Studies on the Dead-Stop Titration. VI

When potassium ferricyanide or ferrocyanide reacts with metal ion to form a precipitate, the solubility product of ferro-metal salt is generally smaller than that of ferri-metal salt. In such a case, the use of a ferricyanide-ferrocyanide mixture would result in preferential precipitation of a ferro salt. Consequently, a polarographic titration of various metals with normal solution of ferrocyanide-ferricyanide mixture was carried out and it was found that a determination can be effected according to the normality of the ferrocyanide in the mixed solution. Some of the metals were found to be determined by the normality of the ferrocyanide-ferricyanide mixture.