24 PHYSIOLOGICAL CHEMISTRY. 



of a-naphthol) has been added, so that the sugar solution will not 

 mix with the acid. A reddish-violet zone is produced at the point 

 of contact. The reaction is due to the formation of furfurol, 



HC-CH 



HC C-CHO, 



\/ 

 



by the acid. The test is given by all bodies containing a carbohy- 

 drate group and is therefore not specific and, in consequence, of 

 very little practical importance. 



3. Phenylhydrazine Reaction. Test according to one of the 

 following methods: (a) To a small amount of phenylhydrazine 

 mixture, furnished by the instructor, 1 add 5 c.c. of the sugar solu- 

 tion, shake well and heat on a boiling water-bath for one-half to 

 three-quarters of an hour. Allow the tube to cool slowly and 

 examine the crystals microscopically (Plate III, opposite). If the 

 solution has become too concentrated in the boiling process it will 

 be light-red in color and no crystals will separate until it is diluted 

 with water. 



Yellow crystalline bodies called osazones are formed from certain 

 sugars under these conditions, in general each individual sugar 

 giving rise to an osazone of a definite crystalline form which is 

 typical for that sugar. It is important to remember in this connec- 

 tion that of the simple sugars of interest in physiological chemistry, 

 dextrose and laevulose yield the same osazone. Each osazone has a 

 definite melting-point and as a further and more accurate means of 

 identification it may be recrystallized and identified by the determi- 

 nation of its melting-point and nitrogen content. The reaction tak- 

 ing place in the formation of phenyldextr osazone is as follows : 



C,H 12 0. + 2(H 2 N-NH-C 6 H 5 ) = 



Dextrose. Phenylhydrazine. 



C 6 H 10 4 (N-NH-C 6 H 5 ) 2 + 2H 2 + H 2 . 



Phenyldextrosazone. 



(b) Place 5 c.c. of the sugar solution in a test-tube, add i c.c. of 



lr rhis mixture is prepared by combining one part of phenylhydrazine hydro- 

 chloride and two parts of sodium acetate, by weight. These are thoroughly 

 mixed in a mortar. 



