AMIDES 133 



(2) Action of Sodium Hydroxide. Urea is decomposed with evolu- 

 tion of ammonia by boiling its solution with excess of caustic soda : 



CO(NH 2 ) 2 + 2 H 2 = C0 2 + H 2 + 2 NH 3 . 



(3) Action of Nitrous Acid. On adding dilute hydrochloric acid and 

 a few drops of sodium nitrite solution to some urea solution, an 

 effervescence of nitrogen and carbon dioxide takes place : 



CO(NH 2 ) 2 + 2 HN0 2 = CO, + 3 H 2 + 2 N 2 . 



(4) Action of Hypobromite. Urea is decomposed into carbon dioxide 

 and nitrogen on adding sodium hypobromite to its solution : 



CO(NH 2 ) 9 + 3 NaOBr = CO, + N 2 + 3 NaBr + H 2 O 

 C0 2 + aNaOH = Na 2 C0 3 + H 2 O. 



Note. An effervescence also occurs when sodium hypobromite is 

 added to ammonium chloride. 



(5) Biuret. On heating some urea in a test tube it melts ; on 

 continuation of the heating the mass becomes solid, white and opaque : 

 ammonia is evolved and a ring of sublimed cyanuric acid may be 

 formed on the cooler parts of the test tube. The white residue consists 

 mainly of biuret, but contains also cyanuric acid ; on treating the mass 

 with water the biuret dissolves. On pouring off the water and testing 

 it with caustic soda and I or 2 drops of dilute copper sulphate (i per 

 -cent.) a pink colour is formed (biuret reaction). 



The residue dissolves in dilute ammonia ; if barium chloride be added 

 to a portion of this solution a white precipitate of barium cyanurate is 

 formed ; on adding copper sulphate to another portion an amethyst- 

 coloured precipitate of copper cyanurate is formed : 



NH 2 H 2 N NH 



CO CO = CO CO + NH, 



\ / I I 



NH 2 H 2 N NH, NH 2 



Biuret. 



NH 2 H 2 N NH 



/ \ /\ 



CO CO CO CO 



+ 3 NH 3 



NH, NH., NH NH 



NH; NH; \/ 



/ co 



/ Cyanuric 



CO acid - 



(6) By adding dilute mercuric nitrate solution (i per cent.), urea 

 is precipitated from the solution as a white compound having the com- 

 position CO(NH 2 )2 . Hg(NO 3 ) 2 . HgO. 



