er separates it into the various ingredients, or materials, of
which it is composed. If we were to take a loaf of bread, and separate
the several ingredients of which it is made, the flour, the yeast, the
salt, and the water, it would be very different from cutting or
crumbling the loaf into pieces.

EMILY.

I understand you now very well. To decompose a body is to separate from
each other the various elementary substances of which it consists.

CAROLINE.

But flour, water, and other materials of bread, according to our
definition, are not elementary substances?

MRS. B.

No, my dear; I mentioned bread rather as a familiar comparison, to
illustrate the idea, than as an example.

The elementary substances of which a body is composed are called the
_constituent_ parts of that body; in decomposing it, therefore, we
separate its constituent parts. If, on the contrary, we divide a body by
chopping it to pieces, or even by grinding or pounding it to the finest
powder, each of these small particles will still consist of a portion of
the several constituent parts of the whole body: these are called the
_integrant_ parts; do you understand the difference?

EMILY.

Yes, I think, perfectly. We _decompose_ a body into its _constituent_
parts; and _divide_ it into its _integrant_ parts.

MRS. B.

Exactly so. If therefore a body consists of only one kind of substance,
though it may be divided into its integrant parts, it is not possible to
decompose it. Such bodies are therefore called _simple_ or _elementary_,
as they are the elements of which all other bodies are composed.
_Compound bodies_ are such as consist of more than one of these
elementary principles.

CAROLINE.

But do not fire, air, earth, and water, consist, each of them, but of
one kind of substance?

MRS. B.

No, my dear; they are every one of them susceptible of being separated
into various simple bodies. Instead of four, chemists now reckon upwards
of forty elementary substances. The existence of most of these is
established by the clearest experiments; but, in regard to a few of
them, particularly the most subtle agents of nature, _heat_, _light_,
and _electricity_, there is yet much uncertainty, and I can only give
you the opinion which seems most probably deduced from the latest
discoveries. After I have given you a list of the elementary bodies,
classed according to their properties, we shall proceed to examine each
of them separately, and th