AMMONIA OF THE ATMOSPHERE. 81 



1. TJie putrefaction of animal substances is always attend- 

 ed by the revolution of ammonia, as a gaseous product. The 

 nitrogen which animals contain, is separated, mostly, in this 

 form.* In the decay of plants also, ammonia is given off. 

 The quantity thus formed, is very great. " A generation of 

 a thousand million men is renewed every thirty years, thou- 

 sands of millions of animals cease to live, and are reproduced 

 in a much shorter period." 



The ammonia, thus produced, is partly thrown off into the 

 atmosphere, and partly retained in the soil in the form of 

 salts, or condensed in the pores of the humus, clay, water, or 

 other ingredients of the soil. Some of it enters the roots of 

 plants, a large portion is washed into the sea by rivers, or 

 carried there in rains. A part of that which remains in the 

 atmosphere is liable to be decomposed by thunder storms, so 

 that but a small quantity of that which is derived from this 

 source, exerts any agency upon vegetation. 



2. When vegetable substances which contain no nitrogen 

 decay or are oxidized in the open air, they exert a catalytic 

 force upon the nitrogen of the atmosphere and the hydrogen 

 of the plant, and ammonia is formed in considerable quantities. 



In a similar way, also, when inorganic substances suffer 

 oxidation in air or water, ammonia is formed ; thus Faraday 

 found, that when oxides were decomposed by potassium in the 

 air, this gas was evolved ; and Chevalier produced it by ex- 

 posing moist iron filings to the influence of the atmosphere. 

 The action of nitric acid on metallic oxides often produces it. 



3. But the most abundant source of ammonia has been 

 pointed out, I believe, by Daubeny. In volcanic districts im- 

 mense quantities are evolved. This is formed in the interior 

 of the volcano by means of heat and the decomposition of wa- 

 ter, the hydrogen of which unites with the nitrogen of the air. 

 This explanation is rendered evident by a very simple exper- 



* In hot countries, the ammonia of fermenting dung heaps, is part- 

 ly transformed into nitric acid. 



7* 



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