Experimental data from aqueous solutions of sodium chloride indicate that critical temperature, pressure, and density are strongly dependent on the salt concentration, φ, especially in the limit of pure water. This dependence has been accurately described using an empirical equation of state by Povodyrev et al. [1] However, the theory shows that electrolyte solutions require the Debye-Huckel theory to incorporate ionic interactions. We have developed a new equation to describe and predict the vapor-liquid critical locus for aqueous solutions of sodium chloride. Our approach follows the work of Kim and Fisher [2] and accounts for the non-analytic anomalous φ^3/2 dependence of the critical locus.

[1] A.A. Povodyrev, M.A. Anisimov, J.V. Sengers, W.L. Marshall, J.M.H. Levelt Sengers, Intl. J. of Thermophysics, 20 1529 (1999).

[2] Y.C. Kim and M.E. Fisher, J. Phys. Chem. B, 105 11785 (2001).