CHAPTER V. 

 NITRIFICATION AND DENITRIFICATION. 



NITRIFICATION. 



The pulling of the organic nitrogen compounds to pieces does 

 not in itself bring the nitrogen into the best available condition for 

 plants. It is in the form of nitrates that plants most readily absorb 

 nitrogen, and at the end of the decompositions noticed ammonia 

 compounds are formed, but no nitrates. Plants may be able to 

 absorb nitrogen in the form of ammonia salts, but this occurs only 

 to a slight extent, and by far the largest amount is assimilated in 

 the form of nitrates. Consequently, if these decomposition pro- 

 ducts are to be utilized by plants, they need to be changed from 

 ammonia salts into nitrates. This process has been called nitri- 

 fication. 



Nitrification is a process of oxidation. In the oxidation of am- 

 monia compounds to form nitrates there are two separate stages. 

 The first is one by which the ammonia is oxidized into a nitrite. 

 A nitrite is a salt of nitrous acid (HNO 2 ), and it contains less oxygen 

 than a nitrate. Nitrites are not plant foods, for, as far as known, 

 ordinary plants never absorb nitrogen in this form. The second 

 change is the addition of another atom of nitrogen to the nitrite, 

 giving a nitrate or salt of nitric acid (HNO 3 ), the form in which the 

 nitrogen is most completely available for plants. 



Nitrates are really of very great significance in nature. They 

 are readily soluble in water, so that they are easily taken up by the 

 soil and absorbed by the roots; thus nitrates feed the whole world of 

 green plants. In addition to this, nitrates form the basis of most 

 explosives. Gunpowder has saltpeter as its basis, and saltpeter is 

 nitrate of potash. Nitroglycerin, too, is made from nitric acid, and 

 practically all the other commonly used explosives are produced 



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