18 CHARACTERISTICS OF AMMONIA SALTS 



little sulphate of lime. The action would then stop if all the 

 products remained side by side. The power of combining with 

 carbonate of ammonia possessed by the humus, by some of the 

 hydrated silicates, and by the hydrated oxide of iron contained in 

 the soil, now, however, steps in ; the carbonate of ammonia which 

 has been produced is absorbed by these substances, and as 

 soon as it is removed from the sphere of action the reaction 

 between the carbonate of lime and the sulphate of ammonia 

 again goes forward, and if the supply of carbonate of lime 

 and the absorptive power of the soil for ammonia are equal to 

 the task the reaction proceeds till the whole of the sulphate of 

 ammonia has been decomposed, its sulphuric acid combined 

 with lime, and its ammonia stored up in the soil. The 

 ammonia is now fairly fixed, and rain may fall upon the soil 

 without removing more than an insignificant amount in the 

 drainage water. 



The ammonia has now reached a condition in which it is 

 probably capable of acting as a food for plants. Its changes, 

 however, are not yet over. In a fertile soil oxidation of the 

 ammonia proceeds with considerable rapidity ; the ammonia 

 disappears, and nitrites and nitrates are successively produced. 

 The successive stages of oxidation are effected by two 

 species of bacteria, one of w T hich converts the ammonia into a 

 nitrite, while the other converts the nitrite into a nitrate. 

 The two actions proceed simultaneously in an ordinary soil, 

 so that a nitrate is apparently the only substance produced. 

 The whole process is known as nitrification. Nitrification will 

 not take place unless there is a base for the nitrous acid to 

 combine with. There is thus in the nitrification of the 

 ammonia a further consumption of the carbonate of lime con- 

 tained in the soil. The final outcome of the whole reaction is 

 the entire disappearance of the sulphate of ammonia, and its 

 replacement by two soluble salts, the sulphate and nitrate of 

 lime. If chloride of ammonium has been employed instead of 

 the sulphate, the series of changes which occur will be per- 

 fectly similar, the final products being chloride of calcium and 

 nitrate of lime. 



If the field to which the ammonia salt is applied is 



