( 343 ) 
e right side is necessarily negative ¢ ‘efore we always hav 
Th ht sid ecessaril gative and therefore we always have 
Tr > Tijs, which also necessarily follows from the meaning of the 
critical point of contact. In the same way we find by means of 
equation (52) : 
tien mr m* Mok 1 /m* 
01 01 01 Okee 01 wal 
Papl Par 3 py. \ pan “fs Tei eh a Tomer ney ETT 4 Mii wv. (66) 
a ie io ee (aed dah k ZN Lun 
01 
12. The condensation. 
The line which indicates the relation between the pressure and 
the volume during the condensation, the so-called experimental isother- 
mal, extends between the two points p’,, v’, and p’, , v’, (the points 
where the condensation begins and ends) but we can also imagine it 
to extend beyond those two points, although there it has only a mathe- 
matical meaning; for beyond those two points the quantity of one 
of the phases would be negative. In order to find the equation of 
the experimental isothermal we must seek at each volume for the 
pressure at which the two phases into which the mixture splits, can 
co-exist. For this purpose I return to the projection on the z, v-plane 
($ 8) of the y-surface belonging to the temperature 7. If v,, xv, and 
v,, ©, are the phases into which the mixture w splits when the volume 
v is reached (v,>v>v,), the point v, # lies on the straight line con- 
necting the points v,, 2, and v,, «, and hence we have this relation : 
Sides AS NN eR SIRE 9 
LUT s 
where ®, Z, p and § have the same meaning as in $ 5. If p, is the 
pressure at which the two phases 2, and 2, co-exist then we obtain 
the. equation of the experimental isothermal by expressing the quan- 
tities ®, =, p and § of equation (67) in p, by means of the equations 
(22), (23), (24) and (25). 
That this experimental isothermal passes through the two points 
v’,, e and v’,, w follows directly from the way in which its equation 
has been derived ; we also obtain it from the substitution of v’, , ©’, — 
or v’,, #, — for v, «, which involves the substitution of v’,, 2’, 
fore, Un ORP a SOE U, Oz... 
By successive approximations (67) is brought to the form : 
pg 
01 . 
P, = pre + Mo, (©—# TK) — aa (v—ory) a +....; « … (68) 
I 
if we consider only the three first terms, this is the equation of a 
straight line, hence of that connecting the two phases where the 
condensation begins and ends. In connection with (18) we find, 
neglecting terms of higher order, 
23 
Proceedings Royal Acad. Amsterdam. Vol. V. 
