What is "vitriol of mars"

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.)

1. A sulphate of any one of certain metals, as copper, iron, zinc, cobalt. So called on account of the glassy appearance or luster.

2. Sulphuric acid; -- called also oil of vitriol. So called because first made by the distillation of green vitriol. See Sulphuric acid, under Sulphuric.

   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.

n. (context inorganic compound English) iron(III) sulfate