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.
       [Colloq.]
       [1913 Webster]

   Blue vitriol. See under Blue.

   Green vitriol, ferrous sulphate; copperas. See under
      Green.

   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
      solution.

   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]