The thermodynamic activity of calcium ion in sodium chloride-calcium chloride electrolytes.

Experimental data on the mean activity coefficient of CaCl(2) in NaCl-CaCl(2) mixtures at ionic strengths below 1 m have been used to prepare a table of activity coefficients for Ca(++) in solutions of physiological interest. The establishment of an empirical calcium ion activity scale is discussed, and a number of possible assumptions are examined. The assumption gamma++ = (gamma+/-)(2) is suggested as being the simplest with a theoretical basis.