44 PHYSIOLOGICAL CHEMISTRY 



CH 2 OH CH 2 OH +H 2 NC 6 H 5 +NH 3 



I 

 (CH OH) 3 -> (CHOH) 3 



I 



CHOH +H 2 N NH C 6 H 5 C=0 



I I 



CH=N NH C 6 H 5 CH=N NH C 6 H 5 



A third molecule of phenyl hydrazine now reacts, forming 

 the osazone. 



CH 2 OH 



I -> I 



(CHOH) 3 + H 2 N NH C 6 H 5 (CHOH) 3 + H 2 



I 

 C==0 C=N NH C G H- 



I I 



CH=N NHC 6 H 5 C =N NH C H, 



I 

 H 



In place of phenyl hydrazine, its hydrochloride often is used, 

 as this compound is more soluble and more stable than the 

 free base. 



The Molisch Test. If to a solution containing a carbohy- 

 drate a few drops of 15% alcoholic oc naphthol are added, and 

 concentrated sulphuric acid carefully poured down the side of 

 the test tube so that it will form a layer at the bottom of the 

 tube, a violet or reddish ring will form at the juncture of the 

 two liquids. This test will detect not only free carbohydrate, 

 but also carbohydrate in combination with other substances. 

 The reaction is so delicate, however, that it will be given by very 

 small traces of carbohydrate material, even fibers of filter paper 

 (cellulose) so that as a general test it is more valuable in a 

 negative than in a positve result. A negative Molisch reaction 

 is good evidence that carbohydrates are absent, whereas a posi- 

 tive test may be due to the presence of filter paper or other 

 casual impurities. As little as 0.2 mg. filter paper is said to 

 give a strong reaction. 



