22 PHYSIOLOGICAL CHEMISTRY 



Phenylhydrazine Reaction (3) in the absence of a positive Resorcinol- 

 Hydrochloric Acid Reaction (see page 35), 



1. Solubility. Test the solubility of glucose hi the "ordinary solvents" and 

 in alcohol. (In the solubility test throughout the book we shall designate the 

 following solvents as the "ordinary solvents"; H 2 O; 10 per cent NaCl; 0.5 per 

 cent Na 2 CO 3 ; 0.2 per cent HC1; concentrated KOH; concentrated HC1.) 



2. a-Naphthol Reaction (Molisch). Place approximately 5 c.c. of concen- 

 trated H 2 SC>4 in a test-tube. Incline the tube and slowly pour down the inner 

 side of it approximately 5 c.c. of the sugar solution to which 2 drops of Mo- 

 lisch's reagent (a 15 per cent alcoholic solution 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 furfural, 1 



HC CH 



II II 

 HC C-CHO, 



\/ 



o 



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

 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 (enough to fill the 

 rounded portion of a small test-tube) furnished by the instructor, 2 add 5 c.c. 

 of the sugar solution, shake well and heat on a boiling water-bath for one-half to 

 three-quarters of an hour. Allow the tube to cool slowly (not under the tap) 

 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 connection that, of the 

 simple sugars of interest in physiological chemistry, glucose and fructose 

 yield the same osazone. Each osazone has a definite melting-point 

 and as a further and more accurate means of identification it may be 



According to v. Ekenstein and Blanksma (Ber. d. d. chem. GesdL, 43, 2358, 1910), 

 oxymethylfurfural is formed. 



2 This mixture is prepared by combining 2 parts of phenylhydrazine hydrochloride and 

 3 parts of sodium acetate by weight. These are thoroughly mixed in a mortar. 



