otion communicated to the air, but
rather a smart stroke which produces sound, and that the explosion of
but a few particles of fixed air may be capable of causing a loud noise,
provided they all recover their spring suddenly, and in the same
instant.

The above experiments lead us also to conclude, that volatile alkalis,
and the common absorbent earths, which lose their air by being joined to
acids, but shew evident signs of their having recovered it, when
separated from them by alkalis, received it from these alkalis which
lost it in the instant of their joining with the acid.

The following are a few experiments upon three of the absorbent earths,
made in order to compare them with one another, and with _magnesia_.

Suspecting that _magnesia_ might possibly be no other than a common
calcarious earth, which had changed its nature, by having been
previously combined with an acid, I saturated a small quantity of chalk
with the muriatic acid, separated the acid from it again by means of a
fixed alkali, and carefully washed away the whole of the salt.

The chalk when dryed was not found to have suffered any alteration; for
it effervesced with the vitriolic acid, but did not dissolve in it; and
when exposed to a violent fire, was converted into a quick-lime, in all
respects similar to that obtained from common chalk.

In another experiment of the same kind, I used the vitriolic acid with
the same event.

Any calcarious matter reduced to a fine powder, and thrown into a warm
solution of alum, immediately raises a brisk effervescence. But the
powder is not dissolved; it is rather increased in bulk: and if the
addition be repeated until it is no longer accompanied with
effervescence, the liquor loses all taste of the alum, and yields only a
very light cloud upon the admixture of an alkali.

From this experiment we learn, that acids attract the calcarious earths
more strongly than they do the earth of alum; and as the acid in this
salt is exactly the same with the vitriolic, it composes with the
calcarious earth a neutral substance, which is very difficultly soluble
in water, and therefore falls down to the bottom of the vessel along
with the earth of alum which is deprived of its acid. The light cloud
formed by the alkali proceeds from the minute portion of the calcarious
compound which saturates the water.

The earth of animal bones, when reduced to a fine powder and thrown into
a diluted vitriolic acid, gradually a