This is a 1915 Lincoln cent struck in nickel. Pollock sites the description from Elder's 2/19 sale which is as follows:
"The mint officials thinking to invent a new cent which would not rust, like the bronze one [sic], had half a dozen samples struck off in nickel. Subsequently all these trials were rejected and destroyed, except this one."
Mike Byers notes: "This fascinating piece requires further study because it weighs 50 grains and is an off-metal. A normal copper cent weighs 48 grains. The closest foreign blank which is 75% copper and 25% nickel is a 1919 El Salvador 1 Centavo, which weighs 38 grains."
We believe these explanations ares dubious. It is more likely that this is a mint error struck from planchet strip originally intended for foreign coinage - the Mint struck Cuban 2 centavos which weighed 54 grains or was struck on nickel 5 cent stock which was inadvertently rolled and punched into U.S. cent planchets. Should any exist on a 38.6 grain planchet, they would have been struck on stock for the Venezuela 5 centismo. For more on this, we recommend Mike Diamond's article for Coin World published on July 14, 2014, and titled "Scrutinize claims of experimental planchets, test strikes".
The illustrated example appeared in the June 10, 2002 edition of Coin World. It is presently owned by Michael Byers as is a recently discovered second example.
Photo courtesy of Mike Byers.