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tical liquidum vapour line passes through point /’; if this equilibrium 
occurs in the stable condition, the liquidum and the vapour line of the 
heterogeneous region must then also pass through the point /’; this 
is the case when, incidentally, a ternary maximum, minimum or 
stationary point occurs in £. If, however, this equilibrium appears in 
the metastable condition, the liquidum and vapour line of the hetero- 
geneous region do not pass through / which is then situated between 
these two. As, from the equilibria solid # + liquid #’-+ vapour F 
and solid /’+ vapour #, it follows that the saturation and the 
vapour saturation line of /’ coincide to one point in /’, the meta- 
stable triple point S must be situated in the liquidum gas region 
of fig. 3. 
We now choose a temperature Tc (tig. 3) lower than the upper 
sublimation point 7), of fig. 3; the vapour saturation line of / has, 
therefore, not yet disappeared when the vapour line of the hetero- 
geneous £ + G passes through the point /. Starting from high 
pressures and then reducing the same there is first formed fig. 4 (1) 
wherein, at first, the gas and heterogeneous regions are still wanting, 
then figs. 1(D, 2(D and 3(I) which is now converted into 8 (I); 
then are formed figs. 9 (1) and 10 (I) and finally a figure which we 
will call 10a and which is formed from fig. 10 when the vapour 
saturation line of / coincides with the point /. 
During this lowering of the pressure, as shown from the figures, 
the substance /’ only occurs solid in the stable condition; the sub- 
stance /’, therefore, traverses the solid region of fig. 3. Not until 
the pressure has been so reduced as to form fig. 10a can solid F 
be in equilibrium with vapour #. We then proceed in fig. 3 from 
the solid region to a point of the sublimation Jine a A. 
On continued reduction of pressure the vapour saturation line of 
[’ disappears from fig. 10a, so that # lies within the gas region; 
hence, /’ can occur only in the form of vapour, so that in fig. 3 we 
proceed to the vapour region. 
In the conversion of fig. 3 (1) into fig. 8 (1) the substance / passes 
through different metastable conditions. On reduction of pressure the 
metastable piece a 5 of the liquidum line passes throngh the point / 
first, then the theoretical liquidum-vapour line and then the meta- 
stable piece a, 6, of the vapour line of the heterogeneous region 
L+G. This also agrees with fig. 3; on lowering the pressure at 
the temperature Ze we meet in the solid region, successively, the 
metastable curves e’ FI’, g’ S, and /’ A. 
When in a system liquid-gas a liquid and a vapour of the same 
composition are in equilibrium, we will call this a singular point of 
