Clausius[3] at one time supposed that free atoms of oxygen might exist in an uncombined state, and his hypothesis on the nature of ozone was that this substance consisted of a mixture of molecules and free atoms of oxygen. In a later paper[4], however, he abandoned this view and regarded ozone as consisting of one or more atoms of oxygen feebly united, (lose verbunden) with molecules of ordinary oxygen. The idea that a third form of oxygen existed also obtained support from the fact that certain organic substances when exposed to the light in the presence of oxygen or air, acquire oxidizing properties. In 1850 Schönbein[5] stated that ether turpentine, and oil of lemons if allowed to stand in diffused light in contact with the air acquires the power of decomposing potassium iodide, and decolorizing indigo. In a subsequent paper[6] he shows that methyl and ethyl alcohols, tartaric and citric acids and even sulphuretted and arsenuretted hydrogen in the presence of sun light can decolorize indigo. These studies led Schönbein to publish a theory on the different modifications of oxygen. In this paper[7] he states that besides ordinary oxygen there are two other conditions in which it may exist one of these is ozone, or positively electrified oxygen, the other _antozone_ or negatively electrified oxygen. The union of ozone and antozone gives ordinary oxygen. He also stated that antozone was formed by the action of light on turpentine and air, and subsequently in 1862[8] he claimed that antozone was identical with the gas obtained when barium superoxide is treated with acids. Meissner[9] also supported the views of Schönbein and claimed that antozone was formed in two ways:--1st, By treating barium dioxide with concentrated sulphuric acid, 2nd, By the electrification of oxygen; being produced simultaneously with the ozone.