283 
M. Gay Lussac’s Reflections on Volcanoes. 
stances mixed with the hydrochloric acid should make its smell 
be mistaken. It would be desirable that M. Monticelli, who is 
so well situated for studying Vesuvius, would place water con- 
taining a little potash, in open vessels, in several places of that 
volcano. This water would become gradually charged with acid 
vapours, and, at the end of some time, it would be easy to de- 
termine their nature. 
If the hydrogen furnished by water to combustible substances 
in the volcanic foci entered entirely into combination with the 
chlorine, the quantity of hydrochloric acid disengaged by vol- 
canoes would be enormous. It would therefore be matter of 
surprise, that this acid had not been oftener observed. 
Further, it would be necessary that the metals of the silica, 
alumina, lime, and oxide of iron, were combined with the 
chlorine ; and in order to explain the high temperature of vol- 
canoes, we must still suppose that the contact of the chlorates of 
silicium and aluminum with water, produced a great disengage- 
ment of heat. Such a supposition is not altogether improbable ; 
but admitting it, we still want data for making a satisfactory 
application of it to volcanic phenomena. 
If the combustible metals are not in the state of chlorides, 
the hydrochloric acid is then a secondary result ; it is produced 
by the action of the air on some chlorate, (probably that of 
sodium) ; an action which is favoured by the mutual affinity of 
oxides. M. Thenard and myself have shown, that when rau- 
riat of soda and sand, both of them perfectly dry, are heated to 
a red heat, no hydrochloric acid is disengaged ; but if the va- 
pour of water be made to pass over a mixture of sand or clay 
with muriate of soda, the hydrochloric acid is immediately disen- 
gaged in very great abundance. 
Now, the production of this acid, by the meeting of water 
and of some oxide with a chloride, must be very frequent in vol- 
canoes. Lavas contain chlorides, since they exhale the acid a- 
bundantly on being exposed to the air. MM. Monticelli and 
Covelli obtained, by simple washing in boiling water, more than 
9 per cent, of muriate of soda, from the lava of Vesuvius of 
1822. It is exhaled also by the mouth of volcanoes, for we see 
very beautiful crystals of it in the scorios which cover the incan- 
descent lava. If, consequently, these lavas are placed in con- 
