of the tank to produce a differential in level of the electrolyte e on opposite sides of each cathode c as the electrolyte flows in its alternating downward and upward path between the anodes and cathodes indicated by the arrows the tank t may be formed of a suitable insulating and corrosion resistant material such as a suitable plastic normally reinforced by fiberglass or the like in this embodiment the electrodes are connected in a parallel circuit i e all the anodes are electrically connected to a bus bar 17 and all of the cathodes are electrically connected to a bus bar 18 on opposite sides of the tank each of the interior sides of the tank as in fig1 and 3 has a series of vertically disposed spacer bars 20 and 21 fastened to or molded into said sides to provide vertically disposed slots the side edges of anodes a and cathodes c fit loosely in alternate sequence into said slots anodes a are pressed by the differential hydraulic pressure against the edge of spacer bars 20 to prevent or minimize flow of electrolyte around the side edges of said anodes cathodes c are similarly pressed by the differential in hydraulic pressure against the edges of spacer bars 21 to prevent or minimize the flow of electrolyte around the side edges of said cathodes with the edges of the cathodes as in fig4 preferably being provided with u shaped.