that of the oxyd
which emits it, is, in all probability, owing to some particles of the
metal which are volatilised and carried off by the caloric.

CAROLINE.

It is then a sort of metallic gas.

EMILY.

Why is it reckoned so unwholesome to breathe the air of a place in which
metals are melting?

MRS. B.

Perhaps the notion is too generally entertained. But it is true with
respect to lead, and some other noxious metals, because, unless care be
taken, the particles of the oxyd which are volatilised by the heat are
inhaled in with the breath, and may produce dangerous effects.

I must show you some instances of the combustion of metals; it would
require the heat of a furnace to make them burn in the common air, but
if we supply them with a stream of oxygen gas, we may easily
accomplish it.

CAROLINE.

But it will still, I suppose, be necessary in some degree to raise their
temperature?

MRS. B.

This, as you shall see, is very easily done, particularly if the
experiment be tried upon a small scale. --I begin by lighting this piece
of charcoal with the candle, and then increase the rapidity of its
combustion by blowing upon it with a blow-pipe. (PLATE XII. fig. 1.)

[Illustration: Plate XII.
Apparatus for the combustion of metals by means of oxygen gas.

Fig. 1.
Igniting charcoal with a taper & blow-pipe.

Fig. 2.
Combustion of metals by means of a blow-pipe conveying a stream of
oxygen gas from a gas holder.]

EMILY.

That I do not understand; for it is not every kind of air, but merely
oxygen gas, that produces combustion. Now you said that in breathing we
inspired, but did not expire oxygen gas. Why, therefore, should the air
which you breathe through the blow-pipe promote the combustion of the
charcoal?

MRS. B.

Because the air, which has but once passed through the lungs, is yet but
little altered, a small portion only of its oxygen being destroyed; so
that a great deal more is gained by increasing the rapidity of the
current, by means of the blow-pipe, than is lost in consequence of the
air passing once through the lungs, as you shall see--

EMILY.

Yes, indeed, it makes the charcoal burn much brighter.

MRS. B.

Whilst it is red-hot, I shall drop some iron filings on it, and supply
them with a current of oxygen gas, by means of this apparatus, (PLATE
XII. fig 2.) which consists simply of a closed tin cylindrical vessel,
full of oxygen gas, with two apertures and s