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  • I'm really excited. We've got two beautiful demonstrations to show you

  • One's a real classic - the ammonia fountain.

  • The other one is a completely new one we've invented ourselves called Neil's balloon

  • They're both based on the fact that ammonia gas is very soluble in water

  • and when it dissolves in water the water goes alkaline.

  • So if you put in an indicator that is colourless in water and red in alkaline.

  • When the ammonia goes in, the water goes red.

  • And we use the indicator Phenolphthalein.

  • The classic experiment is called the ammonia fountain.

  • It consists of a large glass bowl filled with ammonia

  • which has a cork or bung in the bottom with a glass tube going through it about halfway up the flask.

  • And the idea is, if you put the bottom of the tube into water, the ammonia starts dissolving in the water.

  • It creates a partial vacuum because you're absorbing gas and so the pressures going down

  • and the pressure of the atmosphere pushes more water into the flask.

  • More ammonia dissolves, so more water goes in.

  • Now the problem was we set it all up,

  • Neil set it all up. He put ammonia into the flask.

  • Ammonia is lighter than air. So you can just fill the flask in up by putting the tube inside it

  • And he then put the bung into the flask

  • And then before we started, we had the tube just above the surface of a large jar of water

  • And enough ammonia was coming out to start triggering the indicator

  • And the most beautiful red threads started appearing in the jar

  • I was so excited I nearly wanted to stop there

  • Then, we lowered the tube into the water,

  • But, there wasn't enough difference in pressure to get it started

  • So Neil and I decided to pour some liquid nitrogen over the top

  • which cooled the ammonia, reduced its pressure

  • and therefore began to suck in the water

  • And once the water started going in, it was really beautiful

  • [Music]

  • Neither Neil or I had ever seen it before

  • There was a slight problem that the bung hadn't been pushed in quite hard enough

  • So little air was leaking in as well

  • But that caused bubbling which probably added to the effect

  • And for reasons that I don't quite understand

  • that as it went on, the form of the liquid film that was on the glass surface changed a bit

  • So there was an ever-changing patterns

  • And also the color of the indicator changed quite a bit So it was really nice

  • Before we go on to the next one, just let me remind you

  • the reaction here is ammonia dissolving in water making it slightly alkaline

  • And the red colour is not part of the reaction - that's an indicator to show you that the water is alkaline

  • The next demonstration ...or really it's an experiment because we didn't know whether it would work,

  • began with my idea that we should try filling a balloon with ammonia

  • because ammonia is lighter than air, so I just wondered whether a balloon of ammonia would float

  • Not something you'd want to use at a party because if it bursts, there'd be a smell, but it does float quite nicely

  • Then we remembered that if you put sticky tape onto a balloon

  • you can then stick a pin or a needle through the tape into the balloon without bursting it

  • The reason for this is that when you normally prick a balloon...

  • when you make the first hole, the fabric runs from that hole and a slit goes up through the fabric and it breaks

  • But if you have the rubber held by sticky tape, it can't move

  • So we had the idea that we should try injecting water with Phenolphthalein into the balloon

  • What we hoped was that

  • the water would absorb the ammonia so the pressure would go down and the balloon would shrink

  • Of course, with the fountain, the size of the flask can't change and of course it fills up with just more and more water

  • So the idea here was [this'd] be a much simpler demonstration that we could do perhaps more quickly

  • Before we started filming, Neil practiced with a syringe needle in a nitrogen balloon

  • Just sticking the needle in - it worked perfectly

  • But then when we started filming, the first balloon, needle went in, there was an enormous bang

  • [bang]

  • And we all ran out of the room because of the smell of ammonia

  • The ammonia disperses very quickly so it's not dangerous

  • [bang]

  • So for the third time, I suggested we went to cello tape or scotch tape rather than plastic tape

  • And we used a bigger needle so we could inject the liquid faster

  • And it worked beautifully

  • [Music]

  • When the liquid went in, the ammonia started being absorbed and the balloon beautifully shrank

  • But what we didn't realize - because Neil was holding it - was that

  • when ammonia dissolves in water, it produces a lot of heat

  • There is a positive heat of dissolution - a heat of reaction

  • So the balloon was actually getting hotter and hotter and Neil nearly dropped it

  • However he managed to hang on till the balloon went from this sort of size to about the size of my clasped hands

  • We were all really very pleased

  • In a way, it's a nicer demonstration to show how the gas is disappearing into the liquid than the traditional ammonia fountain

  • Because in that, the size of the flask doesn't change

  • But really, both of them are fun and I hope you enjoyed them

  • [Music]

I'm really excited. We've got two beautiful demonstrations to show you

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