URINE AND ITS NORMAL CONSTITUENTS. 376 



Urea forms with acids definite salts and with certain oxides 

 and salts definite compounds. 



Urea is formed artificially by numerous decompositions, as, 

 for instance : 



a. By a process similar to the one taking place in the animal 

 system, viz., by limited oxidation of alburfninous substances by 

 potassium permanganate. 



b. By oxidation of uric acid in the presence of water : 



C 5 H 4 N 4 O S + H 2 + O = = CO(NH 2 ) 2 -f C 4 H 2 N 2 O 4 . 



Uric acid. Urea. Altoxan. 



c. By the action of caustic alkalies upon kreatin : . 



C 4 H,N 5 0, -f H 2 = CO(NH 2 ) 2 + C 3 H 7 NO 2 



Kreatin. Urea. Sarcosine. 



d. By the molecular transformation of ammonium cyanate, 

 which takes place when its solution is evaporated and allowed 

 to crystallize : 



NH 4 .CNO = CO(NH 2 ) 2 . 



Ammonium Urea, 



cyanate. 



e. By the action of ammonia on carbonyl chloride : 



COC1 2 + 2NH 3 = 2HC1 + CO(NH 2 ) 2 . 



Carbonyl Ammonia Hydrochloric Urea, 



chloride. . acid. 



/. By the action of ammonia on ethyl carbonate : 



(C 2 H 5 ) 2 C0 3 + 2NH 3 = : 2(C 2 H 5 HO) + CO(NH 2 ) 2 . 



Ethyl Ammonia. Ethyl alcohol. Urea, 



carbonate. 



Urea may be obtained from urine by evaporating it to the 

 consistency of a syrup and mixing the cooled residue with an 

 equal volume of nitric acid, when crystals of urea nitrate, 

 CO(NH 2 ) 2 .HN0 3 , form. These crystals are washed with a little 

 cold water, dissolved in hot water, and the solution decomposed 

 by potassium carbonate, in which case potassium nitrate, free 

 urea, carbon dioxide, and water are formed. Upon evaporating 

 the solution crystals of potassium nitrate form, which are sepa- 

 rated from the mother liquor, which is evaporated to dryness 

 and exhausted by alcohol, which dissolves the urea; the some- 



