Left photo shows the Dewar with the cap. Note that this allows the gas to escape and is not a tight seal otherwise the thing will explode! The meter has a thermocouple but is way out of rated range although is reading -129 C. Liquid nitrogen (LN2) is at -196 C. The right photo shows a small balsa boat floating in the LN2.
Left and centre photos show the classic rose-in-Liquid N2 which causes it to become so brittle and glass-like that if thrown to the ground, it will shatter. The right photo shows the brittle petals snapping off spontaneously. Lots of other things can be made had or brittle things with zany results. Eg freeze an egg, peel it and let it warm. Or, use a banana to hammer in a nail.
I'm not sure I should show this photo but here is me (carefully) throwing
all the safety precautions to the wind and putting my hand in liquid N2 (for
about 0.5 secs). The gas generation keeps a gas layer between you and the
liquid and reduces the rate of freezing. Sensation is like a
cold breeze and no discomfort but I am not pushing the boundaries here.
Of course touching a solid, particularly metal, at liquid N2 temperature
will give rapid severe frostbite and it might stick to you. To treat
warts and other skin lesions it is applied with a cotton bud and will rapidly kill tissue.
Here is a banana hammer. The banana becomes extremely hard and brittle such that hammering a nail in is easy. Even worked for quite a heavy galvanised nail until the banana hammer handle broke.
point to run video (1.5 M)
Above is a liquid nitrogen popper. Put some in a plastic film canister and close the lid.
point to run video (600 k)
Liquid nitrogen in a plastic drink container filmed from some distance. It took about 2 minutes for this to explode but it has taken over 5 minutes. You can judge the loudness from the echo. The sharp plastic shards were only a few cm long and went a long way. It is very dangerous to approach an unexploded container. If nothing happens for over 10 minutes, throw a blanket over it might be the safest then hit it with a long stick with body/eye/ear protection.
Left photo shows what happens If you pour liquid N2 down a PVC tube to constrain it in the pool, then cover the top... It all blows out the bottom. The right photo shows a plastic cap placed over a blob of floating liquid N2. As the gas is produced, it 'burps' a bubble which has fog in it. This happens repeatedly. The bubble bursts after a second or so. Kind of strange. The pool ripples are seen on the bottom indicating movement. Enough liquid N2 will cause an iceberg to form, particularly if it is constrained by a floating polystryrene ring.
Left photo shows some LED's appearing to smoke. Actually the picture
is upside down and the 'smoke' is just a condensation trail. You can
just see the frosting on the LED's. The right photo shows a
variable capacitor with air spacing after removal from the liquid N2 when
water vapour frosts on it.
This photo shows a spark UNDER LN2 with a 1 mm gap. It would spark about as readily as 20 mm in free air. The green is laser illumination for a narrow light source to go down the neck of the Dewar flask. You can see some bubbling present and ripples on the surface. HV supply was my Candy box HV.
This photo shows a 256 Hz tuning fork which is measured at 256.2 Hz at room temperature. It is made of a magnetic steel which is chrome or nickel plated and with a small NIB magnet and a pickup coil out of the turntable motor from a microwave oven, gives a nice signal for my counter for about 20 seconds.
After immersing in LN2 the frequency
increases to 260.6 Hz. This is a change of 1.7% Simple coefficient of
expansion of steel would account for shortening of 0.000012/K for steel.
Given room temp 24 C and LN2 of -196 C this gives a 220 K range. Hence thermal
expansion is .00264. This would on its own change frequency from 256 Hz to
256.67 Hz. Clearly not the full explanation. Perhaps not even any explanation
as shortening will be accompanied by increased density which may compensate ?
I have frozen some ferrofluid and cut it in half with a saw.
Above left photo shows the LN2 dewar for transport from the gas company. It has a soft sponge plug which is loose and the cap sits on top. Center photo shows the medical oxygen cylinder with the gauge on the left reading 3 litres per minute. Right photo shows my own dewar out of its protective box. Next to it is the copper coil condensor which fits inside it. Oxygen gas intake is at the top and the lower end drains the liquid oxygen into the test tube. This test tube sits in the pool of LN2 to keep it cold.
Above left photo shows a view down into the dewar. The copper coil is around a larger collecting container and the oxygen outlet is the blurred tube at top right which is splashing LOX into the container. The right photo shows the blue tinge of LOX against white paper. By contrast, LN2 is colourless. There is a magnet suspended in it keeping cold. The container was just out in the air for a moment but frosting starts within seconds.
I have been able to confirm that LOX will adhere to a magnet due to its paramagnetic properties. The close up photos above left and center show a small NIB magnet with a crown of LOX over the top giving the muffin like appearance to the NIB. The center photo also shows the blanket of cold oxygen above it from the boiling LOX which in still air was very clearly defined. The setup was on an upside down styrofoam cup as a very shallow insulating dish. The right photo shows how LOX remains on the ends of a magnet where the field is strongest. This does not happen with liquid nitrogen.
This page was last updated July 26, 2009