The writer has already published a series of reports on the diffusion of powdered metals or sometimes of non-metals exhibiting metallic properties (Zn, Sh, Al, Sn, Cr, Si, Mn, Ti, Be, W, Mo, V, Ta, B), that is, metallic cementation in technical words on other solid metals, such as Fe, Ni, Cu, etc., at various high temperatures. For the present work the cementation of cadmium, by making use of diffusion agent containing 25% Cd+65% Al₂O₃+10% CdCl₂, on copper, nickel and silver at various temperatures between 250° and 500° for copper, 250° and 600° for nickel, or 270° alld 600° for silver, for 1 to 5 hours was executed. For the surface layer of the cemented specimens, the measurement of Vickers hardness and depth of penetration, microscopic examination, chemical analysis as well as corrosion test by some acids were carried out. From the experiment the following facts were found: Cadmium diffuses into the metals above mentioned at a temperature lower than. 270°, - and the rate of diffusion increases as the temperature rises, The relation between the weight increase of the specimen (ΔW) or the depth of penetration (P) and the absolute temperature of cementation (T) or the time (θ) required for the treatment is given by an exponential function ΔW=αe, -b/T or ΔW=ae^tθ, where a and bare different constants in each case. Also the log ΔW (or logP) --1 /T×10⁴ curves show an abrupt change at the temperature corresponding to the melting point of cadmium. The cemented surfaces of copper, nickel, and silver are harder than the original material. The cemented surfaces of copper and silver resist against both diluted sulphuric and hydrochloric acids, while that of nickel is readily attacked even by the diluted solution of the strong acids.

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It is a well known fact that the Mg-Mn alloy belongs to one of the highest corrosion-resisting magnesium alloys. The present research has been undertaken in order to improve further the corrosion-resisting properties of the Mg-Mn alloys, by the addition of the third alloying elements. Taking the results obtained in the previous reports (Jour. Iron Steel Inst., Japan, 21 (1935), 85: 24 (1938), 34; This Jour., 3 (1939), 257) into consideration, as the third alloying elements, 0-5_??_2%, of Ca, Hg, As, Sb, Bi, Se and Te have been chosen and added to the Mg-Mn alloys, containing 0-5_??_2% of the latter element. The results of the corrosion-test against 2.5% salt-water as well as the tensile and the hardness-test of the alloys may be summarised as follows:
(1) The third alloying elements, which improve the corrosion-resistance of the Mg-Mn alloys conspicuously, were found to be Ca, Hg, As and Te. Although the actual content of Te in the alloys was small, the Mg-Mn-Te alloy showed the highest corrosion-resistance.
(2) The addition of small amount of Sb and Bi improved the corrosibility of the alloys to a certain extent. The addition of Sb over 1%, however, was fatal, Although Se was hard to alloying, its addition has been found to act effectively on the corrosibility of the alloys.
(3) No high tensile alloys have been detected in the alloys prepared in the present investigations.

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The principal purpose of the study is to compare the tempered structure of Al-Si alloys with the quenched one. The precipitation of large amount of Si-granules from α-solid solution at the temperature between 200_??_300° was confirmed by the microphotography with the magnification 1500x. The precipitation is on climax at 250°. It was pointed out from the curve of the damping factor suddenly rising at the temperature, which was taken by the experiment of torsional vibration of the tempered specimens in vacuum chamber. For the purpose, the special damping tester with an inertia mass was devised. The temperature range is probably divided in three portions; that is, the first portion 0_??_200° is for the preparation of precipitation, and second portion 200_??_300° is for the actual precipitation of the Si-granules, and the third portion over. 300° is for the coagulation of the granules. The testing of hardness with 5mm-ball and 40kg-weight were made on the tempered alloys. As the origins of temper hardening, the following two phenomena are concidered; one of, it is in the form of atomic disorder which occurred prior to the precipitation the other is the coagulation of the precipitates. The hardnesses from these origins superpose with each other and make the effective value against the temperature of tempering, Since the former has a maximum at 200° and the latter at 330°C, the superposed curve of the hardness has a softening point at 250° between them coinciding with the climax of the precipitation, , The form of the curve of damping factor has been compared with the curve of hardness, and the relation has been discussed with our theory of internal friction.
In the study, an experiment on the annealing of 8% Si-alloys was also conducted;- It has been interpretted that the change of internal strain in the Si-granules was the principal cause of the decrease of hardness and change of internal, friction.

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