8 CHEMICAL CONSTITUENTS OF BOD Y AND FOOD. 
(d) Phenylhydrasdne test. — This is carried out in the following 
way :— 
To 5 c.c. of a solution of sugar (which should not be stronger than - 5 per 
cent.) 1 decigramme of phenylhydrazine hydrochloride and 2 decigrammes of 
sodium acetate are added, and the mixture heated on the water bath for 
half an hour. On cooling, if not before, a crystalline or amorphous pre- 
cipitate separates out. If amorphous it may be dissolved in hot alcohol, 
the mixture diluted with water, and boiled to expel the alcohol, whereupon 
FlG. 1— Crystals of phenylglucosazone. 
the compound or osazone separates out in yellow crystals, 
that there should be an excess of phenylhydrazine. 
It is important 
Dextrose gives a precipitate of phenylglucosazone (CjJT^XjO.,), 
which crystallises in yellow needles (melting-point 205° C). Levulose 
and mannose yield osazones identical with this. 
Galactose yields a very similar osazone (phenylgalactosazone). 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 : — 
