1 This International Standard specifies a method for the determination of acidic constituents in petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-ol. It is applicable for the determination of acids whose dissociation constants in water are larger than 10~9; ex-tremely weak acids whose dissociation constants are smaller than 10~9 do not interfere. Salts react if their hydrolysis constants are larger than 10~9.
NOTE — In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak base constituents, acid salts of polybasic acids, and additives such as inhibitors and detergents.
2 This method may be used to indicate relative changes that occur in an oil during use under oxidizing conditions regardless of the colour or other properties of the resulting oil. 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. No general relationship between bearing corrosion and acid or base number is known.
NOTE — A colour-indicator titration method is also available in ISO 6618 (see bibliography in annex A). The acid numbers obtained by the potentiometric method may or may not be numerically the same as those obtained by ISO 6618, but they are generally of the same order of magnitude.
3 New and used petroleum products may contain acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products. The relative amounts of these materials can be determined by titrating with bases. The acid number is a measure of this
SIS SS-ISO 6619:1990 history
1990SIS SS-ISO 6619:1990 Petroleum products and lubricants — Neutralization number — Potentiometric titration method