THEORY OF DEPOSITION OF POTASH SALTS 515 



thing, that is to say, chlorin and sulfuric acid, potassium and mag- 

 nesium. The experimental treatment of this question may be best 

 shown by means of an example. Let us start from L (Fig. 45), 

 where the solution at 25 is saturated with potassium chlorid and 

 potassium sulfate simultaneously. Taking care that both potas- 

 sium salts are present in excess and in contact with the solution, 

 we add magnesium in the form of chlorid or sulfate. The solu- 

 tion then takes up magnesium but remains still saturated with 

 potassium sulfate and potassium chlorid. Finally its capacity 

 for taking up magnesium becomes exhausted, and a solid mag- 

 nesium salt is deposited. This in the case before us is schonit 

 (K 2 Mg(SO 4 ) 2 .6H,O). After this, further addition of the mag- 

 nesium salt will not lead to any being dissolved ; the consequence 

 will simply be an increase in the amount of schonit. The solu- 

 tion will retain its constant composition, since it is and remains 

 saturated with potassium sulfate and potassium chlorid. We de- 

 termine the composition of this solution by analysis, using a mix- 

 ture which at 25, after prolonged agitation, is seen to be in contact 

 with all the three salts and is found to have attained a constant 

 composition. The result is represented by the following formula : 



ioooH 2 0+25K 2 Cl 2 +iiMgS0 4 +2iMgC! 8 . 



Our task is thus finally limited to finding the solutions satura- 

 ted with three salts and analyzing those solutions. Many such 

 are a priori possible, if we consider the seven different com- 

 pounds which have to be taken into account. The possible num- 

 ber would be : 



7 X6X 5_ 

 1X2X3 



As a matter of fact, however, only a few of these possibilities 

 are realized, and when a solution obtained in the above manner is 

 systematically evaporated at 25, and the salt deposits are con- 

 tinually removed, the possibilities which are actually realized are 

 found to be limited to four, in addition to the one described. 



After potassium chlorid and schonit have come out, magnesium 



