Analysis of Recent Measurements of the Viscosity of Glasses.—ii 1

Viscosity of two series of four component glasses .—The results recently reported by S. English 2 are here analyzed by the method used in a previous paper. 3 (1) Series 6SiO 2 , 1.2Na 2 O, 0.8 (CaO+MgO). The temperature at which the difference between the viscosity of a glass and the viscosity of 6SiO 2 ,2Na 2 O at the same temperature makes a sharp bend is called the aggregation temperature T a . It seems to correspond to the devitrification temperature. For this series T a reaches a sharp minimum for the composition 6SiO 2 , 1.15Na 2 O, 0.45MgO, 0.39CaO. The viscosity for any temperature also reaches a minimum at or near this composition. (2) Series 6SiO 2 , 1.1Na 2 O, 0.9 ( CaO+Al 2 O 3 ). The curves are similar to those for the first series, TA reaching a sharp minimum for the composition 6SiO 2 , 1.11Na 2 O, 0.81Ca0, 0.14Al 2 O 3 .