106 CHEMICAL FERTILIZERS 



About 2 % of either of these materials gives a good result. 

 The nitrogen is generally delivered under pressure into the 

 furnaces, which are heated to about 800 C. (1470 F.) 

 by the passage of an electric current through a thin 

 carbon pencil. The absorption of nitrogen is allowed 

 to proceed for 30 or 40 hours, and saturation becomes 

 apparent by a controlling gas meter. During the process 

 the carbide is converted into a hard mass, not unlike coke. 

 It is removed from the furnaces, ground either to a coarse 

 grit or to a fine powder, and is then sold under the name of 

 nitrolim. This substance usually contains from 50 to 60 % 

 of true calcium cyanamide, with 20 % of lime, 28 % of 

 silica and 14 % of carbon in the form of graphite. As 

 calcium cyanamide picks up moisture from the air, its 

 nitrogen content slowly decreases, so that by the time it 

 arrives in the hands of the consumer the nitrogen varies 

 from 18 to 20 %. 



Calcium cyanamide generally contains traces of dicyana- 

 mide or dicyanodiamide. Cyanamide has either of the 

 tautomeric forms N : C . NH 2 or HN : C : NH, the hydrogen 

 being replaced by calcium. Cyanamide polymerizes to 

 either 



H 2 NC CNH 2 or HN= 



according to which form of cyanamide is concerned. The 

 balance of evidence seems slightly in favour of the second 

 formula. Cyanamide readily forms ammonia and nitric 

 acid, dicyanodiamide forms ammonia, but poisons the 

 nitrifying organisms, so that no nitrate is formed in the soil. 

 Very little harm is observed in practice from traces of dicyano- 

 diamide, but large percentages of the latter might be harmful. 

 Morrell, Burgen and Werner have shown that polymeri- 

 zation to dicyanodiamide is caused by small amounts of 

 acids and alkalies, of which alkalies are the more potent. 

 The process does not seem to be reversible. After application 

 to the soil, cyanamide which contains dicyanodiamide does 

 not produce its full amount of nitrate, but Rothamsted 



