Abstract: Apparatus for the electrolysis of solutions. The apparatus comprises bipolar elements formed of a conductive plate peripherally surrounded by an insulating frame provided with feeding and discharging channels along peripheral zones of the frame. A cavity is formed with the conductive plate as the bottom and the frame as wall. Separating elements can be inserted between the bipolar elements. The separating elements consist of a porous diaphragm and an insulating frame also having feeding and discharging channels. Electrodic structures, consisting of cut and expanded metal sheets, nets or other material having high internal porosity may fill up the remaining space between two lateral bipolar elements and a central separating element.