64 



THE SUN'S GIFT OF HEAT 



matter. Man can neither create it nor destroy it. He 

 may only transform it. This great truth has been deter- 

 mined by a vast amount of most careful investigation, and 

 is called the law of conservation of energy. 



Some Effects of Heat. The following experiments illus- 

 trate a common effect of heat. 



Heat. Experiment 18. Fit a glass flask with a one-hole rubber 

 stopper through which passes a glass tube about 20 cm. long. 

 Place this on a ringstand so that the end of the 

 tube extends down into a bottle nearly filled with 

 water. (Figure 24.) Gently heat the flask. The 

 air expands and bubbles rise in the water. When 

 / the flask cools, the air contracts and water rises in 



the tube. 



Experiment 19. Fill the flask used in the last 

 experiment with colored water. See that the end 

 of the glass tube passing through the rubber 

 stopper is just even with the bottom of the stopper. 

 Smear the lower part of the stopper with vaseline 

 and insert it in the flask, being careful that the 

 flask and a few centimeters of the tube are filled 

 with the colored water and that there are no air 

 bubbles in the flask. Mark, by slipping over a 

 rubber band, the end of the water 

 column in the tube. (Figure 25.) 

 Heat the flask. The water expands. 

 Experiment 20. Pass the ball 

 of a ball-and-ring apparatus through 

 the ring. (Figure 26.) Notice how 

 closely it fits. Heat the ball in a 

 Bunsen flame for several minutes. 

 See if the ball will now go through the ring. 

 FIGUBE 26 Explain why it does not. 



We saw in these experiments that heat caused the gas, 

 the liquid, and the solid to expand. Cooling had the reverse 



FIGURE 24 



FIGURE 25 



