We have the case of the
combustion of a candle; we have the case of a candle being put out by the
want of air; and we have now the case of imperfect combustion; and this is
to us so interesting, that I want you to understand it as thoroughly as
you do the case of a candle burning in its best possible manner. I will
now make a great flame, because we need the largest possible
illustrations. Here is a larger wick [burning turpentine on a ball of
cotton]. All these things are the same as candles, after all. If we have
larger wicks, we must have a larger supply of air, or we shall have less
perfect combustion. Look now at this black substance going up into the
atmosphere; there is a regular stream of it. I have provided means to
carry off the imperfectly burned part, lest it should annoy you. Look at
the soots that fly off from the flame: see what an imperfect combustion it
is, because it cannot get enough air. What, then, is happening? Why,
certain things which are necessary to the combustion of a candle are
absent, and very bad results are accordingly produced; but we see what
happens to a candle when it is burnt in a pure and proper state of air. At
the time when I shewed you this charring by the ring of flame on the one
side of the paper, I might have also shewn you, by turning to the other
side, that the burning of a candle produces the same kind of
soot--charcoal or carbon.
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