506 SOILS: PROPERTIES AND MANAGEMENT 



oxide by the combustion of atmospheric nitrogen, accord- 

 ing to the simple equation : — 



N2 + 02=2NO 

 NO + - NO2 



A very high power is required for this synthesis, in- 

 volving a temperature of 2500° to SOOO'^ C, and the 

 expense of the operation is determined almost entirely by 

 the cost of the electricity. 



The nitric oxide gas is passed through milk of lime, 

 giving basic calcium nitrate : — 



Ca(0H)2 + 2 HNO3 = Ca(N03)2 + 2 H2O 



The calcium nitrate resulting from this process has a 

 yellowish white color, and is easily soluble in water but 

 deliquesces very rapidly in the air. This last property 

 can be overcome by adding an excess of lime in the manu- 

 facture, thus producing a basic calcium nitrate which 

 contains only 8.9 per cent of nitrogen. Another way of 

 avoiding the difficulties involved by the deliquescent 

 property of the nitrate is practiced by the factory at 

 Nottoden, Norway. This consists in first melting the 

 product, then grinding it fine and packing it in air-tight 

 casks. The fertUizer thus prepared contains from 11 to 

 13 per cent of nitrogen. 



Calcium nitrate contains its nitrogen in a form directly 

 available to plants. It resembles sodium nitrate in its 

 solubility, avaHability, and lack of absorption by the soil. 

 It may be spread on the surface of the ground, as it exerts 

 no poisonous action and does not tend to form a crust, as 

 does sodium nitrate. 



The relative values of the different soluble nitrogen 

 fertilizers vary with a great many conditions and can be 



