Decomposition voltages of Na(2)O (30-50 mole % )-SiO(2) binary system were estimated at the temperature range of 700~1200℃ by commutator technique. As the experimental procedure, relations between electrolytic current and resulting polarization potential without ohmic loss were observed by 20 cps mechanical commutator, using Pt|Na(2)O-SiO(2)|Pt electrochemical system. Experimental decomposition
voltages determined from above relationship were the value of 1.5~2.0 V at the temperature beyond about 800℃ with comparatively less reproducibility. Further investigations on the decomposition reaction mechanisms were made in reference to both a series of reversible decomposition voltages derived from thermodynamic calculations on the several proposed decomposition reactions and chemical equilibrium in vitreous silicates.