Patent GB-1317200-A (GB)
Title: Apparatus for the determination of surface tension of liquids
IPC: G01N13/02
Filed: 1970-10-01
Abstract: 1317200 Measuring surface tension FULMER RESEARCH INSTITUTE Ltd 24 Sept 1971 [1 Oct 1970 13 April 1971 9 June 1971(2)] 46648/70 9191/71 19602/71 and 19603/71 Heading G1S To determine the surface tension of a liquid which in certain cases is directly relatable to the concentration of impurities therein, a probe is provided with first and second tubes 10, 11, the tube 10 having an orifice at its tip 14 to provide in use a steady succession of bubbles of accurately known radius, and the tube 11 having an end positioned at substantially the same horizontal level below the liquid surface as the orifice, the tube 11 also having means for maintaining at its end a substantially horizontal interface between gas in the tube 11 and the liquid under test, the probe being provided with the supplies 15, 16 of inert gas, e.g. purified helium and nitrogen respectively, to the tubes 10, 11 and a meter, e. g. a silicone oil manometer 19 or a pen recorder operated from a bellows, for measuring the maximum pressure difference between the gases in the tubes 10, 11 from which measurement the surface tension of the liquid can be derived. Preferably an open-ended escape tube 12, plugged at 17 with a material impervious to the liquid but pervious to gas e.g. porous alumina, P.T.F.E. or nylon, is provided within the tube 11 such that if the interface at the end of the tube 11 becomes convex then gas will leak from the tube 11 into tube 12 to restore the interface to its substantially horizontal form, a meter (not shown) being provided to control the flow of gas into tube 12 in dependence on the rate of gas escape at 18. In alternative arrangements, Figs. 7-10 (not shown), the tube 10 is positioned within the tube 11 and has a U-bend at its lower end to provide an upwardly directed orifice, the tube 10 is positioned within the tube 12 so that the bubbles pass into the tube 12, and an impervious thin rubber membrane is provided to close the lower end of the tube 11 and act as a valve maintaining the gas-liquid interface substantially horizontal, this last arrangement being particularly useful for measuring the surface tension of oils which tend to wet almost any surface from with the tube 11 might be made. Alternatively the flatness of the interface could be maintained by maintaining the conduction path between two electrodes positioned in the liquid beneath the tube 11 since if the interface became convex the path would be broken, or by monitoring the intensity of a light beam reflected from the interface which intensity will depend on the curvature of the interface. By measuring the surface tension, impurity concentrations can be estimated from known relationships. The probe and method are particularly useful for measuring the concentration of minor solute ingredients in molten metal, e.g. sulphur, oxygen, phosphorus or nitrogen in liquid iron, sulphur or oxygen in liquid copper, and bismuth, lead, magnesium, antimony or tin in liquid aluminium, and for estimating aqueous solutions of surfactants, oils and alcohol levels in blood or urine.