Red precipitate was one of the first preparations of mercury known.
It is traced to Geber, but when the works attributed to that chemist
were written is doubtful. Avicenna in the tenth century was acquainted
with it. In his writings he says of the metal mercury that “warmed in a
closed vessel it loses its humidity, that is to say its liquid state,
and is changed into the nature of fire and becomes vermilion.” Being
obtained direct from mercury acted on by the air, it became known to
the early chemical experimenters as “precipitatus per se.” Paracelsus
obtained it by acting on mercury with aqua regia and heating the
solution until he got the red precipitate. Then he reduced it to the
necessary mildness for medicinal purposes by distilling spirit of wine
from it six or seven times. Charas described a method of obtaining the
precipitate by nitric acid but by a complicated process, and to the
product he gave the name of arcana corallina. Boyle obtained the red
oxide by boiling mercury in a bottle fitted with a stopper which was
provided with a narrow tube by which air was admitted. The product was
called Boyle’s Hell, because it was believed that it caused the metal
to suffer extreme agonies.