Metallic Conductance of Supercritical Mercury Gas at High Pressures

The electrical conductivity of mercury has been measured at fourteen temperatures between 800 and 1700^∘{}C and at pressures between 1200 and 2100 bar. From the discontinuities of the conductance observed with increasing temperature at constant pressures, the vapor-pressure curve beyond 800^∘{}C has been derived; it has a critical point at Tc=1490±15 ^∘{}C and pc=1510±30 bars. The specific conductivity of liquid mercury in the lower temperature range increases only slightly with pressure (at 0^∘{}C from 1.06×{}10⁴ to 1.14×{}10⁴ Ω^-1 cm^-1 between 1 and 2100 bar; at 1200^∘{}C from 1.6×{}10³ to 2.4×{}10³ Ω^-1 cm^-1 between 610 and 2100 bar). Beyond 1200^∘{}C the conductivity becomes strongly pressure-dependent. At 1520^∘{}C the specific conductivity of supercritical mercury increases continuously by more than 4 orders of magnitude from 10^-2 Ω^-1 cm^-1 to 5×{}10² Ω^-1 cm^-1 if it is compressed from 1580 to 2100 bar. At higher supercritical temperatures the behavior is similar, although the increase of the conductance with pressure becomes less steep. It follows that supercritical gaseous mercury exhibits metallic conductance if compressed to sufficiently high density.