242 DERIVATIVES OF URIC ACID. 



alloxantine with a boiled solution (freed of air) of sal- 

 ammoniac ; it is then deposited in the form of fine 

 white crystals. Colorless, white needles, which become 

 red in the air ; insoluble in cold water, somewhat solu- 

 ble in boiling. Nitric acid converts it into alloxan. 

 It dissolves without change in ammonia ; if this solu- 

 tion is boiled, however, it is converted into murexide. 

 If boiled with water, and mercury oxide be gradually 

 added, it is converted into murexide, metallic mecury 

 being thrown down. 



Thionuric acid, C 4 H 5 N 3 S0 6 . If a solution of alloxan 

 be saturated at the ordinary temperature with sulphuric 

 acid and afterwards with ammonia and then heated to 

 boiling, it deposits, on cooling, a difficultly soluble salt, 

 crystallizing in thin scales of a mother-of-pearl lustre, 

 ammonium thionurate, C 4 H 3 E" 3 S0 6 (OTI 4 ) 2 + H 2 0. The 

 same salt is produced by warming violuric acid with 

 ammonium sulphite. The free acid separated from 

 this salt is a white, crystalline, easily soluble, acid 

 mass. The ammonium salt precipitates metallic silver 

 from dissolved silver salts. By boiling its aqueous 

 solution, it is decomposed, forming uramile and sul- 

 phuric acid. 



Purpuric acid, C 8 H 5 TO 6 . Unknown in the free 

 state. 



Acid ammonium purpurate (Murexide), C 8 H 4 N 5 

 6 .NH 4 -f H 2 0, is produced, when ammonia gas is con- 

 ducted for a long time over dried alloxantine at 100 ; 

 or when a solution of alloxantine and alloxan is mixed 

 with ammonia and diluted with half a volume of hot 

 water. The formation of murexide is the cause of the 

 reaction of uric acid mentioned above (p. 233). -Pre- 

 pared most practically by heating slowly to boiling 4 

 parts uramile and 3 parts mercury oxide with water. 

 The boiling hot, filtered solution yields crystals of 

 murexide. Crystallizes in four-sided columns or plates 

 of an exceedingly beautiful green color of a metallic 

 lustre, greatly resembling the color of the wings of the 



