POTASSIUM FERTILIZERS 165 



saturation may often prevail for a limited period, but as a 

 rule the vessels and implements used contain the crystals 

 necessary to promote crystallization. Rapid movement 

 with paddles assists the crystallization of super-saturated 

 solutions in the presence of those crystals on which the 

 salts in solution can grow. Many salts, which ordinarily 

 are not expected to form super-saturated solutions, may fai 

 to crystallize until cooled well below the temperature at which 

 separation of solid should occur. By the introduction of 

 small quantities of solid crystals and by rapidly stirring the 

 solidifying mass, time may frequently be saved in many 

 crystallizing operations. Where many miscellaneous salts are 

 present in solution, the purity of the crystals separated out 

 may often be largely improved by obtaining such a thorough 

 mixture of crystal and mother liquor that there is only one 

 substance that will crystallize out; on the other hand, 

 should admixture be very imperfect, there is a much greater 

 probability of one substance crystallizing out in one part of 

 the crystallizing vat, and some other salt crystallizing out 

 in another portion. A finer product, both as regards size of 

 grain and quality, can often be obtained by the methods 

 of " seeding " and agitation. 



The Manufacture of Potassium Chloride. The raw 

 material for the manufacture of potassium chloride is some- 

 times obtained from sylvine, a mixed salt of potassium 

 chloride and sodium chloride. When a saturated solution 

 of sylvine, made at a high temperature, cools down, nothing 

 but potassium chloride crystallizes out. For manufacturing 

 purposes, a solution of sylvine is made at the boiling point, 

 cleared by subsidence, and allowed to crystallize. The 

 crude potassium chloride first obtained can be brought up 

 to 98 % of potassium chloride by washing. From the mother 

 liquor, sodium chloride can be separated out by concentration 

 when sodium chloride crystallizes out near the boiling temper- 

 ature. The mother liquor from this separation, after cooling 

 down again, deposits more potassium chloride. Again, the 

 mother liquor may be used to dissolve fresh sylvine, when, 

 since the solution is already nearly saturated with sodium 

 chloride, potassium chloride alone dissolves. 



