Samples were selected out of metallic ions, anions, and organic compounds having one of the following five properties and their effects on the internal stress were investigated.
(a) Corresponding to compounds, commonly added to the plating bath for buffer action of pH in operation.
(b) Corresponding to compounds, acting as reducing agents to prevent oxidation of ferrous ion.
(c) Corresponding to compounds, producing complexes with ferrous ion.
(d) Corresponding to compounds, indicating possibility of codeposition with iron.
(e) Corresponding to impurities introduced during the employment of mild steel as an anode.
The results obtained were summarized as follows:
1) Cobalt linearly increased the internal stress at a rapid rate. The stress was rapidly increased with the increase in Ni²⁺ concentration and decrease in Fe²⁺ concentration.
2) The internal stress was decreased with the increase in concentration of urea or E. D. T. A.
3) The stress value was lower with the rise of temperature. The value was also lower with the increase in Fe²⁺ concentration at a definite temperature.
4) The stress value was higher with the increase in NH₄HF₂ concentration in the concentration range of 2-20g/l. Addition of a very small amount of saccharin rapidly decreased the stress.

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The effects of sulfur co-deposits in a bright nickel on the corrosion were investigated by studing the corrosion behavior, hydrogen embrittlement, crystal structure, and polarization curves.
The results obtained were as follows:
1) The differences of the corrosion behavior of nickel in HCl, H₂SO₄, and HClO₄ were explained by the effects of anions on the co-deposited sulfur.
2) The bright nickel had twin boundaries of (111) and (200) orientations, and was subjected to a strong hydrogen embrittlement in HCl. The embrittlement was explained as follows:
(a) The co-deposited sulfur was converted into H₂S by the action of adsorbed hydrogen (active hydrogen) and was removed from the boundary.
(b) Hydrogen gas accumulated along the grain boundaries caused the embrittlement.
3) The hydrogen overvoltage of nickel in an acidic solution at pH=3 was extremely high. Such a high value of voltage was theoretically interpreted by the evaluation of pH near the nickel electrode as functions of bulk pH, rate of hydrogen evolution, diffusion coefficients of ions, and buffer concentration.

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In order to solve the faults of electrodeposited cobalt described in the previous papers, the authors studied a new type of bath containing cobalt sulfate and sodium citrate.
The following conclusions were reached.
1) Components and conditions suitable for plating were as follows:
(a) Concentration of cobalt sulfate was above 0.5mol/l.
(b) Ratio of concentration in mol between cobalt sulfate and sodium citrate was 1:0.5-1:1.3.
(c) The value of pH was 4-7, and preferably 5-6 in practice.
(d) Ammonium sulfamate and 2. butyne-1.4 diol were possible to be used as additive agents.
2) The plating baths mentioned above contained complex ions and excess of cations.
3) These baths were suitable for being used for insoluble anode, because they had a wide range of controlling conditions as mentioned above.

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In recent years, the sintered body of aluminum powder, which is very cheaper in price than tantalum, has been used as a dielectric material element; and a solid electrolytic condenser of sintered aluminum has been developed in industry.
Since 1965, the authors have studied on sintering mechanism of aluminum powder and the development of solid electrolytic condenser of sintered aluminum.
The sintering of aluminum for condensers had never been attempted, because aluminum has a considerably low melting point and easily be oxidized. Sauerwald (Germany) pointed out in 1922 that an oxide, which is hardly reduced by hydrogen, appears on the surface of aluminum powder so that its sintering is made impossible.
The authors considered that it would be possible to sinter the aluminum powder in vacuum and succeeded in its trial as expected. As the results of studies, the surface area of the sintered body was made larger to increase electric capacity.
The sintering mechanism of aluminum powder and characteristics of electrolytic condenser of sintered aluminum are discussed in this paper.

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Studies were made of the relation between the thickness of boride layer and the composition of bath in boriding of iron.
The samples were dipped in a hot salt bath containing ferroaluminum or aluminum for reducing agent of borax. Sometimes, boron carbide (B₄C) was used in place of ferroboron. Therefore, the principal components of the bath were ferroboron (or B₄C), borax, and ferroaluminum.
The results obtained were summarized as follows:
1) A salt bath containing 55% of borax, 40.5% of ferroboron and 4.5% of ferroaluminum had the highest bonding power. However, the addition of carbonates or neutral salts to the bath decreased thickness of the boride layer.
2) When ferroboron was replaced by B₄C, the composition of bath was preferable at 70% of borax, 24% of B₄C, and 6% of ferroaluminum. The addition of carbonates or neutral salts seemed to increase thickness of the layer.
3) When borax was reduced by aluminum, the preferable composition was at 65% of borax and 35% of aluminum. The addition of cryolite or neutral salts decreased thickness of the layer.

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