A series of corrosion tests of Fe-Cr-Co alloys containing 12% and 18.5% Cr with varying Co content, 4.51_??_49.96%, and a trace of carbon, a same ternary alloy containing 20.93% Cr, 50.48% Co and 0.06% carbon and also Fe-Cr-Cu alloys containing 6% Cr, 13% Cr. 18% Cr and 24% Cr with varying Cu content, 0.27_??_2.06%, and a trace of carbon, were carried out by the dip method. The corrosion resistance was examined in 10% aqueous solutions of HNO₃, HCl and H₂SO₄ at 25° by measuring the loss in weight, and the extent of corrosion was expressed as mg/cm²/hour. The Fe-Cr-Co alloy containing 20.93% Cr, 50.48% Co and 0.06% C and Fe-Cr-Cu alloys containing 24% Cr with Cu 0.47_??_2.06% and a trace of carbon were found to be resistant against the corrosive action of 10% aqueous solutions of both HNO₃ and H₂SO₄ at 25° The results were discussed by referring equilibrium diagrams of the Fe-Cr-Co and Fe-Cr-Cu systems.

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Among the various properties required by electrical high conductive materials, the strength and electrical conductivity are the essential elements, which could be supplied only by age-hardenable alloys, but they are limited to such alloys that conform the following requirements: - as apparent from the Le Chatelier-Guertlers' law, the elements alloyed into copper must be firstly in low concentration in order to raise the electrical conductivity, and next, the structural changes due to heat treatment must occur in such way that in the quenched state, the added elements dissolve as much as possible into solid solution of copper, and in the tempered state, the greater part of them precipitates out from the supersaturated solid solution, remainig the solid solution matrix almost as pure copper.
With these requirements in mind, about 250 specimens of copper base alloys containing small amount of other elements were prepared, and the changes in electrical conductivity, mechanical properties (mainly hardness), forgeability as well as the microstructures of them due to various heat treatments were examined. The alloys were discussed by classifying them conventionally into four groups from the result of the systematic investigation, as follows.
1 st. kind group-containing neither P, As, Si nor Be,
2 nd. kind group-containing P or As but not Si and Be,
3 rd. kind group-containing Si but not Be;
4 th. kind group-containing Be,
In the 1 st. kind alloys none but Fe-Co-Zn-Cu alloys were comparatively good in strength. In the 2 nd. kind alloys there are Ni-P-Cu, Ni-Fe-P-Cu alloys, the properties of them being very worthy to be noted. There are Ni-Si-Cu, Ni-Co-Si-Cu and Co-Si-Cu alloys in the 3 rd. group. In the 4 th. kind alloys containing less than 0.5% Be many superior alloys can be found. Among them it may be said that Ni-Be-Cu base alloys are the best in conductivity and agehardenability, the amounts of Ni less than 3% and of Be not more than 0.5% being beneficial. The existence of Si, Mn or Al with Be greatly diminished the beneficial effect of Be.
Besides the above alloys, the properties of Co-Be-Cu and Ni-P-Be-Cu alloys were also to be noted.

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The measurement of the volume shrinkage due to solidification of 67 kinds of Cd base bearing alloys, such as Cd-Ni, Cd-Ag, Cd-Cu, Cd-Hg, Cd-Ag-Cu, Cd-Ni-Hg, Cd-Ni-Cu and Cd-Hg-Cu, was carried out. The additional elements in these alloys varied from 1 to 10%. The specific volume of melt and solid of these alloys at various temperatures was measured by means of a specially designed pycnometer made of pyrex glass and also a by dilatometer, and the temperature of beginning and ending of the solidification was determined by thermal analysis, From these results, the volume shrinkage due to solidificatien was calculated.
Following alloys showed low volume shrinkage.
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The corrosion resistace of some dental substitutional alloys now in uses in our country was testedd by dipping them in dil HCl-, lactic acid-, NaCl-, Na₂S- solutions, etc. at 37° for 1 week. The results show that Cu-alloys and Acolite were corroded by any of the above solutions, Ni-Cr alloys by only acid solutions, while none of the solutions attacked 18-8 stainless steel and Ag-Pd alloys. The electrolytic potential of the, dental alloys in 1% NaCl and Ringer's solution was then measured against N-calomel electrode. 18-8 stainless steel and some Ni-Cr alloys became much nobler with time, and the potential difference between them and 22 K gold was only 0.02-0.08 V after 24 hrs, while other metals and alloys became baser or slightly nobler under the same condition. The galvanic current between each substitutional alloy and 22 K gold in 1% NaCl and lactic acid solutions with electrodes o_??_ 1cm² and 1cm appart was measured for 3 hrs by a milliammeter, microammeter or a mirror galvanometer in accordance with the amount of current, and the initial current in the instance of short circuiting two electrodes was measured with an oscllograph. The initial current instantaneously-decreases by polarization and alter 1/30-1/10 sec nearly horizontal value is attained and then the current decreases very slowly, taking after several minutes nearly steady-value. The steady galvanic current for several alloys, which is very small compared to the initial value, is as _??_ollows (10^-6 A unit; Palladium-s (Ag-Pd alloys)=0.01), 18-8 Stainless steel=0.13, N-Cl (Ni-Cr alloy)=0.06, Ni=3, Cu-9.7 Randolf=14.5, Acolite=35 Amalgam=100 in 1%, NaCl solution.

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