204 Mr. W. Sutherland on the Spontaneous, 



Thus, then, a process of association or combination of the 



2 molecules to form 3 , that is, ozone, explains one of 

 Bohr's equations, and the cessation of anomaly in Crookes's 

 experiments on deflecting force. It is necessary that in 

 compressing pure 3 a pressure should be reached at which 

 the 3 begins to dissociate into 2 , and progressive increase 

 of pressure produces progressive dissociation of 3 into 2 . 

 This result is so contrary to the ordinary experience of dis- 

 sociation amongst gases that it calls for the closest exam- 

 ination before we proceed farther. Now the most striking 

 result so far is that over a considerable range of values of B 

 there is to be a constant value of N 2 /B, and this gives us at 

 once an insight into the remarkable character of this disso- 

 ciation ; for N 2 /B is proportional to the number of collisions 

 of a molecule of 3 with other molecules of 3 in unit time, 

 and as long as this is below a certain value 6ct'/mv 2 , as we 

 have just seen, there is no dissociation, but when by com- 

 pressing the pure 3 a volume is reached at which N 2 /B = 

 6a!/mv 2 , that is, at which the number of encounters of 3 

 with its fellow molecules attains a certain value, some of the 

 molecules are on the point of being dissociated, and if the 

 pressure is increased the dissociation proceeds until the 

 number of collisions of an 3 with its fellows falls to the value 

 given by N 2 /B = Qa'/mv 2 , at which the number of molecules 

 of 3 remains constant until further compression is attempted; 

 thus, then, we have evidence that there is a certain periodic 

 collision with one another which the 3 molecules cannot 

 stand, and this implies that the period is identical with some 

 natural period of vibration in the molecule : we have a case 

 of molecular resonance leading to the destruction of the 

 resonating molecules. 



So far as we have gone it appears as though a collision of 

 an 3 with an 2 occurring between its collisions with other 



3 is of no account, and we can understand how the presence 

 of a number of 2 molecules is really of little importance to 

 the final result ; for even if a collision wdth an 2 has an 

 inimical result as regards the dissociation, still, according to 

 the laws of probability, there will be a number of successive 

 collisions of some of the 3 molecules with others without 

 intermediate collisons with 2 which would suffice to produce 

 the destruction of the 3 molecules, and therefore the only 

 effect of the 2 molecules is to make the process of disso- 

 ciation slower. 



But at last a stage will be reached at wdiich the dissociation 

 is so slow that it is only able to neutralise the combination 

 that goes on, and then further diminution of volume will 



