EFFECTS OF EVAPORATION 



from the bulb. The other thermometer is called the dry thermom- 

 eter. Find out how many degrees cooler the wet thermometer 

 is than the dry thermometer. Show how this 

 experiment proves that heat is absorbed when 

 water evaporates. , 



If we wet one hand in warm water and 

 let the other hand remain dry, we shall soon 

 realize the effect of moisture evaporation from 

 the body. Although we may come from a 

 warm bath, we soon feel cold unless the water 

 is removed from the body almost immediately 

 before it has time to evaporate. If the 

 evaporation is slow, not so much heat is ab- 

 sorbed in evaporation at any one time, but if 

 the evaporation is rapid, a great deal of heat is 

 absorbed. 



This may be easily shown by placing a 

 small amount of ether in a watch glass and 

 placing the watch glass on a drop of water 

 on a cork. A thin film of water will form 

 on the under side of the glass. Blow through FIG. 3. Why does the 

 a piece of glass tubing directly on the wet thermometer read 



, , less than the dry? 



ether. 



Why will blowing on the ether make it evaporate more quickly? 

 Why does the thin film of water turn into ice and freeze the 



watch glass to the cork? 



Why would not the thin film 

 of water turn to ice if the ether 

 were allowed to evaporate slowly? 

 Manufacture of Ice. This 

 principle of evaporation is used 

 commercially for the manufac- 

 ture of ice. Liquid ammonia, 

 when evaporating, consumes large quantities of heat. This does not 

 mean aqua ammonia, such as we buy at the drug store, which is 

 common water with a large amount of ammonia gas absorbed. 

 If this gas is put under great pressure, it will change to a liquid. 



WATCH GLASS 

 CONTAINING ETHtR 



FIG. 4. 



