COEXISTENCE CURVE OF PERFLUOROMETHYLCYCLOHEXANE-POINT IN COMPOSITION-PRESSURE AND COMPOSITION-TEMPERATURE SPACE(CARBON TETRACHLORIDE NEAR THE CRITICAL)

Coexistence curves in volume fraction-temperature (phi-T) space and in volume fraction-pressure (phi-p) space have been measured for the bin ary system perfluoromethylcyclohexane+carbon tetrachloride in the temp erature range T-c-T<0.8 K and in the pressure range p-p(c)<3.2 MPa nea r the critical point (T-c,p(c),phi(c),). The observed coexistence curv es were expressed by the simple scaling relation phi(+)-phi(-)=B-T(T-c - T)(beta T) in phi-T space and by phi(+)-phi(-)=B-p(p-p(c))(beta p) i n phi-p space. The exponent was determined as beta(T)=0.326+/-0.001 an d beta(p)=0.330+/-0.006, which agree with each other and with the theo retical value beta=0.327 for the Ising model. The observed coefficient s give (B-p/B-T)(1/beta) = 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 lig ht of a thermodynamic argument. This means that the pressure range is converted into the temperature range with the slope (dT/dp)(c) as a sc ale factor. (C) 1998 American Institute of Physics.