-,
tested demonstrations Hot and Cold Running Methane Submitted by Daniel M. ~ t a m m ' Frederick Douglass High School Atlanta, GA
GEORGE L. GILBERT Denison University Granville,OH 43023
are seen to go in opposite directions. (Beware of the flying stopper!) 7. "Hat and Cold Running Methane" stands out in its flamhovanee and reauires auite a bit of emlanation. It consists of lquefylng natural gas, lightingit and pouring it un the n o o r The liquid hrraks up inro numrrow small flaming blobs thnt glide nmrlg frirtionlrssly nrruss the nwr In I darkened room this lwks fantastic
Checked by
David A. Franz Lycoming College Wiiliamsport, PA 17701 Liquefied gases are fascinating materials, probably because we normallv encounter onlv a verv limited ranee of temperatures. he extremely l o 6 tempkrature of bokng liquid nitrogen (-196 C)allows some interesting demonstrations of phase change, (almost) frictionless motion, and conversion of heat into work. Freauentlv. demonstrations using N2(1) involve little more than sho:ng how cold it is bv freezing flowers or fruit. or more recentlv, bv causing a magnet tohover above a ~;~erwnductor. The demonscations below are more informative. The excitement generated by some of them is satisfying in itself, but more importantly, the weird phenomena set the stage for fairly simple explanations illustrating important physical principles. The simpler ones are listed immediately below, followed by the procedure for "Hot and Cold Running Methane". 1. As an intmdudian, explain the construction of the Dewar
2.
flask in terms of minimizing the three modes of heat transfer, and explain that the fog observed is condensed water vapor fram the air, cooled by the Nz(l) as it is poured. Place the corner of a sealed air-fdled plastic bag into Nz(l) in an expanded polystyrene cup. At first the air shrinksin volume according to Charles's Law, hut it then condenses completely, because the boiling (and eondensation) point of the~ 0-N., ~ mixture. ' ~.as
