"We had better keep," said the Captain, "to the same instances of which
we have already been speaking. Thus, what we call limestone is a more or
less pure calcareous earth in combination with a delicate acid, which is
familiar to us in the form of a gas. Now, if we place a piece of this
stone in diluted sulphuric acid, this will take possession of the lime,
and appear with it in the form of gypsum, the gaseous acid at the same
time going off in vapor. Here is a case of separation; a combination
arises, and we believe ourselves now justified in applying to it the
words 'Elective Affinity;' it really looks as if one relation had been
deliberately chosen in preference to another.

"Forgive me," said Charlotte, "as I forgive the natural philosopher. I
cannot see any choice in this; I see a natural necessity rather, and
scarcely that. After all, it is perhaps merely a case of opportunity.
Opportunity makes relations as it makes thieves; and as long as the
talk is only of natural substances, the choice to me appears to be
altogether in the hands of the chemist who brings the creatures
together. Once, however, let them be brought together, and then God have
mercy on them. In the present case, I cannot help being sorry for the
poor acid gas, which is driven out up and down infinity again."

"The acid's business," answered the Captain, "is now to get connected
with water, and so serve as a mineral fountain for the refreshing of
sound or disordered mankind."

"That is very well for the gypsum to say," said Charlotte. "The gypsum
is all right, is a body, is provided for. The other poor, desolate
creature may have trouble enough to go through before it can find a
second home for itself."