VII. SPECIAL MANUEES 139 



with an alkaline reaction and the unpleasant odour characteristic of 

 commercial calcium carbide. It contains much impurity, indeed 

 usually only from 48 to 58 per cent of real calcium cyanamide, the 

 remainder consisting of lime (16 to 30 per cent), carbon (12 to 16 per 

 cent), oxide of iron (2 to 4 per cent), and sand (4 to 7 per cent). The 

 " nitrolime " form contains 5 or 6 per cent of calcium chloride. 



Its nitrogen content is usually about 20 per cent ; pure calcium 

 cyanamide would contain 35 per cent. 



When exposed to the air, it absorbs moisture and carbon dioxide, 

 but does not become damp. 



The constitution of the real calcium cyanamide is shown by the 

 formula 



Ca 



which is to be regarded as derived from cyanamide H 2 N-CN by the 

 replacement of the two atoms of hydrogen by calcium. 



By exposure to air, the calcium is slowly converted into hydroxide 

 and carbonate, and cyanamide is liberated : 



Ca : N.CN + 2H O = CaBL0 2 + H 2 : N.CN 

 and Ca : N.CN + H 2 6 + CO 2 = CaCO 3 + H 2 : N.CN 



The cyanamide then polymerises, yielding dicyano-diamide. 

 2H 2 : N.CN = NH : C (NH 2 ) NH.CN 



This substance, cyano-guanidine according to Bamberger, 1 has a 

 toxic action on plants. When calcium cyanamide is applied to soils, 

 however, it undergoes nitrification and produces much the same effect 

 as an equivalent amount of nitrogen applied as sulphate of ammonia. 

 At first, however, nitrification is inhibited, especially if the dressing be 

 a large one. Probably another portion of the cyanamide may split up, 

 yielding ammonia and dicyanamide 



2H 2 : N.CN = NH 3 + H.N : (CN) 2 



According to Kappen ' 2 the micro-organisms of soil are capable of 

 readily bringing about the decomposition of cyanamide or of calcium 

 cyanamide, but affect dicyanamide or dicyano-diamide very little, 

 if at all. 



Field experiments show that, as a nitrogenous manure, calcium 

 cyanamide is nearly equal to sulphate of ammonia and that the fears 

 expressed that if applied at the same time as the seed, it was injurious 

 to germination (deduced from pot experiments) are not justified on the 

 large scale provided excessive quantities of the manure are not used. 3 



The cost of production of calcium cyanamide is mainly determined 

 by that of calcium carbide, which, in turn, depends chiefly upon that 

 of electricity. Only where large sources of power are obtainable at a 

 cheap rate (i.e., water-falls), can the process be carried out economically 



ifier., 1893, 26, 1583; Jour. Chem. Soc., 1893, Abstracts, i, 494. 

 '*Bied. Zentr., 1908, 37,204; Jour. Chem. Soc., 1908, Abstracts, ii, 414. 

 3 Hendrick, Trans. High and Agric. Soc. Scotland, 1909, 133, and Mnntz and 

 Nottin, Compt. Eend., 1908, 147, 902; Jour. Chem. Soc., 1908, Abstracts, ii, 88. 



