When moving into our new chemistry building, my graduate student uncovered a relic made in the 1930’s. It was a cast-iron Du Nuoy ring tensiometer, but we didn’t know that. We guessed that it had something to do with surface tension, and he did a literature search. Up popped a 1930’s paper by Harkins and Jordan on the ring method for determining surface tension.
We quickly improved this instrument by placing an analytical balance on top of two cinder blocks. The RS-232 printer interface made this a digital tensiometer. Other students improved on the design yielding this instrument and a paper.
Williams, D. L.; Jupe, C. L.; Kuklenz, K. D.; Flaherty, T. J., An Inexpensive, Digital Instrument for Surface Tension, Interfacial Tension, and Density Determination, Industrial & Engineering Chemistry Research, 47(12), 4286-4289 (2008) .
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.