Definition of red precipitate in US English:

red precipitate

noun

Chemistry Medicine
historical
  • A red crystalline form of mercuric oxide, HgO, prepared by heating a solution of mercuric nitrate and formerly used medicinally, especially in ointments for the treatment of chancre and various skin diseases.

Origin

Late 17th century; earliest use found in Walter Harris (1647–1732), physician. After French mercure precipité rouge red precipitate of mercury; compare post-classical Latin praecipitatus ruber, mercurius praecipitatus ruber.