The author studied the relations among the tensile, compressive and transverse strengths, hardness, microscopic structure, density and the amount of combined carbon in some plain and nickel-chromium pearlitic cast irons when annealed for 2 hours at different temperatures up to 900°C.

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The ordinary high speed steel usually contains about 0·6%carbon, while Mr. Rinpei Kikuchi has laid stress on the supriority of high speed steels with about 0·25%C. The author tried to ascertain if such temper-hardening of the low-carbon high speed steel has a mechanism similar to that of the heretofore current high speed steels. A low-carbon high speed steel containing 0·26% C, 3·03% Cr, 22·2% W, and 17·5% Co was examined with reference to the change of hardness, thermal expansion and specific resistance in accordance with tempering in order to study its temper hardening mechanism. The result revealed that the temper hardening mechanism of the low-carbon high speed steel is quite different from that of the ordinary high speed steel; and that the matrix which causes precipitation is the martensitic over-saturated alpha-crystals while the temper-hardening is due similarly to the precipitation of carbides.

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In the previous report (Journal, Iron and Steel Institute, Japan, XXVII, No.3, pp. 184-190) the modified Orsat gas micro-analysis apparatus for the determination of hydrogen in iron and steel was informed. In the present report, the heating fornace of the steel specimen and the pumping and collecting equipments of the gas from the speeimen was described.
The quartz tube in which the steel specimen had been placed, was heated by the wire-wound furnace. The gas issued from the specimen was pumped by a threestage mercury diffusion pump of glass and then collected by a mercury drop pump in a collectingvessel. When the gas collection was complete, it was transferred to the gas analysis apparatus for determination.

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The proeedure of the analysis and the results of the analysis of steel specimens were described.

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The approximate functional relation between the porosity and the electric conductivity of carbon or graphite electrodes was derived thcoretically, and the probability of the formula showing the relation was confirmed by experiment.

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