FLINN SCIENTIFIC
Morning of Chemistry
March 30, 2012
Indianapolis, IN
Liquid Nitrogen Light
When a bare filament from a standard 100W light bulb is immersed in liquid nitrogen the
filament glows brightly and does not burn out! Gorgeous!
Materials
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2 - 100W standard light bulb with the glass bulb removed
2 - utility lamp cords with socket
About 2 L of liquid nitrogen
Pliers
Goggles
Insulated gloves
1 or 2 L beaker
Procedure
Remove the glass bulb covering the filament in two light bulbs. You can either tap the glass bulb to break it
or heat it with a flame at one point then plunge the heated glass bulb into a beaker of cool water to break the
glass with thermal shock. I prefer this method as I have found that there is less trauma to the filament and a
greater chance that the filament will be damaged by the breaking glass. Note: Some light bulbs have more
pressure inside the glass bulb and some have less pressure inside the bulb than outside. Either way, the glass
may pop a bit when broken which is why I like to use the water method to insulate the break.
Gently remove the remaining bits of glass from the broken bulbs and screw the light bulbs into the utility lamp
cord sockets. You can then demonstrate how quickly the filament will burn out when exposed to the
atmosphere containing oxygen.
Pour about 1 L of liquid nitrogen into a 1 L beaker. Lower the unlit light bulb filament into the liquid
nitrogen. Turn on the light bulb filament . . . . a beautiful bright light will be seen glowing in the liquid
nitrogen! It is GORGEOUS!
The filament will stay lit in the liquid nitrogen a long as there is liquid nitrogen surrounding the filament and
insulating it from the atmosphere.
Safety Precautions
Use extreme care when handling liquid nitrogen. At atmospheric pressure, the temperature of liquid nitrogen
is below its boiling point of -77 K (-196°C). Severe frostbite can result from contact with bare skin or
clothing. Wear chemical splash goggles, Zetex™ gloves, and a chemical resistant apron. Please consult your
current Material Safety Data Sheets for additional safety, handling, and disposal information.
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Liquid Nitrogen Light
Continued
Discussion
Tungsten has been used in incandescent light bulb filaments since 1906. Tungsten is a great choice for a
filament in that it is very resistant to corrosion at high temperatures and is relatively cheap. Although the
glowing temperature of the tungsten filament varies a bit with current and resistance, a normal tungsten
filament glows white hot in a range of 2500°C to 3000°C.The tungsten in a light bulb filament needs to be
insulated from oxygen in the atmosphere in order for the filament to glow and not burn as it reacts with
oxygen in the air. Normally this is accomplished by removing the atmospheric gases inside the bulb, via a
vacuum pump, then pumping an inert gas into the bulb and sealing it.
The tungsten filament will glow for about 2-4 seconds if it is turned on while it is exposed to oxygen in the
atmosphere. However, if the filament is submerged in -196°C boiling nitrogen, the filament is insulated from
the atmospheric oxygen and will light up and glow for as long as the filament is insulated from the nitrogen.
One interesting aspect of this demonstration is that even though the tungsten is in the -196°C, the resistance in
the filament is high enough that the tungsten can still reach a temperature high enough for the tungsten to
reach a “glowing” temperature. There is actually a small layer of nitrogen gas surrounding the filament inside
the liquid nitrogen, which is known as the Leidenfrost effect. The filament that is submerged in the nitrogen
can be reused many times.
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with a school purchase order or credit card at www.flinnsci.com.
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