88 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



iii. -CCH-CH^N-NHCeHg + 

 = -CCH=NNHC 6 H 5 



NNHC 6 H 5 



Osazone 



Ketose 



i. -COCH 2 OH + H 2 NNHC 6 H 5 = -CCH 2 OH 



Ketose group || + 



NNHC 6 H 5 



Hydrazone 



ii. -CCHjOH 



|| + C 6 H 5 NHNH 2 



NNHC.H, 



CCHO 



= || +C 6 H 5 NH 3 + 



NNHC 6 H 5 



Aldehyde compound 



in. -CCHHO+'Kj-NNHC 6 H 5 



II 

 NNHC 6 H 5 -CCH=NNC 6 H 5 



Osazone 



In both cases it will be seen that the osazone grouping is 

 the same whether derived from an aldose or a ketose ; if two 

 sugars, therefore, yield different osazones it is a proof that they 

 differ in constitution in portions of the molecule other than the 

 aldose or ketose group. 



As the osazones are mainly soluble, crystallisable compounds 

 with definite melting-points, they are exceedingly useful both 

 in isolating and identifying the various sugars. 



Sugars can be obtained from osazones by the action of 

 strong hydrochloric acid which eliminates the phenyl- hydra- 



