394 



points of intersection whicti represent four-phase equilibria on addition 

 of heat, until one of the phases has been completely converted. 



It is known that especially the equilibria with carbon are com- 

 paratively slowly established below 800°, which is the reason that 

 in experiments with flowing gas, the just mentioned stage-wise 

 reactions are found at temperatures above those corresponding with 

 the points a, h, and c. 



Derivation of the P,T-Fic)nre of the System 0—Fe from the Equilibria 

 of the Iron-Oxides nnth Reducing resp. Oxidising Gases. 



When it is borne in mind that an equilibrium as the following. 



Fe.O, -f H,:;t3FeO-|- H,() (1) 



may be conceived as consisting of the two equilibria: 



2Fe,0,^6FeO-hO, (la) 



and 



2H,0:;!:2H, -hO, {lb) 



and likewise 



Fe,0, + CO;^3FeO + CO, (2) 



as consisting of the equilibria- 



2Fe30, ;16FeO-hO, (2a) 



and 



2C0, ;^ 200 -1-0, {2b) 



it is clear thai from the ecjuilibria (i) and {lb) resp. (2) and {2b) 

 the situation of {\(i) can be derived, and the same thing may be 

 said in reference to the other equilibria that are considered here. 



It also follows from this that where the three-phase line for 

 FeO -f Fe,0, + (CO + CO,) was studied, also FeO -\- Fe^O, + 0, 

 were in equilibrium with each other. Hence the shape of part of 

 the P,T-projection of the system -)- Fe can be derived from the 

 situation of the determined lines of equilibrium. 



Thus it is immediately seen that, the three-phase lines for Fe -|- 

 FeO + (CO -I- CO,) and for FeO + Fe,0, + (CO + CO,) intersecting 

 this must also be the case with the three-phase lines of Fe -)- FeO -|- G 

 and of FeO + FcjO, -f G in the system 0— Fe. 



When we express this in a diagram, and when we also assume 

 the existence of the three-phase line Fe^O» -|- FejO^ -|- G, we arrive 

 at the following P,T-projection (Fig. 10) on the assumption, as was 

 also supposed in fig. 7, that the three-phase lines FeO + Fe^O^ -1- G 

 and Fe,0^ — P'öjOg -|- G do not intersect in stable points. 



Accordingly this projection presents the peculiarity, which up to 

 now has never yet been observed in a case like this, that 



