The question of whether chemical properties, such as polarity or hydrogen bond donation or acceptance, can be measured in aqueous solvent mixtures by means of indicator probes, or whether their use is obviated because of preferential solvation, is examined. In some cases, such as the Kamlet–Taft π* or β parameters, the use of several probes yielding convergent results provides acceptable values of the properties. In another case—i.e. the Kamlet–Taft α parameter—this question must remain open because of the relatively large spread of values obtained with different probes, which is not necessarily related to preferential solvation. A single probe such as the betaine used for the E_T(30) polarity parameter, cannot provide an answer.

The electrostriction of aqueous hydrogen and hydroxide ions at infinite dilution was calculated by the shell-by-shell method over the temperature range 0 to 200 °C. The calculation required an estimate of the ionic radius of these ions, and comparison with data for aqueous lithium, sodium, and fluoride ions provided values for the nominal sizes of the hydrogen and hydroxide ions in solution. From the volumetric standpoint, these sizes are surprisingly smaller than the size of a water molecule.

Single ion volumes calculated using different procedures are compared and are found to be strongly linearly correlated. Since these correlations demonstrate that the (independent) methods are mutually supportive, it is possible to obtain values for any one method from data generated by the other methods. The validity of this procedure is demonstrated for a small selection of ions.