TRANSACTIONS OF WAGNER 



FOOD FROM THE AIR 



FIXATION OF NITROGEN BY OXIDATION 



The element nitrogen ordinarily shows in the free state very low chemical 

 affinity. It was, indeed, formerly considered as one of the most indifferent of 

 elements, but research has brought to light a few elements — gases at ordinary 

 temperatures and existing in small amount in the air — which are apparently 

 without chemical affinity. Free nitrogen combines directly even under the 

 influence of high temperature with but few elements, one of which is mag- 

 nesium. Under the influence of the electric spark direct combination of the 

 nitrogen and oxygen of the atmosphere can be secured. This was discovered 

 in the i8th century, in the course of researches by Henry Cavendish and Joseph 

 Priestley. Whether the combination is due to the increase of the affinity of the 

 nitrogen or the oxygen or both, is not definitely known and is not important here. 

 It is known that pure oxygen can be converted by electric discharges, especially 

 the so-called "silent discharge," into a much more highly active form without an 

 alteration in fundamental composition. This form, termed "ozone," manifests 

 itself by a distinct odor and by oxidizing readily many substances — e. g., 

 silver — upon which ordinary oxygen has no action. Evidence of the produc- 

 tion of ozone is noted almost always when electric discharges are occurring, 

 whether these be silent or noisy and whether spark or arc, but the amount of 

 ozone produced is so much dependent on the form of the discharge that in 

 practice both for making ozone as such and for oxidizing nitrogen only certain 

 forms are used. 



Cavendish used the spark of a static machine, and some modern apparatus 

 for producing ozone use discharges of high voltage currents either through a 

 special dialectric or directly through dry air. For nitrogen-fixation on a com- 

 mercial scale, processes entitled to consideration here are three in number, of 

 which one is direct oxidation and the others direct combinations of other types. 



The direct oxidation has been carried out in several ways, but present 

 usage is Hmited to the employment of a flaming arc. The earlier experiments 

 were made with electrodes drawn so far apart as to make the arc unsteady, but 

 the modern forms do not apply this principle. 



One of the best known, and apparently most successful, forms of apparatus 

 for direct oxidation of nitrogen is the Birkeland-Eyde furnace which depends 

 on developing an arc by an alternating current of high voltage in a constant 

 magnetic field. The furnace is usually a sheet-steel drum about eight feet in 



