180 
the composition of the solid-phase mixture then changes from 7 to s. 
Subsequently, in the monovariant equilibrium ///, the composition 
changes from s to ¢ so that finally a mixture of Fe and FeO remains. 
If the original mixture g had been a little richer in carbon a mixture 
of Fe + C might have been left behind at the termination. 
Conversely, by interaction of a gaseous mixture of CO + CO, on 
iron at a sufficient pressure, this gas will be absorbed with sepa- 
ration of C and formation of iron oxides and in succession the 
equilibrium III, Il and I can be attained. 
The isotherm for temperatures between 880° and 1100°. 
At these temperatures iron forms with carbon solid solutions, 
martensite, of which the C-content varies from O to about 2°/,. The 
projection of the spacial isotherm on the x-plane then becomes as 
indicated in Fig. 4. . 
After the 2 monovariant equilibria I and II now follows VI between 
FeO, C and the C-saturated solid solution a. After this comes the 
divariant equilibrium between FeO, the unsaturated solid solutions 
Fe Fed Fe,0, 0 
Fig. 4. Fig. 5. 
and the gaseous phase. The carbon content of the unsaturated solutions 
can vary from « to 0. If we represent the empirical composition 
of these solutions by the formula FeCy, the reaction, applying to 
the divariant equilibria between FeC, and gas, will be represented by 
h. FeO + (1-+-2y)CO = FeC, + (1+ y)CO,. 
For this equilibrium exists the relation 
\ pity zi 
EE PY = constant, 
pity En (1) : 
COs 
