( 540 ) 
approach each other; and also the stable 
and metastable branches on the vapour part 
especially at the side of the component 
melting at the lowest temperature 1 ). For 
if we approach the temperature of the 
triple point of this component the points 
e x and g x of fig. 2 will have coincided 
to the point e 2 g t in fig. 3, which is 
intended for the temperature of Oa{ fig* !)• 
The two derived surfaces intersect each 
other in the tfw-plane of the component 
A; that intersecting line is, of course, 
the tangent to the ip-line for the gas-liquid 
condition of A and just the one which 
is also tangent to the t^4ine of solid A 
(triple point A). 
By consulting fig. 4 it win be easily 
seen what happens at a temperature 
situated between that of the two triple Fig- 3. 
points. The rolling tangent plane coming 
from the A side will now rest first on 
the liquid- and vapour parts; but if a 
certain nodal line pq is thus reached the 
tangent plane will rest also on a point 
r of the surface of the solid phase. The 
angular points of the three-phase triangle 
pqr give us the composition of the three 
possible coexisting G, L, and S phases at 
that temperature. By further motion of the 
tangent plane a derived surface for GS 
equilibria is formed, whilst also a similar 
movement over the liquid part of the fluid 
surface and over the surface of the solid 
phase is possible in the direction of the 
small volumina. Hence a new system of 
connodal lines for LS equilibria is formed 
starting from r and q. Fig. 4, however, 
Fig- 4. will be plainly understood without further 
comment and a discussion of the configurations at higher temperatures 
will also be superfluous. 
The non-related connodal lines ab (solid) and cd (liquid) diverge from each 
other because as a rule the coefficient of expansion of a substance is smaller in 
the solid than in the liquid state. 
