NITROGEN AS AMINE OR PROTEIN 215 



also nitrolim which is the trade name of the fertilizer sold 

 in England. 



(a) How Made. — Calcium carbide is first made by fusing 

 in an electric furnace a mixture of coke and lime. The 

 reaction is as follows: 



CaO + 3C = CaC 2 + CO. 



The carbide is removed, cooled, crushed to a fine powder 

 and placed in perforated steel cans set in brick ovens. A 

 carbon rod carrying a current of electricity, and passing 

 through the center of the can serves to heat up the carbide 

 to about 1100° C, when union takes place between the 

 carbide and a stream of pure nitrogen which is gently forced 

 into the can. The reaction is as follows: 



CaC 2 + N 2 = CaCN 2 + C. 



Pure nitrogen is obtained by passing air over red hot 

 copper when the oxygen unites with the copper to form 

 copper oxide and the nitrogen alone issues from the furnace. 

 The best process, however, is to fractionally distill liquid 

 air. Nitrogen boils at — 195.5° C. and oxygen at — 182.5° C. 

 The nitrogen comes off first and can be obtained very pure. 



The nitrogenous product, which is really an impure calcium 

 cyanamide, is next cooled, pulverized, and treated with 

 water in rotating cylinders. About 30 per cent, of water 

 is taken up, the excess of calcium oxide is hydrated, and a 

 little carbide decomposed to acetylene and hydrated calcium 

 oxide. The material is then pressed into bricks and before 

 use is crushed and screened so that a granulated fertilizer 

 is obtained which is made use of almost exclusively in 

 manufacturing complete fertilizers. The cyanamid as it 

 comes on the market contains about 45 per cent, of calcium 

 cyanamide, 15 per cent, nitrogen, 27 per cent, calcium 

 hydroxide, and 13 per cent, free carbon, besides small 

 amounts of other constituents. 



(b) Availability. — The fertilizing compound in cyanamid 

 is calcium cyanamide: Ca=N— C = N. This compound is 

 soluble in water but not available to plants. Before its use 



