 I'm Bill Hammack. And I'm Don D'Cost. 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. And 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 naive person would see multiplicity or many different things. And Faraday and his scientific view see 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. And recall that 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. Yeah. And what he's doing at the beginning here, he's kind of reminding us of what's going on, especially, you know, here he's 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 its nature is? And 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. And it might be a little different if he did that today. So it might seem like he's doing 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. 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. And 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. And 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. When he places this in pure oxygen, we see that the black smoke goes away. And 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. And 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. So now let's let Michael Faraday explain what he's going to do with carbon dioxide. 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. So this is another example of why we kept the language. I really like that word asunder. He's used it a couple of times. He's used it twice before, I believe, once with the ice bomb and once when he originally took water apart. But what's the really big point here? I think a 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's kind of a subtle point here that I don't think he makes directly. But there's a unity here. Again, there's 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. You know, I recall doing this. You'll see here in just a second that I really jump back because you heat up the magnesium quite a bit and then the whole thing fumes or reacts for, I don't know, two, three minutes, five minutes? Yeah, it takes several minutes. And especially when we put the top on, we now have surrounded the burning magnesium with carbon dioxide. And of course, given it a lot of oxygen to react with. And there you see me moving backwards. I'm never quite sure. I'm a little further here, right? It's very, very bright. Yeah. And 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? 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. And 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. So probably useful to just remind people that dry acid, of course, is just pure CO2. And now when I lift the lid off, then we see there's the magnesium oxide. There's the white powder. Yep. And the carbon. 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. And now I may tell you that whenever carbon burns under common circumstances, it produces carbon dioxide. So now he's going to show us exactly that the carbon dioxide is produced when burning carbon. And kind of interesting to me here is that he uses wood. He's used candles and other things in the past, but he's making that statement at any time, carbon burns or whatever form it is, it's going to produce CO2. And this is also nice because it has a little bit of, it illustrates a control and experiment. He takes just a pure piece of wood, unburned, shakes it up in his lime water 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 it, which of course we know now is CO2, but he's going to prove that to us by having the solution turn cloudy. And it was nice at the beginning of the lecture. He kind of reminded us of the lime water again. So it wasn't something he expected us to remember from our previous lecture without telling us something about that. It's kind of interesting here as he also uses this in a way to prove that there is carbon in wood, right? Yes, yeah. I mean, that's something that is not necessarily obvious and he actually shows us this then 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's some carbon left over as we can see here. And then what's very nice is that he brings this observation back to the candle in the Bunsen burner. In fact, you might ask, why don't I see carbon in there? And remember that he has said that if I get enough oxygen, then I'm not going to get any carbon. And it's going to be complete combustion and all go to CO2, which he showed us with a sponge when he gave it enough oxygen. Now, Faraday next makes a very important point about carbon and as that is that it burns to a gas. And as we'll see later in the lectures, this is absolutely critical for respiration. I have shown you that the carbon in burning burns only as a solid body and yet you'll perceive that after it is burned, it ceases to be a solid. And 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, and we need it to be able to move around the atmosphere and as we'll see, get to the plants, which need the carbon dioxide to survive. 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. 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's 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. So over the course of the next five minutes, Faraday is going to bring together everything that we've seen previously in the lectures or not everything, 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. I mean, 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. Yeah, and he showed us that earlier when he had the products of the candle putting out the flame. And this is what he's reminded us about. Oh, yeah, here it is from lecture four. So this didn't blow it out in a conventional sense, but it blowed out by it smothered the combustion by surrounding it with CO2. 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. So 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, see what happens. And we can see when we do this, there's a close-up of the flame so that you can see that the flame isn't, you know, a little bit of motion obviously because of the exhaled air or the carbon dioxide. But it's not getting blown out. And it's useful to note that he covers up the top partly to be sure the CO2 will build up inside. Otherwise air could re-enter and keep the candle burning. And what he needs to do is displace the air. And it's interesting again to see how he does this. What he doesn't do is to say, I exhale carbon dioxide. He actually starts with an observation. And he reads us really logically through this. He knows that a flame will go out if there's not a fresh supply of oxygen. It'll go out with the products of a burning candle. I know the products of a burning candle, one of them is carbon dioxide and I know the 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's one of them. Now Faraday did use the phrase again of bad air which in lecture four I think it was. Yes. We chastised him a little bit for. But I think it's useful to note that neither Don nor I or trained scientist, 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. Yeah, it would be really clunky. You know, if he said things like, I exhale the products of my combustion as opposed to bad air. And so he used that type of language. He used a little bit of colloquial language, I think, to help people to understand. I mean, there's sometimes precision obscures within help. So this apparatus now is a little hard to understand but to keep the point, 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 that the long end is now in the water and that way that the gases that I'm exhaling here, the Faraday exhales will bubble through the lime water. And if you watch what happens, it takes a little while here, it turns cloudy and then we know that it has CO2. And notice, he did this again kind of as a way of 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 that what he's calling the bad air or our exhaled air, the carbon dioxide. Yeah, and it's interesting that that highlights that there's a change, that we breathe in air and we breathe out something and naively and not unreasonably we would think that would be air also and so he's showing here that a chemical reaction has happened. 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. So now, what comes up next is really a key section of all five lectures and it's his big unity of science moment. He shows us the analogy really deeper than that between respiration and the candle. We consume food, the food goes through that strange set of vessels and organs within us and it's 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 bodies of 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 is 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. So a great point that 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. And 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. And it's a very nice, simple analogy of we're taking in fuel and he uses food as a fuel and of course the fuel of a candle is its wax. 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 the respiration produces CO2 but for now what he wants to do is just show that sugar contains carbon which we know is necessary for a 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 we call with a piece of wood, we also made carbon in that way. And here what we see, 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. Yeah and we can see here we have some time lapse 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. And 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. And 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 and he told us early in the lectures that there's no better window into science than studying the candle. And notice what he's doing now. He's kind of getting into kinetic 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. So I think it's worth noting that when we showed sugar we showed the formula for sucrose which is how table sugar and other sugars are. There's lots of their kinds, glucose and fructose and other kinds of sugars. But 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 and 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. And so here Faraday does another wonderful demonstration one that we still do and this cotton here is actually gun cotton and he has gun powder next to it. And 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. And in both of these cases they're 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 and we can see he's just heating up the glass rod, touches it, there it goes. When he does the same thing with the gun powder 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 gun powder we know is not stable. This is why we use it in guns. But there is a stability to it. There's a kinetic stability. It has a higher activation barrier than the gun cotton does. So again, Faraday talks about this idea of there's no better window into science and here he's getting into a pretty deep discussion of kinetics versus thermodynamics. And gun cotton is something that's probably familiar with us today. It's nitrocellulose. It's what they make flash paper out of that magicians use. And 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 and 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. And he makes his points very clearly. First of all, he notes that respiration in mammals will happen at any temperature as long as it's above freezing. And he also then, you know, looks at how it scales with different kinds of animals and he all does this very vividly. Maybe it's useful to point out here the things that Faraday doesn't discuss and 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 and he alluded to it. But again, that's a detailed kind of atomic level description to really understand that. And of course he didn't discuss how reactions occur, how molecules come apart and how they go back together. And so he didn't understand, you know, the steps or the mechanisms by which they happen. 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 a lot this unity idea, this analogy that we are essentially like a candle. We take in fuel, we give off carbon dioxide and he's used the phrase spoiled air, exhale there and that we can't breathe the same air twice over. But that's because the plants take in the carbon dioxide. The air is spoiled for us but as he says, what's diseased to the one is health to the other. So while we spoil the air for us, the plants need that quote unquote spoiled air and then they spoil the air for themselves by giving off oxygen, which we then of course need. And I recall when recording this last section that as I was saying the words that it felt very much like a sermon and he has a lot of words in here like live and rejoice if I recall, right? And indeed Faraday was a very religious man and it may be that his religious beliefs were coming through in the 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. And one of the reasons we kept his original language as much as we could is just how poetic he is. So let's listen to how beautifully Michael Faraday just sums up everything we've learned in these lectures. Indeed, all I can say to you at the end of these lectures where 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. And so too these commentaries must come to an end. Thanks for listening. I'm Bill Hammack and I'm down to cost.