LIME NITROGEN 329 



accretion through the washing down of ammonia and 

 nitrates by rain-water from the atmosphere, and through 

 the fixation of free atmospheric nitrogen by bacteria; 

 but, without the frequent use of leguminous crops, 

 the supply could not be maintained. Farm practice 

 of the present day requires the application of nitrogen 

 in some form of manure, and, as the end of the commer- 

 cial supply of combined nitrogen is easily in sight, there 

 is urgent need of discovering a new source. This has 

 lately been done by combining calcium with atmospheric 

 nitrogen in the forms of calcium cyanamid and cal- 

 cium nitrate. 



The most successful process for the production of 

 cyanamid consists in passing nitrogen into closed retorts 

 containing powdered calcium carbide heated to a tem- 

 perature of 1,100 C, the product being calcium cyana- 

 mid, and free carbon. 



CaC 2 + 2N = CaCN 2 + C. 



The free carbon remains distributed in the cyanamid 

 and gives it a black color. A modification of the process 

 provides for the use of lime and coke instead of calcium 

 carbide, but this has not yet been used on a commercial 

 scale. The nitrogen required for the process is obtained 

 either by passing air over heated copper, or by the frac- 

 tional distillation of liquid air. 



The fertilizer, as placed on the market, is a heavy, 

 black powder with a somewhat disagreeable odor. At 

 present it is not manufactured in America and is not 

 obtainable except in small amounts. Plants for its 

 production are being promoted, which will doubtless/ 



