16 LABORATORY EXERCISES 



or cotton. What happens when you lay the cork on its side on 

 the table? Try various positions. Account for what happens. 

 Examine the toy called a " tumbler"; why does it always 

 come to an upright position? 



b. Seal tightly an empty Mason fruit 

 jar, and lay it on its side in a pail of 

 water. Does the bottle rest equally well, 

 however you place it, or does it come to 

 rest in some preferred position? Tell 

 why. 



c. Take the cover off from a Mason fruit 

 jar and try to stand the bottle upright 

 on the water. Explain what happens. 



Now put water into the jar until the jar floats right side up. 

 Give the explanation. 



Why do you hold out your hands when walking a rail? Why 

 does a tight-rope performer carry a long pole? Why does a 

 ship carry ballast? 



EXERCISE 12 

 PRESSURE OF THE ATMOSPHERE 



Apparatus and Materials. Glass tube, medicine dropper, water, 

 mercury, glass siphon (either prepared or to be made by the student; 

 if to be made, a glass tube about 30 cm. long may be used). 



a. Put one end of a glass tube into a glass of water, and by 

 suction remove the air from the tube. What happens? Why? 



b. Put the open end of a medicine dropper under water, 

 and pinch the rubber bulb. What happens? Let go of the 

 bulb, and state the result. Why does the bulb expand when 

 released? What effect has this upon the pressure of the air in 

 the bulb? What causes the water to rise? 



c. If there is mercury in the laboratory, put the open end of 



