AND HYDEOGEN PEROXIDE DALTON'S LAW 203 



volume of the gas remains unchanged." Indeed, the researches of 

 Andrews, Soret, v. Babo, and others showed that the quantity of oxygen 

 absorbed by the potassium iodide is equal to the original contraction of 

 the volume of the oxygen that is, in the absorption of the ozone the 

 volume of the gas remains unchanged. From this it might be imagined 

 that ozone, so to say, does not occupy any room is indefinitely 

 dense. 



'3. "By the action of heat ozonised oxygen increases in volume, 

 and is transformed into ordinary oxygen. This increase in volume 

 corresponds with the quantity of oxygen which is given up to the 

 potassium iodide in its decomposition " (the same observers). 



' 4. These indubitable experimental results lead to the conclusion 

 that ozone is denser than oxygen, and that ozone in its oxidising 

 action gives off that portion of its substance which distinguishes it by 

 its density from ordinary oxygen.' 



If we imagine (says Weltzien) that n volumes of ozone consist of n 

 volumes of oxygen combined with m volumes of the same substance, and 

 that ozone in oxidising gives up m volumes of oxygen and leaves n 

 volumes of oxygen gas, then all the above facts can be explained ; 

 otherwise it must be supposed that ozone is indefinitely dense. ' In 

 order to determine the density of ozone (we again cite Soret) recourse 

 cannot be had to the direct determination of the weight of a given 

 volume of the gas, because ozone cannot be obtained in a pure state. 

 It is always mixed with a very large quantity of oxygen. It was 

 necessary, therefore, to have recourse to such substances as would 

 absorb ozone without absorbing oxygen and without destroying the 

 ozone. Then the density might be deduced from the decrease of 

 volume produced in the gas by the action of this solvent in comparison 

 with the quantity of oxygen given up to potassium iodide. Advantage 

 must also be taken of the determination of the increase of volume 

 produced by the action of heat on ozone, if the volume previously 

 occupied by the ozone before heating be known.' Soret found two such 

 substances, turpentine and oil of cinnamon. ' Ozone disappears in the 

 presence of turpentine. This is accompanied by the appearance of a 

 dense vapour, which fills a vessel of small capacity (0- 14 litre) to such an 

 extent that it is impenetrable to direct sun-rays. On then leaving the 

 vessel at rest, it is observed that the cloud of vapour settles ; the 

 clearing is first remarked at the upper portion of the vessel, and the 

 brilliant colours of the rainbow are seen on the edge of cloud of 

 vapour.' Oil of cinnamon that is, the volatile or odoriferous substance 

 of the well-known spice, cinnamon gives under similar circumstances 

 the same kind of vapours, but they are much less voluminous. On 



