Wetting phenomena near the bulk critical point of fluid mercury

We have studied the adsorption of mercury on sapphire at temperatures and pressures close to the liquid-vapour critical point (T-c = 1478 degrees C, p(c) = 1673 bar, p(c) = 5.8 g/cm(3)) of mercury. The mercury film undergoes a first-older phase transition known as prewetting. At low temperatures, the prewetting line meets the bulk coexistence curve tangentially at the wetting temperatures T-w = 1310 degrees C. At high temperatures the prewetting line terminates at the prewetting critical point T-pw(e) = 1468 degrees C and the prewetting pressure p(pw)(e) = 1586 bar lying close to the bulk critical point. In analogy with the line of compressibility maxima extending above the liquid-vapor critical point, we can identify an extension of the prewetting phase line for T>T-pw(e) which marks the maximum bi ty of the prewetting supercritical phase in the two-dimensional compressibility of the prewetting supercritical phase.