The separation of vario us e lements by electrodeposition using a mercury cathode has b een presented in a summarised form1 • However, as stated by Lavrukhina such investigations, especially in the case of trace elements, have not been carried out systematically. Hovewer, it is well known that the d eposition of iron group elements onto a Hg-cath ode is followed by an overvoltage. A number of papers3 - 7 present the application of this method to various systems, but a method to be applied for the separation of trace amounts of iron from large amounts of manganese using a constant potential mercury cathode system has not been described as yet