Tests of Ozone. Several tests of ozone have been contrived; but the one most employed consists of strips of unsized paper, impregnated with mucilage of starch and a solution of iodide of potassium. A very minute quantity of ozone in the air may be detected by this test. The iodine of the iodide is liberated by the oxidizement of the potassium, and then acts on the starch, producing its characteristic blue colour. According to the depth of the colour is the degree of impregnation; and attempts have been made to express this degree by a scale of numbers. This is no doubt a delicate test of ozone, but is not altogether reliable; because there are other substances, occasionally found in the air, which have the same effect as ozone upon the paper, such as the oxides of nitrogen, certain organic acids, essential oils, and chlorine, bromine, and iodine, especially the last, which has been shown to exist in the atmosphere. To obviate this source of error, M. Auguste Huzeau, of Rouen, suggests the use of strips of wine-coloured litmus-paper, one-half only of which should be impregnated with solution of iodide of potassium. The atmospheric impurities which produce on the starch-paper the same effect as ozone, generally form neutral compounds with the potassium, which have no effect on litmus; but, if there is ozone in the air, it will form an alkali with the potassium, which will restore the blue colour of the litmus-paper. (Journ. de Pharm. et de Chim., Fev. 1866, p. 91.)

Use of Ozone. For use on a small scale, as for the disinfection of apartments, whether in private houses or public establishments, nothing is probably more convenient or effective than ozone. One of the readiest methods of developing it for this purpose is by means of the slow spontaneous combustion of phosphorus. A stick of phosphorus, about an inch long, with its surface cleansed by careful scraping, should be put into a plate or saucer containing enough water to cover about one-half of the stick; and this should then be placed in a convenient spot in the room to be disinfected. The presence of water is necessary to the efficiency of the phosphorus, though it is only the uncovered portion of the latter that acts. if ozone is produced in excess, which may be known by its irritant effect on the nostrils or throat, or if there should be a disagreeable smell of phosphorus, the operation should be suspended, which may readily be done by covering the stick with water; and the degree of its operation may be regulated by lessening or increasing the surface exposed by adding or abstracting the liquid. Great care should be taken that the phosphorus be not set on fire; and perhaps it would be best to resort to some other of the disinfectants, if this cannot be intrusted to perfectly reliable hands.

Another method of generating ozone is to expose oil of turpentine in one or more bottles, partly filled, to the direct rays of the sun.

But probably the most rapid and efficient plan is one recommended by Schonbein, by which a large amount of ozone may be prepared with facility. Dissolve permanganate of potassa, finely powdered, in enough pure sulphuric acid, of the sp. gr. 1.85, to form an opaque, deep olive-green solution. Put this into a two-necked, perfectly clean glass bottle, so contrived that finely powdered peroxide of barium may be introduced through one opening, and the gas escape by the other. Bottger recommends two parts of the permanganate and three of the sulphuric acid; and finds the peroxide of barium unnecessary, though without it the escape of the ozone is slower; and this may perhaps be an advantage in the disinfection of ordinary apartments. But caution is required, in the management of the process, to prevent the vicinity of very inflammable substances; for ether, alcohol, and the volatile oils instantly take fire when in contact with the ozone, and sulphur is converted into sulphuric acid with an explosive sound. (Am. Journ. of Pharm., March, 1863, p. 185.)