Effects of some impurities as well as other additives intentionally added on the internal stress were investigated by means of a spiral contractometer. The increase of NO₃^- or PO₂^3- amount increased the stress; whereas, the addition of PO₄^3- or P₂O₇^4- reduced the stress.
Furthermore, characteristics of iron electrodeposited from baths containing urea and ammonium bifluoride were studied.
The following results were obtained.
1) The maximum internal stress was observed at the lowest values of pH and temperature. The stress was decreased with the increase of pH value and rise of temperature at thickness of 30μ.
2) The addition of boric acid and hydrazine reduced the stress, but hydroxylamine had little effects on the stress over the concentration range in these studies.
3) In the range of 5-15amp/dm² of current density, the current efficiency was 60-80% and the surface roughness was 1.5-6S at 70°C of bath temperature.
4) In the range of 5-15amp/dm² of current density, the structure of deposit became gradually finer with the increase of current density.
5) In the range of 1-2amp/dm² of current density, the microphotographs of sections showed amellar figures. However, in its range of 5-15amp/dm², they showed columnar figures.
6) In the range of 5-15amp/dm² of current density, the hardness of deposits was increased with the increase of current density.

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In order to investigate the adaptability of electrodeposited cobalt from citrate bath as sacrifice layer the authors measured electrode potential in CASS solution and electromotive force of corrosion cell produced by copper, nickel, and cobalt (deposited from a citrate bath) in 5% NaCl solution.
The following conclusions were drawn on the basis of the results obtained.
1) The noblest deposit for sacrifice layer was obtained from the following bath composition:
cobalt sulfate 0.6mol/l
sodium citrate 0.7mol/l
ammonium sulfamate 4-10g/l
2·butyne 1·4 diol 0.1g/l
2) The deposit having the same properties as described in the previous papers (Part 2 and 3) was obtained from the following bath composition:
cobalt sulfate 1.0mol/l
sodium citrate 1.0mol/l
3) The electrode potential of deposited cobalt was less noble with the increase of current density.
4) The electrode potential of deposited cobalt was nobler by the addition of a sulfamate to the bath.
5) Zinc was the most toxic ion in the plating bath among cationic impurities which are usually contained by carelessness.

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This paper describes the studies on the limiting current density in nickel plating.
The experiments were carried out under the following conditions.
Composition of electrolyte: nickel sulfate 300g/l
and boric acid 30g/l
Electrolyte temperature: 20-60°C
Interval between electrodes: 1mm
Flow speed of electrolyte: 0-10m/sec.
As the results of experiments, it was found that the limiting current density in nickel plating can be expressed by the following equation:
i_l=1.7×10⁶nFCD²U1/2/1-α
where U=Flow speed of electrolyte
D: Diffusion coefficient
F: Faraday constant
C: Concentration of nickel sulfate
α: Transport number
i_l: Limiting current density
The above equation corresponded well with the results of experiments at Reinolds number of less than 5000. However, the measured values of i_l were higher than those calculated from the above equation at speeds in the range of 0-1 or beyond 5m/sec.

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Studies were made on the non-cyanide electrolytic degreasing baths.
Degreasing effects were investigated by spectrofluorophotometer in various baths. The optimum conditions and bath composition were as follows.
Bath composition
sodium hydroxide 1mol/l
sodium gluconate 0.3 mol/l
potassium pyrophosphate 0.1 mol/l
Operating conditions
bath temperature 50°C
cathodic current density 10amp/dm²
electrolysis time 1min
The derusting effect of the above bath was less than that of the conventional cyanide baths, but it was available in practical use.
The deposition of iron during electrolysis could be prevented by addition of 20g/l of DTPA to the bath.
A surface active agent, called “anion type 6”, was more effective than other active agents.

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The behavior of the hydrated chromium oxide film formed on the steel surface during galvanostatic electrolysis for a few seconds in an electrolyte consisting of 50g/l of chromic acid and 0.5g/l of sulfuric acid was investigated by means of tracer technics using radioactive Cr (⁵¹Cr).
The results obtained were as follows:
1) In the intermittent electrolysis, the film formed in the early stage of electrolysis did not act as intermediate for deposition of metallic chromium.
2) The formation simultaneous with dissolution of the film took place during the electrolysis.
3) The true quantity of the film linearly increased with the progress of electrolysis time, but its value measured increased exponentially, because a part of the film was exponentially dissolved in the electrolyte.
The measured value of the film quantity (m) after galvanostatic electrolysis for t seconds was shown by the following equation:
m=A/B(1-e^-Bt)
where A and B are constants
Therefore, it was suggested that the thickness of the film would develop to a certain limit.

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