the oxygen from the hydrogen. Iron, zinc, tin, and antimony, have a
stronger affinity for oxygen than hydrogen has, therefore these four
metals are capable of decomposing water. But hydrogen having an
advantage over all the other metals with respect to its affinity for
oxygen, it not only withholds its oxygen from them, but is even capable,
under certain circumstances, of taking the oxygen from the oxyds of
these metals.

EMILY.

I confess that I do not quite understand why hydrogen can take oxygen
from those metals that do not decompose water.

CAROLINE.

Now I think I do perfectly. Lead, for instance, will not decompose
water, because it has not so strong an attraction for oxygen as hydrogen
has. Well, then, suppose the lead to be in a state of oxyd; hydrogen
will take the oxygen from the lead, and unite with it to form water,
because hydrogen has a stronger attraction for oxygen, than oxygen has
for lead; and it is the same with all the other metals which do not
decompose water.

EMILY.

I understand your explanation, Caroline, very well; and I imagine that
it is because lead cannot decompose water that it is so much employed
for pipes for conveying that fluid.

MRS. B.

Certainly; lead is, on that account, particularly appropriate to such
purposes; whilst, on the contrary, this metal, if it was oxydable by
water, would impart to it very noxious qualities, as all oxyds of lead
are more or less pernicious.

But, with regard to the oxydation of metals, the most powerful mode of
effecting it is by means of acids. These, you know, contain a much
greater proportion of oxygen than either air or water; and will, most of
them, easily yield it to metals. Thus, you recollect, the zinc plates of
the Voltaic battery are oxydated by the acid and water, much more
effectually than by water alone.

CAROLINE.

And I have often observed that if I drop vinegar, lemon, or any acid on
the blade of a knife, or on a pair of scissars, it will immediately
produce a spot of rust.

EMILY.

Metals have, then, three ways of obtaining oxygen; from the atmosphere,
from water, and from acids.

MRS. B.

The two first you have already witnessed, and I shall now show you how
metals take the oxygen from an acid. This bottle contains nitric acid;
I shall pour some of it over this piece of copper-leaf . . . . . . .

CAROLINE.

Oh, what a disagreeable smell!

EMILY.

And what is it that produces the effervescency and that thi