  Applying semi-analytical models of nonideal plasma, we evaluate the behavior
of the metallic phase in metal-ammonia solutions (MAS). This behavior is mainly
controlled by the degenerate electron gas, which remains stable down to 5 MPM
due to high solvent polarizability and strong dielectric screening of solvated
ions. Comparing the behavior of the metallic state with those of localized
solvated electrons, we have estimated the miscibility gap $\Delta n$ for
various alkali metals and found $\Delta n$(Na)$> \Delta n($K$)$. It is rather
narrow in Rb-NH$_3$ and does not occur in Cs-NH$_3$ solutions, which is in full
agreement with the experiments. The case of Li is discussed separately. The
difference calculated in the excess free energies of the metallic and
nonmetallic phases is in the order of $k_BT$, yielding a thermally fluctuating
mixed state at intermediate metal concentrations. It results in a continuous
metal-nonmetal (MNM) transition above the consolute point $T_c$ and a phase
separation below $T_c$. We propose a criterion for the MNM transition which may
be attributed to the line of the maximum of compressibility above $T_c$. This
line crosses the spinodal one at the critical temperature. Finally, we assert
that a new electronic phase similar to microemulsion should also arise between
the spinodal and the binodal lines.
