2 9 o PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Uric acid is a weak acid and forms two series of salts, neutral and 

 acid salts. The formation of salts can be explained either by the 

 tautomeric formula in which hydroxyl groups attached to the carbon 



N=c . OH 

 HO . C C NH 



^ C.OH 



-C-/ 



atoms are present, evidence of which is shown by the action of phos- 

 phorus trichloride upon uric acid, which gives trichloropurine, or by 

 assuming that the acid character of the CO groups influences the pro- 

 perties of the hydrogen atoms attached to the N atoms so that they 

 are acidic in character and replaceable by metals. 



The neutral salts, such as C 5 H 2 Na 2 N 4 O 3 , are comparatively easily 

 soluble in water and are obtained on dissolving uric acid in alkali 

 hydroxides or in hot solutions of the carbonates. Lithium urate is 

 the most soluble salt of uric acid. 



Uric acid is insoluble in cold solutions of the carbonates and may 

 thus be separated from other acids such as benzoic acid. 



The acid salts, such as C 5 H 3 NaN 4 O 8 , are soluble with difficulty in 

 water. They are obtained on passing carbon dioxide into a solution 

 of the neutral salt. 



One part of acid sodium urate is soluble in 1 100-1200 parts of cold 

 water and 125 parts of hot water; I part of acid potassium urate is 



FIG. 49. Sodium urate. 

 (After Funke.) 



FIG. 50. Ammonium urate. 

 (After Funke.) 



soluble in 800 parts of cold water and in 70 parts of hot water ; 

 I part of acid ammonium urate is soluble in 1600 parts of cold water, 

 more easily in hot water and is insoluble in ammonium chloride solution. 



