183 
Between VI and VII is situated the region of the divariant 
equilibria of FeO with mixed erystals « to d, 
The p-x-diagram (Fig. 7) much resembles that for temperatures 
above 880° (Fig. 5) with this difference, however, that the line / is 
not stable as far as the foot of the line c, but only as far as» VII, 
where it cuts the line c. Below this point of intersection, the line ec, 
the equilibrium FeO —Fe, becomes stable. | 
Below the stability region of the mixed crystals F thus appears a 
region for pure’ iron, B. The demarcation between the regions is 
given by the line 2 which indicates the equilibrium 
| FeC, + yCO, 2 Fe + 2y00, 
to which applies the relation: 
The line 7 is, therefore, like d and m an ordinary cubic hyper- 
bole of which the parameter 4; changes with the*temperature in 
that sense that it becomes nought at 880° (the isolated region B 
disappears) and equal to fq at + 700° (the region F where the 
mixed crystals are stable disappears). 
The metastable equilibria, in case Fe,C does not separate instead 
of carbon, are analogous to those for temperatures above 880°. 
Instead of VI we thus obtain the equilibrium. VIII and a demarcation 
of the mixed-erystal region not by the line d but by m. 
Influence of the temperature; the p-T-lines. 
An inerease of the temperature causes the equilibrium to shift 
very strongly to the right. The constant 4, of the reaction thus 
becomes greater and the line d much steeper. 
The temperature has comparatively little influence on the equi- 
libria of the iron oxides with CO and CO, *) The consequence is 
that the points of intersection I, II and III, which indicate the 
pressures of the different monovariant equilibria, strongly rise with 
the temperature. The lines indicating this relation: have a similar 
course as the well known dissociation lines for hydrated salts, car- 
bonates ete. They also can, as referring to the monovariant equilibrium 
between a gaseous and 3 solid phases of constant composition, be 
represented by the equation : 
1) Baur and Guagssner, Zeitschr. f. physik, Ch: 48, 354 (1903). 
