General
Fully refined petroleum oils normally contain no naptha insoluble material. Semirefined or black oils frequently contain some naptha insoluble material, sometimes referred to as asphaltenes. This test nieasures the amount of naptha insoluble material in the steam cylinder stocks, black oils, and lubricating oils. This quantity is reported as the precipitation nuniber.
Test
Ten mL of lubricating oil is mixed with 90 mL of ASTM precipitation naptha, and centrifuged for 10 mm at a rcf of between 600 and 700. Volume on the bottom of the centrihige cone is read until repeat centrifugation gives a reading within 0.1 mL. This reading is reported as the precipitation number.
Precision
In the precipitation number range of 0,00 to 1.20, the test repeatability is 10 % of the mean, and the test reproducibility is 30 % of the mean. This procedure is empirical, and no statement of bias can be made.