_APPLICATION 24._ A woman brought me a glass-stoppered bottle of smelling salts and asked me if I could open it. The stopper was in so tightly that I could not pull it out. I might have done any of the following things: Tried to pull the stopper out with a pair of pliers; plunged the bottle up to the neck in hot water; plunged it in ice-cold water; tried to loosen the stopper by tapping it all around. Which would have been the best way or ways? [Illustration: FIG. 45. But notice how it sags when it is hot.] _APPLICATION 25._ I used to buy a quart of milk each evening from a farmer just after he had milked. He cooled most of the milk as soon as it was strained, to make it keep better. He asked me if I wanted my quart before or after it was cooled. Either way he would fill his quart measure brim full. Which way would I have received more milk for my money? INFERENCE EXERCISE Explain the following: 121. Billiard balls will rebound from each other and from the edges of the table again and again and finally stop. 122. In washing a tumbler in hot water it is necessary to lay it in sidewise and wet it all over, inside and out, to keep it from cracking; if it is thick in some parts and thin in others, like a cut-glass tumbler, it is not safe to wash it in hot water at all. 123. The swinging of the moon around the earth keeps the moon from falling to the earth. 124. A fire in a grate creates a draft up the chimney. 125. Telegraph wires and wire fences put up in the summer must not be strung too tightly. 126. Candy usually draws in somewhat from the edge of the pan as it hardens. 127. A meat chopper can be screwed to a table more tightly than you can possibly push it on. 128. A floor covered with linoleum is more easily kept clean than a plain wood floor. 129. Rough seams on the inside of clothes chafe your skin. 130. You can take the top off a bottle of soda pop with an opener that will pry it up, but you cannot pull it off with your fingers. SECTION 16. _Cooling from expansion._ We get our heat from the sun; then why is it so cold up on the mountain tops? What is coldness? Here is an interesting and rather strange thing about heat and expansion. Although heat expands things, yet expansion does not heat them. On the contrary, if a thing expands without being heated from an outside source, it actually gets cold! You see, in order to expand, it has to push the air or something else aside, and it actually uses up the energy of its own heat to do this. You will understand this better after you do the next experiment.