almost always used as manure, and for the present concerns 

 us most. 



When first applied to the land, sulphate of ammonia, being 

 readily soluble in water, is dissolved by the water which the 

 soil contains. When used as a top-dressing, especially on 

 grassland, so that it does not come into close contact with 

 the soil, it may sometimes remain undissolved until rain 

 falls ; but the soil generally contains enough water to dis- 

 solve sulphate, if in close enough touch with it. 



In a state of solution, the sulphate of ammonia spreads all 

 through the soil ; and unless some change takes place in its 

 condition, it may be gradually washed away in the drainage 

 from the soil. We have already referred to the fact that 

 clay and humus in a soil have the power of fixing or 

 absorbing ammonia ; and, of course, the majority of soils 

 contain a certain proportion of one or both of these consti- 

 tuents. In what way the ammonia is fixed, is not clearly 

 understood ; but it is probably chiefly by chemical com- 

 bination, though capillary action may possibly assist in 

 retaining it. 



The humus and clay of the soil, however, can only absorb 

 ammonia when it is either in the free state i.e., not com- 

 bined with other substances or in the state of carbonate. 

 The ammonia of sulphate of ammonia must, therefore, be 

 converted into one of these forms before it can be fixed. 

 This is brought about by chemical action in the soil be- 

 tween the sulphate of ammonia and carbonate of lime, a 

 substance which most soils contain. It will be remem- 

 bered that sulphate of ammonia is a compound of ammonia 

 and sulphuric acid, and carbonate of lime consists of lime 

 and carbonic acid. When these two substances come into 

 contact in the soil, an exchange takes place ; the ammonia 

 and carbonic acid combining to form carbonate of ammonia, 

 and the lime and sulphuric acid forming sulphate of lime. 

 That this action does really take place, is shown by the fact 

 that after the application of sulphate of ammonia to the 

 land the drainage water contains large quantities of sul- 

 phate of lime, and little or no ammonia. 



The carbonate of ammonia thus formed can then be 

 absorbed and fixed by the clay and humus, when it is prac- 

 tically safe from loss by drainage at least, until nitrifica- 

 tion takes place. Brustlein has shown experimentally that 

 without the presence of carbonate of lime, absorption of 

 ammonia does not take place when it is applied in the form, 

 of sulphate, or any other compound of ammonia except the 

 carbonate. 



The requirements for the absorption of ammonia applied 

 as sulphate may therefore be summarized as : 



i. The presence of enough carbcnate of lime in the soil 

 to convert the sulphate into carbonate of ammonia. 



