306 CHEMICAL MANUEES. 



When the shaft revolves the blades turn up the salt, and the roller 

 which follows makes them into a cake again, so that the surfaces are 

 coQtinually renewed. When the dryiog is finished the salt is run out 

 through a shoot and bagged up. In a general way factories which 

 work according to the processes described above are content with 

 producing 80 per cent potassium chloride ; they rarely push the 

 clarifications so far as to make 97 to 98 per cent products, although 

 the potassium chlorides dissolved by the clarification can be re- 

 covered immediately in the crystallizers, whilst the mother liquor 

 is used to dissolve the crude salt. To obtain 98 per cent salt without 

 effort, the method of dissolving the raw salt is altered. The mother 

 liquor, the small amount of clarifying liquor and finally the liquor 

 used to boil the residual salt, are alone used as solvent ; all addition 

 of water is avoided. After having brought the solvent solution in 

 the pan to the boil, the raw salt is run in as before and the whole 

 boiled without interruption until the solution tests 35 to 36" B. At 

 that density the carnallite in the crude salt easily dissolves if the 

 liquid be hot enough, i.e. if the steam be of sufficient tension. 

 Certain factories insert an agitator whose action contributes to mix 

 the solution, consequently to obtain a better result from the crude 

 salt. Nevertheless, the residue is sometimes still rich in potassium 

 chloride ; it is boiled a second time with pure mother liquor. The 

 solution so obtained is clarified in the same way as in the first 

 method ; on cooling it deposits not potassium chloride but carnallite, 

 which is allowed to drain and then dissolved in boiling w^ater to ex- 

 tract the potassium chloride. As common salt as well as kieserite 

 only dissolves slightly w^hen hot in a concentrated solution of magne- 

 sium chloride, whilst potassium chloride is very soluble therein, it 

 is clear that the solution prepared by this process should contain very 

 little common salt, and also that the carnallite which crystallizes 

 therein should contain very little, and the chloride of potassium 

 furnished by the latter should be of high strength. This method, 

 however, has the draw^back of yielding a large amount of carnallite, 

 the removal and solution of which require much labour and steam 

 and consequently fuel. This drawback is obviated by diluting the 

 solution which flows from the clarification vats with water, so that 

 after complete cooling it yields chloride of potassium of high strength 

 directly, and no longer carnallite. In this way the crystallization 

 and solution of carnallite are conducted in a single operation. The 

 advantages of this method of working are evident. Instead of treating 

 as before two different solutions and two different salts, only a 

 single solution and a single salt have now to be treated. The 

 potassium chloride so produced is so pure that when it is freed from 

 magnesium chloride by a little water it only contains 0*5 per cent 

 of common salt, all the rest is potassium chloride with a little 

 moisture and some slight impurities. 



