The use of naphthidine as indicator in the determination of zinc in metallurgical analysis

Using naphthidine as an internal indicator in the titration of zinc with standard potassium ferrocyanide solutions, suitable procedures are recommended for the determination of zinc in various non-ferrous alloys and in rubber ashes. With aluminium alloys, aluminium bronzes and white metals the zinc is separated from interfering elements by hydrogen sulphide procedures, whereas with tin bronzes the separation is best accomplished by an 8-hydroxyquinoline procedure. After the solution of rubber ashes in hydrochloric acid, the major interfering elements are removed from the zinc by filtration after making the solution ammoniacal. With samples giving large precipitates with ammonia, it is necessary to redissolve them and determine the entrained traces of zinc.