Ozone

Ozone (Greek, ozein, “to smell”), allotropic form of oxygen having three atoms in each molecule, formula O₃. It is a pale blue, highly poisonous gas with a strong odour. Ozone boils at -111.9° C (-169.52° F), melts at -192.5° C (-314.5° F), and has a relative density of 2.144. Liquid ozone is a deep blue, strongly magnetic liquid. Ozone is formed when an electric spark is passed through oxygen, and causes a detectable odour near electrical machinery. The commercial method of preparation consists of passing cold, dry oxygen through a silent electrical discharge. Ozone is much more active chemically than ordinary oxygen and is a better oxidizing agent. It is used in purifying water, sterilizing air, and bleaching certain foods. Low level ozone formed in the atmosphere from nitrogen oxides and organic gases emitted by cars and industrial sources, however, is a health hazard, and it may cause serious crop damage in some areas. (see Acid Rain; Environment).