THE ATMOSPHERE 207 



as in a thunderstorm, causes the combination of nitrogen and 

 hydrogen to form ammonium nitrite, 2N + 2H 2 = NH 4 N0 2 . It 

 has been calculated that about 1 5 kg. of N 2 are thus carried down 

 by the rain per acre per annum. (3) Ammonia salts, nitrites 

 and nitrates in the soil and water. (4) Organic nitrogenous 

 compounds from dead plants and animals, such as acid amides, 

 amido-acids, amines, and other proteid derivates. Such are the 

 supplies. On the other hand, every combustion of organic 

 matter, whether by fire or by denitrifying bacteria, sets nitrogen 

 free. Bunge has calculated that in 50 years 10 men die for 

 each sq. kilometre of land of the earth's surface. If cremation 

 becomes universal so much poorer must the land become in 

 nitrogen. An additional loss for the present time is the vast 

 amount of sewage thrown into the sea and the enormous mass 

 of organic matter burnt. Already the older countries, such as 

 England, must be manured to ensure the raising of good crops, 

 and to-day the combined nitrogen of the virgin soils of America 

 are poured down the English sewers into the sea. 



Denitrifying bacteria are very numerous in dung heaps, &c. 

 They act only in anaerobic conditions and in the presence of 

 carbohydrate. These organisms have been regarded as the 

 farmer's enemy, as destroyers of the nitrogenous food of plants. 

 Probably the conditions are such in the soil (e.g. presence of 

 oxygen) that their action is not energetic. The small amount 

 of animal life in the Pacific Ocean has been attributed to the 

 presence of denitrifying bacteria, to these bacteria robbing the 

 plants of nitrates, and so preventing a sufficient growth of food 

 supplies for animals. The process of denitrification probably 

 consists of two stages, each stage being induced by the enzymic 

 action of a different organism. The first stage is the reduc- 

 tion of nitrate to nitrite, the second the decomposition of the 

 nitrite and evolution of nitrogen. Such a decomposition occurs 

 in a solution of ammonium nitrite near the boiling-point 

 NH 4 N0 2 ^N 2 + 2H 2 0, and is accelerated by platinum black 

 acting as a catalyser. The nitrifying bacteria probably reverse 

 the action of the denitrifying bacteria. 



Nitrification bacteria were discovered by Winogradsky. The 

 nitrosomonas oxidises ammonia into nitrates, while the nitro- 

 bacteria oxidises nitrites into nitrates. These organisms only 



