Fire Syringe

So, uh, what have we got here? Oh, we've got something called a fire syringe. And what does it do? Oh, well, I'll show you what it does. Some cotton wool in there. Okay, I'm just going to compress the air in it, and hopefully it will... I don't know what it's going to do. Wow, that's pretty cool! You made a spark in there. Was there any source of fire, like a match or anything down there?

Well, as you can see, it's pretty transparent. There was no match in there. Um, it was actually just the compression of the air on top of it, um, which was able to ignite the, um, the cotton wool that we had in there. So you're saying if we compress air we can make it hot enough to ignite cotton?

Yeah, because air is made up of particles. So when you're actually compressing it, you're forcing those particles to collide closer together, which is actually going to raise the temperature in the inside of that tube there.

Okay, can you describe the apparatus for me? Well, all there is, is there's a glass chamber in there where the cotton wool sits, and as you can see, there's this piston that moves up and down into that glass chamber. And as it moves up and down, you can actually compress the air. So, it's like a little plunger.

Like a little plunger, yeah. Okay, so, uh, why don't we set one up, uh, so we can do it again? Do it again!

Okay, I'll clean the remnants out. What are the tricks here? Uh, the trick is to get not too much, but not too little cotton wool, and it's good to get it aerated so that there's a lot of air around it. So, it makes it much easier to, um, ignite just like a good fire.

Is it just me, or do you feel like we're on a cooking show? I feel like we're on a cooking show! Yes! Who do you think would be Jamie Oliver in this situation? Would it be you or me?

I'm more manly, so he's more like Nigella Lawson, let's face it! That's a good play on words! I wish! All right, we're ready for this! Yes, simple as that. Obviously, no matches, no switches, no anything.

Okay, um, we'll try it again. You want me to try? You can try it! Do you have the strength? We're going to find out. We'll find out. This is going to be awkward for Derek, I think.

Okay, so what I'm going to try to do is compress the air in there, and by compressing it, I'm going to increase its temperature, 'cause we're pushing all these air molecules together. And if I get it hot enough to the ignition point of cotton, hopefully the cotton will catch on fire.

Yeah, I've heard that the, um, auto ignition temperature of cotton is about 400°C, so you can get quite enormous amounts of temperature from a very quick compression.

3, 2, 1... Oh, surprise! Beginner's luck! Yeah, check that out! So, I guess we could generalize and say if you do the compression quite slowly, then there is time for the heat to escape out of the air, and so we don't actually get a high enough temperature to cause the cotton to ignite.

Yeah, and there's actually a word for that. It's called adiabatic compression. That's the one where there's enough heat generated quickly enough so that we can get that auto ignition.

Yeah, so an adiabatic compression would be one in which the heat doesn't escape from the gas, doesn't have the time to. Absolutely!

Yeah, all right, well let's go see if we can autoignite some other things! Yeah, maybe some hair. Okay, maybe not a good idea.