It is shown that the excess thermodynamic properties calculated from the mean spherical approximation (via the energy integrals) for the primitive model of ionic mixtures, that is, electrolytes atid molten salts, can be expressed as functions of a single parameter . The expressions are quite simple, and for what we call low concentrations (up to 1 N of a simple salt) reduce to the same relations that Debye found for the finite size ions, only that 2 takes the place of the Debye length. The interpretation that 2 is in fact the correct screening parameter for finite size ions is borne by the asymptotic form of the pair correlation function at small densities.