On the intrinsic volumes of ions in aqueous solutions

Various methods that have been proposed in the literature for the estimation of the intrinsic volumes of electrolytes in aqueous solutions are briefly discussed. Most of these depend on the radii of the constituent ions. A method that is independent of the radii but requires a long extrapolation from the temperatures involved in salt melts is also mentioned. A new method is developed here, independent of ionic radii, which employs the partial molar volumes of salts in their concentrated solutions (and is, therefore, limited to highly soluble salts). These are extrapolated to a virtual concentration at which all the water present is as closely packed as possible, hence no longer capable of being electrostricted. The resulting intrinsic volumes of salts are reasonable when compared to other estimates of these quantities.