I told you, when we last met, a good deal about carbonic acid. We found,
by the lime-water test, that when the vapour from the top of the candle or
lamp was received into bottles, and tested by this solution of lime-water
(the composition of which I explained to you, and which you can make for
yourselves), we had that white opacity which was in fact calcareous
matter, like shells and corals, and many of the rocks and minerals in the
earth. But I have not yet told you fully and clearly the chemical history
of this substance--carbonic acid--as we have it from the candle, and I
must now resume that subject. We have seen the products, and the nature of
them, as they issue from the candle. We have traced the water to its
elements, and now we have to see where are the elements of the carbonic
acid supplied by the candle. A few experiments will shew this. You
remember that when a candle burns badly, it produces smoke; but if it is
burning well, there is no smoke. And you know that the brightness of the
candle is due to this smoke, which becomes ignited. Here is an experiment
to prove this: so long as the smoke remains in the flame of the candle and
becomes ignited, it gives a beautiful light, and never appears to us in
the form of black particles. I will light some fuel, which is extravagant
in its burning. This will serve our purpose--a little turpentine on a
sponge. You see the smoke rising from it, and floating into the air in
large quantities; and, remember now, the carbonic acid that we have from
the candle is from such smoke as that. To make that evident to you, I will
introduce this turpentine burning on the sponge into a flask where I have
plenty of oxygen, the rich part of the atmosphere, and you now see that
the smoke is all consumed. This is the first part of our experiment; and
now, what follows? The carbon which you saw flying off from the turpentine
flame in the air is now entirely burned in this oxygen, and we shall find
that it will, by this rough and temporary experiment, give us exactly the
same conclusion and result as we had from the combustion of the candle.
The reason why I make the experiment in this manner is solely that I may