APRIL,1934
251
COOLING EFFECT of EVAPORATION. A LECTURE DEMONSTRATION ALTON L. MARKLEY Skidmore College, Saratop Springs, New York
HE FOLLOWING experiment for producing a lowering of temperature by the evaporation of ether has been found convenient because of the simple method of disposing of the ether vapor. An ordinary gas-collecting bottle (260 cc., widemouthed) is filled almost half full of ether and fitted with a stopper bored to bold a test-tube, an inlet tube, and an outlet tube. The test-tube extends into the ether as far as possible, the inlet tube extends almost to the bottom of the bottle, and the outlet tube extends just through the bottom of the stopper. The inlet tube is connected to the gas jet, and the ether caused to evaporate by bubbling gas through it. The outlet tube is connected to a Bunsen burner where the mixture of gas and ether vapor is burned. A thermometer, and 5 to 10 CC. of water are Put into the test-tube. If the part of the test-tube filled with
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water is completely immersed in ether the water will freeze solid in about 30 minutes. If the test-tube is removed and held in a stream of water for a few seconds the ice will be loosened and may then be withdrawn as a chunk on the end of the thermometer. A record of the drop in temperature may be put on the board, readings being taken every few minutes. The temperature usually drops several degrees below the freezing point before ice forms, and consequently the phenomena of undercooling and the liberation of heat during crystallization can also be demonstrated. The effect of different solutes on the freezing point may also be shown by this experiment, as suggested by Hauben.' I HAUBEN, S n a s., "A demonstration of cooling by evaporation," J. CHEM.EDUC., 9, 1115 ( ~ u n e 1932). ,
