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]. There is plenty of carbon in the gas; but, because the
atmosphere can get to it, and mix with it before it burns, you see how
pale and blue the flame is. And if I blow upon a bright gas-flame, so as
to consume all this carbon before it gets heated to the glowing point, it
will also burn blue: [The Lecturer illustrated his remarks by blowing on
the gas-light.] The only reason why I have not the same bright light when
I thus blow upon the flame is, that the carbon meets with sufficient air
to burn it before it gets separated in the flame in a free state. The
difference is solely due to the solid particles not being separated before
the gas is burnt.

You observe that there are certain products as the result of the
combustion of a candle, and that of these products one portion may be
considered as charcoal, or soot; that charcoal, when afterwards burnt,
produces some other product; and it concerns us very much now to ascertain
what that other product is. We shewed that something was going away; and I
want you now to understand how much is going up into the air; and for that
purpose we will have combustion on a little larger scale. From that candle
ascends heated air, and two or three experiments will shew you the