Using a newly designed high-stability sing-around circuit ultrasonic velocities in aqueous salt solutions down to concentrations of 2 × 10−4mole/liter have been measured. Adiabatic apparent molal compressibilities at infinite dilution, and where possible standard molal compressibilities, have been determined for some aqueous solutions of tetra-alkylammonium bromides, alkali-metal chlorides and sulfates, and MgSO4. The determination of these quantities from precise sound velocity, volumetric, and calorimetric measurements is discussed. The practice of obtaining φKs0 from empirical extrapolation of φKs data is shown to be unreliable and unnecessary.

The determination by cryoscopy of precise values of the osmotic coefficients of ammonium chloride and bromide in water at 0°C shows that earlier reports of abnormal behaviour in dilute solution should be discounted. The osmotic coefficients of the ammonium salts are very similar to those of the corresponding potassium salts. Specific interaction coefficients are reported.

An apparatus is described for the precise measurement of freezing-point depressions for nonaqueous solutions by a heating curve method. The apparatus has been used for measurements on solutions in dimethyl sulphoxide and in sulpholane (tetrahydrothiophene-1 ,l-dioxide), the relevant physical properties of which are critically discussed. Osmotic coefficients have been determined with an accuracy of 0.2-1 % for solutions of some alkali metal perchlorates and of lithium chloride. The salts studied behave differently in the two solvents. The ionic solvating power of dimethyl sulphoxide is much greater than that of sulpholane, which results in opposite sequences of osmotic coefficients for the alkali metal perchlorates, and striking differences in degrees of ion association in the two solvents, particularly for lithium chloride. The interpretation of these observations is discussed, together with the behaviour of lithium halides in a range of solvents.

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Ultrasonic absorption measurements over a frequency range of 10-250 MHz are reported for some trivalent lanthanide nitrates, perchlorates, and chlorides in aqueous solution. Thermodynamic and kinetic parameters for the formation of MN032+ complexes of neodymium and gadolinium have been determined. The approximations and assumptions made in this calculation are discussed. Changes in relaxation frequency with cation across the lanthanide series are discussed in terms of changes in cation coordination number.