The physical and chemical conditions of the metal surface contribute to the adhesion to the paint film, being a matter of concern in protective coating of aluminium and its alloys. And the extensibility of the film should be a not-slight factor too in consideration of the flexibility, the heat-expansibility and etc. of aluminium alloys. Therefore, the effect of surface preparation for painting is investigated. Namely, the non-treated specimens and the others treated with alcohol-phosphate are coated with zinc chromate phthalic resin enamel and benzylcellulose enamel under the same conditions respectively, and offered to bending-test, drawing-test, erichsen-test and corrosion-test.

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The test-pieces of castings, each of which is previously treated mechanically with sand paper, or chemically by alcohol-phosphate or B. V. method, or by anodic oxidation method, are enameled, and offered to drawing-test and corrosion-test. Then these surface preparations are compared and discussed on the effect on the enameling coats. It seems that the baking enamels, more anticorrosive, are generally used foraluminium alloy castings, but here for the comparative investigations zincchromate phthalic resinenamel and benzyl-cellulose enamel, picked out formerly, are used together with baking melamineresin enamel and vinyl-acryl-co-polymer enamel. In general anodic oxidationmethod is most effective, the next is alcohol-phosphate method, and B. V. method little inferior to them. But sand paper method is not effective in contrast of them.

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To get excellent chromium oxide for polishing use, chromium oxides prepared by various methods were studied.
In Part I, tests of abrasive ability were carried out for chromium oxides. Chromium oxides having suitable abrasive ability were principally prepared by following two methods:
(1) Roasting in air or decomposing of suitable chromium compounds (for example CrCl₃ anhydride, Cr₂(SO₄)₃ anhydride etc.) at relative low temperature (700-800°C).
(2) High temperature (1100-1300°C) roasting. of fine chromium oxides prepared at low temperature (for example Na₂Cr₂O₇+S, CrO₃).

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Chromium oxides prepared by various methods were observed by the electron microscope. The results obtained are as follows:
(1) The sizes of chromium oxides having suitable abrasive ability are 0.2-0.6μ.
(2) There are two kinds of shapes in chromium oxide, massy and laminated.
(3) The shapes of chromium oxides gradually segregated from fused salt (for example, from fused K₂Cr₂O₇) are large and hexagon-lamellar.
(4) The growth of the particle of chromium oxide by roasting was destinctly recognized.

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The systematical observation is developed pertainning to the various changes of the bath voltage with given circling of an electric current, which indicate us the situation of the proper decomposition voltage and the passivation voltage as well.
The surface of the copper which is an anode and turned into a state of passivity is generally making an appearance of the protective oxide coating of metals, stable and of high classed compound, which keeps and prevents the metals from ionizing.
In the electroplating solution which has been using up to this time, the momentary changes of the bath voltage rise and electric current falls at about 0.5volt and 1.5volt (at 0.5volt it changes slightly and at 1.5volt it changes violentaly) and the form of the metal deposits changes strongly at this bath voltage and especially at the passivation voltage it indicates violent changes.
In the case of the passivation of the anode, the current falls and there will be many faults which the metal deposits at the cathode.
It is strongly required to deal with the bath voltage within the scope of the condition under which the anode can be active, in case of the electroplating solution composed of sulphic acid and sulphic copper solution, which is generally utilized for the electroplating of copper.
But in this case, the bath voltage will be, needless to say, changed automatically with the circumstances of the electroplating solution, or the purity of the anode at the time, etc.
Further more, I developed the studies on the problem (2), which has caused me to put forth, as a result, the effective explanation for the similaritical relations with the A-V curve, coming to the final conclusion on the processes of the reaction after careful performance of the foundamental experimentation for the matter.

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