or less; and a great deal of it comes out of the earth in some places.
Carbonic acid gas is what stupefies the dogs in the Grotto del Cane.
Well, but how is carbonic acid gas made by the candle?"

"I hope with your candle you'll throw some light upon the subject,"
said Uncle Bagges.

"I hope so," answered Harry. "Recollect it is the burning of the
smoke, or soot, or carbon of the candle, that makes the candle-flame
bright. Also 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.