ASTM D3339 Test Method for Acid Number of Petroleum Products
ASTM D3339 Standard Test Method for Acid Number of Petroleum Products by Semi-Micro Color Indicator Titration
4. Summary of Test Method
4.1 To determine the acid number a sample of the oil is dissolved in a solvent consisting of toluene, isopropyl alcohol, and a small amount of water. The resulting single-phase solution is titrated at room temperature under a nitrogen atmosphere with standardized 0.01 M potassium hydroxide (KOH) in isopropyl alcohol to the stable green color of the added p-naphtholbenzein indicator.
5. Significance and Use
5.1 This test method measures the acid number of oils obtained from laboratory oxidation tests using smaller amounts of sample than Test Methods D974 or D664. It has specific application in Test Method D943 in which small aliquots of oil are periodically removed for testing by Test Method D3339. This test method, therefore, provides a means of monitoring the relative oxidation of oils, by measuring changes in acid number, at different time intervals and under the various oxidizing test conditions.
