70 LABORATORY MANUAL 



Directions: A. Convection of Gases. 



Place the wire gauze on the ring stand and adjust a 

 low flame under the gauze. Over the wire gauze 

 drop very small bits of cotton or the fruits of dande- 

 lion or milk-weed. Make a drawing indicating with 

 arrows the path taken by the moving particles. How 

 do you explain this action? 



B. Convection of Liquids. 



Place a small amount of fine sawdust in the bottom 

 of the test tube. Fill the test tube three-quarters full 

 of water. Adjust the Bunsen burner for a low flame. 

 Hold the test tube at a small angle over the flame and 

 heat it gently at one point at the base. Note very 

 carefully the movements of the sawdust particles as 

 the water becomes heated. Make a drawing, indicat- 

 ing with arrows the direction taken by the particles 

 in the water. How do you explain these movements? 

 How does this result compare with that obtained with 

 gas? 



Convection is the process by means of which heat 

 is carried from a hotter to a colder substance by a 

 moving fluid. 



Crystals of potassium permanganate may be used 

 effectively in place of sawdust to show convection cur- 

 rents in liquids. 



Exercise 43. Moisture in the Atmosphere Con- 

 densation. 



Object: To show the presence of water- vapor in the 

 atmosphere. 



