Labortory Manual for South African Sugar Factories

QUT Library

LABORATORY MANUAL F O R

S O U T H A F R I C A N S U G A R F A C T O R I E S

S O U T H A F R I C A N S U G A R T E C H N O L O G I S T S ' A S S O C I A T I O N

2 2 8 1 0 6 1 7 B

First published 1962 by the S O U T H A F R I C A N S U G A R TECHNOLOGISTS ' ASSOCIATION

c/o S.A.S.A. EXPERIMENT STATION M O U N T EDGECOMBE, N A T A L

Text set in 10 Pt. Times Roman Printed in the Republic of South Africa

by Hayne and Gibson Ltd. 50-60 Ordnance Road, Durban

P R E F A C E

One of the outstanding services rendered by the South African Sugar Technologists' Association to our Sugar Industry has been its contribution to chemical control in our factories. This subject has formed an integral part of our activities ever since the inception of our Association in 1926 and the "Official Methods of the S.A. Sugar Technologists' Association for Chemical Control" were published in 1927 as part of the Proceedings of the first Annual Conference of the Association. Revised editions were published in 1930 and 1931 in the Proceedings of the fourth and fifth Annual Congresses. After a later major revision, these methods, suitably augmented, appeared in a separate booklet under the title "South African Sugar Technologists' Association Recommended Methods of Chemical Control in which are included the Official Methods". This publication became known as the "Recommended Methods" and served the Industry well for more than 25 years. The need for further revision and also the inclusion of additional useful methods has however now been felt for some years and in fact "The Committee for Standardization of Chemical Control" has remained most active throughout the intervening years.

This first edition of the "Laboratory Manual for South African Sugar Factories" is in fact the fifth publication of methods of chemical control issued by the South African Sugar Technologists' Association and it supersedes the "Recommended Methods of Chemical Control". The loose cover now used will facilitate future alterations or additions which can now be done by simply replacing or adding the necessary pages.

Members of the Chemical Control Committee have spent very many hours over a period of years in endeavouring to give the Industry the best. On behalf of the South African Sugar Technologists' Association I wish to extend to the Committee and its members our most grateful thanks.

The South African Sugar Industry is justly proud of the chemical control practised in its factories, and there can be no doubt that this manual will prove a great asset in the laboratories. I therefore have pleasure in welcoming the "Laboratory Manual for South African Sugar Factories" as a further worthwhile contribution by our Association to the chemical control of the South African Sugar Industry.

J. L. DU TOIT President

JUNE, 1962. S. Afr. Sugar Technologists' Association

C O N T E N T S PAGE

Chapter I Definitions 1 - 1962

Chapter II The determination of factory weights 1. General 7 - 1962 2. Cane 7 - 1962

a. The weighbridge, tares . . . . . . 7 - 1962 b. S.A.R. trucks 8 - 1962 c. Tram trucks . . . . . . . . 8 - 1962 d. Wagons, lorries and trailers . . . . 8 - 1962 e. Chains 9 - 1962 f. Loading poles . . . . . . . . 9 - 1962

3. Imbibition water . . . . . . . . . . 9 - 1962 4. Mixed juice 9 - 1962

a. General 9 - 1962 b. Non-automatic scales . . . . . . 9 - 1962 c. Automatic scales . . . . . . . . 10 - 1962

5. Bagasse 11 - 1962 6. Final molasses . . . . . . . . . . 11 - 1962 7. Filter cake 11 - 1962 8. Sugar 11 - 1962 9. Burnt lime, Sulphur and Phosphoric acid . . 11 - 1962

Chapter III Calculations 1. General 1 2 - 1962 2. Calculation of quantities in stock .. .. 12 - 1962 3. Recording of decimal fractions .. .. . . 13 - 1962 4. Rules for rounding off . . .. . . . . 14 - 1962 5. Standardization of methods of calculation .. 14 - 1962

a. Weights 14 - 1962 b. Percentages and ratios . . . . . . 16 - 1962 c. Miscellaneous formulae . . . . . . 16 - 1962

6. Sugar Milling Research Institute monthly period calculation sheet . . . . . . . . 18 - 1962

7. Sucrose balances . . .. . . . . .. 2 0 - 1962

Chapter IV Description and use of standard equipment 1 . General 2 2 - 1962 2. Instruments . . . . . . . . . . 22 - 1962

a. Saccharimeters . . . . . . . . 22 - 1962 b. Light filters 22 - 1962 c. Illumination . . .. . . . . 22 - 1962 d. Saccharimeter tubes and cover glasses. . 22 - 1962 e. Quartz plates 23 - 1962 f. Thermometers for the Clerget analysis . . 23 - 1962 g. Brix hydrometers . . . . . . . . 23 - 1962 h. Hydrometer jars . . . . . . . . 24 - 1962 j. Volumetric glassware . . . . . . 24 - 1962 k. Sugar flasks 24 - 1962 1. Pipettes 25 - 1962

m. Beaker flasks 26 - 1962 n. Bagasse digestion apparatus . . . . 26 - 1962 o. Counterpoise weights . . . . . . 26 - 1962

Laboratory Manual for S. Afr. Sugar Factories 1962 — V

PAGE Chapter V Sampling

1. General 27 - 1962 2. Cane 28 - 1962 3. Bagasse 29 - 1962 4. First expressed juice . . . . . . . . 30 - 1962 5. Mixed juice 33 - 1962 6. Last expressed juice . . . . . . . . 33 - 1962 7. Sulphited mixed juice . . . . . . . . 33 - 1962 8. Clarified juice and filtered juice . . . . . . 33 - 1962 9. Filter cake 33 - 1962

10. Syrup 33 - 1962 11. Massecuite (from pan) .. . . . . . . 35 - 1962 12. Massecuite (from crystallizer) . . . . . . 35 - 1962 13. Molasses 3 5 - 1 9 6 2 14. Sugar 35 - 1962

Chapter VI Reagents 1. General 3 8 - 1962 2. Clarifying reagents . . . . . . . . 38 - 1962

a. Lead subacetate solution for general use 38 - 1962 b. Neutral lead acetate solution . . . . 38 - 1962 c. Dry subacetate of lead . . . . . . 38 - 1962 d. Alumina cream (aluminium hydroxide) 40 - 1962

3. Indicators 40 - 1962 a. Indicators for measurement of pH .. 40 - 1962 b. Neutral water for dilution of indicators 40 - 1962 c. Buffer solutions . . . . . . . . 40 - 1962 d. Indicator solutions made up in the

laboratory . . . . . . . . 40 - 1962 4. Standard acid and alkali solutions . . . . 41. - 1962 5. Iodimetry 42 - 1962

a. General 42 - 1962 b. Preparation of N/32 sodium thiosulphate

solut ion. . . . . . . . . . 4 2 - 1962 c. Standardization of N/32 sodium thiosul

phate solution . . . . . . . . 42 - 1962 d. Preparation of iodine stock solution,

N / 1 . 6 approx 4 3 - 1 9 6 2 e. Preparation of N/32 iodine solution . . 43 - 1962 f. Standardization of N/32 iodine solution 43 - 1962

6. For the determination of sucrose . . . . 43 - 1962 a. Hydrochloric acid solution . . . . 43 — 1962 b. Sodium chloride solution. . .. .. 43 - 1962

7. For the determination of reducing sugars .. 43 - 1962 a. Preparation of standard invert sugar

solution . . . . . . 43 - 1962 b. Preparation of Fehling's solution,

Soxhlet's modification . . . . 44 - 1962 c. Standardization of Fehling's solution . . 44 - 1962 d. Preparation of Luff-Schoorl solution . . 44 - 1962

8. Juice preservative . . . . . . . . . . 45 - 1962 9. For the determination of calcium and mag

nesium . . . . . . . . . . .. 45 - 1962 a. Ethylenediaminetetraacetic a c i d . . .. 45 - 1962 b. Standard calcium chloride solution . . 45 - 1962 c. Buffer solution (according to Saunier

and Lemaitre) . . . . . . . . 45 - 1962 d. Eriochrome black T . . . . . . 45 - 1962 e. Murexide . . . . . . . . 45 - 1962 f. Caustic soda solution . . . . . . 46 - 1962 g. Standardization of ethylenediaminetetra

acetic acid solution . . . . . . 46 - 1962

VI — 1962 Laboratory Manual for S. Afr. Sugar Factories

For the determination of available phosphate .. 46 - 1962

a. Ammonium molybdate solution . . .. 46 - 1962 b. Reducing solution . . . . . . 46 - 1962 c. Standard phosphate solution . . . . 46 - 1962 d. Diluted standard phosphate solution . . 46 - 1962

11. For the determination of sulphur dioxide (modified Monier-Williams method) . . . . 46 - 1962 a. Hydrogen peroxide solution . . . . 46 - 1962 b. Hydrochloric acid, concentrated. . .. 46 - 1962 c. Sodium hydroxide solution, N/50 . . 46 - 1962 d. Alkaline pyrogallol solution . . . . 46 - 1962

Laboratory Manual for S. Afr . Sugar Factories 1963 — V I I

Chapter VII General methods of analysis 1. Temperature .. . . . . . . . . 47 - 1962 2. Filtration 47 - 1962 3. Brix 47 - 1962 4. Polarization, pol or apparent sucrose . . . . 48 - 1962

a. Horne 's dry lead method . . . . 48 - 1962 b. Normal weight method . . . . . . 48 - 1962

5 . Sucrose 4 9 - 1962 a. Using acid inversion (modified Jackson

and Gillis method IV) . . 49 - 1962 b. Using invertase . . . . . . . . 50 - 1962 c. The "chemical" method . . 51 - 1963

6. Reducing sugars . . . . . . . . 52 - 1963 a. The Lane and Eynon method . . 52 - 1963 b. The Luff-Schoorl method . . . . 5 3 - 1 9 6 2

7. Sulphur dioxide 53 - 1962 a. The iodine-titration method .. 53 - 1962 b. The rapid method of determining avail

able SO s in sugars 53 - 1962 c. The Monier-Williams method . . . . 54 — 1962

8. The conductivity of solutions of white sugars .. 55 - 1962 9. Calcium and magnesium (by a modification of

the Schwarzenbach method) . . . . . . 55 - 1962 10. Moisture 56 - 1962 11. p H 5 6 - 1 9 6 2 12. Titrated acidity or alkalinity . . . . . . 56 - 1962 13. Sulphated ash 5 6 - 1962 14. Test for traces of sugar in waters (Skarblom

test) 57 - 1962

Chapter VIM Analysis of products 1. Cane 58 - 1962

a. Sucrose % cane . . . . . . . . 58 - 1962 i. General factory method . . . . 58 - 1962

ii. Java ratio method . . . . 58 - 1962 iii. Test mill analysis . . . . . . 58 - 1962

b. Fibre % cane 59 - 1962 i. General factory method . . . . 59 - 1962

ii. Direct method 59 - 1962 iii. Indirect method . . . . . . 60 - 1962

2. Final bagasse . . . . . . . . . . 60 - 1962 a. Pol % bagasse . . . . . . . . 60 - 1962 b. Moisture % bagasse . . . . . . 60 - 1962

3. Bagacillo 61 - 1962 4. All juices other than mixed juice . . . . 61 - 1962

a. Brix 61 - 1962 b. Pol 61 - 1962 c. Reducing sugars . . . . . . 61 - 1962 d. Acidity or alkalinity . . . . . . 61 - 1962

V I I I — 1963 Laboratory Manual for S. Afr. Sugar Factories

PAGE e. Sulphur dioxide . . . . . . 61 - 1962 f. p H 62 - 1962 g. Calcium and magnesium . . . . . . 62 - 1962

5. Mixed juice 62 - 1962 a. Brix 62 - 1962 b. Pol 62 - 1962 c. Clerget sucrose by the Jackson and Gillis

method IV 62 - 1962 d. Clerget sucrose by the invertase method 64 - 1963 e. Reducing sugars . . . . . . 65 - 1962 f. Calcium and magnesium . . . . . . 65 - 1962 g. Available phosphate . . . . . . 65 - 1962

6. Syrup 66 - 1962 a. Brix 66 - 1962 b. Pol 66 - 1962 c. Reducing sugars . . . . . . 66 - 1962 d. Sulphur dioxide . . . . . . 66 - 1962 e. Hydrogen ion concentration (pH) 66 - 1962

7. Filter cake 66 - 1962 a. Pol 66 - 1962 b. Moisture . . 66 - 1962

8. Massecuites . . . . . . . . 66 - 1962 a. Brix 67 - 1962 b. Pol 67 - 1962 c. Crystal content . . . . . . 67 - 1962

9. Molasses excluding final molasses and wash . . 67 - 1962 a. Brix 67 - 1962 b. Pol (for stocktaking) 67 - 1962

10. Final molasses . . . . . . . . . . 67 - 1962 a. Brix 67 - 1962 b. Dry substance . . . . . . . . 67 - 1962 c. Sucrose 68 - 1962

i. The Jackson and Gillis method IV 68 - 1962 ii. The chemical method, using in

vertase . . . . . . . . 69 - 1963 d. Reducing sugars . . . . . . . . 70 - 1963 e. Total sugars . . . . . . . . 70 - 1963 f. Sulphated ash 70 - 1963

11. Sugars 70 - 1963 a. Pol 70 - 1963 b. Reducing sugars by the Luff-Schoorl

method 71 - 1963 c. Colour of white sugars . . . . 71 - 1963 d. Sulphur dioxide 72 - 1963 e. Moisture 72 - 1963 f. Sulphated ash 7 2 - 1 9 6 3 g. Conductometric ash (for mill white and

refined sugars) . . . . 72 - 1963 h. Grain size distribution . . . . 73 - 1962

T A B L E S

I Table adjusting the B.H.P. coefficient "f" according to the purity of mixed juice .. . . . . . . Chapter III , 43

II Temperature corrections to readings of brix hydrometers (20°C) „ IV, 2, g, v

III Schmitz's table for a normal weight of 26.000 g . . „ VII, 4, a

IV Table giving mg invert sugar required to reduce 10 and 25 ml of Fehling's solution in the presence of different amounts of sucrose . . . . . . . . „ VII, 6, a, ii

Va Table giving the divisor, corrected for the brix of the solution, of the formula to be used in the Jackson and Gillis method IV „ VIII, 5, c, iii

Vb Temperature corrections for the divisors for the Jackson and Gillis method for acid inversion . . „ VIII, 5, c, iii

VI Table to be used for the calculation of the result of the Luff-Schoorl determination of reducing sugars . . „ VIII, 11, b

VII Recommended scheme of analysis of various factory products . . . . . . . . . . . . . . „ VIII

F I G U R E S

1 Counterpoise weight . . . . . . . . . . Chapter IV, 2, o

2 Bagasse container . . . . . . . . . . „ V, 3, a, v

3 First expressed juice sampler .. . . . . . . „ V, 4, a, ii

4 Signalling device for first expressed juice sampler . . „ V, 4, b

5 Mixed juice sampler . . .. .. .. .. „ V, 5, c

6 Brix spindle reading . . . . . . . . . . „ VII, 3

7 Apparatus for determination of SO2 by Monier-Williams method . . . . . . . . . . „ VII, 7, c, ii

Laboratory Manual for S. Afr. Sugar Factories 1962 — IX

C H A P T E R I

D E F I N I T I O N S

A B S O L U T E J U I C E : A hypothetical juice, the weight of which is equal to the weight of cane minus the weight of fibre. It comprises all the dissolved solids in the cane plus the total water in the cane.

A P P A R E N T P U R I T Y : See under Purity.

A S H : The residue remaining after burning off all organic matter. B A G A C I L L O : Very small particles of bagasse separated either from

mixed juice or from the mass of the final bagasse for filtration or other purposes.

B A G A S S E : The residue obtained from crushing the cane in one or more mills known respectively as first mill bagasse, second mill bagasse, etc., and when referring to the residue from the last mill, last mill bagasse, final bagasse, or simply bagasse.

B O I L I N G H O U S E OR F A B R I C A T I O N D E P A R T M E N T : That part of the factory in which the processes of manufacture from mixed juice to weighed sugar are carried out.

B O I L I N G H O U S E P E R F O R M A N C E : The percentage ratio of crystallized sucrose actually recovered in sugar to crystallizable sucrose in mixed juice, as found by the method of calculation described in chapter III, 5, 41.

B O I L I N G HOUSE RECOVERY (RECOVERY OF SUCROSE IN MIXED J U I C E ) : The percentage ratio of sucrose (or pol) actually recovered in sugar to total sucrose (or pol) in mixed juice.

B R I X ( D E G R E E S ) : Unit divisions of the scale of a hydrometer, which when placed in a pure aqueous sucrose solution at 20°C, indicates the percentage by weight of solids in the solution. The reading obtained in an impure sucrose solution is usually accepted as an approximation of its percentage by weight of total soluble solids. The term Brix is used in calculations as a measure of substance e.g., tons Brix. Refractometer Brix: The term used when a refractometer equipped with a scale, based on the relationship between refractive indices at 20°C and the percentage by weight of total soluble solids of a pure aqueous sucrose solution, is used instead of a hydrometer to test the solids concentration of a sucrose-containing solution.

Laboratory Manual for S. Afr. Sugar Factories 1962 — 1

B R I X - F R E E W A T E R : The water associated with the fibre in cane and bagasse. In some respects this sorption water behaves in a manner somewhat similar to water of hydration. It cannot be separated from fibre by mechanical means but is driven off at raised temperatures. It is not available for dissolving sucrose. The amount of brix-free water is approximately 30% on bone dry matter (23% on natural fibre) and for milling control purposes is calculated as indicated in chapter III, 5, 33.

C A N E : The raw material from which sugar is recovered. a. Extraneous matter: Consists of materials which become associated

with the cane after it has been reaped, but does not include those comprised in the definition of 'field trash'.

b. Field trash: Consists of cane trash, tops, roots, dead sticks of cane, mud, leafy material and other vegetable matter from the field in which the cane was grown.

C. C. J . S .: A quantity used only for cane payment purposes and which is calculated using the formula

Sucrose % first expressed juice from this cane Tons of cane x —

100

C L A R I F I E D J U I C E : The juice prepared for evaporation.

C U S H - C U S H : The material removable from mill juice by straining. D I L U T I O N W A T E R : The portion of imbibition water or any other

weighed water present in mixed juice. D R Y S U B S T A N C E : The material remaining after drying the product

to constant weight, or for a specified period. The weight of the dry substance can also be found by deducting from the weight of the product, the weight of moisture, as determined in a specified manner.

E X T R A C T I O N : The percentage ratio of sucrose in mixed juice to sucrose in cane.

F A C T O R Y : The premises on which sugar manufacturing operations and their attendant activities are carried out.

F I B R E : The water insoluble matter of cane and bagasse from which the approximate 23 % brix-free water (30 % on bone dry matter) which it contains, has been removed by drying.

Where associated with brix-free water, fibre is often called natural fibre.

In factory and milling control practice, the fibre content of the final bagasse is calculated as indicated in chapter III, 5, 27.

F I L T E R C A K E : The residue removed from process by filtration including any added filter aid.

2 — 1962 Laboratory Manual for S. Afr. Sugar Factories

F I L T E R L I Q U O R S : a. If filter presses are used—

i. Filter juice: The clear filtrate from the presses. The filtrate produced during the process of washing or sweetening off is usually mixed with the filtrate obtained from juice and is also termed filter juice. When fractional washing is applied, the last runnings from one press are used for sweetening off the next press and are ultimately mixed with filter juice.

b. If rotary vacuum filters are used— i. Cloudy filtrate: The filtrate produced during the initial stage

of the filtration process. ii. Clear filtrate: The filtrate produced during the latter stage of

the filtration process, including the filtrate from the washing process.

c. If the double carbonatation process is applied, the filter juices from the first and second carbonatations are distinguished.

F I R S T E X P R E S S E D J U I C E : The juice expressed by the first two rollers of the tandem.

G R A V I T Y P U R I T Y : See under Purity.

G R A V I T Y S O L I D S : The weight of solids calculated from the brix spindle determination.

I M B I B I T I O N : The process in which water or juice is put on the bagasse to mix with and dilute the juice present in the latter. The water so used is termed imbibition water. General terms in use are:

a. Single imbibition, b. double imbibition, c. compound imbibition,

depending on the manner in which the water and/or juice is added. I N V E R T S U G A R : A mixture of approximately fifty % glucose

(dextrose) and fifty % fructose (laevulose) obtained by the hydrolysis of sucrose.

J A V A R A T I O : The percentage ratio of sucrose (or pol) % cane to sucrose (or pol) % first expressed juice. For distribution purposes, the Java ratio is calculated as indicated in chapter III, 5, 36.

J E L L Y ( S T R I N G P R O O F ) : A boiling which has been concentrated without graining to such a consistency that it may be expected to crystallize spontaneously on standing.

L A S T E X P R E S S E D J U I C E : The juice expressed by the last two rollers of the tandem.

L A S T M I L L J U I C E : The juice expressed by the last mill of the tandem.

M A G M A : A mixture of crystals and sugar liquor produced by mechani-cal means.

Laboratory Manual for S. Afr . Sugar Factories 1962 — 3

M A S S E C U I T E : The mixture of crystals and mother liquor discharged from a vacuum pan. Massecuites are classified in order of descending purity as first, second, etc., or A, B, etc., and jelly massecuite.

M I L L S E T T I N G S : a. Set opening: The set opening of a mill is the distance between the

circumferences escribed by the mean diameters of the top roller and feed or discharge roller with the mill running empty. The mean diameter of a grooved roller is equal to the diameter of the equivalent (same volume and length) solid roller.

b. Work opening: The work opening is equal to the set opening plus the increase in distance between the rollers resulting from the lift during milling operations.

M I X E D J U I C E : The mixture of juices from the mills delivered via ancillary mechanical equipment into the juice scales.

M O L A S S E S : The mother liquor separated from the massecuite by mechanical means. It is distinguished by the same prefixes as the massecuites from which it is separated. Final molasses: The mother liquor separated from the final massecuite by mechanical means. Final molasses is usually discharged from the factory as such.

M U D S : The material removed from the bot tom part of the subsiders. The muds (or mud) contain most of the settled suspended solids.

N O N - S U C R O S E : Strictly, dry substance minus sucrose, often brix minus sucrose.

N O N - S U G A R : Brix minus pol.

N O R M A L W E I G H T : a. That weight of pure dry sucrose which, when dissolved in water

to a total volume of 100 ml at 20°C and read at the same temperature in a tube 200 mm long, gives a reading of 100 degrees on a sac-charimeter scale. If the International Sugar Scale is used, the normal weight of sucrose is 26.000 grams; if the Ventzke scale is used, the normal weight is 26.026 grams, corresponding to a reading of 100°V.

b. The weight of sample equal to the normal weight of sucrose.

N U T S C H S A M P L E : A nutsch sample is any sample of molasses which is separated from a massecuite at any time prior to curing the massecuite in the factory centrifugals.

O V E R A L L R E C O V E R Y : The percentage ratio o f sucrose (or pol), actually recovered in sugar to total sucrose (or pol) in cane.

P O L : The apparent sucrose content of any substance expressed as a percentage by weight, and determined by the single or direct polarization method. The term is used as if it were a real substance.

P O L - A S H R A T I O : The ratio of pol to ash.


P O L E X T R A C T I O N : The percentage ratio of the weight of pol in mixed juice to the weight of pol in the corresponding weight of cane.

P R I M A R Y J U I C E : All the juice expressed before dilution begins.

P U R I T Y : The percentage ratio of sucrose (or pol) to the total soluble solids (or brix) in a sugar product. The following terms are in general use:

a. Apparent purity: The percentage ratio of pol to brix. b. Gravity purity: The percentage ratio of sucrose to brix. c. True purity: The percentage ratio of sucrose to total solids

determined by drying.

R E C O V E R Y ON M I X E D J U I C E : See Boiling House Recovery.

R E D U C I N G S U G A R S : The reducing substances in cane and its products determined as described in chapter VII and calculated as invert sugar. Note: The common practice of referring to reducing sugars as glucose is to be discouraged.

R E D U C I N G S U G A R — ASH R A T I O : The ratio of reducing sugars to ash.

R E D U C I N G S U G A R — S U C R O S E R A T I O : The percentage ratio of reducing sugars to sucrose or pol.

R E S I D U A L J U I C E : The juice left in intermediate or final bagasse.

S A C C H A R I M E T E R R E A D I N G : Actual reading on the scale of a saccharimeter.

S A F E T Y F A C T O R : A number designed to indicate the probable keeping quality of a fresh raw sugar. It is calculated by dividing the percentage moisture in the sugar by one hundred minus the pol of the sugar.

S E C O N D A R Y J U I C E : The dilute juice which together with the primary juice forms the mixed juice.

S U C R O S E : The pure disaccharide, C12H22011, also known as saccharose or cane sugar.

S U G A R : The main product of a sugar factory consisting of crystals of sucrose as removed from a massecuite and containing a smaller or larger portion of natural impurities, depending on the type of sugar.

S U L P H A T E D A S H : The residue remaining after burning off all organic matter in a sample, sulphuric acid being used as described in chapter VII, 13.


U N D I L U T E D J U I C E : A hypothetical juice, whose weight i s equal to the weight of cane minus the combined weights of fibre and brix-free water. For milling control purposes, the weight of undiluted juice is calculated as indicated in chapter III, 5, 12.

W A S H : The diluted molasses thrown off by the centrifugals during washing and/or steaming, and collected separately.


C H A P T E R I I

T H E D E T E R M I N A T I O N O F F A C T O R Y W E I G H T S

1. General All weighings shall be subject to the Weights and Measures Act and Regulations and further to the rulings given by the Superintendent of Assize or the Assizer concerned. The weighing of cane, imbibition water and mixed juice shall be subject to the provisions of any Agreement published in terms of the Sugar Act 1936, or any amendment thereof, or any provisions as may be agreed upon by the South African Sugar Association, and where necessary approved by the Assize Depar tment .

2. Cane a. The weighbridge, tares

i. The weighbridge shall be situated as near as possible to the off-loading site in order to minimize any loss or gain in weight after the cane has been weighed.

ii. Sequence numbered scale tickets, upon which the gross weight of the vehicle shall be recorded by means of the stamping device attached to the weighbridge, shall be used on all weighbridges of the beam type.

iii. Special attention is drawn to regulation 53 (g) of the Weights and Measures Act, which reads:

"Where any self-indicating weighing instrument approved in terms of section twenty-three (1) of the Act after 1st September, 1957, is furnished with a weight-recording or printing device, means must be provided to prevent any recording or printing being effected while the pointer is moving."

iv. The introduction of automatic self-recording weighbridges for the weighing of cane, together with some automatic device to ensure that the vehicle to be weighed is correctly placed on the weighbridge platform, is strongly recommended.

v. The weight of the cane shall be obtained by subtracting the gross tare from the gross weight of the vehicle and its contents.

vi. Gross tare means the weight of the vehicle (nett tare) plus the weight of all loading poles or chains and all extraneous matter, but not the weight of matter originally adhering to the cane in the normal practice of harvesting, which means that no deductions shall be made as tare for trash, tops, roots, soil or mud.


b. S.A.R. trucks i. S.A.R. trucks should be weighed uncoupled and separately,

especially where there exists any possibility of a downward or upward thrust being created by the trucks preceding or following the truck to be weighed. There should be at least 50 feet of straight level track on either side of the weighbridge. If circumstances preclude the possibility of weighing S.A.R. trucks uncoupled, then every precaution shall be taken to ensure that the truck being weighed is free from interference by the S.A.R. trucks preceding and following it.

ii. The nett tare weights which are stencilled on the side of the S.A.R. trucks have been found, in certain cases, to be seriously in error. The miller may re-tare each and every truck. Any coal, lime, rocks or any other extraneous matter which may be found at the bot tom of the truck, shall be included in the gross tare.

iii. Where unloaded S.A.R. trucks are not re-tared in the mill yard, the nett tare, as stencilled on the side of the truck by the Railway Administration, shall be accepted and no addition shall be made thereto for the weight of any extraneous matter remaining in the truck unless such weight has been determined separately. Caution: Portuguese rolling stock is marked with tares in kilograms with or without the equivalent in pounds.

c. Tram trucks i. Tram trucks should be weighed uncoupled and separately,

but where this is not possible every precaution shall be taken to ensure that the t ram truck being weighed is free from interference from the t ram trucks preceding or following it. There should be at least 50 feet of straight level track on either side of the weighbridge.

ii. The gross tare, which shall be distinctly marked on the side of each truck, shall include the weight of the loading chains attached to the t ruck; such gross tare weight shall be deter-mined at the beginning of each season and as often as may be deemed necessary due to repairs and other causes, to the satisfaction of the miller and the supplier of the cane.

d. Wagons, lorries and trailers i. The vehicles shall be weighed after unloading as often as is

agreed upon by the miller and the grower, but at least once daily. The weight shall include side poles and chains used to transport the cane from the field to the factory. This con-stitutes the gross tare of the vehicle.

ii. Where cane is weighed in trailers which are too long to be accommodated on the weighbridge platform, the following


procedure to determine the weight of cane shall be adopted: The mechanical horse and trailer shall be weighed

coupled by first placing the horse dead centre on the weighbridge platform (note weight recorded), then the load is drawn across the scale platform until the trailer wheels reach dead centre of the weighbridge platform (note weight recorded). The sum of the two weights represents the total gross weight of the consignment. Tare weights of the horse and trailer are determined in the same way as described above, while the nett weight of the consignment is the difference between the two sets of weights so determined.

e. Chains i. The tare for loading chains shall be included in the gross

weight of the vehicle and shall be determined either by taking the average weight of a number of typical chains, or by substituting a similar number of chains for loading purposes upon the empty vehicle to be re-weighed.

ii. Where cane is weighed in slings the bundle with sling attached shall be completely disconnected from the crane. The weight of the sling constitutes the tare weight and shall be determined as under i above.

f. Loading poles i. Loading poles should be approximately 8 ft 6 in. long and

3½ in. butt end diameter. The weight of each pole should be not less than 15 lb. nor greater than 30 lb.

ii. The average weight per pole shall be used in conjunction with the total number of poles used per truck to determine the tare for poles in each truck.

The average weight per pole shall be determined by mutual agreement between the miller and the supplier of the cane.

3. Imbibition water The weight shall be determined by weighing. Any water that is used for wash-down purposes which enters the mixed juice shall be determined by weighing and included in the weight of imbibition water.

The provisions under 4, Mixed juice, below, concerning the operation and checking of the scales (non-automatic and automatic) shall also apply to the weighing of imbibition water.

4. Mixed juice a. General

The weight shall be determined by weighing.

b. Non-automatic scales i. The nett weight of each tip shall be found by subtracting from


the weight of the full scale tank the weight of the emptied tank, as determined after each weighing of a full tank.

ii. Sequence numbered tickets stamped with indelible numbers shall be used for each scale tank weighed.

iii. An automatic device which records the filling or emptying of each scale tank (such as the Bristol Recorder) shall be fitted to each scale tank.

iv. An automatic counter for recording the number of loads shall be fitted to each scale.

Automatic scales i. Items iii and iv of paragraph 4, b, shall also apply to automatic

scales, but where the frequency of tips precludes the use of the devices mentioned under 4, b, iii, then three automatic counters shall be used on each scale for recording the number of scale tanks weighed.

ii. Automatic weighing machines of the constant-load type shall be adjusted by the District Assizer or by a person authorized by him to perform such adjustment, and the weight of any load of juice delivered by an adjusted weighing machine shall be assumed to be equal to the capacity for which the machine has been adjusted.

iii. Nevertheless it is strongly recommended that daily verification be obtained of the accuracy of the assized weight of a load in order to detect any deviations in the functioning of the weighing machine. For this purpose ten consecutive loads of juice, obtained under normal operating conditions, shall be re-weighed over another assized or re-assized weighing instrument.

iv. The arithmetical mean of the ten check weights shall be determined, and if this mean weight differs by more than 0 .5% either in excess or deficiency from the assized capacity, the weighing machine shall be re-adjusted.

v. Automatic weighing machines of the variable-load type shall be adjusted by the District Assizer or by a person authorized by him to perform such adjustment.

vi. Nevertheless it is strongly recommended that daily verification be obtained concerning the accuracy of the weight as indicated by the recording mechanism of the weighing machine, using the appropriate check weight.

vii. Re-weighing ten consecutive loads of juice as described in 4, c, iii and 4, c, iv above, provides an even better means of verifying weighing machines of the variable-load type, where a sufficiently accurate and sensitive secondary weighing machine is available.

1962 Laboratory Manual for S. Afr . Sugar Factories

5. Bagasse By inference, assuming the fundamental equation to be exact: weight of cane + weight of imbibition water = weight of mixed juice + weight of bagasse.

Weight of bagasse is therefore: weight of cane plus weight of imbibition water minus weight of mixed juice.

6. Final molasses By weighing.

7. Filter cake Whether obtained from plate and frame or vacuum type fil ters, the weight of the filter cake shall be determined by continuous or periodic weighing of the contents of trucks into which the filter cake is discharged.

8. Sugar By weighing on scales and in such manner as is approved by the Government Assize Depar tment . Where sugar is weighed in bags, provision shall be made previously for the weight of the bags.

9. Burnt lime, Sulphur and Phosphoric acid By weighing.


C H A P T E R I I I

C A L C U L A T I O NS

1. General Control data are required for the purpose of factory control and as a basis for cane payment. The former are recorded in daily, weekly, monthly and annual reports.

Control data are usually calculated from quantities obtained by direct weighing (infrequently by direct measuring) in conjunction with figures obtained by direct analysis.

Quantities obtained by direct weighing are : tons* of cane, tons of imbibition water, tons of mixed juice, tons of filter cake, tons of final molasses and tons of sugar. The methods of weighing are described in chapter II.

2. Calculation of quantities in stock For the purpose of correctly ascertaining sucrose, pol, brix, non-sucrose and other balances, and certain efficiency data, account must be taken of the materials currently being processed.

The estimation of the quantities in process is called stocktaking. In stocktaking a list should be made of the estimated quantities of the various products and their percentages of sucrose and brix. F rom these data the total weights of sucrose and brix in stock and the average purity of the products in stock are calculated. F rom the purity figures, the fraction of sucrose in stock which shall be recovered as sugar is calculated using the S.J.M. formula:

* Wherever the term tons is used it means tons of 2,000 lb. each.


where x = recovery of sucrose % sucrose in the primary product

S = expected purity of the sugar to be produced J = purity of the primary product

M = expected purity of the final molasses to be produced which in Natal is taken as equal to the average purity of the final molasses produced in the preceding week.

x = 100 x S (J—M)

J (S—M)

The use of the formula is illustrated by calculation of the percentage of sucrose which should be recovered from the total stock in process at the end of the week.

Let total tons brix in stock = 2000 and „ „ „ sucrose in stock = 1500

then average purity of stock =

If the expected purity of sugar to be produced = 99 and if the purity of final molasses for the preceding week = 39.7

then from S.J.M. formula

x = 100 x = 78.6

i.e. 78 .6% of the sucrose in stock should be recovered in sugar while the balance (21.4%) should be retained in the final molasses.

Subsequent calculations yield: a. tons of sucrose in stock expected to go into sugar b. tons of sucrose in stock expected to go into final molasses.

The former quantity should be added to tons of sucrose in sugar made yielding tons of sucrose in sugar made and estimated. The latter quantity should be added to tons of sucrose in final molasses made yielding tons of sucrose in final molasses made and estimated.

F rom tons of sucrose in sugar made and estimated, tons of sugar made and estimated can be computed. F r o m tons of sucrose in final molasses made and estimated, tons of final molasses made and estimated can be computed.

As well as making a sucrose balance, other balances, e.g. brix and non-sucrose balances, may be made using the above-mentioned data.

3. Recording of decimal fractions A note of caution is given to chemists that decimal fractions should be used with discretion. If r andom errors alone were considered, then the average of a large number of analyses could be carried to more places of decimals than the result of a single test; but there are constant errors such as errors in apparatus which cannot be reduced in this way. Con-sideration of all types of errors shows that the average of a series of pol or sucrose percentages in sugars or juices should not be reported to more than the second decimal place. The reading of a brix spindle should be recorded to the nearest 0.05° brix and the temperature correction to the nearest second decimal place. The second place of the resultant figure should be discarded and the brix of all products should be recorded to the nearest first decimal place. The calculated average, however, should be recorded to the nearest second place. To record decimal places in the case of the weight of filter cake, which is not continuously and carefully weighed, is wrong and misleading. Alternatively, if sugar or cane is weighed precisely to the third or fourth decimal of a ton, then the third or fourth decimal must always be recorded even when the figure is 0.


x 100 = 75.

In the fundamental equat ion: weight of cane + weight of imbibition water = weight of mixed juice + weight of bagasse, the weight of cane, imbibition water, mixed juice and bagasse are all reported to the third decimal place in tons. Where the weight of the cane is recorded to the nearest pound, this weight should be reported to the nearest 0.0005 tons, in which case the fundamental equation should be carried to the fourth decimal place. (Note: While the weight of bagasse cannot be assumed to be accurate, the third decimal place should nevertheless be recorded, in order to make the fundamental equation balance.) The corresponding weights of sucrose in mixed juice and bagasse should be recorded to the third decimal place in tons, and their sum, which is the weight of sucrose in cane, to the third decimal place.

4. Rules for rounding off Wherever a decimal place to be discarded is represented by a number less than five, the preceding digit (that is the last to be recorded) shall remain as it s tands; but where the number to be discarded is greater than five, one shall be added to the preceding digit. Where the number to be discarded is exactly five, the preceding digit shall be unaltered if it is an even number, but if it is an odd number one shall be added to it.

5. Standardization of methods of calculation The calculations in this section are given with a view to standardization of methods. The formulae do not include all the calculations which the chemist may be required to make in his capacity as statistician. Others will be found in subsequent chapters of this manual .

In the following formulae, numbers in square brackets [ ] refer to the number of decimal places to which calculations should be made, numbers in round brackets ( ) refer to the calculations hereunder.

The letter w signifies a quantity obtained by direct weighing or direct measurement and x denotes a value obtained by direct analysis.

a. Weights

1 . T O N S O F B R I X I N C A N E [3]

Tons of brix in mixed juice (9) + tons of brix in bagasse (5). 2 . T O N S O F S U C R O S E I N C A N E [3]

Tons of sucrose in mixed juice (10) + tons of sucrose in bagasse (6). 3 . T O N S O F F I B R E I N C A N E [3]

Is equal to tons of fibre in bagasse (7).

4 . T O N S O F B A G A S S E [3] Tons of cane w + tons of imbibition water w — tons of mixed juice w.

5 . T O N S O F B R I X I N B A G A S S E [3]

Tons of bagasse (4) x brix % bagasse (26) 100

14 — 1962 Laboratory Manual for S. Afr . Sugar Factories

6 . T O N S O F S U C R O S E I N B A G A S S E [3]

Tons of bagasse {4) x sucrose (pol) % bagasse x l00

7 . T O N S O F F I B R E I N B A G A S S E [3]

Tons of bagasse {4) x fibre % bagasse {27) 100

8 . T O N S O F M O I S T U R E I N B A G A S S E [3]

Tons of bagasse (4) x moisture % bagasse x 100

9 . T O N S O F B R I X I N M I X E D J U I C E [3]

Tons of mixed juice w x brix % mixed juice x 100

10. T O N S O F S U C R O S E I N M I X E D J U I C E [3]

Tons of mixed juice w x sucrose % mixed juice x 100

11. T O N S O F A B S O L U T E J U I C E [3]

Tons of cane w — tons of fibre in cane (3). 12. T O N S O F U N D I L U T E D J U I C E [3]

Tons of brix in cane (1) X 100 Brix % first expressed juice x

13. T O N S O F S U C R O S E I N F I L T E R C A K E [3]

Tons of filter cake w x sucrose (pol) % filter cake x

Too

*14. T O N S O F S U C R O S E I N S U G A R [3] Tons of sugar w x sucrose (pol) % sugar x

100

* These are general formulae; if quantities in stock are to be taken into account the procedure mentioned under 2 above should be followed.


*15. T O N S O F M O I S T U R E I N S U G A R [3]

*16. T O N S O F B R I X ( S O L I D S ) I N S U G A R [3]

Tons of sugar w — tons of moisture in sugar (15). *17. T O N S O F S U C R O S E I N F I N A L M O L A S S E S [3]

Tons of final molasses w x sucrose % final molasses x 100

*18. T O N S O F B R I X I N F I N A L M O L A S S E S [3]

Tons of final molasses w x brix % final molasses x l00

*19. T O N S O F U N D E T E R M I N E D L O S S O F S U C R O S E [3]

Tons of sucrose in mixed juice (10) — tons of sucrose in filter cake (13) — tons of sucrose in final molasses (17) — tons of sucrose in sugar (14).

b. Percentages and ratios 20. S U C R O S E % C A N E [2]

Tons of sucrose in cane (2) X 100 Tons of cane w

21. S U C R O S E % C A N E ( A P P R O X I M A T E C A L C U L A T I O N ) [1]

sucrose (pol) % first expressed juice x x an assumed Java ratio 100

22. F I B R E % C A N E [2]

Tons of fibre in bagasse (7) X 100 Tons of cane w

23. B A G A S S E % C A N E [2]

Tons of bagasse (4) X 100 Tons of cane w

24. I M B I B I T I O N % C A N E [1]

Tons of imbibition water w X 100 Tons of cane w

25. I M B I B I T I O N % F I B R E [0]

Tons of imbibition water w X 100 Tons of fibre in cane (3)

26. B R I X ( S O L U B L E S O L I D S ) % B A G A S S E [2]

Sucrose (pol) % bagasse x X 100 Purity of last expressed juice x

27. F I B R E % B A G A S S E [2] Dry substance % bagasse x — brix % bagasse (26).

28. B R I X % A B S O L U T E J U I C E [2]

Tons of brix in cane (1) X 100 Tons of absolute juice (11)

29. D I L U T I O N % A B S O L U T E J U I C E E X T R A C T E D [2]

Brix % absolute juice (28) — brix % mixed juice x X 100 Brix % mixed juice x

30. A B S O L U T E J U I C E L O S T I N B A G A S S E % F I B R E [0]

Brix % bagasse (26) Brix % absolute juice (28) x fibre % bagasse (27)

31. R E D U C I N G S U G A R / S U C R O S E R A T I O [2]

Reducing sugar % product x X 100

Sucrose (pol) % product x

32. R E D U C I N G S U G A R / A S H R A T I O [2]

Reducing sugar % product x Sulphated ash % product x

c. Miscellaneous formulae 33. B R I X - F R E E W A T E R % F I B R E [0]

Tons of absolute juice (11) — tons of undiluted juice (12) X 100 Tons of fibre in bagasse (7)


X 10,000

34. POUNDS OF FIBRE PER CUBIC FOOT ESCRIBED VOLUME [0] Calculated weekly for the discharge opening of each mill unit. The escribed volume is equal to n n D L K cu. ft where n = the total number of revolutions of the top roller for the week

D = the corrected mean diameter of the top roller, in ft L = the length of the top roller, in ft K = the average work opening, in ft.

K is found from the set opening and the average lift of the top roller using the formula: K = S + 0.8H where S is the set-opening in ft and H is the average lift of the top roller in ft (generally 3 0 % of the total possible lift). Pounds of fibre equals tons of fibre for the week x 2,000.

Hence Pounds fibre per cu. ft escribed volume

37. E X T R A C T I O N [2] Tons of sucrose in mixed juice (10)

Tons of sucrose in cane (2)

x 100

40. E X P E C T E D P U R I T Y O F F I N A L M O L A S S E S ( D O U W E S D E K K E R

F O R M U L A )

Expected (true) purity = 35.886 — 0.08088 R + 0.26047 A where R = reducing sugars % non-sucrose

A = ash % non-sucrose.

41. B O I L I N G H O U S E P E R F O R M A N C E [2]

Laboratory Manual for S. Afr. Sugar Factories

in which sum of tons C.C.J.S. is equal to the sum of the quantities

x 100

1962 — 17

Tons of sucrose in sugar (14) Tons of sucrose in mixed juice (10)

x 100

39. OVERALL RECOVERY [2]

Pounds of fibre for the week Escribed volume for the week

35. J A V A R A T I O [2]

Sucrose % cane (20) Pol % first expressed juice x

x 100

36. J A V A R A T I O F O R D I S T R I B U T I O N P U R P O S E S [4] Tons of sucrose in cane for a certain period

Sum of tons C.C.J.S. x 100

Tons of cane x Sucrose % first expressed juice from this cane 100

for each consignment.

x 100

38. B O I L I N G H O U S E R E C O V E R Y [2]

4 2 . C R Y S T A L L I Z A B L E S U C R O S E [3]

Crystallizable sucrose is calculated using the S.J.M. formula in the form

Percentage crystallizable sucrose = S —

where S is the percentage sucrose in the product B is the percentage brix in the product P is the purity of final molasses (either the expected or actual

purity may be employed). Note : Under particular conditions

e.g. when P = 28.57 this formula is known as the Winter formula or when P = 30.0 „ „ „ „ „ Carp formula.

4 3 . B . H . P . C O E F F I C I E N T (f)

The B.H.P. coefficient which is equal to the term in the

formula for calculating percentage crystallizable sucrose in a product is dependent on the purity of the mixed juice. The values reported in Table I have been adjusted to Natal conditions.

6. Sugar Milling Research Institute monthly period calculation sheet The calculation sheet used by the Sugar Milling Research Institute for the " to da te" and "per iod" figures for Boiling house performance and Lost absolute juice together with Purity of last expressed juice, Brix-free water and Imbibition efficiency which are used as checks on the accuracy of some of the factory data, follows. A typical worked example is included. Boiling House Performance Calculation

1. Tons Brix in mixed juice (To Date) 99888.308 2. Tons Sucrose in mixed juice (To Date) 85241.711

3. Tons Non-Sucrose in mixed juice (To Date) 14646.597 4. f (to three decimal places, according to purity

of M.J.) 0.492

(-)

( x ) _5. Tons Non-Crystallizable Sucrose in mixed juice (To Date) 7206.126


100.00

44. C R U S H I N G T I M E A N A L Y S I S

a. Hours available for crushing [1] is a minimum weekly time of 144 hours.

b. Overall efficiency [2] Hours of actual crushing [1]

Hours available for crushing (44, x) c. Hours of stoppage percentage [2]

Hours ot stoppage LI J Hours available for crushing (44, x) It should be recorded as follows:

i. H.S.P. due to mechanical failures in the mills

ii. H.S.P. due to mechanical failures in the boiling house

iii. H.S.P. due to other causes inside the factory (jams, etc.)

iv. H.S.P. due to shortage of cane v. H.S.P. due to other causes outside the

factory Overall efficiency


85241.711 7206.126

78035.585

75720.955 75012.993

707.962

90.84 37.60

53.24

70.62

75012.993

499.963

74513.030

95.49%

To-Date 651078.770 102672.132

548406.638

242432.185 130066.889

112365.296 102672.132

9693.164 99888.308

109581.472 548406.638

19.98

9693.164 19.98

48514.334 102672.132

47.25

74513.030 62349.459

12163.571

78035.585 65336.107

12699.478

95.78%

Period 106151.520 17326.585

88824.935

41805.640 22882.386

18923.254 17326.585

1596.669 16267.461

17864.130 88824.935

20.11

1596.669 20.11

7939.677 17326.585

45.82

Lost Absolute Juice Calculation

Tons of Cane crushed

Tons of Fibre in Cane

Tons of Absolute Juice

Tons of Bagasse Tons of Moisture in Bagasse Tons of Dry Matter in Bagasse Tons of Fibre in Bagasse Tons of Brix in Bagasse Tons of Brix in Mixed Juice

Tons of Brix in Cane Tons of Absolute Juice

( x 1OO) Brix % Absolute Juice

Tons of Brix in Bagasse Brix % Absolute Juice

( x 1OO) Tons of Absolute Juice in Bagasse Tons of Fibre in Bagasse

( x 1OO) LOST ABSOLUTE JUICE % FIBRE

2. Tons Sucrose in mixed juice (To Date)

5. Tons Non-Crystallizable Sucrose in mixed juice (To Date)

6. Tons Crystallizable Sucrose in mixed juice . . (To Date)

7. Tons Solids in Sugar made and estimated . . (To Date) 8. Tons Sucrose in Sugar made and estimated . . (To Date) 9. Tons Non-Sucrose in Sugar made and estimated (To Date)

10. Brix % final molasses (To Date) 11.. Sucrose % final molasses (To Date)

12. Non-Sucrose % final molasses (To Date) 13. Sucrose % Non-Sucrose in final molasses

100x11/12 (To Date)

8. Tons Sucrose in Sugar made and estimated . . (To Date) 14. Tons Non-Crystallizable Sucrose in sugar made

and estimated 9 x 13/100 (To Date)

15. Tons Crystallizable Sucrose in Sugar made and estimated (To Date)

16. BOILING HOUSE PERFORMANCE 1 0 0 X 1 5 / 6 . . (To Date)

15.. Tons Crystallizable Sucrose in Sugar made and estimated (To Date)

17. Dit to to-date quantity of the previous report . .

18. Tons Crystallizable Sucrose in sugar made and estimated (Period)

6. Tons Crystallizable Sucrose in mixed juice . . (To Date)

19. Dit to to-date quantity of the previous report . .

20. Tons Crystallizable Sucrose in mixed juice . . (Period)

21. BOILING HOUSE PERFORMANCE 1 0 0 X 1 8 / 2 0 . . (Period)

Purity of Last Expressed Juice Calculation

Tons of Sucrose in Bagasse Tons of Brix in Bagasse

( x 1OO) Weighted Mean of PURITY OF LAST EXPRESSED JUICE

Brix-free Water % Fibre Calculation

Tons of Brix in Cane Brix % First Expressed Juice

(x 1OO) Tons of Undiluted Juice

Tons of Absolute Juice Tons of Undiluted Juice

Tons of Brix-Free Water Tons of Fibre

(x 100) BRIX-FREE WATER % FIBRE

Imbibition Efficiency Calculation

Tons of Fibre Tons of Bagasse

(x 1OO) Fibre % Bagasse

Brix of Last Expressed Juice Purity of Last Expressed Juice

(x 100) Sucrose % Last Expressed Juice

Fibre % Bagasse

(100 —Fibre % Bagasse) Sucrose % Last Expressed Juice

(x 100) Sucrose % Bagasse (Calculated) Sucrose % Bagasse (Analysis)

(x 100) IMBIBITION EFFICIENCY

Period 1230.614 1596.669

77.07

To-Date 7267.915 9693.164

74.98

Period 17864.130

21.32

83790.478

To-Date 109581.472

21.00

521816.533

88824.935 83790.478

5034.457 17326.585

29.06

548406.638 521816.533

26590.105 102672.132

25.90

Period 17326.585 41805.640

41.45

To-Date 102672.132 252432.185

40.67

4.26 77.07

3.28

3.41 74.98

2.56

100.00 41.45

58.55 3.28

1.92 2.94

65 .31%

100.00 40.67

59.33 2.56

1.52 2.88

52.78%

7. Sucrose balances The sucrose balance offers a convenient means of detailing losses of sucrose in process of manufacture. The use of two such balances is recommended:

a. balance as sucrose % sucrose in cane

b. balance as sucrose % sucrose in mixed juice.


These balances should be drawn up as follows:

Product

Final Bagasse

Filter Cake

Final Molasses made and estimated

Sugar made and estimated

Undetermined

Mixed Juice

Cane

Weight of sucrose in product

Sucrose Balances

Sucrose % sucrose in

cane

100.00

Sucrose % sucrose in mixed juice

100.00


C H A P T E R I V

D E S C R I P T I O N A N D USE O F S T A N D A R D E Q U I P M E N T

1. General a. Standardized equipment shall be used for the determination of

sucrose in cane. b. All volumetric glassware, brix hydrometers and saccharimeter tubes

shall be standardized at 20°C. This apparatus, together with the thermometer used in the estimation of sucrose by the Jackson and Gillis method or by the direct polarization method, must have been tested by the Sugar Milling Research Institute and provided with a Certificate of Accuracy.

2. Instruments a. Saccharimeters: It is recommended that saccharimeters be equipped,

wherever possible, with the International Sugar Scale (°S), corresponding to a normal weight of 26.000 grams. For saccharimeters still equipped with the Ventzke scale (°V) a normal weight of 26.026 grams shall be used.

All saccharimeters must be marked with either a large S or a V indicating whether an International Sugar Scale or a Ventzke Scale is fitted.

b. Light filters: When saccharimeters are provided with light filters in the form of dichromate cells, these cells shall be filled with a solution

containing 9/L grams of potassium dichromate per 100 ml, where L

is the length of the cell in centimetres.

c. Illumination: The source of illumination shall be fixed relative to the saccharimeter and therefore saccharimeters which have the lamp attached by a metal a rm to the instrument are recommended. For the same reason, screw-type and not bayonet-type globe fittings are approved.

d. Saccharimeter tubes and cover glasses i. Tubes of three different lengths are required, 100 mm, 200 mm

and 400 mm. Tubes with a side opening are recommended as most suitable for all types of routine analyses. If solutions in tubes with side openings are not to be read immediately, closure of the opening should be effected to prevent evaporation.


ii. Saccharimeter tubes and cover glasses shall satisfy the requirements given in Polarimetry, Saccharimetry and the Sugars (N.B.S., U.S. Depar tment of Commerce, Circular C440), Washington, United States Government Printing Office, pages 102-106. They shall be covered by a certificate of accuracy issued by the Sugar Milling Research Institute.

e. Quartz plates: Every factory shall have at least two quartz plates. The value of one shall be near 100°S and the value of the other between —10°S and —15°S. Quartz plates shall be procured from a reputable firm and their value shall be checked once a year by the Sugar Milling Research Institute. When warranted, a certificate of accuracy shall be provided after checking.

f. Thermometers for the Clerget analysis i . T H E 0 ° - 1 0 0 ° O R 1 1 0 ° C T H E R M O M E T E R

This thermometer shall be graduated in single degrees (tolerance ± 0.5°C) and shall not exceed 10 mm in diameter so as to ensure the unimpeded flow of the hydrochloric acid which is added to the solution at 65°C. Its length shall be such that the 65°C mark is visible above the top of the inversion flask.

ii. T H E " I N V E R S I O N " T Y P E T H E R M O M E T E R

This thermometer should have a range from 10°C to 35°C and shall be graduated in l /10th degrees (tolerance ± 0.2°C). Thermometers of this type are used for measuring the temperatures of the solutions to be polarized in the inversion method of analysis.

All thermometers selected for the Clerget inversion analysis shall be kept and used only for that purpose.

g. Brix hydrometers i. The graduation of the brix hydrometers shall be based on

Plato's table giving the relationship between the concentration

of pure sucrose solutions and the density at 200/40 C.

ii. A set of six hydrometers covering the following ranges is recommended:

N o . 0 from 0°bx to 5° bx ; graduation interval 0.05°bx No . 1 from 2°bx to 13.5°bx; graduation interval optional but

not greater than 0.1 °bx N o . 2 from 13°bx to 21° bx; graduation interval optional but

not greater than 0.1 °bx N o . 3 from 19°bx to 27° bx; graduation interval optional but

not greater than 0.1 °bx


N o . 4 from 26°bx to 48° bx; graduation interval 0.1 °bx N o . 5 from 46°bx to 68° bx; graduation interval 0.1 °bx

iii. The length of the brix scale shall be approximately: N o . 0 220 m m ; No . 2 250 m m ; N o . 4 320 m m ; N o . 1 270 m m ; No . 3 250 m m ; No. 5 320 mm.

iv. The stems of the instruments shall be flattened at two opposite sides, the graduation being printed on both sides of the paper scale. The ratio between the axes of the elliptical section of the stem shall be approximately 2 :1 . The distance between the top of the instrument and the highest graduation mark shall be 20-60 mm, between the lowest graduation mark and the top conical part of the bulb 10-30 mm.

v. The thermometer shall be located within the bulb of the instrument. The thermometer scale shall cover the range from 10°C-35°C. The scale on the left of the capillary shall be graduated in °C (graduation interval 0.5°C, tolerance ± 1°C) while the scale on the right shall indicate the brix corrections. If desired the positive corrections may be in black and the negative corrections in red. The corrections are given in Table II.

vi. The instruments shall be made of a boro silicate glass. The error of the instruments at any point on the scale shall be less than 0.1 °bx and the difference between any two readings shall be correct to within 0.1 °bx.

h. Hydrometer jars: These may be of glass or metal and should be made without a lip. Glass jars only are recommended for mixed juice. Hydrometer jars attached to troughs to catch overflows are not recommended. Jars shall be constructed so that they always stand vertically. Dimensions:

Overall length: 610 mm Inside diameter: 73 mm.

j . Volumetric glassware i. The unit of volume adopted is the litre (1) and is defined

as the volume occupied by one kilogram of pure water at its temperature of maximum density (4°C) under normal atmospheric pressure. The millilitre is 1/1000th part of the litre.

ii. In general, the requirements for volumetric glassware shall be those of the U.S. Bureau of Standards (Treadwell & Hall, Analytical Chemistry, New York, John Wiley & Sons, Inc., 7th edition, Vol. II, p. 448 et seq.).

k. Sugar flasks: The following types of flasks are recommended for the analysis of sugars and sugar products :


i. 1 0 0 - 1 1 0 ML D I L U T I O N F L A S K : The total height shall be 210 mm. The 100 ml mark shall be at least 10 mm above the top of the conical portion, and the 110 ml mark at least 60 mm below the top of the flask. The error in volume shall not be greater than 0.2 ml at the 100 and 110 ml marks, but the difference between the two volumes shall be correct to within 0.1 ml.

ii. 100 ML K O H L R A U S C H F L A S K F O R T H E D E T E R M I N A -T I O N O F S U C R O S E I N J U I C E

Internal diameter of narrow part of neck:

Internal diameter of wide part of neck: Length of cylindrical portion of narrow

part of neck: Overall height:

Diameter of base to be at least: Length of tube of uniform bore above and below graduation mark to be at

least: Tolerance:

9 mm to 12 mm 23 mm to 27 mm

30 mm to 40 mm 150 mm to 160 mm 34 mm

5 mm ± 0.05 ml.

iii. 200 ML K O H L R A U S C H FLASK FOR THE D E T E R M I N A T I O N O F P O L I N F I L T E R C A K E Internal diameter of narrow part of

neck: Internal diameter of wide part of neck: Length of cylindrical portion of narrow

part of neck: Overall height:

Diameter of base to be at least: Length of tube of uniform bore above and below graduation mark to be at

least: Tolerance:

10 mm to 14 mm 28 mm to 32 mm

35 mm to 45 mm 180 mm to 190 mm 40 mm

6 mm ± 0.2 ml.

iv. 100 ML P O L A R I Z A T I O N FLASKs—Type 2 sugar flasks which conform in respect of materials, workmanship and dimensions to B.S. 675: 1953 are recommended for the polarization of raw sugars.

1. Pipettes: For the Clerget sucrose determination the following pipettes are recommended:

i. 50 ml certificated pipette of the standard type with one mark. Tolerance ± 0.04 ml.

For the discharge of pipettes, hold in a vertical position with the tip of the pipette touching the wall of the vessel.


When the continuous discharge has ceased, the tip is held in contact with the side of the vessel for 15 seconds draining time, after which the vessel is removed taking with it any drop adhering to the outside of the pipette.

ii. 10 ml automatic pipette for addition of sodium chloride and hydrochloric acid solutions.

m. Beaker flasks: Beaker flasks for the Clerget sucrose determination should be made of heavy glass and have a wide neck to facilitate cleaning. For direct polarizations similar metal or plastic beaker flasks may be used.

n. Bagasse digestion apparatus: A brass or copper digester of cylindrical form, 200 mm inside diameter and 254 mm high, having a 3 mm thick machined flange 25 mm wide to form an airtight joint with the cover. The flange should carry four hinged bolts with wing nuts for securing the cover. The cover should be 3 mm thick, having in the centre a hole 38 mm in diameter, encircled with a collar 13 mm in height and very slightly tapered to hold a rubber stopper through which passes the lower end of an efficient reflux condenser. Where the double lid type of condenser is used, the collar need not be tapered and can be of convenient height to receive the incoming cold condenser water. Between the centre and the periphery, a hole shall be provided to take a rubber stopper holding a thermometer, the bulb of which shall be in the vapour space.

o. Counterpoise weights: The counterpoise or tare weights which may be used for the weighing out of the requisite amounts of bagasse and water for the determination of sucrose in bagasse, moisture in bagasse, or any other weighing such as molasses, syrup, etc., shall be constructed in brass, cylindrical in shape, in varying sizes to suit the analysis undertaken. The top of such a counterpoise weight shall be so constructed that it may be screwed into the main body of the counterpoise weight, the centre of which shall be provided with a cavity to accommodate any lead shot needed to adjust the mass of such counterpoise weight (Figure 1).


C H A P T E R V

S A M P L I N G 1. General

a. Samples are taken in the sugar industry either from distinct quantities of material like a tank of syrup, a lorry load of cane, a bag of sugar, or from material which is moving past a sampling point. Examples of the latter are the sampling of juice from a gutter, syrup from a continuously running sampling cock, etc. If the distinct quanti ty of material to be sampled were truly homogeneous, the composition of the sample would be identical to that of the material and the size of the sample would be decided only by the amount required for the actual analysis. In practice this is rarely, if ever, the case. Hence the sample should be composited from a large number of primary samples taken at various spots in the mass to be sampled. The larger the number of these primary samples, the closer the composition of the composite sample will be to the average composition of the sampled material. If the weight of the composite sample becomes excessive due to a very large number of primary samples being used in compositing, the composite sample, after thorough mixing, should be sub-sampled. To do this, various suitable methods are available. Where moving material is being sampled, sampling is either continuous or semi-continuous. We speak of continuous sampling when the sample is withdrawn uninterruptedly and of semi-continuous sampling when the samples are taken at, usually pre-determined, t ime intervals. Sampling sugar by taking a primary sample from each or every fifth bag which is filled, is semi-continuous. Sampling of final bagasse by taking a primary sample once every quarter of an hour can also be called semi-continuous, but due to the relatively large time interval between two primary samples, one could also speak of snap samples being taken.

The particular method of sampling to be employed in each separate case should be decided on very carefully. It should be remembered that the aim is to produce a sample, the composit ion of which is as similar to that of the mass of the material which is being sampled as is required by the use of the analytical da ta determined on the sample. For this reason where great accuracy is not required, catch samples taken at fairly large time intervals will often be adequate, particularly when the variability in the composition of the material to be sampled is relatively small.


However where great accuracy is required, continuous sampling should be employed and care should be taken that the ratio between the weight of the fraction of the sample extracted in each unit of time and the weight of the material it represents, is constant.

It is sometimes better to take a number of catch samples than a continuous sample, for example if it is desirable to get some information on the variability of the composition of the sampled material. Catch samples are also taken when it is feared that a continuous sample will deteriorate during the sampling period.

b. In order to obtain correct results, cleanliness of sample receptacles and strict periodic supervision of the sampling are essential. With regard to the state of cleanliness, seamless stainless steel or copper buckets with seamless rounded bot toms shall be used because such vessels are readily kept clean. Sample buckets should be provided in duplicate sets so that when one set is in use the other may be cleaned.

c. With regard to supervision, it is essential that a record of all sampling devices be kept in each laboratory, that all sampling devices and receptacles be inspected at least once in twenty-four hours, and that the results and time of the inspection be logged and kept as a permanent record of sampling conditions throughout the season.

d. A summary of the sampling procedures recommended for taking the routine samples has been included in Table VII.

2. Cane a. The very nature of cane makes representative sampling a precarious

undertaking and special care is required to achieve some measure of accuracy.

To sample a field of cane for the purpose of studying changes in its sucrose content as an indication of the ripening process, or for other purposes, in each sampling operation one stalk should be taken from a large number of marked stools randomly distributed over the field. If a second sample has to be taken, it too should consist of one stalk from each of the marked stools used for the first sampling operation.

b. If a fairly large sample has to be sub-sampled to obtain a quantity sufficiently small to be crushed conveniently in a laboratory mill, the following procedure should be used. Sticks are arranged in descending order of length with tops all one way. Each stick is then cut into three (approximately equal) lengths and replaced in position. Sub-sampling is done by taking the top sections from the first, fourth, seventh, etc., the middle sections from the second, fifth, eighth, etc., and the butt sections from the third, sixth, ninth,


etc. This gives one sub-sample. Two more sub-samples may be obtained by taking alternate lengths from each section.

3. Bagasse a. Since representative sampling and sub-sampling of bagasse are

matters of considerable difficulty, routine sampling of bagasse for pol and moisture determinations shall be done at all factories in the following manner :—

i. Regardless of chokes or other irregularities of crushing, a sample of bagasse shall be taken at least every quarter of an hour throughout the width across the discharge of the mill as the bagasse emerges from the last two rollers of the milling train.

ii. The sample shall be taken by using a small trough-shaped sampler, the length of which shall be the same as the width across the discharge of the last mill chute. A simple but effective sampler comprises a length of galvanized iron guttering 5 inches wide and 3 inches deep, closed at one end and strengthened by two supports which also serve as handles,

iii. The sampler should be constructed to hold, when full, approximately 3 to 7 lb. of final bagasse. When sampling is carried out the sampler is held across and below the falling bagasse and as a precaution against the sampler being dislodged during sampling by the weight of material above it, protective guide lugs to support each end of the sampler should be welded to the side of the mill discharge chute.

iv. The quarter hourly samples shall be placed in a closed container which has a capacity of approximately 30 lb. of final bagasse.

v. Such a container shall be constructed in accordance with the diagram shown in Figure 2.

FIGURE 2

B A G A S S E C O N T A I N E R


vi. At the end of each hour the sub-samples so collected shall be thoroughly mixed, coned and quartered. Two opposite quarters shall be rejected, the remaining two quarters shall be intimately mixed. This whole operation must be done as thoroughly and quickly as possible to avoid selective sub-sampling and loss of moisture.

vii. This constitutes the hourly sample for analysis from which 520 g for the pol test and 100 g for the moisture test are drawn at random.

4. First expressed juice a. Sampling procedure

i. The sampler is continuous and automatic. The fundamental purpose of this device is to give a continuous sample of the juice as it flows from all points along the whole width of the first two rollers of the crushing train. The sampler is designed to make it possible to adjust the rate of delivery in accordance with the size of sample required.

ii. Figure 3 is a diagram of the first expressed juice sampler which shall be used. In the diagram the size of the sampler relative to that of the mill has been enlarged. A convenient length for each rotating sampling pipe is about six inches. The sampler receiving tank shall be made of stainless steel, copper or heavily enamelled metal, while the rotating dippers shall be made of stainless steel or copper. Exception will be made in the case of a mill operating a 2-roller crusher where a dipper sampler in the juice gutter shall be permitted.

iii. Cleanliness of the apparatus is maintained by the installation of a steaming system. Great care shall be taken that cleaning operations are not carried out while sampling is in progress, otherwise dilution of the sample, due to condensation of steam, will take place.

iv. The rate of flow and the size of the receiving container shall be proport ioned so that the container is not more than filled during the period of taking the sample. At the end of the sampling period the contents of the container shall be well mixed before a sub-sample is taken to the laboratory.

b. Signalling devices In order to indicate to the sample taker the time when the

beginning and end of any consignment of cane has reached the first pair of rollers, an automatic signalling device shall be installed. Figure 4 is a diagram of the signalling device which shall be used. The details governing the time of switching the bulbs on and off will vary according to the conditions obtaining, being dependent largely on the length of the main cane carrier.


SHAFT WITH CONTACT DRUM FOR A.C. ONLY 220V.

5. Mixed juice a. Mixed juice shall be sampled after it has been weighed and at the

point of weighing. b. The sample shall be proportionally representative of the weight of

juice and of the juice at every depth in the scale tank. c. Figure 5 is a diagram of the automatic juice sampler recommended

for sampling cold juice. It has the following constructional details. i. A copper tube of 25 to 32 mm diameter is placed so that one

end of it is in the outflow during the discharge of the juice from the scale tank.

ii. This tube is inserted in the stream of juice to a depth such that sufficient juice is collected to provide an aliquot sample per scale tank.

iii. Care should be taken to exclude an excessive amount of froth which may enter the sampler at the end of the discharge.

iv. In order to minimize evaporat ion and deterioration during sampling, the distance between the point of sampling and the discharge into the sample bucket should be kept as short as possible.

v. The sample bucket shall be situated so that contaminat ion of the contents from outside sources is avoided.

vi. A spare sampling tube shall be provided to permit cleaning which shall be carried out at least once per shift.

vii. The mixed juice bucket and contents shall be taken to the laboratory every hour and the juice sub-sampled for analytical purposes on a p ro ra ta basis in relation to the total weight of juice weighed during each hour.

6. Last e x p r e s s e d ju ice When a continuous sample is not taken, a catch sample shall be drawn along the full length of the roller at the same time as the bagasse is sampled, and the juice sub-sampled in the laboratory.

7. Sulphited mixed juice A catch sample of mixed juice for acidity and sulphur dioxide determination should be taken from the juice-tempering tanks .

8. Clarified ju ice and filtered ju ice These samples should be taken automatically wherever possible, or catch samples may be taken at frequent intervals.

9. Filter cake This sample should be taken from the truck which is receiving the filter cake. The sample should be taken with a long tube.

10. Syrup This sample should be taken automatically wherever possible or catch samples may be taken immediately before the syrup enters the pans.


FIGURE 5

MIXED JUICE SAMPLER


11. Massecuite (from pan) A catch sample is required as the massecuite comes from the pan, avoiding the first runnings and steamings.

12. Massecuite (from crystallizer) A catch sample is taken as required.

13. Molasses a. Run-off molasses from centrifugals: A catch sample is required, as

nearly as possible representative of the bulk of the run-off. b. Molasses prepared for boiling: A catch sample is required. c. Molasses for sale: A representative continuous or catch sample

should be taken as each tank car is being filled. d. Final molasses: Samples should be taken continuously from the

discharge side of the molasses pump or from the scales. Otherwise catch samples should be taken as frequently as required for representative sampling.

14. Sugar a. Sampling procedures

i. To enable the factory manager to check effectively the quality of his product , sugar is usually sampled, either continuously or semi-continuously, at a suitable point before being bagged, shipped in bulk or leaving the factory for storage.

Sampling procedures may differ according to local conditions but it is always essential that the sample is thoroughly representative and that it will no t undergo any change before analysis.

Samples may represent one strike or all the sugar produced during a fixed period of time. Composi te samples representing the sugar produced during a day or a week are often prepared.

ii. When sugar is bagged and sampling at the scales is feasible, the primary samples should be drawn from not less than one in every 5 to 10 bags and should be at least in the propor t ion of 10 g per 200 lb. of sugar.

iii. Where sampling at the scales is not feasible, the same frequency of sampling and propor t ion of weights should be aimed at.

iv. Where raw sugar is shipped in bulk, samples can often be taken suitably from a conveyor belt or from the chute leading to the railway truck. For automatic sampling through an opening in a chute, a mechanically operated device to extract the sample regularly is strongly recommended.

v. To sample closed jute , hessian or cot ton bags (sampling of sugar packed in paper bags is often not practicable) a trier


should be used. The trier should be the "short trier"* as used by the United States Treasury Depar tment and specified by the United States Bureau of Standards. The dimensions of the trier should be as follows:

Overall length: 40.6 cm Length of spoon: 22.9 cm Length of shank: 17.8 cm

Length of handle: 26.7 cm Width of spoon: 2.7 cm Depth of spoon: 0.8 cm

Diameter of handle: 3.8 cm vi. In the sugar industry it is normal to sample one in every 5

to 25 bags, depending on the size of the lot. vii. The S. A. Bureau of Standards specifies that from lots compris

ing 10-1000, 1001-3000 or more than 3000 containers 10, 20 or 30 containers respectively shall be taken at random. The trier should be plunged into the middle of the package and withdrawn filled with sugar. If the trier has the correct length, all the layers of sugar, from the outside to the centre of the package should be correctly represented. Great care should be taken not to obtain a surface sample, because of the variations caused by drying or absorption of moisture. The total contents of each trier should be emptied into a suitable receptacle and the trier left clean for the next sample, the whole operation being conducted as rapidly as possible.

b. Receptacles i. A suitable model is seamless, 260 mm high and 178 mm in

diameter, fitted with a funnel shaped concave lid with a hole 32 mm in diameter. The funnel should have a depth of 45 mm.

When sampling hot sugars in particular, a receptacle with a close-fitting t rapdoor operated by a foot lever has certain advantages,

ii. Before removing the sample, the receptacle should be well shaken to redistribute regularly over the sugar any moisture which may have condensed on its inside wall,

iii. The frequency at which receptacles should be replaced and emptied depends on local conditions. Once every hour, or once per 50 tons of sugar, is often adequate.

c. Sub-sampling i. Whether sub-samples are prepared from the contents of one

or of more than one receptacle depends on local conditions, but mixing the contents of more than three receptacles is

* An illustration of the trier will be found in Spencer and Meade, Cane Sugar Handbook, New York, John Wiley and Sons, Inc., 8th edition, p. 506.


normally not done. Mixing and sub-sampling should be done with the utmost despatch to avoid loss or absorpt ion of moisture by the sugar,

ii. The contents of the receptacle(s) are passed through a wire screen with openings of 9 to 10 mm (or th inch mesh) on to a metal table-top. All lumps on the screen are broken up and added to the sample. Bits of bag, fibre, bagasse, string and other foreign matter are discarded,

iii . The preparat ion of the sub-samples should be done by the standard procedure of "coning and quarter ing". The final sub-sample should weigh not more than 350 g but must be sufficient to completely fill the sample bottle of 250-275 g capacity. After filling, the sample bottle must be closed with a lid which hermetically seals it.

d. Analysis of sub-samples The quantity to be weighed out for analysis should be removed from the bottle by means of a suitable trier which penetrates the sugar completely from top to bot tom. The trier must be constructed so that a similar quantity will be removed from each layer of sugar in the bottle and it is recommended that the dimensions of the trier should be such that the quanti ty extracted in one operation be as close as practicable to the amount which it is desired to weigh.


C H A P T E R V I

R E A G E N T S 1. General In addition to the name and strength of the reagent, the date of its preparation should be shown on the label. Solutions should be made in distilled or deionized water. Volumes should be completed at a temperature as near 20°C as circumstances will allow.

2. Clarifying reagents a. Lead subacetate solution for general use: Lead subacetate solution

of 30° Be is prepared by dissolving dry subacetate of lead powder in hot distilled water and subsequently diluting to 30° Be (54° Bx, 1.25 S.G.). Note : Bottles containing solutions of lead subacetate should always be provided with a soda-lime tube as a protection against the carbon dioxide of the atmosphere.

b. Neutral lead acetate solution: Dissolve neutral lead acetate crystals in distilled water to make a saturated solution, then add glacial acetic acid to render the solution faintly acid to litmus paper. Dilute to 30° Be (54° Bx, 1.25 S.G.).

c. Dry subacetate of lead i. The salt produced shall be dry and conform to the following

specifications of the American Chemical Society which, together with the methods of testing, have been taken from I. & E.C., Anal. Ed., 16 (1944) 282.

Basic lead (PbO): not less than 33 % Insoluble in acetic acid: not more than 0.05 %

Insoluble in water: not more than 2 .0% Moisture (loss at 100°C): not more than 1.5%

Chloride (CI): not more than 0.005 % Nitrate ( N 0 3 ) : to pass test (limit about 0.003 %)

Substances not precipitated by hydrogen sulphide: not more than 0.30%

Copper (Cu): not more than 0.005 % I r o n ( F e ) : not more than 0.005 %

The salt must also conform to the following specifications for fineness:

1. 100% to pass through a sieve with aperture 0.42 mm (35-mesh Tyler sieve).

2. 7 0 % to pass through a sieve with aperture 0.125 mm (115-mesh Tyler sieve).


ii. Whenever containers of bulk quantities of this powder are opened, the powder shall be transferred to air-tight glass receptacles. This clarifying agent should be kept out of contact with the atmosphere (in so far as is compatible with routine laboratory practice).

iii. P R O C E D U R E S F O R T E S T I N G B A S I C L E A D A C E T A T E The methods of analysis given below are those specified by the American Chemical Society. B A S I C L E A D : Weigh accurately about 5 grams and dissolve in 100 ml of carbon dioxide-free water in a 500 ml volumetric flask. Add 50 ml of normal acetic acid and 100 ml of a carbon dioxide-free 3% solution of sodium oxalate. Mix thoroughly, dilute to volume with carbon dioxide-free water, and allow the precipitate to settle. Titrate 100 ml of the clear supernatant liquid with normal sodium hydroxide, using phenolphthalein indicator. Each millilitre of normal acetic acid consumed is equivalent to 0.1116 gram of PbO. I N S O L U B L E I N A C E T I C A C I D : Dissolve 5 grams in 100 ml of water and 5 ml of acetic acid, warming if necessary to complete solution. If an insoluble residue remains, filter and wash until the washings are no longer darkened by hydrogen sulphide. Dry at 105-110°C. The weight of the residue should not exceed 0.0025 gram. I N S O L U B L E IN W A T E R : Agitate 1 gram in a small stoppered flask with 50 ml of carbon dioxide-free water and filter at once. Wash with carbon dioxide-free water and dry at 105-110°C. The weight of the residue should not exceed 0.0200 gram. M O I S T U R E : Weigh accurately about 0.5 gram and dry for 2 hours at 105-110°C. Cool and reweigh. The loss in weight should not exceed 1.5%. C H L O R I D E : Dissolve 1 gram in 50 ml of water and add 1 ml of nitric acid and 1 ml of 0.1 N silver nitrate. Any turbidity should not be greater than is produced by 0.05 mg of chloride in an equal volume of solution containing the quantities of reagents used in the test. N I T R A T E : Dissolve 1 gram in 9 ml of water containing 5 mg of sodium chloride. Add 0.7 ml of acetic acid, 0.2 ml of indigo carmine solution (1 to 1000), and 10 ml of sulphuric acid. Stir thoroughly and allow to stand for 10 minutes. The blue colour of the clear solution should not be completely discharged. S U B S T A N C E S N O T P R E C I P I T A T E D B Y H Y D R O G E N S U L P H I D E : Dilute 10 ml of solution A (see footnote) to 100 ml, pass hydrogen sulphide through the solution to precipitate all the lead, and filter. Evaporate 50 ml of the filtrate to dryness and ignite gently. The weight of the residue should not exceed 0.0015 gram. C O P P E R : To 25 ml of solution A (see footnote) add about 0.05 gram of aluminium chloride and a few crystals of ammonium persulphate. Neutralize with ammonium hydroxide and add a very slight excess. Heat to boiling, cool and filter. Save the precipitate for the determination of iron. Neutralize the filtrate to phenolphthalein, add 0.25 ml of acetic acid in excess and 0.25 ml of a freshly prepared 10 % solution of potassium

Solution A: Dissolve 5 grams in 42 ml of water and 3 ml of acetic acid, and add 5 ml of sulphuric acid. After standing for about 10 minutes, filter the solution.


ferrocyanide. Any pink colour produced should not exceed that pro-duced by 0.125 mg of copper in an equal volume of solution containing the quantities of reagents used in the test.

I R O N : Wash the precipitate of iron and aluminium hydroxides obtained in the previous test sufficiently to remove most of the acetate. Dissolve the precipitate in 10 ml of hot dilute hydrochloric acid (1 + 5 ) , wash the paper and dilute to 50 ml. Dilute 20 ml of this solution to 45 ml and add a few crystals of ammonium persulphate, 3 ml of hydrochloric acid, and 3 ml of a 30% solution of ammonium thiocyanate. The colour should not be more than is produced by 0.05 mg of ferric iron in 45 ml of water to which are added 3 ml of hydrochloric acid and 3 ml of a 3 0 % solution of ammonium thiocyanate.

d. Alumina cream {aluminium hydroxide): To a cold saturated solution of common alum (aluminium potassium sulphate) in water, add ammonia with constant stirring until in slight excess, and allow the precipitate to settle. Pour off the supernatant liquid and wash the precipitate by decantation until the wash water shows only a slight content of sulphate when tested with barium chloride solution. The excess water is poured off and the creamy suspension stored for use.

3. Indicators a. Indicators for measurement of pH: A complete list of indicators

with directions for their preparation is given in Browne and Zerban, Sugar Analysis, New York, John Wiley & Sons, Inc. (3rd edition), p. 559. While it is agreed that indicators can be successfully employed in chemical control when proper precautions are taken, it is nevertheless recommended that use be made, wherever possible, of pH meters of which reliable models are available. The use of indicator paper for pH control in the factory is not recommended since such paper has often been found to yield erroneous results.

b. Neutral water for dilution of indicators: Distilled water which has been boiled for about 5 minutes and cooled in a flask fitted with a soda-lime tube, if continuously protected from the atmosphere, will read 7.0 pH (very nearly) and will constitute a suitable unbuffered water for dilution.

c. Buffer solutions: Ranges of buffered solutions may be purchased. The use of these commercial buffers is recommended, but chemists who prefer to make their own buffer standards are referred to Browne and Zerban, Sugar Analysis, New York, John Wiley & Sons, Inc. (3rd edition), p. 556.

It may be recorded that the pH of a 1 % solution of ammonium acetate is very nearly equal to 7.0 and again that a solution of 1.02 g of potassium hydrogen phthalate crystals in 100 ml of distilled water has a constant pH of 4.0 between 18° and 40°C. These buffer solutions will be found suitable for readjusting pH-meters.


d. Indicator solutions made up in the laboratory

i . P H E N O L P H T H A L E I N : A 1% solution of the powder in rectified spirits. The phenolphthalein may be dissolved in about half the required volume of alcohol and diluted with water. The solution should always be rendered very faintly

pink before use by addition of an alkali,

ii. METHYLENE BLUE: 1 %aqueous solution. iii. A L P H A - N A P H T H O L : 4 % alcoholic solution. iv. S T A R C H F O R I O D I N E T I T R A T I O N S : A starch indicator

which keeps indefinitely may be prepared by dissolving 1 g of salicylic acid in 100 ml water, boiling and pouring into it 1 g starch mixed with a little water. Boil gently till the starch is dissolved, let cool somewhat, then dilute with cold water to one litre.

4. Standard acid and alkali solutions a. A reagent solution, of which the strength has been accurately

determined, is called a " s t anda rd" solution.

b. A " n o r m a l " solution of a reagent is one that contains in one litre that proport ion of its molecular weight in grams which corresponds to 1.008 g of available hydrogen, or its equivalent.

c. Preparation of standard acid and alkali solutions

i. N - H Y D R O C H L O R I C A C I D S O L U T I O N : Dilute 100 ml

concentrated hydrochloric acid (S.G. 1.15) to 1 litre. F rom this solution diluted standards such as N/10 HC1, etc., may be prepared. These solutions can be standardized against sodium carbonate or s tandard caustic soda, as described under 4, d, below.

ii. N - S O D I U M H Y D R O X I D E S O L U T I O N : Weigh out rapidly

approximately 41 g caustic soda (A.R.) and dissolve in a one litre flask. Allow the solution to cool while being protected from the carbon dioxide of the atmosphere by a soda-lime tube. Then dilute to one litre, and keep the solution protected from carbon dioxide.

F rom this solution diluted standards such as N/10 N a O H , etc., may be prepared.

These solutions may be standardized against potassium hydrogen phthalate or s tandard hydrochloric acid solution as described under 4, d, below.

d. Standardization of acid and alkali solutions: Weigh out an exact amount of about 4.1 g potassium hydrogen phthalate, C 6 H 4 .COOH.COOK. Prior to use this salt should be dried at 120°C for 2 hours and allowed to cool in a desiccator. Dissolve in


recently boiled distilled water and titrate 20 ml aliquots with N - N a O H solution contained in a burette, using phenolphthalein as indicator.

5. lodimetry a. General

A standardized iodine solution is generally used for measuring the amount of what is usually termed " S O 2 in juice". Since one litre of N/32 iodine solution corresponds to 1 g of S 0 2 , it is convenient to titrate the juice with an iodine solution of this concentration.

The (unstable) N/32 iodine solution is prepared from N/1.6 iodine stock solution and at least once per 24 hours titrated against N/32 sodium thiosulphate solution. The thiosulphate solution should be standardized against potassium iodate at least twice per month .

b. Preparation of N/32 sodium thiosulphate solution i. A solution of sodium thiosulphate prepared from the pure

salt in pure water (conductivity water) is quite stable. Slow decomposition, however, usually occurs, partly due to an excess of carbon dioxide in the water, partly as a result of the growth of micro-organisms. Thiosulphate solutions therefore must be standardized twice per month,

ii. N/32 sodium thiosulphate solution contains 7.753 g/litre N a 2 S 2 0 3 . 5 H 2 0 , but it is not possible to prepare sodium thiosulphate solutions of definite strength by weighing out the pure salt as purchased because sodium thiosulphate penta-hydrate effloresces very easily,

iii. Dissolve 7.75 g of the pentahydrate in 1 litre of freshly boiled, cooled water, and add 0.1 g of sodium carbonate to the solution in order to retard deterioration.

c. Standardization of N/32 sodium thiosulphate solution Potassium iodate reacts with potassium iodide in acid solution to liberate iodine which can be titrated with thiosulphate:

K I 0 3 + 5KI + 3 H 2 S 0 4 = 3 K 2 S 0 4 + 3I2 -+- 3 H 2 0 Potassium iodate has an equivalent weight of 35.67 and the A.R. salt has a purity of 99.9 per cent. It should be dried at 120°C before use. Weigh out accurately about 1.2 g of pure potassium


iodate, say 1.213 g. Dissolve in water and make up to one litre in a volumetric flask. Pipette out 25 ml of this solution into a 250 ml Erlenmeyer flask, add 0.5 g pure potassium iodide and 2 ml of N-sulphuric acid. Titrate the liberated iodine with the thiosulphate solution and when the colour has become a pale yellow dilute to about 200 ml with distilled water. Add 2 ml of starch solution and continue the ti tration until the blue colour just vanishes. Suppose that 21.7 ml of the thiosulphate solution were used. Then the normality of the solution is

d. Preparation of iodine stock solution, N/1.6 approximately: Weigh out 180 g of potassium iodide and transfer to a clean one litre volumetric flask. Dissolve in the minimum quantity of distilled water and add 80 g of iodine. Rota te until iodine is completely dissolved then dilute with distilled water to 1000 ml. Keep the stock solution in a cool dark place.

e. Preparation of N/32 iodine solution: 100 ml of the stock solution diluted to 2 litres constitutes the N/32 solution required for SO2

determinations. This diluted iodine solution should be standardized against N/32 thiosulphate solution every 24 hours .

f. Standardization of N/32 iodine solution: Thiosulphate is oxidized to tetrathionate by iodine:

The solution should be faintly acid otherwise par t of the thiosulphate may be converted into sulphate:

Add 1 ml of 3 0 % sulphuric acid to 25 ml N/32 iodine solution pipetted into a 250 ml Erlenmeyer flask and titrate with standardized N/32 thiosulphate solution until a faint yellow shade is obtained. Add a few drops of starch solution and titrate until colourless.

6. For the determination of sucrose a. Hydrochloric acid solution: Dilute concentrated hydrochloric acid

to 24.85° bx (add approximately 1750 ml concentrated hydrochloric acid to 1000 ml water), corresponding to approximately 2 0 % by weight

b. Sodium chloride solution: A solution containing 231.5 g A.R. sodium chloride per litre is required.

7. For the determination of reducing sugars a. Preparation of standard invert sugar solution: For this solution the

sugar used should be of the highest s tandard obtainable, e.g. A.R. sucrose or high grade refined sugar. This sugar should be dried and kept in an air-tight glass container.


Dissolve 9.500 g of the above dried sugar in 70 ml water in a 1 litre volumetric flask. Add 10 ml hydrochloric acid solution— see under 6, a above—and set aside at laboratory temperature for 5 days. Add sodium hydroxide solution to raise the pH to about 3 (a separate titration against 10 ml hydrochloric acid indicates the quantity of alkali required) followed by 2 g benzoic acid dissolved in distilled water. Make up to volume with distilled water. This solution contains 1 g invert sugar per 100 ml.

For use 50 ml of this 1% invert solution is pipetted into a 100 ml volumetric flask and made up to volume with distilled water. This solution contains 0.5 g invert sugar per 100 ml.

b. Preparation of Fehling's solution, Soxhlet's modification: Large quantities of the component solutions comprising the Fehling's solution are generally required. A.R. salts should be used in the preparation of the solutions which are made up in quantities of 2 litres as follows:

Solution A — dissolve 138.556 g of copper sulphate, C u S 0 4 . 5 H 2 0 , in water and dilute to 2000 ml in a volumetric flask.

Solution B — dissolve 692 g of sodium potassium tartrate (Rochelle salt) in about 1000 ml of water, mix with 400 ml of a solution containing 200 g sodium hydroxide and complete the volume to 2000 ml.

It will be found sometimes that a slight sediment settles in both solutions on standing. This sediment may be removed by decanting the clear supernatant liquids. It is necessary to keep solutions A and B separate, and these should be mixed in equal proportions only when required and immediately before use. In every case where Fehling's solution is mentioned, a mixture of exactly equal parts of solutions A and B is understood.

c. Standardization of Fehling's solution: The neutralized invert sugar solution prepared as under a above, is titrated against 25.0 ml Fehling's solution. If the Fehling's solution is of correct strength, 24.8 ml of invert solution will be used. If less than 24.8 ml of invert sugar solution is required, the Fehling's solution is too weak and copper sulphate should be added to solution A until the desired 24.8 ml is used. Similarly, if more than 24.8 ml is used, solution A should be diluted until 25 ml Fehling's solution corresponds to 24.8 ml invert sugar solution.

d. Preparation of Luff-Schoorl solution i . S O L U T I O N A: Prepare solution A by dissolving with

slight heating 17.3 g A.R. copper sulphate ( C u S 0 4 . 5 H 2 0 ) and 115 g A.R. citric acid in 200 ml water.

ii. S O L U T I O N B: Dissolve 185.3 g of anhydrous sodium carbonate, analytical reagent, previously dried for 30 minutes at 250°C in a hot-air oven, in 500 ml water.


iii. L U F F S O L U T I O N : Add solution B slowly and with constant shaking to solution A. Never add solution A to solution B. Cool and make up to 1 litre.

iv. P O T A S S I U M I O D I D E S O L U T I O N : Dissolve 20 g A.R. potassium iodide in 80 ml of water. (This solution must be iodate-free.)

v. D I L U T E S U L P H U R I C A C I D ( 1 : 5 ) : Prepare from ana-lytical reagent-grade sulphuric acid by adding 1 vol. acid to 5 vols water.

vi. S T A R C H I N D I C A T O R S O L U T I O N : See under 3, d, iv above.

vii. T H I O S U L P H A T E S O L U T I O N ( N / 1 0 ) : Dissolve 25 g of A.R. sodium thiosulphate crystals plus 0.2 g anhydrous sodium carbonate in distilled water and make up to 1 litre. Standardize against A.R. potassium iodate as described under 5, c above.

8. Juice preservative Dissolve 150 g of mercuric chloride in hot water and add solid potassium iodide until the precipitate first formed is redissolved. Dilute to 1 Utre. Use 0.2 ml of the solution for every litre of juice.

9. For the determination of calcium and magnesium a. Ethylenediaminetetraacetic acid: The solution consists of approxi

mately 8 g of the disodium salt of ethylenediaminetetraacetic acid ("versenate") and 1.5 g of A.R. caustic soda dissolved in water and made up to 1 litre.

b. Standard calcium chloride solution: This solution may be prepared by accurately weighing out 1.5 g of A.R. calcium carbonate, dissolving in a small excess of hydrochloric acid, and making up to one Utre. This solution is used to standardize solution a above.

c. Buffer solution (according to Saunier and Lemaitre): 6.75 g of ammonium chloride, 57 ml of ammonia solution (S.G. 0.9) and 0.1 g of potassium chromate are dissolved in water and made up to 100 ml. This solution is then mixed with 100 ml of a saturated solution of sodium potassium tartrate.

d. Eriochrome-black T: 0.5 g of the dye-stuff is ground in a mortar with 100 g of A.R. sodium chloride or A.R. sucrose. The mixture is kept in an airtight jar.

e. Murexide: 0.2 g of murexide and 1.5 g naphthol green B are ground with 100 g of A.R. sodium chloride to a fine powder. The mixture should be protected from the damp atmosphere. The naphthol Green B which acts as a screening agent may be omitted if so desired.

f. Caustic soda solution: This should be made from A.R. caustic soda, and should be approximately 6N i.e. 240 g per litre.

g. Standardization of the ethylenediaminetetraacetic acid solution: The solution of ethylenediaminetetraacetic acid should be standardized against a calcium chloride solution. To do this, 80 ml of tap water (containing magnesium salts), 4 ml of the buffer solution and 0.2 g of Eriochrome black T indicator are measured into a 350 ml Erlenmeyer flask. The solution of ethylenediaminetetraacetic acid is then added drop-wise from a burette until the colour of the indicator changes from red to blue. 20 ml of the standard calcium chloride solution is then added by means of a pipette, and after the burette has again been filled to the 0 ml mark, the titration is continued until the endpoint is again reached. Since the molarity of the calcium chloride solution is known, the strength of the titrating solution can be calculated in terms of millimols of calcium or magnesium per litre.

10. For the determination of available phosphate a. Ammonium molybdate solution: 15.0 g ammonium molybdate is

dissolved in 300 ml water at 50°C. After filtering and cooling, 350 ml of concentrated hydrochloric acid is added. The solution is cooled and made to 1 litre. The solution should be stored in a dark bottle and made up freshly every 2 months .

b. Reducing solution: 90 g sodium metabisulphite is dissolved in 800 ml of water. 7 g anhydrous sodium sulphite and 1.5 g 1-amino-2-naphthol-4-sulphonic acid are dissolved in 100 ml of water. The two solutions are mixed and diluted to one litre. Store in an amber glass bottle under refrigeration.

c. Standard phosphate solution: Dissolve 0.7668 g A.R. monopotassium phosphate ( K H 2 P O ) in distilled water, and transfer quantitatively to a 1 litre flask. Add 10 ml of sulphuric acid (S.G.1.3) and make to the mark. This standard, of which 1 ml is equivalent to 0.4 mg P205 , keeps indefinitely.

d. Diluted standard phosphate solution: 25 ml of the above stock solution is diluted to 1 litre. 1 ml = 0.01 mg P 2O 5 .

11. For the determination of sulphur dioxide (modified Monier-Williams method)

a. Hydrogen peroxide solution: A 3% solution adjusted to pH 4 with N/100 HC1, using a pH meter.

b. Hydrochloric acid, concentrated: Analytical reagent grade.

c. Sodium hydroxide solution: N/50 accurately standardized.

d. Alkaline pyrogallol solution: Dissolve 10 g of sodium hydroxide and 30 g of pyrogallol in water and dilute to 100 ml.


C H A P T E R V I I

G E N E R A L M E T H O D S O F A N A L Y S I S

1. Temperature Saccharimeters, volumetric glassware and brix hydrometers recommended for this industry are all standardized at 20°C and departure from this temperature introduces errors. Temperature corrections can and should be applied where necessary but it must be realised that these are only approximations. Every at tempt should therefore be made to install constant temperature laboratories operating at 20°C. In all cases however, apparatus should be used at the laboratory or room temperature so as to maintain a uniform temperature in the solution under test, e.g. in cases where polarizations are to be made in a constant temperature room at 20°C, care must be taken to ensure that other operations such as making to volume are also carried out at 20°C.

2. Filtration Where filtration is slow or delayed, adequate precautions must be taken against evaporation by setting the funnel directly on the receiving vessel and covering with a watch glass. For ordinary rapid working, this precaution is not regarded as necessary for dilute solutions such as mill juices or products diluted to the same density, or the dilute solutions from bagasse or filter press cake. In testing sugar however, this precaution must always be taken.

The first runnings from the filter must in all cases be discarded after rinsing the receiving vessel.

3. Brix Before filling hydrometer jars to overflowing, samples should be well mixed and strained through a 14 mesh copper wire sieve, the whole operation being carried out as near room temperature as possible. The reason for straining is to remove bagasse particles which may affect the reading of the brix spindle. Samples should be left to stand at least twenty minutes to allow all air bubbles to rise to the surface. Care must be taken to ensure that the brix spindle, which must be clean and dry, floats freely. To improve the accuracy, the approximate reading is noted and after drying the spindle above the reading, it is carefully reinserted to keep the stem dry above the liquid. A final reading to the nearest 0.05° is taken, after the spindle has been floated for at least two minutes, by bringing the eye level with the surface of the liquid and noting where the meniscus intersects the scale. The film of liquid


drawn up around the stem should be disregarded. In Figure 6 the correct reading is 2.1. Immediately after taking the reading (which is the uncorrected brix) the temperature should be taken, or when the hydrometer is provided with a scale showing the temperature corrections to the brix readings, the appropriate correction should be applied to provide the corrected brix.

BRIX SPINDLE READING

Polarization, pol or apparent sucrose a. Home's dry lead method: To an unmeasured quantity of solution

(say about 100 ml) in a beaker, add a minimum (usually about 1 g/100 ml) of powdered dry subacetate of lead, shake or stir vigorously and when the clarification is complete, filter. Polarize in a 200 mm tube.

The pol is calculated by means of the formula:

Pol normal weight x saccharimeter reading Sr

Weight in grams of 100 ml solution

where: the normal weight is either 26.000 or 26.026 grams, depending on the scale of the saccharimeter used. the weight in grams of 100 ml solution is equal to 99.718 X specific gravity solution at 20/20°C.

In practice, the pol is found from Table III (Schmitz's Table) or a modification of this table when a saccharimeter fitted with the Ventzke scale is used.

b. Normal weight method: Weigh out the normal weight or a multiple or fraction thereof into a 100 ml sugar flask. Make to the mark with distilled water, add the minimum quantity of dry basic lead acetate necessary for clarification, shake vigorously and filter.


FIGURE 6

48 — 1962

Instead of dry basic lead acetate, a solution of basic lead acetate may be used by adding the minimum quanti ty necessary for clari-fication before making to the mark . Polarize in a 200 mm tube. If the normal weight has been used, the pol is equal to the sacchari-meter reading, but when a multiple or a fraction of the normal weight has been used, the saccharimeter reading must be multiplied by the reciprocal of the normality used.

5. Sucrose a. Using acid inversion (modified Jackson & GUI is method IV)

i. The solution to be analysed should be clarified with dry subacetate of lead as described under 4, a above. If desired, and this practice is recommended for molasses solutions, the clarified filtrate is deleaded by adding pulverised anhydrous potassium oxalate and filtering. Two 50 ml port ions of the filtrate (both port ions should be taken either from the clarified or from the deleaded filtrate, not one port ion from the clarified and the other from the deleaded fi l trate) are pipetted in to two 100 ml sugar flasks. To the first flask add 10 ml of sodium chloride solution containing 231.5 g per litre. If after addition of the sodium chloride solution there develops a cloudiness which cannot be removed by filtration, clearing by the addit ion of a few drops of acetic acid is often practised. Make up to 100 ml with distilled water and shake thoroughly.

ii. To the flask containing the second 50 ml por t ion add 20 ml water. Heat in a water bath to 65°C and add immediately 10 ml hydrochloric acid =1 .1029. Mix by rotat ing and set aside for at least 30 minutes. Cool to room temperature and make to the mark with distilled water, mixing the contents by rotating just before the liquid reaches the level of the neck. Shake thoroughly.

iii. Fill two jacketed tubes with these two solutions. Insert an "inversion" type of thermometer into each tube, place the tubes on a rack and leave them for 30 minutes in the sac-charimeter room before polarizing. This procedure will avoid a possible error due to mutarota t ion and will ensure a constant temperature which should be similar in both tubes. The temperature of the solution at the time of taking the invert reading, should be recorded to the nearest 0.1 °C. The temperature of the two solutions should not differ by more than 0.2°C. The reading of the first solution is termed the direct saccharimeter reading (Dr) and that of the second solution the invert saccharimeter reading (Ir). The method for calculating the percentage of sucrose in the solution being analysed is given in detail under Mixed juice, chapter VIII, 5, c, iii, and Final molasses, chapter VIII , 10, c, i.


b. Using invertase i. The invertase method is the only method which can be

depended upon to give correct sucrose values for cane products which may contain fructose, reversion products, and amino compounds, provided that the solution used for the direct reading and the inverted solution have approximately the same pH. Although invertase may be prepared in the labora-tory from yeast, it is recommended that the commercial product be purchased. In both cases a check on the activity of the invertase solution is desirable.

ii. C H E C K O N A C T I V I T Y O F I N V E R T A S E S O L U T I O N :

Instead of determining the k-value of the solution (which should be approximately 0.1) it is usually adequate for practical purposes to carry out the following test:

Dilute 1 ml of the invertase preparat ion to 200 ml. Transfer 10 g of pure sucrose (no. 1 refined) to a sugar flask graduated at 100 and 110 ml, dissolve in 75 ml of water, add 2 drops of glacial acetic acid, and dilute to the 100 ml mark. Make to the 110 ml mark with the diluted invertase solution and mix thoroughly and rapidly, noting the exact time at which the solutions are mixed. At the termination of exactly 60 minutes make a port ion of the solution just alkaline to litmus paper with small amounts of anhydrous sodium carbonate and polarize in a 200 mm tube at 20°C. If the invertase solution is sufficiently active, the alkaline solution will polarize approximately 31°S without correcting for the dilution to 110 ml and the optical activity of the invertase solution.

Example: 10 grams of sucrose in 110 ml aqueous solution show a reading in a 200 mm tube of 34.96°S and after complete inversion the reading will be —11.22°S. If the invertase solution is the correct strength, the reading in the above test should be 31°S, corresponding to a d rop of

(34.96—31.00) X 100 = 8.58 %

46.18

A reading lower than 31°S indicates that the invertase con-centrate is stronger than usual. If for example the reading is 26°S instead of 31°S which corresponds to a d rop in pol of 19.4%, the activity of the invertase is

19.40 -------- = 2.26 so a correspondingly smaller volume of the

8.58

invertase solution shall be required for the analysis, as des-cribed in 5, b, iii, below and in chapter VIII, 5, d and 10, c, ii.


19.40

8.58

(34.96—31.00)

46.18

X 100 = 8.58%

50 — 1962

iii. T H E D E T E R M I N A T I O N : To determine sucrose using in -vertase, the clarified solution 4, a, above, must be deleaded with the minimum of anhydrous potassium oxalate and filtered again. Three 50 ml portions are pipetted into three 100 ml flasks. The first flask is made up to the mark and thoroughly mixed. The second port ion is used to determine the quantity of glacial acetic acid required to reduce the pH to 4.7 ± 0.2. The volume of acetic acid required is noted and this volume is added to the third flask. Then add the requisite quantity of the invertase solution (10 ml of the invertase concentrate is adequate), and mix thoroughly. Place the flask in a water-bath and allow it to maintain a temperature of 57—58°C for fifteen minutes with occasional shaking. Cool and add carefully with constant shaking a concentrated solution of sodium carbonate until distinctly alkaline to a minute piece of litmus paper in the flask. Dilute to the mark and mix thoroughly. Fill two jacketed tubes with these two solutions. Insert an inversion type of thermometer into each tube, place the tubes on a rack and leave them for 30 minutes in the saccharimeter room before polarizing. The reading of the first solution is termed the direct saccharimeter reading (Dr) and the second reading, which must be corrected for the rotat ion of the invertase present, the invert saccharimeter reading (Ir). The temperature of the solution at the time of taking the invert reading should be noted to the nearest 0.1°C. The temperature of the two solutions should not differ by more than 0.2°C.

The saccharimeter readings are converted into the sucrose percentage of the analysed solution as described in detail under Mixed juice, chapter VIII, 5, d, iii and Final molasses, chapter VIII, 10, c, ii.

iv. When very accurate results are required it is preferable to carry out the inversion at room temperature by allowing the solution, after addition of invertase, to stand overnight before taking the invert reading. A further reading is taken several hours later and if there is no change from the previous reading, the inversion is complete.

c. The "chemical" method: Sucrose may be estimated chemically by the determination of reducing sugars, both before and after in-version, either by acid or invertase. If the difference between the percentages of reducing sugars obtained is multiplied by 0.95, the result will represent the weight of sucrose before hydrolysis. This method of sucrose determination is recommended in the case of molasses where solutions are often too dark to obtain accurate optical readings (see chapter VIII , 10, c, ii).


6. Reducing sugars a. The Lane and Eynon method

For solutions of unknown titre an approximate titration is carried out as described under "Incremental me thod" Sub. Par. a, i. This is followed by the "Standard method" Sub. Par. a, ii. If the approxi-mate titration is known proceed as under a, ii, omitting a, i.

i . I N C R E M E N T A L M E T H O D O F T I T R A T I O N

Usually 10 ml (but sometimes 25 ml) Fehling's solution is pipetted accurately into a flat-bottomed narrow neck boiling flask of 300—400 ml capacity. The sugar solution is added from a 50 ml burette. Initially 1 5 ml is run into the flask and the mixture heated to boiling. If after the liquid has been boiling for 10 to 15 seconds its colour shows that much of the Fehling's solution has not been reduced, further additions of sugar solution are made, e.g. 10 ml or 5 ml at a time, with a few seconds actual boiling after each, until it is judged unsafe to add more without risk of exceeding the end-point. At this stage 3—4 drops of methylene blue are added, and the addition of sugar solution is continued, 1 ml or less at a time, at intervals of about 10 seconds, until the indicator is completely decolourized. The boiling reaction liquid then resumes the bright orange appearance (due to cuprous oxide) which it had before the indicator was added. The burette reading is the approximate titration. During the additions to the boiling liquid, the burette is held in the hand, keeping the main burette tube out of the steam.

ii. S T A N D A R D M E T H O D O F T I T R A T I O N

Proceed as in the "Incremental Me thod" but the initial addition of sugar solution should be to within 1 ml (but not closer than 0.5 ml) of the final titration. The contents of the flask are well mixed in the cold by shaking and then heated to boiling over a suitable flame or hot plate. The liquid is kept in moderate ebullition for 2 minutes, and 3—4 drops of methylene blue solution then added preferably without touching the sides of the flask. The titration is completed in another minute by the addition of 2—3 drops of the sugar solution at intervals of about 10 seconds, until the colour of the indicator is completely discharged. Thus the titration is completed in 3 minutes from the commencement of the ebullition and during this time the mixture must be kept boiling continuously as the emission of steam from the neck of the flask is an effective safeguard against back oxidation of the Fehling's solution or the indicator by air.

Duplicate titrations by this method should agree to within 0.1 ml in the volume of sugar solution required. In


the titration of glucose, fructose or invert sugar in the presence of an excess of sucrose it is especially important that the total boiling time of 3 minutes be adhered to closely.

The concentration of invert sugar in mg per 100 ml is obtained from Table IV. The following example illustrates the calculations involved. The dilute final molasses solution used in the titration contains 1.3 g molasses per 100 ml. Sucrose % molasses = 40%. Hence sucrose concentration in titration solution is 1.3 x = 0.5 g/100 ml.

This figure indicates the column in Table IV which must be consulted. Titre = 25.5 ml. From the 2nd column and by interpolation the concentration of invert sugar is 199 mg/100 ml or 0.199 g/100 ml

... R.S. % molasses = x 100 = 15.31%

b. The Luff-Schoorl method: This method which is recommended for sugars and is laid down in the Specifications of the S.A. Bureau of Standards for commercial sucrose, is described in chapter VIII, 11, b.

7. Sulphur dioxide Methods a. and b. given below yield results which are frequently higher than the true concentrations of sulphur dioxide present due to the presence of some other reducing substances in the samples being analysed. However these methods are sufficiently accurate for factory control purposes. When highly accurate analyses are required, method c, the Monier-Williams method, should be employed.

a. The iodine titration method: This method is applied especially for the determination of S 0 2 in juices. The specified volume of juice (see chapter VIII , 4, e) or any other solution is diluted with the appropriate volume of water and titrated against N/32 iodine solution, using a few drops of starch indicator to determine the end-point. The end-point may be made sharper by adding a few drops of concentrated hydrochloric acid when near the end of the titration.

b. The rapid method of determining available S 0 2 in sugars: Available sulphur dioxide may be determined rapidly in sugars by ti tration with an iodine solution. 100 g of the sugar is dissolved in 150 ml distilled water in a 500 ml Erlenmeyer flask. 5 ml of approximately 6 N sulphuric acid is added followed by a measured amoun t of N/32 iodine solution run in from a burette until there is a slight excess of iodine. Add 1 ml of starch solution and back-ti trate the excess iodine with N/32 thiosulphate solution until the colour due to the starch iodine complex just vanishes. The available S 0 2 content of the sugar in parts per million = 10 x (number of ml N/32 iodine used — number of ml N/32 thiosulphate used).


c. The Monier-Williams method i. This method should be used, if only occasionally, to check

the iodine titration method. The method is also laid down in the Specifications of the S.A. Bureau of Standards for commercial sucrose.

ii. Connect a 750 ml round-bot tomed resistance glass flask B (see Figure 7) to a sloping reflux condenser D, the lower end of which has been cut off at an angle. Pass nitrogen from a cylinder through the alkaline pyrogallol solution in a wash bottle A to remove traces of oxygen. Where nitrogen is not readily available, scrubbed carbon dioxide may be

FIGURE 7

A P P A R A T U S FOR D E T E R M I N A T I O N O F SO2 B Y M O N I E R - W I L L I A M S M E T H O D

used. Connect a dropping funnel K to B by a three-holed stopper C. Use tube E to connect the upper end of the condenser to a 100 ml Erlenmeyer flask F, which is followed by a Peligot tube G. The delivery tube extends to the bot tom of the receiver F. One Peligot tube is sufficient to t rap traces of sulphur dioxide swept through flask F. Use rubber stoppers throughout . The receiver F contains 25 ml of 3 % hydrogen peroxide while the Peligot tube contains 5 ml of hydrogen peroxide. After connecting the apparatus, introduce 200 ml of water and 20 ml hydrochloric acid into flask B and boil for a short time in a current of nitrogen. Add 250 g of the sample directly by means of the dropping funnel with the aid of as little distilled water as possible. After the introduction of the sample, boil the mixture for 1 hour in a slow current of nitrogen, stopping the flow of the water in the condenser


just before the end of the distillation. This causes the condenser to become hot and drives over residual traces of sulphur dioxide retained in the condenser. When the delivery tube just above the receiver F becomes hot to the touch, remove stopper J immediately. Wash the contents of the delivery tube and the Peligot tube into the flask F.

iii. Titrate the solution at room temperature with N / 5 0 N a O H to pH 6 using a pH meter and note the volume of sodium hydroxide used. Alternatively Bromophenol Blue may be used as an indicator for the titration. 1 ml of N/50 sodium hydroxide 0.64 mg sulphur dioxide.

8. The conductivity of solutions of white sugars a. After thoroughly rinsing the conductivity cell with conductivity

water it is filled with the conductivity water to be used and its conductance measured. Any batch having a specific conductivity greater than 1.8 reciprocal megohms is rejected.

b. 5.00 g of sugar are weighed into a 100 ml volumetric flask which has been rinsed with conductivity water. The sugar is dissolved and the flask made to volume with conductivity water. The con-ductivity of the solution is then measured at 20°C.

c. If a temperature slightly lower or higher than 20°C is used for measurement, a correction of 2% per degree centrigrade should be made. For temperatures below 20°C, the correction should be added while for those above 20°C, the correction should be subtracted.

d. The conductivity of the sugar solution minus 0.4 times the conducti-vity of the water used in making up the sugar solution, gives the nett specific conductivity of the sugar solution.

e. For the determination of the cell constant, a standard potassium chloride solution is most convenient. An N/100 KC1 solution has a specific conductivity of 0.001225 ohm - 1 cm - 1 at 18°C; 0.001278 at 20°C; 0.001413 at 25°C; and 0.001552 at 30°C. Thus if the resistance of a cell in N/100 KC1 solution at 20°C is found to be R ohms, the cell constant is 0.001278 x R. The specific conductance of a solution is found by dividing the cell constant by the resistance of the solution in the cell.

f. Further information concerning details of instruments and pro-cedures may be found in Browne & Zerban, Sugar Analysis, New York, John Wiley & Sons, Inc. (3rd edition), pp . 1021—1032.

9. Calcium and magnesium (by a modification of the Schwarzenbach method)

a. Calcium and magnesium: A solution of the product to be analysed must be prepared as described in chapter VIII , 4, g. A 20 ml port ion of this prepared solution is pipetted into a 350 ml conical


flask and diluted with 80 ml of distilled water. 4 ml of the buffer and approximately 0.2 g of the indicator are added, and the solution is titrated with ethylenediaminetetraacetic acid until there is no further colour change. The concentration of calcium and magnesium in the solution may be calculated in millimols per litre.

b. Calcium only: For the determination of calcium alone, murexide indicator is used (see chapter VI, 9, e). In accurate work it is necessary to restandardize the ethylenediaminetetraacetic acid with this indicator. 20 ml of the standard calcium solution is diluted with 60 ml of distilled water and 5 ml of 6 N caustic soda solution. 0.2 g of murexide indicator is added and the solution is titrated immediately with the ethylenediaminetetraacetic acid solution until the colour changes from olive-grey to clear blue-green. A blank determination should be carried out on 80 ml of distilled water and the blank titre subtracted from the titre obtained in the standardization. The strength of the titrating solution is calculated as before. For the actual determination 20 ml of the prepared solution is used instead of the standard calcium chloride solution and the titration is carried out as described above. The concentration of calcium in the unknown may be calculated in millimols per litre. The concentration of magnesium is found by subtracting the calcium concentration from the total concentration of calcium and magnesium found as above. To convert millimols per litre to milligrams of CaO per litre, multiply by 56.08; to milligrams of M g O per litre, multiply by 40.32.

10. Moisture See special directions for each material in chapter VIII.

11. pH The pH of solutions is best determined by glass electrode pH meters, which are strongly recommended.

12. Titrated acidity or alkalinity The determination of pH has largely superseded the measurement of acidity by titration. Whereas pH gives the effective acidity or hydrogen ion concentration, the titration method gives the total acidity or alkalinity.

The titration of acid juices (diluted if necessary) is carried out with N/10, N/28, or N/32 N a O H using phenolphthalein as indicator. The results are expressed as milligrams CaO or SO2 (where acidity is due to SO2) per litre.

Alkaline juices are titrated with N/10 or N/28 HC1 and the results expressed as milligrams CaO per litre of juice.

13. Sulphated ash Weigh out into a platinum or porcelain dish 5—25 g of the material depending on its ash content. Add 25 to 30 drops of concentrated


sulphuric acid. Heat gently until carbonized, then ignite in an oxidizing atmosphere and muffle at 550°C. Cool and add a few drops of concen-trated sulphuric acid to moisten the ash thoroughly. Heat gently over a flame to drive off the excess acid and then ignite for one hour in the muffle at 800°C. Cool and weigh. Results should be expressed as per-centage sulphated ash without deduction.

14. Test for traces of sugar in waters (Skarblom test) A test tube approximately 10 mm in diameter and 80 mm in length is filled with a sample of the water and inverted for a few seconds, allowing most of the water to drain. Upon replacing the test tube in an upright position approximately 0.2 ml of water will accumulate in the bottom of the tube. To this is then added one to two drops of 4% alcoholic alpha-naphthol solution followed by 15 to 20 drops of concentrated sulphuric acid. On mixing the contents of the tube by shaking, the development of a violet colour within 30 seconds is indicative of the presence of sugar.


C H A P T E R VIII

A N A L Y S I S O F P R O D U C T S

a. Sucrose % cane: The method used to determine sucrose % cane depends mainly on the size of the parcel of cane to be analysed.

i. G E N E R A L F A C T O R Y M E T H O D : The weight of sucrose

in a quantity of cane crushed in a period which begins and ends with an empty mill train is determined by adding the weights of sucrose in the mixed juice and the bagasse produced from that quantity of cane. This method is generally used by the factories to assess the weight of sucrose in cane crushed in a weekly period. The method is also applicable for shorter periods but the results are less accurate owing to the difficulty of assessing the weights of mixed juice and bagasse corres-ponding to a relatively small quantity of cane.

ii. J A V A R A T I O M E T H O D : The percentage of sucrose in an

individual consignment of cane is assessed by a different method. The consignment is crushed and the sucrose (po1) percentage of the first expressed juice is determined. Sucrose % cane is found by multiplying sucrose % first expressed juice by the so-called Java ratio. This factor is the average ratio of sucrose % cane to sucrose (pol) % first expressed juice determined for the weekly period in which the consignment is crushed. One of the drawbacks of this method is that the juice content of the cane of the individual consignments is not taken into account. The method is applied for cane payment purposes.

i i i . T E S T M I L L A N A L Y S I S : Owing to the considerable varia-tion in the composition of the units constituting a parcel of cane, a satisfactory method of assessing its sucrose content by obtaining a representative sample has not yet been found, in spite of extensive attempts carried out in many countries including South Africa.

The following test mill analysis of a sample is carried out when the greatest accuracy is not required. The sample, after being weighed, is crushed in a test mill. Usually, only the weight of the bagasse produced is determined and the weight of the juice is calculated as the difference between the


weight of the cane and the weight of the bagasse. If facilities exist for the weighing of bo th bagasse and juice this should be done. Any shortage from the total weight of the cane is then divided between the bagasse and the juice in the ratio of 1:2.

The juice is analysed in the ordinary way for brix and pol (sucrose)—see under Mixed juice, chapter VIII, 5; the analysis of the bagasse however is more complicated.

The bagasse is shredded or chopped, the operation being conducted as quickly as possible to avoid loss of moisture. The pol is then determined as under Final bagasse, altering the amount of water taken to allow for the weight of fibre in bagasse, so as to give an approximately half normal solution. N.B. In the case of chopped bagasse, care should be taken that the final sample is representative of the trash, rind and pith originally present.

Then pol % cane =

Fibre % cane =

where Fibre % bagasse = Dry matter % bagasse—brix % bagasse

and brix % bagasse = X 100.

This method is generally used by the factories to assess the fibre percentage of the cane crushed in a weekly period.

ii. D I R E C T M E T H O D : The fibre percentage of a sample of 50-100 lb. of cane can be determined with sufficient accuracy as follows: The sample is sub-sampled as described in chapter V, 2, b. The sub-sample is passed through a suitable laboratory disintegrator or shredder and all the shredded material is collected in a large bucket. When the material has been well mixed 100 g are weighed out in duplicate into tared 500 ml beakers. The samples are transferred quant i -tatively to strong linen bags which are then tied with string. The bags are placed in briskly boiling water for an hour and


X 100.

b. Fibre % cane i. G E N E R A L F A C T O R Y M E T H O D : The fibre percentage of

a quantity of cane crushed in a period which begins and ends with an empty mill train is determined by substituting the relevant data in the expression,

then in cold running water for another hour. During the second hour the bags should be squeezed at intervals. Finally the bags are pressed to eliminate surplus water and are dried at 110-130°C to constant weight. The bags are cooled in a desiccator before weighing. The fibre is then removed from the bags and the bags are weighed empty. The percentage of fibre in cane is found by subtracting the weight of the empty bag from the weight of the bag + fibre in each case.

iii. I N D I R E C T M E T H O D : I f an experimental mill i s available, the fibre percentage of a sample of cane can be assessed by a method similar to that described in 1, b, i above. The weighed sample is crushed and the purity of the expressed juice and the weight, pol and moisture content of the bagasse is determined. Pol % bagasse and moisture % bagasse are determined by the methods described under 2, a and 2, b below. The method of calculating the final result is similar to that described in 1, b, i above.

2. Final b a g a s s e a. Pol % bagasse: Since the error made is insignificant, sucrose %

bagasse is generally assumed to be equal to pol % bagasse and this latter value is determined. The apparatus for the determination of pol in bagasse is described in chapter IV, 2, n. 520 g of unchopped bagasse are weighed out into a digester and 3,775 g of hot water containing 80 ml of a 5 % sodium carbonate solution are added. These quantities have been selected so that the resulting extract is a half normal solution, as explained below. The average moisture content of Natal bagasse being 53 % and its brix content being 3.25%, its average fibre content F is 43.8%. Assuming 30% brix-free water to be present, the amount of juice in bagasse available to mix with the water added is:

520 x = 225 g (approximately 225 ml)

hence: 4000 — 225 — 3775 ml water required to bring the extract volume to

4000 ml.

The perforated plate is placed on the bagasse and pressed below the surface of the liquid. The cover and condenser are attached and the water is brought to the boil. After boiling continuously for one hour, a sample of the solution is withdrawn and cooled to room temperature. It is clarified with the minimum amount of powdered lead sub acetate necessary for clarification and polarized in a 400 mm tube. The reading gives the percentage pol (sucrose) in bagasse directly.

b. Moisture % bagasse: 100 g of bagasse are weighed into trays 20 cm by 20 cm by 2 cm made with suitable gauze bot toms and dried for 8 hours at 100-105°C.


Although a normal drying oven can be used, a Spencer type oven is recommended. In order to reduce the time required for an analysis, a special type of oven in which heated air is blown through the sample placed on a tray provided with a metal gauze bot tom is used in some factories. Special care is required to ensure that fine particles are not blown out of the tray and that the openings of the gauze are not blocked. Where greater accuracy is required, samples of 1000 g must be used for the analysis. Appara tus for this purpose is on the market .

3. Bagacillo A rough test to assess the value of bagacillo as a filter aid for use with rotary vacuum filters. One hundred grams bagacillo are dried for 4 hours at 105°C. The dried sample is sieved on an 8 inch diameter 20 mesh Tyler screen. Sieving is carried out manually for 4 minutes using a rotary mot ion only. The weight of bagacillo passing through the screen is expressed as a percentage of the weight of the dried sample. The bagacillo may be classified as follows:

4. All juices other than mixed juice a. Brix: Brix is determined as described in chapter VII, 3. b. Pol: Normally the method given in chapter VII , 4, a is used.

Otherwise the method in chapter VII, 4, b may be used. c. Reducing sugars: A solution of juice should be prepared so that

15-50 ml will be used in the ti tration. With a juice containing 0.6 to 0.7 % of reducing sugars, 50 ml may be pipetted into a 200 ml flask and the solution made up to volume. This solution is titrated against Fehling's solution in the manner described in chapter VII, 6, a. When the sucrose content of the solution is known, the concentration of reducing sugars per 100 ml solution is found from the appropriate column in Table IV, interpolating if necessary. Percentage of reducing sugars in juice =

x 100.

d. Acidity or alkalinity: See chapter VII, 12. e. Sulphur dioxide: 10 ml of a sample of sulphited juice or 50 ml of

clarified juice are used for the determination of sulphur dioxide by the iodine method (see chapter VII , 7, a). A 10 ml measuring


Percentage passing 20 mesh

90 85 80

Rating

Excellent Satisfactory Minimum requirement

X 100.

cylinder or a pipette with a large tip should be used for measuring out sulphited juice. Millilitres of iodine solution (N/32) used are multiplied by 100 (when 10 ml of the sample were taken) or by 20 (when 50 ml of the sample were taken) to obtain the concentration of sulphur dioxide in milligrams per litre. If the volume of iodine required is abnormally large, an N/16 solution of iodine may be used. In this case the factor becomes 200 (when 10 ml of the sample were taken) for sulphited juice.

f. pH: See chapter VII, 11.

g. Calcium and magnesium: The following procedure may be used to prepare either mixed or clarified juices for the titration. Approximately 200 ml of juice are treated with 2 g of basic lead acetate and the precipitate filtered off. A fast, calcium-free filter paper such as Whatman No . 4 should be used. The filtrate is collected in a dry 350 ml Erlenmeyer flask and heated to 60°C. The flask is fitted with a rubber stopper through which pass a delivery and an exit tube. Hydrogen sulphide from a Kipps apparatus is passed through the solution for 30 seconds (in a fume-cupboard), then the exit tube is clamped and the flask left for 3-5 minutes with occasional shaking under pressure of hydrogen sulphide. After filtering through a fast, calcium-free filter paper, an aliquot is tested with potassium iodide solution to ensure complete removal of lead. If a yellow precipitate forms, the treatment with hydrogen sulphide must be repeated. 20 ml of the cooled filtrate is measured out in duplicate from a burette or pipette into conical flasks. The titration is carried out as described in chapter VII, 9, a and 9, b.

5. Mixed juice a. Brix: As described in chapter VII, 3.

b. Pol: The pol of mixed juice should normally be determined using the method given in chapter VII, 4, a. Sometimes, for example, when juice contains much suspended matter (clay) it is advisable to use the method given under chapter VII, 4, b.

c. Clerget sucrose by the Jackson and Gillis method IV

i. The cooled sample of mixed juice is brought into the laboratory and thoroughly mixed. The density of the hourly sample is determined in the usual manner with a brix hydrometer. A sub-sample from each hourly sample is added to a wide-mouthed glass-stoppered bottle. The weight of each sub-sample must always be in the same proport ion to the weight of juice recorded by the factory mixed juice scales during the period in which the sample was collected. Dry basic lead acetate is added to the composite sample with every sub-sample at the rate of 1 g per 100 ml of juice. The amount of sub-sample and the weight of basic lead acetate


added must be carefully controlled. At the end of four hours the composite sample is shaken and filtered.

ii. Two 50 ml portions are pipetted into 100 ml sugar flasks. The sucrose determination is carried out as described in chapter VII, 5, a.

iii. C A L C U L A T I O N : The formula given in chapter VII, 4, a shows how to convert the saccharimeter reading into the pol (apparent sucrose content) of the solution analysed. A similar formula (or Schmitz's table) should be used to convert the readings Dr and Ir into PD and P I , i.e., the readings which would have been obtained if a normal weight solution of the juice had been analysed. To convert the " n o r m a l " readings PD and Pj into the sucrose percentage of the juice, the following formula should be used when the Jackson & Gillis method IV has been followed:

where t = the temperature in °C of the invert solution at the time of polarization and m = the total weight in grams of dry substance in 50 ml undiluted juice and may be calculated using the formula:

For routine purposes it is recommended to calculate the divisor by the use of Tables Va and Yb. Table Va gives the sum of the first two terms of the divisor as a function of the corrected brix before dilution whilst Table Vb gives the temperature correction.

Alternatively Dr and Ir are converted into S' using a formula similar to the one used to calculate S. Then S' is converted into S (the sucrose percentage of the juice) either by applying the formula given in chapter VII, 4, a or by using Schmitz's table (Table III).

The divisor of this formula can also be found by using Tables Va and Vb.

This method of calculating S' from Dr and Ir and correcting S' for normali ty is generally used in the Nata l sugar industry and shall be used for cane payment purposes. N.B. In the direct pol (Home ' s dry lead) method a 200 mm tube is used, but in the double polarization method 400 mm tubes must be used to take account of the dilution (50 to 100 ml) of the clarified juice.


Example: It is assumed that the four hourly samples are of equal weight. Otherwise a weighted average must be used when calculating the brix of the sample.

Sample

1st hour 2nd „ 3rd „ 4th „

Average

Observed Brix

18.40 19.25 17.50 17.95

Temperature

17°C 19°C 21°C 21°C

Corrected Brix

18.24 19.20 17.56 18.01

18.25 1 i

Calculation of S ' : Temperature at time of Polarization: 22°C

D r : 60.2° I r : - 1 8 . 3 °

D r - I r : 78.5° Divisor corrected for m (from Table Va) : 132.37

Correction for t (from Ta le Vb) : — 1.00 Corrected divisor: 131.37

d. Clerget sucrose by the invertase method i. Catch samples should be clarified by adding dry lead sub-

acetate at the rate of 1 g per 100 ml and filtering. Composite samples should be prepared as discussed in 5, c, i above. The filtrates are de-leaded by adding a minimum quantity of anhydrous potassium oxalate and filtering and are analysed as described in chapter VII, 5, b, iii.

ii. Since 50 ml of the undiluted solution is diluted to 100 ml, readings should be taken in 400 mm tubes, provided that the solutions are sufficiently light in colour to permit accurate readings. If 200 mm tubes are used, readings should be multiplied by 2. The reading of the invert solution should be corrected for the optical activity of the invertase solution.

iii. Calculation: The formula used to calculate S' from Dr and Ir is:

S'= 100 (Dr — Ir)

132.1 + 0.0833 (m — 13) — 0.5 (t — 2 0 ) where t = the temperature of the invert solution at the time of polarization and m = the total weight in grams of dry sub-stance in 50 ml undiluted juice. S' is converted to S (the sucrose percentage of the original solution) by the formula given in the example above or by referring to Schmitz's table (Table III).


e. Reducing sugars: Reducing sugars should be determined on a four-hourly composite sample of mixed juice which has been preserved with pulverised mercuric chloride (250 mg/litre). This composite sample should be prepared in accordance with the principles given under 5, c, i above but substituting pulverised mercuric chloride for basic lead acetate. The sample which has been preserved with basic lead acetate for sucrose analysis should not be used since this practice often leads to low results.

It is not necessary to clarify the sample but where it contains sand or other suspended matter which is liable to block the delivery jet of the burette, it is advisable to filter or screen the sample before proceeding with the analysis.

The Lane & Eynon method of analysis is followed. A port ion of the sample is pipetted off and suitably diluted so that 15-50 ml will be used in the titration. (With an average mixed juice containing 0 .6-0 .7% reducing sugars, 50 ml may be pipetted into a 200 ml volumetric flask and made to volume.)

Titrate against 10 ml Fehling's solution in the manner described in chapter VII, 6, a. The percentage of reducing sugars is calculated as described above for juices generally—see under 4, c above.

f. Calcium and magnesium: The same procedure is used for mixed juice as for other juices—see under 4, g above.

g. A vailable phosphate i. Sufficient mixed juice is filtered to obtain about 20 ml of fairly

clear filtrate. 10 ml of this filtrate is pipetted into a 200 ml volumetric f lask and made up to volume. An aliquot of this (usually about 20 ml depending on the amount of P 2 O 5

expected in the juice) is pipetted into a 100 ml flask. The solution is diluted to approximately 70 ml with distilled water and then 20.0 ml of ammonium molybdate solution is pipetted into the flask, followed by 10.0 ml of the reducing solution, after which it is made to the mark.

ii. The intensity of the blue colour developed is measured on a suitable absorptiometer or spectrophotometer 15 minutes after addition of the reducing solution. The equivalent amount of P 2 0 5 is determined from a standard graph drawn beforehand, using solutions of accurately known P2O5 content.

When the degree of accuracy required is not great, the colour developed may be compared visually with standards of known P 2O 5 content using various volumes of diluted s tandard instead of juice for colour development. When the equivalent amount of P 2 O s in the unknown has been ascertained, either from the standard graph or by visual matching, it is multiplied by the dilution factor to obtain the P2O5 content of the original juice.


Example: 10 ml of filtered juice was diluted to 200 ml and 10 ml of this solution was used for development of the blue colour the intensity of which was found to be equivalent to 0.2 mg P2O5

The P2O5 content of the original mixed juice = 0.2 x 20 mg/10 ml juice = 0.2 x 20 x 100 mg/litre

juice = 400 mg/litre of juice.

6. Syrup A quantity of the sample is accurately diluted with twice its weight of water and this diluted sample is used for all determinations except the measurement of p H .

a. Brix: As described in chapter VII, 3. The corrected brix multiplied by 3 represents the brix of the original sample.

b. Pol: By method a in chapter VII, 4, a. The value of the pol found from Table III, using the uncorrected brix of the diluted sample, must be multiplied by 3 to give the pol of the original sample.

c. Reducing sugars: 50 ml of the diluted sample is made up to 200 ml and titrated against Fehling's solution as described in chapter VII, 6, a. The percentage of reducing sugars found for the diluted sample must be multiplied by 3 to give the percentage of reducing sugars in the original sample.

d. Sulphur dioxide: 50 ml of the diluted sample is used for the determination of sulphur dioxide by the iodine titration method as described in chapter VII, 7, a. Millilitres of N/32 iodine solution required multiplied by 60 gives the concentration of SO2 in milligrams per litre in the original sample.

e. Hydrogen ion concentration ( pH) : The pH of syrup is usually determined on the original sample. If the sample were diluted prior to measurement a higher pH value would often be found.

7. Filter cake a. Pol: 25.5 g of the sample are triturated with water in a mor tar

and washed with water into a 200 ml Kohlrausch flask. The volume of liquid is made up to the 200 ml mark and the minimum quantity of dry basic lead acetate needed for clarification is added. The contents of the flask are thoroughly mixed by shaking, filtered, and polarized in a 400 mm tube. The reading gives the sucrose % filter cake directly.

b. Moisture: For moisture determination 50 g of the sample are dried to constant weight in a flat-bottomed dish at a temperature not exceeding 105°C.

8. Massecuites From every strike a sample is diluted accurately with four times its weight of water. Care should be taken that all crystals of sugar are dissolved.


If hot water has been used for this purpose, the solution should be cooled to about room temperature before proceeding with the analysis.

a. Brix: See chapter VII, 3.

b. Pol: See chapter VII, 4, a. For both brix and pol, all readings must be multiplied by 5.

c. Crystal content: The crystal content of a massecuite may be calculated from the analyses of the massecuite and its mother liquor (molasses). It is possible to use the true sucrose (or pol), dry solids (or brix) or true purity (or apparent purity) data, but the use of true sucrose or true purity data is recommended. Brix should never be used as the basis of calculation. The formula using sucrose data is as follows:

where C = crystal % massecuite Smass = sucrose % massecuite Smol = sucrose % mother liquor.

The formulae for use with pol or dry solids data are analogous to that given above for use with sucrose data. When purity is used as the basis of calculation, the formula is

where C = crystal % massecuite Pmass = purity of massecuite Pmol = purity of mother liquor D.S.mass = dry solids % massecuite.

9. Molasses (excluding final molasses) and wash The sample should represent as nearly as possible run-offs from individual massecuites.

a. Brix: A quantity of the material is diluted accurately with four times its weight of water. The brix of the solution is determined as described in chapter VII, 3. Brix of material = corrected brix of solution x 5.

b. Pol {for stocktaking): Determined on a further port ion of the diluted solution. Pol of material = pol of solution x 5.

10. Final molasses a. Brix: A quantity of the material is dissolved in six times its weight

of distilled water and the brix determined as in chapter VII , 3. The reading multiplied by 7 = brix of the original sample.

b. Dry substance: Approximately 40-50 g acid washed and ignited


quartz sand (about 40-100 mesh) in an aluminium dish together with a small glass stirring rod are dried in an oven and cooled in a desiccator. The dish shall have a tightly fitting lid, be 8 cm in diameter, 1.5 cm in height and be made of 24 gauge aluminium. The length of the glass stirring rod shall be slightly less than the diameter of the aluminium dish.

About 20 g molasses are weighed accurately into a tared weighing bottle provided with a stirrer and closely fitting lid. Approximately 80 g water are added, the mixture stirred until homogeneous (a mechanical stirrer is recommended), the lid replaced and the weighing bottle and contents reweighed.

From this diluted molasses a sample of approximately 10 ml is pipetted into the weighed aluminium dish which is then reweighed. The diluted molasses is mixed intimately with the sand using the glass rod which, after mixing, is allowed to remain in the dish.

The International Commission for Uniform Methods of Sugar Analysis specifies that the drying be carried out at a temperature not exceeding 70°C, preferably 60°C, under a pressure not exceeding 5 cm Hg until successive weighings at two-hourly intervals do not differ by more than 0.5 mg. The dried sample is cooled in a desiccator before weighing.

Sucrose i. T H E J A C K S O N & G I L L I S M E T H O D I V : Weigh out

32.5 g of molasses. Dissolve and make up to the mark with water in a 250 ml flask. Part of this solution is used for the determination of reducing sugars as described in 10, d below. To the remainder add sufficient dry lead sub-acetate for clarification (usually about 6 g), shake well and allow to stand for a few minutes before filtering. To the filtrate add the minimum of anhydrous potassium oxalate necessary for de-leading (usually about 4 g), shake well and again filter. Now pipette 50 ml portions into 100 ml flasks and proceed with either method a or b of chapter VII, 5. The readings are made in 200 mm tubes. If the solution is very dark, add a pinch of zinc dust for decolourizing.

1962 Laboratory Manual for S. Afr . Sugar Factories

The actual saccharimeter readings multiplied by 4 in each case will give PD and PI . To convert ( P D — PI) into S , the modified Clerget Formula in 5, c, iii (for acid inversion) or 5, d, ii (for invertase inversion) above, should be used, where m is the weight in grams of dry substance in the 50 ml of solution taken for inversion. However, since the accuracy of the sucrose determination in final molasses by the Jackson and Gillis method is not very great, no significant error is made if a constant value of 132.0 is taken for the divisor when t is within the limits 19° to 21°C.

When t is either more than 21°C or less than 19°C the value 132.0 shall be corrected for t in the normal way. The above simplification is permitted only if a sample of ordinary final molasses is analysed. In other cases the usual concentra-tion correction shall be calculated and applied, and if Table Va is used the "Corrected brix before di lut ion" is the brix of the half normal solution of the sample,

ii. T H E C H E M I C A L M E T H O D * , U S I N G I N V E R T A S E : 2 6 g of final molasses are weighed out and transferred quanti tatively to a 200 ml volumetric flask. After making to volume this solution is used for the determination of reducing sugars before and after inversion as follows:—

a. 20 ml of the filtrate are pipetted into a 200 ml volumetric flask and made to volume. This solution is titrated against 10 ml of Fehling's solution for the determination of reducing sugars.

b. 50 ml of the filtrate are pipetted into a 100 ml Erlenmeyer flask and diluted to approximately 80 ml and brought to pH 4.7 ± 0.2 by the addition of a pre-determined volume of glacial acetic acid. To this solution is added the invertase, the appropriate quantity of which was determined by the method given in chapter VII, 5, b, ii. If the concentrate is of normal activity 2.5 ml are added, otherwise a pro rata volume. The flask is placed in a water bath at 57-58°C for 15 minutes with occasional shaking. After cooling the solution is transferred quantitatively to a 500 ml volumetric flask and made to volume. This solution is ti trated against 25 ml of Fehling's solution for the determination of reducing sugars after inversion.

The amount of reducing sugars found after inversion gives the percentage of total sugars present. To calculate the sucrose percentage both reducing sugar concentrat ions are expressed as a percentage of the original sample. The percentage reducing sugars before inversion is deducted from the

* Especially for dark-coloured molasses, this method yields more accurate results than the Jackson & Gillis method.


total sugars and the difference multiplied by 0.95. This is necessary to compensate for the fact that 95 parts of sucrose on hydrolysis yield 100 parts of reducing sugars.

d. Reducing sugars: Pipette 20 ml of the diluted solution prepared for the determination of sucrose (10, c above) into a 200 ml volumetric flask and make to the mark with distilled water. Titrate this solution, which is a 1.3% solution of original molasses, against Fehling's solution as described in chapter VII, 6, a. F rom the column for 0.5 g sucrose per 100 ml in Table IV obtain the concentration of reducing sugars per 100 ml and express this concentration as the percentage of reducing sugars in original molasses.

e. Total sugars: As a gauge for the value of final molasses to secondary industries, the percentage of total sugars is often calculated. The percentage is found by adding the percentage of reducing sugars and 1.05 x the percentage of sucrose.

f. Sulphated ash: As described in chapter VII, 13. About 5 g is normally adequate for ashing.

11. Sugars a. Pol

i. The preparation of the solution of the sugar and the reading of the saccharimeter should be carried out at or as near as possible to 20°C. The time of the day for the analysis of composite samples should be chosen accordingly. If it is not possible to work at 20°C the volume of the solution in the 100 ml flask should be completed at the same temperature at which the saccharimeter is read and the reading should be corrected for the deviation of the temperature from 20°C. For every degree above 20°C, 0.03°S should be added to the pol ; for every degree below 20°C, 0.03°S should be deducted from the pol.

ii. Dissolve the normal weight of the sugar in distilled water in a 100 ml volumetric flask. Dilute to approximately 80 ml and add 1.0 ml of lead sub-acetate solution. Mix the solution by swirling and add water until the volume is roughly 96 ml. Thoroughly mix and then wash down the sides of the flask until the volume is approximately 99.5 ml. Disperse any bubbles which have collected at the surface with one drop of diethyl ether. Dry the inside neck of the flask above the solution level with rolled filter paper and make the volume to exactly 100 ml by adding water from a fine dropper. Mix the solution thoroughly and allow to stand for 5 minutes. Filter through an 18.5 cm fluted filter paper contained in a plain stemless funnel, pouring all the contents of the flask into the


paper. Immediately cover the funnel with a cover glass. Discard the first 10 ml of filtrate and collect a further 30 ml of filtrate for polarization in a 200 mm tube at 20°C. It is preferable to use a jacketed tube to prevent warming by the hands.

All operations after weighing should be carried out at a temperature as near 20°C as possible. The funnel should be sufficiently large to prevent the paper projecting above it and during filtration should remain covered with a clock glass.

b. Reducing sugars by the Luff-Schoorl method: Weigh out accurately 20 g of the sample and transfer to a 100 ml volumetric flask. Dissolve in distilled water and make up to volume. Shake well. (Normally no clarification of the solution is required.) In the case of refined and mill-white sugars, accurately pipette a 25 ml aliquot of the solution into a 500 ml Erlenmeyer flask containing 25 ml of the Luff solution. For raw sugars a 25 ml aliquot is normally satisfactory but for raw sugars containing a high percentage of reducing sugars it may be necessary to decrease the aliquot taken. In such a case the volume must be made up to 25 ml with water, e.g. if a 10 ml aliquot is taken 15 ml water must be added. To prevent boiling over add a few pieces of washed and ignited unglazed porcelain. Fit an upright condenser to the flask which rests on a copper gauze over a circular opening with a diameter slightly less than that of the bot tom of the flask. Heat the flask so that the solution boils within 3 minutes and continue boiling for exactly 5 minutes longer. Cool the solution rapidly in running water, taking care that the precipitated cuprous oxide does not come into contact with the air. Immediately add 15 ml of potassium iodide solution and then slowly, with careful swirling, 25 ml of sulphuric acid solution. As soon as the evolution of carbon dioxide ceases titrate the liberated iodine with the N/10 thiosulphate solution. When the end point is approached add I ml of the starch solution. Carry out a blank determination using 25 ml of distilled water in place of the sugar solution. Refer the difference between the volume of N/10 thiosulphate solution required by the blank and the test, corrected for normality, to Table VI and calculate the percentage reducing sugars in the sample.

c. Colour of white sugars i . S A M P L E P R E P A R A T I O N : H o t distilled water a t a tempera

ture of 90-100°C is added to the weight of sugar required to prepare a solution of a concentration of 50 ± 0 .2% refracto-meter solids. The sugar-water mixture is stirred gently to bring the sugar into solution. Cool the solution to about room temperature before measurement. No filtration should be made nor should the pH be adjusted.


N.B. Stainless steel or glass bottles or beakers should be used to prepare the solution. Aluminium beakers should not be used as they introduce turbidity.

ii. M E A S U R E M E N T : The solution should be measured in a 10 cm cell using a suitable spectrophotometer at wavelengths 420 my. and 720 my.. The cell should be located as close to the photocell as possible.

iii. R E F E R E N C E S T A N D A R D : The reference standard should be a 50 ± 0-2% solids colourless sucrose solution. For practical purposes the reading with a colourless sugar solution may be correlated with a secondary standard such as distilled water or air and a balance point established on the scale which will give the equivalent of a colourless sucrose solution.

d. Sulphur dioxide: For raw and refined sugars either the rapid method or the Monier-Williams method is used—see chapter VII, 7, b and 7, c.

e. Moisture: For white sugars and raw or similar type sugars take 25 and 10 g of sample respectively. Accurately weigh the sample of the sugar into a polished aluminium dish provided with a tight-fitting cover. The dish shall be 8 cm in diameter, 1.1 cm in height and made of 24-gauge aluminium sheet. Dry in an oven at 105°C for 3 hours. Replace the cover of the dish, cool in a desiccator and weigh.

f. Sulphated ash: See chapter VII, 13.

g. Conductometric ash {for mill white and refined sugars): The gravimetric determination of bisulphated ash on a refined sugar containing less than 0 .03% ash requires the use of a precision


analytical balance, expensive plat inum ware and very careful analytical technique. A much simpler and often more reproducible method is to measure the electrical conductance of a solution of sugar which will then usually bear a direct relationship to the soluble ash in the sugar. Electrical conductance is the reciprocal of the electrical resistance and in the case of sugar solutions, specific conductivity may be defined as the reciprocal of the resistance of a column of liquid 1 cm long and having a cross-sectional area of 1 cm2 . It is usually reported as reciprocal megohms but may be converted to conductivity ash by multiplying by a factor. The measurement of the conductivity of white sugar in solution at 20°C is described in chapter VII, 8.

h. Grain size distribution: Refined or mill white sugars may be screened as received but with raw sugars it is necessary to remove the film of molasses surrounding the crystals prior to screening. This may be achieved using the method described in I .C.U.M.S.A., 10 (1949) 27. Full details of this method are given below.

E Q U I P M E N T

i . Erlenmeyer flask, 250 ml capacity, wide mouth ( l i in. diam.), with a N o . 8 solid rubber stopper. A wide-mou th bott le of about the same capacity may be used,

ii. A strainer stopper made from the following: N o . 7 rubber stopper, with central hole 3/4 in. to 7/8ths in. d iam.; rubber tubing 11/2 in. wide (used with carbon filter); disc of 100-mesh wire cloth l1/4 in. diam. Cut a band 1 in. wide off rubber tubing. Work this over small end of rubber stopper leaving about 3/16ths in. projecting beyond the end. Peel back projecting tubing, place metal cloth disc on small end of stopper and hold in place by slipping over it the projecting par t of rubber tubing,

iii. Filter flask, 500 ml capacity, with side outlet.

R E A G E N T S

i. Absolute methanol ,

ii. 9 5 % by vol. methanol , prepared by diluting 95 ml

absolute methanol to 100 ml.

iii. 90 % by vol. methanol , prepared from absolute methanol

or from 9 5 % methanol (100 ml to 5 ml H 2 0 ) .

iv. Diethyl ether. P R O C E D U R E

Put 100 g raw sugar in Erlenmeyer flask; add 100 ml 9 0 % methanol ; stop with solid s topper; shake contents to mix;


allow to soak for 1 hour, shaking every 15 min. a few times to mix. Then take flask in one hand, with the index finger over stopper and the flask resting in palm of hand ; rock flask back and forth, causing sugar to be sluiced from one end to the other. Do this for 2 min. making 120 cycles per min. Let sugar settle and, with flask inclined, tilt to wash crystals from around stopper.

Remove solid stopper; replace by strainer-stopper ii, loosely inserted. Pour off methanol through strainer, finally inverting Erlenmeyer flask over filter flask to drain into latter. Apply suction to drain crystals and extract as much methanol as possible.

Add 50 ml 95 % methanol, pouring some through loosened strainer-stopper; then remove stopper and pour remainder of methanol on stopper to wash crystals into flask. Stop with solid stopper and shake for 2 min. as before, etc. Repeat with 50 ml 95 % methanol three times, making in all four applications of the 95 % methanol.

Then wash crystals in the same manner with four 50 ml portions of diethyl ether, shaking for 1 min. instead of 2 min. Most of the diethyl ether of the last wash can be extracted by leaving the Erlenmeyer flask on the filter flask under vacuum for several minutes.

Spread the washed crystals on a piece of clean paper to air-dry; the crystals on the sides of the flask need not be removed. When nearly dry (i.e. when crystals no longer feel cold and begin to cake), return the sugar to the flask and shake a few times; spread again on paper for a few minutes. Return sugar to flask and shake a few times; crystals should now be free running and dry.

S I E V I N G T E S T

For mill white and refined sugars five Tyler s tandard screens (10, 14, 20, 28 and 48 mesh) while for raw sugars four Tyler standard screens (10, 16, 28 and 42 mesh) are used. The sample for screening is weighed prior to placing on the top sieve and sifting is carried out for 10 minutes (the Ro-Tap hand or motor-operated machine is recommended), after which the weights of the fractions are ascertained. The weights of the fractions are expressed as percentages of the total weight of the sugar sifted.

C A L C U L A T I O N O F S P E C I F I C G R A I N S I Z E

The method of calculation given below is that described by Douwes Dekker in S.A.S.T.A. Proceedings, 26 (1952) 46.

The main criterion calculated from the results of the sieving test is the specific surface (U) of the material tested.


U is the ratio between the total surface of all particles and the total surface of the same weight of particles the diameter of which is 1 cm. The particles are supposed to be spheres. U is calculated from Zunker ' s formula,

in which d1 = the diameter of the smallest particle and d2 = the diameter of the largest particle. The specific grain size (S.G.S.) is calculated from U by

the simple formula:

In the following table the values for TJ and S.G.S., as computed from the openings of the Tyler sieves, are given for the six fractions of a sugar-sieving test. d1 of the sixth fraction is assumed to be 0.15 mm. Since the use of three decimals is not necessary and suggests a false degree of accuracy the values of U and S.G.S. which are actually used in the computation of a sugar-sieving test are also given.

First fraction Second „ Third „ Four th „ Fifth „ Sixth „

U

4.712 7.235

10.17 14.37 24.47 48.49

S.G.S. m m

2.122 1.382 0.983 0.695 0.409 0.206

U S.G.S.

For practical use in sugar analysis

4.8 7.2

10.0 14.3 25.0 50.0

2.1 1.4 1.0 0.7 0.4 0.2

To calculate the specific grain size of a sugar from the sieve test results, the weight of each fraction (expressed as a percentage of the total weight) is multiplied by the corresponding value of U. The products are added and the sum divided by 100. The quotient is the specific surface of the sugar tested which, divided into 10 gives the specific grain size in mm. Example:

First fraction Second „ Third „ Four th „ Fifth „ Sixth „

Sieve test result, %

1 15 55 26

2 1

U

4.8 7.2

10.0 14.3 25.0 50.0

Product

4.8 108.0 550.0 371.8

50.0 50.0



The values of U for the fractions obtained when the 10, 16, 28 and 42 mesh screens are used are 4.4, 7.9, 13.2, 22.3 and 41.4 respectively.

T A B L E I I Temperature corrections to readings of brix hydrometers (20°C)

Temperature

I5°C .. . I6°C .. -I7°C .. . I8°C .. . I9°C .. .

2I°C .. . 22°C .. . 23°C .. . 24°C . . . 25°C . . . 26°C .. . 27°C .. . 28°C . . . 29°C . . . 30°C . . . 3I°C .. . 32°C . . . 33°C .. . 34°C . . . 35°C .. .

Hydrometer

No. 0

0.21 0.18 0.14 0.10 0.05

0.05 0.10 0.16 0.22 0.28 0.34 0.40 0.47 0.54 0.61 0.68 0.76 0.84 0.92 1.00

Hydrometer

No. 1

Subtract

0.23 0.18 0.14 0.10 0.05

A d d

0.05 0.11 0.17 0.23 0.29 0.35 0.42 0.49 0.56 0.63 0.70 0.78 0.86 0.94 1.03

Hydrometer

No. 2

Hydrometer

No. 3

From observed percent

0.26 0.21 0.16 0.11 0.05

to observed

0.06 0.12 0.18 0.25 0.32 0.39 0.45 0.52 0.60 0.67 0.75 0.83 0.91 0.99 1 .08

0.29 0.24 0.19 0.13 0.06

percent

0.06 0.13 0.20 0.27 0.33 0.40 0.47 0.55 0.63 0.71 0.79 0.88 0.96 1.04 1.13

Hydrometer

No. 4

0.33 0.27 0.21 0.14 0.07

0.07 0.15 0.22 0.30 0.37 0.44 0.52 0.60 0.68 0.76 0.84 0.93 1.01 1.09 1.18

Hydrometer

No. 5

0.37 0.30 0.22 0.15 0.08

0.08 0.16 0.23 0.31 0.39 0.47 0.55 0.63 0.71 0.80 0.88 0.97 1.05 1.13 1.22


T A B L E I V

Table giving mg invert sugar required to reduce 10 and 25 ml of Fehling's solution in the presence of different amounts of sucrose

ml Sugar Solution Required

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 ..

Og

336 316 298 282 267

255 243 232 222 213

! 205 197 190 184 178

172 166 161 157 152

148 144 140 137 133

130 127 124 121 119

116 114 III 109 107

105

0.5g

335 314 296 280 265

253 241 230 220 211

203 195 189 182 176

170 165 160 155 151

147 143 139 135 132

129 125 123 120 117

114 112 NO 108 106

103

10

mg the

1g

333 312 295 278 264

251 239 228 219 210

202 194 187 180 174

168 163 158 153 149

145 141 137 134 130

127 124 121 118 116

113 111 108 106 104

102

ml Fehling's Solution

deducing Sugars per 100 concentration of s

2g

329 309 291 274 260

249 236 225 216 207

198 191 184 178 171

166 161 156 151 147

143 139 135 131 128

125 122 119 116 114

111 109 106 104 103

100

3g 4g

325 ! 322 305 287 271 257

248 233 222 213 204

196 189 182 175 169

164 159 154 149 145

141 137 133 130 126

123 120 117 115 112

110 107 105 103 102

99

301 284 268 254

242 230 220 210 202

194 186 179 173 167

161 157 152 147 143

139 135 131 128 124

121 118 116 113 110

108 105 103 101 100

98

ml so ution ucrose (g/100 ml)

5g

317 297 280 264 250

238 227 216 207 198

190 183 176 170 165

159 154 149 145 140

136 133 129 126 122

119 116 114 111 108

106 104 102 99 97

95

10g

307 288 271 256 243

231 220 210 200 192

184 177 170 164 159

153 148 143 139 135

131 127 124 120 117

114 III 109 106 103

101 99 96 94 92

90

25g

289 271 255 240 227

217 206 196 187 179

171 164 158 152 147

142 137 132 128 124

121 117 114 111 107

104 102 99 97 94

92 90 88 86 84

82

25 ml Fehling's 1 Sol

when is:—

0g 824 772 727 687 651

619 589 563 539

1 517

496 477 460 444 428

414 401 389 377 366

356 346 337 328 320

312 304 297 290 284

278 272 266 261 255

251

Jtion

1g 817 766 722 682 846

614 585 559 534 512

492 473 456 440 424

410 397 385 373 363

352 342 333 325 316

308 301 294 287 281

275 269 263 258 252

248

Laboratory Manual for S. Af r . Sugar Factories 1963 — 79

T A B L E V a

Table giving the divisor, corrected for the brix of the solution, of the formula to be used in the Jackson & Gillis method IV

Corrected Brix Before Dilution

0 1 2 3 4 5 6 7 8 9

10 11 12 13

Divisor

131.60 131.64 131.68 131.72 131.76 131.80 131.84 131.88 1 31.92 13!.97 132.01 132.05 132.10 132.14

Corrected Brix Before Dilution

14 15 16 17 18 19 20 21 22 23 24 25 26

Divisor

132.18 132.23 132.27 132.32 132.36 132.41 132.46 132.50 132.55 132.60 132.64 132.69 132.74


Temperature corrections for

Temp. (°C)

15.0 15. 1 15.2 15.3 15.4

15.5 15.6 15.7 15.8 15.9

2 0 . 0 20 .1 2 0 . 2 20 .3 2 0 . 4

2 0 . 5 2 0 . 6 2 0 . 7 2 0 . 8 2 0 . 9

2 1 . 0 21 .1 2 1 . 2 21 .3 2 1 . 4

2 1 .5 2 1 . 6 2 1 . 7 21 .8 2 1 . 9

2 2 . 0 22 . 1 2 2 . 2 22 .3 22 .4

2 2 .5 2 2 . 6 2 2 . 7 2 2 . 8 2 2 . 9

2 3 . 0

Correction

2 . 5 0 2 .45 2 . 4 0 2 .35 2 . 3 0

2 .25 2 . 2 0 2 . 15 2 . 1 0 2 .05

0 . 0 0 0 .05 0 . 1 0 0 .15 0 .20

0 .25 0 . 3 0 0 .35 0 .40 0 .45

0 . 5 0 0 .55 0 . 6 0 0 .65 0 .70

0 .75 0 . 8 0 0 .85 0 .90 0 .95

1.00 1.05 1. 10 ! . 15 1.20

1.25 1.30 1.35 1.40 1.45

1 .50

Temp. (°C)

Te

16.0 16. 1 16.2 16.3 16.4

16.5 16.6 16.7 16.8 16.9

Tem

2 3 . 0 23 .1 2 3 . 2 23 .3 2 3 . 4

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

2 4 . 0 24 .1 2 4 . 2 24 .3 2 4 . 4

24 .5 2 4 . 6 2 4 . 7 2 4 . 8 2 4 . 9

2 5 . 0 25 .1 2 5 . 2 25 .3 2 5 . 4

25 .5 2 5 . 6 2 5 . 7 2 5 . 8 2 5 . 9

2 6 . 0

T A B L E V b

the divisors for the Jackson & Gillis method for acid

Correction

Temp. (°C)

Correction

Temp. (°C)

Correction

m p e r a t u r e corrections to be added

2 . 0 0 1.95 1.90 1.85 1.80

1.75 1 .70 1.65 1 .60 1.55

perature

1.50 1.55 1 .60 1 .65 1.70

1.75 1.80 1.85 1.90 1.95

2 . 0 0 2 .05 2 . 1 0 2 .15 2 . 2 0

2 .25 2 . 3 0 2 .35 2 . 4 0 2 .45

2 . 5 0 2 .55 2 . 6 0 2 .65 2 .70

2 .75 2 . 8 0 2 .85 2 . 9 0 2 .95

3 .00

17.0 17.1 17.2 17.3 17.4

17.5 17.6 17.7 17.8 17.9

correcti

2 6 . 0 26 . 1 2 6 . 2 2 6 . 3 2 6 . 4

2 6 . 5 2 6 . 6 2 6 . 7 2 6 . 8 2 6 . 9

2 7 . 0 27 .1 2 7 . 2 27 .3 2 7 . 4

27 .5 2 7 . 6 2 7 . 7 2 7 . 8 2 7 . 9

2 8 . 0 28 .1 2 8 . 2 28 .3 2 8 . 4

28 .5 2 8 . 6 2 8 . 7 2 8 . 8 2 8 . 9

2 9 . 0

1.50 1.45 1 .40 1.35 1.30

1 .25 1.20 1.15 i .10 1.05

18.0 18.1 18.2 18.3 18.4

18.5 18.6 18.7 18.8 18.9

1.00 0 .95 0 . 9 0 0 .85 0 . 8 0

0 . 7 5 0 . 7 0 0 .65 0 . 6 0 0 .55

ons to be subtracted

3 . 0 0 3 .05 3 .10 3 .15 3 . 2 0

3 .25 3 .30 3 .35 3 .40 3 .45

3 .50 3 .55 3 .60 3 .65 3 .70

3 .75 3 .80 3 .85 3 .90 3 .95

4 . 0 0 4 .05 4 . 10 4 . 1 5 4 . 2 0

4 . 2 5 4 . 3 0 4 . 3 5 4 . 4 0 4 .45

4 . 5 0

2 9 . 0 29 .1 2 9 . 2 2 9 . 3 2 9 . 4

2 9 . 5 2 9 . 6 2 9 . 7 2 9 . 8 2 9 . 9

3 0 . 0 30 .1 3 0 . 2 30 .3 3 0 . 4

30 .5 3 0 . 6 3 0 . 7 3 0 . 8 3 0 . 9

31 .0 3 1 . 1 31 .2 31 .3 3 1 . 4

31 .5 3 1 . 6 3 1 . 7 3 1 . 8 3 1 . 9

3 2 . 0

4 . 5 0 4 . 5 5 4 . 6 0 4 .65 4 . 7 0

4 . 7 5 4 . 8 0 4 .85 4 . 9 0 4 .95

5 .00 5 .05 5 .10 5 .15 5 .20

5 .25 5 .30 5 .35 5 .40 5 .45

5 .50 5 .55 5 .60 5 .65 5 .70

5 .75 5 .80 5 .85 5 .90 5 .95

6 . 0 0

Temp. (°C)

19.0 19.1 19.2 19.3 19.4

19.5 19.6 19.7 19.8 19.9

3 2 . 0 32 . 1 3 2 . 2 32 .3 3 2 . 4

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

3 3 . 0 33 .1 3 3 . 2 33 .3 33 .4

33 .5 3 3 . 6 3 3 . 7 3 3 . 8 3 3 . 9

3 4 . 0 34. 1 3 4 . 2 34 .3 3 4 . 4

34 .5 34 .6 3 4 . 7 3 4 . 8 3 4 . 9

3 5 . 0

inversion

Correction

0 . 5 0 0 .45 0 . 4 0 0 .35 0 . 3 0

0 .25 0 . 2 0 0 .15 0 . 1 0 0 .05

6 . 0 0 6 .05 6 . 1 0 6 .15 6 . 2 0

6 . 2 5 6 . 3 0 6 .35 6 . 4 0 6 .45

6 . 5 0 6 .55 6 . 6 0 6 .65 6 . 7 0

6 .75 6 . 8 0 6 .85 6 .90 6 .95

7 .00 7 .05 7 . 10 7 .15 7 . 2 0

7 .25 7 .30 7 .35 7 . 4 0 7 .45

7 .50

Millil itres thiosulphate,

N /10

8 . 0 0 8 . 10 8 . 2 0 8 . 3 0 8 . 4 0 8 . 5 0 8 . 6 0 8 . 7 0 8 . 8 0 8 . 9 0

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

10.00 10.10 10.20 10.30 10.40 10.50 10.60 10.70 10.80 10.90

I f . 0 0 11.10 11.20 11.30 11.40 11.50 11.60 11.70 11.80 11.90

T A B L E V I ( c o n t i n u e d )

Milligrams red

1.25 g sucrose

in aliquot

24 .10 24 .40 24 .70 25 .00 25 .30 25 .65 25 .95 26 .25 26 .55 26 .85

27 .20 27 .50 27 .80 28 .10 28 40 28 .70 29 .00 29 .30 29 .60 29 .90

30 .25 30 .55 30 .85 31 .20 31 .50 31 .80 32 . 10 32 .45 32 .75 33 .05

33 .40 33 .70 34 .00 34 .35 34 .65 34 .95 35 .30 35 .60 35 .90 36 .20

sugars

2 - 5 g sucrose

in aliquot

23 .55 23 .85 24. 15 24 .45 24 .75 25. 10 25 .40 25 .70 26 .00 2 6 . 3 0

26 .65 26 .95 27 .25 27 .55 27 .85 2 8 . 2 0 28 .50 28 .80 29 .10 29 .40

29 .75 30 .05 30 .35 30 .70 31 .00 31 .35 31 .65 32 .00 32 .30 3 2 . 6 0

32 .95 33 .25 33 .55 33 .90 34 .20 34 .55 34 .85 35. 15 35 .50 35 .80

ucing

5 g sucrose

in aliquot

23 .00 23 .30 23 .60 23 .90 24 .20 2 4 . 5 0 24 .80 25 .10 25 .40 2 5 . 7 0

26 .00 26 .30 2 6 . 6 0 2 6 . 9 0 2 7 . 2 0 2 7 . 5 0 27 .80 2 8 . 1 0 28 .40 2 8 . 7 0

29 .05 29 .35 29 .65 29 .95 30 .25 30 .60 30 .90 31 .20 31 .50 3 1 . 8 0

32 .15 32 .45 32 .75 33 .05 33 .40 33 .70 34 .00 34 .35 34 .65 34 .95

Milli l itres thiosulphate,

N /10

12.00 12.10 12.20 12.30 12.40 12.50 12.60 12.70 12.80 12.90

13.00 13.10 13.20 13.30 13.40 13.50 13.60 13.70 13.80 13.90

14.00 14.10 14.20 14.30 14.40 14.50 14.60 14.70 14.80 14.90

15.00 15. 10 15.20 15.30 15.40 15.50 15.60 15.70 15.80 15.90 16.00

Milligrams red

1.25 g sucrose

in aliquot

36 .55 36 .85 37. 15 37 .50 37 .80 38 .10 38 .45 38 .75 39. 10 39 .40

39 .75 40 .05 4 0 . 4 0 4 0 . 7 0 4 1 . 0 0 41 .35 41 .65 4 2 . 0 0 4 2 . 3 0 4 2 . 6 0

42 .95 4 3 . 3 0 4 3 . 6 0 43 .95 4 4 . 3 0 4 4 . 6 5 4 5 . 0 0 4 5 . 3 0 4 5 . 6 0 4 5 . 9 5

4 6 . 2 5 4 6 . 6 0 4 6 . 9 0 47 .25 4 7 . 6 0 47 .95 4 8 . 3 0 48 .65 4 9 . 0 0 4 9 . 3 0 49 .65

sugars

2 - 5 g sucrose

in aliquot

36 . 15 36 .45 36 .75 37 .05 37 .40 37 .70 38 .05 38 .35 38 .65 38 .95

39 .30 39 .60 39 .90 40 .25 40 .55 4 0 . 9 0 41 .20 4 1 . 5 0 4 1 . 8 5 42 .15

4 2 . 5 0 4 2 . 8 0 43 .15 43 .45 4 3 . 8 0 4 4 . 1 0 44 .45 44 .75 4 5 . 1 0 4 5 . 4 0

45 .75 46 . 10 4 6 . 4 0 46 .75 47 . 10 47 .45 4 7 . 8 0 48 .15 4 8 . 5 0 4 8 . 8 0 49 .15

ucing

5 g sucrose

in aliquot

35 .30 35 .60 35 .90 36 .25 36 .55 3 6 . 9 0 37 .20 37 .50 37 .85 38 . 15

38 .50 38 .80 39 . 15 39 .45 39 .80 4 0 . 1 0 4 0 . 4 0 4 0 . 7 5 4 1 . 1 0 4 1 . 4 0

4 1 . 7 0 4 2 . 0 0 4 2 . 3 5 4 2 . 6 5 4 3 . 0 0 4 3 . 3 0 43 .65 4 4 . 0 0 4 4 . 3 0 4 4 . 6 5

44 .95 4 5 . 3 0 4 5 . 6 5 4 6 . 0 0 4 6 . 3 0 46 .65 4 7 . 0 0 47 .35 4 7 . 7 0 4 8 . 0 0 4 8 . 3 0


Product

Final bagasse

First expressed juice

Mixed juice

Last expressed juice

Sulphited juice (sulphur tower)

Clarified juice

Filter juice (clear filtrate)

Filter cake

Syrup

Massecuite

Molasses (run-off)

Wash

Final Molasses

Sugar

Method of Sampling

Catch

Continuous

Continuous automatic

Continuous

Catch

Continuous

Catch

Catch

Catch

Catch

Catch when crystal-lizer about 1/3 down

Catch from tank

Continuous

Semi-continuous

Period covered by sample

1/4 hour

1 hour

1 hour

1/4 hour

2 hours

1 hour

1 hour

1 hour

1 hour (from every tank)

Every strike (at the discharge)

Every crystallizer

8 hours

24 hours

1 hour

Composite sample

1 hour

4-hour sample to be preserved in mill lab.

4-hour sample consisting of aliquot parts of 1 hr. samples

4-hour sample, preservative added

No

4-hour sample, preservative added

No

No

4-hour sample

No

No

No

6 days

Procedure followed depen

Analysis carried out on primary sample

—

Pol Brix

Pol Brix, before addition of lead subacetate

—

S02

pH

Pol Brix

Pol Moisture

—

Pol Brix

Pol Brix

Pol Brix

—

ds on the circumstances

Analysis carried out on composite sample

Pol Moisture

Pol

Pol Sucrose Red. sugars

Pol Brix

-Pol Brix

~

-

Pol Brix Red.sugars

—

—

—

Pol, brix, sucrose, Red sugars, sulph. ash

TABLE III

DEGREES BRIX AND CORRESPONDING PER CENT SUCROSE ~

Labortory Manual for South African Sugar Factories

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