‘Crocus Martis cum Aqua is made by exposing Plates or Filings of Iron to the Rain or Dew, until it hath contracted a Rust, which collected is called Crocus Martis cum Aqua, or ferri Rubigo. This Crocus consisteth of the sulphureous, saline, and terrestrious parts combined together; yea indeed it is the very substance of Iron, having its pores much opened by the Dissolvent or Saline parts of Water; which not only maketh its Pores more open, but by combining with it maketh this Crocus an excellent Aperient medicine, whose Deopilative virtue chiefly dependeth on this Salt.
The Sulphur of Iron being retained in this Preparation renders it a fit ferment for blood, whose active Principles are weak and faint: And the Saline part (being exalted by That of the Dissolvent Water that much laxeth the body of Mars) renders it a good Aperient in Obstructions, as of the Liver, Spleen, Mesentery, Lacteal vessel, or Womb with its coherent parts.’
Samuel Derham, Hydrologia philosophica or, An account of Ilmington waters in Warwick-shire; with directions for the drinking of the same. Together with some experimental observations touching the original of compound bodies (1685)