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IRA FLATOW, host:

You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. Up next this hour, how to add a little bang, spark and sizzle to your Fourth of July holiday. I'm sure many of you have probably set off a firecracker or two in your day, but have you ever tried to make one or a smoke bomb? Would you know where to start?

Well, we can help. We've rounded up a team of backyard science experts to help you put a little more spark and some science into your Fourth of July weekend. We've got instructions for Oreo-powered rockets, Cincinnati fire kites - I didn't know what they were, either. So you're in the boat with me. And then also homemade firecrackers, or for those of you who prefer a different kind of Fourth of July thrill, how about whipping up some liquid nitrogen ice cream? Yeah, it's easy to do, or some red, white and blue shooters.

So grab a pencil, piece of paper in case you need to make a last-minute equipment run, or call in with your questions. Maybe you want to give us some of your backyard experiments to try. We're always looking for suggestions. Our number, 1-800-989-8255, 1-800-989-TALK. Also we are at Tweet - tweetering, twitting…

(Soundbite of laughter)

FLATOW: You can send us a Tweet on Twitter, @scifri, @-S-C-I-F-R-I, and also folks in Second Life are out there willing to talk to you.

We're also going to talk about - I want to be very careful to mention this -we're also going to talk about this hour some experiments that you should probably not do at home. You know how we always say, yes, you can try this at home? Well, we're going to say, yes, you can try this at home, but it's dangerous. It's a dangerous experiment if you want to try to do it, but just be assured that it's dangerous.

We'll explain what that means as we go along, but just a warning. You may think that fireworks can be safely handled, but I can tell you from personal experience that things can and go do wrong - they can go wrong, and they do go wrong. So be very, very careful. So with that caveat out of the way, let me introduce my guest. William Gurstelle is the author of "Backyard Ballistics" and a new book, "Absinthe and Flamethrowers: Projects, Ruminations on the Art of Living Dangerously." Welcome to SCIENCE FRIDAY, Will.

Mr. WILLIAM GURSTELLE (Author, "Backyard Ballistics"; "Absinthe and Flamethrowers: Projects and Ruminations on the Art of Living Dangerously"): Well thank you, Ira, it's great to be here.

FLATOW: You're welcome. Anne Helmenstine is the chemistry guide for About.com. She joins us from the studios of Colorado Public Radio in Centennial. Welcome to the program, Dr. Helmenstine.

Dr. ANNE HELMENSTINE (Chemistry Guide, About.com): Hi Ira, it's great to be here.

FLATOW: You're welcome. Theo Gray is the author of "Mad Science: Experiments You Can Do at Home But Probably Shouldn't." Yeah, he's author of the "Gray Matter" column for "Popular Science" and co-founder of Wolfram Research. He joins us from WFYI in Indianapolis. Welcome back to SCIENCE FRIDAY, Mr. Gray.

Mr. THEODORE GRAY (Wolfram Research): Delighted to be here.

FLATOW: I was trying to give away or to talk about things that we should or we shouldn't do. I got the disclaimer out of the way because I know we're going to get calls about it, and some of these things are pretty dangerous. Let's talk to you, Mr. Gray. "Mad Science: Experiments You Can Do at Home But Probably Shouldn't." Why give out these experiments if you think they shouldn't be done at home?

Mr. GRAY: Well, there's a lot of things that people shouldn't do but that are still interesting to read about. You know, I think, you know, jumping off of cliffs with a wing suit is an example of something that I find very enjoyable to watch videos of other people doing, but heaven forbid I should actually try it myself. I'd undoubtedly kill myself quickly.

So you know, the book has things in it that people could do at home, should do at home, that are perfectly safe, but it also has things in it that are best enjoyed vicariously. But, you know, there's plenty of things in the world that one, you know, should talk about and tell people about and just say, well, you know, this is something that, you know, I can do because of my background or because of whatever equipment I have or experience, but you know, unless you have similar expertise, maybe you shouldn't do it.

FLATOW: Bill Gurstelle, do you think people should be taking these risks?

Mr. GURSTELLE: Oh, I absolutely do, Ira. (Unintelligible) I mean there's a big difference between…

FLATOW: Well, having some audio difficulty.

Mr. GURSTELLE: Having audio trouble with me?

FLATOW: Okay, keep going, we'll try to figure it out. Go ahead.

Mr. GURSTELLE: Okay, well you know, I'm in the middle of the Atlantic Ocean on a ship, so…

(Soundbite of laughter)

Mr. GURSTELLE: I'm serious. So you might get a little trouble.

FLATOW: I know that. I've been there and done that. No, we've got you. Go ahead.

Mr. GURSTELLE: Okay, well you know, you asked about risk-taking. Well, I think risk-taking is usually, usually a good thing. Now, you can take things too far. It's a continuum. You want to be kind of on the smart, risky side, but you don't want to go overboard, Ira.

FLATOW: No, we don't want to do that. Let me start with Anne. Anne, tell us what would be a great experiment that folks should try at home?

Dr. HELMENSTINE: Well, one project I think they should try would be trying to make their own smoke bomb for the Fourth. That's not one of those experiments that's going to blow up on you, but it will teach you quite a lot about science, and it's something that you can pick up the ingredients. It's educational and fun. You don't have to just read about it. It's - go out there and celebrate the Fourth.

FLATOW: How do you do that? Give us some cookbook recipe on that.

Dr. HELMENSTINE: Okay, this is an easy recipe. You only need two ingredients. One ingredient is common, ordinary table sugar, which you'll have in your kitchen, and the other is potassium nitrate, which you would know as saltpeter. You can't go to the grocery store and say, oh, I'd like to pick up some potassium nitrate, but you can go to a Lowe's or a Home Depot or any supply store like that and pick up stump remover, and stump remover is pure potassium nitrate. And what you do is you get out a saucepan.

You put three tablespoons of the potassium nitrate into the pan with two tablespoons of the sugar. You stir it up over medium heat until it's mixed together. You don't want to go on high heat, or then it would turn into one of those experiments you don't want to do where the fire department comes and the smoke alarm goes off. But generally speaking, you can just stir until it's integrated and melted, drop it onto a cookie sheet or some foil, take it outside and light it. You'll get purple fire. You'll get smoke. It's easy and safe.

FLATOW: Wow, that's a good one, pretty simple ingredients we can get anywhere. Bill Gurstelle, my favorite project from "Backyard Ballistics" is the spud gun. It's a potato shooter. Tell us about that.

Mr. GURSTELLE: Well, a spud gun, sometimes called a starch shooter or a - you know, potato cannon. It's got a lot of different names, and it's been around since, well I don't know, like ever since PVC pipe was invented, but it's a simple device. It's constructed, as I said, from PVC pipe and PVC pipe fittings.

You basically put a potato in one end, and you put hairspray in the other because hairspray has a lot of hydrocarbons, (unintelligible), and if you can figure out a way to put, make a spark in the combustion chamber, the potato issues from the muzzle with great velocity and a lot of noise. It's a pretty cool thing to behold.

FLATOW: Theo Gray, you have two different ways of making ice cream in your book.

Mr. GRAY: Yes. So you can do it with liquid nitrogen, or you can do it with a fire extinguisher.

(Soundbite of laughter)

Mr. GRAY: Personally, I find the liquid-nitrogen ice cream tastes a lot better, and it's particularly easy to do, as long as you have a source of liquid nitrogen. Basically, all you do is just mix up your favorite ice-cream recipe. You can use any, you know, any recipe you find as long as it doesn't have alcohol in it. And then sort of pour in liquid nitrogen and keep stirring until it's turned into ice cream, which is usually 20 or 30 seconds later.

The reason you don't want alcohol is because that can depress the freezing point to the point where your ice cream actually gets so cold that it's dangerous without having turned solid yet. And that's really - it's a very good grade of ice cream. It's delicious. It's smooth and creamy because it freezes so fast that crystals are very small. The only catch is you need to find something that's got some liquid nitrogen in it. If you don't own your own dewar, that usually means finding somebody at a university or a medical office somewhere that keeps a tank of it around and inviting them to your picnic.

FLATOW: Or you buy the dewar and go borrow some, fill 'er up at one of those universities.

Mr. GRAY: You could do that, too. Yes, it's just that the dewars are relatively expensive. I got one on eBay fairly cheap, but you know, they're a couple-hundred dollars if you try to buy a new one.

FLATOW: How do you make an Oreo-powered rocket?

Mr. GRAY: Well, it's actually not unlike the recipe we just heard about for smoke bombs. You know, I did that experiment as a way of illustrating the importance of oxidizers, you know, as one of my columns. The point being that if you have a powerful enough oxidizer like, you know, potassium chlorate or perchlorate or ammonium nitrate or any one of these standard sort of oxidizers that one uses, you can burn almost anything with it. It doesn't really matter, almost any kind of organic matter will work.

I originally was going to use a Snickers bar, but I kind of was worried that if I didn't chop the nuts up very finely, they would clog the nozzle. So I decided, you know, an Oreo filling was a nice, good, sort of creamy material that I could use as - just as an illustration of how the fuel is relatively unimportant compared to the oxidizer. Actually, sugar works a lot better. In fact, there's people who have shot rockets, you know, quite high up in the air based on sugar propellants.

FLATOW: 1-800-989-8255 is our number, talking about homemade fireworks for the Fourth. Anne, let me ask you about the recipe for black snakes or glow worms. How do you make those?

Dr. HELMENSTINE: That's another one where you go to your kitchen for the ingredients. This one's even easier. You just need powdered sugar and baking soda, and you can make your own black snake, which is a firework that you would put on a fire-safe surface and light with a lighter, and it makes a black column that grows out, and it's great fun. And it's non-toxic in this version, although the ones that you buy might contain things that you wouldn't want to eat or have kids play with, but what you do as you take, say, four teaspoons of powdered sugar and maybe one teaspoon of baking soda. You mix that up and you set that in a depression in some dirt or some sand. You can pour a fuel on that like alcohol. You could pour Vodka on it. You could pour kerosene, whatever you think you can ignite. You light that on fire and you'll see the black snake, very easy.

FLATOW: Wow. 1-800-989-8255. Let's see if we have some folks on the line who have their own recipes for fireworks. We'll go to Jarred(ph) in Clayton, New York. Hi, Jarred.

JARRED (Caller): Hey, how you doing, Ira?

FLATOW: Hey there.

JARRED: Hey, what would me grandfather do - if you take a piece of iron pipe and you make a canon out of it, and this is like, sort of like the potato gun your caller was talking about but it's sort of like the next double up. And we're here at the border up in New York and Canada and we shoot them at Canada. We might start a war.

(Soundbite of laughter)

FLATOW: They can go pretty far, can't they?

JARRED: Yeah, no kidding.

(Soundbite of laughter)

FLATOW: You could really do some - they can go a few hundred yards, if I remember seeing some of these things getting fired off.

JARRED: Yeah.

FLATOW: You don't want anything in-between.

JARRED: We just try to shoot them as far as we can.

FLATOW: Yeah. Did they ever fire back, ever get any incoming?

JARRED: Thankfully no.

FLATOW: All right, thanks for calling, Jarred. Have happy 4th.

JARRED: Have a great day.

FLATOW: Have a safe 4th. 1-800-989-8255 is our number. Bill, tells us how you make, I saw a video of this, the Cincinnati Fire Kite.

Mr. GURSTELLE: Okay, well the Cincinnati Fire Kite. I actually named it that because back when I was writing my book people knew about it (unintelligible) that they had thought up with (unintelligible) oh, his dad showed him (unintelligible) and I was so taken with it that I named the Cincinnati Fire Kite in his honor. But basically you take a sheet - a full sheet of newspaper and you kind of fold the four corners together so it looks like pillow, okay. And then you either put a staple or piece of tape at the (unintelligible) where they come together and (unintelligible) Now, you get three friends to help you. You each take a match and you light the pointy corner of the kite, this pillow, and as the, you know, the newspaper catches fire and it heats up the air inside this paper kite, and if it's a cool night - now, I have to tell people all the time (unintelligible) cool night because the whole thing is based on buoyancy. The hot air inside the kite is lighter than the cool air outside the kite so the whole thing rises. And when it does rise, Ira, into the night, it's (unintelligible) glowing kite. And finally the paper, you know, burns for a few minutes, it's over. But it's a real simple (unintelligible) elegant little package.

FLATOW: So it's like a little hot air balloon, but a flaming piece of newspaper hot air balloon.

Mr. GURSTELLE: Yeah. It sounds worse than it is. But yeah, you hit the nail right on the head.

(Soundbite of laughter)

FLATOW: 1-800-989-8255. We're talking about the backyard's fireworks this hour on SCIENCE FRIDAY from NPR News. I'm talking with William Gurstelle, author of "Absinthe and Flamethrowers: Projects and Ruminations on the Art of Living Dangerously." Anne Helmenstine who is chemistry guide for About.com, and on that Web site she got all kinds of experiments you can do there. And Theo Gray, who is the author of "Mad Science Experiments You Can Do at Home But Probably Shouldn't."

Our number, 1-800-989-8255. Let's go to the phones. Derek in (unintelligible) New York. Hi, Derek.

DEREK (Caller): Hi. How are you doing today? First time in a long time.

FLATOW: Thank you.

DEREK: You see a bunch of Internet videos of people playing with Mentos and diet soda where they drop a sleeve of Mentos, that candy…

FLATOW: Right.

DEREK: …into the diet soda. And you get a tremendous geyser of diet soda, messy but fun.

FLATOW: Oh, yeah. That's a pretty interesting one…

Mr. GURSTELLE: Yeah. It's a pretty explosive chemical reaction. I don't know what exactly is making it happened but it's definitely a geyser.

FLATOW: That's pretty - well, I'd say that's pretty safe, Anne, is it not?

Dr. HELMENSTINE: It is pretty safe. And how it works isn't that complicated. It's not dangerous. You just - when you put that candy in the Mentos drinks, Mentos are the best candy. But I've heard that others that have kind of that waxy coating will work. But wax comes off of the Mentos and into your diet soda and it lowers the surface tension of the water. And that means that the carbon dioxide bubbles are more able to form and it's easier for them to escape. The other thing that's going on is that Mentos is starting to get little pits in it and that let's the carbon dioxide bubbles form. And all you get in that explosion is just carbon dioxide coming out just like if you shook up a can of Coke except a lot faster.

So it's very safe. You wouldn't want to look right over it. You can make it Fourth of July in red, white and blue using Diet 7-Up or something like that. So that's a fun project.

(Soundbite of laughter)

FLATOW: 1-800-989-8255. Theo, do you have something like that to suggest?

Mr. GRAY: Well, I have something that's a little bit like the Fire Kite, which is one of my favorite experiments, hydrogen soap bubbles, where you take a tank of compressed hydrogen gas and bubble it through a sort of a ball full of soapy water. And because the hydrogen is very light, sort of Hindenburg-like, the bubbles eventually detach themselves and float up into the air. And then you chase after them with the candle at the end of a long stick.

With pure hydrogen, you get really beautiful sort of jellyfish-like shapes out of fire. And if you then mix in some oxygen along with the hydrogen, you get closer to the optimal ratio between the hydrogen and the oxygen. You end up getting this sort of bangs that sound a lot like somebody firing a shotgun in your ear, which makes hearing protection useful and perhaps necessary.

FLATOW: Yeah. That definitely is a don't try this at home one, because you need to have the hydrogen tank and the other stuff.

Mr. GRAY: Yeah. You need a hydrogen tank, but you know, they're not hard to get. But…

(Soundbite of laughter)

Dr. HELMENSTINE: You can make your own hydrogen.

FLATOW: Well, we actually have a video of this on our Web site. It's sciencefriday.com on our homepage. We have a video that you helped supply on this one for this…

Mr. GRAY: Right. And this is actually a standard chemical demonstration that you'll see done at, you know, in college chemistry classes or Christmas lectures quite regularly. And it's very impressive to see the effects of stoichiometry on reaction rates.

FLATOW: Anne, can you do this in school? Is it safe enough to do in school?

Dr. HELMENSTINE: I've seen this done as a demonstration. You could do this in your kitchen. You know, I wouldn't say it's the safest project, but you can make your own hydrogen. Another thing you can do is take canned air and shoot that under some detergent and water. And that's basically the same sort of thing. Sometimes you get hydrogen bubbles or you could get another like an ether bubble. And it gives you the same sort of effect.

FLATOW: Well, then I can…

Dr. HELMENSTINE: You can also do that with taking drain cleaner and nails. And that will give you hydrogen gas. And you can light them. I would do that outside, not as an indoor project. But I think it's safe enough for school kids.

FLATOW: All right. Well, have your parents around when you're doing that, taking the lye out of the drain cleaner.

Dr. HELMENSTINE: That's definitely not an indoor project.

FLATOW: Not an indoor project. All right. We're going to take a break and come back and take more phone calls. Our number, 1-800-989-8255 if you can match the experts on making your own Fourth of July fireworks or maybe things that don't have to have fire in them. Our number, 1-800-989-8255. We're twittering. You can tweet us at scifri, S-C-I-F-R-I. Don't go away. We'll be right back after this break.

(Soundbite of music)

FLATOW: You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. We're talking about backyard experiments, some that you can do in your kitchen too for this holiday Fourth of July weekend. Also, warning you to be careful how you do these.

I'm talking with the authors William Gurstelle, who is author of "Absinthe and Flamethrowers: Projects and Ruminations on the Art of Living Dangerously"; Anne Helmenstine, who is a chemistry guide for About.com; and Theo Gray is author of "Mad Science Experiments You Can Do at Home But Probably Shouldn't."

Theo, are some of these experiments illegal to do?

Mr. GRAY: I wouldn't say illegal, although some of the ingredients are, depending on what state you live in, you know, you need to have sort of an educational institution affiliation. Phosphorous, for example, has been banned due to its use in meth synthesis. Not that it's, you know, particularly dangerous. It's just that you can use if for making meth and therefore it's been banned. But you know, that's really the minority. And of course, if you're, you know, if you have any kind of legitimate reason for having it, you should be okay.

FLATOW: Bill Gurstelle, you know, if you buy a chemistry set these days, they don't have anything dangerous in them anymore.

Mr. GURSTELLE: Yeah. They're kind of gutless. You know, and that's something that really sort of disturbs me. The chemistry sets have kind of gone the way of the diving board. You know, you look at municipal pools, the high board is gone, and because, well, I guess that's too dangerous, and they've kind of done the same thing to chemistry sets. You know, when I was kid - Ira, did you have chemistry set when you were a kid?

FLATOW: Yes, I did. An old Gilbert set.

Mr. GURSTELLE: A what set?

FLATOW: Gilbert. Remember Gilbert chemistry sets? I'm sure we all had one.

Mr. GURSTELLE: Gilbert? Yeah (unintelligible) very best. And you know, they had a lot of good chemicals, a lot of interesting (unintelligible) experiments. The chemistry sets that I see nowadays, and I got to be honest with you, I'm not an expert, I haven't surveyed the whole market. But I don't think they hold a candle to what existed, you know, 30, 40 years ago in terms of what you can do and what you can learn from them.

I've kind of made a study. And there's a lot of people (unintelligible) engineers who got their start, you know, by messing around and doing things with their chemistry set. And I don't think that's available anymore.

FLATOW: Anne, what's you take on that?

Dr. HELMENSTINE: I'm glad that chemistry sets are a little bit safer now. I think the problem wasn't just that people could perform dangerous experiments that might harm themselves. But you still had to worry about disposal of the chemicals whenever you have the heavy metals. I think that it's probably a good idea that those are gone.

But at the same time, I think that people need to actually experience chemistry, and you might not get that when all you have is iron filings and a magnet.

(Soundbite of laughter)

Dr. HELMENSTINE: And then I think that because you don't see the chemistry sets, that people assumed that if it's out there then it must be safe. And that's not a safe perception either. A lot of your household chemicals are every bit as dangerous as what would have been in the chemistry set. But they aren't labeled as such.

FLATOW: Anne, can you - is it possible to make your own homemade firecracker that's safer than you can get legally?

Dr. HELMENSTINE: Well, I don't know about safer, but it's definitely a whole lot of fun, and it's really, really easy. I would not recommend making your own gunpowder. But you can get gunpowder yourself by going to - even a Wal-Mart or any store that sells toy caps for popguns. And you harvest that using a straight pin or a needle. You just scrape the gunpowder onto a plate. You take a two inch piece of scotch tape or masking tape and you pick up the gunpowder with that, and it will stick. And this is a - what makes this safe is you can only get so much gunpowder to stick onto your piece of tape. So you're not going to make an M80 and blow your finger off with this. But you put a little fuse that you got from a fireworks store or you could take a little roll of toilet paper, you roll that up and tape the whole thing up to make your own little firecracker shape. Put that out in your yard, again, not in the house and you light that. The dangerous part is the fuse. If you're making your own homemade fuse, you're not sure if it's burning so there's a little bit of a risk of getting a pop before you're ready. But otherwise it's safe and it's fun. You get a big pop. And you have this I did it myself feeling. Definitely try that.

FLATOW: We used to just take a hammer and hit the whole roll of caps.

(Soundbite of laughter)

Dr. HELMENSTINE: Or that.

FLATOW: That's pretty loud. I don't think I would do that again without some earmuffs on - this time. 1-800-989-8255. Let's go to Ed in South Dakota. Hi, Ed.

ED (Caller): Hi. Thanks for taking my call. A long time listener. My favorite show on the radio. First time getting on the air with you though.

FLATOW: Thank you.

ED: And we always - well, in the last five years or so we've discovered the steel wool firework - kind of a do it yourself. It's a real simple, really magnificent the effects that you can get. You just take a high grade steel wool, a tight one. I think they're like Triple-A or something, or zero, zero, zero. And you kind of tie it into a metal clothes hanger. You take the clothes hangar, extend it so you can kind of swing it around and you light the steel wool. The funnest way to light it, we found, was just a 9-volt battery. You can stick that to it. It ignites it. I think the spinning of the whole apparatus makes the oxygen flow through it. And it makes a really brilliant spiral of sparks…

FLATOW: Hmm.

ED: …shooting, sometimes, 15 feet off of the end of it.

FLATOW: Wow.

ED: It can be dangerous, I guess. You can - little chunks of the steel wool can fall on your head as you do it, but…

FLATOW: Right. Well, maybe wear a football helmet or…

ED: Maybe, yeah, something. And maybe not a straw hat, but…

FLATOW: Not a straw hat. Dale Gray, good project?

ED: What's that?

Mr. GRAY: Yeah. I actually have a - I have a column about that very topic. I didn't think of sticking at the end of a stick and swinging it, though. That's a great idea. I had my daughter blow on it to get it to burn brighter.

ED: Yeah.

Mr. GRAY: I'm told this is actually a technique that they teach Boy Scouts for starting fires, if you're stuck in the woods and all you have is a 9-volt battery and a pad of steel wool.

ED: Yep.

Mr. GRAY: Not exactly sure how practical that is, but…

(Soundbite of laughter)

ED: Yeah. You happen to have those two items, but…

Mr. GRAY: It is an amazingly beautiful demonstration, though. And quite surprising, a lot of people don't realize that you can just light steel with a match, you know?

ED: Yeah. Exactly. You can use a big lighter. You can use anything. The funnest is the 9-volt because even if you get it wet or something you could still use it. And it's so cheap. You go to Wal-Mart, you buy a bunch of that steel wool. I think it's the triple zero grade or something, I can't quite remember, but I think it's…

Mr. GRAY: I - it's four zeros.

ED: Four zero, yep. And that thing is like $2.45 something like that. And then a metal clothes hanger, you just bend a little handle in it, so you can just swing it, you know, real easily or you can just spin it in your hand.

Mr. GRAY: Yeah. I'm going to have to try that. That sounds like a great idea.

ED: That's a lot of fun, too. And I know you guys mentioned earlier the Mentos in the pop. And I don't know if I - hopefully can tell you - about 15 years ago, we tried that. A friend of mine was drinking a Zima when they first came out, and I dropped a Mentos in there and it exploded.

FLATOW: Wow.

ED: Yeah. And about 10 years later, I started hearing about it everywhere. And so…

FLATOW: Yeah.

ED: Yeah. There's a lot of things you can do with that one too, but…

FLATOW: All right. Thanks a lot.

ED: Okay. Thank you very much.

FLATOW: You're welcome. You can try some - you could chew on Wint-O-Green Life Savers in the dark while you're out there and watch little sparks that go off in your teeth. Very safe fireworks that are created by chewing on those sugar crystals there. We have a Tweet that came in from writer Micah(ph). It says, please ask listeners to be aware of their neighbors. Many dogs and other pets will have life-threatening seizures from loud percussions.

And having had a dog who was - used to hide under the table on the Fourth just from firecrackers outside, I can sympathize with that. So be careful when you -if you're doing any of these loud pops or bangs that you watch out for your pets or your neighbor's pets. Also, a Tweet came in from Criselda(ph), who writes, you can make some spectacular flames with various salts in methanol -strontium, cobalt, copper, even boric acid. And I guess Anne knows a way to do that, that kind of stuff?

Dr. HELMENSTINE: That's definitely something to do.

FLATOW: Yeah.

Dr. HELMENSTINE: That's how the fireworks get their colors is from the same salt. You can do that at home because those will dissolve in alcohol or even water in some cases. You can use those to light fires for campfires. Color those or spray them - a good project.

FLATOW: Steve(ph) in Palm Coast, Florida. Hi, Steve.

STEVE (Caller): How are you doing?

FLATOW: Hi, there.

STEVE: Appreciate your show, really good. Anyway, I've got actually two of them. I thought of this one while I was waiting. First one, I use in Halloween. And basically, you get a flash and either a grave stone will drop or something comes streaming down the roof at you. And it's done with nitrocellulose, which you can get at any magic shop, flash cotton, they have flash paper and flash string. And this is the stuff you see magicians throwing balls of fire out of their hands.

You go there, you go to a hobby shop. You get rocket lighters. And you go to hardware store and get some PVC. The diameter of the PVC is going to limit the size of your flash. And I use - you can use a 12-volt battery, but what I use is a light switch hooked up to a Malibu light transformer that steps down the voltage where it's not going to hurt you.

FLATOW: Yeah.

STEVE: And just make sure it's off when you do - your next set. And you put the rocket lighter in the PVC, a couple of holes, a couple of slots, any way you want to do it. Stretch out the flash cotton where it's like relatively thin and you can see through it. And then put that down in the PVC, back up to your light switch and you get a flash…

FLATOW: Wow.

STEVE: …when you throw the light switch. You can have several light switches lined up, makes several of these little flash things. And you can add color, because they have stuff that magicians use to add color to the flashes, so you could…

FLATOW: Oops, we lost Steve. That's okay because we've run out of time. I want to thank my guests for coming on and being with us today. William Gurstelle is author of "Backyard Ballistics" and the new book, "Absinthe and Flamethrowers: Projects and Ruminations on the Art of Living Dangerously." Anne Helmenstine, who is chemistry guide for About.com, and Theo Gray, author of "Mad Science: Experiments You Can Do at Home But Probably Shouldn't." He is the author of the "Gray Matter" column for "Popular Science" and cofounder of Wolfram Research.

Thank you all for taking time to be with us today. Have a happy and safe holiday to all of you.

Mr. GURSTELLE: Well, thank you, Ira. Thanks for having us.

FLATOW: You're welcome.

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