coverings, and gutters, and pipes, would consume and burn, increasing
the combustion.'"

"That would be, indeed, burning 'like a house on fire,'" observed Mr.
Bagges.

"'Think,'" said Harry, continuing his quotation, "'of the Houses
of Parliament, or a steam-engine manufactory. Think of an iron
proof-chest no proof against oxygen. Think of a locomotive and its
train,--every engine, every carriage, and even every rail would be set
on fire and burnt up.' So now, uncle, I think you see what the use of
nitrogen is, and especially how it prevents a candle from burning out
too fast."

"Eh?" said Mr. Bagges. "Well, I will say I do think we are under
considerable obligations to nitrogen."

"I have explained to you, uncle," pursued Harry, "how a candle, in
burning, turns into water. But it turns into something else. besides
that. There is a stream of hot air going up from it that won't
condense into dew; some of that is the nitrogen of the air which the
candle has taken all the oxygen from. But there is more in it than
nitrogen. Hold a long glass tube over a candle, so that the stream
of hot air from it may go up through the tube. Hold a jar over the
end of the tube to collect some of the stream of hot air. Put some
lime-water, which looks quite clear, into the jar; stop the jar,
and shake it up. The lime-water, which was quite clear before, turns
milky. Then there is something made by the burning of the candle that
changes the color of the lime-water. That is a gas, too, and you can
collect it, and examine it. It is to be got from several things,