66 LABORATORY MANUAL 



which the above are the chief ones. If this experiment- 

 is performed at home, a small candle may be lighted 

 under the belljar instead of phosphorus. 



B. In a test tube place about a half teaspoonful of 

 iron filings. Cover them with water. Then invert the 

 test tube and allow the water to run out slowly so that 

 the filings will adhere to the sides of the tube. Place 

 the mouth of the tube in a beaker filled with water and 

 allow the apparatus to stand for twenty-four hours. 

 At the end of that time measure the height to which 

 the water has risen in the tube. What part of the air 

 by volume did the oxygen occupy? What change has' 

 taken place in the iron filings? How do the results in 

 this experiment compare with those in the one above? 



CHAPTER XI 



ATMOSPHERE 



Exercise 39. Does Air Exert Pressure? (Demon- 

 stration.) 



Object: To demonstrate air pressure. 



Apparatus 



Oil can with screw top Bunsen burner 



Magdeburg hemispheres \Yater 



Air pump 



Directions : A. Screw the Magdeburg hemispheres 



on to the plate of the air pump and open the stop-cock. 



'Exhaust the air from the hemispheres and close the 



