292 Common Science 



And when you want to soften it again you rub into 

 it oily substances, like cold cream or vaseline. 



In the same way if harness or shoes get wet and then 

 are dried out, they can be made properly flexible by oil- 

 ing. You could wet them, of course, and this would 

 soften them as long as they stayed wet. But water 

 evaporates rather quickly; so when you want a thing 

 to stay soft, you usually apply some kind of oil or grease. 



Just as diffusion and the forming of solutions are 

 increased by heat, this softening by oil and water works 

 better if the oil or water is warm. That is why you soak 

 your hands in warm water before manicuring your nails. 



Application 67. Explain why women dampen clothes 

 before ironing them; why crackers are put up in water- 

 proof cartons; why an oil shoe polish is better than one 

 containing water. 



Inference Exercise 

 Explain the following : 



421. You can shorten your finger nails by filing them. 



422. You can do it more quickly after washing them than before. 



423. After a flashlight picture is taken, the smoke soon reaches 



all parts of the room. 



424. A jeweler wears a convex lens on his eye when he works with 



small objects. 



425. Shoemakers soak the leather before half -soling shoes. 



426. Lightning often sets fire to houses or trees that it strikes. 



427. The directions on many bottles of medicine and of prepara- 



tions for household use say, " Shake well before using." 



428. If you set a cold tumbler inside of one that has just been 



washed in hot water, the outer one will crack in a few 

 minutes. 



429. A dry cloth hung out at night becomes wet, while a wet cloth 



hung out on a clear day dries. 



430. Putting cold cream or tallow around the roots of your finger 



nails will help to prevent hangnails. 



