Liquid helium

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Liquid helium in a cup

The liquid form of the gas helium, liquid helium, is inert, colorless, odorless, non-corrosive, extremely cold and nonflammable. Vessels and pipes that meet DOT and ASME standards are required for transporting liquid helium because of its extremely cold temperature. ^[1]

Liquid helium, like water, boils at a lower temperature when the pressure is lower. In fact, when liquid helium is kept in containers that are at atmospheric pressure, the helium temperature changes as atmospheric high and low pressure areas pass. These temperature changes are small, but measurable. With vacuum pumps, we can reduce the presssure in a helium container much more than happens with normal atmospheric pressure changes.^[2]

References

http://www-safety.deas.harvard.edu/services/helium.html#general http://cryo.gsfc.nasa.gov/introduction/liquid_helium.html