140 THE CARBOHYDRATES 



official method of the American Association of Official Agricul- 

 tural Chemists is that devised by Munson and Walker.* 



Estimation of Glucose as Osazone. 



The following method of estimating glucose as osazone in 

 the products of the action of malt upon starch is recommended 

 by Davis and Ling : f 20 c.c. of solution containing 2-3 grams 

 of starch products per 100 c.c. are mixed with I c.c. of phenyl- 

 hydrazine and 1-5 c.c. of 50 per cent acetic acid. After heating 

 for an hour % over a water bath, the liquid, which has by this 

 time evaporated to a small bulk, is filtered through a tared 

 Gooch crucible, and the crystalline osazone is washed with 

 20-30 c.c. of boiling water, so that the total filtrate does not 

 exceed 50 c.c. ; the precipitate is then dried in a steam oven 

 and weighed ; under these conditions, o-i gram of glucose 

 gives 0-0505 gram of glucosazone. 



Estimation of Natural Mixtures of Sugars. 



Several methods § have been devised for the estimation of 

 the constituents of sugar mixtures, such as occur in plant 

 extracts and in fermentation liquors, use being made of yeasts 

 to ferment away sugars and of enzymes, such as invertase, 

 to hydrolyse disaccharides, etc.]] 



The following method is that described by Davis, Daish, 

 and Sawyer : ^ The freshly plucked leaf material is dropped 

 into boiling 95 per cent alcohol to which a little 0-88 ammonia 

 is added, to destroy the enzymes. This leaf material is 

 placed in a Soxhlet and is extracted with the same alcohol for 

 eighteen to twenty hours. The extract, after evaporation to 

 a small bulk under reduced pressure, is made up to a known 

 volume with water. A portion is evaporated to dryness for 

 the determination of the dry weight, and the remainder is 

 precipitated with basic lead acetate, filtered, and made up to 



* Munson and Walker : " J. Amer. Chem. Soc," 1907, 39, 541. 



t Davis and Ling : " Journ. Chem. Soc, Lond.," 1904, 85, 24. 



t The heating should not be continued for more than one hour. 



§ See also " Note." p. 514. 



II Davis : " J. Soc. Chem. Ind.," 1916, 35, 201. Nanji and Beazeley : 

 id., 1926, 45, 220. 



^ Davis and Daish : " J. Agric. Sci.." 1913, 5, 437. Davis, Daish, and 

 Sawyer : id., 1916, 7, 255. 



