COMPOUNDS CONTAINING NITROGEN. 553 



phere. When calcium carbide is heated 'to redness in contact with nitrogen, 

 calcium cyanamide is formed, thus : 



CaC 2 + 2N = CN.NCa + C. 



This substance is an excellent fertilizer, and is manufactured in large quanti- 

 ties and sold under the name of nitrolim or lime-nitrogen (Kalkstickstoff). It 

 is slowly decomposed in the soil by moisture and carbon dioxide into calcium 

 carbonate and cyanamide : 



CN.NCa 4- H 2 -f CO 2 = CaCO 3 + CN.NH 2 . 

 The cyanide is further decomposed probably into urea : 

 CN.NH 2 -f H 2 = CO(NH 2 ) 2 . 



Steam under high pressure converts all of the nitrogen of calcium cyanamide 

 into ammonia, which thus furnishes a method of obtaining ammonia from at- 

 mospheric nitrogen. 



When mixed with sodium carbonate and fused, calcium cyanamide forms 

 sodium cyanide. By the action of acids on the calcium compound, cyanamide, 

 CN.NH 2 , is formed, which easily polymerizes to the beautifully crystallized 

 dicyandiamide, C 2 N 2 .N 2 H 4 , which is now made by the ton and used for various 

 purposes. It can very easily be made to unite with water to form urea, which 

 is manufactured thus in great quantities. 



Barium carbide, when heated in nitrogen, acts differently from calcium car- 

 bide, forming barium cyanide, thus: 



BaC 2 + 2N = Ba(CN) 2 . 



Cyanic acid, HCNO, and Sulphocyanic acid, HCNS, are both 

 colorless acid liquids, the salts of which are known as cyanates and 

 mlpho-cyanates. These salts are obtained from alkali cyanides by 

 treating them with oxidizing agents or by boiling their solutions with 

 sulphur, when either oxygen or sulphur is taken up by the alkali 

 cyanide : 



KCN + O = KCNO = Potassium cyanate. 



KCN -f S = KCNS = Potassium sulphocyanate. 

 The acids themselves are obtained by indirect processes, as they 

 decompose when the salts are treated with mineral acids. Sulpho- 

 cyanates give with ferric salts a deep-red color, which is not affected 

 by hydrochloric acid, but disappears on the addition of mercuric 

 chloride. 



Metallocyanides. Cyanogen not only combines with metals to 

 form true cyanides, which may be looked upon as derivatives of 

 hydrocyanic acid, but cyanogen also enters into combination with 

 certain metals (chiefly iron), forming a number of complex radicals, 

 Which upon combining with hydrogen form acids, or with basic 

 elements form salts. It is a characteristic feature of the compound 

 cyanogen radicals, thus formed, that the analytical characters of the 



