being revived by charcoal, when heated red hot, charcoal having a
greater attraction for oxygen than the metals. You need only, therefore,
decompose, or unburn the oxyd, by depriving it of its oxygen, and the
metal will be restored to its pure state.

EMILY.

But will the carbon, by this operation, be burnt, and be converted into
carbonic acid?

MRS. B.

Certainly. There are other combustible substances to which metals at a
high temperature will part with their oxygen. They will also yield it to
each other, according to their several degrees of attraction for it; and
if the oxygen goes into a more dense state in the metal which it enters,
than it existed in that which it quits, a proportional disengagement of
caloric will take place.

CAROLINE.

And cannot the oxyds of gold, silver, and platina, which are formed by
means of acids or of the electric fluid, be restored to their metallic
state?

MRS. B.

Yes, they may; and the intervention of a combustible body is not
required; heat alone will take the oxygen from them, convert it into a
gas, and revive the metal.

EMILY.

You said that rust was an oxyd of iron; how is it, then, that water, or
merely dampness, produces it, which, you know, it very frequently does
on steel grates, or any iron instruments?

MRS. B.

In that case the metal decomposes the water, or dampness (which is
nothing but water in a state of vapour), and obtains the oxygen from it.

CAROLINE.

I thought that it was necessary to bring metals to a very high
temperature to enable them to decompose water.

MRS. B.

It is so, if it is required that the process should be performed
rapidly, and if any considerable quantity is to be decomposed. Rust, you
knew, is sometimes months in forming, and then it is only the surface of
the metal that is oxydated.

EMILY.

Metals, then, that do not rust, are incapable of spontaneous oxydation,
either by air or water?

MRS. B.

Yes; and this is the case with the perfect metals, which, on that
account, preserve their metallic lustre so well.

EMILY.

Are all metals capable of decomposing water, provided their temperature
be sufficiently raised?

MRS. B.

No; a certain degree of attraction is requisite, besides the assistance
of heat. Water, you recollect, is composed of oxygen and hydrogen; and,
unless the affinity of the metal for oxygen be stronger than that of
hydrogen, it is in vain that we raise its temperature, for it cannot
take