- The Bank of England is issuing new bank notes, beginning with the £5 note.
And they're made of plastic, and there've been all sorts of advertisements that you can't break them.
I felt immediately: challenged
and I had the idea, if we froze it with liquid nitrogen...
the strands of the polymer would be frozen rigid...
and you may be able to break it— hitting it with a hammer.
So I gave Neil several of my own £5 notes—
you can't spend university money on things like this
—and he had great pleasure trying to break the professor's bank notes.
And it worked!
He managed to smash one, but it took several attempts.
You had to get the orientation just right and hit it just in the right way,
and then it broke into two or three pieces.
Unfortunately, he lost one of the pieces, so I couldn't glue it together and spend the note,
so it's a souvenir.
Incidentally, it's not illegal to break the notes, though it's illegal to draw pictures
on her Majesty's face.
But Neil felt that this wasn't really quite exciting enough,
so he decided to put this in his special supply of fuming nitric acid.
It's a bit old, so it's gone brown, so it may be even better.
Fuming nitric acid... and there's several sorts, and I'm not sure what Neil's type was particularly,
but essentially, it is a mixture of pure nitric acid—or nearly pure nitric acid
with N2O4 dinitrogen tetroxide added to it.
And N2O4 in itself can dissociate into NO2, so it's quite a witch's brew
or perhaps I should say wizard's brew in the case of Neil.
It is well know as being a very powerful cleaning agent.
If you can't get muck off your glassware, the last resort is fuming nitric acid.
Neil's hypothesis was that he could completely dissolve it—it would just disappear
and he could have a solution of a £5 note.
What happened was actually much more exciting,
that when he put it in, the queen's face quickly faded.
When he took it out, there was some of the writing and stuff still left.
But it just brushed off quite easily and what he was left with, to all our surprise,
was a completely transparent piece of plastic, exactly the same size that he started with.
- yeah, lovely.
- I gave this sample to one of my student who ran an infrared spectrum
and showed that it was polypropylene.
This is the plastic made from propyne.
When it says on the internet these are made from polypropylene, they're right!
It's really fun. I now show this to people and say "what do you think it is"
and they have no idea.
You can see that we did a proper experiment in the sense that we had a control.
I insisted that they also use one of the old paper notes.
The queen didn't fade as much on the paper note, but when they had taken it out and dried it,
it was interesting that the note had gained really quite a lot of weight.
And this was absolutely consistent with my idea
that the fuming nitric acid might nitrate the cellulose of the paper.
This is adding NO2 groups to the paper,
and nitrated paper burns very much better than ordinary paper.
It's used by magicians and conjurers and it's the basis, in fact, of gun cotton,
which is used as an explosive.
It went with a real woosh!
And what was particularly interesting is that it burned without any ash at all.
It just disappeared, and the reason for this is that with the NO2 groups,
you have enough oxygen in the note to make it burn to completion.
So we have a really nice farewell for the old paper bank note.
It just disappears into thin air.
I must stress that we've done this in the interest of science and because we think
it's an important and interesting experiment.
But, on the other hand, we are destroying bank notes, and so we feel that it's only right
that we've given an equal amount of money to charity
to show that we don't really want to destroy money just for the sake of it.
I should say to you that if you want to repeat these experiments,
there are probably cheaper ways of doing it than using bank notes.