CONDUCTING POWER OF METALS. ~ 75 



In considering heat we must put aside the idea of warmth and cold, for 

 they are only different degrees of heat, not the absence of it. 



The study of heat can be briefly undertaken without any complicated 

 apparatus. If we desire a proof of the great conducting power of metals, 

 let us place a fine piece of muslin tightly stretched over a lump of polished 

 metal. On the muslin we put a burning ember, and excite combustion by 

 blowing on it ; the muslin is not burned in the least, the heat being entirely 

 absorbed by the metal, which draws it through the material into itself. 

 Fig. 76 represents a similar experiment : it consists of melting some tin on 

 a playing card, held over the flame of a spirit lamp. The metal becomes 

 completely melted without the card being burnt. It is through a similar 



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Fig. 77, Boiling water in a paper case. 



effect that metals appear cold to us when we take them in our hands ; by 

 their conductibility they remove the heat from our hands, and give us the 

 peculiar impression which we do not experience when in contact with sub- 

 stances that are bad conductors, such as wood, woollen materials, etc. 



Fig. 77 shows the method of boiling water in paper. We make a 

 small paper box, such as those made by school-boys, and suspend it by four 

 threads to a piece of wood held horizontally at a suitable height. We fill 

 this improvised vessel with water, and place it over the flame of a spirit 

 lamp. The paper is not burnt, because the water absorbs all the heat into 

 itself. After a few minutes the water begins to boil, sending forth clouds 



