Liquid nitrogen

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					                                     Liquid nitrogen *




                A funny experiment

                Blow up a balloon. Put the inflated balloon in
                the liquid nitrogen (77 K or - 196°C). It will
                deflate, then take it out and it will inflate as it
                warms up (Charles' law).

                We can see the presence of a liquid in the balloon (liquid oxygen and
                argon). The volume difference between a liquid and a gas is big.
                Liquid nitrogen (at the boiling point, 77 K and 1 atm) is 640 times
                smaller than the gas (273 K, 1 atm).

                What is nitrogen ?

                Nitrogen gas (N2) makes up 78.1% of the Earth’s air, by volume.
                Nitrogen was discovered in 1772. The scientists (Priestley, ...) called it
                “burnt or dephlogisticated air,” which meant air without oxygen. The
                French chemist Antoine Laurent Lavoisier named nitrogen azote,
                meaning without life.

                Other experiments

                   •   Biology: Preservation of biological material (cells, destruction of
                   warts (we just freeze a leaf !), etc.
                   •   Recycling: We submerge a flexible tubing in liquid nitrogen,
                   remove from the dewar and whack the frozen end on a table and
                   watch it break into pieces.
                   •   Singers and magicians: We get a pot of boiling water and pour


*
    July 2003
some nitrogen in it. You will watch the mists of hell shrouding the floor.

   •   Superconductivity

Superconductivity is the ability of certain materials to conduct electricity
without resistance or energy loss, usually at very low temperatures. If we cool
a superconductor in liquid nitrogen, a magnet will levitate (Meissner effect).




The LHC will operate at about 300 degrees below room temperature. The accelerator
will be the largest superconductivity installation in the world (picture: Darren,
HST2003).

				
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