in natural philosophy,
we had better adopt it in chemistry likewise.

MRS. B.

If you have a clear idea of the meaning, I shall leave you at liberty to
express it in the terms you prefer. For myself, I confess that I think
the word Attraction best suited to the general law that unites the
integrant particles of bodies; and Affinity better adapted to that which
combines the constituent particles, as it may convey an idea of the
preference which some bodies have for others, which the term _attraction
of composition_ does not so well express.

EMILY.

So I think; for though that preference may not result from any
relationship, or similitude, between the particles (as you say was once
supposed), yet, as it really exists, it ought to be expressed.

MRS. B.

Well, let it be agreed that you may use the terms _affinity_, _chemical
attraction_ and _attraction of composition_, indifferently, provided you
recollect that they have all the same meaning.

EMILY.

I do not conceive how bodies can be decomposed by chemical attraction.
That this power should be the means of composing them, is very obvious;
but that it should, at the same time, produce exactly the contrary
effect, appears to me very singular.

MRS. B.

To decompose a body is, you know, to separate its constituent parts,
which, as we have just observed, cannot be done by mechanical means.

EMILY.

No: because mechanical means separate only the integrant particles; they
act merely against the attraction of cohesion, and only divide a
compound into smaller parts.

MRS. B.

The decomposition of a body is performed by chemical powers. If you
present to a body composed of two principles, a third, which has a
greater affinity for one of them than the two first have for each other,
it will be decomposed, that is, its two principles will be separated by
means of the third body. Let us call two ingredients, of which the body
is composed, A and B. If we present to it another ingredient C, which
has a greater affinity for B than that which unites A and B, it
necessarily follows that B will quit A to combine with C. The new
ingredient, therefore, has effected a decomposition of the original body
A B; A has been left alone, and a new compound, B C, has been formed.

EMILY.

We might, I think, use the comparison of two friends, who were very
happy in each other's society, till a third disunited them by the
preference which one of them gave to the new-comer.

MR