Chlorine
Chlorine, a chemical element that is a greenish-yellow gas at ordinary temperatures and pressures. The gas is poisonous and has a strong odor. It is about two and one-half times as heavy as air.
Chlorine is not found free in nature. It is commonly found in combination with sodium, forming sodium chloride (common salt). Chlorine is the most abundant member of the halogen family of chemical elements.
Most chlorine is produced commercially by passing an electric current through a solution of water and sodium chloride. This process, called electrolysis, is carried out in a container called an electrolytic cell. The electric current decomposes the solution, producing chlorine and sodium hydroxide (caustic soda).
Chlorine is used in many industrial processes and in the manufacture of many different products. It is widely used in purifying drinking water and in treating sewage. It is also used in the bleaching of paper and other products and in the separation of such metals as copper, lead, zinc, nickel, and gold from their ores.
Important chlorine compounds include hydrochloric acid, sodium hypochlorite, and zinc chloride. Thousands of organic chlorine compounds (compounds containing carbon) have been developed, including ones used in some types of plastic and synthetic rubber.
Free chlorine attacks the mucous membranes of the nose and throat. When it is breathed in large quantities it causes serious congestion of lung tissues, and in extreme cases may cause death. A number of organic chlorine compounds have been found to be a hazard to health.
Chlorine was first isolated by the Swedish chemist Karl Scheele in 1774. Sir Humphry Davy identified it as a distinct chemical element in 1810.
Symbol: Cl. Atomic number: 17. Atomic weight: 35.453. Melting point: -149.8 F. (-101.0 C.). Boiling point: -30.5 F. (-34.7 C.). Specific gravity: gas, 2.49 (air = 1); liquid, 1.56 (water = 1). Chlorine belongs to Group VIIA of the Periodic Table and can have a valence of -1, +1, 3, 5, or 7. There are two stable isotopes: Cl-35 and Cl-37. Common chlorine compounds include sodium chloride, NaCl; hydrochloric acid, HCl; zinc chloride, ZnCl2; and sodium hypochlorite, NaClO.