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CHAPTER V 



NITROGEN AND AIR 



GASEOUS nitrogen forms about four-fifths (by volume) of the atmo- 

 sphere ; consequently the air contains an exceedingly large mass of it. 

 Whilst entering in so considerable a quantity into the composition of 

 air, nitrogen does not seem to play any active part in the atmosphere, 

 the chemical action of which is mainly dependent on the oxygen it con- 

 tains. But this is not an entirely correct idea, because animal life 

 cannot exist in pure oxygen, in which animals pass into an abnormal 

 state and die ; and the nitrogen of the air, although slowly, forms 

 diverse compounds, many of which play a most important part in 

 nature, especially in the life of organisms. However, neither plants 

 nor animals directly absorb the nitrogen of the air, but take it up 

 from already prepared nitrogenous compounds ; further, plants are 

 nourished by the nitrogenous substances contained in the soil and water, 

 and animals by the nitrogenous substances contained in plants and in 

 other animals. Atmospheric electricity is capable of aiding the passage 

 of gaseous nitrogen into nitrogenous compounds, as we shall afterwards 

 see, and the resultant substances are carried to the soil by rain, where 

 they serve for the nourishment of plants. Plentiful harvests, fine 

 crops of hay, vigorous growth of trees other conditions being equal 

 are only obtained when the soil contains ready prepared nitrogenous 

 compounds, consisting either of those which occur in air and water, or 

 of the residues of the decomposition of other plants or animals (as 

 in manure). The nitrogenous substances contained in animals have 

 their origin in those substances which are formed in plants. Thus 

 the nitrogen of the atmosphere is the origin of all the nitrogenous 

 substances occurring in animals and plants, although not directly so, 

 but after first combining with the other elements of air. 



The nitrogenous compounds which enter into the composition of 

 plants and animals are of primary importance ; no vegetable or animal 

 cell that is, the elementary form of organism exists without con- 

 taining a nitrogenous substance ; organic life, before all, evinces itself in 



