SITE ATE OF UEEA. 



11 



perature of boiling water, or when in contact with decaying 

 animal matter, urea readily decomposes. In the latter case 

 it is converted into carbonic acid and ammonia. When 

 heated with the caustic alkalies, urea is decomposed and 

 gives off strong fumes of ammonia. 



Urea is also decomposed by nitrous acid, or by nitric acid 

 containing nitrous acid in solution, by nitrate of the sub- 

 oxide of mercury, and by a solution of hypochlorite of soda. 



Urea is one of the products of the decomposition of uric 

 acid when the latter is heated with peroxide of lead. 



Urea forms several salts, two of which are of great im- 

 portance, as they enable the chemist to separate and deter- 

 mine the amount of urea present in the urine. 



Nitrate of urea (C 2 H 4 N 2 2 , HO, N0 5 ), may be ob- 

 tained in considerable quantities by concentrating urine and 

 then adding an excess of nitric acid. The salt separates in 

 beautiful masses, composed of separate plates. When nitrate 

 of urea is allowed to crystallize under the microscope, the 





Fig. 156. (BEALE.) Crystals of Nitrate of Urea, a, Crystals obtained 

 from urine ; b, Crystals of pure nitrate of urea. X 215. 



crystals are seen to be beautiful rhombic prisms. The rhom 

 bic plates are often combined. (Fig, 156.) 



