Physics. — “On the Critical Quantities of Mercury in Connection 
with the Increase of the Molecular Attraction on Dissociation 
of the Double Molecules.” 1. By Dr. J. J. van Laar. (Com- 
municated by Prof. H. A. Lorentz). 
(Communicated at the meeting of May 29, 1920). 
1. Already twice I published‘) discussions of the critical quan- 
tities of mercury. Starting from the fundamental value 6, = 150.105 
holding for 1 gr. atom Hg (calculated from the densities of the 
solid halogen compounds) and the valueVa,=11.10—? derived from 
it (in connection with the critical temperatures of the said compounds), 
I calculated for mercury, assuming — what is confirmed in different 
ways — that this substance is quite or almost quite bi-molecular 
at 7, (cf. among others loc. cit. p. 9): 
Te = 1260° abs. (= 987° C.); pe == 192 atm. 
From determinations of the vapour pressure the pressure corre- 
sponding to 7’—1260° abs. was calculated < 204 atm. (loc. cit. 
p. 14). When 7, and p are both assumed to be unknown, the 
same vapour-pressure observations, on assumption of V a-=2>11.10-, 
yield for 7, the value 1242° abs., p, becoming = 187 atm. (loc. 
ene p. 15). 
In the second of the cited papers 1 made use of CorLARDFAU and 
Rivizrr’s later vapour pressure observations (1900), which go up to 
Se With be 149.105, Wa, = 107410" (for 1 Gr. atom. 
likewise determined from these observations), I now calculated (loc. 
cit. p. 144): 
Tr 472° abs. (—= 899° Chips 180 atin., 
while for D, about 3,8 was found. Through a simple calculation 1 
got at the same time the certainty that mercury is practically quite 
bi-molecular at 7, (ef. loc. cit. p. 139—140). 
The same value 6. =149.10-5 follows also from the limiting 
density 14,46 at the absolute zero, when 1,2 is assumed for the 
(reduced) coefficient of direction of the “theoretical” straight dia- 
meter. [I determined before 6,=120.10—5 per Gr. atom. for mercury 
itself, starting from D, = 3,77, calculated by Gupsere (le. p. 8)]. 
1) Cf. among others These Proc. 19, p. 6 (1916); 20, p. 138 (1917). Also Zeitschr. 
fir anorg. Chemie 104, p. 84 and 126 (1918). 
18 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
