28 
Proceedings of the Eoyal Society 
the adhesion of the liquid to the salt ; and, conversely, diminished 
solubility with rise of temperature is due to the cohesion being less 
affected by rise of temperature than the adhesion. 
Evidence in support of the above is obtained from experiments 
on the following physical properties of salt solutions - 
Contraction on dilution.* 
Coefficients of expansion.! 
Molecular volumes. J 
Boiling points. § 
Saturation point. || 
Further, the solution of two salts in water is governed by the 
same laws as that of a single salt (when no double decomposition is 
possible) : the solubility of both salts being increased in most 
instances.1T When double decomposition is possible, then the 
amount and nature of it is conditioned by the solubility of the 
possible salts and the strength of the solution.** 
The molecular volume of a salt in solution is a quantity made up 
of two constants , one for the metal, and another for the acid-radical. 
It follows from this, that the replacement of one metal by another 
in combination with an acid-radical is always attended by the same 
change in the molecular volume of the solution, or generally, 
(M - M')R = C' 
M(R-R') = C\ 
where M and M' are two different metals and B and R" two acid- 
radicals. ff 
The presence or absence of water of crystallisation has no effect 
on the above law : it therefore follows that it has the same volume 
in solution as the solvent water. Water of constitution, however, 
shows itself in solution by possessing a volume markedly different 
from water of solution. H 
Finally, when the molecular volumes of a series of solutions of 
* Phil. Mag., February 1883 ; Chem. Soc. Journal , March 1883. 
+ Phil. Mag., February 1883. + Ibid. 
§ Ibid. II Ibid. 
TI Phil. Mag., June 1884. ** Ibid. 
ft Berichte de deut. Chem. Ges., 1884. 
Log. cit., also Phil. Mag., September 1884. 
