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 jnost 
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 
57 
