5. REFERENCES

[1] F. Strohmer, Oesterr-ungar. Z. Zuckerind. Landw. 12, 925 (1883); 13, 185 (1884).

[2] F. Stolle, Z. Ver. deut. Zucker-Ind. 51, 469 (1901).

[3] L. M. Tolman and W. B. Smith, J. Am. Chem. Soc. 28, 1476 (1906).

[4] H. C. P. Geerligs, Arch. Suikerind. 15, 487 (1907).

[5] H. Main, Int. Sugar J. 9, 481 (1907).

[6] O. Schönrock, Z. Ver. deut. Zucker-Ind. 61, 424 (1911).

[7] E. Landt, Z. Ver. deut. Zucker-Ind. 83, 692 (1933).

[8] E. Landt, Int. Sugar J. 39, 225 (1937).

[9] J. Tischtschenko, Z. Ver. deut. Zucker-Ind. 59, 103 (1909). [10] V. Stanek, Z. Zucker Ind. Böhmen 34, 5 (1909).

[11] C. Pulfrich, Z. angew. Chem. p. 1168 (1899).

[12] F. R. Bachler, Facts About Sugar 28, 420 (1933).

XV. DETERMINATION OF MOISTURE

1. GENERAL

An accurate determination of the moisture in sugar products is frequently a matter of great difficulty, and the proper procedure has not been definitely established. Moist sugar or sugar products, sirups, and molasses resist drying with great obstinacy. Sometimes the material is hygroscopic. At ordinary pressures, moisture can be removed only by prolonged heating at a high temperature. But a high temperature frequently exerts a destructive effect on the solid sugars. The destructive action of a temperature of 100° C. is a particularly important consideration in the case of levulose and, to a less extent, in the cases of dextrose and sucrose. Consequently, the best drying methods are those which combine mild temperature and high vacuum. If the substance is in the form of a sirup, drying is facilitated by mixing it thoroughly with dry quartz sand or pumice. The action of the sand is to cause a larger area to be exposed and prevent the formation of a crust. Flaked asbestos or, for fluid substances, a roll of filter paper may be used.

Below are given various methods in common use for determining dry substance. The method to be adopted depends somewhat upon the material. If levulose is present in considerable quantity, the temperature of drying should not exceed 70° C.

2. METHOD OF THE UNITED STATES BUREAU OF CUSTOMS

For control analysis of raw sugars, the Bureau of Customs, Treasury Department, has adopted an arbitrary method which yields readily reproducible results. The procedure is as follows [1]: For the determination of moisture in sugars, dry approximately 4 g in a metal dish 55 mm in diameter and 15 mm in height. Subject each sample to a temperature of 100° C. for 2 hours, care being exercised that the dishes are not in close proximity to the heaters.

In making the determination, dishes of polished aluminum with tightly fitting covers are used. Upon removing from the drying oven, the dish is immediately covered and placed in a desiccator. As soon as the dishes and contents have cooled, they are weighed. The loss of weight is expressed as moisture.

3. METHODS OF THE ASSOCIATION OF OFFICIAL AGRICULTURAL

CHEMISTS

(a) DIRECT DRYING [2]

(Applicable to Cane and Beet Raw and Refined Sugar)

Dry 2 to 5 g of the prepared sample in a flat dish (Ni, Pt, or Al), at the temperature of boiling water, for 10 hours; cool in a desiccator and weigh. Dry again for an hour or until the change in weight is not more than 2 mg. For sugars of large grain, heat at 105° to 110° C to expel the last traces of occluded water. Report the loss as moisture.

(b) VACUUM DRYING [3]

Dry 2 to 5 g of the prepared sample in a flat dish (Ni, Pt, or Al, and with a tightly fitting cover) at a temperature not exceeding 70° C (preferably at 60° C), under a pressure not exceeding 50 mm of Hg, and for 2 hours. Remove from the oven, put cover in place, cool in desiccator, and weigh. Redry for an hour and repeat until the change in weight is not more than 2 mg between successive weighings at 1-hour intervals. The oven should be bled with a current of dry air during drying to insure removal of water vapors.

(c) DRYING ON QUARTZ SAND [2]

(Applicable to massecuites, molasses, and other liquid and semiliquid products) Digest pure quartz sand that will pass a 40-mesh but not a 60-mesh sieve with hydrochloric acid, wash free from acid, dry, and ignite. Preserve in a stoppered bottle. Place 25 to 30 g of the prepared sand and a short stirring rod in a dish approximately 55 mm in diameter and 40 mm in depth, fitted with a cover. Dry thoroughly, cover dish, cool in a desiccator, and weigh immediately. Then add sufficient diluted sample of known weight to yield approximately 1 g of dry matter and mix thoroughly with the sand. Heat on a steam bath for 15 to 20 minutes and stir at intervals of 2 to 3 minutes, or until the mass becomes too stiff to manipulate readily. Dry at 70° C under a pressure of not to exceed 50 mm of mercury. Make trial weighings at 2-hour intervals toward the end of the drying period (about 18 hours) until the change in weight does not exceed 2 mg.

For materials containing no levulose or other readily decomposable substance, the material may be dried at atmospheric pressure by heating 8 to 10 hours in a water oven at the temperature of boiling water. The sample is cooled in a desiccator and weighed; the heating and weighing are repeated until the loss in 1 hour does not exceed 2 mg. The loss of weight is reported as moisture.

(Dry sand, as well as the dried sample, will absorb an appreciable quantity of moisture after standing over most desiccating agents, therefore all weighings should be made as quickly as possible after cooling in the desiccator.)

4. ADDITIONAL METHODS

The length of time required to determine moisture in molasses and other low-grade products by drying on sand has led to the introduction of a number of special methods, such as the method of Spencer

[4] and the method of Rice and Boleracki [5]. In the Spencer method the drying is effected in a specially designed electric oven. The method is applicable to solid sugars as well as liquid sugar products. The samples are placed in aluminum capsules fitted with metallic gauze bottoms which permit free passage of air. When liquid or semiliquid products are to be dried, the sample is absorbed on asbestos [6]. Air, heated by passing over an electric heating element, is passed through the sample and the moist air is continuously withdrawn by

suction.

The Rice and Boleracki method [5] consists in spreading a very thin film of molasses or sirup on thin sheets of silver and drying in a vacuum oven at 70° C. In the hands of an experienced operator the method appears to yield concordant results and has the added advantage of rapidity. It is necessary to exercise some care in preparing the film for drying and also in the manipulation during drying and weighing. The authors recommend the method for the determination of moisture in such products as honey, invert sirup, and blackstrap molasses.

5. REFERENCES

[1] U. S. Customs Regulations (see p. 797 of this Circular).

[2] Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists, 5th ed. p. 484, 485 (1940).

[3] J. Assn. Official Agri. Chem. 21, 89 (1938).

[4] G. L. Spencer, J. Ind. Eng. Chem. 13, 70 (1921).

[5] E. W. Rice and P. Boleracki, Ind. Eng. Chem., Anal. Ed. 5, 11 (1933). [6] G. P. Meade, J. Ind. Eng. Chem. 13, 924 (1921).

XVI. DETERMINATION OF ASH

Although the determination of ash in sugars and sugar products is subject to considerable uncertainty, it is still widely used as an indication of the mineral constituents present. In routine analysis the socalled "sulfated-ash" method is employed, largely on account of its simplicity and reproducibility. In this method any volatile constituents, such as CI, NO3, CO2, etc., are driven off and are replaced by SO4. This replacement is considered advantageous in that it compensates for the losses. A further advantage is the conversion of volatile salts, such as KCl, into the nonvolatile sulfate. The method is as follows:

1. SULFATE METHOD

Weigh 2 to 5 g of the sample in a 50- to 100-ml platinum dish, add 0.5 ml of concentrated H2SO4 or 1.0 ml of 1:1 H2SO4, heat gently on a hot plate until the sample is well carbonized, and then heat in a muffle furnace at a low red heat until all carbon is burned. Cool and add a few drops more of H2SO4, heat until this is fully volatilized, then cool in desicator and weigh. Reignite in the muffle furnace to constant weight. Express the result as the percentage of sulfated ash.

The general practice in many laboratories is to deduct one-tenth of the amount of sulfate ash to reduce to the normal ash. This deduction of 10 percent has been studied by many investigators and found to be in error for cane products. Jamison and Withrow [1] found that the value for sulfate ash in Cuban raw sugar, even with the customary 10-percent correction, was about 34 percent higher than the ash by

direct incineration. Ogilvie and Lindfield [2] found the correction factor to be from 12 to 15 percent for beet sugars and from 6 to 26 percent for cane sugars.

Jamison and Withrow proposed a modification of the sulfate method, in which they added 2 ml of sulfuric acid (2:1) to the sample of sugar, heated the sample on a hot plate until completely carbonized, and finally ignited it in the muffle furnace to a white ash. After cooling the ash, they added 3 or 4 drops of sulfuric acid (2:1) and heated it until the excess acid was driven off. They again ignited the ash in the muffle for 15 minutes.

2. METHODS OF THE ASSOCIATION OF OFFICIAL AGRICULTURAL CHEMISTS [3]

In addition to the sulfate-ash method, the AOAC has adopted as official two methods for carbonated ash, as follows:

Method I.-Heat 5 to 10 g of the sample in a 50- to 100-ml platinum dish at 100° C until the H2O is expelled, add a few drops of pure olive oil, and heat slowly over a flame until swelling ceases. Then place the dish in a muffle and heat at low redness until a white ash is obtained. Treat the residue with a little (NH4)2CO3 solution, reevaporate, and heat again in the muffle at a very dull red heat to constant weight.*

Method II.-Carbonize 5 to 10 g of the sample in a 50- to 100-ml platinum dish at a low heat and treat the charred mass with hot water to dissolve the soluble salts. (In low-purity products the addition of a few drops of pure olive oil may be desirable.) Filter through an ashless filter, ignite filter and residue to a white ash, add the filtrate of soluble salts, evaporate to dryness and ignite to about 525° C to constant weight.*

3. ADDITIONAL METHODS

A number of other methods of determining ash have been proposed by various investigators, the details of some of which have been collected by Jamison and Withrow [1]. The methods are as follows: Oxalic acid method of Grobert [4].

Quartz sand modification of Alberti and Hempel [5].

Benzoic acid modification of Boyer [6].

Zinc oxide modification [7].

Lixiviation modification [8].

Von Lippman advocates taking the dried-out sample on which the water determination has been made, saturating it with vaseline oil (having a boiling point of about 400° C), and igniting the mixture. The carbonized mass is then to be burned to ash in a mixed current of air and oxygen.

Since certain insoluble materials, such as sand and clay, which may be present in the sugar, and would therefore be included in the ash as determined by incineration, have no appreciable effect on the sugar in the process of refining, it is frequently necessary to determine the percentage of soluble ash. This may be accomplished by dissolving the sugar in hot water, filtering, washing the filter thoroughly with hot water, and evaporating the combined filtrate and washings in a platinum dish to dryness. The ash in the dry residue is then determined by one of the standard methods.

*The use of (NH4)2CO3 was dropped in 1940.

The determination of ash by means of conductivity measurements is treated in chapter XVII, p. 275.

4. REFERENCES

[1] U. S. Jamison and J. R. Withrow, J. Ind. Eng. Chem. 15, 386 (1923).

[2] J. P. Ogilive and J. H. Lindfield, Int. Sugar J. 20, 114 (1919).

[3] Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists, 5th Ed., p. 487 (1940).

[4] J. de Grobert, J. Chem. Soc. 58, 670 (1890).

[5] Alberti and Hempel, Deut. Zuckerind. 16, 1069 (1891).

[6] E. Boyer, J. Chem. Soc. 58, 1472 (1890).

[7] A. H. Allen, Commercial Organic Analysis, 4th ed., p. 346 (P. Blakiston's Sons & Co., New York, N. Y., 1909.)

[8] Methods of Sugar Analysis, p. 10 (The Great Western Sugar Co., Denver, Colo., 1920).

XVII. ELECTRICAL CONDUCTANCE OF SUGAR

SOLUTIONS

1. INTRODUCTION

Since the electrical conductance of a liquid may be made a measure of the concentration and mobility of conducting particles in solution, its measurement is useful in determining these qualities in sugar products. It has been used extensively, principally as a rapid method of estimating the ash content of solutions [1, 2, 3] at various stages of manufacture in order to predict their performance in subsequent stages or as an index of the quality of the finished product. Many have found, however, that it is not always necessary to convert the conductance measurement to the more familiar value of sulfate or carbonate ash. In such cases, conductance values are reported in units of specific conductance.

More recently, conductance measurements have come into use in the sugar-manufacturing process to control such operations as boiling [4], crystallization [5], centrifuging [6], and others [7], and in the laboratory to determine purity [8, 9] and concentration of solute [10].

Briefly, electrical conductance is the reciprocal of electrical resistance. In sugar solutions it is expressed in units of specific conductance or reciprocals of units of specific resistance, which in turn may be defined as the resistance in ohms of a column of liquid 1 cm long and having a uniform cross-sectional area of 1 cm 2.

To determine the specific conductance of any volume of liquid containing an electrolyte, it is therefore necessary to measure (a) the resistance in ohms of the liquid, and (b) the dimensions of the volume of liquid causing this resistance. This measurement may be performed with great precision, provided errors depending on the temperature of the solution, the construction of the bridge, oscillator, balancing capacitor, resistance standards, and change of apparent resistance with frequency, have been eliminated or corrected [11, 12]. The resistance of the solution is determined by connecting the cell, Zr, figure 46, in one arm of an alternating-current bridge and adjusting R, and C, until no current flows between the points C and D, as detected by means of head phones, T. Then, if Z, and Z2 are electrically the same, the value of R, may be used to determine the resistance of the column of solution in the cell.