6 9 



when the water boils briskly, hold the pin wheel in 

 the steam. Does the pin wheel rotate ? 



(b} Heat the same quantity of water in a narrow neck 

 flask and when the water boils briskly, hold the pin wheel 

 in the steam. Does the pin wheel rotate (Fig. 58)? 



Can you mention any practical machine in which steam 

 is used to produce motion ? 



CHEMISTRY 

 EXPERIMENT 59. THE CHARACTERISTICS OF ACIDS 



(a) To a few drops of sulphuric acid add a tablespoon- 

 ful of water. Dip a clean stirring rod into the solution, 

 touch the wet end of the stirring rod lightly to the tongue, 

 and determine the taste of the acid. 



(b) By means of the rod, put a drop of the acid on a 

 small piece of blue litmus paper. What is the result ? 



(c) Repeat (a) and (b) for nitric acid, vinegar, butter- 

 milk. Lay a piece of fat on the blue litmus paper and see 

 whether the color of the paper is affected. Dissolve some 

 cream of tartar in warm water and test for acid properties. 



What are the characteristics of acids, and how could you 

 detect the presence of an acid in an unknown substance ? 



EXPERIMENT 60. THE CHARACTERISTICS OF BASES 



(a) Dissolve a small bit of caustic soda (sodium hydrox- 

 ide) or caustic potash (potassium hydroxide) in a few spoon- 

 fuls of water and rub a drop of the solution between the 

 fingers. How does the solution feel ? 



