152 SOILS AND MANUBES 



corresponding compounds of hydrogen are formed, together 

 with some other substances of more complex composition. 

 Similar changes are produced in the soil by the action 

 of micro-organisms. The changes take place more slowly 

 and pass through numerous intermediate stages, but the 

 ultimate result is much the same. In the presence of 

 oxygen all the elements including nitrogen are converted 

 into oxides 



C0 2 ; H 2 0; S0 3 ; N 2 5 



In the absence of oxygen the corresponding compounds 

 of hydrogen 



CH 4 ; OH 2 ; SH 2 ; NH 3 



are produced. The acid oxides S0 3 and N 2 5 combine with 

 bases to form sulphates and nitrates. The process by 

 which they are formed is called nitrification. Slow decom- 

 position in the absence of oxygen is called putrefaction. 

 Strong, disgusting odours are generally evolved, especially 

 if much animal matter is present. 



Artificial Production of Nitrates. Potassium nitrate was 

 artificially produced from nitrogenous organic matter long 

 before it was known that the process of nitrification was 

 due to the action of micro-organisms. Waste organic 

 matter of all kinds the richer in nitrogen the better was 

 mixed with earth and lime and moistened with liquid 

 manure to promote fermentation. After the lapse of a 

 considerable time the heap was lixiviated with water to 

 dissolve out the calcium nitrate which had been formed, 

 and potassium carbonate was added to the solution. These 

 two substances react upon each other, producing calcium 

 carbonate and potassium nitrate thus 



Ca(N0 3 ) 2 + K 2 C0 8 = CaC0 3 + 2 KN0 3 



Calcium Potassium Calcium Potassium 

 nitrate. carbonate, carbonate. nitrate. 



