TTIK NITROGEN PROBLEM. 97 



ill tlie •atmosphere, wliicli plants, except tlie one family men- 

 tioned, were incapable of using-. In tins connection it is worth 

 noting' that twenty million tons of free nitrog-en have been 

 estimated to exist over every square mile of the earth's surface, 

 an amount sufficient, according" to the late Sir William 

 Ramsay, to afford plant food for over 38,000 years at the 

 present rate of consumption. The quantities of available 

 nitrogen from the Chili deposits and coal carbonisation were 

 such that they would in a relatively short period of time prove 

 insufficient to meet the demand created. ( )n the other hand, 

 the use of nitric acid and nitrates, particularly in the manufac- 

 ture of explosives, was also increasing-, thus decreasing- the 

 supply- available for plant nutrition, and other sources of these 

 compounds were, comparatively speaking', neg'lig-ible. 



The problem wliidi therefore presented itself was the 

 conversion of this atmospheric nitrog-en into a form capable of 

 transference to the soil for utilisation by growiiig- plants, more 

 especially wheat. This is now known as the nitrogen problem, 

 and its solution forms one of the g-reatest achievements of this 

 century. The methods by which this has been accomplished 

 are as follows : — ^ 



1. Direct union with oxygen, forming nitric peroxide, and 

 solution of this in water, yielding- nitric acid and its salts. This 

 is effected by the agency of the electric^ arc, the processes in 

 commercial use being (a) the Birkeland-Eyde ; (b) the 

 Schoiiherr; (c) the Pauling. 



2. Direct union -uith hydrogen, forming ammonia, and 

 solution of this in aqueous solutions of acids, yielding 

 ammonium salts, or oxidation to nitric acid, and formation of 

 ammoniam nitrate. This is effected by catalytic action at high 

 temperatures and pressures on the pure mixed gases. The 

 commercial process is known by the name of Professor Haber, 

 Avho successfully investigated the equilibrium of the reaction. 



-.1. Eeaction with metallic carbides, forming cj'anamide 

 and carbon, the commercial process being known by the name 

 of the first product mentioned. 



4. Union with metals, forming nitrides, which are then 

 decomposed, yielding- ammonia and its salts. These processes 

 are still in tiie experimental stage, the most promising being 

 tliat of 0. Serpek, which consists in heating bauxite with 

 carbon to about 1,800° C. and subsequent decomposition of the 

 aluminium nitride thus produced by steam or an. aqueous 

 solution of sodium hydroxide, yielding ammonia and alumina, 

 which is stated to be of sufficient purity for the preparation of 

 the metal by electrolysis. 



5. Conversion into sodium (-yanide by heating a mixture 

 of soda ash and carbon with finely divided iron as catalyst to 

 about 950° C. and passing nitrogen or air through the mass. 

 The cyanide is lixiviated out with water and dried. It is then 

 melted and air passed through, thus yielding- cyanate, which 

 is heated with water to obtain the bicarbonate and ammonia. 

 This process is due to Professor J. F. Buchei and has n^t-j^-et, 

 been worked on the large scale. /''a^^^'4/ 





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