is sufficient to melt copper. When taken out, it weighed
three drams and one scruple, or had lost 7/12 of its former weight.

I repeated, with the _magnesia_ prepared in this manner, most of those
experiments I had already made upon it before calcination, and the
result was as follows.

It dissolves in all the acids, and with these composes salts exactly
similar to those described in the first set of experiments: but what is
particularly to be remarked, it is dissolved without any the least
degree of effervescence.

It slowly precipitates the corrosive sublimate of mercury in the form of
a black powder.

It separates the volatile alkali in salt ammoniac from the acid, when it
is mixed with a warm solution of that salt. But it does not separate an
acid from a calcarious earth, nor does it induce the least change upon
lime-water.

Lastly, when a dram of it is digested with an ounce of water in a bottle
for some hours, it does not make any the least change in the water. The
_magnesia_, when dried, is found to have gained ten grains; but it
neither effervesces with acids, nor does it sensibly affect lime-water.

Observing _magnesia_ to lose such a remarkable proportion of its weight
in the fire, my next attempts were directed to the investigation of this
volatile part, and, among other experiments, the following seemed to
throw some light upon it.

Three ounces of _magnesia_ were distilled in a glass retort and
receiver, the fire being gradually increased until the _magnesia_ was
obscurely red hot. When all was cool, I found only five drams of a
whitish water in the receiver, which had a faint smell of the spirit of
hartshorn, gave a green colour to the juice of violets, and rendered the
solutions of corrosive sublimate and of silver very slightly turbid. But
it did not sensibly effervesce with acids.

The _magnesia_, when taken out of the retort, weighed an ounce, three
drams, and thirty grains, or had lost more than the half of its weight.
It still effervesced pretty briskly with acids, tho' not so strongly as
before this operation.

The fire should have been raised here to the degree requisite for the
perfect calcination of _magnesia_. But even from this imperfect
experiment, it is evident, that of the volatile parts contained in that
powder, a small proportion only is water; the rest cannot, it seems, be
retained in vessels, under a visible form. Chemists have often observed,
in their distillations, that par