,
will assist you in arranging your ideas. It would be in vain to attempt
forming a division that would appear perfectly clear to a beginner: for
you may easily conceive that a chemical division being necessarily
founded on properties with which you are almost wholly unacquainted, it
is impossible that you should at once be able to understand its meaning
or appreciate its utility.

But, before we proceed further, it will be necessary to give you some
idea of chemical attraction, a power on which the whole science depends.

_Chemical Attraction_, or the _Attraction of Composition_, consists in
the peculiar tendency which bodies of a different nature have to unite
with each other. It is by this force that all the compositions, and
decompositions, are effected.

EMILY.

What is the difference between chemical attraction, and the attraction
of cohesion, or of aggregation, which you often mentioned to us, in
former conversations?

MRS. B.

The attraction of cohesion exists only between particles of the _same_
nature, whether simple or compound; thus it unites the particles of a
piece of metal which is a simple substance, and likewise the particles
of a loaf of bread which is a compound. The attraction of composition,
on the contrary, unites and maintains, in a state of combination,
particles of a _dissimilar_ nature; it is this power that forms each of
the compound particles of which bread consists; and it is by the
attraction of cohesion that all these particles are connected into a
single mass.

EMILY.

The attraction of cohesion, then, is the power which unites the
integrant particles of a body: the attraction of composition that which
combines the constituent particles. Is it not so?

MRS. B.

Precisely: and observe that the attraction of cohesion unites particles
of a similar nature, without changing their original properties; the
result of such an union, therefore, is a body of the same kind as the
particles of which it is formed; whilst the attraction of composition,
by combining particles of a dissimilar nature, produces compound bodies,
quite different from any of their constituents. If, for instance, I pour
on the piece of copper, contained in this glass, some of this liquid
(which is called nitric acid), for which it has a strong attraction,
every particle of the copper will combine with a particle of acid, and
together they will form a new body, totally different from either the
copper or the acid.