Abstract: In the production of magnesium by electrolysis of a fused salt the metal is collected over a body of the fused salt under a heavily insulated cover to reduce heat loss from the molten metal under a substantially non-oxidizing atmosphere. The electrolyte is held down to a controlled temperature somewhat above the melting point of magnesium by means of a heat exchanger which projects into the fused electrolyte and is arranged so as to avoid significant uptake of heat from the supernatant molten metal. This arrangement permits the electrolyte temperature to be controlled with reduced formation of sludge and extended cell life by avoidance of exposure of the electrolyte to atmospheric moisture.