DISCUSSION OF EVIDENCE. 161 



EFFECT OF ONE SALT WITH HYDRATING POWER ON THE HYDRATES FORMED 

 BY A SECOND SALT IN THE SAME SOLUTION. 



The effect of adding a salt with strong hydrating power to a solution 

 of another strongly hydrated salt was worked out by Jones and Stine. 1 

 The effect of adding a salt with small hydrating power was also investi- 

 gated. The following pairs of salts were studied : Calcium chloride and 

 potassium chloride; magnesium chloride and calcium chloride; stron- 

 tium chloride and calcium chloride; strontium nitrate and magnesium 

 nitrate; calcium nitrate and magnesium nitrate; aluminium chloride 

 and ferric chloride; calcium chloride and calcium nitrate; lithium 

 bromide and sodium bromide, and ammonium chloride and potassium 

 chloride, as examples of only slightly hydrated salts. 



A large variety of types of salts was used. The first pair contains a 

 binary and a ternary electrolyte with a common anion; the one (calcium 

 chloride) strongly hydrated, the other (potassium chloride) only slightly 

 hydrated. The next four pairs are all ternary electrolytes and are all 

 strongly hydrated salts. 



Aluminium chloride and ferric chloride are quaternary electrolytes 

 and strongly hydrated. The two calcium salts contain a common 

 cation and both are strongly hydrated. The two bromides contain a 

 common anion and are not strongly hydrated, while the chlorides of 

 ammonium and potassium are very weakly hydrated compounds. 



The problem was obviously a complicated one. It was not a 

 simple matter to calculate the composition of the hydrates formed by 

 any one substance when present alone in the solution. It became far 

 more complex and difficult to calculate the composition of the hydrates 

 formed when two hydrating substances were present simultaneously 

 in the solution. We believe, however, that this problem was solved 

 at least approximately. It was found that the amount of combined 

 water increases with increase in concentration in the mixed, as in the 

 separate solutions; the total amount combined with the calcium 

 chloride being less when the potassium chloride was present. The 

 difference between the amount of water combined with the calcium 

 chloride when alone and when potassium chloride is present increases 

 with the concentrations of the two constituents of the mixture. 



We found in general that when two hydrated salts were mixed, each 

 dehydrated the other to an amount that seemed to be controlled by 

 mass action. In order that this law should hold, it would seem that 

 the calculated composition of the hydrates formed by the individual 

 substances must be approximately correct. 



It was early found that both ions and molecules can form hydrates. 

 That the molecules of certain substances have hydrating power, was 

 shown by the fact that certain non-electrolytes undoubtedly combine 

 with water in aqueous solution. Ions were, as a class, found to have 



2 Amer. Chem. Journ., 39, 313 (1908). 



