Margules equations symmetrical solutions

Margules Equations and Slightly Non-ideal, Symmetric Solutions... 

Because most real solutions do not follow the parabolic, symmetrical form of the two-suffix Margules equations, it is necessary to add more flexibility to the equations by adding more coefficients and more terms. One way to do this is to simply define a second Wq term of the type in (15.22), then combine the two Wq terms in a linear equation in X. This can be imagined as the mixing of two solutions, each symmetrical but having different IPg s ... 

Saxena (1973). A general account of the mixing properties of crystalline solutions, with detailed discussions of the van Laar, regular (one coefficient, symmetric), "sub-regular" (two-coefficient, asymmetric) and quasi-chemical models. Margules and other equations for i presented for binary... 

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