ng over the glass tube and put the other
end into a pan of water.

Fill a flask or bottle to the brim with water, letting it
overflow a little; hold a piece of cardboard firmly over the
mouth of the bottle; turn the bottle upside down quickly,
putting the mouth of it under water in the pan; take the
cardboard away. The water should all stay in the bottle.

Now shove the rubber tube into the neck of the bottle until it
sticks up an inch or two. During this experiment, be careful
not to let the neck of the bottle or flask pinch the rubber
tubing; small pieces of wood or glass tubing laid beside the
rubber tubing where it goes under the run of the neck will
prevent this.

Hold, the test tube, tightly corked, over the flame of a
burner, keeping the tube at a slant and moving it slightly
back and forth so that all the material in it will be
thoroughly heated. If you stop heating the test tube even for
a couple of seconds, take the cork out; if you do not remove
the cork, the cooling gas in the test tube will shrink and
allow the water from the pan to be forced through the rubber
tube into the test tube, breaking it into pieces.

When enough gas has bubbled up into the bottle to force all
the water out, and when bubbles begin to come up outside the
bottle, uncork the test tube and lay it aside where it will
not burn anything; then slide the cardboard under the mouth of
the bottle and turn it right side up; leave the cardboard on
the bottle.

Light a piece of charcoal, or let a splinter of wood burn a
few minutes and then blow it out so that a glowing coal will
be left on the end of it. Lift the cardboard off the bottle
and plunge the glowing stick into it for a couple of seconds.
Cover the bottle after taking out the stick, and repeat, using
a lighted match or a burning piece of wood instead of the
glowing stick. If you dip a piece of iron picture wire in
sulfur and light it, and then plunge it into the bottle, you
will see iron burn.

[Illustration: FIG. 165. Filling a bottle with oxygen.]

[Illustration: FIG. 166. The iron really burns in the jar of oxygen.]

Both manganese dioxid and potassium chlorate have a great deal of
oxygen bound up in them. When they join together, as they do when you
heat them, they cannot hold so much oxygen, and it escapes as a gas.
In the experim