Such was the beginning of our knowledge of ozone, the precise nature of which has not yet been completely made out. At the present time it is held to be oxygen condensed. To use a chemical phrase, the molecule of oxygen, which in the ordinary state is composed of two atoms, is condensed, in ozone, as three atoms. By the electric spark discharged in dry oxygen as much as 15 per cent. may, under proper conditions, be turned into ozone. Ozone has also been found to be heavier than air. Professor Zinno says, that compared with an equal volume of air its density is equal to 1,658, and that it is forty-eight times heavier than hydrogen. Heat decomposes it; at the temperature of boiling water it begins to decompose. In water it is much less soluble than oxygen, and indeed is practically insoluble; when made to bubble through boiling water, it ceases to be ozone. The oxidizing power of ozone is very much greater than that of oxygen, and, according to Saret, when ozone is decomposed, one part of it enters into combination, the other remains simply as oxygen. It is remarkable that some substances, like turpentine and cinnamon, absorb ozone and combine with it, a simple fact of much greater importance than has ever been attached to it. I found, for instance, that cinnamon which by exposure to the air has been made odorless and, as it is said, "spoiled," can be made to reabsorb ozone and gain a kind of freshness. It is certain also that some substances which are supposed to have disinfecting properties owe what virtues they possess to the presence of ozone.