CYANAMID MANUFACTURE, CHEMISTRY AND USES 75 



of experimental data that have been reported the results that 

 are consistent with all the known facts, and then to reconcile 

 the apparent disagreements with the consistent facts. 



Formation. — The researches of Ulpiani^ show without doubt 

 that acids do not determine the formation of dicyandiamide 

 from calcium cyanamide. Acids acting on calcium cyana- 

 mide produce calcium salts and free cyanamide. By the 

 further action of the acids, from the weakest to the strongest, 

 there is formed first urea, and secondly, especially in the case 

 of weak acids, ammonium salts. (See also p. 12). F. 

 Lohnis and R. MolP found that even humic acid, in excess, 

 acting upon lime-nitrogen for 8 days at 40° C. produced not 

 the slightest trace of dicyandiamide. There is no evidence of 

 any kind to show that acids ever produce dicyandiamide from 

 cyanamide. Neither do strong alkalies produce dicyandiamide, 

 but always produce urea and free ammonia. Weak alkalies, 

 however, and especially calcium hydroxide, readily effect the 

 polymerization, although in this case also there is formed con- 

 siderable urea. The formation of dicyandiamide in lime- 

 nitrogen is brought about by the combined action of moisture, 

 which causes the hydrolysis of calcium cyanamide to cyan- 

 amide, and lime which determines its polymerization to dicyan- 

 diamide. These reactions take place at ordinary temperatures 

 very slowly, as shown below, but proceed very rapidly above 

 70° C. At about 100° C. other reactions begin with formation 

 of ammonia and small amounts of other derivatives. Water 

 and heat alone do not cause the polymerization to dicyandi- 

 amide; Ulpiani boiled a pure solution of cyanamide 50 hours 

 without any change.^ 



Decomposition. — In a solution of lime-nitrogen, dicyan- 

 diamide forms and decomposes simultaneously. This is seen 



• 

 ^ Gaz. Chim. Ital., 1908, II, No. 4, 358.417. 



» Centl. Bakt. XXII, 276. 



^ Rend. Soc. China, di Roma. p. 4 1906. 



