PURPOSE: To demonstrate the magnitude of atmospheric pressure in a dramatic way.
DESCRIPTION: A cleaned and rinsed 55 gallon drum is placed behind a safety screen at a safe distance of at least 15 feet from the audience. The empty drum is placed atop cinder blocks above three bunsen burners and one gallon of water is poured in. Underneath the drum are placed three gas bunsen burners. Lite the burners and boil the water for 20 or 30 minutes to allow hot steam to displace all the air in the drum. Turn off the flames and quickly cap the drum tightly. Place some ice or dry ice onto the top of the drum to speed up the cooling. After approximetly 20 seconds the steam inside will have condensed sufficiently for atmospheric pressur to collapse the drum violently.
Note that the collapse is very loud. Occasionally the drum will jump in the air, toss the ice across the room and fall over onto the floor. It is well advised to cautiously stand at a safe distance of five feet away. Also, be carefull not to step onto the gas hose and pinch out the flames while the burners are on. This could cause natural gas to fumigate the room. Lastly, be sure to shut off the flames first before sealing the cap on the drum or it will explode from the pressure build up.
EQUIPMENT: 55 gallon drum from the chemistry or the bio-med stockroom. Three burners, hose and gas petcock are stored in the general use drawer in the demo lecture bench. Place them onto a 1/2 size cinder block stored in the Modern Physics cabinet. Three cinder blocks from under the stairway outside room 168. Dry ice from chemistry. Striker from the tool pegboard. Pliers from the tool chest. 1 Gallon water jug from under the sink.
SETUP NOTES: This demo will fail if there is a leak in the cap seal. Be sure that the cap has a gasket.