CHAPTER XXI. 

 NITRIFICATION. 



THE term nitrification refers to the oxidation of ether ammonia 

 or nitrites to nitrates. It is often used in a broader sense to imply 

 the production of nitrates from decomposing organic material. 

 The process of nitrification was made use of in the manufacture of 

 saltpeter to supply the large quantities of gunpowder consumed 

 in the almost incessant wars of Europe. In the eighteen century 

 the artificial production of saltpeter in beds of decaying organic 

 matter reached a high degree of perfection. Especially was this 

 true in Sweden, Switzerland, and France, where nitre was collected 

 as a part of each .farmer's tax. In the year 1777 the French Govern- 

 ment issued special instructions for manufacture of saltpeter. In 

 these there was given special attention to the form of pit to be 

 used, the covering of the organic matter, the arrangement for the 

 free entry of air, the necessity of a mineral base, and the optimum 

 amount of moisture which was best supplied from the drainage of 

 stables. 



Early Theories. Even though the process had reached such a 

 high state of development, the underlying principles were entirely 

 unknown until the last third of the nineteenth century. At this 

 time attempts were made to explain the oxidation of ammonia to 

 nitric acid, on the strength of certain chemical reactions which 

 could be brought about in the laboratory. These were the experi- 

 ments of Kuhlmann and Dumas. The first investigator found, 

 on passing ammonia and air through a heated tube containing 

 a platinum sponge, that they combined with the formation of 

 ammonium nitrate, while Dumas found that nitric acid was pro- 

 duced when air and ammonia were heated to 100 C. with moist- 

 ened lime. It was considered possible that the porosity of the 

 soil could act as did the platinum sponge or the lime of the soil 

 act in a manner similar to that used in Dumas' experiments. After 

 the discovery of ozone by Schonbein this substance was used to 

 explain all natural processes of oxidation, and hence naturally the 

 case with nitrification. Mulder stated that investigations had 

 shown that ozone is capable of oxidizing ammonia to nitric acid 

 and water, and that it is probable that the same reaction could 

 take place in the soil, the soil acting merely as a catalyzer in the 

 reaction. 



