326 Common Science 



455. Striking a match makes it burn. 



456. When you have something hard to cut, you put it in the part 



of the scissors nearest the handles. 



457. A magnet held over iron filings makes them leap up. 



458. Dishes in which flour thickening or dough has been mixed 



should be washed out with cold water. 



459. A woolen sweater is liable to stretch out of shape after being 



washed. 



460. When a telegraph operator presses a key in his set, a piece 



of iron is pulled down in the set of another operator. 



SECTION 49. Chemical change caused by light. 



How can a camera take a picture? 

 Why does cloth fade in the sun? 

 What makes freckles ? 



If light could not help chemical change, nothing would 

 ever fade when hung in the sun ; wall paper and cur- 

 tains would be as bright colored after 20 years as on the 

 day they were put up, if they were kept clean; you 

 would never become freckled, tanned, or sunburned ; 

 all photographers and moving-picture operators would 

 have to go out of business ; but worst of all, every green 

 plant would immediately stop growing and would soon 

 die. Therefore, all cows and horses and other plant- 

 eating animals would die ; and then the flesh-eating 

 animals would have nothing to eat and they would die ; 

 and then all people would die. 



You will be able better to understand why all this 

 would happen after you do the following experiments, 

 the first of which will show that light helps the chemical 

 change called bleaching or fading. 



Experiment 99. Rinse two small pieces of light-colored 

 cloth. (Lavender is a good color for this experiment.) Lay 

 one piece in the bright sun to dry ; dry the other in a dark 



