people initially when we used to show it
they they would just assumed it was
Mercury so because it looks the same
this sodium potassium Fountain liquid
metal Fountain is is a device that
enables you to safely move these liquids
around without letting them get exposed
to the atmosphere or to your skin or to
anything else Knack is an alloy of
sodium Na and potassium K and what makes
it unusual is that when you mix these
two metals you get a metal that is
liquid at room temperature it looks like
Mercury but it's very light in fact it
should float on water and it looks a
little bit like Mercury unlike Mercury
of course it's highly reactive and and
you've got lots of videos that show
reactions of sodium potassium and you
just don't want to uh to have these kind
of things around the atmosphere around
water you start dropping it it's so
reactive that it will react with the
water in the air and it'll be on fire
before it even reaches the water it is a
liquid and therefore the surface is
clean so the oxygen and water in the air
can get to the surface much better than
it could as a solid more than 35 years
ago there was a lot of research here on
Knack they used to use it as a coolant
so it's a liquid so it can be flowed
around quite easily but it's a metal so
it's got really EX excellent thermal
conductivity so this liquid metal was a
coolant and it was particularly used in
the in the nuclear industry neck was
being used for cooling nuclear reactors
particularly the sort of reactor known
as a fast breeder reactor and knck was
chosen as the coolant because as a metal
it conducts heat very well you would
take the the heat away from uh a nuclear
reactor carry that heat away in this
liquid metal deliver it to water without
letting the two Touch of course uh and
then the water would be turned into
steam and that steam would go away and
would power a turbine and create
electricity and sodium and pottassium
can go in intense radiation Fields
without becoming radioactive the problem
is that it could be corrosive and so my
colleagues were doing a whole series of
studies on corrosion which involved
pumping round
knack for days if not weeks over test
pieces of metal to see if any of it
dissolved that is the metal dissolved
Into The Knack because what that would
mean is that if you use those Metals in
a nuclear reactor you could dissolve
them away with a coolant and that would
clearly not be a good situation don't
make your pipes out of that one yes the
problem that they had was they needed to
pump around this liquid that was
enormously corrosive or potentially
corrosive and reactive and to do so when
it was at quite a high temperature
because they were simulating reactors
that had a temperature of 2 or 300°
Centigrade if not more and they devised
a fantastic pump and built one of these
pumps out of glass so that it could be
shown as a demonstration for
visitors
[Music]
unfortunately about 10 years ago or so
before we started periodic videos It was
decided that these demonstrations were
so dangerous that we had to get rid of
them but before it was destroyed my
colleague Steve made a video about it so
let me explain how it works it is based
on the same principle that is used for
electric motors you have
a piece of metal carrying a current
which is in a magnetic field and there
is motion what we have here and this is
a crude analogy we have a powerful
magnet North and South magnetic poles
okay and in between we have the
container with a knack and then there
are two electrodes going in two wires
that carry a current there is a historic
trick in physics for memorizing called
Fleming's left hand rule so it's based
on the thumb and these two fingers which
if you hold them right are all at right
angles and what this says is that if you
have the magnetic field given by this
finger going in this direction from
north to south and the current going
through in that direction you get motion
going upwards in the direction of my
thumb so what you see there is you see
Steve cranking up the current as he
cranks up the current what happens is
that the liquid carrying the current
between the two wires experiences an up
thrust and because it's very light it's
not a dense material it shoots upwards
and you get a little Fountain the pipe
work is such that the liquid then just
goes around and round and round you can
you can see this on the video that you
have the second finger is the current
that's going across the electrodes uh
the first finger is the field that's the
big magnet and when you put those two
together and you turn up the uh the
current and you've seen me doing that in
the video then you get the motion and
the motion is the fountain that gets
flung up through that um through the
guess there an oril office there that
throws it up the fountain goes up and
then the stuff comes down and goes back
down the bottom and then gets thrown up
again so you get this continuing cycle
of liquid metal that's going around and
around because the stuff is so dangerous
the whole apparatus is then surrounded
by a glass bulb which contains argon so
if there is a leak all being well it
doesn't burst into flames so The Knack
was going round and round and round
washing the surface over and over again
and so you could measure the corrosion
quite precisely and sometimes they
measure the corrosion electrically by
measuring the resistance of the piece of
metal that they were studying because
Knack is such a good conductor they
could make the whole apparatus out of
metal and it would still work the one
we've got on the video is glass so you
can see what's happening for the first
20 years that I was here at Nottingham
we used to demonstrate this to visiting
students it would just be sitting in the
corner of the the lab and as we took a
party round we'd say look I switch this
and and they'd go all go o and perhaps
come to Notting him but most of them
didn't realize quite what a historic
piece of equipment it is
my feeling is that probably it was an
act of vandalism to destroy this
equipment and we should have just made
it rather safer and still kept it
because it is really a historic
experiment as far as I know I mean I I
used to use this to demonstrate when it
when it was uh not deemed to be uh too
dangerous to do so but then it was and
it taken away of course you could fill
it with Mercury the problem is that
mercury is very dense the Mercury would
feel EXA exactly the same force from the
current and the magnetic field but it
just wouldn't be enough to lift the
Mercury up because it's so dense what of
course you could do is to put in a very
very much bigger current and then you
could make mercury go around but
probably something unpleasant would
happen it would overheat or Arc or
whatever so it's really designed just
for doing Knack or you could use it at
higher temperature for liquid sodium or
liquid
potassium like everybody dealing with
dangerous chemicals if you know how to
handle them they can be quite safe in
fact on the other side of this building
there was a piece of apparatus that had
two
gallons that is about 8 or n lers of
liquid
sodium at a temperature above its
melting point which is
96° and you could go up there rather
like to te ear and just take a thermos
full of liquid sodium and take it back
to your lab and that was there for
perhaps 10 years before they got rid of
it and so I never heard of any accident
at all from these