AbstractIn two base glasses, the first containing 16% of sodium oxide, 10% of dolomitic lime, and 74% of silica, and the second with 14% of sodium oxide, 12% of dolomitic lime, and 74% of silica, boric oxide was systematically substituted for (a) Na2O, (b) CaO MgO, and (c) SiO2in amounts of 1, 3, and 5%. The effects of these substitutions on such properties as liquidus temperature, viscosity, deformation temperature, fiber softening point, coefficient of expansion, and the resistance of the glasses to dilute acid and distilled water, are presented.