(Equivalent Test Methods: IP 139, ISO 6618, DIN 51558T1, JIS K 2501, and AFNOR T60-112)
EXPLANATION
See discussion under Acid Number for Test Method D974. Although this test has been used for base number of petroleum products for many decades, it may not be truly suitable for this measurement of many basic additive type lubricating oils. Test Method D4739 can be used for this purpose. The values obtained by this test may not be numerically the same as those obtained by Test Method D4739, but they are generally of the same order of magnitude.
TEST SUMMARY
The sample is dissolved in toluene, isopropyl alcohol containing a small amount of water and is titrated at room temperature with standard alcoholic acid solution to the end point indicated by the color change of the added p-naphtholbenzein solution (orange in acid and green-brown in base).
TEST PRECISION
These precision statements do not apply to highly colored oils which obscure the end point of color change. These estimates are based on the use of manual burets; precision using automated burets is not known.
The procedure has no known bias.