The two chambers of the reversal mixing vessel are separated by a tilting lid. The samples (liquid-liquid or liquid-solid) are separately introduced into the vessel outside of the calorimeter. In order to obtain a complete separation of the chambers, a mercury seal on the lid can be used. If the vapor pressures of the samples are low, the mercury seal is not required. After the introduction of the vessels into the calorimeter, the thermal equilibrium is to be achieved in order to have the two separated components at the same temperature. Then, mixing is performed by reversing the calorimeter. If the samples mix easily, only a few rotations of the calorimeter are necessary. In the case of difficult mixing, the reversing mechanism can be maintained during the whole test.