Phase Equilibrium in a Portion of the Ternary System Ba OA‐I 2 ,O 3 ,‐SiO 2 ,

Phase‐equilibrium relations on the liquidus surface in the system Ba0‐A1 2 O 3 ‐SiO 2 have been investigated by the quenching method. The compositions investigated within the ternary area were those containing less than 30%, A1 2 O 3 and more than 20% SiO 2 by weight. Petrographic and X‐ray techniques were employed in the determination of the crystalline phases. The crystal phases that separate from melts within the area investigated are barium orthosilicate (2BaO. SiO 2 ,), barium metasilicate (BaO 2SO 2 ,), solid solutions, sanbornite (BaO 2SiO 2 ), tridymite and cristobalite (SO 2 ), mullite (3A1 2 O 3 2SiO 2 ), and celsian (BaO A1 2 O3 . 2SiO 2 ). Diagrams show the isotherms and indices of refraction of the glasses. Five quintuple points and eleven boundary curves have been determined within = .5yo compositional variations. The liquidus‐surface temperatures have been obtained within limits of ± 125°C.