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  • I seen the barking dog probably 100 times, maybe more, and I never noticed this before because it's just too fast for the eye to see.

  • This reaction is one of really favorites.

  • It's been carried out for many years as a demonstration to our students on particularly by by myself and some of my colleagues, but also by Bt Short Colonel sure who used to do the thunder and lightning lecture many, many times and apply a light.

  • It's called the barking Dog.

  • It produces quite a kind of ah, a barking dog sound.

  • A wolf sounds.

  • It involves a test tube, a really big test tube.

  • This is just a model with a cork, and inside is a mixture of carpet.

  • I sulfide CS, too.

  • On dhe end to a nitrous oxide, the flame shoots out the top of the test tube.

  • So I guess you have this image of this if this flame coming open, consuming your hand if you leave it over the top of the test tube too long.

  • On my first few goals, I was quite You can see me flinching in some of the videos, but I'm as I've done it now probably but tens, if not hundreds of times a flinch, less and less the combustion front racist to the bottom of the tube, giving up this amazing walk.

  • And normally what the audience sees is a great which the note just goes up like the sweet kind made.

  • Then it could be drawn out.

  • It could be roof, or sometimes it goes much quicker.

  • But when you watch it in slow motion, it looks quite different.

  • Now, you may not have seen exactly what happened.

  • What I observed was that although the flame started slowly, it built up speed as it went on.

  • I've never seen it using this really, really ultrafast camera.

  • You still see the flame going down instead of going down in one great bush eggs jumps up and down the tube so it goes down a little bit and then up and down and up and down and so on.

  • And as it gets nearer the bottom, it seems to go up and down more and more.

  • Okay, so we'll take top off.

  • Well, not much.

  • And I thought that this this this flame front used to go very, very smoothly from the top to the bottom and hence the whoop.

  • But actually, what this video footage is shown us is that it actually goes in stages.

  • It's sort of good.

  • Thio chunks its way to the bottom of the tube.

  • We weren't quite sore what was happening.

  • I think what's happening is the pressure wave is bouncing off the bottom of the tube.

  • Now a number of very curious things are going on in this to imagine this hand here, the one with the waltz is the flame front coming down, and as it comes down, it gradually goes faster as it heats up and burns the fuel and eventually gets the stage where it almost explodes and sends a shock wave down to the bottom of the tube.

  • When it gets the boat of the tube, you can't go any further.

  • It's not strong enough to break the glass.

  • The only time it ever went wrong for me was we broke the bottom off the glass, so I guess that the pressure pushed that the tube downwards and we broke the top off the end, and I only know of that happening once and it happened to me.

  • So it's reflected and comes up again.

  • And then when it gets the flame, it gives it to push upwards.

  • So the flame is now burning up here where there isn't quite so much fuel, and it gradually warms up again till it gets here, where the fuel is rich and then another shock wave Good up again.

  • Actually, if you look really carefully, it looks like it's picking up speed as it goes down the tube.

  • And I think that's because the distance between the flame on the bottom of the tube is getting smaller and smaller each time pull up till, in the end is going really quite fast.

  • Well, we still have another you prepared, and so you have another opportunity of observing this effect.

  • I've seen two or three fucking dog experiments since then, but the flame front going down is really too fast to see this bouncing and anywhere I'm too busy blocking my ears.

  • Two really pay attention to the flame front.

  • I think of all the slow motions that I've watched, that one was the most surprising because you could have expected that cesium or rubidium would cause a big explosion.

  • But none of us really expected this motion of the flame front.

  • I suppose once you've seen it, you can think of an explanation.

  • It's no longer such a surprise, but none of us were expecting it.

  • Every time you do a new experiment, you see something subtly different.

  • And that just asked.

  • It makes you ask more questions.

  • Red circle, Read said.

  • Ready on the trigger.

  • Ready?

  • Yeah.

I seen the barking dog probably 100 times, maybe more, and I never noticed this before because it's just too fast for the eye to see.

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A2 tube flame test tube barking bottom front

Barking Dog (slow motion) - Periodic Table of Videos

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    林宜悉 posted on 2020/03/27
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