366 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



The solution is then pumped into solidification pans, under which 

 cold air is circulated to accelerate cooling, and the nitrate of lime 

 stiffens into a brittle, crystalline mass. This is broken up into lumps, 

 which pass to ball crushing mills, where it is reduced to a granular 

 state. The coarse powder is then raised by an elevator into a hopper, 

 from the bottom of which it falls into barrels which hold 2 hundred- 

 weight. These barrels are lined with paper to guard against damp. 

 The analysis of the commercial calcium nitrate, Norwegian saltpeter, 

 or nitrate of lime as it is variously called, is given in Table V. 



Table V. 



With the Birkeland-Eyde process, 1 kilowatt-year gives 500 to 

 550 kilogi-ams of nitric acid, or 853 to 938 kilograms of nitrate of 

 lime. The latter usually contains 13 per cent of nitrogen, which cor- 

 responds to 111 to 122 kilograms of combined nitrogen. It is 

 guaranteed to contain 12f per cent of nitrogen. 



The best result at Notodden has been 900 kilograms of nitric acid 

 per kilowatt-year measured at the arc terminals and allowing for 

 100 per cent nitric acid. 



The percentages of nitrogen and comparative prices of the various 

 artificial manures are about as given in Table VI. 



Table VI. 



Sulphate of ammonia from gasworks. . . 



Nitrate of soda from Chile 



Nitrate of lime made by electricity 



Calcium cyanamide made by electricity 



Content 



of 

 nitrogen. 



Per cent. 

 19.75 

 15.50 

 12.75 

 18.00 



Price 

 per 



ton. 



10 



s. d. 





 15 

 10 







THEORY OF FIXATION. 



The problem is to raise the temperature as quicldy as possible to 

 over the igniting point of nitrogen and oxygen and then immediately 

 to cool the fixed gas and draw it off. The temperature of the burn- 

 ing nitrogen and oxygen flame is lower than the igniting point by. 

 about 200° C. There must be a " hot-cold zone " — that is to say, a 

 zone in which at one part the temperature is enormously high, and 

 at another part the temperature is as low as possible. 



