Silver extraction from copper. Historical engraving showing the equipment used to extract silver from black copper. Two furnaces are shown. The furnace on the left is being prepared for use, while the furnace on the right is in use. The disks (3) are the alloy from which the silver is to be extracted. Silver has a lower melting point than copper, therefore when the alloy is heated the silver melts away first (5). Taken from The Laws of Art and Nature, in Knowing, Judging, Assaying, Fining, Refining and Inlarging the Bodies of Confin'd Metals (1683), John Pettus, a translation of the work by Lazarus Erckern.