High-alkali silicate glasses M-27 containing chloride additives (MCl, where M = Na and K) introduced in the course of synthesis (0, 1, 5, 10, 12.5 wt % Cl) are investigated. The glasses synthesized are analyzed for chlorine content, and their thermal and electrical characteristics are measured. The upper limits of the chlorine content in the glasses are determined. The nonlinear dependence of the as-analyzed chlorine content in a binary glass on the as-batched chlorine content introduced into a batch is explained by structural transformations during which chlorine in the glass interacts with polar groupings that are bonded to at least two polar tetrahedra. Only large-sized associates are able to fix chlorine. The proposed concept of structural transformations is used to interpret the changes observed in the bulk (thermal, electrical) parameters of glasses. It is shown that these changes are governed by two competitive processes, namely, the incorporation of chlorine into the glass structure and the change in the total glass composition due to volatilization of the components in the course of the synthesis. It is noted that the effect of chloride additives on the high-temperature viscosity of glass-forming melts is weaker than that of fluoride additives.