When we were working with Desten and his high-speed camera

We tried one of our favourite experiments, Neil's burning cauldron

Now, the demonstration consists of two parts

The first one is taking a metal vessel, and pouring in liquid oxygen

When you watch it normally, it's just pouring stuff out of a thermal flask

What's interesting in high-speed, is that as it goes in, the oxygen actually breaks up

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There's been a lot of research by different people about how liquids fall

And, it's quite complicated, because it's a combination of surface tension, viscosity

But here, you have the added complication that the liquid is very cold, compared to the air

So it's actually boiling

When it goes in, there's a sort of cloudiness

But that's just the water vapour in the air

You end up with a rather foggy looking liquid

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The second part of the experiment is dropping in a piece of hot charcoal

The first thing that quite surprises me is that as this piece of charcoal comes down

and hits the surface, it actually bounces up again

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But, because it bounces up again, and presumably the hot charcoal has vaporised

a bit more oxygen

It actually starts burning, when it's in the air

And as it comes down again, it burns quite brightly

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I think about it for a moment, you've got a very hot piece of charcoal

on top a very cold liquid

So the liquid immediately under the charcoal will be boiling

and will be generating gas

Which probably, causes the charcoal almost to float above the surface of the liquid

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And if you look carefully, you can see that the charcoal keeps on burning brightly

And then, it goes dimmer again

And then bright, and dim, it's sort of pulsing

And I think, and again, I haven't done any control experiments

but it seems quite likely, that what happens is that, when it's sitting on oxygen gas

It burns rather more brightly, it uses up that gas

And then sinks down onto the surface of the liquid

The hot charcoal vaporises some more, and it starts burning again

lifted up on the oxygen cloud, so it goes up and down

But, the key point

is that, I as a chemist, see that something that I thought was fairly straight forward

is actually more interesting, and more complicated than I thought

Not to, inflame things or try and make too much of the chemistry, physics rivalry

But it seems like in some of those thoughts we had, it's like the chemistry is well understood

But it's the physics that's really interesting, and add in this extra dimension when we see it in high-speed

I think that's a very sensible point

Because, very often, in the short term, in the short time scale, it is the physics

the mixing of the reactions, or the viscosity, or whatever

that determines what happens

And you could uh- you that it's chemical engineering rather than physics

But, it is this combination of the chemical process, and the physical one, that is very interesting

It is important because many of the phenomenon we observe, even when we look at it slowly

Is the result of these two effects, but we don't always realise they're going on