Various methods used to evaluate the correction term for heat exchange in calorimetry by the method of mixtures are compared by applying them to a set of real calorimetric data. The differences between the methods are significant in precision work. By comparison of the enthalpy values for α-alumina measured in the same calorimeter under adiabatic and non-adiabatic conditions, the correction method proposed by King and Grover gives a correct result. Hence much published data on the enthalpy of the calorimetric standard material α-alumina contains errors of ± 0.2 %.