CH. XII.] UREA. 287 



On heating dry urea to 140 C., ammonia is evolved 

 and biuret formed. 



NH a 



NH 9 



\ CO 



NH 3 



NH + NH, 

 NH, I 



/ CO 



CO \ 



NH 2 

 NH, 



On heating beyond 140 C., cyanuric acid and ammonia 

 are formed. Cyanuric acid is QH-jNgOg. 



N 

 HO C C OH 



I II 

 N N 



V 



C OH 



Solutions of urea are decomposed by boiling alkalies 

 into CO 2 and NH 3 . They are also similarly decomposed 

 by heating for several hours at 150 C. with acids. This 

 decomposition is readily effected by the addition of 

 magnesium chloride, zinc sulphate or potassium acetate 

 to the solution for the purpose of raising the boiling 

 point. 



Bacteria, as micrococcus ureae, decompose urea into 

 CO 2 and NH 3 . This accounts for normal urine rapidly 

 becoming ammoniacal on standing in the air. 



Urea is decomposed by the enzyme urease into am- 

 monium carbonate. The enzyme is found in the Soya bean 

 and in other plants. It does not act on any other com- 

 pound, not even on the substituted ureas. It is therefore 

 used both for the detection (Ex. 343) and also for the 

 estimation (Ex. 401) of urea. 



