Temperature Dependence of Ultrasonic Absorption and the Compressional Viscosity Due to Structural Rearrangement in Unassociated Liquids

The ultrasonic absorption in carbon tetrachloride, toluene, chlorobenzene, cyclohexane, cyclohexanone, cyclopentane, and propane has been measured over a range of temperature that extends usually from the boiling to the freezing points. An empirical curve—based on the assumptions (1) that the vibrational contribution to the absorption is linear with temperature and (2) that the ratio of the structural component of the compressional viscosity ηc to that of the shear viscosity ηs is independent of temperature—has been fitted to the measurements. The derived ratio ηc/ηs for carbon tetrachloride is 2.5±1.5, toluene 1.7±0.2, chlorobenzene 1.6±1.0, cyclohexanone 0.4±0.1, cyclopentane <0.7, propane 1.1±0.1, and acetone <2. The empirical basis of the assumptions, the relationship of this method with others for determining ηc, the relationship of these values of ηc/ηs with theoretical and other experimental values are all briefly discussed. It emerges that (1) of the liquids that have been measured the three whose molecules have the most‐spherical force fields have experimental values of ηc/ηs ≈ 1, which compares well with the theoretical value of 5/3 for rigid spheres, and (2) the common assumption that the viscous contribution to the absorption decreases with increasing temperature is true only for sufficiently low temperatures.