Burning the Weeds 



ash is left, which contains the mineral sub- 

 stances existing in the plants. These sub- 

 stances are not affected by combustion 

 because of their power of resistance. The 

 most remarkable of these is potash. All 

 these substances, which formed part of the 

 plants that were burnt, are evidently suitable 

 for assisting in the growth of new plants. 

 The ashes of the weeds that have been des- 

 troyed will be of great use to the plants that 

 will be cultivated by man in the ground that 

 has been burnt. But we may not profit by 

 everything contained in the weeds : all that 

 escapes in smoke is so much loss. The clay 

 burnt in the slabs of turf renders another 

 service in this way. Becoming porous by 

 combustion, it is able to absorb and retain the 

 gases produced by the burning and so far to 

 mitigate the loss. But if there is no clay in 

 the ground the burning is injurious, and it is 

 better to bury the weeds, which will turn into 

 humus, instead of their being dispersed in 

 the air in smoke. 



Ashes are also used as manure, though 

 not often at once, because potash, a very 

 valuable substance, is extracted from them 

 for industrial purposes. After this process 

 t he ashes are called buck-ashes. They contain 



235 



