304: 



CHEMICAL MANUEES. 



Clarifying. — As potassium chloride of 60 to 70 per cent strength 

 is hardly marketable, it is necessary to submit it to new treatment 

 — darification. For this purpose it is run into vats termed clarifying 

 vats, fitted \\^th a double bottom covered by cloth or with a network 

 of osiers. It is covered with water, so that the water is 2 to 3 

 centimetres above that of the salt, and left in contact 5 to 6 hours ; 

 then the clarified solution III is run off through a bung- hole in the 

 bottom of the vat. This liquid runs into a special basin, from which 

 it is run into the dissolving pans by a pump. The liquid from 

 the above clarification of 30^ B. contains : — 



TABLE CIL— ANALYSIS OF MOTHER LIQUOR FROM CLARIFICATION 



OF POTASH SALTS. 



100-000 



If the potassium chloride be not sufficiently enriched by a single 

 clarification, this operation is repeated once or twice until the salt 

 contains at least 80 per cent of dry potassium chloride. The 

 above clarifying liquor constitutes a saturated solution. Now a solu- 

 tion of this nature contains at lo"" C. 25 per cent KCl 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 of the above analysis, it will be seen that the magnesium 

 chloride interferes with the solution of both the potassium chloride and 

 with the common salt. Now as the object of clarification is precisely 

 to eliminate this latter, it follows that a potassium salt with low 

 magnesium chloride content, consequently large -grained, will be 

 more easy to purify in this way than a salt with high magnesium 

 chloride content, fine-grained crystals. But clarification is a costly 

 operation because its object is to redissolve a portion of the finished 

 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 analysed 

 above, an 80 per cent product would be obtained by a single 

 clarification, whilst a fine-grained 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. 



Treatment of the Mother Liquor from the Potassium Chloride. — 

 The mother liquor not used for dissolving is concentrated by evapora- 

 tion, for it still contains an important amount of potassium chloride. 

 It has a densitv of about 32" B., and contains : — 



