The state and stability of oxide film on the surface of electroplated tin plate were studied. The stability was measured with pulse polarizer and the state of oxide film was observed with electron microscope.
When the tin plate was heated in an electric oven, stannous oxide (SnO₂) film developed at the temperature under 100°C, while stannic oxide (SnO) film developed at above 100°C. The stability of SnO₂ film was increased with the growth of its thickness, while that of SnO was decresed with that.
It was also indicated that the stability mostly depended upon the conditions of chemical treatment on the surface of the films of the same weight.

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Effects of the main conditions of chemical copper plating on its local anode and cathode reactions have been investigated by means of potentio-kinetic polarization method.
The main conditions were as follows: (1) pH of the solution, (2) concentrations of the main constituents of the solution, and (3) temperature. Para-formaldehyde was used for the supply source of formaldehyde in the solution.
The results obtained are summarized as follows: (i) Anodic oxidation reaction of formaldehyde greatly depended upon pH of the solution. Maximum anode current decreased when the value of pH was smaller.
Abrupt cease of anode reaction at a certain electrode potential peculiar to pH was proved to be caused by the formation of Cu₂O as reported in the previous paper.
(ii) Local cathode reaction was supposed to be as follows:
Cu(OH)₂(Tart)^2-+2e→Cu+2OH^-+(Tart)^2-
In contrast with the case of anode reaction, cathode reaction was promoted when the value of pH was lowered.
Concentration of copper salt has more significant effects on cathode reaction than the concentrations of the other constituents investigated so far.

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The etched surfaces of (110), (111), and (100) planes of copper single crystal, which had been treated with aq. solution of ammonium persulfate, were observed with electron diffraction and electron microscope.
On (110) plane, it was observed that all of the etched faces were covered with {110} faces consisting of piles of thin rhombic crystals.
When crystal surface was parallel to (111) plane, it was observed that triangular (111) faces appeared on the top of triangular pyramid consisting of {110} faces.
However, {100} faces were not observed on etched surface of (100) plane.

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