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I'm Peter Wothers, a chemist. | 0:00:02 | 0:00:03 | |
Hundreds of years ago, I would have been called an alchemist. | 0:00:03 | 0:00:06 | |
I would have thought everything was made up of just four things - | 0:00:06 | 0:00:09 | |
earth, air, fire and water. | 0:00:09 | 0:00:12 | |
This is my lab in the University of Cambridge, | 0:00:12 | 0:00:15 | |
where I'm going to explore those four ancient elements, | 0:00:15 | 0:00:17 | |
using modern chemistry. | 0:00:17 | 0:00:19 | |
And to help me with this task, | 0:00:19 | 0:00:21 | |
I've invited 12 young students to become my apprentices. | 0:00:21 | 0:00:25 | |
Coming up... | 0:00:28 | 0:00:29 | |
Water. We drink it, we swim in it, but have you ever seen it explode? | 0:00:29 | 0:00:34 | |
Earth. We walk on it, we build houses from it, | 0:00:35 | 0:00:39 | |
but would you know how to make a metal out of it? | 0:00:39 | 0:00:43 | |
Air. It's all around us and we breathe it in, | 0:00:43 | 0:00:45 | |
but have you ever seen a solid lump of it? | 0:00:45 | 0:00:49 | |
Fire. We know it's dangerous, we're always told to be careful, | 0:00:49 | 0:00:53 | |
but how do you get the biggest bang? | 0:00:53 | 0:00:55 | |
BANG! | 0:00:55 | 0:00:57 | |
Three students, one lab and the awesome force of water. | 0:00:58 | 0:01:04 | |
These are the Alchemist's Apprentices. | 0:01:04 | 0:01:07 | |
My name's Peter Wothers | 0:01:11 | 0:01:12 | |
and I'm a chemist here at the University of Cambridge. | 0:01:12 | 0:01:15 | |
And I'm joined today by three apprentices, | 0:01:15 | 0:01:17 | |
who are going to help me explore | 0:01:17 | 0:01:19 | |
some of the very strange properties of water. | 0:01:19 | 0:01:22 | |
-OK, so, what do you know about water? -We drink it. | 0:01:22 | 0:01:24 | |
That's good. OK, what's the chemical formula? | 0:01:24 | 0:01:27 | |
-ALL: H2O. -H2O. So you all know that. | 0:01:27 | 0:01:29 | |
Well, this here represents a little molecule of water. | 0:01:29 | 0:01:32 | |
-So, what's what in that? What do you reckon? -Um... | 0:01:32 | 0:01:35 | |
-What's the formula for water? You just told me. -H2O. | 0:01:35 | 0:01:37 | |
So therefore, two hydrogens and one O. | 0:01:37 | 0:01:40 | |
-What if you cool water down, what do we get? -ALL: Ice. | 0:01:40 | 0:01:43 | |
-What temperature do we have to cool it down to? -ALL: Zero. -OK. | 0:01:43 | 0:01:45 | |
And this is what ice looks like. | 0:01:45 | 0:01:47 | |
But if we give this some energy... What happens if we heat up the ice? | 0:01:47 | 0:01:51 | |
-It turns back into water. -It turns back into water. | 0:01:51 | 0:01:53 | |
So just give this one a jiggle, jiggle it around. OK. | 0:01:53 | 0:01:56 | |
Yeah, OK. You've certainly melted it now. | 0:01:56 | 0:01:59 | |
But what do you notice if we compare this one to this one? | 0:01:59 | 0:02:02 | |
-It's not as organised and as structured. -It's not as organised. | 0:02:02 | 0:02:05 | |
-What about how much space it's taking up? -It takes up less. | 0:02:05 | 0:02:09 | |
Yeah, it's more compact now. It takes up less space. | 0:02:09 | 0:02:12 | |
So in this ice structure, it's a very regular, ordered structure, | 0:02:12 | 0:02:15 | |
but actually, it does take up more space. | 0:02:15 | 0:02:17 | |
And this has very important consequences. | 0:02:17 | 0:02:19 | |
What does this mean if we compare solid water to liquid water? | 0:02:19 | 0:02:23 | |
-It expands. -Yeah. -Well, OK, come over here. | 0:02:23 | 0:02:25 | |
'As my apprentices rightly pointed out, water expands when it freezes. | 0:02:25 | 0:02:30 | |
'This means solid ice takes up more space than liquid water | 0:02:30 | 0:02:35 | |
'and becomes less dense, allowing ice to float. | 0:02:35 | 0:02:38 | |
'But this is actually unusual. | 0:02:38 | 0:02:40 | |
'Normally, substances contract when they freeze | 0:02:40 | 0:02:43 | |
'and, like this cyclohexanol, sink. | 0:02:43 | 0:02:45 | |
'This unusual property explains why rivers and lakes | 0:02:45 | 0:02:49 | |
'don't completely freeze in winter, and how fish survive.' | 0:02:49 | 0:02:52 | |
Now, what do you think would happen | 0:02:52 | 0:02:54 | |
if we filled a container completely full of water | 0:02:54 | 0:02:58 | |
and then turned it into the solid form? | 0:02:58 | 0:03:00 | |
This would take up more space and then expand. | 0:03:00 | 0:03:03 | |
It might expand, yeah. | 0:03:03 | 0:03:05 | |
-The container might crack. -It might crack. | 0:03:05 | 0:03:06 | |
But what if I used a really, really strong one? | 0:03:06 | 0:03:09 | |
What about using a strong one like this? What's it made of? | 0:03:09 | 0:03:12 | |
-Metal? -Yes, it is. It's solid iron. | 0:03:12 | 0:03:15 | |
-So, would this be all right? -Yeah. | 0:03:15 | 0:03:17 | |
-What do you think? -I hope so. -This is the lid. | 0:03:17 | 0:03:20 | |
OK, so we're going to fill this completely with water | 0:03:21 | 0:03:24 | |
and then cool it down. So, we'll see what happens, shall we? | 0:03:24 | 0:03:27 | |
'So our cast-iron flask is filled with water | 0:03:28 | 0:03:31 | |
'and suspended over a beaker of freezing solution. | 0:03:31 | 0:03:34 | |
'We'll slowly lower the flask into the solution | 0:03:34 | 0:03:37 | |
'and observe what happens, as the water inside freezes. | 0:03:37 | 0:03:40 | |
'These experiments should never be carried out | 0:03:40 | 0:03:43 | |
'unless supervised in a proper laboratory. | 0:03:43 | 0:03:45 | |
'Do not try them at home.' | 0:03:45 | 0:03:47 | |
So this splashing around is just as it's cooling, | 0:03:51 | 0:03:53 | |
because, of course, the iron flask there is at room temperature. | 0:03:53 | 0:03:57 | |
So now it should be cooling down | 0:03:57 | 0:04:00 | |
and, hopefully, the water will be changing to ice. | 0:04:00 | 0:04:03 | |
And it's actually broken our beaker there. | 0:04:08 | 0:04:11 | |
This is what's left of our iron flask. | 0:04:11 | 0:04:14 | |
It's actually split into two. | 0:04:14 | 0:04:16 | |
It is the same expansive force which causes damage to homes during winter | 0:04:17 | 0:04:21 | |
if water is allowed to freeze in pipes and tanks. | 0:04:21 | 0:04:25 | |
But there's no risk of damage here | 0:04:25 | 0:04:27 | |
because this is behind a very strong safety screen. | 0:04:27 | 0:04:30 | |
So, what happens if we heat up the water, | 0:04:30 | 0:04:33 | |
the liquid water to higher temperatures? | 0:04:33 | 0:04:35 | |
What do we call gas water then? | 0:04:35 | 0:04:37 | |
-Steam. -Steam, exactly. That's what we're going to do. | 0:04:37 | 0:04:39 | |
We're going to heat up some water | 0:04:39 | 0:04:41 | |
and see how much more space it takes up when we convert it into steam. | 0:04:41 | 0:04:45 | |
'Time to heat things up now | 0:04:45 | 0:04:46 | |
'as we explore another incredible property of water.' | 0:04:46 | 0:04:49 | |
This is forcing hot air over this inner tube. | 0:04:49 | 0:04:53 | |
There's a glass tube inside here, | 0:04:53 | 0:04:55 | |
all the way in here and it's coming out here. You can feel the hot air. | 0:04:55 | 0:04:58 | |
-That's hot. -OK, good. | 0:04:58 | 0:05:00 | |
And in a moment, one of you is going to inject | 0:05:00 | 0:05:03 | |
one cubic centimetre of water using this syringe into here, | 0:05:03 | 0:05:07 | |
and we're going to see how many cubic centimetres of steam we get. | 0:05:07 | 0:05:10 | |
'So as our water turns to steam, | 0:05:10 | 0:05:11 | |
'it expands and pushes out the piston. | 0:05:11 | 0:05:14 | |
'This drives the dial and allows us | 0:05:14 | 0:05:16 | |
'to measure how much steam is generated.' | 0:05:16 | 0:05:18 | |
If you had to guess, how much do you think? | 0:05:18 | 0:05:20 | |
-One? -So one cubic centimetre of water | 0:05:20 | 0:05:22 | |
goes into one cubic centimetre of steam. | 0:05:22 | 0:05:25 | |
-Two maybe. -That means it will double in its volume, | 0:05:25 | 0:05:28 | |
which is quite substantial. And what do you think? | 0:05:28 | 0:05:31 | |
I suspect 100's there for a reason. | 0:05:31 | 0:05:32 | |
You think 100's there for a reason. Well, OK. | 0:05:32 | 0:05:35 | |
'Pretty confident in their guesses, | 0:05:35 | 0:05:37 | |
'Jude thinks it's going to be of equal size. | 0:05:37 | 0:05:40 | |
'Bish thinks it's going to double in size. | 0:05:40 | 0:05:42 | |
'While Ben thinks it's going to go up 100 times as much. | 0:05:42 | 0:05:46 | |
'Let's put it to the test.' | 0:05:46 | 0:05:48 | |
-Who's going to inject the water? -Me. | 0:05:48 | 0:05:50 | |
OK, do you want to come around here, then, please, Ben. | 0:05:50 | 0:05:52 | |
-Ready with the dial? -Yeah. -Off you go then, Ben, push that in. | 0:05:54 | 0:05:57 | |
Are you watching it? How many cubic centimetres? | 0:05:57 | 0:05:59 | |
ALL: 300. | 0:05:59 | 0:06:01 | |
400. | 0:06:01 | 0:06:02 | |
500. | 0:06:02 | 0:06:03 | |
'In fact, none of their guesses were even close, | 0:06:03 | 0:06:06 | |
'as the dial keeps going and going.' | 0:06:06 | 0:06:08 | |
2,300. | 0:06:09 | 0:06:12 | |
Just about stopping there, yeah. | 0:06:12 | 0:06:14 | |
How many cubic centimetres have we got? | 0:06:14 | 0:06:16 | |
2,300 and a bit over. | 0:06:16 | 0:06:19 | |
And a bit more. Wow! | 0:06:19 | 0:06:21 | |
So we've seen that one cubic centimetre of water | 0:06:21 | 0:06:24 | |
turns into more than 2,000 cubic centimetres of steam | 0:06:24 | 0:06:27 | |
at these temperatures. | 0:06:27 | 0:06:29 | |
But what do you think would happen if we didn't try this in a piston, | 0:06:29 | 0:06:32 | |
but in a closed little bottle? What do you think might happen? | 0:06:32 | 0:06:35 | |
The steam would escape. | 0:06:35 | 0:06:38 | |
Might escape. OK. | 0:06:38 | 0:06:39 | |
'This huge expansion is very important as it helps drive turbines | 0:06:39 | 0:06:43 | |
'which provide electricity for our homes and schools. | 0:06:43 | 0:06:46 | |
'Time now for one more experiment to see what happens | 0:06:46 | 0:06:49 | |
'if we try and contain this huge expansion.' | 0:06:49 | 0:06:52 | |
What we've got here is you've seen the little...the glass tube here, | 0:06:53 | 0:06:58 | |
this has again got one cubic centimetre of water in it, | 0:06:58 | 0:07:01 | |
but this time, it's in a sealed glass vessel, | 0:07:01 | 0:07:04 | |
which is something you should never do. | 0:07:04 | 0:07:07 | |
You should never usually heat things up in a sealed vessel. | 0:07:07 | 0:07:09 | |
OK, now if you just step back a bit, please. | 0:07:09 | 0:07:12 | |
So we've got our one cubic centimetre of water | 0:07:14 | 0:07:17 | |
and we're heating this up, OK. | 0:07:17 | 0:07:19 | |
And how many cubic centimetres of steam do we get? Over, 2,000, yeah. | 0:07:19 | 0:07:22 | |
-Yeah, over 2,000. -So just keep an eye on this. | 0:07:22 | 0:07:24 | |
Because the pressure's building up inside there, OK, | 0:07:24 | 0:07:27 | |
and maybe the glass is just going to break. | 0:07:27 | 0:07:30 | |
-BANG! -Oh! | 0:07:32 | 0:07:34 | |
-BANG! -Oh! Oh! | 0:07:34 | 0:07:37 | |
PETER CHUCKLES | 0:07:37 | 0:07:38 | |
-Did you hear it? -Yeah! | 0:07:38 | 0:07:42 | |
'As the water quickly gains energy and turns to steam, | 0:07:42 | 0:07:44 | |
'it has no room in which to expand, leading to the explosive result. | 0:07:44 | 0:07:48 | |
'This is the reason we never heat anything up in a sealed container | 0:07:48 | 0:07:52 | |
'and always need to have a release for the pressure.' | 0:07:52 | 0:07:54 | |
So there we have water, one of the most familiar substances to us | 0:07:54 | 0:07:58 | |
and, yet, well, as the young apprentices have just seen, | 0:07:58 | 0:08:01 | |
it has some really unusual properties. | 0:08:01 | 0:08:03 | |
And this makes it very useful. | 0:08:03 | 0:08:05 | |
Good. | 0:08:05 | 0:08:07 | |
Three students, one lab | 0:08:13 | 0:08:15 | |
and the ultimate goal of getting metal from rock. | 0:08:15 | 0:08:19 | |
These are the Alchemist's Apprentices. | 0:08:19 | 0:08:22 | |
My name is Peter Wothers | 0:08:25 | 0:08:26 | |
and this is my laboratory here in the University of Cambridge, | 0:08:26 | 0:08:29 | |
where I teach chemistry. | 0:08:29 | 0:08:31 | |
And now I'm joined by three apprentices. | 0:08:31 | 0:08:34 | |
And we're going to be looking | 0:08:34 | 0:08:35 | |
at how we can extract the modern elements from the earth. | 0:08:35 | 0:08:39 | |
Can you name a few elements, do you think? | 0:08:39 | 0:08:40 | |
-Hydrogen. -Hydrogen. | 0:08:40 | 0:08:42 | |
-Do you know where we can find hydrogen? -Water. | 0:08:42 | 0:08:44 | |
Hydrogen's in water. Very good. Any other elements? Amy? | 0:08:44 | 0:08:47 | |
-Copper. -Copper is an element, yes. | 0:08:47 | 0:08:49 | |
-Do you know where we get that from? -The earth. | 0:08:49 | 0:08:51 | |
We do get it from the earth. Ed, any other ones? | 0:08:51 | 0:08:53 | |
-Gold. -Gold. Where do we find gold? | 0:08:53 | 0:08:56 | |
Like rivers and streams and stuff. | 0:08:56 | 0:08:57 | |
-OK, also, yes, it may be in rocks and so on, as well. -Yeah. | 0:08:57 | 0:09:01 | |
'They're pretty good on elements, | 0:09:01 | 0:09:02 | |
'but how much do they know about metals?' | 0:09:02 | 0:09:04 | |
Now, do you know the difference between metals and non-metals, then? | 0:09:04 | 0:09:08 | |
Metals are magnetic sometimes. | 0:09:08 | 0:09:10 | |
And they're usually shiny. | 0:09:10 | 0:09:11 | |
They are usually shiny. Any other differences? | 0:09:11 | 0:09:13 | |
They have a high melting point. | 0:09:13 | 0:09:15 | |
'Another clue is that metals conduct electricity | 0:09:15 | 0:09:18 | |
'and we can use this fact to sort out metals from non-metals. | 0:09:18 | 0:09:21 | |
'I've laid out three pieces of material. Which one is the metal?' | 0:09:21 | 0:09:26 | |
Which one do you think is the metal? | 0:09:26 | 0:09:29 | |
-That one. -Yes. | 0:09:29 | 0:09:31 | |
OK, you think this one's definitely not metal? | 0:09:31 | 0:09:33 | |
Well, it kind of could be metal. | 0:09:33 | 0:09:35 | |
Because they're both kind of shiny, | 0:09:35 | 0:09:37 | |
like you've both got tiny bits of shine. | 0:09:37 | 0:09:39 | |
Now, I have some... | 0:09:39 | 0:09:42 | |
These are just some wires here, coming to a little buzzer | 0:09:42 | 0:09:45 | |
and there's a battery in here | 0:09:45 | 0:09:46 | |
and when we complete the circuit... | 0:09:46 | 0:09:48 | |
-BUZZ! -..it buzzes. | 0:09:48 | 0:09:51 | |
Would you like to test these, then? | 0:09:51 | 0:09:53 | |
Do you think this is going to conduct? | 0:09:53 | 0:09:54 | |
-I don't think it is. -No. -No? Well, we could try it. | 0:09:54 | 0:09:57 | |
OK. And what about this one? | 0:09:58 | 0:10:00 | |
-That one might. -It might. -Might. | 0:10:00 | 0:10:02 | |
-Right, do you want to try this one? -No. | 0:10:02 | 0:10:05 | |
Definitely not. | 0:10:05 | 0:10:08 | |
-Do you think this is going to conduct? -Yeah. | 0:10:08 | 0:10:10 | |
-Well, do you want to try it, then? -BUZZ! | 0:10:10 | 0:10:12 | |
It definitely conducts. So this is our copper metal. | 0:10:12 | 0:10:15 | |
We want to see if we can get our copper, | 0:10:15 | 0:10:17 | |
our metal out of this malachite. | 0:10:17 | 0:10:20 | |
So this is the mineral, which is how we would find our copper. | 0:10:20 | 0:10:24 | |
This is the same mineral, actually, this is just polished. | 0:10:24 | 0:10:28 | |
But at the moment, doesn't conduct electricity, | 0:10:28 | 0:10:30 | |
but it has got copper in there, | 0:10:30 | 0:10:31 | |
but it's chemically combined with some other elements. | 0:10:31 | 0:10:35 | |
It's got the elements oxygen and carbon in there, as well. | 0:10:35 | 0:10:38 | |
'Now, then, time for some alchemy | 0:10:45 | 0:10:47 | |
'as we try to extract the copper metal from our rock. | 0:10:47 | 0:10:50 | |
'First, though, a little elbow grease. | 0:10:50 | 0:10:52 | |
'Crushing is just a physical change, but it's still the same substance. | 0:10:53 | 0:10:58 | |
'Extracting our metal will call for a chemical change. | 0:10:58 | 0:11:02 | |
'These experiments should never be carried out | 0:11:02 | 0:11:04 | |
'unless supervised in a proper laboratory. | 0:11:04 | 0:11:06 | |
'Do not try them at home.' | 0:11:06 | 0:11:08 | |
So you're going to heat this up, Nick. OK. | 0:11:08 | 0:11:10 | |
And drive out some of the carbon dioxide from the ore. | 0:11:10 | 0:11:13 | |
We want to test to see if there's some carbon dioxide coming out, | 0:11:13 | 0:11:16 | |
so can we have some limewater? | 0:11:16 | 0:11:18 | |
'The beaker contains limewater, | 0:11:18 | 0:11:20 | |
'which is used to detect the presence of carbon dioxide.' | 0:11:20 | 0:11:23 | |
We're getting quite a few bubbles. | 0:11:23 | 0:11:24 | |
This is where we're driving out the carbon dioxide, | 0:11:24 | 0:11:26 | |
so our malachite, | 0:11:26 | 0:11:28 | |
it contains a carbon and oxygen, combined together with the copper. | 0:11:28 | 0:11:32 | |
We're seeing a colour change. | 0:11:32 | 0:11:34 | |
-OK. I think we're happy that there's carbon dioxide, yes? -Yeah. | 0:11:34 | 0:11:37 | |
Still haven't got our copper. | 0:11:37 | 0:11:39 | |
So we've got copper, combined with oxygen, copper oxide here. | 0:11:39 | 0:11:44 | |
And we need something else to take away this last little bit of oxygen, | 0:11:44 | 0:11:47 | |
to leave the copper behind. | 0:11:47 | 0:11:49 | |
'And that something is hydrogen. | 0:11:49 | 0:11:52 | |
'The hydrogen will combine with the oxygen in our copper oxide | 0:11:52 | 0:11:55 | |
'to make water, leaving just the copper behind.' | 0:11:55 | 0:11:59 | |
We've got copper oxide in here, a big balloon of hydrogen. | 0:11:59 | 0:12:01 | |
In a moment, I'm just going to open this, to let some hydrogen through | 0:12:01 | 0:12:05 | |
and I'm going to light it on here. | 0:12:05 | 0:12:07 | |
-That's a baby flame. -And I'm just going to keep an eye on that. | 0:12:07 | 0:12:10 | |
Oh, whoa! | 0:12:10 | 0:12:12 | |
-Look at that. -It's clearly melting away. | 0:12:12 | 0:12:14 | |
'So our hydrogen has begun taking away the oxygen from the copper. | 0:12:14 | 0:12:18 | |
'But let's see if my apprentices have been paying attention.' | 0:12:18 | 0:12:21 | |
All the oxygen's going out. | 0:12:21 | 0:12:23 | |
-The oxygen is combining... -With the hydrogen. | 0:12:23 | 0:12:26 | |
-Forming...? -Water. -Forming water. | 0:12:26 | 0:12:29 | |
We can see some of the water collecting here, actually. | 0:12:29 | 0:12:32 | |
Look at that. What you're making here is very finely-divided copper. | 0:12:32 | 0:12:36 | |
'Perfect answers from the students. But have we succeeded? | 0:12:36 | 0:12:39 | |
'Time for the conductivity test.' | 0:12:39 | 0:12:42 | |
Let's see if we've got any metallic copper, at all. | 0:12:42 | 0:12:44 | |
BUZZING | 0:12:44 | 0:12:47 | |
It's definitely a metal now. | 0:12:47 | 0:12:48 | |
it'll be really nice, I think, if we can make | 0:12:48 | 0:12:50 | |
a little lump of solid metal, rather than the powder. | 0:12:50 | 0:12:55 | |
'And to do that, we need to heat our metal | 0:12:55 | 0:12:57 | |
'to over 1,000 degrees, to make it melt. | 0:12:57 | 0:13:00 | |
'And a piece of charcoal is the perfect surface to do this on. | 0:13:00 | 0:13:03 | |
'It won't melt, even at that high temperature. | 0:13:03 | 0:13:06 | |
'As always, when working at high temperatures, | 0:13:06 | 0:13:08 | |
'my apprentices stand back, to a safe distance.' | 0:13:08 | 0:13:11 | |
Oh, my God, that's so cool! | 0:13:11 | 0:13:13 | |
HE GASPS | 0:13:13 | 0:13:15 | |
'After a few minutes heating our powder, | 0:13:16 | 0:13:18 | |
'a familiar substance starts to emerge.' | 0:13:18 | 0:13:21 | |
Whoa! | 0:13:27 | 0:13:30 | |
That's cool! | 0:13:30 | 0:13:31 | |
It's started to go harder now. | 0:13:31 | 0:13:33 | |
Yes. I think we've got more of a little lump there. | 0:13:33 | 0:13:35 | |
What do you think it feels like? | 0:13:36 | 0:13:39 | |
It feels like metal. | 0:13:39 | 0:13:40 | |
'Looks good, but will it pass the test?' | 0:13:40 | 0:13:43 | |
BUZZING | 0:13:44 | 0:13:46 | |
-Yeah. -It's quite conclusively metal, isn't it? | 0:13:47 | 0:13:49 | |
Nice and shiny on that side. | 0:13:49 | 0:13:51 | |
BUZZING | 0:13:51 | 0:13:53 | |
-Yeah. -Very good. | 0:13:53 | 0:13:54 | |
'Time to test our conductivity theory, one more time.' | 0:13:54 | 0:13:59 | |
So this is our mineral, our malachite. | 0:13:59 | 0:14:01 | |
Nothing at all. What about the copper oxide? | 0:14:01 | 0:14:03 | |
Nothing at all. | 0:14:03 | 0:14:05 | |
-And what about the metal? -BUZZING | 0:14:05 | 0:14:08 | |
Look at that. Beautiful. What do you think? | 0:14:08 | 0:14:10 | |
-It's pretty cool. -Yeah, pretty cool. | 0:14:10 | 0:14:12 | |
It's quite strange, the way these two will equal this, | 0:14:12 | 0:14:15 | |
but they're all the same thing. | 0:14:15 | 0:14:17 | |
They've all got the same elements in there. | 0:14:17 | 0:14:19 | |
So this one has the copper, combined with oxygen, combined with carbon. | 0:14:19 | 0:14:22 | |
This has just the copper, combined with the oxygen, | 0:14:22 | 0:14:24 | |
and this is just the copper itself. | 0:14:24 | 0:14:26 | |
So they're all in this same mineral, but they do look very different. | 0:14:26 | 0:14:29 | |
We haven't been able to do what the alchemists wanted to do, | 0:14:32 | 0:14:35 | |
to turn one metal, say lead, into another, such as gold, | 0:14:35 | 0:14:39 | |
but we've done something equally exciting. | 0:14:39 | 0:14:41 | |
We've used chemistry to extract the metal copper from its ore, | 0:14:41 | 0:14:47 | |
from its mineral malachite. | 0:14:47 | 0:14:48 | |
And I think that's pretty exciting. | 0:14:48 | 0:14:50 | |
What do you think? | 0:14:50 | 0:14:52 | |
Three students, one lab and the incredible secrets of air. | 0:14:58 | 0:15:03 | |
These are the Alchemist's Apprentices. | 0:15:03 | 0:15:06 | |
My name is Peter Wothers and in my day job as a chemist, | 0:15:10 | 0:15:14 | |
I study the elements and how they make up everything around us. | 0:15:14 | 0:15:17 | |
But today I'm joined by three young apprentices | 0:15:17 | 0:15:21 | |
and we're going to be looking at the properties of the air. | 0:15:21 | 0:15:24 | |
How much air is in this room? | 0:15:24 | 0:15:27 | |
How much do you think all the air in this room would weigh? | 0:15:27 | 0:15:29 | |
How many grams? | 0:15:29 | 0:15:31 | |
2,000 or 3,000? | 0:15:31 | 0:15:32 | |
Well, actually, it would weigh around two million grams. | 0:15:32 | 0:15:36 | |
OK, and that's two tons, which is about the same weight as two cars, | 0:15:36 | 0:15:41 | |
so that's quite a lot of air here, isn't there? | 0:15:41 | 0:15:44 | |
'Thankfully, air is not very dense, so we don't really feel it. | 0:15:44 | 0:15:49 | |
'But what gases make up that air around us?' | 0:15:49 | 0:15:53 | |
So do you know what gases are in the air? | 0:15:53 | 0:15:54 | |
Nitrogen. | 0:15:54 | 0:15:56 | |
-Mainly nitrogen, what else? -A little bit of argon. -Oxygen. | 0:15:56 | 0:15:59 | |
Oxygen is the second most abundant. Any other gases? | 0:15:59 | 0:16:01 | |
Water vapour. | 0:16:01 | 0:16:03 | |
Carbon dioxide. | 0:16:03 | 0:16:04 | |
That's the main components in the air. | 0:16:04 | 0:16:07 | |
'They certainly know a lot about air. | 0:16:07 | 0:16:09 | |
'Let's take a closer look at one of those gases they mentioned.' | 0:16:09 | 0:16:12 | |
What do you know about carbon dioxide then, what can you tell me? | 0:16:12 | 0:16:15 | |
If you burn fossil fuels, carbon dioxide is produced. | 0:16:15 | 0:16:20 | |
That's right. Anything else you know about carbon dioxide? | 0:16:20 | 0:16:23 | |
-You breathe it out and trees breathe it in. -Yes. | 0:16:23 | 0:16:25 | |
'All good answers. | 0:16:25 | 0:16:26 | |
'Using my specially made balance, we're going to explore | 0:16:26 | 0:16:30 | |
'one of the properties of carbon dioxide - its density.' | 0:16:30 | 0:16:33 | |
-We've got two buckets either side, and what's in the buckets? -Air. | 0:16:33 | 0:16:36 | |
Air, oh, very good, yes. | 0:16:36 | 0:16:38 | |
There's nothing other than air, just the air around us in there. | 0:16:38 | 0:16:41 | |
'Let's see what happens | 0:16:41 | 0:16:43 | |
'when we introduce a bucket of pure carbon dioxide gas.' | 0:16:43 | 0:16:46 | |
See if you can pour that into there. | 0:16:46 | 0:16:49 | |
Look at that. | 0:16:51 | 0:16:53 | |
That's amazing. | 0:16:53 | 0:16:55 | |
So you've actually just poured invisible carbon dioxide | 0:16:55 | 0:16:58 | |
from this bucket into that bucket there. | 0:16:58 | 0:17:00 | |
'The oxygen molecules in the air we breathe | 0:17:00 | 0:17:03 | |
'consist of two oxygen atoms. | 0:17:03 | 0:17:05 | |
'Carbon dioxide is made up of two oxygen atoms | 0:17:08 | 0:17:11 | |
'and a carbon atom, so it's heavier. | 0:17:11 | 0:17:14 | |
'This heavier gas tips the balance over.' | 0:17:14 | 0:17:18 | |
So we've seen some of the properties of carbon dioxide, | 0:17:18 | 0:17:21 | |
and now we'll see if we can actually make some carbon dioxide. | 0:17:21 | 0:17:24 | |
'Carbon dioxide can be made in many ways, even just by breathing out. | 0:17:24 | 0:17:29 | |
'For this experiment we are going to make the gas from a rock | 0:17:29 | 0:17:32 | |
'called calcium carbonate. | 0:17:32 | 0:17:33 | |
'First, though, my apprentices need to earn their keep as we set about | 0:17:33 | 0:17:36 | |
'breaking up the rock. | 0:17:36 | 0:17:38 | |
'These experiments should never be carried out, | 0:17:38 | 0:17:41 | |
'unless supervised in a proper laboratory. | 0:17:41 | 0:17:43 | |
'Inside our test-tube, we've got our calcium carbonate rock. | 0:17:45 | 0:17:48 | |
'That contains calcium, carbon and oxygen, and shortly I'll be | 0:17:48 | 0:17:51 | |
'testing my apprentices, to see if they know what it's made from.' | 0:17:51 | 0:17:54 | |
We're going to try and collect some of the carbon dioxide. | 0:17:54 | 0:17:58 | |
We're going to force it out of the calcium carbonate, OK, | 0:17:58 | 0:18:02 | |
and we want to see if we can trap it. | 0:18:02 | 0:18:04 | |
-Now how do you think we can do that? -Liquid nitrogen. | 0:18:04 | 0:18:07 | |
We could use some liquid nitrogen and that would cool it down | 0:18:07 | 0:18:10 | |
and convert it in to the solid form. That's what we'll do. | 0:18:10 | 0:18:13 | |
'Using freezing liquid nitrogen, | 0:18:13 | 0:18:15 | |
'we can cool down our carbon dioxide gas as it's produced. | 0:18:15 | 0:18:19 | |
'This will change its state, into a solid, | 0:18:19 | 0:18:22 | |
'and capture it in a test-tube, before it can escape.' | 0:18:22 | 0:18:24 | |
Now we need pretty high temperatures for this, so I'm going to use 1,000 | 0:18:24 | 0:18:28 | |
degrees C, this particular flame, so the calcium carbonate contains... | 0:18:28 | 0:18:33 | |
..well, which elements do you think it's got in, calcium carbonate? | 0:18:33 | 0:18:36 | |
Calcium. | 0:18:36 | 0:18:37 | |
-Calcium, yes, clearly. -Carbon. | 0:18:37 | 0:18:39 | |
Carbon, yes. And there's one other one. | 0:18:39 | 0:18:42 | |
-Oxygen. -Oxygen, that's right. | 0:18:42 | 0:18:44 | |
Now, I wonder if we're getting anything forming on this side? | 0:18:44 | 0:18:46 | |
Well, we've got some white on the sides, there. | 0:18:46 | 0:18:51 | |
That could be some carbon dioxide. | 0:18:51 | 0:18:54 | |
I think we'll stop heating this, in a moment. | 0:18:54 | 0:18:56 | |
And I'm going to attach a balloon to here, in a minute, | 0:18:56 | 0:18:59 | |
and, then, maybe, when we remove this, as the CO2 turns back into | 0:18:59 | 0:19:03 | |
the gas, it might blow up the balloon. We'll see. | 0:19:03 | 0:19:07 | |
'As we take away the freezing liquid nitrogen, | 0:19:09 | 0:19:12 | |
'the carbon dioxide quickly expands back to its gaseous state. | 0:19:12 | 0:19:15 | |
'This is quite normal, as carbon dioxide is a gas | 0:19:15 | 0:19:18 | |
'at room temperature. | 0:19:18 | 0:19:19 | |
'But there is something unusual happening.' | 0:19:19 | 0:19:23 | |
This is a little block of solid carbon dioxide, | 0:19:23 | 0:19:27 | |
and all it's doing there is turning directly in to carbon dioxide gas. | 0:19:27 | 0:19:33 | |
That's quite cool. It's not melting, at all. | 0:19:33 | 0:19:36 | |
And does anyone know what this is called, | 0:19:36 | 0:19:38 | |
when a solid goes directly to a gas? | 0:19:38 | 0:19:40 | |
-Subliming. -Very good, yes, this is subliming. | 0:19:40 | 0:19:43 | |
'Sublimation is the name of the process when a substance changes | 0:19:43 | 0:19:47 | |
'from it solid state to its gaseous state, without becoming a liquid. | 0:19:47 | 0:19:51 | |
'Because there's never any messy liquid, | 0:19:51 | 0:19:54 | |
'solid carbon dioxide is also known as dry ice. | 0:19:54 | 0:19:58 | |
'So that's the carbon dioxide produced in our experiment. | 0:19:58 | 0:20:01 | |
'But what about the calcium oxide left in the test-tube? | 0:20:01 | 0:20:04 | |
'How has THAT changed?' | 0:20:04 | 0:20:06 | |
This started off just like the rock that you chipped away. | 0:20:06 | 0:20:11 | |
That was calcium carbonate. | 0:20:11 | 0:20:13 | |
We've heated this one up, it's cooled down again now, | 0:20:13 | 0:20:16 | |
but it's changed, so it's no longer calcium carbonate, what is it? | 0:20:16 | 0:20:19 | |
-Calcium oxide. -Calcium oxide. | 0:20:19 | 0:20:21 | |
And I'm just going to put some water on this, so put some water on here. | 0:20:21 | 0:20:25 | |
What's going to happen? What do we get? | 0:20:25 | 0:20:27 | |
-Wet rock. -Wet rock, OK. | 0:20:27 | 0:20:28 | |
But if I give you the watering can, what I'd like you to do, | 0:20:28 | 0:20:32 | |
just sprinkle a little bit on the rocks, both on the rocks there. | 0:20:32 | 0:20:35 | |
And what have we got now? | 0:20:37 | 0:20:39 | |
Carbon dioxide? | 0:20:39 | 0:20:40 | |
No, it's not carbon dioxide. There's no carbon dioxide left in this. | 0:20:40 | 0:20:43 | |
It was only calcium oxide. | 0:20:43 | 0:20:45 | |
'As the water reacts with the calcium oxide ,it gives out heat, | 0:20:45 | 0:20:49 | |
'in what's called an exothermic process. | 0:20:49 | 0:20:52 | |
'The heat turns some of the water to steam. | 0:20:52 | 0:20:55 | |
'And what's being made? | 0:20:55 | 0:20:57 | |
'It's a substance called calcium hydroxide, | 0:20:57 | 0:21:00 | |
'which, when dissolved in water, is called limewater. | 0:21:00 | 0:21:03 | |
'Limewater is used as a test for carbon dioxide.' | 0:21:03 | 0:21:07 | |
The early alchemists thought that the air was a single substance | 0:21:11 | 0:21:14 | |
but, of course, we now know it's a mixture of different gases, | 0:21:14 | 0:21:17 | |
and if we cool these gases down, we can make first the liquids | 0:21:17 | 0:21:20 | |
and then, at even lower temperatures, the solids. | 0:21:20 | 0:21:23 | |
And these gases that make up the air have very different properties. | 0:21:23 | 0:21:26 | |
We've seen the carbon dioxide is heavier than air, | 0:21:26 | 0:21:29 | |
and we can form this by driving it out of some of the minerals | 0:21:29 | 0:21:32 | |
around us, like the calcium carbonate. | 0:21:32 | 0:21:35 | |
'Three students, one lab and lots of fire. | 0:21:42 | 0:21:48 | |
'These are the Alchemist's Apprentices. | 0:21:49 | 0:21:53 | |
My name is Peter Wothers and I'm joined | 0:21:56 | 0:21:59 | |
here in the Department of Chemistry at the University of Cambridge | 0:21:59 | 0:22:02 | |
by three new apprentices, | 0:22:02 | 0:22:04 | |
and we're going to be looking at fire. | 0:22:04 | 0:22:06 | |
So what can you tell me about fire, then? | 0:22:06 | 0:22:09 | |
Isn't it an element? | 0:22:09 | 0:22:10 | |
The Greeks used to think it was an element, | 0:22:10 | 0:22:12 | |
and it used to make up everything around us. | 0:22:12 | 0:22:14 | |
But it's not quite an element, in the modern sense, at all. | 0:22:14 | 0:22:17 | |
Yeah, I think we need to look at some fire | 0:22:17 | 0:22:19 | |
and then that might give us some more clues, all right? | 0:22:19 | 0:22:22 | |
So this is filled with gas, is it going to be very loud, | 0:22:22 | 0:22:25 | |
what do you think? | 0:22:25 | 0:22:26 | |
-Medium. -Medium? -Yeah. | 0:22:26 | 0:22:27 | |
Let's have a look, then, let's see what happens. Are we ready? | 0:22:27 | 0:22:30 | |
LOUD BANG ALL: Oh! | 0:22:31 | 0:22:33 | |
'Don't experiment with flammable materials at home or on your own.' | 0:22:33 | 0:22:36 | |
What did you see? | 0:22:36 | 0:22:37 | |
-Lots of heat. -Did you see the heat? | 0:22:37 | 0:22:39 | |
Yeah. It got, like, warmer. | 0:22:39 | 0:22:42 | |
You felt some heat, did you, you felt a bit of heat? | 0:22:42 | 0:22:45 | |
'An explosive start there, | 0:22:45 | 0:22:46 | |
'but let's see what my apprentices really know about fire, | 0:22:46 | 0:22:49 | |
'with a little help from an old favourite - the Bunsen burner.' | 0:22:49 | 0:22:51 | |
How do they work? | 0:22:51 | 0:22:53 | |
There's a little valve and if you turn it, like if you turn it.. | 0:22:53 | 0:22:56 | |
-Where's the little valve, do you want to show me? -It's just there. | 0:22:56 | 0:22:59 | |
So if you turn it like that, it makes it a roaring flame, | 0:22:59 | 0:23:02 | |
which is the hottest, | 0:23:02 | 0:23:03 | |
and if you turn it like that, it makes it a safety flame. | 0:23:03 | 0:23:05 | |
-Why is this a safety flame, then? -It's hot. | 0:23:05 | 0:23:07 | |
Because everyone can see it. | 0:23:07 | 0:23:09 | |
And if I put this in, then, you can see what's going to happen. | 0:23:09 | 0:23:12 | |
So let's just try this, shall we? | 0:23:12 | 0:23:14 | |
Just put this white tile in. | 0:23:14 | 0:23:15 | |
This black stuff, what would you call it? | 0:23:15 | 0:23:17 | |
-Soot. -Soot, exactly. It's soot. | 0:23:17 | 0:23:19 | |
And this is - well, it's an impure form of carbon. | 0:23:19 | 0:23:22 | |
What does it tell us then? Where was the carbon initially? | 0:23:22 | 0:23:26 | |
Coming from the gas leading to the Bunsen burner. | 0:23:26 | 0:23:28 | |
Exactly. You're absolutely right. | 0:23:28 | 0:23:30 | |
It's coming from the gas that we've lit here. | 0:23:30 | 0:23:32 | |
So what we're seeing, this flame, are very hot, little particles, tiny | 0:23:32 | 0:23:36 | |
little bits of carbon, that's what gives us this nice yellow flame. | 0:23:36 | 0:23:40 | |
'Opening the valve allows more air to mix with the gas | 0:23:40 | 0:23:43 | |
'and use up black carbon. | 0:23:43 | 0:23:44 | |
'This produces a much hotter blue flame which is ideal for cooking | 0:23:44 | 0:23:48 | |
'and heating experiments. | 0:23:48 | 0:23:50 | |
'But let's see if they know exactly how hot it really is.' | 0:23:50 | 0:23:53 | |
I think the blue one's probably about 120. | 0:23:53 | 0:23:56 | |
120. What would you guess at? | 0:23:56 | 0:23:59 | |
-Probably 100. -100. | 0:23:59 | 0:24:01 | |
'Time to put their guesses to the test, using a temperature probe. | 0:24:01 | 0:24:05 | |
'First up is the yellow safety flame.' | 0:24:05 | 0:24:07 | |
It's going up really quickly. | 0:24:07 | 0:24:08 | |
'Like all good chemists, | 0:24:08 | 0:24:10 | |
'my apprentices know they should | 0:24:10 | 0:24:11 | |
'only hold the probe at the insulated end.' | 0:24:11 | 0:24:13 | |
What's the temperature now? It is? | 0:24:13 | 0:24:16 | |
We weren't very good at guessing it. | 0:24:16 | 0:24:18 | |
We're already over 400... coming up to 500C already. | 0:24:18 | 0:24:21 | |
That's quite hot, isn't it? Now, you were guessing 100. | 0:24:21 | 0:24:24 | |
If it was 100 - well, what temperature does water boil at? | 0:24:24 | 0:24:27 | |
A hundred. | 0:24:27 | 0:24:29 | |
A hundred. So it would just be hot enough maybe to boil. | 0:24:29 | 0:24:32 | |
It's definitely much hotter than that. | 0:24:32 | 0:24:34 | |
'Next up, the roaring blue flame. | 0:24:34 | 0:24:36 | |
'Let's see how the introduction of air affects the temperature. | 0:24:36 | 0:24:40 | |
Lauren, if you want to go to the what you think is the hottest part. | 0:24:40 | 0:24:43 | |
'Lauren's right. | 0:24:43 | 0:24:45 | |
'The hottest part of the flame is just above the inner blue cone, | 0:24:45 | 0:24:48 | |
'so the temperature quickly rises.' | 0:24:48 | 0:24:50 | |
-Whoa. -My one's gone red-hot. | 0:24:50 | 0:24:52 | |
Your one's gone red-hot. | 0:24:52 | 0:24:56 | |
And you're up to - well, this is 900C, but you're quite | 0:24:56 | 0:25:00 | |
right, Trinity, your one's actually quite cool, but it does certainly | 0:25:00 | 0:25:04 | |
show that the hottest part of the flame is right above the blue cone. | 0:25:04 | 0:25:09 | |
What if we want to get the best heat out of our fuel? | 0:25:09 | 0:25:14 | |
-We need to mix the fuel with...? -BOTH: The air. | 0:25:14 | 0:25:17 | |
The air. To do that, we can't just burn the gas, | 0:25:17 | 0:25:19 | |
we need to mix it with...? | 0:25:19 | 0:25:21 | |
-Oxygen. -With oxygen, right. | 0:25:21 | 0:25:22 | |
'My apprentices are right again. | 0:25:22 | 0:25:25 | |
'Oxygen is a key ingredient of fire, along with fuel and heat. | 0:25:25 | 0:25:29 | |
'Time for an experiment then, to investigate oxygen, fuel and fire.' | 0:25:29 | 0:25:33 | |
Now, these bottles that you've just brought round, actually just | 0:25:33 | 0:25:37 | |
contain oil and water and I've added some blue food colouring | 0:25:37 | 0:25:40 | |
to the water, so we're using these just to show the ratios that we're | 0:25:40 | 0:25:43 | |
going to mix our fuel and oxygen gas. | 0:25:43 | 0:25:46 | |
And we're trying to work out how to get the loudest bang. | 0:25:46 | 0:25:49 | |
'That's right. | 0:25:49 | 0:25:51 | |
'The aim of this experiment is to discover how much oxygen | 0:25:51 | 0:25:54 | |
'and fuel will make the biggest bang. | 0:25:54 | 0:25:56 | |
'We're going to use a gas called propane as our fuel, | 0:25:56 | 0:25:59 | |
'so which ratios will my apprentices choose?' | 0:25:59 | 0:26:03 | |
I think this one, because it's got more fuel. | 0:26:03 | 0:26:06 | |
So you want the 1:3, do you? OK. | 0:26:06 | 0:26:08 | |
Probably that one. | 0:26:08 | 0:26:10 | |
-So Lauren, you're going to choose the 1:1, are you? -Yeah. | 0:26:10 | 0:26:13 | |
That sounds sensible. | 0:26:13 | 0:26:14 | |
Which means then, Trinity, I'm afraid you're left with the 1:5. | 0:26:14 | 0:26:17 | |
'And know the ratios are chosen. | 0:26:17 | 0:26:19 | |
'Lauren has chosen a ratio of 1:1, Annabel those 1:3, and Trinity 1:5. | 0:26:19 | 0:26:26 | |
'It's time to fill the balloons with our gases. | 0:26:26 | 0:26:29 | |
'We use my apparatus to first measure the volume of gas | 0:26:29 | 0:26:33 | |
'before pushing it into the balloons. | 0:26:33 | 0:26:35 | |
'First up, Lauren, who puts the same amount of oxygen | 0:26:35 | 0:26:38 | |
'and propane in to her balloon, for a 1:1 ratio.' | 0:26:38 | 0:26:41 | |
Push that in, then. | 0:26:41 | 0:26:44 | |
'Next, Annabel fills her balloon with three parts oxygen | 0:26:44 | 0:26:47 | |
'and one part fuel.' | 0:26:47 | 0:26:49 | |
There we are, perfect. | 0:26:49 | 0:26:51 | |
'And finally, | 0:26:51 | 0:26:52 | |
'Trinity adds five parts oxygen | 0:26:52 | 0:26:54 | |
'to her one part of fuel in the balloon.' | 0:26:54 | 0:26:56 | |
Good, and just hold that. Lovely. | 0:26:56 | 0:26:59 | |
'With the sound meter ready and the ear-protection | 0:26:59 | 0:27:01 | |
'securely fastened, it's time to reveal the big bang. | 0:27:01 | 0:27:06 | |
'First to pop is Lauren, with her 1:1 one ratio.' | 0:27:06 | 0:27:10 | |
BANG | 0:27:10 | 0:27:11 | |
105.4. | 0:27:13 | 0:27:15 | |
'Pretty loud.' | 0:27:15 | 0:27:16 | |
OK, ready for the next one? | 0:27:16 | 0:27:18 | |
'Can Annabel do any better, with her 3:1 ratio?' | 0:27:18 | 0:27:22 | |
BANG, BANG, BANG | 0:27:22 | 0:27:24 | |
119. | 0:27:24 | 0:27:26 | |
119? That was better, wasn't it? | 0:27:26 | 0:27:28 | |
'A shocked Annabel takes her place back at the bench. | 0:27:28 | 0:27:31 | |
'It's the turn of Trinity, with her red balloon, containing five times | 0:27:31 | 0:27:34 | |
'as much oxygen as fuel.' | 0:27:34 | 0:27:36 | |
BANG, BANG | 0:27:37 | 0:27:39 | |
116.6. | 0:27:40 | 0:27:43 | |
116.6. | 0:27:43 | 0:27:45 | |
'So Lauren's ratio of 1:1 had a reading of 105.4 decibels. | 0:27:45 | 0:27:51 | |
'Annabel's 1:3 ratio had a 119 decibels. | 0:27:51 | 0:27:55 | |
'While Trinity's 1:5 ratio had a reading of a 116.6.' | 0:27:55 | 0:28:02 | |
It's very important, then, to get the right measure of fuel | 0:28:02 | 0:28:05 | |
and oxygen to get the good combustion. | 0:28:05 | 0:28:08 | |
Did you see the difference between the flames? | 0:28:08 | 0:28:11 | |
So the first one - yes, very yellow, quite big, wasn't it? | 0:28:11 | 0:28:13 | |
it almost looked a bit sooty. But what about the other two ones? | 0:28:13 | 0:28:16 | |
Well, ours went really quickly, you could hardly see the flame. | 0:28:16 | 0:28:19 | |
There was no flame, it just went... | 0:28:19 | 0:28:21 | |
-Black. -Exactly, it just disappeared, yes. | 0:28:21 | 0:28:23 | |
And that's because it was complete combustion there, so we | 0:28:23 | 0:28:26 | |
didn't have the little particles of carbon, of soot that were glowing. | 0:28:26 | 0:28:30 | |
That gives rise to the flame. | 0:28:30 | 0:28:32 | |
When we burn them completely, if we give them enough oxygen, then, | 0:28:32 | 0:28:36 | |
yup, we don't see the flame, we just get a very loud bang indeed. | 0:28:36 | 0:28:39 | |
So we've had some loud bangs there, some flashes, | 0:28:41 | 0:28:44 | |
but my apprentices still seem to be in one piece, which is great, | 0:28:44 | 0:28:48 | |
and I think we've learnt quite a bit about fire. | 0:28:48 | 0:28:51 | |
So thank you very much for coming along. | 0:28:51 | 0:28:54 | |
ALL: Thank you. | 0:28:54 | 0:28:55 | |
What did you like best? | 0:28:55 | 0:28:56 | |
Subtitles by Red Bee Media Ltd | 0:29:02 | 0:29:05 |