o that the candle won't burn without air. Likewise that it
will not burn in nitrogen, or air that has been deprived of oxygen.
So the carbon of the candle mingles with oxygen, in burning, to make
carbonic acid gas; just as the hydrogen does to form water. Carbonic
acid gas, then, is carbon or charcoal dissolved in oxygen. Here is
black soot getting invisible and changing into air; and this seems
strange, uncle, doesn't it?"

"Ahem! Strange, if true," answered Mr. Bagges. "Eh? Well! I suppose
it's all right."

"Quite so, uncle. Burn carbon or charcoal either in the air or in
oxygen, and it is sure always to make carbonic acid, and nothing else,
if it is dry. No dew or mist gathers in a cold glass jar if you burn
dry charcoal in it. The charcoal goes entirely into carbonic acid gas,
and leaves nothing behind but ashes, which are only earthy stuff that
was in the charcoal, but not part of the charcoal itself. And now,
shall I tell you something about carbon?"

"With all my heart," assented Mr. Bagges.

"I said that there was carbon or charcoal in all common lights, so
there is in every common kind of fuel. If you heat coal or wood away
from the air, some gas comes away, and leaves behind coke from coal,
and charcoal from wood; both carbon, though not pure. Heat carbon
as much as you will in a close vessel, and it does not change in the
least; but let the air get to it, and then it burns and flies off in
carbonic acid gas. This makes carbon so convenient for fuel. But it is
ornamental as well as useful, uncle. The diamond is nothing else than
carbon."

"The diamond, eh! You mean the black diamond."

"No: the diamond, really and truly. The diamond is only carbon in the
shape of a crystal."

"Eh? and can't some of your clever chemists crystalize a little bit of
carbon, and make a Koh-i-noor?"

"Ah, uncle, perhaps we shall, some day. In the mean time I suppose we
must be content with making carbon so brilliant as it is in the flame
of a candle. Well; now you see that a candle-flame is vapor burning,
and the vapor, in burning, turns into water and carbonic acid gas. The
oxygen of both the carbonic acid gas and the water comes from the air,
and the hydrogen and carbon together are the vapor. They are distilled
out of the melted was by the heat. But, you know, carbon alone can't
be distilled by any heat. It can be distilled, though, when it is
joined with hydrogen, as it is in the wax, and then the mixed hydrogen
and c