1.1本试验方法涵盖了新的或使用过的石油产品和润滑剂中可溶或几乎可溶于甲苯和异丙醇混合物的酸性成分的测定。本试验方法特别适用于可供分析的样品量太小，无法通过试验方法D 974进行准确分析的情况 或D 664 . 适用于测定水中离解常数大于10的酸 − 9 . 离解常数小于10的极弱酸 − 9 不要干涉。如果盐的水解常数大于10，则滴定盐 − 9 . 1.2本试验方法可用于指示在氧化条件下使用时油中酸值的相对变化。虽然滴定是在确定的平衡条件下进行的，但该方法不能测量可用于预测油在使用条件下的性能的绝对酸性。 轴承腐蚀和酸值之间的一般关系尚不清楚。 1.3由于本试验方法所需样品比试验方法D 974少得多 或D 664 ，它提供了一种有利的方法，通过改变酸值来监测氧化试验( 1. )最大限度地减少酸值分析的试样消耗，从而最大限度地减少对试验的干扰( 2. )允许进行额外的酸值分析，同时保持相同的测试样品消耗，从而提供额外的数据。 笔记 1-一些油，如许多切削油、防锈油和类似的复合油，或颜色过深的油，由于颜色指示剂终点的模糊性，可能更难通过本试验方法进行分析。这些油可以通过试验方法D 664进行分析 如果有足够的样品可用。 然而，与使用试验方法D 974相比，使用试验方法D 3339的可能性要小得多 由于在滴定过程中使用了更高稀释度的样品，并且由于终点颜色变化更稳定。通过试验方法D 3339获得的酸值可能在数值上与通过试验方法D 664获得的酸值相同，也可能不同 但它们应该具有相同的数量级。 笔记 2-使用该方法获得的结果在数值上与使用试验方法D 974获得的结果相同 ，在两种方法的精度范围内，适用于主要用于液压或蒸汽涡轮机类型服务的新型或氧化型润滑剂。使用测试方法D 943获得氧化润滑剂 氧化试验。这种相关性由相关系数表示 r =0.989，带斜率 s =+1.017和截距 y =+0.029，使用精度声明（12.2）所用样品的两种滴定方法获得的酸值计算。 1.4以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.5 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 有关具体的警告声明，请参阅第7节和第9节、A1.1.4、A2.3.1和A2.10.1。 ====意义和用途====== 本试验方法使用比试验方法D 974更少的样品测量从实验室氧化试验中获得的油的酸值 或D 664 . 它在试验方法D 943中有具体应用 通过试验方法D 3339定期取出小份油进行试验。因此，本试验方法通过测量不同时间间隔和不同氧化试验条件下的酸值变化，提供了一种监测油相对氧化的方法。 图1典型装置示意图

1.1 This test method covers the determination of acidic constituents in new or used petroleum products and lubricants soluble or nearly soluble in mixtures of toluene, and isopropyl alcohol. The test method is especially intended for cases in which the amount of sample available to be analyzed is too small to allow accurate analysis by Test Methods D 974 or D 664 . It is applicable for the determination of acids having dissociation constants in water larger than 10 − 9 . Extremely weak acids having dissociation constants smaller than 10 − 9 do not interfere. Salts titrate if their hydrolysis constants are larger than 10 − 9 . 1.2 This test method can be used to indicate relative changes in acid number that occur in an oil during use under oxidizing conditions. Although the titration is made under definite equilibrium conditions, the method does not measure an absolute acidic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid number is known. 1.3 Since this test method requires substantially less sample than Test Methods D 974 or D 664 , it provides an advantageous means of monitoring an oxidation test by changes in acid number by ( 1 ) minimizing test sample depletion for acid number analyses and thus minimizing the disturbance of the test or ( 2 ) allowing additional acid number analyses to be made while maintaining the same test sample depletion and thus providing additional data. Note 1—Some oils, such as many cutting oils, rust-proofing oils, and similar compounded oils, or excessively dark-colored oils, may be more difficult to analyze by this test method due to obscurity of the color-indicator end point. These oils can be analyzed by Test Method D 664 provided sufficient sample is available. However, this situation is much less likely using Test Method D 3339 than using Test Method D 974 due to the use of a more highly dilute sample during the titration and due to the greater stability of the end point color change. The acid numbers obtained by Test Method D 3339 may or may not be numerically the same as those obtained by Test Method D 664 but they should be of the same order of magnitude. Note 2—The results obtained using this method have been found to be numerically the same as those obtained using Test Method D 974 , within the precision of the two methods, for new or oxidized lubricants of the type primarily intended for hydraulic or steam turbine type service. The oxidized lubricants were obtained using the Test Method D 943 oxidation test. This correlation is shown by the correlation coefficient r = 0.989 with slope s = + 1.017 and intercept y = + 0.029, calculated using the acid numbers obtained using both titration methods for the samples used for the precision statement (12.2). 1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see Sections 7 and 9, A1.1.4, A2.3.1, and A2.10.1. ====== Significance And Use ====== This test method measures the acid number of oils obtained from laboratory oxidation tests using smaller amounts of sample than Test Methods D 974 or D 664 . It has specific application in Test Method D 943 in which small aliquots of oil are periodically removed for testing by Test Method D 3339. 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. FIG. 1 Schematic Drawing of Typical Apparatus