In the previous papers of Parts 2 and 3, the authors reported that co-ordination numbers of aluminum atoms in the aluminum anodic coatings were both of 4 and 6 ligands.
The object of the studies in this paper is to make clear the combination of atoms in aluminum anodic coatings by means of differential radial distribution analysis for the purpose of proving the results in the previous papers.
The data necessary for analyzing the combination of atoms were as follows: density of the anodic coatings, kind of elements contained in the coatings, molar ratio of elements, X-ray intensity of the coatings with targets of Cu and Mo, atomic scattering factors of elements, atomic number, and atomic weight.
The values of differential radial distribution function were computed by storing these data in an electronic computer. The function was calculated by the following equation:
4πr²Σ_mK_m(g_m(r)-g_o)=2r/π∫^∞₀Si(S)sin Sr dS
The structural analysis of the coatings was presumed by the comparison of the ionic radius with the radial distance of differential radial distribution patterns.
The results obtained were summarized as follows:
It was supposed that the co-ordination numbers of aluminum atoms in the coatings were both of 4 and 6 ligands. The atoms of 4 ligands were distributed in random configuration in the coatings, and the atoms of 6 ligands were nearly in systematic configuration in the coatings.

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The conditions necessary for decoration in bright copper-zinc alloy plating are uniform color tone, high brightness, and thick plating layer. This paper describes the studies on addition agents to the copper-zinc alloy plating baths for satisfying these conditions.
Addition agents to cyanide plating baths were divided into the following two groups, according to their actions. One was a group of brighteners giving brightening action and the other was a group of color controllers giving uniform color tone. It was found that As and Se belong to the former and ammonia and amines belong to the latter.
Color controllers were not found in these addition agents to the alkali plating baths complexed by tartrates. However, it was found that brightening action was given by the complexing action of amines and sulfamic acid salts in the presence of a small amount of cyanides.
Bright thick platings were obtained by the addition of an adequate amount of these addition agents to each of the baths.

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Investigations were made on the effects of the addition of various metallic salts on anodizing of aluminum in sodium hydroxide and alkaline-acid double electrolytic oxidation, and the properties of the films produced were also discussed.
An anodized film (about 7μ by microscopy) was prepared in NaOH (5×10^-2mol) containing metallic salts of 5×10^-3mol by electrolysis for 30min. under D.C. current density of 1amp/dm².
The result showed that the film had a higher corrosion resistance to acid (10% H₂SO₄) and base (10% NaOH) as compared with the anodized film of nearly the same thickness produced in H₂SO₄, but its scratch hardness (by Martens' hardness tester under a load of 50g) was not so high.
Then, the film produced in the above bath containing zincate had very higher corrosion resistance and hardness (15.0) as compared with the film produced in NaOH bath of the same concentration containing no metallic salts.
In double anodizing process, an anodized film, which had been prepared in the proposed alkaline bath and then electrolyzed in sulfuric acid by D.C. current density of 1amp/dm² for 30min., had a great thickness (about 7μ or more) as expected and a higher corrosion resistance as compared with the single anodized film.

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The boriding of steels was conducted by electrolysis in a bath containing borax and carborandum.
After the electrolysis, each thickness of the both borided layers of FeB and Fe₂B was much more increased as compared with the boriding of the same kind of bath with no electrolysis.
The addition of carborandum into the bath was very effective in preventing the dissolution of iron, nickel, and chromium from the stainless steel crucible into the bath. Therefore, it was considered to be very effective in preserving boriding ability of the bath for a longer time.
The wear resistance of bonded layer of mild steel was higher than that of hard chromium plating.

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Some properties of Ni-Al₂O₃ electro-codeposits on Cu plates were investigated by surface roughness, hardness test, Erichsen test, conical cup test, and measurement of stationary potential-current curve. Specimens were obtained from Watt's bath containing 25-150g/l of alumina particles (1, 0.3, and 0.05μ in particle size).
The results obtained were summarized as follows.
(1) The alumina content in the codeposits was parabolically increased with the increase in concentration of alumina in the plating bath. The rate of increase was lower with the decrease in the particle size of alumina.
(2) Every surface of the specimens had no brightness. When the particle size of alumina was 1μ, the surface was rougher with the increase in alumina content. However, when it was 0.3, or 0.05μ, no effect of alumina content was observed.
(3) The surface hardness was linearly increased with the increase in alumina content, and also increased with the decrease in its particle size.
(4) The forming property was deteriorated after the plating in all specimens, independent of alumina content and particle size.
(5) The corrosion resistance of specimens from 3% NaCl solution was decreased with the increase in alumina contents. The similar tendency was observed for every particle of alumina.

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Anodizing of aluminum in the electrolyte of alkaline solution was studied. This paper describes the relation between the anodizing conditions and thickness of oxide film, and the properties of the film.
The following results were obtained:
(1) In the anodizing of aluminum in alkaline solution, the thickness of anodic oxide film was, increased with the drop of bath temperature and it reached a maximum of 28μ at 1°C.
(2) As long as brown smuts did not adhere to the surface, the thickness of oxide film was linearly increased with increasing current density and anodizing time.
(3) It was shown by electron and optical microscopy that the cell size was larger than that of usual oxide films obtained from acid baths and a number of large pores appeared on the surface.
(4) Anodic oxide films from alkaline baths passed CASS test for 70hrs, and showed a corrosion resistance of 20sec/μ by alkaline drop test.

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In order to obtain economical cobalt platings for decorative purpose of high corrosion resistance, investigations were made for replacing the semi-bright layer of triple nickel platings by copper and replacing thin sulfur rich layer by cobalt.
By using Pb anode and CoSO₄. 7aq. solution or double salt bath, the process was examined for Co⁺⁺ concentration for higher throwing power and higher current density by the determination of cathodic current efficiency and continuous pH determination of the controlled bath. The control of pH was made by neutralization of the solution around the anode with CaCO₃, CoCO₃, or Pb(OH)₂ PbCO₃ or addition of ammonium acetate to the plating bath.
The results obtained were as follows:
(1) The highest throwing power was obtained from the solution containing 0.6mol/l of Co⁺⁺.
(2) The factor most effective for the current density was the variation in pH.
(3) Co⁺⁺ concentration had no effect on the current efficiency at pH=4 in a range of 0.4-0.7mol/l.
(4) The value of pH was required to be kept at above 4.
(5) The method of keeping pH value at constant was to neutralize the solution around the anode with Pb(OH)₂. PbCO₃ or to activate the anode by the addition of ammonium acetate to the plating bath. The optimum conditions of the bath components for the latter method were as follows:
CoSO₄.7aq. 0.6mol/l
(NH₄)₂SO₄ 0.4mol/l
(NH₄)O₂C₂H₃ 0.4mol/l
Anode Pb(containing Sn)
pH 4-4.5

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