Natural History of Volcanos and Earthquakes. 235 
Hifel,) as well as in places where there are no immediate volcanic 
traces, (Hundsriick, the eastern declivities of the Teutoburger 
ald,) and, in general, have found a scarcely measurable quan- 
tity of atmospheric air. According to Boussingault,* the elastic 
fluids, which are evolved from the volcanos at the equator in the 
New World, consist of a great quantity of aqueous vapor, car- 
bonic acid gas, sulphuretted hydrogen gas, and sometimes fumes 
of sulphur ; he considers sulphurous acid gas and nitrogen, on 
the other hand, as accidental. This philosophert also found the 
same gases, viz., carbonic acid and sulphuretted hydrogen gas, in 
the springs which rise in the vicinity of these volcanos. All 
this is by no means favorable to the supposition of the existence 
of vast subterranean cavities filled with air under the craters, and 
an equally unfavorable circumstance is, that, according to Bous- 
Singault, no nitrogen is evolved from the volcanos under the 
*quator, which must necessarily be the consequence of oxidation 
at the expense of atmospheric air. 
Independently of all this, the metals of the earths have been 
ound by more recent experiments to be by no means so easy of 
Oxidation as Davy’s hypothesis assumed. Besides, this proneness 
10 oxidation must be supposed to be a property more especially 
belonging to the metals of silica and alumina, as these earths to- 
gether with oxide of iron, are the principal components of vol- 
canic products—lavas, basalts, &c., generally amounting to about 
0.8, whilst lime and alkalies, although never entirely wanting, 
rm but an inconsiderable proportion. But Berzeliust has shewn, 
that Silicium, the conibustible base of silica, when freed of hy- 
‘gen by being gradually heated to a white heat, is incombus- 
tible even at that heat in the air or in oxygen; and that it is 
‘dually incapable of decomposing water. In like manner Wéh- 
 found,§ that aluminum, the metallic base of alumina, is not 
xidized under a red heat, and decomposes hot water but very 
Slowly, while on cold water it has no influence whatever. — 
Therefore Davy’s hypothesis would be applicable only to the 
Metallic bases of alkaline earths and alkalies. But, as these oc- 
cur only in small proportions in the volcanic rocks, it is scarcely 
“Receivable that so much heat should be evolved by their com- 
hn ction tien 
| 
heco cit. ». lii, p. 5. t Ibid. p. 181. ¢ Poggend. Ann. v. i, p. 221. 
§ Poggend. t, xi, p. 146. 
