222 THE FARMER OF TO-MORROW 



In the light of this discovery, sugar, starch, 

 chloroform, and other chemicals are fertilizers. 

 So is boiling water. How much "plant food" 

 do these substances contain, according to the 

 theory of Liebig? The followers of Liebig 

 value "fertilizers" only in accordance with 

 how much "plant food" they contain. In the 

 strict sense of the term, these materials contain 

 no "plant food." Sugar and starch are made 

 up of carbon, hydrogen and oxygen only. Yet 

 adding them to the soil increases produc- 

 tivity. 



Even without the aid of the "domesticated" 

 bacteria and fungus growths, however, the 

 farmer need never run short of the supply of 

 nitrates required for food. If land becomes 

 too valuable to grow clover in rotation, or to 

 turn under carbonaceous green crops to rot 

 and feed the azotobacter, man has devised a 

 means of extracting nitrogen from the air 

 mechanically. A current of air is ' directed 

 against an electric arc, and the nitrogen be- 

 comes oxidized. This nitrogen can be gathered 

 by spraying the oxidized air against lime, with 

 which the nitrate enters into combination. 

 This discovery was not due to the needs of the 

 farmer. As we have said, the requirements of 



