AbstractThe surface tension of a series of compositions ranging from 0 to 100% PbO in the system PbO‐B2O3and of compositions ranging from 0 to 35% SiO2in the system PbO‐SiO2, was measured by a modification of the anchor ring method. The volatility and changes in composition of members of each system on heating were found to be related to the surface tension and its change with composition. Some correlation between the temperature coefficient of surface tension and expansivity was no