  We analyze the thermodynamical behavior of black holes in closed finite
boxes. First the black hole mass evolution is analyzed in an initially empty
box. Using the conservation of the energy and the Hawking evaporation flux, we
deduce a minimal volume above which one black hole can loss all of its mass to
the box, a result which agrees with the previous analysis made by Page. We then
obtain analogous results using a box initially containing radiation, allowed to
be absorbed by the black hole. The equilibrium times and masses are evaluated
and their behavior discussed to highlight some interesting features arising.
These results are generalized to $N$ black holes + thermal radiation. Using
physically simple arguments, we prove that these black holes achieve the same
equilibrium masses (even that the initial masses were different). The entropy
of the system is used to obtain the dependence of the equilibrium mass on the
box volume, number of black holes and the initial radiation. The equilibrium
mass is shown to be proportional to a {\it positive} power law of the effective
volume (contrary to naive expectations), a result explained in terms of the
detailed features of the system. The effect of the reflection of the radiation
on the box walls which comes back into the black hole is explicitly considered.
All these results (some of them counter-intuitive) may be useful to formulate
alternative problems in thermodynamic courses for graduate and advanced
undergraduate students. A handful of them are suggested in the Appendix.
