OXIDATION STABILITY MEASURING METHOD FOR LUBRICANT

PURPOSE:To provide an oxidation stability measuring method in which the measuring time can be shortened, while enhancing the measurement accuracy, when an index of oxidation stability, i.e., an RBOT value is determined. CONSTITUTION:The inventive measuring method determines an index of oxidation stability, i.e., an estimated value of oxidation induction period (RBOT value), by rotary cylinder type oxidation stability measuring method (RBOT). In the mothod, the residual quantity of antioxidant in a lubricant is measured by chromatograph and the ratio of ultraviolet absorbing area (variation of molecular weight distribution) between low and high molecular regions is determined by means of a molecular weight distribution measuring unit. Thus determined residual quantity of antioxidant and the variation of molecular weight distribution are then introduced into a multiple regression formula determined based on the relationship of the residual quantity of antioxidant, the variation of molecular weight, and the oxidation introduction period thus measuring the RBOT value of unknown lubricant.