COPPERAS, noun Sulphate of iron, or green vitriol; a salt of a peculiar astringent taste, and of various colors, green, gray, yellowish, or whitish, but more usually green. It is much used in dyeing black and in making ink, and in medicine, as a tonic. The copperas of commerce is usually made by the decomposition of iron pyrites. The term copperas was formerly synonymous with vitriol, and included the green, blue and white vitriols, or the sulphates of iron, copper and zink.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI