Abstract: An accurate method for the measurement of the Oxygen index(OI) of non-stoichiometric tungsten oxides was proposed in this paper. In the presence of KOH, tungsten oxide or heterotungstate sample was dissolved in a K₃Fe(CN)₆ solution. In the oxidation-reduction reaction, the tungsten will be oxidized to hexavalent, while the ion Fe(CN)₆^3- in solution will be quantitatively reduced to Fe(CN)₆^4-. By Titrating the Fe(CN)₆ with K₂Cr₂O₇ solution, then OI can be calculated.
An evaluation and error analysis was made in the paper, compared it with·other methods, e.g. the KMnO₄ volumetric method. The results show that the method may be characterized by its high accuracy, simple and quick operation. The method also overcame the shortcomings of the conventional methods.