To clarify the cause of the beneficial effect of copper on the corrosion of steel in a non-oxidizing acid solution, the corrosion test for 12 kinds of copper bearing steels containing 0.03 percent carbon and 0.07-4.75 percent copper was carried out with sulphuric acid solution of various concentrations (1-98%H₂SO₄). The results obtained are as follows:- (1) In the initial period (untill 20 hours in the present experiment), the rate of corrosion of steels is markedly depressed by an addition of about 0.1-0.5% Cu with varying strength of acid (up to 55% H₂SO₄), and the addition of copper above these amount has little influence. (2) The steels containing above 0.8% Cu show a remarkable increase in the rate of corrosion with increasing time of testing, and hence a minimum point in corrosibility are shown at about 0.5% Cu after prolonged period (after 3 days in the present experiment). (3) The relation between the corrosibility and strength of acid shows that the steels containing a very small amount of copper (up to about 0.15% Cu) increase the rate of corrosion almost proportional to the strength of acid and time of testing, showing a maximum rate at 50% H₂SO₄, while the steels containing above 0.3% Cu show a slight increase in the rate of corrosion up to about 40% H₂SO₄ and above this concentration the increase is fairly great showing a maximum rate at 50% H₂SO₄ in prolonged period; this maximum rate at 50% H₂SO₄ is not observed in the initial period. (4) In concentrated sulphuric acid solution above 60% H₂SO₄, in which the mechanism of corrosion of steels differs from that in the weaker solutions, the beneficial effect of copper is not observed.
The above results are explained by an assumption of high over voltage of the Fe-Cu solid solution for hydrogen and the redeposition of copper and its state in the course of corrosion.

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Recently, a new refining method, which depends chiefly upon the partial melting of impure aluminium, has been introduced by one of the present writers. (I. Obinata; Jour. Min. Inst. Japan, 53, (1937), 542. Jap. Pat. No 124398) In this method, the vessel containing the molten aluminium is rotated about a vertical axis and cooled down until the primary crystals of. impurities, FeAl₃ in particular, are separated from the eutectic mother-liquor by the action of centrifugal forces.
In the present paper, aluminiums containing one or more elements, Fe, Si, Ti, Cu, Mg, Zn and Sb as impurities have been subjected for refining under various rates. From the chemical analysis of the results obtained, the follwing conclusions have been drawn; While the elimination of iron and titanium is easy, that of silicon is difficult unless it exists as a ternary compound, FeAl₃ FeSi₂; If aluminium contains a large amount of magnesium or zinc as impurity, the content of iron in the refined parts can be lowered below 0.8%.

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In the case of Precipitation of cementite from austenite, at first, carbon atoms enter regularly into widest spaces of the face centred cubic lattice of iron atoms, and then this lattice causes, at the same time, a sort of simple shear to the directions [001] and [110] in the planes (120) and (113), respectively. By these shears, the carbon atom is surrounded by six iron atoms which form a regular prism of a triangular isoscelses basis and the formation of cementite is completed, if the whole contraction or expansion is neglected. By the similar mechanism, the formation of cementite from martensite is explained.

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Age hardening of 24S type superduralumin containing Si and Mn was investigated by X-ray method using Cu K radiation. When the specimen, fixed to the camera and photographed successively, was quenched, the displacement and deformation of the spot due to ageing was observed. But they were not so remarkable as in the case of superduralumin containing no Si or Mn, which was reported in the previous paper.
The effect of tempering was next studied. The specimens were all cold-rolled after quenching from 550° and then tempered. In superduralumin containing no Mn or Si, precipitation of compound was not so remarkable when tempered at low temperature, and even 250°, long hours were required to attain equilibrium state. But if Si or Mn was added to ternary superduralumin, noticeable precipitation was observed even at 150°. Also in Al-Cu alloy containing 4% Cu, compounds were precipitated easily at 150°, Therefore, by the addition of Si or Mn to superduralumin, precipitation of compound from supersaturated solid solution becomes much easier, but the degree of ageing at room temperature decreases, and the type of ageing of superduralumin changes to that of Al-Cu alloys.

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Using high purity aluminium (99.998%), the equilibrium diagram of the aluminium-zinc system has been re-examined, by means of thermal, differential dilatometric and microscopic analyses as well as a newly devised apparatus. From the results of the experiments, the following conclusions were drawn:-
(1) The liquidus lines of this system have been found in good agreement with the old diagrams.
(2) The solidus lines which were determined by a newly devised apparatus have shown an inflexion point in the range of 58.8% to 80.7% of zinc. (3) An evolution of heat were observed on cooling, in the vicinity of 442°, but it did not accompany sharp peaks. It is probably due to the marked segregation during the process of freezing, because the thermal change is hardly detectable in the heating.
(4) The field of β and β₁+β₂ were determined by means of thermal and microscopic analyses. The results obtained were found in good agreement with those obtained by the X-ray analysis carried out by Dr. Obinata. (Tetsu to Hagane, 8 (1936), 622.)
A small amount of magnesium has been added to the specimens (>55% of zinc) in order to restrain the β phase from decomposition by quenching.
(5) The eutectic and eutectoid transformation points assigned as were 382° and 283° respectively.

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New high tension Silumins were investigated by properly adding several elements, such as Mg, Mn, Cu, Cd, Cr, Sn, Sb, Zn, and Fe in Al-Si alloys, and tested mechanical and anti-corrosion properties on 45 kinds of these alloys. As the base alloy, Al-Si-Mg alloy was taken because Mg is the indispensable element for precipitation hardening effect. Al-Si-Mg alloy containing Cu-Sn-Sb is found to be the best of all the Silumins and the base alloy with Mn-Cu-Cd-Sb, Mn-Cu-Sn-Sb, Mn-Cu-Cd, and Sn-Sb can also be called High Tension Silumins.

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