Baumann then describes results obtained by himself which enable us to clearly distinguish between active oxygen and ozone. Starting from the observation of Remsen[18] and Southworth that carbon monoxide, at ordinary temperatures, is not oxidized by ozone, he suspected that active oxygen would readily effect its oxidation. Palladium hydrogen was therefore sealed up in a capacious glass tube with a few cubic centimeters of clear lime water and a mixture of carbon monoxide and oxygen free from carbon dioxide. At first the lime water remained clear, but after several hours a cloudiness in the lime water became visible and after several days a precipitate of calcium carbonate settled to the bottom of the tube. He then repeated the experiment in a modified form. From a gasometer, containing a mixture of three volumes of oxygen and one of carbon monoxide free from carbon dioxide a slow current of gas was passed, first into a wash bottle containing a clear solution of baryta water, then into a tube containing palladium hydrogen. Then the gases were again passed through a wash bottle containing baryta water. After the current had been passing for four hours, the first baryta water was still perfectly clear, but the second showed a distinct cloudiness of barium carbonate, which slowly increased in the course of twelve hours. The baryta water in the first wash bottle remained clear even to the end of the experiment. The different behavior of ozone and active oxygen was then shown by the following experiment:--“A slow current of air free from carbon dioxide was passed into a flask containing moist phosphorus, from there into a second flask where the ozonized air came in contact with a somewhat slower current, consisting of a mixture of three volumes of oxygen to one of carbon monoxide, carefully purified from carbon dioxide. From the second flask the gases were passed through a clear solution of baryta water.” “After all carbon dioxide had been removed from the apparatus the baryta water remained perfectly clear (völlig klar) after the gases had passed through for six hours.” “But, on the other hand, if the mixture of carbon monoxide and oxygen was passed into the first flask, containing the moist phosphorus and in which according to our theory active oxygen must occur, then the result is quite different, the baryta water becomes cloudy in a short time and in the course of an hour there is formed an _abundant precipitate_ (‘reichlicher Niederschlag’) of barium carbonate.” From these results he concludes that active oxygen may be detected by its power of oxidizing carbon monoxide, and states that this fact enables us to decide whether in oxidations effected by ozone there occur free atoms of oxygen.