( 661 ) 
g§ 2. In order to learn the relation between the compositions. at 
co-existence of two phases, I start from the well-known property 
that in this case: 
d 0 
a= le Set pe eee (1) 
where w represents the free energy, while in the following the index 
1 will always refer to the liquid, the index 2 to the vapour phase. 
As in Communication N° 75 we put: 
y= MRT{(1—a)l (1—2) Hele} dg!) 
where therefore p = — f ij dv. 
ern RG 
If again we write (<*) =, , (1) passes into: 
t, oT 
mer i(-—~) + gy! = MRT (Ee ard + ope. 
It follows from this that for « small we have 
Pal! 
MRT 
y= Tg € 2) e tare (2) 
Now 
1, 
op) 
ee = dv 
de ch le) vT 
Ld 
or by mk theorem : 
Vi 
0 
For small « we Je write: 
— — — dv, 
Pr f@ de vr 
if we are not too near me ad temperature of the pure substance, 
as in that c 
become infinite. Here vj and vs represent 
av 
the molecular aie of saturated liquid and vapour of the pure 
substance. If now we introduce the law of corresponding states by 
means of the relation mentioned in Communication n° 75: 
dp dpak Prk Avr (On\ par Tor (On 
Gr" de vr de AG a Tae dz 5) 
1) Comp. vaN DER Waats, Contin. II, p. 147. 
3) See VAN DER Waats, Arch, Néerl. XXVI, p. 96, Contin. IL p. 148. 
