Solubility of Salts in Water. 371 



were not present, and this last dissolves in the solution of the 

 first in proportions which cannot be determined a priori." 



Kopp found some exceptions to this rule, but believed that 

 in these cases double salts were formed which were capable 

 of existence only in solution, being decomposed on removal 

 of the solvent ; and pointed out that in this respect as in many 

 others sodium behaves quite differently from potassium. 



This second law of Kopp breaks down completely when 

 extended to any large number of salts, as will be seen by an 

 examination of the Table of results of other experimenters 

 given by me in a previous paper*. 



Next in order of time come the experiments of Karsten f , 

 who performed numerous experiments on this subject and 

 arrived at the following conclusions with regard to the mutual 

 solubility of salts in the restricted sense mentioned above. 



1. The salt A precipitates a portion of the salt B from its 

 saturated solution, but this is also conversely true, so that 

 for any given temperature the proportions of A and B are 

 constant. This Karsten calls " Die Auflosung mit wechsel- 

 sei tiger Absonderung." 



2. The salt A precipitates a portion of B from its saturated 

 solution until the quantity dissolved of A is the same as in 

 a saturated solution of that salt alone ; on the contrary, the 

 addition of B does not precipitate A from its saturated 

 solution. "Die Auflosung mit einseitiger Absonderung" 

 (Kopp^s second Rule). 



3. The salt A dissolves in the saturated solution of B, and 

 the salt B in the saturated solution of A, and no precipitation 

 takes place. " Die Auflosung ohne Absonderung." With the 

 salts belonging to this class, three different saturated solutions 

 exist, formed as follows : — 



(a) Excess of A added to saturated solution of B. 



(b) Excess of B added to saturated solution of A. 



(c) Excess of A and B added to water. 



The somewhat cumbrous classification of Karsten resolves 

 itself on reflection into : — 



(1) The solubility of both salts is diminished. 



(2) The solubility of one salt is unaffected, that of the other 

 diminished. 



(3) The solubility of both salts is increased. 



The next important researches on this subject are those of 

 Mulder J, who in 1864 published a monograph on solution 



* Phil. Mag. 1884, xvii. p. 537. 

 t Ann. der Chem. und Pliarm. xl. p. 197. 



\ Bijdragen tot de Geschiedenis van het Scheikimdig gebonden Water t 

 Rotterdam, 1864. 



2E2 



