Part 16

=98. Inversion by Yeast.=—Owing to the difficulty of preparing invertase, O’Sullivan and Thompson propose to use yeast as the hydrolytic agent, as first suggested by Kjeldahl. It is shown that in the use of yeast it is not necessary to employ thymol or any other antiseptic. The method of procedure is as follows: The cane sugar solution of usual strength should not be alkaline, but, if possible, should be exactly neutral. If there be any ferment suspected, the temperature should be momentarily raised to 80° to destroy its activity. The polariscopic reading of the solution is then taken at 15°.5 and the amount of copper reduced by the solution should also be determined.

Fifty cubic centimeters of the solution are poured into a beaker and raised to a temperature of 55° in a constant temperature bath. Some brewers yeast amounting to about one-tenth of the total amount of sugar to be inverted, pressed in a towel, is thrown into the hot solution and the whole stirred until mixture is complete. The solution is left for four hours in the water-bath, at the end of this time it is cooled to 15°.5, a little freshly precipitated aluminum hydroxid added, and the volume made to 100 cubic centimeters. A portion of this solution is filtered and its polariscopic reading observed. The solution is then left till the next day, when another polariscopic reading is taken in order to prove that inversion is complete. The copper reducing power is also determined. The method of calculating the results is the same as when invertase is used. The following formulas are employed.

a = the number of divisions indicated by the polariscopic reading for a 200 millimeter tube:

aʹ = the same number after inversion:

m = the number of the divisions of the polariscopic scale which 200 millimeters of the sugar solution containing one gram of cane sugar per 100, alter at 15°.5 on being inverted: In the case of the ventzke polarimeter scale, one gram of cane sugar in 100 cubic centimeters, indicates +3.84 divisions and after inversion it gives -1.34 div. In experiments of this kind, therefore, m = 5.18.

P = the weight of cane sugar present in 100 cubic centimeters of the original solution:

The formula employed then is

a - 2aʹ P = -----------. m

For the copper reduction data the following are used:

G = the weight of 100 cubic centimeters of the original solution:

Gʹ; = the same for the inverted solution: Allowance must be made here both for the dilution and for the 5 per cent increase of the inverted sugar, but the latter number is so small that it need not be calculated accurately.

w = the weight of the original solution used for the estimation:

wʹ = the same factor for the inverted solution:

k = the weight of cupric oxid reduced by w:

kʹ = the same factor for wʹ:

p = the weight of cane sugar present in 100 cubic centimeters of the original solution: The formula to be employed then is

Gʹ kʹ G k p = 0.4308(2 ------ - -----). wʹ w

This method has been applied to the estimation of cane sugar in molasses, apple juices and other substances. It is recommended by the authors as a simple and accurate means of estimating sucrose in all solutions containing it. The methods of making the copper reductions will be given hereafter.

=99. Application of the Process.=—In practice the process of inversion is used chiefly in the analysis of molasses and low grade massecuites. In approximately pure sugars the direct polarization is sufficiently accurate for all practical purposes. In molasses resulting from the manufacture of beet sugar are often found considerable quantities of raffinose, and the inversion process has been adapted to that character of samples. In molasses, in sugar cane factories, the disturbing factors are chiefly invert sugars and gums. The processes used for molasses will be given in another paragraph. In certain determinations of lactose the process of inversion is also practiced, but in this case the lactose is converted into dextrose and galactose, and the factors of calculation are altogether different. The process has also been adapted by McElroy and Bigelow to the determination of sucrose in presence of lactose, and this method will be described further on. In general the process of inversion is applicable to the determination of sucrose in all mixtures of other optically active bodies, which are not affected by the methods of inversion employed.

=100. Determination of Sucrose and Raffinose.=—Raffinose is a sugar which often occurs in beets, and is found chiefly in the molasses after the chief part of the sucrose has been removed by crystallization. It is also found in many seeds, notably in those of the cotton plant. In a pure solution of sucrose and raffinose, both sugars may be determined by the inversion method of Creydt. The inversion is effected by means of hydrochloric acid in the manner described by Clerget. The following formulas are calculated for a temperature of observation of 20°, and the readings should be made as near that temperature as possible.

C - 0.493A (1) S = -------------- 0.827

A - S 6 (2) R = --------- = 1.017A - ------. 1.57 1.298

In these formulas S and R are the respective per cents of sucrose and raffinose desired, A the polarization in sugar degrees before inversion, B the polarization after inversion read at 20°, and C is the algebraic difference between A and B. It must be understood that these formulas are applicable only to a solution containing no other optically active substances, save sucrose and raffinose.

=101. Specific Rotatory Power.=—In order to compare among themselves the rotations produced on a plane of polarized light by different optically active bodies in solution, it is convenient to refer them all to an assumed standard. The degree of rotation which the body would show in this condition, is found by calculation, since, in reality, the conditions assumed are never found in practice. In the case of sugars and other optically active bodies, the standard of comparison is called the specific rotatory power. This factor in any given case, is the angular rotation which would be produced by any given substance in a pure anhydrous state if it were one decimeter in length and of a specific gravity equal to water. These are conditions which evidently do not exist in the case of sugars, since crystalline sugar particles have no polarizing power, and it would be impossible to pass a ray of light through an amorphous sugar column of the length specified. The specific rotatory power is therefore to be regarded as a purely theoretical factor, calculated from the actual data obtained by the examination of the solution of any given substance. If the length of the observation tube in decimeters be represented by l, the percentage of the polarizing body in 100 grams by p, and the specific gravity of the solution by d, and the observed angle of rotation by a, then the factor is calculated from the formula:

a. 100 [a]{Dj} = ---------------. p. d. l_.

The symbols Dj refer to the character of light employed, D indicating the monochromatic sodium flame, and j the transition tint from white light.

If the weight of the polarizing body c be given or known for 100 cubic centimeters of the solution the formula becomes

a. 100 [a]{Dj} = ----------. c. l_.