W‌e have now seen that we can produce hydrogen
and oxygen from the water that we obtained
from the candle. Hydrogen, you know, comes
from the candle, and oxygen, you believe,
comes from the air. But then you have a right
to ask me, “How is it that the air and the
oxygen do not equally well burn the candle?”
If you remember what happened when I put a
jar of oxygen over a piece of candle, you
recollect that there was a very different
kind of combustion to that which takes place
in the air. Why is this? It is a very important
question, and one I shall endeavor to make
you understand: it relates most intimately
to the nature of the atmosphere, and it’s
most important to us. We have several tests
for oxygen besides the mere burning of bodies.
You’ve seen a candle burnt in oxygen, or
in the air. But we have other tests besides
these, and I am about to show you one of them
for the purpose of carrying your conviction
and your experience further. It is a very
curious and useful one.
I have here a flask
half-filled with a solution of potassium hydroxide,
glucose, and methylene blue indicator and
filled the rest of the way with oxygen gas.
I shake the flask and the oxygen mixes with
the solution.
“What happens?” say you,
“they together produce no such combustion
as was seen in the case of the candle.”
But see how the presence of oxygen is told
by its association with these other substances.
What a beautiful-colored solution I have obtained
in this way, showing me the presence of the
oxygen! In the same way we can try this experiment
by mixing common air with this solution. Here
is another flask containing the same solution,
but this time with air above it. I shake this
flask and you see the result: the solution
turns blue, and that shows me that there is
oxygen in the air—the very same substance
that had been already obtained by us from
the water produced by the candle. But then,
beyond that, how is it that the candle does
not burn in air as well as in oxygen? We will
come to that point at once. The solutions
react with the gas, and the appearance to
the eye is alike in both, and I cannot tell
which of these flasks contains oxygen and
which contains air, although I know they have
been previously filled with these gases. In
order to examine whether there is any difference
between them we simply need to wait.
Notice how the blue color of the solution fades in
this flask, the flask with air. Why is that?
Because there is in air, besides oxygen, something
else present. The solution left something
untouched—there is, in fact, a gas in air,
which the solution cannot touch, and this
gas is not oxygen, and yet is part of the
atmosphere. So that is one way of opening
out air into the two things of which it is
composed—oxygen, which burns our candles,
or anything else; and this other substance—nitrogen—which
will not burn them. This other part of the
air is by far the larger proportion, and it
is a very curious body, when we come to examine
it; it is remarkably curious, and yet you
say, perhaps, that it is very uninteresting.
It is uninteresting in some respects because
of this—that it shows no brilliant effects
of combustion. If I test it with a taper as
I do oxygen and hydrogen, it does not burn
like hydrogen, nor does it make the taper
burn like oxygen.
It has no smell; it is not
sour; it does not dissolve in water; it is
neither an acid nor an alkali; it is as indifferent
to all our organs as it is possible for a
thing to be.
And you might say, “It is nothing; it is
not worth chemical attention; what does it
do in the air?” Ah! then come our beautiful
and fine results shown us by an observant
philosophy. Suppose, in place of having nitrogen,
or nitrogen and oxygen, we had pure oxygen
as our atmosphere; what would become of us?
A piece of iron lit in a jar of oxygen, for
example, goes on burning to the end. When
you see a fire in an iron grate, imagine where
the grate would go to if the whole of the
atmosphere were oxygen. The grate would burn
up more powerfully than the coals—for the
iron of the grate itself is even more combustible
than the coals which we burn in it. A fire
put into the middle of a locomotive would
be a fire in a magazine of fuel, if the atmosphere
were oxygen. The nitrogen lowers it down and
makes it moderate and useful for us, and then,
with all that, it takes away with it the fumes
that you have seen produced from the candle,
disperses them throughout the whole of the
atmosphere, and carries them away to places
where they are wanted to perform a great and
glorious purpose of good to humankind, for
the sustenance of vegetation; and thus does
a most wonderful work, although you say, on
examining it, “Why, it is a perfectly indifferent
thing.” This nitrogen in its ordinary state
is an inactive element; no action short of
the most intense electric force, and then
in the most infinitely small degree, can cause
the nitrogen to combine directly with other
elements of the atmosphere, or with other
things round it; it is a perfectly indifferent,
and therefore to say, a safe substance.
But before I take you to that result, I must
tell you about the atmosphere itself. Here
is a composition of one hundred parts of atmospheric
air. It is a true analysis of the atmosphere,
so far as regards the quantity of oxygen and
the quantity of nitrogen present. By our analysis,
we find that five liters of the atmosphere
contain only one liter of oxygen, and four
liters of nitrogen by bulk. That is our analysis
of the atmosphere. It requires all that quantity
of nitrogen to reduce the oxygen down, so
as to be able to supply the candle properly
with fuel, so as to supply us with an atmosphere
which our lungs can healthily and safely breathe;
for it is just as important to make the oxygen
right for us to breathe, as it is to make
the atmosphere right for the burning of the
fire and the candle. First of all, let me
tell you the weight of these gases. Two liters
of nitrogen weighs roughly 2.29 grams. The
oxygen is heavier: two liters of it weigh
about 2.62 grams. Two liters of air weigh
about 2.37 grams. You might ask “How do
you weigh gases?” I will show you; it is
very simple, and easily done.
Here is a balance,
and here is a plastic bottle. This bottle
is balanced by the weight of the other bottle.
And here is a pump by which we can force the
air into the bottle, and with it we will force
in a certain number of volumes of air.
Now, see how it sinks: it is much heavier than
it was. By what? By the air that we have forced
into it by the pump. There is not a greater
volume of air, but there is the same volume
of heavier air, because we have forced in
air upon it. This bulk of air weighs about
two and a half grams. It is wonderful how
it accumulates when you come to larger volumes.
I have calculated the weight of air in this
room—you would hardly imagine it, but it
is above a ton. So rapidly do the weights
rise up, and so important is the presence
of the atmosphere, and of the oxygen and the
nitrogen in it, and the use it performs in
conveying things to and fro from place to
place, and carrying bad vapors to places where
they will do good instead of harm.
Having given you that little illustration with respect
to the weight of the air, let me show you
certain consequences of it.
When I put my finger on this tube and remove the air
look at what happens.
Why is my finger fastened to this tube, and why am I able to pull the hose about?
It is the weight of the air—the
weight of the air that is above. I have another
experiment here, which I think will explain
to you more about it.
When air is pumped from underneath the plastic
which is stretched over the funnel, you will
see the effect in another shape: the top is
quite flat at present, but I will make a very
little motion with the pump, and now look
at it—see how it has gone down, see how
it is bent in. You will see the plastic go
in more and more, until at last I expect it
will be driven in and broken by the force
of the atmosphere pressing upon it.
Now, that was done entirely by the weight of the air
pressing on it, and you can easily understand
how that is.
The particles that are piled
up in the atmosphere stand upon each other,
as these five cubes do. You can easily conceive
that four of these five cubes are resting
upon the bottom one, and if I take that away,
the others will all sink down. So it is with
the atmosphere: the air that is above is sustained
by the air that is beneath; and when the air
is pumped away from beneath them, the change
occurs which you saw when I placed my finger
on the air-pump, and which you saw in the
case of the plastic, and which you shall see
better in the next demonstration. It is a
little apparatus of two hollow plastic hemispheres,
closely fitted together, and having an outlet,
through which we can exhaust the air from
the inside; and although the two halves are
so easily taken apart, while the air is left
within, yet you will see, when we exhaust
it by-and-by, I will be unable to pull them apart.
Every square inch of surface that is
contained in the area of this vessel sustains
fifteen pounds by weight, or nearly so, when
the air is taken out.
Here is another very
pretty thing: a suction cup. If I clap it
upon the glass you can see at once it holds. I
can easily slip it about, and if I pull it
up, it pulls the glass plate with it. Only
when I lift the edge can I get it off. Why
does it hold? It is only kept down by the
pressure of the atmosphere above. I have a
second one and if I press them together, you’ll
see how firmly they stick. And, indeed, we
may use them as they are proposed to be used,
to stick against windows, or against walls,
where they will adhere for an evening, and
serve to hang anything on them that you want.
Next is an experiment that you can do at home;
it is a very pretty illustration of the pressure
of the atmosphere.
The popgun will confine
the air that is within the tube perfectly
and completely for our purpose. The confined
air will drive the front ball out with a force
something like that of gunpowder; for gunpowder
is in part dependent upon the same action
as this popgun.
I saw the other day an experiment
which pleased me much, as I thought it would
serve our purpose here. By the proper application
of air I expect to be able to drive this egg
out of one cup into the other by the force
of my breath; but if I fail, it is in a good
cause; and I do not promise success, because
I have been talking more than I ought to make
the experiment succeed.
You see that the air which I blew went
downward between the egg and the cup, and made a blast under the egg,
and is thus able to lift a heavy thing—for
a full egg is a very heavy thing for air to
lift. If you want to make the experiment,
you had better boil the egg quite hard first,
and then you may very safely try to blow it
from one cup to the other, with a little care.
I have now kept you long enough upon this
property of the weight of the air, but there
is another thing I should like to mention.
You saw the way in which, in the popgun, I
was able to drive the second yellow ball a
half or two-thirds of an inch before the first
ball started, by virtue of the elasticity
of the air—just as I pressed into the plastic
bottle the particles of air by means of a
pump; now, this depends upon a wonderful property
in the air, namely, its compressibility; and
I should like to give you a good demonstration of this.
If I take anything that confines
the air properly, as does this balloon, which
also is able to contract and expand so as
to give us a measure of the elasticity of
the air, and confine in the balloon a certain
portion of air; and then, if we take the atmosphere
off with this pump—just as in the cases
we put the pressure on—if we take the pressure
off, you will see how it will then go on expanding
and expanding, larger and larger, until it
will fill the whole of this jar.
We will now turn to another very important part of our
subject, remembering that we have examined
the candle in its burning, and have found
that it gives rise to various products. We
have the products, you know, of soot, of water,
and of something else which you have not yet
examined. We have collected the water, but
have allowed the other things to go into the
air. Let us now examine some of these other products.
Here is an experiment which I think
will help you in part in this way.
First, we put our candle under a chimney.
My candle will go on burning, because the air passage
is open at the bottom and the top. You see
the moisture appearing—that you already
know about. It is water produced from the
candle by the action of the air upon the hydrogen.
But, besides that, something is going out
at the top: it is not moisture—it is not
water—it is not condensible; and yet, after
all, it has very singular properties.
You will find that the gas coming out of the top
of our chimney is nearly sufficient to blow
the light out I am holding to it; and if I
put the light fairly opposed to the current . . .
. . . it will blow it quite out. You will say that
is as it should be because the nitrogen does
not support combustion, and ought to put the
match out, since the match will not burn in
nitrogen. But is there nothing else there
than nitrogen? I must now anticipate—that
is to say, I must use my own knowledge to
supply you with the means that we adopt for
the purpose of ascertaining these things,
and examining such gases as these.
If I hold an empty flask to this chimney, I shall capture the combustion of the candle below;
we shall soon find that this flask contains not merely
a gas that is bad as regards the combustion
of a taper put into it, but having other properties.
If I take some of this beautiful clear limewater,
and pour it into this flask, which has collected
the gas from the candle, you will see a change
come about.
You see that the water has become
quite milky. Observe, this will not happen
with air merely. Here is a flask filled with
air; and if I put a little limewater into
it, neither the oxygen nor the nitrogen, nor
anything else that is in that quantity of
air, will make any change in the limewater.
It remains perfectly clear, and no shaking
of that quantity of limewater with that quantity of air in its common state will cause any change.
This is chalk, consisting of the lime in the
limewater, combined with something that came
from the candle—that other product which
we are in search of, and which I want to tell
you about today. This is a substance made
visible to us by its action, which is not
the action of the limewater either upon the
oxygen or upon the nitrogen, nor upon the
water itself, but it is something new to us
from the candle. But we have a better means
of getting this substance, and in greater
quantity, so as to ascertain what its general
characteristics are.
We can produce this substance
in great abundance from a multitude of unexpected
sources. All limestones can produce a great
deal of this gas which issues from the candle,
and which we call carbon dioxide. All chalks,
all shells, all corals can also make a great
quantity of this curious gas. We can easily
evolve carbon dioxide from marble.
Here is a jar containing some hydrochloric acid,
and here is a taper which, if I put it into that
jar, will show only the presence of common air.
There is, you see, pure air down to the
bottom; the jar is full of it. Here is a substance—marble,
a very beautiful and superior marble—and
if I put that piece into the jar, a great
boiling apparently goes on.
That, however, is not steam—it is a gas that is rising up;
and if I now search the jar by a taper
I shall have exactly the same effect produced  upon the
taper as I had from the gas which issued from the end of the chimney over the burning candle.
It is exactly the same action,
and caused by the very same substance that
issued from the candle; and in this way we
can get carbon dioxide in great abundance—
we have already nearly filled the jar. We also
find that this gas is not merely contained
in marble. Here is some common chalk and in
this flask more hydrochloric acid.
It too evolves carbon dioxide,
exactly the same in its nature and properties as the gas we obtained
from the combustion of the candle in the atmosphere.
And no matter how different the methods—
from marble or chalk or candle—by which we prepare
this carbon dioxide, you will see, when we
get to the end of our subject, that it is
all exactly the same, whether prepared in
the one way or another. We will now proceed
to the next experiment with regard to carbon
dioxide. What is its nature?
Here is a vessel full of carbon dioxide, and
we will try it, as we have done so many other
gases, by combustion.
You see it is not combustible, nor does it support combustion.
Neither, as we know, does it dissolve much in water, because
we collect it over water very easily. Then,
you know that it has an effect, and becomes
white in contact with limewater; and when
it does become white in that way, it becomes
one of the constituents to make carbonate
of lime or limestone. It is a very weighty
gas—it is heavier than the atmosphere. I
have put their respective weights at the lower
part of this table, along with, for comparison,
the weights of the other gases we have been
examining. Two liters of this weighs about
3.6 grams. You can see by some experiments
that this is a heavy gas. I have a flask contain
dry ice that is subliming and thus pushing
out the air, replacing it with carbon dioxide.
I’ll pour a little of this carbon dioxide
into another flask filled with nothing but
air.
I wonder whether any has gone in or not.
I cannot tell by the appearance, but I can
in this way.
It extinguishes the flame;
if I were to examine it by limewater I would find it by that test also.
Next is an experiment
where I will show you its density. If I blow
soap bubbles, which of course are filled with
air, into this container filled with carbon
dioxide, they will float.
They are floating by virtue of the greater density of the carbon dioxide than of the air.
And now, having so
far given you the history of carbon dioxide—as
to its sources in the candle, as to its physical
properties and density—in the next lecture
I shall show you of what it is composed,
and where it gets its elements from.
