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  • 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.

You've probably seen our last two videos, one about breaking a tube of sodium

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