Determination of Electrolyte Apparent Molal Compressibilities at Infinite Dilution Using a High-Precision Ultrasonic Velocimeter

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 ${\phi }_{\mathrm{Ks}}^0$ from empirical extrapolation of ${\phi }_{\mathrm{Ks}}$ data is shown to be unreliable and unnecessary.