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So the blue one in the middle of this series is argon, so again this is a
very nice glass tube that we’ve had made with a low pressure of argon
inside. We’ve put a potential across from the two ends, here and here,
and this excites all the argon molecules inside so you can see this
wonderful characteristic eerie blue glow coming off from the argon.
Argon is one of the noble gases or so-called rare gases. It’s not really
quite so rare. It consists in really quite a high percentage, nearly one
percent of the atmosphere.
If I look at the one in the middle I can see lots and lots of lines in the
blue and the green region and these are all specific to the individual
atoms that are in the tubes themselves.
But it’s very un-reactive so early chemists found it quite difficult to
identify, in fact it was only Sir William Ramsey that identified the argon in
1894 and he was in fact the first person in Britain to win a Nobel Prize for
chemistry.
So if we turn off the power to this, we turn off the potential and then we
don’t excite the molecules so what we’d see is just a clear glass tube
with no visible sign of anything inside. And only when we turn on the
potential that we excite the molecules, so they emit and give us these
really quite wonderful colours.