Application of an interferometer method previously used for determining the relative solubility of optical glasses, to a glass which is commonly used for making glass electrodes, gave results leading to the following conclusions:1. The solubility increases rapidly as the pH of most solutions increases above 8.5 or 9.
An interferometer method for determining the chemical durability of glass has been tried on a series of typical glasses over a wide range of temperature and pH. The results emphasize the importance of careful temperature control if comparisons are to be made between the findin gs of different investigators. The relations between amount of attack and pH for some of the glasses show pronounced inflections near p H 7 in the presence of Britton universal buffer, while the attack by distilled wat er for these same glasses is very slight in comparison. Moreover, the results strongly emphasize the fact that there can be no single test by which the durability of glass can be judged with respect to all conditions of service.The method has proved particularly useful in the interpretation of known voltage anomalies of the glass electrode.
CONTENTS Paie
The liquidus te mperature of a glass is t he highest temperature at which equilibrium can coexist between the molten glass and the primary crystalline phase. An improved temperature-grad ient apparatus is d escribed for thc rapid d etermination of liquidus temperatures and rates of crystal growth in glasses. In this method the use of small glass fragmcnts confined in the cells of a platinum a ll oy holder largely eliminates the crror inherent in previous gradient method s. The proced ure is s imple and rapid. Liquidus tempe ratures in the range from 950° to 1,225°C were determined to a precision of 4 d eg rees C.Hates of crystal growth were found to be linear. The usefulness to the glass technologist of data obtained by this method is indicated.
The glass-forming rcgion of thc systcm ZnO-B20 3-Si0 2 was s urveyed. G lasses ,,·e rc Inade wit h composit ions within the foll owing lim its in mole percent: 50 to 62.5 Zn O 20 to 43.5 B20 3, a nd 0 to 20 Si02• They can be melted a nd pOllI·cd bclow 1,400° C. The g lasses have lo w coe ffi cie nts of t herma l expansion , h igh valucs of cla st ic modu li and Po isson 's ratio, and refra ct ive indices fr om 1.6409 to 1.6798.
Glasses in the System Barium Oxide-Boric Oxide-Silica 209havior of clear and opaque plates subjected to the same heattreatment.
V. SummaryA method has been developed for calculating temperature It distributions in glass plates undergoing heat-treatment.has been programmed for a high-speed digital computer and is ready for application to practical problems of glass technology. the differences, both qualitative and quantitative, in the be-
Acknow,edgmenhAcknowledgment is made to E. R. Michalik, formerly of Mellon Institute and now with the Pittsburgh Plate Glass Company, and to Carl Saalbach of the Westinghouse Electric Corporation for programming the high-speed digital computer.
Densities, refractive indices, liquidus temperatures, and primary phases of glass compositions in the glassforming region of the system BaO-BtOrSiOz were determined. Anomalous changesin properties were observed for a continuous change in composition. The possibility that there is a relation between the compounds indicated by the phase diagram and the actual units in the glass is suggested.
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