SURFACE TENSIONS OF SOME OPTICAL GLASSES*

The surface tension of a number of optical glasses made at the National Bureau of Standards was measured by a modification of the anchor ring method. The values for the flint glasses at 1300 °6, were in the range 210 to 230 dynes per cm., the barium crowns ranged from 260 to 310, while the other types of glasses had intermediate values. Most of the glasses had positive temperature coefficients of surface tension. The surface-tension values increased with the increasing periods of time at which the glasses were maintained at high temperatures immediately prior to measurement. Positive rank correlation coefficients of statistical significance were found between seed quality of optical glasses and such factors as surface tension, pot attack, and amount of gas liberated during the melting process.