An Inexpensive, Digital Instrument for Surface Tension, Interfacial Tension, and Density Determination

This article outlines the construction of a large-capacity, digital ring tensiometer, using common laboratory equipment, and reports the validation of this instrument against National Institutes of Science and Technology (NIST) data. A Carver press is used as a hydraulically controlled platform that raises and lowers the temperature-controlled jacketed flask that contains the test solutions. The upper platen of the press supports a four-decimal-place scale with a Pt−Ir ring hanging from the underscale hook. The scale measures the pull on the ring as the solution interface is lowered by the press. The force measurements are transferred to a personal computer (PC) via RS-232 communications. Temperature is controlled via a water-recirculation bath. The experimental surface tension measurements for toluene and water at 13 different temperatures were, on average, 2.7% larger than the NIST data. The 25 °C surface tension measurements for water, 2-butanone, ethyl ethanoate, and toluene were, on average, 1.1% larger than those calculated using the Hansen solubility parameters.