ISO 2488:1973

The principle of the analysis consists in dissolution of a test portion and addition, in a dilute acid medium, of mercuric salts which, with the chloride ions, form soluble and only slightly ionized mercury(II) chloride. Indication of the completion of the reaction by the appearance of a violet coloration due to the reaction between the excess of mercury(II) ions and the diphenylcarbazone used as indicator.