"You fill the jar with water," answered Harry, "and you stand it
upside down in a vessel full of water too. Then you let bubbles of the
gas up into the jar, and they turn out the water and take its place.
Put a stopper in the neck of the jar, or hold a glass plate against
the mouth of it, and you can take it out of the water and so have
bottled oxygen. A lighted candle put into a jar of oxygen blazes up
directly, and is consumed before you can say Jack Robinson. Charcoal
burns away in it as fast, with beautiful bright sparks--phosphorus
with a light that dazzles you to look at--and a piece of iron or steel
just made red-hot at the end first, is burnt in oxygen quicker than
a stick would be in common air. The experiment of burning things in
oxygen beats any fire-works."

"Oh, how jolly!" exclaimed Tom.

"Now we see, uncle," Harry continued, "that water is hydrogen and
oxygen united together, that water is got wherever hydrogen is burnt
in common air, that a candle won't burn without air, and that when a
candle burns there is hydrogen in it burning, and forming water. Now,
then, where does the hydrogen of the candle get the oxygen from, to
turn into water with it?"

"From the air, eh?"

"Just so. I can't stop to tell you of the other things which there is
oxygen in, and the many beautiful and amusing ways of getting it. But
as there is oxygen in the air, and as oxygen makes things burn at such
a rate, perhaps you wonder why air does not make things burn as fast
as oxygen. The reason is, that there is something else in the air that