Plant Food in the Soil 95 



potash, and is also found as a sulphate and as a carbonate, 

 in all of which forms it is readily used by plants. 



One of the most commonly used forms of the crude 

 potash salt is what is known as kainit. Though the pot- 

 ash in kainit is a sulphate of potash it is associated with so 

 large a percentage of chlorine that its action is rather that 

 of a chloride than of a sulphate, and for this reason has 

 been found detrimental to some crops such as tobacco, 

 for which only a pure sulphate should be used. More- 

 over, the expense of freighting a crude salt like kainit, 

 which has but about 12 per cent, of potash, is so great 

 that it is not now so much used as the manufactured and 

 concentrated form called the muriate of potash or chloride. 

 In this concentrated form there is an average of 50 per 

 cent, of actual potash. A very high grade may contain 

 more than 50 per cent. 



The high-grade sulphate of potash is also a manufac- 

 tured article which usually has a httle more actual potash 

 than the muriate and in a better form for crops hke tobacco, 

 Irish potatoes, and crops in which sugar is an important 

 ingredient. Another refined article is what is known as 

 the double manure salt or sulphate of potash and mag- 

 nesia. It has not over one-half the amount of potash 

 that is contained in the high-grade sulphate, and the pot- 

 ash costs more in this form. In the same manner as with 

 phosphoric acid, the soil will absorb and retain potash 

 even to a greater extent than it will phosphoric acid, since 

 it is largely left in the roots, while the phosphoric acid is 

 concerned in the ripening of the grain. Still another 

 source of potash, which has come into use of late years, 

 is the waste stems of tobacco and the tobacco dust from 



