+ 
while for mercury it is complete. To this case belong those substances, | 
for which the heat of dissociation q of the double molecules (i.e. 
the absorbded heat in dissociation) is comparatively small or = 0 (at 
any rate << /7}; hence for ordinary substances <7 7%, when q is 
expressed in gr. cal.). Acetic acid belongs to the other category of 
substances, for which the association in the vapour decreases on 
increase of temperature, till a minimum is reached in the neigh- 
bourbood of 7). At still higher temperature the association in the 
vapour increases again. Here (below the temperature of inversion) 
the temperature-change therefore prevails over the volume-change. 
To this belong those substances, for which the heat of disso- 
ciation of the double molecules is comparatively large (> 7 Tj). 
Accordingly mereury — and we shall also see this confirmed on 
other grounds — is bimolecular at Tj. 
a: 1s. "ay 
—~. in which 2 for substances with 
TU ee, 
Now 27, = sary À by 
a7 a Pk 
high critical temperature has the limiting value *’/,,'), SO that with 
R=1:273,1 we have: 
mae Gace ge ee 
bj. 28 b?}. 
if mow. Uap, — 11.0 x 10-2 15010". for Hem 
we shall find presently, then we get for Hg, : 
eae SLO" or mees 
150 
because for He, War=n (Map), and also 4; will be == (Dj), 
(possible contraction for bj, excluded). 
Hence we find: 
Ty, = n. 630° (abs.) ; pe=192 atm. 
And as the critical temperature of mercury (see § 3) is lying with 
great probability in the neighbourhood of 1260° (absolute) *), and 
< 2 
1) For a we have namely found the expression A= ai ( Z ) in which 
8y—l\y +! 
, (the reduced coefficient of direction of the straight line between Dx and Dy in 
a D,T-diagram, i.e. of the ideal “straight diameter’’) verges to 1. (Cf. These Proc. 
of March 26, (914, p. 8'8, formula (/8)). 
2) Not in all the tables Celsius degrees are distinguished from absolute tempe- , 
ratures with sufficient care in records of temperatures. Thus e.g. in the “Tables 
annuelles” (which contain many errors also in other respects), | find continually 
amidst records of temperatures in Celsius degrees, values which are meant in 
absolute temperature, without this being stated. For the critical temperature of 
mercury I found the value + 1270° C., given somewhere in those tables. The 
value is correct, but the addition: degrees Celsius is faulty. For then Zx would 
be about 1540° absolute, whereas in reality Tp = 1260° absolute. 
