208 NITROGENOUS FERTILIZERS 



ments have shown that sodium nitrate in this way takes 

 the place of a potash fertilizer, in addition to supplying 

 nitrogen to the crop. Another effect of sodium nitrate in 

 the soil is to puddle heavy soils, if used continuously. This 

 is because plants absorb more of the nitrate radicle than 

 thev do of the sodium. The latter unites with carbon 



t/ 



dioxide in the soil forming sodium carbonate which de- 

 flocculates clay particles, giving the soil a very poor physical 

 texture. This fact of its leaving a residue of sodium 

 carbonate in the soil, however, makes sodium nitrate a 

 valuable fertilizer on acid soils, and thus saves the calcium 

 carbonate by supplying an additional base. 



158. Calcium Nitrate. — Some years ago when it was 

 thought that the Chilean nitrate beds were in serious danger 

 of rapid exhaustion, attention was directed to methods of 

 combining the nitrogen of the air with other elements, and 

 so to ward off inevitable destruction when no more nitrate 

 was to be procured ! Although such a danger was very much 

 overrated it served the purpose of stimulating invention and 

 producing competitors for the sodium nitrate industry, a 

 fact which will tend to keep down the price of this fertilizer, 

 now altogether too high. 



(a) How Made. — It has been known for over a century 

 that nitrogen and oxygen would unite if heated to a suffi- 

 ciently high temperature, as by an electric spark. This fact is 

 made use of commercially in Norway where a number of com- 

 pounds of nitrogen are being manufactured, principally cal- 

 cium nitrate and basic calcium nitrate. The union of nitrogen 

 with oxygen is accomplished in a circular furnace in which 

 the combustion chamber is an inch or so wide and about nine 

 feet in diameter (Figs. 47 and 48). Radially in this chamber 

 are placed U-shaped, water-cooled, copper electrodes. An 

 alternating current produces an arc between the electrodes. 

 A powerful electro-magnet placed at right angles to the 

 electrodes has the effect of spreading the arc back along the 

 electrodes, producing a flaming disk through which air is 

 gently forced. Here at a temperature of 3000° C. some of 

 the nitrogen of the air unites with oxygen to form nitric 

 oxide, NO, which after cooling unites with more oxygen 



