404 
If we take this into account for both lines, then it will be clear 
that this quadruple point will present the shape of fig. 6, where 
the angle between L+H, + H, and 
G +4 L+H, does not contain metastable 
prolongations. I shall postpone a discus- 
sion of the further peculiarities which 
appear for inverse melting-points, to a 
later occasion. *) 
Another example, in which the rule 
enables us to infer easily what quadruple 
points are possible, we find among others 
for a dissociating compound in solid 
state by the side of the least volatile 
component, liquid and vapour; then we know that this quadruple 
point can occur on different branches of the three-phase line: 
compound + liquid + vapour. 
Let us consider the case that the pressure continually decreases 
from the first to the second component; then the quadruple point 
can lie in the first place on the three-phase line so that neither 
melting-point, nor maximum sublimation point appear stable. If this 
is the case then the order of the phases is GL VS, in which V 
denotes tbe solid compound, S the solid second component. The 
angle without metastable prolongations lies therefore between G-+-L-+-V 
and L+V-+4S, and in this the coexistences G + L, L + V and 
V + S oceur according to the first formulation of the rule. 
If, however, on the three-phase line of the compound the melting- 
point occurs, but the maximum sublimation point does not occur, 
the succession has become GVLS, so that just as in the preceding 
case we cannot meet with metastable prolongations in the angle 
between G + V+ Land V+ L-+48, and now find the coexistences 
G+vV,V-+L and L+5S between the two lines. As is known this 
case is found among others when a salt-hydrate (before its transition 
to the anhydrous salt or to another hydrate) possesses a melting 
point. 
If the compound has both a melting-point and a maximum point of 
sublimation, the order has become VGLS, and no metastable pro- 
longation occurs in the angle between V + G + L and G+L-+58, 
where the coexistences V + G, G+ L, and L + S are found. 
Led by these considerations we can easily construct the quadruple 
points under discussion. 
Fig. 6. 
1) A. similar type of quadruple points we find also in the system [ron-carbon. 
Smits. Z. f. Elektrochemie 18. 362 (1912). 
