JAMES HOLMES, HAYS CHEMICALS / SCIENCE PHOTO LIBRARY JAMES HOLMES, HAYS CHEMICALS / SCIENCE PHOTO LIBRARY
Worker checking an external radioactive sensor that is used to monitor the level of liquid chlorine contained within the yellow tanks. Chlorine is produced by the electrolysis of brine, aqueous sodium chloride, here at the plant of Hays Chemicals, Cheshire, UK. In the electrolytic process, chlorine gas is liberated at a graphite anode (positive electrode) & sodium at a mercury cathode (negative electrode). Sodium dissolves in mercury to form an amalgam, which is allowed to flow into a second cell to react with water to form hydrogen & sodium hydroxide (caustic soda).
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