Here is the mixture; and when I set
fire to it, you must watch the combustion, and you will see that it is of
two kinds. You will see the gunpowder burning with a flame, and the
filings thrown up. You will see them burning too, but without the
production of flame. They will each burn separately. [The Lecturer then
ignited the mixture.] There is the gunpowder, which burns with a flame;
and there are the filings--they burn with a different kind of combustion.
You see, then, these two great distinctions; and upon these differences
depend all the utility and all the beauty of flame which we use for the
purpose of giving out light. When we use oil, or gas, or candle, for the
purpose of illumination, their fitness all depends upon these different
kinds of combustion.
There are such curious conditions of flame, that it requires some
cleverness and nicety of discrimination to distinguish the kinds of
combustion one from another. For instance, here is a powder which is very
combustible, consisting, as you see, of separate little particles. It is
called _lycopodium_[7], and each of these particles can produce a vapour,
and produce its own flame; but, to see them burning, you would imagine it
was all one flame. I will now set fire to a quantity, and you will see the
effect.
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