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Many people think air is mostly oxygen, because that's the part we care about. In fact, air is about 78% nitrogen, an inert gas whose main contribution is to slow down the rate of burning to something reasonable. Oxygen is an extremely reactive substance, and if our atmosphere were mostly oxygen, the forests and cities of the world would long since have burned to the ground.
Nitrogen gas is almost completely inert, but once nitrogen is taken out of the air and built into chemical compounds in the soil, it becomes a critical nutrient for plant growth. So critical that in many kinds of soils, the limiting factor determining how much plant material you can grow is the amount of nitrogen in the soil. The development of the Haber process for taking nitrogen from the air and turning it into fertilizer was a revolution in humanity's ability to feed itself.
In farm fields around the world you can often see tanks of "anhydrous", by which the farmer means anhydrous, or pure, ammonia, NH3. Ammonia is a nasty, smelly, and dangerous chemical, but if you squirt it down a few inches under the ground when there is a reasonable amount of moisture in the soil, it is instantly dissolved into the earth and becomes nourishment for the crops in the field. By this means vast amounts of nitrogen can be added cheaply and quickly. Unfortunately much of it runs off into streams and ultimately into the ocean, where it causes huge toxic algal blooms, because in sea water as in soil, nitrogen is often the limiting factor in plant or algae growth.
Liquid nitrogen is the cheapest and most readily available liquefied gas, and as such is perfect for things like freezing a flower or leaf, then shattering it into a thousand pieces with a hammer. I have to admit I've never done this myself, but I've seen it done, and any first-semester chemistry teacher worth his salt will do it for the class eventually. It's just too much fun to skip, even though the educational value is probably somewhat questionable.
If you hold some liquid nitrogen in a non-insulating cup (say an aluminum measuring cup), you will see beads of liquid forming and dripping off the outside of the cup. This is not water condensing out of the air: The nitrogen is so cold that water could not possibly stay liquid, and any that condensed would be in the form of frost. No, the liquid dripping off is liquid oxygen! This happens because the boiling point of liquid nitrogen is a bit lower than the boiling point of oxygen, so at the temperature of boiling nitrogen, oxygen is still firmly liquid and will condense right out of the air.
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 Natural sample, 78% Pure.
I collected this sample of naturally occurring air (78% pure nitrogen) from about 20 feet away from the table in May, 2002. The sound for this sample is a beautiful 78% nitrogen, 21% oxygen wind sound borrowed from ftp://ftp.zib.de/ pub/ UserHome/ Luegger/ Urania/Sound/ FX-03.WAV .
I've got a story and video of making ice cream by pouring liquid nitrogen directly into a mixture of cream and chocolate syrup.
Source: Air
Contributor: Theodore Gray
Acquired: 18 May, 2002
Price: $0/Free like the air we breathe
Size: 2.5"
Purity: 78%
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Small "military" cylinder.
These cylinders look like the little CO2 cylinders used in BB guns. A reader, Christoph Loew, reports:
"The cylinders of nitrogen gas are, as far as I know, used for cooling the thermal imaging system of certain man-portable anti-tank missiles, I did some maintenance work on thermal imagers during my time with the german army and was told that the MILAN system used these."
So now I know.
Source: eBay seller janerili
Contributor: Theodore Gray
Acquired: 5 September, 2002
Price: $5
Size: 2.5"
Purity: >95%
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Winekeeper tank.
This is a tank used in a system that lets you preserve wine by purging the bottle with nitrogen. Somehow I'm not surprised it's ended up on eBay: Isn't it a lot easier to just drink the bottle?
What's really amazing about this sample is its incredible perfect purity. As you can clearly see from the label, the manufacturer has achieved absolute 100% purity, a goal that has eluded every other supplier of every known substance. The hyperpure silicon used in chip making is nothing compared to this stuff!
Source: eBay seller djkemme
Contributor: Theodore Gray
Acquired: 6 September, 2002
Price: $10
Size: 9"
Purity: 100%
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Sample from the Everest Element Set.
Up until the early 1990's a company in Russia sold a periodic table collection with element samples. At some point their American distributor sold off the remaining stock to a man who is now selling them on eBay. The samples (excepted gasses) weight about 0.25 grams each, and the whole set comes in a very nice wooden box with a printed periodic table in the lid.
To learn more about the set you can visit my page about element collecting for a general description and information about how to buy one, or you can see photographs of all the samples from the set displayed on my website in a periodic table layout or with bigger pictures in numerical order.
Source: Rob Accurso
Contributor: Rob Accurso
Acquired: 7 February, 2003
Price: Donated
Size: 0.2"
Purity: >99%
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