IX between the phases Fe, FeC,, C and gas 
and X ie ip Be, Kel, sGnBe0 
As these ternary equilibria are subordinate to the binary equili- 
brium between Fe, FeC, and C and as this alters but very little 
with the pressure, the equilibria IX and X will also be almost 
independent of the pressure. 
Beside the stable quintuple point O with C as a participating 
phase there also exists a metastable quintuple point O’, in which, 
instead of carbon, Fe,C participates and where V and VIII come 
in contact with the prolongation of VIL. 
Of these different lines II has been determined experimentally by 
R. Scuenck and V. Fancke') and the line III by different investi- 
gators and that repeatedly*). The equilibria always set in but ex- 
ceedingly slowly and are, as is to be expected, dependent on the 
kind of carbon that is used. With graphite are obtained lower 
pressures than with amorphous carbon. Looking at the fairly con- 
cordant results obtained by the different investigators we find, with 
graphite 680° as the temperature where p,, becomes — 1 atm. 
O’ is situated at about 700° and O therefore certainly above 700°. 
From this it follows that the pressure in the quintuple points will 
be greater than 1 atmosphere. 
As to the other lines of Fig. 8 notbing is known with certainty. 
I probably lies at such low temperatures that the reaction velocity 
is too small to obtain stable equilibria; VI and VII will lie at 
pressures >> 1 atm.; V and VU, however should, without great 
trouble, be accessible to the experiment. As to V, some indications 
are to be found in the different experiments. SCHENCK *) observed that 
on interaction of much CO with comparatively little iron there was 
formed a lower equilibrium pressure and a CO-richer equilibrium 
gas than on the interaction of little CO with much iron. He sup- 
posed that in the first case the equilibrium IV between Fe,C, FeO, 
amorphous C and gas is obtained and then calculates from the 
relation: CO:CO, and the value of %, that for the equilibrium V 
at 650° p= 51.92 atm. at 700° p = 166.38 atm. 
A priori, this assumption and the conclusion drawn therefrom is 
not very acceptable. As shown from Fig. 3, the equilibrium IV, as 
the intersecting point of d with e, which at that place is doubly 
1, Ber. d. Deutsch. chem. Ges. 40, 1708 (1907). 
2) SCHENCK, SEMILLER and FarcKe, Ber. 40, 1704 (1907); van Royen, Disser- 
tation, Bonn 1911; H. Nrepert, Dissertation, Breslau 1913: V. Faroke, Z. f. Elek- 
troch. 21, 37 (1915); 22, 121 (1916). 
3) R. Scuencx, H. SeMiLLeR and V. Faucks, Ber. d. D. chem. Ges. 40, 1710 (1907). 
