IX WORK AND ENERGY 127 



to work simply through an ordinary copper wire which presents 

 little resistance. The current has no work to do beyond heat- 

 ing the wire, and the energy of the current is almost wholly 

 expended in heating the liquids and other parts of the battery, 

 which is of course a very undesirable waste of energy. 



EXPT. 121. Show the motion of a magnet produced by an 

 electric current in a wire held over it. 



Instances of the conversion of the energy of the electric 

 current into mechanical work will doubtless have come under 

 the student's attention. 



Other forms of energy can be converted into that of electri- 

 fication and of electricity in motion. If we heat certain 

 crystals, e.g., tourmaline crystals, it is found that they become 

 electrified, one part of the crystal exhibiting electrification of 

 the kind developed when sealing-wax is rubbed with fur, another 

 exhibiting the kind obtained by rubbing glass with silk. 



Heat can give rise to electric currents. If we solder a piece 

 of the metal antimony to a piece of the metal bismuth and 

 apply heat to the junction, it is found that an electric current 

 passes from the bismuth to the antimony. 



Energy of Chemical Action. EXPT. 122. Place a small 

 piece of dry phosphorus 1 on a plate, and a short distance 

 from it a few grains of solid iodine. Nothing happens. By 

 means of a glass rod push the piece of phosphorus on to the 

 iodine, and notice that when they come into contact the phos- 

 phorus inflames and dense fumes are formed which, as will be 

 understood after reading the chemical section of this book, are 

 a compound of phosphorus and iodine. 



EXPT. 123. Call attention to the heat of the flame of the 

 laboratory burner, where certain chemical actions are going on, 

 which are described in a later chapter, (Chapter XV.) 



In speaking of heat as a form of energy we took the example 

 of the work done by an engine as the result of the heat from the 

 furnace ; but we can now push our inquiry a step further back. 

 What causes the heat of the furnace ? Evidently the burning of 

 the coal, which, as we shall learn, is nothing more than chemical 



1 Great care must be used in handling phosphorus, as it is easily ignited. 



