Vapor Pressure, Critical Isochore, and Some Metastable States of CO2

An experimental method for obtaining precise PVT properties for gases in the critical region is described. Main features are absence of noxious volumes, small height of sample volumes, precise temperature control, and high pressure sensitivity. Some results are presented for CO2. The 0°C fixed point and the vapor-pressure curve have been measured and compared with literature values. Three liquid isochores including their metastable extensions into the two-phase region are also presented. The vapor-pressure data and pressures on the critical isochore above Tc are compared with the predictions of the thermodynamic scaling law and with those of a recently proposed extension of scaling. The equation of extended scaling fits the data between −2 and 46°C with a standard deviation of 1.5× 10−3 bar, for a ``best'' critical exponent α=0.09.