1176 
fn Oe hy ; 
vibration becomes = ————— + const. according to the formula of 
7 
| 
PraNCK-EINsreIN. It could be neglected for the temperatures that are 
to be taken into account for the evaporation’). For very high values 
of the energy of vibration, which, however, will be so rare at not 
too high temperatures that they may be left out of account in the 
caleulation of the mean value, the mutual motion of the atoms is 
no longer a simple sine vibration; and at still greater value of the 
energy the attractive force between the atoms becomes very small, 
they get detached from each other, and the molecule is dissociated.’) 
We may imagine that each of the (spherical) atoms has a pole, 
and that in the molecule the two poles coincide or are removed 
from each other a small distance through the heat motion, however 
in such a way that the axes of the two atoms passing through pole 
and centre are always in the production of each other. 
When the atoms are of different kinds, say A and B, we find 
for the constant of equilibrium of the reaction AB 2 A + BB’): 
hy 
dl 
eae uaa ge A ak fee EF LT 
be eT gay ele teas Fe haan ALOE en hoen 
ny mA +MB J h 2 an 
in which #, resp. m, is the number of split resp. unsplit molecules 
per volume unity, m4 and mg the masses of the atoms, and / the 
moment of inertia of the molecule. c is the heat of dissociation, as 
it would be for the absolute zero. 
For lower temperatures this reduces to: 
Berge Meee ty bh CER NE 
u, m4+mpB 2Ih\ 29 
On the other hand according to thermodynamics: 
2 Ss 1 \2-1 
=de Pils) Secs Tere Cal ae ep ee 
1 
aa Has d-dAB 
; ; 
in which log A= 
3 R 
c has the same meaning as in (20) 
1) If namely a possible zero point energy is not so great that the moment of 
inertia becomes variable in consequence. 
*) In reality it may of course occur that the vibrations are already no longer 
sine-shaped for small values of the energy; it is, however, not possible for the 
present to take this into account theoretically. 
5) J. D. vAN DER Waars Jr., these Proceedings XVI, p. 1082. 
