double extrapolation; experiments in 0.1 and 0.7M solution (NaCl, KCl, MgCl2, or CaCl2, resp.) or mixed electrolyte solutions of different ionic strength containing the major ions of seawater in their appropriate seawater proportions; extrapolation to 1.0 M; free of CO2; fig.6: logK=-5.45 (wrong sign)