The temperature-concentration dependence of electric conductivity of glasses in the PhO-SiO₂ system is investigated. It is shown that the activation energy for electric conduction remains constant within the limits of experimental error. The fact that the Pb²⁺ ions are not involved in the electricity transport is established with the Hittorf gravimetric method (Tubandt's technique). The use of stable hydrogen isotope (deuterium) as a tracer demonstrates that protons (H⁺) are the main current carriers in the electric field.