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which coexist with the solid phase A at a definite pressure which 
is larger than the vapour-pressure of solid A alone, but the same 
for each of them, The three coexisting phases are represented by the 
lines O4G, Oul, Oul? respectively standing for solid, gas and liquid. 
They are situated together on a cylindrical surface, because for equal 
t, also p is equal. The part O42 is also a limitation of the surface 
of two sheets. 
In the same manner we have for the equilibrium of solid B with 
liquid and vapour the three lines OgpH, Opb, OpF, for solid. liquid 
and gas respectively, again situated on a cylindrical surface, while 
the part HOpF thereof forms below a second limitation of the 
surface of two sheets. This cylindrical surface first rises from Op but 
afterwards falls again. 
The surface of two sheets terminates, as far as the liquid-surface is con- 
cerned, finally in //, the gas-surface in J’. This liquid and this vapour 
may exist in contact with solid A (point G) and also with solid B 
(point H). As the points G, F, WM, H belong to the same values of 
p and ¢, they are situated on a horizontal line and represent the 
only possible complex of four phases. 
To the gas-line O4f' a second gas-surface joins, representing 
the vapours capable of coexisting with solid A, when the quantity 
of B in the vapour increases; also to Ogi’ the gas-surface for 
the vapours in equilibrium with solid B with increasing amounts of 
A. From the melting points of the pure substances down to the tem- 
perature of the quadruple-point G / MH these two gas-surfaces 
are not in contact with each other, but each of them singly is in 
contact with the gas-surface of the surface of two sheets. 
Below that temperature they intersect each other immediately, 
forming the line /’Z which represents the vapours capable of coexisting 
with solid A —+ solid B. To this belong the lines GM for solid A 
and HN for solid B which are again situated on a cylindrical surface. 
All complexes of the solid phase A and of the coexisting vapours 
are situated within the space formed by the gas-surface J/O0,FZ, 
the surface of the solid phase /O4GJ/ and the two cylindrical 
surfaces GO4F and MGFL. All complexes of the solid phase B 
and the vapours which can exist in contact with it, are situated 
in the space bounded by the gas-surface KOpFL, the surface 
of the solid phase AOgHN and the cylindrical surfaces HOpF 
and N AFL. 
Both spaces extend to the absolute zero if no new phases are 
formed. 
The three surfaces representing the equilibria of gas with liquid, with 
19* 
