280 



REPORT — 1901. 



Thus, supposing a solution C to contain 12^ molecules of Sodium 

 sulphate, to express its composition, a point in space is plotted by 

 measuring off from the origin 12^ units along the Magnesium sulphate 

 axis and —12^ units along the Magnesium chloride axis ; i.e., downward 

 and therefore along the Potassium sulphate axis. The point c on the 

 diagram is thus obtained. The corresponding point on the model 

 is deduced by measuring off 12^ on the Sodium chloride axis vertically 

 upwards and adding 51 on account of the 51 molecules of Sodium 

 chloride supposed to be present in the solution as such. 



It will be noticed that Magnesium and Potassium sulphates do not 

 appear in the table as single salts which can be used as equilibrators in 

 presence of excess of Sodium chloride, the reason being that new re- 

 ciprocal salt pairs are constituted by the presence of the Sodium chloride, 

 and interactions take place which destroy these sulphates ; e.g., 



MgSO^ + Na2Cl2=Na2SO, + MgCls- 



Tlie remarkable character of the changes brought about by the 

 presence of Sodium chloride will at once be obvious on contrasting figs. 3 

 and 5. The double salts formed by Magnesium and Potassium sulphates 

 with Sodium sulphate occupy the lower portions of the diagram, 

 Potassium sulphate disappearing altogether, and the area of the Mag- 

 nesium sulphate field being much restricted. Moreover, the greater pull 

 on the water molecules exerted by the soluble Sodium chloride molecules 

 brings about the partial dehydration of several of the compounds 

 appearing in diagram 3 : causing, for example, the displacement of the 

 greater part of the Schonite field by Leonite, MgKo(SO,)2.4H.,0, and of 

 the MgSO , . 6H2O field by Kieserite. In addition, a new double sfilt, 

 Kainite, MgS04.KCl,3H20, appears. 



