red precipitate
Chemistry and Medicine (now historical )
noun
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.