102 MANUFACTURE OF FERTILIZING -MATERIALS 



(muriate of potash) the crude salt treated consists 

 of a mixture of all the salts as mentioned on previ- 

 ous page. However, carnallite predominates; it 

 forms 50 to 60 per cent of the crude salt, equal 

 to a potassium chloride content of 13 to 17 per 

 cent. The processes now used in the treatment 

 of the crude salt in the manufacture of more 

 pure potash salts (potassium chloride) are based 

 essentially on the property of carnallite to .de- 

 compose in presence of water into potassium 

 chloride and magnesium chloride; it is therefore 

 dissolved and potassium chloride separated from 

 the solution by crystallization. The process is 

 in itself very simple; what complicates it is the 

 presence of quite a series of foreign salts accom- 

 panying the carnallite, the most important of 

 which are rock salt (NaCl), in the proportion 

 of 20 to 25 per cent, and kieserite, which forms 

 15 to 20 per cent of the crude salt. Other minerals, 

 such as kainit, polyhalite, tachydrite, are rarely 

 met with in large proportion; but they then 

 are very troublesome in the process. 



As the mines deliver the crude salt in big 

 lumps, which were at first delivered ground, 

 they must be crushed before treating. Formerly 

 they were satisfied with crushing lumps by blows 

 from a mallet with a long handle, but now all 

 factories have installed mechanical crushers for 

 the purpose; the machine most used is the jaw- 

 breaker crusher already described. 



The salt is then fed into a pan, in which it 



