t 

 48 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



ferrocyanide of ammonium sulphate, filter, and evaporate at 

 about 60-70 0., at which temperature the ammonium cya- 

 nate is converted into urea. The crystals of potassium sul- 

 phate are removed from time to time and then the solution 

 evaporated to dryness. The urea is obtained from this residue 

 by extraction by absolute alcohol as above described. 



Properties. Urea crystallizes in needles or in long, colorless 

 four-sided, often hollow, anhydrous rhombic prisms, similar 

 to saltpetre. It has a neutral reaction, has a bitter taste, and 

 produces a cooling sensation on the tongue. It melts at 130- 

 132 0., but partly decomposes at about 100 C. At ordinary 

 temperatures it dissolves in equal weights of water and in five 

 parts alcohol. Urea is readily soluble in amyl alcohol. It is 

 insoluble in anhydrous ether, chloroform, and in petroleum 

 ether. Urea combines with salts, such as NaCl, NH 4 C1, and 

 the chlorides of the heavy metals, such as mercury, gold, zinc, 

 copper, etc., producing crystalline combinations. It also com- 

 bines with acids, both inorganic and organic, forming crystal- 

 line salts. 



Uric Acid, 



C 6 H 4 N 4 3 or HN CO 



-NH 



AoL: 



I 



HN C NH 



Preparation. 1. Powdered Peruvian guano is just heated 

 to boiling with 15-20 parts water, in a porcelain dish, and 

 then dissolved by the careful addition of a small amount of 

 concentrated solution of caustic soda or potash, and now 

 boiled until the odor of ammonia has disappeared. Filter and 

 saturate the filtrate with carbon dioxide, when a gelatinous, 

 afterwards granular, precipitate of acid potassium urate is 



