Activity coefficient derivatives of ternary systems based on Scatchard's neutral electrolyte description

Activity coefficient derivatives with respect to molality are presented for the Scatchard Neutral Electrolyte description of a ternary common-ion electrolyte system. These quantities are needed for the calculation of "diffusion Onsager coefficients" and in turn for tests of the Onsager Reciprocal Relations in diffusion. The usually-omitted b(23) term is included. The direct SNE binary approximations and a further approximation are discussed. Binary evaluation strategies other than constant ionic strength are considered.