Emily Dickinson Lexicon

COL-CO'THAR, n.

The brown red oxyd of iron which remains after the distillation of the acid from sulphate of iron; used for polishing glass and other substances. It is called by artists crocus, or crocus martis. – Encyc. Ure. The sulphate of iron is called colcothar or chalcite, when the calcination has been carried so far as to drive off a considerable part of the acid. – Fourcroy. [See Chalcite.]