 I'm Bill Hammack. And I'm Don DeCost. And we created this lecture series, Michael Faraday's The Chemical History of a Candle. And this is a commentary track to just kind of deepen or enrich the lectures. And I would suggest that if possible, you have the subtitles for the lectures turned on. In the first lecture, Faraday gave us an overview of how a candle works. Now let's listen to Faraday's words about the subject of lecture two. Faraday happens in any particular part of the flame, why it happens, what it does in happening, and where, after all, the whole candle goes to. Throughout this lecture, Michael Faraday focuses on the properties of the flame of a burning candle using those properties to understand how a candle works. Now what's interesting is the number of tools he creates to probe the flame. We normally think of sophisticated scientific instruments like microscopes or spectroscopes or balances. But Faraday's simple tools are just as specialized. And of course that's part of science to invent or create tools that let us see the invisible or to quantify nature. You know, and this is one of the things that makes chemistry a difficult subject, especially when you're first studying it. And that is many of the properties are invisible. Now you see here that he's using a specially shaped glass tube to capture what he calls the wax of the candle made into a vaporous fluid. At this point Faraday makes a distinction between a gas and a vapor, noting that a gas is permanent and a vapor can be condensed at least at the pressure and temperature of interest. But the larger issue is that he points out that science makes use of precise terminology. Now that said, we're going to take Faraday to task in a few minutes for some imprecise usage of the word air, but more on that in a moment. You know, there's a couple of different ways to see things. As Bill mentioned, you make tools to do this. You can also take things out of context. And what Faraday is going to do next is he's going to take a large sample of wax and heat it, not burning it like a candle, but heating it in a flask. And this is something deep here. He's going to make an assumption that the sum of the parts equals the whole. And this is a type of reductionism. Let's listen here to the extent that Michael Faraday uses reductionism. This then is exactly the same kind of vapor as we have in the middle of the candle. Of course, there's a limit to this analogy as to all analogies. For example, why does the vapor flame out in the flask, but not in the candle? The idea here is that it's not exactly like a candle. Now, this is one of our favorite demonstrations. It's truly stunning. He shows clearly that it's the vapor that ignites. And he mentions that production and combustion of the vapor occur in two different parts of the flame. And he says this in a single sentence, but it's really a big deal. The key here is to note where the tube is positioned in the flame. It's placed in a point where the production of the vapor is occurring so that he's able to light the vapor as it comes out the top of the tube. So this great demonstration really shows that there are different parts of the flame that it's not homogeneous. In fact, watch what happens when he moves the tube. So what he's done is move his tube from the place of the production of vapor to the place where the combustion has occurred and so the vapor is spent and so it won't relight. And it was at this point that Michael Faraday mentioned the intense chemical action which the air meets the vapor in the candle flame. And this is the first time he's really getting into the chemistry. So now he's going to move from the production and combustion of the vapor to show us about the temperature distribution in the flame. So notice here that he's going to use another tool. It's just a simple tool, but it's extremely effective. And this is another tool that makes the invisible visible. We would think that the whole flame was hot, yet it isn't homogeneous in temperature. The heat generated by the chemical reaction takes place in only parts of the flame where the dark ring appears. Faraday mentions again the chemistry happening between the air and the vapor. But we want to listen carefully to his words because there's a little bit of imprecision in them that we want to talk about later. Air is absolutely necessary for combustion. And what is more, I must have you understand that fresh air is necessary or else we should be imperfect in our reasoning and our experiments. So the problem here is the use of the term fresh air. What exactly does this mean? I mean we know today that what he's trying to get to is the amount of oxygen that's in the air, but it kind of implies that regular air or normal air doesn't have oxygen in it. So let's listen to what he says next, which is just a little bit better. The jar is full of air, partly changed, partly not changed, but it does not contain sufficient of the fresh air which is necessary for the combustion of a candle. And this is better of course because Faraday uses some change, some not changed for the air showing that there's a chemical reaction that's occurring. But he still uses the phrase fresh air and he does this because he doesn't want to prejudge the idea that there's oxygen in the air. What Faraday does as a teacher here is very interesting, he uses this imprecise metaphor of fresh air so he doesn't have to introduce a new topic yet. Now let's watch in this next section how he returns to that notion of reductionism. Here is a larger wick made from these cotton balls. All these things are the same as candles after all. So notice he's saying all of these things are the same as candles, which means that the cotton balls are the same as candles, but of course they're not. And this is one of the really, I think, subtle parts of science. So we use models to capture the essential physical phenomenon. But what we have to do as scientists is we have to know how far to take a model and we have to know when it falls apart. Now his goal here is to reduce the amount of oxygen that can get to the burning cotton. Now he can't reduce that amount yet like he will soon with a Bunsen burner so he creates this giant flame that can not be fed well enough from the surrounding air. So this means that the oxygen is limiting. Now earlier on he showed us that we need something in the air, which we know is oxygen, by putting the jar over the top of the candle. And now he shows us that without enough oxygen there's incomplete combustion. Now what Faraday did here was very interesting or more to the point what he didn't do. He did show us there was black smoke. He didn't tell us what that black smoke is. We probably have guessed that it's carbon particles. And today we would just say, look I'm going to make carbon in the flame and then we would tell you that the carbon makes the candle glow. And Faraday inverts this process. He puts the observation first. He says a candle glows, why does it glow, and then he goes back and looks at what the black inner flame means and shows that it's carbon particles that glow. So up to this point Faraday has done a few things. One, he started by showing us that a flame is not homogeneous with respect to the chemical action. There are different places of production of vapor and combustion of vapor and he showed us that it's not homogeneous with respect to temperature. There's a hottest part of the flame. Now in both of those cases we couldn't really see them and he used tools to do this. Now what he's going to do is he's going to show us that the flame is not homogeneous with respect to brightness which we could see although we have to really be observant to do that. And he's going to discuss this by talking about things that burn with the flame and not with the flame. And he's playing a little bit fast and loose here with the word burn but again a little imprecision to get to a larger point I think is justified. In this case the chemical reaction of the gunpowder with the oxygen produces the heat to form a flame and the iron particles are heated until they glow which we call incandescence. Now of course he's going to show us in a little bit that the carbon particles that are in the flame are what's glowing and of course there's carbon particles in gunpowder. So he's really adding the iron filings here for effect. Now the last thing that he mentions here as well is that the oil, the gas, the candle all of these that we use for illumination. He uses the phrase their fitness depends on these different kinds of combustion which is a really nice way then of expanding this to more than just a candle. So when we were recording the lectures we noticed that this demonstration was redundant it contains really the information of the previous demonstration and we did take a number of these redundant demonstrations out but we really liked this one and it highlights just how great a showman Michael Faraday was because this produces just an absolutely brilliant flame that would have delighted his audience. So what's coming up next is kind of a continuation of what he had done before. Bill had mentioned earlier how it's interesting how Faraday starts with an observation and then goes in search of how to explain that observation. The one observation was when he used the cotton balls to make a large flame we had restricted oxygen and we noticed that we see some black smoke. Now where is that black smoke coming from? Now Faraday uses this simple tool of this glass tube to place it inside a part of the flame in this case the brightest part of the flame and we can see that the black smoke is coming from there. We now know of course that the black smoke is carbon and the carbon actually reacts with the oxygen in the air when it meets the interface of the flame and the air. So here Faraday gives a little chemistry lesson, nice conservation of mass. He points out that the carbon that's coming out of the candle and the smoke was the carbon that was originally in the candle and he makes an observation that shows how science links together all sorts of observations. He mentions the soot that's in London that that's also carbon so carbon is carbon that's a theme that we'll see come up a couple of times particularly when he talks about water. And so here Faraday is reminding us that it's the glowing carbon particles that give us the bright part of the flame just as he showed the iron filings were glowing in the gunpowder. At this point Michael Faraday sums up what he concludes from his experiment so let's just listen to him. What I have to say is applicable to all substances whether they burned or whether they do not burn that they are exceedingly bright if they retain their solid form and that it is to this presence of solid particles in the candle flame that it owes its brilliancy. So Faraday here is using reductionism. He said that carbon particles glow so he's going to isolate the carbon and interestingly what he does here is he makes it human sized so he's got a large chunk of carbon and when he puts it in a flame you can see that it glows and this as he says is what gives the candle its brightness. Let's listen to Faraday comment on a kind of counterintuitive aspect of beauty and nature and we'll talk about it a bit after. Is it not beautiful to think that such a process is going on and that such a dirty thing as charcoal can become so incandescent? You see it comes to this that all bright flames contain these solid particles all things that burn and produce solid particles either during the time they are burning as in the candle or immediately after being burnt as in the case of the gunpowder and iron filings all these things give us this glorious and beautiful light. So when Faraday says that a dirty thing like charcoal has beauty he's really echoing some thoughts that he had in the first lecture where he looked at decorative candles which most people thought were beautiful but they were bad burning and argued that a normal candle is a beautiful thing and also there's a subtle reminder here that science gives us a unified way to look at the natural world. So this demonstration kind of like a podium demonstration is a little bit redundant at this point he's talked about the brightness of flames coming from the solid particles but again it's a spectacular demonstration so Faraday being the showman wants to see this but he also does something interesting from an educational aspect and he asks the audience, I've given you all the tools now you can reason your way through this does this flame contain particles or not? Here Faraday burns propane which of course provides the carbon in a bunch in burner and he's allowed very little oxygen into it and so what happens is you get this very yellow flame because of the carbon particles now watch what happens as he allows a lot of oxygen into the flame all of the carbon burns so he no longer has carbon particles so he no longer has the yellow flame but instead has just a blue flame So it's interesting here that Faraday now is using this bunsen burner as a tool although not as we normally use it in the lab he's doing this to kind of sum up two of the key observations that he's made one, the oxygen controls the amount of particles that we have in the flame and two, it's the particles here that glow brightly and give the flame its brightness so he's using this then to control these variables So here Faraday is again making the invisible visible he's already shown us this once before covering the candle with the jar but before he focused on the flame and now he's focusing on the cloudiness inside the glass jar and he's doing that because it's the products of the candle that actually make this cloudiness and he's hinted a little bit he's talked about this invisible substance when he talked about the carbon burning he'll talk about carbon dioxide in lecture four but what he's really hinting at now is the fact that water is one of the products of combustion and he does this with a spoon, something you can do at home And water is the subject of the next lecture Faraday looks at it thoroughly in lecture three and I hope you join us for commentary on that lecture I'm Bill Hammack and I'm Don DeCost and thanks for listening