Defines a colour-indicator titration method for determining acidic or basic constituents in petroleum products and lubricants which are soluble in mixtures of toluene and isopropyl alcohol. Applies to the determining of acids or bases having dissociation constants in water 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.