apparatus. A very large plant of this kind working at Odda, in Norway, 

 is capable of turning out 13,000 cubic feet of nitrogen per hour with 

 an expenditure of some 200 h.p. 



A current of liquid air is allowed to run down the rectifying 

 column, which is built up of trays, perforated and filled with glass 

 beads. In passing down this column the liquid air meets with an 

 ascending current of gases which are evaporating from the mixture of 

 liquid oxygen in the still; an interchange of heat takes place, some of the 

 oxygen in the gases travelling up the column is condensed to liquid 

 while the heat given up by the liquid causes the evaporation of an 

 equivalent amount of nitrogen. This happens throughout the whole 

 of the passage of the liquid and gases down and up the column, with 

 the result that almost pure nitrogen issues from the top of the column 

 while the liquid in the still becomes so rich in oxygen that it can be 

 drawn off and used for the production of this gas. The nitrogen 

 which is pumped off from the rectifier is passed into holders and so 

 into the retorts containing the heated carbide. 



CaC 2 +N 2 = CaCN 2 



The mixture of calcium cyanamide and carbon which is thus 

 produced is allowed to cool out of contact with air and then ground. 



It has been found that if seeds are sown in land to which cyana- 

 mide has been applied just previously the germination and also the 

 subsequent growth is adversely affected, so that it is desirable to 

 apply cyanamide some little while before sowing the crop. Even then 

 it is rare that cyanamide will give so good results as equivalent amounts 

 of nitrogen applied in the form of either nitrate of soda or lime, or 

 sulphate of ammonia. (See Appendix recording experiments on 

 maize.) 



By treating cyanamide with superheated steam ammonia is 

 produced thus : 



CaCN 2 +3H 2 = CaC0 3 + 2NH 3 . 



This ammonia can then be concerted into nitric acid by the 

 catalytic process invented by Ostwald. In this the ammonia is passed 

 with air or oxygen through porous plugs in which is a quantity of 

 very finely divided platinum ; when the correct conditions are main- 

 tained the ammonia is oxidized with the formation of nitric acid. 



Of the remaining processes for bringing about the combination of 

 nitrogen the method of causing the nitrogen to combine with hydrogen, 

 invented by Haber, is by far the most important. This process 

 was without doubt a very great asset to Germany during the war 

 when it was cut off from outside supplies of nitrates. Unfortunately 

 very few details as to the working of this process have been published. 



