When an electric spark is passed through air a peculiar smell is noticed; this is due to the formation of ozone. The electricity in passing through the air appears to break up the molecules of ordinary oxygen (Fig. 164), and the atoms which are thus dis




Fig. 164. - Diagram to illustrate the formation of ozone by electricity. a represents oxygen, through which a spark is passing; b after it has passed. The double rings are intended to represent molecules of oxygen, each containing two atoms. As the electric spark passes through the oxygen it breaks up the first molecule, carrying one atom on to join the second molecule of oxygen, and form one of ozone. The atom which is left joins another molecule of oxygen, and also forms ozone. (After Lockyer.) sociated join together so as to form ozone. It is also formed by the slow oxidation of phosphorus, and is formed also by protoplasm (p. 69). Two atoms are present in a molecule of oxygen and three in that of ozone. When electricity is passed through a quantity of oxygen, contained in a tube over mercury, so as to convert a portion of it into ozone, it becomes condensed in bulk and acquires much greater chemical activity. On warming it again to about 300° C. the molecules of ozone become again dissociated, ordinary oxygen is formed, the gas then returns to its original bulk, and it loses its active properties. Ozone has a most powerful oxidising property, attacking metals and forming oxides, and destroying organic substances, such as paper and caoutchouc. It has a curious action upon albumen, already described (p. 58), and decomposes blood. As might be expected, it is exceedingly poisonous to low organisms, and is fatal also to the higher animals.

Its effect appears to be due in a great measure to its having such a powerful irritant and even destructive effect on the albuminous tissues of the respiratory passages, that it causes reflex depression of the heart and interferes with the ordinary respiration in the lungs. It thus diminishes instead of increasing oxidation. In animals it causes sometimes quickness, and sometimes slowness of the respiration (vide p. 241), and produces excitement followed by exhaustion and sometimes convulsions.

When it is present only in small quantity in air, it may be inhaled without any disagreeable effects, and is, according to Binz, a decided soporific.

Uses. - It has been recommended in cases similar to those already mentioned under oxygen; and also in infectious diseases, and in diphtheria, where it is likely to be useful by destroying low organisms, which produce the disease.