ASTM D4486 Test Method for Kinematic Viscosity of Volatile and Reactive Liquids
8. Standardization
8.1 Viscometers - Only calibrated viscometers standardized as described in Annex A2 shall be used.
8.2 Thermometers - Liquid-in-glass thermometers shall be checked to the nearest 0.01°C (0.02°F) by direct comparison with a suitable standardized thermometer. Kinematic Viscosity Test Thermometers shall be standardized at "total immersion" which means immersion to the top of the mercury column, with the remainder of the stem and the expansion chamber at the top of the thermometer exposed to room temperature; do not submerge the expansion bulb at the top of the thermometer. It is essential that the ice point of standardized thermometers be determined periodically and the official corrections be adjusted to conform to the change in ice point.
8.3 Timers - Standard time signals available in some nations may be used in checking the accuracy of timing devices. In the United States of America, time signals, as broadcast by the National Bureau of Standards, Station WWV, Washington, D. C. 20234, at 2.5, 5, 10, 15, 20, 25, 30, and 35 MHz are a convenient and primary standard reference for calibrating timing devices; the signals are broadcast 24 h daily. Station CHU from Ottawa, Canada, at 3.330, 7.335, and 14.670 MHz or Station MSF at Rugby, United Kingdom, at 2.5, 5, and 10 MHz may be received better in some locations.
8.4 Viscosity standards may also be used to check the over-all kinematic viscosity procedure in a laboratory. If the measured kinematic viscosity does not agree within +/-0.35 % of the certified value, each step in the procedure should be rechecked, including thermometer and viscometer calibration to locate source of error.
9. Cleaning of Viscometer
9.1 Between successive determinations, clean the viscometer thoroughly by several rinsings with an appropriate solvent completely miscible with the sample, followed by a completely volatile solvent. Dry the viscometer with vacuum attached to Tube A or by placing viscometer in a vacuum oven.
9.2 Periodically clean the instrument with chromic acid (Warning - Causes severe burns. A recognized carcinogen. Strong oxidizer, contact with organic material may cause fire. Hygroscopic. See Annex A1.2) to remove organic deposits, rinse thoroughly with distilled water and acetone, (Warning - Extremely flammable. Vapors may cause flash fire. See Annex A1.3) and dry with clean dry air. Inorganic deposits may be removed by hydrochloric acid (Warning - Poison. Corrosive. May be fatal if swallowed. Liquid and vapor cause severe burns. Harmful if inhaled. See Annex A1.4) treatment before use of cleaning acid, particularly if barium salts are suspected.
NOTE 1 - Do not allow chromic acid or hydrochloric acid to stand in contact with the Kovar fitting on the viscometer. Use a glass pipet to introduce these acids into the viscometer in such a manner that contact with the metal fittings is kept to an absolute minimum.
NOTE 2 - Viscometers used for silicone fluids, fluorocarbons, and other liquids which are difficult to remove by the use of a cleaning agent, should be reserved for the exclusive use of those fluids except when standardizing. Such viscometers should be subjected to standardization checks at frequent intervals.
