is limited or the solution is cooled in such a way that it does not heat to above 25 u00b0 c the acceptable currents are approximately 20 to 100 ma the electric current is carried by the iodomercurate anions hgi 3 the cations of impurities and to a certain extent the cations hgi all these ions are obtained either from the complexing of the iodides of impurities by mercuric iodide according to a general reaction of the following type for sodium iodide for example or a certain auto complexing of the mercuric iodide itself according to the reaction equ3 at the anode the iodomercurate anions discharge and supply the iodine to obviate the iodine concentration a 7 n high purity mercury excess 8 can be placed at the bottom of the round bottomed flask and this reacts with the iodine re forming mercuric iodide in this case the solution is diluted every so often to prevent supersaturation at the cathode the cations of impurities are concentrated in the cathode space for example na k fe 3 ni 2 cu 2 cu cr 3 ca 2 ag etc the cations hgi are discharged and deposit an insoluble mercurous iodide mud 7 certain impurity cations are deposited at the same time as the mercurous iodide mud or are adsorbed in this mud the conductivity.