Excess free energies of mixing at temperatures below 25°. Isopiestic measurements on the systems H₂O-NaCl-Na₂SO₄ and H₂O-NaCl-MgSO₄

Abstract

Isopiestic vapour pressure measurements have been made on the systems H₂O-NaCl-Na₂SO₄ and H₂O-NaCl-MgSO₄ at 15° and 0°. Excess free energies of mixing the aqueous salts hare been calculated for various ionic strengths, and the results have been compared with those previously obtained at 25°.     Within experimental uncertainty the excess free energies of mixing of aqueous NaCl with aqueous Na₂SO₄ are the same at 0°, 15°, and 25°. However, the excess free energy of mixing aqueous NaCl with aqueous MgSO₄ shows differences which may be just larger than experimental uncertainty over the same temperature range.