6) Smelting tests indicated that oversmelting, as evi-were either rutile or anatase; in the large majority of denced by yellow-to-brown coloring of the frit, is detri-cases, rutile was found; effect of composition on form mental to reflectance; color of fired enamel is not af-of TiOz that recrystallizes in firing is not definite from fected by oversmelting; correct smelting temperature results of this investigation. It has been determined seemed to be 2150'F. and glass should be poured as that the crystal form of TiOz added to the smelter does soon as all material is in solution. Undersmelting as not control the form of Ti02 recrystallizing.indicated by some undissolved particles imbedded in the frit did not affect reflectance or color of fired Acknowledgment enamel. The yellow coloring of grass is due in part to reduction of Ti02 to a lower oxide.(7) Firing time and temperatures are important since opacity is produced in the enamel during the firing procoptimum time and temperature are indicated for this type of enamel, above which optimum the reflectance is not increased appreciably for feasible increasesThis investigation was carried out in the Department of Ceramic Engineering a t the University of Illinois and was financed by the Enameled Utensil Manufacturers' Council of Cleveland, Ohio. The authors wish to express their appreciation to the Technical Committee of the Council for its advice, suggestions, and cooperation. Thanks are due J. 0. Kraehenbuehl of the Department of Electrical Engineering for the spectrophotometric analyses. ess;in time or temperature. ABSTRACTThe fundamental condition for glass formation is the existence of stronglybonded large networks or long chains of atoms in the liquid. Such chains or networks prevent or hinder the orderly orientation of atoms in the chains or networks themselves and also that of atoms, not in the networks in the liquid, near the melting point or liquidus temperature. A liquid structure will persist when the liquid is cooled below the melting point or liquidus temperature and will continue until free, long-range movement of atoms becomes impossible. In order to obtain such long chains or large networks, it is necessary that (1) the bond strength of atoms in the chains or networks be verystrong;(2) the small ring formation of these strongly bonded atoms be at a minimum; and (3) the relative numbers of various atoms in the chains or networks be such that at least a continuous chain is configuratively and structurally possible; at the same time, the coordination numbers of the glassforming atoms should be as small as possible to keep the bond strong. The general treatment is applied to all kinds of glasses, particularly oxide glasses. The bond strengths of all M-0 single-bond linkages in these glasses are calculated and tabulated here for the first time. The bond strength of all the glassformers was found to be greater than 80 kilocalories per Avogadro bond, that of the intermediates between 60 and 80, and that of the modifiers below 60; the transition is continu...

The glass-formation region has been determined for the PbO-W03-P205 system$ and certain physical properties of representative glasses have been measured. Glasses of the system show an unusually high X-ray and gamma-ray absorption and are not readily discolored when exposed to X rays. Equations have been developed from which specific volumes and lead equivalents may be calculated from composition. Because of their high index of refraction and relatively low dispersion these glasses are also useful for optical purposes.Works, Corning, N. Y . ; Westinghouse Research Laboratories, East Pittsburgh, Pa.; and the University of Pittsburgh, Pittsburgh, Pa. Patent applied for.ally transparent lead-containing glasses a "glassformer" must be added, and then only in a minimum amount be-1 Ernst Kordes, "Physicochemical Investigation of Fine Structure of Glasses: I, Molar Refraction of Binary Phosphate, Silicate, and Borate Glasses," Z . anorg. allgem. Chem., 241 [I] 1-38 (1939); Ceram. Abstracts, 18 [8] 207 (1939) (abstracted from Ghsfech. Ber., 17 [3] 65-76 (1939)). 153 6 W.

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The difficulty of defining the vitreous state in a rigorous manner, the existence of many borderline cases, and the theoretical requirements which must be met if a substance is to be vitreous are discussed. Silicate glasses and certain other typical classes of vitreous substances are treated in some detail with especial reference to the relation between their structures and vitreous properties.