Sulphur containing selenium, such as occurs in the isle of Vulcano in the Lipari Isles, may be orange-red; and a similar colour is seen in sulphur which contains arsenic sulphide, such as that from La Solfatara near Naples.
The vast works for the refining of sulphur in the volcanic district of Solfatara were erected under his direction.
A triple-peaked volcano in the solfatara stage, extinct at the summit, but displaying considerable activity at its base in the form of numerous fumaroles and boiling sulilhur springs.
Beyond Posilipo is the small island of Nisida (Nesis); and at a short distance inland are the extinct craters of Solfatara and Astroni and the lake of Agnano.
A stream of lava issued in 1198 from the crater of the Solfatara, which still continues to exhale steam and noxious gases; the Lava dell' Arso came out of the N.E.