Metallic-Nonmetallic Phase Coexistence above the Consolute Point of Sodium-Ammonia Solution

The heat capacity under saturated vapors, $C_{\sigma }$, of three different concentrations of NaN${\mathrm{H}}_3$ solution ($X=0.045, 0.046, 0.063$ molar part of Na) has been measured in the temperature range 200-300 K. All three $C_{\sigma }\mathrm{}\left(T\right)\mathrm{}$ curves show anomalies consistent with the existence of a new two-phase region above the well-known liquid-liquid critical point ($X_c=0.0415\mathrm{}$, $T_c=232\mathrm{}$ K). Its location is compatible with the metal-nonmetal transition line; so it is believed that in equilibrium these are metallic and insulating phases with different concentrations of electrons.