THE NITROGEN OF TEE AIR 241 



therefore, expose the air to a very high temperature and then very 

 suddenly cool it to a temperature so. low that the nitrogen oxide already 

 formed does not decompose at an appreciable rate. 



These conditions have been practically realized in only one way — 

 by causing an electric discharge, similar to that in an ordinary arc 

 lamp, to take place in air. The temperature of the arc is enormously 

 high, but the air just outside of it is comparatively cool; so that any 

 nitrogen oxide formed at the boundaries of the arc mixes at once with 

 the colder air and thus escapes decomposition. The excess of air con- 

 taining the oxides of nitrogen is then passed into towers filled with 

 quartz over which water is trickling, whereby nitric acid is formed. 



It is not necessary to enter further into details; for these are the 

 essential features of the commercial process for the manufacture of 

 nitric acid which is now being carried out on a large scale at Notodden 

 in Norway. Aside from the cost of installing and maintaining the 

 electrical and absorbing apparatus, the only large expense involved in 

 the process is the cost of power used in producing the electric discharge. 

 The works must therefore be located where water-power is obtainable 

 at the lowest possible cost; and Norway was naturally chosen as the 

 seat of the industry in Europe. The saltpeter factories there are 

 already utilizing 200,000 horse-power; and thousands of tons of their 

 product have been shipped to this country, for use in fertilizing the 

 fruit orchards of California and the sugar plantations of Hawaii. 



Almost simultaneously with this process for the manufacture of 

 nitrate there is being developed a process for the artificial production 

 of ammonia, its competitor in the fertilizer field. The aim is to pro- 

 duce this compound also from its elementary constitutents, nitrogen 

 and hydrogen. Nearly pure nitrogen can now be obtained cheaply 

 from the air by a commercial process which up to twenty years ago had 

 been carried out only on the smallest laboratory scale; namely, by 

 liquefying air with the aid of a liquid-air machine, and then distilling 

 the mixture of nitrogen and oxygen, much as a mixture of alcohol and 

 water is distilled in the rectification of spirit. The nitrogen, having 

 a much lower boiling-point, passes off first, yielding a gas containing 

 less than half a per cent, of oxygen, which can readily be removed from 

 it by chemical means. Pure hydrogen can be obtained cheaply by the 

 decomposition of water in two or three different ways. The raw ma- 

 terials needed for the production of ammonia, although not costless like 

 the air and water used in making nitric acid, are therefore obtainable 

 at low cost; and the main problem again consists in finding a practical 

 way of causing them to combine. 



It is a curious fact that difficulties are met with here which are 

 just the reverse of those encountered in the synthesis of nitric acid. 

 Ammonia is a compound on which temperature has the opposite effect : 



VOL. LXXXII.— 17. 



