 Prdaj pa všeč nas pači in bila pak in drugi tudi. Vse je pričo, da smo tamo všeljni krič, z nattu, dr Henry Henson, ki tractovali o več za njigovosti, z njigovosti za sovrčno nitozernost, z njigovosti za sovrčno nitozernost v njigovosti. Vse chodimo, da se četite, da bili si neko, ne bo vse, Ne zdarjam, da je bilo se, da jo se so teh v družatih včetni. Daj,azingo, da jega. Tako, zelo... Vljubez sem nekaj, da se je jer bilo v življu, in posredno, z Elizabeta, je zelo, da je mi je kaj. Dojega ne všeč v ampala plasno odrandilo? Vljubez sem nekaj, da všeč v ampala plasno odrandilo? Všeč, da všeč vojimo tudi na ampala plasno odrandilo? Vse možemo vse odličiti, da sem sem tudi prišli, v ko sem treba prezent. Kako je, da se počusti, da se našli z vrštih nekaj neči vrštih. Všeč mi zelo, da sem razimel, da jaz sem, da sem prišli, kako sem, da se prišli, razimel sem, da sem prišli, in ljudi, da sem, da sem prišli, zato sem. Zato, da sem prišli, da sem prišli, da sem prišli, da vših ima nekaj dobro. V neko jen tudi se pričeš, ovo je, da jih je tom, kaj je, a ni to je tudi, in vseč, vseč v neko, vseč bojivo, si to pravati, tukaj zelo mi začeš, vseč bojivo, nekaj ne si neskot, in nekaj se očiče vseč. V neko vseč, tače je, ne kaj ne sem spodobila. je to, da bomo moh zeločiti, je samo, da so dobro zeločiti kaj je temporeč, da so njihojeune vče, ko temporeč je vče, kot vši boj, 100, je, da je dobro, njega je pričo, MPL Bryn. Zaj, za to, da je prič ovo prišli, da se nekaj, da dobro, saj se nekaj. 100 °C, vseč je bilo zdefnit. Vseč, zaznam, še bilo zvršo v kot, ki je v tem na vršu, ki je zvršo v vršu, od 80 °C, ki je zršo v barzat. Na kot vse, ki je v barzat, je vzostaj 240 °C, ki je zršo v barzat. Svršo v barzat ima nekaj zršo v barzat. Na pohle potrebe. Nel kratko je zelo, da je bilo vse. To je zelo, da je zelo. Iko se zelo, da je bilo vse. Što je so dobro, saj sem jistil vse, je vse zelo kripril. Zelo je zdaj zelo povrčeno. Nel kripril tačnog vse je zelo, načo se bo vse uvaj, zelo je vse vse uvaj. A kratko se je zelo, ne bomo vse zelo, da je ne so vse zelo. Vse je bilo prikrat, da je vse prečo, ki se vse naje vrdu zelo. Vse je vse način, da je ročno, da je več nekaz, ki je oveč vzelo za vzelo, da je vse nekaz, da je več nekaz, če so nekaz. Danes nekaz sem da sem ovoril, da se način bilo vse nekaz. imaš tukaj. To je tukaj Dua, inventovalo so James Dua. In je tukaj Klerihu, če je bitno limerik, če je pojem, o so James Dua. To je, So James Dua je klerer, če nekaj Dua. Bez nekaj Dua nekaj zelo, da bomo povolj, to je tukaj držav. Čest vse je dvere, z vse in vse nekaj, je incezato z prihodom vakošodnju, vso vkazobnega vzela in izvečine. Kaj ga polejim v hovoj, zelo kej ta kratil. Vsoj nožel, dvejo, Kaj je to? Kaj je to? Kaj je to? Stine. Stine. Znam, da je dobro. Znam, da je stine. Fog. Fog? Tako je. Vsih je nekaj. Vsih je nekaj. Vsih je nekaj. Vsih je nekaj. Roči zelo. Vojte, da je kaj ni so. Zelo. Zelo. Zelo. Zelo. Zelo, nekaj je. Zelo. Zelo. Zelo. Zelo. Zelo. Zelo. Zelo. To je bilo, da je bojljena voda, zato je bojljena, kaj je tega? 100°C. Kaj je tega? Kaj je to bojljena? Vznikam na toga tabla. Vznikam na vzniku. Mord. Mord? Ne. Minus 180°C. V Celsius minus 196°C. Minus 190°C. Go on. Minus 196°C. That's cold. So this is a liquid that is boiling at minus 196°C. Wow. What can I show you? I can put a tenis boil in this. 500°C. Put hot water in the water in the glass. In glass with break. 100°C break. This. This is called Tim. This is actually a tea thermos flask. It's designed to put your hot tea in there. It's actually got a top that you can put on. To keep your tea nice and hot. I don't just say flask. So I think what I'm saying is, you can put boiling water onto a glass container. And it won't necessarily shatter. So this was an ordinary tenis boil. It is an ordinary tenis boil still now. I should have sort of demonstrated how normal it was. But now I'm cooling it down to hit such hideously towed temperatures. Its properties are going to change by quite a lot. So here we go. It's not bouncy anymore. I'm actually going to use these gloves to hang this because it's pretty cold. I dare say if I throw it hard enough it would shatter. But I'm not going to because I need this for my next demo when I do it again. So I hope that convinces you that this is not just boiling water. You wouldn't expect to see that if it was boiling water. And that brings us to the idea of temperature. Temperature is something to do with the speed of molecules. And if you slow the molecules down they have a lower temperature. Does that make sense? So I thought just for fun. Right, we're kind of all... Could you hold this here? This is the lowest possible... There is a lowest possible temperature. Below which you can't go. And if you think of temperature as being the speed of things moving, what's the slowest things can move at? Stop, stop! Stop, yes! Not moving at all. So you can imagine, if I just keep cooling things down and eventually they're reaching a point where they're not moving at all. So actually philosophically it's quite easy to think of there being a lowest temperature. And that's what you got there, the lowest possible temperature. I did a bit of research when I was sort of putting this story together about the hottest possible temperature. Which is that. Whatever that means. I didn't understand what it meant when I saw that that was there. But apparently there is a hottest possible temperature. It's to do with the physical laws of matter. So you guys, can you be the hottest possible temperature? Right, fine. What about water boiling? What temperature do you get in water? 100. Can you take this? And stand somewhere in between the two. For what it's worth, let's see what that is in Celsius. Yeah, it's stupidly large. No, that's about 100. So you're quite close to her. What's the coldest thing in your house? Freezone. Minus 18 or so. So could you join the temperature scale somewhere between those two? Somewhere over here. When I do this sort of quiz in schools, I take this into schools as well, I usually say what's the coldest thing in your house and some child pipes up my sister's heart. Anyway, no. It's your freezer at about minus 18 Celsius. At that temperature, biology kind of doesn't bother to do anything. It just desicates. I mean you can keep food in a fridge, in a freezer forever and ever and ever. And well, in permafrosts you can dig out a mammoth. It's just, it's dried out during that time. What water does at such low temperatures is it sublimes. It changes from a solid straight into a gaseous form and just kind of disappears off. You might have heard of carbon dioxide subliming from a solid to a gas, but water does that at minus 18. So there's a great experiment where you put some ice cubes in your freezer and then just watch them disappear. It's like they're evaporating off and they come off and they stick to be inside of the freezer and that's why your freezer gets clogged up. So when you see don't keep meat beyond this date it's not that it's not good to eat it's just that it's desicated and it becomes really, really chewy. So that's the reason why meat's got cell by dates. Yes. Yes, absolutely. Yes, you can use that as the desication process. What about a fridge? Can you be a fridge? Yes. Oh yes, it's written on the back. Yes. So a fridge is about plus four and recently we bought some food from a supermarket and we thought we're not going to be able to get home and luckily the outside was about three degrees Celsius so we just left it in the car all day. Ok, water freezing. Can you be water freezing? Go and stand where you think that should go. What's the hottest thing in your house? Gas fire. Gas fire? No. Do you know? Tungsten light bulb. Which is about 2700 Celsius. We let our children play with the light switch and on and off the hottest thing in your house. Ok, so he's going to go. The coldest place on Earth. Would you like to be the coldest place on Earth? It's Vostok research station in Antarctica. In the Antarctic, not only do you not see a lot of the sun, but also you've got quite high mountain ranges and with altitude comes a drop in temperature. South Pole is colder than the North Pole so you're colder than your freezer. Would you like to be the sun's surface? The sun's surface is about 6000 degrees Celsius. Inside the sun it's a lot, lot hotter than that, it's millions of degrees but this is just the sun's surface. There's more. This one has to be you. A healthy Englishman's armpit. Ok. Where do you think that should go? This guy's had a long day so I need to keep him awake by giving him crazy things to do. I'm sure butter would not melt in your mouth so you'd be that one. And we're running out of people. Can you do the hottest bath you can stand? Can you do nitrogen boiling? Are you up for this? Go on for two seconds. You'll be a candle flame, I'll tell you if any punters come in. Can you be nitrogen freezing? And I'll be the temperature on Pluto. Actually, you want to take a photograph, don't you? I'll do two. You take the photo. Right. Nitrogen freezing is somewhere around there. Actually, the number is written on the back. Temperature on Pluto. Can you kind of work out where that is? Right. You can take a photo of this. Candle flame. Candle flame between water boiling and tungsten light. Fantastic. Right. Can you do a photo of this lot? My temperature scale. We've got just one of the people, haven't we? Brilliant. Thank you. I didn't just randomly choose these things. Some of them look completely random. But I have to tell you that these most things here, have at some point been considered as a a point on a temperature scale. Now, we know about water boiling being the hundred degrees Celsius point. We know about water freezing being the zero point. So zero, one hundred. Those are kind of the Celsius scale. Yeah, they're fixed there. But a healthy English mizump, it really was considered to be part of a temperature scale at some point. As was butter melting. As was the hottest bath you can stand. As was Candle flame as well, I think. So these points have all been thought of as places to anchor a temperature scale onto. OK, fantastic. Can you put a little to Mr. Hotest Temperature and he'll collect them up. Thank you very much. You're back to your seats, please. Thank you. Thanks. Let me tell you a little bit more about this temperature, because I did read up a little bit more about it. It's to do with the fact that some physics there's a kind of rule of physics that you can't get smaller than a particular wavelength of light. Just, there's a limit to the way the world can work. And related to that emission of energy, if you like is a particular temperature. So the limit is on the wavelength of light which is very, very, very, very small, which would contain huge amount of energy, and the temperature of something creating that light would be this temperature, which is insanely hot. And I thought about this and I spoke to a cosmologist about it and he said, well if you think about it the universe contains heat. Heat is kind of motion energy of material, and the average temperature of the universe is only 2.7 degrees above the coldest temperature that we spoke about. So the average temperature of the universe is very, very low but there's a lot of universe so there's quite a lot of heat. So if you think about the big bang the fact that we started off as kind of a singularity a point where the entire universe was smaller than the size of an atom all the heat of the universe would have been contained in a very, very small volume. Does that make sense? And you ask yourself the question how small would the volume of the universe be to contain that amount of heat? For that amount of heat to be at that temperature. Another way is how soon after the creation of the universe would that point be? And the answer is in terms of how close you are to the beginning of the creation of the universe 10 to the minus 42th of a second that's very, very soon after the creation of the universe and with the universe extremely small, smaller than an atom before that our physics simply does not work it just doesn't work at all gravity and all the other forces are kind of on the same scale and they'll we just don't understand it it makes absolutely no sense whatsoever and one of Stephen Hawkins' work is involved in trying to look into these things and trying to work out a unification of all of these different forces in terms of how they would behave before 10 to the minus 42th of a second after the beginning of the universe that's a bit over the top, isn't it? I thought this would be a fun thing splashing liquid nitrogen about and I'm talking about creation so let's splash some liquid nitrogen about I talked about taking liquid and converting it from the liquid into a gas let's do exactly the reverse so I've got a container here of liquid nitrogen and I've got a a vessel here into which I'm going to put some gas it's a slightly bizarre balloon, isn't it? so in here is a mixture of about 21% oxygen 78% something like that, nitrogen about 1% argon a little bit of carbon dioxide a little bit of water vapor and a few other bits and pieces and that's gaseous air at about in here it feels like it's about 30 degrees celsius but I think it's probably about 25 I've got a thing here that will measure the temperature so it will tell me actually telling me that the battery is running out on this telling me that the floor is 38 I just don't believe that so in there is some air in gaseous form what do you think will happen if I pour cold liquid nitrogen that's what this is on top of it so it will shrink you've seen this before haven't you yes and the reason it shrinks is because if you think about the atoms the molecules in there as they slow down they take up less space they're not moving around so much and as you change from being a gas to being a liquid you change from being great distances apart as molecules to being really really close to each other as molecules so you need a lot lot less space to be where you are so yeah so I'm using this to cool down the air inside I'm using liquid air to cool gaseous air and you can hear that the rubber of the balloon is kind of going exactly as well that's because normally the rubber of balloons the molecules are quite ductile and they move like soap over each other but when they get cold like a lot of us you get quite quatchity and you get sort of scratchy and that's what you can hear usually you can hear the molecules scratching up against each other so the air is still in here a gas it's a liquid occupying getting on for 700th of a volume we call that a gas constant which is the proportion of volume between the liquid and the gas so liquid air liquid nitrogen if I'm being really specific takes up a 700th of a volume of it's of gaseous air oh my goodness it's coming back to life again because the air is in there all the time it's just when it was in there it was rattling around as a liquid inside the balloon so it was still in there now it's and that's come back to life as a scientist this is great because I can borrow this liquid nitrogen from npl where I work and I can go to the party with all the balloons preinflated in my balloon tARDIS I can fit about 50 balloons in here ouch I'm making sure they're not too cold by the time I throw them at you this has all been whisk assessed so you can feel it's cold you can still feel it just that last bit of growing as it warms up that last bit so there it is can I just splash them on the floor I think I can that may happen so if I just do this you'll notice it rolls across the ground I wouldn't stand on it but then you will love this because this is actually cleaning as it goes it carries the dust front with it so I'll just do some towards you guys ready here we go let me show you what's happening here on the film as well in the video oops so can you see that the little droplets do not boil off immediately they dance around they seem to last a bit longer than they really ought to has anyone seen anything like this before at home snuka yeah but this is pretty frictionless actually how about a hot frying pan if you get a really really hot frying pan you heat it to about 150 or a bit more than that and you put water onto it the droplets start to behave like this they don't boil off instantly they just kind of rattle around two things are happening here one they don't boil off instantly which you might think they would because the temperature difference is so big and two there's this kind of frictionless moving around and the two things are caused by the same physical action going on and that's the fact that these things are boiling they're boiling in all directions the gas is going up sideways and down the gas acts as a kind of barrier one it supports the weight of the droplet but two also it acts as a thermal insulator a barrier preventing the heat of the tray from instantly warming it up and boiling it off so the gas acts as an insulator so it's a bit like you put a rubber glove on the droplet which is fantastic this is called the leading frost effect which sounds like something that happens to people in Austria in the winter but it's not, it's named after I think it's got rid von leading frost and it's this effect that actually makes this stuff curiously safe I would not pour boiling coffee or hot coffee on my hand but I think I know what will happen if I do this the layer of gas between the really really cold liquid here and my hand will protect me I'm going to put my faith in the leading frost effect and the lady with the camera is getting very excited and I'm getting quite scared here we go it really is really really cold it's about minus 200 that's what I pretended but it really is about minus 200 but this gaseous layer is protecting my hand from the insane insanely cold temperature preventing my hand from burning and the burn that I would get from this would be exactly the same as a chemical burn or heat burn it's the disruption of the cell membrane literally my cells bursting but no, that doesn't happen because I'm protected by this gaseous layer are there any adults here so your hand went up very quickly I won't bother to get you to sign the disclaimer for but because you look sensible enough so you're going to ask to pull that up a bit we don't want any sort of cloth in the way hold your hand at about 45 degrees fingers apart downwards no piercings ok, you ready? are you sure? no, it's funny that is funny do it again so what do you feel like? warmer than water warmer than water you feel the weight of it, don't you? but it doesn't feel wet because it doesn't stick to you I think wetness is kind of stickiness, isn't it? tell your mates this bloke through some liquid at minus 196 and would anyone else like your dad is giving permission for this it's ok unfortunately old enough unfortunately old enough so fingers apart ok, ready? that's really smooth it's like I just put hand cream on every self-respecting scientist puts hand cream that is liquid nitrogen on their hands that's quite strange but it wasn't cold you kind of feel a prickly-ish sort of feeling, don't you? yeah, like all of the hair is stunned up but it's not cold and you're not as hairy as us too so he's just tweeting something odd I've just been frozen by some idiot insane person let me out of here as the police you're contacting now you haven't got quite so many hairs that will trap it not that you can see ok, thank you very much, thanks so this is medium frost effect that actually protects you and medium frost effect also comes into play with kettles and if you boil a kettle as the liquid turns into a gas the gas then acts as a thermal insulator so the heating element of the kettle suddenly becomes less efficient in heating the liquid so when a kettle boils suddenly at a boiling point it's not working so well so a well-designed kettle will circulate the water around and will work better and this is more of a problem with a boiler, for example where you're boiling lots of liquid and you want it all at a high temperature now we I told you that as we expand the volume occupied by liquid air to gaseous air the volume increases by a factor of about 700 with water the volume increases 1700 so a steam engine is a fantastic way you just heat the liquid suddenly it wants to occupy 1700 times the volume and that creates a head of pressure that can drive a piston or whatever it is you want to do so in the case of one of these what you wanted to do is to tell you that it's boiling and it does that by having a whistle on here as we have water in this kettle I'm going to put liquid nitrogen in a kettle and as it boils it's going to drive air out of the whistle yeah that works quite well good I have to be careful not to touch that now because that is cold what about other explosions oh yes we could do with this so if I put some liquid air which occupies whatever it occupies and then as it boils off it expands the head of it gas will sometimes blow the top of one of these sometimes not this time these are quite loose fitting lids I think that's where it's gone along let's try again right that way so this is what we call a controlled explosion and it's great fun my family liquid nitrogen show that I take to theatres and schools there are about six of us firing these off simultaneously and they're all going everywhere oh dude people like an explosion is there oh right but that could go on for quite a while and there's a guy called hero in AD 94 AD 94 who noticed this thing with the kettles and the head of steam coming out of a kettle so he built something quite similar to what I've got here a spherical vessel this is a ping pong ball and I've drilled a hole into it and I kind of bent the hole sideways so the hole is going kind of like that does that make sense so I'm going to cool this down hero of course didn't use liquid nitrogen or a ping pong ball he had a sort of kettle thing and he had water in it but it was the same sort of idea what I'm going to do now is just like the balloon the ping pong ball is now cooling down inside so the gas inside the ping pong ball is turning from a gas into a liquid it's also there's less pressure in there so it's sucking some of the liquid in through the hole from the liquid around it so we're going to end up with a cold ping pong ball containing a little bit of liquid air at a low temperature let me just pan out a bit now as it warms up the air is going to start expanding and it will start coming out of that little hole come on there it goes so now we have a steam engine so this was called hero's steam engine AD94 in ancient Greece a guy invented the steam engine and they just thought that's interesting and they left it at that now if they'd just carry on with that just a little bit more we would be technologically in the year 4000 now we would probably be out conquering galaxies so I don't know if that's a good or bad thing that we didn't seize upon that opportunity and notice a fundamental game changer of technology so that's a steam engine literally just converting that head of pressure into motion that could then be used to drive something or just look at and think that's interesting which is what the Greeks did with it so that's my hero's engine let's look at a slightly more modern piece of technology these are really really powerful magnets which is what I've got that sign there that says danger don't get close to these magnets and I've got here a material itrium, barium carbon oxide, YCBO there are little black pucks in there they look like magnets and this almost alchemical collection of mixture of elements if you cool them down below a certain temperature they start to behave in a very very odd way what actually happens is that the electrons gang up in pairs and start to move around extremely freely inside your material and I mean extremely freely so if you applied an electric sort of voltage across it they're just whiz across there feeling no resistance whatsoever it's a super conductor I don't know if you know about electricity but it has zero ohms there's no electrical resistance which is incredible and because these electrons can move really really quickly if you put a magnetic field near them they'll just orientate themselves to it immediately no problem at all so it's kind of strongly magnetic but it doesn't matter whether you put a north pole close to it or a south pole next to it it always aligns itself to be opposite it's like an eternally repulsive thing do you know anything very repulsive? no but anyway this is just incredibly repulsive material when it comes across a magnetic field so I've arranged these magnets here into a sort of track and this thing just always repels the track so there's an air gap between there sorry? and it's the you know they're on one side and they are in a circle one side is one side so amebus strip is the technical term yeah and I've seen it done on one of those that's right the real institution and the University of Cambridge made one of these they spent about 2,000 pounds on lots and lots of magnets the track was a lot longer than this and yes there's a force repelling it but there's also a kind of force attracting it so if I've lifted away it just wants to sit in this well I've arranged these magnets so that they're north south north upwards so there's kind of a C shaped section and the kind of logic of it so if I went that way it would pull me back so it's always going to sit within that well and hover so the Japanese particularly are really really interested in this idea of a levitation device and they want to get a train to work like this I mean this would be a train with no wheels with no contact point hardly any energy needed to get the thing moving I'm not quite sure how the brakes would work but yeah so they have what's called a magnetic levitation train here they're not using superconductors like this but they're using electromagnets that they can adjust really really quickly and they do have to adjust them quickly because there are kind of variations in this magnetic field as you go along the magnets aren't all perfectly the same there are gaps between them in some places the magnetic force is stronger than in other places but by nature getting the electrons to arrange themselves really really quickly according to whatever comes onto them all that automatic switching is done just instantly whereas with a magnetic levitation train from Japan where it's all electronically controlled electromagnets there's some really complicated switching having to go on to make the thing just stick on the track and if that switching stops working that's it, you're all dead slightly worrying in a way but this material at least two little pucks in here we might just about would have said two little black things that's 60 quids worth of material in there and these magnets weren't cheap either hi ok thanks so if we could get something that was like the magnets cheaper if we could get this material that was cheaper and it worked at other temperatures that weren't liquid nitrogen really really low temperatures we might end up with this sort of magic almost floating device now has anyone seen the film Back to the Future the one that's set in the future do you remember they had skateboards that levitated that just reminds me of this do you know what year that was set in 2015 2015, that's this year so we better get cracking on this we really need to get cracking on it otherwise Back to the Future will not be the documentary that I thought it was I've nearly finished and I just want to show you one last demonstration of this which usually goes down a bit old wow I'm not allowed to make ice cream for you I would love to but I can't and ice cream with liquid nitrogen is brilliant he's got the catering franchise, I haven't I'll tell you how it works you get some cream you get some strawberries or chocolate you put in tons and tons of icing sugar you mix it all together and then you stir in some of this stuff and as it boils it agitates it keeps turning over the material so you don't get one large crystal forming so it doesn't end up like an ice cube it flows it's still at minus 18 or whatever but it flows like Mr Whippy ice cream does so you get this lovely slushy cold ice cream it takes about 10 minutes maybe to make something like that so you can get some fresh ingredients to ice cream that's just lovely and tasty in about 10-15 minutes whereas with an ordinary ice cream maker it will take ages to make it and there's agitation required and there's just quite a large involved sort of job I have to tell you that this stuff is actually quite cheap it's only 14p a litre to buy that's because there's a by-product from getting oxygen out of the air which is what British Oxygen Corporation and Air Products do they need the oxygen for scuba divers for hospitals and for the steel industries karting bottles of oxygen around is a very convenient way of transporting huge amounts of the gas that they want in a smaller volume as we talked about the squashing down of a gas into a liquid but in liquifying oxygen they accidentally liquify nitrogen so you're remembering me saying that 78% of the air is nitrogen and that's what they start with so there's enormous amount of by-product more by-product than they really know what to do so that's why it's so cheap and you might think well why isn't the world why hasn't the world got so many ice cream outlets just making liquid nitrogen ice cream for you Hester Blumenthal I think famously has made ice cream using this stuff because London is one of these places where there is nothing I think there is one ice cream place that will make liquid nitrogen ice cream for you that isn't NPL but the point is actually 14p to cool down some ice cream is still a huge cost compared with how cheap electricity is to refrigerate down your ice cream so it really is a cost thing it's as simple as that as transporting this stuff around anyway let's sort of pseudo make some ice cream because why not so it's the bubbling through that stops the solid from forming and at the same time cooling it which is what you want if you've got ice cream and myself an NPL's bubble expert because NPL has a bubble expert of course we were in the car park at NPL and we tried this demonstration and we thought we knew what was going to happen we got our bubble making apparatus was this washing up liquid we put in some liquid nitrogen and we were waiting for the thing to happen and it didn't it just turned to a solid ice cube immediately there was no bubbling through and it was just because it was too cold, too quickly so that's why I'm going to put the secret ingredients and boiling water into here which will then do what I hope it will do warm it up enough so we've got a bubble liquid there bubble making liquid and we're going to this stuff is going to quite furiously bubble through it and make some bubbles are you ready? so is this steam? no it's mist it's water vapor so we have bubbles here filling up with nitrogen that's bubbling out of there but also a little bit of water vapor and if it gets too cold it's it's still going to bit if it gets too cold it will stop doing this but it seems quite happy to carry on for the moment sorry now I know why I bought that so now the bubbles are going solid so these are now frozen bubbles so what do you do? you put some of this into it and you can just keep going between hot and cold making these bubbles happen and I can't think kodajčen in this so that's where I'm going to stop you can applaud me and then you can ask me tricky questions thank you if what never warms up it does warm up in here so there's hot water going in there and there's cold liquid nitrogen in there they mix and eventually they work out what the temperature in there is going to be and if I keep adding liquid nitrogen the average temperature will keep going down and eventually it will just turn to ice because it will be cold a lot of people are curious about how I can just be putting something so cold around all time why isn't it just instantly all boring off and the inside of this container is well the inside the container is about minus 200 it's been cooled down by the liquid nitrogen itself so it's not going to be all off there and at the top of the liquid there's cold air and where the air really meets the liquid it's so cold it's about the same temperature so you have kind of a plug on top so it's almost as though it's a kind of loose lid on here of gas so that's why it's not boiling off instantly in the way that you might think if I had some water at boiling point it's going to carry on boiling off so that's why it doesn't all instantly disappear is this how it's delivered? sorry? no, it's delivered under pressure so bridges oxygen drive around this big tube giant gas canister, well liquid canister effectively and it's under pressure it's held under pressure, very high pressure I mean I have a vent there so if it gets above a particular pressure it will go and then to empty it you just release this and then the pressure of the stuff inside boiling pushes it all out and it comes out and it delivers into here so as bridges oxygen drive around and you may have seen BOC and if you go to a hospital you'll see a great big white vat sometimes it will have oxygen in it sometimes it will have nitrogen in it because they use these for freezing biological specimens in hospitals they squirt a little bit on there and then that burns the vort off so those ones will be under pressure but guys who know how to use the pressure valves and whatever gently ease it off and then can decant into these handling buckets which are not held at pressure deliberately so so this big one here the top is loose and the top is loose the top is loose if that got stuck on here then the pressure would build up and up and up and up and up and eventually it would explode the hazards involved in nitrogen are this threat of exploding if it's under pressure and the fact that it's very cold and also the fact that you can't breathe nitrogen well you can breathe it but if you increase the proportion of nitrogen in this room you'll decrease the proportion of oxygen so, but I've done the maths if I emptied all of this lot into this room and the whole of this expanded 700 times to fill this room would still probably be all right because of air flows and things like that Does that contain a life expectancy that does it degrade? Yes there's low pressure between the outer vessel and the inner vessel so the thermal insulation will degrade with time but when it comes to that you just the opposite of refill it you re-evacuate it in principle it should last a very long time somebody told me that if you just have one of these sitting in the corner of your garage because you're going to use it to make ice cream over the weekend or kill the ants nest or do some weeding it will evaporate off at about a liter a day but I think these are probably less it depends on how good they are as insulators that when you buy them new they're probably about a tenth of a liter a day perhaps even less perhaps a bit more than that and this contains 25 liters so it should be good for three weeks yes I buy this and then in three weeks later I'll come back and there's nothing in it but a 14 per liter that doesn't really bother me yeah about 20 degrees lower than the boiling point so about minus 207 I think 207, 217, something like that it's not that much lower but you think of water being 100 degrees between the boiling point and the freezing point with nitrogen it's only 20 degrees so yeah good question and that goes back to that of things that we had and there was a picture there of some solid nitrogen I think you can get solid nitrogen on Pluto if we look back at those values that we had everything a boiling point and a freezing point and depends on the material exactly where those points are some of them are very close some of them are very far apart and again go back to my opening thing we're used to water boiling we're used to seeing kind of all these things but we're not used to thinking about the air being so cold it turns into a liquid or even so cold it turns into a solid we're used to that idea with water because we live in sorts of places where you can see water boil and you can see water freeze we're used to it no, I can't think of any there's a list of about 30 applications of liquid nitrogen but they're not that great or it wouldn't be that cheap at MPL down the road we use it for cooling detectors so the cameras the chips on these cameras that they're using there they work a lot, lot better if they're cold there's thermal noise generated in the electronics which makes for a cloudy a fuzzy photograph but if you cool that chip down it just works much, much better better signal to noise ratio so we pour the stuff into our detection apparatus cool the electronics down and you get much better signals and to which temperature you cool it down usually like if you have this petrometer or cold you want the chip the machine returns whatever you can get sometimes there are some experiments that we do we go liquid helium temperatures 4 degrees above absolute 0 so we might have the nitrogen as an outer cheap and then the helium in the inside of that but you're right we should be spooning nitrogen granules in there shouldn't we are there any more questions for Andrew? in that case thank you so much thank you so much to Andrew thank you very much for coming thank you thanks much for so the next talk will be in April and it will be the bubble expert don't worry we will probably do this one again so hopefully I hope to see you there thank you so much for coming thank you