88 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



iii. -C-0;fCH=N-NHC6H5 + CeHsNHNH-Hsi 

 = -CCH=NNHC6H5 



+ H,0 



2'- 



Osazone 



NNHCgHs 



Ketose- 



i. -COCH^OH + H^NNHCgHj = -CCH^OH 



Ketose group 1 1 J_ TT O 



NNHC0H5 



Hydrazone 



ii. -CCH,OH 



NNHC„H, 



— CCHO 



NNHCgHg 



+ C^H^NH, + NH3 



Aldehyde compound 



iii. -CCH-|o + H^HNNHCgHg 



NNHCgHg -CCH=NNCgH5 



+ K0 



NNHCgHg 



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, crystaUisable 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- 



