Active and Ordinary Oxygen. 267 



the explanation I originally gave, is connected with the changes 

 in volume which oxygen undergoes when part of it passes from 

 the ordinary into the active condition. 



In the paper above cited, " On the Nature of the Motion 

 which we term Heat/' I have referred all volumetrie relations of 

 gaseous bodies to one theorem, " that for the same temperature 

 the individual molecules of all gases have the same vis viva as 

 regards their progressive motion." If this theorem is correct in 

 the case of all gases, there must for the same temperature and 

 the same pressure be the same number of molecules in the same 

 volume. If we consider a certain quantity of ordinary oxygen, 

 according to my view the atoms are united in pairs forming mo- 

 lecules. If, by the excitation of this oxygen, a number of mole- 

 cules are decomposed into their atoms, it is a question how these 

 atoms are constituted — whether they remain isolated and effect 

 their motions separately, so that each of these atoms in the gas 

 plays the part of a molecule, or whether they enter into any 

 other combination. 



In my first explanation I have assumed that the separated 

 atoms remain separate and form molecules of themselves, so that 

 in excited oxygen there are more molecules than in the same 

 quantity of oxygen in the unexcited condition. There were 

 indeed at that time the experiments of Andrews and Tait* on 

 the density of ozone, which had given the result opposed to that 

 assumption, that oxygen containing ozone, when converted into 

 ordinary oxygen, increases in volume; but these experiments 

 were at that time so isolated, and from their difficulty seemed to 

 contain so many possible sources of error, that, without doubt- 

 ing the skill and care of these experimenters, I believed I must 

 raise an objection to the reliability of the results, and retain my 

 assumption. 



Since then the same gentlemen have continued their investi- 

 gation of the subject, and Babo and Soret have made some obser- 

 vations on the same point. By these investigations, in the de- 

 scription of which the authors in question only speak of ozone, 

 and not of two kinds of active oxygen, the result previously 

 found, that ozonized oxygen fills a smaller volume than the 

 same quantity of oxygen which is completely in the condition of 

 ordinary oxygen, has become completely confirmed; and the 

 special result has been obtained that the difference between the 

 two volumes is just as great as if that part of oxygen which was 

 in the condition of ozone did not exist. 



It becomes now the question whether, and in what manner, 

 my explanation, that active oxygen is distinguished from ordinary 

 oxygen in consisting of isolated molecules, can be made to har- 

 * Proceedings of the Royal Society, vol. viii. p. 498. 



