OZONE, a colorless gas, an allotropic form of oxygen, having a peculiar odor like that of chlorine and extreme chemical activity. Its density is one and one-half times that of oxygen and it is changed into oxygen only at a high temperature. Ozone is found in country atmos phere to a much greater extent than in cities and towns, and on mountain tops to a greater extent than in deep valleys. Its molecular formula is 0, and its molecular weight, 48.00.
The peculiar odor around an electrostatic machine in operation was noticed long before its cause was discovered. In 1840 Schonbein explained the cause of this phenomenon and succeeded in preparing ozone by the electrolysis of water and by the slow combustion of phosphorus.
Physical 1. Ozonized air is colorless and has an odor somewhat similar to that of chlorine. It exerts a stimulating action on the salivary glands. Pure ozone (obtained by liquefaction) is bluish in color and danger ous to handle on account of its tendency to ex plosive decomposition. Like oxygen, ozone is a supporter of combustion.
2. Specific gravity, 1.658 (air =1). Boiling point, 119° C. Decomposing temperature, 270° C. Solubility in water per 100 volumes, 0.88 volume. Ozone dissolves in and combines with the etheral oils, especially turpentine, cin namon oil and with aqueous quinine solutions.
Chemical 1. The formation of ozone is an endothermic reaction, the heat of formation being 36,208 calories.
2. Ozone is a powerful oxidizing agent. It bleaches solutions of litmus and of indigo. It oxidizes phosphorus, sulphur and arsenic to the corresponding acid anhydrides. Sulphides are converted to sulphates; and nitrogen into N20,, ammonium nitrate, and nitrite, in the presence of water. Manganese in solution is quantitatively precipitated as MnO,. It attacks almost all organic compounds and rapidly cor rodes rubber tubing, and cork or rubber stoppers. The albuminoids and saturated hydro carbons are practically unaffected.
3. Unsaturated organic compounds with a double bond between carbon and carbon absorb ozone quantitatively forming characteristic ozonides.
4. Ozone is a strong bactericidal agent.
Laboratory Methods of Preparation, 1. Electrolysis. Fisher and Massanez (1907) obtained oxygen containing 23 to 28 per cent of ozone by electrolyzing between cooled platinum electrodes dilute sulphuric acid (specific gravity 1.223 to 1.07) by a current of 80 amperes per square centimeter at 7.8 volts. They obtained a yield of 7.2 grams ozone per kilowatt hour.
2. Thermal Method. As stated above, the formation of ozone is an endothermic reaction. Nernst has shown that free atoms of oxygen form ozone only when their concentration is 10 to 20 times greater than in ordinary oxygen. Therefore ordinary oxygen should be readily transformed into ozone when exposed to high temperatures and pressure. To minimize the decomposing effect of the high temperature on the ozone the air must be rapidly cooled after exposure to heat.
A current of dry air is brought in contact with an electrically heated Nernst filament.
Better results, however, are obtained by im mersing the incandescent filament in liquid oxygen. (German patent 195, 985; 1906).
3. By Ultra-Violet Rays. A current of air is subjected to the influence of the rays from a mercury vapor lamp. The lamp has a bulb of quartz (transparent to ultraviolet rays) and the air is passed spirally between the bulb and an outer wall of glass (fairly impervious to the ultraviolet rays). (United States patent 845,965).
Commercial Methods of Manufacturing Ozone. Of the methods which have been tried for making ozone, the only practical ones have been those involving the passage of air or oxygen through an apparatus and subjecting it to the influence of the silent electrical dis charge. A very good ozonizer is the Siemens and Halske machine. Each ozone tube (of which there are six or eight set in a suitable metal tank through which water flows for cool ing purposes) consists of a cylinder of glass around one of aluminum. The aluminum cylinders are connected to the alternating cur rent, the glass being grounded by contact with the cooling water in the tank. Air enters a lower chamber beneath the cooling tank, passes through the ozone tubes, where it is subjected to the influence of a silent electrical discharge, and passes off as ozonized air from an upper chamber. The tension of the current will vary between 10,000 and 90,000 volts at, at least, 100 alternations per second. A higher tension yields a greater output of ozone. The Siemens Halske ozonizers yield about 60 grams of ozone per horse-power hour. For further de tails regarding this machine and several other modifications, consult Martin, 'Industrial Uses of Ozone finds some application in the bleaching of sponges and straw. (2) The principal use of ozone depends upon its bactericidal property. It is used for sterilizing water, as well as air. The advan tage in the use of ozone for purifying water lies in the fact that it is non-toxic and leaves no objectionable residue. Furthermore it does not attack the salts usually found in water which give it its characteristic taste. (3) The disagreeable effects of air in crowded rooms are not entirely produced by the excess of carbon dioxide present. They are partly due to organic substances given off from the skin and lungs of the people present. The intro duction of a slight amount of ozone into such rooms is found to offset the bad effects by oxidizing these impurities. However, the bac teria present in such crowded rooms cannot be destroyed by the amount of ozone permis sible, for the concentration required to kill bacteria would be such as to make the air intolerable to those present. (4) Ozone has recently found application in the commercial manufacture of vanallin from iso-eugenol and in the production of artificial camphor. Consult Martin, Thorpe, of Applied Vosmaer, Alexander, Its Manufacture, Properties and Uses' (New York 1916).