Low-frequency sound velocity near the critical point of xenon

By measuring the resonant frequency of an azimuthal mode in a horizontal annular resonator, it was possible to determine the sound velocity in xenon at ∼ 1 kHz without difficulties caused by gravity-induced density gradients near the critical point. It was shown that the resulting velocity data along the critical isochore above $T_c$ and in the coexisting vapor below $T_c$ correspond to the thermodynamic (zero-frequency limiting) values. The experimental data were fitted with a theoretical curve based on the linear-model parametric equation of state, and the resulting value of 0.08 for the critical exponent $\alpha$ is in good agreement with the value determined previously from specific-heat data.