I will now take such a flame as I had a moment since, and set free from it
the particles of carbon. Here is some camphine, which will burn with a
smoke; but if I send these particles of smoke through this pipe into the
hydrogen flame, you will see they will burn and become luminous, because
we heat them a second time. There they are. Those are the particles of
carbon re-ignited a second time. They are those particles which you can
easily see by holding a piece of paper behind them, and which, whilst they
are in the flame, are ignited by the heat produced, and, when so ignited,
produce this brightness. When the particles are not separated, you get no
brightness. The flame of coal-gas owes its brightness to the separation,
during combustion, of these particles of carbon, which are equally in that
as in a candle. I can very quickly alter that arrangement. Here, for
instance, is a bright flame of gas. Supposing I add so much air to the
flame as to cause it all to burn before those particles are set free, I
shall not have this brightness; and I can do that in this way:--If I place
over the jet this wire-gauze cap, as you see, and then light the gas over
it, it burns with a non-luminous flame, owing to its having plenty of air
mixed with it before it burns; and if I raise the gauze, you see it does
not burn below[10].
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