You see there is no color change at all, and that is because here, we have a physical effect. The two colorless liquids, which I have mixed together, are now changing their state. One of them is changing from the liquid state to the solid state; that is the water.
And the other one, the liquid nitrogen, is turning from the liquid state to the gaseous state. So, here we have the three states of matter in one very straightforward experiment.
Now, as the liquid nitrogen continues to boil away, you may hear a slight crackling sound. Now, this is because, when water freezes, it expands slightly, and as it it expands, the crystals take up a greater volume, and they push against one another, and they set up enormous mechanical forces, which is what the crackling is about, and sometimes the beaker may actually crack.
So we shall keep our eyes on this, allow the process to continue, and I can just hear the beginnings of a crackling sound.
Now, I just top it up, make sure we continue to freeze our water. And I wanted to tell you that when liquid nitrogen was first made, at the end of the 19th century, it did set off an entirely new era in the history of technology, and that’s liquid gas technology. And thanks to that, today we have frozen food, and we have a huge number of all sorts of effects that we benefit from; among them, of course, are refrigerators.
Now, to continue then on our experiments – and also the science of cryogenics. To continue with our experiments with low temperatures – these, by the way, approximately five to six minutes, you’ll hear the bangs, so please be warned.
I’m now going to show you an experiment with a solid. Here we have a piece of rubber tubing, and it’s elastic. The reason why it’s elastic is because, when you stretch it, it returns back to its original shape.
Now, the reason why it’s elastic is because – I can hear the pressure being taken up, so you may hear a bang shortly. Now, the reason why it’s elastic, from a thermodynamic point of view, is because it’s very warm in here. (Banging)
And because it’s very warm in here, these molecules in here have lots of energy. However, I will now place the rubber tubing into liquid nitrogen, and please observe carefully what happens as we lower the temperature. And you’ll notice this most interesting effect of a shower, a shower which is issuing from the end of the rubber tube.
Now, why does this happen? Well, it’s for the same reason that the bottles are exploding in there, and that is because, as the liquid nitrogen boils fiercely when it comes into contact with the very hot rubber tubing – so it expands enormously, as I said, by a factor of about 800. That boiling, therefore, pushes the liquid nitrogen out, setting up a pressure that forces it out there.
As you saw there, it did not have anywhere to escape, and that’s why the bottle finally gave way.
Now, let us inspect our rubber tubing which we have here, and let us see what has happened to the elastic property. It went in as an elastic solid, but now, you see, it’s no longer elastic. And if I whack it well on this table – please watch carefully – then it will shatter into 1,000 fragments.
Now, the reason why it shatters into 1,000 fragments is because, at high temperatures, the molecules are all vibrating. We have lots of energy, the molecules of the rubber tubing have lots of energy, so they’re all going around like that.
But when you drop them into liquid nitrogen, there is very little energy, and so the molecules suddenly freeze; they go like this. They freeze solid. I’m, of course, being silly, but I’m illustrating an important scientific principle.
Now, I wanted just to show you here – we’re just going to see – in the meantime, I just wanted to show you, our beaker has indeed cracked. There it is; a piece of glass has fallen away from it, and what that shows you is, it just shows you the huge forces, intermolecular forces, which are set up when water freezes. It freezes; the molecules rearrange themselves to form an open lattice.
Now, here I have a beautiful balloon, a beautiful balloon. And why does it have the pressure? It has pressure inside it because the molecules of nitrogen and oxygen in the air are moving around because they have lots of energy because it’s very warm.
But if we reduce the energy by pouring liquid nitrogen over the balloon, then you will notice a very, very interesting effect. So please, watch carefully. I’m going to pour liquid nitrogen over the balloon, and as you notice, the balloon starts to contract. And as the balloon starts to contract – so, you’ll notice, getting smaller and smaller, and it undertakes a shape which has no elasticity; it has completely collapsed.
Now, why is this? Well, once again, it’s the same reason: at the low temperatures – sorry, I think the floor is cracking underneath me. Bear with me. Everything is freezing all around, but we’re still alright. Please look carefully. The balloon has now collapsed; it looks very sorry for itself.
But if we allow it to warm up a little bit by shaking it up, throwing it up in the air, in a very short space of time – let’s see if I can catch it. I’m sorry, it’s escaping from me. It’s escaping. And as you see, it has been restored to its full shape.