80 THE farmers' handbook. 



ever, absorbed by tbe water, as it is so diluted, with the air which passes over 

 with it that at least half escapes absorption. This is passed into a tower 

 charged with milk of lime, where it is converted into nitrite and nitrate of 

 calcium. By further treatment with nitric acid, a calcium nitrate, contain- 

 ing about 13-2 per cent, nitrogen, is formed (pure Ca (NO,). = 17 per cent, 

 nitrogen). It is placed in the market, either in this form (either fused or 

 in crystals), or, preferably, by converting it (Messel's process) into a basic 

 salt by calcining it with lime, this product being non-hygroscopic, whereas 

 ordinary calcium nitrate absorbs water from the air and becomes moist. 

 This is a point of considerable importance in determining its value as a 

 manure. 



Calcium nitrate appears to be just as effective as sodium nitrate contain- 

 ing the same amount of nitrogen. The determining factor is, of course, the 

 cheapening of the unit-cost of the current, by the provision, for example, of 

 water supply adequate to produce the requisite power at a cheap rate. 



More Recent Processes. 



Instead of combining atmospheric nitrogen with oxygen to form nitric 

 acid, as in the above processes, it may be combined directly with hydrogen to 

 form ammonia. 



Haber Process. — This process, or some modifications of it, has been the 

 basis of most of the recent processes for the fixation of atmospheric nitrogen. 

 Hydrogen, obtained from water by the decomposition of steam by iron or 

 coal or coke, is directly combined with the nitrogen of the air under the- 

 influence of a catalyst, such as finely-divided iron. The ammonia thus 

 obtained can be converted into sulphate of ammonia or oxidized to nitric 

 acid. 



Oxidation of Ammonia to Nitric Acid. — The ammonia produced by the 

 Haber process or its modifications, or by any other process, such as the de- 

 structive distillation of coal in the manufacture of coal-gas, can be converted 

 directly into nitric acid. A mixture of air and ammonia can be so oxidized 

 in contact with metallic platinum, the platinum acting as a catalyser. 



Recent Developments Drought about by the War. — The need for nitric 

 acid nitrates in the manufacture of high explosives, brought about by the 

 war, caused a rapid development of methods for extracting nitrogen cheaply 

 from the air. When Germany declared war she was in a position to be in- 

 dependent of the Chilean nitrate supplies. She was in possession of the- 

 Haber process for the production of ammonia and the Ostwald process for 

 its oxidation to nitric acid, and these processes were heavily subsidised by 

 the Government. 



The world's consumption of fixed nitrogen went up rapidly and enor- 

 mously. Germany alone, for example, which consumed about 250,000 tons 

 nitrogen in 1913, consumed 400,000 in 1917. Many modifications of the 

 Haber process for the production of ammonia and its subsequent oxidation 

 to nitric acid have been introduced, and the cost of production of both ferti- 

 lisers and explosives from the air very considerably reduced. 



Cyanide Process. — This has been developed principally in the United 

 States. In this process sodium cyanide is produced from carbonate of soda,. 

 coke, iron, and atmospheric nitrogen, a process which does not involve the 

 use of electricity. The cyanide can be converted into ammonia and this in 

 turn, as with the processes referred to above, into ammonium sulphate or 

 nitric acid. 



