( 767 ) 
It is clear that this may cause a new phase to appear, and that 
besides equilibrium between the vapour phase and the liquid phase 
as in the ordinary theory of vaN per WaAALs, under particular 
circumstances equilibrium may occur between the vapour phase and 
the third phase, or between the liquid phase and the new phase. 
This phase, the molecular volume of which is somewhat less for 
positive Ad than that of the liquid phase, and for negative Ad 
somewhat larger, cannot be anything but a solid phase (amorphous 
or crystalline), which distinguishes itself from the liquid one in this, 
that the degree of dissociation of the double molecules (see $ 3) is 
found in the neighbourhood of 0, so that the molecules are for the 
greater part in the state of double molecules; in the liquid state, 
however, this degree of dissociation can lie between the values 1 
and almost 0, depending on whether we have to deal with so-called 
non-associating or with strongly associating liquids. 
It is self-evident that formation of triple or multiple molecules 
is not excluded in this, but for the sake of simplicity I shall only 
work out the theory for partially dissociated double molecules in 
the following pages. The phenomena will not show any quantitative 
change by the occurrence of multiple molecules. 
2. Before proceeding to a fuller discussion of the above formula (a), 
we shall first briefly repeat its derivation, and also set forth the 
influence of pressure and temperature on the equilibrium *). 
In the condition of equilibrium: 
Fie Se ety. oy en ae eae (BY 
0g 0g 
in which p, = eg and u, =a represent the molecular thermody- 
n, Ne 
namic potentials resp. of the double and of the simple molecules, 
we must substitute the well-known values for u, and u,. 
Now: 
0 ¢ a 
a Cae a [@ — RT Sn, . log Sn,)] + RT log e, | 
Ny 
9 
0 
u, = C, — ~— [2 — RT Sn, . log Zn] + RT loge, | 
3 
On, 
in which the functions of the temperature C, and C, are given by: 
C, TA k, td (log her 1) in [(e)o ip KCR | 
C, are kT (log dt 1) a (€), re T(s)o| 
while 
1) Cf, Arch. Teyler, Lc. 
52* 
