1. J.W. Gibbs, “On the Equilibrium of Heterogeneous Substances,” in Scientif ic Papers, Vol. 1, pp. 55–353 (Dover reprint). Often cited, rarely read
2. I. Prigogine and R. Defay, Chemical Thermodynamics (Longmans, Green and Co., London 1954).
3. I.M. Gelfand and S.V. Fomin, Calculus of Variations (Prentice-Hall, Inc., Englewood Cliffs, NJ 1963).
4. C. Lanczos, The Variational Principles of Mechanics (Dover reprint).
5. F.P. Buff, “The Theory of Capillarity,” in Handbuch der Physik, Vol. 10, pp. 281–304 (Springer-Verlag, Berlin 1960).