Handbook of the polariscope and its pracitcal applications / adapted from the German editon of H. Landolt, by D.C. Robb and V.H. Veley.

  • Hans Heinrich Landolt
Date:
1882
Catalogue details

Licence: Public Domain Mark

Credit: Handbook of the polariscope and its pracitcal applications / adapted from the German editon of H. Landolt, by D.C. Robb and V.H. Veley. Source: Wellcome Collection.

    207/320 (page 187)
    (f.) Determination of Cane-Sugar in the Presence of other Active Substances. § 95. Another source of inaccuracy met with in the sacchari- metric analyses of beet-liquors, inferior natural sugars, and molasses, is the occurrence along with cane-sugar of a whole series of other substances, capable of affecting in different ways the plane of polariza- tion of light. Of such substances the following have been found, viz. :—Malic acid (—), asparagin and aspartic acid (both + in acid solutions and — in alkaline), glutamic acid ( + ), invert-sugar ( —), beet-gum ( —), dextran ( + ), the two last-named possessing very high rotatory powers. In molasses these substances may be present in such quantity as to render the determination of the sugar in the highest degree inaccurate, and even with beet-liquors some uncer- tainty is thereby involved in the results. It is true that by clearing with basic acetate of lead such substances are precipitated in part; but a method of certainly removing them entirely or of optically neu- tralizing them is still a desideratum. Eisfeldt and Follenius1 attempt this, by heating with a solution of copper sulphate and caustic soda, so as partly to precipitate and partly decompose them by oxidation. Sickel2 has proposed a method, which consists in adding to 18*024 grammes of beet-juice 1 cubic centimetre of basic acetate of lead, and diluting to 50 cubic centimetres with absolute alcohol. In this way the asparagin, aspartic acid, malic acid, gum, and dextran are precipi- tated, and the rotatory power of the invert-sugar almost completely annulled by the presence of the alcohol. This method appears to be serviceable, but requires further confirmation. § 96. When invert-sugar alone accompanies the cane-sugar, the effect of which is to reduce the rotation, the correct percentage of the cane-sugar present can be determined by employing the so-called inversion method of Clerget.3 When a saccharimeter with Soleil scale is used, the method is as follows:—The usual normal solution, containing 16*35 grammes of the sugar is prepared in the ordinary way, cleared, if necessary, with basic acetate of lead, and the rotation determined. Then 50 cubic centimetres of the solution 1 Eisfeldt and Follenius: Zeitsch. des Vereins fur Rub enzucker Industrie, 1877, 728 and 794. 3 Sickel: Idem., 1877, 779 and 800. 3 Clerget: Ann. Ghim. Rhys. [3], 26, 175.