You've probably seen our last two videos, one about breaking a tube of sodium
under water and the next one breaking two tubes of potassium under water.
Now the real reason that Neil devised his special device for breaking glass
tubes underwater was because for years he's been holding a 5 gram sample
of caesium in his cupboard and he wanted to see what would happen with breaking
that caesium underwater.
Now, the caesium sample is different from the other ones that we had because
that's a commercial sample which was sealed under vacuum so there's no gas
at all and the other difference, which is a physical difference, is that caesium
metal is much denser than water
so there is no way that caesium metal itself can spontaneously float up to the
surface of our trough and for those of you who watched their earlier videos
it's important to realize that the five grams of caesium have about the same
number of atoms as the weights of potassium and sodium that we were using
in the earlier experiments
so you have three experiments you can compare.
I should also say, like the others, this was filmed outside but it was filmed a
bit later in the day so the sun was at a different angle and you can see this
because as Neil started turning the screw
there were some interesting ripples on the surface from the vibrations and gave
quite nice patterns in the high-speed video but this is not chemical this is
just vibrations again like the other two as the test tube begins to break you see
some bubbles of hydrogen coming out now this time we know its hydrogen because
there was no gas at all
inside the vessel
one part of the test tube you can see shoots across the screen and ends up on
the left hand side close to the wall of the vessel but that piece near the wall
still has a lot of caesium in it and the water will then rush in again
it reacts with the caesium so there's another big explosion and it's really big
because if you look at the side of the plastic vessel which is pretty rigid it
bulges out and the surface of the water looks like a model tank when they are
videoing a disaster movie of the storm
huge waves and potassium it was just a few ripples
so a lot of energies come out.
And this video is probably the best demonstration
that I've ever seen that shows that cesium is a lot more reactive than
potassium because we have had the conditions very much the same with one
we get to reasonable reaction here we get something where Neil was worried
that his plastic vessel might be ruined
we have also with this tank of water a sort of crude energy meter
the more the waves go the more energy is released and here if you look at them
side-by-side, potassium: slight waves, caesium: hurricane! of course we didn't do
rubidium because Neil didn't have rubidium stashed away and so if any of
you've got five grams of rubidium we're always up for trying it.