959 
forces from the simple initial assumptions made by vaN ber WAALS. 
Such changes in ap might originate from three causes: change in the 
dy, in the by, or in the Ry of the chief equation, as a result of the 
radius of the sphere of action being but slightly greater than_that 
of the molecule, a circumstance ') revealed in apparent association. 
Since 
0? dy, 
ijn i — u Yo 
OLEN Ov Jr 
dee 
the question as to whether oe is independent of the temperature 
5 
dp 
and therefore | ~~ 
Dael =0, is most intimately connected with the 
Oy» 
question as to whether Ë ) =—=0 or not. For a long time this 
v id . 
question remained undecided on account cf the lack of experimental 
data. We now know that, at least for a number of substances, 
Op 
ia is in general a function of the temperature, and that therefore 
v 
ped 
—_ | does not vanish. 
7 
If we now compare the behaviour of argon with respect to 
OP “ : 
Ti with that of isopentane we find correspondence in many respects. 
Vv 
Youre *)*) deduced from his observations upon isopentane that 
or 
volumes up to vrp—400c.c. it increases with falling temperature, 
while it remains practically constant at still greater volumes. For 
argon, for which the volumes are expressed in terms of the normal 
volume as unit, if the law of corresponding states were accurately 
obeyed these volumes would correspond to vy = 0.00877 and 
vy = 0.328 or ox = 265 and on = 3.05. 
The argon observations embraced by VIL A. 3 lie entirely within 
these limits, and from Table I we see that argon agrees with 
isopentane within the region of observation. Over the entire region 
Op 
fs : 3) decreases with falling temperature for vr < 4.6 c.c. ; at greater 
(Op | | 
(37), falls with increasing temperature. At the lowest argon density 
1) This circumstance causes a change in bw also, cf. H. KAMERLINGH Onnes and 
W. H. Keesom, Suppl. N° 23, Nr. 47. 
2) M. RersGANuM, Diss. Göltungen. 1899, pg. 42. 
3) S. Youne, Proc. phys. soc. Londen 13 (1895), p. 602. 
