b 



No. 1 v.— 0;i the Solfatara of Pozzuoll 139 



as far as our limits permit us to dwell upon this part of our 

 subject, we may, in conclusion, notice those volcanic craters 

 occurring in different parts of the world, in a state similar to 

 the one before UvS. The general congruity of such phenomena, 

 however, the small stock of information which we compara- 

 tively possess relative to inter-tropical volcanos, and the supe- 

 rior interest of the Solfatara of Pozzuoli, as well as the care 

 with which it has been examined, admit only a moment's atten- 

 tion to this subject. 



Since sulphur is converted into vapour at 290° of Fahren* 

 heit, the habitual temperature of any spot which exhibits it as 

 a characteristic product must be below that point, and, it il; 

 hardly necessary to add, must be free from those paroxysms 

 which would destroy the nature of the crater, and probably 

 change the emanating gases. Now, as it is known that sul* 

 phurous acid and sulphuretted hydrogen gases mutually de- 

 compose each other, the portion of either emitted from any 

 crater is understood only to be the excess of the one above the 

 other.* But in all active volcanos the sulphurous acid ap- 

 pears to predominate, and does not lead to any direct and ex- 

 tensive deposition of native sulphur, while, on the other hand, 

 sulphuretted hydrogen becomes the characteristic gas of ex- 

 tinct emissaries. Thus, to take only Italy and its neighbour- 

 hood, whilst at the Solfatara, at Sermoneta, at Terracina, at 

 Castelamare, at Acerra, at Jaci Reali, (Sicily ;) among the 

 least active of the Lipari Isles, and other examples almost in- 

 numerable, the hydrogen abounds ; at Etna, Vesuvius, and 

 Volcano, the only true modern emissaries, it is wholly unknown. 

 Such then are the general conditions of the formation of a Sol- 

 fatara. 



The most accurate examples of Solfataras with which we 

 are acquainted are in the West Indies, and I shall notice no 

 others, for the Lipari Isles, the crater of the Peak of Tene- 

 ritfe,-(- and other more imperfect examples, can hardly be clas- 

 sed under this denomination. Among the Carribbee Islands 

 the most important is Guadaloupe, of which we have some ac- 

 count in the " Menioires de VAcademie^^^X in the Annates des 



• Daubeny. t Humboldt, Fers. Nar. 



X For 1750, Histoircj p. 48, 12mo Edit. 



