A 1792 US silver-centre cent sold for $1.9m at Heritage Auctions' US Coins Signature Auction in Chicago on August 9.  

The coin was the first to be designed and struck in the newly opened US Mint in Philadelphia (earlier pieces, like the 1792 half disme, were designed in temporary buildings near the site).

The 1792 silver cent features a silver plug at its centre

It features a silver plug at its centre that was introduced to limit the size of the coin. This was the result of a newly passed bill, which stated that the value of the metal used had to be equal to the value of the coin.

The cent would have been significantly larger had copper alone been used, around the size of a half dollar.

Thomas Jefferson explained in a letter to George Washington at the time: "Th. Jefferson has the honor to send the President two cents made on Voigt's plan by putting a silver plug worth ?� of a cent into a copper worth ?? of a cent.

"Mr. Rittenhouse is about to make a few by mixing the same plug by fusion with the same quantity of copper.

"He will then make of copper alone of the same size, and lastly he will make the real cent as ordered by Congress, four times as big."

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