 I'm Bill Hammack and I'm Don DeCost and we created this lecture series with Alex Black and this is a commentary track designed to enrich and enhance the lecture and so let's start with what Faraday is trying to do in lecture number three. So in this lecture we're going to be looking at the main products of the combustion in this particular case water and its constituent elements hydrogen and oxygen and we combined a couple of Faraday's lectures because one of the things we wanted to do was take out some of the redundant demonstrations that he did. There was also some dangerous demonstrations. He did some producing of hydrogen gas near open flames and things like that and some of the demos too didn't have a lot of payoff in terms of the overall narrative of trying to actually figure out what is happening when a candle is burning. 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 rearranged a bit and we brought the water hydrogen and oxygen together for this lecture. 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 or very much support that they were there and so we arranged things because we brought things in a little bit earlier. So the drop of water that you're looking at here is from the products of the candle and what Faraday's 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. A small piece of potassium shows the presence of water by lighting up and floating about burning with a violent flame. 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 someone's substance and it reacts like this, it's water. 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. You might need to do more tests but I think Faraday would really think that this is a victory because what he has now is he has you asking questions about this. I remember that in the first lecture he said that we're here to be scientists and one thing about being a scientist is that you're going to ask these questions. And we can see this throughout all of the lectures. This is one of the big themes of all of the lectures and that is every scientific answer can be potentially refined. So now let's listen to Michael Faraday as he introduces the next big idea from this lecture. 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. So the big idea that Michael Faraday just introduced with his phrase water is water. It's 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 being like chemical change like like TNT or something but really it's just a physical change. 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 we give it a little bit of thought we can see why it's such a difficult topic. And so now let's listen to Michael Faraday's words that highlight just how difficult this concept is. And although it changes in condition and form and in many other qualities it still is water. So put yourself 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. You know and what does this mean? 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. So one way that we introduce or differentiate a physical change from a chemical change is we often say 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 at least at first physical versus chemical changes. And this is another kind of big theme in science right? We have black and white categories when we first introduce them like physical versus chemical change or like solid versus liquid versus gas or like polar bond versus non-polar bond. We know that there are gray areas with all of these but we introduce them as black or white. 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. And one thing Bill and I noticed in reading these these lectures again and try to think about how to film them is just how many of Faraday's demonstrations are 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. So let's listen again to Michael Faraday just because this little segment is coming up highlights why we kept his language. It's it's lyrical almost poetic. And so the vessel is obliged to give way and has crushed inwards. As in the other case by the further application of heat it would have been blown outwards. So that phrase obliged to give way is just it's just lovely. But we weren't always slavish about you know retaining everything that was in the lectures. I mean you can see here that we used animations which of course Faraday would not have had. So here of course is another classic Faraday demonstration. Really shows his great showmanship. It's very dramatic. And while it's 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. Yeah I think everybody knows that these things are gonna are gonna burst apart. Now when Faraday did this he actually used ice and water and we tried that at first and found that it took 30 minutes for it to happen. So we changed the dry ice and acetone which is I think minus 78 degrees and make it happen very quickly as you'll as you'll see here. And this is also coming up here another great example of why we kept Michael Faraday's language. No communication will take place you 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. Now I want you to look very carefully at the enclosure that I have here that was made in our machine shop. That is I don't remember about three quarters inch I think or half inch thick plexiglass. And when I tossed that thing in I did run I ran across the room and I did say this was faster than ice water and it is but you can see that we condensed a little bit I think it took five or six minutes. And we're 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 could see views just like that. We actually didn't want to just hear the explosion we wanted to see what was going on. And so we actually win this thing when I lift this up. I want you to watch because it is really stunning. Those are our 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. 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 learn something new. 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. To return to our quiet philosophy. We shall not in future be deceived therefore by any changes that are produced in water. Water is the same everywhere where they're produced from the ocean or from the flame of the candle. So Faraday had talked about physical changes three times so obviously they're very important and in this case he's 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. It is neither in one nor the other but it comes from their combined action. Apart from the candle apart from the air. Now of course he hasn't used these terms yet but the part from the candle is hydrogen and apart from the air is oxygen. In an order to show that the 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. I'll use electricity to pull water to pieces. So notice he uses a phrase pull the water to pieces and at some level that could imply a physical change where we're pulling to use modern terms we're pulling the water molecules away from each other. But Faraday wants us to see that we're actually pulling the water apart into its elements hydrogen and oxygen. 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 and 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 you know 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. Now next Faraday makes a very important point about hydrogen. We may obtain the substance equally from water produced from the candle flame as from any other source. So this is a statement similar to his statement water is water and what he's doing is pointing out the the universality of science that it gives a uniform description. So there's a thing called hydrogen and no matter how we make it it is going to be the same thing. 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 a control here. He makes sure that he he reacts the air or tries to react the air with the flame and then he shows us that the hydrogen actually is different. Now Faraday knew that substances differ in the number of atoms of each element that are present but as P.W. Atkins of 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. This is what we get from water the same substance which is contained in the candle. So there are a couple interesting points here. One first of all is about conservation and 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. And I think it's worth noting that we added that graphic just a few seconds ago of the water and the hydrogen and oxygen atoms that something that Faraday would not have had in his lectures and he would not have thought about molecules in that way. Now as we mentioned Faraday has already talked about density once he figured out that this was hydrogen he looked at the properties in one of these for 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 shillman 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 float up in a very dramatic fashion but he also talks 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. Now here he just he deduces oxygen just saying that there's oxygen in water and you might say well he hasn't proved to us 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 you know help you to prove it. So what he's doing though is 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 in his is in the air does not aid combustion and here we turn to that in lecture four for now though he's going to point out that oxygen is necessary for all types of combustion but it does not affect merely the combustion of hydrogen or carbon or the candle but it exalts all combustions of the common kind. So that's another statement about how science gives a unified view of nature that every kind of combustion 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 rule of nitrogen there. So now we're reaching the close of the lecture and we'll 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 go over everything that we've learned of this but then he's also going to show us again that water is water. 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 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 then potassium in analogy here takes oxygen from water and he's reminding us of elements of continuity he notes again and again that water is water and so here it's really nice that he uses ice instead of liquid water which he used at the beginning and again that's a reminder that water is water it doesn't matter what he uses And so Faraday ends here again hoping that we're thinking of a question and that question is well if oxygen is so quote unquote 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 So that's the end of our commentary for lecture number three I'm Bill Hammack And I'm Don DeCost Thanks for listening