Two cases are considered: sulphuric acid contents equal to or lower than 98 % (m/m) and sulphuric acid contents higher than 98 % (m/m). The principle is based on oxidation of a test portion with hydrogen peroxide and titration of the total acidity with a standard volumetric sodium hydroxide solution, in the presence of methyl red as indicator. - Replaces ISO Recommendation R 910-1968.