46 LABORATORY MANUAL 



all the liquid has evaporated, being careful not to 

 burn the substance left in the dish. Taste the residue. 

 What is it? Has its form changed? Its nature? 

 Changes which do not involve a change in the composi- 

 tion of substances are called physical changes. 



Exercise 23. Chemical Change. 

 Object: To determine the nature of a chemical 

 change. 



Apparatus 



Sugar Wire gauxe 



Sulphuric acid Test tube 



Evaporating dish Potassium iodide crystals 



Bunsen burner Mercuric chloride crystals 



Glass stirring rod (poison) 



Ring stand Mortar and pestle 



Directions : A. Cover some sugar in the evaporating 

 dish with sulphuric acid. Stir the substance with the 

 glass rod. What happens? Place the solution on the 

 wire gauze and slowly heat it. What happens? Does 

 the resulting substance resemble either the acid or the 

 sugar with which you started? 



Changes which involve a change in the composition 

 of substances and result in' the formation of new sub- 

 stances are called chemical changes. 



Classify the following under the head of chemical 

 or physical change respectively : A change from ice to 

 water; water to ice; water to gas; gas to water; action 

 of hydrochloric acid on marble as used in Exercise 6; 

 burning of wood; cider to vinegar. 



B. The following experiments are to be performed 



