Investigations into the Question of the Presence of Compounds in Molten Glass

JSGT 1936 V20 T144-T151

Comments are made on the results of recent determinations made by Heidtkamp & Endell of the density and viscosity at high temperatures of the soda–silica glasses. The likelihood of changes of curvature in the temperature–viscosity–composition curves being indicative of the presence of the compounds Na₂O.2SiO₂ and Na₂O.SiO₂ is discussed. The form of the density–composition curves at different temperatures is also abnormal in the same sense as those of viscosity and probably for the same reasons. Comparison with other work only emphasises these differences. The evidence afforded by the study of glass-making reactions, and the volatilisation of alkali from a similar series of glasses in connection with this problem is pointed out, and also the obvious chemical changes taking place in coloured glasses. The compounds Na₂O.SiO₂ and Na₂O.2SiO₂ known to be stable at their melting points, should not be denied existence in the liquid state without experimental proof, and any theory of the constitution of glasses should not ignore the elementary facts of chemical combination.

Eric Preston & W. E. S. Turner