236 NATURE STUDY AND AGRICULTURE 



of a boiling teakettle. Can you see anything close to the 

 spout? What is there, although you cannot see it? Why 

 can you see steam at a short distance from the spout? 

 Here, of course, the invisible vapor is changing back into a 

 liquid state. 



Now examine the cup that you set in. a warm place. 

 Can you see any steam coming from it? Measure the 

 water carefully. Has any of it disappeared? What has 

 become of it? We say it has evaporated, which means 

 that the water has changed into an invisible gas or vapor. 

 The same thing happened as when you boiled the water, 

 with one difference; the evaporation went on more slowly. 

 When evaporation takes place rapidly we sometimes use 

 the term vaporize instead of evaporate. 



What are some of the conditions that influence the 

 evaporation of liquids? 



Experiment. — Measure exactly in the measuring cup a 

 half cup of water and put it into a tumbler. Put the same 

 amount into a shallow pan or plate, and the same into a 

 pickle bottle. Set the three side by side and let them stand 

 until the next day. Now measure carefully. From 

 which has the most water evaporated ? The least ? What 

 caused the difference? From this we learn that extent of 

 surface has a certain effect on the rapidity of evaporation. 

 What is it? 



Place equal amounts of water in two tumblers or cups 

 of exactly the same size and shape. Put one in a warm 

 place, the other in a cool place, and leave for twenty-four 

 hours. Measure and note difference. What is your con- 

 clusion as to the effect of temperature upon evaporation ? 



Place equal amounts of water in cups as suggested in 



