270 SOILS AND MANUEES 



presence of the sodium apparently does no harm. Quite 

 recently, however, a method has been devised by which 

 it can be prepared directly from the air on a commercial 

 scale. It is obtained by the Birkland and Eyde pro- 

 cess, in which the nitrogen of the air is oxidised to nitric 

 oxide by means of an electric arc furnace, i.e., in much 

 the same way as nitric acid is formed naturally in the air. 

 The nitric oxide is easily oxidised 'to nitrous and nitric 

 acids, and the products are absorbed by powdered slaked 

 lime, forming nitrate of lime. The commercial product 

 contains about 13 per cent, of nitrogen which is equal to 

 76'5 per cent, of calcium nitrate. About a fourth of the 

 total lime remains unchanged. As a manure, it does not 

 tend to decalcify the soil; on the contrary it slightly 

 increases the proportion of available lime. It might, there- 

 fore, be expected to produce a rather better effect than 

 equivalent quantities of other nitrogenous manures, but 

 reports on this point are conflicting. It is a highly deli- 

 quescent substance and must be kept free from damp. 

 The very fine state of division in which it is sold makes it 

 difficult to handle. It cannot be sown broadcast as it 

 injures the hands and eyes of the workmen, and if dis- 

 tributed by a machine it runs .so freely that it is apt to 

 be spread too thickly. This objection may soon be sur- 

 mounted by the manufacturers, and, in any case, it could 

 probably be overcome by mixing the manure with an equal 

 bulk of fine dry soil. To compete successfully with the 

 Chilian nitrate it will probably have to be offered at a more 

 tempting price. At present the difference is about 2 

 per ton in favour of the nitrate of lime, but this corres- 

 ponds to only a small difference in the price per unit of 

 nitrogen. The Norwegian Hydro-electric Company of 

 Christiania produced 1,059 tons of " lime nitrogen," as 

 it is sometimes called, in the first three months of last year 

 (1908), and this was more than the total output for the 



