185 
tiating the different quantities with respect to h and taking into 
consideration that p, has a constant value, we obtain: 
dM,' = dp, + dM = dp + dM'. 
Omitting the constant we can write for the energy at the height / 
c‚d'o c, d‘o 
laa Bd 
where e= Splitting this energy into a part €, corresponding to 
the homogeneous phase and a part €”, we may write 
eze He 
Now the stationary equilibrium demands that both in the homo- 
geneous phase and in the passage layers fluid-vapour and fluid- 
solid wall 
&é—1y + pv uM 
has a constant value. Here p, represents therefore the pressure in 
the direction of the passage layer; in the homogeneous phase it has 
the same value as the constant pressure in the vessel. The equation 
expresses that layers lying in each other’s neighbourhood will exchange 
the same number of particles in the same time. 
The change of the attraction (molecular pressure) in the direction 
of h from point to point is: 
dM,' = — 29 de = — 20 (de + de") = 2a9 dg—2o de". 
This follows from the value of 
2 2 
M,' = ag’-+-¢,0 =< — ; (5) 
in conneetion with 
€ = & — ag — = 
dp + dM'= dp + 2uo do 
and so — 2ode"= dp or — 2de'"=rdp, whence oe Jode". 
For e— ty + p‚v=—=uM we may write & He’ —ru tpv 
+ (p.—p)v=uWM. By differentiation we find vdp de" +-d (p‚—p)v=0, 
as de — td + pdv=0; this is evident when we regard the unit 
of mass (as homogeneous phase) as having first had the volume v 
at the height A and afterwards the volume v + dv at the height 
h + dh. For the passage from one state into the other we have: 
tdy = de’ + pdv. 
As further vdp= — 2de", we have — de"+ d(p,—p)v=0 and so 
