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 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 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.