DR. DAUBENY ON THE ERUPTION OF VESUVIUS. 157 



way round its brim in a direction nearly horizontal, except in one part, where, from 

 some shock or fracture, they had sunk abruptly downwards. These strata consisted 

 of loose volcanic sand and rapilli, coated with saline incrustations of common salt, 

 coloured red and yellow by peroxide of iron, and presenting a beautiful and brilliant 

 appearance. I could perceive no dykes intersecting these strata, as at the Monte 

 Somma. 



In order to collect the vapours, I caused to be constructed an apparatus, consisting 

 of the head of a large alembic, fitted on to a cylindrical vessel of tinned iron with 

 riveted joints, which, being open at bottom, and introduced a little way into the 

 ground, served to conduct the exhalations into the receiver connected with it above. 

 By this contrivance I succeeded in the course of an hour or two in condensing a suf- 

 ficient quantity of the vapour for chemical examination at Naples. In the liquid 

 collected I could detect no saline ingredient, and there appeared only a slight trace 

 of sulphurous or sulphuric acids. The principal body condensed along with the steam 

 was muriatic acid, which was uncombined with any base. 



Whether carbonic acid might be disengaged from the crater I could devise no un- 

 exceptionable method of determining ; yet by comparing the quantity of carbonate 

 of barytes precipitated, by exposing a given quantity of barytic water for five minutes 

 in the vapour of one of the Fumaroles, with what was obtained from the same quan- 

 tity in equal times exposed to the open air out of the Fumaroles, I am led to con- 

 clude that this gas was exhaled. 



Of nitrogen, the air of the Fumarole appeared to contain the same proportion, as 

 atmospheric air does in general. 



No sulphuretted hydrogen was emitted from the crater, neither could I discover, 

 either in the condensed vapour or in the sublimations lining its walls, any trace of 

 muriate of ammonia. 



Muriatic salts principally were detected among the latter, but sulphates of lime, 

 alumina, and iron were likewise present. 



The next point in the volcano which arrested my attention was the vent on the 

 eastern side of the great cone, from which issued one of the principal streams of lava 

 that burst from the mountain in August last. 



The vapours here collected appeared to agree in composition entirely with those 

 from the interior of the crater ; and the sublimations were of the same nature, with 

 the addition of much specular iron ore and some muriate of copper. 



The lava, which had been emitted in August, continued, when I visited it in Novem- 

 ber, to give out throughout the whole of its course white vapours ; and even after the 

 copious rains which fell subsequently, many of the spiracles, so late as the end of De- 

 cember, continued to emit the same. The interior of the current appeared also at both 

 these periods to retain a considerable proportion of its original temperature. After 

 removing about six feet of loose scoriae, I at length reached the upper surface of the 

 bed of lava itself, into which it would have been impossible to penetrate without the 



