Electro-generated quinone from hydroquinone at a platinum anode in a 0.5-10 N sulphuric acid medium has been used as a coulometric titrant.Current-potential curves for oxidation of hydroquinone showed an efficiency of nearly 100 percent in generation of quinone.Coulometric titrations of milligram quantities of titanous ion and hypovanadous ion give errors less than 1 per cent.The quantitative reduction of vanadate or vanadyl ions to the divalent state can be conveniently accomplished by means of a small zinc amalgam reductor as shown in Fig.3.Chromium and molybdenum interfere with the determination of vanadium, whereas titanium and manganese do not.