me quantity: from whence it is evident, that the
air, which quick-lime attracts, is of a different kind from that which
is mixed with water. And that it is also different from common elastic
air, is sufficiently proved by daily experience; for lime-water, which
soon attracts air, and forms a crust when exposed in open and shallow
vessels, may be preserved, for any time, in bottles which are but
slightly corked, or closed in such a manner as would allow free access
to elastic air, were a vacuum formed in the bottle. Quick-lime therefore
does not attract air when in its most ordinary form, but is capable of
being joined to one particular species only, which is dispersed thro'
the atmosphere, either in the shape of an exceedingly subtile powder, or
more probably in that of an elastic fluid. To this I have given the name
of fixed air, and perhaps very improperly; but I thought it better to
use a word already familiar in philosophy, than to invent a new name,
before we be more fully acquainted with the nature and properties of
this substance, which will probably be the subject of my further
inquiry.

It is, perhaps, needless to mention here, that the calcarious substances
used in making the above experiments should be of the purest kind, and
burnt with the utmost violence of heat, if we would be sure of
converting them into perfect quick-lime. I therefore made use of chalk
burnt in a small covered crucible with the fiercest fire of a
Black-smith's forge, for half an hour, and found it necessary to employ,
for this purpose, a crucible of the _Austrian_ kind, which resemble
black lead; for if any calcarious substance be heated to such a degree
in an ordinary or _Hessian_ crucible, the whole of it is melted down,
together with part of the vessel, into glass.

I now prepared to inquire into the properties of the caustic alkali; in
order to which, I made a caustic or soap ley in the following manner.

Twenty six ounces of very strong quick-lime made of chalk, were slaked
or reduced to a sort of fluid paste, with eleven pounds of boiling
water, and then mixed in a glass vessel with eighteen ounces of a pure
fixed alkaline salt, which had been first dissolved in two pounds and a
half of water. This mixture was shaken frequently for two hours, when
the action of the lime upon the alkali was supposed to be over, and
nothing remained but to separate them again from one another. I
therefore added 12 pounds of water, stirred up the li