Osmotic coefficients are reported for the system NH4Cl + (NH4)(2)SO4 + H2O at 298.15 K over a wide range of concentrations. Scatchard's mixed electrolyte equation is used to fit these data with six fitting parameters, b(ij). For comparison, we insert extended Debye-Hijckel equations and separately Pitzer's equations as the necessary binary salt equations within Scatchard's equation. Three sets of the six bij are obtained in each case from fits with two subsets and the full set of the osmotic coefficients. We examine the consequence of including different binary osmotic coefficient expression equations and applying different data ranges in these fits. The results are combined with available ternary diffusion coefficients to calculate and report solvent frame thermodynamic transport coefficients, (L-ij)(0). These are intercompared relative to the Onsager Reciprocal Relations requirement. Finally, we use Pitzer's mixed electrolyte equation to calculate thermodynamic properties of the ternary system directly and to calculate (L-ij)(0) coefficients for comparison with the (L-ij)(0) obtained using Scatchard's equations.