Isotope effects in aqueous systems. VI. partial molal free energies in NaCl−H2O−D2O by freezing-point measurements. The heat of fusion of D2O

The freezing-point depressions of solutions of NaCl in normal and heavy water have been measured between 0.01 and 2m. Extrapolation of the isotope effect data to infinite dilution yields a new value for the heat of fusion of D₂O at its melting point (?1507±3 cal-mole^?1). The freezing-point data were employed to obtain osmotic coefficients at the feezing points of the solutions, which were corrected to rounded temperatures up to 40°C using the enthalpy data reported by Craft and Van Hook (previous paper). The data for H₂O solution are in quantitative agreement with well-established results. Those for the D₂O solvent establish the NaCl?D₂O system as an isopiestic reference. In contrast to the statements of earlier authors, examination of the isotope-effect data reveals a (surd overline m) dependence within experimental error.