268 Common Science 



Application 64. Explain why you beat fudge as it cools; 

 why the paper around butter becomes encrusted with salt 

 if it is exposed to the air for some time. 



Inference Exercise 

 Explain the following : 



391. Dynamos have copper brushes to lead the current from the 



coils of wire to the line wires. 



392. A megaphone makes the voice carry farther than usual. 



393. Copper wire is used to conduct electricity, although iron 



wire costs much less. 



394. A flute gives notes that differ in pitch according to the stops 



that are opened. 



395. There are usually solid pieces of sugar around the mouth of a 



syrup jar. 



396. You can beat eggs quickly with a Dover egg beater. 



397. When ocean water stands in shallow open tanks for some 



time, salt begins to form before the water has all evapo- 

 rated. 



398. In a coffee percolator the boiling water goes up through a 



tube. As this water drips back through the ground coffee 

 beans, it becomes brown and flavored, and the coffee is 

 made. 



399. Kerosene will clean off the run of soap and grease that forms 



in bathtubs. 



400. Beating cake frosting or candy causes it to sugar. 



SECTION 43. Diffusion. 



How does food get into the blood ? 



Why can you so quickly smell gas that is escaping at the 

 opposite side of a room? 



On our imaginary switchboard the DIFFUSION switch 

 would not be safe to tamper with. It would be near 

 the SOLUTION switch, and almost as dangerous. For 

 if you were to make diffusion cease in the world, the 

 dissolved food and oxygen in your blood would do no 

 good ; it could not get out of the blood vessels or into 



