A copper surface anodically etched in aqueous solutions of orthophosphoric acid becomes as bright as though it had been polished, if voltage and current density are kept within definite limits. If properly controlled, anodic etching will reveal the crystalline structure of the metal. The phenomenon seems to be based on the passivation of the anode and is a function of concentration polarization. The anodic etch method has been applied to metal sections intended for metallographic examination ; excellent results were obtained. As compared with the usual polishing method, the anodic has the advantage of being much more rapid and less expensive.INTRODUCTION.

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Certain hydrophilic colloids (proteins and their disintegration products) form adsorption films on metal surfaces (copper, nickel, iron, platinum), and these films materially reduce the adhesion of electrolytic deposits to such surfaces. On the basis of the adsorption phenomenon, we have evolved a method for the determination of the degree of adhesion of electrodeposits on any basis metal. As a rule, results are reproducible to about 10 to 20 per cent. The measurements are limited by the distortion of the deposit, this limit being a function of the thickness of the deposit. For copper deposited on nickel, a thickness of 0.30 mm. (12 mil.) is sufficient for the study of the effect of various factors on the degree of adhesion of electrodeposit to basis metal. The less the mechanical strain developed in the copper plate during deposition, the better will it adhere to the nickel. During the operation of an acid copper sulfate bath a gradual but continuous change in the composition of the bath takes place. This ageing of the bath is indicated by the determinations of the degree of strain developed in the successive deposits from the same bath. The ageing of the bath has a marked effect on the adhesion of the copper to the nickel. The ageing appears to be due to a progressive enrichment of the electrolyte in cuprous ions. For strongly adherent deposits it has been shown by two chemical tests, H 2 S and K4Fe (CN) e, that after pulling off the copper deposits from the basis nickel surface, a copper layer or residual film remains on the nickel surface, nearly always continuous. Thus the force necessary to detach the copper deposit from the basis metal does not Correspond to the true adhesion of the deposit, but represents what might be called a shearing stress of the copper. When copper is deposited from a copper bath with a very low content of free sulfuric acid, the true adhesion of the deposit 1 Manuscript