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 $T_c$ . After proper weight assignment, it is established that the top of the coexistence curve is asymptotically symmetric: ${\rho }^{\pm }{\mathrm{\hspace{0.17em}=\hspace{0.17em}\rho }}_c{\mathrm{\hspace{0.17em}\pm \hspace{0.17em}Bt}}^{\beta }$ ; that the exponent $\beta$ 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 $\mathrm{\beta ,\; B}$ , 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.