238 THE POPULAR SCIENCE MONTHLY 



Before discussing the present and prospective sources of supply of 

 useful compounds of this element, it should be mentioned that, though 

 the consumption of these compounds in fertilizers exceeds all other 

 uses of them, yet enormous quantities are required in other industries. 

 Thus, the powerful modern explosives which have made practicable 

 great engineering works, like the Panama Canal and the Hudson River 

 tunnels, are all nitrogen compounds — made by the action of nitric 

 acid on glycerin, cotton, or some other material. Most of the so-called 

 coal-tar products, the artificial clyestuffs, drugs and perfumes, are also 

 prepared from the substances distilled out of the tar by first treating 

 these substances with nitric acid. Ammonia, too, a compound of 

 nitrogen with hydrogen, is used in large quantity in refrigerating 

 plants and in various chemical industries. 



Up to a few years ago, there were only two important commercial 

 sources of nitrogen-compounds — the great natural deposits of sodium 

 nitrate (the so-called Chili saltpeter) in Chili, Peru and Bolivia; and 

 the crude ammonium sulfate obtained in the manufacture of gas and 

 coke from coal. But the saltpeter deposits will, at the present rate of 

 exploitation, become exhausted within a period variously estimated at 

 from 30 to 100 years; and, in the meantime, owing to increased cost of 

 production, the price of the saltpeter is steadily rising, thus restricting 

 its availability as a fertilizer. The ammonia produced in gas and 

 coke works is only a by-product; and the quantity of it can not of 

 course be increased beyond that corresponding to the demand for the 

 main products, gas and coke. The total quantity of ammonia thus 

 produced is in fact entirely insufficient to furnish the nitrogen used in 

 fertilizers; and by far the larger proportion of commercial nitrogen is 

 still derived from the saltpeter deposits of South America. 



The nitrogen from these sources costs to-day in American or Euro- 

 pean markets not far from 15 cents a pound — a price which is causing 

 a nitrogen famine among the crops of the world; for the cost is too 

 high to admit of spreading it in adequate quantity over the millions of 

 acres of land under cultivation. This condition of things offers a 

 challenge to the scientific investigator. For, though nitrogen is one 

 of the commonest elements, forming as it does, four fifths of our 

 atmosphere, yet we are drawing nearly all our nitrogen from South 

 American mines or from gas works and are paying fifteen cents a 

 pound to get it in a form available for plant life. 



It might seem as if the problem of converting the nitrogen of the 

 air into compounds that can be assimilated by plants was essentially a 

 chemical one; but recent discoveries have opened also to the biologist 

 a great field of investigation in this direction. For it has been found 

 that, although the higher plants can not utilize directly the nitrogen 

 of the atmosphere, there are certain common kinds of bacteria, which 



