SURFACE PROPERTIES OF FUSED SALTS AND GLASSES: I SESSILE‐DROP METHOD FOR DETERMINING SURFACE TENSION AND DENSITY OF VISCOUS LIQUIDS AT HIGH TEMPERATURES *

A bstract An apparatus is described which allows measurements to be made of the contact angle and the exact dimensions of a sessile drop of liquid resting on an electrode graphite surface in vacua or in nitrogen atmosphere. Temperatures up to 1100°C have been employed. Under these conditions, surface tension and gravity are the only forces acting on the drop, and the exact shape, surface, and volume may be computed from the tables of Bashforth and Adams. The method may be used with liquids having viscosities up to 600 poises, whereas the bubble‐pressure method used by Jaeger is limited to liquids of viscosity less than 70 poises. On the basis of internal evidence, the surface‐tension values obtained by the sessile‐drop method are considered correct within 5%. They also agree with data by Jaeger, but are, roughly, twice as great as those of Washburn and Libmart, who used a ring method. The probable error in Washburn and Libman's work appears to be in their assumption of zero contact angle.