The diffractive scattering by crystals of thermal neutrons, which have the de Broglie wave-length of about 1.6 A, had been investigated by several authors. It gives many intersting facts, which may offer some means of supplementing the X-ray study of the solid state. In the present experiments the total cross section of thermal neutrons have been measured for Fe, Cu and Al as a function of the degree of cold-working. The thermal neutrons from a paraffin “howitzer” with 200_??_300 mC Rn-Be source are detected by a BCl₃ ionization chamber and a linear amplifier as shown in Fig. 1. About 2000 counts per minute are obtained without a scatterer, and the residual counts due to higher energy neutrons above Cd cut-off are 5% or less. Completely annealed plates of electrolytic iron, Armco iron, pure Cu and pure Al are subjected to various degrees of cold-working (rolling). The final thickness of the scatterers is so regulated as to give about 50% transmission in each case. The experimental results are illustrated in Fig. 5, which shows the relative variation in the total cross. section as a function of the degree of working. It can be seen that the annealed samples of Fe and Cu show small cross sections which quickly increase to the saturation values by, a cold-working of an order of only a few per cent reduction of thickness. On the other hand, Al shows no marked change beyond the limit of experimental errors. After analysing the experimental results of Beyer and Whitaker on Fe, Halpern, Hamermesh and Johnson suggested, the existence of secondary extinction in the scattering of thermal neutrons by a single crystal. They also reaches the conclusions that the primary extinction must be negligible on account of the small interaction of neutron and nucleus, provided that the size of the mosaic block of Fe be of the order of 10^-5cm. It would, however, be premature to conclude that Fe had such a small mosaic block, though-Miller and DuMond had determined the size of a block of Al to be of that order of magnitude from X-ray investigations; because, in general, the lower limit of the size of a mosaic block in metals-is considered to be in the order of 10^-4cm after Bragg. The present results seem to point out the existence of the effect of primary extinction in annealed polycrystalline Fe and Cu. If we neglect the incoherent part of elastic scattering, the size of the mosaic block can be calculated by the same method as described in a previous paper by one of us (M. K.). According to Darwin, a measure of the degree of extinction is given by tanh mq/mq, where q is the, amplitude of the wave reflected by a certain net plane, and m is the number of net planes forming a mosaic block. By assuming that the primary extinction is completely removed by sufficient working, the size of a mosaic block is determined to be in the order of 5×10^-4cm for annealed Armco iron, 3.6×10^-4cm for annealed electrolytic iron and 5.8×10^-4cm for annealed Cu. The reason why Al shows no marked decrease of cross section by annealing can be accounted for by the smallness of q and of the size of a mosaic block. Rasetti has found that in the case of Pb or Bi the cross sections are almost the same for the single and polycrystalline states and tried to attribute this fact to the isotope or spin disorder in crystal lattices. It is difficult, however, to explain our results on Al along these lines, because Al has only one isotope.

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The change in electric resistance of alloys of the iron-cobalt system at various temperatures, ranging from -195° to 1150° is measured up to 1600 oersteds in the longitudinal magnetic field. The specimen used is a fine wire, 0.20_??_0.61mm in diameter and 3.9_??_7.1cm in length. The change in resistance of alloys with face-cen tered cubic γ-solid solution is far remarkable than alloys with body-centered cubic α-solid solution on the iron side, and with hexagonal close-packed h-solid solution on the cobalt side, - especially at lower temperatures. The isothermal curves of concentration of magneto-resistance cosist of three portions, that is, α-, γ-and h-solid solution, the curves of α-solid solution alloys are all concave towards the concentration axis.

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From two series of high speed steel containing various amounts of cobalt, whose carbon contents are extremely low or high, I have measured the tempering hardness after quenching and the durability, and then have observed the change of micro structure. The results of the investigation are as follows;- In the case of the steel containing about 0.2% C, the temper hardness is not fully attained unless the cobalt content becomes higher than about 10%. When the carbon content reaches 1.4%, the quenching hardness of steel is considerably low, but the tempering hardness is high, and increases unteil cobalt content reaches about 20%. The highest durability is obtained at 20% Co while carbon content goes down to 0.2%, and at 1.3_??_1.7% Co while carbon content rises to 1.4%. The complex carbide is extremely fine in the former, but it is coarse and numerous in the latter. The hardness is higher in the case of the latter, but the durability is higher in the former when the cobalt content is higher than 15%. Moreover, a series of comparative experiments is carried out of two kinds of high speed steel containing about 18% Co one of which contains about 0.3% C and another, about 0.8% From the study of the change of hardness and durability due to different heat treatment, it is apparent that the steel of low carbon content shows higher durability as in the case of the former experiment.

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In the first report in the same title, we had already made clear of the effect of each alloying element, such as C, Cr, W, V and Mo, on high speed steels containing 0_??_5% Co. In the present investigation, we have repeated the similar study of high speed steels containing 10 and 15% Co, changing the content of each element above mentioned. We have researched change in hardness of steel caused by the different heat treatment, and conducting actually a series of cutting tests, we have ascertained the effect of each element, and have determined the proper compositions for the high cobalt high speed steels of these classes. The results obtained from the present study are as follows:-(1) The highest durability is obtained when carbon contents are 0.9_??_1.0% for the steel containing 10% Co; and about 0.6% for that containing 15% Co. (2) Cr contents in 3_??_4% are most appropriate for the steel either 10 or 15% Co content. (3) Almost the same durability is given within the range of 12_??_20% W contents for the steel containing 10% Co, and of 12_??_22% W contents for that containing 15% Co. (4) The contents of 1.5_??_1.8% V are most appropriate for the steel either containing 10 or-15% Co. (5) Mo contents up to 2.5% do not give any appreciable influence on durability of the high speed steel.

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