Velocity of sound at 4 MHz in mercury near its liquid-vapour critical point

The sound velocity of mercury near its liquid-vapour critical point has been measured at 4 MHz with a pulse transmission-echo method. Accurate data could be obtained along several isotherms just below and above the critical temperature. The resulting velocity data along the critical isochore above T-c and in the liquid along the vapour-pressure curve show a finite velocity minimum at the critical point. The existence of such a minimum is consistent with the view that the critical behaviour of the metal mercury does not differ from that typical for molecular fluids.