The Tension of Metallic Films Deposited by Electrolysis

It is well known that metallic films deposited electrolytically are in many cases liable to peel off if deposited to any considerable thickness. This is the case with nickel which, when deposited over a certain thickness, will curl up into beautiful close rolls, especially if it does not adhere very tightly to the body on which it is deposited. For example, if a piece of glass is silvered by any of the usual silvering solutions, and then nickel is deposited on the silver, it is found that the nickel and silver peel off the glass in close tight rolls almost at once. In ‘Practical Electro-Chemistry,' by Bertram Blount, reference is made on pp. 114 and 272 to the tendency of nickel to peel off, and it is stated that it “will peel—spontaneously and without assignable cause” (p. 272), but that a thick coating can be obtained by keeping the solution at between 50° and 90°C. The late Earl of Rosse tried, about 1865, to make flat mirrors by coating glass with silver chemically, and then electroplating with copper; but he found that, owing to the “contraction” of the copper film, it became detached from the glass. I have had the' same experience in protecting silver 61ms in searchlight reflectors by a film of electro-deposited copper, it being found that if the film of copper is more than 0.01 mm. thick peeling is apt to take place.