POTASSIUM SULFATE 5OI 



occurring naturally is very small, and, therefore, it has no com- 

 mercial importance. When, however, kainit is washed with water 

 the common salt and magnesium chlorid which it contains being 

 more soluble, are the first leached out, and the residue has ap- 

 proximately the composition of the pure mineral. This mixture, 

 as prepared in the way mentioned above, has the following aver- 

 age composition: 



Per cent. 



Potassium sulfate 50.40 



Magnesium sulfate 34.00 



Sodium chlorid 2.50 



Water 11.60 



The percentage of potash corresponding to the above compo- 

 sition is 27.2. This substance being so rich in potash, and prac- 

 tically free of chlorids, is well suited to transportation to great 

 distances and for general use in the field. Since, however, a 

 considerable expense attends the manufacture of the artificial 

 schonit, the advantages above named give it very little, if any, 

 advantage in competition with the other potash salts, as they 

 come from the mines. It has, however, an especial value for the 

 fertilization of tobacco and vines. 



430. Potassium Sulfate. Several grades of potassium sulfate 

 are found in the market for fertilizing purposes, some of them 

 quite pure, containing over 97 per cent, of the pure sulfate. The 

 following data show the composition of a high grade and low 

 grade potassium sulfate of commerce : 



High grade. Low grade. 

 Per cent. Per cent. 



Potassium sulfate 97-2O 90.60 



Potassium chlorid 0.30 1.60 



Magnesium sulfate 0.70 2.70 



Magnesium chlorid 0.40 1 .00 



Sodium chlorid 0.20 1.20 



Insoluble 0.20 0.30 



Water 0.70 2.20 



Naturally, high grade sulfates of this kind can only be pre- 

 pared in chemical factories built especially for the work. The 

 result is that the potash per unit is raised greatly in price. When, 

 however, the fertilizers are to be transported to a great distance, 



