TRANSACTIONS OF WAGNER 



FOOD FROM THE AIR 



Beginning with the complex proteins, such as albumin and fibrin, that 

 form the basis of living tissues, the first change is the sphtting of these into 

 somewhat simpler forms, and by successive cleavages finally into ammonium 

 compounds, water and carbon dioxid. Most higher proteins contain sulfur 

 and phosphorus, which are ultimately converted into sulfates and phosphates 

 respectively, but these accessory products do not need attention here. Am- 

 monium is converted into nitric acid, and this at once acts upon the alkaline 

 material of the soil, calcium or magnesium carbonate, and less frequently 

 sodium, or potassium carbonate, by which nitrates are formed, which become 

 directly the food of the higher plants, and these in turn become the food of 

 animals, complex animal proteins are again produced, and the cycle repeated 

 indefinitely. As these changes go on mostly under the influence of minute 

 organisms, and as the growth and multiplication of such organisms are generally 

 restrained by free acid, it is necessary that the soil should contain some sub- 

 stances capable of neutralizing the acid as fast as formed. This function is 

 performed, as noted above, by the carbonates. Any carbonate will neutralize 

 nitric acid, but only a few are commonly found in soil. Calcium carbonate 

 is the most abundant. In the form of limestone it constitutes immense de- 

 posits in many parts of the world. It is but little soluble in water under 

 ordinary conditions, but when the water contains notable amounts of car- 

 bonic acid, the solvent action is much increased. Now arable soil is rich in 

 microbes, and the processes of the nitrogen cycle just described give rise to 

 much carbon dioxid. This dissolves in the water percolating through the 

 pores of the soil, and thus the calcium (and also magnesium) carbonate, other- 

 wise but slightly soluble, can be brought into solution and readily act on the 

 nitric acid formed by the microbes. The well-known fertihty of limestone 

 soils is explained on this principle. 



The amount of nitrogen in the part of the universe with which we are 

 acquainted is immense and much of it is in the free state in the atmosphere, 

 which is a mixture of about four volumes of nitrogen with one volume of oxygen 

 and small amounts of other substances, of which water and carbon dioxid are 

 the most important. In view of possible near exhaustion of the sodium nitrate 

 deposits of South America, and the slowness with which nitrates can be pro- 

 duced by ordinary methods of decomposition, agricultural chemists have for some 

 years been turning their attention to the discovery of methods of causing the 

 nitrogen of the atmosphere to unite with other elements so as to produce com- 



