Direct measurements of the functional dependencies of the electric resistivity and the molar volume on enthalpy and pressure have been performed for graphite and liquid carbon. It has been found that for graphite at the pressures P  ⩽  1 GPa the isochoric temperature coefficient of resistance is positive, while for liquid carbon it is negative over the entire pressure range investigated where P  =  0.5-3.5 GPa. These observations probably indicate that graphite is a metal whereas liquid carbon is not a metal, so that the melting of graphite under such pressures coincides with a metal-to-nonmetal transition.

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