ARTIFICIAL AND CONCENTRATED MANURES. 99 



upon yield is not believed to be superior to the muriate. 

 Commercial forms of sulphate of potash contain on the 

 average fifty per cent of actual potash. 



Double Sulphate of Potash and Magnesia. This 

 product is similar to the high-grade sulphate in its 

 effect. It contains, in addition to the sulphate of pot- 

 ash, over thirty per cent of sulphate of magnesia. The 

 potash contained in the product, as usually found, is 

 equivalent to about twenty-six per cent of actual pot- 

 ash, though lower grades are made. These are known 

 under the name of "double manure salts." The mag- 

 nesia is regarded as of considerable value, particularly 

 in potato manures. The cost of potash in the double 

 sulphate is also greater than in the muriate. 



Appearance of Potash Salts. Although all these 

 products exist in the form of salts, they differ in appear- 

 ance and character. The sulphates are usually in the 

 form of a fine powder, in color ranging from nearly white 

 to a dirty gray. The muriate is in the form of small, 

 though distinct crystals, varying in color from grayish 

 white to light brown. The kainit is composed of crys- 

 tals, varying in color from white to dark gray, giv- 

 ing the ground salt a rather pepper-and-salt appearance. 

 Upon standing, all of these salts have a tendency to 

 become hard, though, with the exception of kainit, they 

 are easily pulverized. Kainit often becomes very hard, 

 and requires regrinding in order to make its application 

 possible. 



The Uses of Potash Salts. Although these salts 

 are regarded mainly as sources of potash to the manure 

 manufacturer, their direct use upon the land is increasing 



