112 
and the substance with the greater vapour pressure has here even 
the greater molecule. Instead of in the righthand half of the general 
isobaric figure of vaN DER Waars we are now in the lefthand part. 
Accordingly the unmixing found here must not be ascribed to the 
b 
same cause, the high value of Be but (so long as we assume that 
1 
we have not to do with abnormal systems, and with the systems 
mentioned we may do so to all probability) to a smaller value of / 
than generally occurs. 
Let us take as an example the system aniline-hexane. hb, is here 
b, b 
0,006115, a = 0,007849, so 6, == 1,284, and =a = 1,186 follows 
1 1 
d°b 
3 US k dit, 
from the formula of LorENtz, so h=0,1153, and Agee 0017 
Further a, = 0,04928 and a, = 0,05282, so == 0,9659. If we sub- 
stitute these values in the equations (2) and (4), we get: 
dlp. af 5 En ; 
ey) a (0588471035) 4 240, 7694 BEE 
da Jr) m, 
and 
1? 1; Cc : - x 
TE NE ne 
dt m, 
dlp. 9 
So we get (5 =] == de OR == with y and == a 
Hine 
(Tj, hexane = 235° and the temperature of the upper mixing point 
= 68°,9). So we have not to expect unmixing, at least in the 
neighbourhood of the border, nor for greater concentrations, 
dlp d?l 
because —"° must at least be — 4 to make 1-+ 2(1—2) a 
dix” dx? 
3 F ee ae dlp, 
negative. In agreement with the complete miscibility Tt 2,62, and so 
AL 
Se ees | : : ; ae 
; aa and accordingly van ‘r Horr’s law is fulfilled 
mr vi 
with pretty close approximation. As soon, however, as / becomes 
dlp. 
smaller, this is changed. For /= 0.9 we get = = 0.66, and so 
ALL 
1—z, 
1 ; : 
; >>, and the lowering of the vapour pressure of the second 
—a,~ 2 
component by addition of the first will therefore amount to only 
dlp. 
half of what van ’r Horr’s rule would require. But as — has the 
U 
