URIC ACID, ALLANTOIN. 1003 



on a filter, and is obtained perfectly white. From the brown 

 liquid filtered from the urate of potash, an additional quantity 

 of uric acid may be obtained by supersaturation with hydro- 

 chloric acid, but the product has a brownish colour. 



Uric acid crystallizes in thin scales of a silky lustre and 

 brilliant whiteness, is inodorous and insipid, loses nothing at 

 2J2. This acid is nearly insoluble in cold water, requiring, 

 according to Prout 10,000 parts of water at 60 for solution, 

 and but slightly soluble in hot water ; its solution has a feeble 

 reddening effect upon litmus. It is insoluble in alcohol and 

 ether. It dissolves in concentrated sulphuric acid, and is again 

 thrown down on dilution with water. It is also more soluble 

 in concentrated hydrochloric acid than in water. In nitric acid, 

 uric acid dissolves with lively effervescence, the gases disengaged 

 being carbonic acid and nitrogen in equal volumes. The solu- 

 tion contains alloxan, alloxantin, urea, parabanic acid and 

 ammonia. The concentrated liquor becomes of a purple red 

 (from murexide), when an excess of ammonia is added, affording 

 a character by which uric acid may be recognised. (Liebig). 



Urates. Metallic oxides appear to combine with uric acid 

 without displacing the basic water of the acid which remains 

 in the salt. The urates of the alkalies and alkaline earths are 

 sparingly soluble in cold, but more freely soluble in boiling 

 water. Urate of ammonia dissolves, according to Dr. Prout, 

 in 480 parts of water at 60. Urate of potash forms crystalline 

 scales soluble in about 500 parts of cold water, but is much 

 more soluble in boiling water, especially if there be an excess of 

 alkali present. All the urates are decomposed by acetic acid. 

 Urate of soda forms the principal constituent of gouty con- 

 cretions. 



ALLANTOIN. 



Formula: C 4 H 3 N 2 O 3 , or Cy 2 -f3HO (Liebig and Woehler). 

 This is a crystalline substance found in the allantoic fluid of 

 the cow, and produced artificially by boiling uric acid with the 

 puce-coloured oxide (peroxide) of lead. It is deposited from 

 the allantoic fluid of the cow when concentrated by a gentle 

 heat to one-fourth of its bulk, upon cooling, in crystals, which 

 are treated with animal charcoal and obtained perfectly pure. 



