bild

Industrial production of chlorine by the electrolysis of brine, aqueous sodium chloride. A worker surveys the chlorine cooling & drying tower at the plant of Hays Chemicals, Cheshire, UK, in early evening. 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) - secondary products that are widely used in the chemical industry. (KEYSTONE/SCIENCE PHOTO LIBRARY/JAMES HOLMES, HAYS CHEMICALS)