  Analytical equations of state are presented for fluid mercury in metal,
nonmetal, and in metal-nonmetal transition states. Equations of state for metal
and nonmetal states are simple in form but the complexities of transition state
leads to a complex fourth-order equation. The interatomic potential function
used to describe the metal state have a hard repulsive wall, and that of
nonmetal state is the same as potential function of non-polar fluid with
induced dipole intermolecular interaction. Metal-nonmetal transition occurs in
the liquid density range 11-8 g/cm3, and a density dependent interaction
potential which gradually changes from a pure metal interaction to a nonmetal
interaction, on going from metal state to nonmetal state in the transition
region, is used. Well-depth and the position of potential minimum are presented
as temperature dependent quantities; their calculated values for the metal
state are typically within 5.0% and 0.33% of the experimental value,
respectively. The calculated well-depth for nonmetal state is smaller than the
experimental value indicating the effect of high pressure PVT data used, which
pushes a pair of mercury atom further together into the repulsive side. In the
transition region, calculated well-depths are 2-3 order of magnitudes larger
than for the metal state, and contain a sharp rising edge and a steep falling
having a singularity characteristic of phase transition.
