7. Reagents and Materials
7.1 Chromic Acid Cleaning Solution, or a nonchromium-containing, strongly oxidizing acid cleaning solution. (Warning - Chromic acid is a health hazard. It is toxic, a recognized carcinogen, highly corrosive, and potentially hazardous in contact with organic materials. If used, wear a full face-shield and full-length protective clothing including suitable gloves.Avoid breathing vapor. Dispose of used chromic acid carefully as it remains hazardous. Nonchromium-containing, strongly oxidizing acid cleaning solutions are also highly corrosive and potentially hazardous in contact with organic materials, but do not contain chromium which has special disposal problems.)
7.2 Sample Solvent, completely miscible with the sample. Filter before use.
7.2.1 For most samples a volatile petroleum spirit or naphtha is suitable. For residual fuels, a prewash with an aromatic solvent such as toluene or xylene may be necessary to remove asphaltenic material.
7.3 Drying Solvent, a volatile solvent miscible with the sample solvent (see 7.2) and water (see 7.4). Filter before use.
7.3.1 Acetone is suitable. (Warning - Extremely flammable.)
7.4 Water, deionized or distilled and conforming to Specification D1193 or Grade 3 of ISO 3696. Filter before use.
8. Certified Viscosity Reference Standards
8.1 Certified viscosity reference standards shall be certified by a laboratory that has been shown to meet the requirements of ISO 17025 by independent assessment. Viscosity standards shall be traceable to master viscometer procedures described in Test Method D2162.
8.2 The uncertainty of the certified viscosity reference standard shall be stated for each certi?ed value (k = 2, 95% confidence). See ISO 5725 or NIST 1297.
9. Calibration and Verification
9.1 Viscometers - Use only calibrated viscometers, thermometers, and timers as described in Section 6.
9.2 Certified Viscosity Reference Standards (Table A1.2) - These are for use as confirmatory checks on the procedure in the laboratory.
9.2.1 If the determined kinematic viscosity does not agree within the acceptable tolerance band, as calculated from Annex A4, of the certified value, recheck each step in the procedure, including thermometer and viscometer calibration, to locate the source of error. Annex A1 gives details of standards available.
NOTE 4 - In previous issues of Test Method D445, limits of more or less 0.35% of the certified value have been used. The data to support the limit of more or less 0.35% cannot be verified. Annex A4 provides instructions on how to determine the tolerance band. The tolerance band combines both the uncertainty of the certified viscosity reference standard as well as the uncertainty of the laboratory using the certified viscosity reference standard.
9.2.1.1 As an alternative to the calculation in Annex A4, the approximate tolerance bands in Table 1 may be used.
9.2.2 The most common sources of error are caused by particles of dust lodged in the capillary bore and temperature measurement errors. It must be appreciated that a correct result obtained on a standard oil does not preclude the possibility of a counterbalancing combination of the possible sources of error.
9.3 The calibration constant, C, is dependent upon the gravitational acceleration at the place of calibration and this must, therefore, be supplied by the standardization laboratory together with the instrument constant. Where the acceleration of gravity, g, differs by more that 0.1%, correct the calibration constant as follows:
C2 = g2/g1 x C1
where the subscripts 1 and 2 indicate, respectively, the standardization laboratory and the testing laboratory.
