Internal Pressure of Carbon Tetrachloride between —7° and 70°

Measurements of (∂P/∂T)_V of carbon tetrachloride at ten different temperatures between —7° and 70°C yield an equation for the internal pressure (∂E/∂V)_T=3346[1—2.97×10^—3(t—25)—12.6×10^—6(t—25)²] atmospheres. Comparison with the cohesive energy density ${\mathrm{(\Delta E}}^v\mathrm{/V)}$ confirms previous observations (Hildebrand and co‐workers) that the ratio of the internal pressure to the cohesive energy density is approximately unity and further shows this ratio to be remarkably constant over the entire 77° range of temperature. The experimental data on the internal pressure are in marked disagreement with the predictions of ``free‐volume theory'' (Lennard‐Jones and Devonshire, Hirschfelder and co‐workers).