The equilibrium diagram of Fe-Cu-Fe₃C presented by Ishihara, Ishigaki and Yonekura in 1932 is revised in the present investigation, The research was carried out by thermal and dilatometric. analysis and by microscopic examination, using electrolytic iron, electrolytic copper and pure white cast iron as raw materials. The following three points are of special value. to mention. (1) The monoteetic reaction suspected by many authors do not exist on the Fe-Cu side. The region consisting of two liquid layers extends from the Cu-Fe₃C side so closely to the Fe-Cu side and the critical point lies at 1435° and at the composition containing 40% of Cu, 60% of Fe and 0.1% of C. (2) The ternary eutectoid of Fe, Cu and Fe₃C lies at 702° and it contains 6.5% of Cu and 0.85% of C. The structure consists of alternate layers of ferrite and cementite, and the fine globules of copper in ferite. (3) The equilibrium state of copper corner is precisely investigated and a peritecto-eutectic point was found of 1092°, which contains 2.7% of Fe and 0.008% of C. The whole results obtained are represented in the diagram of Fig. 36.

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In order to complete the equilibrium diagram of the iron-aluminium system, the authors have very carefully studied the alloys between O and 42 per cent of aluminium by differential -dilatometric, , magnetic, and X-ray analysis and also by microscopic examination. From the results of this investigation a new diagram has been established as shown in Fig. 2, which may be summarized as follows; in the diagram, three compounds, a₂, a₃ and a₄, are added which have newly found by the authors.
(1) The a₁ phase (Fe₃Al, a super-structure of a-iron already found by Bradly and Jay) is formed at a temperature of 570° by the following peritectoid reaction, a+a₂_??_a₁, its homogeneous range is 7.5 per cent at room temperature.
The Curié point of this phase is measured to be 510° at Fe₃Al composition.
(2) The a₂ phase has a new super-structure and is formed at a composition of Fe₅Al₃ (22.5 per cent aluminium) and a temperature of 1050° by the following peritectoid reaction, a+a₃_??_a₂.
(3) The a₃-phase being also a super-structure is probably formed at the composition FeAl, 32.6 per cent aluminium, by the following peritectic reaction, melt+a_??_a₃, and is stable only at high temperature:-this phase decomposes into a₄ and θ phase at 35 per cent aluminium and 670° by the following eutectoid reaction, a₃_??_θ+a₄.
(4) The a₄-phase shows a super-structure having same composition as the a₃-phase, but it is stable at temperature below 780° and is formed by the following reaction, a₃+a₂_??_a₄.
(5) ε-phase is formed by the peritectic reaction, a₃+melt_??_ε and not by a+melt_??_ε, and it decomposes to θ+a₃ at a temperature of 1080°, not to θ+a.
(6) The lattice constant-concentration curves of a, a₁, a₂, a₄, and a₃ phases are shown in Fig, 8.
(7) The curié point-concentration curves of a and a₁, phases are given in. Fig, 5.
(8) The space group adopted for the phase, Fe₅Al₃ is any one among T_h⁵ O₁⁵, O_h² and O_h³ and 2 atoms being included in its unit cell.
(9) The phases a₃ and a₄ have the same chemical composition, and the space group determined for one of them is T_h⁷ or T⁵ with 8 molecules of FeAl including in its unit cell, and O_h¹ for the other with one molecule of FeAl, and the exact space groups to be adopted for the phases a₃ and a₄ could not be determined, as their difference in atomic structure and calculated and actual spectrum lines was very little.

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Regarding the determination of oxygen in the steel, the vacuum fusion method and the hydrogen reduction method are already will studied, and proved successful. But, until now, the chlorine method for the determination of oxides is not fully investigated, and hence the writers made a study of this method on carbon steel that
1. The chlorination is carried at 300°.
2. By passing through sugar charcoal heated at 800°, the effect of oxygen in the chlorine gas in removed.
3. The non-volatile residue is washed by hot water, 5% HCl solution and finally by 5% Na₂CÓ₃ solution, and then by gravimetric method, the various oxides are separated and determined.
By the procedure above described, the blank test about various metals and oxides were examined, and the effect of impurities such as S. P. C. etc. on the determined value was studied. The results are as follows:
1. FeO, Al₂O₃, SiO₂ can be determined exactly.
2. MnO, determination is not satisfactory.
3. In the determination of S, P, and C, the loss of oxygen occurs, but it is very little.
4. The total oxygen by the chlorine method is much smaller than that by the hydrogen reduction
method, and it will agrees with that by the vacuum fusion method.
Lastly, after comparing the oxygen in the deposit metal of welding with those of the mechanical pro-perties, it is assured that the higher the oxygen content the worse the mechanical properties.

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As is well known that aluminium bronze containing about 10% aluminium possesses high tension, excellent mechanical properties, superior resistance for wear and corrosion, and furthermore that these properties are remarkably improved by heat treatments.
The author investigated the effect of a third element on the heat treating temperature of the aluminium bronze and found that the proper heat treating temperature of this alloy differs from those given in the reports of previous investigators and moreover that nickel-free aluminium bronze can be used efficiently if a proper quantity of manganese is added.

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