CONCERNED WITH NITRIFICATION 125 



is required to change the ammonia into nitrites and the nitrites into 

 nitrates. 



2. Nitrification 



This oxidation is performed by the nitrifying micro-organisms, 

 and the process is known as nitrification. It should be clearly 

 understood that the process of nitrification may, so to speak, dovetail 

 with the process of denitrification. No exact dividing line can be 

 drawn between the two, although they are definite and different 

 processes. In a carcase, for example, both processes may be going 

 on concomitantly, so also in manure. There is no hard-and-fast line 

 to be drawn in the present state of our knowledge. Other organisms 

 beside the true nitrification bacteria may be playing a part, and it is 

 impossible exactly to measure the action of the latter, where they 

 began and where the preliminary attack upon the nitrogenous com- 

 pounds terminated. In all cases, however, according to Professor 

 Warington, the formation of ammonia has been found to precede the 

 formation of nitrous or nitric acid. 



It was Pasteur who (in 1862) first suggested that the production 

 of nitric acid in soil might be due to the agency of germs, and it is 

 to Schlosing and Miintz that the credit belongs for first demonstrat- 

 ing (in 1877) that the true nature of nitrification, the conversion of 

 ammonia into nitric acid, depended upon the activity of a living 

 micro-organism.* Partly by Schlosing and Miintz and partly by 

 Warington (who was then engaged in similar work at Rothamsted), it 

 was later established (1) that the power of nitrification could be com- 

 municated to substances which had not hitherto nitrified by simply 

 seeding them with a nitrified substance, and (2) that the process of 

 nitrification in garden soil was entirely suspended by the vapour of 

 chloroform or carbon disulphide. The conditions for nitrification, 

 the limit of temperature, and the necessity of plant food, have 

 furnished additional proof that the process is due to a living organism. 

 These conditions, according to Warington, are as follows: 



1. Food (of which phosphates are essential constituents). "The 

 nitrifying organism can apparently feed upon organic matter, but it 

 can also, apparently with equal ease, develop and exercise all its 

 functions upon purely inorganic food " (J. M. H. Munro).f Wino- 

 gradsky prepared vessels and solutions carefully purified from 

 organic matter, and these solutions he sowed with the nitrifying 

 organism, and found that they flourished. Professor Warington has 

 employed the acid carbonates of sodium and calcium with distinct 

 success as ingredients of an ammoniacal solution undergoing nitrifi- 

 cation. 



2. The next condition of nitrification is the presence of oxygen. 



* Compt. Rend., 1877, pp. 84, 301. t Trans. Chem. Soc. y 1886, etc. 



