VOL.9, NO. 6
COOLING BY EVAPORATION
1115
A DEMONSTRATION OF COOLING BY EVAPORATION SAULS. HAUBEN, BROOKL.YN TECHNICAL HIGHSCHOOL, BROOKLYN, NEWYORK
One of the common methods in use for the removal of ether from extractions is by evaporation through the use of the electric fan. If this is done on a hot, humid day, one notices that ice forms on the outer surface of the dish in which the evaporation is being carried out. This method may well be used to demonstrate the principle of the modern refrigerator which uses the gases ammonia, sulfur dioxide, or carbon dioxide. In experimenting, the following apparatus was used: (1) Petri dishes, 7 em. diameter, (2) watch glasses, 10.7 cm. diammter, (3) electric fan, 10 in. diameter, 60 cycles, 110 volts, 0.35 ampere. Tap water, temperature 15'C., was poured into a Petri dish until about two-thirds full. The watch glass was placed over the dish with the convex surface touching the water. Enough ether to fill the concavity of the watch glass was then added. The fan, 6 in. away, was then turned on at high speed. The ether was replaced as soon as evaporated. In all, about 125 cc. of ether was used. Within fifteen minutes, a concave-convex layer of ice 0.95 cm. in thickness had formed on the convex surface of the watch glass. The work was carried on a t an open window. This experiment was repeated several times with similar results. A comparative demonstration may be shown a t the same time by evaporating ether over Petri dishes containing varying amounts of alcohol or glycerin added to the water. Smaller amounts of ice or none a t all are formed, depending upon the amounts of these liquids added to the water. This experiment is of value in explaining the use of anti-freezes for automobiles in the winter. The addition of soluble solids or liquids to water or other solvents, in definite amounts, causing a lowering of the freezing point of the solvent, may also be demonstrated by this method.
=
