Pure copper is obtained by means of electrolysis.* Bars of impure copper are melted in an ordinary furnace and are granulated by being placed on a copper tray at the bottom of a tank of cold water. This highly concentrated alloy of copper serves as the anode of a battery. The cathode is an exceedingly pure bar of copper (about 99.93% pure). The electrolyte is a copper sulphate solution containing free sulphuric acid. The principle of the process is that by electrolytic action the metal to be refined is dissolved from the anode by the free acid in the electrolyte. The current of electricity passing through the solution deposits the copper from the electrolyte on the cathode in a pure form. The foreign metals and impurities remain on the anode or in the anode slime. The cost of the electrolytic process is covered first by the high price of the refined metal and second by the value of the silver and gold that is recovered from the copper. To have high electric conductivity the copper must be free from arsenic and antimony.