Gives the potentiometric and visual methods als alternatives for the final titration. The principle consists in the combustion of the sulphur in a current of oxygen. Oxidation and fixation of the sulphur dioxide and trioxide gases in chromic and sulphuric acid solutions. Absorption of the carbon dioxide formed in a solution of barium hydroxide, followed by titration in the presence of phenolphthalein and screened methylorange (by xylene cyanol FF) as indicator. Has also been approved by the IUPAC.