XVII.
��PRODUCTION OF OZONE,
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��The presence of chlorine or oxidation products of nitrogen hinders the formation of ozone. Presence of hydrogen pro- motes the yield, if formation of water be rigidly avoided (i.e. if the tension is not too high). Silicon fluoride greatly aids the formation. If an induction apparatus be used, the current must not be made and broken too many times per second, otherwise it is not possible to keep the air sufficiently cool. Shenstone (S6) recommends 16 breaks per second ; but, of course, if the air be changed rapidly tliis number may be increased.
The Siemens and Halske ozoniser consists of two con- centric tubes, coated inside and outside, separated by a thin mica plate placed close to the inside of the outer tube, and by a narrow space through which the air to be ozonised must pass. The apparatus is very similar to the Berthelot tube. It works with an alternating current of 6500 volts ; the yield, i.e. the quantity of heat consumed in the ozone .per cent, of the electrical energy spent. The yield is, how- ever, nine times as great £is that calculated on the assumption that the process is an electrolytic one which follows Faraday's law. The inner tube of the ozoniser is kept cold by a cuixent of water.
Andreoli (^7) has recently described an ozoniser which is said to give a yield of ozone about five times as great as grams of ozone per kUowatt-hour. The apparatus consists of a number of square aluminium plates of about 70 cm. length
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