Bill: I’m Bill Hammack.
Don: and I’m Don DeCoste.
Bill: . . . and this is a commentary version
of Lecture Five of Michael Faraday’s The
Chemical History of a Candle. We created this
series with Alex Black, a chemistry undergraduate
at the University of Illinois. So this commentary
is designed to enhance and enrich the lecture.
So in this lecture, Faraday really drives
home his point that science gives us a unified
description of the world. So a naïve person
would see multiplicity or many different things
and Faraday in his scientific view sees unity,
and that’s illustrated very deeply in this
lecture by the connection between the burning
of a candle and human respiration. And so,
this is the capstone to all the lectures.
Recall that when he started his first lecture,
he claimed I will teach you all you need to
know about science from a candle, and I’d
say he does pretty well.
Don: Yeah. What he’s doing at the beginning
here, he’s kind of reminding us of what’s
going on especially here he is telling us
about the water that came from the candle.
He tells us about the carbon dioxide as well.
And since we could take apart water, he then
says well can we take apart the carbon dioxide
and figure out what it’s nature is. So that’s
one of the things that we’re going to do.
Notice he doesn’t really talk about atoms.
He talks more about real things, the carbon
and oxygen gases. It might be a little different
if we did that today.
Bill: So it might seem like he’s going through
a whole bunch of convolutions coming up to
show us that carbon dioxide contains carbon
and oxygen, but we did change the language
in his lecture. At the time, he would have
called carbon dioxide “carbonic acid.”
Don: Now this is an interesting demonstration
that he’s going to show us. He did something
similar to this before when he made a big
flame with cotton balls and showed us the
black smoke. Now he’s going to say that
--- you know, we should see that as well.
We’re going to see these carbon particles
in the flame of the candle. We can see here
the black smoke. Why don’t we see this in
a candle? Because as he said, there was a
different ratio of oxygen. In this case, the
flame is too big, but when he places this
in pure oxygen, we see that the black smoke
goes away. So this is an analogy then to a
candle. We can see this flame here; we don’t see the black smoke because we have plenty of oxygen.
This is another example of where
he does not anticipate. He actually shows
us before he tells us, which is really good.
He does this one as a reminder because we’re
going to need this idea later in the lecture,
but it’s also really great because he shows
us this in a different way. Before he showed
us the black smoke, but he didn’t add the
extra oxygen, and by doing so here, we get
the point in a different way.
Bill: So now let’s let Michael Faraday explain
what he’s going to do with carbon dioxide.
Faraday: Being a compound body consisting
of carbon and oxygen, carbon dioxide is a
body that we ought to be able to take asunder
and so we can. As we did with water, so we
can with carbon dioxide, take the two parts
asunder. The simplest and quickest way is
to act upon the carbon dioxide by a substance
that can attract the oxygen from it and leave
the carbon behind. You recollect that I took
potassium and put it upon water or ice, and
you saw that it could take the oxygen from
the hydrogen. Now suppose we do something
of the same kind here with this carbon dioxide.
Bill: So this is another example of why we
kept the language. I mean I really like the
word ‘asunder’. He’s used it a couple
of times. He used it twice before I believe.
Once with the ice bomb and once when he originally
took water apart, but what’s really the
big point here.
Don: Yeah, I think the big point here is the
analogical thinking that he’s using. He
reminds us that he used potassium to remove
oxygen from water. And he’s going to do
the same thing here. He’s going to use the
magnesium to remove the oxygen from the carbon
dioxide. And there is kind of a subtle point
here that I don’t think he makes directly,
but there is a unity here again. There is
a common set of principles that guide all
chemical reactions. So if we could take a
metal and remove oxygen from one compound,
maybe we can take a different metal and remove
oxygen from a different compound.
Bill: Now I recall doing this. You’ll see
here in just a second that I really jumped
back because you heat up the magnesium quite
a bit and then the whole thing fumes or reacts
for, I dunno, two-three minutes, five minutes.
Don: Yeah, it takes several minutes especially
when we put the top on. We now have surrounded
the burning magnesium with carbon dioxide,
and of course giving it a lot of oxygen to
react with.
Bill: I know . . . you see me moving backwards.
I’m never quite sure . . . I move a little
further here.
Don: It’s very, very bright.
Bill: Yeah. If I remember right, we’re going
to see the part where we kind of condensed
the time . . . So, what is the chemistry that’s
going on here?
Don: So, in this case, it’s like Faraday
says, what’s going on is that magnesium
needs oxygen to burn. And it finds the oxygen
from the carbon dioxide. So it’s removing
the oxygen from the carbon dioxide. It’s
actually then going to give us some products
here that we’re going to see in a minute.
We’re going to actually see the magnesium
oxide with the magnesium reacting with the
oxygen and we’ll see some carbon as well.
Bill: So probably useful — at this point
— just to remind people that dry ice of
course is pure CO2. Now when I lift the lid
off, then we see the – there is the magnesium
oxide.
Don: That’s the white powder . . .
Bill: Yep.
Don: . . .and the carbon.
Bill: So next Faraday gives us a truth about
how carbon burns. And then he’s going to
use that truth in order to make an observation
in the next section of the lecture.
Faraday: And now I may tell you that whenever
carbon burns, under common circumstances it
produces carbon dioxide.
Bill: So now he is going to show us exactly
that, that carbon dioxide is produced when
burning carbon. Kind of interesting to me
is that he uses wood. He has used candles
and other things in the past, but he’s making
that statement that any time carbon burns,
whatever form it is, it’s going to produce
CO2. This is also nice because it has a little
bit of a . . . it illustrates a control in
the experiment, he takes just a pure piece
of wood unburned, shakes it up in his limewater
solution, which we know turns cloudy when
you have CO2, shows nothing happens. And now
he takes the piece of wood, and he’s going
to capture the emissions from that -- the
gas that comes off, which we know now is CO2
— but he’s going to prove it to us by
having the solution turn cloudy.
Don: It was nice at the beginning of the lecture
he kind of reminded us of the limewater again.
So it wasn’t something he expected us to
remember from a previous lecture without telling
us something about that.
Bill: It’s kind of interesting. He also
uses this in a way to prove that there is
carbon in wood, right.
Don: Yes. I mean that’s something that is
not necessarily obvious. He actually shows
us this in a little bit with the burnt piece
of wood showing us that because it’s incomplete
combustion, it doesn’t turn the wood completely
into carbon dioxide, but there is some carbon
leftovers as we can see here.
Bill: And then what’s really nice is that
he brings this observation back to the candle
and the Bunsen burner. In fact, you might
as why don’t I see carbon in there. Remember
that he has said that if I get enough oxygen
that I’m not going to get any carbon. It’s
going to be complete combustion and all go
to CO2, which he showed us with the sponge
when he gave it enough oxygen.
Now Faraday next makes a very important point about carbon,
and that is that it burns to a gas. As we’ll
see later on in the lectures, this is absolutely
critical for respiration.
Faraday: I have shown you that the carbon
in burning burns only as a solid body. Yet,
you perceive that after it burns, it ceases to be a solid
Don: It’s critical because of the analogy
between combustion and respiration. We need
to be able to get rid of the waste, the carbon
dioxide, which is a gas. We need it to be
able to move around the atmosphere. As we’ll
see get to the plants which need the carbon
dioxide to survive.
Bill: So let’s now return to Michael Faraday,
because he’s now going to bring everything
together that the lectures have been aimed
toward, which is the analogy between the burning
of a candle and human respiration.
Faraday: Now I must take you to a very interesting
part of our subject to the relation between
the combustion of a candle and that living
kind of combustion, which goes on within us.
In every one of us, there is a living process
of combustion going on very similar to that
of a candle. And I must try to make that plain
to you. For it is not merely true in a poetical
sense, the relation of the life of humans
to a candle. And if you follow, I think I
can make this clear.
Bill: So over the course of the next five
minutes, Faraday is going to bring together
everything that we’ve seen previously in
the lectures — not everything, but a lot
of it — and demonstrate to you that what
is coming out of our bodies when we exhale is CO2.
And so he wants you to recall right now
that a candle can’t burn in CO2. So he’s
going to exhale into this pipe, cover the
candle with whatever comes out of our lungs
— we know it’s CO2 — and show that it
can’t burn anymore. Now, it’s important
to note that he’s not blowing out the candle,
I guess we call it mechanically . . . .
Don: Yeah, he showed us that earlier when
we had the products of the candle putting
off the flame. This is what he’s reminding us of.
Bill: Yes, here it is from lecture four. So
this didn’t blow it out in the conventional
sense, but it blowed it out by --- it smothered
the combustion by surrounding it with CO2.
Don: Which he kind of showed by putting his
thumb over that as well. If CO2 is a product
of the candle, the CO2 will fill that vessel
and then smother the candle, the flame.
Bill: This is actually a stunning set of experiments
and I think unexpected from where he starts
with the candle. I guess let’s watch him
exhale here and see what happens.
Don: We can see when we do this, there is
a close-up of the flame, so that you can see
that the flame is in little bit of motion
obviously because of the exhaled air or the
carbon dioxide, but it’s not getting blown
out.
Bill: It’s useful to note that he covered
up the top part to be sure that CO2 will build
up inside. Otherwise, air could re-enter and
keep the candle burning. What he needs to
do is displace the air.
Don: It’s interesting again to see how he
does this. What he doesn’t do is say I exhale
carbon dioxide. He actually starts with an
observation. He leads us really logically
through this. He knows that a flame will go
out if there is not a fresh supply of oxygen.
It will go out with the products of a burning
candle. I know that the products of a burning
candle. One of them is carbon dioxide, and
I know that flame goes out with my breath.
So what could we conclude. Well, it might
be that our breath has carbon dioxide in it,
but we can look at this with other tests and
here is one of them.
Bill: Now Faraday did use the phrase again
of bad air, which in lecture four I think
it was . . . .
Don: Yes.
Bill: . . . we chastised him a little bit
for. But I think it’s useful to note that
neither Don nor I — who are trained scientists,
engineers — didn’t notice that until we
were reviewing the lectures. So I suspect
that we heard what we wanted, and I kind of
suspect Michael Faraday heard what he wanted.
Don: Yeah, it would be really clunky if he
said things like I exhaled the products of
my combustion as opposed to bad air, so he
used that type of language.
Bill: He used some of the colloquial language
I think to help people to understand. I mean
sometimes precision obscures rather than helps.
So this apparatus, now it’s a little hard
to understand but the key point to note here
is that the pipe on the left in this drawing
doesn’t touch the water, the other pipe
does touch it. So he’s able to draw in air
as he just did and then flip it around or
he flips it around, so it’s long end is
now in the water. That way the gases that
I’m exhaling here or that Faraday exhales will
bubble through the limewater. If you watch
what happens, it takes a little while here.
It turns cloudy, and then we know that it
has CO2.
Don: Notice he did this again kind of as a
way of a control but also to show that there
is something going on in their breathing by
inhaling the air from the outside first and
showing that nothing went on. He can show
that it must be what he calls the bad air
or our exhaled air, the carbon dioxide.
Bill: It’s interesting that that highlights
that there is a change. We breathe in air
and we breathe out something. Naively and
not unreasonably we would think that would
be air also. He’s showing here that a chemical
reaction has happened.
Don: At this point, Faraday used an interesting
phrase. He said that the atmosphere is "spoiled"
by us breathing; kind of like saying bad air.
He doesn’t really explain what this means
yet. He will later and we’ll see that it’s
spoiled for us but not for the plants.
Bill: So now what comes up next is really
a key section of all five lectures. It’s
his big unity of science moment. He shows
us the analogy really deeper than that between
respiration and the candle.
Faraday: We consume food. The food goes through
that strange set of vessels and organs within
us and is brought into various parts of the
body into the digestive parts especially.
The air that we inhale is drawn into the lungs,
absorbed into the bloodstream and transported
throughout the body so that the oxygen and
the food come close together. In the body,
a curious wonderful change takes place. The
oxygen combines with the carbon. Not carbon
in a free state but as in this case placed
ready for action at the moment and makes carbon
dioxide, and is so thrown out into the atmosphere
and thus the singular result takes place.
The oxygen can thus act upon the food producing
precisely the same results in kind as we have
seen in the case of the candle. The candle
combines with parts of the air forming carbon
dioxide and evolves heat. We may thus look
upon the food as fuel.
Don: So a great point Faraday just made here
is that we as humans rely on chemical reactions
to survive, and that’s something that’s
not really an obvious point. These chemical
reactions of course he’s discussed at length
and he’s differentiated from physical changes.
He also then as Bill mentioned earlier, he’s
making a nice analogy here between our respiration
and then the combustion of a candle. It’s
a very nice simple analogy of — we’re
taking in fuel and he uses food as a fuel.
Of course, the fuel of a candle is it’s wax.
Bill: So what’s coming up then next is a
really stunning and vivid demonstration of
how sugar is like the fuel of a candle. Well,
almost at least. He’s going to show in a
moment that respiration produces CO2, but
for now what he wants to do is just show that
sugar contains carbon, which we know is necessary
for fuel. He’s made that point earlier.
In fact, we know from his many demonstrations
and comments so far that carbon is produced
when a candle is burned — it goes off as
CO2 — although, recall with a piece of wood,
we also made carbon in that way. Here what
we see - what we’re going to see clearly
here is that carbon is produced when sugar
is — and I’ll put it in quotes here — “burned.”
Although, it’s a chemical reaction happening
here, not really strictly combustion.
Don: Yeah. We can see here, we have some time
left, what’s going on. It takes a few minutes,
but what’s happening here is that the sulfuric
acid removes the oxygen and the hydrogen from
the sugar and it leaves only carbon. Now the
analogy here is really deep. To bring these
two processes together calls for a sophisticated
theory of chemical reactions. So his discussion
is part analogy that humans and candles make
carbon as a byproduct and this produces heat,
but it’s part exact as well once we have
a theory of chemical reactions. It’s not
merely an analogy, although you have to dig
really deeply into the chemistry to see how
the combustion of the candle and the reaction
of the sugar and the sulfuric acid are deeply
related.
So what’s coming up next is Faraday
is going to remind us of when he added the
potassium to water. His point here is that
a candle doesn’t always burn even though
we know that it will burn if we start the
wick on fire. Just being in contact, the wick
in contact with the air won’t have it burn,
but if potassium is in contact with water,
it happens right away. He mentioned a phrase
earlier: “these reactions are different
in form but not in kind.” So he’s again
bringing this unity to chemistry, to chemical
reactions. He told us early in the lectures
that there is no better window into science
than studying the candle. Notice what he’s
doing now. He’s kind of getting into kinetics.
Something that wouldn’t be obvious in studying
a candle. As he mentioned, potassium reacts
at once if it’s with water, but carbon in
a candle can wait as he said days, months,
weeks, years before it reacts.
Bill: So I think it’s worth noting that
when we showed sugar, we showed the formula
of sucrose, which is how table sugar and other
sugars are. Although there is lots of other
kinds –- glucose, fructose and other kinds
of sugars. They all do about the same thing.
I think another point to make is Faraday reorganized
the chemical formula for sugar to show these
waters. You shouldn’t view the waters tucked
around the carbon. It’s actually just carbon,
oxygen, hydrogen all bonded together, but
it’s a useful fiction though. In fact, we
often call sugar “carbohydrates” because
of this way to represent them. In fact, in
biochemistry, the reaction of sugar with sulfuric
acid is often called a dehydration reaction.
Don: And so here Faraday does another wonderful
demonstration; one that we still do. This
cotton here is actually gun cotton. He has
gunpowder next to it. Again, what he’s going
to do with these is kind of show the difference
between a reaction that happens right away
and a reaction that doesn’t. In both of
these cases, they are stable enough to not
just react with the air, but by applying a
little bit of activation energy. So he gets
into this idea of an activation barrier. The
gun cotton has a smaller activation barrier.
We can see he is just heating up the glass
rod, touches it, there it goes. When he does
the same thing with the gunpowder, it’s
not reacting even though he’s using the
same amount of heat in both cases. Now this
is a little bit surprising because gunpowder
we know is not stable. This is why we use
it in guns, but there is a stability to it.
There is a kinetic stability. It has a higher
activation barrier than the gun cotton does.
So again Faraday talks about this idea that
there is no better window into science. Here
he’s getting into a pretty deep discussion
of kinetics versus thermodynamics.
Bill: Gun cotton is something that’s not
probably familiar with us today. It’s nitrocellulose.
It’s what they make flash paper out of that
magicians use. It was also used for a film
base or film stock in the first part of the
20th century. But of course, the films were
very flammable. It’s very dangerous. In
the 1930s, they changed to a nitrate based
film that was much less flammable. In these
final sections, Faraday turns his attention
to carbon dioxide that's emitted by humans, and
as we’ll see as well other mammals. He makes these
points very clearly. First of all, he notes
that respiration in mammals will happen at
any temperature as long as it’s above freezing.
He also then looks at how it scales with different
kinds of animals. He also does this very vividly.
Maybe it’s useful to point out here the
things that Faraday doesn’t discuss that
were really not part of his 19th century science.
He doesn’t really go into why reactions
occur. That took a detailed atomic level understanding
of the second law of thermodynamics; something
that came across with Boltzmann. Faraday doesn’t
talk about what initiates a chemical reaction.
We talked a little bit about activation barriers
there. He alluded to it, but again that’s
a detailed atomic level description to really
understand that. Of course, he didn’t discuss
how reactions occur, how molecules come apart
and how they go back together. So he didn’t
understand the steps or the mechanisms by
which they happen.
Don: So at this point, Faraday is now going
to link us as humans with what he calls our
fellow creatures or our fellow existers. He’s
already made the point, and we’ve mentioned
it a lot, this unity idea, this analogy that
we are essentially like a candle. We take
in fuel. We give off carbon dioxide. He’s
used the phrase “spoiled air” or exhaled
air, and that we can’t breathe the same
air twice over. But that’s because the plants
take in the carbon dioxide. That the air is
spoiled for us, but as he says, what’s disease
to the one is health to the other. So while
we spoil the air for us, the plants need that
“spoiled air,” and then they spoil the
air for themselves by giving off oxygen which
we then of course need.
Bill: I recall when recording this last section
that as I was saying the words that it felt
very much like a sermon. He has a lot of words
in here like “live” and “rejoice,”
if I recall right. Indeed, Faraday was a very
religious man. It may be that his religious
beliefs were coming through in a language
that he chose to use to sum up the lectures.
So here at the end of the lecture, let’s
give Michael Faraday the last word.
Don: One of the reasons we kept his original language as much as we could is just how poetic he is.
Bill: So let’s listen to how beautifully Michael
Faraday sums up everything we’ve learned
in these lectures.
Faraday: Indeed, all I can say to you at the
end of these lectures, for we must come to
an end at one time or other, is to express
a wish that you may in your generation be
fit to compare to a candle, that you may,
like it, shine as lights to those about you,
that in all your actions, you may justify
the beauty of the taper by making your deeds
honorable and effectual in the discharge of
your duty to humankind.
Bill: So too, these commentaries must come
to an end. Thanks for listening. I’m Bill Hammack . . .
Don: . . . and I’m Don DeCoste.
