46 



HEAT 



c. Fill the bottle with cold water and in- 

 sert the stopper. The water should run up 

 the tube not more than two inches. Mark the 

 surface of the water with a piece of string tied 

 tightly around the tube. Heat the bottle 

 gently and tell what happens. Explain. Let 

 the water cool and explain what happens. 



Some materials expand more than others 

 when they are heated. Thus tin expands 

 twice as much as does steel, while lead and zinc 

 expand still more. Steel expands the least 

 and zinc the most. This difference of expan- 

 sion leads to results which appear strange until 

 we think about what is occurring. A common example is 

 the loosening of preserve jar covers when the jars are 

 turned upside down and the covers placed in hot water. 

 The metal cover expands more than the glass does and 

 becomes loose. 



Experiment 25. The Result of Unequal Expansion. 

 Apparatus: Apparatus as shown in cut, consisting 



of a bar of brass and a bar of iron fastened together, 

 alcohol or gas lamp, bottle to hold apparatus. 



Materials: Ice, salt. 



a. Notice that the bars are straight. Heat very 

 hot by holding the bars in the flame. Which way do 

 thev bend, with the brass or the iron outside? Which 



