6 CYANAMID — MANUFACTURE, CHE:MISTRY AND USES 



Carbon dioxide also destroys the calcium cyanamide with 

 formation of calcium oxide, carbon monoxide and free nitro- 

 gen. 



The reaction by which calcium cyanamide is formed is 

 reversible : 



CaC, + N, = CaCN, + C. 



The temperature of reversal at atmospheric pressure varies 

 greatly with the composition of the carbide used. Thus the 

 temperature of reversal lies at about 1,360° C.,^ for a crude 

 calcium cyanamide containing 21.1 per cent, combined nitro- 

 gen, and made from a commercial carbide of the following 

 composition : 



Per cent. 



CaCj 82.30 



C 1.20 



CaO 14.72 



CaSi 0.06 



CagPj 0.07 



CaS 0.13 



Ferrosilicon - o, 72 



Not determined 0.80 



An increase of the free lime in the carbide greatly lowers 

 the critical temperature. Thus with a carbide containing 75 

 per cent. CaQ the equilibrium point lies at about 1150° C.^ 



The effect of nitrogen pressure on the equilibrium point has 

 been investigated by M. Thompson, who found that the tem- 

 perature at equilibrium varies directly as the pressure.^ Since 

 calcium cyanamide is decidedly volatile at the equilibrium tem- 

 perature, even as low as 1,050° C, and distils to the colder 

 parts of the apparatus the determination of the equilibrium 

 conditions is open to some errors, but these may not be large 

 enough to vitiate the general conclusions that have been drawn. 



It is owing to the reversibility of the reaction that nitrogen 



^ Caro, Cheni. Trade Jour., 1909, p. 622. 



2 LeBlanc & Eschmann, Zeit. fiir Elek., 1911, 17, 20-34. 



^ Thompson & Lombard, Met. and Chem., Eng., 1910, 617, 682. 



