Coexistence curve of perfluoromethylcyclohexane+carbon tetrachloride near the critical point in composition-pressure and composition-temperature space

Coexistence curves in volume fraction-temperature (φ–T) space and in volume fraction-pressure (φ–p) space have been measured for the binary system perfluoromethylcyclohexane+carbon tetrachloride in the temperature range Tc–T<0.8 K and in the pressure range p–pc<3.2 MPa near the critical point (Tc,pc,φc). The observed coexistence curves were expressed by the simple scaling relation φ+–φ−=BT(Tc−T)βT in φ–T space and by φ+–φ−=Bp(p–pc)βp in φ–p space. The exponent was determined as βT=0.326±0.001 and βp=0.330±0.006, which agree with each other and with the theoretical value β=0.327 for the Ising model. The observed coefficients give (Bp/BT)1/β=0.42±0.02 K/MPa, which may be compared with the slope (dT/dp)c=0.38 K/MPa of the p–T critical line in light of a thermodynamic argument. This means that the pressure range is converted into the temperature range with the slope (dT/dp)c as a scale factor.