Reactions in mixtures of solid alkali metal sulphates with barium chloride were investigated by DTA. The decisive role of an intermediate liquid was demonstrated.It was established that the application of DTA with simultaneous recording of electrical conductivity in the investigation of the mechanism of interaction of mechanical non-equilibrium mixtures of anhydrous salts leads to data on the transitory existence of a labile eutectic, which to a certain extent affects the course of the reactions of the mixtures of solids.