Transactions of the Electrochemical Society Volume 4 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1903 edition. Excerpt: ...a small amount of another metal present to facilitate the solution, so I think the chemical solution of the anode is probably facilitated by the presence of copper or other impurity. Dr. Rudolph Gahl: I should not think that the impurities of the nickel could cause much local action. Nickel causes strong local action on account of its low overvoltage on metals of higher overvoltage; for example, on copper. But the metals which are generally contained in nickel as impurities have a higher overvoltage than nickel has, and, therefore, I do not think that they can cause local action. Pres. Richards: You state that they have a lower overvoltage effect? Dr. Gahl: Yes, sir. Pres. Richards: Platinum with zinc intensifies the local action, but platinum has a lower overvoltage effect than zinc, so that it is rather the short-circuit effect of which I am thinking that the presence of the impurity in the body of the anode may have. Dr. Gahl: It depends on the amount of the overvoltage. Platinum has a very low overvoltage, and, therefore, causes an especially great local action; the other metals of higher overvoltage than platinum when deposited on zinc do not cause so much local action as platinum does. For example, the local action caused by copper is less than that caused by nickel, and the local action of nickel is much less than that of platinum, therefore, you cannot cause local action on nickel at all by copper, nor by lead nor by zinc, if these metals are deposited upon nickel. Mr. C. J. Reed: How is the overvoltage determined? The overvoltage of platinum, for instance, or nickel? Dr. Gahl: Overvoltage of a metal is the excess of voltage which is required for developing hydrogen on this metal, over that required for developing hydrogen on...