130 METHODS OF ANALYSIS [Chap. 



All products which contain dextrose or other reducing sugars in the crystalline 

 form, or in supersaturated solution, exhibit the phenomenon of birotation. The con- 

 stant rotation only should be employed in the Clerget formula, and to obtain this 

 the solutions prepared for direct polarization should be allowed to stand overnight 

 before making the reading. If it is desired to make the direct reading immediately, 

 the birotation may be destroyed by heating the neutral solution to boiling for a few 

 minutes or by adding a few drops of strong ammonium hydroxid before completing 

 the volume. 



23 Method II. {Double dilution method.^)— Tentative. 



(Substances in which the volume of the combined insoluble matter and 

 precipitate from clarifying agents is more than 1 cc. from 26 grams.) 



Weigh out a half normal weight of the sample and make up the solution to 100 

 cc, employing the appropriate clarifier (basic lead acetate for dark colored con- 

 fectionery or molasses and alumina cream for light colored confectionery). Also 

 weigh out a normal weight of the sample and make up a second solution with the 

 clarifier to 100 cc. Filter and obtain direct polariscopic readings of both solu- 

 tions. Invert each solution as directed in 22 and obtain its invert reading. 



The true direct polarization of the sample is the product of the two direct read- 

 ings divided by their difference. 



The true invert polarization is the product of the two invert readings divided 

 by their difference. 



Calculate the sucrose from the true polarizations thus obtained by the formula 

 given under VIII, 14. 



COMMERCIAL GLUCOSE (APPROXIMATE). 



24 Method I— Tentative. 



(Substances containing little or no invert sugar.) 



Commercial glucose can not be determined accurately owing to the varying 

 amounts of dextrin, maltose, and dextrose present in this product. However, in 

 sirups, in which the amount of invert sugar is so small as not to appreciably affect 

 the result, commercial glucose may be estimated approximately by the following 

 formula:^ 



^ (a - S) 100 . , . , 



G = in which 



175 



G = per cent of commercial glucose; 



a = direct polarization; 



S = per cent of cane sugar. 



Express the results in terms of commercial glucose polarizing +175°V. 



Method II. — Tentative. 



25 (Substances containing invert sugar.') 



Prepare an inverted half normal solution of the substance as directed under 

 VIII, 14 except that after inversion cool the solution, make neutral to phenol- 

 phthalein with sodium hydroxid solution, slightly acidify with hydrochloric acid, 

 and treat with 5-10 cc. of alumina cream before making up to the mark. Filter 

 and polarize at 87°C. in a 200 mm. jacketed tube. Multiply the reading by 200 and 

 divide by the factor 103 to express the amount of glucose present in terms of glu- 

 cose polarizing +175°V. 



