Activities of fluoride and foluorosilicate in chromium plating baths were studied by using a fluoride electrode, and the following results were obtained.
(1) In chromium plating baths, the activity of fluoride was less than that of the additional fluoride. The reason for this was that F^-+H⁺→HF.
(2) The activity of fluoride well corresponded with the value calculated from pH of the plating bath and ionization constant of HF, 7.2×10^-4.
(3) The activity of fluorosilicate was quite the same as that of fluoride at concentrations of less than 10^-3mol/l or at higher pH. The reason was that the fluorosilicate was completely decomposed at low concentrations, and it was decomposed to fluoride at higher pH as follows:
SiF₆^2-+6OH^-→6F^-+[Si(OH)₆]^2-
(4) The difference between activities of fluoride and fluorosilicate under other conditions was due to the formation of complex salt by fluorosilicate.

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The pitting and protection potentials for pure aluminum in 0.5N NaCl solutions (pH=4, 6, 8, 10, and 12) were investigated by means of an apparatus consisting of a potentiostat and a high sensitive recorder.
The results obtained were as follows.
The pitting potentials determined by polarization curves of aluminum in 0.5N NaCl solutions (pH=4, 6, and 8) showed two kinds of different values.
(1) In the solution of pH=4, the 1st pitting potential was -1.15V (vs. S.C.E.) and the 2nd one was -0.73V (vs.S.C.E.); and the protection potential was -1.20V (vs.S.C.E.).
(2) In the solution of pH=6, the 1st pitting potential was -1.16V (vs.S.C.E.) and the 2nd one was -0.72V (vs.S.C.E.); and the protection potential was -1.20V (vs.S.C.E.).
(3) In the solution of pH=8, the 1st pitting potential was -1.16V (vs.S.C.E.) and the 2nd one was -0.70V (vs.S.C.E.); and the protection potential was -1.16V (vs.S.C.E).
(4) The pitting and protection potentials for aluminum in 0.5N NaCl solution (pH=10) were -0.70V (vs.S.C.E.) and -1.16V (vs.S.C.E.), respectively.
(5) The pitting and protection potentials for aluminum in 0.5N NaCl solution (pH=12) were -0.52V (vs.S.C.E.) and -1.89V (vs.S.C.E.), respectively.

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In this paper, the dry-sliding wear properties of SKD 11 and SKH 9 under conditions of high pressure and low velocity are discussed; these samples are industrially utilized as mold forming materials in cold forming. Particularly, these alloy steels were used as stators, while sulfurized or phosphated low carbon steels were used as rotors cooperating with the side stators.
The results showed that in the range of contact pressure of 500-1500kg/cm² and sliding velocity of 0.05-1.00m/sec., the surface layers of phosphated rotors broke away at their earlier stage of wear, which resulted in metal transfer due to adhesion.
Whereas, little adhesion was observed on the sulfurized rotors. A part of porous sulfurized layers spalled away as wear powder, which adhered to the sliding surface of counter experimental piece. Then, the wear loss between the two sulfurized layers grew remarkably less.
It was also observed that when the wear ratio varied in the velocity-wear property curve, the wearing mechanisms were nearly identical with those mentioned above.
It was further observed that the wear of underhardened material was slightly larger than that of ordinarily quenched and tempered one, because the hardness of the former was much lower than that of the latter.

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This paper describes the results of experiments on the coagulation mechanism of metal ion and oxidation reactivity of metal hydroxide at high temperatures with respect to chromium ion (Cr³⁺) and chromium hydroxide causing public discussion in waste water treatment and sludge disposal.
The following results were obtained:
(1) The water content of chromium hydroxide was maximum when the coagulation of chromium ion occurred at pH of 7-9. (It was less when the coagulation occurred at higher or lower values). As the result, the apparent specific gravity of chromium hydroxide produced at pH of 7-9 was minimum and its sedimentation rate was also minimum.
(2) Na content of chromium hydroxide increased with the increase of pH value at which coagulation occurred. Therefore, the Cr⁶⁺ content of the burned chromium hydroxide was also greater with the increase of pH value at which coagulation occurred.
(3) The Cr⁶⁺ content of the burned chromium hydroxide containing Na was maximum at about 300°C. However, when the oxidation temperature was higher than that, the Cr⁶⁺ content decreased owing to its decomposition.

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