it follows, that, by adding to it a sufficient quantity
of alkali saturated with air, the lime will recover the whole of
its air, and be entirely restored to its original weight and
condition: and it also follows, that the earth separated from
lime-water by an alkali, is the lime which was dissolved in the
water now restored to its original mild and insoluble state.

III. If it be supposed that slaked lime does not contain any parts
which are more firey, active or subtile than others, and by which
chiefly it communicates its virtues to water; but that it is an
uniform compound of lime and water: it follows, that, as part of it
can be dissolved in water, the whole of it is also capable of being
dissolved.

IV. If the acrimony of the caustic alkali does not depend on any
part of the lime adhering to it, a caustic or soap-ley will
consequently be found to contain no lime, unless the quantity of
lime employed in making it were greater than what is just
sufficient to extract the whole air of the alkali; for then as much
of the superfluous quick-lime might possibly be dissolved by the
ley as would be dissolved by pure water, or the ley would contain
as much lime as lime-water does.

V. We have shewn in the former experiments, that absorbent earths
lose their air when they are joined to an acid; but recover it, if
separated again from that acid, by means of an ordinary alkali: the
air passing from the alkali to the earth, at the same time that the
acid passes from the earth to the alkali.

If the caustic alkali therefore be destitute of air, it will separate
magnesia from an acid under the form of a magnesia free of air, or which
will not effervesce with acids; and the same caustic alkali will also
separate a calcarious earth from acids under the form of a calcarious
earth destitute of air, but saturated with water, or under the form of
slaked lime.

These were all necessary conclusions from the above suppositions. Many
of them appeared too improbable to deserve any further attention: some
however, I found upon reflection, were already seconded by experience.
Thus _Hoffman_ has observed, that quick-lime does not effervesce with
spirit of vitriol;[7] and it is well known that the caustic spirit of
urine, or of salt ammoniac, does not emit air, when mixed with acids.
This consideration excited my curiosit