Laboratory Manual for Queensland Sugar Mills - Fifth Edition

BUREAU OF SUGAR EXPERIMENT STATIONS QUT j Library I

LABORATORY MANUAL FOR

Q U E E N S L A N D SUGAR M I L L S

FIFTH EDITION

Registered at the General Post Office, Brisbane, for transmission by post as a book.

Wholly set up and printed in Australia by WATSON, F E R G U S O N AND COMPANY Brisbane, 1970

PREFACE TO FIFTH EDITION

D u r i n g t h e past eight years the technology of t h e cane sugar industry has changed considerably. Many new items of apparatus have been introduced i n t o sugar mill laboratories, and analytical methods and techniques have been modified to take advantage of this improved equipment. This new edition of t h e Laboratory Manual has, as far as possible, been brought up to to date as at the middle of 1969 and, w h i l e t h e f o r m of t h e Fourth Edition has been retained, each chapter has been subjected to a critical review and changed or completely r e - w r i t t e n to conform to present day knowledge. The equipment and methods of analysis set o u t are those w h i c h , in t h e considered opinion of t h e officers of t h e Mill Technology Division, are t h e most suitable presently available, but t h e r e w i l l doubtless be some sections w h i c h are t h e subject of diversity of o p i n i o n , and t h e r e are some sections which are in such a state of rapid change t h a t the procedures set d o w n w i l l be o u t of date in t h e near f u t u r e . W h e r e v e r possible, descriptions and illustrations of apparatus cover t h e most modern equipment available, and sections on such new equipment as t h e automatic polarimeter and t h e spectrophotometer have been included. The chapter on analytical methods has been broadened to include many new aspects of sugar analysis, and such o t h e r new subjects as t h e direct analysis of cane. W i t h the increasing importance of boiler w a t e r t r e a t m e n t t h e section dealing w i t h this subject has been expanded. A new chapter has been w r i t t e n to cover t h e subject of metrology, w h i l e t h e chapter dealing w i t h soil analysis has been deleted, as it is felt t h a t this subject is better covered in specialized t e x t - b o o k s . The Bureau of Sugar Experiment Stations wishes to acknowledge t h e assistance given by the following organizations and individuals w i t h t h e preparation of this m a n u a l : — D r . W. H. Steel and Mr. G. A. Bell of t h e National Standards Laboratory. D r . R. A. M. W i l s o n of t h e Colonial Sugar Refining C o . L t d . Mr. J. L. Clayton of t h e Central Sugar Cane Prices Board. The Sugar Research Institute. The Colonial Sugar Refining C o . L t d . The Queensland Health Department. and a number of individuals in t h e sugar industry w h o f o r w a r d e d suggestions f o r this new Edition. The following reference books w e r e used freely in t h e compilation of this E d i t i o n : — The System of Cane Sugar Factory C o n t r o l , Second Edition (I.S.S.C.T.). Cane Sugar Handbook, N i n t h Edition, Spencer-Meade. Polarimetry, Saccharimetry and t h e Sugars, Circular C.440, National Bureau of Standards. ICUMSA Methods of Sugar Analysis, 1964 Edition. Report of the Fourteenth Session of ICUMSA, 1966. Various Publications of t h e British Standards I n s t i t u t i o n , and t h e Standards Association of Australia. We also gratefully acknowledge t h e provision of illustrations by various d i s t r i b u t o r s of laboratory apparatus. 1st February, 1970

N o r m a n J. King, Director Bureau of Sugar Experiment Stations, Brisbane

PREFACE TO FIRST EDITION

The Division of Sugar Mill Technology was created in 1929. One of the early duties of the Division was to introduce a definite plan of campaign for mill control, which was not possible at that time due to the confusion of methods employed and the lack of specific standards. In 1930, Mr. Norman Bennett (then Mill Technologist) instituted the Mutual Control scheme, which was voluntarily subscribed to by the majority of the Queensland mills. The International Standards laid down at the Java Conference of 1929 were adopted as the basis for this work, and a brief statement of standard analytical methods and specifications foi laboratory apparatus was prepared and issued to the mills participating. It was most gratifying to find that practically all mills were eager to adopt the new standards in their entirety, which made possible the present standardised method of reporting mill data and enabled comparisons to be made of the work of different mills. Doubtless the scheme has been directly or indirectly responsible for many of the marked improvements in milling work which have characterised the accomplishments of the Queensland mills during the past five years. In order to assist the mills in obtaining accurately standardised equipment, the Division undertook the calibration of all glassware employed by the industry; at the present time practically all mills submit their apparatus for checking purposes, and hardly any new apparatus is obtained unless accompanied by the Bureau's guarantee. It is felt that the time is opportune for the publication of a Manual which will provide the mill chemist with the desired analytical methods, together with the tables employed in the subsequent calculations, in a readily accessible form. This publication of the Bureau is therefore presented in the hope that it may fill a long-felt want. Further, it was appreciated that the student in sugar chemistry often finds it difficult to obtain a work which will provide him with the fundamental principles of the subject presented in an elementary form. Chapters, have, therefore, been included in Definitions, Optical Instruments, Balances, Densimetric Methods, and Calibration of Glassware, with this end in view. The present work is the result of the combined efforts of members of the Bureau staff, who would welcome any reconstructive criticism and advice from those engaged in the industry. The authors wish to acknowledge their indebtedness to those excellent text-books of C. A. Browne, G. L. Spencer, and J. Reilly and W. N. Rae, which sources have been freely drawn on in the preparation of this Manual; and also to those manufacturers from whose catalogues several of the illustrations have been taken. H. W. KERR, Director. Bureau of Sugar Experiment Stations, Brisbane. 14th July, 1934.

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CHAPTER SAMPLING OF SUGAR M I L L PRODUCTS

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CHAPTER DENSIMETRIC METHODS OF ANALYSIS

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CHAPTER T H E BALANCE

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CHAPTER X I I I . .

R E F E R E N C E TABLES

CHAPTER I DEFINITIONS Whilst the majority of definitions from the previous Edition have been carried forward, several general terms which have recently come into prominence and some of the more important definitions associated with the milling train have been added. Absolute Juice—All the solids in solution in the cane, together with all the water in the cane; i.e. Absolute Juice = Cane - Fibre. Apparent—The word apparent is applied to figures and analyses based on Brix and pol, as distinct from dry substance and sucrose, for example, apparent purity. Brix and pol analyses are widely used for factory control purposes, and unless a specific instance arises where pol and Brix have to be divorced from sucrose and dry substance, the term "apparent" is often omitted. Ash—The residue remaining after burning off all organic matter. In practice the proportion of residue remaining as "ash" is influenced by the conditions of combustion, so that ash, as actually determined, is not an absolute quantity. Back Roller Juice—The juice expressed between the top and delivery rollers of any mill of a tandem. The term is synonymous with last expressed juice only when it refers to the last mill of a tandem. Bagacillo—A fraction of the fine particles separated from bagasse. Bagasse—The residue after extraction of juice from cane in one or more mills. Hence the terms, First Mill bagasse, Second Mill bagasse etc. and in the case of the last mill Final bagasse or simply bagasse, are used. Brix—The Brix of a solution is the concentration (in g solute per 100 g solution) of a solution of pure sucrose in water, having the same density as the solution at the same temperature. If refractive index be adopted as an alternative basis of comparison the value derived should be termed Refractometer Brix. Obviously, for solutions of pure sucrose in water, the Brix is equal to the dry substance, but in the presence of soluble impurities this may not be, and usually is not the case. Although gases and insoluble solids in suspension may alter the density of a solution the term Brix refers exclusively to soluble solids. Bulk Density—Prepared Cane—The bulk density of prepared cane is used as a measure of the degree of cane preparation and is defined as the weight of a prepared cane sample, divided by its bulk volume under standard test conditions. Cane—The raw material delivered to the mill, including clean cane, trash and any other extraneous matter. C C S . (Commercial Cane Sugar)—That percentage by weight of a quantity of cane which would be recovered as pure sucrose (100 n.t.) if

2

DEFINITIONS

milling and refining operations were conducted at a prescribed standard of efficiency. The prescribed standard of efficiency is such that for every pound of soluble impurities in the cane one-half pound of sucrose is lost in process, there being no other losses of sucrose. Hence C.C.S. = Sucrose per cent cane 2

Impurities per cent cane

In the normal application of this formula the following assumptions are made:— 1. Brix = Total soluble solids (dry substance). 2. Sucrose = Pol. 3. Impurities = Brix — Pol. 4. Brix per cent cane . 100 - (F + 3) J . = Brix per cent first expressed juice x 100 5. Pol per cent cane „ . . = Pol per cent first expressed juice X

100 - (F + 5) TT^TJ

Hence C C S . = Pol in cane — | (Brix in cane — Pol in cane) 2 V 109 J 2 V where P — pol per cent first expressed juice B = Brix per cent first expressed juice F = fibre per cent cane.

100

)

Clarified Juice—Juice which has passed through the clarifiers. This juice is fed to the evaporators and as such can also be referred to as Effect Supply Juice or E.S.J. Coefficient of Work—The percentage ratio of the weight produced to the weight of c.c.s. in the cane from was derived. Hence, jr - ^ r „r , Tons 94 n.t. sugar made x Coefficient of Work = —: Ions c.c.s. in cane (A discussion on this formula is contained in the "Calculations Involved in Chemical Control").

of 94 n.t. sugar which the sugar 100 Chapter entitled

Compression Ratio (Milling)—The no-void volume of original cane, divided by the volume occupied by the bagasse (or cane) at the conditions being considered. Condensate—Water which has been condensed, either from vapour liberated from boiling juice, or from steam. Crystal Content—The percentage by weight of crystalline sugar present in a massecuite, magma or similar material. Crystallizer Drop—The decrease in purity of the mother liquor of a massecuite resulting from treatment in a crystallizer. Cyclone Purity of Molasses—Usually this term refers to the purity of the mother liquor of a massecuite at the completion of the pan boiling operation. The term, suitably qualified, is often extended to refer to the purity of any sample of mother liquor extracted from a massecuite for examination, and not as part of the normal factory operations.

DEFINITIONS

3

Dextran—A polysaccharide formed by the action of certain species of bacteria on sucrose during cane and juice storage. Dilution Indicator (D.I.)—A factor used to forecast the keeping and handling quality of raw sugar. It is the ratio of moisture to dry nonsugars expressed as a percentage. moisture Dilution indicator = —— -—— — . X 100 100 — (pol + moisture) A value of dilution indicator below 40 is considered satisfactory, for values between 40 and 50 the keeping quality of the sugar is doubtful, whilst for values above 50 the probability of deterioration is considerable. Dilution Water—The quantity of added imbibition or maceration water which is present in mixed juice. Dilution water is usually expressed as dilution per cent first expressed juice. Dry Substance—The weight of material remaining after drying the product examined under specified conditions, expressed as a percentage of the original weight. The determination of dry substance represents an attempt to measure the total solids, both soluble and insoluble, or, in the absence of insoluble solids, the total soluble solids. The degree of accuracy achieved depends upon the constitution of the sample and the drying technique. Escribed Volume—The volume escribed by a pair of mill rolls in a given time. Escribed volume is equal to the roller length multiplied by the work opening multiplied by the surface speed of the rolls. Extraction (Pol)—The percentage of pol extracted from the incoming material by a train of mills either individually or cumulatively. Analogous definitions apply to Sucrose Extraction, Brix Extraction, and Juice Extraction, the juice, in the case of the last mentioned, being undiluted juice. Extraneous Matter—That portion of the material received as cane which, by arbitrary standards, is considered not to form part of clean cane. It consists of trash, tops, roots, dirt, etc. Fibre—Technically, fibre is the dry, water-insoluble matter in the cane. For commercial purposes a standard method of determination of fibre per cent cane is specified. Filling Ratio—A term used in milling calculations to define the ratio between the no-void volume of fibre passing between a pair of rolls in a given time, and the escribed volume for the same period of time. Filling ratio is actually volumetric coefficient divided by fibre density. Filterability—The filterability of a raw sugar is measured by comparing the filtration rate of the sugar with that of a standard sucrose solution under specified conditions. The result is expressed as a percentage of the filtration rate of the standard sugar. Filter Cake—The washed residue discharged from mud filters. Filtrate—Liquid which has passed through the filtration process. First Expressed Juice—The juice expressed by the first two rollers of a mill tandem.

DEFINITIONS Gravity Purity—See Purity. Gravity Solids—Synonymous with Brix q.v. Gums—A general classification given to polymers of high molecular weight which can be precipitated from sugar products by a strong alcohol solution. Substances included in this category are pectins, hemicelluloses, oligosaccharides, dextrans and solubilised starches. Hygroscopic Water—The Brix-free water absorbed by cane fibre, the amount of which varies with the condition of the solution with which the fibre is in contact. For sugar solutions of low Brix and at normal temperatures, such as those experienced in bagasse analysis, it appears that hygroscopic wrater is some 20 to 25 per cent on fibre. Imbibition—The process whereby water or juice is added to bagasse to dilute the juice contained therein. Impurities (Soluble)—A collective term for all substances other than sucrose present in the total soluble solids contained in a sample. Sometimes expressed as a percentage of the whole material, as in the c.c.s. formula, and sometimes as a percentage of the total soluble solids as in Impurities = 100 — purity Frequently based on apparent analyses, in which case it is synonymous with Non sugars. Invert Sugar—The equimolecular mixture of glucose and fructose which results from the hydrolysis or inversion of sucrose. Java Ratio—The percentage ratio of the pol per cent cane to the pol per cent first expressed juice. Hence. Last Expressed Juice—The juice expressed between the top and delivery rollers of the final mill in a tandem. Maceration—The process in which the bagasse is steeped in an excess of wyater or juice, generally at a high temperature. The water added for this purpose is termed maceration water. Magma—A mechanical mixture of sugar crystals with a liquid such as syrup, juice or water. Massecuite—The mixture of sugar crystals and mother liquor discharged from a vacuum pan. Massecuites are classified according to descending purity as first, second, etc., or A, B, etc. Milling Loss—The percentage ratio of pol in bagasse to fibre in bagasse. Mixed Juice—The mixture of juices leaving the milling train for further processing. Molasses—The mother liquid separated from a massecuite. It is distinguished by the same term as the massecuite from which it was extracted. Mud Solids—Insoluble matter other than bagacillo in subsider mud, filter cake and associated materials.

DEFINITIONS

5

Net Titre (N.T.)—An empirical value used as a measure of the percentage of pure sugar which m a y be recovered from a batch of raw sugar. Sugars of various qualities are commonly reduced to a common basis of 94 n.t. as follows:—

Non-Sucrose—The difference between dry substance and sucrose. Non-Sugars—The difference between Brix and pol. Normal Weight—That weight of pure sucrose which, when dissolved in water to a total volume of 100 ml at 20 °C, gives a solution reading 100 degrees of scale when examined in a saccharimeter, in a tube 200 mm long, at 20 °C. The normal weight according to the International Sugar Scale is 26.000 g weighed in air with brass weights. No-Void Volume—The volume of cane (or bagasse) calculated on the basis that it consists of juice and fibre only i.e. that all air and/or gas has been removed. Other Organic Matter (O.O.M.)—The sum of the constituents of raw sugar other than pol, reducing sugars, ash and water. i.e. o.o.m. = 100 — (pol + reducing sugars -j- ash -j- water) Pol—The pol of a solution is the concentration (in g solute per 100 g solution) of a solution of pure sucrose in water having the same optical rotation at the same temperature. For solutions containing only pure sucrose in water, pol is a measure of the concentration of sucrose present; for solutions containing sucrose and other optically active substances, pol is the algebraic sum of the rotations of the constituents piesent. Primary Juice—All the juice extracted without dilution. Primary Mud—The discharge from the underflow of a clarifier prior to the addition of bagacillo. Purity—Three classes of purity—Apparent, Gravity and True purity—are recognized. Ideally, purity is the percentage of sucrose in the total solids in a sample. The purities mentioned above are derived as follows:—-

The term purity alone generally signifies apparent purity. Gravity purity is not used in Queensland.

6

DEFINITIONS

Reabsorption Factor—The ratio between the no-void volume of bagasse leaving a mill opening in a given time, and the escribed volume for the opening, over the same period of time. Reduced Extraction—A formula used to express normal mill extractions on a common basis of 12.5 per cent original fibre in cane. The formula is usually expressed in the general form, (100 —extraction) (100— fibre) Reduced extraction = 100 = ^r 7 x fibre Reducing Sugars (R/S)—The reducing substances in cane and sugar products calculated as invert sugar. The most familiar examples of sugars having reducing power are glucose (dextrose) and fructose (laevulose). Reducing Sugar/Ash Ratio—The ratio between reducing sugars and ash. Refractometer Brix—See Brix. Remelt—A solution of low grade sugar in either syrup, clarified juice or water. Residual Juice—The juice left in bagasse after milling. Seed—Fine sugar crystals, generally suspended in a liquid medium, in which case the mixture is known as seed slurry. Seed is used either to provide the crystal surface for deposition of sucrose, or to promote spontaneous crystal formation from a super-saturated solution. The latter is referred to as shock seeding. Set Opening—The distance between the tips of the teeth of a pair of rollers. Where the roller teeth are set in mesh, this distance will be negative. Sucrose—The pure chemical compound with the formula C 1 2 H 2 2 O u . This is commonly referred to in the industry as pure cane sugar. Sugar—The crystals of sucrose, together with any adhering molasses, as recovered from the massecuites. The various grades are commonly identified in terms of the grade of massecuite processed, or in terms of the avenue of disposal of the sugar—hence, A sugar, C sugar, Shipment sugar. Suspended Solids—Solids in juice or other liquid, removable by mechanical means. Syrup—The concentrated sugar solution leaving the evaporators. Total Sugars—The combined percentages of sucrose and reducing sugars in a sample. Turbidity—A measure of the material in suspension in a sugar solution as determined by a spectrophotometer. Undiluted Juice—The juice expressed by the mills or retained in the bagasse, corrected for dilution water. For purposes of calculation the Brix of the undiluted juice is taken to equal that of the primary juice, or in Queensland, the first expressed juice. Volumetric Coefficient—A term used to designate the fibre loading of a mill opening. Using the British system of measurement, it is quoted as pounds of fibre per cubic foot of escribed volume.

DEFINITIONS

7

Work Opening—The mean opening between a pair of mill rolls. This opening takes into account the set opening and the allowance for mill grooving. No allowance is made for juice grooves, but where a dirtytop roller is employed, this must be taken into account. Work Ratio—Where a three roller mill has rollers of equal circumference rotating at a common speed, this ratio is the ratio between the feed work opening and the delivery work opening. Where openings with rollers of different diameter or different peripheral speed are to be compared, it is necessary to calculate the ratio from the two escribed volumes.

CHAPTER II OPTICAL I N S T R U M E N T S The optical properties of sugar solutions afford rapid and convenient methods for their analysis and the chemist's most important piece of apparatus is the polarimeter or saccharimeter. The refractometer is used in a limited degree for the rapid determination of total solids in juices and syrups. The introduction of colorimetric methods into sugar laboratory analyses demands the use of the spectrophotometer, and clarification studies require the use of this instrument as a turbidimeter. The microscope is used where raw sugars are examined for grain quality. Each of these instruments will, therefore, be described in some detail. Recent trends to automation have resulted in the development of automatic polarimeters; these will be discussed fully while the principles involved in automatic refractometers will also be mentioned. Properties of Light Light is a form of electromagnetic radiation and it consists of trains of waves vibrating transversely—that is, at right angles to the direction in which the waves are travelling. The most familiar case of a transverse wave is probably that which travels along a rope or string when one end is suddenly jerked sideways. If the end of the rope is moved continuously, a continuous wave will be produced.

Fig. 1—Illustrating the principle of a light wave.

Fig. 1 represents a wave in which the vibration is at right angles to the direction of motion, P Q. The distance A B is the amplitude of the wave, while the distance 0 E, which includes one complete crest and trough, is known as the wavelength and denoted by the symbol A. For light, wavelengths are expressed either in nanometers (formerly called millimicrons; 1 nm = 10- 9 metre) or in angstrom units (1 A = 10- 10 metre = 0 . 1 nm). Light of different wavelengths appears to the eye as different colours; the following wavelengths have the colours given: 683 nm red 615 nm orange 559 nm yellow 512 nm green 473 nm blue 410 nm violet These represent pure spectral colours; colours of most objects, however, are due to light having a range of wavelengths. The intensity of the light depends on the amplitude of the wave; in fact, it is proportional to the amplitude squared.

OPTICAL INSTRUMENTS The number of complete waves passing any point each second is the frequency, denoted by v. This is measured in hertz (Hz), formerly called cycles per second. For visible light the frequencies range from 4 x 1014 to 8 x 1014Hz. The speed v at which the wave advances is then given by v = v X. In a vacuum, light has a constant speed, no matter what its wavelength; this is denoted by c. In transparent matter, light has a lower speed and this speed varies with the wavelength of the light. It is this slowing down of light by matter that enables optical measurements to give an estimate of, for example, the total dissolved solids in a solution; the more material in solution the greater the "slowing down" of light. In general, the vibration of a light wave occurs in the two dimensions at right angles to the direction of travel. However, light can be made to vibrate entirely in a single plane just as a water wave vibrates only up and down. The light is then said to be plane polarized or linearly polarized. When such light passes through certain media, the orientation of this plane is changed. This change is caused only by special materials, said to be optically active, of which sugars are examples. The amount the direction is changed depends on the concentration of the optically active material in a solution, so polarimeter measurements give concentrations of active materials (such as sugars), rather than total solids. Refractive Index In a homogeneous medium light travels in straight lines. If, however, a beam of light in one medium meets the surface of a second medium, it will in general be refracted or bent from its original path. The incident ray of light, denoted by L O in Fig. 2, arrives at the boundary between the media

Fig. 2—Illustrating the law of refraction. M and M' in a direction represented by the angle LOP between the ray and the normal (perpendicular) to the boundary. This angle is called the angle of incidence i. Part of the light is reflected along O L' at the same angle i on the opposite side of the normal. The bulk of the light, however, is transmitted into the second medium along O S, which makes an angle SOQ with the normal. This is called the angle of refraction. If this angle is smaller than the angle of incidence, the first medium is said to be the rarer medium and the second the denser. This terminology relates to the effect, discussed earlier,

that as the concentration and hence the density of a medium increases, the speed of light in it decreases. (This should not be confused with the "optical density" of a medium, which refers to its light-absorbing properties). The angles of incidence and refraction are related by the expression n sin i = n2 sin r where n and n 2 are constants describing each medium; they are the refractive indices of the media. For any transparent medium, the refractive index is the ratio of the speed of light in air to its speed in the medium. Thus, a "denser" medium, having a lower speed of light, has a higher refractive index than a "rarer" medium. For a stricter theory, the refractive index should be defined with respect to speed of light in vacuum rather than in air, namely n = c/v. This is the absolute refractive index and it is 1.000 28 times the refractive index relative to air, 1.000 28 being the absolute index of air itself. For practical purposes, however, it is always the index relative to air that is used and this is what is meant by the simple term "the refractive index". Another way of writing the relation between the angles of incidence and refraction is sin i -. = n sin r where n = n 2 /n 1 and is the ratio of the two refractive indices or the relative refractive index. This ratio is the same whether absolute indices or indices with respect to air are used. Since the speed of light in any medium other than vacuum varies with wavelength, so does the refractive index. Light of different wavelengths is therefore refracted by different amounts. When a beam of white light, which is a mixture of all visible wavelengths, is refracted at a boundary, it is spread out into a series of colours, known as a spectrum. This is the phenomenon of dispersion, sometimes called prism dispersion to distinguish it from the rotatory dispersion discussed later. When a refractive index of a material is quoted, it is therefore desirable to specify the wavelength for which it has been measured. Certain spectral lines are known by letters, for example, the D line of sodium and nD denotes the refractive index for this line. Important lines are: Symbol Wavelength (A) Colour Element C 6563 red hydrogen D 5893 orange sodium d 5876 yellow helium e 5461 green mercury F 4861 blue hydrogen When the line is not specified, it is commonly the D index that is meant. Although useful for measurements of moderate accuracy, this is really two lines, close together. The modern tendency, particularly for accurate work, is to replace the D line by either the helium d line or the mercury e line. The dispersion of a medium is given by the difference between the refractive indices for the blue and red lines of the hydrogen spectrum, i.e. nF—nC. The refractive index of a material also varies with the temperature and a complete 2description of a refractive index should also include this, as, for example nD 0 °. The rate of variation for glass is small, between 1 x 10- 6 and 6 6 x 10- per degree Celsius, and is usually positive, the index increasing as

OPTICAL INSTRUMENTS 11

the temperature increases. For liquids, the rate of change is much greater and in the opposite sense; an increase of temperature by 1 degC decreases the refractive index of water by 8 x 10-5. For sugar solutions, the te for organic liquids it may be even greater. The Refractometer For the most accurate measurements of refractive index the material, if a solid, is made into the form of a prism. If liquid, it is poured into a hollow prism. The deviation of the light through the prism is then measured. For routine measurements of refractive indices of liquids, however, methods based on the critical angle are used. Critical-Angle Refractometers When light passes from a rarer to a denser medium, the angle of refraction is smaller than the angle of incidence. Thus, while all values up to 90° are possible for the angle of incidence, until the incident light grazes the boundary surface, the angle of refraction has a maximum value that is smaller than this. This maximum value is the critical angle r c and is the angle of refraction that corresponds to an angle of incidence of 90°. Then sin i — 1 and nn1 = n2 sin rc. Thence an unknown index n 1 can be found by measuring the critical angle r c for light refracted from the sample into a denser medium of known index n2. The method is illustrated in Fig. 3, where M 1 is the rarer and M 2 the denser medium. In Fig. 3(a) the light is incident from the rarer medium and rays 0x-0b are shown at increasing angles of incidence. A small amount of the

(o)

(b)

Fig. 3—Illustrating the measurement of critical angle, (a) by transmission (b) by reflection. energy from each ray is reflected at the boundary; the rest is transmitted in the refracted ray. Since the ray 05 arrives at an angle of incidence of 90°, it is the critical ray. No light from Mx can penetrate into M2 at a larger angle of refraction. Hence, if the emergent light into M2 is viewed by a telescope aimed along the direction 05, the observer will see light on one side of the field of view, darkness on the other. Obviously, it is impossible for the telescope to be inside the denser medium M 2 , but this medium can be made as a prism, the second surface of which refracts these emergent rays into the air. This second refraction will change the direction of the critical ray but the

final direction will still depend only on the known refractive index of the prism M2 and the unknown index of the sample M1. The angle of the critical ray is measured and the index n 1 of the sample found from tables provided with the refractometer, or the instrument is calibrated to read, instead of angle, the index n1 directly or a Brix value derived from n1. The reverse process to that described above is shown in Fig. 3(b). In this case the light is incident from the denser medium and the rays O1-05 are again part reflected and part refracted at the boundary, passing into the rarer medium at a larger angle to the normal until, for 05, the angle of refraction has reached 90° and the ray leaves grazing the boundary. The angle of incidence for this ray is thus the critical angle. If the angle of incidence is increased further, as in O 6 or 0 7 , no light can be refracted into the rarer medium. All the energy is reflected at the boundary giving the phenomenon known as total internal reflection. Again if the light emerging in the denser medium, now the reflected light, is examined by a telescope aimed along 05, a divided field of view is seen with one side brighter than the other. The brighter side, at angles greater than 05, corresponds to rays for which there is total reflection, while the darker side corresponds to partial reflection. For this case sin r = 1 and n1 = n2 sin ic.

Fig. 4—The essential parts of an Abbe refractometer.

OPTICAL INSTRUMENTS

13

The critical angle is now an angle of incidence. Since on reflection, the angles of incidence and reflection are equal in magnitude, the unknown refractive index is found from a measurement of the angle of reflection that corresponds to this critical angle of incidence, ic. For either method of critical-angle refractometry, the solid or liquid sample M1 is placed on a prism of the material M2. For the first method, the boundary is illuminated from the sample; for the second, from the prism. In both cases the illumination should cover a range of angles: in the first case right up to 90° incidence, and in the second the range must include the critical angle. The emergent light, refracted or reflected according to the method, is examined through a telescope, the inclination of which can be altered to set it in the direction of the critical ray. The field of view of the telescope has a light and a darker side and the boundary between them is set on a pair of cross lines in the telescope eyepiece. In the first method, the darker side of the field would be completely dark, but for scattered light. In the second method there is only the less obvious distinction between total and partial reflection. Hence the first

Fig. 5—The principle of the Abbe refractometer.

14

OPTICAL INSTRUMENTS

method is therefore by far the more sensitive method of measurement and it is the one normally used. The second method is only used when the specimen is so strongly absorbing {e.g. a sample of molasses) or scattering, that insufficient light can be sent through it to the boundary. One of the most widely used refractometers that is based on the measurement of the critical angle is the Abbe refractometer. An early model made by Zeiss Jena is shown in Fig. 4 and, in conjunction with Fig. 5, is convenient for explaining the operating principle. Two prisms A and B of a flint glass of high refractive index (nD) = 1.75) allow samples to be measured with refractive indices up to 1.7. Each prism is contained in a metal mount, the mount of the lower prism B being hinged to that of A and held in the closed position by a clamp. The two prisms are connected through the main bearing of the instrument to the arm J, which carries a cross line and eyepiece L. Rotating independently about the same axis is a second arm which carries the telescope F and the sector S, upon which the refractometer scale is engraved. The angle between the prisms and the telescope is read as the position of the cross line on the a r m / relative to this scale, while this angle is adjusted to set the boundary line on the cross line in the telescope by turning the knob T. In Abbe refractometers, the scale is not normally graduated directly in angle but either in refractive index or in Brix. In use, the two arms are rotated together until the prism B is uppermost, the clamp released, and prism B opened away from A. It will be noticed that the top (hypotenuse) surface of A is polished while the corresponding surface of B is roughly ground. If a solid sample is being examined, such as the test piece normally supplied by the manufacturer, a drop of a liquid, such as monobromonaphthalene (n — 1.658), that is known to have a higher index than the test piece is first placed on the top of A, which should be horizontal, and the large polished face of the test piece is pressed down on this, the small face to the front of the instrument (away from the telescope). This small face is pointed towards a window or another diffuse source of light and the telescope set on the boundary between the light and dark fields with the instrument in this "upside-down" position. The same position is also used for absorbing liquids, when the second method of measurement is used. The light is sent through the window C of prism A (normally closed by a cover) from the mirror R. In both these measurements, prism B is not used. For the usual measurements on reasonably clear liquids, a drop of the liquid is placed on the surface of prism A. Prism B is then clamped into position so that the liquid forms a film about 0.15 mm thick between the faces of the two prisms. The instrument is swung back so that the telescope is upright and light is reflected from a diffuse source from the mirror R into the open face of prism B. This light is then scattered by the ground face of this prism which serves simply as a means of giving incident light inside the liquid at all angles up to 90°. Prism A gives the critical refraction. The path of the light through the instrument is shown in Fig. 5, with the light entering through prism B, and being scattered at the ground surface. In this figure, the thickness of the sample is greatly exaggerated, and in practice the rays p q and p' q' are almost parallel to the prism surface ef. These rays enter the prism A at the critical angle and are brought to a focus along a line at L in the eyepiece of the telescope. Other rays are focussed to the left of L, so that L represents the boundary between light and dark fields. This boundary is set to intersect the centre of the cross lines, as shown. To measure the D index, a sodium lamp may be used as the light source. When a source of white light is used, the boundary becomes a band of colours since a different critical angle is obtained for each wavelength. To compensate

OPTICAL INSTRUMENTS

15

for this dispersion, Abbe refractometers are equipped with a pair of compensating or Amici prisms. These prisms are placed on the telescope tube, in front of the objective and can be rotated simultaneously in opposite directions by the screw head M. They then act as an adjustable prism that produces no deviation of the light but has a variable dispersion that can compensate for the dispersion of the critical refraction. Attached to the prisms is a scale z that can be used to give the dispersion of the sample, that is nF — nC. The Amici prisms are adjusted until the boundary between the light and dark fields becomes as sharp as possible. It is then not quite colourless but is seen to have a narrow band of a magenta colour on one side, yellow-green on the other. Unless the refractometer is used in a temperature-controlled room, the sample should be kept at a constant temperature during the measurement by circulating water at a constant temperature through the metal mountings which carry the prisms. The temperature is indicated by the thermometer Th. When a measurement has been made, the liquid should be removed from the prism surfaces with absorbent paper, the surfaces washed with a suitable solvent (usually water or alcohol) and dried with a soft cloth. As the prisms are made of a soft flint glass, they are easily scratched and great care must

Fig. 6—Abbe refractometer by Carl Zeiss, W. Germany.

be taken not to wipe grit across their surfaces or close them with dust in between. A scratched or pitted prism will give an indistinct boundary. The adjustment of the refractometer should be checked periodically on a sample of known refractive index. This can be the glass test piece provided with the instrument, freshly distilled water free from air (nD20° = 1-3330) or another liquid that has been specially calibrated. When making this check, the telescope is set at the refractive index of the calibrating sample and the adjusting screw V turned until the boundary is at the cross line. When using liquids as standards, it is essential to control their temperature to that for which they have been calibrated.

Fig. 7—High accuracy refractometer by Bellingham and Stanley, London.

Provided the sample gives a clear boundary between the light and dark fields, an Abbe refractometer should be capable of measuring its refractive index to an accuracy of about two units in the fourth decimal place (2 x 10-4). Fig. 6 shows a modern instrument made by Carl Zeiss, Oberkochen, W. Germany.

OPTICAL INSTRUMENTS

17

There are however more accurate critical angle refractometers which will measure the refractive index of solutions to an accuracy of three units in the fifth decimal place (less than 0.02° Brix). Figures 7 and 8 illustrate two types of high accuracy refractometers. The bench model (Fig. 7) is used with a monochromatic light source and readings may be obtained over the range 0 to 80° Brix with a single measuring prism. The Dipping or Immersion refractometer (Fig. 8) is fitted with a compensator for light dispersion correction, so that it may be used with white light. It is supplied with a series of interchangeable prisms, each one covering a portion of the total range of 1.32 to 1.64 refractive index. This refractometer may be fitted with either non-heatable or heatable prisms. In the former instance

Fig. 8—High accuracy immersion refractometer with temperature controlled prisms by Carl Zeiss, \V. Germany.

it is used with the measuring prism dipping into the solution to be tested. The heatable prisms are similar to those of the Abbe type refractometer and are water jacketed to permit temperature control of the sample. This heatable prism assembly is usually preferred by Queensland sugar mills. Flow through cells are also obtainable for these instruments. It must be stressed that constant temperature control is essential for precision measurement.

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OPTICAL INSTRUMENTS

With high accuracy refractometers the scale is not calibrated in refractive index but is an arbitrary scale of equal divisions. As the scale is linear it may therefore be subdivided by means of a vernier so that readings to one tenth of one scale division are possible. Tables are provided for conversion of the scale reading to refractive index from which the degrees Brix may be determined. Simpler but less accurate than the Abbe refractometer are the hand refractometers, an example of which is shown in Fig. 9.

Fig. 9—Hand refractometer by Atago Optical Works, Japan.

Tables have been prepared which show the relationship between the concentration and the refractive index of sugar solutions. This relationship varies only slightly for different sugars, so the refractometer is quite satisfactory for determining the total sugars present in a solution of mixed sugars. With respect to speed, ease of manipulation, and amount of sample required, the procedure is superior to specific gravity methods. As recently as 19(H) ICUMSA has adopted new equations developed by the Physikalisch-Technische Bundesanstalt in West Germany. These now form the basis of the International Table of Refractive Indices (1966) of sucrose solutions from 0 to 85 per cent. The new table is very similar to the former table based on work by Schonrock; however, precise refractive index values can now be obtained to the fifth and at lower concentrations, the sixth decimal place. The new table of refractive indices of sugar solutions at 20 0 C in air at 20 0 C, 760 mm pressure and 50 per cent relative humidity is found in Table VII. Where it is necessary to correct refractometer results for temperature, this is done by converting the refractometer reading to its corresponding Brix value and applying the corrections for refractometer Brix shown in Table VIII. As ICUMSA has not yet studied temperature corrections in detail, the values shown in Table VIII are still the original ones based on Schonrock's work. With impure sugar solutions, such as low-grade molasses, it is found that the refractive index affords a closer approximation to the actual amount of dry substance present than does the specific gravity. The percentage dry matter in massecuites or moist sugars can be determined with the refractometer after dissolving all soluble matter in a known amount of added water. Since the refractometer indicates the amount of dissolved solids only, any insoluble matter which is present will introduce an error in the estimation of dry substance. Where dark-coloured solutions are being examined, it is often difficult to eliminate completely the effects of dispersion. This may be corrected in some degree by dilution with water, but with impure solutions an error is introduced just as is the case with specific gravity determinations. A close approximation is obtained if a solution of pure sugar is used for the dilution. Most modern refractometers can be obtained with a Brix scale for the direct determination of the Brix of sugar solutions. The hand refractometer, of which one type is illustrated in Fig. 9 is useful for the approximate checking of Brix, particularly for maturity testing in the field. The model illustrated is of the double prism type and is to be preferred to the single prism instruments which are also available. In both cases, when a sample is introduced,

OPTICAL INSTRUMENTS

19

the eye placed to the telescope will see a division line between light and dark fields superimposed on a scale of the type shown in Fig. 10. The scale is read at the junction of the two fields. These instruments are made to cover various ranges of Brix, e.g., 0-30°, 0-50°, 40-80°. So long as an adequate number of sticks is suitably sampled, it is possible to obtain a reasonably accurate estimate of the dry substance present in the juice from a crop, and the concentration of solids from the several portions of the stalk of cane provides a useful guide in the determination of the state of maturity of the crop. The instrument is also of great value in affording a rapid estimate of the relative sugar content of large numbers of cane seedlings when these are being selected for further trials.

Fig. 10—Typical field of a hand refractometer.

Automatic Refractometers Although automatic refractometers are not yet used in the Australian Sugar Industry, they have found wide use in the sugar industry overseas. Three methods are commonly used for measuring the effect of a liquid on a light beam directed at the liquid surface: (i) the lateral shift, or sometimes the dispersion, of the transmitted beam as a result of refraction. (ii) the position of the critical angle (the angle of incidence for which the emergent beam is tangential to the interface). (iii) the intensity of the reflected beam for angles of incidence less than the critical angle. Measurement of refractive index by the "transmission principle" (i) is possibly the most precise of the three methods; however it is only suitable for light coloured solutions. For dark coloured solutions it is essential to use small measuring cells and this can cause difficulty if any particulate matter is present. Automatic refractometers using the "critical angle principle" (ii) of operation are generally the most robust for process control work and are claimed to be unaffected by aeration, turbidity, and colour. Automatic refractometers working on the "reflected light principle" (iii) are widely used as Brix controllers on clear factory streams. They are however usually affected by aeration, turbidity and colour. The principle employed by the Waters Inline Refractometer which works on the critical angle principle is described as follows:

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OPTICAL INSTRUMENTS

A light beam from an incandescent lamp is directed through a lens to a glass prism in contact with a liquid sample. The beam is refracted at the interface between the prism and the process fluid and directed back through a beam deflector to two cadmium sulphide photocell detectors. As the refractive index changes the critical angle changes causing more or less light to fall on one photocell detector. The other photocell (comparison cell) remains in the full intensity portion of the beam. As the light changes on the detector cell, a signal is generated by the photocells and amplified, causing a servo motor to drive a glass restorer plate in the beam. The amount of movement of the glass required to restore the beam to a null balancing position is a measure of the process stream concentration. Prisms covering different refractive index ranges are available. There are many automatic refractometers currently available from well known manufacturers throughout the world. Polarized Light Linearly polarized light, in which the vibration occurs entirely in one plane, is one type only of polarized light. The vibration may be in two dimensions, at right angles to the direction of travel. Thus it can be a circular vibration around the direction of travel, and, in the most general case, vibration in an ellipse. If all the light in a beam has its vibrations following the same figure (straight line, circle or ellipse) the light is polarized, either linearly, circularly, or elliptically. Natural light is not polarized, but consists of a random mixture of all polarizations. In practice, linearly polarized light is the most important. It is obtained from natural light by means of a polarizer, a system that transmits vibrations in one direction only. Since the random vibrations of natural light can be resolved into two components along two directions at right angles and these two components are, on the average, equally intense, a perfect polarizer will transmit half the intensity of natural light. The light reflected from the boundary between twro transparent media is linearly polarized for a certain angle of incidence, but only a small part of the intensity is reflected. A more efficient polarizer is made from dichroic films. A dichroic material is one that transmits light linearly polarized in a certain direction (with respect to the orientation of the material molecule) and absorbs that polarized in the direction at right angles. The early experiments on polarized light used the dichroic crystal tourmaline as polarizers. As it proved difficult to produce large dichroic crystals artificially, later polarizers have been made from small crystals embedded in a plastic sheet, all aligned in the same direction by stretching the sheet. This is the original form of Polaroid, the crystals used being herapathite or iodosulphate of quinine. These microcrystalline sheet polarizers are now quite obsolete. The present-day polarizers made by the Polaroid Corporation use a molecular dichroic material. A sheet of polyvinyl alcohol is stretched to align the molecules and then its surface converted into a dichroic material by treatment either with iodine or oxygen to give two types of Polaroid, called H or K sheet. For use in optical instruments, the sheet polarizer is cemented between discs of glass. Other manufacturers such as Zeiss in Germany and Barr and Stroud in Scotland also make sheet polarizers. The properties of sheet polarizers vary somewhat, depending on the dichroic material used and how much of it there is on the sheet. All absorb some of the linear polarization that they should transmit and transmit a

OPTICAL INSTRUMENTS

21

small amount of the polarization they are intended to absorb. Good sheet polarizers, however, are now as good as the polarizing prisms described later and are gradually replacing these prisms in polarimeters and other optical instruments. Prism polarizers are made of transparent crystals that have the property of being birefringent or doubly-refracting. The crystal commonly used is calcite or Iceland spar, a clear form of calcium carbonate that cleaves readily into rhombohedra. If an object is viewed through such a crystal, a double image is seen. Both images are found to be linearly polarized with their polarizations at right angles. The crystal thus splits natural light into two linearly polarized rays and refracts these rays in different directions. (A dichroic crystal does the same splitting, but it absorbs one ray). Each crystal has a direction known as the optic axis, fixed with respect to the rhombohedral planes, in which both rays have the same refractive index, 1.658 for calcite. In other directions, one ray still has the same refractive index; it is called the ordinary ray. The other ray, however, the extraordinary ray, has a refractive index that varies with direction from 1.658 to 1.486 and so does not obey the simple law of refraction. In Fig. 11 the effect of sending a beam of light through a crystal of calcite is illustrated.

Fig. 11—Illustrating double refraction of light in calc spar.

The natural light is split into two polarized beams that leave the crystal with a slight separation, about 1/9 of the thickness of the crystal. This separation is usually too small to be useful for making a polarizer, and before such a crystal of calcite may be utilized for this purpose, one set of emergent rays must be eliminated. One method is to use the phenomenon of total internal reflection. This is usually accomplished by the method devised by Nicol. A crystal is selected (Fig. 12) of which the length is about three times the width. Wedge shaped sections are cut or ground from each end of the crystal so as to reduce the acute angles GBC and FDA from 71° to 68°. The crystal is then halved in the direction AC, at right angles to the modified faces. The cut surfaces are next polished and reunited with Canada balsam which has a refractive index about 1.54. A beam of light PR entering such a crystal

Fig. 12—Illustrating the principle of the Nicol prism.

(Fig. 12) is resolved into two rays, RO and RE. That which is the more highly refracted (the ordinary ray, RO) meets the film of Canada balsam AC at such an angle that it is completely reflected and is thus eliminated. The

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OPTICAL INSTRUMENTS

e x t r a o r d i n a r y r a y R E i s less h i g h l y r e f r a c t e d , a n d e m e r g e s a s p l a n e p o l a r i z e d light from t h e e n d surface o f t h e c o m p o s i t e p r i s m . It should be of the ordinary Canada balsam. ordinary ray to balsam.

noted t h a t the separation of the two rays and the elimination r a y a r e a c h i e v e d b y t h e half p r i s m A B C a n d t h e film o f T h e o t h e r half p r i s m A D C s e r v e s o n l y t o r e s t o r e t h e e x t r a i t s original d i r e c t i o n , a n d t o p r o t e c t t h e film o f C a n a d a

T h i s early t y p e o f Nicol p r i s m d o e s n o t n e e d t o b e g r o u n d a n d p o l i s h e d o n t h e o u t s i d e faces, o n l y a l o n g t h e d i a g o n a l — w h e r e t h e t w o half p r i s m s a r e c e m e n t e d w i t h t h e C a n a d a b a l s a m . I t h a s t h e d i s a d v a n t a g e s o f a s m a l l useful angle a n d o f d i s p l a c i n g t h e b e a m o f l i g h t t o o n e side. I t i s n o w r e p l a c e d e n t i r e l y b y r e c t a n g u l a r p r i s m s , w i t h all faces p o l i s h e d . T h e s e a r e , h o w e v e r , still s o m e t i m e s called " n i c o l s " . A s calcite i s a m u c h softer m a t e r i a l t h a n glass, c a l c i t e p r i s m s s h o u l d b e c l e a n e d o n l y w i t h e x t r e m e c a r e o r t h e y will s c r a t c h . T h e y a r e difficult t o h a v e r e c o n d i t i o n e d a s t h e p o l i s h i n g o f c a l c i t e i s h i g h l y specialized o p t i c a l w o r k and each prism m u s t be separated then re-cemented with a cement of index s u i t a b l e to t h e p r i s m a n g l e . A s i m p l e r class of m a i n t e n a n c e is s o m e t i m e s r e q u i r e d , h o w e v e r , i f t h e b l a c k p a i n t o n t h e side o f t h e p r i s m b e c o m e s d e tached. This paint is important as it absorbs the ordinary ray and so prevents i t b e i n g s c a t t e r e d b a c k b y t h e g r o u n d surface. A c o m b i n a t i o n of t w o p o l a r i z e r s in series is t h e b a s i s of a p o l a r i m e t e r . W h e n l i g h t from t h e first p o l a r i z e r (Fig. 13 I) p r o c e e d s to a s e c o n d p o l a r i z e r , k n o w n as an analyser, it is c o m p l e t e l y t r a n s m i t t e d if t h e p o l a r i z i n g d i r e c t i o n s of t h e t w o a r e p a r a l l e l , losses in i m p e r f e c t p o l a r i z e r s b e i n g n e g l e c t e d . If, h o w e v e r , t h e a n a l y s e r i s r o t a t e d a b o u t t h e l i g h t b e a m (Fig. 1 3 I I ) , t h e i n t e n s i t y o f t h e e m e r g e n t l i g h t will d e c r e a s e u n t i l t h e t w o p o l a r i z i n g d i r e c t i o n s a r e a t r i g h t angles, w h e n t h e light i s e x t i n g u i s h e d . I n t h e first p o s i t i o n , t h e p o l a r izers a r e s a i d to be parallel: in t h e second, t h e y a r e s a i d to be crossed.

I. Parallel Nicols.

II. Crossed Nicols. Fig. 13—Illustrating the principle of polarizer and analyser. W h e n linearly polarized light passes t h r o u g h a birefringent crystal, it also c a n b e split i n t o t w o r a y s w i t h different r e f r a c t i v e i n d i c e s . I f t h e c r y s t a l is thin, these rays are not noticeably separated and recombine as t h e y leave t h e c r y s t a l . B e c a u s e o f t h e i r different s p e e d s , h o w e v e r , t h e y d o n o t r e c o m b i n e in s t e p a n d , i n s t e a d of l i n e a r l y p o l a r i z e d l i g h t , e l l i p t i c a l l y p o l a r i z e d l i g h t is obtained.* E l l i p t i c a l p o l a r i z a t i o n c a n also b e o b t a i n e d i f l i n e a r l y p o l a r i z e d

OPTICAL INSTRUMENTS

23

light passes through strained glass. Glass is not ordinarily doubly refracting but, when strained, because of poor annealing or a mount that introduces strain, it becomes slightly birefringent. Optical Activity Quartz is also a crystal that is birefringent with about one-twentieth the birefringence of calcite. As with calcite, this effect is greatest in directions at right angles to the optic axis. Along the optic axis, however, a new effect occurs; if linearly polarized light is sent through a crystal of quartz in this direction, the angle at which the light is polarized is changed. The amount of change depends on the thickness; the direction of polarization can be imagined as rotating around the ray like a corkscrew as the light proceeds through the quartz. This property of rotating the plane of polarization is known as optical activity. It is possessed by certain crystals and also by some liquids and solutions, including sugar solutions. Materials such as glass that are not ordinarily optically active, can rotate the plane of polarization when they are placed in a magnetic field; this is known as the Faraday effect. The amount of rotation depends directly on the thickness of the sample through which the light passes and, in the case of a solution, on the concentration of the optically active substance in the solution. It also depends on temperature and wavelength, so these must be specified. An active substance in solution is characterized by its specific rotation a, i.e. the rotation of a solution of unit concentration and 1 decimetre length. For the D line at 20 °C this 20 is written ay-. If a sample has a concentration c (in g per 100 ml, weighed in vacuo) and a length / (in dm), the angular rotation will be 20 0 = a ^ C //100, 6 being measured in degrees. In the case of the Faraday effect, the amount of rotation depends on the field strength and its length, and therefore for an electromagnetic coil, on the current in the wire and the number of turns. A normally non-optically active substance, such as glass or air, when placed in an electromagnetic coil is characterised by its Verdet constant V, i.e. the rotation caused by the substance in unit field strength and 1 decimetre long. As 20 above the angular rotation can be expressed as 6 — V — H Z/100, where H is the field strength in gauss. The measurement of this rotation is the technique of polarimetry; it is a method of measuring the concentration of a substance of known specific rotation when placed in a tube of known length.

Sucrose +66.54 Laevulose —92.5 Dextrose +52.5 Invert —20.0 A solution of sucrose or dextrose, which has a positive specific rotation, rotates the plane of polarization in a clockwise direction when viewed towards the light source, and is said to be dextrorotatory. Laevulose, on the contrary, rotates the plane in an anti-clockwise direction and is said to be laevorotatory. Crystals of quartz occur in two different forms that are either dextro- or laevorotatory. They are called right-handed and left-handed quartz. In the case of the Faraday effect, the direction of rotation depends upon the direction of the magnetic field and therefore for an electromagnetic coil on the direction of the current in the coil.

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OPTICAL INSTRUMENTS

In any method of polarimetry, the solution is placed in a cell of known length between two polarizers. In a polarimeter, these are set crossed with the cell empty and the extra rotation of the analyser, required to restore extinction after the sample is introduced, measures the rotation of the sample. In a saccharimeter, the analyser is not rotated, but the rotation due to the sample is compensated by the rotation in a plate of quartz of variable thickness. In certain automatic polarimeters, the same principle of balancing is used, but instead of quartz, a rod of glass in a variable magnetic field gives a Faraday rotation; the current used to produce the field indicates a measure of the sample rotation. The variation of rotation with the wavelength of the light used is known as rotatory dispersion. It has the practical result that measurements of rotation must be made with monochromatic light, as are measurements of refractive index. Traditionally, the D line of sodium has been used, but there is a modern tendency to use the e line of mercury (5461 A) for very accurate measurements; it must be remembered that the specific rotations for these two lines are quite different. Thus a polarimeter is used with either a sodium or mercury lamp. In a saccharimeter, the quartz and sugar solution have similar rotatory dispersions, at least in the red-to-yellow part of the spectrum, so that white light that has been passed through an orange filter can be used. The Polarimeter The essential parts of a visual polarimeter are shown in Fig. 14. An aperture B is illuminated by a source of monochromatic light C, either directly or through a lens which focuses C on B. The light passes on through a fixed polarizer P, with a field stop F, and the analyser A which may be rotated;

Fig. 14—Showing the essential parts of the simple polariscope.

the latter is fitted with a scale S on which the rotation can be read. It is usually graduated so that the crossed position of the analyser corresponds to the zero of the scale. The light is viewed by the eye E of the observer. If a cell X containing an optically active solution is now placed between the polarizer and analyser, it will be found that the light is no longer extinguished by A, which will have to be rotated to a new orientation to restore extinction. The angle through which the analyser is rotated is the rotation of the specimen. The scale 5, as well as being marked in angular degrees, is often also marked in terms of the International Sugar Scale discussed later. A simple polarimeter of this type would not be very accurate, for setting an instrument to extinguish light cannot be done with high precision. It is well known in the technique of measurement that a setting to a maximum or a minimum, such as this, is less precise than a balancing of two quantities to equality or coincidence; for example, setting a needle on a scale division, aligning a line to a crosswire, or matching the intensity of two adjacent fields of view. Settings of this last type are known as null settings. The eye looking through the polarimeter has a field of view located at the stop F near the fixed polarizer. To convert the instrument into an

OPTICAL INSTRUMENTS

25

instrument with a null setting, this field is split into two parts as shown in Fig. 15 or in some cases into three parts. The polarizations of these two regions are in directions that differ by a small angle (when three regions are used, the two outer ones are polarized in the same direction and the centre one is different) so that, as the analyser is rotated, first one field, then the other is extinguished. When the analyser is crossed with the direction midway between the two polarizations, the two fields have equal intensity. A setting to this position is thus a null setting and is much more accurate than a simple setting to extinction.

I

II

III

Fig. 15—Illustrating the principle of the Lippich polarizer for double field.

The three-field alternative has an even greater sensitivity but, if the two outer fields are not polarized exactly in the same direction, it loses its advantage, since two balance-points are obtained. Under ordinary laboratory conditions, the simpler two-field balance is preferable. The angle between the polarizations of the two fields is known as the half-shadow angle. Theory shows that, the smaller the half-shadow angle used, the greater is the sensitivity of the instrument. However, the smaller this angle, the closer the two sides of the field are to extinction at the balance point, and the less light there is available to judge the balance. Since the sensitivity also depends on the light intensity, when the light source is as bright as can be obtained, a compromise is required on the half-shadow angle between the loss of sensitivity due to too large an angle and the loss due to too little light. In practice angles of 1° to 10° are used. In the saccharimeter described later an angle about 7° to 8° has been found a good compromise for accuracy and available light. There are several methods used to make polarizers that give a split field. The simplest to understand are forms of the Jellet-Cornu polarizer. Imagine a polarizing prism with a narrow-angle V taken longitudinally from its centre. The two separate prisms are then cemented together to give two adjacent polarizers with a fixed half-shadow angle, the angle of the V cut. Another polarizer with a fixed half-shadow angle is made from two long natural rhombs of calcite; this is one example of the use of the rhomb itself, instead of a prism, to separate the ordinary from the extraordinary ray. The most common method of obtaining the split field is the Lippich polarizer, shown in Fig. 16. In front of the main polarizer is placed a smaller polarizer covering half the field. This is rotated through the half-shadow angle from the main polarizer. This rotation changes the direction of polarization across this half of the field and also slightly reduces the

26

OPTICAL INSTRUMENTS

intensity. The reduction of intensity affects the position of the setting slightly; it is no longer exactly midway between the angles at which the two fields extinguished. The small polarizer is also tilted slightly so that the observer does not look along its face (and hence see a broad band separating the two fields) but sees only a sharp edge. When the triple field is used, two such small polarizers are employed. The Lippich system has the advantage that the half-shadow angle is adjustable and can be altered to suit the intensity of the illumination. When it is altered, however, there is an alteration of the zero point of the analyser. But, in the Bates Fric saccharimeter a special set of gears is fitted so that, when the large polarizer is rotated to change the halfshadow angle, the analyser is rotated by the amount required to correct for the change in zero point. The need to use monochromatic light with a polarimeter was a great practical disadvantage when it had to be obtained by feeding metal salts into a flame. Now spectral lamps, such as sodium and mercury, are readily available and easy to use. Most of the visible light from the sodium lamp is in a pair of orange lines, called the D line, and it is usually used with a yellow filter to cut out the light from a fainter pair of green lines. Sodium lamps have a fixed, rather low brightness. Mercury lamps can be obtained with a wide range of brightness. The bright, high-pressure lamps, however, give broadened spectral lines and this can cause errors. Thus for polarimetry, a low-pressure mercury lamp is required with a filter to separate out the green e line.

Fig. 16—Showing the construction of Lippich polarizer for double field.

The Saccharimeter Formerly a saccharimeter was considered to be a polarimeter graduated not in angular degrees but in relative concentration of sugar or degrees of sugar o S. However some polarimeters today have both angle and sugar scale graduations and modern automatic polarimeters can be arranged to display the rotation in any chosen unit. This applies equally whether the sample rotation is compensated by turning the analyser prism, or by placing a suitable amount of optically active substance, such as a piece of quartz, or a glass rod in a magnetic field, immediately before a fixed analyser. Therefore it seems best to describe a polarimeter with a sugar scale merely as a sugar polarimeter and to confine the term saccharimeter to an instrument which by virtue of its principle of operation should be used only on sucrose solutions. As a result, it is becoming common, therefore, to reserve the name saccharimeter for an instrument that uses quartz wedges for compensation. When a polarimeter is designed specifically for use with sucrose solutions, that is, as a saccharimeter, it becomes possible to adopt an alternative means of eliminating the ill-effects of rotatory dispersion and the need to use rather

OPTICAL INSTRUMENTS

27

low intensity spectral lamps. (When white light is used with a simple polarimeter, no extinction is obtained since different colours are rotated different amounts.) By chance, quartz has practically the same rotatory dispersion as sucrose solution. The rotation produced by the sugar is balanced out by a quartz compensator, wavelength by wavelength, and extinction can now be obtained with white light. The extinction is improved further if the blue end of the spectrum, where the dispersions match worst, is not used. The light is therefore filtered through a bichromate filter (15 mm thickness of a 6 per cent solution of potassium bichromate) or a plate of glass having similar transmittance characteristics. The quartz compensator consists of two wedges of quartz of equal angle mounted so that one can be moved past the other, as shown in Fig. 17. The pair of wedges then acts as a parallel-sided plate of quartz of adjustable

Fig. 1 7—Showing the construction of single wedge quartz compensation. I Dextrorotatory system. II Laevorotatory system.

thickness and it gives a controlled rotation to the light going through it. This rotation is never zero, since the plate formed by the two wedges can never be zero thickness. To obtain zero rotation, the wedges are "backed off" by a fixed plate of quartz of the opposite hand; i.e. if the wedges are made of left-handed quartz, this plate is right-handed. This system, known as a single-wedge compensator, is the one most commonly used in commercial saccharimeters. The optical system of a saccharimeter is shown in Fig. 18. The lens a condenses white light from a clear filament lamp, with a ground glass disc in front of it, on the aperture in b; the light is brought to a focus at the objective of the telescope by a lens c; d is the polarizer (with fixed half-shadow angle); e is a stop to limit the size of the light beam and / a glass protecting

Fig. 18—Illustrating the parts of a saccharimeter.

plate. The sugar solution under examination is contained in the cell g; h is a second protecting plate; i and m are stops for cutting out stray light; j, k, and I make up the single-wedge compensator; n is the analyser; o the objective of the viewing telescope; p a field stop in the focal plane of the eyepiece; and q and r form the eyepiece of the telescope. Two separate optical parts of the instrument are thus in dust-proof enclosures, protected from juice splashes by the optically inactive protecting glasses. The whole system is mounted in a rigid metal tube which is held horizontal on a stand. Formerly, saccharimeters were supplied for both

200 mm and 400 mm sample cells but the former has almost disappeared from the modern sugar-mill laboratory; the longer cell is needed for such solutions as bagasse extracts, which are of low optical activity. On the latest models (Fig. 19) the lamp housing is built on as an extension to the instrument so that the light source is fixed in relation to the instrument and is held in its correct position. With the Schmidt and Haensch instrument a small focusing disc is provided. This is placed at the end of the trough towards the analyser, and if the light be correctly placed, a sharp image of the filament of the lamp will coincide with the horizontal diameter marked on the disc. The ground glass disc with which the lamp is fitted should, of course, be removed when making this test. The scale is usually graduated from —30 °S through zero to +105 °S (with extended graduations at both ends), or occasionally, from —150 °S to +150 °S. The angular rotation that corresponds to 100 °S depends on the length of cell used, the normal weight specified for the instrument, and on the wavelength for which the rotation is measured.

Fig. 19—Illustrating a Schmidt and Haensch saccharimeter.

The scale is viewed through a lowpower microscope, being illuminated by some of the light that has been deflected from the main path. Two types of scale are now in common use. The type employing a vernier is illustrated in Fig. 20. It will be observed that the main scale is graduated at intervals of one degree of sugar. A centre-zero vernier is provided, one side for positive readings and the other for negative, both divided to read to 0.1 °S. In Fig. 21 is illustrated the scale employed in the current Schmidt and Haensch saccharimeter. The scale moves vertically as opposed to the former horizontal scale and the main scale is divided into 10 °S divisions. A fixed engraved scale

Fig. 20—Illustrating the double vernier scale of a saccharimeter. Reading 73.4° S.

OPTICAL INSTRUMENTS

29

Fig. 21—Direct reading scale employed in the Schmidt and Haensch saccharimeter. Reading 66.3° S.

of 10 °S subdivided into 100 divisions is also provided whereby the reading may be made directly to 0.1 °S and estimated to 0.02 °S. The zero adjustment for each scale is carried out as follows:— In the vernier type scale the field is set to the balance position with the trough empty and the zero of the vernier is adjusted, with the key provided, to the zero of the main scale. With the direct reading scale the zero on the movable scale is set to the zero on the fixed scale first and the field is then balanced for equal intensity by the knurled knob situated at the base of the analyser housing. At the balance point the two halves of the field should appear identical. The appearance of a difference in colours at the balance point, one side appearing yellowish and the other nearly white indicates the need for internal adjustment. This should not be attempted by unskilled technicians. Effect of Illumination As stated earlier, the rotatory dispersion of sucrose solution is close, but not exactly equal to that of quartz, the sugar having the greater dispersion. Since the difference in the two dispersions is greatest for blue light, the quartz-wedge saccharimeter is designed for use with white light filtered to remove the blue end of the spectrum. A movable glass filter, that approximates closely to the characteristics of a six per cent potassium bichromate solution of 15 mm thickness, is now usually built into the saccharimeter. This filter transmits red, orange, and yellow light but absorbs the rest of the spectrum; the transmitted radiation has a mean wavelength of about 6000 A. If white light is used without a filter, a saccharimeter will give readings that are in error by about +0.12 °S at the 100 °S point. Only when the solution is coloured and acts as its own filter should the filter be omitted. If a sodium lamp is used with a quartz-wedge saccharimeter, there is again a small error, now about 0.03°S at 100 °S, whether a filter is used or not. Automatic Polarimeters The modern tendency in optical measuring instruments is to replace the eye by some photoelectric detector. Such instruments do not require as highly skilled an observer and are less fatiguing to use. In addition, the

30

OPTICAL INSTRUMENTS

results obtained are more reliable and often more accurate and, being in the form of an electrical signal, can be recorded by means of the large variety of data-recording equipment now available. If calculations are made on the results, this is done by connecting in the appropriate calculating circuits and the result is obtained with very little delay. An automatic polarimeter is normally used with a flow-through cell so that samples can be readily introduced and flushed away; many installations use an automatic sample feeder which introduces samples to the instrument at regular intervals of, say, 60 seconds and actuates the read-out device. Certain instruments allow the polarisation to be recorded continuously as the sample flows through the cell. However, the precision of the measurement usually surfers seriously as a result of striations. A photoelectric polarimeter could be made by using a conventional split-field polarizer and taking the light from each half of the field to a separate photocell. At the balance point, the two electrical signals from the photocells would be equal. Such a system would give continuous d.c. signals from the photocells and would require d.c. amplifiers, which are notoriously more unreliable and more unstable than a.c. amplifiers. Modern automatic polarimeters, therefore, use a.c. balancing. Instead of a field split in space and two photocells, one photocell is used with a field "split in time". The plane of polarization changes backwards and forwards between the two positions it would have for the split field, either in jumps or continuously. The electrical signal from the photocell then consists of a d.c. background superimposed on which is an alternating current of the same frequency as that at which the polarization is being switched. This a.c. component of the signal is an error signal: it becomes zero at balance. The instrument balances itself by using the error signal to drive the balancing system; when the error signal vanishes, this drive stops. It is thus a servo-system. To oscillate the direction of polarization one of three methods is used. The first, employed by Schmidt and Haensch and also by Perkin Elmer in their automatic saccharimeters and polarimeters, uses a synchronous motor coupled to the polarising prism, which is caused to rotate backwards and forwards so that the direction of polarisation oscillates. The second, used by the National Physical Laboratory (N.P.L.) in the standard polarimeter that they use to calibrate quartz control plates and also by Jobin-Yvon, has a rotating plate, around the edge of which is a series of holes, each covered by a quartz plate. These plates are of equal thickness and alternatively left- and right-handed. As the plate rotates, these quartz plates pass in turn in front of the polarizer to give a direction of polarization that switches first to the left, then to the right. Hilger and Watts use a similar system consisting of a vibrating reed supporting and oscillating two pieces of quartz side by side, one left-handed and the other right-handed, and oscillating them across the light beam. The third method makes use of a Faraday cell and is employed by Zeiss and Jouan. It is also used in the polarimeter designed by N.P.L. which is made by Thorn Bendix. As stated earlier, if a glass rod with light passing through it is placed in a magnetic field, the field being in the direction of the light, the plane of polarization of the light is rotated by an amount that depends on the type of glass and the strength of the magnetic field. Very dense flint glasses give the largest rotation. The sense of rotation depends on the direction of the field and, if this is alternated, the rotation alternates. To give an oscillating direction of polarization the glass rod is enclosed in a solenoid through which passes an alternating current.

OPTICAL INSTRUMENTS

31

The polarimeter is balanced in one of three ways, corresponding to the above methods of modulation: Either a conventional analysing prism is rotated (Hilger and Watts, Zeiss, Perkin Elmer), or compensating quartz wedges are driven up and down (Schmidt and Haensch, Jobin-Yvon), or a d.c. Faraday cell is used as a compensator to balance the rotation due to the sample (Bendix, Jouan). The rotating analyser is turned to balance by a motor that is driven by the amplified error-signal, and the rotation can be read from an angle scale by an electrical method e.g. by using a potentiometer. In the Hilger and Zeiss instruments a digital output of the rotation in sugar degrees is obtained using a shaft encoder. The compensation quartz wedges are driven to balance by a motor in a similar fashion to the rotating analyser, and the sugar value of the rotation of the sample is read from a linear scale. (The Schmidt and Haensch instrument uses moire gratings, for example). In the Bendix polarimeter, the current in the compensating Faraday cell is a measure of the rotation. In the Hilger and Zeiss instruments, the servo motor drives the rotating analyser at a constant rate, and so the time taken to reach a balance depends on the range to be traversed: for instance if a cane juice sample reads 90 °S, the instrument will take twice as long to give a reading if the previous sample read 70 °S than if it had read 80 °S. In the Bendix instrument the balancing is done electronically, not mechanically, and equilibrium is approached at an exponentially decreasing rate. Therefore the time taken to reach balance depends only slightly on the range to be traversed. The accuracy of the final setting depends, however, on the time allowed for the equipment to reach a balance; the longer the time permitted, the higher the accuracy that can be obtained, until the instrument's limit of accuracy is reached. To be precise, the accuracy increases as the square-root of the time, so that, to double the accuracy, the instrument would take four times as long to reach a balance. The Hilger M560, Zeiss OLD 3 and Bendix-NPL 700 A automatic polarimeters have been built to comply with the Australian Standard Specification for an Automatic Sugar Polarimeter, AS K157 - 1968. Australian Standard Specification AS K157 - 1968 "Automatic Sugar Polarimeter" covers the requirements which are considered desirable for an automatic sugar polarimeter suitable for use in the analysis of cane juice and sugar products in Australian sugar factories. It was approved by the Standards Association of Australia in 1968. They have a range of —120 °S to +120 °S with a digital readout to 0.01 °S, and are suitable for cane juice, raw sugar and molasses. Most of the other commercially available automatic polarimeters are built for the European beet sugar industry, and have a range of 0 to 30 °S or 0 to 100 °S, with a readout to the nearest 0.05 °S or 0.10 °S. The Hilger and Zeiss instruments are basically automated verisons of conventional polarimeters. Their components are shown in Figs. 22 and 23, respectively. The Hilger M560 polarimeter normally uses a mercury vapour lamp and an absorption filter to provide monochromatic radiation of 546 nm. However, it can be fitted with a sodium light source. The light is linearly polarised by a calcite prism of the Lippich type. A small oscillating biplate of left- and right- rotating quartz modulates the beam, which passes through the sample, normally contained in a 200 mm tube, and on to the analyser prism and the photomultiplier. Jacketed flow-through cells are available, and the tube trough is also provided with a water jacket for more effective temperature control. The "out of balance" signal from the photomultiplier is amplified and used to drive a servo motor which rotates the analyser prism until balance is reached. The shaft of the servo motor also drives the electro-

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OPTICAL INSTRUMENTS

SCHEMATIC LAYOUT OF M560 AUTOMATIC POLARIMETER

Fig. 22—Schematic layout of Hilger M560 automatic polarimeter.

mechanical digitizer disc; this consists of a number of miniature commutator type brushes which touch contacts on an opposing fixed disc. This instrument is not being commercially produced. The Zeiss OLD 3 polarimeter uses a mercury spectral lamp and an interference double-band filter for a wavelength of 546 nm. The light is polarised by a prism of the Glan-Thompson type, and then passes through a Faraday modulation coil. The modulator rod is made of special stress-free glass, 50 mm long; the modulation is at 50 Hz and the angle is about ± 2 ° at

Fig. 23—Diagram of Zeiss OLD digital polarimeter.

OPTICAL INSTRUMENTS

33

546 nm. The modulated beam then passes through a sample cell, 98.13 mm long; this length being chosen so that 100 °S is equivalent to 20° of angle. Jacketed flow-through cells are available, and the sample space is also provided with a water jacket for more effective temperature control. From the cell the light passes through the analyser prism to the photomultiplier. The Zeiss is a full circle polarimeter; the analyser is permanently coupled to an analogue-digital convertor (shaft encoder) with 5 decades and a transmitting potentiometer. The two decades representing the most significant figures (tenths and hundredths of a sugar degree) are photoelectric: the other three decades are electro-mechanical with suitable reduction by epicyclic gears. The components of the Bendix-NPL polarimeter are shown in Fig. 24. Since the instrument uses a magnetic field to give the balance, it is itself sensitive to the earth's magnetic field and, if horizontal, the reading given

Fig. 24—Diagram of Bendix-NPL automatic polarimeter Type 700.

would change if the instrument were turned around on a table. It is therefore made upright so that it always stands vertical at a constant angle to the earth's field (at one place). In addition it is made of non-ferrous metals. It should be kept away from large pieces of iron or steel during use since, if these are moved near it, the field through the Faraday compensation coil could be changed in the middle of a measurement. Road traffic closer than 15 ft may also affect the reading. The light source, a filament lamp with a stabilized electrical supply, is at the top. This light is passed through an interference filter to give a band of mean wavelength corresponding to the mercury e line (546 nm), with a band width at 50 per cent transmission of about 20 nm. An interference filter can be fitted to give a mean wavelength corresponding to the sodium D line (589 nm). The light then passes through two stops and a condenser lens, which control the beam size, the polarizer (a sheet polarizer), and the first Faraday cell (the modulator cell). An alternating current through the coil of this cell provides the required oscillation of the direction of polarization

34

OPTICAL INSTRUMENTS

about the direction given by the polarizer. A modulation frequency of 380 Hz is chosen because it is not harmonic with either 50 Hz or 60 Hz. Below this Faraday cell is the compartment for the sample cell. This is much shorter than those used with visual polarimeters and saccharimeters. The Faraday cell type of automatic polarimeter is much more precise than the visual type instrument for the measurement of angle; it can therefore use a shorter sample and still achieve the same precision in terms of the sugar scale. The shorter cell is really forced on the instrument; a large range of rotations cannot be covered because of the limitation in rotation imposed by the Faraday compensator cell. Below the sample chamber is the compensator which is followed in turn by the fixed analyser and photomultiplier. The polariser and analyser are normally in the crossed position, and when modulation is applied the intensity of light reaching the photomultiplier varies sinusoidally. In one period of oscillation the plane of polarisation passes twice through the null position, and the light intensity at the photomultiplier therefore has a frequency of 760 Hz. The output signal from the photomultiplier includes a 760 Hz inbalance component, and a 380 Hz out-of-balance component when a sample is introduced. The signal is fed to the input of a selective amplifier in the electronic unit. The amplifier only accepts a narrow band of frequencies centred on 380 Hz. After passing through a phase sensitive detector, followed by rectification and amplification, the out-of-balance signal is fed back to the Faraday compensator cell until null balance is restored. The current in the compensator is then a measure of the rotation, which can be read from a meter on the electronic unit, recorded on a separate chart recorder, or fed to and displayed on a digital voltmeter from which a print-out or punch-out can be obtained. The small Bendix Model 143 C polarimeter covers a range of rotations of ±.5° and has a sensitivity of 0.0001°. Thus, if the sample cell were 2 mm thick only, it would allow measurements on solutions up to about 120 °S (with the mercury e line) to an accuracy of about 0.025 °S; such a thin cell is very difficult to make accurately. The angular range has been increased in the large Model 700 A polarimeter by providing water cooling on the compensator cell so that larger currents can be used without generating too much heat, and ±.5° of rotation is covered. In use, the amplifier must be switched on at least 30 minutes before use, so that it can stabilize. When used frequently, it should be left on continuously, that is 24 hours a day seven days a week. With each set of readings, it is advisable to check the zero of the instrument with the sample cell containing distilled water. The coarse adjustment to the zero is done by rotating the polarizer. An additional Faraday cell between the compensator and the analyser allows fine control of the zero to be made electrically (see Fig. 24). Effects of Birefringence As stated earlier, materials such as glass become doubly refracting if they are strained. If linearly polarized light passes through such strained glass, it may come out elliptically polarized. If it is now followed by an analyser, the intensity seen varies as the analyser is rotated, but it no longer drops to zero at any position; the extinction is only partial, not complete. At the position of minimum intensity, the analyser is crossed with the direction of the longer axis of the ellipse of polarization. This may not be in the same direction as the original linear polarization, so that the strained glass

OPTICAL INSTRUMENTS

35

has this the and

i n t r o d u c e d a n e r r o r i n t o t h e m e a s u r e m e n t . I t i s n o t possible t o e l i m i n a t e e r r o r b y r e - a d j u s t i n g t h e z e r o o f t h e p o l a r i m e t e r since t h e d i r e c t i o n o f ellipse a n d h e n c e t h e e r r o r c a n c h a n g e w h e n t h e s a m p l e i s i n t r o d u c e d rotates the polarization. T h e s e e r r o r s d u e t o birefringence c a n b e c a u s e d b y s t r a i n e d glass i n t h e e n d p l a t e s o f t h e s a m p l e cells o r i n o t h e r p r o t e c t i v e p l a t e s b e t w e e n t h e polarizer a n d t h e analyser. In visual polarimeters a n d saccharimeters t h e y a r e n o t u s u a l l y l a r g e e n o u g h t o b e serious, b u t i n a u t o m a t i c p o l a r i m e t e r s , w h e r e t h e a c c u r a c y o f angle m e a s u r e m e n t m u s t b e g r e a t e r t o allow for t h e s h o r t e r s a m p l e , t h e y c a n b e significant. T h e e r r o r s i n t e r a c t s o t h a t s t r a i n i n glass p l a t e s before a n d after t h e c o m p e n s a t i o n cell c a n g i v e rise t o t w o sets o f e r r o r s , o n e fixed, t h e o t h e r d e p e n d i n g o n t h e s a m p l e . T o a v o i d birefringence e r r o r s i n a u t o m a t i c p o l a r i m e t e r s , n o t o n l y m u s t all glass u s e d b e v e r y well a n n e a l e d , b u t i t m u s t also b e m o u n t e d w i t h o u t s t r a i n a n d c l e a n e d c o r r e c t l y ; w i p i n g w i t h a c i r c u l a r m o t i o n i n t r o d u c e s less b i r e f r i n g e n c e t h a n w i p i n g always in the one direction. Standardization of Polarimeters J u s t as t h e reading of a refractometer is checked periodically by m a k i n g a m e a s u r e m e n t on a t e s t piece, a p o l a r i m e t e r s h o u l d be c h e c k e d r e g u l a r l y w i t h a s t a n d a r d of k n o w n r o t a t i o n . F o r v i s u a l p o l a r i m e t e r s , t h i s is a q u a r t z c o n t r o l p l a t e , a p l a t e of q u a r t z of k n o w n r o t a t i o n m o u n t e d in a t u b e t h a t f i t s i n t o t h e p o l a r i m e t e r i n p l a c e o f t h e s a m p l e cell. T h e s e c o n t r o l p l a t e s a r e n o r m a l l y m a d e close t o 2 5 °S, 5 0 °S, 7 5 ° S a n d 100 ° S a n d t h e l a s t t w o a t least s h o u l d b e a v a i l a b l e for use. T h e q u a r t z c o n t r o l p l a t e s a r e t h e m s e l v e s checked by a standardizing laboratory. In Australia, t h e recognized standardizing laboratories are the National S t a n d a r d s L a b o r a t o r y a n d those registered by t h e N a t i o n a l Association of Testing Authorities.

Q u a r t z p l a t e s a r e n o r m a l l y u s e d t o s t a n d a r d i z e t h e H i l g e r a n d Zeiss a u t o m a t i c p o l a r i m e t e r s . T h e a c c u r a c y r e q u i r e d for B e n d i x p o l a r i m e t e r s i s s o h i g h t h a t q u a r t z c o u l d n o t , i n t h e p a s t , b e g r o u n d a n d p o l i s h e d sufficiently flat a n d p a r a l l e l for v a r i a t i o n s o f r o t a t i o n t o b e negligible. T h e N a t i o n a l P h y s i c a l L a b o r a t o r y ( L o n d o n ) h a s recently- o v e r c o m e t h e s e p r o b l e m s , a n d have a suitable plate available. The International Sugar Scale A t t h e 1932 m e e t i n g o f t h e I n t e r n a t i o n a l C o m m i s s i o n for U n i f o r m M e t h o d s o f S u g a r A n a l y s i s , t h e following r e s o l u t i o n s w e r e a g r e e d t o : — (1) T h a t t h e C o m m i s s i o n a d o p t a s t a n d a r d scale for t h e s a c c h a r i m e t e r a n d t h a t t h e scale b e k n o w n a s t h e " I n t e r n a t i o n a l S u g a r S c a l e " . R o t a t i o n s e x p r e s s e d i n t h i s scale shall b e d e s i g n a t e d a s d e g r e e s s u g a r (°S). (2) T h a t t h e p o l a r i z a t i o n of t h e n o r m a l s o l u t i o n (26.000 g of p u r e s u c r o s e d i s s o l v e d i n 100 m l . , a n d p o l a r i z e d a t 2 0 ° C i n a 2 0 0 m m t u b e , u s i n g w h i t e light a n d t h e d i c h r o m a t e filter a s defined b y t h e C o m m i s sion) b e a c c e p t e d a s t h e b a s i s o f c a l i b r a t i o n o f t h e 100° p o i n t o n t h e I n t e r n a t i o n a l S u g a r Scale. (3) T h a t t h e following r o t a t i o n s s h a l l h o l d for t h e n o r m a l q u a r t z p l a t e of the International Sugar Scale:— N o r m a l Q u a r t z P l a t e = 100 °S = 4 0 . 6 9 0 ° ± 0 . 0 0 2 ° (A = 5461 A) at 20°C N o r m a l Q u a r t z P l a t e = 100 °S = 3 4 . 6 2 0 ° ± 0 . 0 0 2 ° (A = 5892.5A) at 20°C T h i s definition o f t h e " I n t e r n a t i o n a l S u g a r S c a l e " d o e s n o t h o w e v e r m a k e mention of t h e rotations of t h e normal sugar solution, at t h e n o r m a l

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OPTICAL INSTRUMENTS

Fig. 25—Polarimeter tubes, a

Fig. 25 b

Fig. 25 c

Fig. 25 Id

Fig. 25 lid

Temperature Effects. When a sugar solution is made up and polarized at temperatures other than 20 °C, the reading obtained will be influenced by the temperature difference on the instrument, the apparatus used and the substance in solution. Therefore the reading obtained must be corrected to 20 °C to give the true polarization in °S of the solution under consideration and in addition this corrected polarization reading must be corrected further if the solution was not made up at 20 °C. R. A. M. Wilson (1965) of the Colonial Sugar Refining Coy. Ltd. has classified the corrections for temperature effects into the "polarization reading

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OPTICAL INSTRUMENTS

Tr

= T e m p e r a t u r e of s o l u t i o n or q u a r t z p l a t e w h e n r e a d i n g t h e p o l a r i z a t i o n (°C) N = N o r m a l i t y of s o l u t i o n . A n o r m a l s o l u t i o n c o n t a i n s 26g of s a m p l e in 100 m l 5 = W e i g h t p e r c e n t s u c r o s e in t h e s a m p l e R = W e i g h t p e r c e n t r e d u c i n g s u g a r in t h e s a m p l e Tp = T e m p e r a t u r e of p o l a r i m e t e r (°C) Tm = T e m p e r a t u r e of s o l u t i o n w h e n m a k i n g to t h e m a r k (°C) T] = C o n s t a n t e q u a l to 1 for q u a r t z w e d g e s a c c h a r i m e t e r s a n d e q u a l to 0 for o t h e r t y p e s of p o l a r i m e t e r s a n d s a c c h a r i m e t e r s F o l l o w i n g on t h e w o r k of W i l s o n a n d a s u b m i s s i o n to I C U M S A in 1966 b y t h e A u s t r a l i a n N a t i o n a l C o m m i t t e e o f I C U M S A , t h e following simplified f o r m u l a e w e r e a d o p t e d a s u s u a l l y sufficient for t e m p e r a t u r e c o r r e c t i o n s t o t h e p o l a r i z a t i o n o f r a w s u g a r . F o r o t h e r p r o d u c t s , for q u a r t z c o n t r o l p l a t e s a n d for h i g h p r e c i s i o n w o r k , a p p r o p r i a t e f o r m u l a e m a y b e o b t a i n e d b y suitable combination of the equations above. F o r quartz wedge saccharimeters the temperature correction to be m a d e t o t h e observed polarization shall b e : — (t r — 20) (0.00033 S — 0.004 R) where t r (°C) is t h e t e m p e r a t u r e of t h e s o l u t i o n as r e a d in t h e s a c c h a r i m e t e r S is t h e a p p r o x i m a t e per cent sucrose in t h e s a m p l e R i s t h e a p p r o x i m a t e p e r c e n t r e d u c i n g s u g a r s (as i n v e r t s u g a r ) i n the sample. For sugar polarimeters (without q u a r t z wedge compensation) the correct i o n t o b e m a d e t o t h e o b s e r v e d p o l a r i z a t i o n s h a l l be:-— (tr — 20) (0.00019 5 — 0.004 R) w h e r e t h e s y m b o l s a r e a s defined a b o v e . For accurate work it is desirable t h a t control of t e m p e r a t u r e to 20.0-^ 0.5 °C be o b t a i n e d for all p o l a r i m e t r i c a n a l y s e s of n o r m a l s u g a r s o l u t i o n s t h u s eliminating a n y major t e m p e r a t u r e corrections. I C U M S A h a s r e c o m m e n d e d t h a t for t h e p o l a r i z a t i o n o f r a w s u g a r t h e t e m p e r a t u r e of p o l a r i z a t i o n s h a l l be as close to 2 0 . 0 °C as p o s s i b l e a n d in a n y case i t shall n o t b e o u t s i d e t h e r a n g e 1 5 t o 2 5 °C. The Spectrophotometer Q u a n t i t a t i v e m e a s u r e m e n t s based on t h e colour of solutions h a v e been e m p l o y e d b y c h e m i s t s for m a n y y e a r s . T h e s e m e a s u r e m e n t s , w h i c h a r e covered by t h e general t e r m colorimetric analysis, m a y be carried out in a n u m b e r of different w a y s . T h e simplest m e t h o d s of colorimetric analysis are visual methods, which m a y i n v o l v e m a t c h i n g of an u n k n o w n c o l o u r w i t h a series of s t a n d a r d c o l o u r s , d i l u t i o n of an u n k n o w n colour in a p a r a l l e l - s i d e d t u b e u n t i l it m a t c h e s a t u b e filled w i t h a s t a n d a r d c o l o u r a n d t h e n c a l c u l a t i n g t h e s t r e n g t h o f t h e u n k n o w n s o l u t i o n from t h e h e i g h t s of t h e l i q u i d s in t h e t u b e s , or by t h e use of a colour c o m p a r a t o r s u c h a s t h e D u b o s c q . A m o r e a d v a n c e d f o r m o f c o l o u r m e a s u r e m e n t i s o n e w h e r e t h e h u m a n e y e i s r e p l a c e d b y a p h o t o e l e c t r i c cell, t h u s largely eliminating t h e errors due to t h e personal characteristics of each observer. I n s t r u m e n t s based on this principle are k n o w n as photoelectric

OPTICAL INSTRUMENTS

41

colorimeters, or, more correctly, photoelectric absorptiometers. These instruments usually employ light consisting of a comparatively narrow range of wavelengths, and this is achieved by passing white light through filters. The most modern instruments employed for colorimetric analysis operate with light of a definite wavelength, with a very narrow band-width, and these instruments are called spectrophotometers. A spectrophotometer, as its name implies, is a combination of a spectrometer and a photometer. The spectrometer portion of the instrument provides light of any selected colour, by employing a prism or a diffraction grating, and is usually termed a monochromator, while the photometer portion of the instrument measures the intensity of the monochromatic light produced. The spectrophotometer most commonly in use in Queensland mills is the Bausch and Lomb Spectronic 20, which is shown in Fig. 26. A schematic diagram of the optical system of this instrument is shown in Fig. 27. The

Fig. 26—The Spectronic 20, Bausch and Lomb

operation of the instrument is as follows:—White light emanating from the tungsten lamp passes through the entrance slit, being focused by the field lens onto the objective lens. The objective lens is of such a focal length as to focus an image of the entrance slit at the exit slit, the reflection-type diffraction grating being interposed before the exit slit in order to reflect and

Fig. 27—Schematic optical diagram of Spectronic 20.

42

OPTICAL INSTRUMENTS

d i s p e r s e t h e light. T o o b t a i n t h e v a r i o u s w a v e l e n g t h s a t t h e e x i t slit, t h e grating is rotated, by m e a n s of an a r m which rides on t h e wavelength cam. In setting the wavelength, the cam rotates t h e grating so t h a t light of t h e d e s i r e d w a v e l e n g t h p a s s e s o u t t h r o u g h t h e e x i t slit. T h i s m o n o c h r o m a t i c l i g h t w h i c h p a s s e s t h r o u g h t h e e x i t slit c o n t i n u e s o n t h r o u g h w h a t e v e r sample m a y be contained in a test t u b e or c u v e t t e placed in t h e light p a t h , a n d finally t e r m i n a t e s a t t h e m e a s u r i n g p h o t o t u b e , w h e r e t h e l i g h t e n e r g y i s c o n v e r t e d i n t o a n electric signal. W h e n e v e r t h e s a m p l e i s r e m o v e d f r o m t h e i n s t r u m e n t , a n o c c l u d e r a u t o m a t i c a l l y falls i n t o t h e l i g h t b e a m s o t h a t t h e zero m a y b e set w i t h o u t f u r t h e r m a n i p u l a t i o n . A l i g h t c o n t r o l i s also p r o v i d e d in order t h a t t h e i n s t r u m e n t m a y be set at zero absorbance with a b l a n k or reference s o l u t i o n i n t h e s a m p l e c o m p a r t m e n t . V a r i o u s o t h e r s p e c t r o p h o t o meters are available, some with a wider range of light wavelengths t h a n is o b t a i n a b l e w i t h t h e S p e c t r o n i c 20, b u t all w o r k o n t h e s a m e p r i n c i p l e o f a p r i s m or diffraction g r a t i n g m o n o c h r o m a t o r p r o v i d i n g a s o u r c e of m o n o c h r o m a t i c light for a light s e n s i t i v e p h o t o t u b e . A c t u a l l y , t o refer t o t h e s e instruments in terms of "light" is rather misleading, because even the simple S p e c t r o n i c 2 0 i n s t r u m e n t h a s a scale r a n g e f r o m 3 2 5 n m ( t h e u l t r a v i o l e t region) u p t o 9 7 5 n m , w h i c h i s well i n t o t h e i n f r a - r e d r e g i o n .

Colorimetry The operation of such instruments for colour determination is relatively simple, but several points must be borne in mind, in the interests of accuracy. Firstly, for the instrument to be stable, the light output from the lamp must be constant. This requires a stable power supply, and voltage stabilizers may have to be installed to ensure this, or in some instances battery operation of the lamp must be reverted to in order to overcome line voltage variations. Secondly, for accurate results, scrupulous cleanliness must be practised with the handling of the delicate and expensive glass cuvettes used as sample containers, and, whenever possible, these cuvettes should be kept in their matched sets. This last factor will avoid errors caused by standardization of the instrument with a blank in one cuvette and reading the unknown in another cuvette which does not have a precisely equal cell width. When using spectrophotometers for colour measurement the manufacturer's instructions should, of course, be adhered to, but the procedure basically consists of setting the wavelength to that specified for the determination, setting the zero of the instrument, setting the optical density to zero with a blank solution as sample, and then reading the optical density of the unknown sample. The concentration of the unknown solution is then read off a standard graph prepared from solutions of known concentration. Turbidity Measurement Spectrophotometers are also used to measure the turbidity of such mill products as clarified juice. For this determination the wavelength is set to 975 nm, well into the infra-red region, to avoid the effect of juice colour, and the amount of "light" absorbed, read as an optical density, gives a measure of turbidity. For convenience, turbidity is usually recorded as one hundred times the optical density. The Microscope In sugar factory operations the most important use of the microscope is for the examination of proof samples withdrawn from vacuum pans and for the determination of the sizes of crystals in sugar, massecuite, magma, seed, etc. For these purposes a comparatively low order of magnification is required. The microscope also enters essentially into the determination of saturation temperature by the optical method and has numerous other casual

OPTICAL INSTRUMENTS

ACTUAL PATH OF LIGHT. RAY PATH OF VIRTUAL IMAGE.

i Fig. 28—The essential parts of a microscope.

43

44

OPTICAL INSTRUMENTS

uses for w h i c h a fairly h i g h d e g r e e of m a g n i f i c a t i o n is r e q u i r e d . H e n c e , w h i l s t t h e p r o v i s i o n of a s i m p l e low p o w e r e d m i c r o s c o p e for u s e on t h e p a n s t a g e is u n i v e r s a l l y a c c e p t e d , t h e r e is also n e e d for a m o r e v e r s a t i l e i n s t r u m e n t of b e t t e r q u a l i t y for l a b o r a t o r y use. The Structure and Operation of the Microscope T h e e s s e n t i a l p a r t s of t h e t y p e of m i c r o s c o p e in g e n e r a l u s e in t h e laboratory are illustrated in Fig. 28. T h e h e a v y b o x of cast metal A s u p p o r t s a s h o r t rigid u p r i g h t pillar B to w h i c h t h e a r m or l i m b D is h i n g e d at C. T h e a r m w h i c h i s c o n v e n i e n t l y c u r v e d for e a s y g r a s p i n g b y t h e h a n d w h e n t h e m i c r o s c o p e h a s t o b e m o v e d f r o m p l a c e t o p l a c e , i s also o f h e a v y m e t a l a n d t h e h i n g e C s h o u l d allow o n l y a stiff m o v e m e n t in a v e r t i c a l p l a n e a n d no m o v e m e n t whatsoever sideways. At the upper end the a r m bears the t u b u l a r b o d y E , w h i c h carries t h e m a g n i f y i n g lenses, a n d j u s t n e a r t h e h i n g e t h e s t a g e F i s r i g i d l y a t t a c h e d t o it. B e n e a t h t h e s t a g e a n d fitted t o i t i s t h e condenser G, commonly known as the substage condenser, a n d below t h a t t h e d o u b l e m i r r o r H , w h i c h i s flat o n o n e side a n d c o n c a v e o n t h e o t h e r . M o v e m e n t o f t h e b o d y d o w n to, a n d u p from, t h e s t a g e i s p r o v i d e d b y a coarse a d j u s t m e n t o p e r a t e d b y t u r n i n g t h e milled h e a d I a n d a fine a d j u s t m e n t working t h r o u g h a smaller head J. At t h e t o p t h e tubes of most microscopes are fitted w i t h a g r a d u a t e d d r a w t u b e s o t h a t t h e d i s t a n c e b e t w e e n t h e eye-piece K a n d t h e nose-piece M in w h i c h t h e o b j e c t i v e s N are m o u n t e d , c a n b e v a r i e d t o suit t h e r e c o m m e n d a t i o n s o f t h e m a n u f a c t u r e r o f t h e lenses. T h e eye-piece fits easily i n t o t h e t o p o f t h e t u b e . T h e o b j e c t i v e s d o n o t lit d i r e c t l y i n t o t h e t u b e , b u t a r e s c r e w e d i n t o a r e v o l v i n g p l a t e called t h e nosepiece. T h i s m a y h o l d from o n e t o four o b j e c t i v e s . F o r p u r e l y r o u t i n e use a t t h e o n e m a g n i f i c a t i o n a s i n g l e - o b j e c t i v e nose-piece is q u i t e s u i t a b l e , b u t w h e n a r a n g e of m a g n i f i c a t i o n is r e q u i r e d t h e m u l t i - o b j e c t i v e nose-piece is e s s e n t i a l in t h a t it allows t h e r e a d y c h a n g i n g of o b j e c t i v e s w i t h o u t risk of damage to the object a n d with a m i n i m u m of delay. The substage condenser is n o t n e c e s s a r y w i t h l o w - p o w e r o b j e c t i v e s (when t h e c o n c a v e side of t h e m i r r o r p e r f o r m s t h e s a m e f u n c t i o n ) , b u t i t i s e s s e n t i a l for h i g h - p o w e r o b j e c t i v e s w h i c h m u s t h a v e a c o n c e n t r a t e d b e a m o f i n t e n s e light. T h e c o n d e n s e r m u s t b e u s e d o n l y w i t h t h e p l a n e m i r r o r , o t h e r w i s e i t loses m u c h of its efficiency. T h e r a c k a n d p i n i o n g e a r O is u s e d for m o v i n g t h e c o n d e n s e r u p a n d d o w n a n d t h e r e i s u s u a l l y s o m e p r o v i s i o n for s w i n g i n g t h e c o n d e n s e r o u t o f t h e o p t i c a l axis w h e n n o t r e q u i r e d . T h e v e r t i c a l m o v e m e n t o f t h e c o n d e n s e r i s v e r y i m p o r t a n t b e c a u s e t h e s y s t e m o f lenses f o r m i n g t h e c o n d e n s e r h a s to be focused j u s t as carefully as t h e o b j e c t i v e s if a h i g h q u a l i t y i m a g e o f t h e o b j e c t i s t o b e o b t a i n e d . T h e iris d i a p h r a g m P u s e d t o r e g u l a t e t h e a m o u n t o f light c o m i n g i n t o t h e c o n d e n s e r , i s a n i n t e g r a l p a r t of it a n d is o p e r a t e d by a s m a l l l e v e r facing t o w a r d s t h e front of t h e i n s t r u m e n t . General Principle of Operation: By s u i t a b l e p o s i t i o n i n g of t h e m i r r o r in r e l a t i o n t o t h e c o n d e n s e r a n d t h e s o u r c e o f light, r a y s o f light a r e reflected from i t a n d i n t o t h e c o n d e n s e r w h e r e t h e y a r e c o n c e n t r a t e d i n t o a m o r e intense b e a m a n d so pass through the object under examination. This is m o u n t e d on a glass slide, u s u a l l y m e a s u r i n g 3 x 1 in h e l d firmly by s p r i n g clips t o t h e s t a g e , a n d for s a t i s f a c t o r y e x a m i n a t i o n s h o u l d b e e i t h e r c o m p a r a t i v e l y t r a n s p a r e n t , o r consist o f s m a l l p a r t i c l e s s e p a r a t e d b y clear liquid. T h e light p a s s i n g t h r o u g h t h e m o u n t e d o b j e c t e n t e r s t h e o b j e c t i v e , t h e f u n c t i o n of w h i c h is to form an e n l a r g e d i m a g e of t h e o b j e c t for f u r t h e r m a g n i f i c a t i o n b y t h e eye-piece. T h e front lens o f t h e e y e collects t h e light r a y s c o m i n g t h r o u g h t h e eye-piece a n d p r o j e c t s a n i m a g e o n t h e r e t i n a w h i c h t h e b r a i n r e c o r d s a s a n o b j e c t s i t u a t e d a b o u t 1 0 i n a w a y from t h e e y e . T h e a c t u a l p i c t u r e seen by l o o k i n g d o w n a m i c r o s c o p e is in r e v e r s e a n d if o n e

OPTICAL INSTRUMENTS

45

wishes to move an object from, say, the left edge of the field of view to the centre, one must move the stage (and slide) from right to left and not left to right. The same reversal, of course, occurs for other movements also. Lenses and Magnification: The objectives are the most important components of the microscope since on their perfection depends the efficiency of the instrument. They each consist of a series of lenses in a brass cylinder and are made to give various degrees of magnification: the higher the magnification the more lenses have to be incorporated, and so the more expensive the objectives become. The lower powered objectives are known as "dry" lenses, but objectives giving a magnification of 80 of more are always "oil immersion", i.e., they can only operate when a film of special oil, having a refractive index the same as glass, makes contact with both the front of the lens and the top of the glass slip covering the object. Oil immersion lenses represent the peak of the lens maker's skill and are essential for critical work at high magnifications, but they are quite unnecessary for practical sugarhouse control, and the special conditions for their satisfactory use will not be considered here. Two types of dry lens are obtainable, viz., achromatic and apochromatic. The aprochromats are more corrected for colour errors inherent in any glass magnification system, but their advantage is only apparent in critical work at the higher magnifications and for the practical requirements of a sugar mill the much cheaper achromats are quite suitable. Objectives are designated by a number—expressed in inches or millimetres, and engraved on the objective—which represents the "focal length" of the particular lens and indicates its magnifying power. The common objectives are the 2/3 in (16 mm) or lower power, the 1/6 in (4 mm) or high power and the 1/12 in (2 mm) which is an oil immersion. The focal length is measured from a point within the objective so that when the object is in focus the distance between it and the front lens of the objective is always less than the focal length. This reduced distance is called the working distance of the lens and becomes quite an important factor in the use of supersaturation apparatus. The table below shows the approximate magnification obtained with various objectives and eye-pieces: Objective focal length

Objective or initial | magnification

in

mm

2/3

16

1/3

8 4 2

1/6 1/12

!

!

Final magnification x 6 eye- piece

10 20 40 80

!

60 120 240 480

| X 10 eye-piece 100 200 400 800

An objective is always designed to be used with a certain tube length, usually 160 mm, but objectives for a 200 mm length are also obtainable. Increasing the tube length by withdrawing the sliding drawtube L increases the magnification of the object, but it does not increase the amount of detail that can be seen; in other words, the resolution, which is a function of the objective alone, is not altered. Like the objectives the eye-pieces are also compound lenses. Their function is to pick up the enlarged image of the object formed by the objective and magnify it still further. The total magnification thus obtained is the product of the objective magnification multiplied by the eye-piece magnification. Eye-pieces are made with various powers of

46

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m a g n i f i c a t i o n ; x 6 a n d X 10 a r e t h e m o s t c o m m o n , b u t for c e r t a i n w o r k i n t h e mill i t m a y b e d e s i r a b l e t o o b t a i n o n e w i t h a h i g h e r m a g n i f i c a t i o n . The a d v a n t a g e of t h e high magnification in t h e eye-piece c o m p a r e d w i t h t h a t obtained with a higher powered objective a n d a low power eye-piece is t h a t w i t h t h e former a r r a n g e m e n t t h e w o r k i n g d i s t a n c e i s m u c h t h e g r e a t e r . Source of Light: W h i l e o r d i n a r y d a y l i g h t , n o t d i r e c t s u n l i g h t , is often u s e d as a s o u r c e of i l l u m i n a t i o n for m i c r o s c o p i c w o r k , artificial l i g h t is g r e a t l y t o b e preferred. I t s use allows t h e g e n e r a l l i g h t i n g i n t h e r o o m t o b e r e d u c e d t o a c o m f o r t a b l e level for m i c r o s c o p e w o r k a n d s o e x t r a n e o u s a n n o y i n g g l a r e c a n b e e l i m i n a t e d . I t also gives t h e o p e r a t o r c o m p l e t e c o n t r o l o v e r t h e i n t e n s i t y o f t h e i l l u m i n a t i o n a n d allows t h e m i c r o s c o p e t o b e s i t e d w h e r e v e r convenient. There are various types of microscope lamps on t h e m a r k e t , some of t h e m very expensive, b u t a cheap a n d quite satisfactory l a m p can be easily m a d e b y m o u n t i n g a b u l b , p r e f e r a b l y w i t h p e a r l glass, i n a s m a l l b o x o r t i n . S o m e v e n t i l a t i o n i s n e c e s s a r y a n d t h e light s h o u l d c o m e o u t t h r o u g h a piece of g r o u n d glass s e t at t h e s a m e level as, or s l i g h t l y below, t h e f i l a m e n t of t h e b u l b . A s m a l l h o o d a r o u n d t h e g r o u n d glass will confine t h e light to a b e a m not m u c h wider t h a n the microscope mirror. Operation: T h e m i c r o s c o p e m u s t be set on a firm t a b l e or b e n c h at a c o m f o r t a b l e h e i g h t for t h e o p e r a t o r , a n d v i b r a t i o n f r o m m a c h i n e r y , p e o p l e w a l k i n g o n t h e floor, e t c . , e l i m i n a t e d a s far a s possible. A n eye-piece a n d t h e objectives having been placed in position, t h e operator p u t s the microscope s q u a r e l y i n front o f h i m w i t h t h e m i r r o r facing d i r e c t l y t o w a r d s t h e s o u r c e o f light. T h e d i a p h r a g m P i s o p e n e d t o i t s fullest e x t e n t a n d t h e p l a n e m i r r o r a d j u s t e d s o t h a t t h e m a x i m u m a m o u n t o f l i g h t i s reflected t h r o u g h t h e c o n d e n s e r a n d t h e w h o l e field of v i e w is i l l u m i n a t e d as e v e n l y as possible. I t i s c o n v e n i e n t a t t h i s j u n c t u r e t o focus a n o b j e c t o n a slide w i t h t h e low p o w e r o b j e c t i v e e v e n t h o u g h t h e light m a y n o t b e s a t i s f a c t o r y . When bringing an object into focus never rack the tube downwards with the eye looking through the eye-piece; always rack down carefully as close to the object as possible with the eye on a level with the stage and then rack upwards until the object is in focus. M a n y e x p e n s i v e lenses a n d i r r e p l a c e a b l e o b j e c t s h a v e b e e n r u i n e d b y failure t o o b e y t h i s s i m p l e rule. W i t h t h e o b j e c t i n focus t h e c o n d e n s e r i s t h e n b r o u g h t i n t o focus also. T h i s i s d o n e b y m o v i n g t h e c o n d e n s e r u p w a r d s t o w a r d s t h e slide a n d c o n c u r r e n t l y m o v i n g t h e m i r r o r s l i g h t l y from t i m e t o t i m e u n t i l t h e edge o f t h e l a m p or t h e filament of t h e b u l b or, if d a y l i g h t is b e i n g used, a p o r t i o n of t h e w i n d o w f r a m e o r a m a r k o n t h e w i n d o w glass, c o m e s i n t o view. T h i s i m a g e is t h e n m a d e to disappear by m o v i n g t h e condenser d o w n w a r d s slightly, a n d t h e illumination restored to its previous uniformity by m a n i p u l a t i o n of the mirror. The condenser is then transmitting t h e m a x i m u m a m o u n t of light, w h i c h i n g e n e r a l will b e t o o m u c h for u s e w i t h t h e low p o w e r s a n d s h o u l d be r e d u c e d by use of t h e d i a p h r a g m , or a screen of g r o u n d or c o l o u r e d glass i n s e r t e d b e t w e e n t h e s o u r c e o f light a n d t h e m i r r o r . T h e coarse a d j u s t m e n t i s o p e r a t e d b y t h e m i l l e d h e a d s I a n d i s all t h a t i s n e c e s s a r y for t h e lower p o w e r s . F o r t h e h i g h e r p o w e r s t h e fine a d j u s t m e n t / i s n e c e s s a r y t o b r i n g t h e o b j e c t i n t o s h a r p focus. T h e low p o w e r o b j e c t i v e s h o u l d a l w a y s be e n g a g e d first a n d s h o u l d it be d e s i r e d to v i e w a s e c t i o n of t h e field i n g r e a t e r d e t a i l , t h e s e c t i o n i s m o v e d i n t o t h e c e n t r e o f t h e field, a n o b j e c t i v e o f h i g h e r p o w e r t u r n e d i n t o p o s i t i o n , a n d t h e focus carefully a d j u s t e d . T h e l o w p o w e r i s t h e r e c o n n a i s s a n c e lens a n d t h e e x a m i n a t i o n o f a n y o b j e c t s h o u l d c o m m e n c e w i t h t h i s before u s i n g t h e h i g h e r p o w e r . O b j e c t s m o u n t e d on t h e u s u a l 3 X 1 i n c h g l a s s slides m a y b e s t be o b s e r v ed by s u b m e r g i n g t h e m in a t h i n film of a colourless l i q u i d a n d c a r e f u l l y p l a c -

OPTICAL INSTRUMENTS

47

ing a coverslip over t h e whole. F o r pan-stage observations w i t h v e r y low p o w e r s , e.g., i n c h focal l e n g t h l e n s m a g n i f y i n g four t i m e s , a c o v e r s l i p is n o t n e c e s s a r y , b u t c r y s t a l s a r e seen m u c h m o r e c l e a r l y i f m o u n t e d i n a c o u p l e o f d r o p s o f a s a t u r a t e d s o l u t i o n o f refined s u g a r . M a s s e c u i t e s m a y b e t h i n n e d d o w n for e x a m i n a t i o n b y m i x i n g w i t h a d r o p o f t h e s a t u r a t e d s o l u t i o n . B l a c k circular air bubbles m a y interfere with t h e observation of some preparations, b u t a d r o p o f a l c o h o l e i t h e r n e a t o r s u g a r - s a t u r a t e d will u s u a l l y c a u s e t h e m to disappear. Direct Measurement of Objects: It is f r e q u e n t l y d e s i r e d to m e a s u r e accurately t h e dimensions of an object u n d e r t h e microscope. It is manifestly i m p o s s i b l e t o p l a c e a fine r u l e r i n t h e s a m e field a n d m a k e d i r e c t r e a d i n g s a s o n e w o u l d d o w e r e t h e o b j e c t o f a size e a s i l y m e a s u r a b l e b y c o m p a r a t i v e l y gross i n s t r u m e n t s s u c h a s calipers a n d rules. R e c o u r s e h a s t h e n t o b e m a d e to an eye-piece m i c r o m e t e r . T h i s is a glass disc on o n e surface of w h i c h a r e a c c u r a t e l y e t c h e d lines o r s q u a r e s o f u n i f o r m s p a c i n g . T h e t o p o f t h e eye-piece is unscrewed a n d t h e micrometer dropped in to come to rest on a ledge within t h e eye-piece. T h e t o p i s t h e n r e p l a c e d a n d t h e e y e - p i e c e l o o k e d i n t o while held v e r t i c a l l y o v e r a s o u r c e o f l i g h t . T h e m i c r o m e t e r r u l i n g s s h o u l d n o w b e i n s h a r p focus: i f t h e y a r e n o t , t h e m i c r o m e t e r m a y b e f o u n d t o h a v e l a n d e d upside down on t h e ledge or it m a y be necessary to screw t h e t o p out slightly t o give a s h a r p focus. I t will b e f o u n d t h a t w h e n p r o p e r l y p o s i t i o n e d a n d i n s h a r p focus t h e m i c r o m e t e r r u l i n g s will lie i n t h e s a m e p l a n e a s t h e i m a g e of t h e o b j e c t a n d t h e size of t h e o b j e c t in t e r m s of divisions c a n be r e a d d i r e c t l y . T h e a p p a r e n t size of t h e s e divisions in m i l l i m e t r e s or f r a c t i o n s of an i n c h is, h o w e v e r , n o t k n o w n a n d m u s t b e a s c e r t a i n e d b y reference t o a s t a g e m i c r o m e t e r . T h i s c o n s i s t s o f a s t o u t 3 x 1 i n c h glass slide w i t h a p o r t i o n i n t h e c e n t r e r u l e d a c c u r a t e l y w i t h lines a k n o w n d i s t a n c e a p a r t . A c o m m o n t y p e h a s lines s e v e r a l m i l l i m e t r e s l o n g 0.1 m m a p a r t w i t h o n e 0.1 m m s e c t i o n s u b d i v i d e d i n t o 0.01 m m . B y focusing o n t h i s m i c r o m e t e r o n t h e s t a g e t h e eye-piece r u l i n g s c a n b e s u p e r i m p o s e d o n t h e scale r e a d i n g s a n d t h e v a l u e o f t h e eye-piece m i c r o m e t e r divisions easily m e a s u r e d . T h i s m e a s u r e m e n t o f t h e a p p a r e n t a c t u a l size o f t h e eye-piece m i c r o m e t e r division i s t e r m e d " c a l i b r a t i o n " of t h e eye-piece m i c r o m e t e r a n d v a r i e s w i t h t h e m a g n i f i c a t i o n , so a s e p a r a t e d e t e r m i n a t i o n m u s t b e m a d e for e a c h c o m b i n a t i o n o f eye-piece a n d objective at a particular t u b e length. Eye-piece micrometers are not expensive a n d s h o u l d be p a r t of t h e e q u i p m e n t of e v e r y m i c r o s c o p e : as a m a t t e r of fact t h e y c a n b e k e p t p e r m a n e n t l y i n t h e eye-piece a n d s o r u n n o risk o f b e i n g m i s l a i d . T h e s t a g e m i c r o m e t e r s a r e m o r e e x p e n s i v e b u t officers o f t h e B u r e a u will b e p l e a s e d t o c a l i b r a t e a n y m i c r o s c o p e s a n d eye-piece m i c r o m e t e r s u p o n request. T h e c a l i b r a t i o n d o e s n o t p r o v i d e a m e a s u r e of t h e m a g n i f i c a t i o n , i.e,. t h e size o f t h e o b j e c t a s seen b y t h e e y e t h r o u g h t h e m i c r o s c o p e c o m p a r e d w i t h i t s a c t u a l size. T h i s c a n often b e o b t a i n e d b y a k n o w l e d g e o f t h e m a g n i f i c a t i o n p r o v i d e d b y t h e o b j e c t i v e a n d t h e eye-piece, b u t s o m e t i m e s t h i s i s n o t a v a i l a b l e . A r o u g h a p p r o x i m a t i o n c a n t h e n b e m a d e w i t h lowp o w e r e d o b j e c t i v e s b y t h e following m e t h o d : — P l a c e an o b j e c t of k n o w n s u i t a b l e size, e.g., a d i v i s i o n on an e n g i n e e r i n g rule, o n t h e s t a g e a n d b r i n g i t i n t o s h a r p focus. T h e n h o l d a s h e e t o f w h i t e c a r d or stiff p a p e r at a d i s t a n c e of 10 in f r o m t h e e y e a n d close to t h e l i n e of t h e microscope body. By looking i n t o t h e microscope with one eye a n d focusing t h e o t h e r o n t h e w h i t e p a p e r a t t h e s a m e t i m e , a n i m a g e o f t h e o b j e c t will b e seen t o b e s u p e r - i m p o s e d o n t h e p a p e r . T h e e n d s c a n b e m a r k e d with a pencil as one watches a n d then t h e distance m e a s u r e d between t h e t w o p e n c i l lines. T h e r a t i o o f t h i s d i s t a n c e t o t h e a c t u a l size o f t h e o b j e c t

48

OPTICAL INSTRUMENTS

gives the magnification of the particular optical set-up of the microscope. The method sounds rather complicated but after a little practice it is found possible to reproduce the measurements quite readily. The Projection Microscope A projection microscope is of value when a large image is to be thrown on a screen for demonstration purposes or on to a table for the purpose of making a drawing. Outfits are available for converting a standard microscope into a projector, the main requirements being a stand to provide rigid mounting and an efficient illumination train of high intensity. Complete projection microscopes may also be obtained. Various models are available ranging from expensive high power units to much simpler ones when only low to medium magnification is required. A projection microscope of medium cost is shown in Fig. 29. This microscope is of a type suitable for use in the examination of proof samples withdrawn from vacuum pans etc. The slide with the sample to be examined is placed on the stage and brought into focus on the viewing screen

Fig. 29—A projection microscope of medium cost (Maruzen).

OPTICAL INSTRUMENTS

49

of nearly 7 in diameter. The standard lens supplied (x 10) is of sufficient power for pan stage operation, however, other objectives up to x 40 are also available. A squared grid may be placed over the screen and calibrated for size depending on the objective used. Photomicrography Photomicrography is the process of recording on film the image produced by the microscope. The fact that a real image of the microscopical object is projected, without the aid of any equipment other than a brilliant source of illumination, by the eye-piece onto a screen located above it, makes photographic reproduction possible. If a light-sensitive plate or film is substituted for the screen and all extraneous light excluded a negative can be secured. The simplest form of equipment consists of a light-tight box with a ground glass screen fitted into the top, which can be exchanged for a film pack or plate holder. The box is arranged over the microscope so that the image can be focused onto the screen, which is then exchanged for the film. The exposure can be made by turning the microscope light on for the required period. Another simple method involves a camera with the lens removed, connected in a light-tight manner to the microscope tube. A single-lens reflex camera or one with a ground glass focusing screen is required so that accurate focusing on the focal plane of the camera can be done, for the point of best focus for the camera will not be identical with the best visual focus through the microscope. If a camera with a focal plane shutter is used this can be used for making the exposure, otherwise the microscope light can be used. Complete photomicrographic equipment, ranging from extremely simple to very elaborate, is available from microscope manufacturers. If serious work is contemplated these commercial products are to be preferred, however very good results can be obtained with improvised outfits. The Care of Optical Instruments All too frequently optical instruments are treated as though they were a piece of laboratory furniture and not as delicate instruments built by the manufacturers to a degree of high precision. If treated and used carefully the life of a good instrument is practically unlimited. Optical instruments should be set up in situations which are not exposed to dampness or corrosive fumes, or subjected to jarring or vibration. In tropical conditions dampness favours mould growth which etches the polished surfaces of prisms. It has been found in practice that mould growths on calcite prisms will render a saccharimeter useless within a short period of time from when they first become visible. The instrument should be forwarded for attention to an instrument maker who is thoroughly conversant with it. If the instrument is subjected to vibration or jarring the optical system may be thrown out of adjustment. Where it is not practicable to build the laboratory sufficiently far from the mill to avoid all vibration, the instrument should be mounted on a suitable anti-vibration table. The instrument should be examined regularly and kept scrupulously clean. This applies, in the case of saccharimeters, to splash glasses and the trough. If juice is allowed to accumulate in the trough thus penetrating to the threads of the screw caps holding the splash glasses, great difficulty will

50

OPTICAL INSTRUMENTS

be experienced when an attempt is made to remove them. In some saccharimeters the splash glass holder is held in position by means of a tension spring and is constructed for ready removal by the fingers. It should be maintained in such a condition. The prisms of a refractometer should always be thoroughly cleaned and dried after use and a piece of lens tissue placed between the prisms before closing them. This assists in keeping the polished face of the measuring prism in good condition. A microscope, even one in the cheaper range, is an instrument of precision and as such should be treated with every care, if it is to give satisfactory results over a long period. The operation and manipulation should be entrusted only to people who have shown themselves capable of handling it with the respect it deserves. Special precautions should be taken to ensure that dust is kept out of the lenses at all times and they should never be exposed to direct sunlight, for this will quickly result in permanent fogging. When not in use, objectives should be placed carefully in the small plastic or metal cans provided by the manufacturers. There should always be an eyepiece in position otherwise damaging grit is likely to enter the draw tube, body, nose-piece and objectives. Eye-pieces should never be left dismantled, for dust inside the eye-piece will spoil the image. The condenser remains attached to the microscope permanently and should be wiped over from time to time with a dust-free silk or cotton cloth or cigarette paper, care being taken that the top lens surface is not scratched. The diaphragm and mirrors should be quite dry and dust-free. While a very small amount of lubrication is required for the adjustment threads and racks, oil or grease elsewhere is to be avoided at all costs. Not only is it unnecessary, but it damages lenses and specimens and in removing it permanent harm can easily occur to the instrument. Care in the actual use of the microscope is also of importance in maintaining the instrument in a good working condition. It should never be subjected to sudden jolts or bumps and never allowed to get sticky or dirty. The under side of the slides should always be dry and clean before being placed on the stage and no liquid should be allowed to run off the. mounted slide. The technique for avoiding the fouling of the front lens of the objective when bringing the object into focus has been explained and it should be followed at all times. When not in continuous use, all optical instruments should be kept under a cover. At the end of the season they should be cleaned and stored away in a dry atmosphere. REFERENCE Wilson, Robert A. M. (1965), Polarization Temperature Corrections. Int. Sug. J. 67, 234-6, 265-8.

CHAPTER III THE BALANCE A sugar laboratory should be provided with three balances of the following general types— (1) An analytical balance for accurate work; (2) A sampling balance for work of moderate accuracy; (3) A balance of higher capacity for coarse weighing of large masses. The Analytical Balance This balance is required for all analytical purposes, for determination of specific rotations, for calibration of small items of volumetric glassware,

Fig. 30—-A modern single pan constant load balance (Sartorius).

52

T H E BALANCE

for the weighing of pycnometers and all other operations where precision weighing is required. It should have a capacity of at least 160 grammes and a sensitivity reciprocal of 0.1 rnilligramme per scale division or less. The great majority of balances of this class utilise the two knife edge, constant load principle, employing built in weights, critical damping of the swing of the beam and an optical projection system for reading the beam deflection. A modern balance of this type is shown in Fig. 30 while the diagrammatic representation in Fig. 31 shows the components.

1 2 3 4 5 6 7 8 9 10 11 12

Compensating stirrup Front knife edge Pan brake Weight carriage Built-in weights Pan Weight control mechanism Recording disc Projecting scale Micrometer mirror Weight shaft Arrestment shaft

14 15 16 17 19 19 20 21 22 23

Bulb Arrestment Objective regulator Scale and objective Damping Sensitivity adjustment Zero adjustment Beam Center bearing plate Center knife edge

Fig. 31—Diagrammatic representation of a single pan constant load balance (Sartorius).

The sensitivity of a balance is defined as the deflection produced by the addition of unit mass to the pan and is usually expressed in divisions per milligramme. The more useful term sensitivity reciprocal, S.R., is the mass which must be added to the pan to change the reading by one scale division. The value of the sensitivity depends on the position of the centre of gravity of the moving system in relation to the axis of rotation of the beam. For stability, the centre of gravity of the beam must lie below the axis but the smaller the separation the more sensitive the balance becomes. In a three knife edge equal arm balance the sensitivity varies with the load being weighed unless the three knife edges are accurately co-planar. The two knife edge balances, in which weighing is made by substitution, operate at constant load and the sensitivity remains constant irrespective of the value of the load being weighed. A small weight moving on a vertical screw fixed to the beam is provided to vary the vertical distance of the centre of gravity from the main knife and hence the sensitivity of the balance. A constant load balance having a sensitivity reciprocal of 0.1 mg per division should be adjusted so that the error in reading at the full deflection of the beam is less than 0.2 mg. A three knife edge balance should be adjusted, with half full load in each pan, to the same order of accuracy.

T H E BALANCE

53

In all balances provision is made for poising the beam and adjusting the zero reading by means of poising nuts carried on horizontal screwed rods parallel with the beam. In all balances with optical projection reading, fine adjustment of the zero is made by moving the reading index of the balance. All precision balances are equipped with an arresting mechanism which supports the pans, stirrups and beam of the balance, so protecting the knife edges and bearings from damage when the pan or pans are loaded and unloaded. When loading has been completed and the case closed the balance is released and the pan, stirrup and beam are released, preferably in that order. Weights: The majority of modern balances have the weights built in to the balance, the weights being applied and removed by the manipulation of controls external to the case. Balances of the older type require to be used in conjunction with a set of standard weights. Irrespective of which type of weights is used they must conform with certain basic requirements. To ensure both long and short term stability the weight must be constructed in one piece from a hard inoxidisable material, the surface must be smooth and free from sharp edges and the material must be non-magnetic. These requirements are met by well made weights of nonmagnetic stainless steel containing approximately 25% chromium, 20% nickel, which has a density between 7.8 and 8.0 g c m - 3 a t 20°C. Weights of this material are far superior to those of brass, either plain or with a protective plating of gold, chromium or any other material. It is customary for precision weights to be adjusted to their nominal value on the assumption that they are all of uniform density—8.0 g cm - 3 . That is, the weights are adjusted to balance a standard weight of true nominal mass and of density 8.0 g c m - 3 when in air of density 0.0012 g cm - 3 . This practice is followed by N.S.L. Australia, and by most national standardizing laboratories. It follows from this that in weighing of the highest precision, where air buoyancy corrections must be applied, they should be calculated on the basis that the density of the weights is 8.0g cm~3 and using the actual value of the density of the air in the balance case. Weights must never under any circumstances be touched with the fingers. They should be manipulated only with plastic-tipped or chamois covered forceps. Setting up the Balance: In the case of a new balance it is most desirable if possible to have the balance set up and adjusted by the maker's representative. The balance must be set up on a firm bench, free from vibration and in a room in which the temperature is reasonably constant or varies only slowly during the day. A good criterion for an acceptable level of vibration is the appearance of the image of the optical scale. This should, of course, be focussed until the lines appear quite sharp, and the balance then released. The appearance of the lines is closely observed and any slight blurring is a good indication of the presence of excessive vibration. If this occurs, steps should be taken to isolate the balance from the bench by means of anti-vibration mountings. The balance should be placed on the bench and the inside of the case thoroughly cleaned. The case should be levelled using the circular level bubble or plumb bob provided and the rest point adjusted to zero. The sensitivity should be adjusted to its nominal value by placing on the pans a weight which should give full scale deflection of the reading index.

54

THE BALANCE

After these adjustments have been made the balance case should be closed and (he balance left to stand for at least one hour to settle down. After this period the zero reading and sensitivity should be re-checked and any further minor adjustments made if required. General Precautions in Weighing Objects should never be weighed until they have attained the temperature of the balance case. Hot bodies should never be placed on the balance case but should be allowed to cool, preferably in a desiccator, until they are approximately at ambient temperature. The time taken by a body to cool to room temperature depends on its initial temperature, its size, and the material from which it is made. Hygroscopic materials can only be weighed when contained in an airtight vessel. Under no circumstances should any chemical come into contact with the scale pan. All material to be weighed should be placed in a clean dry tared container of suitable material such as platinum, glass, aluminium etc. In the case of non-hygroscopic crystals a piece of clean dry paper may be used. Method of Weighing: The operator must first make sure that the pan and the interior of the weighing compartment are clean. The operation of weighing with a direct reading balance with weight loading facility is very simple. With the weight selector dials set to zero, release the balance, and when the image comes to rest adjust the balance to read zero. Arrest the balance. Place the object to be weighed on the balance pan, and close the balance case. Select a weight which is judged to be close in value to the mass of the object being weighed. Release the balance and note whether the object is heavier or lighter than the weight selected. Arrest the balance and select the appropriate greater or smaller weight and read again. Repeat the process until a reading on the scale is obtained. Allow the beam to come completely to rest and read the weight of the body. Some balances of this type have a partially released position of the beam in which it is possible to change the dial settings and watch the change in scale reading without having to arrest the beam between settings. In making weighings with an equal arm three knife edge balance the following procedure is observed. The pans are wiped with a small camel-hair brush, the case is closed, and the beam is carefully released. The pointer will now swing slowiy over the scale, and when the amplitude has fallen to about five scale divisions, the readings of the extremities of the swing are taken for five successive swings. Care should be taken to avoid parallax in the readings. It is best to number the scale continuously from left to right rather than to call the centre division O and those to the right positive and to the left negative. Suppose the central point to be numbered 10, and that the following numbers represent observations: —

THE BALANCE The beam is then arrested, taking care that this is done when the pointer is at the centre of the scale, so as to avoid damaging the knife-edges. The object to be weighed should be removed from a desiccator in which it has been placed in order that it may be free from moisture, and at the same temperature as the balance. The object is placed on the left-hand pan. A large weight should then be put on the right-hand pan, and the beam released just sufficiently to determine the direction in which the beam will move. The beam is again arrested and a larger or smaller weight applied as required. Each weight is tried in turn until equilibrium has been obtained as closely as possible. The balance case is then closed, and the further adjustments made by means of the rider. It is not necessary to adjust the weight so that the resting point is identical with that initially found, provided the precise sensitivity of the balance is known. Suppose the following turning-points were determined with a mass of 21.682 g on the right hand pan:— Right

Mean

9.53

12.05

The weight is, therefore, insufficient and should be increased by an amount which would change the resting point by 10.79-10.03 or 0.76 division. If, from a previous determination, it has been found that the sensitivity at 20 g load is 4.0 scale divisions per mg the correction to be added is:—-

It will be observed that the average of the last left-hand and the last right-hand swing of the balance gives a result which would be indistinguishable on the scale from the true resting point. A skilled operator makes use of this fact to determine when the correct mass is on the scale pan. By a careful release of the mechanism he may confine the first deflection to one or two divisions and observe if the next two are at equal distances from the centre of the scale. Testing a Precision Balance The essential attributes of any precision balance are:— (1) The reading of the balance must be consistent for any given condition of loading. (2) The balance must give weighings which are closely reproducible. In the case of balances fitted with optical projection reading and inbuilt weights the following are additional requirements. (3) The sensitivity must be close to its nominal value and must be constant over the full range of the scale.

56

T H E BALANCE (4) T h e e r r o r i n a n y w e i g h t o r c o m b i n a t i o n o f w e i g h t s s h o u l d n o t e x c e e d t h e c o r r e s p o n d i n g Class A t o l e r a n c e specified b y t h e N a t i o n a l Standard Laboratory. (5) I n t h e case o f t w o p a n t h r e e knife e d g e b a l a n c e s t h e effective l e n g t h s o f t h e b a l a n c e a r m s s h o u l d b e e q u a l t o w i t h i n 1 0 p a r t s i n a million.

Methods of Test: (1) T h e g e n e r a l c o n d i t i o n of a b a l a n c e c a n n o t be c h e c k e d q u a n t i t a t i v e l y b u t a n i n s p e c t i o n s h o u l d s e r v e t o c h e c k t h e following p o i n t s . T h e b a l a n c e s h o u l d b e c l e a n a n d all p a r t s s h o u l d b e free f r o m c o r r o s i o n . The arrestment should operate smoothly and should not cause a n y unwanted motion of the pointer or pans. M a n i p u l a t i o n o f t h e b u i l t i n w e i g h t s s h o u l d n o t c a u s e a n y significant j o l t i n g or s w i n g of t h e p a n . (2) R e p r o d u c i b i l i t y o f r e a d i n g s . T h i s i s c h e c k e d b y t a k i n g t w e n t y c o n s e c u t i v e r e s t p o i n t r e a d i n g s , t h e b a l a n c e case b e i n g k e p t closed a n d t h e balance arrested between each reading. T w o c r i t e r i a of s t a b i l i t y a r e u s e d : (a) T h e m a x i m u m difference b e t w e e n a n y t w o c o n s e c u t i v e r e s t p o i n t s a n d (b) T h e s t a n d a r d d e v i a t i o n of t h e r e s t p o i n t s . (a) is a m e a s u r e of e r r a t i c v a r i a t i o n in t h e r e s t p o i n t a n d (b) gives a m e a s u r e of drift or slow c h a n g e in t h e r e s t p o i n t . If S is t h e a c c u r a c y of e s t i m a t i o n of t h e r e a d i n g e i t h e r by v e r n i e r or by v i s u a l e s t i m a t i o n , b o t h c r i t e r i a (a) a n d (b) s h o u l d be less t h a n 2 8 for a g o o d balance. (3) T h e s e n s i t i v i t y of t h e b a l a n c e is to zero and t h e n adding to the p a n a deflection of t h e scale. T h e d e p a r t u r e n o m i n a l v a l u e s h o u l d n o t e x c e e d 2 S in a n d 10 8 in t h e case of t h r e e knife edge

m e a s u r e d by s e t t i n g t h e o p t i c a l scale weight equivalent to the m a x i m u m of t h e full scale deflection f r o m i t s t h e case of a c o n s t a n t l o a d b a l a n c e balances with optical projection.

(4) T h e l i n e a r i t y of r e s p o n s e of t h e b a l a n c e is t e s t e d by u s i n g successive

r a n g e of t h e scale. (5) T h e t e s t i n g of t h e a c c u r a c y of t h e i n d i v i d u a l w e i g h t s is a m o s t inv o l v e d process b u t a n i n d i c a t i o n o f t h e p r e s e n c e o f a n y gross e r r o r s c a n b e obtained by checking the sum of various groups of weights against appropr i a t e s t a n d a r d s . F o r e x a m p l e if a b a l a n c e h a s an o p t i c a l r a n g e of 0.100 g r a m m e and groups of weights 0, 0 . 1 - 0 . 9 g 0, 1 - 9 g check

0, 1 0 - 9 0 g 0.9 + scale a g a i n s t 1 g 9.9 + scale a g a i n s t 10 g 99.9 + scale a g a i n s t 100 g

A m e t h o d of c a l i b r a t i o n of i n b u i l t w e i g h t s , u s i n g all a v a i l a b l e d a t a , h a s b e e n d e s c r i b e d ( H u m p h r i e s , 1961), w h i c h y i e l d s self c o n s i s t e n t r e s u l t s of an accuracy comparable with the discrimination of the balance.

T H E BALANCE

57

Balance for Coarse Weighing For general approximate work at heavier loads a speedier balance of more robust construction is used. A balance having a maximum load of 3 or 4 kilogrammes and a discrimination of 0.1 gramme is suitable for this purpose. Single pan balances with optical scale and taring facility are available and they are very suitable for this purpose. Although these balances are robust they should nevertheless be kept clean and their accuracy periodically checked with known weights. REFERENCE Humphries, J. W. (1961). The calibration of the weights built into a balance. Aust. Jour, of Ap. Sci. 2, 3, 360

CHAPTER IV DENSIMETRIC METHODS OF ANALYSIS The quantity of mass in unit volume of a substance is known as the density of that substance, and is expressed in such units as grammes per millilitre, or pounds per cubic foot. Mathematically

where d is the dens-

ity, m the mass and v the volume of the substance. The volume of a given mass may, and almost invariably does, vary with temperature and pressure. For liquids and solids the change of volume with temperature is quite significant, but the effect of variation in pressure is usually negligible, so t h a t it suffices to specify the temperature to which any statement of density is related. At any given place the mass of any body is proportional to its weight in vacuo. The ratio of the masses (weights in vacuo) of equal volumes of a substance and some standard material is known as the relative density of the substance. Customarily, when the standard material is water, the ratio is known as specific gravity, so that specific gravity (s.g.) may be defined as a number which indicates how much heavier or lighter a material is than water. The derivation of specific gravity involves two densities each of which must be qualified by a temperature and so the ratio

Since one ml of pure water at 4 °C (the temperature at which the density of water is a maximum) weighs one gramme in vacuo* and thus has a density of 1 g per ml, the temperature of 4 °C is frequently adopted as a basis for expression of specific gravities. It follows that the density of a substance at ts in g per ml and its specific gravity

are numerically the same.

For convenience it is customary to adopt a standard temperature for which the density of the test material is specified. In the Queensland sugar industry the accepted standard temperature is 20 °C and specific gravities are usually quoted as s.g By reference to tables showing the density of water at various temperatures it is possible to derive a factor for the conversion of specific gravities based on water at 4 °C to values based on water at some other selected temperature, e.g., s.g. 20 °C. The relationship between two masses is correctly expressed by the ratio of their weights in vacuo. When a weighing operation is conducted under normal laboratory conditions, the buoyant effect of the atmosphere is exerted on both the sample and the weights, and as these usually differ in volume, the resultant force creates a difference between the weight of the sample in air and its weight in vacuo. A weight "in air, with brass weights" is con*This follows from the old definition of the millilitre, i.e., the volume occupied by 1 g of water at the temperature of its maximum density.

DENSIMETRIC METHODS OF ANALYSIS vertible to the weight in vacuo if the density of the test sample is known. Hence, densities and specific gravities may be expressed in terms of weight in air with brass weights, and as most weighings are conducted under these conditions, tables of density on this basis have great practical value. Great care should be taken to avoid confusion between density figures based on weight in vacuo and those based on weight in air with brass weights. The determination of specific gravity is one of considerable importance in sugar analyses. This is due to the interesting fact that solutions of different sugars of equal concentrations have almost identical specific gravities. The following values for 10 per cent solutions of nine distinct sugars illustrate this fact:—

Further, the mean value for all sugars approximates closely to that for sucrose. It is possible, therefore, to determine very closely the percentage of dissolved substance in any solution of sugar or mixture of sugars simply by determining its specific gravity. While the application of specific gravity tables established for sucrose may be applied with reasonable accuracy for the estimation of dissolved substance in a solution of mixed sugars, this is not the case where other dissolved substances are present. The errors resulting from this cause are at times very great as, for example, with final molasses. The influence of the salts present in such a solution may be gauged from the following data showing the concentration of solutions of sodium-potassium tartrate and potassium carbonate in comparison with sucrose solutions of equal specific gravity.

When the specific gravity of such solutions is determined after dilution with water, the error is still further intensified, owing to the difference in contraction between sugar and dissolved impurities in aqueous solution, as is seen from the above table. Concentrations determined by this method for other than pure sugar solutions must, therefore, be regarded as rough estimates only.

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DENSIMETRIC METHODS OF ANALYSIS

The Pycnometer A highly accurate instrument for the determination of specific gravity is the pycnometer or specific gravity bottle (Fig. 32).

Fig. 32—Illustrating the types of pycnometer in use in Queensland.

It is simply a glass vessel which is designed to contain an accurately reproducible volume of liquid at any particular temperature. The best pycnometers are vacuum jacketed for thermal insulation, and are fitted with a thermometer. By weighing the bottle filled first with water and then the given solution at constant tempeiature the weights of equal volumes of the two fluids may be determined, and hence the specific gravity of the test solution. The pycnometer is mainly used in the sugar mill laboratory for the determination of the Brix of dilute sugar solutions extracted in the analysis of cane or bagasse. To Determine the Volume of the Pycnometer at a Standard Temperature.—This determination has little practical use, but serves to describe the technique and develop the theory. The bottle is thoroughly cleansed, using in turn glass cleaning solution, water and alcohol. It is then dried in a stream of dry air and weighed. It is next filled with distilled water which has recently been boiled to expel dissolved air and cooled to 2 to 3 °C above ambient temperature. The stopper is inserted*, care being taken to prevent the introduction of air bubbles, and the excess water is carefully removed by means of a filter paper (from the stopper and also from the capillary in the side-arm type). *The temperature of the water must be determined at the instant the stopper is fully inserted. Where a thermometer is incorporated in the stopper, the stopper is lightly set in place and the thermometer allowed to come to reading; where a stopper only is provided, a thermometer is inserted first, read and withdrawn. The stopper is inserted immediately.

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61

The pycnometer is then placed in a water bath at a temperature lower than that of the water employed to fill the bottle (ambient or preferably a lower temperature). The liquid meniscus is thus drawn down the ground glass joint or the capillary depending on the type of pycnometer used. The pycnometer is then wiped perfectly dry. In drying the surface considerable care must be taken and the following technique is recommended. The outside is first wiped thoroughly with a piece of clean, damp flannel, then the damp surface is dried with a clean chamois, after which a final rub is given with a second chamois. During these manipulations and the subsequent weighing the pycnometer must not come in contact with the fingers. Several determinations are made with distilled water, the temperature being noted to 0 • 1 °C for each weighing. The total weight minus the weight of the empty vessel is the weight, in air, of the water contained, at the observed temperature. This weight in air has to be converted to weight in vacuo by applying corrections for the buoyancy of the water and the weights.*

This volume VT is fixed for any pycnometer. It will be noted that the measured weight of water W1 is related to the standard volume VT by a complex factor which involves the density of water, the correction for buoyancy and the thermal expansion of glass. The value of this factor for water in a glass vessel is fixed for any temperature t1 referred to a standard temperature T. Values for various temperatures are available from tables. For added convenience, tables have been prepared in which the correction is made additive or subtractive (see Tables X X I I I and XXIV). Hence, in practice the measured weight of water contained at t1 (in grammes) is converted, either by a factor or a correction, directly to the standard volume of the pycnometer at T (in millilitres). This procedure is adopted as the basis in the testing of standard volumetric glassware. |The accepted values for y are (B.S.S. 1797: 1952) soda glass + 0.00003, borosilicate glass + 0.00001 per 1 °C rise in temperature. *It being assumed that the weighings have been made in air of average density 0.0012 g/ml using weights of density 8.0 g/ml.

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DENSIMETRIC METHODS OF ANALYSIS

To Determine the Specific Gravity of a Test Solution. The pycnometer is filled with the solution at a temperature 2 to 3 °C above ainbient and the weight of the contents determined as before. Let the weight of the contents be W2 at t2. The density of the solution at the temperature of the determination t2 may be determined by dividing the true weight of the contents at t 2 by the volume of the pycnometer at t2, the latter being determined either by direct measurement using pure water at t 2 or by correction of the volume at the standard temperature to the volume at t 2 in accordance with the coefficient of expansion of the glass of which the vessel is made. This procedure has the disadvantage that the observed weight of the solution must first be converted to weight in vacuo. If it were convenient to conduct tests on the solution and on pure water at temperature t2, the buoyancy corrections on the two weights would be practically equal and could be neglected. Hence,

Without special precautions, it is very difficult to conduct two determinations at the same temperature. Hence, in general, the test with water will be conducted at t 1 and that with the solution at t2. Then, if the density of the solution at t2 be designated D,

Determination of Brix. In using the pycnometer for the determination of the Brix of sugar solutions a modified procedure is adopted for simplicity. If the true weight of the contents of a pycnometer at t2 be divided by the standard volume of the pycnometer at T, the result derived is known as the apparent density at t2. It is assumed that, as before, the weight of pure water contained at t1 is W1.

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63

The apparent density at t 2 is the value which would be observed by taking a glass hydrometer calibrated to read correctly at the standard temperature T and immersing it in the test solution at t2. A Brix hydrometer is calibrated to read correctly at a standard temperature T, and, if used at another temperature t2 will give a reading which differs from the actual Brix. If the apparent density at t2, referred to above, be converted to Brix by using the standard tables for conversion at temperature T the value derived will coincide with the actual reading of the Brix hydrometer at t2. Thus, in the determination of Brix, the apparent density is first derived. This apparent density is converted to "observed" Brix, using the standard table, and the observed Brix is then corrected for temperature according to the normal method for the Brix hydrometer. It will be noted that, to derive the apparent density, the observed weight W 2 must be divided by the term

culated for various values of t1 and a table of factors could be compiled. However, it is simpler, and sufficiently accurate, to make use of Table X X I I I , subtracting 1.05 from the values listed therein and then reducing the correction as usual in proportion to the approximate volume of the pycnometer. The procedure is most easily followed by reference to the examples. In the compilation of Table X X I I I it has been assumed that the coefficient of expansion of glass is 0.00003. Such a coefficient is not likely to be associated with any borosilicate glass, and even some glasses nominally of the soda type display coefficients of expansion significantly different from the figure stated. The existence of a coefficient different from 0.00003 will be manifested in systematic variation of the determined pycnometer constant with the temperature at which it is determined. *ln the second edition of the Laboratory Manual this characteristic constant of the pycnometer was referred to incorrectly as the Volume. It might leniently be regarded as an "apparent volume" but the word "apparent" is overworked, and the term pycnometer constant is preferred.

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DENSIMETRIC METHODS OF ANALYSIS

For general scientific work it is possible and would be desirable to analyse the results of tests over a range of temperatures to determine the actual coefficient of expansion of the glass, and hence the true constant. However, in the sugar laboratory the pycnometer is used almost exclusively for the determination of Brix, in the course of which reference is made to Table I. This table incorporates an allowance of 0.000025 for the coefficient of expansion of glass. Hence in practice, whatever be the material of construction of the pycnometer, the coefficient of expansion of the material should be taken as 0.000025 for the calculation of the constant. If the coefficient of expansion of the material is, in fact, 0.000025 the constant will be independent of temperature. For all other cases the so-called constant will vary with temperature. For any vessel displaying this characteristic it is necessary, from the results of tests over a range of temperatures, to draw up a temperature scale of constants and, in practice, to adopt the value of constant corresponding to the temperature of a determination. The apparent density thus derived may be converted to observed Brix with the aid of Table XIV and the Brix may then be adjusted by reference to Table I. Examples: For the purposes of the following examples the pycnometer is constructed of glass having a coefficient of expansion of 0.00003 per 1 °C rise in temperature. Determination of Volume of Pycnometer.--

This specific gravity may be converted to or any other reference temperature for the water, but, without tables applying specifically to the solution, the reference temperature of 25 °C for the solution may not be converted to any other temperature. If a value for density at a selected temperature t is required, a density determination must be conducted at that temperature. This does not apply to sugar solutions for which temperature correction tables are available.

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65

Hydrometers. A second method of determining the specific gravity of solutions, and the one most commonly employed in sugar laboratories, is by means of the hydrometer. It provides by far the easiest and most direct method of determination of this factor. In its usual form this instrument consists of a hollow glass body, cylindrical in shape, and terminating at its lower extremity in a bulb, which can be weighted with mercury or lead shot and at its upper extremity in a slender, hollow stem within which a paper scale is sealed. If this instrument be allowed to float in a solution, the weight of liquid displaced is equal to the weight of the hydrometer. If placed in solutions of different specific gravity the instrument will sink to varying depths; and the scale is so graduated that the point on the stem which corresponds with the liquid surface indicates the density or percentage of dissolved substance for the given temperature. In practice the hydrometer scale is standardized at a few points only, and the intermediate divisions are determined by interpolation. The density of a solution is equal to the weight W of the hydrometer divided by the volume V of the portion submerged.

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DENSIMETRIC METHODS OF ANALYSIS

ThenThe difference between the volume submerged for any two divisions v is— v

=nr2d

where d = distance between divisions and r = the radius of the stem. The following table shows the relationship between the stem divisions of a hydrometer weighing 75 g and with a cross sectional area of stem (nr2) equal to 0-2 cm2.

It is clear that as the density increases the distance between scale divisions decreases. To effect this progressive reduction it is customary, in practice, to employ a dividing engine. In the graduation of a hydrometer scale for indicating direct percentages of sugar (Brix) the distance between scale divisions is more uniform, due to the partial compensating effect of the non-linear relationship between Brix and density. At 20 °C the change in density from 0 to 10 °Brix is 0-03901 g per ml, whilst the corresponding change from 50 to 60 °Brix is 0-05089 g per ml. This effect is illustrated in the following table, where the dimensions of the hydrometer are the same as before:—

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67

It is, therefore, customaryingraduating hydrometers which read direct percentages of sugar, to calibrate at, say, three points, and then divide the intervals between these points into equal subdivisions. Though not absolutely accurate, the error introduced is probably less than the errors of observation. Brix Hydrometer The construction of the hydrometer which reads direct percentages of cane sugar is due to Balling. The scale as later recalculated by Brix constitutes the form at present in general use. The divisions of the scale are called degrees Brix, and express weight per cent of sugar; that is, a sucrose solution of 20 °Brix is composed of 20 g of pure sucrose dissolved in 80 g of pure water. It should be observed that there is no reference in this definition to volume. A solution of 20 °Brix at 20 °C is still a 20 °Brix solution at 80 °C. The confusion which frequently arises in this connection is due to the fact that the Brix hydrometer responds primarily to the density of the solution tested, which varies with temperature. As the glass of which the hydrometer is made has a much lower temperature coefficient of volume than sugar solutions, it follows that, with increasing temperature, the hydrometer will sink deeper and yield lower readings. The Brix scale marked on the hydrometer is related to the density of the solution at the standard temperature (20 °C). Hence, at any other temperature, whilst the equilibrium position of the hydrometer is closely related to the actual density of the solution, the reading cannot be interpreted directly as Brix. A correction must be applied to the observed reading to compensate for the change in reading which would result from bringing the temperature of the solution to 20 °C. In the derivation of temperature correction tables it is assumed that a hydrometer of a standard type of glass is immersed in a solution of sucrose in water. One type of hydrometer which is used in Queensland mills is illustrated in Fig. 33. The approximate dimensions are:— Overall length—36 cm Length of scale—15 cm Diameter of cylindrical bulb—3 cm Diameter of upper tube—5 mm Length of scale division (0.1 °Brix)—1 -5 mm The following ranges have been specified as the most convenient for sugar-mill laboratory use:— 0—10°, 10—20°, 15—25°, 20—30°, 30—40°, 40—50°, 50—60°, 60—70°. Fig. 33—Illustrating a Brix hydrometer.

CHAPTER V VOLUMETRIC EQUIPMENT The Units of Volume The units of volume should be based, theoretically at least, on units of length, and, in the metric system, the cubic metre, cubic decimetre and cubic centimetre are recognized units purely based on length. However, for a major part of the last century, units of volume based on mass have not only been recognized but accepted as standard. In the metric system, the familiar ones are the litre and millilitre. The originators of the metric system of weights and measures attempted to make mass units compatible with volume units by defining the kilogramme as the mass of one cubic decimetre of water at the temperature of its maximum density (4 °C). With the best accuracy available at the time this mass unit was determined and reproduced in a mass of metal—the standard kilogramme. Subsequent experience with masses based on the standard kilogramme and volumes based on the standard metre revealed small discrepancies, indicating that the original correlation was slightly in error. The volume of one kilogramme of water at 4C was demonstrated to measure 1.000027 cubic decimetres. This volume, based on the kilogramme was designated the litre, with a sub-unit, the millilitre. Two slightly different sets of units were then available, and in 1901 the litre was officially defined and adopted for volumetric work. This was apparently not regarded as of much significance at the time, for, at least 20 years later, volumetric glassware was still being calibrated in cc. now written as cm3. However the millilitre triumphed, and, for the past generation, volume and derived quantities such as density have been expressed in terms of the litre. In 1950 the conversion factor was amended to 1. 000028. In 1964 the 12th General Conference of Weights and Measures resolved to revert to the purely linear basis of volume and redefined the litre to be exactly one cubic decimetre. This means that the term litre may now represent either of two volumes, and for clarity it is necessary to invoke the officially unrecognized terms "old" litre and "new" litre. Once again, public response is very slow and even now (1969) many chemists are hardly aware of the change. Confusion will be avoided by the use of the term cm 3 rather than ml, and for the most part, the difference between the cm 3 and the old ml does not matter anyway. The Laboratory Manual, in all editions to date, has used the old litre and millilitre as units; that policy has been adhered to in the current edition because it does not yet appear possible to adopt the new standards throughout. The normal solution for the International Sugar Scale is 26.000 g in 100 old ml; is it to become 25.999 g in 100 cm3? It may be decided to let the weight stand unchanged. This book deals with a variety of subjects, involving a wide range of precision of results. In the analysis of factory products the difference between the old ml and the cm 3 matters not one bit; in pycnometry it cannot be ignored. It must be left to the reader, conscious of the different units, to

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69

decide when they are interchangeable, when not. The important item of record is that the volume units are of the pre-1964 era, the old litre and the old millilitre, based on the kilogramme. It should be stressed that the ml is absolute, and does not alter with change of temperature. At 4 °C the volume occupied by 100 g of pure water is exactly 100 ml. If the temperature be raised the water will expand and occupy a greater volume than 100 ml, but the unit itself does not alter.* As 20 °C is the standard temperature for all sugar laboratory apparatus, all volumetric glassware must be standardized at this temperature. For example, the 100 ml flask used in determining the polarization of sugars will contain, at 20 °C, 100 times the volume occupied by 1 g of water at 4 °C. Volumetric Glassware The volumetric glassware used in the sugar laboratory includes flasks, burettes, pipettes and measuring cylinders. For general purposes, volumetric equipment of class B standard is satisfactory and it is recommended that the use of class A glassware be restricted to those operations which necessitate the highest degree of accuracy being attained. Various standards authorities—The National Physical Laboratory England, National Standards Laboratory Australia, The National Bureau of Standards USA, The British Standards Institution, the Standards Association of Australia and others have developed and laid down specifications for class A and class B volumetric glassware. However the accuracy of an individual piece of equipment is not guaranteed by any more than the reputation of the manufacturer. The first essential in standardization is to have the glassware thoroughly clean. Traces of grease are particularly to be avoided. The vessel should be rinsed with water and loose contamination should be removed mechanically as far as possible in the usual way. The vessel should then be filled with an aqueous solution of a soapless detergent, shaken vigorously and allowed to stand for several hours. After pouring off the solution the vessel should be rinsed with distilled water several times until all traces of the detergent have been removed. If the vessel is not sufficiently clean after this treatment it should be filled with chromic acid cleansing solutionf, allowed to stand overnight if possible and then repeatedly washed with distilled water. The vessel is rinsed with pure alcohol, then with pure ether and finally dried by a current of dry air free from dust. The vessel should not be heated. The capacity of a graduated glass vessel is defined by the volume of water (or mercury) it contains or delivers at its standard temperature, when the meniscus i.e. the concave (or convex) liquid surface in the vessel is brought to the graduation line in a specified manner. In the case of a water meniscus the top edge of the graduation line is set tangentially to the lowest point of the meniscus. The provision of a strip of black paper 1 mm below the meniscus and viewed against a white background will be found to facilitate the setting. It should be noted that volumetric apparatus is graduated either to contain or to deliver the particular volume. This is usually indicated on apparatus made to British or Australian specifications by the inscription " I n " which has been adopted in place of "C" to indicate that the vessel is graduated to contain, and " D " is used as the inscription to indicate to deliver. Pipettes *It may appear superflous to labour this point, but the true significance of this fact is so frequently overlooked that students fail to make intelligent use of it. See p. 86 for the preparation of this solution.

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VOLUMETRIC EQUIPMENT

and burettes are obviously used only to deliver known volumes, but graduated flasks and more especially cylinders are used either to contain or to deliver, and when ordering these goods the method of using them should be considered. Since the capacity of a glass vessel varies with the change of temperature, any given vessel can be correct at only one temperature. The particular temperature at which a vessel is intended to contain or deliver its nominal capacity is the "standard temperature" of the vessel. In Australia 20 °C has been adopted as the standard temperature for volumetric glassware. Flasks The volumetric flask is a vessel designed to contain a known volume of liquid. The usual form of flask consists of a pear shaped body with a long narrow neck of approximately cylindrical shape on which a mark is etched to indicate the required capacity at a given temperature. The bottom should be flat or slightly dished to allow the flask to stand stably. The neck of the flask is made as narrow as is consistent with convenience in order that the error involved in filling to the mark may be as small as possible. The method usually employed in standardizing a flask is to first weigh the vessel empty and again when filled to the mark with a liquid of known density. Corrections must be applied for the buoyancy of air and the temperature of the liquid. Pure water, either distilled or demineralized, is most generally used, although mercury gives a higher degree of accuracy, particularly with vessels of low capacity. The flask should be weighed to a precision better than 10 per cent of the tolerance prescribed. This can be achieved with a good quality analytical balance having a capacity suitable to the requirements. A substitution method of weighing is generally used. With modern single pan balances of constant load it is the only method which can be employed, whilst with a two pan balance it avoids any errors due to inequality in the lengths of the arms. When using an ordinary two pan balance the clean dry flask is placed on one pan together with standard weights slightly in excess of the amount of water to be weighed. Tare weights are added to the other pan until the balance is in equilibrium. The flask is then removed from the pan, filled with water to a distance of a few millimetres above the graduation line and the surplus water is withdrawn by means of a fine jet so that the lowest point of the meniscus is well formed and distinct in outline. After filling, the flask is replaced on the pan and the weights are readjusted so that the balance is again in equilibrium. The tare weights are left undisturbed. The difference between the weights used in the first and second weighings is equal to the weight of water contained in the flask. The temperature is noted immediately after completion of the last weighing. The weight of water may then be converted to the volume at 20 °C by adding or subtracting corrections from Tables X X I I I and XXIV. The main correction compensates for the expansion of water at temperatures rising above 4 °C and the buoyancy effect of a standard atmosphere on the flask and weights. The smaller correction is for departure of the atmospheric conditions from the standard. The latter correction is negligible for most flasks used in sugar laboratories. The tables apply to a unit volume of 1000 ml and for other volumes the corrections must be reduced or increased in the ratio of the volumes. Example for 100 ml flask filled with water at a temperature of 23 °C and an atmospheric pressure of 755 mm of mercury. Empty flask + standard weights on pan = 100.000 g Filled flask + readjusted weights on pan = 0.385 g

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Weight of water contained in flask = 99.615 g Correction for 100 ml at 23 °C (Table XXIII) = +0.340 g Correction for 755 mm pressure (Table XXIV) = —0.002 g Capacity of flask at 20 °C = 99.953 ml When a single pan balance is used normal weighings are made with the flask empty and when it is filled. To minimize errors due to changes in the buoyancy of air the second weighing should follow the first without delay. The tolerances permitted for class B flasks are specified in Table XXV. Burettes The burette is employed either to deliver a measured volume of liquid or to measure a volume of liquid delivered. It consists of a cylindrical tube graduated usually in tenths of a ml and with a total capacity of 25 or 50 ml. It is provided at the lower end with a glass tap, or for use with alkaline solutions, with a rubber tube connected to a glass outlet jet and closed with a pinch clip. A good burette is of uniform bore, the tap is well fitting and the graduations are accurate. The fit of the tap may be improved when necessary by using the finest grade of carborundum paste as a grinding material. In reading a burette, care should be exercised to avoid errors due to parallax. Various devices are employed to ensure this; the best burettes have the graduation marks etched completely around them, so that in reading, the front of the etching conceals the back portion. Some burettes (Schellbach type) are manufactured with a longitudinal strip of white glass with a blue stripe running down the centre of it. The meniscus then presents the appearance illustrated in Fig. 34. This and similar devices are, however, not recommended for precise work, as they introduce the possibility of irregularity in bore. The accuracy of a burette is also a function of its rate of delivery; a satisfactory rate for a 50 ml burette of B class accuracy is between 75 and 150 seconds. The delivery time is determined from the zero line to the lowest graduation line and is taken with the stopcock fully open with the jet NOT in contact with the side of the receiving vessel. A burette is first tested for leakage. It is clamped in a vertical position with the stopcock free from grease, the barrel and key wetted with water and the burette filled initially to the zero line with water. The rate of leakage with the key in the closed position shall not exceed one half of one scale subdivision in 10 minutes for class B burettes during a test of at least 20 minutes.

Fig. 34 — Illustrating the appearance of the meniscus of the Schellbach burette.

The tolerances permitted for class B burettes are set down in Table XXV. In order to record corrections from point to point through the length of the burette, the errors (positive or negative) may be plotted as ordinates, against the burette scale graduations as abscissae. For calibration, the burette is clamped in a vertical position with the jet downwards and filled through the jet to a few millimetres above the zero graduation line. It is usual to test at five points of the scale, starting from zero on each occasion. Delivery is made into a tared weighing vessel, the outflow being unrestricted until the meniscus is about 1 cm above the graduation line of the test point. The rate of flow is then reduced to allow the final setting

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to be made without any allowance for drainage time. The drop adhering to the jet of the burette is removed by bringing the side of the weighing vessel in contact with the tip of the burette. The weighing vessel is then weighed, the temperature noted and the volume delivered at 20 C is calculated from Tables X X I I I and XXIV. The substitution method of weighing as outlined for flasks is recommended.

Fig. 35—Illustrating common types of pipette.

Pipettes The function of the pipette is to deliver a particular volume or a range of measured volumes of liquid; it may be of the bulb type shown in Fig. 35(1) or a graduated type illustrated in Fig. 35(11). In construction the bulb pipette consists of a straight suction tube above the bulb and a straight delivery tube below the bulb. The top of the suction tube should be ground smooth and square with the axis of the tube, the outer edge of the top being slightly bevelled. The graduation mark should be a fine clean line of uniform thickness completely encircling the suction tube. The delivery tube should terminate at its lower end in a delivery jet made with a gradual taper. The end of the jet should be ground smooth and square with the axis of the jet. The outer edge of the jet should be slightly bevelled. The delivery time of a pipette is important for the volume of liquid delivered is less than the volume contained, by an amount equal to that adhering to the walls of the pipette. This volume of adhering liquid will vary if the delivery time is reduced or increased. However provided the delivery time is within the specified limits, the change in volume of the film adhering to the walls will not introduce any gross errors into the volume delivered. The delivery time is the time occupied by the descent of the water meniscus from the graduation line to the position at which it appears to come to rest in the jet. The determination of the delivery time is made with the pipette in a vertical position and the jet in contact with the side of the receiving vessel. For the determination of capacity, the pipette is clamped in a vertical position with the jet downwards and filled as described for a burette. The water is retained by pressure of the finger on the tip of the suction tube and the outside of the jet is wiped free of water with a cloth. The pressure of the finger is reduced and the water allowed to run out slowly until the lowest point of the meniscus coincides with the top of the graduation line. The drop of water adhering to the jet is removed and the volume now contained in the pipette is delivered into a tared vessel with the tip of the jet in contact with the inside of the vessel. A waiting time of approximately 3 seconds after movement of the water has ceased, before removing the pipette, is now specified in international

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recommendations for one mark pipettes. The natural rate of delivery should not be increased by force such as blowing and the small quantity of water remaining in the jet should not be expelled. The vessel is now weighed and the weight of water may then be converted to the volume at 20 °C by adding or subtracting corrections from Tables X X I I I and XXIV. The tolerances for capacity and delivery time for pipettes are specified in Table XXV. Graduated Pipettes Graduated pipettes may be obtained in various types, some examples being as follows:— (a) Calibrated downwards from a zero graduation. (b) Calibrated upwards with the residual volume in the jet as the zero datum. Standardization of these graduated pipettes is carried out in a similar manner to burettes for delivery times and for the volume of water delivered at 20 °C corresponding to the graduation mark tested. The tip of the jet is held in contact with the receiving vessel and no drainage time is allowed. The tolerances allowed for graduated pipettes are shown in Table XXV. Measuring Cylinders Cylinders are in common use for rapid approximate estimation of liquid volumes but they cannot be employed for accurate work. They may be standardized by the usual method of weighing the water which they contain or deliver. Thermometers Although not a volumetric instrument, the thermometer is so often closely associated with volumetric determinations that it may well be considered in this connection. A good thermometer must be made of sound glass, contain pure mercury and be filled with inert gas at a suitable pressure. The mercury thread must be free from breaks. The dividing and figuring of the scale should be clear and distinct and graduation lines should be of uniform thickness. If the thermometer is of the solid stem type the graduations are etched on the stem, or if of the enclosed scale type the scale is permanently marked on suitable material and rigidly supported within the glass tube carrying the capillary. The divisions should be at equal spacing. For routine laboratory work a general purpose thermometer as described in British Standard 1704 is most suitable. The maximum error of 1°C is allowed for general purpose thermometers in the range —5 to +105 °C graduated at each degree. For more accurate work thermometers as described in British Standard 593 are recommended where the maximum error allowed for a thermometer in the range —5 to +105 °C graduated at each degree, is 0.3 °C. A thermometer is subject to changes in bulb volume caused by the gradual recovery of the glass from the strain introduced during the treatment it receives in manufacture. This slow alteration is most noticeable in the first year or two after the thermometer is made but may proceed for years. Such changes are also modified by the heat treatments to which the thermometer is subjected in practice. In using a thermometer which is calibrated for total immersion it should be arranged as far as practicable for the entire mercury column to be immersed

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i n t h e l i q u i d . W h e r e t h i s i s n o t possible i t b e c o m e s n e c e s s a r y t o a p p l y a c o r r e c t i o n for t h e e m e r g e n t p o r t i o n o f t h e c o l u m n w h i c h i s n o t a t t h e s a m e t e m p e r a t u r e a s t h e b u l b . T h e following f o r m u l a i s a p p l i c a b l e for a p p r o x i m a t e corrections:—• Tc = T 0 + 0.000156L (To — T m ) where Tc = corrected temperature To — observed temperature Tm = temperature of the mid point of the emergent thread taken by another short thermometer and L = l e n g t h in degrees of t h e e m e r g e n t c o l u m n . In g e n e r a l for t e m p e r a t u r e s b e l o w 100 °C, t h e m a g n i t u d e of t h i s c o r r e c t i o n will n o t e x c e e d o n e or t w o t e n t h s of a d e g r e e . T h e r m o m e t e r s d e s i g n e d for a l i m i t e d d e g r e e of i m m e r s i o n a r e a v a i l a b l e — t h e c o r r e c t d e p t h of i m m e r sion b e i n g i n d i c a t e d b y a line e n g r a v e d o n t h e s t e m .

CHAPTER VI THE BUREAU'S METROLOGY LABORATORY The Bureau maintains a testing service for certain apparatus used in sugar mill laboratories. According to Regulation 57 of "The Regulation of Sugar Cane Prices Act 1962-1966", "Only such measuring instruments as are certified by the Bureau of Sugar Experiment Stations to be within the required limits of accuracy shall be used in the determination of Brix, pol and fibre for cane payment purposes". Such instruments include volumetric glassware, Brix hydrometers, polarimeters or saccharimeters, polarimeter tubes, refractometers, balances, weights and thermometers. The metrology laboratory of the Bureau retains standard equipment certified by the National Standards Laboratory, Sydney, and is registered with the National Association of Testing Authorities Australia for classes of tests for the examination of all the abovementioned apparatus. Examination of apparatus calibrated at 20 °C is conducted in a room in which the temperature is controlled at 20 + 1 °C and the relative humidity at 5 5 + 5 per cent. When the equipment being tested is made to a specified standard the tests are conducted for compliance with that standard. In the absence of any nominated standard, the equipment is examined for compliance with tolerances which apply to Class B requirements of the relevant British or Australian standards for the particular item of apparatus, or for compliance with the specifications for apparatus used in the analysis of cane for payment purposes as outlined in Table XXV. Reports are issued for all apparatus tested and when the tests are conducted in accordance with the terms of registration with NATA, the reports are endorsed to this effect. In addition if the apparatus is approved for use in the analysis of cane for payment purposes the report is endorsed accordingly. As outlined in the introduction to Chapter V the unit of volume is based on the kilogramme, i.e. the old litre and millilitre have been retained throughout this edition of the manual. Thermometers All thermometers should be carefully tested before being put into use. The service available at the Bureau is for thermometers in the range 0 to 110 °C. They are calibrated for use in the vertical position either partially immersed or immersed to the reading, by comparison with mercury-in-glass thermometers which have been standardized by the National Standards Laboratory Australia. It is customary to test at the icepoint (0 °C) and the highest graduation mark, as well as at three or four intermediate points. Brix Hydrometers The testing of Brix hydrometers covers all ranges within the limits of 0 to 70° Brix. The method of standardization is by comparison of readings of the test hydrometer with those of a standard hydrometer of known corrections. This is carried out in solutions contained in glass cylinders of sufficient size

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to allow both hydrometers to float freely side by side. This method is independent of temperature but a constant temperature is desirable. At the Bureau the testing is carried out in a constant temperature room at The reading of each hydrometer is obtained by viewing, from below the liquid surface, the point where the level of the liquid surface intersects the stem of the hydrometer. This point is clearly defined when a screen painted with the top section white and the lower section black is placed behind the cylinder

fig. 36- A dual comparator used by the Bureau for checking the length of sacchari meter tubes.

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with the junction of the black and white sections slightly below the surface of the solution when both hydrometers are immersed. This screen provides a dark ellipse around the stem of the hydrometer. This ellipse becomes a thin straight line as the head is raised to bring the eye to a position exactly on the level of the surface of the liquid. With the eye at this level the reading of each hydrometer is taken without altering the position of the head. Readings are thus obtained on the two hydrometers under identical conditions. The scale is checked at each end of the range and at a third point approximately in the middle. Polarimeter Tubes For the calibration of length of polarimeter tubes a comparator (Fig. 30) which incorporates two dial gauges is employed. Each tube is compared with a standard bar of known length, the dial gauge measuring the difference between the lengths of the tube and the bar to an accuracy better than 0.01 mm. The two dial gauges provide a check on the accuracy of measurement; a difference between the two readings indicates that a check on the dial gauges is necessary. This calibration is carried out in the constant temperature room Tolerances for tubes are shown in Table XXV. Cover Glasses ("over glasses for polarimeter tubes are checked for strain by means of a strain viewer. They are also examined to ensure that the surfaces are plane parallel and free from scratches or other defects. Saccharimeters The scales of saccharimeters are calibrated bv by means of live standard quartz plates. nlates. These plates cover a range from Saccharimeters are also examined for correct mechanical and optical operation and anv any defective parts are replaced where possible. The tolerance is shown in Table XXV. Quartz Plates Ouartz control plates for use with quartz wedge saccharimeters are tested in a Hates Fric saccharimeter for S rotation. The rotation in angular degrees for subsequent conversion to S is also determined in a Schmidt and Haensch polarimeter using the sodium yellow 5892 A or the mercury green 5461 A wavelengths of light. Ouartz plates are also tested for uniform thickness and lor any strain due to incorrect mounting. Refractometers Abbe refractometers are tested against calibrated liquids and glass standards covering the range 1.33 to 1.65 refractive index at 20 C. Balances Balances up to a maximum capacity of five kilogrammes are tested according to the principles set out in Chapter III. Weights Weights of values up to 1(H) gramme are standardized on the basis of weighings made in air of density 0.00120 g/ml against standard weights of density S.O g/ml. The method of double weighing is used. Volumetric Glassware Calibration of volumetric glassware is determined according to the method set out in Chapter V for each item of glassware.

CHAPTER VII SAMPLING OF SUGAR MILL PRODUCTS In the preceding chapters considerable attention has been paid to the necessity for precision in all apparatus employed in sugar laboratory control work. However, accurate apparatus and refined methods of analysis are totally worthless if the material analysed is not representative of the total substance, the composition of which it is desired to determine. Sugar-mill products in particular present a most difficult problem in this regard, but unless complete and accurate methods of sampling are employed the laboratory control must be regarded as only approximate and indefinite. The method of sampling depends, of course, on the nature of the particular product; and further, an accurate analytical result is of little value for control purposes if the total quantity of substance is not, in turn, accurately determined. Thus, a true analysis of a representative sample of mixed juice gives no measure of the quantity of sugar entering manufacture, unless the true quantity of such juice is also known. The necessity for the highest degree of precision in both sampling and measuring cannot be overemphasized. Yet all too often one finds that the supervision of these operations is placed in the hands of juniors, while the expert technician performs the analyses. It is certainly true that greater precision in results is often obtained by having the chief chemist carry out the sampling and by leaving the analyses to the laboratory junior, but it must be emphasized that, whoever takes the sample, it must be taken in a completely unbiased manner. It must always be remembered that even the best sampling methods are approximate, and chemists should be continually on the watch for improvements in technique. The following methods are regarded by the Bureau as being simple and practicable, and at the same time, not unscientific. Cane The correct sampling of a field of cane is quite a difficult matter. As the result of studies which have been carried out, it has been found that a large number of individual sticks must be selected at random from all parts of the field if an accurate estimate of its c.c.s. is desired. The number of stalks necessary depends on the degree of variation in crop growth from point to point in the block, particularly if the crop is far removed from maturity. From 20 to 50 sticks should be regarded as the range of sampling necessary. The best method for determining the degree of maturity of a crop is to carry through a series of systematic tests. The collection of stick samples for fibre analysis was formerly a universal practice at Queensland mills. This method of cane sampling is fully described in Regulation 57 of the Regulation of Sugar Cane Prices Act, but it has been largely replaced by the practice of sampling prepared cane. Prepared cane samples can be used for the determination of cane fibre by disintegrating the sample in a hammermill or cutter grinder, transferring the sample to a fibre bag and determining fibre in the usual manner; or the prepared cane samples can be used for direct analysis of cane, utilizing the wet disintegrator to determine Brix and pol and a Spencer or similar type of air stream oven to determine moisture. Prepared cane is usually obtained from the elevator feeding into the number one mill hopper by means of a hydraulically or

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pneumatically operated door in the b o t t o m of t h e elevator. In order to avoid t h e risk of i n c o r r e c t s a m p l i n g c a u s e d by t h e p o s s i b i l i t y of s e g r e g a t i o n in t h e carrier, i t i s i m p o r t a n t t h a t t h e d o o r c o v e r a s m u c h o f t h e w i d t h o f t h e e l e v a t o r a s possible. T h e d o o r o p e n i n g s h o u l d also b e sufficiently w i d e t h a t a free fall of t h e full d e p t h of t h e c a n e in t h e e l e v a t o r o c c u r s . T h e p r e p a r e d c a n e is u s u a l l y allowed to fall o n t o a l a r g e s a m p l i n g t a b l e w h e r e it is s p r e a d o u t a n d s u b - s a m p l e d b y h a n d for h a m m e r - m i l l i n g o r d i s i n t e g r a t i o n . V a r i o u s a v e n u e s for a u t o m a t i c m e c h a n i c a l s u b - s a m p l i n g a r e a t p r e s e n t b e i n g i n vestigated.

Juice Various devices are employed for obtaining continuous samples of juice from the mills and juice gutters. The simplest form is probably a metal container provided with a conical lid in which a small hole has been drilled. This hole is covered with fine gauze to exclude bagasse particles. The container is usually suspended in the stream of juice from the first roller of the train. Tests have shown that if three such vessels are suspended beneath the same roller the samples collected may vary in composition within relatively wide limits, and, therefore, it is essential to collect a sample from the full length of the roller. This may be done by fitting a trough beneath the roller in such a way that the entire quantity of juice expressed by the roller is collected. At the centre of the trough a cup is provided to which is attached a large downpipe several inches long. The sampler is placed directly below the centre of the outlet. This method suffers from a serious disability. The sample is collected at a uniform rate, irrespective of the rate of juice flow. With normal crushing the variation will not be great, and the sample obtained should be fairly representative of the entire juice; but this limitation should be borne in mind in those areas where the cane supply is frequently highly variable. The size of the hole in the container determines the capacity of the sampler. If the hole is too large frequent changes are necessary, while if too small the sample is insufficient. For normal sampling the hole is made of such dimensions as to provide a gallon of sample juice every four hours. For first expressed juice sampling this method has now been superseded by automatic continuous devices. Several types are in use in Queensland, but in all the collection of the sample involves the use of a trough to catch the juice, this trough being constructed to conform with Regulation 57 of the Regulation of Sugar Cane Prices Act. All of the juice flow from this trough is collected and fed into the suction of a juice sampling pump. By means of a proportioning device, part of the juice flow from the pump is diverted to a sample can system located adjacent to the first mill or in the laboratory, and the remainder returned to the mill bed. Normally the sample cans are held in an automatic sampling device which changes the sample flow from one can to the next as each successive rake of cane comes through the first mill. The samples are identified by means of pins or balls in sample wheels which have their speeds geared to the speed of the carrier or elevators, or, in the most recent type of automatic sampler, the samples are tracked through the conveying system electronically. This electronic sampler also has the facility of being able to alter the proportioning device so that a more or less constant quantity of juice is collected for each rake of cane, irrespective of the length of the rake. Sampling from juice gutters also presents difficulties. The best device for this purpose is a small under-shot water wheel. One of the spokes is made

SO

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SUGAR MILL PRODUCTS

hollow and terminates in a spoon-shaped blade. This spoon takes up a little of the juice, which flows down the spoke to the hollow axle which is provided, and thence into the container. The main objection to this type is that the small pipes are liable to become choked, after which sampling will cease. In order to ensure a true average sample, small baffles should be fitted in the trough upstream from the wheel to effect a thorough mixing of the juice. Sampling of mixed juice, particularly where suspended matter deter minations are to be carried out on the juice, is best accomplished by means of a pitot-tube type sampler placed in the delivery pipe from the mixed juice pump. In this way, a sample of the juice is taken before the suspended solids have had a chance to settle, and a reasonably accurate sample can be obtained. A moving receiving tube which passes at regular intervals through the juice flowing from the sampling tube comprises an efficient method of subsampling the main sample flow. Syrup With the replacement of reciprocating syrup pumps by centrifugal pumps, samplers such as the Calumet described in earlier editions of this Manual are no longer applicable for the purpose of syrup sampling. Continuous sampling of syrup may be effectively carried out by piping a small sample of syrup from the pump delivery line and sub-sampling this smaller flow by means of a sample splitter. Syrup samplers must be checked and cleaned at regular intervals to ensure that crystallization does not occur, thus blocking the sampler. If continuous sampling is not used, syrup may be snap sampled at regular intervals and the snap samples composited over a period. Preservative is not required for syrup, molasses, or massecuite samples. Massecuites and Molasses The composition of massecuite varies from point to point within the pan, due to imperfect circulation, and therefore the sample should be taken continuously as the massecuite is discharging. For control purposes a "snap" sample is usually sufficient, though for preference three such samples should be taken and composited for each strike. These should be drawn at regular intervals as the massecuite is discharged, but the first should not be taken from the first flow of massecuite. In compositing samples of massecuite, care must be taken that the respective portions are proportional to the quantity of massecuite which each represents. Molasses may be sampled similarly to syrup (q.v.) and similar precautions as with syrups should be taken in preparing a representative composite sample. It is preferable to obtain a continuous sample of final molasses. A convenient sampler for those mills using molasses scales is to fit a small pipe leading from the receiving tank to a sample container. Each time the weighing tank discharges, the inlet to this pipe is submerged to a similar depth, and the quantity of molasses transferred to the container is uniform. Raw Sugar Raw sugar is now handled in bulk in Queensland, and sugar sampling at the bulk terminals is carried out by removing a portion of the sugar from the bulk containers as they are being discharged. At the mill various devices are being used for sugar sampling. Theoretically, it is best to sample from a stream in free fall, and, if the practical difficulties could be overcome, this could be achieved on a sugar belt if the belt were fitted with a sampling gap, almost the full width of the belt, and a sample can placed under the belt at the feed point. This is however, a rather difficult and expensive method of

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sampling and samples are usually obtained by means of motor-driven sampling spoons or other devices. The disadvantages of these devices are that, unless very sophisticated control equipment is used, they are not strictly proportional to sugar rate and are easily fouled by wet sugar. Bagasse The accurate sampling of bagasse is a very difficult problem. Here, again, no satisfactory continuous sampler has been devised and hand sampling is necessary. In general the analyses of final bagasse samples are not considered individually, but only with reference to their average value, hence advantage may be taken of the fact that bagasse can be preserved for reasonable periods. In this way samples may be taken at frequent intervals without increasing the number of analyses to be made by the chemist. For final bagasse the compositing of samples taken at short intervals, and the subsequent analysis of the well mixed sample, is strongly recommended in preference to the taking of "snap" samples once or twice per shift. The former method is far more representative of the bagasse in process, and the sampling procedure described below does not inflict any extra work on the analyst. For sampling bagasse a small chute the width of the bagasse blanket is provided. This chute is held across and below the falling bagasse, and when it is full the contents are transferred to a closed container containing preservative. A suitable type is shown in Fig. 37. The chute should hold 2 or 3 lb of final bagasse so that the resulting total sample is about 30-50 lb. When the composite is completed the large sample is spread out, rapidly but effectively mixed, and then sub-sampled for analysis. The mixing must be carried out thoroughly, otherwise the whole sampling process will have been wasted; but it must be done quickly to avoid moisture loss by evaporation. This loss is to a certain extent minimized by the fact that, by the time mixing is carried out, the temperature of the sample will have dropped to approximately that of its surroundings. In mills where sudden changes in varieties and conditions occur, half an hour should be the maximum interval, whilst in others where conditions are comparatively uniform a one-hour period is permissible. The time schedule for sampling should be adhered to, irrespective of milling conditions, as long as the mill is crushing. The composite sample Fig. 37—Illustrating container recommended is preserved by means of a pad for compositing samples of bagasse.

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s a t u r a t e d w i t h s t r o n g a m m o n i a a n d c h l o r o f o r m ( p r o p o r t i o n s 6 : 1) or t o l u e n e . W h i l e , a s m e n t i o n e d p r e v i o u s l y , final b a g a s s e c a n b e p r e s e r v e d for a r e a s o n a b l e l e n g t h of t i m e , four h o u r l y a n a l y s i s p e r i o d s a r e c o n s i d e r e d p r e f e r a b l e to a o n c e p e r shift a n a l y s i s of t h e c o m p o s i t e . S a m p l e s f r o m earlier mills i n t h e t r a i n a r e u s u a l l y i n t e n d e d t o s u p p l y t h e e n g i n e e r w i t h specific i n f o r m a t i o n a n d m a y n o t b e i n t e n d e d for c o n t r o l p u r p o s e s . H o w e v e r , s o t h a t t h e s e s a m p l e s c a n b e reliable, t h e y s h o u l d b e t a k e n o v e r a p e r i o d o f t i m e w i t h a shovel. I t i s i m p o r t a n t t h a t t h e full d e p t h o f b a g a s s e b e s a m p l e d since t h e t o p s u r f a c e m a t e r i a l h a s a h i g h e r j u i c e c o n t e n t t h a n t h e r e m a i n d e r . Also s a m p l i n g s h o u l d b e c a r r i e d o u t a c r o s s t h e full w i d t h of t h e roller.

Filter Cake With the rotary filter, next to weighing at regular intervals the complete out-turn of cake in a given time, the following procedure is recommended. The length of the filter is divided into a suitable number of equal portions. At half hourly intervals the mud from one or more screen segments (depending on the size of the screens and the length of the portion) is caught on a suitable tray. This quantity of mud from the known area of screen is then weighed, and a small area removed by means of a sampler resembling a scone cutter. The weight of mud in each trayful is recorded and the small samples composited in a closed container for subsequent analysis. At the end of a period the total weight of cake produced by the filter can be calculated from the following expression:—

where W = total weight of cake for the period, in tons w = average weight contained on mud sample tray in pounds n — revolutions of filter during period (preferably obtained from revolution counters) a = area of cake removed by the mud sample tray A = area of screen surface on the filter. The weight of pol in mud can then be calculated from the cake weight and the pol per cent cake determined on the composited sample. Composite mud samples cannot be effectively held for pol determination for periods much longer than four hours, and analysis of mud samples for pol twice per shift is recommended. Care of Samplers and Containers All sugar-mill products are susceptible to rapid deterioration due to bacterial activity; it is therefore imperative that all sample containers be maintained in a thoroughly clean condition and be subjected to frequent sterilization. Sample jars should be washed with hot water after each usage and thoroughly dried. Metal containers (preferably of stainless steel) should be frequently washed and steamed. Preservation of Samples Preservation of certain specific samples has been discussed in this chapter, but details of common preservatives and recommendations for their use will be found in the chapter on laboratory reagents.

CHAPTER VIII LABORATORY R E A G E N T S This chapter has been re-arranged by listing, wherever possible, the various reagents under each specific analysis. Celite and Triethanolamine, for example, are included under the heading of "Filterability Determination". It is anticipated t h a t this method of presentation will expedite analytical procedure. Poisons: A good analyst is familiar with the reagents being used and their individual properties. The repeated use of common reagents, however, C o m m o n Toxic Materials

General Toxicity

Highly toxic. Avoid inhalation of the vapour. Poisonous, combustible, volatile with steam. A narcotic agent with insidious chronic effects. Prolonged exposure to low concentrations can result in chronic irritation of the nervous system—an acute narcotic agent in high concentrations. Highly toxic gas. Not readily detected by the senses at a concentration of one p.p.m. Highly corrosive. Explosive when mixed with certain organic solvents. Toxic. Included in this table for comparative purposes. A very poisonous gas. A chemical commonly taken too lightly. Higher concentrations are very dangerous as the sense of smell becomes paralysed. Cumulative poisons. Refer to the special precautions listed in this chapter. Highly toxic. Can be absorbed via the respiratory tract or by contact with the skin. Corrosive to all tissues. Permanent damage to the respiratory tract can result from prolonged contact. Highly corrosive. Severe lung damage can result from inhalation of the vapour. Prolonged exposure to low concentrations can cause inflammation of nasal and throat tissues. Narcotic agent. Its toxicity is considered to be associated with the benzene concentration present as an impurity. Highly toxic. Do not inhale or allow this chemical to come in contact Avith the skin. Parts of gas or vapour per million parts of air by volume. No specific level adopted at this stage by the National Health and Medical Research Council of Australia.

84

LABORATORY REAGENTS

can t e n d to allow a "familiarity b r e e d s c o n t e m p t " a t t i t u d e to arise. T h e m a j o r i t y of c h e m i c a l s u s e d in s u g a r l a b o r a t o r i e s a r e highly toxic substances, a n d for t h e s a f e t y o f all c o n c e r n e d , t h i s p o i n t c a n n o t b e e m p h a s i z e d t o o strongly. Some general information on t h e toxic properties of some of t h e more commonly used chemicals in sugar laboratories is listed above in t a b u l a r f o r m . T h e m a x i m u m p e r m i s s i b l e levels i n t h i s t a b l e a r e t h e t h r e s h o l d l i m i t values which h a v e been proposed by t h e American Conference of Governm e n t a l I n d u s t r i a l H y g i e n i s t s , a n d w h i c h h a v e also b e e n r e c o m m e n d e d b y t h e N a t i o n a l H e a l t h a n d Medical Research Council of Australia. However, t h e fact t h a t a chemical is n o t listed in this table does n o t necessarily m e a n t h a t i t i s n o t t o x i c , a n d all l a b o r a t o r y c h e m i c a l s a n d r e a g e n t s s h o u l d b e h a n d l e d as if t h e y were poisonous. W h e n k n o w n toxic or corrosive chemicals are being used the wearing of the appropriate protective equipment, such as goggles, g l o v e s , a n d r e s p i r a t o r s , i s s t r o n g l y r e c o m m e n d e d . Boiler Water Analysis Alkalinity Barium Chloride Solution—Dissolve 10 g of b a r i u m c h l o r i d e B a C l 2 . 2 H 2 0 i n d i s t i l l e d w a t e r a n d d i l u t e t o 100 m l . Methyl Orange Indicator—Dissolve 0.10 g of m e t h y l o r a n g e in 100 ml of h o t w a t e r , cool, f i l t e r i f n e c e s s a r y a n d a d j u s t t o v o l u m e . Phenolphthalein Indicator—Dissolve 1.0 g of p h e n o l p h t h a l e i n in 60 ml of industrial m e t h y l a t e d spirits. W h e n dissolved, a d d 40 ml of water, m i x well, filter i f n e c e s s a r y a n d a d j u s t t o v o l u m e . Sodium

Sulphate

Crystals—Reagent

grade

Na2S04.10H2O.

Sulphuric Acid 0 . 0 2 N — D i l u t e 10.0 ml of 1 . 0 0 N s t a n d a r d s u l p h u r i c a c i d to 500 ml w i t h distilled water. T h e p r e p a r a t i o n of 1 . 0 0 N s t a n d a r d acid is described elsewhere in this chapter. Phosphate Acid Molybdate Solution—Dissolve w i t h o u t h e a t i n g , 8.8 g of a m m o n i u m m o l y b d a t e i n 100 m l o f w a t e r . I n a s e p a r a t e c o n t a i n e r , c a r e f u l l y a d d 3 8 m l of concentrated sulphuric acid to a p p r o x i m a t e l y 300 ml of water. Allow t h e d i l u t e d a c i d t o cool t o r o o m t e m p e r a t u r e a n d t h e n t r a n s f e r t h i s s o l u t i o n a n d t h e a m m o n i u m m o l y b d a t e t o a 5 0 0 m l v o l u m e t r i c flask. D i l u t e t o v o l u m e w i t h distilled w a t e r . Hydroquinone—Dissolve 0.5 g of h y d r o q u i n o n e in 50 ml p h u r i c acid. S t o r e i n a d a r k o r a m b e r c o l o u r e d b o t t l e .

of

0.02N

sul-

Carbonate—Sulphite Solution—Dissolve 130 g of a n h y d r o u s p o t a s s i u m c a r b o n a t e a n d 24 g of s o d i u m sulphite ( N a 2 S 0 3 . 7 H 2 0 ) in 500 ml of w a t e r . Hardness Wanklyns Soap Solution—This is u s u a l l y p u r c h a s e d as a p r e p a r e d r e a g e n t from a chemical supplier. Sodium Sulphite Potassium Iodate—Iodide Solution—Dissolve 0 . 7 1 3 g of p o t a s s i u m i o d a t e in 2 0 0 ml of w a t e r a n d t h e n a d d 7 g of p o t a s s i u m i o d i d e a n d 0.5 g of s o d i u m b i c a r b o n a t e . W h e n d i s s o l v e d , t r a n s f e r t o a o n e l i t r e v o l u m e t r i c flask a n d dilute to volume. Starch Indicator Solution—Mix 0.5 g of s o l u b l e s t a r c h w i t h 5 ml of c o l d w a t e r , a n d t h e n a d d 100 m l o f b o i l i n g w a t e r . H e a t o n a b o i l i n g w a t e r b a t h

LABORATORY REAGENTS

85

for 5 m i n u t e s , cool a n d s t o r e in a r e f r i g e r a t o r . (A c o m m e r c i a l solid i n d i c a t o r p r e p a r a t i o n c a n also b e u s e d ) . Sulphuric Acid, 6.5 per cent v/v.—Carefully a d d 65 ml of c o n c e n t r a t e d s u l p h u r i c a c i d t o a p p r o x i m a t e l y 9 0 0 m l o f distilled w a t e r . Cool t o r o o m t e m p e r a t u r e a n d dilute to a volume of one litre. Sulphate Barium Chloride, 0 . 0 4 N — D i s s o l v e 4 . 8 8 6 g of b a r i u m c h l o r i d e ( B a C l 2 . 2 H 2 0 ) in distilled w a t e r a n d dilute to a volume of one litre. EDTA—(Diaminoethanetetra—acetic acid, disodium salt), 0.02N.—Dissolve 3.72 g of E D T A in d i s t i l l e d w a t e r a n d d i l u t e to a v o l u m e of o n e l i t r e . Hydrochloric Acid, 0 . 5 N approximately—Measure o u t 45 ml of c o n c e n t r a t e d h y d r o c h l o r i c a c i d ( d 1.18) a n d p o u r i n t o a p p r o x i m a t e l y 5 0 0 m l o f water. Mix a n d t h e n dilute to a volume of one litre. Solochrome Black Indicator—Weigh o u t 0.5 g of s o l o c h r o m e b l a c k W . D . F . A . a n d d i s s o l v e in a b o u t 2 ml of h o t w a t e r . A d d 10 g of s o d i u m chlori d e , m i x t h o r o u g h l y a n d d r y a t 105 °C. W h e n d r y , a d d 9 0 g o f s o d i u m c h l o r i d e a n d g r i n d t h o r o u g h l y . T h i s i n d i c a t o r c a n also b e p u r c h a s e d i n t a b l e t f o r m . Sulphate Buffer Solution—To 56.5 ml of a m m o n i a (d = 0.880) a d d 4.125 g o f a m m o n i u m c h l o r i d e a n d m a k e u p t o 5 0 0 m l w i t h w a t e r . A d d 3.72 g o f E D T A , m i x a n d t h e n a d d 2.03 g o f m a g n e s i u m c h l o r i d e ( M g C l 2 - 6 H 2 0 ) . Buffer S o l u t i o n s pH 4 . 0 0 Potassium Hydrogen Phthalate Buffer—Dissolve 10.21 g of d r y p o t a s s i u m h y d r o g e n p h t h a l a t e A . R . i n freshly distilled w a t e r . D i l u t e t o o n e l i t r e . T h e p H o f t h i s s o l u t i o n i s defined a s b e i n g 4.00 a t 1 5 ° C a n d 4 . 0 1 a t 3 0 °C. pH 6.85 Mixed Phosphate Buffer—Dissolve 3.402 g of p o t a s s i u m d i h y d r o g e n p h o s p h a t e K H 2 P 0 4 a n d 4.45 g of disodium h y d r o g e n p h o s p h a t e N a 2 H P 0 4 . 2 H 2 0 i n freshly distilled w a t e r a n d d i l u t e t o o n e l i t r e . T h e p H o f t h i s buffer i s 6.85 a t 2 5 ° C a n d i t h a s a negligible p H c h a n g e o v e r t h e r a n g e of ordinary room t e m p e r a t u r e . pH 9.18 Borax Buffer—Dissolve 19.071 g of s o d i u m b o r a t e N a 2 B 4 0 7 . 1 0 H 2 O i n f r e s h l y distilled w a t e r a n d d i l u t e t o o n e l i t r e . T h e s o l u t i o n h a s a p H of 9.18 a t 2 5 °C a n d 9.07 a t 38 °C. Clarifiability T e s t Lime-Sucrose

Reagent

T w o solutions are initially required: S o l u t i o n A:

D i s s o l v e 150 g of refined s u g a r in a p p r o x i m a t e l y 60 ml of hot water.

Solution B:

Slowly add, with stirring, 15 g of A . R . calcium oxide to 100 ml of a l m o s t b o i l i n g w a t e r . Carefully m i x s o l u t i o n B i n t o s o l u t i o n A . F i l t e r t h e h o t s o l u t i o n t h r o u g h a 6 3 3 A o r s i m i l a r t y p e o f filter p a p e r u n d e r v a c u u m , u s i n g S u p e r c e l f i l t e r a i d . T h e filtered s o l u t i o n m u s t b e s t o r e d i n a r e f r i g e r a t o r , w h e r e i t will k e e p for a p p r o x i m a t e l y three weeks. Filterability Determination Triethanolamine Buffer Solution—Two in 50 per cent w/w glycerol solution.

solutions

are

prepared

separately

86

LABORATORY REAGENTS

Solution A: Dissolve 15.0 g of A.R. calcium acetate in approximately 300 ml of 50 per cent glycerol solution in a beaker. Mild heating may be used. Solution B: In a second beaker, dissolve 400 g of triethanolamine with approximately 200 ml of 50 per cent glycerol. N.B.—Triethanolamine can cause severe skin irritation. Avoid direct contact. Transfer solutions A and B to a one litre volumetric flask and use 50 per cent glycerol to rinse both beakers and to dilute to volume. Mix well and allow to stand overnight. Add a small quantity of filter aid and filter. Store in a stoppered clear glass bottle. Celite—This is a standard filter aid No. 505, wrhich has been standardized by the C.S.R. Company. No other type of filter aid is directly applicable to this test. Glass Cleaning Solution Dissolve 80 g of potassium bichromate (K 2 Cr 2 0 7 ) in 300 ml of water in a litre pyrex beaker and cool to room temperature. Carefully add 460 ml of concentrated sulphuric acid with stirring. The addition of the acid precipitates chromic acid, and the solution will act as an effective cleaning agent while red crystals of this compound are present. Glass cleaning solution is extremely toxic and highly corrosive. All necessary precautions should be observed and it is advisable to stand the bottle in a lead tray so that damage to bench surfaces can be minimized. Indicators The preparation and characteristics of indicators for selected pH ranges are listed below: Indicator

Preparation

pH Range

Colour Change

Methyl Violet Ouinaldine Red Methyl Orange Bromphenol Blue

0.25 g per 100 ml of water 0.10 gin 100 ml of ethyl alcohol 0.10 g per 100 ml of water 0.10 g in 8.6 ml of 0.02 x. NaOH. Dilute to 250 ml with water. 0.10 g in 7.15 ml of 0.02 N. NaOH. Dilute to 250 ml with water. 0.10 g in 18.6 ml of 0.02 x. NaOH. Dilute to 250 ml with water. 0.10 g in 9.75 ml of 0.02 x. NaOH. Dilute to 250 ml with water. 0.10 g in 8.0 ml of 0.02 x. NaOH. Dilute to 250 ml with water. 0.10 g in 14.2 ml of 0.02 N. NaOH. Dilute to 250 ml with water. 0.10 g in 13.1 ml of 0.02 x. NaOH. Dilute to 250 ml with water. 1.0 g in 60 ml of ethyl alcohol. Dilute to 100 ml with distilled water. 0.10 g in 100 ml of ethyl alcohol. 0.10 g in 100 ml of 50% ethyl alcohol.

0.1—1.5 1.4—3.2 3.1—4.4 3.0—4.6

Yellow to blue Colourless to red Red to orange Red to orange

3.8—5.4

Yellow to blue

4.2—6.2

Red to yellow

5.2—7.0

Yellow to red

6.0—7.6

Yellow to blue

6.8—8.4

Yellow to red

7.2—8.8

Yellow to red

Bromcresol Green Methyl Red Bromphenol Red Bromthymol Blue Phenol Red Cresol Red Phenolphthalein Thymolphthalein Alizarin Yellow

8.2—10.0 Colourless to red 9.3—10.5 Colourless to blue 10.0—12.0 Yellow to lilac

LABORATORY REAGENTS

87

Phosphate Analysis Acid Molybdate Solution—Dissolve 16.6 g of ammonium molybdate in 600 ml of distilled water. Gentle heating may be used, but the temperature must not rise above 60 °C. Carefully add 96 ml of concentrated sulphuric acid and cool. Dilute to one litre with distilled water. Store in a dark bottle in a cool place. Acid Reagent—Carefully add 96 ml of concentrated sulphuric acid to 600 ml of distilled water. Cool and dilute to one litre. Acid Washed Supercel—Add 50 g of supercel to one litre of distilled water. Add 50 ml of concentrated hydrochloric acid and stir for 5 minutes. Vacuum filter the slurry and wash with distilled water until no trace of acid remains (silver nitrate test). Dry the supercel at 100 °C for 6 hours and store in a screw top jar. Amidol Reagent—Dissolve 1.0 g of amidol and 20 g of sodium metabisulphite in distilled water. Dilute to a volume of 100 ml. Add a level teaspoon of acid washed supercel and filter under vacuum through two Whatman No. 5 filter papers. Store in a dark bottle and hold under refrigeration. Prepare freshly each week. Standard Phosphate Stock Reagent—Dry approximately 2 g of A.R. potassium dihydrogen phosphate (KH 2 P0 4 ) for 1 hour at 110 °C. Weigh out 1.0984 g of the dried salt, dissolve in distilled water and dilute to 250 ml in a volumetric flask. This reagent contains 1.00 mg/ml of P and should keep for about two years if a few ml of chloroform are added and it is stored in a refrigerator. Standard Phosphate Solution—Pipette 10.0 ml of the stock reagent into a one litre volumetric flask and dilute to volume. This solution contains 0.01 mg/ml of P and is used for the preparation of the standard phosphate graph as described in Chapter IX. Pol Determination Acetic Acid 1 + 4—This solution is usually prepared in relatively large quantities. Apart from its use in pol determinations, the solution is effective for removing precipitated lead salts from volumetric glassware. To prepare a litre of 1 + 4 solution, add 200 ml of glacial acetic acid to distilled water in a litre measuring cylinder and dilute to volume. Herles' Reagents—Two separate stock solutions are prepared in the following manner : Solution A—Dissolve 50 g of A.R. sodium hydroxide pellets with distilled water in a litre volumetric flask. Dilute to volume after cooling. Solution B—Dissolve 500 g of lead nitrate with distilled water in a litre volumetric flask. Dilute to volume. Reagent Check—Dispense an equal volume of solution A and solution B into a beaker. Determine the pH of the resultant mixture. If the value obtained is not below 7 pH, solution A must be diluted until the resultant mixture gives an acid reading. N.B.—Sodium hydroxide and lead nitrate are dangerous solutions when prepared to the above concentrations. They should not be dispensed with mouth aspirated pipettes.

88

LABORATORY REAGENTS

Lead Acetate Safety Precautions with Lead Compounds:—Lead s a l t s a r e c u m u l a t i v e p o i s o n s a n d t h e following r u l e s s h o u l d b e o b s e r v e d w h e n a n y l e a d c o m p o u n d s or solutions containing lead are being used. 1 . Vessels c o n t a i n i n g l e a d s o l u t i o n s m u s t b e l a b e l l e d " P o i s o n " . 2. Do not open containers of d r y lead a c e t a t e in an enclosed room. A v o i d b r e a t h i n g t h e fine d u s t o f t h i s s u b s t a n c e , e s p e c i a l l y w h e n transferring it from one container to another. 3. Always wash the h a n d s thoroughly after handling d r y lead a n d polarizing solutions. 4 . A v o i d w i p i n g t h e face o r e y e s w i t h a l a b o r a t o r y glass t o w e l a n d d o n o t u s e t h e s e t o w e l s for w i p i n g e a t i n g u t e n s i l s . 5. K e e p t h e reagents a n d polarizing solutions a w a y from cuts or a b r a sions. 6 . D o n o t u s e p o l a r i z a t i o n filter-glasses for d r i n k i n g p u r p o s e s . 7 . T h e a p p a r a t u s a n d p r o c e d u r e s u s e d for p r e p a r i n g o r t r a n s f e r r i n g w e t or d r y lead should be such t h a t there is no risk t h a t an analyst m a y ingest or absorb a n y of t h e reagent. 8. A s u p p l y of a n t i d o t e s s h o u l d be p r o v i d e d in a c e n t r a l p l a c e in a laboratory, together with instructions as to how they should be used, viz. 1 0 p e r c e n t a q u e o u s m a g n e s i u m s u l p h a t e , followed b y m i l k o r a l b u m e n i n cold w a t e r . 9. A n o t i c e c o n t a i n i n g t h e a b o v e p r e c a u t i o n s s h a l l be p o s t e d in a p r o m i n e n t place in t h e laboratory. Basic Lead Acetate Powder—The m o r e i m p o r t a n t specifications p e r t a i n ing to t h e quality of basic lead a c e t a t e powder are shown below: T o t a l L e a d (as P b O ) * * : N o t less t h a n 7 5 . 0 p e r c e n t B a s i c L e a d (as P b O ) * * : N o t less t h a n 3 3 . 0 p e r c e n t Moisture*: N o t m o r e t h a n 1.5 p e r c e n t Insoluble in water: N o t m o r e t h a n 2.0 p e r c e n t Insoluble in acetic acid: N o t m o r e t h a n 0.05 p e r c e n t A n a d d i t i o n a l specification t o m e e t A u s t r a l i a n r e q u i r e m e n t s i s t h a t 7 5 p e r c e n t m u s t p a s s t h r o u g h a 115 m e s h T y l e r sieve a n d 100 p e r c e n t m u s t p a s s t h r o u g h a 3 5 m e s h T y l e r sieve. * M o i s t u r e is d e t e r m i n e d by d r y i n g 1 g of s a m p l e at 100 °C for 2 h o u r s . **Total a n d Basic Lead are determined by the National B u r e a u of S t a n d a r d s M e t h o d ( b a s e d o n C i r c u l a r C . 4 4 0 p . p . 120-122). Basic Lead Acetate Solution (Wet Lead)— D i s s o l v e 5 6 0 g of b a s i c l e a d a c e t a t e p o w d e r ( c o n f o r m i n g t o t h e a b o v e r e q u i r e m e n t s ) i n o n e l i t r e o f freshly boiled distilled w a t e r , w h i c h h a s p r e v i o u s l y b e e n cooled, i n a s e a l e d c o n t a i n e r . Boil for 3 0 m i n u t e s a n d a l l o w t o s e t t l e o v e r n i g h t i n a sealed c o n t a i n e r . S t a n d a r d i z a t i o n : D e c a n t t h e s u p e r n a t a n t l i q u i d . D i l u t e w i t h freshly b o i l e d distilled w a t e r to 1.25 specific g r a v i t y (54 B r i x ) . T h e m e t h o d s o f a n a l y s e s p r e v i o u s l y specified for b a s i c l e a d a c e t a t e powder are again employed, with t h e variation t h a t 25 ml of wet lead solution a r e s u b s t i t u t e d for t h e o r i g i n a l 5 g s a m p l e w e i g h t . I C U M S A specifies t h a t w e t l e a d m u s t c o n t a i n b e t w e e n 9.6 a n d 10.5 g of b a s i c l e a d ( e x p r e s s e d as P b O ) p e r 100 m l o f s o l u t i o n . I f t h e q u a n t i t y d e t e r m i n e d i s a b o v e t h i s r a n g e , t h e calculated volume of glacial acetic acid should be a d d e d a n d t h e analysis repeated.

LABORATORY REAGENTS

89

N.B.—The basic lead acetate solution should be stored in a stoppered container and labelled "Poison". Neutral Lead Acetate Solution—A 10 per cent solution is used i.e. dissolve 100 g of lead acetate Pb(C 2 H 3 0 2 ) 2 in distilled water and dilute to one litre. The pH of the solution is then determined and adjusted to 7.0 with either acetic acid or sodium hydroxide. Preservatives Mercuric Chloride—Highly toxic. Prepare a saturated solution of the salt in alcohol. Store in a suitable automatic dispenser and use at the rate of 0.5 ml per litre of juice. N.B.—Mercuric chloride cannot be used in samples taken for reducing sugar analysis. Phenyl Mercuric Acetate {P.M.A.)—Prepare a solution containing 1 g of the salt per litre. Label "Poison" and store in a suitable automatic dispenser. The following table is presented as a rough guide for the preservation and storage of samples for routine mill analysis. The recommendations are of a general nature but should provide effective preservation of normal samples under average factory conditions. Preservation of Samples

*The calculated amount of lead acetate should be added with each aliquot in order to avoid overleading of initial portions of the sample.

90

LABORATORY REAGENTS

Reducing Sugar Analysis Methylene Blue Solution—Dissolve 1 g of methylene blue powder in 100 ml of distilled water. This reagent must be freshly prepared at least every six months. Phosphate-Oxalate, Deleading Solution—Dissolve 30 g of C.P. potassium oxalate (K 2 C 0 0 4 ) in 400 ml of distilled water, and 70 g of disodium phosphate (Na 2 HP0 4 .12H 2 0) in another 400 ml portion of distilled water. Pour the two solutions into a one litre volumetric flask, mix and dilute to volume. Fehling's Solution—Two reagents are separately prepared and mixed in equal volumes just prior to use: Fehling's A—Dissolve 34.639 g of C.P. copper sulphate (CuS0 4 .5H,0) in a 500 ml flask and dilute to volume. Filter through prepared asbestos. Fehling's B—Dissolve 173 g of Rochelle salt (sodium-potassium tartrate) in about 250 ml of water, mix with 100 ml of solution containing 50 g of sodium hydroxide, in a 500 ml volumetric flask. Allow to stand for two days. Dilute to volume and filter through prepared asbestos. Standard Invert Sugar Solution—Weigh out 9.500 g of A.R. sucrose and wash with approximately 100 ml of distilled water into a one litre volumetric flask. Dissolve by gently swirling the flask. Transfer 5.0 ml of concentrated hydrochloric acid into the volumetric flask. Stopper with a cotton wool plug. Allow the flask and contents to stand at room temperature from three to seven days, according to the prevailing temperature. In a separate operation, determine the volume of a prepared sodium hydroxide solution required to adjust 5.0 ml of concentrated hydrochloricacid to 3.0 pH. Use methyl orange as an indicator. Add the determined quantity of sodium hydroxide to the semi-prepared invert solution. Dissolve 2.0 g of benzoic acid in a beaker. Gentle heating may be used. Add the benzoic acid to the invert solution, cool and carefully dilute to a volume of one litre. The prepared invert solution now contains 1 gramme of invert sugar per 100 ml of solution. Standardization of Fehling' s Solution—Pipette 50.0 ml of standard invert sugar solution into a 250 ml volumetric flask. Add one drop of phenolphthalein indicator and carefully neutralize with 5 N sodium hydroxide solution. Dilute to volume with distilled water. Rinse and fill an offset burette with this solution. Pipette 5.0 ml of each of the Fehling's A and B solutions into a 200 ml conical boiling flask. Add approximately 24.5 ml of the neutralized standard invert. Heat to boiling and titrate in the manner described in Analytical Methods, Chapter IX. Repeat the determination until two successive titres agree to within 0.1 ml. The calculated titration value is 25.64 ml. If the actual result varies by more than 0.5 ml from this value, the strength of the Fehling's A must be adjusted. If the actual value is within the 0.5 ml range, but different from the calculated value of 25.64 ml, a correction factor must be calculated and applied to all determinations involving that batch of Fehling's solution.

LABORATORY REAGENTS

91

Standard Acids and Alkalis Sulphuric Acid 1.00 Normal (0.5 M)—Cautiously add 28 ml of concentrated sulphuric acid (Sp.Gr. 1.84) via a measuring cylinder to approximately 900 ml of distilled water. Cool, transfer to a one litre volumetric flask and dilute to volume. Standardize as follows: Transfer 1.0599 g of predried A.R. sodium carbonate to a 300 ml Erlenmeyer flask. Add 100 ml of distilled water, dissolve and add 2 drops of methyl orange indicator. Titrate against the unstandardized acid. The titration should require exactly 20.0 ml of 1.00 N sulphuric acid. Adjust the strength of the solution until this is obtained. Hydrochloric Acid 0.20 Normal (0.2 M)—Measure out 18 ml of concentrated hydrochloric acid (Sp.Gr. 1.18). Pour this into approximately 500 ml of water and then dilute to a volume of one litre in a measuring cylinder. Agitate to obtain thorough mixing. Standardize as follows: Weigh accurately two portions, each between 0.240 and 0.280 g, of pre-dried A.R. sodium carbonate. Carefully transfer each to wide necked 250 ml conical flasks containing about 50 ml of distilled water. Swirl gently until dissolved. Add 3 drops of methyl orange indicator and titrate against the unstandardized acid until the colour changes from yellow to orange. If V ml of acid are used for titrating W g of sodium carbonate, then W Strength of acid (factor) F = ° 0.010b x V From the two portions of sodium carbonate originally weighed out, two independent factors will be obtained. These should be in close agreement before the mean value of F is accepted. Adjustment—Note the volume of 0.2 N acid left in the one litre measuring cylinder (V ml). Add Y(F — 1) ml of water to it, mix well and repeat the standardization. The final factor (F) should be 1.00+0.005. Sodium Hydroxide, 0.20 Normal (0.2 M).—The water used for the preparation of this reagent must be free from dissolved carbon dioxide. If in doubt, boil the water just before use and cool to room temperature in a sealed vessel. Prepare a stock solution of sodium hydroxide by dissolving 53 g of the chemical in 50 ml of distilled water. Store in a polythene bottle for three days. Decant off 12 ml of the stock solution and transfer to a one litre measuring cylinder. Dilute to volume and thoroughly mix. The solution is then standardized as follows: Pipette 25.0 ml of the diluted solution into a 250 ml conical flask and add 3 drops of methyl orange indicator. Titrate with 0.2 N hydrochloric acid until the colour changes from yellow to orange. Repeat the standardization. If V ml of acid (mean of the two determinations) are required, then

Adjustment—Note the volume of 0.2 N sodium hydroxide left in the litre measuring cylinder (V ml). Add V(F — 1) ml of water to it, mix well and repeat the standardization. The final factor (F) should be 1.00^0.005. Sodium Carbonate 1.00 Normal (0.5 M)—The water for the preparation of this reagent must be free from dissolved carbon dioxide. If in doubt, boil the water just before use and cool to room temperature in a sealed vessel.

92

LABORATORY REAGENTS

W e i g h o u t 2.650 g o f a n h y d r o u s s o d i u m c a r b o n a t e a n d d i s s o l v e i n a p p r o x i m a t e l y 50 ml of w a t e r . Transfer t h e solution to a 500 ml v o l u m e t r i c f l a s k a n d d i l u t e t o v o l u m e . M i x well a n d s t o r e i n a g r o u n d glass s t o p p e r e d bottle. Starch Analysis—Sugar Calcium Chloride Dihydrate Solution—To 5 3 0 g of U n i v a r c a l c i u m c h l o r i d e d i h y d r a t e , a d d 4 7 0 g o f d i s t i l l e d w a t e r . A d j u s t t o 8.2 p H w i t h 1 N s o d i u m h y d r o x i d e . S t o r e in a s e a l e d c o n t a i n e r . Acetic Acid 1 N . — D i l u t e 57 ml of g l a c i a l a c e t i c a c i d to a v o l u m e of one litre. Calcium Chloride—Acetic Acid Reagent—Add 11 ml of 1 N a c e t i c a c i d to one litre of calcium chloride d i h y d r a t e solution. Potassium Iodate Solution 0.01 N . — W e i g h a c c u r a t e l y 0.3566 g of A . R . p o t a s s i u m i o d a t e a n d d i s s o l v e i n a l i t r e v o l u m e t r i c flask. D i l u t e t o v o l u m e a n d p o u r into a b r o w n glass s t o p p e r e d bottle. Store in a d a r k c u p b o a r d . Concentrated Potassium Iodide—10% W/V—Dissolve 10 g of A . R . p o t a s s i u m i o d i d e in a 100 ml v o l u m e t r i c flask. S t o r e in a p l a c e a w a y f r o m l i g h t in a b r o w n glass s t o p p e r e d b o t t l e . T h i s r e a g e n t m u s t b e d i s c a r d e d w h e n t h e s o l u tion becomes yellow. Potassium Iodide—Iodate Reagent—This r e a g e n t m u s t be p r e p a r e d on t h e d a y it is to be used. To one p a r t of concentrated potassium iodide 10 per cent solution a d d 9 p a r t s of distilled w a t e r a n d m i x . To this solution a d d an e q u a l v o l u m e o f 0.01 N p o t a s s i u m i o d a t e r e a g e n t . M i x a n d s t o r e i n a b r o w n s t o p p e r e d b o t t l e for n o l o n g e r t h a n o n e d a y . Standard Starch Solution—Determine t h e m o i s t u r e c o n t e n t of t h e s t a r c h b y d r y i n g 2 g a t 105 ° C for t w o h o u r s ; d i s c a r d t h i s p o r t i o n . W e i g h i n t o a 3 0 ml b e a k e r t h e q u a n t i t y of u n d r i e d s t a r c h equivalent to a d r y weight of 0.400 g. A d d 500 ml of distilled w a t e r i n t o a conical flask a n d boil gently. A d d 5 ml o f cold d i s t i l l e d w a t e r t o t h e w e i g h e d q u a n t i t y o f s t a r c h a n d m i x t o a t h i n slurry consistency. Transfer to t h e boiling w a t e r as r a p i d l y as possible. R e m o v e a n y residual s t a r c h from t h e beaker w i t h additional 5 ml aliquots of c o l d w a t e r . B o i l t h e s o l u t i o n for t h r e e m i n u t e s . T i m i n g s h o u l d c o m m e n c e f r o m t h e first a d d i t i o n o f s t a r c h t o t h e b o i l i n g f l a s k . T r a n s f e r t h e h o t s o l u t i o n q u a n t i t a t i v e l y , via a funnel, to a one litre volumetric flask, which h a s previously been rinsed with h o t water. By w a y of t h e original 30 ml beaker, wash t h e boiling flask w i t h h o t distilled w a t e r a n d transfer to t h e volumetric flask. Continue this operation until the total volume in the flask is approxim a t e l y 9 0 0 m l . M i x , cool i n r u n n i n g w a t e r a n d d i l u t e t o v o l u m e . S t o r e u n d e r r e f r i g e r a t i o n . T h i s s o l u t i o n s h o u l d k e e p for o n e w e e k . Sucrose Analysis Jackson and Gillis Hydrochloric Acid Solution—Dilute c h e m i c a l l y p u r e h y d r o c h l o r i c a c i d to a specific g r a v i t y of 1.1029. T h i s is e q u i v a l e n t to 2 4 . 8 5 B r i x a t 2 0 °C. Jackson and Gillis Sodium Chloride Solution—Dissolve 2 3 1 . 5 g of c h e m i c a l l y p u r e s o d i u m c h l o i i d e i n distilled w a t e r . D i l u t e t o o n e l i t r e i n a v o l u m e t r i c flask. Sugar Detection Alpha Naphthol—This s o l u t i o n d a r k e n s r a p i d l y o n e x p o s u r e t o l i g h t a n d s h o u l d b e p r e p a r e d freshly e a c h w e e k . T h e s o l u t i o n i s u s e d a t a r a t e o f 5 d r o p s

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93

per sample. On this basis the quantity required can be estimated before alcohol and dilute to volume with ethyl alcohol. Phenol Reagent—Dissolve 50 g of A.R. phenol dilute to one litre. N.B.—A.R. grade phenol is stipulated. If this is not of other grades of phenol should be carried out before This reagent is also used for the determination gums.

in distilled water and available, redistillation it is used. of alcohol precipitated

Water Analysis—Chlorides Potassium Chromate Indicator—Dissolve 5.0 g of potassium chromate (K 2 Cr0 4 ), in approximately 75 ml of distilled water. Add silver nitrate solution by drops, until a permanent brick-red precipitate is established. Cover the container and allow to stand overnight. Filter into a 100 ml volumetric flask and dilute to volume with distilled water.

the preparation of this reagent. It is also advisable to visually check that no haze forms when a crystal of silver nitrate is added to a sample of this water. Dry approximately 5 g of silver nitrate on a watch glass at 100 °C for 15 minutes. Transfer to a desiccator and cool to room temperature. Weigh out 4.786 g of the dried chemical and transfer to a 1000 ml volumetric flask. Dissolve and dilute to volume. Store in a dark bottle away from light.

CHAPTER IX ANALYTICAL METHODS The various methods of analysis have been grouped under headings, for ease of reference and are located as follows: — Contents Subject Page Brix Pol

Dry Substance Bagasse Analysis Cane Analysis

Sucrose-High Purity Materials Sucrose-Low Purity Materials ReducingJSugars Ash

Sugar Analysis

Mud Analysis

Mill Products Dry Lead Method Normal Weight Method Herles' Method Notes on Pol Determination Pan Products Sand Method Josse Filter Paper Method Moisture Pol

Pol by Disintegrator Method Brix by Disintegrator Method Pol in Open Cells Fibre Optical Invertase Method Jackson and Gillis Modification No. IV Chemical Method Dane and Eynon Method Gravimetric Method Conductometric Method Polarization Moisture Filtcrability Grain Size Starch Total Colour Attenuation Insoluble Solids—Vacuum Filtration Method Insoluble Solids—Aluminium Dish Method Moisture Pol

Gums Phosphates

Sugar in Effluents Quality of Mill Lime Caustic Cleaning Solution Laboratory SettlinglTest Cyclone S a m p l i n g and Supersaturation Boiler Water Analysis

Water Analysis

Fibre Determination of Gums in Juice Total Phosphate in Raw Sugar Total Phosphate in Syrups and Clarified Juice Total Phosphates in Juices Soluble and Insoluble Phosphate Phenol-Sulphuric Acid Method Bartholomae Method Alpha-Naphthol Test Neutralizing Value Available CaO Determination of Concentration C.S.R. Procedure Pressure Filtering Device Theory of Supersaturation Saturation Cell Alkalinity Phosphate Sulphite Hardness Total Dissolved Solids Sulphate Chlorides

95 97 98 99 99 100 100 101 102 103 105

105

100 107 108 110 112 113 115 115 110 119 119 121 123 124 124 125 126 126 126 127 128 129 129 129 130 131 131 132 132 133 133 135 136 137 139 140 141 141 142 142 143

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T h e p r e v i o u s E d i t i o n listed t h e v a r i o u s a n a l y s e s w h i c h w o u l d b e r e q u i r e d for e a c h p r o d u c t "if a c o m p l e t e c h e m i c a l c o n t r o l on all f a c t o r y o p e r a t i o n s were to be obtained . . . " The advances of the last decade in m a t t e r s pertaining t o f a c t o r y efficiency a n d s u g a r q u a l i t y h a v e h o w e v e r , r e s u l t e d i n t h e i n t r o d u c t i o n o f m a n y n e w m e t h o d s o f a n a l y s i s t o o u r I n d u s t r y . A s far a s possible t h e l a t e s t m e t h o d s o f a n a l y s i s h a v e b e e n i n c l u d e d i n t h i s c h a p t e r . I t i s r e a l i z e d t h a t local c o n d i t i o n s m a y n e c e s s i t a t e s m a l l d e v i a t i o n s f r o m r e c o m m e n d e d m e t h o d s , a n d t h a t t h e f r e q u e n c y w i t h w h i c h a n a l y s e s for r o u t i n e c o n t r o l p u r p o s e s a r e c a r r i e d o u t i s a q u e s t i o n w h i c h s h o u l d b e left to t h e d i s c r e t i o n of t h e c h e m i s t in c h a r g e of e a c h f a c t o r y . A f a c t o r for c o n sideration in this regard however, is t h a t while t h e frequent analysis of certain p r o d u c t s i s e s s e n t i a l for b o t h r o u t i n e c o n t r o l a n d r e c o r d k e e p i n g p u r p o s e s , the practical value of each analysis should be considered and the general l a b o r a t o r y routine reviewed from t i m e to time. If procedures are not reviewed, t h e s i t u a t i o n c a n arise w h e r e a l a r g e n u m b e r o f a n a l y t i c a l d a t a i s c o m p i l e d on samples which m a y b e a r little or no relationship to t h e actual material in p r o c e s s . T h e m o r e p r a c t i c a l s y s t e m i s o n e w h i c h p e r m i t s sufficient a n a l y s e s for b a s i c c o n t r o l , a n d w h i c h still l e a v e s s o m e t i m e for t h e a n a l y s t s t o s t u d y various aspects of the process which m a y w a r r a n t investigation. T h e f o r m o f p r e s e n t a t i o n h a s b e e n r e v i e w e d w h e r e v e r possible i n t h i s C h a p t e r i n a n e n d e a v o u r t o assist b o t h t h e a n a l y s t a n d t h e s t u d e n t t o o b t a i n a brief r e s u m e of t h e g e n e r a l p r i n c i p l e s of e a c h m e t h o d , m e r e l y by reference t o t h e a p p r o p r i a t e s u b - h e a d i n g s . S o m e m e t h o d s h a v e b e e n c o n d e n s e d for sake of brevity, a n d although t h e essential details and procedures h a v e been r e t a i n e d , a n a l y s t s e n t i r e l y u n f a m i l i a r w i t h a specific a n a l y s i s a r e a d v i s e d t o resort to original publications to obtain a m o r e comprehensive b a c k g r o u n d of t h e fundamentals of t h e particular m e t h o d . A d d i t i o n s t o t h i s C h a p t e r since t h e F o u r t h E d i t i o n h a v e b e e n o b t a i n e d f r o m t h e Colonial S u g a r R e f i n i n g C o m p a n y L i m i t e d , t h e S u g a r R e s e a r c h I n s t i t u t e and various other sources. Their permission to publish these m e t h o d s is g r a t e f u l l y a c k n o w l e d g e d . T h e l i b e r a l u s e of t h e 1964 E d i t i o n of the ICUMSA Methods of Sugar Analysis, and the R e p o r t of the Proceedings of t h e F o u r t e e n t h Session of I C U M S A 1966, as reference s t a n d a r d s is also acknowledged. Brix T h e m e t h o d of Brix determination is dependent u p o n the t y p e of analysis to be performed. T h e majority of Brix determinations are usually carried out b y m e a n s o f a B r i x h y d r o m e t e r , b u t i n d i r e c t c a n e a n a l y s i s , for e x a m p l e , B r i x i s d e t e r m i n e d b y precision r e f r a c t o m e t e r , o r b y p y c n o m e t e r . Brix by Hydrometer M a n y s a m p l e s s u c h a s juice, m a c e r a t i o n f l u i d a n d s y r u p a r e sufficiently l o w in v i s c o s i t y for a d i r e c t h y d r o m e t e r d e t e r m i n a t i o n to be c a r r i e d o u t . Samples of relatively high viscosity, such as massecuites a n d molasses, req u i r e p r i o r d i l u t i o n w i t h w a t e r i n a k n o w n w r eight t o w e i g h t r a t i o . F o r p u r p o s e s of u n i f o r m i t y t h e s t a n d a r d d e g r e e of d i l u t i o n in Q u e e n s l a n d is o n e p a r t of w a t e r to o n e p a r t of s a m p l e i.e. a 1:1 d i l u t i o n , a n d t h i s is a c c o m p l i s h e d as follows:— T a r e a c o n t a i n e r of a c a p a c i t y in excess of o n e l i t r e on a s u i t a b l e b a l a n c e . Mix t h e s a m p l e a n d a d d 5 0 0 . 0 g t o t h e t a r e d c o n t a i n e r . A d d a p p r o x i m a t e l y 300 m l o f h o t w a t e r a n d s t i r u n t i l d i s s o l u t i o n i s c o m p l e t e . Cool a n d f u r t h e r d i l u t e t h e c o n t e n t s w i t h cold w a t e r t o a t o t a l w e i g h t o f 1000.0 g . T h o r o u g h l y

96

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m i x t h e solution. W h e n t h e Brix reading is finally taken, t h e reading of t h e d i l u t e d s a m p l e m u s t b e c o r r e c t e d for t e m p e r a t u r e . T h i s t e m p e r a t u r e corrected Brix is then multiplied by a factor of t w o to o b t a i n t h e Brix of t h e original sample. Preparation—The p r o c e d u r e defined in R e g u l a t i o n 57 of t h e S u g a r C a n e P r i c e s A c t for t h e d e t e r m i n a t i o n o f B r i x for c a n e p a y m e n t p u r p o s e s a p p l i e s i n p r i n c i p l e t o all B r i x d e t e r m i n a t i o n s b y h y d r o m e t e r , n a m e l y : — "A brixing cylinder, d r y or well-drained, is set up and, w i t h o u t stirring, sufficient o f t h e s a m p l e j u i c e i s p o u r e d i n t o f i l l t h e c y l i n d e r . I f a n y a p p r e c i a b l e q u a n t i t y o f b a g a s s e , t r a s h , o r o t h e r foreign m a t t e r i s s u s p e n d e d i n t h e j u i c e , the juice should be d e c a n t e d t h r o u g h a strainer into the cylinder. T h e c y l i n d e r a n d c o n t e n t s a r e a l l o w e d t o r e m a i n u n d i s t u r b e d for 2 0 m i n u t e s o r t h e c o n t e n t s m a y b e p l a c e d u n d e r a p r e s s u r e n o t e x c e e d i n g 1 0 in. H g a b s . for a p e r i o d o f 5 m i n u t e s . I n t h e l a t t e r case t h e j u i c e m u s t b e a l l o w e d t o s t a n d u n t i l a t least 2 0 m i n u t e s h a v e e l a p s e d since t h e j u i c e w a s l a s t stirred . . . " Three i m p o r t a n t facets of t h e d e t e r m i n a t i o n are as follows:— Temperature—The t e m p e r a t u r e of t h e s o l u t i o n m u s t be a p p r o x i m a t e l y t h a t o f t h e s u r r o u n d i n g s . I f i t i s t o o h i g h , t h e s o l u t i o n m u s t b e cooled, a n d c a r e s h o u l d b e t a k e n t o e n s u r e t h a t t h e e n t i r e s a m p l e i s cooled u n i f o r m l y . Preferably t h e c o n t e n t s of t h e cylinder should be t h o r o u g h l y m i x e d after cooling. Suspended Matter—Coarse p a r t i c l e s in t h e s a m p l e a r e r e m o v e d by s t r a i n ing through a fine mesh gauze as the sample is being poured into t h e cylinder. T h e h e a v y p a r t i c l e s o f s m a l l e r size t h a t p a s s t h r o u g h t h e s t r a i n e r will u s u a l l y settle in the b o t t o m of the cylinder during the obligatory 20 m i n u t e s standing p e r i o d . S o m e p a r t i c l e s h o w e v e r will still r e m a i n i n s u s p e n s i o n . T h e s e c a n h a v e a significant effect o n t h e h y d r o m e t e r r e a d i n g a n d s h o u l d b e r e m o v e d b y e i t h e r f i l t r a t i o n o r c e n t r i f u g i n g i f precise r e s u l t s a r e r e q u i r e d . Air Bubbles—Samples of b o t h low a n d h i g h B r i x fluids f r e q u e n t l y c o n t a i n a c o n s i d e r a b l e q u a n t i t y of air b u b b l e s at t h e t i m e of s a m p l i n g . F u r t h e r air c a n also b e e n t r a p p e d i n t h e p r o c e s s o f p o u r i n g t h e l i q u i d i n t o t h e c y l i n d e r . R e m o v a l of t h i s air is a c c o m p l i s h e d e i t h e r by t h e a p p l i c a t i o n of v a c u u m or b y a l l o w i n g t h e s a m p l e t o s t a n d for 2 0 m i n u t e s a s s e t o u t i n t h e R e g u l a t i o n . Procedure—The c l e a n e d , d r i e d h y d r o m e t e r s h o u l d b e l o w e r e d i n t o t h e c y l i n der, c a u s i n g t h e l i q u i d t o overflow a n d c a r r y a w a y w i t h i t a n y f r o t h floating o n t h e surface. T h e h y d r o m e t e r i s l o w e r e d u n t i l i t f l o a t s freely, a n d c a r e s h o u l d be t a k e n to see t h a t t h e s t e m is w e t t e d for o n l y a few t e n t h s of a u n i t above the point at which the h y d r o m e t e r comes to rest. If in the above o p e r a t i o n t h e h y d r o m e t e r s t e m is w e t t e d m o r e t h a n a few t e n t h s of a u n i t a b o v e t h e m e n i s c u s , t h e r e a d i n g s h o u l d b e n o t e d , t h e h y d r o m e t e r lifted, a n d t h e emergent portion of t h e s t e m wiped dry. T h e h y d r o m e t e r is t h e n carefully lowered to the reading first observed. I f t h e r e i s a n y a p p r e c i a b l e difference i n t e m p e r a t u r e b e t w e e n t h e s o l u t i o n a n d t h e h y d r o m e t e r , t h e l a t t e r s h o u l d b e a l l o w e d t o f l o a t freely u n t i l t e m p e r ature equilibrium is established. I f t h e s o l u t i o n i s clear a n d l i g h t c o l o u r e d t h e p o i n t a t w h i c h t h e p l a n e o f t h e l i q u i d s u r f a c e w o u l d i n t e r s e c t t h e scale i s r e a d i l y o b s e r v e d . F r e q u e n t l y t h e r e a d i n g o f t h e u p p e r edge o f t h e m e n i s c u s m u s t b e t a k e n a n d a c o r r e c t i o n a p p l i e d . F o r t h e class o f h y d r o m e t e r g e n e r a l l y u s e d i n Q u e e n s l a n d t h e m e n i s c u s c o r r e c t i o n i s close t o + 0 . 1 5 ° B r i x , s o t h a t i f r e a d i n g s a r e t o b e m a d e t o t h e n e a r e s t 0.1° i t i s justifiable t o a d d e i t h e r 0.1° o r 0.2° a c c o r d i n g t o t h e

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r e a d i n g a t t h e t o p o f t h e m e n i s c u s . W h e n e v e r possible a n effort s h o u l d b e m a d e to estimate the t r u e point at which t h e surface plane would intersect t h e scale. T h i s e l i m i n a t e s a n y d o u b t s a s t o w h e t h e r t h e m e n i s c u s c o r r e c t i o n s h o u l d b e 0.1 o r 0.2. I n a n y case, t h e r e a d i n g a t t h e t o p o f t h e m e n i s c u s s h o u l d n e v e r b e s e t d o w n a s a r e s u l t , b u t s h o u l d b e c o r r e c t e d m e n t a l l y before b e i n g entered on the records as observed Brix. The t e m p e r a t u r e of the solution should be determined immediately t h e hydrometer reading has been m a d e a n d t h e necessary correction applied to give t h e t r u e B r i x v a l u e . E x a m p l e : —

Significance of the Brix Determination—The d e t e r m i n a t i o n of B r i x as a s e p a r a t e entity can be of i m p o r t a n c e in measuring such factors as Brix of massec u i t e , B r i x o f m a c e r a t i o n fluid e t c . B r i x m e a s u r e m e n t h o w e v e r , i s n o r m a l l y associated with t h e determination of pol in order to obtain a measure of t h e q u a n t i t y of i m p u r i t i e s p r e s e n t in a s o l u t i o n . In t h i s r e g a r d , t h e a s s o c i a t i o n of a Brix test with the determination of pol by the d r y lead m e t h o d has a dual purpose. The Brix of the solution is obtained, and, in addition, the Brix r e a d i n g is u s e d to give a m e a s u r e of t h e d e n s i t y of t h e s o l u t i o n , a n d h e n c e t h e w e i g h t of 100 ml of t h e s o l u t i o n in air. A B r i x h y d r o m e t e r is, of c o u r s e , c a l i b r a t e d in d e g r e e s B r i x , b u t e v e r y graduation corresponds to a particular density. W h e n a h y d r o m e t e r calibrated at 20 °C i m m e r s e d in a l i q u i d at 20 °C r e a d s , for e x a m p l e , 25.0 ° B r i x , it is e s t a b l i s h e d t h a t t h e d e n s i t y of t h e s o l u t i o n is 1.103557 g p e r m l . If t h e h y d r o m e t e r itself w e r e n o t affected b y t e m p e r a t u r e , t h e n i r r e s p e c t i v e o f t h e t e m p e r a t u r e of t h e s o l u t i o n , a r e a d i n g of 25.0° w o u l d i n d i c a t e a d e n s i t y of 1.103557 g p e r m l . In a c t u a l fact, t h e h y d r o m e t e r itself is affected v e r y l i t t l e by t e m p e r a t u r e ; the substantial t e m p e r a t u r e corrections which are applied t o o b s e r v e d B r i x r e a d i n g s (for t e m p e r a t u r e s o t h e r t h a n 2 0 °C), a r e d u e a l m o s t e n t i r e l y t o t h e effect o f t e m p e r a t u r e o n t h e s u g a r s o l u t i o n a n d , for p r a c t i c a l p u r p o s e s , t h e t e m p e r a t u r e coefficient of v o l u m e of t h e h y d r o m e t e r is i g n o r e d , a n d a r e a d i n g at t °C is t a k e n as an i n d e x of t h e d e n s i t y of t h e s o l u t i o n a t t °C. Pol T h r e e m e t h o d s for t h e d e t e r m i n a t i o n o f p o l i n j u i c e s a n d s i m i l a r l i q u i d s c o n t a i n i n g u p t o 2 5 p e r c e n t s u c r o s e a r e listed i n t h i s E d i t i o n . I n t h e first m e t h o d a n d o n e version o f t h e t h i r d m e t h o d , t h e B r i x o f t h e s a m p l e m u s t also b e d e t e r m i n e d . The analyses obtained The reagents

u s e o f t h e d r y l e a d m e t h o d i s o b l i g a t o r y for f i r s t e x p r e s s e d j u i c e for c a n e p a y m e n t p u r p o s e s . O n l y i f u n s a t i s f a c t o r y clarification i s b y the d r y lead m e t h o d m a y the other m e t h o d s b e used. specification o f l e a d a c e t a t e p u r i t y a n d t h e p r e p a r a t i o n o f H e r l e s ' are listed in C h a p t e r V I I I .

Dry Lead Method In order to obtain t h e pol per cent of a solution, a s e p a r a t e Brix determ i n a t i o n is required with this m e t h o d . In t h e procedure outlined below, attention is d r a w n to t w o aspects, the addition of lead acetate powder a n d t h e choice o f c o n t a i n e r . T h e q u a n t i t y o f l e a d a c e t a t e a d d e d s h o u l d b e j u s t

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ANALYTICAL METHODS

sufficient to achieve satisfactory clarification, and overleading must be avoided. The most suitable container for this determination is a flat-bottom conical flask of approximately 150 ml capacity, with a neck opening just wide enough to permit easy addition of the lead powder, but narrow enough to be easily stoppered for the purpose of shaking the contents. Procedure—Transfer approximately 100 ml of juice to a flask. Add 1 g of dry lead acetate, stopper and shake vigorously. Allow a reaction time of several minutes. A further mixing of the contents at this stage is recommended. Filter. Add the juice to a maximum safe level and cover the top of the filter to minimize evaporation. Discard the first 10 ml of filtrate, and read the optical rotation of the solution in a 200 mm tube. Calculation—This is simplified by the use of Schmitz's Table for undiluted solutions (Table II), which has been derived from the formula—

The table is used in the following manner:— Suppose the uncorrected Brix = 18.1 (without temperature correction) and the polariscope reading = 60.5 CS. Under the column headed 18 (the closest approximation provided) and opposite 60 (the whole number of the polariscope reading), the value of 14.57 is found. Add to this the amount of 0.12 (equivalent to 0.5 pol reading found in the inset table for tenths of a degree pol reading). The pol of juice then = 14.57 + 0.12 = 14.69. If it is desired to work out results for cases not shown in Schmitz's Tables, the pol may be derived from the formula—

Values of apparent density at 20 °C for corresponding Brix values are available from Table XV. Normal Weight Method This method is not recommended for general use, but it occasionally has some application where, for example, the pol per cent of a juice is required without an accompanying Brix determination. Unlike the previous method, the normal weight method is affected by the presence of insoluble matter in the juice, and also by the volume of precipitate formed when wet lead clarification is used. Procedure—Transfer three normal weights of juice (78.00 g) to a 100 ml volumetric flask. Wash in any residual juice with a small quantity of distilled water. Addition of Lead Acetate—Two alternatives are available: A. Dry Lead—Dilute the flask contents to 100 ml with distilled water and then add approximately 0.8 g of dry lead acetate. Shake thoroughly, allow to stand and filter as in the previous method. Read in a 200 mm tube. B. Wet Lead—Add 2 ml of wet lead solution and then dilute to the 100 ml mark. Shake, allow to stand and filter. Read in a 200 mm tube.

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99

Herles' Method This method has been found to be of considerable benefit for clarifying juices that will not respond satisfactorily to lead acetate addition. Two variations of the method are presented: A. Gravimetric Method— Procedure—Weigh out 2 normal weights of juice into a 100 ml volumetric flask. Add 5 ml of reagent B, followed by 5 ml of reagent A. (Chapter V I I I : Herles' reagents). Add distilled water short of the mark and mix well by swirling. Dilute to 100 ml. Mix, filter and polarize in a 200 mm tube. B. Volumetric Method—A separate Brix measurement is required in this case. Procedure—Add 50 ml of juice into a 100 ml volumetric flask. Proceed as above to the stage where a polariscope reading is obtained. Calculation—Multiply polariscope reading by 2. Refer to Schmitz's table (Table II) and derive pol per cent juice from the undiluted polariscope reading and the uncorrected Brix of the sample. Notes on Pol Determination Of the three methods described, the dry lead method is preferred and is used almost exclusively throughout the Industry. The notable exception to this is when juices from canes in an advanced stage of deterioration are encountered. In this instance, Herles' method will generally prove to be the most effective. The formula on which Schmitz's Table is based, namely—

should theoretically be applied only when solutions are analysed at 20 °C. At temperatures other than 20 °C however, the influences of polariscope and tube coefficients are very minor items in practice, and the formula is used as if it were independent of temperature, with the one qualification that the polariscope reading and Brix determination are carried out at the same temperature. However, while the use of the observed Brix compensates adequately for the changes in density of undiluted juice at different temperatures, the effects of temperature on the optical rotation of sucrose, reducing sugars, etc., must also be considered. Sucrose solutions display a rotation which decreases with temperature. Invert sugar solutions display a much higher change of rotation in the reverse direction. When the reducing sugars (considered as invert sugar) constitute 6f per cent of the sucrose, the temperature coefficient of the mixture vanishes. An empirical formula suggested for the correction of the observed polarization of juices as read in a quartz wedge compensated saccharimeter is

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ANALYTICAL METHODS

N o t e t h a t w h e n t h e p o l a r i s c o p e r e a d i n g i s 80, t h e c o r r e c t i o n i s z e r o . T h e polariscope readings of undiluted juices a p p r o x i m a t e to 80 so t h a t , according t o t h i s f o r m u l a , t h e o m i s s i o n o f a t e m p e r a t u r e c o r r e c t i o n i s justified. H o w e v e r , i n d i v i d u a l s a m p l e s o f j u i c e s h a v e b e e n f o u n d t o d i s p l a y significant t e m p e r a t u r e coefficients a n d t h e p r a c t i c e o f c o n d u c t i n g j u i c e a n a l y s e s a t o r n e a r 20 °C is r e c o m m e n d e d . T h e d e t e r m i n a t i o n of t h e pol of o t h e r m a t e r i a l s is best discussed in r e l a t i o n t o specific p r o d u c t s a s follows:—• Pan Products For the determination of pol in p a n products, b o t h t h e concentration of s o l u t i o n a n d t h e a m o u n t o f clarifying a g e n t m u s t b e v a r i e d t o s u i t t h e n a t u r e o f t h e p r o d u c t . F o r p u r p o s e s o f u n i f o r m i t y , t h e following d i l u t i o n s a n d a m o u n t s o f d r y l e a d a r e s u g g e s t e d . T h e s e s h o u l d b e a d e q u a t e for t h e m a j o r i t y of s a m p l e s e n c o u n t e r e d in e a c h c a t e g o r y . Product

Syrup A and B Massecuite A and B Molasses Magma C Massecuite Final Molasses

Aliquot

1 normal weight of straight syrup/100 ml 1 normal weight of 1:1 dilution/100 nil 1 normal weight of 1:1 dilution/100 ml 1 normal weight of 1:1 dilution/100 ml 2 normal weights of 1:1 dilution/300 ml 2 normal weights of 1:1 dilution/300 ml

Weight of Dry Lead

1 3 2 5 8

g g g g g

T h e effects of o v e r l e a d i n g a r e m o r e p r o n o u n c e d in C m a s s e c u i t e a n d final m o l a s s e s a n a l y s e s a n d a c o n s i d e r a b l e inflation of t h e p o l r e a d i n g s c a n r e s u l t . F o r C m a s s e c u i t e a n d final m o l a s s e s a n a d d i t i o n a l s t e p s h o u l d b e e m p l o y e d in t h e d e t e r m i n a t i o n as follows: — After n o r m a l l e a d i n g a n d f i l t r a t i o n , a d d 5 0 m l o f t h e f i l t r a t e t o a 50-55 m l v o l u m e t r i c flask. T h e n a d d 2 ml of 1 + 4 a c e t i c a c i d r e a g e n t a n d d i l u t e to 5 5 m l w i t h distilled w a t e r . Mix t h o r o u g h l y a n d p o l a r i z e i n a 200 m m t u b e . T h e c a l c u l a t i o n for t w o n o r m a l w e i g h t s i n 300 m l o f 1:1 d i l u t e d s a m p l e a n d filtrate d i l u t i o n f r o m 5 0 t o 5 5 m l t h e n b e c o m e s P o l p e r c e n t = p o l r e a d i n g X 3.3 This additional step is necessary due to the relatively high concentration of laevulose in these products. Lead in solution combines with laevulose to give a s o l u b l e c o m p o u n d o f l o w o p t i c a l r o t a t i o n . A c e t i c a c i d s p l i t s u p t h i s compound, thereby restoring t h e rotation of t h e laevulose. Dry Substance T h r e e m e t h o d s a r e a v a i l a b l e for t h e d e t e r m i n a t i o n o f d r y s u b s t a n c e b y drying under controlled conditions, t h e Sand m e t h o d , t h e T a t e and Lyle V a c u u m O v e n M e t h o d , (De W h a l l e y 1964), a n d t h e J o s s e F i l t e r P a p e r m e t h o d . Of the three, t h e Josse Filter Paper m e t h o d w i t h v a c u u m drying is considered t o b e t h e m o s t s u i t a b l e for Q u e e n s l a n d c o n d i t i o n s . T h e S a n d m e t h o d i s still used b y some factories, b u t its replacement b y t h e Josse Filter P a p e r m e t h o d is recommended. Sand Method Sand Preparation—A s u p p l y of fine p r e p a r e d s a n d is r e q u i r e d . T h e r e c o m m e n d e d m e t h o d of preparation is as follows:—

*

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101

Use only sand that will pass through a 40 mesh and be retained on a 60 mesh screen. Digest the sand in hot hydrochloric acid, and then wash in running water until the tailings will not give a positive reaction with silver nitrate. Oven dry and then ignite in a muffle furnace at a temperature in excess of 600 °C. Special Apparatus—Flat bottomed aluminium dishes, approximately three inches in diameter with 3/4 inch vertical walls and close fitting lids, are used for the determination. A glass stirring rod of such a length that it will just fit inside the dish on a slope is also required. Procedure—Pre-dry approximately 50 g of sand in the aluminium dish. Allow to cool in a desiccator just prior to use. Weigh dish plus sand and stirrer. Add a known weight of sample. This varies from 10 g for juices to 6 to 10 g of 1:1 dilution for massecuites and molasses. Mix sand and sample thoroughly with the glass stirring rod. Great care must be taken during this operation to avoid any loss of sand. Dry, either in a hot air oven at 103-105 °C for four hours, or preferably, under a vacuum of 28 inches Hg at 70 °C until successive weighings at two hourly intervals do not differ by more than 0.5 mg. This usually takes about 16 hours. The air bleed into the oven should be fitted with a double calcium chloride drying tower. After completion of drying, replace the lid and allow to cool to room temperature in a desiccator. Complete the final weighing with a minimum of delay. Calculate the weight of dry solids and express as a percentage of the weight of the original undiluted sample. Josse Filter Paper Method The determination of dry substance by this or any other drying method can be subject to errors from various sources, unless analytical procedure, drying conditions and timing between operations are rigidly controlled. Two of the main sources of error in this regard are evaporation effects between addition and weighing of sample, and re-absorption after drying. Special Apparatus—Glass weighing bottles approximately 3 cm diameter and 7 cm in height with ground glass stoppers are required. Strips of filter paper 60 x 4.5 cm are rolled in loose coils and placed inside the bottles. Procedure—Pre-dry the bottle and paper in a vacuum oven at 63 °C for a minimum of 6 hours. Stopper immediately after removal from the oven and cool in a desiccator for 20 minutes. Weigh the sealed bottle plus paper. The sample, undiluted in the case of juices, or diluted 1:1 in the case of massecuites or molasses, is then added in the following manner. Remove the paper, introduce approximately 2 g of sample and weigh. Then add 1 ml of distilled water, mix by swirling, insert the paper coil and allow to stand for 30 minutes before commencement of drying. The sample is then dried at 63 °C for 16 hours under a vacuum of from 26 to 29 inches Hg. A slight bleed of air, which is dried in double calcium chloride towers, is allowed to pass into the oven during the drying period. At the end of the drying period the vacuum is released slowly, the air entering through the drying towers. The bottles are then closed and cooled in a desiccator for 20 minutes before weighing. The weight of dry solids is calculated and expressed as a percentage of the weight of the original undiluted material.

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Bagasse Analysis Preparation of Sample The method of collecting and compositing bagasse has been described in Chapter VII. The sub-sampling of a large quantity of bagasse is facilitated by hammer-milling, which comminutes and mixes the bagasse. This is particularly useful for first mill bagasse where large pieces are usually present. Drying of the sample will also be facilitated by the finer subdivision. When hammer milling is carried out, care must be taken to avoid contamination of the samples, and care should be exercised during any bagasse sampling to minimize loss of moisture. Moisture Large capacity drying ovens based on the principle of the old Spencer type oven are now standard equipment in most mill laboratories. Bagasse is placed in a cylindrical container measuring approximately 11 inches by 7

inches in diameter, the base of which is covered by a layer of 22 mesh gauze supporting a layer of 100 mesh gauze. Hot air is then passed through the sample. When a number of drying containers are to be used continuously, it is convenient to adjust all the containers to the same tare weight.

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Procedure—Add 1000 g of bagasse sample to the container and dry at a temperature of from 105 to 115 °C until the weight loss is less than 2 g in 30 minutes. This usually takes from three to four hours. Weighings are made while the container is still hot. Pol The wet disintegrator method of pol determination has now almost completely replaced the old hot digestion method. Several minor changes have been made to the machine described by Foster (1955), but the same

Fig. 39—Wet-Disintegrator.

basic principle is still employed. The procedures described in this Manua are, however, designed for use with the modified type of wet disintegrator i.e. a machine fitted with three six inch blades at half inch intervals up the shaft, shaft end one eighth inch from the bottom of the can, and a water-cooled baffled can. The blades on these machines must be kept sharp. Procedure—Weigh out 1200 g of first mill bagasse or 1000 g of bagasse from subsequent mills. Transfer to the disintegrator can and add 10 kg of

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water. Disintegrate for 30 minutes at approximately 5600 rev/min and ensure that an adequate flow of cooling water is applied to the waterjacketed disintegrator can. Remove approximately 200 ml of extract for pol analysis, strain through a 40 mesh gauze into a 250 ml conical flask, stopper and cool to room temperature. Clarify with a minimum amount of dry lead acetate, shake, and allow to stand for at least five minutes. Filter, discard the first 10 to 15 ml of filtrate and polarize in a 400 mm tube. Calculation—It is assumed in the following formula that the specific gravity of the extract is 1.000 and that the fibre contains 25 per cent hygroscopic water.

where R W B M Q

= = = = —

pol reading of extract weight of water added weight of bagasse moisture in total bagasse (B) purity of residual juice

neglected. For the routine analysis of final bagasse, where a 10:1 ratio of water to bagasse is used, a simplified formula, which neglects the influence of hygroscopic water, is frequently employed, and the formula reads as follows:—

where w = moisture per cent bagasse Q = purity of residual juice. The purity of residual juice is frequently assumed to be 70, and a table, based on this assumption, and on the simplified formula given above, mav be found in Table III. Cane Analysis The present Queensland cane payment system evaluates cane for payment purposes in terms of c.c.s. or commercial cane sugar. The c.c.s. is calculated from the pol and Brix of cane, which are determined by means of an empirical formula involving the pol and Brix of first expressed juice and the fibre per cent cane. The need for a more exact method of cane analysis has resulted in the development of a system for direct cane analysis. In direct analysis, pol and Brix of cane are determined by use of the wet disintegrator on a sample of prepared cane. Moisture is also determined on the prepared cane sample and fibre calculated using the formula: Fibre per cent cane = 100 — Brix per cent cane — water per cent cane. The method of sampling cane for direct analysis is described in Chapter VII.

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Sample Preparation Thoroughly mix the sample of prepared cane. If cane preparation is considered inadequate, the sample may be given additional preparation by passing the cane through a hammer mill or cutter-grinder. Care must be taken to minimize loss of moisture if comminution of the sample is carried out and if a cutter-grinder is used, the blades must be kept sharp. Transfer the sample to a sealed container and commence the following analyses with a minimum of time delay. Moisture This is determined in the manner described for moisture per cent bagasse. Brix and Pol Procedure—Weigh out accurately 2000 g of prepared cane and transfer to the water jacketed disintegrator can. Add 6000 g of water from a suitable dispenser. Disintegrate the material as described in the procedure for pol per cent bagasse. Brix of Extract—To a separate portion of extract, add approximately 2 g of filter aid per 100 ml and filter. Discard the first runnings. Take all necessary precautions to minimize evaporation. Determine the Brix of extract by a precision refractometer after having previously checked the zero point of the instrument with distilled water, or by means of a pycnometer. Calculations (Deicke 1959)—

and

y = x = z = w = For 2000 g of cane, 6000 content of 25 per cent, the

weight of cane weight of water per cent hygroscopic water moisture per cent cane g of water and an assumed hygroscopic water formula is simplified to

Pol of Extract—For dry lead clarification and polarization of the extract in a 400 mm tube. Pol per cent cane =

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ANALYTICAL METHODS

Pol in Open Cells An estimate of the percentage of broken and unbroken cells in cane can be obtained from the determination of pol in open cells as opposed to pol of the total sample; The determination is seldom used for routine control purposes, but it is of value in establishing the degree of cane preparation obtained prior to crushing. The basis of the method is that sugar can be rapidly leached from broken cells under conditions which do not induce diffusion of sugar from unbroken cells. It must also be assumed that the pol content of broken cells is the same as the pol content of unbroken cells. The forementioned must be viewed with some reservation and results should be considered more on a comparative than an absolute basis. A version of the method of Aldrich and Rayner (1962) as modified by the Sugar Research Institute, is listed below. Special Apparatus—A 3 gallon bottle neck container of the type and dimensions shown in Fig. 40 is required. Procedure—The prepared cane should be thoroughly mixed before subsampling. Pol in open cells—Weigh out 1000 g of prepared cane and transfer into the special container. Add 10,000 g of water, seal and rotate on a jar mill for 10 minutes at 70 rev/ min. Determine the pol reading of the extract in a 400 mm tube. Pol in total sample—Transfer 2000 g of prepared cane and 6000 g of water to a wet disintegrator and disintegrate for 30 minutes. Determine the pol reading of the extract in a 400 mm tube. Pol in total sample—Transfer 2000 g of prepared cane and 6000 g of water to a wet disintegrator and disintegrate for 30 minutes. Determine the pol reading of the extract in a 400 mm tube.

ratio of the pols of the extracts, and if this ratio is designated r, the formula for percentage of pol in open cells reduces to

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107

Fibre The direct determination of fibre for cane payment purposes is carried out by either of the two methods described below. It should be emphasized however that the form of presentation of these methods does not constitute an official interpretation of the Cane Prices Regulations. Whole Stalk Method -The use of this method has been superseded in most factories by the prepared cane method, but whole stalk selection and analysis is still required for certain milling and agricultural experiments. Procedure—Sticks should be selected in a manner which will ensure that they are a representative selection of the original parcel of cane. A group of 12 sticks constitutes a suitable unit for fibre analysis, and if the amount of cane to be sampled cannot be adequately represented by this number, it is preferable to take as many groups of 12 as required and to analyse each group separately. Sub Sampling—Lay the 12 sticks on the ground in descending order of length and with all tops in the same direction. Cut each stalk into three equal sections, top, middle and butt. Sections are then selected and laid out as follows:— Stalk Section Direction 1 2 3 4 5 6

Top Middle Butt Top Middle Butt

Unchanged Unchanged Unchanged Reversed Reversed Reversed

This sequence is repeated for the second group of six sticks. Preparation—When the old Queensland type fibrator is employed the 12 sections are fibrated, without reversal, to the extent of half the length of each section. The resultant fibrated material should represent two complete stalks of cane. It is important that the fibrator should be sharp and in good order. The fibrated material should be mixed thoroughly and quickly on a shallow tray and a representative portion selected and placed in an airtight container. The actual analysis is then carried out in a similar manner to that described for the prepared cane method. An alternative and more efficient preparatory device is the Jeffco type cutter-grinder. When this is employed however, the full sections are fibrated. Prepared Cane Method—The method previously described has several limitations, the more important being that it is extremely difficult to obtain a representative sample of cane. The lengthy procedure of stick selection and preparation also limit the number of determinations that may be carried out in any one period. The need for an improved method of fibre determination resulted in the development of a technique which permits the sampling and analysis of prepared cane just prior to milling. A more detailed discussion of this subject may be found in a paper by Anderson and Petersen, (1959). Sample Preparation—A sample of prepared cane is removed from the carrier to a table by the method as described in Chapter VII. After rapid but thorough mixing, a sub-sample is transferred to a Waddell type hammer mill which has previously been conditioned with a discarded portion of the sample.

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Procedure—Hammer m i l l t h e c a n e for a p p r o x i m a t e l y 15 s e c o n d s a n d again rapidly b u t thoroughly mix the prepared sample. Transfer a representa t i v e s u b - s a m p l e t o a closed c o n t a i n e r . W e i g h a p r e d r i e d f i b r e b a g i n a n airt i g h t c o n t a i n e r a n d r e c o r d t h e w e i g h t of b a g + c o n t a i n e r (Wl). R a p i d l y t r a n s f e r a p p r o x i m a t e l y 150 g o f t h e h a m m e r m i l l e d s a m p l e t o t h e b a g . F a s t e n the top of the bag and transfer to the airtight container. Weigh the bag + c o n t a i n e r a n d r e c o r d as (W2). Washing—Immerse t h e b a g i n c o l d r u n n i n g w a t e r a n d s q u e e z e a t t h e c o m m e n c e m e n t of w a s h i n g a n d at 15 m i n u t e i n t e r v a l s for a p e r i o d of o n e hour. R e m o v e the bag, squeeze or spin d r y to remove surplus w a t e r a n d t r a n s f e r t o b o i l i n g w a t e r , r e p e a t i n g t h e p r o c e d u r e for a f u r t h e r h o u r . Drying—Remove s u r p l u s w a t e r b y s q u e e z i n g o r s p i n d r y i n g a n d t r a n s f e r t o a n air o v e n . D r y t o c o n s t a n t w e i g h t a t 100 t o 105 °C. W h e n r e m o v e d f r o m t h e o v e n for w e i g h i n g t h e b a g s a r e p l a c e d i n t h e a i r t i g h t c o n t a i n e r . R e c o r d t h e w e i g h t o f c o n t a i n e r + b a g + f i b r e (W3). E m p t y t h e b a g s a n d r e m o v e all a d h e r i n g fibre. R e - d r y in t h e o v e n for o n e h o u r at 100 to 105 o C. Cool in t h e a i r t i g h t c o n t a i n e r a n d r e - w e i g h (W4).

N.B.—The determination should be carried out in duplicate whenever practicable. Sucrose in High Purity Materials The present methods for the determination of sucrose in relatively high purity materials e.g. first expressed juice, clarified juice and syrup, are based on the original Clerget method whereby the polarization of the sucrose solution is determined both before and after inversion. The method is based on the assumption that optically active materials other than sucrose are not affected by the inversion. The inverting agents employed are either the enzyme invertase or hydrochloric acid. The former is considered to yield more correct results, due to the fact that it is an enzyme specific to sucrose, but because of the necessity of maintaining and storing a supply of suitable invertase, this method has in the past received only partial acceptance for factory control analysis. Attempts to eliminate the defects of hydrochloric acid as an inverting agent have led to the development of numerous modifications of Clerget's method. The method most widely accepted is the Jackson and Gillis Modification No. IV, in which sodium chloride is added to the solution used for the direct polarization, to offset the effect of the chloride ions in the acid added to the inverted solution. Two methods of analysis are presented. Both require a high degree of analytical precision to obtain reproducibility, and it is recommended that for reliable results the determination of sucrose on any one sample be carried out at least in duplicate. Optical Invertase Method Preparation—Dissolve t w o a n d a half t i m e s t h e n o r m a l w e i g h t of t h e s u b s t a n c e i n w a t e r i n a 2 5 0 m l v o l u m e t r i c f l a s k . ( D e p e n d i n g o n t h e colour, multiples or fractions of this weight m a y be used a n d t h e weights calculated to a b a s i s of 26 g p e r 100 ml.)

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Add sufficient dry lead to just clarify the solution, mix by swirling and dilute to volume. Mix by shaking and filter, keeping the funnel covered with a watch glass. Reject the first 25 ml of nitrate. If the filtration rate is slow, it is advisable to use two filters in parallel. Delead the filtrate by adding ammonium dihydrogen phosphate in as small an excess as possible. Mix well, filter and again reject the first 25 ml of filtrate. Direct Reading—Pipette 50.0 ml of lead-free filtrate into a 100 ml volumetric flask. Dilute to volume, mix well and transfer to a 200 mm water jacketed tube. Allow to stand for approximately 10 minutes, record the temperature and polarize. The polariscope reading multiplied by 2 is taken as the direct reading, designated P. Invert Reading—Two alternatives are available, either a 24 hour inversion using 5 ml of invertase for the actual inversion, or a rapid inversion at elevated temperatures using 10 ml of invertase. 24 Hour Inversion—In a separate operation accurately determine the quantity of acetic acid required to reduce 50 ml of the filtrate to a pH of 4.4. To another 50.0 ml portion in a 100 ml volumetric flask add the requisite quantity of acid and 5 ml of invertase solution. Dilute almost to volume and allow to stand overnight, preferably at a temperature of not less than 20 °C. Dilute to volume, mix well and polarize in a water jacketed tube at 20 °C. Determine the optical activity of a similar portion of the invertase previously used by diluting this portion to 100 ml and polarizing. Correct the invert polarization for the effect of the optical activity of the invertase solution, and multiply by 2 to obtain the corrected invert reading for a normal solution, designated P 1 . Determine the total solids of the original sample by refractometer, multiply this figure by the density at 20 °C and use the result to calculate total solids from the original solution in 100 ml of the invert solution, designated g. Rapid Inversion—If this procedure is used, add 10 ml of invertase solution to 50.0 ml of nitrate in a 100 ml volumetric flask. Transfer to a water bath and hold at 55-60 °C for 15 minutes with occasional swirling. Cool the flask and contents, add soduim carbonate until distinctly alkaline to litmus paper, adjust to volume and polarize in a water jacketed 200 mm tube. Record the temperature to the nearest 0.1 °C. Allow the solution to remain in the tube for approximately 15 minutes and again determine the polarization. If there is no change from the previous reading, mutarotation is complete. If it is necessary to work at a temperature other than 20 °C, both the direct and invert polarizations should be made at the same temperature, which should be as near as possible to 20 °C. Calculation—The percentage sucrose, S, in the original sample is derived from the formula

N.B.—The strength of each batch of invertase should be periodically checked to ensure that it complies with the A.O.A.C. specification. This is

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defined as invertase which under the specified conditions of the test will produce a drop in polarization of 3.96 in a solution of 10 g of sucrose in 110 ml. The test is carried out as follows:— Dilute 1 ml of invertase concentrate to 200 ml with distilled water. Dissolve 10.00 g of pure sucrose in a 100-110 ml volumetric flask, using approximately 60 ml of distilled water. Add two drops of glacial acetic acid and make up to a volume of 100 ml. Add 10 ml of the diluted invertase to the sugar solution, mix thoroughly and allow to stand for exactly 60 minutes at 20 CC. Render alkaline to litmus by the addition of solid sodium carbonate. Polarize in a 200 mm tube to obtain a reading P.

If the activity is unity or greater, the invertase complies with the A.O.A.C. specification. Jackson and Gillis Modification No. IV This method is applicable in the presence of invert sugar, as the effect of hydrochloric acid inversion on this substance is balanced by the addition of sodium chloride ions to the solution used for the direct polarization. As previously mentioned, the method is not recommended for low purity materials or materials containing appreciable quantities of optically active non sugars, the specific rotations of which can be subject to significant changes during acid inversion. Preparation—Juices are taken undiluted, while sugar, syrup and high grade pan products are prepared at a concentration of 2 normal weights in 200 ml. Clarify the appropriate preparation with dry lead (as for pol determination) and filter. Delead the filtrate with anhydrous potassium oxalate. The quantity required is determined by a potassium iodide test on small portions of the filtrate. Direct Polarization—Pipette 50.0 ml of filtrate into a 100 ml volumetric flask. Add 10.0 ml of Jackson and Gillis sodium chloride solution. Dilute to volume with distilled water and filter only if necessary. Stopper and retain so that this solution and the one from the next stage are read at approximately the same time and at the same temperature. Polarize in a water jacketed 200 mm tube and multiply the result by 2. Designate as P. Invert Polarization—Pipette 50.0 ml of filtrate into a 100 ml volumetric flask. Either of the following procedures may be adopted for inversion but the U.S. Customs method is considered to be more precise and is preferred. A. Walker Method—Insert a thermometer in the flask and heat in a water bath until a temperature of 65 °C is attained. Remove the flask and add 10.0 ml of Jackson and Gillis hydrochloric acid solution. Mix by swirling and set aside for 30 minutes. Cool to room temperature, wash any adhering liquid from the thermometer and dilute to volume. Polarize in a water jacketed 200 mm tube at the same temperature at which the direct reading is determined and multiply the reading by 2. Designate as P1. Record the temperature of the polarization to the nearest 0.1 °C.

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Or B. U.S. Customs Method—Transfer 10 ml of Jackson and Gillis hydrochloric acid solution to the cold 50 ml of nitrate. Insert a thermometer and transfer to a water bath. Heat to 60 °C and hold for 10 minutes. Agitate the flask during the first 3 minutes. Rapidly cool to room temperature, wash adhering liquid from the thermometer and dilute to volume. Polarize as described in the previous alternative. Calculation— The concentration of sucrose is calculated from P and P1 using the formula In the case of an undiluted solution this formula gives an apparent sucrose reading which is used in conjunction with Schmitz's Table as if it were a pol reading. A separate Clerget divisor is required for each method. Walker Method Divisor = 132.63 + 0.0794 (m —13) —0.53 (t — 20) U.S. Customs Method. Divisor = 132.56 + 0.0794 (m —13) —0.53 (t — 20) where t = temperature of polarization °C and m = total solids, g per 100 ml, in the actual invert solution N.B.—The divisors for the Walker Method for solutions ranging from 8 to 26 Brix are shown in Table IX, while the temperature corrections are shown in Table X. The divisors for the U.S. Customs Method may be obtained by deducting 0.07 from those listed in this table. Brix P at 25.7 °C P1 at 25.7 °C

= 18.1° = 60.2 = —18.3

P—P1

=

78.5

Divisor for 18 Brix = 132.31 Temperature correction = —3.02 Corrected divisor

= 129.29

In the case of solutions of normal strength, or related thereto by a simple ratio, the values of P and P 1 must be expressed as for a normal solution. Hence, if the original solution were of half normal strength the direct and invert readings would be made at quarter normal strength and the readings must be multiplied by four to give P and P1.

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The Clerget divisors may be calculated from the formulae given above. For sugars (1 N.W. in 100 ml) the value 132.63 at 20 °C may be taken, and for final molasses (1 N.W. in 300 ml) 131.88 at 20 °C. These apply to the Walker method of inversion, and must, of course, be corrected to the temperature of the operation. The formula shown above S = (P — Pl) X 100 Clerget divisor then gives the percentage of sucrose S directly, when P and P 1 are expressed in terms of a normal solution. Sucrose in Low Purity Materials Optical methods are not recommended for the determination of sucrose in low purity materials. A more suitable technique is that known as the Chemical Method. Basically the chemical method involves the determination of the original reducing sugar content of the sample, followed by another reducing sugar determination after the sucrose present has been inverted to reducing sugar. Two methods for carrying out the inversion are given. Chemical Method The weights and suggested dilutions shown below are normally suitable for final molasses samples. They may have to be varied to suit local conditions. (If B molasses is to be analysed, a concentration 10 g of sample in 250 ml, and titration of the undiluted filtrate should suffice). Procedure—Accurately weigh out approximately 4 g of final molasses. Transfer to a 250 ml volumetric flask. Dissolve and dilute to volume. Warm the flask and contents to 40 °C. Add 1 g of powdered potassium oxalate. (This precipitates the calcium from the solution.) Shake well and cool. Filter through a No. 1 Whatman paper after having added a small amount of kieselguhr to assist filtration. Direct Reducing Sugar Determination—Pipette 50.0 ml of filtrate into a 100 ml flask. Dilute to volume and shake. Prepare Fehling's solution by adding 5.0 ml of No. 1 and 5.0 ml of No. 2. Fehling's into a 250 ml boiling flask. Add four drops of methylene blue indicator and titrate as described in the section on reducing sugars determination. Estimation of Total Sugars A. Invertase Method—Pipette 50.0 ml of filtrate into a 250 ml volumetric flask. Add two drops of glacial acetic acid followed by 10 ml of invertase. Heat in a water bath to 57.5 °C for 25 minutes. Agitate continuously for the first three minutes and then intermittently for the remainder. Cool to 20 °C and make to volume with distilled water. Titrate against 10.0 ml of mixed Fehling's solution using methylene blue as an indicator. B. Acid Inversion Method—Pipette 50.0 ml of filtrate into a 200 ml volumetric flask. Add 10.0 ml of Jackson and Gillis hydrochloric acid solution. Insert a thermometer and heat the flask and contents to 60 °C in a water bath. Agitate the flask during the initial three minutes of heating. After a total heating time of ten minutes, remove the flask, cool in water and dilute to volume. Add one drop of phenolphthalein indicator and neutralize with 4 N sodium hydroxide to the first darkening of the solution. Dilute to

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volume. Titrate against 10.0 ml of mixed Fehling's solution using methylene blue as an indicator. Calculation—(Example for the Acid Inversion method using the weights and dilutions as stipulated).

Per cent sucrose = (total sugars — reducing sugars) X 0.95 Note 1. In this calculation the 0.5 g sucrose column in Table V is used. Note 2. In this calculation the 0.0 g sucrose column in Table V is used. Reducing Sugars Of the numerous methods available for the determination of reducing sugars, only one is listed in this Edition, namely the Lane and Eynon method, as this has now received almost universal acceptance by the Queensland Sugar Industry. Briefly, this method consists of the titration of a sugar solution of unknown reducing capacity against standard strength Fehling's solution. For accurate results the level of reducing sugars in the test sample should be approximately 0.2 g per 100 ml of solution. If the test solution has a concentration greater than this it must be diluted. If the test solution has a reducing sugar concentration less than 0.1 g per 100 ml, a known quantity of standard invert solution should be added to the test solution to laise the reducing sugar concentration to a level of approximately 0.2 g per 100 ml. The amount of added invert is later subtracted from the final result. In the case of high polarization sugars, this can normally be obtained by adding 20 ml of standard invert solution to a 200 ml flask. One drop of phenolphthalein indicator is added, and the excess acidity is then neutralized with caustic soda solution. The weighed quantity of sugar (usually 50 g) is then added to the flask, dissolved and diluted to volume. For other sugar mill products the dilution required must be ascertained by a process of trial and error. Clarification of samples is not usually carried out, but when any appreciable quantity of calcium is present this is precipitated by adding 0.1 g of potassium oxalate per 100 ml, and filtering off the precipitate. Method of Lane and Eynon Incremental Method of Titration—Prepare the Fehling's solution just prior to the titration, by pipetting 5 ml of Fehling's A solution and 5 ml of Fehling's B solution into a 250 ml boiling flask. N.B.—If water is added at this point to obtain a more workable volume, the quantity added must be standardized. This same volume must also be used in the initial standardization of the Fehling's solution. Exploratory Titration—Add approximately 15 ml of the test solution from an offset burette to the prepared Fehling's. Heat to boiling. The colour of the boiling solution will give an indication of the additional quantity of test liquid required to reduce the remaining copper. If the end point appears to be reasonably close, continue boiling for two minutes and add four drops of methylene blue indicator. Continue the titration in aliquots of 1 ml or less until the colour is completely discharged.

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N.B.—The liquid must be kept boiling during all stages of the titration. Final Titration—Repeat the above in a modified form i.e. To 10 ml of mixed Fehling's solution, add the volume determined from the rough titration less approximately 0.5 ml. Heat to boiling, and boil for exactly two minutes. Add four drops of methylene blue indicator, and recommence the titration 15 seconds after the commencement of indicator addition. Complete the titration within a total boiling time of three minutes. Calculation of Results—The reducing power of an invert sugar solution is affected by both the volume of the final solution and the concentration of sucrose present in the solution. Allowances for these factors have been calculated in Table IV and the expanded version in Table V. Example {A) Undiluted Juice Uncorrected Brix of juice Pol of juice Approximate density of juice (Table XIV) Grammes sucrose per 100 ml (pol x density) Titration (ml) mg R.S. per 100 ml (Table IV) Per cent R.S. in sample

= = = = = =

Example (B) Sugar with Added Invert Added invert Sucrose concentration Titration (ml) mg R.S. per 100 ml (Table IV) After deduction for added invert Per cent R.S. in sample

= = = = =

19.7 17.8 1.08 grammes per ml 19.0 approx. 20.0 222 222 x 100 = 1000 x 108 = 0.21 per cent 100 mg per 100 ml 25 g per 100 ml 27.5 155 55 55 x 100 = 1000 x 25 = 0.22 per cent

Ash Theoretically, ash is defined as the residue remaining after burning off all organic matter. In practice however, the position is more complicated, as the total removal of "ash" from all sugar products is not always possible. A further complication arises from the fact that the chemical form in which the ash is determined is normally not the form in which the ash is present in a sugar product. Furthermore, a diversity of opinion still exists on such points as whether single or double sulphation should be used and whether or not a ten per cent deduction should be applied. The overall quantity of sulphuric acid to be used for the determination is also a matter of debate. Apart from the variations in registered quantities that result from changes in technique, the influence of these changes on working formulae such as R.S./Ash ratio, and the effect on the difference between actual and expected purity when considering final molasses exhaustion criteria, should also be borne in mind. In an endeavour to remedy this situation and to obtain some uniformity in reporting results for Mutual Control purposes, we strongly recommend that the following be adopted for control analysis—double sulphation, no deduction, concentrated acid addition of 0.5 ml before the first incineration followed

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by five drops before the second incineration. For the analysis of sugar for payment purposes, the practice of single sulphation, using 2 ml of concentrated acid and the application of 10 per cent deduction to the result, is still followed in Queensland. Gravimetric Ash Determination Three items of importance that are associated with the ash determination are listed below:— Quality of Sulphuric Acid—Check each bottle of sulphuric acid to be used for ash determination as follows:— Transfer 25 ml of the acid from a measuring cylinder to a prepared platinum crucible. Evaporate cautiously in a fume cupboard. Transfer to a muffle oven and ignite at 500 °C. Cool in a desiccator. The weight of residual ash from the 25 ml aliquot should not exceed 0.001 g. Acids with a residue in excess of this figure should not be used for this work. Preparation of the Platinum Crucible—Wash the crucible and polish both inside and out with moistened keiselguhr. Rinse with distilled water and remove excess droplets with filter paper. Heat to 800 °C for approximately 30 minutes and allow to cool in a desiccator. Health Hazard—It is important that the preparatory stages of heating should be carried out in a fume cupboard effectively vented to the atmosphere. Sulphuric acid vapour can cause severe damage to the respiratory tract. The vapour also has a highly corrosive action on metallic laboratory fittings. Procedure—The following sample weights for the various sugar products are recommended. Sugar 5g First Expressed and Clarified Juices 20 g Syrup and A Massecuite 3g Products of lower purity 2g Weigh out the recommended weight of sample into a prepared platinum crucible. Add 0.5 ml of concentrated sulphuric acid by drops over the surface of the sample. Heat the crucible gently on a hot plate to carbonise the sample. (Dilute solutions should be evaporated to syrup consistency in a water bath to avoid loss of solids.) Continue heating on a hot plate until frothing has ceased. Incinerate in a muffle oven at 550 °C until no trace of unburnt carbon is visible. Remove the crucible, cool and add five drops of concentrated sulphuric acid to wet the residue. Transfer to a muffle oven and again incinerate until a temperature of 800 °C is attained. Remove after 15 minutes at 800 °C and transfer to a desiccator. Weigh when cool and express the weight of residue as a percentage of the original sample. Conductometric Ash An approximation of the ash content of raw sugar products can be obtained rapidly by the conductometric method. When sugar is dissolved in water, the soluble impurities disperse into electrically charged particles called ions. As the passage of an electric current through a solution is dependent upon the concentration of ions present, a measure of the concentration of soluble impurities can be obtained from a simple conductivity measurement. One shortcoming of the conductometric method is that the relationship between gravimetric and conductometric ash must be known for each grade

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of sugar product. This relationship is then assumed to be valid for all samples tested in each category. Significant departures from these standards can occur in actual practice however, but the method is a useful adjunct to routine factory control purposes. Apparatus—A special electrolytic conductivity meter known as an "ash bridge" is used. A suitable conductivity meter is illustrated in Fig. 41. Procedure—Weigh out 10 g of sample (if below one per cent ash) and transfer to a 200 ml volumetric flask. Dissolve and dilute to volume. N.B.—If the sample has an ash content above one per cent, a mixture of sample and pure sucrose should be substituted to give a 10 g sample with an ash content equal to approximately 0.5 per cent. Determine the conductivity of the solution, making corrections for the temperature at which the determination is carried out. Calculation— where C

= the predetermined relationship between gravimetric and conductometric ash for the particular grade of product.

Sugar Analysis The majority of methods for the routine analysis of raw sugar are presented under this sub-heading. The procedures for reducing sugars, ash and phosphates however, may be located under their specific sub-headings as their procedures have a general application to other types of sugar products. Polarization The procedure for raw sugar polarization has been the subject of much debate for a number of years. Investigations into this analysis are still being carried out, and, no doubt, the pending introduction of automatic polarimeters into the industry will result in considerable changes in this section. The polarization of a sugar is one of the most exacting analyses carried out by a sugar chemist, and rigorous adherence to a standard procedure is essential if reproducible results are to be obtained. At the 14th Session of ICUMSA in 1966, a recommendation was duly adopted for a method to be referred to as ICUMSA polarization Method 1. This method is based on the use of the International Sugar Scale, clarification by the standard wet lead solution, a standard specification for apparatus, and for the procedures to be followed during preparation of the solution, filtration, polarization of the filtrate and the corrections to be applied to the observed polarization. The following procedure is based in principle on ICUMSA polarization Method 1.

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Apparatus This should conform to the standards laid down by ICUMSA (1966). Included in the apparatus are saccharimeters or sugar polarimeters, quartz plates, balances, flasks, polarimeter tubes or cells, cover glasses, funnels, filter paper and basic lead acetate. Although the specification for flasks includes various types, it is recommended that the flask made to the British Standard 675 Type 2, be the only flask used for the polarization of raw sugar. This flask has been specifically designed for this purpose not only in its dimensions, but also for ease of mixing after completion to volume. All sugar polarizations should be conducted in a room maintained at a constant temperature and relative humidity (20° ± 0.5 °C and 65-70 R.H.). If this temperature is not attainable the range 15 to 25 °C should not be exceeded, if possible. Preparation of Solution Thoroughly mix the sugar samples received for analysis prior to weighing capsule, on a balance with a sensitivity reciprocal of 0.1 milligrammes per scale division. Transfer by washing with about 60 ml of distilled water into a 100 ml flask conforming to B.S. 675 Type 2 specification. Dissolve the sugar, without any loss from the flask, and add 1.0 ml of basic lead acetate solution, (made to the specification as detailed in Chapter VIII) from a reservoir protected from atmospheric carbon dioxide. Mix in the added lead solution by swirling gently, then add further distilled water until the bulb of the flask is filled. Allow to stand at least 10 minutes making sure that no air bubbles are entrapped in the flask. Dilution to Volume Add distilled water to bring the meniscus level to about five mm below the graduation line. If necessary, ether or alcohol vapour from a blower may be used to clear the meniscus before finally making to volume with distilled water. For setting of the meniscus to the graduation line it is recommended that a strip of black paper be secured around the neck of the flask with a clip, at about 1 mm below the graduation mark. Place the flask on a stand at eye level and add the distilled water from a fine jet until the lowest point of the meniscus is at the top edge of the graduation line. Remove any drops of water adhering to the neck of the flask by means of a rolled strip of filter paper. Stopper and thoroughly mix the solution. Allow it to stand for at least five minutes to permit settling of the precipitate. Filtration Filter the solution through a single paper (the moisture content of which is in the range 6-8 per cent when dried for 3 hours at 100 °C), fitted neatly without any overlap in a stemless funnel made of non-corrosive material. Cover the filter with a suitable cover of non-corrosive material to minimize evaporation during filtration. Discard the first 5 to 10 ml of filtrate and do not return any of the filtrate to the filter. N.B.—The nitration should be carried out as rapidly as possible and the funnel must be seated firmly in the mouth of the filter glass and not in a filter stand. Rinse a clean dry glass pol tube of 200 i 0.03 mm length (previously tested so that no detectable change in reading is observed on rotating the tube

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in the trough of the saccharimeter), at least twice with filtrate. This rinsing assists in wetting the walls of the tube and washes out any unobserved foreign matter. When the tube is finally filled with the filtrate, close off with a cover glass made of good optical glass with plane parallel faces free from defects. The cover glasses are held in position with the threaded cap ends complete with good quality rubber washers of the correct size. Do not overtighten the caps as this could cause strain to the cover glasses, resulting in their becoming optically active. With enlarged end tubes any air bubbles in the tube are collected in the enlarged end by inverting the tube a few times, so that on placing the tube in the trough of the saccharimeter a continuous path of solution is presented to the polarized light. To avoid undue temperature rise in the filtrate, the tube must be handled as little as possible before being placed in the trough of the saccharimeter. The saccharimeter used shall be fitted with the International Sugar Scale in compliance with the ICUMSA (1966) standards. Reading of the Filtrate The saccharimeter shall be standardized at the time of reading, by means of a standard quartz plate of the value close to the observed polarization. The value of the quartz plate shall have been checked by an authorized authority. Determine the reading of the filtrate, making at least five settings of the instrument and averaging the result. Each setting should be read to the accuracy of the instrument. A scale correction based on the reading of the standard quartz plate is then applied to the observed reading. Determine the temperature of the filtrate as soon as practicable after the saccharimeter readings, by immersing a thermometer graduated in tenths of a degree in the tube after a little of the solution has been removed. To minimize handling, it is recommended that the tube be placed upright in a clean dry container whilst the temperature is being determined. After the temperature of reading has been measured, the correction to be applied to adjust the observed polarization to 20 °C is made as follows: — When the reading is obtained in a quartz wedge saccharimeter P20 = pt +. 0.00033 S (ty — 20) — 0.0047R (tv — 20) where P20 = polarization at 20 °C Pt = polarization at t °C S = per cent sucrose in sample R = per cent reducing sugars in sample tr = temperature of solution as read °C. When a sugar polarimeter is used the coefficient 0.00033 S is smaller and may be taken as 0.00019 5. The temperature used in the above formulae for correcting polarizations to 20 °C is the actual temperature of reading, and the assumption is made that this temperature is the same as that at which the solution was made to the mark. Even if all operations are carried out in a constant temperature room, this assumption will not necessarily be correct. Any change in concentration of the solution caused by a change in temperature between making to the mark and polarizing should be allowed for. For this reason if it is not possible to carry out the preparation of solutions, the nitrations, and the

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readings in a constant temperature room, it is important that the temperature should vary as little as possible from the start to finish of the operations i.e., by not more than 0.5 degree C. If however, there is reason to suspect that the temperature of reading the filtrate differs from the temperature of making to the mark by more than 0.5 degree C, the temperature of making to the mark shall be determined. This shall be done by placing a clean dry thermometer, graduated in tenths of a degree C, in the flask immediately after shaking and before the solution is poured on the filter. This temperature should be noted and recorded to the nearest tenth of a degree, and if necessary the quantity 0.027 (tr —• tm) should be added to the observed polarization, where tr is the temperature of reading the filtrate in the saccharimeter, and t m is the temperature of making the solution to the mark. The pol of the sugar reported will be the observed reading, corrected for scale error, corrected if necessary for errors in flask and tube, and corrected for temperature when observations are made at temperatures other than 20°C. Moisture For routine control purposes, the moisture content of raw sugar is taken as the loss of weight resulting from the air drying of a 5 g sample at 103 to 105 °C for a period of three hours. The value recorded should be regarded as relative rather than absolute, as some thermal degradation of the sample occurs under these test conditions. Although a simple procedure, the moisture determination can give varying results unless both technique and test conditions are adequately standardized. Determinations should be carried out in duplicate and repeat determinations carried out if the duplicates differ by more than 0.05 per cent. Drying Dishes- -These are approximately two inches in diameter, half an inch deep and should be fitted with close fitting lids. Procedure—Prepare the requisite number of dishes by drying overnight in an air oven. Transfer the covered dishes to a desiccator and allow to cool to room temperature. Weigh the dish plus lid to ^O.OOOl g. Rapidly add approximately 5 g of sample evenly over the dish surface and replace the lid. Determine the weight accurately. The sample addition and weighings should be carried out as rapidly as possible. Transfer the dish and contents to an air oven and dry for three hours at 103 to 105 °C. At the completion of drying, replace the lid and allow to cool to room temperature in a desiccator. Weigh the dish plus dried sample again to ±0.0001 g. Express the loss of weight as a percentage of the original sample weight. Filterability The test involves the constant pressure filtration of a raw sugar solution under standard conditions. The filtration rate of the test solution is compared with the filtration rate of a pure sugar solution which has been filtered under identical conditions. Strictly speaking, the per cent filterability is defined at 20 ±1 °C, and the procedure and calculation tables are designated for temperature controlled laboratories. Temperature control of ±1 °C is difficult to maintain however, and if the test is performed at a temperature outside this range, the result can only be validly expressed as "filterability at t°C". Table XXXVII will permit the calculation of "filterability at t °C" between the ranges of 12 and 32 °C. As temperature changes are likely to

ANALYTICAL METHODS occur during the test, the average of the temperatures taken before and after the test should be used. Special Apparatus—Pressure Filter. The C.S.R. type filter shown in Fig. 42 is assembled in the following order:— rubber gasket, filter disc, Whatman No. 54 filter paper, retaining ring and second rubber gasket. Air Pressure. A supply of compressed air or nitrogen at 50 pounds per square inch is required. Stirrer. This should have a running speed between 1000 and 1200 rev/min. Excessive and prolonged stirring should be avoided so that damage to filter aid particles is minimized. Procedure—Mix the sample thoroughly and weigh out the appropriate amount of sugar (listed in the following table) into a 400 ml beaker. Add 99.4 ml (equivalent to 99.1 g in air) of distilled water. Then add 0.720 g (equivalent to 0.48 per cent on solids) of standard filter aid, and dissolve the sugar using the stirrer. This usually requires 25 to 35 minutes of stirring. Minimize evaporation by keeping the solution away from draughts and covering it when not being stirred. Add 2.0 ml of standard buffer solution (Chapter VIII), and stir for two minutes ±lO seconds. Cover the solution and allow to stand for 15 minutes ±0.5 minutes. Assemble the filter, stir for a further 60 seconds and pour the liquid into the filter body. Read the temperature of the solution to ±0.1 °C. Per cent Moisture of Sugar 0.0 0.2 0.5 0.8

— — — —

0.2 0.5 0.8 1.0

Sample Weight g ±0.05 149.0 150.0 151.6 152.6

Close filter, apply air pressure of 50 lb/in 2 gauge and commence timing of filtration immediately the pressure is applied. Discard the filtrate for the first two minutes and collect the filtrate for the next five minutes in a tared 100 ml beaker. Release the air pressure and determine the temperature of the residual solution. Calculation—Average the initial and final temperatures to 0.1 °C. Reweigh the beaker to determine the amount of filtrate collected between two and seven minutes of filtering. Refer to Table X X X V I I and find the corre-

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sponding weight of pure sugar syrup equivalent to the weight obtained at the temperature of the determination. Calculate per cent filterability as

Notes on the Determination (i) (ii) (iii) (iv) (v)

Keep the filter and gaskets thoroughly clean. Keep the filter disc, when not in use, in the lightly assembled filter. Make sure that the gaskets are not perished or damaged in any way. Check the pressure gauge at regular intervals. The filter disc should be calibrated once every two months to check its performance. (vi) For affined or good filtering sugars, twice the amount of solution may be required. In these cases, twice the amount of buffer solution and filter aid will have to be added. Calibration of Pressure Filter Discs—The performance of a filter disc must be checked at regular intervals against the standard flow rates in Table XXXVII, before any routine filterability determinations are carried out. If the discrepancy is greater than four per cent, a replacement filter is required. The calibration is carried out as follows:— Prepare about 500 g of 60° Brix syrup using A.R. sucrose and distilled water. Add a weight of standard filter aid equal to 2 1/2 per cent of the weight of the solids in the syrup. Mix and pressure filter in two separate portions through Whatman No. 54 filter papers. Discard the first 20 ml of filtrate from each filtration. Mix both portions of clear filtrate, weigh, and adjust the Brix to 60.0 ± 0 . 1 ° Brix. Determine the amount of filter aid equal to 0.48 per cent of the solids in the syrup. Add about 50 ml of syrup to the weighed amount of filter aid in a separate beaker and mix to a smooth slurry consistency by means of a rubber tipped stirring rod. Avoid grinding of the filter aid. Transfer the slurry to the bulk of the syrup and recover any residual slurry with original syrup. Add 1.4 ml of standard buffer solution. Mix for two minutes using the electric stirrer, cover and allow to stand for 15 minutes as before. Filter the syrup as previously described. N.B.—(i) The quantity of syrup collected should be within 4 per cent of the corresponding quantity shown in the table. (ii) If a check reveals faults, and the pressure gauge is correct, renew the filter disc. Calibrate the new disc before use. Grain Size Distribution: Grist Analysis The results obtained from previous routine methods for grist determination were often influenced by the amount of syrup film surrounding the crystals, and by the conditions of humidity and temperature prevailing at the time of the determination. The C.S.R. method presented below, however, minimizes the tendency of crystals to adhere to each other, by removal of most of the syrup film with successive washings of methyl and isopropyl alcohol.

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ANALYTICAL METHODS

Special

Apparatus—

Drying Oven—This should have an explosion proof rating and should be so situated that any emerging alcohol vapours can be directly removed to outside atmosphere. Sieves—Three British Standard screens or their equivalents in the Tyler rating are employed. The recommended screens are as shown:— !

Tyler Screen

British Standard Screen Mesh

i 18 25 36

Size of Opening mm

Mesh

Size of Opening mm

0.853 0.599 0.422

20 28 35

0.833 0.589 0.417

!

Jar Mill—A jar mill with a speed of approximately 75rev/min is required for the mixing process. Several commercial units are available, but some items of laboratory machinery can be modified for this purpose. A two pint Agee jar with the normal sealer cap is required for mixing. The outer surface of the jar should be covered wdth one thickness of bandage impregnated with Araldite. Also required are an Agee lid ring covered with 100 mesh gauze, and an outer rubber sealing ring, which will form a seal when the jar is inverted over a Buchner funnel. Sample Preparation—Thoroughly mix the sugar sample and transfer approximately 11.0 g to the Agee jar. Add 250 ml of 99 per cent methyl alcohol, seal and rotate for three minutes at 75 rev/min on the jar mill. Substitute the gauze covered cap, invert the jar over a Buchner funnel and draw off the alcohol under vacuum. Add 250 ml of 99 per cent isopropyl alcohol, rotate for three minutes and again remove the alcohol under vacuum. N.B.—The preceding alcohol washings should be repeated at this stage, if the sugar sample is below 98 polarization. Oven dry the sugar on a flat tray at 80 to 90 °C. Occasionally disturb the sugar with a spatula to prevent caking. Allow the sugar to cool in a desiccator. Sieve Separation—Weigh out 100.00 g of prepared sample and sieve for 10 minutes on a Ro-tap shaker or Pascall sieve vibrator. Empty the sugar crystals caught on each sieve onto sheets of glazed paper, brushing out the sieve with a firm tapping brush, taking care not to damage the screens. Transfer the sugar from each section to a tared container and weigh the fractions to 0.01 g. Round off weights so that the weights of the four fractions add up to 100.0 g. Report the results as a percentage. The percentage of fines is defined as the percentage passing through the B.S.25 mesh screen, and by plotting cumulative weight fraction against sieve aperture (linear axis) on arithmetic probability paper, mean aperture and coefficient of variation can be obtained in the following manner. Mean aperture == sieve aperture corresponding to 50 per cent weight fraction.

ANALYTICAL METHODS

123

Starch The C.S.R. method for the determination of starch in raw sugar is presented below in a slightly abbreviated form. The method involves hot, mild digestion of an aqueous solution of raw sugar in calcium chloride/acetic acid to ensure that any starch present is in a form suitable for subsequent reaction with iodine. The starch/iodide complex is then determined colorimetrically at 700 nm. This complex is essentially a colloidal suspension which is stable for at least five minutes. Standardization—A standard graph is prepared using B.D.H. Laboratory Reagent Potato Starch Batch No. 2499440. Refer to Chapter VIII for preparation of the standard starch and other starch reagents. Prepare aliquots of the standard starch solution, increasing in concentration from 0 to 500 p.p.m. starch on solids. These are obtained by adding 40 g of standard starch-free sugar to each of eight 100 ml volumetric flasks and then adding 0, 5, 10, 15, 20, 25, 30 and 50 ml aliquots of standard starch solution. Add distilled water to each flask to make a total volume of approximately 75 ml, and dissolve. Dilute to volume, stopper and mix. Pipette 15 ml of each solution into separate 50 ml volumetric flasks and then add 25 ml of calcium chloride/acetic acid reagent from an automatic burette or graduated cylinder. Mix thoroughly. Hold each flask in boiling water for 15 minutes and swirl at five minute intervals to facilitate the escape of gaseous materials. After exactly 15 minutes of heating, cool the flasks in running water, dilute to volume, stopper and mix. From each 50 ml flask, pipette 15 ml aliquots into each of two 25 ml volumetric flasks designated (a) blank sample and (b) test sample. Then add 2.5 ml of 1 N acetic acid reagent to each 25 ml flask. Flask (a) from each set is then diluted to volume, stoppered, mixed and later used as a separate blank for each test sample. Prepare and analyse each of the flask (b) test samples as a separate entity in the following manner:— Add 5 ml of freshly prepared potassium iodideiodate solution (Chapter VIII). Swirl during the addition of this reagent and then make to the mark, stopper and mix. Transfer to a 1 cm cuvette. Determine the optical density at 700 nm against the corresponding blank. The determination should be completed as rapidly as practicable after the iodideiodate solution has been added. Plot p.p.m. starch on solids against optical density. Procedure—-The procedure used for raw sugar is basically the same as that used to obtain the standardization curve. Dissolve 40.0 g of sugar in 50 ml of distilled water in a 100 ml volumetric flask. Make up to the mark and mix. Pipette 15 ml of this solution into a 50 ml volumetric flask, add calcium chloride/acetic acid reagent, mix, digest in a boiling water bath, cool and make up to the mark as previously described. Pipette 15 ml aliquots into each of two 25 ml volumetric flasks. Add 2.5 ml of 1 N acetic acid to each flask, mix well and make one flask up to the mark, stopper and mix. This is the sample blank solution. Fill a 1 cm cuvette with this solution and use it to adjust the spectrophotometer for infinity and zero optical densities at a wavelength setting of 700 nm. Add 5 ml of potassium iodide-iodate reagent to the other flask, make up to the mark, stopper and mix. Transfer this solution to a 1 cm cuvette and read the optical density at a wavelength of 700 nm, within five minutes.

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ANALYTICAL METHODS

Read the concentration of starch as p.p.m. on raw sugar solids from the standard graph. Total Colour Attenuation Two methods of colour attenuation have been issued by the C.S.R. Company. The more precise of these is not included in this Edition as it requires the use of a precision spectrophotometer of a type which is not generally available in mill laboratories. The procedure for the routine method for colour measurement of raw sugar is given below. The method is also applicable to low polarization sugars, but in this case, the initial sample weight should be reduced to maintain maximum sensitivity on the spectrophotometer scale. Special Apparatus—A millipore vacuum filtering apparatus or a C.S.R. type pressure filter may be used. Filtration is affected through Millipore type A.P.30 prefilter discs and type PH (0.3 micron) filter membranes. Sample Preparation—Weigh out 12.50 g of raw sugar and transfer to a 100 ml volumetric flask. Dissolve in approximately 40 ml of distilled water and dilute to volume. Mix thoroughly. pH Adjustment—By means of a graduated measuring cylinder, transfer 50 ml of the solution to a beaker and determine the pH. Adjust the pH of the solution to 7.00 ± 0.05 pH by drops of either 0.1 N NaOH or 0.1 N HC1, stirring vigorously during the addition. Filtration—Filter the solution through a Millipore prefilter disc and 0.3 micron filter membrane. If insufficient sample is collected before the filtration rate slows appreciably, the filter and prefilter should be renewed. Reading—Determine the optical density at 420 nm in a 1 cm cuvette against a distilled water blank. Calculation— Total colour attenuation @ 420 nm = 1000 x optical density (concentration of solution g/ml) x (cell size in cm) N.B.—If less than ten drops of alkali or acid are used for neutralization, the calculation, for an original sample weight of 12.50 g per 100 ml, may be abbreviated to— Total colour attenuation = 8000 x optical density If more than ten drops are used for neutralization, the refractometer Brix should be accurately determined and converted to g/ml concentration, using Table VII of the Manual. Mud Analysis Insoluble Solids The measurement of insoluble solids in clarifier feed and primary mud is usually carried out in conjunction with the laboratory settling test for the assessment of clarifier performance, while the determinations on filter feed and filter cake are carried out to assess rotary filter performance. Two methods are given below. Vacuum Filtration Method—Weigh out 200 g of well mixed sample and filter through a Buchner funnel. Do not wash the cake with water.

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125

Peel off the cake from the filter paper and weigh the wet cake. Dry to constant weight at 96 to 100 °C. Determine the soluble solids content of a separate quantity of gravity filtered filtrate. This is required to correct for the weight of soluble solids contained in the cake. Calculation— Per cent insoluble solids =

Aluminium Dish Method—This method has been used extensively by the Bureau in clarifier investigations and is useful where a large number of samples have to be analysed. Its accuracy is mainly dependent upon accurate subsampling of a relatively small quantity of material, and the minimizing of evaporation effects. When samples with a relatively low insoluble solids content are encountered, the accuracy of the determination may be improved by prethickening before subsampling. If this is carried out the formula must be modified accordingly. Equipment—Flat bottomed aluminium dishes with close-fitting lids. A deep welled measuring spoon to contain approximately 3 g of sample. Procedure—Prepare the aluminium dishes by pre-drying and cooling in a desiccator. Weigh . . .. .. .. .. .. .. .. W1 Thoroughly but rapidly mix the sample and transfer approximately 3 g to the aluminium dish. Immediately seal the dish and weigh dish plus contents .. .. .. .. .. .. . .. .. W2 Remove the lid and rotate the capsule to spread the sample in an even film over the bottom of the container. Oven dry for 16 hours at a temperature of 70 °C. Seal the container and allow to cool in a desiccator for 30 minutes. Weigh and record as ..W3 Soluble Solids Correction—Filter a separate portion of the original sample, taking care to minimize evaporation effects. Determine the Brix to an accuracy of ±0.03 units by means of a precision refractometer. Calculation—

N.B.—In the case of materials containing an appreciable amount of fibre, the fibre content must be determined as described below, and subtracted from the insoluble solids content to obtain the actual percentage of mud solids. In the case of filter cake, it may be necessary to apply some compression to the sample in order to obtain a juice sample for the determination of refractometer Brix.

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ANALYTICAL METHODS

Moisture Low temperature drying of mud is recommended for experimental purposes. For comparative routine determinations on filter cake however, drying at 100 °C will not introduce serious errors. Procedure—Weigh out 5.0 g of well mixed sample into a tared aluminium container. Dry at 70 °C for 16 hours or for four hours at 100 °C. Cool in a desiccator and reweigh. Calculate moisture per cent original sample. Pol In the determination of per cent pol in mud by wet lead clarification an arbitrary adjustment is made to the weight of sample taken, to correct for the error introduced by the presence of insoluble solids. Procedure—Thoroughly mix the sample and weigh out 50 g into a nickel weighing dish. Add a small quantity of water to promote mobility and transfer into a wide mouthed (Kohlrausch type) 200 ml volumetric flask. Add sufficient wet lead to clarify. This usually requires from 2 to 5 ml. Dilute to volume with distilled water, shake and allow to stand for at least 5 minutes. Filter and then polarize in a 400 mm tube. Calculate pol per cent mud by halving the polariscope reading. Fibre For the determination of fibre in mud, a 3 inch diameter 3 inch high cylindrical container fitted with a 100 mesh gauze base is employed. An old style Spencer over drying capsule is ideal for this purpose. Procedure—Transfer 50 g of the premixed mud sample into the drying capsule. Hold over a sink and wash with a steady stream of water until the runnings are clear. Allow surplus water to drain off and then dry to constant weight in a Spencer-type oven. The fibre per cent mud will equal double the dry weight of the fibre (in g), weighing to an accuracy of ± 0.C1 g. Gum Analysis The following is a revised version of the U.S.D.A. method for the determination of gums in cane juices by alcohol precipitation. The method has been used extensively in cane deterioration studies as it provides a quantitative index of changes that occur in gum content during cane storage. Other methods of gum determination are available, and although the results of the method described below may not agree precisely with these, the alcohol precipitation method is considered to be the most suitable for routine analyses. Preparation of Standard Graph—Prepare aqueous solutions of A.R. dextrose (C 6 H 12 0 6 ) to the following concentrations:—0.001 per cent, 0.05 per cent and 0.01 per cent. To a separate test tube for each concentration, add 2.0 ml of dextrose solution and 1 ml of phenol reagent. (See Chapter VIII under Sugar Detection). Rapidly add 10 ml of concentrated sulphuric acid to each test tube, holding the tip of the safety pipette about two inches above the liquid surface. Take care in case the mixture boils and ejects from the tube. Swirl to mix and allow to stand for ten minutes.

ANALYTICAL METHODS

127

After t h e r e a c t i o n t i m e h a s e l a p s e d , cool i n w a t e r for t e n m i n u t e s a n d determine optical density at 485 nm against a blank prepared as above using distilled w a t e r in place of t h e dextrose solution. N.B.—The p h e n o l - s u l p h u r i c acid m e t h o d r e q u i r e s a n e l e v a t e d r e a c t i o n temperature to convert the polysaccharides present to dextrose and other monosaccharides. F r o m the optical density results a s t a n d a r d graph of polysaccharide concentration (expressed as anhydroglucose) versus optical density is obtained. The concentration of anhydroglucose is calculated by deducting ten per cent from t h e concentration of t h e dextrose solutions originally used. T h e r e a s o n for t h i s d e d u c t i o n c a n b e seen f r o m t h e following f o r m u l a e : — D e x t r o s e C 6 H 1 2 0 6 , M o l e c u l a r W e i g h t 180.156 P o l y - D e x t r o s e ( C 6 H 1 0 O 5 ) n , M o l e c u l a r W e i g h t 162.141 A difference of 18.015 or 9.9997 p e r c e n t . Determination of G u m s in Juice Sample Preparation—Sieve a p o r t i o n of t h e j u i c e s a m p l e t h r o u g h a 3 2 5 m e s h s c r e e n . C e n t r i f u g e for six m i n u t e s a t n o less t h a n 2000 g . P r o v i d e d t h e j u i c e i s u n h e a t e d , t h e a b o v e p r o c e d u r e will r e m o v e s t a r c h i n t e r f e r e n c e . I f t h e juice or p r o d u c t has been heated, t h e starch c a n n o t be isolated, a n d " t o t a l g u m s " will b e d e t e r m i n e d . Alcohol Precipitation—Pipette 10 ml of t h e s u p e r n a t a n t l i q u i d i n t o a s e p a r a t e c e n t r i f u g e t u b e c o n t a i n i n g 3 0 m l o f a b s o l u t e alcohol, m i x a n d allow t h e p r e c i p i t a t e t o f o r m b y s t a n d i n g for a t l e a s t five m i n u t e s . R e c e n t r i f u g e for six m i n u t e s t o c o n c e n t r a t e t h e g u m s i n t h e b o t t o m o f t h e c e n t r i f u g e t u b e . D e c a n t t h e s u p e r n a t a n t l i q u i d a s q u i c k l y a s possible t o a v o i d loss o f g u m s . I n v e r t t h e t u b e s o v e r a t o w e l a n d allow excess alcohol to d r a i n off. Purification of Gums—Add a few d r o p s of 80 p e r c e n t alcohol i n i t i a l l y t o assist i n r e s u s p e n d i n g t h e g u m s , a n d s t i r w i t h a glass r o d . W a s h t h e t u b e w i t h m o r e alcohol u s i n g a t o t a l of 30 ml of 80 p e r c e n t alcohol. Allow to s t a n d for five m i n u t e s . C e n t r i f u g e for six m i n u t e s a t n o less t h a n 2000 g . D e c a n t t h e s u p e r n a t a n t l i q u i d a n d a g a i n allow t o d r a i n o v e r a t o w e l . D i s s o l v e t h e g u m s i n distilled w a t e r a n d d i l u t e to a v o l u m e of 100 ml in a v o l u m e t r i c flask. Blank and Test Solution—Pipette 2.0 ml of g u m s o l u t i o n i n t o a t e s t t u b e a n d p r o c e e d w i t h t h e a d d i t i o n of 1 ml of p h e n o l r e a g e n t a n d 10 ml of s u l p h u r i c acid as described in t h e section on p r e p a r a t i o n of t h e s t a n d a r d graph. T h e b l a n k solution is p r e p a r e d in a similar m a n n e r , w i t h the exception t h a t 2.0 m l o f d i s t i l l e d w a t e r i s s u b s t i t u t e d for t h e g u m s o l u t i o n . Determine the optical density of t h e test against t h e blank solution at 485 n m . Calculation—Read off t h e p e r c e n t g u m s in j u i c e for t h e o p t i c a l d e n s i t y o n t h e s t a n d a r d g r a p h . (If t h e o p t i c a l d e n s i t y limits of t h e graph, t h e g u m solution m u s t be rediluted). A Brix i s c a r r i e d out o n t h e o r i g i n a l j u i c e a n d t h e r e s u l t s e x p r e s s e d a s solids.

corresponding is outside the determination gums per cent

128

ANALYTICAL METHODS Phosphate Analysis

T h e C . S . R . a m i d o l m e t h o d i s r e c o m m e n d e d for t h e d e t e r m i n a t i o n o f p h o s p h a t e in r a w sugars, syrups a n d juices. P h o s p h a t e is d e t e r m i n e d by measuring t h e intensity of t h e blue coloration developed in t h e presence of acid m o l y b d a t e a n d amidol at a wavelength of 660 n m . F o r purposes of u n i f o r m i t y , i t i s s u g g e s t e d t h a t all p h o s p h a t e r e s u l t s b e e x p r e s s e d a s p a r t s p e r million p h o s p h o r u s i.e. p . p . m . P . W h e n u s i n g t h i s m e t h o d o f a n a l y s i s t h e following p o i n t s s h o u l d b e b o r n e in mind: (a) I n h a l a t i o n o f t h e v a p o u r f r o m a m i d o l s o l u t i o n s s h o u l d b e carefully a v o i d e d a t all t i m e s . T h i s s u b s t a n c e i s v e r y t o x i c . (b) T h e m e t h o d specifies a c i d w a s h e d s u p e r c e l a s s o m e b a t c h e s o f s u p e r cel, a s r e c e i v e d , h a v e b e e n f o u n d t o c o n t a i n a p p r e c i a b l e q u a n t i t i e s o f p h o s p h o r u s . E a c h b a t c h o f filter p a p e r s s h o u l d also b e c h e c k e d t o e n s u r e t h a t phosphorus cannot be e x t r a c t e d from t h e paper into t h e sample. (c) It is a d v i s a b l e to h a v e a s e t of flasks a n d c u v e t t e s w h i c h a r e k e p t solely for p h o s p h a t e a n a l y s i s a s m i n u t e t r a c e s o f t h e r e d u c i n g a g e n t u s e d i n t h i s d e t e r m i n a t i o n c a n affect t h e r e s u l t s o f o t h e r a n a l y s e s . Preparation of Standard Graph—The p r e p a r a t i o n of t h e s t a n d a r d p h o s p h a t e s o l u t i o n ( c o n t a i n i n g 0.01 m g P p e r m l ) a n d t h e a s s o c i a t e d r e a g e n t s a r e d e s c r i b e d i n C h a p t e r V I I I . T h e following a l i q u o t s o f t h e s t a n d a r d p h o s p h a t e s o l u t i o n a r e t r a n s f e r r e d i n t o 5 0 m l v o l u m e t r i c flasks: 0 , 1 , 2 , 3 , 4 , 7.5 a n d 10 m l . Colour Development—To e a c h flask a d d t w o d r o p s of c o n c e n t r a t e d h y d r o chloric a c i d followed b y distilled w a t e r t o m a k e t o a t o t a l v o l u m e o f 3 0 m l . T h e n a d d 1 0 m l o f a c i d m o l y b d a t e followed b y 4 m l o f a m i d o l r e a g e n t b y m e a n s of a u t o m a t i c dispensers. Dilute to v o l u m e with distilled water, s h a k e a n d let s t a n d for a t l e a s t 1 0 m i n u t e s t o a l l o w a s t a b l e c o l o u r t o d e v e l o p . Blank Preparation—Prepare a b l a n k s o l u t i o n in a 50 ml flask u s i n g t w o d r o p s o f c o n c e n t r a t e d h y d r o c h l o r i c acid, 1 0 m l o f a c i d r e a g e n t a n d d i s t i l l e d water. Adjust t h e s p e c t r o p h o t o m e t e r w i t h t h e b l a n k solution to r e a d zero o p t i c a l d e n s i t y i n a 1 c m cell a t 660 n m w a v e l e n g t h . Colour Measurement—Determine t h e o p t i c a l d e n s i t y of t h e c o l o u r e d solution after t h e s p e c t r o p h o t o m e t e r h a s been s t a n d a r d i z e d w i t h t h e b l a n k solution. This operation should be carried out between 10 a n d 30 m i n u t e s after t h e addition of amidol reagent. Prepare a s t a n d a r d g r a p h by plotting optical density against mg of P used from t h e s t a n d a r d solution. Total Phosphate in R a w Sugars Preparation—Weigh o u t 4 0 . 0 g of s a m p l e a n d t r a n s f e r to v o l u m e t r i c flask. A d d sufficient w a t e r t o d i s s o l v e t h e c r y s t a l s .

a 2 0 0 ml

p H Adjustment—Reduce t h e p H o f t h e s o l u t i o n t o a p p r o x i m a t e l y 4 . 0 . This usually requires only t w o drops of concentrated hydrochloric acid. Dilute t o volume w i t h distilled w a t e r a n d m i x . Filtration—Prepare a s l u r r y by m i x i n g a p p r o x i m a t e l y 20 ml of t h e solution w i t h a level teaspoon of acid w a s h e d supercel. Use this slurry to precoat t w o W h a t m a n N o . 5 p a p e r s i n a B u c h n e r f u n n e l . R i n s e t h e B u c h n e r flask

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with this filtrate and discard. Filter approximately 50 ml of the test solution through the pre-coated papers. Colour Development—Pipette 20 ml of the filtered solution into a 50 ml flask. Add 10 ml of acid molybdate and 4 ml of amidol by means of automatic dispensers. Dilute to volume, shake and allow to stand for 10 minutes. Blank Preparation— Pipette 20 ml of filtered test solution into a separate 50 ml volumetric flask. Add 10 ml of acid reagent, dilute to volume and shake. Use this solution to adjust the spectrophotometer to zero optical density at 660 nm in a 1 cm cell. Determine the optical density of the coloured solution against the blank. This should be carried out between 10 and 30 minutes after the addition of amidol reagent. Convert optical density to mg P from the standard graph. Then p.p.m. P

Total Phosphate in Clarified Juice and Syrup Sample Preparation—Determine the Brix of the material by refractometer, and calculate the weight of material which contains 10 g of soluble solids. Transfer this amount into a 200 ml volumetric flask, adjust the pH to 4.0, dilute to volume and mix. The solution is then filtered and analysed in the same manner as described for the determination of phosphate in raw sugars. Convert optical density to mg P from the standard graph. Then p.p.m. P on solids = mg P x 1000. Total Phosphate in Raw Juices The same procedure as described for syrups is applied, with the exception that a smaller aliquot of filtered sample is taken for colour development. A 5 ml aliquot should be sufficient for normal juices, and the calculation in this instance would then become:— p.p.m. P on solids = mg P x 4000. Soluble and Insoluble Phosphate The form in which phosphate is originally present, and the efficiency of phosphate removal during clarification, bear an important relationship to the filtering qualities of the raw sugar produced. While on one hand it is desirable to have a relatively high concentration of phosphate present in raw juice, the presence of phosphate in raw sugar is considered to be undesirable. A complication also arises by virtue of the fact that some phosphates are present in cane juice in a form that does not favour their precipitation and subsequent removal during clarification. These are commonly referred to as insoluble phosphates, although the term "organically bound phosphate" is more precise. Soluble phosphate is determined after filtration of the undiluted product at its existing pH value. The level of soluble phosphate in clarified juice is of value as an index of the efficiency of juice clarification, but the figure should always be examined in conjunction with the level of phosphate in unlimed juice, as a marked decline in the latter can result in an increase in the residual phosphate present after clarification.

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t h e presence of sugar in a sample. T h e a l p h a - n a p h t h o l test is n o t r e c o m m e n d e d for c o n t r o l p u r p o s e s w h e n facilities a r e a v a i l a b l e for u s i n g t h e p h e n o l sulphuric acid method. Procedure—Pipette 5 ml of c o o l e d s a m p l e i n t o a c l e a n t e s t t u b e a n d a d d five d r o p s o f a l p h a - n a p h t h o l s o l u t i o n . S w i r l t o m i x . Carefully a d d 5 m l o f concentrated sulphuric acid to t h e inclined test t u b e so t h a t t w o clearly defined l i q u i d l a y e r s a r e f o r m e d . I f s u c r o s e i s p r e s e n t , a v i o l e t r i n g will f o r m a t t h e j u n c t i o n o f t h e t w o liquids a n d t h e intensity of t h e colour of this ring is an indication of t h e q u a n t i t y of sucrose present. T h e test is extremely delicate in t h a t 1 p.p.m. of s u c r o s e will g i v e a slight c o l o r a t i o n . An i n t e n s e b l a c k r i n g will f o r m at a c o n c e n t r a t i o n of a p p r o x i m a t e l y 100 p . p . m . Quality of Mill L i m e T h e q u a l i t y of lime supplied to sugar factories is an i m p o r t a n t b u t often n e g l e c t e d f a c t o r i n t h e j u i c e clarification p r o c e s s . A p a r t f r o m t h e e c o n o m i c a s p e c t , t h e u s e of inferior q u a l i t y l i m e c a n i n t r o d u c e significant q u a n t i t i e s of undesirable impurities into process. T h e composite sampling a n d analysis of all i n c o m i n g l i m e c o n s i g n m e n t s a r e f a c t o r s w o r t h y o f s e r i o u s c o n s i d e r a t i o n . T w o d e t e r m i n a t i o n s a r e r e q u i r e d t o assess t h e s u i t a b i l i t y o f a m i l l l i m e . These are t h e Neutralising Value—expressed as per cent CaO, a n d Available CaO. Sampling Procedure—An i n i t i a l b u l k s a m p l e , r e p r e s e n t i n g a p p r o x i m a t e l y one p o u n d per t o n of lime received, is s u b s a m p l e d d o w n to a p p r o x i m a t e l y o n e p o u n d . T h i s i s t h e n g r o u n d i n a m o r t a r a n d p a s s e d t h r o u g h a n 0.5 m m sieve. I t i s i m p o r t a n t t h a t t h i s o p e r a t i o n b e c a r r i e d o u t a s r a p i d l y a s possible so t h a t recarbonation is kept to an absolute minimum. Sample Preparation—Two o u n c e s of t h e s i e v e d m a t e r i a l a r e o v e n d r i e d for four h o u r s a t 100 °C. T h e s a m p l e i s t h e n s t o r e d i n a s m a l l a i r t i g h t container. Neutralizing Value T r a n s f e r an a c c u r a t e l y d e t e r m i n e d w e i g h t a p p r o x i m a t i n g 1 g of s a m p l e t o a 600 m l E r l e n m e y e r flask a n d a d d 4 0 . 0 m l o f 1.00 N HC1. C o v e r t h e m o u t h o f t h e flask w i t h a w a t c h glass a n d h e a t o n a s t e a m b a t h for 1 5 m i n u t e s . Filter, a n d w a s h t h e residue w i t h h o t distilled w a t e r . Dilute t h e n i t r a t e a n d t o t a l w a s h i n g s t o a v o l u m e o f 100 m l a n d b o i l v e r y g e n t l y for five m i n u t e s . A l l o w t o cool i n a w a t e r b a t h . A d d five d r o p s o f p h e n o l p h t h a l e i n i n d i c a t o r a n d t i t r a t e t o t h e e n d p o i n t w i t h 1.00 N N a O H . Calculation— Neutralizing Value ( e x p r e s s e d as p e r c e n t CaO)

=

ml of 1.00 N HC1 u s e d X 2.80 w e i g h t of s a m p l e

Available Calcium Oxide T h e following m e t h o d i s p r e s e n t e d for o b t a i n i n g a n a p p r o x i m a t e e s t i m a t i o n o f t h e p e r c e n t a g e c a l c i u m o x i d e t h a t will c o m b i n e w i t h s u c r o s e t o f o r m a soluble calcium saccharate. It is i m p o r t a n t t h a t t h e s a m e s t a n d a r d sucrose b e u s e d for all t e s t s , a n d for t h e p u r p o s e o f u n i f o r m i t y , i t i s r e c o m m e n d e d t h a t B . D . H . A . R . sucrose only be used. Procedure—Transfer 1.60 g of s a m p l e to a d r y s t o p p e r e d 2 0 0 ml E r l e n m e y e r flask. A d d 2 . 0 m l o f e t h y l a l c o h o l t o p r e v e n t t h e f o r m a t i o n o f a g g l o m e r -

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a t e s . T h e n a d d 100.0 m l o f 1 0 p e r c e n t s u c r o s e s o l u t i o n p r e p a r e d f r o m B . D . H . A . R . sucrose, t o f o r m a soluble s a c c h a r a t e . Seal t h e flask a n d s h a k e for 3 0 minutes. F i l t e r . D i s c a r d t h e first 5 ml of filtrate. A d d t h r e e d r o p s of m e t h y l o r a n g e i n d i c a t o r to a 50 ml a l i q u o t of t h e n i t r a t e a n d t i t r a t e a g a i n s t 1.00 N HC1. Calculation —

Caustic Cleaning Solution Determination of Concentration Care s h o u l d b e t a k e n t o e n s u r e t h a t t h e s a m p l e o f c l e a n i n g s o l u t i o n i s r e p r e s e n t a t i v e of t h e c o n t e n t s of t h e h o l d i n g vessel. P a r t i c u l a r e m p h a s i s s h o u l d b e p l a c e d o n t h i s p o i n t , especially after m o r e solid c a u s t i c s o d a h a s been added to increase the concentration of t h e solution. T h e determination of caustic strength by a straight acid/base titration c a n give e r r o n e o u s r e s u l t s if significant a m o u n t s of s u l p h a t e a r e p r e s e n t . T h i s interference can be overcome by precipitation of t h e sulphates w i t h b a r i u m c h l o r i d e a n d r e m o v a l o f t h e p r e c i p i t a t e b y filtration. Procedure—To 50 ml of t h e s a m p l e a d d 20 ml of 4 p e r c e n t W / V b a r i u m c h l o r i d e s o l u t i o n . Mix a n d filter. T i t r a t e a 25 ml a l i q u o t of t h e filtrate a g a i n s t 0.50 N h y d r o c h l o r i c a c i d , using m e t h y l red as an indicator. P e r c e n t s o d i u m h y d r o x i d e = t i t r e x N of HCI x 0.224 N.B.—The s t r e n g t h o f t h e s t a n d a r d a c i d c a n b e v a r i e d t o s u i t t h e c a u s t i c solution being analysed. C.S.R. L a b o r a t o r y S e t t l i n g T e s t T h e l a b o r a t o r y s e t t l i n g t e s t i s u s e d t o d e t e r m i n e t h e clarifying p r o p e r t i e s of individual juices a n d to predict factory settling rates. T h e multiple testing o f f a c t o r y m i x e d j u i c e s also p e r m i t s t h e e s t a b l i s h m e n t o f s t a n d a r d s t o e v a l u a t e f a c t o r y p e r f o r m a n c e ( B u r g e s s et al., 1962). Special Apparatus—The Juice Heating

following e q u i p m e n t is required:-— — H e c l a 4 5 0 w a t t A.C. p e r c o l a t o r p l u s a 1500 w a t t i m m e r s i o n h e a t e r . Stirring Mechanism — Laboratory type stirrer operating at app r o x i m a t e l y 1200 r e v / m i n . Lime Addition — A 10 ml g r a d u a t e d pipette w i t h approxim a t e l y 1 i n c h of flexible t u b i n g a t t a c h e d to the delivery end. A hypodermic syringe m a y be used as a suitable substitute. H e a t e d S e t t l i n g B a t h — A s p e r C.S.R. specifications. Settling Tubes — T h e s e s h o u l d be 1.50 i n c h e s i n t e r n a l d i a meter, and graduated in volume per cent o v e r a l e n g t h of 16 i n c h e s .

Lime Requirement—The l i m e r e q u i r e m e n t v a r i e s c o n s i d e r a b l y b e t w e e n ind i v i d u a l juices, b u t a n a p p r o x i m a t e e s t i m a t e o f t h i s q u a n t i t y c a n b e o b t a i n e d i n t h e following m a n n e r : — S e t u p a s t i r r e r a n d p H e l e c t r o d e s i n a b e a k e r c o n taining 600 ml of t h e sample. Slowly a d d t h e lime sucrose solution (Chapter V I I I ) from a b u r e t t e until t h e desired pH is obtained. This q u a n t i t y of lime

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saccharate is then used in t h e actual settling test. A refinement to this procedure is t h e use of a m a g n e t i c stirrer hotplate. This a p p a r a t u s reduces t h e r i s k o f e l e c t r o d e d a m a g e a n d also p e r m i t s t h e d e t e r m i n a t i o n t o b e c a r r i e d out at elevated temperatures. Procedure—Subsample t w o 600 m l a l i q u o t s o f j u i c e . D e t e r m i n e t h e l i m e requirement on one portion. Transfer t h e remaining 600 ml of juice to t h e percolator in which t h e stirrer has already been positioned, a n d h e a t rapidly to boiling using t h e percolator element a n d the immersion heater. The time between sampling a n d boiling should n o t exceed seven m i n u t e s . A f t e r t h e j u i c e h a s b o i l e d for t w o m i n u t e s , t u r n t h e s t i r r e r o n a n d a d d the predetermined a m o u n t of lime at a constant r a t e to t h e outer edge of t h e rotating stirrer blade. T h e addition of lime should t a k e approximately 15 s e c o n d s . C o n t i n u e s t i r r i n g a n d h e a t i n g for a f u r t h e r 1 5 s e c o n d s . T u r n t h e h e a t e r a n d s t i r r e r off a n d t r a n s f e r t h e j u i c e t o a p r e h e a t e d s e t t ling t u b e i m m e r s e d i n b o i l i n g w a t e r . Fill t h e t u b e t o t h e 100 p e r c e n t g r a d u a tion m a r k , stopper a n d commence timing of the settling test. Record per cent m u d v o l u m e a g a i n s t t i m e a t o n e m i n u t e i n t e r v a l s for 1 5 m i n u t e s a n d t h e n a t 2 0 a n d 2 5 m i n u t e s . C o m p l e t e t h e t e s t a t 3 0 m i n u t e s a n d r e c o r d t h e final m u d v o l u m e . A s a m p l e of clarified j u i c e is t h e n r e m o v e d , cooled a n d a n a l y s e d for pH, tubidity and phosphate. Calculation of Settling Area Requirement—Plot a s e t t l i n g c u r v e of p e r c e n t m u d v o l u m e v e r s u s s e t t l i n g t i m e i n m i n u t e s . U s e a scale s u c h t h a t 1 0 p e r c e n t i n m u d v o l u m e i s e q u i v a l e n t t o a t i m e i n t e r v a l o f five m i n u t e s . T h e " c r i t i c a l p o i n t " i.e. t h e p o i n t o f m i n i m u m f l u x , i s l o c a t e d b y t h e following m e t h o d a s s h o w n i n F i g . 4 3 . Determine underflow concentration h by the equation

a n d d r a w a h o r i z o n t a l line a t t h e u n d e r f l o w c o n c e n t r a t i o n level. P r o d u c e t h e i n i t i a l s t r a i g h t line s e c t i o n (free s e t t l i n g zone) of t h e c u r v e t o c u t t h e u n d e r f l o w h line a t point A. Bisect t h e outer angle f o r m e d b y t h e e x t e n d e d free s e t t l i n g line a t t h e i n t e r c e p t o n t h e h line. D r a w a line p e r p e n d i c u l a r t o this bisector a n d tangential to t h e settling curve. Produce this t a n g e n t t o c u t t h e h line a t p o i n t C . R e a d off the time corresponding to point C. Designate this time as T. The unit settling area requirem e n t of the juice tested is t h e n given by the equation:— U n i t A r e a = 0.002 x T square foot/gallon juice /hour

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It should be noted that this formula applies only to settling tubes of the dimensions previously stated. This unit area has been used to calculate the area required in factory clarifiers by multiplying the unit area by the factory mixed juice flow, expressed in gallons per hour. However, while the concept has been a valuable guide in the past, with the present extensive use of flocculating agents and the consequent increase in settling rates obtained with these additives, the areas predicted from this test must now be considered with a good deal of reserve. The advent of flocculating agents has, however, introduced a further use for this settling test as it enables the performance of various flocculants to be compared under laboratory and factory conditions. Due to variations in juice composition, and slight differences in test procedure, a single test is of limited value, and the average of a number of tests is required to provide a valid comparison with factory results. As explained in Chapter I, a cyclone sample is a sample of the mother liquid extracted from a massecuite. For the separation process the laboratory Cyclone Sampling and Supersaturation

Fig. 44—Illustrating a pressure filter for separation of molasses from massecuite.

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b a s k e t t y p e fugal w a s f o r m e r l y r e c o m m e n d e d . T h e u s e o f a fugal h a s t h e d i s a d v a n t a g e t h a t a significant p r o p o r t i o n o f w a t e r i s e v a p o r a t e d f r o m t h e m o l a s s e s i n t h e s e p a r a t i o n p r o c e s s . T h i s d o e s n o t influence p u r i t y o f t h e m o l a s s e s b u t i t d o e s a l t e r t h e s u c r o s e a n d t o t a l solids c o n c e n t r a t i o n s . S u c t i o n filters h a v e b e e n u s e d for t h e s e p a r a t i o n , b u t t h e s e d i s p l a y t h e s a m e d i s advantages. T h e r e c o m m e n d e d d e v i c e for s e p a r a t i o n of c y c l o n e s a m p l e s is a p r e s s u r e filter, of w h i c h o n e e x a m p l e is i l l u s t r a t e d in F i g u r e 4 4 . It c o n s i s t s s i m p l y of a w a t e r j a c k e t e d p r e s s u r e vessel w i t h r e m o v a b l e t o p a n d b o t t o m c o v e r s . T h e b o t t o m plate is provided with drainage channels leading to a central hole a n d supports a screen on which t h e a c t u a l filtration is achieved. W h e n massec u i t e i s p l a c e d i n t h e s e a l e d vessel a n d air p r e s s u r e a p p l i e d a t t h e t o p , t h e m o l a s s e s i s forced o u t t h r o u g h t h e s c r e e n . E x c e p t i n t h e m o s t difficult cases, t h e s e p a r a t i o n i s a c c o m p l i s h e d i n a few m i n u t e s a n d t h e c o m p o s i t i o n o f t h e m o t h e r l i q u o r i s n o t a d v e r s e l y affected i n t h e p r o c e s s . C a r e m u s t b e t a k e n , however, to ensure t h a t the separation is carried out at t h e t e m p e r a t u r e of s a m p l i n g o f t h e m a s s e c u i t e a n d t h e first 5 t o 1 0 m l o f s a m p l e s h o u l d b e rejected. Supersaturation T h e d e t e r m i n a t i o n of t h e d e g r e e of s u p e r s a t u r a t i o n of m o l a s s e s is of considerable i m p o r t a n c e in t h e s t u d y of p a n boiling a n d crystallization. T h e e x p l a n a t i o n of t h e t h e o r y a s s o c i a t e d w i t h t h e d e t e r m i n a t i o n of coefficient of s u p e r s a t u r a t i o n i n v o l v e s t h e u s e o f t e r m s w h i c h a r e defined a s f o l l o w s : — (a) C o n c e n t r a t i o n . T h e p e r c e n t a g e r a t i o b y w e i g h t o f s o l u t e t o s o l v e n t (unless o t h e r w i s e s t a t e d ) . (b) S a t u r a t i o n . T h a t c o n d i t i o n i n w h i c h t h e q u a n t i t y o f s o l u t e d i s s o l v e d in a solvent is t h e m a x i m u m which can be contained in stable equilibrium. (c) S o l u b i l i t y . T h e c o n c e n t r a t i o n of s o l u t e in t h e s o l v e n t g i v i n g a c o n d i t i o n of s a t u r a t i o n . S o l u b i l i t y is r e s p o n s i v e to v a r i o u s influences, of w h i c h t e m p e r a t u r e a n d t h e presence of other solutes in t h e solvent are i m p o r t a n t in the present connection. (d) S o l u b i l i t y Coefficient. T h e r a t i o of t h e s o l u b i l i t y of s u c r o s e in t h e impure w a t e r of t h e sample to t h e solubility of sucrose in p u r e w a t e r at the same t e m p e r a t u r e . Some impurities raise t h e solubility of sucrose in water, o t h e r s lower it. T h e c o m b i n e d effect o f t h e i m p u r i t i e s p r e s e n t i n c a n e m o l a s s e s is usually to lower t h e solubility of sucrose. (e) Coefficient of S u p e r s a t u r a t i o n . T h e r a t i o of t h e a c t u a l c o n c e n t r a t i o n of s u c r o s e p r e s e n t in a s a m p l e to t h e s o l u b i l i t y of s u c r o s e in t h e w a t e r of t h e sample at the same temperature. Supersaturation is an unstable condition; though, in practice, the tendency to revert to the equilibrium condition is s o m e t i m e s v e r y feeble. T h e m e t h o d of d e t e r m i n a t i o n of t h e coefficient of s u p e r s a t u r a t i o n , d e vised by H a r m a n , is based on t h e fact t h a t , if a s u p e r s a t u r a t e d solution is h e a t e d , t h e s u p e r s a t u r a t i o n coefficient will fall, d u e t o t h e rise i n t h e s o l u b i l i t y o f s u c r o s e w i t h t e m p e r a t u r e . A t s o m e t e m p e r a t u r e t h e s o l u t i o n will b e c o m e s a t u r a t e d , a n d i f t h i s t e m p e r a t u r e i s e x c e e d e d , u n d e r s a t u r a t i o n will r e s u l t . A n y c r y s t a l s o f s u c r o s e p r e s e n t i n t h e s o l u t i o n will t h e n c o m m e n c e t o d i s solve, a p h e n o m e n o n w h i c h m a y b e o b s e r v e d v i s u a l l y u n d e r s u i t a b l e conditions.

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For a p u r e solution of sucrose in water, s u p e r s a t u r a t e d at t e m p e r a t u r e t1 and found to be saturated at temperature t2 it m a y be claimed t h a t t h e c o n c e n t r a t i o n o f s u c r o s e a c t u a l l y p r e s e n t i s t h a t c o r r e s p o n d i n g t o t h e solubili t y of s u c r o s e at t2. T h e c o n c e n t r a t i o n of s u c r o s e r e q u i r e d to give a s a t u r a t e d s o l u t i o n a t t 1 i s t h e s o l u b i l i t y a t t 1 . B o t h s o l u b i l i t y figures m a y b e a s c e r t a i n e d for s e l e c t e d t e m p e r a t u r e s f r o m t a b l e s s u c h a s t h a t o f Charles (Table X I I I ) . T h e n if S be t h e coefficient of s u p e r s a t u r a t i o n at t e m p e r a t u r e t 1

F o r i m p u r e solutions, t h e solubility of sucrose is altered due to t h e presence of t h e impurities, and, at saturation, t h e actual concentration of s u c r o s e will b e e q u a l t o t h e s o l u b i l i t y o f s u c r o s e i n p u r e w a t e r m u l t i p l i e d b y t h e s o l u b i l i t y coefficient. If k 1 is t h e s o l u b i l i t y coefficient at t 1 a n d k 2 t h e s o l u b i l i t y coefficient of the same sample at t2 t h e n

H a r m a n points out t h a t , over t h e range of temperatures involved, k1 m a y b e t a k e n e q u a l t o k 2 w i t h o u t a p p r e c i a b l e e r r o r . H e n c e for i m p u r e solut i o n s also

w h e r e s o l u b i l i t y is t h a t of s u c r o s e in w a t e r , i.e. g s u c r o s e p e r 100 g of w a t e r (Table X I I I ) . T h e s t a t e m e n t t h a t k 1 m a y b e t a k e n e q u a l t o k 2 c a n g i v e rise t o v e r y serious e r r o r s i n s o m e cases. W h e n c o r r e c t i o n s a r e m a d e for c h a n g i n g s o l u b i l i t y coefficient i t s h o u l d b e n o t e d t h a t t h i s definition m u s t b e s t a t e d a s b e i n g for c o n s t a n t p u r i t y . I n practice a solution when crystallized does not remain at constant purity, a n d a m o r e f u n d a m e n t a l v a l u e of coefficient of s u p e r s a t u r a t i o n is o b t a i n e d by e x p r e s s i n g it as

N o g a i n o r loss o f w a t e r i s a l l o w e d d u r i n g t h e c r y s t a l l i z a t i o n a n d s o t h i s definition i m p l i e s a c o n s t a n t i m p u r i t i e s / w a t e r r a t i o . Special Apparatus—In t h e d e t e r m i n a t i o n of s a t u r a t i o n t e m p e r a t u r e , a " s a t u r a t i o n cell" is used. T h e t y p e favoured, as shown in Fig. 45, consists of a s h a l l o w c y l i n d r i c a l cell of b a k e l i t e or similar m a t e r i a l . I n s i d e t h e cell is mounted a metal table which supports the sample and accommodates a t h e r m o m e t e r b u l b . A r o u n d t h e i n t e r n a l p e r i p h e r y o f t h e cell a n electric h e a t i n g e l e m e n t is m o u n t e d . A glass w i n d o w in t h e b o t t o m of t h e cell a n d a h o l e i n t h e c e n t r e o f t h e t a b l e a l l o w l i g h t t o p a s s u p t h r o u g h t h e cell. T h e cell i s set o n a m i c r o s c o p e s t a g e , t h e t h e r m o m e t e r i n s e r t e d , t h e s a m p l e m o u n t e d o v e r t h e h o l e i n t h e t a b l e , a n d t h e cell c o v e r e d w i t h a s h e e t o f clear glass. T h e s a m p l e , a s m a l l d r o p of m o l a s s e s , is m o u n t e d on a s m a l l s q u a r e o f m i c r o s c o p e slide glass. I f n o t i n y c r y s t a l s a r e likely t o b e p r e s e n t , a l i t t l e finely g r o u n d s u g a r is s p r i n k l e d o v e r t h e s a m p l e a n d a t h i n c o v e r slip is then placed over t h e sample a n d pressed down to give a t h i n film. T h e m i c r o s c o p e i s t h e n focused o n t h e s a m p l e . ( A c o m b i n a t i o n o f 1 6 m m (2/3

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inch) objective and a X25 eyepiece has been found to be very satisfactory). The field is moved until several small sharp edged crystals are in view. Procedure—The electric heater is turned on, and adjusted so that the temperature rises about 3 °C per minute. Eventually erosion of the crystals will be observed, and at the first sign of this, the temperature should be noted. The experiment should then be repeated with the temperature rising more slowly—about 0.5 °C per minute—in the vicinity of the critical temperature noted earlier.

Hints on the Determination—Materials of high purity crystallize quickly and excessive chilling may even lead to spontaneous crystal formation which would spoil the sample. Such materials must be handled quickly, and before the determination is commenced, the cell should be heated to within a few degrees of the probable saturation temperature. A sample of molasses may be separated from a massecuite by enclosing a small ball of the massecuite in a pocket of a piece of cloth, and squeezing. If the cloth is of fairly open texture, sufficient fine crystals for observation purposes will nearly always be found in the sample. More satisfactory results appear to be achieved with crystals originally present in the sample. The observation is tedious and exacting. The use of a red filter improves the ease of observation; polarized light is even better. Several crystals should be studied in rotation, as there appears to be no means of predicting where the erosion will first be noticed. Beware of a false end point; always maintain the heating until erosion is obviously well advanced, thus verifying the suspected onset of erosion. The saturation cell may be checked for accuracy of temperature reading by using it as a melting point apparatus for various pure chemicals, the actual melting points of which may be established by a recognized method. Boiler Water Analysis The various constituents in both natural and make-up water can result in severe scale formation, boiler corrosion and carry-over unless an effective method of chemical treatment is adopted. Some of the common scale forming constituents encountered in sugar factories are silica, calcium and magnesium, oil and residues from the thermal degradation of sugars. These

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deposits are undesirable because of their adverse effect on heat transfer, and because their presence can lead to localised overheating of the metal with consequent failure and risk of explosion. Corrosion is due to acid conditions in the boiler or the presence of dissolved oxygen. The prevention of carry-over by strict control on the level of total dissolved solids is also essential to prevent damage to the equipment in which steam is utilized. A detailed discussion on the application of recommended systems and methods of boiler water treatment is contained in Chapter X I I . Chapter X I I also permits the analyst to obtain an understanding of the functions of the various chemicals added for effective water treatment and it is suggested that the analyst should become familiar with its contents. The following simple methods of analysis, most of which are extracted from the relevant British Standard, are suitable for routine control of the boiler station. More sophisticated methods of analysis are available in some cases, and if the apparatus is available, these methods may be used at the discretion of the analyst. Alkalinity Three different types of alkalinity determinations are carried out on boiler waters. These are (a) Alkalinity to phenolphthalein, end point at pH 8.3 (b) Alkalinity to methyl orange, end point at pH 4.5 (c) Alkalinity to phenolphthalein after barium chloride addition. If organic matter is present in the sample, the alkalinity to methyl orange is unreliable, and determination of alkalinity to phenolphthalein, both before and after the addition of barium chloride, is carried out. Barium chloride addition also corrects for the presence of any residual trisodium phosphate which would register as alkalinity, unless precipitated. Procedure (a) Alkalinity to Phenolphthalein (P) Measure 100 ml of the sample and transfer to a white porcelain basin. Add 1 ml of phenolphthalein indicator. A pink colour will form if the solution is alkaline to phenolphthalein. Titrate with 0.02 N sulphuric acid until the pink colour just disappears. Retain the solution for procedure (b) Alkalinity to phenolphthalein (P) =

Procedure (b) Alkalinity to Methyl Orange (M) To the solution treated as described above, add 3 drops of methyl orange indicator. Titrate slowly with 0.02 N sulphuric acid, while stirring continuously, until the solution shows the first colour change from yellow to orange. Record the total number of ml of acid used, i.e. including those used in the previous titration with phenolphthalein. Alkalinity to methyl orange (M) =

If the solution is so highly coloured that the indicator end points cannot be detected, a pH meter may be used. When this procedure is adopted, the

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i n d i c a t o r s o l u t i o n i s n o t a d d e d a n d t h e t i t r a t i o n v a l u e s a t p H 8.3 a n d p H 4.5 a r e r e c o r d e d for p h e n o l p h t h a l e i n a n d m e t h y l o r a n g e r e s p e c t i v e l y . Procedure (c) Alkalinity to Phenolphthalein after Barium Chloride addition T h e p r o c e d u r e for t h e n o r m a l i n d i c a t o r t i t r a t i o n i s a s f o l l o w s : — M e a s u r e 100 m l o f s a m p l e a n d t r a n s f e r t o a w h i t e p o r c e l a i n b a s i n . A d d 1 m l of p h e n o l p h t h a l e i n i n d i c a t o r , followed by a c r y s t a l of s o d i u m s u l p h a t e a n d 1 0 m l o f 1 0 p e r c e n t b a r i u m c h l o r i d e s o l u t i o n . S t i r well for t w o m i n u t e s a n d t h e n t i t r a t e w i t h 0.02 N s u l p h u r i c a c i d u n t i l t h e p i n k c o l o u r j u s t d i s a p p e a r s . Disregard a n y r e a p p e a r a n c e s of t h e p i n k colour. Alkalinity to phenolphthalein after b a r i u m chloride addition

Phosphate S e v e r a l m e t h o d s a r e a v a i l a b l e for t h e d e t e r m i n a t i o n o f p h o s p h a t e i n boiler w a t e r s . T h e m a j o r i t y of t h e s e a r e b a s e d on t h e f o r m a t i o n of a b l u e phospo-molybdate complex, t h e intensity of which is directly proportional t o t h e a m o u n t o f P 0 4 ion p r e s e n t i n t h e s o l u t i o n . F o r r o u t i n e c o n t r o l w o r k , the chemist a n d engineer need only to k n o w t h a t a reserve of p h o s p h a t e is p r e s e n t a n d t h a t t h e level i s w i t h i n a c e r t a i n r a n g e . T h i s p e r m i t s a r e d u c t i o n in t h e time spent on carrying out t h e determination. T h e colour formed after reagent addition is compared either in a L o v i b o n d t y p e c o m p a r a t o r or against s t a n d a r d c o l o u r p l a t e s . A s u i t a b l e e x a m p l e of p h o s p h a t e c o l o u r p l a t e s is shown on p a g e 49 of British S t a n d a r d s 1170:1957. A s p e c t r o p h o t o m e t e r m a y be used, if available. Apparatus—Two t e s t t u b e s a p p r o x i m a t e l y 6 i n c h e s in l e n g t h a n d half an inch in diameter. T w o 250 ml bottles, each fitted with a r u b b e r t e a t p i p e t t e g r a d u a t e d at a 2 ml d i s c h a r g e level. U s e o n e b o t t l e for d i s p e n s i n g a c i d m o l y b d a t e a n d t h e o t h e r for c a r b o n a t e - s u l p h i t e . O n e 250 m l b o t t l e f i t t e d w i t h a r u b b e r t e a t p i p e t t e g r a d u a t e d at a 1 ml d i s c h a r g e level for d i s p e n s i n g h y d r o q u i n o n e . W h a t m a n N o . 5 filter p a p e r s . Procedure—The t e m p e r a t u r e o f t h e s a m p l e a n d r e a g e n t s m u s t b e k e p t b e t w e e n 2 0 a n d 3 0 °C. F i l t e r a s a m p l e o f t h e cooled boiler w a t e r t h r o u g h t w o W h a t m a n N o . 5 filter p a p e r s . D i s c a r d t h e first 10 ml a n d refilter t h e e x t r a c t if a clear l i q u i d i s n o t o b t a i n e d f r o m t h e first f i l t r a t i o n . T r a n s f e r 5 ml of t h e s a m p l e to a t e s t t u b e , a d d 2 ml of a c i d m o l y b d a t e and mix thoroughly. Then a d d 1 ml of hydroquinone and again mix thoroughly. Allow t h e c o n t e n t s o f t h e t u b e t o s t a n d for 5 m i n u t e s . A d d 2 m l o f c a r b o n a t e - s u l p h i t e s o l u t i o n t o t h e o t h e r t e s t t u b e . Carefully pour the contents of the first t u b e into the one containing the carbonatesulphite solution. Mix by cautiously transferring several times t h e contents from one t u b e to t h e other. Hold t h e test t u b e containing t h e sample a little distance a w a y from t h e side of t h e s t a n d a r d colour plates, a n d e s t i m a t e t h e P 0 4 level in t h e solution. It is advisable to use a t u n g s t e n filament l a m p when m a k i n g t h e comparison a s i t i s n o t possible t o o b t a i n a g o o d c o m p a r i s o n b y d a y l i g h t o r fluorescent light. Interpretation of Results—A P 0 4 level b e t w e e n 30 a n d 70 p . p . m . is usually considered to be satisfactory. Results are usually recorded as "low", "satisfactory" or "high".

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Sulphite The presence of free sodium sulphite in a boiler water is an assurance that all dissolved oxygen in the feed water has been eliminated. Special attention must be given to the method of sampling for this determination, as sulphite can be rapidly destroyed when the sample is exposed to atmosphere. This is more pronounced at elevated temperatures, but the effect can be minimized if the following sampling procedure is carried out:— A stainless steel or nickel-copper cooling coil which will reduce the outlet temperature to below 30 °C is required. Position the outlet tube into the bottom of the sample container, and allow water to flow until at least five changes have occurred. Withdraw the outlet tube slowly so that the container is filled to maximum capacity, and stopper with an effective sealing device. Analyse the sample as soon as possible. Procedure—Transfer 4 ml of 6.5 per cent V/V sulphuric acid to a white porcelain basin. Add 100 ml of unfiltered boiler water sample and 1 ml of starch indicator. Titrate with potassium iodide-iodate solution and stir continuously during the titration until a faint permanent blue colour is obtained.

Hardness Refined methods are available for the determination of hardness in boiler waters. The majority of these are time consuming, and for ordinary routine control purposes sufficient accuracy can be obtained by titrating a known volume of sample with standard soap solution. During this titration, the soap combines with calcium and magnesium salts in the water until they are precipitated as an insoluble curd, and when all these salts have been converted, the addition of an extra drop of soap solution will produce a permanent soap lather. Thus, the soap solution provides its own indicator, and the formation of this permanent lather corresponds to the point where colour changes occur when indicators are used for the more refined methods of hardness determination. Standardization of Soap Solution—Each batch of Wanklyn's reagent should be checked by titrating the reagent against 100 ml of distilled water. The amount of soap solution required to establish a permanent lather with distilled water is then regarded as the blank, and is subtracted from all other titrations carried out with that particular batch of reagent. Procedure—Measure out 100 ml of filtered boiler water sample and transfer into a glass stoppered bottle of approximately 250 ml capacity. Titrate with Wanklyn's soap solution from a burette, 0.2 ml at a time, replacing the stopper and shaking after each addition. Continue additions until a permanent lather, i.e. one that remains at least 5 minutes, is obtained. It is not necessary to wait 5 minutes between additions, as the immediate breakdown of individual bubbles is an indication that the lather will not be permanent. View the lather by laying the bottle on its side at eye level. It will be noted that the lather rapidly becomes more permanent as the end point is approached and additions of the reagent should then be made in smaller quantities. For a 100 ml sample aliquot,

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Total Dissolved Solids These may be determined either gravimetrically by weighing after drying, conductometrically, or by the determination of specific gravity using a special hydrometer of the type supplied with "Alfloc" testing equipment. The last method is recommended for routine control determinations because of the simplicity of the technique. Two factors which must receive special attention in the determination of T.D.S. by the hydrometer are, firstly, that special care is required when handling and cleaning the hydrometer, and, secondly, that the hydrometer must be restandardized against the gravimetric method at regular intervals to ensure its reliability. Effect of Temperature—Changes in temperature during the determination and a temperature difference between the instrument and surrounding solution can result in considerable discrepancies in the values determined. The analyst must therefore ensure that sufficient time is allowed for each sample to cool to near room temperature, and also for the hydrometer to attain the temperature of the solution. The temperature corrections to be applied to the standard 80 °F type hydrometer are listed in the following table. —• Temp. °F 44 46 48 50 52 54 56 58 60 62

Temperature Corrections—80 °F Type Hydrometer

Correction to observed reading (divisions Subtract

26 26 26 26 26

25.5 24.5 23.5 22.5 21

Temp. °F 64 66 68 70 72 74 76 78 80 82

Correction to observed reading (divisions) Subtract

19 17 15 13

10.5 8 5.5 3

"Nil

Add

Temp. °F 84 86 88 90 92 94 96 98 100

Correction t o observed reading (divisions) Add

5 8 11 14 18 22 26 30 34

2

Procedure—Pour in a sufficient quantity of boiler water sample to fill the hydrometer jar to approximately one inch from the top. Add six drops of wetting agent and mix into the solution. Lower the hydrometer carefully into the solution. If air bubbles are observed to be adhering to the instrument, these can usually be removed by gently spinning the hydrometer. Record the temperature of the solution to the nearest °F. Read the hydrometer scale by looking slightly down on the surface of the liquid. Correct the scale reading for temperature by reference to the above table. Multiply the corrected reading by 100 and record as p.p.m. Total Dissolved Solids. Sulphate Sulphate is precipitated as barium sulphate by the addition of a known amount of barium chloride to the acidified solution. The excess barium chloride is then determined by titrating against EDTA, using either solochrome or eriochrome black as an indicator.

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The test for sulphate is not applicable to waters containing appreciable amounts of calcium and magnesium salts as these also react with EDTA. The test is generally applicable to boiler waters with a hardness value below 20 p.p.m. CaC0 3 . In these circumstances the errors caused by hardness salts can be ignored. Procedure—Pipette 10 ml of the sample into a porcelain basin and acidify with 1 ml of 0.5 N hydrochloric acid. Add exactly 10 ml of 0.04 N barium chloride solution from a suitable automatic dispenser. Pipette into a small beaker 3 ml of the sulphate buffer and add to it 0.2 g of solochrome black indicator. Mix well and pour into the basin containing the sample. Slowly titrate the contents of the basin with 0.02 N EDTA, stirring the sample with a glass rod until the colour begins to change to purple. Then add the EDTA solution, drop by drop, stirring continuously until all traces of red colour have disappeared. The final colour at the end point is usually blue, but with some waters a greyish coloured end point is obtained.

Water Analysis Chlorides Chloride is determined by titrating a neutral or slightly alkaline solution against a standard silver nitrate solution in the presence of chromate indicator. White silver chloride is precipitated, followed by reddish silver chromate when the chloride end point has been reached. The presence of sulphites in some waters can cause considerable interference to this determination. This effect may be overcome by the addition of 1 ml of hydrogen peroxide (10 vol.) prior to the commencement of the titration. Procedure—Pipette 50 ml of sample into a white porcelain basin. Add 1 ml of potassium chromate indicator and commence titrating with silver nitrate solution. Stir continuously with a rubber-tipped glass stirring rod and continue the titration until the first permanent reddish colour change is established. Record the volume of silver nitrate used. Chloride = titre x 20 as p.p.m. CI. REFERENCES Aldrich, B. I. and Rayner, P. C, (1962), Cell-Breakage Determination in Prepared Cane and Bagasse. Proc. I.S.S.C.T., eleventh Conf., 1004-1013. Anderson, G. A. and Petersen, K. J., (1959), Operation of an Individual Fibre System. Proc. Q.S.S.C.T., twenty-sixth Conf., 15. B u r g e s s , I. G., Beardmore, R. H., Fortescue, G. E„ and Davis, G. W. (1962), Development and Application of a Laboratory Clarification Test. Proc. I.S.S.C.T. eleventh Conf., 920-927. Deicke, R. (1959), Investigations with the Wet Disintegrator for Direct Analysis of Cane. Proc. I.S.S.C.T. tenth Conf., 168-174. De Whalley, H. C. S. (Editor) (1964), ICUMSA Methods of Sugar Analysis, Elsevier, 41-44. Foster, D. second H., (1955), Determination of Pol in Bagasse, Proc. Q.S.S.C.T., twenty Conf.,The 279-283.

CHAPTER X THE DETERMINATION OF pH Hydrogen Ion Concentration Pure water exhibits a very high resistance to the passage of an electric current, but its conductivity is markedly increased when substances known as electrolytes are dissolved in it; electrolytes include all acids, bases and salts, whereas substances such as sugars, alcohols and ketones are without influence on the conductivity of the solution and are known as non-electrolytes. An attempt to explain the effect of electrolytes led Arrhenius in 1887 to propound his Electrolytic Dissociation Theory. He postulated that when an electrolyte is dissolved in water, some of the molecules of the substance dissociate into electrically charged particles, which are known as ions. Thus a molecule of hydrochloric acid gives in solution a positively charged hydrogen ion H+, and a negatively charged chlorine ion Cl~. In all cases, the sum of ionic charges must be zero, for the molecule is electrically neutral. The molecules of all electrolytes are not dissociated to the same degree. For example, a normal solution of hydrochloric acid is dissociated to the extent of 80 per cent, while a solution of acetic acid of similar concentration possesses but 0.43 per cent of its molecules in the ionised form. Electrolytes which are highly dissociated in solution are known as strong electrolytes, while those which are but slightly dissociated are called weak electrolytes. The degree of dissociation is a function of the concentration of the solution; the more dilute the solution the higher the percentage of dissociation. Pure water does conduct an electric current in a feeble degree, and is therefore itself a weak electrolyte. The equation for the electrolytic dissociation of water may be represented:—

Since the degree of dissociation of water is so low, no appreciable error will be introduced if the concentration of undissociated molecules be regarded as constant, and therefore [H+] [OH-] = K [HOH] = Kw where Kw is known as the Dissociation Constant of Water. Careful measurements have demonstrated that at 22 °C, pure water possesses a concentration of hydrogen ions equal to 10 -7 gramme ions per litre. It contains also a similar ionic concentration of hydroxyl ions. Thus at 22 °C the dissociation constant of water is equal to 10 - 7 x 10 -7 or 10 -14 . It should be observed, also, that in dilute aqueous solution the product of the concentrations of H+ and O H - is for practical purposes a constant at constant temperature, and equals 10 -14 at 22 °C. As the concentration of hydrogen ions often has a very low value, in order to avoid the nuisance of writing a long decimal expression to describe it, it has been found useful to use an exponential notation. The term pH, first proposed by Sorensen in 1909, is widely used today. It is defined as the negative exponent of 10 which gives the hydrogen ion concentration.

T H E DETERMINATION OF pH

145

Thus, F o r p u r e w a t e r a t 2 2 °C, [H+] e q u a l s 1 0 - 7 g r a m m e s p e r l i t r e , t h e r e f o r e t h e p H is 7. A n acid s o l u t i o n m a y b e defined a s o n e i n w h i c h t h e c o n c e n t r a t i o n o f the H+ exceeds t h a t of O H - ; a n d conversely, an alkaline solution is one w h i c h possesses an excess of O H - o v e r H + . A solution of pH 7.0 is, t h e r e f o r e , r e g a r d e d a s a n e u t r a l s o l u t i o n ; p H v a l u e s less t h a n 7.0 i n d i c a t e a n a c i d solut i o n , while v a l u e s a b o v e 7.0 a r e c h a r a c t e r i s t i c of a l k a l i n e s o l u t i o n s . In employing this convention, it must be remembered always t h a t pH is a logarithmic f u n c t i o n ; a n d t h e r e f o r e a s o l u t i o n of pH 6.0 h a s a H+ c o n c e n t r a t i o n t e n t i m e s t h a t of a solution of pH 7.0. I t will b e o b s e r v e d t h a t t h e v a l u e o f p H for w a t e r a t 2 2 ° C i s 7.0. T h i s v a l u e does v a r y w i t h t h e t e m p e r a t u r e i n q u i t e a m a r k e d degree, a s i s s h o w n by t h e following t a b l e for p u r e w a t e r : — Temperature °C pH 16 7.10 20 7.03 22 7.00 25 6.95 40 6.71 100 6.12 The importance of temperature control must be borne in mind in carrying o u t all p H d e t e r m i n a t i o n s ; s t r i c t l y t h e s e s h o u l d b e m a d e a t a c o n s t a n t t e m p e r a t u r e , so as to be comparable with one another. Measurement of pH Two general m e t h o d s are employed in t h e determination of p H , the c o l o r i m e t r i c m e t h o d a n d t h e e l e c t r o m e t r i c m e t h o d . E a c h possesses i t s advantages and disadvantages; the latter requires a pH meter a n d is more a c c u r a t e , while t h e former r e q u i r e s less s o p h i s t i c a t e d a p p a r a t u s . Colorimetric method C e r t a i n c h e m i c a l c o m p o u n d s h a v e t h e a b i l i t y t o c h a n g e colour w h e n t h e p H o f t h e solution, i n w h i c h t h e y a r e dissolved, c h a n g e s o v e r c e r t a i n r a n g e s . These compounds are known as indicators. Ostwald explained this ability to c h a n g e colour b y a s s u m i n g t h a t c o m p o u n d s o f t h i s n a t u r e b e h a v e a s w e a k acids or b a s e s , t h e m o l e c u l e s of w h i c h a r e a b l e to a b s o r b light of a definite s p e c t r a l r a n g e , w h i l e t h e i r ions h a v e t h e a b i l i t y of a b s o r b i n g light of a n o t h e r s p e c t r a l b a n d . A n a c i d i n d i c a t o r a t l o w p H v a l u e s will e x h i b i t t h e colour c h a r a c t e r i s t i c s of t h e u n d i s s o c i a t e d molecules, w h i l e t h e n e u t r a l i z a t i o n of t h e a c i d by t h e a d d i t i o n of a b a s e r e s u l t s in t h e p r o d u c t i o n of a h i g h l y d i s s o c i a t e d s a l t (since all s a l t s a r e h i g h l y dissociated) a n d t h e s o l u t i o n e x h i b i t s t h e c o l o u r o f t h e ions. I n d i c a t o r s a r e u s u a l l y utilized i n t h e m e a s u r e m e n t o f t h e p H o f s o l u t i o n s by m e a n s of t e s t p a p e r s or a colour c o m p a r a t o r . Test papers: T h e r e a r e n u m e r o u s different t y p e s of t e s t p a p e r s a v a i l a b l e c o m m e r c i a l l y for t h e e s t i m a t i o n o f p H . " U n i v e r s a l " t e s t p a p e r s c o v e r t h e r a n g e 1.0 t o 11.0 p H i n s t e p s o f 1.0 p H ; t h e c o l o u r c h a n g e c h a r t for t h e s e p a p e r s i s p r i n t e d o n t h e inside o f t h e c o v e r . A n o t h e r useful t y p e for s u g a r mill application is t h e " H y d r i o n " short range pH test paper covering t h e r a n g e 6.0 t o 8.0 i n half u n i t s t e p s . T h e s e t e s t p a p e r s a r e p o r t a b l e a n d s p e e d y , but not extremely accurate.

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T H E DETERMINATION OF pH

Comparator: The Lovibond or Hellige comparator comprises a plastic housing into which can be fitted a disc of permanent colour standards together with two glass containers, one for the specimen under test and the other for a blank (to compensate for inherent colour in the sample). Each particular test requires the use of the appropriate disc which contains a number of permanent glass colour standards (usually nine) representing the range of colours produced by different concentrations of the material which is the subject of the test. The discs for pH determinations are usually supplied complete with the appropriate indicator. A useful disc for sugar mill work is the Bromothymol blue disc, containing nine steps of 0.2 pH over the range 6.0 to 7.6. The comparator can only be used for fairly clear solutions. It is slower than the test papers but more accurate. Electrometric method Electrometric methods are based upon the principle of measuring the electromotive force generated, as a function of the hydrogen ion concentration (and temperature), between electrodes of various types immersed in a solution to be tested and in a solution of known and definite characteristics joined thereto by a liquid junction. The standard and classical electrometric method employs the hydrogen electrode and while, because of the many difficulties involved in its use, the hydrogen electrode has found no direct application in the sugar industry, an understanding of its operation is useful to give a clear picture of the method. Hydrogen electrode: The hydrogen electrode consists of a platinum or gold foil carefully plated with platinum, palladium, or iridium, and immersed in the solution being tested, which is saturated to equilibrium with purified hydrogen gas. The hydrogen is bubbled through the solution surrounding the electrode. In order to measure the electric potential of the solution in which the hydrogen electrode is placed, it is brought in contact by liquid junction with another electrode or half-cell, which may be a similar hydrogen electrode, or it may be one of the other types of standard half-cells, such as one of the calomel electrodes. Thus, if two hydrogen electrodes are placed in solutions containing different hydrogen ion concentrations, but joined by a liquid junction, then the potential difference is given by the equation—

and therefore the potential difference is proportional to the difference in pH between the two solutions. If E is measured, and one pH is known, the unknown pH may be evaluated.

T H E DETERMINATION OF pH

147

T h e e l e c t r o c h e m i c a l effects of i o n s in s o l u t i o n a r e influenced n o t o n l y b y t h e c o n c e n t r a t i o n o f t h e ions b u t also b y t h e " a c t i v i t y coefficient", a n d strictly speaking t h e pH is not directly related to t h e hydrogen ion concentrat i o n . H o w e v e r , for p r a c t i c a l p u r p o s e s t h e p H i s a c c e p t e d a n d i n t e r p r e t e d a s b e i n g r e l a t e d t o t h e h y d r o g e n ion c o n c e n t r a t i o n . As previously mentioned, it is not practicable to measure t h e pH of a s o l u t i o n b y m e a n s o f h y d r o g e n electrodes, i t c a n , h o w e v e r , b e m e a s u r e d b y a c o m b i n a t i o n of t w o o t h e r electrodes (half-cells) s u c h as t h e calomel e l e c t r o d e a n d t h e glass electrode. Calomel electrode: T h e c a l o m e l e l e c t r o d e is c o m p o s e d of m e r c u r y a n d c a l o m e l ( m e r c u r o u s chloride) in a w a t e r solution of p o t a s s i u m chloride. T h e s e m a t e r i a l s a r e c o n t a i n e d in a glass vessel of a s u i t a b l e design. O n e s u c h design i s s h o w n i n F i g . 4 6 (b). P r o v i s i o n i s m a d e i n s o m e m a n n e r t o p r o t e c t t h e

Fig. 46—(a) Glass electrode.

(b) Calomel electrode.

e l e c t r o d e from c o n t a m i n a t i o n b y diffusion o f t h e s o l u t i o n b e i n g t e s t e d t h r o u g h t h e liquid j u n c t i o n . T h i s i s n o r m a l l y a c h i e v e d b y m a i n t a i n i n g t h e s o l u t i o n i n s i d e t h e cell a t a h i g h e r level t h a n t h e t e s t s o l u t i o n , t h u s k e e p i n g t h e l i q u i d j u n c t i o n flushed w i t h fresh p o t a s s i u m c h l o r i d e s o l u t i o n . E l e c t r i c a l c o n t a c t t o t h e c a l o m e l cell i s o b t a i n e d t h r o u g h t h e m e r c u r y b y m e a n s o f a p l a t i n u m wire, sealed t h r o u g h t h e b o t t o m o f t h e c a l o m e l e l e c t r o d e , o r fed t h r o u g h t h e t o p o p e n i n g o f t h e vessel i n t o t h e m e r c u r y . T h e p o t e n t i a l o f a calomel electrode is dependent upon t h e concentration of the potassium

148

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chloride solution in contact with the calomel and mercury. One of three concentrations may be used, namely, 0.1 normal, normal, or saturated. The last is used most widely in practice because it is easily prepared; it has the same salt concentration as the salt bridge (liquid junction) and hence eliminates diffusion difficulties; and it has a high conductivity which increases the sensitivity of the system. Glass electrodes: Glass electrodes, as the name implies, are bulbs of thinwalled glass of special composition blown on the end of a glass tube. Inside this tube is an electrode of some type, such as a silver-silver chloride electrode in a hydrochloric acid solution. A typical glass electrode is shown in Fig. 46 (a). It is believed that an actual transfer of hydrogen ions takes place through the bulb, which makes it behave like a hydrogen electrode, and like the hydrogen electrode it needs a reference electrode and salt bridge to complete the hydrogen ion cell. In many respects the glass electrode is considered ideal, in that nothing has to be added to the solution which might alter its hydrogen ion concentration; also the electrode cannot become poisoned, and it can be used for measuring the pH of all kinds of materials, including those which are semisolid in consistency and those which contain active reducing or oxidizing substances. The range of application is normally from about 1 to 13 p H ; however, errors may be introduced in alkaline solutions containing appreciable amounts of sodium salts. With frequent and proper calibration a limit of error of about 0.02 pH is attainable with the glass electrode. Before use, all glass electrodes should be immersed in distilled water for at least 24 hours. When not in use, the glass electrode should be stored in distilled water, as repeated wetting and drying impairs the action of the glass membrane. Several makes of pH equipment using glass electrodes are on the market, all of which operate on more or less similar principles, the main differences between them being in structural detail.

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149

pH Meters: Modern pH meters usually utilize the glass electrode, calomel electrode combination. A typical modern pH meter is illustrated in Fig. 47. Because the conductivity of glass is very low, even a thin membrane exhibits very high resistance (108 ohms), it is necessary to amplify the potential difference across the two electrodes, and to measure the voltage directly with a calibrated galvanometer. The overall potential developed by the complete electrode assembly is of the form— E = K pH + Eo where E = overall measured potential K = a thermodynamic constant varying with temperature Eo = the result of a group of fixed potentials—half cell potentials, asymmetry potential, liquid junction potentials, etc. This also varies with temperature. Due to the fact that asymmetry potential will vary from electrode to electrode, and, even for the same electrode, from time to time, a pH meter must be standardized before being used to measure the pH of an unknown solution. This is carried out in the following manner. A standard buffer solution of known pH is used and the electrode assembly is immersed in the buffer. The temperature effect of the standard buffer solution must be compensated for either by the use of a platinum resistance thermometer connected directly to the pH meter, in which case the compensation is automatic, or by measuring the temperature and manually compensating for it by adjusting the temperature compensating dial on the instrument. When this has been done the correct value of K in the above equation is established in the instrument. The meter is checked for zero reading and this is adjusted if necessary, and then switched to the appropriate scale to measure the pH of the standard buffer solution. By adjustment of a knob provided, the meter is made to read the pH of the buffer solution used and this operation serves to provide the correct value of Eo in the equation. The meter should then indicate correctly the pH of an unknown solution. For strict accuracy the buffer solution and any other solutions tested should be at the same temperature, and the results obtained will then correspond to pH at this temperature. Values of pH at one temperature cannot be converted to the basis of another temperature unless the pH-temperature relationship of the solution is known. Determination of pH values of Sugar Mill Products: The most important aspect of pH measurement in a sugar mill is its use for the control of the clarification process. Almost all mills have now installed automatic equipment for the addition of lime to mixed juice, and this addition of lime is controlled by pH measurements made on the limed juice. This pH measurement is continuous and generally utilizes an industrial glass electrode, which will operate at high temperature and withstand erosion, together with an industrial calomel electrode, which maintains a slight pressure on the potassium chloride solution to ensure that the liquid junction is not fouled. The pH of the limed juice determines the final pH of clarified juice, and the set point of the pH controller is altered up or down according to the value determined on the clarified juice. The pH of clarified juice is the most important pH measurement in the factory, and for preference this quantity should be measured continuously using a pH recorder. Whether a recorder is used or not, periodic laboratory pH determinations should be carried out on clarified juice, to determine its pH value, or to check the accuracy of the recorder. These determinations should be carried out with an accurate laboratory pH meter, which is a most useful instrument for general laboratory work

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and for measurements of pH on other factory products. Laboratory pH measurements are carried out in the following manner:— Check and restandardize the instrument at least once per shift with standard buffer solution as described previously. Cool the solution to room temperature or to the temperature at which the instrument was restandardized. Rinse the electrodes with a portion of the test solution prior to carrying out the determination. Fill the beaker or receptacle with test solution to a level which will ensure that the electrodes and thermometer bulb are well covered. Read the temperature of the solution and adjust the instrument temperature compensator to the desired setting. (Reference tables may have to be used on older model pH meters.) Allow sufficient time for the system to come to equilibrium, and determine the pH. After the determination is completed, thoroughly wash the electrodes with distilled water and keep them immersed in distilled water when not in use. N.B.—Glass electrodes are fragile and susceptible to breakage. Extreme care should be taken when handling these electrodes.

CHAPTER XI CALCULATIONS INVOLVED IN CHEMICAL CONTROL The chemical control of any process is divisible into two fairly distinct phases. One phase involves the study of a group of facts associated with the process—quantities of materials entering process, leaving process or in process; the compositions of original, intermediate and final products; the necessary details of auxiliary materials used in the process; and the conditions under which the various stages are operated. The second phase deals with attempts to express in figures the merit of the results achieved. In industry generally the purely quantitative relationships provide an adequate index of performance, but this is not usually the case in sugar manufacture. For instance, pol extraction and recovery which are purely quantitative figures are not adequate measures of milling or manufacturing efficiency. Other things being equal, a recovery of 86 per cent is better than one of 85 per cent, but in practice other things are not equal and the lower recovery may represent the better performance. In the majority of Queensland sugar factories the analytical and quantitative data are only approximate. Actual weights are available for only a few of the materials involved, pol is used as an approximation for sucrose, Brix instead of total soluble solids, and various empirical formulae are introduced. This provides a set of figures which are substantially accurate and trustworthy for certain "normal" conditions. Should the existing conditions not conform to those assumed the data are rendered incorrect; and the magnitude of the discrepancies which enter depends upon the extent of the divergence from normal. The shortcomings of this control are generally recognized by the mill chemist, but in the absence of means of securing accurate data, the magnitude of the discrepancies at any time cannot be gauged. These shortcomings of the present empirical system for cane analysis have been well known for many years, but there is no point in discarding an accepted system unless some improved method is available. Several years ago an intensive investigation into the juice weighing system of factory control was carried out. The results of this investigation showed the system to be less prone to the large seasonal variations of the empirical system, but it also brought to light several disturbing sources of inaccuracy in the method. Attention has now moved from juice weighing to the direct analysis of cane using a wet disintegrator for the determination of Brix and pol, and a Spencer or similar type of hot air circulating oven for the determination of moisture. At the time of writing this edition the matter is under investigation, and it may well be that the empirical method of analysis will be superseded by direct analysis of cane. Quantitative Data Materials Balances—A materials balance involves a statement of (1) the total quantity of a particular material entering a process from various sources, and (2) the total quantity of the same material leaving the process through various avenues. In the factory, materials balances may be drawn up to cover a single stage of processing, several stages, or the whole operation, and may deal with pol, Brix, impurities, fibre, crystal, etc.

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Pol Balance (Empirical System) The most important materials balance is the pol balance of the factory. Pol enters the factory only in the cane, and leaves mainly in bagasse, mud, molasses and sugar. The total of these quantities of pol leaving will normally be less than that of the pol entering, the discrepancy being due to mechanical losses, destruction of pol in the process and errors in the measurements, analyses and formulae. These losses are grouped under the title of "undetermined" losses. For convenience, each quantity of pol leaving the factory is expressed as a percentage of the quantity of pol entering the factory. Stock—When a materials balance is taken out at an intermediate stage of operation of a process some of the material involved may be only partly treated and held in stock. Such material may be entered in the materials balance as "in stock", but for the purposes of the pol balance it is customary to presume that all the pol in stock will eventually leave the factory in sugar or final molasses, and to calculate how much of the pol in stock should pass into each of these channels. This involves the use of recovery formulae (see later) or recovery tables. A recovery formula or table will predict the percentage of the total pol in stock which may be expected later to pass out in the sugar. It follows that, if x is the percentage "recovered" as sugar, then 100 — x per cent will enter the molasses. Normally when taking out a pol balance over a period, account must be taken of stock at both the beginning and the end of the period. The quantities of recoverable and unrecoverable pol in each stock are calculated and those figures for the beginning of the period are subtracted algebraically from the respective figures for the end of the period. The balances may be positive or negative and are accordingly added to or subtracted from the respective figures for pol in sugar and in molasses actually made during the period. Hence the pol balance becomes:— Pol in sugar, made and estimated, per cent pol in cane Pol loss in bagasse per cent pol in cane Pol loss in mud per cent pol in cane Pol loss in molasses, made and estimated per cent pol in cane Undetermined loss 100 Pol in Cane—The quantity of pol entering the factory is not measured directly but determined from the weight of the cane and the analysis of the first expressed juice, with the aid of an empirical formula—thus:— Tons pol in cane = tons cane x pol per cent cane

where F = fibre per cent cane Pol Loss in Bagasse—From the definition of pol extraction it follows that Pol loss in bagasse = 100 — pol extraction. Pol Loss in Mud—This is derived from the weight of mud and the pol per cent mud.

Pol Loss in Molasses—This is derived from the weight of molasses and the pol per cent molasses, with correction for stock.

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153

Pol loss in molasses =

Pol in Sugar—This is derived from the weight of sugar and the pol of the sugar, with correction for stock. Pol in Sugar =

Undetermined Loss—This is a residual, calculated by difference, either in tons or per cent pol in cane. Pol Balance (Direct Analysis) The only difference between this system and the empirical system just set out, is that pol per cent cane is determined directly, using the wet disintegrator. Thus the empirical formula for pol in cane is not used in this method and one possible source of error is avoided. The accuracy of the direct analysis system, as with all other analytical systems, depends of course, on the accuracy and adequacy of sampling techniques, plus strict adherence to good analytical procedures. Overall Recovery—Overall recovery, frequently simply called recovery is the tons of pol recovered in sugar expressed as a percentage of the tons of pol in cane.

and is identical with the figure for pol in sugar per cent pol in cane. Boiling House Recovery—In the boiling house recovery, the quantity of pol in sugar, made and estimated, is expressed as a percentage of the quantity of pol entering the boiling house, i.e., in the juice leaving the mills. It follows by simple reasoning that

Extraction—This is an important figure from a commercial point of view, since it relates the quantity of pol extracted by the milling plant to the quantity of pol in the cane. It also provides an estimate of the percentage of the pol in cane which enters the boiling house, and thus forms a basis for the evaluation of boiling house recovery. The extraction is calculated from the analysis of bagasse and cane as follows:— Let— P c = pol per cent cane Fc = fibre per cent cane Pb = pol per cent bagasse Bb = Brix per cent bagasse W = moisture per cent bagasse F b = fibre per cent bagasse Then since bagasse consists of fibre, soluble solids and water— Fb = 100— Bb — W

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In practice Bb is frequently calculated by assuming t h a t t h e purity of the juice in t h e bagasse is equal to t h e p u r i t y of last expressed juice, a n d from this assumption:—

where C = p u r i t y of l a s t e x p r e s s e d j u i c e This assumption is not usually correct, t h e p u r i t y of juice in t h e bagasse b e i n g n o r m a l l y lower t h a n t h e p u r i t y o f l a s t e x p r e s s e d j u i c e , b u t t h e e r r o r i n t r o d u c e d i s n o t large a n d i s f r e q u e n t l y t o l e r a t e d . As no fibre is lost or g a i n e d in t h e process, t h e q u a n t i t y of fibre w h i c h enters m u s t eventually appear in the bagasse. Therefore, there are Fc p a r t s of fibre e n t e r i n g a n d p a s s i n g to t h e b a g a s s e , p e r 100 p a r t s of c a n e , so t h a t —

T h e e x t r a c t i o n o b t a i n e d b y i n d i v i d u a l mills s u b s e q u e n t t o N o . 1 mill c a n also be c a l c u l a t e d as a p e r c e n t a g e of t h e pol in t h e b a g a s s e from t h e p r e v i o u s mill i n t h e following m a n n e r : —

where

en

En En - i

= pol e x t r a c t i o n at t h e wth mill e x p r e s s e d as a p e r c e n t a g e of p o l in t h e b a g a s s e from t h e p r e v i o u s (n — 1) mill. = pol e x t r a c t e d p e r c e n t pol in c a n e for n mills of t h e t r a i n . = pol e x t r a c t e d p e r c e n t p o l in c a n e for n — I mills of t h e train.

For example:—Consider t h e following list of p o l e x t r a c t i o n s p e r c e n t pol i n c a n e . No. 1 mill—70.0 No. 2 mill—82.0 No. 3 mill—90.0 No. 4 mill—95.0 T h e n extraction by n u m b e r t h r e e mill, expressed as a percentage of t h e pol in n u m b e r t w o mill b a g a s s e : —

T h e e x t r a c t i o n o b t a i n e d b y e a c h i n d i v i d u a l mill e x p r e s s e d a s a p e r c e n t a g e o f t h e p o l i n t h e feed t o t h e m i l l c a n b e c a l c u l a t e d b y c a r r y i n g o u t a m a t e r i a l s balance over t h e milling train.

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Maceration—The quantity of maceration is logically considered as a percentage of fibre. It is strongly recommended that the maceration water be weighed or measured, since this gives an accurate figure for the water used, which moreover is immediately available as a guide to the correct regulation of the added water. The maceration water per cent fibre for any period is then readily calculated from the weight of water, weight of cane and average fibre in cane for the period. The proportion of water added is often conveniently reported in terms of "dilution", i.e., the portion of the maceration water which passes into the mixed juice. This may be expressed as a percentage of undiluted juice or as a percentage of fibre in cane. Dilution per cent Undiluted Juice—This is calculated by a Brix balance, since the added water introduces no solids and the quantity of Brix in the diluted juice is identical with that in the undiluted juice. Let— 100 — weight of undiluted juice, B = Brix of undiluted juice, b = Brix of diluted juice, x = weight of maceration water in diluted juice, and 100 + x = weight of diluted juice (mixed or clarified juice).

Dilution per cent Fibre—This is obtained by multiplying the dilution per cent undiluted juice by the weight of undiluted juice extracted from cane, expressed as per cent fibre, thus— Dilution % fibre =

The expression for undiluted juice in cane is derived from the first part of the c.c.s. formula from which we have—

Filter Washing Water—The water used in washing filter cake (or in diluting mud prior to filtering) should be metered and the quantity expressed as a percentage of the dry substance in filter cake. The weight of filter cake is determined for rotary niters as described under sampling. Pol Added to Filter Cake by Bagacillo—Some of the pol contained in rotary filter cake was present in the bagacillo added to assist nitration and theoretically had been accounted for as pol lost in bagasse. Hence a portion of the pol in the bagacillo is included in both the pol loss in bagasse and the pol loss in mud.

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A method of correcting the observed pol loss in mud to the basis of original mud without added bagacillo was outlined in a previous edition of this Manual. Some of the reasoning involved in the calculation is open to question and the method is not recommended for adoption. The actual correction is of the order of ten per cent of the observed mud loss and therefore is a relatively small factor on the actual pol balance. Retention (Rotary Filters)—The calculation of retention is based on the assumption that all fibre (bagacillo) in the feed is retained in the cake. Let— Mf and M c be the mud solids contents per cent, and Ff and F c the fibre (bagacillo) contents per cent, in feed and cake respectively. Then—

In measuring retention, the values Mf and Mc, Ff and F c are determined as described in Chapter IX. There are other methods of obtaining an estimate of retention, one of which was shown in the previous edition of this manual. However, the method listed above is the only mathematically correct one which can normally be carried out in practice, and it is recommended that this method be used in preference to the more approximate alternatives. Clarified Juice per cent Cane—This quantity is obtained by means of a pol balance, thus— Tons pol in clarified juice = tons pol in cane — tons pol in bagasse — tons pol in mud

Concentration and Evaporation Formulae—These formulae are similar to those for Dilution, and are calculated as follows:— Let— 100 = weight of original juice, etc. b = Brix of original juice, etc. B = Brix of final product, x = water evaporated, as percentage by weight of original juice, Then— 100 b = (100— x)B

Overall Evaporation Coefficient of Effets—This figure represents the weight of water, in pounds, evaporated per hour per square foot of heating surface, and is readily calculated with the aid of the two preceding formulae as follows:—

N.B.:—The calculation of heating surface area for effets or other vessels must be clearly defined if comparisons between different installations are

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to be m a d e . T h e m e t h o d of c a l c u l a t i o n of h e a t i n g surface is l a i d d o w n in t h e S.A.A. Boiler Code, A S . C B 1 , w h e r e a p p e n d i x A , s e c t i o n R - 9 s t a t e s : — "Evaporators, Vacuum Pans, Etc.—For evaporators, vacuum pans, h e a t e r s a n d o t h e r similar unfired vessels, t h e h e a t i n g surface shall i n c l u d e t h e t o t a l a r e a o f t u b e s , i n c l u d i n g c i r c u l a t i n g t u b e s (if a n y ) , t h e t u b e p l a t e s e x c l u d i n g t h e a r e a of t h e t u b e holes, a n d in t h e case of b a s k e t c a l a n d r i a s , t h e a r e a of t h e shell. F o r t h i s p u r p o s e t h e a r e a o f t h e t u b e s shall b e b a s e d o n t h e e x t e r n a l d i a m e t e r o f t h e t u b e s a n d t h e i r l e n g t h b e t w e e n t h e o u t e r surfaces o f t h e t u b e p l a t e s . T h e n e t t u b e p l a t e a r e a shall b e t h e t o t a l a r e a o f t h e t u b e p l a t e , calculated on t h e external diameter of the calandria, minus the area of t h e t u b e holes. I n t h e case o f b a s k e t c a l a n d r i a s t h e u p p e r t u b e p l a t e , m i n u s t h e t u b e holes, a n d t h e a r e a o f t h e s t e a m inlet shall b e m e a s u r e d , a n d also, i n t h e b a s k e t t y p e , t h e a r e a o f t h e shell shall b e b a s e d o n t h e o u t s i d e d i a m e t e r a n d t h e l e n g t h b e t w e e n t h e o u t e r surfaces o f t h e t u b e p l a t e s . I n t h e case o f e v a p o r a t o r s w i t h coils, h e a t i n g surface shall b e b a s e d o n t h e e x t e r n a l d i a m e t e r o f t h e coil a n d t h e coil l e n g t h b e t w e e n t h e inlet a n d t a i l p i p e . " R e c o v e r y F o r m u l a e — T w o r e c o v e r y f o r m u l a e are i n c o m m o n u s e ; t h e S.J.M. a n d t h e W i n t e r - C a r p . E a c h i s t a k e n t o r e p r e s e n t t h e p e r c e n t a g e o f t h e pol i n t h e original m a t e r i a l r e c o v e r a b l e a s pol i n s u g a r . T h e S.J.M. f o r m u l a is d e r i v e d as f o l l o w s : — L e t — 100 = w e i g h t of p r i m a r y p r o d u c t , J = p u r i t y of p r i m a r y p r o d u c t , P = pol of p r i m a r y p r o d u c t , S = p u r i t y of s u g a r p r o d u c e d , M = p u r i t y of final molasses, x = r e c o v e r y of pol p e r c e n t pol in p r i m a r y p r o d u c t ,

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The Winter-Carp formula was originally derived from the assumption that for every 100 parts of impurity in juice 40 parts of sucrose would be rendered unrecoverable. (Compare this with the c.c.s. formula.) To derive the Winter-Carp formula consider a juice of purity J containing 100 parts of sucrose. Then

It is found that by substituting S = 100 and M = 28.57 in the S.J.M. formula, the Winter-Carp formula may be derived thus—

Hence arises the common impression that the Winter-Carp formula is a special case of the S. J.M. formula. Originally intended to express the recovery of raw sugar, the Winter-Carp formula is now used, like the S.J.M., to express the recovery of pol from the quantity of pol present in the original material. Example— Given 130 tons of massecuite of Brix 95 and pol 66.5—hence 70 per cent purity, calculate the quantity of sugar recoverable. S.J.M. Formula—Assuming 100 purity for sugar, and molasses purity of 35—

Molasses in Stock—The estimation of molasses in stock follows simply from the calculation of recoverable pol, for— Tons pol in molasses = tons pol in stock — tons recoverable pol. The figure for pol in molasses thus derived may be used directly in the calculation of the pol balance. If it be desired to express the quantity as molasses, then

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Taking Stock—All pans, tanks, and other holding vessels should be calibrated so that the volume of the product in stock may be determined readily. Stocktaking is then usually carried out by recording the volume and temperature of each product, analysing a sample for Brix and pol, and entering the results into a table of the following form:— Stock Sheet

Material

Temp. Gal°C lons Brix 1

A

2

3

*Brix at ** FacT°C tor Pol 4

5

Purity

Weight in Tons

Tons Brix

Tons Pol

7

8

9

10

6

Massecuite

AB Massecuite B

Massecuite

C

Massecuite

A

Molasses

AB Molasses B

Molasses

Syrup Juice Magma Totals * Brix corrected for temperature from tables supplied. ** From tables.

Column 1 shows the actual temperature of the material when the volume (column 2) is measured. Columns 3, 6, and 7 are obtained from the analytical data. The values for column 4 must be corrected to the value corresponding to the actual temperature of the material when sampled. The factors of column 5 are obtained from Table XX. The weight in tons (column 8) is obtained by multiplying column 2 by column 5 and dividing by 100, while columns 9 and 10 are calculated by multiplying column 8 by columns 3 and 6 respectively. Totals are obtained for columns 9 and 10, and their ratio multiplied by 100 shows the average purity of the materials in stock. Then from this value and the total tons of pol, the recoverable sugar may be calculated by applying the Recovery Formula. The volume of molasses expected may also be estimated, as outlined above. The method of measuring stock outlined above is not applicable to final molasses, which, after brief storage, is usually found to be highly aerated. The quantity of molasses in storage should be determined using a weight measuring device such as the pneumercator. This device has been available for a number of years and is well described in the paper by W. R. Dunford,

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P r o c e e d i n g s Q.S.S.C.T. 1967. If s u c h a d e v i c e is n o t u s e d , g r e a t c a r e m u s t be t a k e n w h e n s a m p l i n g final m o l a s s e s , i n o r d e r t o e n s u r e t h a t a r e a s o n a b l y accurate estimate of the actual average Brix m a y be obtained. For advice in measuring stocks u n d e r these conditions t h e reader is referred to t h e p a p e r by N . S m i t h , P r o c e e d i n g s Q.S.S.C.T. 1941. In recent years, with the advent of bulk sugar handling, one further stock q u a n t i t y has to be calculated, t h a t of the sugar held in the bulk bin at t h e e n d of a p e r i o d . To o b t a i n an a c c u r a t e e s t i m a t e of t h i s s t o c k , a b e l t w e i g h e r o n t h e b e l t feeding i n t o t h e s u g a r b i n , o r a b i n w e i g h i n g d e v i c e , s u c h a s t h e l o a d cell a r r a n g e m e n t i n s t a l l e d a t o n e Q u e e n s l a n d mill, s h o u l d b e employed, and these are to be recommended. F o r w e e k l y mill c o n t r o l p u r p o s e s c o n s i d e r a t i o n h a s t o b e g i v e n t o t h e d e g r e e o f a c c u r a c y r e q u i r e d w h e n e s t i m a t i n g s t o c k . F o r a w e e k l y figure t h e a m o u n t o f t i m e a n d effort s p e n t i n s t o c k t a k i n g m a y n o t b e c o m m e n s u r a t e w i t h t h e i n c r e a s e d a c c u r a c y o b t a i n e d , b e a r i n g i n m i n d t h e fact t h a t a n y e r r o r s i n s t o c k o n l y affect t h e figure f r o m w e e k t o w e e k . F o r t h i s r e a s o n difficult a n d t i m e c o n s u m i n g s t o c k t a k i n g p r o c e d u r e s , w h i c h o n l y r e s u l t i n a v e r y s m a l l i n c r e a s e i n a c c u r a c y , a r e n o t u s u a l l y e m p l o y e d . I n m a n y mills, where there are no large variations in t h e p u r i t y of materials in process, a n a l y s e s a r e n o t c a r r i e d o u t o n all i t e m s o f s t o c k , t h e w e e k l y a v e r a g e a n a l y s i s for t h e m a t e r i a l c o n c e r n e d i s t a k e n a s t h e a n a l y s i s o f t h e m a t e r i a l i n s t o c k a t t h e e n d o f t h e w e e k . W h e n a d o p t i n g s u c h p r a c t i c e s , h o w e v e r , careful consideration m u s t be given to t h e errors introduced to ensure t h a t the overall e r r o r i n s t o c k does n o t r e a c h a level w h e r e i t m a t e r i a l l y affects t h e w e e k l y r e c o v e r y figure. M a s s e c u i t e C o m p o s i t i o n — I n order to determine the relative q u a n t i t i e s of s y r u p a n d m o l a s s e s r e q u i r e d to p r o d u c e a m a s s e c u i t e of a definite p u r i t y , t h e following f o r m u l a gives a close a p p r o x i m a t i o n . I t i s b a s e d o n t h e assumption t h a t t h e Brix values of b o t h syrup a n d molasses are equal, an approximation which is usually experienced in practice, particularly when t h e quantities are m e a s u r e d in t e r m s of t h e volumes of massecuite boiled on the respective materials. L e t — p = p u r i t y of m o l a s s e s , P = p u r i t y of s y r u p , M = p u r i t y of m a s s e c u i t e , x = p e r c e n t a g e of s t r i k e d e r i v e d f r o m m o l a s s e s , y = 100 — x = p e r c e n t a g e of s t r i k e d e r i v e d from s y r u p . Assuming uniform Brix—

T h e s e f o r m u l a e c a n b e a p p l i e d t o a n y m i x t u r e o f m a t e r i a l s o f different p u r i t i e s , a n d t h e c a l c u l a t i o n i s often c o n v e n i e n t l y c a r r i e d o u t b y u s i n g t h e "cross" m e t h o d as follows:— call this A.

call t h i s B.

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161

When it is desired to know the actual quantities of molasses and syrup necessary to give the strike, the following procedure should be followed:— Let— B — Brix of massecuite, b = Brix of syrup and molasses, X = quantity of molasses used per 100 massecuite, Y = quantity of syrup used per 100 massecuite.

Expected Purity of Molasses—A formula derived statistically by the staff of the Sugar Research Institute is designed to give a target purity which is the lowest purity of molasses which could normally be expected to be attained from the material being processed. The expected true purity is calculated from the reducing sugar to ash ratio of the molasses in the following manner:— Expected purity = 40.67 — 17.80 log X where X = Reducing sugar/ash ratio Equivalent Standard Granulated (E.S.G.)—Not all the pol in raw sugar is recoverable, some being destined to pass out of the refinery in molasses. E.S.G. is intended to represent that portion of the pol in a raw sugar which is recoverable as pure sucrose. In the calculation of E.S.G. use is made of the Winter-Carp formula to derive the E.S.G. factor.

Recovery and boiling house recovery may be expressed in terms of E.S.G. instead of pol by multiplying each by the E.S.G. factor of the s u g a r Recovery E.S.G. = pol recovery x E.S.G. factor In recent years the importance placed on E.S.G. figures has declined, and these figures are now seldom seen in literature. Crystal Content of Massecuite—The crystal content of a massecuite may be calculated from the analyses of the massecuite and the mother liquor of the massecuite. For the purposes of deriving formulae for crystal content it may be assumed that "crystal" has a dry substance content or a sucrose content or a true purity of 100 per cent. Thus three formulae may be derived, based on true analyses. Add to this the three formulae which may be drawn up on the basis of the apparent analyses, Brix, pol, and apparent purity, and it is found that six formulae are available for the calculation of crystal content.

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Suppose that the massecuite and mother liquor be analysed for sucrose contents. Then the crystal content may be derived as follows:— Suppose 100 parts of massecuite, of sucrose content S mass per cent, contain C per cent of crystal. Let the sucrose content of the mother liquid be S mol. Then, from a sucrose balance

The formulae involving dry substance, Brix and pol are derived similarly and are analogous in form. If purity be adopted as a basis of calculation, the derivation is slightly different. It is convenient to regard crystal content as the recoverable sucrose, of 100 purity, per cent massecuite. The S. J.M. formula may be used to derive the recoverable sucrose per 100 sucrose in massecuite and this may be converted simply to the basis of per 100 parts of massecuite. Let the purities of massecuite and molasses be P mass and P mol respectively, the dry substance per cent massecuite D.S. mass and the sucrose per cent massecuite Smass.Then

Note that the form of the first term is analogous to that of the previous formulae, but the dry substance per cent massecuite is also involved in the complete expression.

100 parts total solids in massecuite. This is a useful figure, particularly as it may be calculated using only purity figures, which are the most commonly available for pan products. The crystal contents set out in Table XVIII are calculated by this formula. With six formulae available to calculate crystal content, the question arises as to the order of merit of the formulae in practice. Sucrose and true purity figures provide the best bases of calculation; pol and apparent purity figures yield results sufficiently accurate for routine work; dry substance gives reasonably satisfactory results; Brix gives unreliable results and should not be used to calculate crystal contents. If the method of separation of the mother liquor from the massecuite involves any significant degree of concentration or dilution, crystal content calculations must be based on purity. Rapid Method for Determining Weighted Average from Previous Average and Value for N e w Period—In preparing the weekly report, the chemist is required to give "To Date" values for each item, which involves considerable time and labour by the usual arithmetical method. The following is a simple, short method, and should be of interest to those chemists who are not acquainted with the procedure:— The previous "To Date" total (cane, molasses, or sugar) is divided by the new total, thus providing a factor. The value for each item in the new period is then subtracted from the previous average, and the difference is

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multiplied by the factor. The value so obtained is added to the new value to give the new average. If the value for any item, is greater in the new period than in the previous average, the difference will be negative, and the amount is actually subtracted. This is demonstrated by the following example:— Cane Tons Cane Fibre Previous "To Date" values New Period To Date

Fibre Calculation— 13.42 — 14.08 = —0.66 x 0.9039 = 14.08 + (-0.60) =

-0.66 -0.60 13.48

172,108 18,307 190,415

%

13.42 14.08 13.48

Pol

%

16.81 15.75 16.71

Pol Calculation— 16.81—15.75 = 1.06 1.06 x 0.9039 = 0.96 15.75 + 0.96 = 16.71

Obviously the method cannot be applied to calculated values such as dilution, crushing rate, percentage lost time, etc.; these must be determined by employing the usual formulae. Performance Criteria Milling-—Numerous formulae have been devised to measure milling efficiency, but only two have been adopted in Queensland—Reduced Extraction and Lost Undiluted Juice per cent Fibre. Reduced Extraction—In the extraction formula it may be seen that, for constant values of pol in cane and pol and fibre in bagasse, the higher the fibre in cane, the lower the extraction. Accepting this as true in practice, the Reduced Extraction formula sets out to eliminate the effect of variations due to fibre per cent cane by "reducing" this figure to a standard 12.5 per cent. The formula was derived by Deerr, who argued along the following lines:— If e is the actual extraction, and / the fibre per cent cane, then v the absolute juice per cent fibre in bagasse is given by the expression

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criticism for it implies that the pol of the absolute juice is uniform, throughout the cross section of the cane stalk. This is far from correct though a parallel assumption in regard to Brix is much more reasonable. The main weakness of the formula is the implicit assumption that the higher the fibre content of the cane, the lower the extraction. If the higher fibred canes display improved response to milling and maceration the relationship may actually be reversed. The reduced extraction formula would then become even worse than pol extraction as a measure of milling efficiency. Lost Undiluted Juice in Bagasse per cent Fibre—Since from the technical or operating point of view the work of a milling plant consists of the separation of juice from fibre, and since loss of juice in bagasse is caused only by fibre, the logical method of evaluating the technical efficiency of the milling station is by expressing the loss in bagasse in terms of undiluted juice per cent fibre. Obviously the comparison of results on a basis of pol extraction with differing fibre and pol contents of cane can be quite misleading if used as a criterion of efficiency of milling work. The lost undiluted juice per cent fibre is calculated by expressing the Brix in bagasse in terms of an equivalent amount of undiluted cane juice (the Brix of which is taken as equal to that of first expressed juice), as follows:— Lost undiluted juice per cent fibre =

or, using the same nomenclature as for calculating extraction, and Bf for Brix of first expressed juice—

It will be noted that the quantities involved in this expression are all determined directly and involve neither the assumptions of the c.c.s. formula nor the use of the figure for fibre in cane. Like reduced extraction, lost undiluted juice per cent fibre compensates for the quantity of fibre handled but can take no account of its quality. This formula is based on sounder principles than the reduced extraction formula, but suffers from the disadvantage of providing a value of zero for the limit of perfection and an upper limit approaching 1000. On this scale relative merits are not easily appreciated. In the absence of any complete criterion of the milling quality of cane, milling efficiency figures must continue to give only moderate satisfaction. Boiling House Efficiency—The influence of the purity of the raw material on recovery is so pronounced that recovery figures serve as a poor guide to efficiency. In Boiling House Efficiency the actual boiling house recovery is expressed as a percentage of the recovery indicated by the Winter-Carp recovery formula. Strictly the Winter-Carp recovery should be based on the purity of mixed juice, but as this is not generally available, the purity of first expressed juice is taken instead.

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165

T h e w e a k n e s s o f t h e boiling h o u s e efficiency f o r m u l a i s t h a t i t a c c e p t s all t h e p o l i n t h e s u g a r a s r e c o v e r a b l e pol. T o c o m p e n s a t e for t h i s t h e E . S . G . R e c o v e r y m a y b e t a k e n , t h e figure d e r i v e d b e i n g Boiling H o u s e Efficiency E . S . G . , o r Boiling H o u s e P e r f o r m a n c e . A n o t h e r w e a k n e s s i s t h a t t h e b a s i c r e c o v e r y d e p e n d s o n l y u p o n t h e p u r i t y o f t h e original j u i c e , t h e r e b y t a k i n g account of the quantity, b u t not the nature of the impurities. V a r i o u s a t t e m p t s h a v e b e e n m a d e t o e l i m i n a t e t h e effects o f p u r i t y o f original m a t e r i a l on recovery, by " r e d u c i n g " t h e p u r i t y of t h e m i x e d juice t o a s t a n d a r d o f 8 5 p e r c e n t . H e n c e s u c h t e r m s a s R e d u c e d Boiling H o u s e Recovery a n d R e d u c e d Overall Recovery h a v e been derived. There is disa g r e e m e n t o v e r t h e r e a s o n i n g i n v o l v e d i n r e d u c i n g t h e recoveries t o a s t a n d a r d based on juice of 85 per cent purity, and, as t h e reduced recoveries are not used in Queensland, t h e formulae h a v e been o m i t t e d from this Manual. B e c a u s e of t h e n u m e r o u s deficiencies in t h e Boiling H o u s e Efficiency formula it is not normally considered to be of great importance. C o e f f i c i e n t o f W o r k — A s s t a t e d i n t h e Definitions,

I r r e s p e c t i v e of i t s m e r i t s as a c r i t e r i o n of f a c t o r y p e r f o r m a n c e , t h e coefficient of w o r k is t h e m o s t i m p o r t a n t figure in mill c o n t r o l in Q u e e n s l a n d since i t r e l a t e s t h e s u g a r m a d e t o t h e c a n e c r u s h e d i n t e r m s o f t h e b a s i s o n w h i c h t h e s e c o m m o d i t i e s a r e b o u g h t a n d sold. H e n c e t h e figure h a s h i g h significance financially. As a m e a s u r e of f a c t o r y p e r f o r m a n c e t h e coefficient of w o r k e m b o d i e s t h e deficiencies of t h e c.c.s. a n d n e t t i t r e f o r m u l a e a n d must be accepted with caution. As s t a t e d earlier, t h e c.c.s. f o r m u l a p o s t u l a t e s a s t a n d a r d loss of sucrose in process. W o r k i n g to t h i s s t a n d a r d , a mill t r e a t i n g 100 t o n s of c.c.s. w o u l d r e c o v e r 100 t o n s o f p u r e s u g a r (100 n . t . ) , w h i c h w o u l d b e e q u i v a l e n t t o n e a r l y 106.4 t o n s of 94 n . t . s u g a r . T h e coefficient of w o r k w o u l d be n e a r l y 106.4. T h i s is s o m e t i m e s r e g a r d e d as t h e u p p e r l i m i t of t h e coefficient of w o r k . T h e i d e a s t h a t (1) t h e u p p e r l i m i t of coefficient of w o r k is 100, a n d (2) t h e u p p e r l i m i t i s a b o u t 106.4 a r e b o t h e r r o n e o u s . T h e u p p e r limit i s v a r i a b l e , b u t r e p r e s e n t s a p e r f o r m a n c e in w h i c h all t h e sucrose in t h e c a n e is r e c o v e r e d as p u r e s u g a r . A coefficient of w o r k of 106.4 a p p r o x i m a t e l y is t h e minimum v a l u e at which this condition could exist. This m i n i m u m value would be obtained f r o m c a n e w i t h a m a x i m u m c.c.s. for i t s pol c o n t e n t , i.e. c o n t a i n i n g no i m p u r i t i e s i n t h e j u i c e . I f all t h e sucrose i n t h e c a n e c o u l d b e r e c o v e r e d f r o m c a n e c o n t a i n i n g i m p u r i t i e s in i t s juice, a coefficient of w o r k h i g h e r t h a n 106.4 w o u l d be o b t a i n e d , e.g. consider c a n e of t h e following analysis. pol p e r c e n t c a n e = 16.0 Brix per cent cane = 18.0 c.c.s. = 15.0 P o l r e c o v e r e d a s p u r e s u g a r f r o m 100 t o n s c a n e = 16.0 t o n s 16.0 t o n s at 100 n . t . = 17.02 t o n s at 94 n . t . T o n s of c.c.s. f r o m 100 t o n s c a n e = 15.0

CHAPTER X I I THE BOILER S T A T I O N Introduction The large quantity of steam required by the factory for power and heating purposes is supplied by a boiler station where the chemical energy stored in the fuel is released by combustion in the furnaces and as much as possible transferred, in the form of heat, to the boilers proper. The steam generated by the boilers provides a very flexible medium for applying heat wherever it may be wanted and, when generated at a suitable working pressure, it may first be used in prime movers to supply all the mechanical and electrical power needed by the various factory processes. Boiler Efficiency It should be the aim in every factory to operate the boiler station at an efficiency which enables all steam requirements to be met by burning only the bagasse fuel which is available from the milling process. Boiler efficiencv for any period of time may be stated as:

To carry out an efficiency test it would be necessary to measure the quantities of steam produced and fuel used during the time of the test and to determine the heat required per lb of steam and the calorific value of the fuel used. Suggestions covering these items will now be given. Steam Produced For the measurement of steam output, a positive type meter on the feedwater is recommended, together with a recording thermometer. Where any blowing down is done during the period concerned, the weight of water blown down must be estimated and deducted from the total weight of feed water. This is readily done by noting the depth of water removed from the boiler drum each time by blowing down, and calculating its volume and weight from the dimensions of the drum. With most mills the normal amount of blowing down during a weekly working period will probably be negligible (well below 1 per cent of total steam) and the blow-down need be estimated only in abnormal circumstances. Steam output may also be measured by flow meters; this, however, necessitates careful correction of the flow meter records for variations in steam pressure and temperature, as well as frequent checking of the meter. In this case no correction foi blowing down is required; on the other hand, steam blown off through the safety valves will, if of sufficient amount, cause an error in the figures for steam output. Heat Required per lb of Steam The pressure and (when superheated) temperature of the steam should be registered and also the temperature of the feed water. Average values for the period of test are then calculated. For superheated steam the heat required per lb = H —(t — 32),* where H is the total heat of superheated steam in Btu per lb at the average temperature and pressure obtaining during the test period and t is the average feedwater temperature in °F. •Steam tables using the British system of units are based on a datum of 32 °F.

Fuel Used The most accurate way of determining the amount of fuel used is by direct weighing. Hand weighing by feeding the bagasse into a large box mounted on platform scales and then hand feeding the furnaces would be quite feasible for an efficiency test of a few hours' duration on a single boiler, but would be almost impossible for a test on the whole station. A continuous weigher would be ideal for such an overall test and when these weighers are installed for the purpose of chemical control the testing of boiler station efficiency will be very much simplified. In the meantime it is necessary to determine the weight of bagasse from the weight of cane crushed, and the percentages of fibre in the cane and the bagasse during the period, thus— , weight of cane x fibre per cent cane Weight of bagasse = —~ -^-^ fibre per cent bagasse Should the above method be used for determining the weight of fuel, allowance must be made for any bagasse removed from the boiler station for other purposes, also for any bagasse which might be saved during the period of the test. It is suggested that such quantities may be determined with sufficient accuracy by volume measurement allowing 10 lb/ft 3 for piled bagasse. Allowance has also to be made for any extraneous fuel used during a test. However, as the furnaces are designed essentially for bagasse burning it would be more satisfactory to conduct any tests at a time when the mill had settled down to a steady crushing rate. There would then be little likelihood of the boiler's requiring extraneous fuel. Calorific Value of the Fuel When a fuel is burned, heat is generated, and the quantity of heat liberated per unit weight of fuel is known as the calorific value and expressed in Btu per pound. Most fuels contain hydrogen which, when it burns, yields water in vapour form; furthermore, any water originally present in the fuel is also converted to vapour. This water vapour contains latent heat, representing a portion of the heat liberated by the combustion. If the water vapour be condensed the latent heat becomes available for inclusion in the total quantity of heat released. The calorific value determined under these conditions is known as the Gross Calorific Value, represented by the symbol Bh. The heat released per pound of fuel, not including any latent heat in the products of combustion, is known as the Net Calorific Value, designated Bi. It is customary to base all boiler calculations on gross calorific value, but comparisons between fuels, as between, say, bagasse and coal, or between bagasses of different moisture contents, are more reliably drawn on the basis of net calorific value. In practical boilers only the heat corresponding to the

168

T H E BOILER STATION

net calorific value is available for absorption, but, as stated above, boiler efficiencies and allied figures are related to gross calorific values. Bagasse.—Formulae giving the calorific value of bagasse have been worked out from determinations on Queensland bagasse and are as follows: Gross cal. value (Bh) = 8345 — 22 • 1 pol — 83-45 water Net „ „ {Bi) = 7783 — 22-1 pol — 88-27 water In these formulae pol and water represent the percentage of pol and moisture obtained from the analyses of final bagasse leaving the milling plant. Strictly speaking, a correction should be made for a reduction in moisture by evaporation between the mills and the boiler station. While such a collection may readily be established and applied, it is suggested that for routine calculations the figures for the bagasse leaving the final mill may be employed. This would under-estimate somewhat the calorific value (Bh) of the bagasse and so over-estimate the boiler efficiency and, in effect, credit the boiler house with any drying of bagasse between the final mill and the boilei furnaces. In any case the discrepancy in Bh would be fairly uniform and of no consequence for comparative purposes. Values of Bh for normal ranges of pol and moisture are given in Table XXXV. Wood.—The calorific value of wood depends mainly on its condition, i.e , how much moisture it contains. If no other information is available a B ^ value of 6000 may be taken for air-dried wood containing 20 to 40 per cent moisture. The corresponding B\ is about 5300. Furnace Oil and Diesel Fuel.—The average gross calorific values of these fuels can be taken as 18,800 and 19,200 respectively. Molasses.—The calorific value of molasses depends on its moisture content and ash. The average values oi Bh and B\ for normal molasses can be taken as 5380 and 4600 respectively. Coal and Tar.—Coal and tar are about the only remaining substances which are likely to be used as supplementary fuels in the sugar industry. The gross calorific values can be taken as 11,000 and 16,500 respectively. Equivalent Bagasse.—Equivalent bagasse is assumed to be bagasse having a net calorific value of 3300 Btu per pound, calculated from bagasse of 50 per cent moisture and three per cent pol. This value is accepted as the standard for bagasse and all extraneous fuels. Therefore to calculate tons equivalent bagasse, the weight of bagasse produced is multiplied by the net calorific value (Table XXXV(b)) divided by 3,300. The extraneous fuels are calculated to equivalent bagasse, from the following formulae:— Tons equivalent bagasse = tons wood X 1.6 = tons molasses x 1.4 = tons coal X 3.5 = tons oil X 5.5 Measuring Boiler Efficiency Indirectly A certain proportion of the theoretical heat available from the bagasse fed into a boiler furnace is used to generate steam while the remainder is absorbed by various losses. It is possible to calculate the major losses fairly accurately while a reasonable estimate of the minor losses may be made from results obtained in previous tests on boilers of similar type. As the losses are

T H E BOILER STATION

169

e x p r e s s e d as a p e r c e n t a g e of t h e Bh v a l u e of t h e b a g a s s e , t h e efficiency =. 100 — losses. T h e m e t h o d gives a r e a s o n a b l y a c c u r a t e w a y of m e a s u r i n g b o i l e r efficiency w i t h o u t t h e l a b o u r o f w e i g h i n g a n d h a n d feeding b a g a s s e a n d w i t h o u t t h e difficulty o f m e a s u r i n g t h e s t e a m p r o d u c e d . Moreover, for a n y p a r t i c u l a r boiler, t h e losses w h i c h a r e e s t i m a t e d c a n , u n d e r n o r m a l w o r k i n g c o n d i t i o n s , b e e x p e c t e d t o r e m a i n c o n s t a n t while t h e losses w h i c h a r e c a l c u lated include those which are u n d e r t h e operator's control. T h e m e t h o d therefore gives a t r u e g u i d e as to h o w efficiently a boiler is b e i n g w o r k e d . T h e v a r i o u s losses a r e discussed below a n d f o r m u l a e g i v e n for t h o s e which can be calculated. Condensation Loss T h e t e r m c o n d e n s a t i o n loss i s a p p l i e d t o t h e h e a t lost i n t h e flue g a s d u e t o w a t e r v a p o u r . P a r t o f t h i s v a p o u r c o m e s from t h e o r i g i n a l b a g a s s e a n d p a r t i s f o r m e d i n t h e c o m b u s t i o n process. 100 (562 + 4 . 8 2 w ) C o n d e n s a t i o n loss = = p e r c e n t BhBh where w = p e r c e n t m o i s t u r e in b a g a s s e . Sensible Heat Loss T h e f l u e g a s l e a v e s t h e boiler a t a t e m p e r a t u r e a b o v e t h a t o f t h e a t m o s p h e r e , a n d t h u s p a r t o f t h e h e a t o f c o m b u s t i o n leaves t h e boiler a s sensible heat in the flue gas. Table of values for lOOOK for use in formula for sensible heat loss. Per cent COa in flue gas, mt

Per cent moisture in bagasse, w

404 0

46

48

50

52

54

56

5 6 7 8 9

78.9 67.3 58.9 52.6 47.6

79.3 67.7 59.3 52.9 48.0

79.6 68.1 59.7 53.4 48.5

80.0 68.4 60.0 53.7 48.8

80.5 68.8 60.4 54.1 49.2

81.0 69.4 60.9 54.6 49.6

81.5 69.9 61.4 55.1 50.1

82.1 70.5 61.9 55.7 50.7

82.7 71.0 62.5 56.2 51.3

10

43.8 42.1 40.6 39.2 37.9

44.1 42.4 40.9 39.6 38.2

44.5 42.8 41.3 39.9 38.6

44.9 43.2 41.7 40.4 39.1

45.3 43.6 42.1 40.7 39.4

45.8 44.1 42.6 41.2 39.9

46.3 44.6 43.1 41.7 40.4

46.8 45.1 43.6 42.2 41.0

47.4 45.7 44.2 42.8 41.5

36.7 35.6 34.7 33.7 32.9

37.1 36.0 35.0 34.1 33.2

37.4 36.4 35.4 34.4 33.6

37.9 36.9 35.9 34.9 34.1

38.3 37.2 36.2 35.2 34.4

38.7 37.6 36.7 35.7 34.9

39.2 38.2 37.2 36.2 35.4

39.7 38.7 37.7 36.7 35.9

40.3 39.3 38.3 37.3 36.5

32.1 31.3 30.6 29.9 29.3

32.4 31.6 31.0 30.2 29.6

32.7 32.0 31.3 30.6 30.0

33.2 32.5 31.7 31.1 30.5

33.6 32.9 32.1 31.4 30.8

34.1 33.3 32.6 31.9 31.3

34.5 33.8 33.1 32.4 31.7

35.1 34.3 33.6 33.0 32.3

35.6 34.9 34.2 33.5 32.9

10.5 11

11.5

12

12.5 13

13.5 14

14.5 15

15.5 16

16.5 17

42

44

Sensible h e a t loss = K (tF—tA) p e r c e n t Bhw h e r e K is a c o n s t a n t d e p e n d i n g on t h e C O a c o n t e n t of t h e flue g a s a n d t h e w a t e r c o n t e n t o f t h e b a g a s s e (values for 1000K a r e given in t h e accompanying Table). tp = flue g a s temperature °F. tA = air temperature ° F .

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T H E BOILER STATION

Unburnt Gas Loss In the combustion of hydrocarbon fuels gaseous intermediate products are formed. The existence of such products in the flue gas represents a loss of heat. The most common instance is of carbon burning to CO instead of C0 2 The unburnt gas loss may be determined from the following formula:—

m2 = average reading of per cent unburnt gas registered by a Mono or similar type of recorder. The CO 2 and per cent unburnt may best be determined from a flue gas analyser of the Mono type. The Mono is a recording instrument and very convenient to use as the difference between the readings of alternate strokes of the pen gives a measure of the unburnt gas. It is reasonable to assume that this unburnt gas is made up of CO and H 2 , in which case the actual quantity of unburnt would be two-thirds of the percentage shown by the difference between alternate strokes. Miscellaneous Losses These are made up of radiation loss, sensible heat loss in the ash, unburnt material in the ash and unburnt material in the fly ash. It is almost impossible to measure these losses, but in a series of tests cairied out by the Bureau on five water tube boilers they were found to have an average value of 8 • 3 per cent Bh at an average rate of evaporation of 4 -9 lb per ft2 of heating surface per hour. Two of the miscellaneous losses relate to ash. Rough calculations show that the sensible heat lost when hot ashes drop through the grate and are raked out of the ashpit would be of the order of 0 • 1 per cent Bh- Observations show that the amount of unburnt in the ash would also be very small when stated as a percentage of heat available in bagasse. It is therefore suggested that these two ash losses be neglected and the miscellaneous losses regarded as being made up of fly ash and radiation losses. Experiments carried out in 1950 indicate that fly ash loss is proportional to boiler rating and that a reasonable figure to adopt for a water tube boiler would be 2 per cent at a rating of 4 • 9 lb per ft2 of heating surface per hour. If the actual steam consumption of the factory is not known the following estimates of steam (from and at 212 °F)* per ton of cane could be used to arrive at the boiler rating:— Using quadruple evaporation without bleeding 61 per cent steam on cane Using quadruple with bleeding 58 Using quintuple without bleeding 57 ,, ,, Using quintuple with bleeding 55 It is generally accepted that radiation loss, expressed as per cent Bh, does not increase with rating, but, if anything, tends to decrease. Reasonable results should be obtained, however, if this loss be taken at 8-3—2 = 6 - 3 per cent Bh for all ratings. Large boilers with water wall furnaces would tend to have a still smaller radiation loss and in such boilers it is probable that the miscellaneous losses would not exceed 6 per cent Bh•Steam raised from water at 212 °F without any change in temperature. The heat required for this conversion is 970.6 Btu/lb.

THE BOILER STATION

171

Flue Gas Flue Gas Composition For any particular flue gas temperature, boiler efficiency will improve as the amount of excess air going into the furnace is reduced—provided always that the air is supplied in such a way that there is little if any unburnt in the flue gas. The adjacent Table shows the relationship between the C0 2 reading, which is really a measure of excess air, and the sensible heat loss. The last column also shows the importance of complete combustion, e.g.., the reduction in heat loss brought about by improving the C 0 2 from 11 to 14 per cent would be completely nullified if the combustion efficiency deteriorated sufficiently to yield an unburnt gas reading of one per cent on a Mono or similar recorder. Table showing sensible heat and unburnt gas losses. (Based on a flue gas temperature of 500 °F and a bagasse moisture of 50 per cent.)

co2

Excess air per cent

Sensible heat loss in flue gas per cent Bh

20.3

0 19 27 35 44 56 68 84 102

13.0 13.5 14.1 14.8 15.6 16.5 17.6 19.6

17 16 15 14 13 12 11 10

Loss caused by 1 per cent unburnt in flue gas per cent Bh

_2 . 5 2.6 2.8 3.0 3.2 3.5 3.8 4.2

Flue Gas Temperature The higher the flue gas temperature the greater will be the sensible heat loss. The temperature must go up as the boiler rating is increased and the operator has no control over the efficiency in this regard. He can, however, obtain maximum efficiency at any given rating by making sure that the heating surfaces, on both water and gas sides, are kept as clean as possible. The sensible heat loss when the bagasse contains 50 per cent moisture and the flue gas 12-5 per cent C 0 2 varies with temperature as follows:— Flue gas temperature °F 300 400 500 600 70C Sensible heat loss per cent B h 8-5 12-4 16-2 20-2 24•( Operation at moderate rating would give a temperature of between 500 and 600 °F. By fitting an economiser or air heater this could be brought down to 350 °F, which shows that such a unit can be worth up to about 8 per cent in efficiency. Volume of Flue Gas To specify the capacity of an induced draught fan or fans for a boilei station it is necessary to determine the volume of flue gas which will t*

172

T H E BOILER STATION

produced per minute when the factory is working at maximum crushing rate and all the bagasse is being burnt in the furnaces. The weight of flue gas which will be produced by each pound of this bagasse may be found from the following formula:—

where w = per cent moisture in bagasse m \ == P e r cent CO 2 in flue gas. Over the range of C 0 2 and moisture values likely to be met, the specific volume of the flue gas may be taken as 25 • 1 ft 3 /lb at 500 °F. For any other

It is suggested that the fan capacity be determined for a C 0 2 figure of 12 1/2 per cent and increased by 10 per cent to allow for depreciation in service. The flue gas temperature could be taken as 600 °F. At full capacity the fan should be capable of giving a draught of 2 in water at the back of all boilers. The draught at the fan inlet should, for a simple installation and reasonably well designed flues, not have to exceed 2 1/2 in. If an economiser or fly ash eliminator be fitted extra draught must be provided to compensate for the resistance of these units. Horsepower Required for a Fan The following formula gives the horsepower required for a fan:—

Effect of Density on Fan Performance It is necessary to remember that most manufacturers state fan performance in terms of "standard air" which has a density of 0-075 lb/ft 3 The volume delivered by a fan at a certain speed is independent of density but the pressure (or draught) will be proportional to the density. Therefore if a pressure of 3 in is required when handling flue gas at 500 °F (specific volume 25-1 ft 3 /lb = 0 - 0 4 lb/ft 3 density) a fan giving a pressure

Forced Draught Fans To determine the capacity of a forced draught fan the maximum rate of burning of bagasse in the furnace must first be estimated and air required found from the following formula:—

The volume of air per minute may then be determined. However, if the fan is to be used with an air heater, the capacity must be increased to allow for a certain amount of recirculation as the only sure

T H E BOILER STATION

173

way to avoid corrosion in a tube or plate type air heater is to arrange foi the in-going air to be at a temperature at least equal to the dewpoint temperature of the flue gas. This dewpoint temperature depends on the moisture content of bagasse and per cent CO2 in the flue gas. At 50 per cent moisture and 12.5 per cent C 0 2 it would be 148 °F and sufficient hot air must be added to the in-going atmospheric air to give a mixture of this temperature. Taking an atmospheric temperature of 70 °F and a hot air temperature of 370 °F the recirculation needed would be

The combustion air required under the assumed conditions of moisture and C 0 2 would be 4.65 lb per lb of bagasse = 7 1 - 5 ft3 at 148 °F. Therefore3 the volume of air to be handled by the fan would be 71.5 x 1.35 = 96.5 ft per lb of bagasse burnt. This figure is suggested as being suitable for average Queensland conditions. Bagasse Moisture Bagasse moisture has a very big influence on the steaming capacity of the boilers and if steam troubles are being experienced an effort should be made to arrange mill settings so that the moisture in final bagasse does not exceed 50 per cent. Apart from making the bagasse easier to burn, reducing the moisture content is equivalent to increasing the fuel supply. For moistures in the neighbourhood of 50 per cent, one per cent reduction is equivalent to obtaining one per cent more fuel from the same quantity and quality of cane. The Treatment of Water for Boilers* The supply of unsuitable water to steam generating plants is not only uneconomical, but may be dangerous if adequate steps are not taken to minimize the cumulatively deleterious results. The desirable feed to all boilers is a suitably conditioned water, free from all unwanted salts and gases, and the maximum possible amount of such suitable water as is available must be fed to boiler plant. Where raw make-up or other unsuitable water must be fed to boilers there is, however, no excuse for allowing the impurities in this water to remain in the boiler in a harmful form. The problems of boiler water treatment have become magnified in recent years with the advent of large, modern, bent-tube, water-walled, high capacity boilers into the industry. Such boilers are particularly prone to damage from overloading and inadequate water conditioning, and it is false economy to run the risk of ruining or damaging an investment worth some half a million dollars for the sake of a small outlay on boiler feed water treatment. There are a number of British Standards available dealing with the subject of water treatment and it is strongly recommended that the following standards be purchased. B.S. 2486 "Treatment of Water for Land Boilers" B.S.1427 "Routine Control Methods of Testing Water Used in Industry" B.S. 1328 "Methods of Sampling Water Used in Industry" *The recommendations made under this section are approved by the Chief Inspector of Machinery.

174

T H E B O I L E R STATION

There are also a number of reputable commercial firms with long experience in this field, and, providing their recommendations are within the limits prescribed by British Standards, the advice of such firms can be profitablyfollowed. The indiscriminate addition of boiler water additives whose composition is not specified by the manufacturer, should, however, be avoided. The objects of boiler water treatment are threefold, namely:— 1. The prevention of scale on heating surfaces 2. The prevention of corrosion and caustic embrittlement 3. The production of clean steam free from entrained water or solids and these three criteria will now be discussed separately. The Prevention of Scale on Heating Surfaces The avoidance of scale on heating surfaces is most important, for, as well as reducing the efficiency of heat transfer to a boiler, heavy scale will cause overheating of the tube metal which, if sufficiently severe, can cause tube failure. Scale can be described as a hard adherent deposit on heating surfaces and is caused by the presence of three main chemical substances in the water; salts of calcium, magnesium, and silica. It is therefore important to provide a boiler feed water containing as few of these impurities as possible but, if the impurities must unavoidably be introduced, as they are in small quantities even in very efficient steam plants, they must be removed from the water before feeding it to the boiler, or additives must be introduced to the water so that scale will not form. The ideal answer to the problem is not to introduce water containing these compounds to the boiler. This is done, as far as possible, by returning condensed steam to the boiler as feed water wherever this can be obtained in an uncontaminated form. This practice reduces the usage of raw water, i.e. untreated water from outside the steam-condensate cycle, as far as possible. The use of clean condensate is the greatest single factor in the avoidance of boiler feed treatment problems. Where raw water make-up containing scale forming constituents must be added the scale-forming constituents of this water can be dealt with in three ways either singly or in combination, by distillation {i.e. evaporation), external water treatment (softening or ion exchange), or by internal water treatment. The use of distillation processes or external water treatment systems is, however, not economical under sugar industry conditions, and boiler water conditioning is carried out by what is known as internal treatment. Internal treatment entails the chemical treatment of the boiler water in such a manner that the scale forming substances are not deposited on the heating surface as scale, but precipitated as a mobile sludge which flows to the lowest point in the boiler and is removed in the blowdown. This is usually achieved by adding phosphate to the boiler water and by maintaining an excess of alkalinity, by the addition of caustic soda. Under the alkaline conditions prevailing, the phosphate precipitates any calcium present as calcium phosphate sludge. The caustic alkalinity precipitates magnesium salts as magnesium hydroxide, also a mobile sludge. Any silica present will normally be absorbed on the magnesium hydroxide precipitate and removed, or may co-precipitate with magnesium as magnesium silicate. Thus all harmful concentrations of scale forming compounds can be removed from the boiler

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in the blowdown, providing the correct concentrations of phosphate and alkalinity are maintained at all times. The consumption of phosphate and alkali obviously depends on the quantity of scale forming compounds fed to the boiler, so that the cost of the treatment depends entirely on this factor. It is therefore of great importance that the maximum possible amount of good condensate be returned to the boiler and the minimum of poor quality water added. Thus make-up should be kept to a minimum and, where alternative sources of make-up water are available, the best source should be used. There is also a secondary reason for the avoidance of feed contamination by scale forming materials. The scale forming materials add solids to the boiler water and the chemicals added to control the scaling add further solids. This necessitates increased blowdown to maintain a safe solids level in the boiler water, as will be discussed in a subsequent section, and this results in some of the treatment chemicals being lost in blowdown. This causes an increased chemical demand to maintain the correct chemical concentrations, and this adds further solids to the water and so on. The net result is that the system can reach a stage where it chases its own tail, so to speak, and chemical costs are high due to wastage of chemicals in blowdown. Therefore the maximum usage of good condensate for boiler feed is of the utmost importance. The Prevention of Corrosion and Caustic Embrittlement Corrosion—Corrosion in a boiler is produced by two main causes, acidity and oxygen. Acidic conditions are corrosive to iron and steel, so that the material of a boiler will be eaten away if acid conditions are allowed to prevail for any length of time. The control of this problem is a relatively simple one. The boiler water must be kept alkaline at all times. This is in conformity with the internal method for the prevention of scale, as discussed in the previous section, and the provision of the correct alkalinity serves a dual purpose. The presence of dissolved oxygen in a boiler can cause very severe corrosion. Corrosion from this source, and sometimes from acids as well, normally occurs in the form of pits in the boiler shell or as wasting away at the tube ends. The fact that the corrosion is concentrated in small areas and not evenly distributed over the whole surface means that the effects are more severe. In extreme cases of pitting, the boiler drum finally becomes holed by pits which extend right through the metal. The theory of corrosion caused by the presence of oxygen is rather complex, but the process is actually a form of galvanic action. Due to stresses in a boiler shell, and to lack of complete uniformity of metal composition, under operating conditions certain areas of a boiler become anodes while others become cathodes. A current will pass between the anodic and the cathodic areas and this will cause the removal of metal from the anodic areas. The metal removed forms an hydroxide, under the alkaline conditions in the boiler, but in order to proceed, the galvanic action requires oxygen. If oxygen is present the action can continue indefinitely and the anodic areas can be continually denuded of metal. The anodic areas, once established, remain localized, and severe corrosion occurs at these localized points, giving the typical pitting of oxygen corrosion. The answer to this problem is obviously to ensure that the boiler water contains no dissolved oxygen. The oxygen enters the boiler in the feed water and so conditions in the feed should be maintained so that a minimum amount of dissolved oxygen is present. The solubility of oxygen in water depends

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upon temperature and pressure. The solubility decreases with temperature, at a given pressure, so that it is obviously advantageous to maintain the boiler feed water at as high a temperature as possible. It is also essential to provide venting to the atmosphere in the feed system, so that any oxygen or other gases released from condensate, or raw water make-up, can be expelled. The vent should release a certain amount of vapour, in order that no atmospheric oxygen can enter the system. Condensate collection vessels and feed tanks should be covered, except for the venting, and pump glands maintained in good order for the same reason. Thus once again the need for a maximum of steam condensate return is paramount, and for the purposes of oxygen content the condensate should be as hot as possible. In any steam plant some make-up must be used to replace unavoidable losses and the make-up should also be as hot as possible in order to have the minimum oxygen content. In large boiler plants feed de-aerators are used to remove oxygen before feed entry into the boiler. These units consist essentially of a combination heater and flash tank in which the boiler feed is heated and flashed, to allow dissolved oxygen to be released and removed. The residual oxygen left in the feed after the de-aerator is treated inside the boiler. For sugar mill installations de-aerators are usually uneconomical, as the oxygen present in the feed water can be removed chemically inside the boiler. This is normally achieved by the use of hydrazine or sodium sulphite. Hydrazine, a compound of nitrogen and hydrogen, N 2 H 4 , is used in high pressure installations where dissolved solids are a problem, because both products of the reaction are inert, one being water and the other nitrogen. The latter goes out in the steam and is vented through the non-condensible gas vents. The commonly used substance for internal oxygen removal is sodium sulphite. This chemical absorbs oxygen to form sodium sulphate. The sodium sulphate formed is not scale forming and is beneficial from the point of view of embrittlement control, as will be seen later. This chemical, if added in the correct manner and in such quantities as to keep a reserve of sulphite in the boiler at all times, can completely remove all significant oxygen corrosion and, coupled with alkalinity control, should result in the complete avoidance of boiler corrosion. Once again, as with scale-forming materials, the feeding of oxygen or acids to the boiler should be avoided, as these cause increased dosage of chemicals, with consequent higher solids, greater blowdown and the resultant chemical wastage. Caustic Embrittlement—There has been a certain amount of argument as to the existence and severity of cracking caused by a caustic environment, but it is now generally agreed t h a t caustic embrittlement can only occur under the following conditions:— (a) The water in the boiler must contain free hydroxide alkalinity. (b) The caustic soda must become concentrated to an extent which is usually only possible in a joint or seam where evaporative leakage can take place. (c) The tensional stress in the steel must be high at the point where the concentration of caustic soda is occurring. There are several ways of ensuring that this cracking does not occur. If the phosphate level is high enough in a boiler, all the free hydroxide will be reacted with to form the harmless compound tri-sodium phosphate. This needs a very fine degree of chemical control, and while most of the alkalinity in a boiler will, under correct conditions, be in the form of tri-sodium phosphate, inhibitors are usually added to ensure that embrittlement cannot

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occur. Three c o m m o n inhibitors are used, sodium sulphate, sodium nitrate, and quebracho tannins. Providing these are used correctly t h e incidence of c a u s t i c e m b r i t t l e m e n t , w h i c h i s r a r e i n a n y case, c a n b e d i s c o u n t e d . T h e Production of Glean S t e a m Free f r o m Entrained Water or Solids T h e p r e v e n t i o n o f p r i m i n g , o r c a r r y o v e r , i n boilers d e p e n d s u p o n t h r e e main factors:— (a) T h e d i s s o l v e d solids c o n c e n t r a t i o n i n t h e w a t e r . (b) T h e p r e s e n c e of f o a m p r o d u c i n g solids. (c) T h e d e g r e e a n d s e v e r i t y of l o a d fluctuations. A boiler w a t e r c o n t a i n i n g a h i g h solids c o n t e n t is m o r e p r o n e to f o a m t h a n o n e w i t h a l o w solids w a t e r , a n d to t h i s e n d , t h e solids c o n t e n t of a boiler water m u s t be kept under control. This is achieved by means of blowdown. All feed w a t e r will c o n t a i n s o m e dissolved solids, a n d o b v i o u s l y , if s t e a m free from e n t r a i n e d solids i s b e i n g p r o d u c e d , t h e solids will c o n c e n t r a t e i n t h e boiler w a t e r . To c o u n t e r a c t t h i s , s o m e of t h e boiler w a t e r is b l o w n d o w n o u t of t h e boiler, a n d r e p l a c e d b y low solids feed. T h e a m o u n t o f b l o w d o w n necess a r y will t h u s o b v i o u s l y d e p e n d u p o n t h e solids c o n t e n t o f t h e feed w a t e r a n d t h e a c c e p t a b l e solids level i n t h e boiler. B l o w d o w n s h o u l d b e k e p t t o a m i n i m u m , a s s t r e s s e d before, t o a v o i d c h e m i c a l losses, a n d t h e r e f o r e t h e solids content of the feed water should be kept to a m i n i m u m . Yet another reason for t h e u s e of u n c o n t a m i n a t e d c o n d e n s a t e for feed. T h e a l l o w a b l e solids level in a boiler will v a r y w i t h t h e t y p e of boiler in use a n d t h e c o n d i t i o n s u n d e r w h i c h i t o p e r a t e s . T h e n e w e r w a t e r wall boilers o f h i g h h e a t l o a d i n g will n o t t o l e r a t e t h e solids level a c c e p t a b l e i n t h e o l d e r t y p e s o f boiler a n d m u s t b e w a t c h e d m o r e carefully, p a r t i c u l a r l y u n d e r c o n d i t i o n s o f f l u c t u a t i n g l o a d . F l u c t u a t i n g l o a d causes v a r i a t i o n s i n h e a t t r a n s f e r across t h e boiler h e a t i n g surface a n d v a r i a t i o n s i n p r e s s u r e i n t h e boiler d r u m . A s u d d e n i n c r e a s e in l o a d c a u s e s d r u m p r e s s u r e to d r o p w h i c h r e s u l t s in a r a p i d rise in w a t e r level, w h i c h , if severe, c a n c a u s e c o n s i d e r a b l e p r i m i n g . T h e m a i n f o a m p r o d u c i n g c o n d i t i o n s a r e excessive a l k a l i n i t y a n d t h e p r e s e n c e o f oil. E x c e s s i v e a l k a l i n i t y c a n b e a v o i d e d b y c h e m i c a l c o n t r o l a n d t h e i n c i d e n c e o f oil s h o u l d b e k e p t t o a m i n i m u m b y e l i m i n a t i n g oil c o n t a m i n a t i o n of t h e s t e a m as far as possible. S o m e of t h e oil u n a v o i d a b l y fed to a boiler will b e c a r r i e d d o w n w i t h t h e a l k a l i - p h o s p h a t e p r e c i p i t a t e , b u t oil c o n t a m i n a t i o n s h o u l d b e m i n i m i z e d a s i t h a s a n o t h e r serious effect. Oil globules c a n a t t a c h t h e m s e l v e s t o t h e h e a t i n g surfaces o f t h e boiler. I f t h i s occurs, t h e h e a t transfer resistance at this point increases m a r k e d l y a n d t h e t u b e m a y o v e r h e a t a n d fail. S o m e t i m e s a n t i - f o a m c h e m i c a l s , u s u a l l y c o m p l e x polyamides or polyoxides, are introduced into t h e boiler to reduce t h e danger of f o a m i n g . B l o w d o w n f r o m a boiler also s e r v e s t o r e m o v e t h e alkali p h o s p h a t e p r e c i p i t a t e , s o t h a t b l o w d o w n p o i n t s a r e p l a c e d a t t h e l o w e s t levels i n t h e boiler. T h e s e p o i n t s a r e o p e n e d a t i n t e r v a l s , t h e f r e q u e n c y a n d i n t e r v a l o f opening depending upon the a m o u n t of blowdown required. In some of the m o d e r n b o i l e r s a c o n t i n u o u s b l o w d o w n i s i n s t a l l e d a s well, u s u a l l y i n t h e t o p d r u m , t o effect c o n t i n u o u s r e m o v a l o f s o m e o f t h e h i g h solids w a t e r . Sampling, Methods of Analysis and Chemical Dosage B . S . 1328 " M e t h o d s o f S a m p l i n g W a t e r u s e d i n I n d u s t r y " c o v e r s t h e s u b j e c t o f s a m p l i n g fully a n d i t will suffice t o s a y t h a t t h e w a t e r i n e a c h boiler m u s t b e s a m p l e d s e p a r a t e l y a n d t h e s a m p l e cooled before collecting. Coil t y p e coolers a r e u s u a l l y u s e d for t h i s p u r p o s e . T h e s a m p l e i s g e n e r a l l y t a k e n from

T H E B O I L E R STATION

the boiler shell or from the water gauge. The sampling container should be a closed vessel, for accuracy of sulphite results, and it is axiomatic that the water from the sampling point should be allowed to run for a sufficient time before the sampling commences, to ensure that a representative sample is obtained. For good control it is recommended that the samples should be analysed, at least once a day, for: — Alkalinity, Phosphate, Sulphite, Hardness, Total Dissolved Solids Determination of pH at more frequent intervals can indicate whether any abnormal incidence of contamination has occurred. If sulphate is used for caustic embrittlement control, the sulphate to caustic ratio should be determined periodically. The methods of carrying out these analyses and the levels recommended in the boiler may vary slightly between treatment systems, but can be generally stated as follows:— Alkalinity—This is best determined by titration, as this is a more accurate and sensitive method than pH measurement, although pH is useful for quick checks on boiler conditions. There are several methods of carrying out alkalinity titrations and the limits of alkalinity set out in the treatment being used should be adhered to. A minimum alkalinity is required for acidity control and for the correct operation of the alkali-phosphate treatment. This usually coincides with an alkalinity, to phenolphthalein, of approximately 150 p.p.m. expressed as CaC0 3 . A maximum alkalinity is obviously set to avoid foaming, and this is normally at about 800 p.p.m. of total alkalinity. These figures coincide with a pH range of approximately 10.5 to 11.5. Phosphate—Once again set limits vary a little but a figure of 50 to 60 p.p.m. expressed as P 0 4 is normal. Excess phosphate is not harmful except in that it adds solids to the water. Sodium sulphite—The limits necessary for this compound to act effectively depend upon the reaction time available and whether or not a catalysing agent is used. Sodium sulphite takes a definite time to absorb oxygen depending on the temperature and, if possible, the reaction should have time to proceed before the feed enters the boiler. The sulphite is thus best added well back in the feed system, but should be added after the system is vented. Adding sulphite before venting results in wastage of chemicals, because the sulphite will absorb oxygen which would have been removed in any case by venting. The rate of reaction can be speeded up by two methods, an increase of sulphite concentration and the presence of a catalyst (usually a cobalt salt) with the sulphite. The first method has the only objection that the solids content of the boiler is increased and more sulphite is lost in blowdown, while the catalyst has the drawback t h a t the sulphite must sometimes be added and given time to react before the caustic is added, as high alkalinity may precipitate certain types of catalyst. With the first method a sulphite reserve of 100 to 200 p.p.m. as Na 2 S0 3 , is usually kept in the boiler, while with the second method a minimum reserve of some 40 p.p.m. is kept. The analysis for sulphite is a titration method which is a little more complex than an alkalinity determination, and is based on an iodimetric titration using starch as an indicator.

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Hardness—If t h e a l k a l i n i t y level a n d p h o s p h a t e level a r e c o r r e c t , boiler w a t e r h a r d n e s s will always be zero. A s o a p m e t h o d is sufficiently a c c u r a t e for t h i s d e t e r m i n a t i o n , a n d i t i s m e r e l y u s e d a s a d o u b l e c h e c k for p h o s p h a t e a n d alkalinity. Total Dissolved Solids—This is m o s t c o n v e n i e n t l y d e t e r m i n e d as a r o u t i n e m a t t e r b y u s i n g a special t y p e o f h y d r o m e t e r . T h i s m e t h o d s h o u l d b e c h e c k e d p e r i o d i c a l l y by a l a b o r a t o r y m e t h o d i n v o l v i n g t h e e v a p o r a t i o n of a s a m p l e o f w a t e r a n d w e i g h i n g t h e r e s i d u e . T h e l i m i t s for t o t a l dissolved solids v a r y , a s s t a t e d before, d e p e n d i n g o n t h e t y p e o f boiler, t y p e o f w a t e r , s t e a d i n e s s o f t h e l o a d a n d use o f a n t i f o a m . T h e m a n u f a c t u r e r ' s r e c o m m e n d a t i o n s s h o u l d b e a d h e r e d t o i n t h i s case. A n t i f o a m s , w h e n used, a r e n o r m a l l y a d d e d i n a fixed r a t i o t o feed w a t e r f l o w . Caustic Embrittlement Control—Where t a n n i n s a r e u s e d t h e s e a r e n o r m a l l y a d d e d w i t h , a n d i n a fixed p r o p o r t i o n t o p h o s p h a t e . N i t r a t e , w h e n used, is a d d e d so t h a t t h e ratio of n i t r a t e to alkalinity is a certain m i n i m u m figure. T h e s a m e i s t r u e o f s u l p h a t e . T h e r a t i o o f s o d i u m s u l p h a t e t o c a u s t i c soda should be a m i n i m u m of 2.5. A n y sulphate required, additional to t h a t produced by the oxidation of sulphite, is added as sodium sulphate. These n i t r a t e a n d sulphate tests need normally only be done occasionally a n d a r e often c a r r i e d o u t , a s a service, b y t h e c h e m i c a l t r e a t m e n t s u p p l i e r . T h e a n a l y s e s r e q u i r e d for t h e s e d e t e r m i n a t i o n s a r e r a t h e r c o m p l e x i n n a t u r e . D e t a i l s of s i m p l e m e t h o d s of a n a l y s i s for a l k a l i n i t y , p h o s p h a t e , s u l p h i t e , h a r d n e s s , t o t a l dissolved solids, a n d s u l p h a t e will b e f o u n d i n t h e r e l e v a n t c h a p t e r o f t h i s m a n u a l a n d f u r t h e r i n f o r m a t i o n c a n b e f o u n d i n B . S . 1427 a n d B.S. 2690. O t h e r suitable l a b o r a t o r y m e t h o d s m a y be used at t h e discret i o n of t h e o p e r a t o r . Methods of Chemical Dosage—Chemicals c a n be a d d e d to a boiler c o n t i n u o u s l y o r i n slug doses. I n o r d e r t o m a i n t a i n c h e m i c a l c o n c e n t r a t i o n a t a n e v e n level, c o n t i n u o u s d o s i n g i s u s e d w h e r e v e r possible. T h u s c a u s t i c s o d a , s o d i u m s u l p h i t e a n d a n t i f o a m (where used) a r e n o r m a l l y d o s e d c o n t i n u o u s l y . I f t h e s o d i u m s u l p h i t e i s n o t u s e d w i t h a c c e l e r a t o r all t h r e e c h e m i c a l s c a n b e m i x e d t o g e t h e r a n d a d d e d c o n t i n u o u s l y after t h e feed v e n t . I f accelerator is used, t h e sulphite should be added, by a separate dosing p u m p , a s e a r l y i n t h e s y s t e m a s possible, a n d t h e c a u s t i c a d d e d j u s t before t h e feed e n t e r s t h e boiler. T h e q u a n t i t i e s a d d e d a r e c a l c u l a t e d from t h e a n a l y s e s o f ,the w a t e r a n d b a s e d o n e s t i m a t e d d e m a n d . Sufficient c h e m i c a l s for t h e n e x t 2 4 hours are usually mixed in a predetermined q u a n t i t y of water, and the dosing p u m p set to deliver this volume in t h e 24 h o u r period. U n f o r t u n a t e l y , p h o s p h a t e c a n n o t b e a d d e d c o n t i n u o u s l y t o t h e feed lines, a s u n d e r t h e s e c i r c u m s t a n c e s , c a l c i u m p h o s p h a t e c a n b e p r e c i p i t a t e d i n t h e feed lines t h u s g r a d u a l l y b l o c k i n g t h e m . A h i g h p r e s s u r e slug d o s i n g p u m p , w i t h individual connections t o e a c h boiler, i s n o r m a l l y u s e d t o a d d p h o s p h a t e a c c o r d i n g t o e a c h b o i l e r ' s d e m a n d . T h i s p u m p i s also c o n v e n i e n t l y u s e d t o a d d c a u s t i c o r s u l p h i t e t o i n d i v i d u a l boilers t o m a i n t a i n b a l a n c e d c o n c e n t r a t i o n s b e t w e e n boilers, i f t h e y v a r y d u e t o v a r y i n g l o a d o r feed c o n d i t i o n s . S l u g d o s a g e o n c e in 24 h o u r s is n o r m a l l y sufficient, b u t if t h i s is n o t so, a p H a n d t o t a l dissolved solids c h e c k c a n b e t a k e n once a shift, t o decide w h e t h e r a n y t h i n g abnormal has occurred, and further action t a k e n if r e q u i r e d . P r o b l e m s of Boiler Feed Treatment Peculiar to the Sugar Industry T h e r e a r e c e r t a i n p r o b l e m s o f boiler feed t r e a t m e n t w h i c h a r e p e c u l i a r t o t h e s u g a r i n d u s t r y . A s well a s h a v i n g t o c o n t e n d w i t h t h e u s u a l c o n t a -

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minants, such as scale-forming compounds and oxygen, contamination of condensates by the material being processed may be caused by leaking heater tubes, and other faults. This results in sugar entering the feed water and, unfortunately, from the point of view of boiler feed treatment, this is most undesirable. Sugar and reducing sugars, under the influence of heat, break down in solution to form a series of acidic compounds known collectively as saccharic (or sugar) acids. It has been stressed, in the section under corrosion, that acid conditions are most corrosive to steel. Sugar contamination to any extent can result in very acid conditions in the boiler, and this will cause serious corrosion. To counteract the acidity from sugar contamination more caustic soda must be added to the boiler, resulting in increased, and sometimes dangerously high, solids levels in the boiler. This can cause carryover of water and solids. Cases of serious turbine trouble, due to carbon and other products building up on the turbine blades, are not unknown. The elimination of sugar contamination is therefore most important. To this end checks for sugar must be made regularly on the feed water and, if sugar in any significant concentration is found, the source must be located by further testing. The most serious contamination can be obtained from a split juice heater tube, as the juice in the heater is under pressure, and this can lead to gross contamination of condensates. Leaking effet and pan tubes can, of course, cause serious trouble, but this normally only occurs when the effets or pan concerned are shut down. Condensate checking can be carried out by various chemical means, from the simple, roughly quantitative alpha-naphthol test, to the more precise and complex methods. Obviously an instrument to monitor condensate contamination continuously, is the ideal answer. Various instruments using chemical methods have been developed for this purpose but, as yet, they are slow in reaction and rather tedious to maintain. Sugar contamination in a raw sugar factory is always in the form of impure solutions which carry other materials besides sugar. Many of these impurities are electrolytes, that is, they are ionized in solution, and are conductors of electric current. Thus the conductivity of a condensate can be a guide to its sugar content. At present sizeable contamination can be detected in this way, and the method can be used in conjunction with a multipoint conductivity recorder, which can monitor every source of boiler feed in rapid succession, and operate automatic valves to divert any contaminated condensate away from boiler feed. It can therefore be seen that for a sugar mill, the boiler feed should consist mainly of hot, un-contaminated exhaust steam condensate. Some make-up is always required and the make-up water should ideally be hot, to avoid dissolved oxygen, and as free from contamination as possible, to avoid scaling problems. The best source of make-up is usually the condensate from the steam space of the second effet vessel. This water is hotter and usually less contaminated with entrained juice than is water from vessels further down the set. At times, cold, raw water must be used as make-up. If possible, this should be heated and vented before pumping to the feed tank, so that the entry of dissolved oxygen is reduced to a minimum. The use of raw water can also be minimized by the provision of a reasonable amount of feed storage, as this can tide the boilers over short mill stops. A storage capacity approaching an hour's feed supply is desirable, if possible, and raw water should only be added once this storage is exhausted. If boiler water conditions are maintained correctly, at all times, the incidence of corrosion should be negligible, and the cleaning of boiler tubes completely avoided.

CHAPTER X I I I FIRST AID Shock Shock occurs with all injuries to a greater or lesser extent and may be serious enough to cause death. The symptoms are paleness, moist skin and trembling, and an expression of extreme anxiety. Keep the patient warm and cover with blankets or coats. The patient should lie flat, preferably with a pillow or two under the lower limbs. Lowering the head is usually uncomfortable and not always essential. Do not move unnecessarily. Do not give fluids of any kind by mouth. Remove from danger, check haemorrhage, make comfortable. Await ambulance. Electric Shock Quickly switch off the current or cautiously remove contact from the patient with an insulator, e.g., a dry stick or dry towel. Start artificial respiration and external cardiac massage immediately (see later). Keep the patient warm with blankets and jars of hot water. Do not regard early rigidity as a sign for ceasing artificial respiration. It should be maintained for at least four hours. Heat Exhaustion After it is certain that the patient has collapsed due to heat exhaustion, plenty of cold water in which a salt tablet has been dissolved may be given, provided the patient is not nauseous or vomiting. Removal to hospital is imperative. Fainting The patient should lie flat as indicated under "Shock". Loosen the clothing round the patient's neck and see that he gets plenty of fresh air. Sprinkle face and chest with cold water. Give stimulants when the patient can swallow. Burns Dry Heat and Scalds—In the treatment of burns the main object is to exclude the air as quickly as possible from the injured part. For minor burns wash with plenty of soap and water. For such burns on the face and hands apply dressings with gauze or lint impregnated with sterile vaseline. On other parts of the body burns should be covered with tannic acid jelly. No dressing should be applied and cloths must not be replaced until the coagulum is dry. For serious burns apply sterile vaseline on gauze and remove to hospital. Acid—Wash immediately and thoroughly with cold water and then with dilute sodium bicarbonate solution. Apply picrate or boric ointment or acriflavine solution. Alkali—Wash immediately with large quantities of water then with a five per cent solution of acetic acid. Dress with picrate or boric ointment or sterile vaseline. Prepared in collaboration with the Division of Industrial Medicine, Department of Health.

182

FIRST AID

Burns in the Eyes—Flush immediately with large quantities of water. Irrigation of the eye should be continued for at least ten minutes, and often for longer periods after alkali splashes. Cover eye, refer to hospital for further treatment. Wounds Even severe bleeding may be stopped by the application of a very firm pressure bandage over the wound. A tourniquet should only be applied if it is obvious that the wound is unmanageable. If the wound is on the arm, leg, hand or foot and the blood is scarlet, apply the tourniquet four inches below the armpit or four inches below the groin. If the blood is dark and purplish apply the tourniquet below the wound. A piece of rubber tubing or a necktie will make a good tourniquet. NOTE—Under no conditions should the tourniquet be held tight for longer than 15 minutes at a time. Loosen it and allow blood to flow for a few seconds, then retighten it. Loosen but do not remove the tourniquet as soon as the blood clots. If the bleeding is copious and the wound is in a position where a tourniquet cannot be applied, place a pad of sterile gauze, soaked with acriflavine in the wound and apply a bandage. For slight cuts, clean the wound with acriflavine solution (1 in 1000) and apply a dressing of this material. General: All cases must be removed to hospital as soon as possible after first aid treatment is carried out. Poisoning Strong Acids—Mouth and lips may be stained. Do not induce vomiting. Give magnesium oxide, milk of magnesia or lime water immediately. Repeat at short intervals and wash out the mouth with one of the above materials. Do not give carbonates but milk or white of egg should be given. Combat collapse by placing patient in reclining position, and applying blankets, hot water bottles, etc. Alkalies—Mouth and lips may be stained. Do not induce vomiting, but give a five per cent solution of acetic acid, or vinegar until the alkali appears to be neutralised. Give white of egg or milk and combat collapse. Note—Cream or any vegetable oil may be given in each case. Carbolic Acid—Give milk or vegetable oil, induce vomiting, repeat oil, remove to hospital. Cyanide—Speed is essential. A doctor should be telephoned immediately and advised that intravenous antidotes and the necessary syringes are held by the laboratory concerned if such is the case. Unless cyanide accidents are more than a remote possibility, it should not be necessary to hold ampoules of the antidotes, but the capsules described hereunder are essential. If cyanide has been swallowed or if the patient has been poisoned in a contaminated atmosphere, observe the following procedure:— (1) Remove patient immediately to uncontaminated atmosphere. (2) Break capsule of amyl nitrite under the patient's nose every five (5) minutes. (3) Inject ten ml of sodium nitrite three per cent intravenously, followed immediately by 50 ml of sodium thiosulphate 25 per cent.

FIRST AID

183

(4) Artificial respiration must be maintained continuously if patient is not breathing. Phosphorus—Induce vomiting, give four oz of mineral oil, followed by saline purge, e.g. Epsom salts. Note—To induce vomiting, give fairly large amount of milk, water, coca-cola etc. and push finger far down back of tongue. Gases and Fumes Corrosive Gases—Carry the patient into fresh air and apply artificial respiration if necessary. Combat collapse. Give oxygen if available. Carbon Monoxide, Hydrogen Sulphide and Nitrous Fumes—Remove the patient to fresh air. Apply artificial respiration and give oxygen. Combat collapse. Artificial Respiration Artificial respiration may be applied in any circumstances where the patient has ceased to breathe, e.g., drowning, electrocution, cyanide poisoning, gassing or other causes. Mouth-to-mouth resuscitation is the most effective method and may be applied as follows:— Place patient on his back and rapidly clear obstructions in the mouth. Stretch the neck by tilting the head back as far as possible. Hold the head back at all times. Pinch nostrils closed with thumb and fore-finger of one hand and keep the jaw open and the chin up with the other hand. Take a deep breath, open your mouth wide, and seal your lips around the patient's mouth. Blow air into the patient and watch to see that his chest rises. If this does not happen, tilt the head further and lift the chin up again. If the chest rises, remove your mouth and the patient's chest will collapse. Continue inflation in this way at least ten to 12 times a minute. External Cardiac Massage If the patient is unconscious, not breathing and apparently pulseless, immediately initiate both mouth-to-mouth resuscitation as above, and cardiac (heart) massage. Place patient face up. Get someone else to proceed with mouth-to-mouth resuscitation. Kneel beside patient. Apply palm of one hand over the bottom of the chest plate (breast bone). Bring palm of the other hand on top of the first. Now bring your weight rhythmically down at about a rate of 50 to 60 times a minute. Continue for 20 minutes. Foreign Body in the Eye If possible remove with corner of a clean handkerchief, but use great care; if not, wash out with boracic lotion. Apply a pad and bandage firmly to prevent movement of the eyelid. If the surface of the eyeball is injured use only irrigation and send for a doctor. Alternate treatment—Apply eyedrops of albucid soluble ten per cent in water (sodium sulphacetamide) by pulling forward lower lid and using a small rubber sponge. Remove foreign body with the sponge if possible. If this fails apply a pad and bandage as before and send for expert treatment. If the surface of the eyeball is injured apply the albucid drops, the pad and bandage, and send for a doctor.

REFERENCE T A B L E S Table No. I

TITLE Page Temperature Corrections to Readings of Brix Hydrometers (Calibrated at 20 °C.) 186

II

Schmitz's Table for Sucrose (Pol) in Juice for Use in the Dry Lead Method with Undiluted Solutions. Normal Weight of 26.000 g.

188

III

Pol Bagasse from Polariscope Reading (400 mm Tube) and Moisture Content. (Ratio of water to bagasse =10:1). (Clarified with dry lead).

193

IV

Milligrammes of Reducing Sugars Required to Reduce 10 ml Fehling's Solution (Lane and Eynon Method).

195

V

Milligrammes of Reducing Sugars Required to Reduce 10 m Fehling's Solution (Lane and Eynon Method) at Low Sucrose Concentrations. To be Used with the Chemical Method of Sucrose Analysis.

196

Specific Rotation of Sugars.

197

VI VII VIII IX X XI XII XIII

Refractive Indices of Sugar Solutions at 20 °C in Air at 20 °C, 760 mm Pressure and 50 per cent Relative Humidity. International Table of Temperature Corrections for the Abbe Refractometer Calibrated at 20 °C.

199

Clerget Divisors.

200

198

Subtractive Temperature Corrections for Clerget Divisors.

200

Dilution Indicator of Raw Sugar.

201

Solubility of Sucrose in Water in g Sucrose (S) per 100 g Water According to Charles, Amer. Chem. S o c , 1958 Abst. of Papers p. 100. Reported in Honig "Principles of Sugar Technology", 2, 228. Solubility of Sucrose in Water in g Sucrose (S) per 100 g Solution (Charles).

201 202

XIV

Densities of Solutions of Cane Sugar at 20 °C in g/ml. (This table is the basis for standardizing hydrometers indicating per cent of sugar at 20 °C).

XV

Brix, Apparent Density, Apparent Specific Gravity, and Grammes of Sucrose per 100 ml of Sugar Solutions. (NBS—C440, 1942, p. 632).

206

Weight per Unit Volume of Sugar Solutions at 20 °C.

216

XVI XVII XVIII

203

Degree of Supersaturation—All Values Being Prefixed by 1.

217

Crystal Content of Massecuites.

218

X I X (a) Stock Recovery.

219

X I X (b) Stock Recovery.

220

X I X (c) Stock Recovery.

221

XX

Factors to be Used in Calculating Weight per Gallon of Molasses.

222

XXI XXII

Weights as Decimals of Ton. Density (g/ml) of Water at Temperatures from 0 to 102 °C. According to M. Thiesen, Wiss. Abh. der Physikalisch-Technischen Reichsanstalt, 4, No. 1; 1904.

222 223

XXIII

Corrections for Temperature (in g) to Be Added to Weight of Water Contained to Obtain Volume (in ml) of Vessel at 20 °C. Nominal Capacity 1,000 ml. (For vessels made of soda glass).

224

R E F E R E N C E TABLES Table No. XXIV XXV XXVI XXVII XXVIII

XXIX XXX

Corrections for Atmospheric Pressure (in g) to Be Added to or Subtracted from the Weight of Water Contained to Obtain Volume (in ml) of Vessel at Standard Temperature and Pressure.

225

Requirements for Apparatus for Use in the Analysis of Cane for Payment Purposes.

226

Properties of Saturated Steam.

229

Temperature Conversion Table.

231

Equivalents Volume and Capacity Equivalents. Mass Equivalents. Density Equivalents. Linear Measure Equivalents. Surface and Area Equivalents. Pressure Equivalents. Heat, Energy and Work Equivalents. Heat Flow Equivalents. Mensuration of Surfaces and Solids.

232 234

Circles: Diameters, Areas, Circumferences.

235

Capacities of Vertical Cylindrical Tanks (UK gal).

235

Capacities of Rectangular Tanks (UK gal) for Each Foot of Depth.

236

XXXIII

Capacity of Horizontal Cylindrical Tanks at Varying Levels. i = depth of liquid, d = diameter of vessel.

237

XXXIV

Amount of CaO in Milk of Lime of Various Densities at 15 °C.

237

XXXI XXXII

XXXV XXXVI

Fuel Value of Bagasse.

238

Boiling Point Elevation of Sugar Solutions and Cane Juices (°F) at 760 mm Pressure.

239

XXXVII

Table for Rapid Filterability Test.

240

XXXVIII

International Atomic Weights, 1966 (Published by the C.R.C. Handbook of Chemistry and Physics).

242

Table I—Temperature Corrections to Readings of Brix Hydrometers (Calibrated at 20 °C) Temperature '

°C 0

5

10

15

£

Observed per cent of sugar 20

25

30

35

40

50

55

60

65

70

75

80

85

90

cent. 1.37 1.05 0.72 0.65 0.58 0.51 0.44 0.36 0.29 0.22 0.15 0.08

1.41 1.08 0.74 0.66 0.59 0.52 0.45 0.37 0.30 0.23 0.15 0.08

1.44 1.10 0.75 0.68 0.60 0.53 0.46 0.38 0.31 0.23 0.15 0.08

1.47 1.12 0.76 0.69 0.61 0.54 0.46 0.38 0.31 0.24 0.16 0.08

1.49 1.14 0.77 0.70 0.62 0.55 0.47 0.39 0.32 0.24 0.16 0.08

1.50 1.16 0.78 0.71 0.63 0.56 0.47 0.39 0.32 0.25 0.16 0.09

1.50 1.17 0.79 0.72 0.64 0.56 0.48 0.40 0.33 0.25 0.16 0.09

1.51 1.18 0.80 0.73 0.64 0.57 0.48 0.40 0.33 0.25 0.17 0.09

1.51 1.19 0.81 0.74 0.65 0.57 0.48 0.41 0.34 0.26 0.17 0.09

per cent. 0.08 0.08 0.15 0.16 0.23 0.24 0.31 0.32 0.38 0.39 0.47 0.47 0.54 0.55 0.62 0.63 0.70 0.71 0.78 0.79 0.87 0.88 0.95 0.96 1.04 1.05 1.12 1.13 1.21 1.22

0.08 0.16 0.24 0.32 0.39 0.48 0.56 0.64 0.72 0.80 0.88 0.97 1.05 1.14 1.22

0.08 0.16 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.89 0.97 1.06 1.14 1.23

0.08 0.16 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.89 0.97 1.06 1.14 1.23

0.09 0.16 0.24 0.32 0.39 0.48 0.56 0.64 0.72 0.81 0.89 0.97 1.06 1.14 1.22

0.09 0.17 0.25 0.33 0.39 0.49 0.57 0.65 0.73 0.81 0.89 0.97 1.06 1.14 1.22

0.09 0.17 0.25 0.33 0.39 0.49 0.57 0.65 0.73 0.81 0.89 0.97 1.06 1.14 1.22

0.09 0.17 0.25 0.33 0.38 0.48 0.56 0.64 0.72 0.81 0.89 0.97 1.06 1.14 1.22

0.09 0.17 0.25 0.33 0.38 0.48 0.56 0.64 0.72 0.81 0.89 0.97 1.05 1.13 1.21

45

0 5 0 1 12 13 14 15 16 17 18 19

0.30 0.36 0.32 0.31 0.29 0.26 0.24 0.20 0.17 0.13 0.09 0.05

0.49 0.47 0.38 0.35 0.32 0.29 0.26 0.22 0.18 0.14 0.10 0.05

0.65 0.56 0.43 0.40 0.36 0.32 0.29 0.24 0.20 0.15 0.10 0.05

0.77 0.65 0.48 0.44 0.40 0.35 0.31 0.26 0.22 0.16 0.11 0.06

0.89 0.73 0.52 0.48 0.43 0.38 0.34 0.28 0.23 0.18 0.12 0.06

0.99 0.80 0.57 0.51 0.46 0.41 0.36 0.30 0.25 0.19 0.13 0.06

Subtract from observed per 1.08 1.16 1.24 1.31 0.86 0.91 0.97 1.01 0.60 0.64 0.67 0.70 0.55 0.58 0.60 0.63 0.50 0.52 0.54 0.56 0.44 0.46 0.48 0.49 0.38 0.40 0.41 0.42 0.32 0.33 0.34 0.36 0.26 0.27 0.28 0.28 0.20 0.20 0.21 0.21 0.13 0.14 0.14 0.14 0.07 0.07 0.07 0.07

50 21 22 23 24 25 26 27 28 29 JO M 12 J3 \4 \5

0.04 0.10 0.16 0.21 0.27 0.33 0.40 0.46 0.54 0.61 0.69 0.76 0.84 0.91 0.99

0.05 0.10 0.16 0.22 0.28 0.34 0.41 0.47 0.55 0.62 0.70 0.78 0.85 0.93 1.01

0.06 0.11 0.17 0.23 0.30 0.36 0.42 0.49 0.56 0.63 0.71 0.79 0.87 0.95 1.02

0.06 0.12 0.17 0.24 0.31 0.37 0.44 0.51 0.59 0.66 0.74 0.82 0.90 0.98 1.06

0.06 0.12 0.19 0.26 0.32 0.40 0.46 0.54 0.61 0.68 0.76 0.85 0.93 1.02 1.10

0.07 0.13 0.20 0.27 0.34 0.40 0.48 0.56 0.63 0.70 0.79 0.87 0.96 1.04 1.13

0.07 0.14 0.21 0.28 0.35 0.42 0.50 0.58 0.66 0.73 0.82 0.90 0.99 1.07 1.16

Add to observed 0.07 0.07 0.14 0.14 0.21 0.22 0.29 0.30 0.36 0.38 0.44 0.46 0.52 0.54 0.60 0.61 0.68 0.70 0.76 0.78 0.84 0.86 0.93 0.95 1.01 1.03 1.10 1.12 1.18 1.20

Table I—continued. Tmperature °C

Observed per cent of sugar 0

p

5

10

15

20

25

30

35

40

45

50

per cent. 1.30 1.31 1.39 1.39 1.47 1.48 1.56 1.56 1.65 1.65

55

60

65

70

75

80

85

90

1.31 1.39 1.48 1.56 1.65

1.32 1.40 1.49 1.57 1.66

1.32 1.40 1.49 1.57 1.66

1.31 1.39 1.48 1.56 1.65

1.31 1.39 1.48 1.56 1.65

1.30 1.39 1.47 1.56 1.64

1.30 1.39 1.47 1.56 1.64

1.29 1.38 1.46 1.55 1.63

1.07 1.15 1.24 1.33 1.42

1.09 1.17 1.26 1.35 1.45

1.12 1.21 1.29 1.38 1.47

1.15 1.24 1.33 1.42 1.51

1.19 1.28 1.36 1.45 1.54

1.22 1.31 1.39 1.48 1.57

Add to observed 1.25 1.27 1.29 1.34 1.36 1.38 1.42 1.44 1.46 1.51 1.53 1.55 1.62 1.62 1.64

1.51 1.61 1.71 1.81 1.91

1.54 1.64 1.74 1.84 1.94

1.56 1.66 1.76 1.86 1.96

1.60 1.70 1.80 1.90 2.00

1.63 1.73 1.83 1.93 2.03

1.67 1.76 1.86 1.95 2.05

1.69 1.79 1.88 1.98 2.07

1.71 1.81 1.90 2.00 2.09

1.73 1.82 1.92 2.01 2.10

1.74 1.83 1.92 2.01 2.10

1.74 1.83 1.92 2.01 2.10

1.74 1.83 1.92 2.01 2.10

1.75 1.84 1.92 2.01 2.10

1.75 1.83 1.92 2.00 2.09

1.74 1.82 1.91 1.99 2.08

1.73 1.82 1.90 1.99 2.07

1.72 1.81 1.89 1.98 2.06

1.72 1.80 1.89 1.97 2.05

1.71 1.79 1.88 1.96 2.04

2.01 2.12 2.23 2.35 2.46

2.05 2.16 2.26 2.37 2.48

2.07 2.18 2.28 2.39 2.50

2.11 2.21 2.32 2.42 2.53

2.14 2.24 2.35 2.45 2.56

2.15 2.26 2.36 2.47 2.57

2.17 2.27 2.38 2.48 2.58

2.19 2.29 2.39 2.49 2.59

2.20 2.30 2.39 2.49 2.59

2.20 2.29 2.39 2.48 2.58

2.20 2.29 2.39 2.48 2.58

2.19 2.29 2.39 2.48 2.57

2.19 2.28 2.38 2.47 2.56

2.18 2.27 2.36 2.45 2.54

2.17 2.26 2.34 2.43 2.52

2.16 2.24 2.33 2.41 2.50

2.14 2.23 2.31 2.40 2.48

2.13 2.21 2.30 2.38 2.46

2.12 2.20 2.28 2.36 2.44

2.58 2.70 2.81 2.93 3.05

2.60 2.72 2.83 2.95 3.07

2.62 2.74 2.85 2.97 3.09

2.64 2.76 2.87 2.99 3.12

2.67 2.78 2.90 3.01 3.12

2.68 2.79 2.90 3.01 3.12

2.69 2.80 2.90 3.01 3.12

2.69 2.80 2.90 3.01 3.11

2.69 2.79 2.90 3.00 3.10

2.68 2.78 2.88 2.98 3.08

2.68 2.78 2.87 2.97 3.07

2.67 2.76 2.86 2.95 3.05

2.65 2.75 2.84 2.94 3.03

2.63 2.72 2.82 2.91 3.00

2.61 2.70 2.79 2.88 2.97

2.59 2.68 2.76 2.85 2.94

2.57 2.65 2.74 2.82 2.91

2.54 2.63 2.71 2.80 2.88

2.52 2.60 2.69 2.77 2.85

3.18 3.20 3.31 3.33 3.43 ! 3.46 3.56 ! 3.59 3v69 3.72

3.22 3.35 3.47 3.60 3.73

3.23 3.35 3.48 3.60 3.73

3.24 3.36 3.48 3.60 3.72

3.24 3.35 3.47 3.58 3.70

3.23 3.34 3.45 3.56 3.67

3.22 3.33 3.43 3.54 3.65

3.20 3.31 3.41 3.52 3.62

3.18 3.29 3.39 3.50 3.60

3.17 3.27 3.37 3.47 3.57

3.15 3.25 3.34 3.44 3.54

3.12 3.22 3.31 3.41 3.50

3.09 3.19 3.28 3.38 3.47

3.06 3.15 3.25 3.34 3.43

3.03 3.12 3.21 3.30 3.39

3.00 3.09 3.17 3.26 3.35

2.97 3.05 3.14 3.22 3.31

2.93 3.02 3.10 3.19 3.27

This table is calculated using the data on thermal expansion of sugar solutions by Plato assuming the instrument to be of Jena 16111 glass. The table should be used with caution and only for approximate results when the temperature differs much from the standard temperature or from the temperature of the surrounding air.

Table H—Schmitz's Table for Sucrose (Pol) in Juice for Use in the Dry Lead Method with Undiluted Solutions. Normal Weight of 26.000 g. Polariscope reading

-

2 3 4 5

6 7 8 9 10

Degrees Brix

Polariscope reading

10

15

20

2 5

30

3 5

40

4 5

5 0

5 5

6 0

6 5

7 0

7-5

8 0

8-5

9 0

9 5

10 0

10 5

11 0

0-26 0-52 0-78 104 1-30

0-26 0-52 0-78 1-04 130

026 0-52 0-78 1-04 1-29

026 0-52 0-78 103 129

0-26 0-62 0-77 103 1-29

0-26 0-51 0-77 1-03 1-29

0-26 0-51 0-77 103 1-28

0-26 0-51 0-77 103 1-28

026 051 0-77 102 1-28

0'26 0-51 0-77 102 1-28

0-25 0-51 0-76 102 1-27

0-25 0-51 0-76 102 1-27

0-25 0-51 0-76 1-02 1-27

0-25 0-51 076 1-01 1-27

025 0-51 0-76 1-01 1-26

0-25 0-50 0-76 1-01 1-26

0-25 0-60 0-76 1-01 1-26

025 0-50 0-75 101 1-26

0-25 0-50 0-75 1-00 1-25

0-25 0-50 0-75 1-00 1-25

0-25 0-50 0-75 100 1-25

2 3 4 5

1-56 1-82

1-55 1-81 2-07

1-55 1-81 207 2-33

1-55 1-81 2-06 2-32 258

1-54 1-80 2-06 232 2-57

1-54 1-80 2-06 2-31 2-57

1-54 1-80 2-05 2-31 2-56

1-54 1-70 205 2-30 2-56

1-53 1-79 2-04 2-30 2-55

1-53 1-78 204 2-29 2-55

1-53 1-78 2 04 2-29 2-54

1-52 1-78 203 2-29 2-54

1-52 1-77 203 2-28 253

1-52 1-77 202 2-28 2-53

1-51 1-77 2 02 2-27 2-52

1-51 1-76 2-02 2-27 2-52

151 1-76 2-01 226 2-51

1-51 1-76 201 2-26 2-51

1-50 1-75 2 00 2-25 2-50

150 1-75 2-00 2-25 2-50

6 7 8 9 10

2-84

2-83 3-09 3-35

2-83 308 3-34 3-60 3-85

2-82 308 3-33 3-59 3-85

2-82 3>07 333 3-58 3-84

2-81 3-07 3-32 3-58 3-83

2-80 306 3-31 3-57 3-82

2-80 305 331 3-56 3-82

2-80 3 05 3-30 3'56 3-81

2-79 3-04 3-29 3-55 3-80

2-78 304 329 3-54 3-79

2-78 303 3-28 3-53 3-79

2-77 302 3-28 353 3-78

2-77 3 02 3-27 3-52 3-77

2-76 3-01 3-26 3-51 3-76

275 301 3-26 351 3-76

2-75 300 3-25 3-50 3-75

11 12 13 14 15

4-10 4-36

410 4-35 4-61 4-86

4-09 4-34 460 4-85 511

4-08 4-33 4-59 4-84 5-10

4-07 433 4-58 4'83 5-09

406 4-32 4-57 4-82 508

4-06 4-31 4-56 4-82 5-07

4-05 4-30 4-55 4-81 5-06

4'04 4-29 4-54 4-80 5-05

403 4-28 4-54 4-79 5-04

4-02 4-27 4-53 4-78 5-03

4-02 4-27 4-52 4-77 5-02

401 4-26 4-51 4-76 5-01

400 4-25 4-50 4-75 500

16 17 18 19 20

5-36

5-35 5-61 5-86

534 5-60 5-85 611 6-36

5-33 5-59 5-84 6 09 6-35

5-32 5-58 5-83 6-08 634

5-31 5-56 5-82 6-07 6-32

5-30 5-55 5-81 6 06 6-31

5-29 554 5-79 605 6-30

5-28 5-53 5-78 6 03 6-29

527 5-52 5-77 6-02 627

5-26 5-51 5-76 601 6-26

5-25 5-50 5-75 6-00 6-25

21 22 23 24 25

6-60 6-86

6-59 6-84 7-10 7-35

6-58 6-83 7-08 7-34 7-59

656 6-82 707 7-32 7-57

6-55 6-80 7-05 7-31 7-56

6-54 6-79 7-04 7-29 7-54

6-52 6-78 7-03 7-28 7-53

6-51 6-76 7-01 7-26 7-51

6-50 6-76 700 7-25 7-50

26 27 28 29 30

7-84

7-83 8-08 8-33

7-81 8-06 8-31 8-57 8-82

7-79 8 05 8-30 8-55 8-80

7-78 803 8-28 8-63 8-78

7-76 801 8-26 8-52 8-77

7-75 8-00 8-25 8-50 8-75

31 32 33 34 35

9-05 9-30

9 03 9-29 9-54 9-79

902 900 9-27 9-25 9-52 9 5 0 9-77 9-75 10-02 10-00

36 37 38 39 40

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 26 29 30

BRixl-OtolOO

31 32 33 34 35

Tenths of the polariscope reading

36 37 38 39 40

0-1 0-2 0-3 0-4 0-5

Per cent sucrose

Tenths of the polariscope reading

Per cent sucrose

0-02 0-05 0-07 0-10 0-13

0-6 0-7 0-8 0-9

0-15 0-18 0-20 0-23

1

_

Table II—continued. Polariscope 1 readmg 11-5 1 12-0 1 12-5 1 13-0

Degr ees Brix 13-5

14-0

145

15 0

15-5

16 0

16 5

17 0

17-5

18 0

18 5

190

19 5

20 0

Polariscope reading 1 2 3 4 5

5

0-25 0-50 0-75 1-00 1-25

0-25 0-50 0-75 1-00 1-24

0-25 0-50 0-74 0-99 1-24

0-25 0-50 0-74 0-99 1-24

0-25 0-49 0-74 0-99 1-24

0-25 0-49 0-74 0-99 1-23

0-25 049 0-74 0-99 1-23

0 : 74 0-98 1-23

0:98 1-23

7 8 9 10

1-50 1-75 2-00 2-24 2-49

1-49 1-49 1-74 1-74 1-99 1 1-99 2-24 2-24 2-49 2-48

1-49 1-74 1-98 2-23 2-48

1-48 1-73 1-98 2-23 2-47

1-48 1-73 1-98 2-22 2-47

1-48 1-73 1-97 2-22 2-46

1-48 1-72 1-97 2-21 2-46

1-47 1-72 1-96 2-20 2-45

1-47 1-71 1-96 2-20 2-45

1-96 2-20 2-44

2-44

11 12 13 14 15

2-74 2-99 3-24 3-49 3-74

2-74 2-99 3-24 3-49 3-73

2-73 2-98 3-23 3-48 3-73

2-73 2-98 3-22 3-47 3-72

2-72 2-97 3-22 3-46 3-71

2-72 2-96 3-21 3-46 3-70

2-71 2-96 3-20 3-45 3-70

2-71 2-95 3-20 3-44 3-69

2-70 2-95 319 3-44 3-68

2-69 2-94 3-18 3-43 3-67

2-69 2-93 318 3-42 3-67

2-93 317 3-42 3-66

2 : 92 317 3-41 3-65

3-40 3-64

16 17 18 19 20

3-99 4-24 4-49 474 499 1

3-98 4-23 4-48 4-73 4-98

398 4-22 4-47 4-72 4-97

3-97 4-22 4-46 4-71 4-96

3-96 4-21 4-45 4-70 4-95

3-95 420 4-45 4-69 4-94

3-94 4-19 4-44 4-68 4-93

3-94 4-18 4-43 4-67 4-92

3-93 417 4-42 4-66 4-91

3-92 416 4-41 4-65 4-90

3-91 4-16 4-40 4-64 4-89

3-90 415 4-39 4-64 4-88

3-90 414 4-38 4-63 4-87

3-89 413 4-37 4-62 4-86

3-88 412 4-36 4-61 4-85

4-'36 4-60 4-84

4-83

21 22 23 24 25

5-24 5-49 5-74 6-99 6-24

5-23 5-48 5-73 5-97 6-22

5-22 5-47 5-71 5-96 6-21

5-21 5-45 5-70 5-95 6-20

5-20 5-44 5-69 5-94 6-19

5-19 6-43 5-93 6-17

5-18 5-42 5-67 5-92 6-16

5-17 5-41 5-66 5-90 6-15

5-15 5-40 565 5-89 614

5-14 5-39 5-63 5-88 612

513 5-38 5-62 5-87 611

512 5-37 5-61 5-86 610

511 5-36 5-60 5-84 6-09

510 5-35 5-59 5-83 6-07

5 09 5-33 5-58 5-82 606

508 5-32 5-57 5-81 605

507 5-31 5-55 5-80 604

5-30 6-54 5-78 6-02

21 22 23 24 25

26 27 28 29 30

6-49 6-74 6-98 7-23 7-48

6-47 6-72 6-97 7-22 7-47

646 6-71 6-96 7-21 7-45

6-45 669 6-94 7-19 7-44

6-43 6-68 6-93 7-18 7-42

6-42 6-67 6-91 7-16 7-41

6-41 6-65 6-90 7-15 7-39

6-39 6-64 6-89 7-13 7-38

6-63 6-87 7-12 7-36

6-37 6-61 6-86 7-10 7-35

6-36 6-60 6-85 7-09 7-33

6-34 6-59 6-83 7-08 7-32

6-33 6-57 6-82 706 7-30

6-32 6-56 6-80 7 05 7-29

6-30 6-55 6-79 7-03 7-27

6-29 6-53 6-78 7-02 7-26

6-28 6-52 6-76 7-00 7-24

6-27 6-51 6-75 6-99 7-23

26 27 28 29 30

31 32 33 34 35

7-73 7-98 8-23 8-48 8-73

7-72 7-97 8-22 8-46 8-71

7-70 7-95 8-20 8-45 8-70

7-69 7-93 8-18 8-43

7-67 7-92 8-17 8-41 8-66

7-66 7-90 8-15 8-40 6-64

7-64 7-89 8-13 8-38 8-63

7-62 7-87 8-12 8-36 8-61

7-61 7-85 8-10 8-35 8-59

7-59 7-84 8-08 8-33 8-57

7-58 7-82 8-07 8-31 8-56

7-56 7-81 8-05 8-30 8-54

7-55 7-79 8-03 8-28 8-52

7-53 7-78 8-02 8-26 8-50

7-52 7-76 8-00 8-24 8-49

7-50 7-74 7-99 8-23 8-47

7-49 7-73 7-97 8-21 8-45

7-47 7-71 7-95 819 8-43

31 32 33 34 35

36 37 38 39 40

8-98 9-23 9-48 9-78 1 9-98 1

8-96 9-21 9-46 9-71 9-96 1

8-94 919 9-44 9-69 9-94

8-93 9-17 9-42 9-67 0-92

8-91 9-16 9-40 9-65 9-90

8-89 9-14 9-38 9-63 9-88

8-87 912 9-37 9-61 9-86 I

8-85 9-10 9-35 959 9-84 I

8-84 908 9-33 9-57 9-82

8-82 906 9-31 9-55 9-80

8-80 9 05 9-29 9-53 9-78

8-78 903 9-27 9-51 9-76

8-77 901 9-25 9-50 9-74

8-75 8-99 9-23 9-48 9-72

8-73 8-97 9-21 9-46 9-70

8-71 8-95 9-20 9-44 9-68

8-69 8-94 918 9-42 9-66

8-68 8-92 916 9-40 9-64

36 37 38 39 40

1 2 34

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Table II—continued.

R E F E R E N C E TABLES

191

Table II—continued.

REFERENCE TABLES Table IIA—Table of Factors for the Calculation of Pol Per Cent Juice from Pol Reading for U s e in the Dry Lead Method with Undiluted Solutions Pol per cent juice = Degrees Brix

Factor

Pol Reading Pol Factor Degrees Brix

Factor

0.5 1.0 1.5 2.0 2.5

3.84273 3.85023 3.85769 3.86519 3.87273

16.5 17.0 17.5 18.0 18.5

4.09450 4.10285 4.11119 4.11962 4.12804

3.0 3.5 4.0 4.5 5.0

3.88027 3.88785 3.89546 3.90308 3.91077

19.0 19.5 20.0 20.5 21.0

4.13650 4.14496 4.15350 4.16204 4.17062

5.5 6.0 6.5 7.0 7.5

3.91842 3.92615 3.93388 3.94165 3.94942

21.5 22.0 22.5 23.0 23.5

4.17923 4.18788 4.19658 4.20527 4.21400

8.0 8.5 9.0 9.5 10.0

3.95723 3.96512 3.97296 3.98088 3.98881

24.0 24.5 25.0 25.5 26.0

4.22277 4.23158 4.24042 4.24931 4.25819

10.5 11.0 11.5 12.0 12.5

3.99677 4.00473 4.01277 4.02081 4.02885

26.5 27.0 27.5 28.0 28.5

4.26712 4.27608 4.28508 4.29412 4.30315

13.0 13.5 14.0 14.5 15.0 15.5 16.0

4.03696 4.04508 4.05327 4.06146 4.06965 4.07792 4.08619

29.0 29.5 30.0 30.5 31.0 31.5 32.0

4.31227 4.32138 4.33054 4.33973 4 34896 4.35823 4.36750

The values have been calculated to sixteen significant figures and rounded to six significant figures using the rounding rule in British Standards 1957 NOTE 2.— Due to rounding errors and differences in original data there may be discrepancies in the second decimal place of pol between values calculated using these factors and those obtained from Table II. Providing sufficient significant figures are used in the calculation the values obtained using the pol factors of this table are to be considered the correct results.

Table III'—Pol Bagasse from Polariscope Reading (400 mm Tube) and Moisture Content. (Ratio of water to bagasse = 10:1). (clarified with dry lead).

Table III—continued.

R E F E R E N C E TABLES Table IV—Milligrammes of Reducing Sugars Required to Reduce 10 ml Fehling's Solution (Lane and Eynon Method).

•Calculated by extrapolation.

195

196

R E F E R E N C E TABLES T a b l e V — M i l l i g r a m m e s o f R e d u c i n g S u g a r s Required t o R e d u c e 1 0 m l Fehling's Solution (Lane a n d Eynon Method) at Low Sucrose Concentrations.

R E F E R E N C E TABLES T a b l e VI—Specific R o t a t i o n of S u g a r s .

197

198

R E F E R E N C E TABLES T a b l e VII—Refractive I n d i c e s of S u g a r S o l u t i o n s at 20 °G in A i r at 2 0 °G, 760 m m P r e s s u r e a n d 5 0 p e r c e n t R e l a t i v e H u m i d i t y .

The following values are according to t h e smoothed measured values of t h e Physikalisch-Technische Bundesanstalt in West Germany, and have been computed from t h e polynomial adopted by t h e ICUMSA 1966.

P = sugar concentration as percentage by weight in air at 20 °C 760 mm pressure and 50 per cent relative humidity.

200

R E F E R E N C E TABLES

L a b o r a t o r y M a n u a l for Q u e e n s l a n d S u g a r M i l l s T a b l e IX—Glerget D i v i s o r s . W h e n analyses are conducted according to Jackson Gillis Method IV, t h e presently accepted formula for conversion of polariscope (saccharimeter) readings to sucrose concentration is: where

S = P1 = P = m =

sucrose per cent in sample. direct reading calculated to basis of normal solution. invert reading calculated to basis of normal solution. concentration of dissolved solids in g per 100 ml of solution as read in polariscope. t = temperature in °C. The basic value 132.63 applies to the Walker method of inversion (heat to 65 ° C , a d d acid, allow to cool). For inversion by t h e U.S. Customs method (add acid, immerse in 60 °C bath, stir for 3 min, hold for 7 more min, cool quickly) t h e basic value is 132.56, whilst for inversion at room temperature (24 h) the value is 132.66. For invertase inversion the Clerget divisor is given by t h e formula— 132.1 + 0.0833 (m — 13) — 0.53 (/ — 20). Using the Walker method of inversion some useful Clerget divisors, at 20 ° C , a r e : J u i c e s — T h e divisor is related to t h e Brix as follows: T a b l e IX (a)

S u g a r s — F o r all sugars the value 132. 63 at 20 °C m a y be adopted. M o l a s s e s — F o r normal samples of molasses t h e value 131.88 at 20 °C m a y be adopted. For other materials or other methods of inversion the divisor m u s t be calculated from t h e specific data. All Clerget divisors must be corrected for temperature according to t h e table.

T a b l e X — S u b t r a c t i v e T e m p e r a t u r e C o r r e c t i o n s for C l e r g e t D i v i s o r s .

REFERENCE TABLES Table XI—Dilution Indicator of R a w S u g a r .

T a b l e XII—Solubility of Sucrose in Water in g Sucrose (S) per 100 g Water A c c o r d i n g to Charles, A m e r . C h e m . S o c , 1958 Abst. of P a p e r s p. 10D. Reported in Honig "Principles of S u g a r Technology", 2, 228.

201

202

REFERENCE TABLES Table XIII—Solubility of Sucrose in Water in g Sucrose (S) per 100 g Solution.* (Charles.)

°c 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

S 64.41 64.48 64.56 64.64 64.73 64.82 64.92 65.02 65.11 65.22 65.33 65.44 65.56 65.68 65.80 65.93 66.06 66.19 66.33

°C 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

S 66.47 66.61 66.75 66.90 67.05 67.21 67.36 67.52 67.69 67.85 68.02 68.19 68.36 68.54 68.72 68.89 69.08 69.26

°C 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

S 69.45 69.64 69.83 70.02 70.22 70.41 70.61 70.81 71.01 71.21 71.42 71.63 71.84 72.05 72.26 72.47 72.68 72.90

°C 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72

*Beware of confusion between this Table and Table XII.

S 73.11 73.33 73.55 73.77 73.99 74.21 74.43 74.66 74.88 75.10 75.33 75.56 75.78 76.01 76.24 76.46 76.69 76.92

°C 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

S 77.15 77.38 77.60 77.83 78.06 78.29 78.52 78.75 78.97 79.20 79.43 79.66 79.88 80.11 80.33 80.56 80.78 81.01

Table XIV—Densities of Solutions of Cane Sugar at 20 °C in g/ml.*. (This table is the basis for standardizing hydrometers indicating per cent of sugar at 20 °C). Per sugar

.2

.3

.4

.5

.6

.7

.8

.9

0.998622 1.002509 1.006405 1.010327 1.014277

0.999010 1.002897 1.006796 1.010721 1.014673

0.999398 1.003286 1.007188 1.011115 1.015070

0.999786 1.003675 1.007580 1.011510 1.015467

1.000174 1.004064 1.007972 1.011904 1.015864

1.000563 1.004453 1.008363 1.012298 1.016261

1.000952 1.004844 1.008755 1.012694 1.016659

1.001342 1.005234 1.009148 1.013089 1.017058

1.001731 1.005624 1.009541 1.013485 1.017456

1.017854 1.021855 1.025885 1.029942 1.034029

1.018253 1.022257 1.026289 1.030349 1.034439

1.018652 1.022659 1.026694 1.030757 1.034850

1.019052 1.023061 1.027099 1.031165 1.035260

1.019451 1.023463 1.027504 1.031573 1.035671

1.019851 1.023867 1.027910 1.031982 1.036082

1.020251 1.024270 1.028316 1.032391 1.036494

1.020651 1.024673 1.028722 1.032800 1.036906

1.021053 1.025077 1.029128 1.033209 1.037318

1.021454 1.025481 1.029535 1.033619 1.037730

1.038143 1.042288 1.046462 1.050665 1.054900

1.038556 1.042704 1.046881 1.051087 1.055325

1.038970 1.043121 1.047300 1.051510 1.055751

1.039383 1.043537 1.047720 1.051933 1.056176

1.039797 1.043954 1.048140 1.052356 1.056602

1.040212 1.044370 1.048559 1.052778 1.057029

1.040626 1.044788 1.048980 1.053202 1.057455

1.041041 1.045206 1.049401 1.053626 1.057882

1.041456 1.045625 1.049822 1.054050 1.058310

1.041872 1.046043 1.050243 1.054475 1.058737

1.059165 1.063460 1.067789 1.072147 1.076537

1.059593 1.063892 1.068223 1.072585 1.076978

1.060022 1.064324 1.068658 1.073023 1.077419

1.060451 1.064756 1.069093 1.073461 1.077860

1.060880 1.065188 1.069529 1.073900 1.078302

1.061308 1.065621 1.069964 1.074338 1.078744

1.061738 1.066054 1.070400 1.074777 1.079187

1.062168 1.066487 1.070836 1.075217 1.079629

1.062598 1.066921 1.071273 1.075657 1.080072

1.063029 1.067355 1.071710 1.076097 1.080515

1.080959 1.085414 1.089900 1.094420 1.098971

1.081403 1.085861 1.090351 1.094874 1.099428

1.081848 1.086309 1.090802 1.095328 1.099886

1.082292 1.086757 1.091253 1.095782 1.100344

1.082737 1.087205 1.091704 1.096236 1.100802

1.083182 1.087652 1.092155 1.096691 1.101259

1.083628 1.088101 1.092607 1.097147 1.101718

1.084074 1.088550 1.093060 1.097603 1.102177

1.084520 1.089000 1.093513 1.098058 1.102637

1.084967 1.089450 1.093966 1.098514 1.103097

1.103557 1.108175 1.112828 1.117512

1.104017 1.108639 1.113295 1.117982 1 1.122705

1.104478 1.109103 1.113763 1.118453 1.123179

1.104938 1.109568 1.114229 1.118923

1.105400 1.110033 1.114697 1.119395 1.124128

1.105862 1.110497 1.115166 1.119867 1.124603

1.106324 1.110963 1.115635 1.120339 1.125079

1.106786 1.111429 1.116104 1.120812 1.125555

1.107248 1.111895 1.116572 1.121284 1.126030

1.107711 1.112361 1.117042 1.121757 1.126507

0

0.998234 1.002120 1.006015 3 ' 1.009934 1.013881 4

1 2

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Per

Tenths of per cent

.1

.0

1 1.122231

1 1.123653

*All weights in vacuo—International Critical Tables 2, 343.

cent sugar

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 ©

REFERENCE TABLES

R E F E R E N C E TABLES

206

R E F E R E N C E TABLES TABLE XV B r i x , A p p a r e n t Density, A p p a r e n t Specific Gravity, a n d G r a m m e s of S u c r o s e p e r 100 ml of S u g a r S o l u t i o n s (NBS—C440, 1942, p. 632)

Column 1 gives Brix»or percentage of sucrose in the solution. Column 2 gives apparent density, t h a t is, the weight in air with brass weights of 1 ml of solution at 20 °C. The values in this column correspond to the values of true density (table XIV), having been obtained by means of the formula

which m a y be utilized for converting apparent density into true density, and vice versa, by considering t h a t M, the weight in vacuo, and W, the apparent weight, refer to 1 ml, since true density is defined as the weight in vacuo of 1 ml, and the apparent density as the weight of 1 ml of substance in air with brass weights, p is the density of air, which has been taken as 0.0012046; d 1 the density of the solution, d 2 the density of the weights, which has been taken as 8.4 g/ml. Column 3 gives the a p p a r e n t specific gravity at 20 C C. The values in this column were obtained by dividing the apparent density in column 2 by the apparent density of water at 20°C, which was taken as 0.997174. Column 4 gives the grammes sucrose (weighed in vacuo) per 100 ml of solution. The values in the table were calculated in three sections by different individuals; t h u s from 40 to 60 Brix by Peters and Phelps (BS Tech. Paper T338, 1927); 60 to 83.9 Brix by Brewster and Phelps (NBS Research Paper RP536, 1933); and the remaining values, 0 to 40 and 84 to 93 Brix by Snyder, Saunders, and Golden of t h e National Bureau of Standards. After the computations were completed, the tabulations were made by rounding off the values to the last figure given. The values are considered exact to ± 1 in the fifth decimal. Grammes of |

Apparent density at 20 °C

gravity at 20 °C/20 °C

4

1

2

3

4

1.00000 .00039 .00078 .00117 .00156 .00194 .00233 .00272 .00312 .00351

0.000 .100 .200 .300 .400 .500 .600 .701 .801 .902

2.0 .1 .2 .3 .4 .5 .6 •7 .8 .9

1.00495 .00534 .00574 .00613 .00652 .00691 .00730 .00769 .00809 .00848

1.00780 .00819 .00859 .00898 .00937 .00977 .01016 .01055 .01094 .01134

2.012 .113 .215 .317 .418 .520 .622 .724 .826 .928

1.00390 .00429 .00468 .00507 .00546 .00585 .00624 .00663 .00702 .00741

1.002 .103 .203 .304 .405 .506 .607 .708 .809 .911

3.0 •1 .2 .3 .4 .5 .6 .7 .8 .9

1.00887 .00927 .00966 .01006 .01045 .01084 .01124 .01163 .01203 .01243

1.01173 .01213 .01252 .01292 .01331 .01371 .01410 .01450 .01490 .01529

3.030 .132 .234 .337 .439 .542 .644 .747 .850 .953

Apparent density at 20 °C

Apparent specific gravity at 20 °C/20 °C

1

2

3

0.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

0.99717 .99756 .99795 .99834 .99872 .99911 .99950 .99989 1.00028 .00067

1.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

1.00106 .00145 .00184 .00223 .00261 .00300 .00339 .00378 .00417 .00456

per 100 ml weight 1

Apparent

Grammes of sucrose per 100 ml weight

Percentage of sucrose by weight (Brix)

Percentage of sucrose by weight (Brix)

R E F E R E N C E TABLES T a b l e XV—continued

207

208

R E F E R E N C E TABLES T a b l e XV—continued

R E F E R E N C E TABLES T a b l e XV—continued

209

210

R E F E R E N C E TABLES T a b l e XV—continued

R E F E R E N C E TABLES T a b l e XV—continued

211

212

R E F E R E N C E TABLES T a b l e XV—continued

Percentage of sucrose by weight (Brix)

Apparent density at 20 °C

Apparent specific gravity at 20 °C/20 °C

1

2

3

54.0 54.1 54.2 54.3 54.4 54.5 54.6 54.7 54.8 54.9

1.25084

1.25439

141 197 254 311

495 552 609 666

1.25367

1.25723

55.0 55.1 55.2 55.3 55.4 55.5 55.6 55.7 55.8 55.9

1.25651

1.26007

708 765 822 879

064 122 179 236

1.25936 1.25993 1.26050

1.26293

108 165

350 408 465 522

56.0 56.1 56.2 56.3 56.4 56.5 56.6 56.7 56.8 56.9

1.26222

1.26580

279 337 394 452

637 695 752 810

1.26509

1.26868

57.0 57.1 57.2 57.3 57.4 57.5 57.6 57.7 57.8 57.9

1.26797

1.27156

854 912 970

214 272 330 388

58.0 58.1 58.2 58.3 58.4 58.5 58.6 58.7 58.8 58.9

424 481 538 594

566 624 682 739

1.27028 1.27086

4

780 836 893 950

925

1.26983 1.27041 098

1.27446

143 201 259 317

504 562 620 678

1.27375

1.27736

433 492 550 608

794 853 911

1.27664 724 782 841 899

Grammes of sucrose per 100 ml weight

1.27969 1.28028 086 145 203 262

by weight (Brix)

Apparent density at 20 °C

gravity at 20 °C/20 °C

Grammes of sucrose per 100 ml weight in vacuo

1

2

3

4

Percentage

Apparent

67.601 .757 .912 68.069 .225 .381 .537 .694 .851 69.008

59.0 59.1 59.2 59.3 59.4 59.5 59.6 59.7 59.8 59.9

1.27958 1.28017

1.28320

075 134 193 251 309 367 426 485

379 437 497 556 614 672 731 789 849

69.164 .322 .479 .636 .794 69.951 70.109 .267 .425 .583

60.0 60.1 60.2 60.3 60.4 60.5 60.6 60.7 60.8 60.9

1.28544

1.28908

074

084 143 203 262 321 380 439

70.742 70.900 71.059 .217 .376 .535 .694 71.854 72.013 .173

61.0 61.1 61.2 61.3 61.4 61.5 61.6 61.7 61.8 61.9

1.29133

1.29498

193 252 311 370 430 489 548 608 667

559 618 677 736 796 855 915 975

1.30034

72.332 .492 .652 .812 72.973 73.133 .293 .454 .615 .776

62.0 62.1 62.2 62.3 62.4 62.5 62.6 62.7 62.8 62.9

1.29726

1.30093

786 845 905 966 085 145 205 265

153 212 273 334 393 453 513 573 633

73.937 74.098 .260 .421 .583 .744 74.906 75.068 .230 .393

63.0 63.1 63.2 63.3 63.4 63.5 63.6 63.7 63.8 63.9

1.30325

1.30694

385 446 506 566 626 686 747 807 867

754 815 875 936 994

602 661 720 779 838 897 956

1.29015

1.30025

966

1.29025

1.31055 117 177 237

75.555 .718 .880 76.043 .207 .369 .533 .696 .860 77.024 77.188 .351 .515 .680 .844 78.009 .173 .338 .503 .668 78.833 .999 79.165 .330 .496 .662 .828 .995 80.161 .328 80.494 .661 .828 .995 81.162 .329 .497 .665 .833 82.001 82.169 .337 .506 .674 .843 83.012 .180 .360 .519 .688

R E F E R E N C E TABLES

213

T a b l e XV—continued Grammes of

Apparent density at 20 °C

Apparent specific gravity at 20 °C/20 °C

1

2

3

4

64.0 64.1 64.2 64.3 64.4 64.5 64.6 64.7 64.8 64.9

1.30927

1.31297

988

359 418 479 540 600 661 723 784 845

69.0 69.1 69.2 69.3 69.4 69.5 69.6 69.7 69.8 69.9

1.33992 j 1.34371 433 1.34054

108 169 229 290 350 412 473

83.858 84.028 .198 .367 .538 .708 .879 85.049 .220 .391

65.0 65.1 65.2 65.3 65.4 65.5 65.6 65.7 65.8 65.9

1.31533

1.31905

081

70.0 70.1 70.2 70.3 70.4 70.5 70.6 70.7 70.8 70.9

1.34616

089 150 210 271 332 393 455

85.561 .733 .904 86.076 .248 .419 .591 .763 .935 87.107

66.0 66.1 66.2 66.3 66.4 66.5 66.6 66.7 66.8 66.9

1.32142

1.32516

203 264 325 385 446 509 570 632 693

577 638 699 759 820 884 945

87.280 .453 .626 .798 .971 88.142 .318 .492 .666 .839

67.0 67.1 67.2 67.3 67.4 67.5 67.6 67.7 67.8 67.9

1.32754

1.33129

816 878 939 062 124 186 248 309

192 254 315 377 438 500 562 625 686

68.0 68.1 68.2 68.3 68.4 68.5 68.6 68.7 68.8 68.9

1.33371

1.33748

433 495 557 619

810 872 935 997

681

1.34059

1.31048

594 655 716 777 837 898 959

1.32019

1.33001

743 805 867 930

966

1.32028

1.33007 068

121 183 245 309

per 100 ml weight in vacuo

Percentage j of sucrose j Apparent by weight density at (Brix) 20 °C

Apparent specific gravity at 20°C/20°C

Percentage of sucrose by weight (Brix)

1

2

3

116 179 241 304 366 429 491 554

Grammes of per 100 ml weight 4

92.524 .701 495 .878 558 93.056 621 .233 684 .411 746 .589 809 .767 871 1 .945 934 94.123

1.34997 1.35060 123

119 182

186 248 311 375 438 501 564

94.302 .481 .660 .839 95.017 .197 .376 .556 .736 .916

71.0 71.1 71.2 71.3 71.4 71.5 71.6 71.7 71.8 71.9

1.35245

1.35627

308 371 434 498 561 625 688 751 814

691 754 817 881 944

96.096 .276 .456 .636 .817 .998 97.179 .360 .541 .722

89.012 .187 .361 .536 .711 .885 90.060 .235 .411 .585

72.0 72.1 72.2 72.3 72.4 72.5 72.6 72.7 72.8 72.9

1.35877

1.36261

940 067 131 194 258 322 385 450

324 389 452 516 579 643 707 771 836

90.761 .937 91.112 .288 .464 .641 .817 . 993 92.169 .347

73.0 73.1 73.2 73.3 73.4 73.5 73.6 73.7 73.8

1.36514

1.36900

73.9

679 742 805 867 930 993

1.35056

1.36004

578 642 705 769 833 896 960

1.37024

088

1.36008

072 135 198

964

1.37028

092 156 220 283 347 411 476

97.904 98.085 .268 .449 .632 .814 .997 99.179 .362 .545 99.728 .912 100.095 .278 .462 .646 .827 101.014 .198 .383

214

R E F E R E N C E TABLES T a b l e XV—-continued Grammes of

Grammes of

per 100 ml weight

Percentage of sucrose by weight (Brix)

Apparent density at 20 °C

Apparent specific gravity at 20 °C/20 °C

4

1

2

3

79.0 79.1 79.2 79.3 79.4 79.5 79.6 79.7 79.8 79.9

1.40409 475 541 607 674 740 806 872 939 1.41005

1.40806 872 938 1.41005 072 138 204 270 337 404

111.002 .195 .388 .581 .775 .968 112.161 .354 .549 .743

103.423 .609 .796 .983 104.170 104.356 .543 .731 .919 105.106

80.0 80.1 80.2 80.3 80.4 80.5 80.6 80.7 80.8 80.9

1.41072 138 204 271 337 404 472 537 604 671

1.41471 537 603 670 737 804 872 937 1.42004 072

112.938 113.131 .326 .521 .715 .911 114.106 .301 .497 .692

1.38835 902 967 1.39032 097 162 228 293 358 423

105.294 .482 .670 .859 106.047 .236 .424 .613 ,802 .991

81.0 81.1 81.2 81.3 81.4 81.5 81.6 81.7 81.8 81.9

1.41737 804 871 938 1.42005 072 139 206 273 340

1.42138 205 272 339 406 474 541 608 675 742

114.888 115.084 .280 .477 .673 .870 116.067 .264 .461 .658

1.39096 161 225 291 356 422 488 554 619 685

1.39489 554 619 685 750 816 882 949 1.40014 080

107.181 .370 .560 .750 .940 108.130 .320 .511 .701 .892

82.0 82.1 82.2 82.3 82.4 82.5 82.6 82.7 82.8 82.9

1.42407 475 543 610 677 744 811 878 946 1.43013

1.42810 878 946 1.43013 080 148 214 282 350 417

116.856 117.053 .252 .449 .647 .845 118.044 .243 .442 .641

1.39751 816 882 948 1.40013 079 145 211 277 343

1.40146 211 277 344 409 475 541 607 674 740

109.084 .274 .466 .657 .848 110.041 .232 .425 .617 .809

83.0 83.1 83.2 83.3 83.4 83.5 83.6 83.7 83.8 83.9

1.43081 148 216 283 351 419 488 555 623 691

1.43486 553 621 688 756 824 894 961 1.44029 097

118.840 119.039 .239 .438 .638 .838 120.039 .238 .439 .640

Apparent

Percentage of sucrose by weight (Brix)

Apparent density at 20 °C

gravity at 20 °C/20 °C

1

2

3

74.0 74.1 74.2 74.3 74.4 74.5 74.6 74.7 74.8 74.9

1.37153 217 281 345 410 475 539 604 668 733

1.37541 605 669 733 798 864 928 993 1.38057 122

101.568 .753 .937 102.122 .308 .493 .679 .865 103.050 .237

75.0 75.1 75.2 75.3 75.4 75.5 75.6 75.7 75.8 75.9

1.37797 862 926 991 1.38055 119 184 249 314 379

1.38187 252 316 381 445 1.38510 575 640 705 770

76.0 76.1 76.2 76.3 76.4 76.5 76.6 76.7 76.8 76.9

1.38444 510 575 640 705 770 835 900 965 1.39030

77.0 77.1 77.2 77.3 77.4 77.5 77.6 77.7 77.8 77.9 78.0 78.1 78.2 78.3 78.4 78.5 78.6 78.7 78.8 78.9

per 100 ml weight 4

R E F E R E N C E TABLES

215

T a b l e XV—continued

Percentage of sucrose by weight (Brix) l

Apparent density at 20 °C 2

Apparent Specific gravity at 20 °C/20 °C 3

Grammes of sucrose per 100 ml weight in vacuo 4

Percentage of sucrose by weight (Brix) 1

Apparent density at 20 °C 2

gravity at 20 °C/20 °C

Grammes of sucrose per 100 ml weight in vacuo

3

4

Apparent

1.47199 .47269 .47339 .47409 .47479 .47548 .47618 .47688 .47758 .47828

1.47616 131.096 .47686 .305 .47756 .515 .47826 .725 .47897 .935 .47967 132.145 1.48037 .355 .48107 .565 .48177 .776 .48247 .987

1.47898 .47968 1.48039 .48109 .48179 .48249 .48320 .48390 .48460 .48531

1.48317 133.198 .48388 .409 .48458 .620 .48529 .832 .48599 134.043 .48669 .255 .48740 .467 .48810 .680 .48881 .892 .48951 135.104

91.0 •1

1.48601 .48672 .48742 .48813 .48883 .48954 1.49024 .49095 .49166 .49236

1.49022 135.317 .49093 .530 .49164 .743 .49234 .956 .49305 136.170 .49376 .383 .49447 .597 .49518 .811 .49588 137.025 .49659 .239

1.46225 126.943 .46294 127.149 .46364 .355 .46433 .562 .46502 .768 .46572 .975 .46641 128.182 .46710 .389 .46780 .596 .46849 .803

92.0

1.49307 .49378 .49449 .49520 .49591 .49662 .49733 .49804 .49875 .49946

1.49730 137.454 .49801 .668 .49872 .883 .49944 138.098 1.50015 .313 .50086 .529 .50157 .744 .50228 .960 .50299 139.176 .50371 .392

1.46919 129.011 .46989 .219 1.47058 .426 .47128 .635 .47198 .843 .47267 130.051 .47337 .260 .47407 .468 .47477 .677 .47547 .886

93.0

1.50017 .50088 .50159 .50230 .50302 .50373 .50444 .50516 .50587 .50659

1.50442 139.608 .50513 .824 .50585 140.041 .50656 .257 .50728 .474 .50799 .691 .50871 .908 .50942 141.126 1.51014 .343 .51086 .561

84 . 0 .1 .2 .3 .4 .5 .6 .7 .8 .9

1.43758 .43826 .43894 .43962 1.44030 .44098 .44166 .44234 .44303 .44371

1.44165 120.841 .44234 121.042 .44302 .243 .44370 .444 .44438 .646 .44507 .847 .44575 122.049 .44643 .251 .44712 .453 .44780 .655

89.0

85 . 0 .1 .2 .3 .4 .5 .6 .7 .8 .9

1.44439 .44507 .44576 .44644 .44712 .44781 .44849 .44918 .44986 1.45055

1.44848 122.858 .44917 123.061 .44985 .263 1.45054 .466 .45123 .670 .45191 .873 .45260 124.076 .45329 .280 .45397 .484 .45466 .688

90.0

86 . 0 .1 .2 .3 .4 .5 .6 .7 .8 .9

1.45124 .45192 .45261 .45330 .45398 .45467 .45536 .45605 .45674 .45743

1.45535 124.892 .45604 125.096 .45673 .301 .45741 .505 .45810 .710 .45879 .915 .45949 126.121 1.46018 .326 .46087 .531 .46156 .737

87 . 0 .1 .2 .3 .4 .5 .6 .7 .8 .9

1.45812 .45881 .45950 1.46019 .46088 .46157 .46227 .46296 .46365 .46434

88 0 1 2 3 .4 .5 6 7 8 9

1.46504 .46573 .46643 .46712 .46782 .46851 .46921 .46990 1.47060 .47130

.1 .2

.3 .4 .5 .6 .7 .8 .9 .1 .2 .3 .4 .5 .6 .7 .8 .9

.2 .3 .4 .5 .6 .7 .8 .9

.1 .2 .3 .4 .5 .6 .7 .8 .9 .1 .2 .3 .4 .5 .6 .7 .8 .9

216

R E F E R E N C E TABLES Table XVI—Weight p e r U n i t V o l u m e of S u g a r S o l u t i o n s at 20°C Weight in air

Weight in air

Brix

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Brix lb/ft3

lb/gal

ton/100 gal

62.253 62.492 62.739 62.978 63.225 63.472 63.727 63.973 64.228 64.482 64.744 65.006 65.260 65.522 65.791 66.053 66.322 66.592 66.868 67.138 67.414 67.691 67.975 68.260 68.544 68.828 69.113 69.404 69.696 69.995 70.287 70.586 70.893 71.192 71.499 71.806 72.112 72.426 72.741 73.055 73.376 73.698 74.020 74.349 74.678 75.007 75.336 75.673 76.017 76.354 76.690

10.00 10.038 10.078 10.112 10.156 10.196 10.237 10.276 10.317 10.358 10.400 10.442 10.483 10.525 10.568 10.610 10.653 10.697 10.741 10.785 10.829 10.874 10.919 10.965 11.011 11.056 11.102 11.149 11.196 11.244 11.291 11.339 11.388 11.436 11.485 11.535 11.584 11.634 11.685 11.735 11.787 11.839 11.890 11.943 11.996 12.049 12.102 12.155 12.211 12.265 12.319

.4456 .4474 .4491 .4509 .4526 .4544 .4562 .4580 .4598 .4616 .4635 .4653 .4672 .4691 .4709 .4728 .4748 .4767 .4786 .4806 .4826 .4846 .4866 .4886 .4906 .4927 .4947 .4968 .4989 .5010 .5031 .5053 .5074 .5096 .5118 .5140 .5162 .5184 .5207 .5229 .5252 .5275 .5298 .5321 .5345 .5369 .5392 .5416 .5440 .5465 .5489

51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100

lb/ft3

lb/gal

ton/100 gal

77.042 77.386 77.738 78.089 78.441 78.800 79.151 79.518 79.877 80.244 80.618 80.984 81.358 81.732 82.114 82.488 82.877 83.258 83.647 84.036 84.425 84.822 85.218 85.622 86.018 86.430 86.834 87.238 87.647 88.068 88.480 88.898 89.317 89.744 90.170 90.597 91.023 91.457 91.891 92.325 92.766 93.207 93.649 94.097 94.546

12.376 12.431 12.487 12.543 12.600 12.658 12.714 12.773 12.831 12.890 12.950 13.009 13.069 13.129 13.190 13.250 13.312 13.374 13.437 13.499 13.562 13.625 13.689 13.754 13.817 13.884 13.949 14.013 14.095 14.147 14.213 14.280 14.347 14.414 14.484 14.553 14.621 14.691 14.760 14.831 14.901 14.972 15.043 15.115 15.187

.5514 .5539 .5564 .5589 .5614 .5640 .5665 .5691 .5717 .5743 .5769 .5796 .5823 .5850 .5877 .5904 .5931 .5959 .5986 .6014 .6042 .6070 .6099 .6127 .6156 .6185 .6214 .6243 .6273 .6302 .6332 .6362 .6392 .6422 .6453 .6483 .6514 .6545 .6576 .6607 .6638 .6670 .6702 .6733 .6765 .6798 .6830 .6862 .6895 .6928

Table XVII—Degree of Supersaturation—All Values Being Prefixed by 1.

218

R E F E R E N C E TABLES T a b l e XVIII—Crystal Content of M a s s e c u i t e s * Purity drop P 20

Mass. puritjT

15

16

17

18

19

90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 75 74 73 72 71 70

60.0 57.7 55.6 53.6 51.7 50.0 48.4 46.9 45.5 44.1 42.9 41.7 40.5 39.5 38.5 37.5 36.6 35.7 34.9 34.1 33.3

61.5 59.3 57.1 55.2 53.3 51.6 50.0 48.5 47.1 45.8 44.4 43.2 42.1 41.0 40.0 39.0 38.1 37.2 36.4 35.6 34.8

63.0 60.7 58.6 56.7 54.8 53.1 51.5 50.0 48.6 47.2 45.9 44.7 43.6 42.5 41.5 40.5 39.5 3S.6 37.8 37.0 36.2

64.3 62.1 60.0 58.1 56.3 54.5 52.9 51.4 50.0 48.6 47.4 46.2 45.0 43.9 42.9 41.9 40.9 40.0 39.1 38.3 37.5

65.5 63.3 61.3 59.4 57.6 55.9 54.3 52.8 51.4 50.0 48.7 47.5 46.3 45.2 44.2 43.2 42.2 41.3 40.4 39.6 38.8

69 68 67 66 65 64 93 62 61 50 59 68 57 56 55

!

66.7 64.5 62.5 60.6 58.8 57.1 55.6 54.1 52.6 51.3 50.0 48.8 47.6 46.5 45.5 44.4 43.5 42.6 41.7 40.8 40.0

21 65.6 63.6 61.8 60.0 58.3 56.8 55.3 53.8 52.5 51.2 50.0 48.8 47.7 46.7 45.7 44.7 43.7 42.9 42.0 41.2

22

23

24

25

64.7 62.9 61.1 59.4 57.9 56.4 55.0 53.7 52.4 51.2 50.0 48.9 47.8 46.8 45.8 44.9 44.0 43.1 42.3

63.9 62.1 60.5 59.0 57.5 56.1 54.8 53.5 52.3 51.1 50.0 48.9 47.9 46.9 46.0 45.1 44.2 43.4

63.2 61.5 60.0 58.5 57.1 55.8 54.5 53.3 52.2 51.1 50.0 49.0 48.0 47.1 46.2 45.3 44.4

62.5 61.0 59.5 58.1 56.8 55.6 54.3 53.2 52.1 51.0 50.0 49.0 48.1 47.2 46.3 45.5

15

16

17

18

19

20

22

24

26

28

30

32.6 31.9 31.2 30.6 30.0 29.4 28.8 28.3 27.8 27.3 26.8 26.3 25.9 25.4 25.0

34.0 33.3 32.7 32.0 31.4 30.8 30.2 29.6 29.1 28.6 28.1 27.6 27.1 26.7 26.2

35.4 34.7 34.0 33.3 32.7 32.1 31.5 30.9 30.4 29.8 29.3 28.8 28.3 27.9 27.4

36.7 36.0 35.3 34.6 34.0 33.3 32.7 32.1 31.6 31.0 30.5 30.0 29.5 29.0 28.6

38.0 37.3 36.5 35.8 35.2 34.5 33.9 33.3 32.8 32.2 31.7 31.1 30.6 30.2 29.7

39.2 38.5 37.7 37.0 36.4 35.7 35.1 34.5 33.9 33.3 32.8 32.3 31.7 31.3 30.8

41.5 40.7 40.0 39.3 38.6 37.9 37.3 36.7 36.1 35.5 34.9 34.4 33.8 33.3 32.8

43.6 42.9 42.1 41.4 40.7 40.0 39.3 38.7 38.1 37.5 36.9 36.4 35.8 35.3 34.8

45.6 44.8 44.1 43.3 42.6 41.9 41.3 40.6 40.0 39.4 38.8 38.2 37.7 37.1 36.6

47.5 46.7 45.9 45.2 44.4 43.8 43.1 42.4 41.8 41.2 40.6 40.0 39.4 38.9 38.3

49.2 48.4 47.6 46.9 46.2 45.5 44.8 44.1 43.5 42.9 42.3 41.7 41.1 40.5 40.0

*With apparent purities t h e crystal content per cent Brix is derived. The use of true purities gives crystal per cent dry substance. To obtain crystal per cent massecuite multiply by Brix or dry substance per unit of massecuite.

R E F E R E N C E TABLES

219

Table X I X (a)—Stock Recovery. Total pol and recoverable pol in tons per 100 gallons of stock, when the apparent purity of final molasses is 30. Total Brix pol(T) of pro— Recov. duct pol(R)

Apparent purity of product 45

50

55

60

65

70

75

80

85

90

64 1

T R

.169 .080

.187 .107

.206 .134

.225 .160

.243 .187

.262 .214

.281 .241

.300 .267

.318 .294

.337 .321

66

T R

.175 .084

.195 1 .214 .111 .139

.234 .167

.253 .195

.273 .223

.292 .251

.312 .278

.331 .306

.351 .334

68

T R

.182 .087

.203 .116

.223 .145

.243 .174

.263 .203

.284 .232

.304 .261

.324 .290

.345 .319

.365 .347

70

T R

.190 .090

.211 .120

.232 .150

.253 .180

.274 .211

.295 .241

.316 .271

.337 .301

.358 .331

.379 .360

72

T R

.197 .094

.219 .124

.240 .156

.262 .187

.284 .219

.306 .250

.328 .281

.350 .312

.372 .343

.393 .375

74

T R

.204 .097

.227 .130

.249 .162

.272 .194

.295 .227

.317 .259

.340 .292

.363 .324

.385 .356

.408 .389

76

T R

.212 .101

.235 .134

.259 .168

.282 .202

.306 .235

.329 .269

.353 .302

.376 .336

.400 .369

.423 .403

78

T R

.219 .104

.244 .139

.268 .174

.292 .209

.317 .244

.341 .278

.365 .313

.390 .348

.414 .383

.438 .417

80

T R

.227 .108

.252 .144

.277 .180

.303 .216

.328 .252

.353 .288

.378 .324

.403 .360

.429 .396

.454 .432

82

T R

.235 .112

.261 .149

.287 .186

.313 .224

.339 .261

.365 .298

.391 .335

.417 .373

.443 .410

.470 .447

.323 .231

.351 .270

.378 .308

.405 .347

.432 .385

.459 .424

.486 .462

84

T R

.243 .116

.270 .154

.297 .193

86

T R

.251 .120

.279 .159

.307 .199

.335 .239

.362 .279

.390 .319

.418 .358

.446 .398

.474 .438

.502 .478

88

T R

.259 .123

.288 .165

.317 .206

.346 .247

.374 .288

.403 .329

.432 .370

.461 .411

.490 .453

.518 .494

90

T R

.268 .127

.297 .170

.327 .212

.357 .255

.387 .297

.416 .340

.446 .382

.476 .425

.505 .467

.535 .509

92

T R

.276 .132

.307 .175

.338 .219

.368 .263

.399 .307

.430 .351

.460 .394

.491 .438

.522 .482

.552 .526

94

T R

.285 .136

.317 .181

.348 .226

.380 .271

.411 .316

.443 .362

.475 .407

.506 .452

.538 .497

.570 .543

96

T R

.294 .140

.326 .186

.359 .233

.392 .280

.424 .326

.457 .373

.490 .420

.522 .466

.555 .513

.587 .559

98

T R

.303 .144

.336 .192

.370 .240

.404 .288

.437 .336

.471 .384

.504 .432

.538 .480

.572 .528

.605 .577

100

T R The tons pol from tons

.312 .346 .381 .416 .450 .485 .520 .554 .589 .624 .149 .198 .247 .297 .346 .396 .445 .495 .544 .594 pol in residual molasses m a y be obtained by subtracting tons recoverable pol in stock.

220

R E F E R E N C E TABLES

T a b l e X I X (b)—Stock Recovery. Total pol and recoverable pol in tons per 100 gallons of stock, when the apparent purity of final molasses is 35. Total Brix pol(T) of Recov. duct pol(R)

Apparent purity of product 45

50

55

60

65

70

75

80

85

90

64

T R

.169 .058

.187 .086

.206 .115

.225 .144

.243 .173

.262 .202

.281 .230

.300 .259

.318 .288

.337 .317

66

T R

.175 .060

.195 .090

.214 .120

.234 .150

.253 .180

.273 .210

.292 .240

.312 .270

.331 .300

.351 .330

68

T R

.182 .062

.203 .094

.223 .125

.243 .156

.263 .187

.284 .218

.304 .249

.324 .281

.345 .312

.365 .343

70

T R

.190 .065

.211 .097

.232 .130

.253 .162

.274 .194

.295 .227

.316 .259

.337 .291

.358 .324

.379 .356

72

T R

.197 .067

.219 .101

.240 .135

.262 .168

.284 .202

.306 .235

.328 .269

.350 .303

.372 .336

.393 .370

74

T R

.204 .070

.227 .105

.249 .140

.272 .174

.295 .209

.317 .244

.340 .279

.363 .314

.385 .349

.408 .384

76

T R

.212 .072

.235 .108

.259 .145

.282 .181

.306 .217

.329 .253

.353 .289

.376 .325

.400 .362

.423 .398

78

T R

.219 .075

.244 .112

.268 .150

.292 .187

.317 .225

.341 .262

.365 .300

.390 .337

.414 .375

.438 .412

80

T R

.227 .077

.252 .116

.277 .155

.303 .194

.328 .233

.353 .271

.378 .310

.403 .349

.429 .388

.454 .427

82

T R

.235 .080

.261 .120

.287 .160

.313 .201

.339 .241

.365 .281

.391 .321

.417 .361

.443 .401

.470 .441

84

T R

.243 .083

.270 .124

.297 .166

.323 .207

.351 .249

.378 .290

.405 .332

.432 .373

.459 .415

.486 .456

86

T R

.251 .086

.279 .129

.307 .173

.335 .214

.362 .257

.390 .300

.418 .343

.446 .386

.474 .429

.502 .472

88

T R

.259 .089

.288 .133

.317 .177

.346 .222

.374 .266

.403 .310

.432 .354

.461 .399

.490 .443

.518 .487

90

T R

.268 .091

.297 .137

.327 .183

.357 .229

.387 .274

.416 .320

.446 .366

.476 .412

.505 .457

.535 .503

92

T R

.276 .093

.307 .142

.338 .189

.368 .236

.399 .283

.430 .330

.460 .378

.491 .425

.522 .472

.552 .519

94

T R

.285 .098

.317 .146

.348 .195

.380 .243

.411 .292

.443 .340

.475 .389

.506 .438

.538 .487

.570 .536

96

T R

.294 .100

.326 .151

.359 .201

.392 .251

.424 .301

.457 .351

.490 .402

.522 .452

.555 .501

.587 .552

98

T R

.303 .103

.336 .155

.370 .207

.404 .259

.437 .310

.471 .362

.604 .414

.538 .466

.572 .517

.605 .569

T R

.312 .107

.346 .160

.381 .213

.416 .266

.450 .320

.485 .373

.520 .554 .589 .624 .426 .480 .533 .586 The tons pol in residual molasses m a y be obtained by subtracting tons recoverable pol from tons pol in stock. 100

R E F E R E N C E TABLES

221

Table X I X (c)—Stock Recovery. Total pol and recoverable pol in tons per 100 gallons of stock, when the apparent purity of final molasses is 40. Total Brix pol(T) of Recov. duct 1 pol(R)

Apparent purity of product 45

50

55

60

65

70

75

80

85

90

.169 .031

.187 .062

.206 .094

.225 .125

.243 .156

.262 .167

.281 .218

.300 .250

.318 .281

.337 .312

R

.175 .032

.195 .065

.214 .097

.234 .129

.253 .162

.273 .194

.292 .227

.312 .259

.331 .292

.351 .235

68

T R

.182 .034

.203 .068

.223 .101

.243 .135

.263 .169

.284 .202

.304 .236

.324 .270

.345 .303

.365 .338

70

T R

.190 I . 2 1 1 .035 .070

.232 .105

.253 .140

.274 .175

.295 .210

.316 .246

.337 .280

.358 .315

.379 .351

72

T R

.197 .036

.219 .073

.240 .109

.262 .145

.284 .182

.306 .218

.328 .255

.350 .291

.372 .327

.393 .364

74

T R

.204 .038

.227 .076

.249 .113

.272 .151

.295 .189

.317 .227

.340 .265

.363 .302

.385 .340

.408 .378

76

T R

.212 .039

.235 .078

.259 .118

.282 .157

.306 .196

.329 .235

.353 .274

.376 .314

.400 .353

.423 .393

78

T R

.219 .041

.244 .081

.268 .122

.292 .163

.317 .203

.341 .244

.365 .284

.390 .325

.414 .366

.438 .406

80

T R

.227 .042

.252 .084

.277 .126

.303 .168

.328 .210

.353 .252

.378 .294

.403 .336

.429 .379

.454 .420

82

T R

.235 .043

.261 .087

.287 .130

.313 .173

.339 .217

.365 .260

.391 .304

.417 .347

.443 .392

.470 .435

84

T R

.243 .045

.270 .090

.296 .135

.324 .180

.351 .225

.378 .269

.405 .315

.432 .359

.459 .405

.486 .450

86

T R

.251 .046

.279 .093

.307 .139

.335 .186

.362 .232

.390 .279

.418 .325

.446 .371

.474 .418

.502 .465

88

T R

.259 .048

.288 .096

.317 .144

.346 .192

.374 .240

.403 .288

.432 .336

.461 .384

.490 .432

.518 .480

90

T R

.268 .050

.297 .099

.327 .149

.357 .199

.387 .248

.416 .298

.446 .347

.476 .397

.505 .447

.535 .495

92

T R

.276 .051

.307 .102

.338 .153

.368 .205

.399 .255

.430 .307

.460 .358

.491 .408

.522 .460

.552 .511

94

T R

.285 .053

.317 .105

.348 .158

.380 .211

.411 .263

.443 .316

.475 .369

.506 .421

.538 .474

.570 .527

96

T R

.294 .054

.326 .109

.359 .163

.392 .217

.424 .272

.457 .326

.490 .381

.522 .435

.555 .489

.587 .544

98

T R

.303 .056

.336 .112

.370 .168

.404 .224

.437 .280

.471 .336

.504 .392

.538 .448

.572 .504

.605 .560

64 66

T R

T

.554 .450 .485 .520 .589 .624 T .312 .346 .381 .416 .346 .404 .462 .519 .577 .288 R .115 .173 .231 .058 The tons pol in residual molasses may be obtained by subtracting tons recoverable pol from tons pol in stock. 100

222

R E F E R E N C E TABLES

T a b l e X X — F a c t o r s to be U s e d in Calculating W e i g h t per Gallon of M o l a s s e s . Temp. °C

Factor A

Factor B

Temp. °C

Factor A

Factor B

10 11 12 13 14

0.99975 0.99978 0.99980 0.99983 0.99985

1.0013 1.0014 1.0015 1.0016 1.0017

25 26 27 28 29

1.00013 1.00015 1.00018 1.00020 1.00023

1.0040 1.0043 1.0046 1.0048 1.0051

15 16 17 18 19

0.99988 0.99990 0.99993 0.99995 0.99998

1.0019 1.0021 1.0023 1.0025 1.0027

30 31 32 33 34

1.00025 1.00028 1.00030 1.00033 1.00035

1.0054 1.0057 1.0060 1.0064 1.0067

20 21 22 23 24

1.00000 1.00003 1.00005 1.00008 1.00010

1.0028 1.0030 1.0033 1.0035 1.0038

35 36 37 38 39 40

1.00038 1.00040 1.00043 1.00045 1.00048 1.00050

1.0070 1.0074 1.0077 1.0081 1.0085 1.0089

T a b l e X X I — W e i g h t s as D e c i m a l s of T o n . lb

ton

lb

ton

lb

ton

lb

ton

1 2 3 4 5 6 7

.00045 .00089 .00134 .00178 .00223 .00268 .00312

8 9 10 11 12 13 14

.00357 .00401 .0045 .0049 .0054 .0058 .0062

15 16 17 18 19 20 21

.0067 .0071 .0076 .0080 .0085 .0089 .0094

22 23 24 25 26 27 28

.0098 .0103 .0107 .0111 .0116 .0120 .0125

2 qr = . 025 ton,

3 qr = . 0375 ton and 4 qr = 1 cwt = . 05 ton.

R E F E R E N C E TABLES

223

Table XXII—Density* (g/ml) of Water at T e m p e r a t u r e s f r o m 0 to 102 °C. According to M. Thiesen, Wiss. Abh. der Physikalisch-Technischen Reichsanstalt, 4, No. 1; 1904. Temp. °C

Density

Temp. °C

Density

Temp. °C

Density

0 1 2 3 4

0.99987 0.99993 0.99997 0.99999 1.00000

35 36 37 38 39

0.99406 0.99371 0.99336 0.99299 0.99262

70 71 72 73 74

0.97781 0.97723 0.97666 0.97607 0.97548

5 6 7 8 9

0.99999 0.99997 0.99993 0.99988 0.99981

40 41 42 43 44

0.99225 0.99186 0.99147 0.99107 0.99066

75 76 77 78 79

0.97489 0.97428 0.97368 0.97307 0.97245

10 11 12 13 14 15 16 17 18 19

0.99973 0.99963 0.99952 0.99940 0.99927 0.99913 0.99897 0.99880 0.99862 0.99843

45 46 47 48 49 50 51 52 53 54

0.99024 0.98982 0.98940 0.98896 0.98852 0.98807 0.98762 0.98715 0.98669 0.98621

80 81 82 83 84 85 86 87 88 89

0.97183 0.97120 0.97057 0.96994 0.96930 0.96865 0.96800 0.96734 0.96668 0.96601

20 21 22 23 24

0.99823 0.99802 0.99780 0.99756 0.99732

55 56 57 58 59

0.98573 0.98524 0.98478 0.98425 0.98375

90 91 92 93 94

0.96534 0.96467 0.96399 0.96330 0.96261

25 26 27 28 29

0.99707 0.99681 0.99654 0.99626 0.99597

60 61 62 63 64

0.98324 0.98272 0.98220 0.98167 0.98113

95 96 97 98 99

0.96192 0.96122 0.96051 0.95981 0.95909

30 31 32 33 34

0.99567 0.99537 0.99505 0.99473 0.99440

65 66 67 68 69

0.98059 0.98005 0.97950 0.97894 0.97838

100 101 102

0.95838 0.95765 0.95693

1 imperial gallon of water at 62° F (16.7°C) weighs 10.0 lb. 1 cubic foot of water at 62° F (16.7° C) weighs 62.288 lb. *The values in the above table, when divided by 0.099892, give the weight in pounds of 1 gallon of water at the corresponding temperatures.

R E F E R E N C E TABLES

225

226

R E F E R E N C E TABLES Table XXV

R e q u i r e m e n t s for A p p a r a t u s for U s e in the A n a l y s i s of Cane for Payment Purposes When apparatus is used for the analysis of cane for payment purposes it must conform either to a specification from a recognised Standards authority or to the following requirements. Brix Hydrometers The hydrometer must be of an approved shape, size and construction. The scale shall correspond to one of the following ranges: 0 to 10, 10 to 20, 15 to 25, 20 to 30. It shall be calibrated to read degrees Brix at 20 °C and the range shall be divided in intervals of one tenth of one degree with full numbering at each unit graduation mark. The graduation lines shall be fine, of uniform thickness and at right angles to the axis of the hydrometer. The scale shall be firmly secured inside the stem and without twist. The readings must conform to a tolerance of ± 0.1° Brix at any point of the scale. The following inscriptions shall be clearly marked on the scale within the stem and shall not encroach on the scale or numbering. (a) The makers name (b) Serial number (c) Brix or per cent of sugar by weight (d) Temp. 20 °C P o l a r i m e t e r or S a c c h a r i m e t e r t u b e s The tube must be straight. The length of the tube at 20 °C shall be within ± 0.03 per cent of the nominal lengths of 100 and 200 mm. The ends of the tube must be parallel and ground flat in a plane at right angles to the axis of the tube and no detectable change in reading should be observed on rotating the tube. Each end must project beyond the ferrule or threaded collar to a distance not exceeding 1 mm, such t h a t a cover glass placed over the end of the tube does not touch any other p a r t of the tube. Cover g l a s s e s Cover glasses for polarimeter or saccharimeter tubes must be made of clear optical glass and free from strain. They must have plane parallel surfaces free from scratches. The edges should be slightly bevelled to prevent chipping. A thickness of 1. 5 to 2 mm is desirable for tubes of 200 mm length. Polarimeters and Saccharimeters These must be in a satisfactory condition mechanically and optically. The error at any point of the scale must not exceed ± 0 . 1 scale degrees. It is recommended t h a t they should be calibrated in terms of the International Sugar Scale corresponding to a normal weight of 26. 000 grammes. Thermometers Thermometers are to be of mercury in glass, solid stem, or of an approved enclosed scale type. All ranges up to a maximum of 110 °C to include zero. The maximum error allowed is 1.0 °C. Total immersion thermometers are preferred. Inscriptions should include the maker or vendors name or mark and the immersion for which the thermometer is calibrated. Refractometers These must be in satisfactory condition mechanically and optically. The maximum error at any point of the scale should be the equivalent of 0. 2 degrees Brix. Balances These should be within accepted tolerances for sensitivity and reproducibility corresponding to the maximum capacity of the balance. Efficient damping is required for rapid weighing. Weights Weights to lOOg should conform to Class B tolerances as specified by the National Standards Laboratory Australia. Weights of nominal values from lOOg to 1kg should conform to tolerances of 15 parts in 100,000.

R E F E R E N C E TABLES

227

Table XXV—continued T o l e r a n c e s (B Class) for Apparatus for General U s e in S u g a r Factory Laboratories The tolerances shown in this Table have been compiled from specifications issued by the British Standards Institution. They are recommended as being suitable for apparatus for general use. Flasks—One mark volumetric Nominal capcity ml Tolerance ± ml

5

10

25

50

100

200

250

500

1000 2000

0.04 0.04 0.06 0.10 0.15 0.30 0.30 0.50 0.80 1.20

(British Standard 1792:1960 endorsed as Australian Standard R.20-1961) Sugar Flasks Type 1—two graduation marks. Type 2—single graduation mark for polarization of sugars.

Nominal capacity ml Tolerance ± ml (British Standard 675:1953)

Nominal capacity ml

1 2 5 5 10 10 25 25 50 100

Subdivision

Tolerance on capacity ± ml

ml

Delivery times

0.01 0.02 0.02 0.04 0.02 0.05 0.05

0.01 0.02 0.02 0.05 0.02 0.1

0.05

0.1 0.1 0.2

0.1 0.1 0.2

min.

max.

20 20 50 20 100 15 85 35 75 65

50 50 120 50 200 40 170 70 150 130

(British Standard 846:1962 endorsed as Australian Standard R. 10-1964) Pipettes—One mark bulb Nominal capacity ml Tolerance ± ml Delivery times (seconds) minimum maximum

.015

2 .02

5 .03

10 .04

15 .05

20 .06

25 .06

50 .08

100 .12

5 15

5 15

10 25

10 25

15 30

20 40

20 40

20 50

30 60

1

(British Standard 1583:1961 endorsed as Australian Standard R. 16-1962)

228

R E F E R E N C E TABLES T a b l e XXV—continued Graduated P i p e t t e s Type 1—for delivery from zero mark to graduation marks. Type 2—for delivery down to jet. 2 .02 .02

1 .01 .01

Nominal capacity ml Subdivisions ml Tolerance ± ml

5 .05 .05

25 .10 .20

10 .10 .10

Delivery times, all sizes Type 1 Minimum 15 s Maximum 30 s Type 2 Minimum 10 s Maximum 25 s (British Standard 700:1962, amendment No. 1 published 7/5/1963) M e a s u r i n g Cylinders,—unstoppered Nominal capacity ml Tolerance ± ml (British Standard 604:1952 endorsed as Australian Standard R.6-1953) T h e r m o m e t e r s — M e r c u r y in glass type British Standard

Range °C

— 5 to + 1 0 0 — 20 to + 6 0 50 to 110 99 to 160 150 to 210 — 5 to + 1 0 5 — 5 to + 1 0 5 — 5 to + 1 0 5 — 5 to + 2 5 0 — 5 to + 3 6 0 95 to 205

Graduation interval deg C

593 593 593 593 593 1704 593 1704 1704 1704 593

Tolerance ± °C Total immersion

Partial immersion

0.2 0.3 0.3 0.4 0.6 0.5 0.3 1.0 1.0 2.0 0.5

0.4 0.4 0.6 0.8 1.2 0.6 0.6 1.0 1.0 3.0 1.0

0.1 0.2 0.2 0.2 0.2 0.5 1.0 1.0 1.0 1.0 1.0

Metric Weights Nominal value kg Tolerance ± rag

5

3

2

250

150

100

Nominal value g

500

300

200

100

Tolerance ± mg

25

15

10

5

1 50

50

30

20

10 to 0.1

0.05 to 0.001

2.5

1.5

1.0

0.5

0.2

For values not tabulated the tolerances are the same as those given for the next larger tabulated value. The tolerances for burettes, graduated pipettes, graduated cylinders, and thermometers apply to the whole of the graduated portion or to any fraction of it.

R E F E R E N C E TABLES

231

Table XXVII—Temperature Conversion Table. (Albert Sauveur.)

c — 17.8 -17.2 — 16.7 -16.1 — 15.6 — 15.0 -14.4 -13.9 — 13.3 -12.8 -12.2 — 11.7 -11.1 -10.6 -10.0 - 9.44 — 8.89 - 8.33 - 7.78 - 7.22 - 6.67 - 6.11 - 5.56 — 5.00 — 4.44 - 3.89 — 3.33 - 2.78 - 2.22 — 1.67 - 1.11 — 0.56 0.00 0.56 1.11 1.67 2.22 2.78 3.33 3.89 4.44 5.00 5.56 6.11 6.67 7.22 7.78 8.33 8.89 9.44 10.0 10.6 11.1 11.7 12.2 12.8 13.3 13.9 14.4 15.0 15.6 16.1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61

F

C

32.0 33.8 35.6 37.4 39.2 41.0 42.8 44.6 46.4 48.2 50.0 51.8 53.6 55.4 57.2 59.0 60.8 62.6 64.4 66.2 68.0 69.8 71.6 73.4 75.2 77.0 78.8 80.6 82.4 84.2 86.0 87.8 89.6 91.4 93.2 95.0 96.8 98.6 100.4 102.2 104.0 105.8 107.6 109.4 111.2 113.0 114.8 116.6 118.4 120.2 122.0 123.8 125.6 127.4 129.2 131.0 132.8 134.6 136.4 138.2 140.0 141.8

16.7 17.2 17.8 18.3 18.9 19.4 20.0 20.6 21.1 21.7 22.2 22.8 23.3 23.9 24.4 25.0 25.6 26.1 26.7 27.2 27.8 28.3 28.9 29.4 30.0 30.6 31.1 31.7 32.2 32.8 33.3 33.9 34.4 35.0 35.6 36.1 36.7 37.2 37.8 38.3 38.9 39.4 40.0 40.6 41.1 41.7 42.2 42.8 43.3 43.9 44.4 45.0 45.6 46.1 46.7 47.2 47.8 48.3 48.9 49.4 50.0 60.6

62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123

F

C

143.6 145.4 147.2 149.0 150.8 152.6 154.4 156.2 158.0 159.8 161.6 163.4 165.2 167.0 168.8 170.6 172.4 174.2 176.0 177.8 179.6 181.4 183.2 185.0 186.8 188.6 190.4 192.2 194.0 195.8 197.6 199.4 201.2 203.0 204.8 206.6 208.4 210.2 212.0 214 216 217 219 221 223 225 226 228 230 232 234 235 237 239 241 243 244 246 248 250 252 253

51.1 51.7 52.2 52.8 53.3 53.9 54.4 55.0 55.6 56.1 56.7 57.2 57.8 58.3 58.9 59.4 60.0 60.6 61.1 61.7 62.2 62.8 63.3 63.9 64.4 65.0 65.6 66.1 66.7 67.2 67.8 68.3 68.9 69.4 70.0 70.6 71.1 76.7 82.2 87.8 93.3 98.9 100 104 110 116 121 127 132 138 143 149 154 160 166 171 177 182 188 193 199 204

F 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 170 180 190 200 210 212 220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400

255 257 259 261 262 264 266 268 270 271 273 275 277 279 280 282 284 286 288 289 291 293 295 297 298 300 302 304 306 307 309 311 313 315 316 318 320 338 356 374 392 410 413 428 446 464 482 500 518 536 554 572 590 608 626 644 662 680 698 716 734 752

232

R E F E R E N C E TABLES T a b l e XXVII—continued.

c 210 216 221 227 232 238 243 249 254 260 266 271 277

410 420 430 440 450 460 470 480 490 500 510 520 530

F

C

770 788 806 824 842 860 878 896 914 932 950 968 986

282 288 293 299 304 310 316 321 327 332 338 343 349

540 550 560 570 580 590 600 610 620 630 640 650 660

F

C

1004 1022 1040 1058 1076 1094 1112 1130 1148 1166 1184 1202 1220

354 360 366 371 377 382 388 393 399 404 410 416 421

F 670 680 690 700 710 720 730 740 750 760 770 780 790

1238 1256 1274 1292 1310 1328 1346 1364 1382 1400 1418 1436 1454

NOTE.—The numbers in bold face type refer to the temperature either in degrees Centigrade or Fahrenheit which it is desired to convert into the other scale. If converting from degrees Fahrenheit to degrees Centigrade the equivalent temperature will be found in the left column, while if converting from degrees Centigrade to degrees Fahrenheit, the answer will be found in the column on the right.

T a b l e XXVIII—Equivalents. V o l u m e and Capacity Equivalents. in» 1 1,728 277.42 231 61.03

ft3

U K gal

U S gal

0.0005787 1 0.1605 0.1337 0.03531

0.00360 6.225 1 0.833 0.22

0.00433 7.481 1.2 1 0.2642

litres 0.01639 28.32 4.546 3.785 1

m« 1.639 x 0.02832 4.546 x 3.785 x 1 x

I0-« 10~3 10~ s 10-»

M a s s Equivalents.

kg

oz

lb

Long ton

Short ton

Metric (tonne)

1 0.02835 0.4536 1,016 907.2 1,000

35.27 1 16 35,840 32,000 35,274

2.205 0.0625 1 2,240 2,000 2,205

0.0009842 0.0000279 0.0004464 1 0.8929 0.9842

0.001102 0.00003125 0.0005 1.12 1 1.102

0.001 0.00002835 0.0004536 1.016 0.9072 1

R E F E R E N C E TABLES

233

T a b l e XXVIII—continued. D e n s i t y Equivalents. g/ml

lb/ft 3

lb/UK gal

1 0.01602

62.43

10 .1604

Linear M e a s u r e Equivalents. km 6

102.54 x 10- 5 3.048 x 10-* 9.144 x 10-*

cm

105 1 2.54 30.48 914.4

in

39,370 0.3937 12 36

ft

3,280.83 0.032808 0.0833 1 3

yd

1,093.61 0.010936 0.02778 0.3333 1

Surface and Area Equivalents.

P r e s s u r e Equivalents.

mile 0.62137 0.62 x 10~4 0.158 x 10-4 3 0.1894 x 100.5682 x 10~ 3

micrometre

10» 10* 25,400 304,801 914,402

R E F E R E N C E TABLES Table XXVIII—continued. Heat, E n e r g y a n d W o r k Equivalents.

H e a t F l o w Equivalents. cal/sec cm 1 .0002778 .0000754

2

cal/h cm 2

Btu/h ft 2

3,600 1 0.2714

13,263 3.684 1

REFERENCE TABLES Table XXX—Circles: Diameters, Areas, Circumferences.

235

Table XXXII—Capacities of Rectangular Tanks (UK gal) for Each Foot of Depth. Tank width (ft in)

Tank length (ft in) 2—0

2—6

3—0

3-6

4—0

4—6

5-0

5—6

6-0

6—6

7—0

0—6 . 1—0 .

1.56 3.12

3.12 6.24

4.68 9.36

6.24 12.48

7.80 15.60

9.36 18.72

10.92 21.84

12.48 24.96

14.04 28.08

15.60 31.20

17.16 34.32

18.72 37.44

20.28 40.56

21.84 43.68

1-6 . 2—0 .

4.68 6.24

9.36 12.48

14.04 18.72

18.72 24.96

23.40 31.20

28.08 37.44

32.76 43.68

37.44 49.92

42.12 56.16

46.80 62.40

51.48 68.64

56.16 74.88

60.84 81.12

65.52 87.36

2-6 . 3—0 .

7.80 9.36

15.60 18.72

23.40 28.08

31.20 37.44

39.00 46.80

46.80 56.16

54.60 65.52

62.40 74.88

70.20 84.24

78.00 93.60

85.80 102.96

93.60 112.32

101.40 121.68

109.20 131.04

3—6 . 4—0 .

10.92 12.48

21.84 24.96

32.76 37.44

43.68 49.92

54.60 62.40

65.52 74.88

76.44 87.36

87.36 99.84

98.28 112.32

109.20 124.80

120.12 137.28

131.04 149.76

141.96 162.24

152.88 174.72

4—6 . 5—0 .

14.04 15.60

28.08 31.20

42.12 46.80

56.16 62.40

70.20 78.00

84.24 93.60

98.28 109.20

112.32 124.80

126.36 140.40

140.40 156.00

154.44 171.60

168.48 187.20

182.52 202.80

196.56 218.40

5—6 . 6-0 .

17.16 18.72

34.32 37.44

51.48 56.16

68.64 74.88

85.80 93.60

102.96 112.32

120.12 131.04

137.28 149.76

154.44 168.48

171.60 187.20

188.76 205.92

205.92 224.64

223.08 243.36

240.24 262.08

6—6 . 7—0 .

20.28 21.84

40.56 43.68

60.84 65.52

81.12 87.36

101.40 109.20

121.68 131.04

141.96 152.88

162.24 174.72

182.52 196.56

202.80 218.40

223.08 240.24

243.36 262.08

263.64 283.92

283.92 305.76

7—6 . 8-0 .

23.40 24.96

46.80 49.92

70.20 74.88

93.60 99.84

117.00 124.80

140.40 149.76

163.80 174.72

187.20 199.68

210.60 224.64

234.00 249.60

257.40 274.56

280.80 299.52

304.20 324.48

327.60 349.44

0-6

1—0

1-6

R E F E R E N C E TABLES

237

Table XXXIII—Capacity of Horizontal Cylindrical T a n k s at Varying Levels. i = depth of liquid d = diameter of vessel. i/d .01 .02 .03 .04 .05 .06 .07 .08 .09 .10 .11 .12 .13 .14 .15 .16 .17 .18 .19 .20 .21 .22 .23 .24 .25

fraction of total .0017 .0048 .0087 .0134 .0187 .0245 .0308 .0375 .0446 .0520 .0598 .0680 .0764 .0851 .0941 .1033 .1127 .1224 .1323 .1424 .1527 .1631 .1737 .1845 .1955

i/d .26 .27 .28 .29 .30 .31 .32 .33 .34 .35 .36 .37 .38 .39 .40 .41 .42 .43 .44 .45 .46 .47 .48 .49 .50

fraction of total .2066 .2178 .2292 .2407 .2523 .2640 .2759 .2878 .2998 .3119 .3241 .3364 .3487 .3611 .3735 .3860 .3986 .4112 .4238 .4364 .4491 .4618 .4745 .4873 .5000

i/d .51 .52 .53 .54 .55 .56 .57 .58 .59 .60 .61 .62 .63 .64 .65 .66 .67 .68 .69 .70 .71 .72 .73 .74 .75

fraction of total .5127 .5255 .5382 .5509 .5636 .5762 .5888 .6014 .6140 .6265 .6389 .6513 .6636 .6759 .6881 .7002 .7122 .7241 .7360 .7477 .7593 .7708 .7822 .7934 .8045

i/d .76 .77 .78 .79 .80 .81 .82 .83 .84 .85 .86 .87 .88 .89 .90 .91 .92 .93 .94 .95 .96 .97 .98 .99

1.00

fraction of total .8155 .8263 .8369 .8473 .8576 .8677 .8776 .8873 .8967 .9059 .9149 .9236 .9320 .9402 .9480 .9554 .9625 .9692 .9755 .9813 .9866 .9913 .9952 .9983 1.0000

T a b l e X X X I V — A m o u n t of CaO in Milk of L i m e of Various D e n s i t i e s at 15 °C.

R E F E R E N C E TABLES

238

T a b l e X X X V — F u e l Value of B a g a s s e . (a) G r o s s Calorific Value (B h ). Formula B h = 8345 — 22.1 pol — 83.45 water Btu/lb. Pol per cent bagasse Moisture per cent bagasse

1.0

1.5

2.0

2.5

3.0

3.5

4.0

38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

5,152 5,068 4,985 4,901 4,818 4,735 4,651 4,568 4,484 4,401 4,317 4,234 4,150 4,067 3,984 3,900 3,817 3,733

5,141 5,057 4,974 4,890 4,807 4,723 4,640 4,557 4,473 4,390 4,306 4,223 4,139 4,056 3,972 3,889 3,806 3,722

5,130 5,046 4,963 4,879 4,796 4,712 4,629 4,546 4,462 4,379 4,295 4,212 4,128 4,045 3,961 3,878 3,795 3,711

5,119 5,035 4,952 4,868 4,785 4,701 4,618 4,535 4,451 4,367 4,284 4,201 4,117 4,034 3,950 3,867 3,783 3,700

5,108 5,024 4,941 4,857 4,774 4,690 4,607 4,523 4,440 4,357 4,273 4,190 4,106 4,023 3,939 3,856 3,772 3,689

5,097 5,013 4,930 4,846 4,763 4,679 4,596 4,512 4,429 4,346 4,262 4,179 4,095 4,012 3,928 3,845 3,761 3,678

5,085 5,002 4,919 4,835 4,752 4,668 4,585 4,501 4,418 4,334 4,251 4,168 4,084 4,001 3,917 3,834 3,750 3,667

Interpolations: per cent moisture. subtract

.1 8

.2 17

.3 25

4 33

.5 42

.6 50

.7 58

.8 67

|

.9 75

Approximate formula B h = Dry Substance x 82 Btu/lb. (b) N e t Calorific Value (B 1 ). Formula B 1 = 7783 — 22.1 pol — 88.27 water Btu/lb. Moisture per cent bagasse 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55

Pol per cent bagasse 1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

4,407 4,318 4,230 4,142 4,054 3,965 3,877 3,789 3,701 3,612 3,524 3,436 3,347 3,259 3,171 3,083 2,994 2,906

4,396 4,307 4,219 4,131 4,043 3,954 3,866 3,778 3,690 3,601 3,513 3,425 3,336 3,248 3,160 3,072 2,983 2,895

4,385 4,296 4,208 4,120 4,031 3,943 3,855 3,767 3,679 3,590 3,502 3,414 3,325 3,237 3,149 3,061 2,972 2,884

4,373 4,285 4,197 4,109 4,020 3,932 3,844 3,756 3,668 3,579 3,491 3,403 3,314 3,226 3,138 3,050 2,961 2,873

4,362 4,274 4,186 4,098 4,009 3,921 3,833 3,745 3,657 3,568 3,480 3,392 3,303 3,215 3,127 3,039 2,950 2,862

4,351 4,263 4,175 4,087 3,998 3,910 3,822 3,734 3,646 3,557 3,469 3,381 3,292 3,204 3,116 3,028 2,939 2,851

4,340 4,252 4,164 4,076 3,987 3,899 3,811 3,723 3,635 3,646 3,458 3,370 3,281 3,193 3,105 3,017 2,928 2,840

4,329 4,241 4,153 4,064 3,976 3,888 3,800 3,712 3,624 3,535 3,448 3,358 3,270 3.182 3,094 3,006 2,917 2,829

Interpolat ions: per cent moisture subtract

.1 9

.2 18

.3 26

4 35

.5 44

.6 53

.7 62

.8 70

.9 79

239

REFERENCE TABLES Table XXXVI—Boiling Point Elevation of Sugar Solutions and Cane Juices (°F) at 760 mm Pressure. Brix

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 94

Purity 100

90

80

70

60

50

40

0.2 0.4 0.5 0.7 1.1 1.4 1.8 2.5 3.2 4.1 5.4 6.8 9.2 12.6 16.9 23.4 35.3 54.9

0.2 0.4 0.5 0.9 1.3 1.6 2.0 2.7 3.4 4.5 5.8 7.4 9.9 13.5 18.0 24.7 36.9

0.2 0.4 0.5 0.9 1.3 1.8 2.3 3.2 4.0 5.0 6.5 8.1 10.8 14.4 18.9 25.9 38.2

0.2 0.4 0.7 1.1 1.4 2.0 2.7 3.6 4.5 5.6 7.2 8.8 11.7 15.5 20.3 27.5 40.3

0.4 0.5 0.7 1.3 1.8 2.3 3.1 4.0 5.0 6.3 7.9 9.6 12.8 16.9 22.1 29.5 42.7

0.4 0.5 0.9 1.4 2.0 2.5 3.4 4.3 5.6 7.0 8.8 10.8 13.9 18.2 23.6 31.3 45.5

0.4 0.7 1.1 1.6 2.2 2.9 3.8 4.9 6.1 7.7 9.7 11.7 14.9 19.4 25.4 34.4

240

R E F E R E N C E TABLES

T a b l e XXXVII Showing weights of pure sugar syrup filtered (between 2 and 7 minutes after application of pressure) at various temperatures, under t h e standard conditions of the Rapid Filterability Test, viz. 0.48 per cent filter aid on solids 9 . 0 pH obtained by buffer (This table applies only to Celite 505 standardized in October 1966. When this batch is exhausted, any further supply of filter aid will be accompanied by a table appropriate to the new batch.)

R E F E R E N C E TABLES

241

T a b l e XXXVII—Continued Temp. °C

Wt. of nitrate (grammes)

Temp. °C

Wt. of nitrate (grammes)

22.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

177 178 179 179 180 180 181 182 182 183

27.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

208 208 209 210 210 211 212 212 213 213

23.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

183 184 185 185 186 186 187 188 188 189

28.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

214 215 215 216 217 217 218 218 219 220

24.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

189 190 191 191 192 192 193 194 194 195

29.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

220 221 222 222 223 224 224 225 225 226

25.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

196 196 197 197 198 199 199 200 200 201

30.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

227 227 228 229 229 230 231 231 232 233

26.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

202 202 203 204 204 205 205 206 207 207

31.0 .1 .2 .3 .4 .5 .6 .7 .8 .9

233 234 234 235 236 236 237 238 238 239

242

R E F E R E N C E TABLES Table XXXVIII—International A t o m i c W e i g h t s , 1966 (Published by the C.R.C. Handbook of Chemistry and Physics.)

N O T E : The above atomic weights are based on the isotope CI2, whereas previous tables were based on 0 = 16.000.

INDEX First Aid, 181 A Absolute juice, 1 Absorptiometer, 41 Acid, definition of, 145 dissociation of, 144 normal solutions, 91 Air in juice, 96 Alkali, definition, 145 Alkalinity, 139, 178 Alkalis, normal solutions, 91 Amici prisms, 15 Analyser prism, 22 Analysis of— bagasse, 102 boiler water, 138, 177 cane, 104 effluents, 130 filter cake, (see mud) gums, 126 lime, 132 mud, 124 sugar, 116 water, 143 Analytical methods— contents for, 94 for specific analyses, refer to the individual analysis involved, Angular rotation, 23 Apparent (analyses), 1 Ash, 1 determination, 114 B Back roller juice, 1 Bagacillo, 1 pol added to filter cake by, 155 Bagasse—• analysis, 102 Brix, 153 moisture, 102 pol, 103 calorific value, 168 definition, 1 equivalent, 168 per cent cane, 154 preparation of sample, 81, 102 samples, preservation, 81 sampling, 81 wet disintegrator, 103 Balance— analytical, 51 constant load, 52 for coarse weighing, 51, 57 requirement for cane payment (table XXV) sensitivity, 52 setting up the, 53 testing, 55, 77 weighing, 54 weights, 53 Basic lead acetate— analysis, 88

dry, 88 safety precautions, 88 solution, 88 specification, 88 Bichromate filter, 27 Birefringence, effect of, 21, 34 Boiler efficiency, 166 condensation loss, 169 measurement, 168 miscellaneous losses, 170 sensible heat loss, 169 unburnt gas loss, 170 Boiler water— alkalinity, 84, 139, 178 analysis, 138, 178 reagents for, 84 chemical dosage, 179 hardness, 141, 179 phosphates, 140, 178 removal of oxygen, 176 sampling, 177 sugar in, 180 sulphates in, 142, 179 sulphites in, 141, 178 total dissolved solids, 142, 177, 179 treatment, 139, 173 prevention of scale, 174 problems in sugar industry, 179 Boiler station, the, 166 Boiling house efficiency, 164 E.S.G., 165 recovery, 153, 165 reduced, 165 Brix— definition, 1 determination— by hydrometer, 95 by pycnometer, 62 by refractometer, 18, 95, 105 for cane payment, 96 indirect cane analysis, 105 of mill products, 95 of sugar solution, 67 significance of, 97 temperature corrections in, 97 refractometer, 1 Brix hydrometer— calibration, 75 dimensions, 67 for cane payment, 96 ranges, 67 requirement for cane p a y m e n t (table XXV) scale, 66, 67 temperature of calibration, 67 temperature corrections, 67, table 1 tolerance, (table XXV) Buffer solutions— reagents for, 85 Bulk density, prepared cane, 1 Burettes— calibration, 71 specification, (table XXV) tolerance, 71

244

c Calcite, 21, 22 Calculations in chemical control, 151 boiling house efficiency, 164 boiling house recovery, 153, 165 c.c.s. formula, 2, 106 clarified juice per cent cane, 156 coefficient of work, 165 concentration and evaporation, 156 crystal content, 161 dilution, 155 equivalent standard granulated, 161 evaporation coefficient, 156 expected purity of molasses, 161 extraction, 153 reduced extraction, 163 maceration per cent fibre, 155 materials balances, 151 overall recovery, 153 pol balance, 152 empirical system, 152 direct analysis, 153 recovery formulae, 157 S.J.M., 157 Winter-Carp., 157 retention (rotary fiters), 156 taking stock, 159 weekly report, 160 to date averages, 162 Calibration of— Brix hydrometers, 75 pol tubes, 75, 77 thermometers, 75 volumetric glassware, 69, 77 burettes, 71 flasks, 70 measuring cylinders, 73 pipettes, 72 Calomel electrode, 147 Calorific values of fuels, 167 Canada balsam, 21 Cane— analysis, 104 direct, 104 whole stalk, 107 Brix by disintergrator method, 105 C.C.S., 1, 106 definition, 1 fibre, 107 maturity, 19, 78 moisture, 105 pol in cane, 152 pol by disintergrator method, 105 pol in open cells, 106 sample preparation, 105 sampling, 78 Cane maturity, 78 by refractometer, 19 Caustic cleaning solution— determination of concentration, 133 Caustic embrittlement, 175, 179 CCS — definition, 1 formula, 2 CellFaraday, 30, 33 saturation, 137 Chemical control, calculations, 151 Chemical dosage of boilers, 179

Clarifiability test, 133 reagents, 85 Clarified juice— definition, 2 per cent cane, 156 pH measurement, 149 phosphates, 129 turbidity measurement, 42 Cleansing solution, glassware, 69, 86 Clerget— divisors, 111 method for sucrose, 108 Coal, calorific value, 168 Coefficient of supersaturation, 136 Coefficient of work, 165 definition, 2 upper limit, 165 Colorimetry, 42 Colorimetric determination— p H , 145 phosphates, 128 starch, 123 Colour, in raw sugar, 124 Commercial cane sugar— definition, 1 formula, 2 Co mparator— colour, 140 measurement of pol tubes, 77 measurement of p H , 146 Compression ratio (milling), 2 Concentration, definition, 136 Concentration and evaporation formulae, 156 Condensate, 2 sugar in, 180 Condensation loss, 169 Continuous sampler, 79 Corrosion, in boilers, 139, 175 Cover glasses, 77 requirement for cane payment (table XXV) strain, 37, 77 Crystal content, 2, 161 Crystallizer drop, 2 Cutter-grinder, 105 Cyclone purity of molasses, 2, 136 Cylinders, measuring, 73 D

Definitions, 1 Densimetric methods of analysis, 58 hydrometer, 65 pycnometer, 60 Density of a substance, 58 relative, 58 Dextran, 3 Dextrorotation, 23 Dichroic film, 20 Diffraction grating, 41 Dilution indicator, 3 Dilution, per cent clarified juice, 155 per cent fibre, 155 per cent mixed juice, 155 per cent undiluted juice, 3, 155 Dilution water, 3, 155 Disintegrator, wet, 103, 104 Dispersion— prism, 10 rotatory, 24, 26 Dissociation constant of water, 144

INDEX Dosage of chemicals to boilers, 179 Double refraction, 21 Dry substance— definition, 3 determination, 100 Josse method, 101 sand method, 100 Drying oven, Spencer type, 102 E E.D.T.A., 85 Effets, overall evaporation coefficient of, 156 Effluents, sugar detection in, 130 Electrode— calomel, 147 glass, 148 hydrogen, 146 Electrolytes, 144 Electrolytic dissociation theory, 144 Equivalent bagasse, 168 Equivalent Standard Granulated (E.S.G.), 161 Escribed volume, 3 Evaporation coefficient of effets, overall, 156 Evaporation formula, 156 Expected purity of molasses, 161 Extraction— calculation, 153 definition, 3 pol, 3, 153 reduced, 6, 163 Extraneous matter, 3 F Fans— boiler, 171 forced draught, 172 horse power required, 172 induced draught, 171 performance, 172 Faraday effect, 23 Faraday cell, 30, 33 Fehling's solutions— reagents, 90 standardization, 90 Fibre— definition, 3 determination— prepared cane method, 107 whole stalk method, 107 in bagasse, 153 in cane, 78, 107 in mud, 126 Filling ratio, 3 Filter— retention, 156 washing water, 155 Filterability— definition, 3 reagents for, 85 test, 119 Filter cake (see Mud), 3, 125 sampling, 82 Filtrate, 3 Final molasses (see molasses) First aid, 181 First expressed juice, 3 Flasks, 69, 70

245

specification, (table XXV) standardization, 70 sugar polarization, 117 tolerance, 71 Flue gas— composition, 171 heat losses in, 171 temperature, 171 volume, 171 Formula— c.c.s., 2 crystal content, 161 expected purity of molasses, 161 gross calorific value of bagasse, 168 lost undiluted juice per cent fibre, 164 net calorific value of bagasse, 168 recovery, 157 S.J.M., 157 Winter-carp, 158 reduced extraction, 163 Fuel—• bagasse moisture influence, 173 calorific value, 167 equivalent bagasse, 168 used, 167 weight of fuel, 167 G Glass electrode, 148 Glassware—calibration, 69, 77 cleansing solution, 69, 86 volumetric, 69 specifications, 69 tolerances, (table XXV) Grain size, raw sugar, 121 Gravity solids, 4 purity, 4 Grist, raw sugar, 121 Gums, 4 analysis, 126 reagents for, 93 H Half shadow angle, 25 Hand refractometer, 18 Hardness analysis, boiler water, 141, 179 Heatin steam, 166 losses, 168 condensation, 169 in flue gas, 171 sensible heat, 169, 171 unburnt gas, 170 required, by factory, 170 Herles' reagent, 87 Hydrochloric acid— for sucrose inversion, 92 normal solution, 91 Hydrogen electrode, 146 Hydrogen ion concentration (see pH), 144 Hydrometer, 65 Brix, 66, 67 requirement for cane payment (table XXV) for total dissolved solids in boiler water, 142, 179 scale, 65 testing of, 75 Hygroscopic water, 4, 104, 105

INDEX

246 I Imbibition, 4 Impurities, 4 Indicators, 86, 145 pH range, 86 preparation, 86 Insoluble solids— in clarifier feed, 124 in mud, 124 International sugar scale, 24, 35 ICUMSA definition, 35 Interference filter, 32, 33 Inversion of sucrose— by hydrochloric acid, 108, 110 by invertase, 108 Walker method, 110 U.S. Customs method, 111 Invertase, 108, 110, 112 Invert sugar, 4 standard solution, 90 Ions, 144 J Jackson-Gillis modification IV, 110 divisors, 111 method, 110 reagents, 92 J a v a ratio, 4 Juice— absolute, 1 air bubbles in, 96 back roller, 1 Brix, 1, 95 clarified, 2 per cent cane, 156 p H , 149 extraction, 3 first expressed, 3 gums in, 127 last expressed, 4 lost undiluted, per cent fibre, 164 mixed, 4 p H , 149 phosphate, 129 pol, 97 preservation, 89 primary, 5 residual, 6, 104 sampling, 79 suspended matter in, 96 temperature, 96 undiluted, 6 lost in bagasse, 164 L Laboratory reagents, 83 Laevorotation, 23 Last expressed juice, 4 Lead acetate— basic, 88 neutral, 89 powder, 88 solution, 88 specifications, 88 Lead compounds, 88 safety precautions, 88 Lenses, 45

I Lightamplitude of wave, 8 dispersion, 10, 15, 18, 24, 27 double refraction, 21, 34 filter, 27, 29, 31, 32 frequency, 9 linearly polarised, 9, 20 monochromatic, 17, 24, 26, 41 nature of, 8 plane polarized, 9, 22 refraction, 9 source, 10, 26 spectrum, 8, 10 wavelengths, 8 Lime— addition, 149 automatic to juice, 149 analysis— available CaO, 132 neutralizing value, 132 pH control, 149 quality, 132 Lime sucrose reagent, 85 Lippich polarizer, 25 Litre, 68 Losses— heat, 169 miscellaneous, 170 pol, 152 undetermined, 152 Lost undiluted juice per cent fibre, 164 M Maceration—definition, 4 per cent fibre, 155 Magma, 4 Magnification, 45 Massecuite— composition formula, 160 crystal content, 161 definition, 4 purity, 4 sampling, 80 Materials balances— pol balance, 152 quantitative data, 151 stock, 152, 159 Maturity testing, 19, 78 Meniscus— correction, 96 setting of, 69, 70, 71 Metrology laboratory, 75 N.A.T.A. registration, 75 Microscope, 8, 42 construction, 43 micrometer eyepiece, 47 micrometer stage, 47 projection type, 48 table of magnifications, 45 Millilitre, 68 Milling— efficiency, 163 extraction, 3, 153 loss, 4 lost undiluted juice in bagasse, 164 performance criteria, 163 reduced extraction, 6, 163 Mixed juice, 4

INDEX Moisture— bagasse, 102 cane, 105 filter cake, (see mud) mud, 126 raw sugar, 119 Spencer-type oven for, 102 Molasses— analysis— Brix, 95 pol, 100 reducing sugars, 112 sucrose, 112 total sugars, 112 calorific value, 168 cyclone purity, 2, 136 definition, 4 expected purity ,161 in stock, 158 measuring device, 159 sampling, 80 supersaturation coefficient, 136 Monochromatic light, 17, 24, 26, 41 Mudanalysis, 124 fibre, 126 insoluble solids, 124 moisture, 126 pol, 126 soluble solids, 125 solids, 4 N N.A.T.A. registrations, 75 Net titre, 5 Nicol prism, 21 Non sucrose, 5 Non sugars, 5 Normal quartz plate, 35 Normal solutions, 91 Normal sugar solution, 35 definition, 36 formula for calculation of wavelengths, 37 rotation of, 35 Normal weight, 5, 36 No-void volume, 5

o Oilcalorific value, 168 Optical activity, 9, 23 quartz, 23 sugar solutions, 23 Optical instruments, 8 care of, 49 microscope, 42 projection type, 48 polarimeter, 24 refractometer, 11 saccharimeter, 24, 26 spectrophotometer, 40 Optic axis, 21, 23 Other organic matter, 5 Oven— Spencer type, 102 Overall evaporation coefficient of effets, 156 Overall recovery, 153 Oxygen, in boiler water, 175

247

P Pellet's continuous tube, 37 pH— brom. thymol blue disc, 146 buffer solutions, 85, 149 clarified juice, 149 colour comparator, 146 control, 149 definition, 144 determination, 144, 149 indicators, 86, 145 measurement, 145 colorimetric method, 145 electrometric method, 146 meters, 149 recorder, 149 sugar mill products, 149 temperature compensation, 149 test papers, 145 value of boiler water, 178 Phosphates— analysis, 87, 94, 128 reagents for, 87 colour comparator, 140 determination in— boiler water, 140, 178 juice, 129 raw sugar, 128 syrup, 129 soluble and insoluble, 129 Photomicrography, 49 Photomultiplier, 31, 34 Pipettes— calibration, 72 delivery time, 72 graduated, 73 specification, (table XXV) tolerance, 73 Pneumercator, 159 Poisons, 83 Poladded to filter cake by bagacillo, 155 balance— empirical system, 152 direct analysis, 153 definition, 5 determination— bagasse, 103 cane, 105 juice, 97 molasses, 100 mud, 126 pan products, 100 sugar, 116 temperature corrections, 38, 99, 118 extraction, 3, 153 indirect cane analysis, 105 in open cells, 106 losses, 152 methods of analysis— dry lead, 97 Herles', 99 normal weight, 98 reagents for, 87 Polarimeter— automatic, 8, 24, 29 construction of, 24, 30 photo electric, 30 requirement for cane payment (table XXV)

248

INDEX

standardization, 35 sugar, 26 Polarimeter tubes, 37, 75 calibration, 75, 77 requirement for cane p a y m e n t (table XXV) Polarimetry, 23 Polariscope (see Polarimeter and saccharimeter) Polarized light, 20 by dichroic film, 20 extraordinary ray, 21 linearly, 20, 23 ordinary ray, 21 Polarizer prism, 21 Prepared cane analysis, 104 Preservation of samples— for analysis, 81, 89 for storage conditions, 89 Preservatives, 89 reagents for, 89 Pressure filter, 120 purity of molasses, 136 Primary juice 5 Primary mud, 5 Prisms— amici, 15 analyser, 22 calcite, 21 dispersion, 10, 15 Nicol 21 polarizer, 21, 25 refractometer, 14, 17 Purity— apparent, 1, 5 gravity, 5 true, 5 Pycnometer, 60 constant, 63 temperature effects, 63 determination— Brix 62 specific gravity, 62 volume, 60 Q Quartz plates, 35 compensator, 27 for Bendix polanmeter, 35 normal, 35 specification (table XXV) standardization of polarimeters by, 35 strain, 77 testing, 35, 77 Quartz wedge compensation, 26 R Raw sugar— analysis, 116 ash, 115 colour, 124 moisture, 119 phosphates, 128 polarization, 116 reducing sugars, 113 starch, 123 dilution indicator, 3 filterability test, 119 gram characteristics, 121

net titre, 5 other organic matter, 5 sampling, 80 temperature corrections for pol, 39, 118 tons E S G , 161 Reabsorption factor, 6 Reagents for— boiler water analysis, 84 buffer solutions, 85 clarifiability test, 85 filterabihty, 85 glass cleaning solution, 86 indicators, 86 phosphate analysis, 87 pol determination, 87 preservatives, 89 reducing sugar analysis, 90 standard acids and alkalis, 91 starch analysis, 92 sucrose analysis, 92 sugar detection, 92 water analysis, 93 Recovery— boiling house, 153 E S G , 161 formula, 157 overall, 153 pol in stock, 159 reduced overall, 165 Reduced extraction, 6, 163 Reducing sugars— definition, 6 determination, 113 molasses, 112 reagents for, 90 total, 112 Reducing sugar ash ratio, 6, 114 Refractive index, 9 angle of incidence, 9, 11 angle of refraction, 9 impure sugar solutions, 18 measurement, 11, 19 temperature effect, 10, 18 Refractometer, 8, 11 Abbe, 14 adjustment, 16 automatic, 8, 19 critical angle, 11, 19 dipping or immersion, 17 dry substance determination by, 18 hand, 18 high accuracy, 17 requirement for cane p a y m e n t (table XX 1 scale, 18 testing of, 77 Refractometer Brix, 1, 6, 18 Relative density, 58 Remelt, 6 Residual juice, 6 Retention, rotary filter, 156 Rotatory dispersion, 24, 26

S Saccharimeter, 8, 24, 26 automatic, 30 calibration of scale, 28, 77 construction, 27 definition, 26 effect of illumination, 29

INDEX

249

examination, 77 trace sugars, 130 influence of temperature, 39 turbidity measurement, 42 International sugar scale, 24, 35 Spencer-type drying oven, 102 light filter, 27, 29, 31, 32 Standard invert sugar solution, 90 quartz wedge compensation, 27 Standardization— requirement for cane payment (table XXV) acids and alkalis, 91 scale, zero adjustment, 29 Fehling's solution, 90 standardization, 35 normal solutions, 91 tolerance, 77 polarimeters, 35 Sample— quartz plates, 77 container, 79, 82 refractometers, 18 identification, 79 soap solution, 141 preservation, 82, 89 weights, 56, 77 Sampler— Starchautomatic, 79 indicator solution, 84 care of, 82 in raw sugar, 123 continuous, 79 reagents for analysis, 92, 123 pitot tube type, 80 standard solution, 92, 123 Sampling— Steam— bagasse, 81 dry saturated, 167 boiler water, 177 heat required, 166 cane, 78, 107 produced, 166 prepared, 78 superheated, 166 filter cake, 82 Stock— juice, 79 bulk sugar in, 160 massecuite, 80 materials balance, 152 molasses, 80 molasses in, 158 raw sugar, 80 taking, 159 syrup, 80 Strain, in glass, 23, 34 Saturation-definition, 136 Sucrose— Saturation cell, 137 analysis, 92, 108, 112 Scale on boiler heating surfaces, 174 reagents, 92 Schmitz's table for pol, formula, 99 definition, 6 Seed, 6 in high purity material, 108 Sensible heat loss, 169 in low purity material, 112 Set opening, 6 methods— Settling test, C.S.R. laboratory, 133 chemical, 112 Sieves— Clerget, 108, 110 British standard, 122 invertase, 108 Tyler, 122 Jackson and Gillis modification IV, 110 S.J.M. formula, 157 normal weight, 5, 36 Sodium D line, 10 recoverable, 157 Solidssolubility, definition, 136 dissolved, in boiling water, 142, 179 Sugar analysis— in mud, 124 ash, 115 insoluble, 124 filterability, 119 soluble, 125 grain size, 121 soluble, 1 moisture, 119 suspendedphosphate, 128 definition, 6 polarization, 116 in juices, 96 reducing sugars, 113 total dissolved—boiler water, 142 starch, 123 Solubility coefficient, 136 total colour attenuation, 124 Specific gravity— Sugar, definition, 6 bottle, 60 Sugars— definition, 58 by refractometer, 18 determination, 59 detection of, in effluents, 130 by hydrometer, 65 in boiler water, 180 by pycnometer, 60, 62 influence of temperature on rotation, 38 sugar solutions, 59 99, 118 Specific rotation, 23 optical rotation of, 23 Spectrophotometer, 8, 40 reducing, 6, 113 optical system, 41 specific gravities of, 59 use of— total, 112 Sugar detection— colour, total, 124 methods, 130 gums, 126 reagents, 92 phosphate determination, 128, 140 Supercel, 87 starch determination, 123

INDEX

250 Supersaturation— coefficient, 136 determination, 136 Suspended solids, 6 in juice, 96 Syrup— definition, 6 phosphate determination in, 129 sampling, 80 T

Tar, calorific value, 168 Temperature e f f e c t s boiler feed water analysis, 142, 177 pH determination, 145 pol reading, 38, 99, 118 refractive index, 10 sugar solutions, 38, 99, 118 Thermometer, 73 calibration, 75 emergent column error, 74 requirement for cane payment (table XXV) To date, averages, 162 Tolerances for laboratory apparatus (see table XXV) Total dissolved solids—boiler water, 142, 179 Total sugars— by refractometer, 18 definition, 6 estimation of, 112 Toxic materials, 83 True purity, 5 Turbidimeter, 8 Turbidity, 6 Turbidity measurement, clarified juice, 42 U Unburnt gas loss, 170 Undetermined loss, 152

Undiluted juice, 6 dilution per cent, 155 lost in bagasse per cent fibre, 164 V

Verdet constant, 23 Volumetric coefficient, 6 Volumetric equipment, 68 units of volume, 68 Volumetric glassware, 69 calibration, 77 meniscus setting, 69, 70, 71 specifications, 69 standard temperature, 69, 70

W Water— analysis— chlorides, 143 reagents, 93 dilution, 3 dissociation constant, 144 hygroscopic, 4 Weighing— by substitution, 52 coarse, 57 general precautions in, 54 method of, 54 Weighted average for " t o d a t e " figures, 162 Weights— requirement for cane p a y m e n t (table XXV) standardization, 77 tolerances (table XXV) Winter-Carp formula, 158 Wood, calorific value, 168 Work opening, 7 Work ratio, 7