2l6 METHODS IN TEACHING 



beauty, its rarity, and its durability, is one of the most 

 valued of gems. 



Children in general have little knowledge of the common 

 metals. Specimens of these arc easily secured, and should 



form a part of every school equipment. 

 Metals Where practicable, there should also be a 



collection of the common metallic ores. Of 

 the various useful metals perhaps iron is best known; for 

 this reason it should be studied first. Draw from the class 

 what is already known concerning the sources of the iron 

 supply in this country; distinguish between the terms 

 wrought iron, cast iron; steel and cast steel. Discuss with 

 the class such properties of iron as its strength, hardness 

 in various forms, elasticity in tempered steel, weight, color, 

 and ductility. Discuss its uses, adapting the discussion to 

 the age and experience of the pupils. Direct attention to 

 some of the many ways in which it is used in the school- 

 room or building; in the home; in the city. What Andi- 

 tions hasten its decomposition? (Oxidation or nf^ng.) 

 Why do we paint iron? By what other means 'do we ex- 

 clude the air from iron and steel? The use of oil, zinc, 

 tin, or silver for these purposes. The use of iron as a con- 

 ductor of heat. Compare with wood in this respect; with 

 copper; lead; aluminum. For this purpose place rods of 

 several different metals in such a position that one end of 

 each is in contact with an alcohol or gas flame. At the 

 same distance from the heating ends of the rods, stick 

 pieces of paraffin or tallow. Note on which one of the rods 

 the tallow melts soonest, and the order in which it melts on 

 all of them. Which metal is the best conductor of heat? 

 Which is the poorest? 



