SOLFATARA  , a volcanic vent emitting vapours chiefly of sulphurous

character, whence the name, from the Italian solfo (sulphur) . The typical example is the famous Solfatara, near Puzzuoli, in the Phlegraean Fields, west of Naples . This is an old crater which has not been in active eruption since A.D . 1198, but which is continuously exhaling heated vapours, chiefly hydrogen sulphide, sulphur dioxide and steam . These issue from orifices in the crust, on the walls of which are yellow incrustations of sublimed sulphur, sometimes orange-red by association with arsenic sulphide, whilst the trachytic rocks of the volcano are bleached and corroded by the effluent vapours, with formation of such products as gypsum and alum . Sal ammoniac occurs among the sublimates . The term solfatara has been extended to all dormant volcanoes of this type; and a ' volcano which has ceased to emit lava or ashes but still evolves heated vapours, is said to have passed into the " solfataric stage." Examples are to be found in many. volcanic districts . By French geologists the term soufriere is used instead of the Italian solfatara .