What is "ferrous sulphate"

Copperas \Cop"per*as\, n. [OE. coperose, F. couperose, fr. (assumed?) L. cuprirosa, equiv. to G. cha`lkanqos, i. e. copper flower, vitriol. See Copper and Rose.] Green vitriol, or sulphate of iron; a green crystalline substance, of an astringent taste, used in making ink, in dyeing black, as a tonic in medicine, etc. It is made on a large scale by the oxidation of iron pyrites. Called also ferrous sulphate.

Note: The term copperas was formerly synonymous with vitriol, and included the green, blue, and white vitriols, or the sulphates of iron, copper, and zinc.

n. (context dated inorganic compound English) (alternative form of ferrous sulfate English)