vessels, or even in bottles
which are but slightly covered, for a considerable time, without
absorbing a sensible quantity of air.

In order to know how much lime it contained, I evaporated ten ounces in
a small silver dish over a lamp, and melted the salt, after having
dissipated the water.[8]

The caustic thus produced was dissolved again in a small quantity of
water, and deposited a trifling portion of sediment, which I imagined at
first to be lime; but finding that it could easily be dissolved in a
little more water, concluded it to be a vitriolated tartar, which always
accompanies the fixed alkali of vegetables.

I then saturated the solution of the caustic salt with spirit of
vitriol, expecting thus to detect the lime; because that acid
precipitates a calcarious earth from its ordinary solutions. During the
saturation, a large quantity of white powder was formed; but this
likeways turned out to be a vitriolated tartar, which had appeared in
the form of a powder, because there was not enough of water in the
mixture to dissolve it.

Lastly, I exposed a few ounces of the ley in an open shallow vessel so
long, that the alkali lost the whole of its causticity, and seemed
entirely restored to the state of an ordinary fixed alkali; but it did
not however deposite a single atom of lime. And to assure myself that my
caustic ley was not of a singular kind, I repeated the same experiments
with an ordinary soap-ley, and with one made by mixing one part of a
pure fixed alkaline salt with three parts of common stone lime fresh
slaked and sifted; nor could I discover any lime in either. The first of
these contained a small quantity of brimstone, and was far from being
perfectly caustic, for it made a pretty brisk effervescence with acids;
but the last was so entirely deprived of its air, that it did not
diminish in the least the transparency of lime-water.

These experiments seem therefore to support the fourth proposition, and
to shew that the caustic alkali does not contain any lime.

As it seems probable, from the quickness and ease wherewith the alkali
was rendered caustic, that more lime had been employed than what was
just sufficient to extract the whole of its air, we are surprised to
find that little or none of the superfluous quick-lime was dissolved by
the water. But this _phaenomenon_ will become less surprizing, by
comparing it with some similar instances in chemistry. Water may be made
to deposite a salt, by