e I take a glass containing nothing else but air, and from this
vessel containing the carbonic acid I attempt to pour a little of this gas
into that glass; I wonder whether any has gone in or not. I cannot tell by
the appearance, but I can in this way [introducing the taper]. Yes, there
it is, you see; and if I were to examine it by lime-water, I should find
it by that test also. I will take this little bucket, and put it down into
the well of carbonic acid--indeed, we too often have real wells of
carbonic acid--and now, if there is any carbonic acid, I must have got to
it by this time, and it will be in this bucket, which we will examine with
a taper. There it is, you see; it is full of carbonic acid.

[Illustration: Fig. 30.]

There is another experiment by which I will shew you its weight. I have
here a jar suspended at one end of a balance--it is now equipoised; but
when I pour this carbonic acid into the jar on the one side which now
contains air, you will see it sink down at once, because of the carbonic
acid that I pour into it. And now, if I examine this jar with the lighted
taper, I shall find that the carbonic acid has fallen into it, and it no
longer has any power of supporting the combustion. If I blow a
soap-bubble, which of course will be filled with air, and let it fall into
this jar of carbonic acid, it will float.

[Illustration: Fig. 31.]

But I shall first of all take one of these little balloons filled with
air. I am not quite sure where the carbonic acid is; we will just try the
depth, and see whereabouts is its level. There, you see, we have this
bladder floating on the carbonic acid; and if I evolve some more of the
carbonic acid, the bladder will be lifted up higher. There it goes--the
jar is nearly full; and now I will see whether I can blow a soap-bubble on
that, and float it in the same way. [The Lecturer here blew a soap-bubble,
and allowed it to fall into the jar of carbonic acid, when it floated in
it midway.] It is floating, as the balloon floated, by virtue of the
greater weight of the carbonic acid than of the air. And now, having so
far given you the history of the carbonic acid--as to its sources in the
candle, as to its physical properties and weight--when we next meet I
shall shew you of what it is composed, and where it gets its elements
from.

LECTURE VI.

CARBON OR CHARCOAL--COAL GAS--RESPIRATION AND ITS ANALOGY TO THE BURNING
OF A CANDLE--CONCLUSION.

A lady, who