302 AGRICULTURAL ANALYSIS 



dent of the processes commonly associated therewith, may some- 

 times take place. 03 



The influence of oxid of iron in the soil in rendering available 

 the nitrogen of the air, has received special attention. Bonnema 

 has given to this subject careful consideration and has come to 

 the conclusion that the so-called fixation of atmospheric nitrogen 

 in the soil is dependent upon the presence of ferric hydroxid. 

 This substance appears to have the property of oxidizing ele- 

 mental nitrogen and changing it into nitrous acid, which is capa- 

 ble of conversion into nitric acid in the usual manner. 



It appears from this investigation that the first step in the 

 nourishment of a plant by atmospheric nitrogen is not necessarily 

 one of biological chemistry, but rather one of a simple elementary 

 process. 64 



This problem has lately been studied more closely by Sestini. 65 

 It appears from the investigation made by Sestini that it is not 

 the elemental nitrogen of the air, but the ammonia which is con- 

 tained therein which is oxidized by ferric hydroxid into nitric acid. 

 This is an important observation in view of the fact that it is 

 generally supposed that the ammonia which enters the soil from 

 the air is converted into nitrous acid through the activity of nitri- 

 fying ferments. The utilization of the oxid of iron, therefore, is 

 not directed to the increase of the total quantity of assimilable 

 nitrogen, but only to the change of the ammonia into an assimi- 

 lable form. This has an important bearing upon the study of 

 the chemical processes relating to fertilizing materials by reason 

 of the relation of ammonia to fertility. The highly beneficial ef- 

 fects produced by the application of ammonia salts have long 

 been recognized. Most observers claim that these salts are only 

 useful when converted into nitric acid, and others that they are 

 useful in the absence of ferments which can produce this change. 

 In either case, however, it is evident, in view of the observations 

 above mentioned, that ammonia is not directly assimilable ever. 



61 Wiley, Principles and Practice of Agricultural Analysis, 2nd Edition, 

 1906, 1 : 568. 



64 Chemilcer-Zeitung, 1903, 27 : 149. 



65 Die landwirtschaftlichen Versuchs-Stationen, 1904, 60 : 103. 



