Phase transitions and critical phenomena in mercury fluid probed by sound

The velocity of sound in mercury has been measured at a frequency of 10 MHz for temperatures to 1900 K and pressures to 1750 bar. The studied region of state parameters include the liquid and gas phases, together with the coexistence curve up to the critical point and the supercritical region. The error in the sound velocity data is less than 0.4%. The determined critical parameters of mercury are 1764 K and 1670 bar. Considerable attention was paid to the measurements in the vicinity of the critical point. The data obtained confirm an abnormal behavior of the velocity of sound in mercury in the gas phase near the coexistence curve and in the vicinity of the critical point. The critical behavior of the absorption of sound is also discussed.