A new method for “ferrous iron” and “excess oxygen” in rocks, minerals, and oxides

A new method is given whereby oxygen excess or deficiency in many minerals and oxides may be simply determined. The method depends on the stability in phosphoric acid-pyrophosphate mixtures of both Mn^III and Mn^II. The sample is dissolved in a phosphoric acid mixture containing excess Mn^II, with or without the addition of standard oxidant, and Mn^III remaining in solution or produced by reaction with the sample is titrated with ferrous ammonium sulphate, using barium diphenylamine sulphate as indicator. The method is useful in many cases where existing methods are inapplicable or unsatisfactory. Accurate results can be obtained using relatively small samples.