Cryogenics with Liquid Nitrogen

Cryogenics is a branch of physics that deals with the production and effects of very low temperatures.

Here are demonstrations of some of those effects.
I will add more as time and my liquid nitrogen supply permit.

This page has gotten very large so if you came to this site to see a particular demonstration this list  may help you find it quickly. 
The demos are all on this page so just scroll down and don't bother with the list if you want to see lots of them.
If you are going to try any of the demos please read the precautions in the red text.

Leidenfrost effect
Superconductivity
Hero's engine, ping-pong ball, heat engine
Frozen balloon, uninflated
Brittle metal
Lead bell
Solder spring
Liquid to gas, balloon inflation
Slow chemistry, light stick
Liquid to gas, soap solution
Frozen flower
Explosion 1, bucket launch
Modeling clay, broken ball
Liquid nitrogen canon
Make liquid oxygen
Magnetic liquid oxygen
Electrical resistance change
Flashlight change
Bare light filament
Broken penny, zinc
Balloons in liquid nitrogen
Helium balloon
Frozen marshmallow
LED band gap change
Banana hammer
Rubber ball
Gasoline candle
Solid butane fire
Wizard ice cream in 12 seconds
Ice cream drops, Dippin' DotsŪ
Water balloon
Plastic containers
Clouds, fog, frost and snow
Explosion 2, in a barrel
Lenz's law repulsion coil


    

Please be very careful if you try any of these demonstrations.

Liquid nitrogen is dangerously cold.
Direct contact with the liquid or gas that is boiling off or with materials/containers cooled by it can cause severe frostbite very quickly.

It expands more than 700 times when it goes from a liquid to a room temperature gas.
If confined it can produce pressures that can burst nearly any container. Pressures of over 40,000 pounds per square inch are possible.
A pop bottle or a thermos with the lid on is an invitation for disaster
Sealed containers are bombs if there is no way for pressure to be released.

Some materials become very brittle and are easily broken when cold.
This includes some steel, other metals, and many plastics.
Don't use untested materials.

As it boils nitrogen gas is released.
It is not poisonous but it will dilute the oxygen content of air thereby reducing it.
If the oxygen level gets too low you will lose consciousness and at still lower concentrations you will die.
Make sure of adequate ventilation during your experiments.

It is possible to make liquid oxygen by condensation of oxygen from the air, even accidentally.  This can result in a fire or explosion hazard if the liquid or the high concentration of oxygen gas that results when it evaporates contacts combustible materials.  This includes materials that you wouldn't ordinarily think of as flammable.  Eliminate all sources of ignition including flames, sparks, and ground apparatus to avoid static discharges.

Gloves (even ones designed for cryogenic work) will not provide protection from immersion in liquid nitrogen.  If the glove is wetted with the liquid it will soak in and freeze your hand inside the glove. 

You must be careful.  These warnings cover most but not all possible ways that you might get into trouble when using liquid nitrogen.  Do your own safety research, take adequate precautions, and please be careful

The temperature of liquid nitrogen which is boiling at normal atmospheric pressure is:
77 ° Kelvin
-196° Celsius
-320° Fahrenheit
139° Rankine
-157 Reaumur
These are just different ways of representing the same temperature.  Just like we can measure the same distance in inches, centimeters, miles or other units depending on just what we are doing.
To give you some sense of how cold it is, it is about as much below room temperature as a pizza oven is above it.

Many things change their physical, chemical and electrical properties when cooled to the temperature of liquid nitrogen.  The pictures below show some of these effects.

One of the simplest experiments to try is to just spill a few cc's of liquid nitrogen on a hard smooth floor.  You will see that each droplet forms a bead and moves quickly around on the floor as if it were frictionless.   Close examination of one of the droplets will show that it isn't touching the floor at all.  Instead it is sitting on a thin film of gas that is coming from the bead.  This is called the Leidenfrost effect, named for a German experimenter who investigated it using water and a hot metal plate in the mid 1700s.  The film of gas that is formed is an effective insulator so the evaporation rate is considerably slower than you might expect.  The droplets also have the tendency to pick up dust from the surface and as they evaporate the dust is concentrated often forming a tiny ball when the nitrogen has completely evaporated.  These pictures show some liquid nitrogen when it was initially poured on a surface and later when dust and possibly frost has collected on it.

  

This video shows the effect in a pan.  You can see that this is much different from water or other liquid since there is almost no friction and very low viscosity.

Superconductivity can be demonstrated with a disk of  yttrium barium copper oxide (Y Ba2 Cu3 O7) ceramic and a neodymium-iron-boron (or other strong) magnet.  What you see in the pictures below are the ceramic disk with a small powerful magnet sitting on it.  As the disk is cooled by the liquid nitrogen the Meissner effect forces the magnet's field out of the disk which causes the magnet to rise supported by its magnetic field.  The magnet is quite stable (if you poke at it it will bob around and return to its starting position). If you do manage to knock it off it can be picked up and set back in place by using non magnetic tweezers.

    

In this video the tip of the plastic tweezers can then pass between the superconducting disk and a cubic magnet.  When the magnet is tapped with the tweezers it spins on its magnetic axis.


If you use a pin to poke two holes in a Ping-Pong ball tangential to the surface you can use it to make a Hero's engine.  Drop it into a container of liquid nitrogen and hold it under the surface for a few seconds.  As the air in the ball cools the pressure in the ball drops and atmospheric pressure forces some liquid nitrogen into the ball.  Take the ball out and put it on the floor and as the nitrogen boils and is discharged the ball will spin rapidly.  You don't need much liquid in the ball for it to spin so don't try to fill it up.  There is the possibility that if the ball is too full the pressure could build up to the point that the ball would burst so don't stand too close when you try this.  I have done this experiment many times and haven't had one burst yet but I can't be sure that all Ping-Pong balls can take the pressure.

  

Here is a video of the "engine".  There are marks on the ball to make it's rotation easier to see.  You will notice that at the start I hold the ping-pong ball in my hand very briefly so the liquid nitrogen will boil and start the rotation quickly. 


You can demonstrate how the properties of some materials are changed when they are cooled to cryogenic temperatures.
Here an uninflated long skinny balloon like those used to make animals and such was dipped into liquid nitrogen and then stretched.  The kink will break before it straightens.  That is not what some might expect for thin and normally flexible rubber.

  


Metals can also become brittle when they are cooled in liquid nitrogen. The first two, copper and aluminum, flex easily but the tin strip breaks with almost no force. If you are wondering, the metal is very cold but because it isn't very thick and I didn't hold on for more than more than a couple of seconds so I didn't have any ill effects.

Here is a still photo of strips of brass (on left), copper (next to it) and tin (last two)   The brass and copper remain flexible as in the video above the tin became so brittle that it was easily broken when it was cooled and bent.  If you want to repeat this make sure that you have actual sheet of tin metal not tin plated steel that is often sold as tin sheet.

When you tap a sheet of lead you shouldn't expect to hear music but when it is cooled to the temperature of liquid nitrogen you can easily hear that the normal temperature dull click takes on a more musical ping.


A spring made from solder doesn't work all that well.  When stretched it deforms rather than returning to its original length.  The bottom half of this spring was dipped into liquid nitrogen and behaves like you would expect a spring to until it warms up.  The top part wasn't cooled and deforms easily and does not come back to it's original shape.   This demonstration is more effective if you can find some old  lead/tin solder rather than the newer lead free type.


Ten cc's or so of liquid nitrogen were put into this bottle then the balloon was put over the top.  As the nitrogen boils the gas fills the balloon with the expected result.  The difference in volume between the liquid and gas is brought home vividly. It expands about 730 times as it warms to room temperature. The pop can be loud enough to make ears ring if you use a high quality balloon so warn your audience to cover their ears.
  


Cool temperatures cause chemical reactions to slow down.  The chemiluminescent glow of a light stick is quickly extinguished by cooling it.  The light returns when the reaction resumes as it warms up. If you cool only half of the light stick this is what happens.  You can demonstrate this with dry ice or even ice water to a lesser degree. (pun intended)
  

A simple, dramatic, and messy way to show the change of volume that liquid nitrogen undergoes as it changes to a gas is to dump a small amount of it into a soap and water solution.  The nitrogen boils and generates a lot of bubbles rather quickly.  It helps if the soap solution is warm and you use only a few cc's of liquid nitrogen.  This both makes the change in volume more dramatic and is less likely to result in frozen liquid and bubbles.   You can add more later to see just what frozen bubbles are like.

 


The old frozen flower trick.  Take a flower and dip it in the liquid nitrogen.  It looks much the same except for the frost and fog.  I usually point out that the flower won't wilt or decay no matter how long it is kept in the liquid nitrogen.  In fact it could be studied many years later and would be just as it was immediately after it was frozen.  Many types of biological specimens are stored this way to preserve them.  However, we have to avoid mechanical damage.  To illustrate this I rapidly crush the bloom and let the fragments fall on a hard surface.  Usually someone will say that they sound like broken glass.  You can crush the flower with your bare hand if you release it very quickly and use a flower that doesn't have a lot of places that the liquid could be trapped.  Chrysanthemums are a particularly bad choice. 

    
The surface here isn't hard enough to make the glass like sound.




Here is a video of a liquid nitrogen explosion.
Remember I said "A pop bottle with the lid on is an invitation for disaster.  Sealed containers are bombs if there is no way for pressure to be released."

For this experiment I put a 100 cc's or so of liquid nitrogen into a two liter plastic pop bottle. Put the lid on and quickly dropped it into a 5 pound coffee can with about 2 inches of water in it.  Covered the whole works with a 5 gallon plastic bucket and got back about 120 feet. 
You see the result. 
Calculations based on measurements we made give a peak height for the bucket of 88 feet. 

Liquid Nitrogen Explosion 

You should be aware that fragments of the bottle landed more than 70 feet away from the launch point.
There is no guarantee that is the greatest distance they can travel so get way back if you decide to repeat this.

A ball of modeling clay will freeze and when dropped or struck will shatter nicely.  There are a lot of different kinds of clay available and some probably will be harder to break than others.  If you discover one that is particularly durable let me know about it.


During a demonstration of the properties of liquid nitrogen I was challenged to a duel.  The canons were loaded with a gallon of hot water and Styrofoam packing peanuts.  At the count of three the combatants dumped liquid nitrogen into their canons.  It boiled rapidly and you see the results.


Here is a way to produce a few drops of liquid oxygen. Put liquid nitrogen in an aluminum can.  The outside of the can will quickly cool to just above the temperature of the nitrogen.  Frost will quickly form and then it will appear to be wet.  The frost is created from water vapor from the air. The liquid that is wetting it is oxygen that is condensing out of the air. This happens because the temperature at which oxygen changes from a gas to a liquid is about 13 degrees Celsius above that of nitrogen.  The oxygen can be seen dripping from the can just as on a humid day you can see drops of water condense and drip from a can you take from the refrigerator.  Be sure to observe the special precautions for liquid oxygen in the red text at the top of the page.



Liquid oxygen is magnetic.  I filled a small nonmagnetic aluminum container with liquid oxygen then brought a strong magnet near to it.
You can see it is attracted to the magnet.



The resistance of most conductors goes down as the temperatures falls.  Here is a flashlight bulb connected to a battery through a coil of wire.  At room temperature the resistance of the coil is high and the bulb barely glows.  When the coil is cooled the bulb gets much brighter.

  

Here a 200 watt light bulb is powered through the coil of wire seen in this picture.

The resistance of the wire reduces the voltage to the light.  When the coil is cooled with liquid nitrogen the coil's resistance goes down and the light gets brighter.  The increase is most easily seen on the cloth behind the lamp.


What is the effect of immersing a small flashlight in liquid nitrogen?   I usually ask the audience what they think will happen.  If I do it right after the demonstration just above or the superconductor experiment, most will predict that it will get brighter.  If I do it soon after showing the light stick most will predict that it will get dim or go out.  In fact it goes out, but it takes several minutes for the battery to cool down and slow the chemical reactions that make it work.  It does come on again when it warms up.  It would not surprise me if some batteries or flashlights may be damaged and the light won't come back on but I haven't found it to be a problem with the ones I use. There is also the potential for the flashlight to leak and get some liquid nitrogen inside it which will boil and expand as it warms up causing the flashlight to burst.


In another electricity/light experiment I removed the glass from a 12 volt light bulb and immersed it in liquid nitrogen and powered it up.  If I did this in air it would immediately burn out but the nitrogen prevents oxygen from getting to it so it continues to work.  It may be surprising that the filament is able to become incandescent even though it is being cooled by the liquid nitrogen but the Leidenfrost effect shown at the top of the page provides enough thermal insulation for it to work.  This picture shows the bare filament with a wire cage around it to keep it from being broken if I happen to bump it into the liquid nitrogen container.


The video shows the light being switched on and off while under the liquid nitrogen. Each time it was switched on the video camera compensated by reducing the exposure so the rest of the image gets dark. When the power is switched off the camera again compensates and the background of the image gets brighter again.


Break a penny? US pennies minted after 1983 have a zinc core clad with a very thin coat of copper. Prior to that time they were solid copper. The zinc becomes brittle when cooled in liquid nitrogen and can be broken by tapping it with a hammer. At room temperature they remain intact as do the solid copper ones at either temperature.



An inflated balloon pushed into a container of liquid nitrogen will slowly collapse as the air inside it contracts and condenses.  The part of the balloon that is cooled becomes quite stiff and crinkles like a plastic bag.  When it has nearly completely deflated you can take it out and show the liquid air by swirling it in the bottom of the balloon.  If you haven't cracked the balloon by bending it when it was frozen and there is a reasonably large part of the balloon that isn't so hard that it won't stretch, it will reinflate to it's original size demonstrating that all of the air is still in there.


Putting several balloon animals in a container makes a real impression.  I usually say that I have collected this menagerie on my visit to another planet and I didn't have room to bring them back in my space ship so I cooled them to make them smaller.  Having the kids give them names is also fun.

A helium filled balloon was weighted so that it would barely rise. It was then cooled with liquid nitrogen. The helium contracted and the balloon became less buoyant. When I touched it with my hands it warmed enough for the gas to expand and it could rise again.


Put a marshmallow on a stick and freeze it.  Marshmallows are good insulators so they take a couple of minutes to freeze.  Take it out and rap it on a hard surface and it will shatter.  I recommend that you don't do this where it will be hard to clean up because those shards of marshmallow will quickly warm up and they are incredibly sticky.  (The first time I did this it was in my kitchen and my wife hasn't forgotten it yet.)




A light emitting diode (LED) is a semiconductor that converts electrical energy to light.  The color of the light depends on the size of the "step" between the valence and conduction bands in the material from which it is made.  When an LED is cooled the band gap and therefore the color of light it produces is changed.  The change in the band gap also changes the voltage drop across the diode which, depending on the circuit providing the current, may change the current through it.  If the current changes, the intensity of the light as well as the color will change.  The two pictures below show the same LED, first at room temperature then after it was cooled in liquid nitrogen.
 
This picture shows the effect on several different colors of LEDs.  The set on the right has been cooled and the colors are all shifted to slightly shorter wavelengths. 
The same current is flowing through the corresponding LEDs in each set and, as you can see, the cooled ones are much brighter.


Freeze a banana.  It can be used as a hammer to drive a nail.  Take care to only hold on to the part that hasn't been immersed in the liquid nitrogen. Bananas that are less than fully ripe are not as likely to break

When one does break you have a new way to examine the structure of a banana.  Compare it to a sliced one.  Let it warm up and check it again.  The results are interesting and you don't need to use liquid nitrogen to check what happens.  You can just put a banana in a home freezer and leave it there for at least 24 hours to be sure that it is completely frozen.  Take it out and check what happens as it warms up.  Be sure to wait long enough (at least 1 day) for it to completely change. 


Freeze a rubber ball.  The solid high bouncing rubber balls still bounce on hard surfaces but they sound like marbles or pool balls.  Hollow handball type balls are easily broken but if you decide to do that be aware that the fragments can fly quite a distance and could hurt if they hit someone.



Here are identical balls being bounced, one frozen one not.

Make a candle from vegetable oil or any liquid hydrocarbon.  When frozen most will look a lot like paraffin.  Alternately dip a wick into the liquid and into the nitrogen.  When you get a reasonable size candle you can put it in a holder and light it.  Of course as it burns and warms from the air it will entirely liquefy and you will have an oil lamp with a long wick that may fall in any direction.  Please be aware of the potential fire hazard and take appropriate precautions.  The white candle was made using vegetable oil and the greenish one was made from gasoline (use extreme care).



A lump of solid butane was made by cooling a container of butane with liquid nitrogen. The lump was put on a piece of cardboard and ignited. Because the evaporation of the butane cools the cardboard the cardboard doesn't catch fire. The only change is some soot deposited on it.


Wizard ice cream.  Use any good homemade ice cream recipe.  Put it in a metal bowl and add about an equal volume of liquid nitrogen while stirring vigorously with a wooden spoon. You won't be able to see what is going on in the bowl because of the vapor cloud that is produced.  The record time for going from liquid to finished product is 12 seconds for a half gallon of ice cream.  Be sure that you don't use too much liquid nitrogen.  If you do the ice cream will be rock hard and if you manage to serve some there will be a real chance of frostbite of the tongue.

As of May 14, 2014 more than 12,168 kids and adults have enjoyed our ice cream.


Our recipe
1 quart egg whites
6 cups sugar
2 quarts of cream
1 gallon whole milk
2 oz. vanilla
1/4 tsp salt
Liquid nitrogen
Whip egg whites until they start to stiffen.
Continue beating while you slowly add sugar.
Stir in remainder of ingredients.
Using about 1/4 of the mixture at a time add liquid nitrogen while mixing.
It will take about the same volume of liquid nitrogen as the mix you use.
Enjoy!

A lot of people have told us that our ice cream is better than either home made or commercial brands.
It is probably because it is all natural, very fresh, and frozen very fast.
That last point is important because there isn't time for any ice crystals to grow as sometimes happens with homemade ice cream.

You can make tiny ice cream balls by dripping the mix directly into a container of liquid nitrogen.  It doesn't make much very fast but it is an interesting product similar to Dippin' DotsŪ.



A water balloon dropped into liquid nitrogen will freeze into a shell of ice with liquid water inside.  The balloon may split because it becomes brittle and the water expands as it turns to ice.  The picture shows a hole chipped in the ice shell to see if the center was still liquid.  It was.



Styrofoam cups also make good containers if you can be sure that no one will mistake them for a cup of beverage.  You shouldn't have cups of  beverage in any laboratory setting in any case.

 

A two liter plastic pop bottle that has been cut off  near the top of the wide part also makes a good container for liquid nitrogen.  It can be seen to be boiling looking through the side of the container.  The cloud that forms and cascades from the bottle is like formation of clouds when warm moist air is cooled  by rising to higher altitudes where it is cooler.   Fog is also formed when the ground is cooled by radiation of heat into space and it cools the air and the moisture condenses out.  If you tap on the bottle the frost that has formed on it will fall off and feels just like snow so you have a few elements of a meteorology demonstration.  It is a good idea to use a sheet of styrofoam to insulate the surface where you set the container to keep it from cracking because of the cold. 


And if you have a little liquid nitrogen left when you have had fun with the other experiments you can extend the meteorology demonstration by tossing the contents of a container into the air.  Moisture in the air condenses and forms a cloud of water droplets. The process continues when the nitrogen hits the ground about 15 ft below.

Here I take a 2 liter pop bottle containing about 100 cc's of liquid nitrogen, put a cap on it, and drop it into a barrel that has a couple of inches of water in it.  If you recall my comments about putting a lid on a container of liquid nitrogen you know what happens next.  The pressure builds up until the pop bottle explodes.  Notice the barrel jump from the force.  It was a lot louder than it seems in the video, in fact even though we warned the audience to cover their ears some folks in the front row said that it was the loudest noise that they had heard indoors.



Lenz's law repulsion coil.  A coil of wire with an alternating current flowing through it will induce a current in any conductor near it. The current in that conductor (the ring) will make a magnetic field that is in the opposite direction so it will be repelled. Initially the ring is at room temperature and is repelled to just over the top of the column. When the ring is cooled with liquid nitrogen its resistance is much lower and it is tossed about 1.5 times as high.


For more information you can go to these pages.


Superconductivity
Hero's engine
Lightstick chemistry

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