Green Vitriol (Copperas) from Weathered Pyrites, Ure 1839

Copperas, green vitriol, was made by leaving pyrites out in the weather. Andrew Ure (1839): spread it on a sloping platform until it takes up oxygen and blooms with salt, wash the salt out, sweeten the acid liquor with old iron and boil it down to crystals. It made black dyes, ink, prussian blue and the old oil of vitriol. Roasting pyrites gives off a choking, deadly gas: do it only in the open with a respirator. The picture: green crystals of iron(II) sulfate.