The reduction of iron in the iron blast furnaces may be regarded to be due to both of C and CO. The reduction amount due to CO gas amounts to 60 70% of the total iron content, and the rest is due to the direct reduction of carbon. The amount of coke used in the direct reduction corresponds to 10-15% of the total consumption and its rate is called the direct reduction percentage "D.R%". The magnitude of D.R% is represented by the combustion velocity of coke and the charging velocity. The production capacity of a blast furnace is mostly determined by the direct reduction pereentage, the gas reduction percentage and the blast quantity. It is possible to presume the highest capacity of the furnace by defining the limit value of the aforementioned three. Espeoially the magnitude of D.R% greatly influences the furnace status and the produetion capacity. The author theoretically explained that D.R% varys with the preheating capacity of the blast stove and the quantity of materials used, and thus intellded to contribute to the operation of a blast furnace.

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Knowledge of the characteristics of the vapor tension of gas dissolved in the molten bath is primarily needed for dealing with the growth of blow holes and shrinkage cavities in cast iron. For instancerthe boiling condition of the molten bath develops in case the total vapor tension has excelled the total external pressure consisting of the atornospheric and liquid pressures.
In other words, blow holes appear in the molten bath, where
The vapor tension of the dissolved gas varys with the change of temperatures. Above all, the change at the instant of solidification is predominant. At first, P'CO causes segregations at the solidification stage and enhances the gas pressure, the increase of which is, however, checked by the coexistent Si at a certain pressure (Fig. 2.). Nextly P'N2 tends to increase with cooling of the molten pig, but on the contrary does not cause segregations at the solidification stage. Therefore it does not increase the vapour pressure in solidification. Thirdly segregations are most prominent in P'H2 and its vapour pressure remarkably increases with the process of solidification. Therefore, while the P'H2 at the ordinary melting stage is as low as below 0.05 atm, the pressure at the solidification stage becomes as high as 0.5 atm, causing the boiling of the molten pig (Fig. 7.). The author gives some interesting explanations by combining the characteristics of the abovementioned three kinds of vapor tensions with the gowth of blow holes and shrinkage cavities in cast iron.

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Resistance to the corrosion by sea water was experimented with specimens of cast steel with scales and shaper-finished specimens without scales. As for painted specimens, three kinds such as the blank, specimens those coated with the ship's bottom paint and those coated with zinc were experimented. The comparative experiments covered the change of weight, the solution potential and the tensile properties after corrosion. The result of the experiments was summarised as follows:
(1) In case the immersion time is short, the corrosion resistance of specimens with scales is higher than the shaper-finished ones without scales. However, as the time of immersion increases, the corrosion develops and scales peel off, when the weight abruptly decreases and the attack is more remarkable than in the finished specimens.
(2) The scales are electrochemically positive against the finished specimens and favors the corrosion resistance. However, with the increase of the immersion time the difference of the solution potential becomes less and the effect of aforementioned factor prevails.
(3) In either case, the zinc-coating is effective, but the ship's_bottom paint is the best coating.
(4) Considering from the results of the tensile test, no brittleness due to corrosion is observed in such degree of corrosion.

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18-4-1 standard high speed stee's, which are generally used, contain as much as 18 % tungsten. Owing to the scarcity of production of tungsten in Nippon, it is essential to decrease the content of tungsten or to add small amount of other elements, instead of large amount of tungsten in high speed steels. Following the first and second report (Tetu to Hagane, Vol.23, 1937, No.8, p. 787-798 & Vol. 27, 1941, No. 6, p. 373-404) the present paper dealt mainly with the following standard type and substitute materia's of high speed steels:-
(1) 18-4-1 series (standard type).
(2) 14-4-1 series.
(3) 12-4-1 series.
(4) 8-4-1; 8-4-3; 8-4-5 series
(5) 4-4-1 series.
(6) 2-4-1 series.
(7) 0-4-1; 0-4-4 series.
(8) 0-8-1; 0-18-4 series.
(9) 0-12-1; 0-12-4 series.
Moreover the author dealt with the comparative study of acid and basic high speed steels by hardness test at normal and high temp ratures, microscopic examination and cutting test, etc.

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