26 



LABORATORY MANUAL 



Exercise 7. Diffusion of Gases. { Demonstration.) 

 Object: Will gases diffuse through a porous wall? 



Apparatus 



Porous cup with glass tube Cup of colored liquid 



inserted Belljar 



Ring stand Air pump 



Directions : From the ring stand suspend the porous 

 cup apparatus with the free end of the glass tube 



projecting into the cup of 

 colored liquid. Place the 

 belljar over the porous 

 cup. Is there any change 

 at the end of the glass tube 

 in the colored liquid ? With 

 an air pump force air into 

 the belljar over the porous 

 cup. Is there any change 

 now at the end of the glass 

 tube in the colored liquid? 

 Thus the air currents have 

 no effect. Fill the belljar 

 with illuminating gas, then 

 quickly lower it over the 

 porous cup. What change 

 of the glass tube in the 

 What change 



Fig. 



takes place at 

 colored liquid? 



the end 

 Remove the belljar. 



do you now observe? In the first instance what were 

 the bubbles escaping ? Where did they come from ? 

 What must have been the condition in the porous cup 



