134 Mr Forbes's Physical Notices of the Bay of Naples. 



Scrope *, a peculiar concretionary form, which he attributes to 

 a play of chemical affinities. It is ascertained, too, that here, 

 as at the spring of La Pisciarella, the calcareous particles form 

 an oolitic concretion named pisolite or peastone, well known 

 as a production of the hot spring of Carlsbad. It has been a 

 subject of remark that the disintegrated matter of the Solfatara 

 much resembles tripoli, and might probably be employed for 

 the same purposes. 



We have now considered in sufficient detail the general 

 characters of the Solfatara, and we may proceed to the second 

 object of the present paper, by giving a very short accoimt 

 of the products of this curious spot, by which we mean such 

 as are daily forming by the action of subterraneous volcanic 

 agency. 



The " fumerole," or emissaries through which these are 

 emitted, rise on the eastern side of the plain. The temperature 

 of one of them, during a series of observations made by Breis- 

 lak in the month of June, remained within the extremes of 75° 

 and 78° Reaumur. The humidity contained in them is very 

 great, and of course rapidly condenses on reaching the exter- 

 nal air, which the same observer employed as a means of pro- 

 curing the requisite supply of water for the solution of the 

 salts used in commerce. 



United with the steam of the fumerole, we find sulphuretted 

 hydrogen and a small quantity of muriatic acid gas, and ac- 

 tompanying it, nitrogen and carbonic acid. We shall very 

 briefly state some facts regarding the origin and eflects of these 

 elastic fluids, borrowing chiefly from the excellent work of Dr 

 Daubeny, professor of chemistry at Oxford, and from Breis- 

 Jak's detailed account of the Solfatara. 



If we adopt the theory that volcanic action is superinduced 

 by the affusion of the metallic alkaline bases by sea water, 

 these effects are easily explained. The oxygen of the water 

 rapidly uniting with the potassium and sodium disengages its 

 hydrogen, which combines with the sulphurous deposits un- 

 doubtedly existing at a great depth below the surface of the 

 earth, and appears with the steam produced by the calorific 



• Geolog. Trans, ut sup. p. 346. 



