eruption of the greatest degree of violence, to see if
there was any inflammation occasioned by this natural electric
spark--any indication of the presence of inflammable gas; but in
vain."[765]

May not the hydrogen, Gay Lussac inquires, be combined with chlorine,
and produce muriatic acid? for this gas has been observed to be evolved
from Vesuvius--and the chlorine may have been derived from sea salt;
which was, in fact, extracted by simple washing from the Vesuvian lava
of 1822, in the proportion of nine per cent.[766] But it was answered,
that Sir H. Davy's experiments had shown, that hydrogen is not
combustible when mixed with muriatic acid gas; so that if muriatic gas
was evolved in large quantities, the hydrogen might be present without
inflammation.[767] M. Abich, on the other hand, assures us, "that
although it be true that vapor illuminated by incandescent lava has
often been mistaken for flame," yet he clearly detected in the eruption
of Vesuvius in 1834 the flame of hydrogen.[768]

M. Gay Lussac, in the memoir just alluded to, expressed doubt as to the
presence of sulphurous acid; but the abundant disengagement of this gas
during eruptions has been since ascertained: and thus all difficulty in
regard to the general absence of hydrogen in an inflammable state is
removed; for, as Dr. Daubeny suggests, the hydrogen of decomposed water
may unite with sulphur to form sulphuretted hydrogen gas, and this gas
will then be mingled with the sulphurous acid as it rises to the crater.
It is shown by experiment, that these gases mutually decompose each
other when mixed where steam is present; the hydrogen of the one
immediately uniting with the oxygen of the other to form water, while
the excess of sulphurous acid alone escapes into the atmosphere. Sulphur
is at the same time precipitated.

This explanation is sufficient; but it may also be observed that the
flame of hydrogen would rarely be visible during an eruption; as that
gas, when inflamed in a pure state, burns with a very faint blue flame,
which even in the night could hardly be perceptible by the side of
red-hot and incandescent cinders. Its immediate, conversion into water
when inflamed in the atmosphere, might also account for its not
appearing in a separate form.

Dr. Daubeny is of opinion that water containing atmospheric air may
descend from the surface of the earth to the volcanic foci, and that the
same process of combustion by which water is decompo