l8 CYANAMID — MANUFACTURE^ CHE:MISTRY AND USES 



tion to a syrup and allowing to crystallize. It forms trimetric 

 plates or thin leaves, melting at 205° C. It is decomposed by 

 heating, with evolution of ammonia and formation of mela- 

 mine, melam, and other derivatives. Dicyandiamide is some- 

 what easily soluble in water and alcohol, but almost insoluble 

 in ether. It combines with ammonium chloride at 150°, giving 

 diguanide hydrochloride, C2H7N5HCI; with HCl at 150° gives 

 guanidine hydrochloride, CH5N3HCI; on boiling with baryta 

 it gives amidodicyanic acid and ammonia; with zinc and HCl 

 yields methylamine and ammonia; with H^S it gives guanyl- 

 thiourea; on heating with urea or cyanuric acid it forms 

 ammelin, C3H5N5O, and ammonia. 



Treated with weak or strong acids, or with strong 

 alkalies, dicyandiamide goes over to dicyandiamidine, 



NH : C^ , caustic crystals, easily soluble in 



^NH.CO.NH, 



water and alcohol. 



Dicyandiamide, treated with silver nitrate solution, forms 

 additional compounds containing, according to the conditions, 

 one, two and three molecules respectively, of dicyandiamide 

 per molecule of silver nitrate. Cold caustic potash added to 

 a dicyandiamide solution containing sufficient silver nitrate 

 causes a white to brown mixture of precipitates of silver 

 dicyandiamide and silver oxide. Silver dicyandiamide is 

 slightly soluble in water, easily soluble in ammonia, soluble in 

 hot nitric acid; on prolonged boiling with caustic potash is 

 converted into silver cyanamide, CN.NAgg, and cyanamide, 

 which polymerizes again to dicyandiamide. 



If silver nitrate, then nitric acid, is added to a solution of 

 dicyandiamide, a white precipitate is formed, insoluble in 

 cold, soluble in hot nitric acid or in excess of ammonia. (Iden- 

 tification in mixtures of cyanamide and dicyandiamide. Cyan- 

 amide, it will be remembered, gives a yellow precipitate with 

 dilute silver nitrate, soluble in nitric acid, but insoluble in 

 ammonia.) 



