THERMAL DECOMPOSITION OF OZONE 439 



changes. For this reason, H. E. Clarke, H. E. Jones and the 

 writer have undertaken a research on the reconversion of ozone 

 into oxygen ; the results of this inquiry are brought together in 

 the present article. 



Although the classical memoirs of Andrews, Soret and Brodie 

 deal mainly with the question of the constitution of ozone, they 

 contain accounts of some interesting observations on the mode 

 of production and on the stability of the compound. Andrews 

 showed that the presence in the ozonised oxygen even of traces 

 of the oxides of nitrogen will cause the ozone to revert to oxygen 

 with great rapidity. Brodie discovered that the highest per- 

 centage of ozone could be prepared from oxygen which was kept 

 in contact with concentrated sulphuric acid during the produc- 

 tion of the ozone. He believed that this fact was due to the 

 circumstance that ozone is more easily formed from dry oxygen 

 than from the gas in a moist condition ; but we shall see later on 

 that the true explanation of the observation is to be sought in 

 the circumstance that concentrated sulphuric acid absorbs the 

 nitrogen peroxide produced, together with the ozone, by the 

 influence of the silent discharge on the oxygen and the small 

 amount of nitrogen which the latter contains. The difficulties 

 experienced by the earlier workers in obtaining ozone from 

 moist oxygen are now known to have arisen from the ineffective- 

 ness of the silent discharge between the moist glass surfaces of 

 the apparatus used by them, not from diminished stability of the 

 ozone. Another remarkable fact recorded by Brodie, which still 

 awaits a satisfactory explanation, is the very high proportion of 

 ozone — as much as 85 per cent. — contained in the oxygen formed 

 when carbon dioxide is acted on by the silent discharge. 



An interesting modern investigation carried out with the sole 

 object of elucidating the chemical properties of pure ozone was 

 that of Shenstone and Cundall published in 1887. Convinced 

 of the importance of working with highly purified material, these 

 investigators took extreme precautions to obtain oxygen possess- 

 ing a very high degree of purity and dryness. They proved that 

 such oxygen is easily converted into ozone and they showed 

 incidentally that dry ozone is completely destroyed by contact 

 with mercury, after several hours, without oxidation of the 

 mercury being perceptible such as occurs, to a greater or less 

 extent, when the metal and imperfectly dried ozone come into 

 contact. Seven years later, in 1894, Baker confirmed Shenstone 



