he hydrogen of our bodies. Besides, should the air
be slightly caustic, we are in a great measure sheltered from its
effects by the skin; you know how much a wound, however trifling, smarts
on being exposed to it.

CAROLINE.

It is a curious idea, however, that we should live in a slow fire. But,
if the air was caustic, would it not have an acrid taste?

MRS. B.

It possibly may have such a taste; though in so slight a degree, that
custom has rendered it insensible.

CAROLINE.

And why is not water caustic? When I dip my hand into water, though
cold, it ought to burn me from the caustic nature of its oxygen.

MRS. B.

Your hand does not decompose the water; the oxygen in that state is much
better supplied with hydrogen than it would be by animal matter, and if
its causticity depend on its affinity for that principle, it will be
very far from quitting its state of water to act upon your hand. You
must not forget that oxyds are caustic in proportion as the oxygen
adheres slightly to them.

EMILY.

Since the oxyd of arsenic is poisonous, its acid, I suppose, is fully as
much so?

MRS. B.

Yes; it is one of the strongest poisons in nature.

EMILY.

There is a poison called _verdigris_, which forms on brass and copper
when not kept very clean; and this, I have heard, is an objection to
these metals being made into kitchen utensils. Is this poison likewise
occasioned by oxygen?

MRS. B.

It is produced by the intervention of oxygen; for verdigris is a
compound salt formed by the union of vinegar and copper; it is of a
beautiful green colour, and much used in painting.

EMILY.

But, I believe, verdigris is often formed on copper when no vinegar has
been in contact with it.

MRS. B.

Not real verdigris, but compound salts, somewhat resembling it, may be
produced by the action of any acid on copper.

The solution of copper in nitric acid, if evaporated, affords a salt
which produces an effect on tin that will surprise you, and I have
prepared some from the solution we made before, that I might show it to
you. I shall first sprinkle some water on this piece of tin-foil, and
then some of the salt. --Now observe that I fold it up suddenly, and
press it into one lump.

CAROLINE.

What a prodigious vapour issues from it--and sparks of fire I declare!

MRS. B.

I thought it would surprise you. The effect, however, I dare say you
could account for, since it is merely the consequence of the oxygen o