ON SOLUBILITY. 461 



consequently the excess of those ' ions ' separate from solution in 

 union with the requisite number of oppositely charged ' ions.' He 

 also introduced the conception of a ' solubility product ' (vide Section 

 V. C (iii), (1889). 

 ft A communication by Riecke 17i on the thermal potential for 



' dilute solutions furnished results which are in agreement with 

 experimental data for the distribution of a substance between two 

 solvents and also for the diminution of solubility of a substance when a 

 second substance is added. These results were arrived at mathemati- 

 cally from an application of Gibb's equation to dilute solutions. 



Masson 175 discussed the analogy between the dissolution of a solid 

 and the vaporisation of a volatile substance; he mentioned, among other 

 points, that, when regarding these phenomena as related, it becomes 

 necessary that there should be some relationship between the true 

 melting-point of salts and the rates of increased solubility with the 

 temperature; further, 178 substances should exhibit an infinite solubility. 

 The former having been generally established by Tilden and Shenstone, 

 the latter, only in the case of liquids, by Alexejeff. 



In an important communication entitled ' The Solubility of Mixed 

 Crystals, more especially of two Isomorphous Substances,' Rooze- 

 bourn* 1S2 considered the question of solubility with the object of throw- 

 ing light on the analogy between solid and liquid solutions. He 

 adversely criticised Duhem's explanation of the behaviour of iso- 

 morphous salt pairs based on Gibb's Phase Eule, and from measure- 

 ments of the solubility of the mixed crystals of the isomorphous salts, 

 potassium chlorate and thallium chlorate, he expressed views 183 as to 

 the limitations of Nernst's law of the relative lowering of solubility. 



These limitations were not acceptable to Nernst, 188 as is 

 " seen from his communication entitled ' The Solubility of Mixed 

 Crystals.' 



Pickering 189 published evidence to show that a substance in solution 

 was in a condition different from that of a gas (vide Section V. A (ii) ). 



The change in the internal friction of the solvent was considered by 

 Winkler 190 to be the real cause of the decrease in the absorption powei 

 of liquids for gases as the temperature was raised. 



Etard 186 concluded from his work on the solubility of mercuric 

 chloride and cupric chloride in various organic solvents, that union takes 

 place between salt and solvent. In some cases, for example, with 

 cupric chloride and methylic alcohol, he was able to isolate the complex 

 that is formed. 



Some interesting results were published by Noyes 195 which revealed 

 considerable imperfections in the ' ionic ' conception as advanced by 

 Nernst. 1 * 4 The assumption was made that thallous chloride is disso- 

 ciated to the same degree as the chlorides of the alkali metals at the 

 same concentration, and the dissociation of potassium chloride was 

 calculated from solubility measurements. The results thus obtained dif- 

 fered greatly from the values found from measurements of conductivity. 



Etard 20 ° investigated the solubility of hydrocarbons in organic 

 liquids at low temperatures, and was led to regard the melting-point of 

 the solute as the superior limit of solubility and the melting-point of the 



1910. h ii 



