  In this paper we present the construction of the Maxwell equal area law in
the Hawking temperature graph for a charged black hole in Anti-deSitter
background. We are able to find exact solution for the corresponding isotherm
and entropies for "gaseous" (large) black holes and "liquid" (near-extremal)
black holes. Isothermal construction removes the unphysical, negative heat
capacity, regions. Furthermore, extremal black holes turn out to be dual to
"un-shrinkable" molecules of Van der Waals real fluid, which may explain their
thermodynamical stability.
