THERMAL DECOMPOSITION OF OZONE 445 



catalysis and especially on the question of the remarkable effect 

 exercised by water vapour on most chemical changes. It has 

 been shown by Dixon, Baker and others that a very large 

 number of chemical changes will not take place below a certain 

 temperature unless water vapour be present and it has been 

 concluded that water vapour is essential for the progress of 

 these changes at all temperatures, indeed that the presence of 

 water vapour is necessary in all cases of chemical change. 



As it is probable that there is no really essential difference 

 between the decomposition of ozone and any other simple 

 chemical change, inasmuch as the decomposition of ozone can 

 proceed without the assistance of water, the ground for the 

 view that any change can proceed without the aid of water, 

 provided that the temperature be sufficiently high, is consider- 

 ably strengthened. In the opinion of the writer, the right view 

 to take of the catalytic effect of water is that the vapour enables 

 a change to take place at a temperature at which it could not 

 proceed without its assistance : more precisely, that the rate of 

 a chemical change is the sum of two terms, the first correspond- 

 ing with the rate of change without the catalyst, the second 

 with the increase in rate due to the catalyst ; and that the first 

 term can and often does become negligibly small in comparison 

 with the second at low temperatures. 



The mode in which the catalyst assists the chemical change 

 is an entirely different question. Armstrong thinks that the 

 powerful catalytic effect of moisture must be attributed to the 

 fact that water is an effective electrolyte and. that it can there- 

 fore introduce into the system the possibility of electrolysis 

 taking place. The theory is in agreement with the principal 

 facts. Chemical change is undoubtedly facilitated by the com- 

 bined agency of an electrolyte and a metallic conductor, that is, 

 by the process commonly known as electrolysis. If the metallic 

 conductor be removed and the circuit be so small that an 

 exchange of electrons can take place without its assistance (as 

 Armstrong postulates), there is no ground for supposing that 

 the electrolyte could not still aid the change to proceed. But 

 on the other hand, if the metallic conductor be unnecessary, the 

 only effect of its removal being that the change proceeds with 

 greater difficulty, it seems to me that the electrolyte cannot be 

 absolutely essential. 



