294 EGYPTIAN AGRICULTURE. 



is concentrated until it soli lifias. The mass thus obtained 

 contains some 13'^ nurogen equal to la% nitrate of 

 calcium Ca(-X0s)j. It is highly de.iquescent which 

 necessitates the use of air-tight drums in its transport. 

 For agricultural purposes it is usually converted into a 

 basic nitrate by the introduction of excess of lime, as in 

 rhis form it is less difficult to deal with. 



As a manure it is of equal value to nitrate of soda, 

 equal amounts of nitrogen being considered. 



LIME NITROGEN OR NITROGEN LIME. 



This is a fine dark dusty powder, rather like basic slag 

 in appearance but smelling of acetylene, especially when 

 moistened. It contains approximately 55 to 60 % of the 

 compound CaCN 2 , calcium cyanamide, equal to some 20^ 

 nitrogen, and is therefore a manure of about the same 

 nitrogen content as sulphate of ammonia. 



In its preparation calcium carbide Ca C 2 is first 

 formed by heating together chalk and coke in an electric 

 furnace. The carbide is then coarsely powdered and heated 

 ia a kind of gas retort and nitrogen is passed over it. 

 Combination takes place with the formation of calcium 

 cyanamide. The nitrogen is obtained from air, the oxygen 

 being removed by passing the air over red-hot copper. 

 The copper oxide formed is reduced to the metallic state 

 again by heating in coal-gas. 



In contact with water, calcium cyanamide decomposes 

 slowly at ordinary temperatures giving rise to calcium 

 carbonate and ammonia and this change is what takes 

 place in the soil, aided probably by some bacterial action. 



