(, 332) ) 
point on the imaginary part of it. If the temperature is lower than 
the critical temperatures of the two components the plait occurs 
between the limits «=O and «w—1, but, except for mixtures of the 
second type, according to formula 26 the plaitpoint lies outside these 
limits. Hence the case is physically not without significance, but the 
plaitpoint cannot be observed. 
Equation (26) may be written: 
C "11 ry” 1 
2 T pl == nmr (T—Ty), . . . . (26) 
“~~ RT, k,,a—m>,, ( 
and this form shows that #7,; will be positive or negative as 77—T7, 
and RT? kem’, have different or the same signs. R7?, k,,a>m?,, 
is only possible if @a<c 0; R1°,k,,a< m*,, will always be the case 
if a >0, but may occur with @< 0. The different cases that may 
occur are shown in the following table. 
RTM, ka Mn | RT7,k,, a < mo 
| 
Í a > 0 | 8570 
O> are > erpl (Are > e791 > 0 | zap > 0 > an 
Ly J} | > » land . . 
| figs. 5 and 11 || figs. 1 and 7 | figs. 3 and 9 
i] 
| LT) > LT. > 0 IK) = LP > &TE | LTE SD LT pl | 
Te [ag 
See figs..6 and 12 || figs. 2 and 8 | figs. 4 and 10 
| 
| 
1. The border curve in the p‚v‚,a diagram at the temperature T. 
Ps Y / 
Along the border curve v=v7,+P+ ¢, so that the equation of 
the border curve may be written 
0 = (o—o7,)—2 P (v — vry) +-P2—g?. . (30) 
Where d> and g must be replaced by the expressions as functions 
of p,. To the first approximation we can take therefor the expres- 
sions (22) and (23) and neglect 7%; the equation (30) then repre- 
sents a parabola of the second degree. The apex of this parabola does 
not, as im the p,v, diagram of a simple substance eo-incide with 
the critical point (pri, Vri), but with the plaitpoint. 
Along that parabola 
d°p 2M. model Bm kr Telg 
dv? mt Rm, RT ke Mm 
(31) 
