CHAPTER Xyill 



NITRIFICATION 



The term nitrification is used to designate the change 

 of humus-nitrogen, or of any nitrogen in vegetable 

 and animal substances, into a nitrate. It is also used, 

 at times, to designate the change of ammonia, or of 

 nitrites, into nitrates. The first definition is broader 

 and includes the work not only of the nitrifying bacteria 

 proper, but, also, that of the ammonifying bacteria. 

 A nitrate (NO3) contains one more atom of oxygen than 

 does a nitrite (NO2). 



Until within a generation ago it was not known that 

 nitrification is a bacterial process. The transformation 

 of organic nitrogen into nitrate was regarded as a purely 

 chemical reaction and was extensively studied from 

 that standpoint. Important economic issues were in- 

 volved in such studies. The matter was of lively con- 

 cern, not only to agriculture, but, also, to military 

 organizations. Since gunpowder is composed largely 

 of saltpeter (nitrate of potassa, or potash), some pro- 

 cess whereby this could be obtained was eagerly sought. 

 Numerous methods were discovered and employed 

 with various degrees of efficiency. 



The fact that saltpeter has its origin in organic sub- 

 stances was suspected by at least a few chemists early 

 in the eighteenth century. It was stated in 1717 that 



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