108 MANUFACTURE OF FERTILIZING MATERIALS 



nature contains at 15 C. 25 per cent KC1 when 

 it is prepared from pure potassium chloride, 

 27 per cent NaCl when it is made from common 

 salt. If these figures be compared with those 

 above, it will be seen that the magnesium chlo- 

 ride interferes with the solution of both the 

 potassium chloride and the common salt. Now 

 as the object of clarification is precisely to elim- 

 inate this latter, it follows that a potassium salt 

 with low magnesium chloride content, conse- 

 quently large-grained, will be more easy to 

 purify in this way than a salt with high mag- 

 nesium chloride content, fine-grained crystals. 

 But clarification is a costly operation because 

 its object is to redissolve a portion of the fin- 

 ished salt, therefore to work economically it 

 must be done in such a way as to clarify as 

 little as possible, that is to say, to produce large- 

 grained crystals as far as possible. Starting 

 from the salt an 80 per cent product would be 

 obtained by a single clarification, while a fine- 

 grain salt often requires two, sometimes three, 

 clarifications to get a product of the same strength. 

 It is clear that by this operation 95 per cent 

 products and higher may be obtained. 



The mother liquor not used for dissolving 

 is concentrated by evaporation, for it still contains 

 an important amount of potassium chloride. 

 In the evaporation the greater part of the com- 

 mon salt separates out, because it is less sol- 

 uble when hot than when cold, at the same 



