84- M. Gay-Lussac on Volcanos. 



volcanos; and from the knowledge which has been obtained of 

 the true nature of these substances, by the admirable discoveries 

 of Sir Humphry Davy, it is probable that the greater part, 

 if not all of them may exist in a metallic state. There is no 

 difficulty in conceiving that by their contact with water they 

 might decompose it, become changed into lava, and produce 

 sufficient heat to account for the greater part of the volcanic 

 phaenomena. But as my object is not to consti'uct a system, 

 but, on the contrary, to examine the probability of the two 

 hypotheses under consideration, and to direct the attention of 

 future observers towards those facts which are most likely to 

 throw light upon the causes of volcanos, I shall proceed to 

 point out the consequences which must result from the adop- 

 tion of the latter hypothesis. If water be really the agent 

 which sustains the volcanic fires by means of its oxygen, we 

 must admit, as a necessary and very important consequence, 

 that an enormous quantity of hydrogen, either free or com- 

 bined with some other principle, would be disengaged through 

 the craters of volcanos. Nevertheless it does not appear that 

 the disengagement of hydrogen is very frequent in volcanos. 

 Although, during my residence at Naples in 1805, with my 

 friends M. Alexander de Humboldt and M. Leopold de Buch, 

 I witnessed frequent explosions of Vesuvius, which threw up 

 melted lava to the height of more than 200 metres^ I never 

 perceived any inflammation of hydrogen. Every explosion 

 was followed by columns [tourbillons) of a thick and black 

 smoke, which must have been ignited if they had been com- 

 posed of hydrogen, being traversed by bodies heated to a tem- 

 perature higher than was necessary to cause their inflammation. 



This smoke, the evident cause of the explosions, contained 

 therefore other fluids than hydrogen. But what was its true 

 nature ? If we admit that it is water which furnishes oxygen 

 to volcanos, it will ibllow that, as its hydrogen does not disen- 

 gage itself in a free state, it must enter into some combination. 

 It cannot entev into any compound inflammable by means of 

 heat at its contact with the air ; it is however very possible that 

 it unites with chlorine to form hydrochloric acid. 



A great many observations have in fact been recently given 

 to the woi-ld on the presence of this acid in the vapours of 

 Vesuvius; and, according to that excellent observer M. Breis- 

 lack, it is at least as abundant in them as sulphurous acid. 

 M. Menard de la Groye (whose conclusions on volcanos I 

 however think too precipitate to be adopted), and M. Mon- 

 ticelli to whom the public is indebted for some excellent ob- 

 servations on Vesuvius, also regard the presence of hydro- 

 chloric acid in its vapours as incontestable. I have my- 

 self 



