Abstract
Beam-bending method that one used to measure the sag point of glass was tried to apply to the viscosity measurement of the relatively unstable glasses. An electrical circuit making connections between the differential transformer and the recording millivoltmeter was newly designed. This enables the viscosity measurement in range of 107-1016 poises involving annealing point and sag point. Annealing point of a commercial soda-lime glass measured by this method coincided with that obtained by the fibre-elongation method. Furthermore, results of viscosity measurements of glasses in the systems of Li2O-B2O3-SiO2-Al2O3, Li2O-Al2O3-SiO2 and Na2O-Al2O3-SiO2 were given. The glasses in the two former systems are so apt to crystallize or separate into two phases at a temperature near the sag point that they can hardly be obtained in a form of relatively long fibre as homogeneous state. The present method is especially suited for measuringt he annealing point and sag point of glass in case that the glass to be subjected cannot be got in a large amount because of the preciousness or the experimental situation.
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