text: The cell used in this process consists of an iron tank lined with carbon at the bottom.
  A molten alloy of copper, crude aluminium and silicon is used as the anode. It forms the lowermost layer in the cell.
  The middle layer consists of molten mixture of fluorides of sodium, aluminium and barium (cryolite + BaF).
  The uppermost layer consists of molten aluminium.
  A set of graphite rods dipped in molten aluminium serve as the cathode.
  During electrolysis, Al ions from the middle layer migrate to the upper layer, where they are reduced to aluminum by gaining 3 electrons.
  Equal numbers of Al ions are produced in the lower layer. These ions migrate to the middle layer. Pure aluminium is tapped off from time to time. The Hoopes process gives about 99.99% pure aluminium.