The experimental apparatus for measuring the PVT-data, electrical and optical properties of expanded fluid mercury near the liquid-gas critical point are reviewed. By using these apparatus, the equation-of-state, optical absorption spectrum, thermopower data can be obtained accurately over the wide temperature and pressure range. In fluid mercury the metal-non-metal transition occurs near the density of 9 g/cm3 and the thermopower has a considerably large negative value in the vicinity of the critical point. The optical data for fluid iodine and chalcogen mixture are also included.