ATMOSPHERIC NITROGEN FIXATION 



By Eric A. Lof 



Formerly with the Poiver and Mining Engineering Department, General Elec- 

 tric Co.; now with the American Cyanamid Co. 



[With 4 plates] 



The three essential food constituents of living matter are carbo- 

 hydrates, fats, and proteins; the two former chiefly for the produc- 

 tion and storage of energy and the latter for building up the body 

 substance. They are alike in the respect that they all contain the 

 three elements carbon, hydrogen, and oxygen, but differ in that pro- 

 tein also contains nitrogen, which, therefore, becomes one of the in- 

 dispensable substances of life. 



Nitrogen is a colorless, tasteless, and odorless gas, slightly lighter 

 than air. It comprises about four-fifths of the volume of the atmos- 

 phere, where it occurs in a free state mechanically mixed with 

 oxygen. In this free state, it is an exceedingly inert element and 

 combines only with difficulty with certain other elements as will be 

 explained later. In combined form, it is found chiefly in certain 

 natural nitrate deposits, and natural manures such as guano also 

 contain large quantities of nitrogen compounds. 



FREE NITROGEN 



The atmosphere is the inexhaustible source for our nitrogen sup- 

 ply, and every bit of nitrogen in plants, animals, and the soil has 

 originated from free atmospheric nitrogen. Arrhenius estimates 

 that no less than 400,000,000 tons of nitrogen are annually with- 

 drawn from the atmosphere; and as nitrogen does not accumulate 

 to any great extent in the soil, this enormous quantity must again be 

 set free as inert nitrogen gas by the decomposition of organic matter 

 and restored to the atmosphere. An immense and endless circulation 

 of nitrogen is therefore continually going on, as shown in the ac- 

 companying diagram. 



'Reprinted by permission from the General Electric Review for March and April, 1923. 



203 



