MANUFACTURE OF CARBIDE OF CALCIUM. 141 



of carbide. They tliereupon passed nitrogen across barium carbide 

 and alkalies, and obtained bariimi cyaniinide according to the equa- 

 tion — 



BaC2 + N2 = Ba(CN)2. 

 As barium carbide is expensive, they substituted calcium carbide, and 

 found that at a temperature of 1000 degrees C. it would fix nitrogen 

 direct without any alkalies being present. The reaction is given by the 

 equation — ■ 



CaC2 + N2 = C + CaCN2. 

 And it will be noticed that free carbon is given off. 



Theoretically, the content of nitrogen in the calcium cyanimide 

 should be 30 per cent., but on accoimt of impurities in the carbide, 

 and the changes which it undergoes during transformation, the actual 

 content is about 20 per cent. 



When united with water under high pressure all the nitrogen 

 changes into ammonia, thus — 



CaCNa + SHgO - CaCOg + 2NH3. 

 This suggested the thought that cyanimide would make an excellent 

 manure, and such has really been the case. When the cyanimide is 

 mixed in the soil the above reaction takes place slowly, and the 

 nitrogen is taken up by the plants. 



The question is whether cyanimide can compete in price with Chili 

 nitrate, sulphate of ammonia, and other manures. Professor P. A. 

 Guye has investigated the matter, and the following is his estimate : — 



Professor P. A . Guile's Estimate of Cost of Ton of Calcium Cyanimide 

 that contains 20 yer cent. Nitrogen. 



1 ton carbide, containing 80 per cent. CaC2 



200 kilos nitrogen ... 



Manufacture, pulverisation of carbide, 

 charge and discharge of retorts, heat- 

 ing retoi-ts 20 ... 20 



Necessary repairs of mills, retorts, liquef}- 

 ing machines ... 



General expenses ... ... " 



Packing ... ... 



Transport 



Depreciation and interest on capital in- 

 vested 



Cost price per ton ... 

 Price of 1 kilo of nitrogen 



The price will partly be governed by the market price of Chili 

 nitrate. Until artificial fertilisers came on to the market and began 

 to threaten the position which natural nitrate had so long held, there 

 Avas a tendency for the latter to increase in price. Farmers have to 



