The metallic compound called electron is described by Strabo p. 146 as the mixed residuum, or scouring, (κάθαρμα) left after the first smelting of gold ore. Pliny (H. N. xxxiii. 23) describes it as containing 1 part silver to 4 gold. cf. Soph. Antig. 1038, and Herod. i. 50.