The mercury goes into a chamber underneath, where water flows in the opposite direction. A pump returns the mercury to the top chamber. Chloride ions are oxidised to chlorine. The chlorine gas is taken off and collected. The sodium dissolves in the mercury.
Water flows from right to left.
The water reacts with the dissolved sodium. This forms sodium hydroxide solution and hydrogen gas. The sodium hydroxide solution flows out on the left. Hydrogen gas is taken away and collected.