ASTM D2502 Test Method for Estimation of Molecular Weight (Relative Molecular Mass) of Petroleum Oils From Viscosity Measurements
5. Procedure
5.1 Determine the kinematic viscosity of the oil at 100 and 210°F (37.78 and 98.89°C) as described in Test Method D445.
5.2 Look in Table 1 for 100°F (37.78°C) viscosity and read the value of H that corresponds to the measured viscosity. Linear interpolation between adjacent columns may be required.
5.3 Read the viscosity - molecular weight chart for H and 210°F (98.89°C) viscosity. A simplified version of this chart is shown in Fig. 1 for illustration purposes only (Note 1). Interpolate where necessary between adjacent lines of 210°F viscosity. After locating the point corresponding to the value of H (ordinate) and the 210°F viscosity (superimposed lines), read the molecular weight along the abscissa.
Example:
Measured viscosity, cSt:
100°F (37.78°C) = 179
210°F (98.89°C) = 9.72
Look in Table 1 for 179 and read the corresponding value H = 461.
Using H = 461 and 210°F viscosity = 9.72 in conjunction with chart gives molecular weight (relative molecular mass) = 360 (see Fig. 1).
NOTE 1 - A 22 by 28-in. (559 by 711-mm) chart available as an adjunct to this test method was used in cooperative testing of the method. If other charts are used, the precision statements given in the Precision Section will not apply.
5.4 Report the molecular weight to the nearest whole number.
