The oxidation of thallium(I) by selenious acid

A new and simple method for the quantitative determination of thallium based on the oxidation of TI(I) to TI(III) by selenious acid has been described. The precipitated selenium is weighed directly. Furthermore, the thallic hydroxide obtained by the addition of excess alkali to the filtrate is dissolved in HCl and determined iodometrically. The excess selenious acid in the filtrate is also estimated iodometrically or by gravimetric method after reduction to metallic selenium. Under the specified operative conditions the results are reproducible and accurate within the limits of experimental error.