40 LABORATORY EXERCISES 



through the hole in the cover. When no more gas comes off, 

 remove the dish from the flame, and let it cool. Then take 

 off the cover, and examine what remains in the dish. What 

 is it? Save it for the present. 



6. Repeat experiment a, using soft coal instead of wood. 



c. Repeat it again, using half a teaspoonful of sugar. 



d. Repeat it again, using a lump of starch. What is the 

 residue called in each case? 



EXERCISE 39 

 HOW ORES ARE REDUCED TO METALS 



Apparatus and Materials. Small iron dish of Exercise 38, piece of 

 wire, powdered charcoal, lead oxide, burner or stove, limewater. 



a. Powder some of your charcoal, or get some powdered 

 charcoal from the bottle, and mix half a teaspoonful of it very 

 thoroughly with the same volume of powdered lead oxide (it 

 is called litharge). Put the mixture in a heap in your iron dish 

 (Fig. 19), push in the cover, and heat the dish very hot for about 

 10 minutes. While the heating is going on, hold over the hole 

 in the cover a drop of limewater. You can hold the limewater 

 in a loop made at the end of a piece of wire. 



What happens to the limewater? What gas must be formed 

 from lead oxide and charcoal? From what substance does the 

 carbon of the charcoal get the oxygen? 



Let the dish remain covered until it is cool; then examine 

 its contents. What change has occurred? Do you get any 

 evidence of a metal? If necessary, wash away any unused 

 charcoal in a stream of water. What is the metal? Try to 

 cut it with a knife. 



