Chemical Processes in Plants. 331 



Complex Nitrogenous Compounds. 



4 [ 

 $ I Ammonia 



Si Nitrites 

 Nitrates 



Gaseous 

 Nitrogen 



The loss of nitrogen either in gaseous form or as ammonia 

 or nitrates is far from being compensated for by the action 

 of the nodule bacteria, azobacter, etc., so that without 

 artificial manures, the soil would be ultimately depleted of 

 the nitrogen necessary for the growth of crops. This loss 

 has, up to the present, been very largely replaced by the 

 addition to the soil of Chili saltpetre, of which big natural 

 deposits have been discovered. The supply of nitrogen 

 from this source is, however, by no means inexhaustible, 

 and many investigations have been carried out with the 

 object of finding methods for obtaining the nitrogen of the 

 air in such a form that it can be available as a source of 

 food supply to plants. 



The loss of nitrogen in a form suitable for plant nutri- 

 tion, and the prospective exhaustion of natural nitrate 

 stores, such as the Chili saltpetre, have stimulated investi- 

 gation within recent years on the economical preparation 

 of nitrates and other compounds in which the nitrogen 

 derived from the air can be rendered available as a plant 

 food. Nictric acid has been obtained by the oxidation of 

 atmospheric nitrogen by an electrical discharge. Nitrogen 

 has also been made to combine with hydrogen at high 

 temperatures in the presence of a catalyst to form ammonia 

 from which nitrate can be obtained by oxidation. Another 

 method by means of which atmospheric nitrogen can be 

 rendered available depends on the fact that when the 



