NITRIFICATION 119 



ments turned their attention to the development of the process 

 of nitrification. Therefore, in the eighteenth 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 niter was collected as a part of 

 each farmer's tax. In the year 1777 the French Government 

 issued special instructions for the manufacture of saltpeter. In 

 these there was given special attention as 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 Ideas. — 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 basis of certain chemical reactions which could 

 be brought about in the laboratory. These were the experiment 

 of Kuhlmann and Dumas. The first investigator found that on 

 passing ammonia and air through a heated tube containing a plati- 

 num sponge that they combined with the formation of ammonium 

 nitrate, while Dumas found that nitric acid was produced when 

 air and ammonia were heated to 100° C. with moistened 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. 



It may be seen that in all the early theories nitrification was 

 supposed to be a purely chemical process; it was not until the time 

 of Pasteur that the biological explanation for the formation of 

 nitrates received any support. 



