236 Natural History of Volcanos and Earthquakes. 



bastion 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 volcanic phenomena.! 



Gay-Lussac,J assuming that water supplied the oxygen in vol- 

 canos, endeavored to account for the absence of uncombined hy- 

 drogen among the exhalations of volcanos, 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 hydrogen, 

 which would result from an oxidation by means of water, were 

 to enter into combination with chlorine. But it would be strange 

 that such an exhalation should not have been remarked sooner. 

 In order to account for the formation of muriatic acid, he men- 

 tions the experiments made by him and Thenard, 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 and 

 Covelli extracted more than 0.09, and in the slags which cover 

 the white hot lava, and which sometimes contain very beautiful 



* Also the latest experiments, made with admirable exactness by Prof. Reicli 

 in Freiberg, with the assistance of the torsion-balance, have given 5.44 for the 

 density of the earth, as a mean of 14 experiments which afforded very nearly the 

 same results. Versuche Ober die mittlere Dichtigkeit der Erde mittelst der Dreh- 

 wage von F. Reich. Freiberg, 1838. This result accords very nearly with that, 

 which was found by Cavendish and Hutton. 



t Davy, however, afterwards abandoned his hypothesis. See Consolation in 

 Travel, or the Last Days of a Philosopher. 



t Loco cit. § Loco cit. iii, p. 57 and 94. 



jj L. c. p. 172. See also Daubeny's Description of Active and Extinct Volca- 

 nos. Lond. 1826. p. 372, and v. Humboldt's Reise, etc. t. i, p. 195. 



