[SOUND] Each topic, we're going to have a how things work segment. Today's is on fireworks. So if you see a large hanging collection of firecrackers, you're just so tempted to go over there and just light that. Well you've seen that probably a few times, and will see it some more. Well what's really inside one of those? Let's take a look. The different between a firework and a hand grenade is the casing. The key thing is that we have an explosion. In a firework, it's typically something called flash powder or before that, black powder. Let me tell you the difference about those in the few minutes. Then you see that there's this clay plug. Basically it's something to hold the pressure in. You see when the flash powder or the gun powder actually explodes, what happens is a solid turns into a gas and that increases an enormous amount of pressure. You need that pressure to build up to a certain point or you won't get the loud bang. So the clay plugs and the casing, which is always made out of cardboard is what's needed to be able to build that pressure up until it explodes. If this was something dangerous like a hand grenade or a pipe bomb, the casing would be made out of metal. And if the explosion was large enough, the metal fragments that would fly everywhere, could really hurt people. I mean that's sort of the point of a hand grenade. In fireworks, the little pieces of cardboard that blow out, and the clay at the ends that blow out won't hurt you, unless of course it's very close. And that's why you never light these things in your hands. I actually took a firework and cut it open once, because I really wanted to see what was inside. And just like you saw in the diagram, you can see that we have the clay plugs, we have the fuse. We have a chamber where the flash powder would actually go and of course, a very thick casing. So when this actually explodes, you get a very large bang. Fireworks are brought to us from China. And in China, the very first recording of things that make bangs were called Baozhu. That's spelled B-A-O-Z-H-U. It was a segment of bamboo. Have you ever looked at a bamboo cane, bamboo fishing pool? It's in segments and each of those segments is sealed. Now, if you took one of those segments and you tossed it in a fire, if you got it just right. The water vapor inside that chamber would heat up, heat up and expand and the thing would blow up like a fire cracker. Of course, if you didn't get it quite right, maybe the bamboo would start on fire, burn through, and you wouldn't get a bang at all. But that was the first recorded time, and this was way back in 200 BC. So a fascination with exploding bamboo led through the ages to the first recorded use of fireworks. Which is 7th century China And in 9th century China a very important invention. The invention of black powder of gunpowder. Now gunpowder is 75% potassium nitrate, 15% charcoal and 10% sulphur, and this is by weight. You might say, potassium nitrate, that seems an odd thing to just have on hand in the 800s. Well you see, this can be distilled from bat guano, bat poop. Go to some cave, got a whole bunch of bats live there. Got this white stuff lining the grounds of the cave where the bats have been for probably thousands of years, you scrape it up, you've got yourself some potassium nitrate. Who first figured it out, you take this stuff you mix it with some charcoal, half burnt wood. An oxygen starved environment from sulphur, we dig up from some sulphur spring this yellow crusty stuff. Mix it up like this together stick it inside some clay shell or other type of plug, maybe a piece of bamboo, you put clay in on the end. Throw that in the fire, you got yourself a big bang. [SOUND] You see what happens is that all three of these things are solids. But when you combust them, when you rearrange the molecules together, they make products like carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen, right? Nitrous oxide and O, I don't know, two or three, or some number here. All of these are gases, and this reason you have 75% of this is it's the thing that carries the oxygen. So all the compounds that get combined the more stable states are gasses since the gasses have of course, much more pressure than the solids. There's a 10,000 to 1 expansion just turning the same amount of substance from a solid to a gas. That builds up this huge pressure and the thing explodes. [NOISE] So for many years, black powder was used in fireworks, and it was also used, of course for ammunition for guns. For putting the black powder in something and not making a completely enclosed case like a bomb, but rather a propellent to shoot out a bullet eventually. And before that to have the shells explode, an instrument of war. Black power is dangerous. I would not suggest you go try and make it. In fact, modern fireworks are even since the 1900s, what people use instead of black powder which can be very dangerous, very volatile. Something called flash powder. Now, flash powder is the silvery stuff you see. And you'd see this silvery, very silvery colored stuff inside. The reason it's that color is because it's 30% aluminum, maybe ten micron size flakes with a lot of surface area. And the other ingredient, and there's only one is 70% potassium chlorate. Probably easier to get than the back guano potassium nitrate. But the same principle is here, this carries oxygen. And it will combine with the aluminum into one of the most absolutely stable elements that exists, aluminum oxide, alumina. The outside coating of every aluminum can, which you can't help but get. Because if you expose aluminum to the air, it will turn into this extremely stable compound. When something goes to an extremely stable compound of course, that means there's a lot of energy to be given off. You have to have that energy balance. And when you have that, that excess energy of course goes into the motion of the particles, heat. And the other product that's made here, is potassium chloride. Now that's a salt, that's also a solid, and you're saying so where in this case is this conversion to a gas? Well so much heat is given off that this potassium chloride is actually hot enough to be a gas. And your fireworks still go bang without the use of black powder which could be very dangerous. Flash powder. [SOUND] The thing that makes it even less dangerous is the limit of the amount of the flash powder that is allowed to be in a given firework. Long ago, there were these things when I was a kid called M80s. And they had something like 2.5 grams of flash power in them. They could make really big explosions. They looked something like this, maybe just a little bit bigger than this. But this isn't allowed anymore as any type of consumer firework. Now the biggest firecracker you're allowed to buy in the United States has 0.05 grams. But everyone still wants to by an M80, so what they did is they take a tiny little firecracker with this much in it. And they pat it in a huge amount of clay, so that you still get a bigger bang, not a big enough one to blow up a mailbox. But a bigger bang because you have all that pressure held in for a longer amount of time. So far we've been talking about firecrackers basically, things that just make bangs. What about fireworks? The things that make the beautiful displays in the sky. Well here, we have a couple more elements. First, it has to get up in the air. So you usually put some shell like this, a mortar shell into a tube. When you put it into a tube and you light the fuse, it will immediately blow up this lift charge. Basically, you've made a model rock. Because you have the outside tube and because this is at the bottom. The hot gases that are released propels the shell up into the air. You'll also notice that there's this timer fuse. The lift charge lights the back of this timer fuse, it's a very slow burning fuse. The white thing you see in there is an insulator, and it's the green part that's actually a fuse on fire. And it's timed by its length to be the right amount. So when that shell gets to the maximum part and before it starts falling down, you should get to the end of that fuse. And you get to the end of the fuse, you'll notice it will light the burst charge. Basically, this is still a whole bunch of flash powder that makes a explosion. That explosion does two things. One, each of these little stars and that's the fun part, gets set on fire. Good, and because these stars are lined up on the shell on the outside of this, those stars go out in a circular pattern. Each of the stars was not simply flash powder. But it's a substance that burns mixed with particular metal or compound that gives off a specific color. So when those things are on fire and they're being propelled outward by this first charge. They make the long beautiful lines of color that you see in a firework. Sometimes, each of those little stars is itself a tiny shell. So that the shell is burst out, and then inside that shell it's lit and it makes its own bang. And that's why sometimes, you don't just see these balls of color going out. But sometimes at the very end of these these will also produce some kind of pretty burst. It's very interesting to actually look into one of these in person. I took a rocket here okay, and cut it open. If we look closely inside you can see that we have our propellant, our lift charge here. And then at the very top of the rocket are a whole bunch of these stars, the things that will have the different colors that will actually produce the burst when we are up in the air. And the pretty little plastic nose cone is just sort of to give it some aerodynamics and make it look like a rocket going off. But it's really just a lift charge that then lights these. Which will then just because the whole thing is moving up produce some [SOUND] going up into the air. Here's a illustration of the different colors. And by adding different compounds to the small little stars that are responsible for these trails of light as they burn or as they burst here. You can get a large variety of colors. You might wonder, who first figured this out? I bet that was a lot of fun. Hey, let's put this in something and see what color it gets. It didn't get any color. Let's try this, let's try this. Certainly it was trial and error and this was in the 7th and 9th century in China. It took a long time for the knowledge of these types of fireworks to reach the west. There was Jesuit priest that went to China in the late 1750s. And he observed not only these wonderful colorful firework displays, but also was able to talk to the people making them. He eventually went back to Europe, and when he was in France, he wrote a manuscript, a published scientific paper. It took about five years for this whole process to go. But in 1763, an article was written in a scientific journal explaining how to do this. It didn't take too long after that till people in the west were also making the fireworks types of displays. Today in the US, a given firework is limited to 500 grams of the explosive material flash power. Those are not the kind of fireworks you want to hold in your hand. Because clearly they make very large explosions and very beautiful displays. That's what you need to know about fireworks. [MUSIC]
