ABSTRACT
This chapter aims to give illustrations of some important concepts for liquids and solutions taken from some approximate lattice theories of gases and liquid mixtures. Since these theories have a quite simple mathematical structure, they are pedagogically useful in order to help in the understanding of the concepts via explicit formulas that can quite easily be explained. The Ising model is a model for interacting particles located on lattice sites. Originally, it was used as a model for ferromagnetism in the solid state, but it has been used for many other kinds of problems. The Ising model for a lattice fluid, where the lattice has filled and vacant sites, can be used as a model of a gas when the number of particles is low, a so-called lattice gas. An important kind of system that can be approximately treated by lattice theories are polymer solutions and polymer mixtures.
