ABSTRACTVarying mixtures of BaO, MgO, and SiO2were made into cones and fired to determine the temperature at which they would fuse. The direction of falling temperature as determined by their relative fusion temperatures converged to an area whose center represented a mixture, the composition of which was approximately 46.0% by weight of BaO, 8.0% by weight of MgO, and 46.0% by weight of SiO2. The first signs of fusion occurred in this mixture at standard pyrometric cone 1 (3 o'clock).