OZONE (Greek, όζωh, I smell) is a peculiar variety of oxygen, characterised by its greater weight, its peculiar chlorous smell, its intensely active oxidising powers, and, finally, by the ease with which it passes into common oxygen. The history of ozone may be summed up as follows:—In 1785 Van Marum observed the production of a peculiar smell when electric sparks were passed through oxygen. This smell, which every one who has worked with an electric machine must have noticed, Van Marum regarded as the “smell of electricity,” thinking that electricity was a substance. In 1840 Schönbein, of Basle, proved the existence of a definite substance, to which he assigned the name of ozone, and discovered several modes of producing it, a delicate test for it, and several of its most striking properties. He subsequently added many new facts, but to the time of his death he never held a correct theory in regard to its nature. Later researches by
Marignac and Dedalline, Becquerel and Fremy, Andrews and Tait, Soret, Brodie, and others, have established the true nature of this remarkable body. It is now generally admitted that it only differs from common oxygen in containing three atoms of oxygen in each molecule instead of two. In fact, as the formula for oxygen is O2, that of ozone is O3. It follows that ozone is half as heavy again as oxygen, and it has accordingly been demonstrated that its specific gravity is 24 (H = 1), that of oxygen being 16. All the known reactions of ozone are easily explained in accordance with this view.
Ozone may be generated in several ways. 1. By the action of electricity on oxygen or air, sparks are far less efficacious than the silent or ‘slow’ discharge; but the best apparatus is the induction-tube of Siemens. This consists of two tubes, one inside the other. The inner side of the inner and the outer side of the outer tube are coated with tinfoil, and these coatings are connected with the terminals of a powerful induction-coil. Dry air or oxygen streams between the tubes and passes out, strongly charged with ozone.
2. M. Boillot has proposed a modification of Siemens’ apparatus, which consists of two glass tubes, one fitting within the other, and each coated externally with powdered coke made to adhere by means of gelatin. The coatings of the two tubes are connected with the poles of an induction coil, and a stream of oxygen is made to pass between the tubes, and becomes thus exposed to the influence of the silent discharge, as in Siemens’ contrivance.
3. Hozeau has invented an apparatus which he calls an ‘ozoniser,’ by means of which ozone is produced in considerable quantities. In an ordinary straight gas-delivery tube is placed a wire of copper, lead, or, better, platinum, 4 to 6 décimètres long, with one of its extremities passing through the side of the upper portion of the tube. On the exterior of the tube is coiled a similar wire over the path of the preceding. When the two are placed in communication with a Ruhmkorff’s coil, giving a 2 or 3 centimètre spark, a slow stream of oxygen passing through the tube will be strongly charged with ozone. By this apparatus Hozeau has prepared oxygen containing 60 to 120 (once 188) milligrams of ozone per litre. Electrolysis of water furnished only 3 to 5 milligrams, barium peroxide and sulphuric acid 10 milligrams per litre.[84]
[84] ‘Comptes Rendus’ (‘Watt’s Dictionary,’ second supplement), lxx, 1286.
4. During certain processes of oxidation a piece of phosphorus, half covered with water in a bottle of air, absorbs a portion of the oxygen, while another portion becomes partially ozonised.
5. By plunging a clean glass rod heated to about 260° C. into a jar containing a few drops of ether.
6. By mixing very gradually 3 parts of
strong sulphuric acid and 2 of permanganate of potash.