VI.] OTHER SOURCES OF POTASH 163 



soluble and greedy of moisture ; and as both chlorides 

 and magnesium are present in all but the purest grades 

 of sulphate of potash, the salts used for manurial 

 purposes are always somewhat deliquescent. 



These salts constitute practically the only sources of 

 potash for manurial purposes ; wood ashes are a little 

 used occasionally, a small amount of sulphate of potash 

 is derived from kelp, and the ashes which form the final 

 waste product in beet sugar refining are used for the 

 carbonate of potash they contain ; but the whole amount 

 is trifling compared with the increasing output of the 

 Stassfurt mines. 



Attempts have been made from time to time to 

 utilise as fertilisers various minerals which occur in large 

 quantities and contain considerable amounts of potash ; 

 for example, orthoclase felspar, K^AloO^, 6Si02, with 17 

 per cent, of potash, and leucite, KjAlgO^, 2Si02, with 

 22 per cent, of potash. In some cases these minerals 

 have been simply reduced to a very fine powder, in 

 others they have been heated with lime or soda salts 

 in order to bring the potash into a more soluble form. 

 Though the results show that the potash can thus 

 be rendered comparatively available for the plant, 

 the great cheapness of the completely soluble Stassfurt 

 salts has prevented any general adoption of the 

 processes. 



The question of which of these salts it is advisable 

 to apply as a manure has excited a good deal of 

 attention, but cannot be said to have reached any 

 very definite settlement, probably because the problem 

 is complicated by a secondary action of the salts on the 

 texture of the soil, which will be discussed later. But, 

 speaking generally, it may be said that for grass and 

 mangolds, and wherever the salts can be put on in the 

 winter months so as to allow the magnesium chloride 



