can form on the sides to a thickness which is adapted to the thermal equilibrium within the electrolysis furnace fig2 is a cross sectional view of an electrolysis furnace arranged for delivery of the aluminum oxide charge in the region of the longitudinal center axis of the furnace with such a manner of charging the longitudinal sides of the furnace must be unstressed electrically and thus thermally in favor of the cathode surface disposed below the anode an aluminum oxide hopper 20 is located between anodes 12 and the aluminum oxide is continuously or intermittently charged into the electrolysis furnace from this hopper and forms the cover layer 22 a mass of electrolyte 15 and layer of molten aluminum 16 are disposed between cover layer 22 and cathode 13 cathode 13 is located above steel bars 14 supported on furnace floor 23 a loading chisel 21 is provided to break up the electrolyte crust according to the invention the cathode is provided with insulation portions 18 located to cause the electrolyte current to flow vertically through the carbon cathode blocks 13 this promotes establishment in the furnace of a temperature drop extending from the center of the furnace to the longitudinal sides thereof which.