We tried several experiments and consideration on the system of GaO-SiO₂-Al₂O₃.
(a) It was found that molten slags were ionic by the measurements of voltage-current relations.
(b) Molten slags were decomposed by D.C. source in some conditions and after that they were analysed by the new improved polarograph with Hg-dropping cathode, and ionic behaviors during electrolysis were examined.
So it was presumed that Al⁺⁺⁺, AlO₃^--- were more sensitive for electrolysis than Ca⁺⁺ and were playing larger parts for the electric conductivity.
(c) Movable oxygen ions, probably existing in molten slags, jump from positive ions to negative complex ions by electric conductance belonging to Grotthuss type, and they determine the acidic or basic strength of the slags.

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It is said that molding sand repuires gas permeability in any casting practice.
But, it has been unknown how much the property of permealility is effective on casting. In the present study the author mearsured the internal pressure in the molding sand in casting, and found a relation between the internal pressure and permeability. He also found the reason of occurrence of scabs and blow holes.

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The auther formerly recognized that when a steel plate or bar was bent by compression, a defect which is a sort of flaws occured at the inside of bent part. As the result of study on the nature of flaws which was made by experiments under various conditions, following results were obtained.
(1) The flaws are not caused by the deformation of surface layer of steel, but are caused by the fracture of steel itself due to partially concentrated stress at the inside of bent part.
(2) The flaws occur in almost every kind of steel.
(3) The depth of flaws differs according generally to the principles of strength of materials.
(4) The flaws occur considerably affected by temperature, grain size and properties of surface of steel.

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The authors carried out the experiment on the effect of cobalt on the tool steel for hot working by the same method as previous reports. (1), (2), (3), (4).
As the results of this investigation, it is ascertained that the cobalt gives better effect to tool steel for hot working, because the resistance for temper softening and the properties at high tem perature increase highly as cobalt content increases.

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If the carbon content in a molten steel bath is constant, also the oxygen content should be constant, as viewed from the stand point of carbon-oxygen equilibrium.
In the practical steel making process, however, the oxygen content in the bath is not always equilibrium to the carbon content, but it is rather higher than the equilibrium value. That is, steels always contain different oxygen value according to the various conditions of carbon-oxygen reaction.
There are many problems how and why these differences in oxygen content influence on the properties of iron and steel.
In order to study this influences, the author prepared steel samples which contain contant carbon and various oxygen in laboratory furnaces, and then, by using these samples, investigated their grain size and hardenability.
Results obtained are as follows.;
1) In the pure carbon steels containing little oxygen and much oxygen have greater tendency to form grain growth than that of containing medium quantity of oxygen.
2) In the pure carbon steels containing much oxygen, abnormal structures are apt to appear in the carburized samples.
3) The pure carbon steels containing much oxygen have distinctly lower hardenability than that containing little oxygen.
4) It is said that steel with coarse and uniform grains has good hardenability, but even in steel with fine and ununiform grains, if it contains little oxygen, the hardenability of it is much improved.
However, it is not yet clarified that whether these results depend upon only the effect of oxygen content or not.
Anyhow, in the practical steel making process, it is clear that the refining operation has to be performed standing on the base of preventing oxidation of the molten steel bath.

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Some examinations of the fracture test of quenched specimen for measuring the austenite grain size are described. It was found that the fracture test measuring austenite grain size don't show the correct grain size such as by means of double quenching method on the steel containing below 0.4% of carbon. Also the fracture test applied to the steels for carburizing is not allowed.
And it was shown that the austenite grain size by means of fracture test, as well as on the double quenching method appears smaller as that by means of McQuaid test.

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There are many cases that steel contains such high melting point oxides as Al₂O₃ or Cr₂O₃, and to determine exactly the oxygen content in steel, it is necessary to ascertain that oxygen from these oxides is to be satisfactory extracted or not by vacuum fusion method.
However, to ascertain this, it is thought that the extracting temperature have to be rised to their melting point.
So the authers tried to improve a carbon-spiral furnace to be able to rise the degassing temperature to 2300°C.
As the results of our improvement, it became possible to examine the extraction of oxygen from above mentioned oxides at their melting point, and besides at previous extracting temperature (1600°-1700°C), it became possible to shorten the degassing time and to decrease the blank value.
But it became clear that, it is impossible to obtain a complete extraction of oxygen from the pure Al₂O₃ and Cr₂O₃ powder by vacuum fusion method.
It seems possible to obtain a complete extraction of oxygen included in steel samples as Al₂O₃.

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