ON THE SOLUBILITY OF ANHYDROUS CALCIUM SULPHATE AND OF GYPSUM IN CONCENTRATED SOLUTIONS OF SODIUM CHLORIDE AT 25 °C, 30 °C, 40 °C, AND 50 °C

Abstract

The solubilities of anhydrous CaSO4 and CaSO4.2H2O in concentrated aqueous solutions of NaCl at a series of temperatures—25 °C, 30 °C, 40 °C, and 50 °C, have been determined. It was found that the transition temperature for the reaction[Formula: see text]which in pure water has a value of 42 °C, is shifted progressively to lower temperatures with increasing NaCl concentration. It was also found that the variation of the transition temperature with NaCl concentration could be adequately represented by the equation[Formula: see text]where ΔG, ΔH, and ΔS are the Gibbs free energy, enthalpy, and entropy of the reaction and P0 and P are the vapor pressures of pure water and the solution respectively at the absolute temperature T.