  The aim of this paper is to investigate the conditions for the coexistence of
phases in a Lennard Jones fluid. The calculation has been performed within the
virial developement mathod and, as a result, a simple approximate relation has
been obtained between the number densities of two coexisting densities and the
interparticle potentials in them. The calculation is preliminary,in the sense
that it does not take into account the equality of the chemical potentials. The
results of this work may have implications for modelling of the giant planets.
More than 300 exoplanets have been discovered, so this has become more
important than ever.
