We review and correct the classical critical exponents characterizing
the transition from negative to positive black hole's heat capacity at
high charge-angular momentum. We discuss the stability properties of
black holes as a thermodynamic system in equilibrium with a radiation
bath (canonical ensemble) by using the Helmholtz free energy potential
. Finally we analytically extend the analysis to any value of the vari
ables in the Helmholtz potential and show that this leads to the consi
deration of negative mass holes. We then study their curious thermodyn
amical stability behavior.