1911 Encyclopædia Britannica/Copperas

COPPERAS (Fr. couperose; Lat. cupri rosa. the flower of copper), green vitriol, or ferrous sulphate, FeSO4·7H2O, having a bluish-green colour and an astringent, inky and somewhat sweetish taste. It is used in dyeing and tanning, and in the manufacture of ink and of Nordhausen sulphuric acid or fuming oil of vitriol (see Iron).