(1214 ) 
(3 SED Ne dl Rel ae: 
av), \ar Mi ie critical point, we get: 
d 
In this last equation (5) represents the increase of tension of the 
a kr 
saturate vapour, as it is at the critical temperature. We may also 
write : 
T' dp 
sis Late AEN 
pal) i, PIV 
or 
a 
Dr == 
: [rar 
ve | ——— 1]. 
p dp Wee 
And putting vs = rb, 
a 1 
Dn == == 
af bi | LT dp n 
7 eren Tas een 
p dT 6 (7) 
For a number of substances the tension of the saturate vapour 
has been experimentally determined up to 7, — and especially the 
values of p for some thirty substances have been given by SYDNEY 
Youre in “The Scientific Proceedings of the Royal Dublin Society” 
(June 1910. These tensions have been determined for temperatures 
between 7}. and about 4 7%. 
By approximation they are indicated by the empirical formula: 
) TT 
— NN ep log — =f 
Ph 1 
or 
1—m 
— Nep log a =f : 
m 
But the quantity f is somewhat variable with m; starting from 
T;. or m=1 there seems to be at first some diminution of f with 
descending value of m, which, however, has already been replaced 
by a rise for m< 4, while for m=} the value of m has again 
risen above f;,. For still smaller value of m the observation is 
prevented by the appearance of the solid state. From some pheno- 
mena I have concluded as probable that e.g. at fp = 7 the limiting 
value of f would rise to about 9 at the absolute zero. 
From this empirical formula we derive: 
dx Tm 1—m dfn 
adm m? m dm 
