red vitriol

From The Collaborative International Dictionary of English v.0.48:

Vitriol \Vit"ri*ol\, n. [F. vitriol; cf. Pr. vitriol, vetriol,
   Sp. & Pg. vitriolo, It. vitriuolo; fr. L. vitreolus of glass,
   vitreus vitreous. See Vitreous.] (Chem.)
   (a) A sulphate of any one of certain metals, as copper, iron,
       zinc, cobalt. So called on account of the glassy
       appearance or luster.
   (b) Sulphuric acid; -- called also oil of vitriol. So
       called because first made by the distillation of green
       vitriol. See Sulphuric acid, under Sulphuric.
       [1913 Webster]

   Blue vitriol. See under Blue.

   Green vitriol, ferrous sulphate; copperas. See under

   Oil of vitriol, sulphuric or vitriolic acid; -- popularly
      so called because it has the consistency of oil.

   Red vitriol, a native sulphate of cobalt.

   Vitriol of Mars, ferric sulphate, a white crystalline
      substance which dissolves in water, forming a red

   White vitriol, zinc sulphate, a white crystalline substance
      used in medicine and in dyeing. It is usually obtained by
      dissolving zinc in sulphuric acid, or by roasting and
      oxidizing certain zinc ores. Formerly called also {vitriol
      of zinc}.
      [1913 Webster]
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