184 
Also the metastable equilibrium V_ will give a similar p-T-line 
which, however, lies above line III. 
The equilibrium VII in which the mixed crystals participate has 
a totally different course, which, however, is quite comparable to 
the monovariant equilibrium liquid-solid-gas in a binary system. 
The pressure which at the starting point at + 700° has a finite 
value, falls to O at 880°, where the existible region of iron termi- 
nates. According to the thermic effect Qyyz, of the reaction between 
the different phases of the equation VII 
1 
xt ~ ) Re C0; Puch ss Fel, + xFeO 
which for small values of y (close to 880°) is negative, is also 
negative for large values of (at lower temperature) or then becomes 
positive, the p-Z-line VII will on raising the temperature always 
presenta falling course or attain’) a maximum between 700°—880°. 
Of the equilibrium VI represented by the reaction: 
x Fe) + 1 + xy) C2 x FeCy 4+ COx + Qui 
the heat of reaction is sure to be always negative’). In connexion 
therewith the p-7-line of Vl is continuously rising. 
The line VIII indicating the equilibrium between Fe,C, FeCy, FeO 
and gas also has a course similar to VI. 
The entire p-7-projec- 
tion now becomes as indi- 
cated in Fig. 8°). 
The lines III, VI and VII 
meet in the quintuple point 
O, where there is equili- 
brium between the phases 
Fel),, C, Fe, FeO. and gas. 
Besides these three lines 
Fig. 8. there also meet the lines 
for two other monovariant equilibria, namely 
1) We disregard here the transformation z-iron = Biron at 720°. The line 
VII thus consists in fact of 2 parts, one relating to the equilibrium with z-iron 
and one relating to #-iron. 
2) The heat of formation of FeO is about 67,3 [Baur and GLAESSNER, Z. plays. 
Ch. 48, 368 (1903)], that of CO 29,3 and of CO, 97 calories. The heat of forma- 
tion of FeCy will be but trifling in all cases where y is very small. If we neglect 
it. then Qyr becomes —67, 3x + 29,3 (2—x) + 97,0 (z—1) = (—38,4 + 0,47) cal, 
that is about —38 cal. 
8) In this figure VI should be drawn steeper than III (and VIII steeper than V), 
as for temperatures above 700° the pressure in the metastable equilibrium ITG as 
lower than that in the stable equilibrium VI. (See Fig. 7). 
