Mercury replaced graphite with

The electrode assembly shown (Figure 1) is fairly versatile and has been used by the submitter in flasks with electrolyte volumes of ca. 40 mL to 4 L. Additionally, the platinum electrodes may be replaced by other electrodes that fit directly into the thermometer adaptor, e.g., commercially available A in. graphite or stainless-steel rods. In the present example the electrodes are positioned vertically and are of opposite polarity. In other cases they may be positioned horizontally (parallel to a mercury cathode) and are both anodic. 

Castner-Kellner process A process once used to produce chlorine and sodium hy-droxidebythe electrolysis of sodium chloride solution. The electrolysis took place in a cell with a mercury cathode and graphite anode. The cell consisted of three compartments with a common bed of mercury and solution of sodium chloride above. The cathode was in the central com partment and anodes in the other two. It was invented independently by American industrial chemist Hamilton Young Castner (1858-99), who was working in the UK at the time, and Austrian chemical engineer Karl Kellner (1851-1905). The process was abandoned due to concerns over mercury pollution and replaced by various diaphragm-based electrolytic processes. 

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