236 Natural History of Volcanos and Earthquakes. 
bustion at the ordinary temperature as would be sufficient to melt 
the pure earths, or to inflame their metals, supposing them to 
exist at the seat of the volcanic action. 
The slight specific gravity of the metals of the alkalies, also 
proves fatal to Davy’s hypothesis ; for, if the mean density of the 
earth surpass that of all kinds of rocks, those metals cannot exist, 
at least not in great quantities, in the interior of the earth.* 
Davy’s hypothesis, therefore, according to the present state of 
science, will not account for voleanic phenomena.t 
Gay-Lussac,{ assuming that water supplied the oxygen in vol- 
eanos, endeavored to account for the absence of uncombined hy- 
drogen among the exhalations of voleanos, by supposing it to 
form such combinations with other bodies as would not inflame 
by coming into contact with the air. This is the case when it 
combines with chlorine to form muriatic acid gas. He here re- 
fers to the observations of Breislak,$ and of Monticelli and Covelli,|| 
which shew that this acid is among the exhalations of volcanos. 
He himself, however, observes, that an enormous quantity of mu- 
riatic acid must be evolved from the craters, if the hydroge, 
which would result from an oxidation by means of water, were 
to enter into combination with chlorine. But it would be strangé 
that such an exhalation should not have been remarked soonel- 
In order to account for the formation of muriatic acid, he men 
tions the experiments made by him and Thénard, in which they 
evolved that acid, by introducing aqueous vapor into a mixture 
of sand and common salt heated to a red heat. In support of his 
position, he mentions the occurrence of common salt in the lavas; 
from one of which, (that of Vesuvius in 1822,) Monticelli 
Covelli extracted more than 0. 09, and in the slags which cover 
the white hot lava, and which sometimes contain very beautifil 
* Also the latest experiments, made with admirable exactness a Prof. Reich 
in Freiberg, with the assistance of the torsion-balance, have given 544 for = 
density of the earth, as a mean of 14 experiments which afforded vary — oh 
same results. Versuche iber die mittlere Dichtigkeit der Erde mittelst der Dr a 
wage von F. Reich. Freiberg, 1838. ae result accords very nearly with thal 
which was found by Cavendish and Hutte 
“+ Davy, however, afterwards hustonds his hypothesis. 
Travel, or _ Last Days of a Philosopher. 
t Loco e Loco cit. iii, p. 57 a 
Eee, ‘ ‘72. See also Daubeny’s Description of Active an 
nos. Lond. 1826. p. 372, and v. Humboldt’s Reise, ete. t. 
d Extinet Volea 
See Consolation 
. 
* 
a 
ts: 
