In SINCONA Auction 72 in November 2021, we offered as lot 870 one of four known specimens with a reeded edge. This piece with a plain edge has not been published so far.
Thomas Graham, master of the Mint from 1855 until his death in 1869, was an eminent chemist, renowned for his pioneering work on dialysis and the diffusion of gases (Grahams Law). His interest in metallurgy prompted the striking of coins in various metals and establishing their reaction to gases, including the absorption of hydrogen gas by palladium. According to his calculations this piece is said to contain 900 times its volume in hydrogen.