( 321 ) 
Here v is the same quantity as above; vj: and vg, however, are 
now the molecular liquid and vapour volumes; 2’, zj and 29 are 
respectively the composition of mixture, liquid and vapour. We may 
write this equation : 
v= vy + 
ph 
Ly — 
val 
(vg —= Vol } 
vy 
Here we must not neglect the second term with regard to the 
first, as the factor «'— zj approaches 0, but in the second term 
By 
we may neglect v‚7 with respect to vg and put for the latter 
differentiation we get now: 
: MRT ar! —= Ly 
tr ( ) 
Lg — ®) 
or, if we take the molecular liquid volume as invariable: 
MRT 2' — 2, 
dod eee ) 
Bn rm el 
and so proceeding in this way we arrive also at the general formula 
for the shape of the empiric isothermal given on p. 140 of my thesis. 
Let us apply this formula in the case that the pr, line is a 
straight one, what comes to about the same thing as equal critical 
pressure for the two components. '). 
In this case the pg line is a hyperbola ®, so if p4 and pg °) represent 
the vapour-tension of the components : 
p= pa(l —'a) + par 
and 
a PA PB 
pB(l — 73) + PA %3 
If we now take p, and pg for the greatest and the smallest 
co-existing pressure which can occur with the composition 2’, so 
1) See Zeitschrift fiir phys. Chemie 36, p. 52. 
2) Van DER Waals. Proc. IX p. 172. 
3) We shall allways assume pz > pa. 
