text: The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode.  The electrolyte is an acidic solution of copper sulphate.  By passing electricity through the cell, copper is dissolved from the anode and deposited on the cathode.  However impurities either remain in solution or collect as an insoluble sludge.  This process only became possible following the invention of the dynamo; it was first used in South Wales in 1869.