M. Guy-Lussac on Volcanos. 85 



self no longer any doubt on this fact, though during my stay 

 in the neighbourhood of Vesuvius I could never distinguish 

 by the smell any thing but sulphurous acid ; it is, hov/ever, very 

 possible that the extraneous substances mixed with the hydro- 

 chloric acid disguised its odour. 



It is very much to be wished that M. Monticelli, who is so 

 favourably situated for observing Mount Vesuvius, would 

 place some water, containing a little potass, in open vessels on - 

 different parts of this volcano ; the water would gradually be- 

 come charged with acid vapours, and after some time it ^\ oukl 

 be easy to determine their nature. 



If the whole of the hydrogen furnished by water to the com- 

 bustible substances contained in volcanic furnaces becomes 

 combined with chlorine, the quantity of hydrochloric acid dis- 

 engaged by volcanos ought to be enormous. It would then 

 become a matter of surprise that the existence of this acid 

 had not been observed isooner. Besides, the chlorine must 

 enter into combination with the metals of silica, alumina, lime, 

 and oxide of iron ; and in order to explain the high tempera- 

 ture of volcanos, we must suppose that the contact of the chlo- 

 rides of silicium and aluminium with water produces a great 

 evolution of heat. Such a supposition is by no means impro- 

 bable ; but even if we admit it, we are still in want of a great 

 many data, before we can render its application to volcanic 

 phfenomena satisfactorj-. 



If the combustible metals are not in the state of chlorides, 

 hydrochloric acid is then a secondary result; it must proceed 

 from the action of the water upon some chloride (probably tliat 

 of sodium), an action which is favoured by the mutual affinity 

 of oxides. M. Thenard and I have already shown that if 

 perfectly dry sea-salt and sand are both heated red hot, no 

 hydrochloric acid is evolved : we found also that sea-salt un- 

 dergoes no alteration from the agency of water alone ; but if 

 aqueous vapour is suffered to pass over a mixture of sand or 

 of clay with sea-salt, hydrochloric acid is immediately disen- 

 gaged in great abundance. 



Now the production of this acid by the conjoint action of 

 water and some oxide upon a chloride, must be very fi-equent 

 in volcanos. Lava contains chlorides, since it gives them out 

 abundantly when it comes in contact with the air. MM. Mon- 

 ticelli and Covelli extracted, merely by rejreated wasliings 

 with boiling water, more than nine per ceiu. of sea-salt from 

 the lava of Vesuvius in 1822. It is exhaled through the 

 mouths of volcanos; for very beautiful crystals of it are found 

 in the scoria covering incandescent lava. If" therefore, lava 

 comes in contact with water, either in the interior of the vol- 

 cano, 



