Improvements in the Lattice Model of a Liquid

A new type of approximation is introduced, with the objects of examining further the transition of a fluid of non-attracting rigid molecules, and of improving the lattice model of a liquid by reducing the ratio of mesh size to molecular volume. The approximation is first checked by applying it to some simple two-dimensional lattices, reproducing many known results and predicting some new ones. The probable qualitative behaviour of the isotherm of a two-dimensional fluid of rigid non-attracting molecules is determined, available evidence suggesting the existence of a finite region in which the fluid phase is metastable. Some preliminary results on the effect of reducing the lattice mesh size suggest that simple lattice models of a liquid do give physically sensible results in spite of their crudity.