HEAT OF THE GliOUND. 
79 
a couckoidal fracture. These masses, which will one day 
perhaps be objects of commerce, are constantly bedewed 
with sulphurous acid. 1 laid the imprudence to wrap up a 
jew, in order to preserve them, but I soon discovered that 
tie acid had consumed not only the paper which contained 
t n cm, but a part also of my miueralogical journal. The 
beat oi the vapours, which issue from the crevices of the 
caldera, is not sufficiently great to combine the sulphur 
wlule in a state of minute division, with tho oxygon of the 
atmospheric air ; and after the experiment I have just cited 
on the temperature of the soil, we may presume that tiie 
sulphurous acid is formed at a certain depth,* in cavities to 
which the external air lias free access. 
The vapours of heated water, which act on the fragments 
ol lava scattered about on the caldera, reduce certain parts 
ot It to a state ol paste. On examining, after I had reached 
America, those earthy and friable masses, I found crystals of 
sulphate of alumme. MM. Davy and Gay-Lussac have 
akeady made the ingenious remark, that two bodies highly 
inflammable, tlie metals of soda and potash, have probably 
an important part in the action of a volcano ; now the potash 
necessary to tho formation of alum is found not only in 
feldspar, mica, pumice-stone, audaugito, but also in obsidian, 
tins last substance is very common at Teneriffe, where it 
forms the basis of the tenhrinie lava. These analogies 
between the peak of Teneriffe and the Solfatara of Puzraoli, 
might no doubt he shown to be more numerous, if' the 
former were more accessible, and had been frequently visited 
bv naturalists. J 
. A n expedition to the summit of the volcano of Teneriffe 
IS interesting, not solely on account of tlic great number of 
phenomena winch are the objects of scientific research ; it 
has still greater attractions from the picturesque beauties 
winch it lays open to those who are feelingly alive to the 
majesty ot nature. It is a difficult task to describe the 
An observer, in general very accurate, M. Breislack, asserts that the 
muriatic acid always predominates in the vapours of Vesuvius. This 
asseition is contrary to what M. Cay-Lussac and myself observed, before 
lie gieat eruption of 1805, and while the lava was issuing from the 
mater, I he smell of the sulphurous acid, so easy to distinguish, was 
perceptible at a great distance; and when the volcano threw out scorise, 
the smell was mingled with that of petroleum. 
