A process once used to produce chlorine and sodium hydroxide by the 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 compartment 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.