The oldest method of separation and purification was the electrolytic reduction of mercury cathode.
The electrolytic cell had two chambers: anode and cathode, which were connected by a salt bridge.
Electrolytic reduction is the preferred method of reduction.
More reactive metals, such as alkali and alkaline earth metals, can be easily reduced by external potential and have a higher affinity for oxygen than carbon. As a result, electrolysis is chosen over chemical reduction.
Applying an external potential from the outside is a simple way to induce electrolytic reduction.
Furthermore, more reactive metals than carbon have a stronger affinity for oxygen.