372 Dr. W. W. J. Nicol on the Mutual 



which is of the greatest possible interest and importance. In 

 it he not only gives the results and conclusions from his own 

 experiments, but has incorporated the work of all previous 

 experimenters. He worked with a very large number of salts, 

 his experimental skill and accuracy are of the highest order, 

 and, as a rule, his results are completely to be depended on, 

 not by any means a common thing in researches on solution. 

 I need not therefore apologize for devoting some considerable 

 space to an examination of his results. 



Mulder states, as the results of his experiments, that he 

 knows of no better classification of salts, so far as their 

 mutual solubility is concerned, than into the three following 

 divisions : — 



(1) Salts the amounts of which in a saturated solution are 

 dependent entirely on the nature of the solid salts. 



(2) Salts the saturated solutions of which are dependent on 

 the affinity of the respective salts for water. 



(3) Salts which resemble those in both of the foregoing 



classes, and consequently behave now in one way and 

 now in another according to the amount of either salt 

 present. 



(1) Solutions of salts belonging to this class contain, when 

 saturated, according to Mulder, the constituent salts in simple 

 equivalent proportions, and the saturated solution has the 

 same composition whether it is prepared by adding salt A to 

 a saturated solution of B, or vice verm, or by adding both salts 

 in excess to water. 



(2) This second class of salts is divided into two sub- 

 classes : — 



(a) The solubility is dependent on that of one of the salts. 

 In this case we have to deal, according to Mulder, with 



double salts in solution, one of the constituents of which be- 

 haves as if it were the only salt present, dissolving in the 

 water as if it were alone and yet permitting of the solution of 

 a quantity of the other salt, with the result that the salts are 

 present in a simple molecular proportion. 



(b) The solubility is dependent on that of both salts. 



We have here the remarkable fact that in a saturated 

 solution of one salt another may be dissolved, and that to the 

 same extent as in pure water, while the solubility of the first 

 salt also remains unaffected. In this case also the salts are 

 present in simple molecular proportions. 



Mulder lays great stress on the existence of this simple 



molecular relation between the salts present in a saturated 



solution, and sees in it clear proof of the existence of double 



' salts in solution and of the chemical nature of solution in 



