Tales from the Prep Room: Lighting a match
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- Andrew Marmery
- London, UK
- Filmed in:
- The Prep Room
- Collections with this video:
- Tales from the Prep Room
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01:49 Water boiling point
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WolframAlphaWater boiling point
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01:59 Autoignition temperature
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I've just sent the better of my hot plates to Japan.
None of this stuff is quite straight.
This is my apparatus for, which we're going to use to light a match with water. Sounds an improbable thing to do, but that's what's going to happen hopefully. I have never actually done this before, so maybe it won't happen, but we'll see.
So we're going to boil water in here, over a Bunsen. The steam is going to boil off, flow through these tubes, into the coil, and out here. And while it's flowing around the coil, we're going to try and superheat it with a blowtorch. So when it comes out, it's a few hundred degrees centigrade. And hopefully that will be enough to light a match.
Of course it would have been helpful if I'd filled that from the hot tap.
Oop. Classic schoolboy error.
OK. That will take a couple minutes to come to the boil, I think.
You can't normally light a match with water, or even steam. Because it's just not hot enough. The normal steam you get off boiling water will condense pretty much immediately on anything because it's only just above its boiling point. So as soon as it hits anything cooler, it will just condense.
It's getting hotter quickly, actually. We want to really heat the steam up to a few hundred degrees. At which point, hopefully we'll exceed the autoignition temperature of the head of the match.
So the head will have a temperature at which, if you raise it to that temperature, it will spontaneously ignite. And that's what we're trying to do. Just to heat this water hot enough that that will happen.
OK. So the thermometer is reading quite a lot less than 100 degrees. But that's probably not really a surprise. We've got this huge coil, which at the moment is acting like a condenser. So we're probably not getting water above 100 degrees out the end. Which is where the blowtorch comes in.
So you saw just now, before I started using the blowtorch, there was a lot of condensed water dripping out the end of the pipe. The plume of droplets, the plume of water mist that you saw coming out as the water condensed, is now pretty much disappeared completely. Because it's now too hot, and it's not condensing when it comes out at the end of the pipe.
It's a bit of a problem juggling all these extremely hot objects. But - I'll probably just take the blowtorch away while I do this. Oh. Not bad. I've never seen a match do that before. It sort of smoldered without igniting. Didn't know that was possible.
I wasn't convinced that there was enough heating going on there. So I've got another Bunsen out. We'll see how we get on with that. So I've set the water boiling off again. Let's light this other Bunsen.
Now we've got our copper coil actually glowing red hot. So I think this is going to do the job now. I don't think it is that easy to melt copper. I think it'll radiate a lot of heat before it gets to that point.
OK. So let's give the thermometer a go. See if we're - see how hot we might be. It's really racing up. Nope. Hm. I see. Well, I've learned something new today. I've learnt that my thermometer only goes up to 200 degrees. So we've maxed it out.
Oh. There we go. That's a really interesting observation, actually. And I think that the problem we had before was not so much that it wasn't hot enough, but that I was just holding the match too directly in the stream of steam. And not pulling out as it started to smolder.
And obviously, there is no oxygen in what's coming out of here. This is pure gaseous water. So there's no oxygen there. So the match wasn't actually able to ignite. And I think that was probably the problem.
And now: A, we've increased the heat. But B, if I just stick it into the stream and then withdraw it, to allow the air to get to it, at that point the match ignites.
About this video
Lighting a match with water.
Ri Demo Technician Andy Marmery shows us how to light a match without striking it. Using a Bunsen burner, a blowtorch and a super heated copper coil, Andy ignites the match in a stream of pure gaseous water.
The key to producing a flame is getting the water hot enough so that it exceeds the match’s auto-ignition temperature – the temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition.
To activate this reaction, Andy boils the water and superheats the copper coil through which the steam passes. The temperature of the steam exiting the coil is high enough to ignite the match – as long as the match is moved back out of the stream and into the oxygen present in the Prep Room air.
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