Enthalpy increments for sodium chloride and potassium bromide were measured from 4.5 K to 350 K with an adiabatic calorimeter. These measurements were combined with other selected values from the literature to generate models that represented the thermal properties of crystalline sodium chloride and potassium bromide to the melting points. The entropy, enthalpy relative to 0 K, and the heat capacity of sodium chloride and potassium bromide were calculated from these models. The new measurements and models were compared to previous measurements of the thermodynamic properties of crystalline sodium chloride and potassium bromide. Additionally, the equation for the thermodynamic properties of copper given by Martin (Rev. Sci. Instrum. 1987, 58, 639), which is useful for calibration of calorimeters for temperatures below 310 K, was adjusted for the difference of the International Temperature Scale of 1990 from the International Practical Temperature Scale of 1968.