170 NATUBE-STUDY LESSONS. 



XLVIII.-C0NDU0TION. 



1. (a) Place one end of a piece of iron wire, six or 



eight inches long, in the flame of a lamp or 

 of a stove ; hold the other end in the hand. 

 (^) What change takes place in the wire ? 



(c) How do you know ? 



(d) How is the temperature of the wire affected ? 



(e) What caused this change of temperature ? 

 (/) What is the source of the heat ? 



(g) How has the heat got from this source to the 



hand? 



The heat is said to have been transmitted from the flame to the hand 

 along the wire by conduction, and the wire is called a conductor. 



2. (a) Test similarly pieces of copper wire, wood, slate- 



pencil and glass. 

 (J>) Which of these substances is the best conductor? 

 Which the poorest ? 



(c) Which would be the better material for the 



handle of an oven door, iron or glass or 

 wood? Give reasons for your answer. 



(d) Why is wood sometimes used to make part of 



tea-pot handles ? 



3. Examine the handles of such articles as tea-kettles, 

 lid-lifters, coffee-pots, to discover how the conduction of 

 heat to the hand is prevented. 



4. (a) Take a test-tube nearly filled with water. Hold 



it in an inclined position with the upper sur- 

 face directly over the flame of a lamp. 



(fi) After a short time, what takes place ? 



{c) When the water is boiling, what must be the 

 temperature of the water at the mouth of the 

 tube? 



