1198 
dE AN! | 
eh ke, NO RE eg SON 
AT WAV 
Herein 4H represents the increase of entropy and A V the increase 
of volume with the reaction, which may occur in the equilibrium £,. 
As on curve Z, the quantity of one of the components becomes 
zero, the region / must terminate (or begin) in curve £,; for this 
reason we call Z, the limit-line of the region £. We shall refer to 
this later. In fig. 1 ab and cd are the limit-lines of a region 
abed; on eurve ab one of the components is missing e.g. A,, on 
curve cd an other component e.g. A, is missing in the equilibrium 
E. When we go, starting from a point / of a limit-line towards a 
point 2 or m within the region, then the equilibrium £, passes 
into the equilibrium Z. 
Let us take now the second case, viz. that an equilibrium Zr 
occurs. The equilibrium Ep consists of 7 components in 7 phases, 
between which the phase-reaction (2) may occur. Er is, therefore, 
a monovariant equilibrium and it may be represented by a curve 
in the P,7-diagram. It is defined by (3) in which AH and AV relate 
now to reaction (2). In order to examine the position of the region 
in the vicinity of this curve, we use the property: when in a system 
of n components in » phases a phases-reaction may occur, then at 
constant 7’ the pressure and under constant P? the temperature is 
maximum or minwnum’). 
Let ef be in fig. 2 a curve ER. When we trace the region along 
a horizontal line (P constant) then in the point of intersection of 
this line with ef the temperature must be maximum or minimum. 
Let g be this point of intersection and let us assume that 7), is a 
maximum, then consequently the region must be situated at the left 
of curve ef. At 7, + dT (dT > 0) then viz. no equilibrium # exists, 
at TdT two different equilibria H exist, however; consequently 
the region is two-leafed in the vicinity of curve ER. In fig. 2 the 
one leaf of the region is dotted, the other leaf is striped. When we 
trace the region along a vertical tine, then the pressure on ef is a 
minimum. 
Consequently curve ER is also a limit-line of the region £, but 
in connection with the property of the region in the vicinity of this 
curve, we call it “turning line” of the region Z. 
Also on the turning-line ER the concentration of one of the 
components may become zero at a definite 7’ (and corresponding P); 
') F. A. H. Scuretvemaxers, Die heterogenen Gleichgewichte von BakHurs 
Roozesoom. III}. 285, 
