402 Mr. W. M. Hicks on some Effects of Dissociation 



take place in an elementary gas, the molecule being composed 

 of two atoms. How the atoms are bound together we do not 

 know ; but, from what we can gather, there seems to be some 

 attractive force between them which at very close quarters 

 changes into a repulsive one. Equilibrium is sustained by the 

 attraction between the two atoms and their motion about one 

 another. If, then, the two atoms of a molecule become sepa- 

 rated, there seem only two ways of accounting for it. Either 

 their relative motion becomes so large as to overcome the 

 force of attraction ; or some external force must act upon them, 

 which can be nothing else than a reaction between them and 

 some other molecule. The latter is the hypothesis I have 

 adopted in the following investigation. 



2. I consider the atom to be smooth, spherical, and perfectly 

 elastic, and, in order to bring the dissociation under mathe- 

 matical treatment, suppose 



(1) That when a molecule experiences a blow greater than 

 a certain blow c, it breaks up into its component atoms, 



(2) That when two atoms impinge with a blow less than c, 

 they combine to form a molecule. 



Now it is exceedingly improbable that any of these sup- 

 positions is absolutely true ; but yet I venture to think, since 

 the mathematical form would be similar, that the state of such 

 a gas would differ only slightly from that of real gases. As 

 was said before, the reaction between two molecules is pro- 

 bably a varying one, and it is unlikely that they ever come 

 into real contact ; still the mean effect will be similar to the 

 case under our hypothesis. We must look upon c as a mean 

 blow for different directions of incidence, or as some quantity 

 which in the real state determines whether the molecules will 

 break up or not. For instance, if the force between two atoms 

 were inversely as the square of the distance, c would determine 

 whether the resulting orbit of two atoms coining together 

 would be an ellipse, or a parabola or hyperbola. So also the 

 radii of action must be taken as average quantities. Further, 

 it is not likely that they are absolutely independent of the 

 temperature ; for it is conceivable that as the internal energy 

 increases they will fly further apart, and thus become more 

 liable to blows from the other molecules. Neither are we 

 perhaps warranted in assuming that c is constant ; since c 

 constant involves the invariability of the distance of the two 

 atoms ; for if the distance increased, the force between would 

 diminish, and therefore c also. Nevertheless, although 

 numerical results would be affected by this cause, the general 

 laws would be of the same form in the two cases ; and in 

 either case our experimental knowledge is neither wide 



