Darkening aluminum by boiling water containing silica, was investigated. Silica was added to water in the form of sodium silicate, which did not affect the degree of darkening and the tone of surface color, when the ratio of SiO₂ to Na₂O was 2:1, 1:1, or 1:2.
Addition of some calcium sulfate, zinc sulfate or carbonate to sodium silicate solution promoted the darkening effect and black surface was obtained.
It was observed by X-ray test that the surface film on aluminum formed in boiling water was amorphous. Only the film formed in boiling distilled water showed a weak diffraction pattern of boehmite. From the result of the test of calcining the films at 1300°C it was found that the film formed in the water containing silica had the pattern of 3Al₂O₃⋅2SiO₂, and that formed in silica-calcium salt solution and well-water the mixture of 3Al₂O₃⋅2SiO₂ and CaO⋅Al₂O₃⋅2SiO₂. It seemed, therefore, that silica, calcium carbonate and calcium sulfate in water would be absorbed to hydrated aluminum oxide layer, and the absorption of silica might be considered as one of the most important factors of darkening.

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Superior corrosion resistivity of nickel-chromium coating can be presumed to some extent from the electrochemical investigation previously reported.
A series of corrosion tests, including outdoor exposure at seaside, was carried out to study the performance of copper-nickel-chromium and double nickel-chromium plated steel test pannels.
As a result, the following conclusions were obtained:
(1) In the salt spray and sulfur dioxide test, any superiority of the double nickel-chromium coatings to the copper-nickel-chromium coating was not observed.
(2) In the Korrodkote and CASS test, the performance of the former was excellent, regardless of the thickness. On the other hand, the latter was rapidly deteriorated.
(3) In the outdoor exposure at seaside, the former with total thickness of 30μ was excellent, but the former with total thickness of 20μ was often inferior to the latter with total thickness of 40μ.
(4) As the proportion of semibright nickel in a double nickel coating is increased, its durability in the outdoor exposure increases. Contrary to this, quite reversed phenomenon was observed in the Korrodkote and CASS tests.

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The anodic behavior of copper has been studied in connection with the elucidation of the mechanism of its electropolishing in orthophosphoric acide media. The horizontal section of the current-potential curve, which was considered by Jacquet as being uniform, has been investigated in greater detail by means of the potentiostatic method with a copper rod electrode in quiet media and with a rotated copper wire electrode.
Extrapolation to zero current of the plot of current at zero time against potential indicates that the initial step of the electrode reaction occurring in the entire potential range corresponding to the horizontal part of the current-potential curve is represented by
2Cu+H₂O→Cu₂O+2H⁺+2e.
The initial current is controlled by the charge transfer process of the above reaction, while the steady-state current is controlled by the mass transfer process involved in the dissolution process of the cuprous oxide.
Depending on the shape of current-time curves, the horizontal part of the current-potential curve may be divided into three ranges; i. e. high, intermediate, and low potential ranges. The mode of transition of current-controlling process from the charge transfer to the mass transfer process is different in different potential regions.

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In earlier work by C. M. Loucks et al. on citric acid cleaning test employed for preoperational mill-scale removal from the boiler tube, a black-iron boiler tube 28 in long and 1/2 in in diameter, was used as test specimen. But as the specimen was uneconomical for the factorial experiment to determine the cleaning condition, a semi-micro specimen prepared by halving length wise a black iron tube, 50mm long and 48-56mm in diameter, was used. Acid cleaning test was carried out by immersing the semi-micro specimen into 3% citric acid hot aq. solution poured and agitated in a 500cc beaker, and the descaling effect was measured by the difference of mean contact electric resistance, before and after the cleaning of the inside walls of each pieces. At the same time, ageing of acid solution was measured by photoelectric photometry. From the statistical analyses of the results of the experiment to determine the cleaning condition, it wes found that the temperature of acid solution was significant for cleaning hours but liquid velocity (agitation) was not always significant.

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