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.

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Fabrication of a new pressure jump cell made entirely from Plexiglas is described. Chemical relaxation effects greater than 50 jusec can be measured when the pressure on a chemical system is suddenly released from 40 atm by means of a bursting phosphor-bronze diaphragm and the resulting conductance change is measured by a Wheatstone bridge arrangement.