Fireworks, Explosions and Chemistry

06 November 2005

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In this explosions extravaganza, John Emsley and Jacqueline Akhavan describe the chemistry behind the bangs on bonfire night, George Pendle talks about Jack Parsons and the history of rocketry, Mark Schrope comes back down to earth to describe his experience of flying into the eye of Hurricane Rita, and Dave and Derek cool us off with a home made fire extinguisher in kitchen science.

In this episode

How To Get Rumbled By your Stomach

Forget polygraph tests to flush out a liar, criminals could soon be given away by their stomachs according to new research carried out at the University of Texas by Pankaj Pasricha and his colleagues. The team gave 16 volunteers an electrogastrogram (EGG for short), which sounds misleadingly like an email food greeting but is in fact a measurement of the nerve activity in the stomach. The subjects were asked to lie about some things, and tell the truth about others. Intriguingly, their stomach nerve activity shot up whenever they told a porky, but remained unchanged when they were honest, evidence, says Pasricha "that the gut has a mind of its own". Moreover, the team suggest that the addition of an EGG to a standard lie-detector test could help to improve the overall reliability of the test.

Is Tanning Addictive?

We hear about drug addiction, nicotine addiction, alcohol addiction and even chocolate addiction – but addiction to the sun? Surely not! But yes - according to a recent study, tanning is addictive too. American scientists adapted a questionnaire normally used to diagnose people with drug and alcohol addiction and tested 150 beach goers. They found that over half of these people could be classified as ‘ultraviolet tanning dependent’ (Also know as Brits-on-holiday syndrome!!). It is thought this addiction is due to release of endorphins – feel good chemicals that are released when you’re exposed to UV light - giving beach babes a sun-induced emotional high. This may explain why despite the risks of skin cancer many people would rather bare all on the beach than reach for the fake tan.

- Flying Into Hurricane Rita

The Naked Scientists spoke to Mark Schrope, freelance journalist in Florida, USA

Flying Into Hurricane Rita
with Mark Schrope, freelance journalist in Florida, USA

Mark - I wanted to learn about a programme called RAINEX, which look sat why it is that hurricanes can dramatically shift from a category 3 to a much more devastating category 5 really in the space of a few hours. I tagged along on a research flight into Hurricane Rita.

Chris - It sounds like a pretty crazy thing to do to get on a plane and fly straight into the heart of a hurricane. But this is actually standard practice isn't it?

Mark - It is, and it's been going on since the 1970s, so on the one side you can feel safe because they know what they're doing, but then on the other side you feel they've been doing it a long time and so their time is coming!

Chris - So you took off and were heading into the heart of Hurricane Rita.

Mark - We left from tamper, which is where the planes are based, and started seeing the storm within about 30 minutes of leaving the coast of Florida. It was so massive it just about filled to Gulf of Mexico. It's quite funny really because they had a fasten seat belt sign like you'd have on a commercial airline. It comes on and off, so you'd see it and run back to your seat and then get up again after a minute when it'd gone back off.

Chris - You were experiencing wind speeds one would presume of 110 miles per hour or so. But what was it actually like flying through the eye, and into the eye wall, where the winds are most intense?

Mark - One side of the hurricane wasn't as bad as the other side. It would be rough on one side, but on the other you would get quite beaten up. There was a complete white out when we went through the eye wall. You couldn't see anything but cloud and could only feel the turbulence we were flying through. When we flew into the eye, it calmed down and got a little sunnier. But on the day I was flying there was still a bit of cloud cover, so there were some clouds in the eye.

Chris - What was your most vivid memory of the experience?

Mark - Probably taking hits when we were going through the eye wall. There was one time when my arm flew up above my head from the impact. I think that was one of the times when there was a 2G force there. One of the other planes up there at the same time got hit with a 3.5G impact.

Chris - So how are the measurements collected? Have you got a group of scientists on board with you looking out of the window or is it all down to clever machinery?

Mark - Doppler radar is one of the big tools. They have these instruments called drop suns that they drop out of the bottom of the plane. We had about 17 or 18 people including the flight crew working pretty frantically through the whole nine hour flight. There were lots of computer stations and people looking at radar and other data coming back in.

Chris - Have there been any data produced so far that have led to a better understanding, or is that why there are three planes up there this year rather than the normal one?

Mark - The reason for the three planes is that they have this theory that there are rain bands that in a classic hurricane shape are feeding into the eye. They think those rain bands are actually transferring energy into the eye. Then you go through places in the cycle where the bands on the outside of the eye make their own secondary eye wall and starve the eye of power. This weakens the eye, allowing the secondary eye to become the eye and gain strength. The reason for the three planes was so that there would be people simultaneously at each of these different points. They have somebody flying into the eye, somebody flying on the outside of a rain band and somebody flying into a rain band.

- The Chemistry of Fireworks

The Naked Scientists spoke to Dr Jacqueline Akhavan, University of Cranfield

The Chemistry of Fireworks
with Dr Jacqueline Akhavan, University of Cranfield

Chris - So as a pyrotechnics expert, you like blowing things up. What a great job to have for a living!

Jacqueline - Yes it's fascinating. It means I can practice my chemistry. Explosions and fireworks are just chemistry.

Chris - How did you get into blowing things up?

Jacqueline - Well, when I became a lecturer at Cranfield University, I was trained in polymer chemistry. My professor at the time was an expert in explosives. I then realised that polymers and explosives come together quite nicely in polymer bonded explosives and so I got involved with putting explosives intoa polymeric network.

Chris - So for the lay person, a polymeric network means what?

Jacqueline - Polymers are like plastics, so what you do is take explosive crystals and embed them in a plastic network, which holds all of the explosives together.

Chris - What, so they're held together in just the right way that they go off efficiently?

Jacqueline - Well not really. It's like a binder. So if you think of when you're making bread dough and how eggs bind flour together, and then when it's cooked you get bread. Polymers are exactly the same. They start off wet, and then when you put it in the oven, it reacts and forms a solid lump, embedding all the explosive crystals.

Chris - Now let's talk about fireworks for a bit. How do you make fireworks so that they produce these fantastic shapes? How do you make a starburst that has arms that spread out equally and then have secondary explosions that turn from red to blue to green?

Jacqueline - First of all, the various shapes are called mortar bombs. It's like a very large football that has small fireworks in called fountains. To make the design you want to see in the sky, you put it together on a much smaller scale. For instance, if you want a heart, you arrange these small little fireworks into a heart shape. When the mortar is sent up into the sky and bursts apart, the small fireworks are sent out and burn in a heart shape. To get the change in colour, you have small pellets. One pellet will contain a substance that will burn red, and then you add a compound called strontium to that, and you attach that to another pellet that might burn with green. When it's I the sky with a mortar bomb, the red bit burns first, and then when it burns through and meets a green composition, you get a green colour second.

John - I was once told that the way to judge a firework display was the quality of the blues that can be produced in the sky. And I know for example that purples are very rare indeed. Why is that?

Jacqueline - Blue is a really hard colour to produce. To get blue, you need to add a composition that contains copper. The blue you are actually seeing is copper chloride. We have to add some chlorine to it because chlorine seems to intensify flame colour. Copper chloride is a very unstable species, and if the flame temperature is too high, copper chloride breaks apart and you don't see blue. So we have to try and keep the flame cool long enough so that the copper chloride stays stable and you get to see that blue colour.

John - And why do you never see purple?

Jacqueline - Well purple again is quite a difficult colour to produce. To get purple you have to mix to compounds together. You can mix for instance red with yellow to get orange, but blue is so unstable that it's hard to mix it with other compositions.

Catherine - When you see fireworks that make noise, such as whistling and crackling, what's the chemical basis behind making those kinds of noises?

Jacqueline - The crackling noise is produced by burning titanium metal flakes. Titanium has a oxide layer, but the oxide layer is very thick compared to the oxide layer around magnesium or aluminium.

Chris - And that's what stops the air getting to it to burn, is that what you're saying?

Jacqueline - All metals will have an oxide layer. What happens is, when you've got titanium inside a flame, the metal actually melts and the oxide layer cracks open. So the metal doesn't actually burn, it melts. When the oxide layer cracks open, then you start getting your white sparks. So the breaking open of the thick oxide layer is the crackle sound.

Chris - But what about the squeaky noises? Do they embed something into the firework so it makes a whistle sound?

Jacqueline - No. What happens with the whistler rocket is that you have your rocket whistler composition, and it's in a cardboard tube that's only filled a quarter of the way at the top end of the tube. The rest of the tube is open. When you ignite your whistler from the open ended cardboard tube, as it burns, you get small sparks and explosions occurring. These small explosions cause the cardboard tube to vibrate. As it's vibrating, just like a tuning fork, you actually get a resonant sound occurring.

Catherine - What do you think the future of fireworks is? Where do you think we're going to see them going next?

Jacqueline - There are some new fireworks being developed, but the most important thing for fireworks will be the safety aspect. At the moment, all fireworks are made by hand, and most commercial ones are being imported from China. If there are accidents, people can die. Automating the process would make it much safer. That's the first thing. The second thing is safety of the users.

Catherine - And the third thing is surely the biggest firework in the world!

- The History of Rocketry

The Naked Scientists spoke to George Pendle, author of Strange Angel, New York

The History of Rocketry
with George Pendle, author of Strange Angel, New York

Chris - You've written this book Strange Angel. It traces the history of rocketry, but where did rocketry actually come from in the first place?

George - It's really interesting, because when we think of rocket scientists today we think of men in white lab coats pressing buttons at Mission Control with brains the size of small planets, but this hasn't always been the case. Up until the middle of the 20th century, rocket scientists, or at least those dabbled in rockets were seen as lunatics and crazy men dealing with things that were ludicrously dangerous. Many of the people working with rockets in the early days blew themselves up in the process.

Chris - So when did it become a really serious science?

George - It became a serious science in around the 1930s. To trace it back, we really have to go back 1000 years. Rocketry is an old science, even though it hasn't been treated as one. If we go back to ancient China, some of the earliest writings about rockets describe them being used as weapons. They could be launched a thousand feet, and caused great terror among the ranks. But this is a thousand years ago, and for a thousand years after that there were no real breakthroughs in rocketry.

Chris - So when did things begin to change?

George - Well in about the 1930s, rocketry was really at its lowest ebb. Rocketry wasn't being taught at any of the universities and it wasn't being funded by governments. In fact, the only place it existed was in the science fiction pages of science fiction magazines. It really began to change when young enthusiasts, around twenty years old, were fuelled by the stories of Jules Verne and H.G. Wells and wanted to make the tales a reality.

Chris - And this is when Jack Parsons comes in I guess.

George - That's correct. He was a self-trained young guy who was fanatical about science fiction. He lived in Los Angeles in the United States in the 1930s. He went to the California Institute of Technology, and said that he wanted to build rockets. No-one took him seriously apart from one man who thought that there might be something in this rocket business.

Chris - And did he actually succeed?

George - He did. If you look at Jack Parsons, he's on the very first step of the road towards walking on the moon. He got the US government interested in rocketry, and if you look at a similar young man in Germany at the time called Wernher von Braun, he came up with the idea for the V2 and also allowed it to become a reality.

- How do liquid hand-warmers work?

I have recently bought these cool hand warmers that are filled with a gel and a metal disc. When you bend the metal disc, the gel goes ha...

How do liquid hand-warmers work?

I'm pretty sure that what they work with is sodium acetate. What you've got is a super-saturated solution of sodium acetate, and as this begins to crystallise, it gives off a constant heat of about 55 degrees centigrade, which is a nice comfortable temperature for something like a hand warmer. Now how do you get this to work? Well as you bend the metal, I think you create surfaces that are like the crystals that could be formed from the solution. Once you've done this, you're really seeding the crystals, and so one forms and then another and another until it spreads throughout the bulk of the hand warmer. All the time it is giving off this heat. Eventually, the heat will stop because you've crystallised the whole thing. You can repeat the whole process by putting the used hand warmer in something like and oven, until the crystal is all melted again.

- Why do we feel better after sneezing?

Why do we feel better after sneezing?

Why do we feel better after sneezing?

A sneeze is a bit like an itch in your nose. When you have an itch, it's extremely pleasurable to scratch it. Unless you have really long fingers, it's not that easy to scratch that far up your nose! So what sneezes do is use air to perform a metaphorical scratch. What we know about itching is that there is a special class of very small nerve fibres, and they signal itchiness. In fact, you can switch off the signals into the spinal cord and brain for itchiness if you cause a little bit of pain. That's why scratching an itch actually helps to relieve an itch, because you cause a little bit of pain and it switches off the itch signal. In sneezing, you get that pleasant relief because you've got rid of the itchy sensation, and also dislodged some of the gunge that's in your sinuses.

- How's a rainbow made in the sky?

How's a rainbow made in the sky?

How's a rainbow made in the sky?

The reason that you get a rainbow, is that sunlight shines into a raindrop. Raindrops are very tiny and the surface of it is like a mirror. As the light waves go into a raindrop, they hit the mirror like surface and reflect. The light bounces off the back inside surface of the raindrop and comes back out of the front. Now if you've ever seen a prism, what that does is split white light into all the colours of the rainbow. White light is actually a mixture of lots of different colours. When the light comes back out of the front of the raindrop, it splits up into all the different colours of white light, and that's how you get a rainbow.

- What is the best way to burn fat from the abdominal area

What is the best way to burn fat from the abdominal area, or in other words, a beer belly?! And why does it collect there?

What is the best way to burn fat from the abdominal area

This is a Nobel Prize winning level of question, and if either of us could answer that, we'd probably be straight of to Scandinavia! The easy answer is, have you noticed that men tend to put weight on round their middle, and women tend to put it on round their bum? So there has to be a genetic component to this. The old saying goes that women have lots of fat around their hips and bums because that's their store for pregnancy. However, we don't know exactly why and how the body decides on the distribution of fat in the body. What we do know is that you can lose weight from those areas just as easily as you can anywhere else, if you resort to the right kind of exercise regimen. Energy in equals energy out, plus or minus any weight gain. So if you're not burning up the energy that you're putting into your body, the energy has to go somewhere. You body thinks that the most efficient way to store it is as fat, which it puts under the skin, or if, a man, as a bit of a beer belly.

- How do glowsticks work?

When you snap a glowstick, what makes it glow?

How do glowsticks work?

It's luminol, or a dye like it, that you're activating. This is a chemical that can absorb chemical energy and then release it as visible light. In a glowstick, the chemical reaction that energises the luminol is usually the oxidation of an ester, called phenyl oxalate, by hydrogen peroxide (H2O2) in the presence of a strong alkali, like sodium hydroxide (NaOH). If all of these chemicals were present in the same tube when the glowstick was manufactured, they would begin reacting immediately and, by the time you needed it, the glowstick would be exhausted.

Instead,the chemicals are kept apart by putting the luminol and the ester and the alkali in one tube and the peroxide into a separate tube, usually made of thin glass, which is floating inside the tube containing the luminol.

This means that the reaction will only begin when you break the glass by bending the glowstick and allowing the chemicals to mix.

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