The electrical conductances of calcium nitratendash;potassium nitrate solutions have been measured as a function of temperature to 200deg;C and pressure to 3000 atm, by imposing oil pressure directly on samples held within an externally heated bomb. Log (conductance) varies linearly with pressure at high temperatures, but curvilinearly at low temperatures, the ldquo;activation volumerdquo; appearing to increase with increasing pressure. ldquo;Activation volumesrdquo; increase rapidly with decreasing temperature. The observations may be accounted for if the ldquo;ideal glass transition temperaturerdquo;T0is taken to be the only pressurehyphen;dependent variable in a simple equation previously found to describe temperature and compositionhyphen;dependent variations in conductance in this, and other, systems. Within uncertainty limits,T0varies linearly with pressure and mole fraction, thus pressure equivalents of given composition changes can be simply stated. Using a thermodynamic relation applicable at the glass transition, the observed dependence ofT0on pressure is used to predict the change of heat capacity at the glass transition. The value is confirmed within error by direct measurements. Application of the Adamndash;Gibbs theory of relaxation processes leads to the derivation of approximate ldquo;constant (configurational) entropyrdquo; parameters,E lpar;Scrpar;, which exhibit qualitatively the properties of ldquo;constant volumerdquo; parameters,Elpar;Vrpar;, observed in studies of nonionic liquids.
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