22 THE CHEMISTRY OF THE FARM. 



Burning is occasionally resorted to as a means of in- 

 creasing the available plant food, and improving the 

 texture of a heavy soil. The soil is burnt in heaps, which 

 are then spread over the land. If the soil contains lime- 

 stone it is easy to see that the phosphates of the limestone 

 may become more available by the complete disintegration 

 which attends the conversion into lime. The lime will 

 also attack the silicates of the soil at a high temperature, 

 and liberate a part of the potash from its insoluble com- 

 binations. To produce the best results it is essential that 

 the burning should take place at a low temperature. This 

 treatment by burning is a very extreme one, and can be 

 recommended only in few cases ; it must always be at- 

 tended with an entire loss of the nitrogen in the soil burnt. 

 The ploughing in of burnt clay is of use in improving the 

 texture of heavy land. 



