This paper discusses recent experimental results in the liquid-vapour
critical region of mercury. These results show that the existence of t
he metal-non-metal transition noticeably influences electronic, thermo
dynamic, structural and interfacial features. Optical reflectivity exp
eriments were conducted for mercury in contact with an optically trans
parent sapphire substrate. The experiments were carried out with the m
ercury close to the vapour-liquid coexistence curve. The temperature a
nd density dependence of the reflectivity reveal clearly the existence
of a prewetting transition of mercury on the sapphire substrate. At h
igh temperature, the transition line terminates at a surface critical
temperature T-sc lying below the bulk critical temperature T-c. At low
temperature, it terminates at the wetting transition temperature T-w.
Furthermore, the transition lies close to the bulk vapour-liquid coex
istence curve and occurs when the bulk vapour pressure is within a few
percent of its saturation value.