  We derive the interfacial tension of a semi infinite two phase binary mixture
of partially miscible fluids in contact with a planar surface. In our model we
take a surface free energy term into account omitted by Cahn [J. W. Cahn, J.
Chemical Physics, 66:3667-3672,1977]. Our analysis applied to the case of
regular solutions shows that this extra surface free energy term cannot a
priori be neglected.
