FREE INSTITUTE OF SCIENCE 



FOOD FROM THE AIR 



pounds that may be employed for enriching the soil. These processes are also 

 invaluable in another department of human industry, namely, the manufacture 

 of explosives. While explosives are largely used in the destruction of Ufe and 

 property, they are also of the greatest value in the arts of peace. In mining, 

 the construction of roads, tunnels, canals, the removal of river and harbor ob- 

 structions, and even in agriculture the modern high explosives are used in 

 enormous amount. It has been discovered that by overturning the soil by 

 dynamite a notable increase of fertiHty is assured. As civihzed nations are 

 impressed with the importance of both Hberal food supplies and Hberal suppHes 

 of explosives, there is a double incentive to discovery and invention along the 

 line of utilization of the nitrogen of the air. 



A pecuHar and interesting utiHzation of nitrogen takes place in soil, in 

 connection with the growth of some plants, especially those belonging to the 

 large and widely distributed natural order, Leguminosce. To this order belong 

 several important food plants, such as peas and beans, important grazing 

 plants, such as clover and alfalfa, and many trees, such as the honey-locust 

 the Kentucky coffee-tree and the acacias. The roots of many of these plants 

 bear nodules that are collections of bacteria, which use the roots as a physical 

 support and which carry on processes by which nitrogen is fixed and rendered 

 available for the use of the host plant. This is not a true parasitism, but more 

 like a mutual relationship, and hence it is known to the biologist as "symbiosis " 

 (joint life). It has long been known that the fertiHty of land can be materially 

 increased by planting clover, and, after it has reached good growth, plowing it 

 in. The reason for this effect is now understood. It appears that each 

 species of leguminous plant is best served by a particular species of micro- 

 organism. It is now a practice to inoculate the seeds of such plants with pure 

 cultures of the appropriate organism and thus increase the yield. 



These processes of nitrogen-fixing are slow and can be appHed only to 

 farming areas and made applicable only to certain crops, except indirectly. 

 The nitrogen compounds must be utilized in the place in which they are pro- 

 duced for the growth of plants, so that one very important appHcation of fixed 

 nitrogen, that for the manufacture of explosives, is not met by this method, 

 hence chemists have been seeking energetically of late years for methods of 

 nitrogen-fixation available under a great variety of conditions and in many 

 locations. 



