ASTM D971 for Interfacial Tension of Oil Against Water by the Ring Method
5. Apparatus (Figs. 1 and 2)
5.1 Tensiometer - Force measurement on the tensiometer may be made using a torsion wire, load cell, or any other means of linearly determining tension in the range of 0 to 100 mN/m.
5.1.1 Horizontal platform to hold the sample container should be capable of movement upward or downward using a mechanical screw, lever mechanism, electronic drive, or any other means of precisely changing vertical position of the sample.
5.2 Rings made of platinum or platinum-iridium alloy may be used. The ring should be welded into a continuous circle and attached to at least two parallel stirrups. Circumference of the ring should be minimum 40 mm and diameter of the ring wire should be about 0.3 mm. Ratio of the ring major radius (R) and the wire radius (r) should be known (R/r) to at least three significant figures. Stirrups should be at least 25 mm long.
5.2.1 The ring may be suspended from or rigidly fixed into the tensiometer force measuring system.
5.3 Sample Container - Glass beaker or clear cylindrical container having a minimum diameter of 45 mm.
6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in the test.
6.2 Purity of Water - Unless otherwise indicated, references to water shall be understood to mean distilled water or water of equal purity.
