OZONE is a gas which possesses (the odour of chlorine or of moist phosphorus. It may be formed (a) by chemical action; (b) by electrolysis; (c) by the electro-static field; (d) by ultra violet rays; (e) by the radioactive elements; (f) by incandescent solids in air; (g) by the evaporation of water. Ozone has found quite general usage in many countries for the purification of water. At Philadelphia a Vosmaer sterilizing tower 33 ft. high and 3 ft. in diameter has been shown to be capable of sterilizing so,000 gallons of water per hour, using an ozone concentration of one gram per cu. metre; the plant supplying Paris deals with 24 millions of gallons of water daily. Ozonized air has been utilized in food preservation, in surgery and therapeutics, in the bleaching and refining of oils, fats and varnishes. Its use in the fine chemical industry is of increasing importance. It is successfully employed in the manufacture of the flavouring material, vanillin, and the perfume, heliotropin.
Ozone, allotropic oxygen, chemical symbol 03 (see ALLOTROPY), is normally a colourless gas. In great thickness or under pressure the colour is blue. It is sparingly soluble in water (coefficient of solubility, it has been liquefied to a deep blue liquid which is, however, dangerous to handle owing to its tendency to spon taneous explosion. Its boiling point is variously given as — o6° C (Olszewski) and C (Troost). Ozone is seven times as soluble in carbon tetrachloride as in water. Its solutions in this solvent and in acetic acid, acetic anhydride and chloroform are blue and fairly stable.
The simplest form of laboratory ozonizer was due to W. von Siemens (1857) and consists of two concentric glass tubes, the inner surface of the inner one and the outer surface of the outer one being coated with tin foil, and each of the tin foil conductors being in metallic contact with the terminals of an electrical induc tion coil. A slow stream of dry oxygen is passed through the ozonizer and under the influence of the silent electric discharge the gas becomes charged with from 3 to 8% of ozone. Two types of ozonizers are employed on a large scale : those which have dielectrics in the path of the discharge—the Siemens and Halske, and Linder ozonizers—and those which have no dielectrics—the Schneller and the Vosmaer ozonizers. In the "ozonair" system a
series of mica or micanite plates covered on both sides with a gauze of aluminium alloy are mounted side by side in a case into which air can be passed. Alternate plates are charged and earthed. The production is about 4o-6o gm. of ozone per kilowatt-hour of energy at a concentration of 2 gm. of ozone per cu. metre of air.
The first recorded observation on ozone was by Van Marum (1785) who found that electrified oxygen had a peculiar smell and tarnished mercury. In 1840 C. F. Schonbein noticed these prop erties in air subjected to the silent electric discharge, in oxygen generated by electrolysis of water and in the slow aerial corn bustion of phosphorus. He gave to the new gas the name ozone (h ay, to smell). Ozone is evolved in many chemical reactions, as by the action of sulphuric acid on barium or sodium peroxide and on many per-salts (perborates, percarbonates, permanganates, persulphates, etc.). Fluorine decomposes water with the produc tion of blue ozonized oxygen (H. Moissan, 1891). The least volatile portions of liquid ozone contain a denser gas of great chemical activity to which the name oxozone has been given with a molecular formula 04. (C. D. Harries, 1911. See OzoNmEs.) The constitution of ozone as 03 was demonstrated by T. An drews and P. G. Tait (186o), J. L. Soret (1866-67) and B. Brodie (1872), by making use of the fact that certain essential oils (cin namon and turpentine) absorb ozone without taking up any marked amount of oxygen. The loss in volume by absorption of the ozone from ozonized oxygen was twice that observed during the original ozonization of the gas. It was inferred from these experiments that 3 volumes of oxygen are condensed to produce 2 volumes of ozone. This conclusion was confirmed by comparing the rates of diffusion of ozone and chlorine, when the density of ozone calculated on the basis of T. Graham's law of gaseous dif fusion was approximately 24 (H=i), agreeing with a molecular formula of (48).