Chemical Change and Energy 335 



dioxid are the main things a plant needs to make its 

 food, the animals really are as helpful to the plants as 

 the plants are to the animals. For the animals furnish 

 the materials to the plants for making their food in ex- 

 change for the ready-made food furnished by the plant. 

 And both plants and animals would die if light stopped 

 helping to bring about chemical change. 



Application 74. Explain why the heart of a cabbage is 

 white instead of green like the outside leaves ; why a photog- 

 rapher works in a dark room with only a ruby light; why 

 you get freckled in the sun. 



Inference Exercise 



Explain the following : 



461. If a pin is put through a lamp cord, a fuse is likely to blow out. 



462. The wall paper back of a picture is often darker than that 



on the rest of the wall. 



463. If you wet an eraser, it rubs through the paper. 



464. Clothes are hot after being ironed. 



465. If you drop candle grease on your clothes, you can remove 



the grease by placing a blotter over it and pressing the 

 blotter with a warm iron. 



466. Milliners cover hats that are on display in windows where 



the sun shines in on the hats. 



467. You pull down on a rope when you try to climb it. 



468. In taking a picture, you expose the sensitive film or plate 



to the light for a short time. 



469. Good cameras have an adjustable front part so that the lens 



may be moved nearer to the plate or film, or farther from 

 it, according to the distance of the object to be photo- 

 graphed. 



470. A pencil has to be resharpened frequently when it is much 



used. 



SECTION 50. Chemical change caused by electricity. 



How are storage batteries charged? 

 How is silver plating done by electricity? 



