A continuous electrolytic process used to produce aluminium from alumina. The alumina is dissolved in a bath of sodium aluminium chloride called cryolite that contains alumina fluoride and calcium fluoride. The solution is heated to 950ºC in a steel tank with a carbon liner. Carbon anodes are lowered into the solution with the liner being the cathode. Electrolytic action separates the alumina into liquid aluminium, which collects at the cathode, and oxygen at the anode, which combines with the carbon to form carbon dioxide gas. It was invented in 1886 simultaneously and independently by American chemist Charles M. Hall (1863–1914) and French scientist Paul L. T. Héroult (1863–1914).