Bill: I’m Bill Hammack . . .
Don: . . . and I’m Don DeCoste.
Bill: . . . and we created this Lecture series
with Alex Black and this is a commentary track
designed to enrich and enhance the Lecture.
So let’s start with what Faraday is trying
to do in Lecture Number Three.
Don: So in this Lecture, we are going to be
looking at the main products of the combustion.
In this particular case water and it’s constituent
elements hydrogen and oxygen and we combined
a couple of Faraday’s lectures because one
of the things we wanted to do is take out
some of these redundant demonstrations that
he did.
Bill: There was also some dangerous demonstrations.
Don: Yeah, he did some producing of hydrogen
gas near open flame and things like that and
some of the demos too did not have a lot of
payoffs in terms of the overall narrative
of trying to actually figure out what is happening
when a candle is burning.
Bill: So, in his original Lecture Number Three
that was about water, his Lecture Four was about
hydrogen and they seem to go together because
he talked about hydrogen at length in his
Lecture Number Three on Water and so we re-arranged
a bit and we brought the water, hydrogen and
oxygen together for this lecture.
Don: So, Faraday’s audience had a little
bit less chemical knowledge than we have today
and so he would do a lot of things where he
would be hesitant to introduce a term like
carbon dioxide or hydrogen or oxygen until
he could kind of prove with very much support
that they were there. And so we arranged things because we brought things in a little bit earlier.
Bill: So the drop of water that you’re looking
at here is from the products of the candle
and what Faraday is about to introduce here
is really a big thing because he’s about
to discuss the chemistry of what is happening
in the candle. So let’s listen to Michael
Faraday as he introduces us to the technique
by which he determines that this is water.
Michael Faraday: A small piece of potassium
shows the presence of water by lighting up
and floating about burning with a violent
flame.
Bill: Now, what we see here is Faraday doing
elementary analytical chemistry. He develops
a test for water and what he does is, he shows
that if potassium is added to water, you get
a particular kind of phenomenon and that he’s
going to say that every time he adds potassium
to some unknown substance so it reacts like
this, it’s water.
Don: And of course, this isn’t logically
rigorous in the sense that it’s not sufficient
just because something reacts with potassium
similarly to the way water does, doesn’t
necessarily mean that that substance is water.
Bill: You might need to do more test but Faraday
would really think that this is victory because
what he has now, he has you asking questions
about this. You remember in the First Lecture
he said there were here to be scientists and
one thing about being a scientist is you’re
going to ask these questions.
Don: And we can see this throughout all of
the lectures. This is one of the big themes
of all the lectures and that is every scientific
answer can be potentially refined.
Bill: So now, let’s listen to Michael Faraday
as he introduces the next big idea from this lecture.
Michael Faraday: Water is one individual thing.
It never changes. We can add to it by careful
adjustment for a little while or we can take
it apart and get other things from it. But
water as water remains always the same either
in a solid, liquid or fluid state.
Bill: So, the big idea that Michael Faraday
just introduced with his phrase “water is
water” is the idea of a physical change
as contrasted to a chemical change. And in
this lecture he’s going to give us several
very dramatic examples of what water can do
when it just changes form. It can crush vessels,
it can explode and we might think of this
change to be like a chemical change, like
TNT or something. But really it’s just a
physical change.
Don: And it’s kind of interesting because
this is one of the first topics taught to
High School chemistry students, this idea
of physical versus chemistry and if you do
this with High School students you find out
it’s surprisingly difficult to understand
. . . or at least it seems surprisingly difficult
. . . but this is what Faraday is good at,
understanding what students have trouble with
and if you give it a little bit of thought,
we can see why it’s such a difficult topic.
Bill: Now let’s listen to Michael Faraday’s
words that highlight just how difficult this concept is.
Michael Faraday: “And although it changes
in condition, in form, and in many other qualities,
it’s still is water.”
Bill: So put yourselves in the mindset of
a first time chemistry student. Faraday has
just said that it changes in condition and
form and many other qualities but it’s still
water. And you know what does this mean?
Don: Yeah, how can something change so much
and still be water. And of course, we know
the answer now, is that water is water because
water, liquid water, and ice and steam all
consist of water molecules that if water is
going to be water, it consists of two hydrogen
atoms bonded to one oxygen atom and if we change that, then we’re actually changing the water.
Bill: So, one way that we introduce or differentiate
a physical change from a chemical change is
we often say a physical change is something
reversible as opposed to a chemical change
which is irreversible. Now this needs to be
nuanced greatly but it’s a way to approach
it at least at first physical versus chemical
changes.
Don: And this is another kind of big theme
in science, right? We have black and white
categories when we first introduced them like
physical versus chemical change or like solid
versus liquid versus gas or like polar bond
versus nonpolar bond. We know that there are
gray areas with all of these but we introduce
them as black and white.
Bill: Now what’s coming up is a very famous
demonstration. Chemistry teachers still do
this today they fill a soda can or pop can
with steam and then just turn it upside down
in an ice bath.
Don: And one thing Bill and I noticed in reading
these lectures again and trying to think about
how to film them is just how many of Faraday’s
demonstrations are still done today and I
don’t think it’s an exaggeration at all
to say that he’s kind of the Godfather of
the chemistry demonstrations because again
most of those are still used.
Bill: So let’s listen again to Michael Faraday
just because this little segment coming up
highlights why we kept this language. It’s
lyrical, almost poetic.
Michael Faraday: And so the vessel is obliged
to give way as it is crushed inwards. As in
the other case by the further application
of heat it would have been blown outwards.
Bill: And so that phrase “obliged to give
way” is just lovely. But we weren’t always
slavish about retaining everything that was
in the lectures. I mean you could see here
that we used animations which of course Faraday
would not have had.
Don: So, here of course is another classic
Faraday demonstration. It really shows his
great showmanship, it is very dramatic. While
its a classic demonstration we don’t often
see it because it’s so dangerous but everyone’s
really aware of the phenomena of what’s
going to happen.
Bill: Yeah, I think everyone knows it that
these things are going to burst apart. Now
when Faraday did this, he actually used ice
and water and we tried that at first and found
out that it took 30 minutes for it to happen.
So, we changed to dry ice and acetone which
is I think minus 78 degrees and makes it happen
very quickly, as you will see here. And this
is also coming up here: another great example
of why we kept Michael Faraday’s language.
Michael Faraday: No communication will take
place you will observe between the water in
the bottle and the ice in the outer bowl.
But there will be a conveyance of heat from
one to the other.
Bill: Now I want to look very carefully at
the enclosure that I have here. It was made
in our machine shop . . . that is I don’t
remember about three-quarters inch I think
or a half-inch thick plexiglass and when I
tossed that thing in I did run . . . . I ran
across the room . . . and I did say that was
faster than ice-water, and it is but you can
see the condensed a little bit, I think it
took 5 or 6 minutes.
Don: And we are not sure how Faraday did it.
We have seen this online before and people
have put this in wooden boxes but one of the
reasons we made this enclosure is so that
we can see views just like that. We actually
didn’t want to just hear the explosion,
we wanted to see what was going on.
Bill: And so actually when this thing, when
I lift this up, I want you to watch, because
it’s really stunning. Those are cast iron
vessels you can buy them just for this experiment,
that’s what we did and it truly is just
broken into little pieces.
Don: And Faraday notes that ice floats on
water and he links it to this phenomenon,
so he takes something that we already know
and helps us to learn something new.
Bill: So let’s listen to Michael Faraday
as he reiterates again the idea of a physical
change before he turns his attention to chemical changes.
Michael Faraday: To return to our quiet philosophy,
we shall not in the future be deceived therefore
by any changes that are produced in water.
Water is the same everywhere whether produced
from the ocean or from the flame of a candle.
Don: So Faraday had talked about physical
changes three times. So obviously they are
very important. And in this case, he is looking
knowing that water is coming from the candle.
So does that mean that water was in the candle?
Now if it was just a physical change it would
be, but it turns out it is a chemical change
that makes the water. Let’s listen to him.
Michael Faraday: It is neither in one nor
the other. But it comes from their combined
action, a part from the candle, a part from
the air.
Don: Now of course he hasn’t used these
terms yet. But the part from the candle is
hydrogen and the part from the air is oxygen.
Bill: In order to show that water is made
of hydrogen and oxygen, he’s going to use
electrolysis which is a chemical change to
extract both of them. So, let’s listen to
how he describes that process.
Michael Faraday: I’ll use electricity to
pull water to pieces.
Don: So notice he uses the phrase “to pull
the water to pieces” and at some level that
could imply a physical change. We are pulling,
to use modern terms, we are pulling the water
molecules away from each other. But Faraday
wants us to see that we are actually pulling
the water apart into its elements, hydrogen
and oxygen.
Bill: In fact, I think one of the most interesting
things here is how well he knows his audience.
So, his audience would think this was boiling.
He actually addresses that explicitly because
you’re applying a power source, you have
bubbles, it’s water. Wouldn’t that be
boiling? And in fact it’s hard not to believe
that’s boiling. And then he takes you through
a scientific method to understand that it
isn’t boiling. He points out that what comes
out is not condensable, so it’s not steam.
And also that it will ignite and steam doesn’t
ignite. So this must be hydrogen or oxygen.
Bill: Now, next Faraday makes a very important point about hydrogen.
Michael Faraday: We may obtain this substance
equally from water produced from the candle
flame as from any other source.
Bill: So this is a statement similar to his
statement “water is water” and what he’s
doing is pointing out the universality of
science; that it gives a uniform description,
so there is a thing called hydrogen and no
matter how we make it, it is going to be the same thing.
Don: So, now that Faraday knows that this
is hydrogen, he decides to test it and he
looks at its properties. He actually looks
at its density and then how it reacts with
the flame. It’s interesting he does a few
things here. One, he makes, the invisible
visible because we can’t see that there’s
anything in either of those vials and he shows
one is air and one is hydrogen. The other
thing . . . he does is a control here. He
makes sure that he reacts the air or tries
to react the air with the flame and then he
shows us that the hydrogen actually is different.
Bill: Now, Faraday knew that substances differ
in the number of atoms of each element that
are present. But as P.W. Atkins, a physical
chemist, pointed out Faraday had little conception
of the patterns in which the atoms are linked together to form the molecular structure of
a compound. Listen to him here.
Michael Faraday: This is what we get from
water. The same substance which is
contained in the candle.
Don: So there are a couple of interesting
points here. One, first of all, is about conservation,
that is conservation of atoms. We have hydrogen
that’s in the candle, the candle burns and
gives water as one of the products and we
can then take water apart to get the hydrogen
back and so hydrogen is not destroyed then,
the atoms are not destroyed. However, Faraday
uses the term “same substance.” So he says what we have here— the hydrogen gas — is the
same substance that’s in the candle and
so, as Bill mentioned before this clip, Faraday
wasn’t thinking about the molecular structure: we know that hydrogen gas is really not in the candle.
Bill: And I think it is worth noting is that
we added that graphic just a few seconds ago
of the water and the hydrogen and oxygen atoms.
That’s something that Faraday would not
have had in his lectures and he would not
have thought about molecules in that way.
Don: Now as we mentioned Faraday’s already
talked about density once he figured out that
this was hydrogen he looked at the properties
and one of these were density. But he goes
back to this and he does this for a couple
of reasons. One, of course, as we mentioned
before, he’s a good showman and so it’s
very visual for him to blow bubbles, something
very familiar to everyone. But then when he
blows the bubbles with hydrogen, we see them
fold up in a very dramatic fashion. But he
also talks then about then the utility of hydrogen.
So the fact that it’s less dense than air
allows it to be used for example in hydrogen
balloons which were used at that time. Now
this is something that Faraday has done a
lot though. He finds a substance, he gets
a good amount of that substance and then he
plays with it and tests it and shows us its
properties.
Bill: Now, here he just . . . he introduces
oxygen just saying that there’s oxygen in
water and you might say well he hasn’t proved
to us that there’s oxygen in water and I
think that he hasn’t but I think he would
say, you know, that’s good for you to ask
a question and maybe ask you to come up with
a way to prove it or help you to prove it.
So what he’s doing though, he’s preparing
to discuss oxygen in the next lecture and
he tells us that a candle needs oxygen to
burn, reminds us that a candle burns in air
which contains oxygen and then he shows us
the burning of a candle in pure oxygen and
at that point it burns brighter as we’ll
see here. He implies that whatever else is
in the air, it does not aid combustion, and
he’ll return to that in Lecture Four. For
now, though, he’s going to point out that
oxygen is necessary for all types of combustion.
Michael Faraday: But it does not affect merely
the combustion of hydrogen or carbon or the
candle but it exalts all combustions of the
common kind.
Bill: So that’s another statement about
how science gives a unified view of nature
that every kind of combustion is, in Faraday’s
thinking, is going to involve oxygen. Now
he’s going to return to combustion and to
oxygen in Lecture Four that follows in detail
and introduce the role of nitrogen there.
Don: So now we’re reaching the close of
the lecture and listen to how he’s going
to start that. But what he’s going to do
here is, remember at the beginning of the
lecture, he reacted potassium with water and
he did that to show us that the stuff coming
off of the candle was also water. But remember
the first lecture he said we come here to
be scientists, we must ask why and so now
he’s going to ask why is it that the potassium
reacts with the water? And in explaining this,
he’s going to do a couple of things. One,
he’s actually going to essentially review
the entire lecture and go over everything
that we’ve learned of this. But then he’s
also going to show us again that “water is water."
Michael Faraday: Why does a piece of potassium
decompose water? Because it finds oxygen in
the water. What is set free when I put it
in the water? It sets free hydrogen and the
hydrogen burns. But the potassium itself combines
with oxygen and this piece of potassium in
taking the water apart, the water you may
say derived from the combustion of the candle
takes away the oxygen which the candle took
from the air and so sets the hydrogen free.
Bill: And what he’s showing is the potassium
reacts violently because it finds oxygen in
the water and it sets free the hydrogen. And
note how this captures in many ways everything
in this lecture. First, hydrogen we’ve seen
is explosive and so that’s why this is so
violent. And second, he retraces the complete
process of the candle. The candle takes oxygen
from the air to make water and the potassium
in analogy here takes oxygen from water. And
he’s reminding us about elements or continuity.
He notes again and again that “water is
water” and so it nice that he uses ice instead
of liquid water which he used at the beginning
and then again that’s reminded that the
“water is water” — It doesn’t matter
what he uses.
Don: And so Faraday ends here again hoping
that we were thinking about the question in
that question is, well if oxygen is so “dangerous”,
if it’s going to cause all this combustion
then why aren’t we in trouble with all this
oxygen around us? And that’s where he’s
going to talk about nitrogen in the next lecture.
Bill: So, that’s the end of our commentary
for Lecture Number Three. I’m Bill Hammack.
Don: And I’m Don DeCoste.
Bill: Thanks for listening.
