24 



What practical application do we make in our homes 

 of the absorption of heat by a melting 'solid, or the heat 

 of fusion ? 



EXPERIMENT 13. THE COOLING EFFECT OF EVAPORATION 



(a) Allow bottles of water, alcohol, and ether to stand in 

 a room until they have acquired the temperature of the 

 room. Pour equal quantities of each of these liquids into 

 three test tubes and allow the liquids to stand about three 

 minutes. Then record the temperature of each liquid, 

 being careful to have the bulb of the thermometer entirely 

 below the surface of the liquids. Can you suggest why 

 the temperature has changed in each case ? 



(b) Pour equal quantities of these liquids into three 

 shallow dishes and after allowing them to stand about two 

 minutes, record the temperatures of each. Are the respec- 

 tive temperatures of the three liquids higher or lower than 

 in()? Why? 



(c) Place a drop of water, alcohol, and ether on the 

 hand, and note which disappears most rapidly. Did the 

 drop which disappeared first seem warmer or colder than 

 the other two ? Note also which drop disappeared most 

 slowly. Did it seem warmer or colder than the others ? 

 From your results explain the difference in the tempera- 

 ture changes in (a) and (b) respectively. 



Why is an alcohol bath valuable in sickness ? 



EXPERIMENT 14. CONDENSATION 



Arrange the apparatus as shown in Figure 18, having 

 carefully weighed the water in B and recorded its temper- 



