COOLING BY EVAPORATION 



105 



When the ether was dropped on the air thermometer 

 bulb it evaporated and the water column rose just as it did 



FOG 

 A low cloud formed near the surface of the earth. 



in Experiment 27. Ether is one of a number of liquids, 

 such as gasoline and alcohol, that evaporate more rapidly 

 than water. The more rapidly a liquid evaporates, the 

 more rapidly it takes up heat from its 

 surroundings. That is why ether feels 

 colder to the hand than water. In many 

 places, at the present time, advantage is 

 taken of rapid evaporation in the con- 

 struction of ice and cold-storage plants. 



The canvas desert water-bag (Figure 

 52) illustrates a simple application of the 

 principle of cooling by evaporation. The 

 water seeps very slowly through the bag, FIGURE 51 

 and the evaporation of this seeping water 

 absorbs the heat from the water in the bag and keeps 

 it cool enough to refresh the thirsty traveler. Nature 



