Mercurimetric determination of chloride with diphenylcarbazide disodium disulfonate as an indicator

A procedure is given for the use of diphenylcarbazide disodium disulfonate as an indicator in the direct titration of chloride with mercuric nitrate. By adding ferric nitrate to form the carbazone and an inert green substance to serve as a color screen, a sharp and reversible endpoint changing from green to grey to purple is obtained. Studies were made on the indicator reaction and other factors, such as mercuric chloride concentration, pH, volume, temperature and the effect of various added salts. The pH must be adjusted to 1.8 to 2.0 for best results. A series of ten determinations on a sample gave a standard deviation of ±0.16 part per thousand.