onia, although principally extracted from this salt, can
also be produced by a great variety of other substances. The horns of
cattle, especially those of deer, yield it in abundance, and it is from
this circumstance that a solution of ammonia in water has been called
hartshorn. It may likewise be procured from wool, flesh, and bones; in a
word, any animal substance whatever yields it by decomposition.

We shall now lay aside the alkalies, however important the subject may
be, till we treat of their combination with acids. The next time we meet
we shall examine the earths.

CONVERSATION XV.

ON EARTHS.

MRS. B.

The EARTHS, which we are to-day to examine, are nine in number:

SILEX,
ALUMINE,
BARYTES,
LIME,
MAGNESIA,
STRONTITES,
YTTRIA,
GLUCINA,
ZIRCONIA.

The last three are of late discovery; their properties are but
imperfectly known; and, as they have not yet been applied to use, it
will be unnecessary to enter into any particulars respecting them; we
shall confine our remarks, therefore, to the first five. They are
composed, as you have already learnt, of a metallic basis combined with
oxygen; and, from this circumstance, are incombustible.

CAROLINE.

Yet I have seen turf burnt in the country, and it makes an excellent
fire; the earth becomes red hot, and produces a very great quantity of
heat.

MRS. B.

It is not the earth that burns, my dear, but the roots, grass, and other
remnants of vegetables that are intermixed with it. The caloric, which
is produced by the combustion of these substances, makes the earth red
hot, and this being a bad conductor of heat, retains its caloric a long
time; but were you to examine it when cooled, you would find that it had
not absorbed one particle of oxygen, nor suffered any alteration from
the fire. Earth is, however, from the circumstance just mentioned, an
excellent radiator of heat, and owes its utility, when mixed with fuel,
solely to that property. It is in this point of view that Count Rumford
has recommended balls of incombustible substances to be arranged in
fire-places, and mixed with the coals, by which means the caloric
disengaged by the combustion of the latter is more perfectly reflected
into the room, and an expense of fuel is saved.

EMILY.

I expected that the list of earths would be much more considerable. When
I think of the great variety of soils, I am astonished that there is not
a greater number of earths to