270 
in consequence of the dissociation of the double molecules. According 
to my recent investigations, this case is met with everywhere where 
the dissociation (as for He,) leads to free atoms, for which the 
increased attractions of valency are so enormously much greater 
than for the compounds *). 
4, Vapour Pressures and Values of the Vapour Densities D,. 
We shall start with the treatment of the experimental material 
known at present. To supplement this, it is however necessary 
approximately to know the values of D, (the density of the saturate 
vapour). But for this purpose first the values of the vapour pressures 
must be known insapproximation. 
When the critical temperature is -assumed°—= 1427° U. = 1700° 
abs., and p,==1100 atm., then follows from the known formula 
Pe Ï 
lon == 
: a uC ) 
at 100°, 200°, 300°, 500°, 700° and 880° C., where p resp. = 0,28 mm., 
17,2 mm., 246 mm., 8 atm., 50 atm. and 162 atm.’): 
f= 1582.4, 81. 1,80... 178i, BOD: 
increases become resp. 47,7, 54,3 and 47,6 0/, for ideal substances with the same 
values of x. Hence already on an average 50 °/, between 2 =!/; and x = 2/s, 
which amount is still considerably increased for ordinary substances, and for the 
case that /b is not = 0. 
But when besides ,@ is so enormously large as in mercury e.g. (formerly we 
always supposed Aa =O, because we had only to do with substances that do not 
appear as isolated atoms with the so greatly increased attractions of valency), Te 
and especially pc is increased in a still much greater degree, even though the 
value of x be only slight. 
1) These Proc. 18 —21; especially 21 (1918), p. 644. Cf. also Z. f. anorg. Ch. 
104, 56 —156 (1918) and J. d. Ch. Ph. 16 (1918), p. 411. 
2) pe = 1150 atm. instead of 1100 atm. would give 1,83 for the first value of 
f, 1,80 for the last, which would render the almost constant course of this quantity 
still slightly better. The more pc is assumed to be below 1100 atm., the greater 
the unjustifiable decrease of the f-values on rise of the temperature. The value of 
1100 atm. is therefore to be regarded as a minimum, and pe will sooner be found 
somewhat greater than this amount than smaller. We remind that the course of 
the values of f is a strict criterion for the determination of the critical pressure. 
For in the neighbourhood of the critical temperature these values always increase 
on rise of temperature; for ordinary substances there is a minimum at about 
T=3/, Te; for substances as He, Hy, etc., where a continually decreases instead 
of increasing at falling temperature, f will also continue to decrease from 7, to lower 
temperatures, without passing through a minimum. (Cf. also Recueil des Tr. Ch., 
N°. Bland 5 of 1920), 
