No. IV.— On the Solfafara of Po%%uoll 135 



agency in the form of sulphuretted hydrogen gas. The small 

 quantity of muriatic acid accompanying it is easily explained 

 by the decomposition of the muriate of soda in the sea water. 

 The nitrogen may be accounted for by the accidental access 

 of atmospheric air to the seat of volcanic oxidation. Carbonic 

 acid, as we had occasion to mention when speaking of the 

 Grotto Del Cane in the last number of these Notices, probably 

 owes its origin to the effect of internal heat upon calcareous 

 strata, and its prevalence in those volcanos only which are near- 

 ly extinct has been ingeniously explained by the fact, that po- 

 tassium, and probably the other alkaline and earthy bases when 

 heated, decompose this gas. Such is one of the most modern 

 and most elegant explanations of the origin of these elastic 

 t fluids, though I shall not venture here to give an opinion 

 > upon the plausibility of the great chemical theory upon which 

 they are built. The subsequent action of these gases, how- 

 ever, is sufficiently obvious, and accounts for all the varied 

 products of this crater. The principal of these \^e shall short- 

 ly notice. 



The sulphuretted hydrogen combining with the various sub- 

 stances contained in the rock of the Solfatara forms the class 

 ©f hydrosulphurets, which being decomposed by the union of 

 carbonic acid with the bases, the sulphuretted hydrogen is 

 separated into hydrogen, which forms water with the oxygen 

 of the atmosphere, and sulphur, first forming hyposulphates 

 of the earthy bases, and finally sulphates, but a great part % 

 precipitated into the natural forms of sulphur. 



This substance occurs either crystallized or compact ; but 

 \i is a curious fact that it seems to be entirely the production 

 of the " fumerole,"" as no sulphur has been detected in the 

 5 natural plain of the Solfatara. For a long time the manufac- 

 ture of sulphur was continued during the last century with 

 little profit, and the usual inattention to the economy of labour, 

 and management in general, which too often characterizes 

 manual operations in Italy : the product was annually only 

 270 cwt., selling at sixteen livres per cwt., * which was found 

 so little profitable, that about fifty years ago, when the Solfatara 



• Lalande, Voyage en liaLe, vii. 329. 



