General Perturbation Calculation, for Solutions

Let us now consider a binary mixture of the constituents A and B. We shall present here a theory which im ludes in particular the cases of small dipolar interactions and of inductive effects (Balescu [1955]. This, calculation applies in general to all cases where the perturbed potential has the same (6-12) form as the initial one. In this paragraph we shall not q ecify the exact nature of the perturbation, and thus give 

We assume that the interaction between two molecules i, is given by 

as opposed to the Lennard-Jones law, we suppose that the interaction parameters ey, and ry are not molecular constants but functions of the temperature and of one or several structural parameters (such as dipole moment, polarizability, etc) which we shall not specify at this point 

The letters affected with a superscript will always refer to unpertijxbed quantities. The functions 9 y and are related to the average value of the orientational forces (as we have seen in the example of the preceding section). We shall suppose their numerical value be small as compared to unity. We suppose in this paragraph that the two perturbations and 9 y are independent. 

According to the general ideas of the average potential theory of solutions (cf. Ch. IX-XI) we shall now introduce parameters which characterize the average potential around a particle i, (A or B) which may be written in the form 

---