THE NITROGEN OF THE AIR 237 



THE UTILIZATION OF THE NITROGEN OF THE AIR 



By ARTHUR A. NOYES 



PROFESSOR OF THEORETICAL CHEMISTRY IN THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY 



A GERMAN geographer has estimated that the world contains 

 1,700 million people, and that they are increasing at the rate 

 of twelve million a year. During each succeeding decade, therefore, 

 provision must be made for feeding a new population greater than the 

 present population of the United States. This demands an enormous, 

 steadily growing increase in the world's output of agricultural products. 

 How to provide for this increase is one of the largest material problems 

 that confronts our generation and the generations to come. Many 

 factors must contiibute to its solution. New land must be brought 

 under cultivation by a wider distribution of population, by increased 

 facilities of transportation, by better utilization of the available water- 

 supply through storage and irrigation. A larger yield per acre must 

 be secured by improvement of the varieties of food-yielding plants 

 through biological selection and breeding, through the adoption of more 

 economical methods of farming, and especially through increasing and 

 maintaining the fertility of the land by the scientific use of fertilizers 

 in adequate amount. 



This last aspect of the problem is the one with which this article is 

 concerned. It is a vital part of the food problem, one which can not 

 be eliminated by advances in any of the other directions just referred 

 to; for plants can not live on water and air alone. They consist, to be 

 sure, in largest proportion of compounds of carbon, hydrogen and 

 oxygen; and they have the marvelous power of producing these 

 compounds under the influence of sunlight from the carbon di- 

 oxide of the air and the water of the soil. But they contain also 

 as essential constituents certain other elements, especially nitrogen, 

 phosphorus and potassium, which they can not obtain from the air, 

 which they must therefore extract from the soil. These elements 

 are, however, present only in small quantity even in virgin soil; 

 and they soon become exhausted through the harvesting of successive 

 crops. It is therefore necessary, in the long run, to return to the soil 

 the quantities of nitrogen, phosphorus and potassium that are contained 

 in the vegetable products taken from it. 



The sources from which we can obtain these three plant-foods 

 cheaply and abundantly is so large a question that only one of them, 

 nitrogen, will be here considered. Of the three this is by far the most 

 expensive — by far the most difficult to obtain in sufficient quantity at 

 low cost. 



