THE ORGANIC CONSTITUENTS OF THE URINE. 22i) 



and ammonia, respectively. This decomposition is, however, also 

 noted during the process of ammoniacal fermentation. 



On heating the substance in aqueous solution in a sealed tube to 

 a temperature of 100 C. ammonia and carbon dioxide likewise 

 result. 



Nitrous acid when added in excess decomposes urea, with the 

 formation of nitrogen, carbon dioxide, and water, but the acid is at 

 the same time decomposed, as is seen in the equation : 



CO(NH 2 ) 2 -f 2HNO, = C0 2 + 4N + 3H 2 O. 



This reaction is utilized when it is desired to remove nitrous acid 

 from a solution. 



On heating the dry substance in a test-tube to a temperature of 

 about 150-170 C., fumes of ammonia are freely evolved, owing to 

 the decomposition of the urea with the formation of biuret, as shown 

 in the equation : 



X NH 2 

 C0< 

 2CO(NH 2 ) 2 = NH 3 -f )>NH 



\~Aj'-. 



X NH 2 

 Biuret. 



On further heating, more ammonia is given off ; the melted mass 

 finally solidifies, and may be shown to contain both biuret and 

 cyanuric acid. The reaction which takes place may be represented 



as follows : 



(1) 3CO(NH 2 ) 2 == 3CONH + 3NH 3 

 Cyanic acid. 



(2) 3CONH == C 3 N 3 (OH) 3 

 Cyanuric acid. 



To demonstrate the presence of the biuret, the residue is dis- 

 solved in a dilute solution of sodium hydrate, when upon the care- 

 ful addition of a dilute solution of copper sulphate a beautiful, 

 purple-red color develops (see also page 34). 



A very delicate test also is the following : 2 c.c. of a concentrated 

 solution of furfurol are treated with 4-6 drops of strong hydro- 

 chloric acid. If to this mixture, which should not present a red 

 color, a small crystal of urea is then added, a deep violet develops 

 in the course of a few minutes. 



Synthetic Formation. As has been mentioned, urea was the first 

 organic substance formed in the animal body which was made syn- 

 thetically in the chemical laboratory. Wohler in 1828 produced the 

 substance artificially by heating ammonium cyanate to a temperature 

 of 1 00 C., when a rearrangement of atoms occurs and urea results : 



NH 2 



(NH 4 )CNO == C0( 



X NH 2 



Other methods now exist by which urea can also be made svn- 



