OZONE (from the Greek 410, to smell) is the name given by Professor Schonbein of Basle to an odour evolved during the progress of certain electrochemical decompositions. It is also produced by common electrie sparks, and by the working of an ordinary electrical machine in the air. This odour attracted no particular notice until M. Schonbein called the attention of the British Association to it in 1840, since which time it has undergone much examination, and various theories have been propounded as to its nature and compo sition.
Ozone is evolved at the anode, or positive pole of a galvanic battery, at the same time with oxygen, during the electrolisation of any of the following bodies : namely, water, dilute sulphuric acid, solu tions of phosphoric and nitric acids, potash, and many oxysalts. Of these, dilute sulphuric acid mixed with chromic acid yields it in the greatest quantity. It may also be obtained from atmospheric air, by passing the electrodes through a closely-fitting cork into a jar filled with air, and frequently making and breaking contact. Under the influence of heat ozone disappears, and it cannot be obtained from heated solutions, or solutions of hydracids, chlorides, bromides, or iodides, the presence of which, even in small quantity, prevents its evolution from solutions otherwise yielding it abundantly. It may be developed by electrolising a solution of chloride of sodium with platinum electrodes, by placing the gas collected at the anode over ammonia and water to absorb the chlorine. Ozone can be preserved for a length of time with the oxygen collected with it in well-closed bottles. It possesses the property of bleaching litmus-paper and pager coloured with indigo or a solution of that substance. It is readily absorbed by mercury and the oxidisable metals, farming oxides with them; and when the solutions employed are heated, its affinity for metals is so greatly increased that it oxidises platinum and gold. Water absorbs it. The inspiration of ozone is very injurious, the effects being similar to those resulting from chlorine and bromine. A mouse is killed with it in five minutes ; and M. Schonbein states that he was seriously affected by breathing an atmosphere charged with it.
The electrodes employed in these experiments have a great influence In respect to the evolution of ozone.. With water or acid solutions they must be of platinum or gold; for when the more oxidisable metals are used it enters immediately into combination with them.
It can be obtained from air when the positive electrode is copper, iron, silver, or platinum, and zinc negative, but not when these arrange ments are reversed, or both electrodes are of zinc. On electrolising a solution of sulphuric acid the following results are obtained :—With platinum electrodes the odour is very powerful; but it is not produced when copper, zinc, or iron electrodes are employed. With boxwood charcoal, the gas given off from the positive pole has no smell ; but when absorbed by lime-water it turns it milky, proving the gas to be carbonic acid. With gas charcoal, sulphuretted hydrogen is evolved at the negative pole and carbonic acid at the positive, but no odour of ozone is produced. With a solution of chloride of sodium, the odour is not perceptible until the gas obtained from platinum electrodes at the positive pole is placed over ammonia and water to absorb the chlorine. The residual gas emits the peculiar odour.
There exists much variance in the experimental results with this new substance, and not less in the opinions concerning its nature. Professor Schonbein and Dr. Andrews regard it as oxygen in an allotropic condition, whilst Dr. Williamson and M. Baumert consider it to be a teroxide of hydrogen. The latter chemist has even succeeded in analysing ozone, and thus quantitatively demonstrating its compo sition; nevertheless, Dr. Andrews calls in question tho accuracy of these experiments, and adduces others in proof of his view of the composition of this substance.
Tests for Ozone.—Notwithstanding the remarkable characters of this body, no reliable test of its presence in minute quantity (in the air, for instance) is known. Paper imbued with starch and iodide of potassium is rendered blue by ozone, but the same effect is produced by acid gases; and this test, as used for the detection of ozone in the air, is utterly worthless. Paper soaked in solution of sulphate of manganese, which is turned brown, or impregnated with black sulphide of lead, which is bleached by ozone, are more reliable tests ; but even these are open to so many sources of fallacy as to render their indi cations of little value. [HYDROGEN, Tiroxide of.]