104 EXPERIMENTAL GENERAL SCIENCE 



time. The mist or the insensible perspiration will soon be 

 deposited on the object. The danger of remaining in wet 

 clothing is due to the fact that the evaporation of the moisture 

 takes a great amount of heat out of the body and so chills it. 

 If one happens to be exercising vigorously and thus producing 

 considerable amounts of heat, he is not likely to become chilled 

 in wet clothing. If one happens to get wet, therefore, the best 

 way to avoid a cold is to keep moving. In the absence of ice, 

 housewives often contrive to keep milk from souring by cooling 

 it through evaporation. The vessel containing the milk is 

 wrapped in a cloth which is allowed to dip into a dish of water. 

 The moisture rises in the cloth and evaporates, taking the heat 

 out of the milk for the purpose. A great deal of the water 

 taken up by plants is evaporated from the leaves and other 

 parts, thus keeping them cool, as our perspiration keeps us 

 cool. 



Practical Exercises 



1. Put a drop of water, a drop of alcohol, and a drop of ether on the 

 back of your hand and note which evaporates first. Which feels coldest? 

 Why? 



2. Where does a fog go when it disappears? 



3. When fog disappears does it warm or cool the air (68)? 



4. Of what advantage is it to give people alcohol baths when they 

 have a fever? 



5. How does hanging wet cloths in a room cool it? 



6. Why are wet soils likely to be cold for a long time in spring? 



7. Why is it cooler on land in a wet bathing suit than in the water? 



