ining it to the nitrous and vegetable acids, than to the
vitriolic. Those earths, when combined with spirit of nitre, cannot be
reduced to a crystalline form, and if they are dissolved in distilled
vinegar, the mixture spontaneously dries up into a friable salt.

Having thus found _magnesia_ to differ from the common alkaline earths,
the object of my next inquiry was its peculiar degree of attraction for
acids, or what was the place due to it in Mr. _Geoffroy's_ table of
elective attractions.

Three drams of _magnesia_ in fine powder, an ounce of salt ammoniac, and
six ounces of water were mixed together, and digested six days in a
retort joined to a receiver.

During the whole time, the neck of the retort was pointed a little
upwards, and the most watery part of the vapour, which was condensed
there, fell back into its body. In the beginning of the experiment, a
volatile salt was therefore collected in a dry form in the receiver, and
afterwards dissolved into spirit.

When all was cool, I found in the retort a saline liquor, some
undissolved _magnesia_, and some salt ammoniac crystallized. The saline
liquor was separated from the other two, and then mixed with the
alkaline spirit. A coagulum was immediately formed, and a _magnesia_
precipitated from the mixture.

The _magnesia_ which had remained in the retort, when well washed and
dried, weighed two scruples and fifteen grains.

We learn by the latter part of this experiment, that the attraction of
the volatile alkali for acids is stronger than that of _magnesia_, since
it separated this powder from the acid to which it was joined. But it
also appears, that a gentle heat is capable of overcoming this
superiority of attraction, and of gradually elevating the alkali, while
it leaves the less volatile acid with the _magnesia_.

Dissolve a dram of any calcarious substance in the acid of nitre or of
common salt, taking care that the solution be rendered perfectly
neutral, or that no superfluous acid be added. Mix with this solution a
dram of _magnesia_ in fine powder, and digest it in the heat of boiling
water about twenty four hours; then dilute the mixture with double its
quantity of water, and filtrate. The greatest part of the earth now left
in the filtre is calcarious, and the liquor which passed thro', if mixed
with a dissolved alkali, yields a white powder, the largest portion of
which is a true _magnesia_.

From this experiment it appears, that an acid qui