Hydrogen-embrittlement caused by Zn-cyanide plating process was stronger than that by the acidic process in the same current efficiency. Therefore, the embrittlement by the former process seemed to be caused by other factors than the amount of hydrogen discharged. At first, electrolytic con-ditions in the process of plating were studied for hydrogen or zinc polarization by potentiostatic method in the eight baths reported in the previous paper.
The results obtained were as follows:
1) The degree of brittleness of the specimens corresponded well with that of the hydrogen polarization before Zn deposition. Then, the cause of embrittlement was considered to be the action of hydrogen discharged on the naked iron cathode of low hydrogen overvoltage.
2) As the results of equilibrium potential measurements and activity of OH^-, it was concluded that most of Zn from so-called Zn cyanide bath was deposited from zincate solution.

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Some mechanical properties of electroplated ABS plastics were measured. It was found that its tensile strength conformed to a simple composite law; namely, the value of its tensile strength was equal to the sum of each value of the electroplated metal and the base, and there was no interaction between both materials.
S-N curves in fatigue tests were obtained for the plastics the etched one and the electroplated one When the fatigue limit was expressed in terms of the strain amplitude, the value of the electroplated plastics was much lower than that of the base. The above tendency also appeared in bending tests and the electroplated plastics were essentially “brittle”. The fatigue limit of the etched one, was decreased from that of unetched one.
Initiation and growth of cracks were observed during the fatigue tests and the behavior was varied according to the thickness of the film.

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The cathodic polarization characteristics of pure chromic acid solution were measured by potentiostatic method for the investigation of its chathodic reaction.
The following results were obtained:
1) Electro-deposition of metallic chromium appeared in the chromic acid solution to which anions had been added in the potential range of the 4th branch on the polarization curve; whereas, in pure chromic acid solution, deposition of hydrated chromium oxide film appeared at first, and subsequently black chromium plating occurred.
2) Significant hysteresis was observed in pure chromic acid solution when in was polarized to the potential range of the 4th branch.

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Studies were made on the conditions of anodic oxidation of Ag⋅AgCl electrodes during its preparation by electrochemical chlorination of Ag plate in HCl solution.
The results obtained were as follows:
1) The optimum quantity of electricity was 1mAmp. hr./cm² in the chlorination for 10-120min, under the current density of 2mAmp./cm² and in the anodic polarization test of these electrodes in 1mol NaCl solution.
2) Better polarization characteristics were obtained in the electrode chlorinated under the current density of 2mAmp./cm² by the experiments in the range of 1-10mAmp./cm².
3) The effect of concentration of HCl for chlorination on the limiting current density for anodic oxidation in 1mol NaCl solution was examined. It was shown that the optimum concentration of HCl was 1N.
4) The limiting current density for anodic polarization in 1mol NaCl solution was higher with the rise in both temperatures of HCl and NaCl solution. However, the overvoltage of anodic polarization in 1mol NaCl solution was higher with the rise in temperature of HCl.
5) The overvoltage of the electrode specimen in anodic polarization was lower and the limiting current density in 1mol NaCl solution was higher by the chlorination of the Ag plate in 1N HCl containing a small amount of H₂O₂.

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Reduced Ni films were obtained on iron substrate from the electroless plating bath containing NaBH₄ as an reducing agent.
The initial precipitation behavior of the plated Ni films was examined by direct observation and electron diffraction method with an electron microscope.
The following results were obtained:
1) No difference of precipitation behavior was observed between the inoculation process by an instantaneous galvanic contact with Al and the process by a momentary current. At first, Ni micro-granules of less than 150Å in diameter were precipitated in the early stage, and then, developed to the diameter size of 300-1300Å, when nebulous crystals were distributed independent of the granular crystals. The nebulous crystals grew into acicular form with the progress of plating time.
2) The granular crystals of 300-1300Å had no coherency with the substrate and did not grow up to above 1300Å. The precipitation density of these granules was 10⁶/mm².
3) The diffraction pattern of the nebulous crystals observed consisted of rings having an intense spot.
4) The granular crystals were precipitated on the substrate from a new bath only. Whereas, the nebulous crystals were immediately precipitated from an old bath which had been practised for a long period.
5) The initial precipitation behavior of Ni films electroplated from a plating bath not containing NaBH₄ was observed to be under the same conditions as in the electroless plating.

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This paper reports the research on etching mechanism for plating of ABS resin. After etching with sulfuric-chromic acid solution, the resin was examined by infrared spectroscopy, adsorption of dyes, weight loss, surface roughness, etc.
A linear relationship was observed between the immersion time in the solution at 60°C and the amount of adsorption or other factor (such as weight loss or surface roughness) in the normal etching reagent (for example, saturated chromic acid containing 60% sulfuric acid).
The results showed that polybutadiene particles only were preferentially oxidized and dissolved into the etching reagent.
A further relation was examined between the immersion time and adhesion of plating on the resin. The adhesive strength was rapidly increased during the first several minutes and attained to a peak after 5-20 minutes, when the peeling strength obtained was 11kg/in. After etching with a solution of sulfuric-chromic acid (both acids were in higher concentrations), a layer insoluble in methyl ethyl ketone (MEK) was formed on the resin surface, which was examined by differential scanning calorimetry and elementary analysis. The effect of the solution was so remarkable that the resin remained in network structure insoluble in MEK, which seemed to be degraded.
It was further found by the results of weight loss, surface roughness, etc. that AS resin matrix as well as polybutadience was attacked and dissolved into the solution.
It was also shown that the immersion time in the solution had powerful effects on the adhesive strength and the resin etched for a long time had very little adhesive strength.

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