NITRIFICATION 29 



three weeks nitrates began to appear in the effluent and 

 increased to such an extent that finally the filtered sewage 

 contained no ammonia. After this had continued for 

 some weeks chloroform vapour was passed at the same 

 time through the tube, with the result that in ten days 

 after the introduction of the chloroform all nitrates dis- 

 appeared from the effluent. 



Subsequently the passage of chloroform vapour was 

 discontinued, but nitrification did not resume until the 

 washings from 10 grm. of garden soil were added. Eight 

 days after this addition nitrates again appeared in the 

 effluent (this was confirmed by Warington). Evidently 

 the chloroform vapour acted as an antiseptic and killed 

 the nitrifying organisms, while the addition of soil washings 

 re-inoculated the material. 



Shortly after this Schloesing and Miintz found that 

 exposure of soil to 100 C. for an hour destroyed the 

 power of mducing nitrification. Soils thus treated were 

 exposed to a current of air, purified by ignition, without 

 nitrification taking place ; the addition of a little un- 

 heated mould was, however, sufficient to cause nitrifica- 

 tion to recommence. They also tried seeding the sterilised 

 soils with various Hyphomycetes, etc., without result. 



In 1884 Warington concluded that the factor deter- 

 mining the formation sometimes of nitric acid and some- 

 times of nitrous acid was a difference in the character of 

 the organisms ; for it is possible to have two similar 

 solutions under identical conditions, and for nitrites to be 

 produced in the one, and nitrates in the other. 



In 1886 Munro showed that the process of nitrification 

 could take place in solutions practically destitute of 

 organic matter. 



Nitrification in the soil takes place in three stages : 



I. Ammonisation. When complex organic compounds 

 such as albuminoids are applied to the land they are 



