288 
It is to be expected that probably the value of 6,: 7, at the 
triple point will possess the same value for certain groups of elements. 
That in other words the solid state then occurs when the molecular 
volume shail have become a definite fraction of the total volume. 
To investigate this we shall determine the general value of ,:v, 
from the equation of state (when, namely, at the triple point p can 
be neglected) 
a 
a (v,—b,) = RT,, 
aa 
from which follows: 
v,—6, RT, a 
v a]: “2 
4 B eren ge En 
Now RT,=-—-4—, in which A lies between 1 and */,, (for 
at OE 
substances with high critical temperature). For most substances with 
which we shall occupy ourselves in what follows, we may put 
fF 2 ar A “on 
RT, = ——, hence ap=" , RT;. bx. In consequence we get: 
( Ok 
nb 
Sys 
: rs am, m 
age a oY 
vs" i a, by by. 
in whieh (a, and a, not differing much) the factor g will never be 
far from ?/,. Hence we tind: 
If therefore 6,:7, or (v,—b,):v, has a constant value, also the 
value of v,: bj >< m, must be constant. In this by: v, is the factor 
of the above formula (1), which we shall eall f,, so that 
molt dm. oe eN 
Y 
EE Ma Sk 6 ss 
Hence 
? 9 
If eg: f,:m,=6; then’ Wbp */, X le = "lev SO that 
then the solid state would oceur, when the free (available) space 
between the molecules has become */,, of the total volume. 
If instead of m,— 7, : 7; the reciprocal quantity u,= 7%: 7, is 
introduced, then becomes: 
in which: 
