VARIATIONS OF REFRACTIVE INDEX OF GLASS WITH TIME AND TEMPERATURE IN ANNEALING REGION*

The refractive index of a rapidly cooled fiber of borosilicate glass was found to increase according to the equation, 1/(N₆–N) – 1/(N₆–N₀) =At, where t is time, N₆ is equilibrium index, and A is a constant at constant temperature. Index data were plotted according to this equation to determine, graphically, values of N₆ and A for several temperatures between 914° and 1060°F. Values of N₆ for temperatures from 1060° to 1180°F. were determined by prolonged heating of the glass at each 20° interval. The change of A with temperature was found to be well represented by the equation, log A=K/T+C, where T is the absolute temperature and K and C are constants.