The method of numerical solution of Poisson - Boltzmann equation for polyelec-trolyte solutions containing simple salt presented by Vink is used to calculate the distribution of electric potential around the polyion in cylindrical cell model. Combining with the thermodynamics of polyelectrolyte solution

the activity coefficients of counterion

coion and polyion are obtained from those electric potential data. The osmotic coefficients of solvent are also obtained. These numerical data are correlated with general function of parameter of electric charge density ε parameter of polyelectrolyte concentration X and the ratio of concentrations of simple salt and polyelectrolyte f. The mean activity coefficients of simple salt calculated by this work for systems of NaPP - NaCl

NaPP - NaBr and Napp - Nal are agreement with the experimental data

better than that predicted by Mannings model.