726 
In the point 7 viz. the equilibrium: A + Hs + L,z oecurs; as 
the melting-line of H, represents the equilibrium H, + La, r is, 
therefore, also a point of this melting-line. In the same way i 
appears that 7 is also a point of the melting-line of H‚. 
The melting-line of H, is represented in fig. 10 by aa, that of 
H; by 85. The three curves aa, 35 and (M), therefore must go in 
fig. 10 through a same point 7. 
In the deduction of fig. 10 we have assumed that the gas-phase 
G consists of watervapour only: now we shall briefly diseuss the 
case that the compounds H; and H, are also volatile. 
Then G contains, besides the watervapour. still the substance SS. 
When we represent in fig. 9 the compositions of the gas-phases 
which may be in equilibrium with the liquids of curve dec, then 
a curve d’a’c’ arises, which is not drawn in fig. 9. This curve is 
the vapourcurve belonging to dac. Also a vapourcurve «’p’2’ which 
is not drawn belongs to curve «sz. Now we assume firstly that the 
vapours, which are in equilibrium with the liquids, contain less of 
the substance S than the liquids. Branch d’c’ is then situated in 
fig. 9 more towards the left than da, branch c’a’ more than ca, 
branch #3’ more than #3 and branch 2’?’ more than 2. 
The two vapourcurves d'«’c’ and 3/2’ intersect one another in 
fig. 9 in g and g,; the vapour g is in equilibrium with the liquid g ; 
the vapour gy, with the liquid g,. The point g is always situated at 
the left of the line «3; the point g, may be situated also, 
however, just as e.g. g, at the right of the line ag. We first 
consider the case that the vapour. which is in equilibrium with the 
liquid g,, is represented by g,. 
In the same way as we have deduced above fig. 10, we now 
find that the P,7-diagram keeps the form of fig. 10. 
The vapours of the equilibrium (2) = H, + H,; + Gand of(L), 
=H, + H;+G are represented in fig. 9 by curve gy,. The equi- 
librium ML, + H: + G has a point of maximum- or of minimum- 
temperature, when the vapour G has the composition H, = Hg. 
When we produce in fig. 9 curve gg, until it meets in 7, the line 
ag, then the tangent in 7, is horizontal. Consequently in 7, the 
equilibrium MH, + H, + Gs occurs, in which Gp represents a vapour 
of the composition H, = Hg. 
In fig. 10 this point 7, is situated somewhere on the metastable 
part of the (J/)-curve, viz. on the part, descending starting from 
the point g,. This point 7, is the metastable terminating-point of 
the curves (4) and (L),; at the same time it is, as we easily see, 
