87 
previously mentioned saturation lines of / and the liquidum and 
vapour lines of the heterogeneous region £ + G. For this, we first 
choose a temperature 7’, corresponding with point A of fig. 3 and 
a very high pressure so that we find ourselves in the solid region. 
On the pressure being reduced we arrive from the solid region 
into the liquidum region, then into the liquidum-gas region and 
finally into the gas region. If we choose a temperature 7’; corre- 
sponding with point 6 of fig. 3, the substance /#’ on reduction of 
pressure first traverses the solid region, then the liquidum-gas region 
and finally the gas region. Reduction of pressure at the temperature 
Tc transfers the substance from the solid region to the gas region. 
We now start from the temperature 74 and a very high pressure: 
the corresponding diagram then consists of fig 1 (1) wherein, howe- 
ver, is still wanted the gas region and the heterogeneous region 
L+G of this figure. It is now evident that the compound # can 
only exist in the solid condition; it can, of course, be in equilibrium 
with a liquid, but this liquid cannot form unless to the compound 
is added a little of at least one of its components. The pure com- 
pound 4 which we have still under consideration can only occur 
in the solid condition. 
On reduction of pressure, the saturation line of /” contracts so as 
to coincide finally with point of fig. 1 (1). At this pressure occurs, 
therefore, the equilibrium solid /’+ liquid #, so that in fig. 3 we 
proceed from the solid region to a point of the melting point line 
fd. The heterogeneous region L + G of fig. 1 (1) niay, or may 
not, have appeared at this pressure; in any case, however, it has 
not yet extended to the point /’ of this tigure. : 
As, on further reduction of pressure, the saturation line of # 
disappears from fig. 1 (1) (in order to keep in with fig. 3 we take 
V>v) £ is now situated in the liquidum region of fig. 1 (4). 
Hence, in fig. 3 we must also arrive in the liquidum region. As on 
further reduction of pressure the gas region of fig. 1 (1) is further 
extended, the liquidum line ed of the heterogeneous region. passes, 
at a definite pressure, through the point /. This means that the 
liquid # can be in equilibrium with vapour. This is in agreement 
with fig. 3; therein we proceed from the liquidum region to the 
line Le. 
On further reduction of pressure, the heterogeneous region 1 + G 
shifts over the point /’; the compound # is now resolved into a 
liquid of the Jiquidum line and into a vapour of the vapour line 
which on further decrease in pressure always change their compo- 
sition. Hence “the compound / traverses the liquidum gas region 
