A consistent thermodynamic substantiation is given for interpolation formulas that are applied in treatment of high-temperature measurements of thermodynamic properties of solids. The physical meaning of empirical interpolation coefficients is established. Expressions for the thermodynamic potential, enthalpy, heat capacity, and entropy are given. Using lead as an example, it is shown that the approach suggested ensures good agreement between calculated and experimental data over the whole range of the solid state of metals except in the immediate vicinity of the melting point. The energy of formation and concentration of vacancies in metals are determined from the deviations of the experimental heat capacity data near the melting point from those calculated in terms of the Frenkel vacancy model.