Summary of Work on Atomic Arrangement in Glass*

A bstract The present picture of the atomic arrangement in glass has developed from four kinds of information, namely, the laws of crystal chemistry, the X‐ray diffraction study of glass, the various measured physical properties of glass, and the kinds of materials and the ranges of composition in which glassforming properties exist. X‐ray diffraction studies establish the predominant type of bonding in the glass, for example, the tetrahedral bonding in silicate glasses. Secondary structural features such as those which change with annealing or conditioning do not show up in the X‐ray pattern. Most of the proposed structures are those which are suggested and are partially substantiated by X‐ray studies, those which fit the laws of crystal chemistry, and those which seem best able to explain the physical properties of the glass. The preliminary theory of immiscibility in glass systems has been extended to include a consideration of the temperature dependence. A study of thermal expansion in terms of the number of glassforming bonds allows a simple correlation between thermal expansion coefficients in the silica‐boric oxide and the soda‐boric oxide systems. The same kind of considerations used in discussing immiscibility may be used to give a quantitative treatment of the change in the coordination number of the boron atom when boric oxide is present with soda.