Based on thermodynamic calculations of possible reactions of interaction between sodium tungstate and oxygen-containing compounds of boron, carbon, phosphor, sulphur, metals of VI-B group the probability of possible reactions was evaluated. The experimental verification of the assumptions was accomplished by the methods of potentiometry and IR-spectroscopy. The possibility of existence of equilibrium (reversible) melted systems with the electrodes from metals of VI-B group and their carbides was proved by the electrochemical measurements and thermodynamic calculations.