in the bottom. Now put your finger and
thumb over the hole in the bottom of the burner. What happens
to the flame? Turn the valve so that it will close the hole
in the same way. Now hold a white saucer over the flame, being
careful not to get it hot enough to break. What is the black
stuff on the bottom of the saucer?

Examine the gas plate (small gas stove) in the laboratory.
Light it, and see if you can find the place where the air is
fed in with the gas. Close this place and see what happens.
Open it wider and see what happens. If the air opening is too
large, the flame "blows"; there is too much cold air coming in
with the gas, and your flame is not as hot as it would be if
it did not "blow." Also, the stove is liable to "back-fire"
(catch fire at the air opening) when the air opening is too
wide.

[Illustration: FIG. 168. The Bunsen burner smokes when the air holes are
closed.]

_APPLICATION 69._ An oil lamp tipped over and the burning oil
spread over the floor. Near by were a pail of water, a pan of
ashes, a rug, and a seltzer siphon. Which of these might have
been used to advantage in putting out the fire?

_APPLICATION 70._ My finger was burned. I wanted the flesh
around it to heal and new skin cells to live and grow rapidly
around the burn.

"Put a rubber finger cot on the finger and keep all air out,"
one friend advised me. "Air causes decay and will therefore be
bad for the burn."

"He's wrong; you should bandage it with clean cloth; you want
air to reach the finger, I've heard," said another friend.

"Oh, no, you don't; air makes things burn, and the burn will
therefore get worse," still another one said. What should I
have done?

_APPLICATION 71._ Two students were discussing how coal was
formed.

"The trees must have fallen into water and been completely
covered by it, or they would have decayed," said one.

"Water makes things decay more quickly; there must have been
a drought and the trees must have fallen on dry ground," said
the second.

Which was right?

[Illustration: FIG. 169. Regulating the air opening in a gas stove.]

_APPLICATION 72._ A gas stove had a yellow flame. In front,
by the handles, was a metal disk with holes so arranged that
turning it to the left allowed air to mix with the gas on the
way to the flame,