the stomach, and
that its effect is therefore proportional to the quantity of this acid.

Altho' _magnesia_ appears from this history of it to be a very innocent
medicine, yet having observed, that some hypochondriacs who used it
frequently, were subject to flatulencies and spasms, he seems to have
suspected it of some noxious quality. The circumstances however which
gave rise to his suspicion, may very possibly have proceeded from the
imprudence of his patients, who, trusting too much to _magnesia_, (which
is properly a palliative in that disease,) and neglecting the assistance
of other remedies, allowed their disorder to increase upon them. It may
indeed be alledged, that _magnesia_, as a purgative, is not the most
eligible medicine for such constitutions, as they agree best with those
that strengthen, stimulate and warm; which the saline purges commonly
used are not observed to do. But there seems at least to be no objection
to its use when children are troubled with an acid in their stomach; for
gentle purging in this case is very proper, and it is often more
conveniently procured by means of _magnesia_ than of any other medicine,
on account of its being intirely insipid.

The above-mentioned Author observing, some time after, that a bitter
saline liquor, similar to that obtained from the brine of salt-petre,
was likewise produced by the evaporation of those waters which contain
common salt, had the curiosity to try if this would also yield a
_magnesia_. The experiment succeeded: and he thus found out another
process for obtaining this powder, and at the same time assured himself
by experiments, that the product from both was exactly the same.[3]

My curiosity led me some time ago to inquire more particularly into the
nature of _magnesia_, and especially to compare its properties with
those of the other absorbent earths, of which there plainly appeared to
me to be very different kinds, altho' commonly confounded together under
one name. I was indeed led to this examination of the absorbent earths,
partly by the hope of discovering a new sort of lime and lime-water,
which might possibly be a more powerful solvent of the stone than that
commonly used; but was disappointed in my expectations.

I have had no opportunity of seeing _Hoffman's_ first _magnesia_ or the
liquor from which it is prepared, and have therefore been obliged to
make my experiments upon the second.

In order to prepare it, I at first employed th