Abstract: A glass for sealing a beta-alumina tube in a sodium-sulphur cell has a composition suitable to resist attack by sodium at elevated temperatures and a coefficient of thermal expansion suitable for use with beta-alumina. The glass consists essentially of 28-48 mol % B.sub.2 O.sub.3, 0-20 mol % SiO.sub.2, 16-28 mol % Al.sub.2 O.sub.3, together with 18-33 mol % of at least one alkaline earth oxide selected from the group consisting of BaO, SrO, CaO and MgO, the proportions of the constituents being such that the combined total of B.sub.2 O.sub.3 and SiO.sub.2 is 40 to 60 mol % and furthermore being such that 0.0517 A.sub.1 +0.0354 A.sub.2 -0.0063 A.sub.3 +0.168 A.sub.4 +0.1336 A.sub.5 +0.098 A.sub.6 +0.1597 A.sub.7, lies between 5.7 and 6.4 where A.sub.1, A.sub.2, A.sub.3, A.sub.4, A.sub.5, A.sub.6 and A.sub.7 are the respective molar percentages of B.sub.2 O.sub.3, SiO.sub.2, Al.sub.2 O.sub.3, BaO, CaO, MgO and SrO.A cell sealed with such a glass is described.