a is usually employed
medicinally; it then differs but little in appearance from its simple
form, which is that of a very fine light white powder. It dissolves in
2000 times its weight of water, but forms with acids extremely soluble
salts. It has not so great an attraction for acids as lime, and
consequently yields them to the latter. It is found in a great variety
of mineral combinations, such as slate, mica, amianthus, and more
particularly in a certain lime stone, which has lately been discovered
by Mr. Tennant to contain it in very great quantities. It does not
attract and solidify water, like lime: but when mixed with water and
exposed to the atmosphere, it slowly absorbs carbonic acid from the
latter, and thus loses its causticity. Its chief use in medicine is,
like that of lime, derived from its readiness to combine with, and
neutralise, the acid which it meets with in the stomach.

EMILY.

Yet, you said that it was taken in the state of carbonat, in which case
it has already combined with an acid?

MRS. B.

Yes; but the carbonic is the last of all the acids in the order of
affinities; it will therefore yield the magnesia to any of the others.
It is, however, frequently taken in its caustic state as a remedy for
flatulence. Combined with sulphuric acid, magnesia forms another and
more powerful medicine, commonly called _Epsom salt_.

CAROLINE.

And properly, _sulphat of magnesia_, I suppose? Pray why was it ever
called Epsom salt?

MRS. B.

Because there is a spring in the neighbourhood of Epsom which contains
this salt in great abundance.

The last alkaline earth which we have to mention is STRONTIAN, or
STRONTITES, discovered by Dr. Hope a few years ago. It so strongly
resembles barytes in its properties, and is so sparingly found in
nature, and of so little use in the arts, that it will not be necessary
to enter into any particulars respecting it. One of the remarkable
characteristic properties of strontites is, that its salts, when
dissolved in spirit of wine, tinge the flame of a deep red, or blood
colour.

CONVERSATION XVI.

ON ACIDS.

MRS. B.

We may now proceed to the acids. Of the metallic oxyds, you have already
acquired some general notions. This subject, though highly interesting
in its details, is not of sufficient importance to our concise view of
chemistry, to be particularly treated of; but it is absolutely necessary
that you should be better acquainted with the acids,