  Using phenomenological equations of state, we study the chemical and
mechanical instabilities in hot isospin-asymmetric nuclear matter. Both
instabilities are found to depend strongly on the isospin asymmetry of the
nuclear matter. For a chemically and mechanically stable asymmetric nuclear
matter, a lower neutron excess is found in the liquid phase than in the gas
phase. Furthermore, the neutron excess in the mixed phase at densities between
that of the liquid and the gas phases is limited by certain maximum value.
Also, for the nuclear equations of state considered here the boundary of
chemical instability in the pressure-density plane is found to be more extended
than that of mechanical instability. However, locations of these boundaries
depend sensitively on both the bulk compressibility of nuclear matter and the
density dependence of the symmetry energy.
