APPARENT MOLAR VOLUMES OF AQUEOUS CALCIUM-CHLORIDE TO 250-DEGREES-C, 400 BARS, AND FROM MOLALITIES OF 0.242 TO 6.150

Relative densities of CaCl2(aq) with 0.242 less than or equal to ml(mo l-kg(-1)) less than or equal to 6.150 were measured with vibrating- tu be densimeters between 25 and 250 degrees C and near 70 and 400 bars. Apparent molar volumes V-phi calculated from the measured density diff erences were represented with the Fitter ion-interaction treatment, wi th appropriate expressions chosen for the temperature and pressure dep endence of the virial coefficients of the model. It was found that the partial molar volume at infinite dilution V-phi(O), and the second an d third virial coefficients B-V and C-V, were necessary to represent V -phi near the estimated experimental uncertainty. The ionic-strength d ependent beta((1)v) term in the B-V coefficient was included in the fi t. The representation for V-phi has been integrated with respect to pr essure to establish the pressure dependence of excess free energies ov er the temperature range studied. The volumetric data indicate that th e logarithm of the mean ionic activity coefficient, In gamma(+/-)(CaCl 2), increases by a maximum of 0.3 at 400 bars, 250 degrees C, and 6 mo l-kg(-1) as compared with its value at saturation pressure.