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Brightening solutions for aluminium. The chemical brightening of aluminium in mixtures based on phosphoric acid formed the subject of a series of experiments in which commercial purity aluminium panels were used in order to assess the influence of the aluminium content of the bath, and the effect of temperature upon the amount of metal removed. Four mixtures were employed: phosphoric‐sulphuric acid, phosphoric‐sulphuric‐nitric acid, phosphoric‐acetic‐nitric acid and phosphoric acid‐water‐nitric acid. If a highly specular finish is required, then the presence of about 5% (by volume) of nitric acid is essential. Acetic acid reduces the tendency for the rate of attack to increase with temperature, while water increases the maximum aluminium content which can be tolerated before the bath becomes unusable. Weight loss‐time curves are given for S1, S1B, S1C, NS4, HS10WP, HS15W and an Al (99.99%), 1.25% Mg, alloy treatment times up to 5 min. in the four solutions investigated. Except for HS15W, the response was found to be good for most materials, but a loss of brightness occurred with the lower‐purity materials on anodising.— (A. W. Brace and T. S. de Gromoboy, Trans. Inst. Met. Finishing, 1956, 33, advance copy No. 2.)

Cathodic protection by galvanic or impressed current techniques is probably the most favoured method of obviating the corrosion of buried and immersed metals. The theoretical principles and the economics involved in such protection are well established now and have been the subject of numerous papers, monographs and reviews. Cathodic protection is, however, still far from being an infallible method of corrosion prevention primarily because (a) the cathodic protection conditions necessarily change with the environment, (b) complete corrosion protection is rarely achieved in practice (see below), and (c) corrosion of an apparently protected structure may occur through the presence of stray currents