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Liquid Nitrogen

Introduction
Various demonstrations with liquid nitrogen
Explanation
Explanation: 

Doing various experiments using liquid nitrogen including:
# Showing it in double walled pint glasses
# Smashing flowers
# Smashing rubber gloves
# Shrinking baloons
# Blowing the lids off tins
# Creating huge quantities of foam

First READ THE RISK ASSESMENT!! This experiment can only be done in venues where we have access to a suitable local supply of liquid nitrogen (e.g. the Cavendish teaching labs)

Liquid nitrogen is great as a teaching aid, and I like to get lots of bits of science in while people are interested in the subject

There is more stuff than you need here, pick what to talk about depending on how with it the audience is.

What is Liquid Nitrogen

This is cold - go through temperature line down to nitrogen. For example, -71 deg. C was the coldest temperature ever recorded on Earth. Possibly mention absolute zero

Pour some nitrogen into a double thin plastic pint glass

# What is nitrogen - 80% of air
# This is what happens when you cool nitrogen down to -196°C
# Why is it bubbling? - like water in a 400&degC oven

Smashing things
Flower:

What is a flower made of mostly? - water

What will happen to it? - freeze

Smash the flower, you can give out the ex-frozen petals

Notice the petals are all floppy, and smell really strongly

This is because the ice crystals break the cell walls apart

-imagine a cell as a polythene bag of water and gunk

- what happens to water when it freezes? The crytals are also sharp

Rubber glove

Rubber is made of long string like molecules that straighten out when you strech it by each string wriggling past the others.

When you cool it down the the molecules stop wriggling, and the only way it can deform is by breaking

When it warms up it goes back to normal

Shrinking Balloons

Use long thin balloons as they fit in buckets better. Start off with a helium balloon if you have got it, otherwise fudge with an air one.

Cool it down, it shoudl shrink 30% or so - and stop floating which you can get in

Do you think that warm or cold things have more energy? - is a cooker adding or removing energy to water

Hot -> lots of energy - what do you do when you have lots of energy? - run about

It often helps to run about and bounce off some walls here

Hot ->Molecules moving fast -> push sides hard -> big baloon

Cold->Molecules slow -> push weakly -> small baloon

Shrink air balloon

Some of the air will liquefy in end of balloon - do not get it too close to audience as it may explode

Blowing lids off tins

Little liquid blows up a whole baloon so what will happen in the tin?

Put nitrogen in tin, bang on lid

Make sure you have a lever to trigger it in case it doesn't go off of it's own accord

Pressure builds up and lid blows off

Foam

Only do outside,with a floor that doesn't mind getting slippy

What happens when we put liq. N2 in wasing up water...

Chuck in about 1-200ml

You get a lot of gas produced so a lot of foam, and some of the foam will freeeze if you chuck in enough nitrogen

Risk Assessment
Date risk assesment last checked: 
Tue, 01/01/2019
Risk assesment checked by: 
Andrei Ruskuc
Date risk assesment double checked: 
Wed, 12/12/2018
Risk assesment double-checked by: 
Mattlem
Risk Assessment: 

General- READ THIS!!

Liquid nitrogen is quite safe, if you handle it correctly, but can be dangerous if you are stupid. If it pours over your skin and doesn't pool it is fine, but if it is held on your skin by pooling or by clothes it can get unpleasant.

  • Keep it well away from eyes. Wear eye protection and shoes which cover your whole foot (ie. not sandals)
  • Always think about what is going to happen if you drop it/the container fails etc.
    • If you are doing the experiment on a table, do not let the public come up to the edge of the table as nitrogen has almost no friction on a smooth surface and it will fly
    • If there is a slope on the ground make sure it is away from the audience
    • Don't let the audience sit on the floor - nitrogen on shoes is fine, bottoms is not!
    • Make sure that no one is going to creep up on you from behind.
    • Think about ventilation and asphyxiation - only use a large or well-ventilated room if you use liquid nitrogen indoors.
    • Give the audience a line to keep behind otherwise they will creep forward
  • Have a second person to deal with the unexpected
  • Don't stick tubes in it, as they will boil the nitrogen inside and create something like a geyser
  • Things that have been in the nitrogen are often more dangerous than the nitrogen itself as they can stick to skin.
  • Don't stop thinking!
  • Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
    Extreme cold not very dangerous on skin for a short period but can be very dangerous if poured on clothes and collected near skin. Objects exposed to it, particularly metals, are very dangerous. Risk of cryogenic burns 3 4 12 Volunteers with previous experience of using liquid nitrogen to demonstrate only. Do not allow children to put their hands near it or to touch cold things. Another volunteer to police this. Do not let audience members sit on the ground. Follow guidelines above. Use in small quantities in a very controlled manner. Use one clear plastic pint glass inside another to hold a sample of liquid nitrogen for the audience to see. This means no-one needs to come close to see the liquid nitrogen. In the case of a cryogenic burn, loosen clothing around the affected area that may be restricting the blood flow. Flush with tepid (not warm) water. Call first aider. then cover with clean plastic and wrap in warm clothing (do not allow fabric to touch burn). 3 3 9
    Sharp smashed fragments Cuts etc. 2 2 4 Smash objects at a safe distance from visitors, without sending fragments flying. 1 2 2
    Flying tin lids Impact with face or similar. 2 3 6 Anchor the tin well. Do experiment away from visitors. 1 2 2
    Transport/storage Transporting and storing liquid nitrogen safely to avoid asphyxiation and leaks 2 2 4 Carry in a dewar with car windows open. Make sure dewar cannot fall over. Place dewar in separate compartment from the passengers and driver. Ensure the dewar is appropriate for carrying liquid nitrogen. If these conditions cannot be met in full, liquid nitrogen must not be transported. [NB: CHaOS should rethink this if we wish to transport again, we have not needed to or done so in over a decade] AVOID AT ALL COSTS. 1 2 2
    washing up liquid slip hazzard 2 1 1 Do experiment outside. Clear up area after demonstration 1 1 1
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