COMMERCIAL FERTILIZER MATERIALS 451 



nitrogen supply for agriculture may be appreciated when it 

 is considered that nitrates are being carried off in the drain- 

 age water of all cultivated lands at a surprisingly rapid rate. 

 A Dunkirk silty clay loam at Cornell University, 1 carrying 

 a rotation of maize, oats, wheat, and hay, lost in crop and 

 drainage water in a period of ten years over 77 pounds to the 

 acre of nitrogen annually. This is equivalent to 520 pounds 

 of commercial sodium nitrate or to about 380 pounds of com- 

 mercial ammonium sulfate. 



The exhaustion of the supply of nitrogen in most soils may 

 be accomplished within one or two generations, unless a re- 

 newal of the supply is brought about in some way. Natural 

 processes provide for an annual accretion through the wash- 

 ing-down of ammonia and nitrates by rain-water from the 

 atmosphere, and through the fixation of free atmospheric 

 nitrogen by bacteria. Farm practice of the present day re- 

 quires the application of nitrogen in some form of manure, 

 and, as the end of the commercial supply of combined nitro- 

 gen is easily in sight, there is urgent need of discovering a 

 new source. The world war has given great impetus to the 

 study of the artificial fixation of nitrogen and a number of 

 compounds thus produced are on the market or will appear 

 shortly. 



250. Calcium cyanimid (CaCN 2 +). 2 — The manufacture 

 of this fertilizer begins with calcium carbide (CaC 2 ) which 

 is produced by heating lime and coke together. 



CaO + 3C = CaC 2 + CO 



This impure carbide is then powdered and heated elec- 

 trically in special ovens. At the proper temperature nitro- 

 gen gas is passed through the carbide with the following re- 

 sult: 



CaC 2 + N 2 = CaCN 2 + C 



*For complete data, see par. 163, this text. 

 a Pranke, E. J., Cyanamid; Easton, Pa., 1913. 



