Notes on the freezing of simple substances

Experimental data on the freezing of argon and the helium isotopes at high pressures are analyzed. It is found that attractive forces in argon can be adequately described by the van der Waals mean field theory. An analogous approximation may also be applicable to helium, but this cannot be established conclusively because of quantum effects. However, an analysis of experimental results on the freezing of helium intuitively suggests that the solid-phase stability region is enlarged by quantum effects.