  A new equation of state for argon has been developed in view to extend the
range of validity of the equation of state previously proposed by Tegeler et
al. (Ref. 4) and to obtain a better physical description of the experimental
thermodynamic data for the whole fluid region (single-phase, metastable and
saturation states). As proposed by Tegeler et al., this equation is also based
on a functional form of the residual part of the reduced Helmholtz free energy.
However in this work, the fundamental equation for the Helmholtz free energy
has been derived from the measured quantities CV(rho,T) and P(rho,T). The
empirical description of the isochoric heat capacity CV(rho,T) is based on an
original empirical description containing explicitly the metastable states. The
thermodynamic properties (internal energy, entropy, free energy) are then
obtained by combining integration of CV(rho,T). The arbitrary functions
introduced by the integration process have been deduced from a comparison
between calculated and experimental pressure P(rho,T) data. The new formulation
is valid for the whole fluid region from the melting line to 2300 K and for
pressures up to 50 GPa. It also predicts existence of a maximum of the
isochoric heat capacity CV along isochors as experimentally observed in several
other fluids. For many applications, an approximate form of the equation of
state for the liquid phase may be sufficient. A Tait-Tammann equation is
therefore proposed between the triple point temperature and 148 K.
