Activity coefficients of water and sulfolane from the solid + liquid phase diagram

The solid + liquid phase diagram drawn from thermal analysis is presented. It exhibits a eutectic at x₂ = 0.303 and T = 262.2 K and precludes the existence of definite compounds between the two components. Mixed crystals are observed in the sulfolane-rich region. The activity coefficients of water, f_{x, 1}, and of sulfolane, f_{x, 2}, are calculated from the initial freezing points of water. Log f_{x, 1} and log f_{x, 2} show a steady dependence on volume composition, providing evidence for the supposition that strongly self-associated water and monomer sulfolane scarcely interact with one another, and that the thermodynamic properties of the mixtures should rather be related to steric factors.