Coexistence Curves of CO2, N2O, and CClF3 in the Critical Region

The coexistence curves of CO2, N2O, and CClF3 are analyzed in the critical region. The curves were obtained by refractive index measurements which are virtually free of gravity effects and contain much detail near Tc. After proper weight assignment, it is established that the top of the coexistence curve is asymptotically symmetric: ρ± = ρc ± Btβ; that the exponent β is independent of the range, varies little from substance to substance, and is insensitive to impurities; and that the data are in agreement with the law of the rectilinear diameter. “Best” values for β, B, and for the slope of the diameter are presented. An analysis of earlier coexistence curves for CO2 and N2O, including a weight assignment, is presented; there is agreement between the older and newer data.