THEORY OF DEPOSITION OF POTASH SALTS 509 



ing in their pure state, to the formulae 2CaSO 4 .MgSO 4 .K 2 SO 4 . 

 2H 2 O. These deposits are found in alternate layers, having been 

 intermingled with rock salt which diminishes in quantity as the 

 deposits approach the surface. Above these calcium minerals are 

 found other layers in which magnesium plays the principal part, 

 consisting of kieserit MgSO 4 .H 2 O, and carnallit MgCL.KCl. 

 6H 2 O. These may be regarded as the primary or original de- 

 posits. By the action of water of a less degree of concentration 

 these primary deposits have been changed, in some instances, to 

 those of a secondary character, thus potassium chlorid has evi- 

 dently been derived by the action of water upon carnallit and 

 kainit. MgSO 4 .KC1.3H 2 O is evidently derived from carnallit and 

 kieserit. 



A study of these deposits both from the theoretic and practical 

 point of view has been made by van't Hoff in which all the prob- 

 lems of a theoretic character relative to the depositions of these 

 compounds are elaborated. 8 



Van't HofT calls attention to the fact that in considering the 

 natural depositions of salts of this kind, a commonly accepted 

 principle; namely, that the least soluble salts in a mixture of 

 this kind are the first deposited, is not necessarily correct. 9 It is 

 true that if the formation be considered as a whole, the deposits 

 which take place naturally must be in harmony with the commonly 

 accepted principle above stated, and, therefore, that a slightly solu- 

 ble calcium salt would first appear and afterwards the combina- 

 tion of such a salt with more soluble sul fates, then the easily 

 soluble magnesium sulfates, and finally comes the very soluble car- 

 nallit. This principle, however, assumes that all the substances are 

 present in a saturated solution. It is easy to imagine, however, 

 that such would not be the case and that a more difficultly solu- 

 ble salt being present in small quantities would not, perhaps, be 

 precipitated as quickly as a more easily soluble salt present in a 

 saturated solution at the temperature of observation. Therefore, 

 it would be quite impossible that there should be a solution so rich 

 in magnesium sulfate, as van't Hoff states, and so poor in gypsum 



8 Zur Bildung der ozeanischen Salzablagerungen, 1905. 



9 Physical Chemistry in the Service of the Sciences, 1903 : 97. 



