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, H2S and K4Fe(CN)6, 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 seems to be very high, but the shearing stress is relatively low. This fact might be explained by the presence of a certain quantity of cuprous oxide in the metal. The physical state of the basis nickel surface has a great effect on the adhesion of the electrolytic copper : The adhesion is very poor on emery scratched surfaces. As a rule, it is better on polished nickel surfaces than on roughened electrolytic ones.