Natural History of Volcanos and Earthquakes. 235 



Eifel,) as well as in places where there are no immediate volcanic 

 traces, {Hundsruck, the eastern declivities of the Teutohurger 

 Wald,) 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 philosopher! 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 

 equator, 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 

 found by more recent experiments to be by no means so easy of 

 oxidation as Davy's hypothesis assumed. Besides, this proneness 

 to 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 hme and alkalies, although never entirely wanting, 

 form but an inconsiderable proportion. But Berzelius."]: has shewn, 

 that silicium, the combustible base of silica, when freed of hy- 

 drogen 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 

 equally incapable of decomposing water. In like manner Woh- 

 ler found,'§. that aluminum, the metallic base of alumina, is not 

 oxidized 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 

 conceivable that so much heat should be evolved by their com- 



* Loco cit. V. Hi, p. 5. t Ibid. p. 181. X Poggend. Ann. v. i, p. 221. 



§ Poggend. t. xi, p. 146. 



