The co-deposition of a small amount of zinc impurity in the silver cyanide bath has been studied. A lavelled compound ⁶⁵Zn(CN)₂ was added to the bath in the concentration range of 0.05-1.0g/l. The amount of zinc co-deposited with silver increased with increasing zinc concentration, current density, and bath temperature. It was found that the amount of co-deposited zinc did not increase further after 1 min of plating time. This indicates that zinc deposited only in the initial stage of electrodeposition and the further co-deposition was prevented by the subsequent deposition of silver. The X-ray diffraction patterns of the silver deposits did not show any appreciable changes in orientation. Observations by electromicroscopy revealed coarse crystal grain growth and distinct nucleations. The autoradiography of the deposit showed that the co-deposition occurred obviously in polishing flaws on the surface at low zinc concentrations, but occurred around several spots at high zinc concentrations.

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A series of successive transformations of oxalate ions into colored substances is described in terms of E.L., P.L., E.S.R. and oxide color. High-purity aluminum (99. 99%) and 3S-aluminum (1%-Mn) were anodized in a 3% oxalic acid solution at a constant temperature (20°C) with or without pulsed current of varying frequencies. E.L. intensity during anodization and P.L. intensity after anodization were measured by an electronic photomultiplier. The deepness of the film color was determined by a color meter in the degree of L-value. In pulse anodizing, intensive coloration occurred at a frequency of ca. 1000Hz., and the brightest E.L. was observed, but P.L. intensity was almost inversely proportional to the color intensity. The cathodic part of the pulsed current plays an important role in the coloration as well as in E.L. From these results the authors propose the following mechanism: Oxalate ions are originally incorporated into anodic oxide matrix, then excited by high energy electrons, to be partly converted into intermediate compounds of colored substances. This intermediate compounds are the origin of P.L., but not of color. These compounds are further converted into colored substances, which have no P.L. Instantaneous inversion of polarity enhances the internal field strength which accelerates electrons so as to convert oxalate ions into colored substances.

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Electrochemical properties of aluminum oxide films formed chemically in hot water were studied by the measurements of corrosion potential, polarization curves and impedance in a sodium chloride solution. In addition, the films were examined by electron diffraction and scanning electron microscopy. Aluminum specimens of 99.99, 99.8, and 99.3% in purity were pretreated in 2% H₂SO₄-6% HNO₃ and then dipped for 20min in either of the following solutions; (1) distilled water, (2) boiling water containing 0.3% triethanolamine, (3) boiling water containing 0.1N ammonia. Corrosion potential of the aluminum treated in the boiling water was less noble than that of the aluminum pretreated only, because of an increase in cathodic polarization. This tendency is more notable with the specimens treated in super-heated steam at 4kg/cm² for 30min. The corrosion potential becomes less noble for increasing treatment time, water temperature and purity of aluminum. It is shown that thickness of the inner layer adjacent to the metal is increased by super-heated steam treatment.

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A theoretical study has been made of the improvement of rinsing process in plating, in relation to the saving and recycling of rinse water. A theoretical equation has been derived for the salt concentration of rinse water in the batch type intermittent rinsing process:
C_{j, k}={Σ^j_p=1(p+k-2 k-1)(V/V+D)^p-1}(D/V+D)^k⋅C₀
where C₀ is the salt concentration in the plating bath, D the dragout volume of plating solution per rack, V volume of each rinsing tank (D<V), k number of rinsing tanks, j number of racks through a rinsing tank, C_{j, k} the salt concentration in the k-th rinse tank after j rinses, and j and k are arbitary integers, which are greater than 1. This equation can be used in the wider range of j and k values than the similar equations hitherto proposed.

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