precipitation number

precipitation number

[prə‚sip·ə′tā·shən ‚nəm·bər] (analytical chemistry) The number of milliliters of asphaltic precipitate formed when 10 milliliters of petroleum-lubricating oil is mixed with 90 milliliters of a special-quality petroleum naphtha, then centrifuged according to American Society for Testing and Materials test conditions; used to determine the quantity of asphalt in petroleum-lubricating oil.