ISO 6295 Petroleum products - Mineral oils - Determination of interfacial tension of oil against water - Ring method
4 Apparatus
4.1 Leconte du Nouy tensiometer, with platina ring of either 60 or 40 mm nominal circumference.
4.2 Ring, of fine platinum wire in a nearly true circle of 40 or 60 mm circumference welded to a suitable stirrup made of the same wire. It is necessary to know, to three significant figures, the circumference of each ring, and the ratio of the diameter of the ring to the diameter of the wire of which it is made.
4.3 Test portion container, glass beaker or cylindrical vessel having a minimum diameter of 45 mm.
5 Preparation of apparatus
5.1 Clean all glassware by removing any residual oil with petroleum naphtha followed by several washes with methyl ethyl ketone and water and immersion in a hot cleaning solution of chromic acid. Rinse thoroughly with tap water and then with distilled water. Unless it is to be used immediately, drain the test portion container in an inverted position over a clean cloth.
5.2 Clean the platinum ring by rinsing it in petroleum naphtha followed by rinsing in methyl ethyl ketone. Then heat the ring in the oxidizing portion of a gas flame.
6 Calibration of apparatus
Make certain that all portions of the ring are in the same horizontal plane. Calibrate the tensiometer against known masses and adjust its zero point according to the procedure of its manufacturer.
7 Sampling
Carry out the sampling in accordance with one of the methods specified in ISO 3170.
8 Preparation of test portion
Filter the test portion through a 150 mm diameter, unwashed filter paper of medium porosity, using fresh paper for each 25 ml portion of oil.
