174 



MR J. Y. BUCHANAN ON THE 



§ 93. Solubility. — The molecular solubility of each of these salts, that is, its solu- 

 bility expressed in gram-molecules salt per thousand grams of water at 19'5° C, is : — 



Salt. 



RbCl. 



^01 + 1 

 ^ 2 • 



KBr. 



Molecular weight . . 

 Gram-molecules in 1000 grams water . 



121 



7-77 



120-35 



5-83 



119-1 

 5-7 



The discussion will, however, be confined to the relation of solutions of these salts 

 which contain, per thousand grams of water, 5 or a smaller number of gram-molecules 

 of salt. 



Considering the change of specific gravity over a range of concentration varying 

 from 5 to 1 gram-molecules per thousand grams of water, that of rubidium chloride 

 varies from i-351760 to r083782, that of the potassium salt of the mixed halides 

 from 1-336904 to 1-080182, and that of potassium bromide from 1-343255 to 

 1*081211. Although potassium bromide has the lowest molecular weight, there is a 

 closer agreement in the specific gravity of the solutions of this salt with those of 

 rubidium chloride than with those of the potassium salt of the mixed halides. At the 

 same time the nature of the change of values with change in concentration of solution, 

 as indicated by the numbers representing the difi'erences of consecutive specific gravities 

 given in the column d^/dm of the tables, shows that in this respect the potassium salts 

 exhibit a closer relationship among themselves than either of them does with rubidium 

 chloride. Also the nature of the decrease in this value with increasing concentration 

 seems to indicate the fact that the increase in specific gravity becomes more nearly 

 proportional to the increase in concentration in the strongest solutions. 



It will be observed that the actual weight of each salt per thousand grams of 

 water in each solution is slightly diff'erent, and if the specific nature of the salts were 

 the same in each of these solutions, and the masses of them present in the solution 

 were equal, as their molecular weights would in that case be, the specific gravities of 

 these solutions and the constants derived from them would be dift'erent from those in 

 table § 92. 



§ 94. For comparison in this sense the specific gravities have been adjusted to the 

 value which they would have if their gram-molecules had the uniform weight 121, 

 which is the actual molecular weight of the heaviest of the three, namely, rubidium 

 chloride. 



The following table gives the specific gravities adjusted in this sense :— 



1 



Multiples of 121 grams of Salt per 1000 grams Water . 



5. 4. 



1-351760 1-292983 

 1-338724 1-282025 

 1-3487311 1-290140 



1 



3. 



2, 1. 



Observed specilic gravities for solutions of RbCl . 

 Oalculated „ „ „ K „ 

 » » .. >, K:Br . 



1-229284 

 1-220131 

 1-226672 



1-159851 

 1-153815 

 1-157734 



1-083782 

 1-080575 

 1-082507 



