SomeH0measurements in concentrated LiCl solutions are reported. It is shown that theH0values in 1–9 MLiCl, 1–9 MHClO4, and 1–11 MHCl solutions can be calculated using the equationwhereawis the activity of water,Cis either the molar or molal concentration, andnandBare least-squares constants. Values ofn = 2 (molar equation) andn = 1 (molal equation) fit the experimental data better than doesn = 4. With the molar equation a non-integral value ofnfor HClO4is required to give reasonableH0values. The adequacy and significance of integral and non-integral values ofnare considered. The nature of the constantBis also discussed. A more general equation is developed which under certain conditions reduces to the simpler equation. The more general equation is based upon a model which assumes the existence of more than one hydrated form of the indicator base, its conjugate acid, and H3O+. Some of the implications of this more general equation are considered