Sometimes Brady and Neil do experiments that are just for fun
And then they ask me what's going on.
So the experiment they decided to do was to
drop a piece of burning iron wool
this is finely divided iron wire
that looks a bit like my hair.
Slightly darker.
And you can light such iron wool
by putting it across the terminals of a small battery
and it glows red and you can see it burning in the air.
Not very vigorously but enough to stay red.
And then they dropped it into Neil's favourite cauldron
in which he often puts liquid oxygen.
When they dropped it in, and they did it several times,
there were the most amazing colours.
Essentially in all of it the iron burns.
It didn't all burn because at the end there were
bits of iron left in the bottom.
The chemistry is very simple:
The iron is reacting with oxygen.
There are three oxides of iron: FeO, Fe₂O₃, and Fe₃O₄.
Heaven knows which one was formed in these reactions, and it was probably a ghastly mixture of them
but the formation of all of these is highly exothermic:
It gives out a lot of heat.
So you have iron going into the liquid oxygen
producing a lot of heat, and, because it's so hot, it produces a lot of light.
In essence, what was happening is that you have small pieces of very hot iron
in liquid oxygen
and there were really beautiful colours.
A reaction like this is not very reproducible
because it depends exactly where you drop it, how the light is reflected,
where Brady was standing when he took the shot
so every picture is different, and nearly all of them are really beautiful.
Liquid oxygen is at a low temperature, -186 degrees centigrade
and you're dropping in a piece of hot metal
and you would expect that metal to cool down
but it was getting hotter.
The obvious interpretation, if you see these pictures,
is that somehow the iron is burning in this really cold liquid
but that's a contradiction. How can something be very hot
and very cold at the same time?
Now, what I thought was that the iron was so hot that
it was effectively in a bubble of oxygen gas
which comes bubbling up all the time
but was able to sustain the combustion.
But you can't really see that from the top
because you're looking through liquid oxygen.
So we decided we needed to do another experiment
looking at this vessel sideways
so you could see the liquid and at the same time you could see the iron at the bottom
and see what was happening.
But, experimentally, this is not easy.
The first problem is that liquid oxygen is very cold
so the air contains water vapour
which can condense and ice the whole thing up very quickly.
You could get round this by using a transparent Dewar flask,
A Thermos flask,
but they're quite expensive and the last thing you want to do
is to put hot metal inside it and crack your favourite Thermos vessel
and because these are evacuated, if they do crack,
they will explode spectacularly
which might make a good video,
but is unfortunate if it's an expensive piece of kit.
So, after discussion with Neil, we decided that the best thing to do
was to use an ordinary beaker
and to put it in a plastic box,
the one he'd carefully made,
and try and fill the box with either oxygen or nitrogen
which would not condense.
The experiment was moderately successful.
What I was hoping to see was the iron going in, sitting on the bottom,
and burning, surrounded by bubbling gas.
Of course, what happened is that when it went in,
there was such a bright flash
that was pretty difficult to film,
though Brady used some quite good tricks to get round this
and we couldn't get rid of all the ice forming
but the other thing, which we hadn't thought about,
was that the reaction was so violent
that burning bits of iron were pushed out of the beaker pretty quickly
and they landed on Neil's favourite plastic box
and set fire to it.
It wasn't actually the plastic
but it was the silicone sealant which caught fire.
I didn't think that silicone burnt very much at all
but when you see what happened to Neil's box,
we had demonstrated beyond doubt that when you have an atmosphere of oxygen,
silicone burns pretty well.
And I'm sad to say that Neil's box may be ruined.
It's certainly not in a good state.
But what was particularly surprising to me
was that the iron had got so hot
that it had actually gone through the glass of the beaker
and effectively punched a hole through it.
When we looked at the cauldron,
we also found lumps of iron in the bottom
because the molten iron was hot and started forming larger lumps
and these larger lumps have a smaller surface area,
so they don't burn so fast
and eventually they cool down and the reaction stops.
And you could tell that they were lumps of iron
because you could pick them up with a magnet.
So, what's the message?
Well, it's obvious, our experiment failed!
We did see something,
but we're still arguing what exactly we saw
and I don't think we can produce a really neat explanation of what happened
so we've got to go back to the drawing board
and design a better experiment.
The film we have taken has had such nice footage, particularly in the cauldron,
that we really wanted to show it to you
and I think it's really important to stress that when you're doing science,
not every experiment works
and you can still enjoy experiments that fail
and, so, enjoy our failure.
Very nice object.
Now, Steve I have the impression you think you know what this is.
This has got be a Davy lamp.
If you´re a superhero that would be your suit
And I hate to think what my origin story would be, but...
There is a second picture here.