THEORY OF DEPOSITION OF POTASH SALTS 517 



EQPNMLA Potassium chlorid 



EQRF Carnallit 



FRGB Magnesium chlorid 



RGHPQ MgS0 4 .6H 2 



PHCJN MgS0 4 .7H,0 



JKMN Schonit 



KMLD Potassium sulfate 



The progress of crystallization is given in each area by lines 

 which proceed away from the points which represent saturation 

 with the body itself, as a single constituent. Thus in the potas- 

 sium chlorid area, these lines proceed from A in all directions." 



In the application of a theory of this kind to a solution con- 

 taining a gram molecule of magnesium chlorid and a gram mole- 

 cule of potassium sulfate the preliminary evaporation before the 

 appearance of any deposit corresponds to motion from the origin 

 in the vertical direction, until the area line immediately above it, 

 that is, the potassium sulfate area is reached. In this condition, 

 the potassium sulfate should separate theoretically, and in fact, 

 this phenomenon actually occurs. Theoretically, the next move- 

 ment would begin at D and move away from D until the limit KM 

 is encountered and at this point the separation of schonit would 

 begin. The actual experimental data in this case also correspond 

 with the theory. If the salts, as they separate, are continuous- 

 ly removed, the deposit of schonit continues as indicated 

 in the figure until the limit MX is reached at which point, theo- 

 retically a crystallization of potassium chlorid should take place. 

 This theory is also corroborated by the experimental data. 



When the point N is reached on the line MN, theoretically 

 magnesium sulfate begins to be deposited. By consulting the 

 table of the letters at the different points in order to understand 

 just what they represent, the progress of crystallization can be 

 followed theoretically until the complete deposit of the salts takes 

 place. Thus, the figure, as worked out in detail, furnishes a 

 means of comprehending the process of crystallization of these 

 mixed salts, and, theoretically, of predicting in a very certain 

 manner, the entire change which takes place. 



In a similar manner, van't Hoff has worked out the influence 

 of time and the variations of temperature and pressure on the 



