scope:

This International Standard specifies a colour-indicator titration method for the determination of acidic or basic constituents in petroleum products and lubricants soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids or bases whose dissociation constants in water are greater than 10^-9; extremely weak acids or bases whose dissociation constants are less than 10^-9 do not interfere. Salts react if their hydrolysis constants are greater than 10^-9.

NOTE 1 In new and used oils, the constituents considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, and additives such as inhibitors and detergents. Similarly, constituents considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts of heavy metals, and additives such as inhibitors and detergents.

The method is not suitable for measuring the basic constituents of many basic additive-type lubricating oils, for which ISO 3771 can be used.

This International Standard indicates relative changes 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 or basic property that can be used to predict performance of an oil under service conditions.

NOTES

2 No general relationship between bearing corrosion and acid or base number is known.

3 Oils, such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-coloured oils, that cannot be analysed by this method owing to obscurity of the colour-indicator end-point, can be analysed in accordance with ISO 6619. The acid or base numbers obtained by this colour-indicator method may or may not be numerically the same as those obtained by ISO 6619, but they are generally of the same order of magnitude.