1156 
The previous rule is deduced in the supposition that the three- 
phases-triangle is situated in the immediate vicinity of the side with 
the binary terminating-points. As however by this is determined 
the direction in which 7 and P increase or decrease along the 
three-phases-curves, the rule remains also true, when the three- 
phases-triangle moves further away from this side. When the three- 
phases-triangle passes into a straight line, then on the three-phases- 
curves a point of maximum or minimum pressure occurs. 
The previous considerations are also valid when the added new 
substance is not volatile. The threephases-curve a 6c, which indicates 
the composition of the vapour, however, then not goes from a into 
the triangle, but it falls on the side YZ. Of the three-phases-triangle 
bb, 6, the angle-points 6, and 6, are situated, therefore, within the 
concentration-diagram, but, as is drawn in fig. 5, the point b is 
situated on YZ in the immediate vicinity of point a. 
Now we shall indicate by s the point 
of intersection of 6,6, with the side 
YZ, in fig. 5 this point of intersection — 
2 is drawn, inthe other figures, however, 
it is not drawn. We may now disting- 
uish two cases, viz. 
1° the point a (and consequently 
also 6) is situated on the other side of 
s as the points a, and a,,. 
2° the point a (and consequently 
X also 6) is situated on the same side of 
Fig. 5. s as the points a, and a,. 
The first case is represented in fig. 5, the second in the figs. 3 
and 4; we imagine, however, in the two latter figures the point 
bon the side YZ in the immediate vicinity of point a. Now we 
call those figures the new figures 3 and 4. In those new tigures 3 
and 4, the three-phases-triangle 6, 6,6 turns, just as in the old 
figures its vapour point 5 towards YZ; in the new figures (dP)r 
and (d7’)p have consequently the same sign as is indicated in the 
old figures. 
Notwithstanding that also in fig. 5 the point 6 is situated on the 
side YZ, it is yet apparent that we must say here, that the three- 
phases-triangle turns its vapour-point 6 away from the side YZ. 
Consequently (d7’)p and (dP)r must have the sign, indicated in 
fig. 5. 
Consequently on addition of a new substance, which is not volatile, 
