150 



silicates, and liberating the alkalis and other mine- 

 ral food constituents from their unassimilable com- 

 binations, and converting them into available 

 plant-food ; thirdly, its decomposing rapidly any 

 inert organic substances which may be present ; 

 and fourthly, in its neutralizing all acids or other 

 compounds injurious to healthy vegetation. 



