2. The presence of clay or humus to absorb the carbonate 

 of ammonia thus formed. 



It must not be understood that these actions are imme- 

 diate or complete. It is a common mistake, and one which 

 leads to a good deal of confusion of idea, that chemical 

 action takes place as readily and completely in the soil as in 

 the beakers and test-tubes of the chemist's laboratory. It 

 is really quite otherwise ; and in the case we are considering, 

 some sulphate of ammonia may remain unchanged for along 

 time, though the supply of carbonate of lime is plentiful. As 

 this sulphate sinks lower and lower in the soil, most of it is 

 gradually converted into carbonate, and is then fixed; but 

 probably many other actions take place, though generally 

 on a small scale and with quite unimportant results. 



POSSIBLE Loss OF AMMONIA WHEN APPLIED AS SULPHATE. 



Carbonate of ammonia which results from the interaction 

 of sulphate of ammonia and carbonate of lime is a very 

 volatile substance that is, when exposed to the air, it 

 gradually disappears in a state of vapour, unless previously 

 fixed by the clay or humus of. the soil. It has, therefore, 

 been suggested that, on light calcareous soils i.e., those 

 rich in carbonate of lime, and deficient in clay and humus 

 serious loss of nitrogen must take place, owing to the rapid 

 formation of carbonate of ammonia, and the want of enough 

 absorbent material in the soil to save it from volatilization. 

 The amount of this loss, however, has been probably ex- 

 aggerated, and is hardly appreciable, except in cases where 

 the land is particularly rich in carbonate of lime. Even 

 then, according to Pechard,* the loss is prevented if 

 sulphate of lime is present ; for this tends to convert the 

 ammonia in the soil into sulphate of ammonia. As to 

 what occurs under ordinary conditions, Muntz found 

 in an experiment on a light soil, containing 2 per cent. 

 of lime, that the ammonia given off into the air was 

 only at the rate of 8f grains (0-56 gram) per acre per 

 day, during the first five days after a dressing of sulphate 

 of ammonia at the rate of 4 cwt. per acre a heavy dressing. 

 Where farmyard manure was employed, the amount of 

 ammonia lost in the same time was 25 grains per acre per 

 day. These quantities are so small that they may be safely 

 neglected in practice, especially as we may assume that the 

 amount of ammonia given off into the air would be greatest 

 during the first few days after the manure was applied at 

 any rate in the case of sulphate of ammonia. Other experi- 

 ments with a variety of soils have shown even less loss of 

 ammonia. 



* " Comptes Rendus," 109. 



