Lemery in 1675 by distilling green vitriol.
As alum and green vitriol were applied to a variety of substances in common, and as both are distinguished by a sweetish and astringent taste, writers, even after the discovery of alum, do not seem to have discriminated the two salts accurately from each other.
Originally prepared by heating alum, green vitriol and other sulphates, and condensing the products of distillation, sulphuric acid, or at least an impure substance containing more or less sulphur trioxide dissolved in water, received considerable attention at the hands of the alchemists.
Ferrous sulphate, green vitriol or copperas, FeSO47H2O, was known to, and used by, the alchemists; it is mentioned in the writings of Agricola, and its preparation from iron and sulphuric acid occurs in the Tractatus chymico-philosophicus ascribed to Basil Valentine.
By evaporation the green vitriol is obtained as large crystals.
