8 



CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



(cl) Phenylhydrazine test. This is carried out in the following 

 way: 



To 5 c.c. of a solution of sugar (which should not he stronger than 0*5 per 

 cent.) 1 decigramme of phenylhydrazine hydrochloride and 2 decigrammes of 

 sodium acetate are added, and the mixture heated on the water hath for 

 half an hour. On cooling, if not "before, a crystalline or amorphous pre- 

 cipitate separates out. If amorphous it may he dissolved in hot alcohol, 

 the mixture diluted with water, and boiled to expel the alcohol, whereupon 



FIG. 1 Crystals of phenylglucosazone. 



the compound or osazone separates out in yellow crystals. It is important 

 that there should he an excess of phenylhydrazine. 



Dextrose gives a precipitate of phenylglucosazone (C^H^N^), 

 which crystallises in yellow needles (melting-point 205 C.). Levnlose 

 and mannose yield osazones identical with this. 



Galactose yields a very similar osazone (phenylgalactoeazone). It 

 differs from phenylglucosazone by melting at 190-193 C., and in being 

 optically inactive when dissolved in glacial acetic acid. 



The chemistry of the reaction is represented in the following 

 equations : 



