JuLyY 19, 1923 FERGUSON: OXIDES OF IRON 277 
could not be completely reduced though heated for many hours. 
An experiment at a higher temperature was more successful. Experi- 
ment 6 shows that the hypothesis is untenable. 
The results appear to be evidence in favour of the view® that in the 
(H,;H.O, Fe, FeO) system, the iron phase contains no appreciable ° 
amount of oxygen but is practically pure iron. 
II. THE FERROUS IRON PHASE 
That ferrous oxide may take up ferro-ferric oxide in solution seems 
to be fairly well established.6 The available equilibrium measure- 
ments’ indicate that this ferrous oxide phasé is unstable at low tem- 
peratures and Chaudron’ has qualitatively checked this theoretical 
possibility. At 1100°C. Hilpert was able to prepare an iron-free 
ferrous oxide containing 1.5 per cent of ferric oxide but at 700°C. the 
ferrous oxide he obtained, free from metallic iron, contained some 15 
TABLE II.—ANALYSES OF SAMPLES USED 
SAMPLE FREE IRON FERROUS IRON FERRIC IRON TOTAL IRON METHOD OF PREPARATION 
I Trace 78.16 21.84 76.03 750°C. He,H20 
II 0.72 87.48 11.80 800°C. H2,H20 
Ill Trace 84.65 15.35 920°C. CO,COz 
per cent of the higher oxide. The synthetic experiments of Hilpert 
furnish the only information we have upon the relative stability of 
the ferrous oxide solid solutions. This question of relative stability 
seemed to us to merit further investigation. 
We have prepared from pure iron, using suitable gas mixtures of 
hydrogen and water vapour, many samples intermediate in composition 
between FeO and Fe;0,. Twosuch samples and a third sample, made 
with a gas mixture of carbon monoxide and carbon dioxide, were 
selected as materials suitable for a study of the invariant point, at 
which the ferrous oxide and iron phases are in equilibrium with the 
4 Similar results are reported by Richards and Baxter. Z. anorg. allgem. Chem. 23: 
245. 1900. 
5 R. B. Sosman, This JouRNAL7: 56. 1917. 
6 Hilpert and Beyer, Ber. deutsch. Chem. Ges. 44: 1908. 1911. Matsubara, Trans. 
Am. Inst. Mining Met. Eng., reprint 1051, issued with Mining and Metallurgy, February, 
1921. 
7 For a summary of these, see the paper by Eastman. Journ. Am. Chem. Soc. 44: 
975. 1922. 
8 Chaudron, Annales de Chimie, 16: 221. 1921. 
