ece of paper by holding it in the flame of
the fire.

MRS. B.

The closer it is in contact with the source of caloric, the sooner will
its temperature be raised to the degree necessary for it to burn. If you
hold it near the fire, the same effect will be produced; but more time
will be required, as you found to be the case with the piece of stick.

EMILY.

But why is it not necessary to continue applying caloric throughout the
process of combustion, in order to keep up the electric energy of the
wood, which is required to enable it to combine with the oxygen?

MRS. B.

The caloric which is gradually produced by the two electricities during
combustion, keeps up the temperature of the burning body; so that when
once combustion has begun, no further application of caloric is
required.

CAROLINE.

Since I have learnt this wonderful theory of combustion, I cannot take
my eyes from the fire; and I can scarcely conceive that the heat and
light, which I always supposed to proceed entirely from the coals, are
really produced as much by the atmosphere.

EMILY.

When you blow the fire, you increase the combustion, I suppose, by
supplying the coals with a greater quantity of oxygen gas?

MRS. B.

Certainly; but of course no blowing will produce combustion, unless the
temperature of the coals be first raised. A single spark, however, is
sometimes sufficient to produce that effect; for, as I said before, when
once combustion has commenced, the caloric disengaged is sufficient to
elevate the temperature of the rest of the body, provided that there be
a free access of oxygen. It however sometimes happens that if a fire be
ill made, it will be extinguished before all the fuel is consumed, from
the very circumstance of the combustion being so slow that the caloric
disengaged is insufficient to keep up the temperature of the fuel. You
must recollect that there are three things required in order to produce
combustion; a combustible body, oxygen, and a temperature at which the
one will combine with the other.

EMILY.

You said that combustion was one method of decomposing the atmosphere,
and obtaining the nitrogen gas in its simple state; but how do you
secure this gas, and prevent it from mixing with the rest of the
atmosphere?

MRS. B.

It is necessary for this purpose to burn the body within a close vessel,
which is easily done. --We shall introduce a small lighted taper (PLATE
VII. Fig. 1.) under this glass recei