Velocity and Absorption of Ultrasonic Waves in Several Nonassociated Liquids Under High Pressure

The ultrasonic-wave velocity and absorption for carbon tetrachloride, benzene, and carbon disulfide are measured by a pulse-reflection method, at several temperatures, in the pressure range of 1 to 1360 atmospheres. Generally similar pressure effects are found in the three liquids. The velocity increases with pressure to about 1.4 times the atmospheric-pressure value, while the relative absorption decreases to about 0.4. The structural relaxation theory, which is examined with reference to carbon tetrachloride, predicts approximately the pressure effect on the absorption at constant temperature, but gives erroneous predictions of the magnitude of the absorption, and of the effects of pressure on the absorption temperature coefficient and on the relaxation frequency. The thermal relaxation theory is partially examined with reference to carbon disulfide, although more extensive data and further refinement of the theory are needed for a rigorous test. In terms of this theory, the absorption data are consistent with approximate theoretical predictions of the effect of pressure upon the relaxation frequency and upon the relaxational portion of the specific heat. Over all, the study tends to confirm the thermal relaxation theory of the excess absorption in nonassociated liquids. It is shown also that the Tonks equation of state gives approximately correct values of the pressure coefficient of sound velocity for carbon disulfide.