650 



volume of 1 Gr. atom H, and c//, the same quantity for H,. As 



CH^ is = 5, and c// = 3 (in Gr. cal.), Q— Q, -\- T may be written 



in the case of H, -»► 2H for Q. 



When, however, the volume becomes smaller and smaller, and the 



a A 



quantities -and larger and larger, at last a (tictitions) volume will 

 r V 



arise, in which the ditference of the two enei-gies has become = 0, 



in consequence of the fact that with respect to the internal energy 



it will then have become quite indilferent whelhei' the atoms are 



separately present in thai .small space, or combined to molecules — 



i.e. when also the energies of translation do not differ, hence at T ■= 0. 



H, 



For the difference Q' = 2E'm 



4.4 



H + H 

 ^' H., ^ve have in this case: 



Q' = Q,--^+-+{2cn~cHXJ\ ..... id) 



in which i\ represents the above mentioned small volume, which 

 we shall have to define more closely. Now it follows immediately 

 from {(l) at T=0, in which case Q' must be =0, that 



iA a 



(1) 



and this is the simple I'elation l»etween the heat of dissociation Qo 

 at T=0 and the two attractions A and a, which we have sought. 

 We must now determine the small volume v^. This will evidently 

 be of the order of the limiting volume, wdiich the molecules theujselves 

 (see the above figure) occupy in the natural state in unconstrained 

 condition, i.e. the volume expressed by b,, — and not e.g. the smaller 

 volume b^ in the liquid state, where the molecules will be com/«'^.y*W 

 in consequence of the smaller space, and which therefore denotes a 

 constrained, and no free, no natural condition '). Now b,j is about = bk, 

 so that we may put : 



V , ^ bg =z yb/c, 



In this it has also been supposed that /></ is not = 4m, when m denotes the 

 real voknne of the molecules, but simply = m itself. According to recent views 

 the latter supposition is theoretically at least as well justified as the former ^v = 4m, 

 which refers specially to collisions of mathematical spheres, and not of real 



