second or zeolitic class of silicates. This process, how- 

 ever, is too slow to be relied upon as an immediate 

 source of plant food. 



In the following table are given the percentage 

 amounts of compounds soluble and insoluble in hydro- 

 chloric acid for a few typical soils : 9 



The insoluble matter, after digestion with hydro- 

 chloric acid, was submitted to fusion analysis, and the 

 figures given under insoluble residue represent the 

 amounts of potash, sqda, etc., insoluble in the acid. In 

 the clay soil, 94 per cent of the total potash was in 

 forms insoluble in hydrochloric acid. 



99. Soluble and Insoluble Potash and Phosphoric Acid. 

 From the preceding table it is to be observed that 



