3IO PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Kainit, correctly speaking, is a mineral composed of sulphate 

 of potash and magnesia, K 2 SO 4 , MgSO 4 , MgCl 2 , 6H 2 O. The 

 term is also used for crude potash salts containing not less than 

 12.4 per cent, potash, which may be crude kainit or mixtures of 

 other crude salts. Since kainit is prepared from crude salts, no 

 expense of manufacturing is attached to it. On the other hand, 

 freight per unit of potash is higher than for the more 

 concentrated potash salts. At a distance from the mines, 

 the freight cost is greater than the manufacturing cost, 

 so that the concentrated salts are cheaper. Since kainit contains 

 chlorides, it is not suitable for use on tobacco or potatoes. Kainit 

 is used as a preservative in saving stable manure, to check attacks 

 of injurious insects, and as a remedy against cotton rust. 



Muriate of potash is a concentrated potash salt prepared from 

 the crude potash minerals by solution and crystallization. Various 

 grades are prepared, ranging from 70 to 98 per cent, muriate of 

 potash equivalent to 46.7 to 62 per cent, potash (K 2 O). 



Sulphate of potash is prepared by reaction between the muriate 

 of potash and. sulphate of magnesia, also found in the potash 

 mines. The two are mixed in solution, and the sulphate of 

 potash, being less soluble, separates out. Various grades are 

 prepared, containing 45 to 53 per cent, potash (K 2 O). 

 2KC1 + MgSO 4 = K 2 SO 4 + MgCL, 



Double Manure Salts. This is an impure sulphate of potash 

 containing about 30 per cent, potash. It contains considerable 

 amounts of sulphate of magnesia. 



Forms of Potash. The compounds of potash used in fer- 

 tilizers are all soluble in water, and there is practically little differ- 

 ence in their availability. Some forms are, however, better 

 adapted to some crops than others. Fertilizers free from 

 chlorides are desirable for potatoes and tobacco, since chlorides 

 make the potato less mealy and injure the burning quality of the 

 tobacco. 



Miscellaneous Fertilizing Materials. The analyses of some mis- 

 cellaneous fertilizing materials are given in the table. Most of 



