From abstract: "The results of recent measurements on the equations of state of sodium and xenon are discussed. The experimental data for each of these are analyzed to show that the isothermal compressibility is solely a function of volume within experimental accuracy. The basic differences between the low temperature PV relationships for sodium and xenon are shown to be easily understandable in terms of the elementary theories of these substances. The range of experimental pressures (to 20 kbars) and temperatures (20°K to the triple point) is sufficiently great so as to produce significant changes in the lattice thermal properties in each case. These changes are indicated through the use of zero pressure heat capacity data in combination with the equation of state data to calculate the volume and temperature dependence of the Debye Θ. The result is quite spectacular for xenon, where a pressure of 20 kbars roughly doubles ΘD."