Some considerations of solution properties and structure of pyrophosphate bath were given for the electrodeposition of iron-nickel alloy.
The absorption spectrum of each solution, potassium pyrophosphate, nickel chloride, ferric chloride and these mixed salts, was observed. A maximum extinction coefficient appears at 720mμ of wave length in the NiCl₂ solution, it is transferred to the longer wave range in the NiCl₂-K₄P₂O₇ system, and it is transferred to the still more longer range and the degree of extinction increases in the K₄P₂O₇-NiCl₂-FeCl₃ system.
From these observations, a complex structure which contained Fe³⁺, Ni²⁺ and P₂O₇^4- was supposed which was endorsed by the measurement of the specific electroconductivity of these solution.
Moreover, the iron-nickel alloy could be successfully electrodeposited on the copper wire from this ternary mixed solution.

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In order to find out the factors significantly affecting the result of Korrodkote test of double nickel-chromium coatings, a series of experiments was carried out by means of experimental design. Statistical analysis of the result has led to several interesting conclusions.
For example:
1) Type of semibright and bright nickel plating bath can be important factors. Among sulfer-free semi bright nickel baths, the coumarin containing bath gave better result compared with the Watts' bath without addition agent, and among bright nickel baths, the TNS containing bath was better than the saccharin containing one.
2) In bright nickel plating, the deposit with higher current density was more corrosion resistant.
3) Thickness of nickel deposit showed more significant effect on corrosion resistivity than that of copper, the latter being almost insignificant.

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