THE EQUATION OF STATE FOR MERCURY-VAPOR AND THE LAW OF CORRESPONDING STATES

The law of corresponding states fails to describe the phase transition region of mercury where a metal-nonmetal transition is superposing th e conventional liquid-gas phase transition. Microscopically, this diff erence to simple liquids is related to the excitation of internal degr ees of freedom of the mercury atom. In the present model, the equation of state for dense mercury vapours is calculated by means of a system of coupled mass action laws which take into account atoms, electrons, as well as simple and double charged ions. The interaction correction s between the various components are taken into account which cause th e transition from a weakly ionized low-density vapour to a highly ioni zed, dense metal. New results for the critical point and the coexisten ce curve are derived which are in reasonable agreement with the experi mentally observed behaviour.