182Chapter FiveGasesFigure5.l.The pressureexertedby the gasesinthe atmospherecan be demonstratedbyboilingwaterin a large metalcan (a) andthen turningoff the heat and sealingthecan. As the can cools,the watervaporcondenses,loweringthe gas pressureinsidethe can. This causesthe can tocrumple(b).1h=760mmHgfor standardatmosphereFigure5.2A torricellianbarometer.The tube,com-pletelyfilledwithmercury,is invertedina dish of mercury.Mercuryflowsout ofthe tubeuntil the pressureof the columnof mercury(shownby the blackarrow)"standingon the surface"of the mercuryin the dish is equal to the pressureof theair (shownby the purplearrows)on therest of the surfaceof the mercuryinthe dish.Soon after Torricelli died, a Germanphysicist named Otto von Guericke in-vented an air pump. In a famous demon-stration for the King of Prussia in 1663,Guericke placed two hemispheres to-gether, pumped the air out of the result-ing sphere through a valve, and showed
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