"I think I'll show you now how I make gas on a small scale."
"What kind of gas?" inquired Alec.
"Oh! such gas as we burn in stores and houses. I've got my pipe already
prepared: if I hadn't, I couldn't show you that experiment very well
to-day. I got the pipe ready to show to a boy who was coming to see me
last week; but he was sick and didn't come, so I didn't use the pipe."
Johnny took a common clay pipe from his closet, and showed Alec and
Belle that the top of the ball of the pipe was closed with plaster of
Paris.
"I pounded a little piece of bituminous coal, such as they use at the
gas-works," said Johnny, "and nearly filled the bowl of the pipe with
it; then I wet a little plaster of Paris, and closed the end of the bowl
to make it air-tight,--that is, to keep out the oxygen. There are
carbon and hydrogen in the coal, and they will both combine with oxygen
very quickly at the right degree of heat: the hydrogen will form a
flame, and the carbon will look bright as you see it in a piece of
burning wood or coal. But you see the pipe is fixed so that the oxygen
can't get at the coal at that end."
"Is the flame of a fire or a lamp caused by the burning of hydrogen?"
inquired Belle.
"Yes: the flame is the hydrogen combining with oxygen, and the glowing
coal or wick is the carbon uniting with oxygen. The gas from the
gas-works is the hydrogen of the coal separated from the carbon. When
we heat it with a match to set it to uniting with oxygen, we have
nothing but a flame. You know the coal is heated in air-tight retorts;
it is heated hot enough to burn, but it can't burn because there is no
oxygen for it to unite with; but the heat causes the hydrogen to
separate from the carbon, and then it finds its way out through the
opening in the retort into the pipes, and when it reaches the air at the
end of a pipe, you can heat it a little with a match, and it will begin
to unite with the oxygen."
"And the coal that is left in the retort is called coke. I have seen it
very often," said Alec: "the reason it looks different from coal, and
burns differently, then, is because it has lost its hydrogen?"
"Yes," replied Johnny: "almost all ordinary combustibles are composed of
carbon and hydrogen,--wood, coal, oil, etc.; and there are a great many
other things that oxygen has a great affinity for, and will combine with
at the right temperature: the things that it won't combine with are such
as have all the oxygen in them that they will contain, like dirt and
stones and ashes."
"And how about the pipe?" asked Alec.
"Why, after Sue gets back with the piece of iron, we will go down and
set the ball of the pipe in Katie's fire. When it gets hot, we shall
see a smoke coming out of the pipe, which will be composed chiefly of
hydrogen gas: we will touch a match to it, and there will be a flame at
the end of the pipe until all the hydrogen which was in the coal in the
ball of the pipe has united with oxygen. That is one way to make gas on
a very small scale."
"And then, if we break the plaster of Paris, and take out what is left
of the coal, we shall have some coke," said Alec.
"Yes," replied Johnny.
Sue now appeared, bringing a small cold chisel. Johnny took a file from
the closet, and, placing the chisel over the flame of the lamp, began to
file it briskly: beautiful little points of light at once commenced to
play about the file and chisel at the point of contact.
"Why don't the filings fall down into the flame?" inquired Alec.
"I suppose the current in the flame blows them up, they are so small,"
replied Johnny, "or perhaps the motion of the file does."
Alec, Belle, and Sue then took turns at making the "fireworks," as Sue
called them.
"I think I understand now about fire being a chemical union between
oxygen and other substances," said Alec; "but I don't understand about
the heat. What makes heat? or why does a chemical union of that kind
produce heat?"
"Why, friction makes heat," replied Johnny; "particles of matter coming
against each other violently. You know the Indians used to get the
oxygen to combining with the carbon and hydrogen in two pieces of dry
wood, by rubbing them together briskly; and before matches were
invented, they kindled a fire by striking flint and steel over tinder;
and a steel peg in your shoe-heel sometimes strikes fire on the pavement
by the heat produced by friction; and I think I have seen it stated,
that, when oxygen is uniting with other substances, it is the very quick
motion of the little particles of matter among themselves that produces
the heat."
"I shouldn't think such little invisible particles as those of oxygen
and hydrogen could make friction enough by their motion as to produce
heat," said Alec.
"Why, Alec," replied Belle, "don't you remember what terrible force the
air has in hurricanes, and even in a common gale?"
"But that is in an immense volume," replied Alec.
"Oxygen is in a comparatively mild and harmless state when it is by
itself," said Johnny; "but when it gets to combining with any thing it
has a great affinity for, it is in a sort of rage. I think myself that
there must be some pretty rapid motion going on in a fire, even if we
can't see it."
Johnny had handed the chisel to Sue, telling her to put it right back
where she found it.
"Well, I will," replied Sue; "but I guess things won't be put back in
their right places much after Felix gets here."
Sue had no sooner said this, than she clapped her hand over her mouth.
"Oh!" she exclaimed, "if I haven't gone and told!"
Johnny's face had grown very long in an instant.
"Is that your bad news?" he said. "When is Felix coming?"
"I don't know," replied Sue: "you'll have to ask mamma, for she was to
decide."