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Liquid Nitrogen


Liquid Nitrogen is a very cold fluid which is popular in science demonstrations and is surprisingly well-known to most people because of its appearance in movies*. Liquid nitrogen is the neutral stuff which 80% of the air is made of, but cooled down to minus 196 degrees Celsius so it is a liquid. This is interesting stuff! It's great fun!

Liquid nitrogen is a clear fluid which is like water in some ways, for example it's WET (unlike mercury). It looks like water which is on the boil, as the room is so hot relative to its boiling point that it's boiling away all the time. Also the vapour is like steam on a cold day, producing a creepy-film movie effect of a witches' brew. You can use liquid nitrogen to freeze various things, even things that will not normally freeze. Freezing with liquid nitrogen is quite fast, but not instantaneous.

If you freeze strawberries in a freezer normally they go all squooshy when you defrost them. But if you put them in liquid nitrogen they are frozen so quickly that even if they are then kept in the household freezer they still defrost perfectly ok! By this effect it is hoped to be able to freeze dead people and bring them back to life in the distant future! See Cryonics

However, on a lighter note, you can do a lot of silly things with liquid nitrogen, which I will now go on about, as I have considerable personal experience of the stuff...

Before I start to recount the tales of liquid nitrogen I think it's only fair to point out a safety warning: Caution! Zyra is a qualified mad scientist. If you are so silly as to try any of these tricks, then you do so at your own risk!

Blu-Tack nails hammered into the wall

Because liquid nitrogen is so very cold, things that are normally soft are changed in surprising and amusing ways. Blu-Tack, normally like putty, can be shaped by hand into the shape of nails, which when put into liquid nitrogen go hard (as nails) and can then be hammered into the wall (well, if the wall is fairly soft). Of course, liquid nitrogen soon evaporates and the nails warm up, and nails made of Blu-Tack turn back into ordinary soft Blu-Tack, leaving a situation which seems to other people impossible! How has someone made a nail of soft Blu-Tack and nailed it into the wall?

Similarly I once made a cutting tool out of Blu-Tack, put it on a power-drill and cut a notch in a desk. Next time you see notches in university desks, you may wonder how they've been done!

Explosives that disappear into thin air

I urge caution here, as the letting off of explosions should always be done in good humour! Seeing a bomb go off - great fun, but ending up dead or in the accident & emergency dept not funny, especially if you've got a really stupid story to tell when they say "how did this happen?". Anyway, liquid nitrogen, about 50ml of it, in a plastic lemonade bottle. At room temperature, liquid nitrogen boils, expanding like steam to fill a volume 2000 times its liquid state. The plastic bottle explodes very violently. being nearer than 30ft is Not Recommended! Boom! It explodes in a great cloud of frozen steam and ice-vapour! The plastic of the bottle is brittle like broken glass and smashes into smithereens, tiny shards going all over the place. Then the scene clears and all the liquid nitrogen literally disappears into thin air. So, explosion investigators will find remnants of a violent explosion but absolutely no trace of any explosives.

Rockets too can be made. As in "the advanced gas-cooled Lilt bottle".

Solid lumps of pure frozen Antifreeze

Antifreeze is a liquid deliberately for preventing freezing. Even dilute quantities in car radiators can save your engine from being destroyed by frost. Even the most severe winter will not freeze a quite strong solution of antifreeze in water. But pure antifreeze, surely that could never be frozen? Not so! Liquid nitrogen will freeze it solid! Pure solid blue crystal lumps of antifreeze - a sight to be seen!

What if it gets in your carpet?

Liquid nitrogen is as wet as water, so it will soak material. On a solid floor it will skitter about like globules of water on a cooker hotplate, as the floor at room temperature is from a nitrogenous perspective as hot as a hotplate. They hover around like tiny hovercraft on their own cushions of evaporating fluid. A carpet is a bit different, and the stuff will soak right through a carpet and then start to evaporate. For this reason it is best to make sure it's a good quality carpet and not foam-backed, as the foam will shatter! Good quality carpets aren't harmed by liquid nitrogen (except for really ancient fibre carpet). Chewing gum in contrast turns to something hard and brittle, so with a hammer it can be smashed! This is a novel way to remove sticky icky gooey things from carpets. The British Museum used liquid nitrogen to get the chewing gum out of their Axminster carpets after thousands of tourists had traipsed through the Tutankhamen exhibition.

In liquid nitrogen, some things become brittle and some don't. Things that don't become brittle even at -196 degrees C include expanded polystyrene, wool, and hair.

Drinking liquid nitrogen

Not recommended! It's about as advisable as fire-eating! However I can do it because I know how tiny a quantity of liquid nitrogen to drink such that I avoid exploding! Even a few ml, swallowed, results in belching forth great clouds of ice-vapour, an excellent party trick! Getting it wrong, though, would be very nasty. I have found that when doing something really silly it is best to be sensible in the silliness! For example, if I were being charged up to a million volts so I could spike my hair I'd be very careful not to touch anything connected to electrical earth.

Rubber

Rubber; flexible, bouncy, stretchy, springy... but with liquid nitrogen it becomes a hard solid a bit like porcelain. Rubber tubes, such as those found on bunsen burners, if dipped in liquid nitrogen, turn into thin pottery tubes and can be smashed! Then when they warm up, the broken pieces are still in the shape of smashed shards but are now made of flexible rubber again. A curious irony.

Killing weeds in the garden

Weeds growing inbetween slabs on paths? No problem! A quick dose of liquid nitrogen freezes them solid! Weeds in garden paths do not survive being frozen to minus 196 degrees C and then melting in the sun. However, the liquid nitrogen is not a poison or a chemical as such and will completely disappear into thin air. As a result, there is no residue. The sterile ground will soon get new seeds dropped on it, so the technique of using liquid nitrogen as weedkiller is not a permanent solution. What's more, though the weeds will come back, your liquid nitrogen will not.

Whistling Kettles

If a whistling kettle is filled with liquid nitrogen it will soon boil, even if just left in the room with no heating applied. A boiling kettle with no heating. It will even whistle and boil in the deep freezer, as the liquid is boiling at room temperature, so the room and the freezer are like an oven in relative terms.

The tale of the exploding Fairy Liquid

This happened in a room in a student hall of residence. I already knew from experience at a student party that if liquid nitrogen is put in a bottle of Fairy Liquid then after an effective delay the top will burst off and hit the ceiling! So, attempting to repeat this is my student room I borrowed the bottle of dish washing liquid from the communal kitchen and placed it in the middle of the carpet where my friends gathered around the room could observe the stunt without (much) danger. Now I'm sure the people who make Fairy Liquid will nod in agreement here about the wisdom of buying a good quality washing-up liquid like Fairy Liquid and not some cheap brand. Because Fairy Liquid is the top-of-the-range stuff and is a bit more expensive, the bottle is more sturdy. The borrowed bottle of shop's own brand was not just cheaper soapy stuff, but a lesser-engineered bottle. What happened next was observed by the onlookers who will not forget, as the liquid nitrogen boiled away and the bottle started to expand, bloating out like a balloon. At last it could take it no more, and suddenly Burst! The contents, a mixture of liquid nitrogen and soap-liquid went all over the carpet!

The nitrogen disappeared within minutes. But how do you clean liquid soap out of a carpet? Use muck? In the end it was never finally resolved, although some of the bravest attempts to clean it up took place on Friday nights. It was a known fact that the cleaners never visited over the weekend, and the heating was always on full because the tower had no separate room controls and therefore had to be heated to the most tropical temperatures so as to please all the residents, some of whom were from very hot places. So, on a Friday night, the twenty gallon transformer wagon on wheels (which just happened to be about) was filled with water and was overturned onto the carpet! This produced loads of suds which could be trampled around in, but the stuff was never exhausted. So, if you're staying in a student hall of residence, you might like to test your carpet to see if it's been soaked in soap.

Case of mistaken identity - The Wrong Pie

It was usual to collect food from the refectory and leave it lying around in the rooms. Because of this, some of the food lying about on plates in rooms was fresh, and some of it was stale. It never really went bad, but because of the high temperatures and dry air it would become preserved and dried-out. On that day I had put a small amount of liquid nitrogen in a champagne bottle and had put the cork in (caution! Silliness!), and I aimed it at a slice of cherry tart which had been lying around for a week or two and I had decided was a bit too stale and was ready to throw out of the window of the high tower to the birds. The cork shot out like a bullet, as expected, and hit the cherry tart with just the right amount of force so as not to smash the plate. But oh shucks, I suddenly realised the mistake and saw the actual stale cherry tart on the bookshelf. I had shot the wrong pie! The shot pie was the fresh one I had acquired that day! What a mess!

I hate wasting food! It really won't do! So I got a spoon and went around carefully eating it off the chairs, curtains, carpets, etc, being very careful to avoid eating any industrial grit and other stuff that had been produced by some of the other silly experiments that had been done in that room. It was an hour before I had got all the pie eaten. Not good, as I could have put that time into studying something scientific. So, the moral is: When aiming a champagne bottle with liquid nitrogen at a cherry tart, make sure to identify the correct target first!

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More Liquid Nitrogen silliness will be added here.

Extra notes:

Solid Nitrogen? - The freezing point of nitrogen, ie the point at which nitrogen becomes solid, is -210 degrees C, which is 63 Kelvin.

And yes, you can freeze nitrogen solid without using high pressure (unlike helium)

Even more notes: Liquid nitrogen was traditionally made using a compressor, but now there's new electrification of the process. It's a ramification of the new improved thermo-diode! See http://www.trnmag.com/Stories/2001/121901/Chips_turn_more_heat_to_power_121901.html

Where to get liquid nitrogen:

This is a question I'm often asked: "Where can I get some liquid nitrogen?". Sometimes the question is phrased in a way which suggests a few assumptions about the stuff. For example "Where can I buy liquid nitrogen in small aerosol cans in shops?". Having received many such requests, I've decided to write a page about it. See Where Can I Get Liquid Nitrogen?

Other notes about the handling of liquid nitrogen:

* Polystyrene cups are very useful. (That is, expanded polystyrene, which is such a good insulator)

* Don't try to keep liquid nitrogen in a closed container to stop it evaporating. It WILL evaporate, even if it has to explode the container to do it.

* If you spill liquid nitrogen on your skin it will usually not harm you, as each droplet will hover on its own cushion of air like drops of water on a hotplate, but don't be lulled into a false sense of security. Any metal objects cooled down to liquid nitrogen temperatures (metal teaspoons for example) are hazardous as they can stick to your skin and cause injury similar to a burn.

* Liquid nitrogen will not hang around for long. The larger the flask, the longer it will last. A five gallon Dewar will still be half full after two weeks, but a two pint tea flask will not have much remaining after a day or two. Also see how a Thermos flask works


** A few movies featuring liquid nitrogen:

Terminator 2 Judgment Day (1991). The line "Hasta la vista, baby!" is spoken by Arnie just before he shoots the T1000 enemy terminator which has been frozen solid on account of a tanker of liquid nitrogen crashing and spilling the liquid all over the steel works floor. Although the foe is shattered into tiny pieces, the heat of the steel factory soon warms up the pieces which flow around like liquid metal mercury which can then reconstitute.

Batman & Robin (1997). Mr Freeze has his wife frozen in liquid nitrogen, displayed in a stylish showcase. (Although plausible, there are condensation issues which are unconsidered. Note that people stored by cryonics are generally kept inside very well-insulated vats).

Goldeneye (1995) (James Bond). Boris, a computer whizkid working for the bad guys, despite claiming to be "Invincible!", is frozen instantly in a deluge of liquid nitrogen. (This is scientifically questionable, as a body tends not to freeze instantly).


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