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Air or oxygen is ozonised on the technical scale by the silent electric discharge. The Siemens and Halske ozoniser
 | Fig: Siemens and Halske ozoniser |
consists of a battery of glass or porcelain tubes with internal tubes of aluminium, enclosed in an earthed iron tank of water to cool the apparatus. The aluminium tubes are charged to a potential of 8000-10,000 volts, each battery of 6-8 tubes requiring half a kilowatt of power. The Ozonair apparatus consists of two sheets of aluminium gauze separated by a plate of insulator, several units being enclosed in a case and alternate plates charged and earthed. The best production amounts to about 40-60 gm. of ozone per kilowatt-hour, at a concentration of 2 gm. of ozone per cu. m. of air. With pure oxygen, 120-180 gm. are obtained. The yields are about 5 and 15 per cent, of the theoretical with air and oxygen, respectively.
Ozonised air is used in the sterilisation of water, when it is bubbled through the filtered water in a tall column (2 gm. of ozone per cu. m. of water); also for purifying air (e.g., in underground railways) and for oxidation processes (e.g., iso-eugenol to vanillin). The purification of water is its most important use: the plant supplying Paris deals with 24,000,000 gallons daily. A small plant is in operation at Knutsford, in Cheshire.
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