VELOCITY OF SOUND AT 4 MHZ IN MERCURY NEAR ITS LIQUID-VAPOR CRITICAL-POINT

The sound velocity of mercury near its liquid-vapour critical point ha s been measured at 4 MHz with a pulse transmission-echo method. Accura te data could be obtained along several isotherms just below and above the critical temperature. The resulting velocity data along the criti cal isochore above T-c and in the liquid along the vapour-pressure cur ve show a finite velocity minimum at the critical point. The existence of such a minimum is consistent with the view that the critical behav iour of the metal mercury does not differ from that typical for molecu lar fluids.