VISCOSITY OF GLASS BETWEEN THE STRAIN POINT AND MELTING TEMPERATURE1

An apparatus is described which employs the elongation of a glass fiber under load for the determination of annealing and strain points. The same apparatus is also used by varying the suspended load for the determination of the temperature-viscosity curve between the annealing range and the softening point of the glass. A description is given of measurements made in this manner on a series of three simple soda-lime-silica glasses at theses low temperatures, as well as measurements made in a rotating cylinder viscomcter between the softening point and the melting temperature. Curves are shown for the viscosities of the three glasses in the two temperature ranges and a complete viscosity curve from 500 to 1400°C is given for one of them. It is found that the two methods yield results that fit a smooth curve between these limits of temperature.