bsorbs the acid in the same manner
as the calcarious earths, but without any remarkable effervescence. When
it is added to the nitrous or to the muriatic acid, it is slowly
dissolved. The compound liquor thence produced is extremely acrid, and
still changes the colour of the juice of violets to a red, even after it
is fully saturated with the absorbent. Distilled vinegar has little or
no effect upon this earth; for after a long digestion it still retains
its sour taste, and gives only a light cloud upon the addition of an
alkali.

By dropping a dissolved fixed alkali into a warm solution of alum, I
obtained the earth of this salt, which, after being well washed and
dried, was found to have the following properties.

It is dissolved in every acid but very slowly, unless assisted by heat.
The several solutions, when thoroughly saturated, are all astringent
with a slight degree of an acid taste, and they also agree with a
solution of alum in this, that they give a red colour to the infusion of
turnsol.

Neither this earth, nor that of animal bones, can be converted into
quick-lime by the strongest fire, nor do they suffer any change worth
notice. Both of them seem to attract acids but weakly, and to alter
their properties less when united to them than the other absorbents.

PART II.

In reflecting afterwards upon these experiments, an explication of the
nature of lime offered itself, which seemed to account, in an easy
manner, for most of the properties of that substance.

It is sufficiently clear, that the calcarious earths in their native
state, and that the alkalis and magnesia in their ordinary condition,
contain a large quantity of fixed air, and this air certainly adheres to
them with considerable force, since a strong fire is necessary to
separate it from magnesia, and the strongest is not sufficient to expel
it entirely from fixed alkalis, or take away their power of effervescing
with acid salts.

These considerations led me to conclude, that the relations between
fixed air and alkaline substances was somewhat similar to the relation
between these and acids; that as the calcarious earths and alkalis
attract acids strongly and can be saturated with them, so they also
attract fixed air, and are in their ordinary state saturated with it:
and when we mix an acid with an alkali or with an absorbent earth, that
the air is then set at liberty, and breaks out with violence; because
the alkaline body attrac