EXERCISE 47 

 WHAT EFFECT HAS EVAPORATION UPON TEMPERATURE? 



Materials. A thermometer ; cotton ; alcohol ; a small cup or drinking glass. 



Directions. Record the temperature of the room. Twist a small piece of cotton about the bulb 

 of a thermometer. This may be fastened on with a rubber band. Place the bulb in water which 

 has stood until it is at about the room temperature. Record the exact temperature of the liquid. 



Remove the bulb from the water. Watch the thermometer carefully, noticing and recording any 

 temperature changes until no further changes occur. How do you account for the temperature 

 changes which you have noted ? 



Wet the bulb of the thermometer again and fan it. How does its temperature change ? Why ? 

 How does the temperature change when the bulb of the thermometer becomes dry ? Repeat the 

 experiment with the same thermometer and the same cotton covering, using alcohol instead of 

 water. Explain the difference in results. 



In your conclusions state what you have learned regarding the effect of evaporation and the 

 rate of evaporation. 



Additional problems. Put a drop or two of ether on the back of your hand and explain the sensation 

 produced. 



What are the principles underlying the use of ammonia in ice making ? 



Why do people fan themselves during hot weather ? 



When bathing in water which is cooler than the atmosphere, one may feel comfortably warm in the 

 water but unpleasantly cool when out of the water. How may this fact be explained ? 



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