CYANAMID — MANUFACTURE, CHEMISTRY AND USES 5 



CaO + 3C --- CaC, + CO. 

 The carbide is removed from the furnace at regular inter- 

 vals, is cooled, crushed to a fine powder, and packed in the 

 nitrifying ovens. These are cylindrical, perforated steel cans, 

 set in heat-insulated brick ovens. A carbon pencil through 

 the axis of the can is used to heat the carbide to the combining 

 temperature. On admission of the nitrogen to the cans the 

 following reaction takes place : 



CaC, + N, ^ CaCN, + C. 



This reaction is accompanied by an evolution of heat which 

 is just about sufficient to maintain the mass at the combining 

 temperature. The commercial calcium carbide used contains 

 about 20 per cent, of impurities, which so influence its physical 

 and chemical properties that the absorption of nitrogen takes 

 place very readily at atmospheric pressure at a temperature of 

 about 1,100° C. The addition of catalytic agents, principally 

 haloids, suggested by various investigators, is not necessary for 

 the fixation of nitrogen, since the manufacturer can easily 

 regulate the reactions by suitable disintegration of materials 

 and by other mechanical means. 



Nitrogen is obtained either by fractional distillation of 

 liquid air, or by means of the copper oxide process. In the 

 latter, air is passed through a red-hot mass of finely divided 

 copper, suspended in asbestos or other inert material. The 

 copper combines with the oxygen and allows the nitrogen to 

 pass through. The copper oxide is easily recovered for use 

 by reduction in situ with a suitable gas, such as natural gas. 



The nitrogen used must be pure and dry, otherwise, at high 

 temperatures, there is destruction of the carbon pencils, and 

 of calcium carbide, according to the following reactions : 



C + O --> CO, 

 C + CO., — 2CO, 

 •c-f H,0— CO+ H„ 

 H,0 + CaC, —- CaO + C,H„ 

 3O -I- CaC, — CaO + 2CO. 



