chlorate with an equal amount of manganese dioxide and place the
mixture in a strong test tube. Close the mouth of the tube with a
one-hole rubber stopper in which is fitted a long, narrow tube, and
clamp the test tube to an iron support, as shown in Figure 22. Fill
the trough with water until the shelf is just covered and allow the
end of the delivery tube to rest just beneath the hole in the shelf.
Fill a medium-sized bottle with water, cover it with a glass plate,
invert the bottle in the trough, and then remove the glass plate. Heat
the test tube very gently, and when gas bubbles out of the tube, slip
the bottle over the opening in the shelf, so that the tube runs into
the bottle. The gas will force out the water and will finally fill the
bottle. When all the water has been forced out, slip the glass plate
under the mouth of the bottle and remove the bottle from the trough.
The gas in the bottle is oxygen.

Everywhere in a large city or in a small village, smoke is seen,
indicating the presence of fire; hence there must exist a large supply
of oxygen to keep all the fires alive. The supply of oxygen needed
for the fires of the world comes largely from the atmosphere.

37. Matches. The burning material is ordinarily set on fire by
matches, thin strips of wood tipped with sulphur or phosphorus, or
both. Phosphorus can unite with oxygen at a fairly low temperature,
and if phosphorus is rubbed against a rough surface, the friction
produced will raise the temperature of the phosphorus to a point where
it can combine with oxygen. The burning phosphorus kindles the wood of
the match, and from the burning match the fire is kindled. If you want
to convince yourself that friction produces heat, rub a cent
vigorously against your coat and note that the cent becomes warm.
Matches have been in use less than a hundred years. Primitive man