40 THE MECHANISM OF LIFE 



The current generated can now be used in various ways; for 

 instance, it can be sent tkrough lamps, when the latter glow; or 

 it can be made to decompose clay, producing aluminium; or it 

 can be fed into motors, generating mechanical energy; or passed 

 through electric fires, generating heat. 



Thus electric energy transforms into radiant (light) energy; 

 into available chemical energy; into mechanical energy; 

 and into heat energy. 



And so on ; summarising the example we have given, and many 

 others that might be quoted, we get our first principle of energetics : 



/ Any form of available energy can be converted into any other 

 ^^ form . . . . . . (1) 



The Diminution o! Available Energy. 



We come now to a very important result. Returning to the 

 series of examples just given, we note that a certain quantity of 

 coal contains chemical energy, and that the latter may be con- 

 verted into heat. The quantity of heat which can be generated 

 by the combustion of the coal can be estimated in the following 

 manner: A small weighed piece is powdered, mixed with some 

 substance which yields free oxygen, and is placed in a kind of 

 bomb, which is put into a vessel containing a known mass of 

 water at a known temperature. The mixture of coal and oxygen- 

 yielding substance is fired electrically, and precautious are 

 taken that all the heat generated goes to raise the temperature 

 of the water. The result is that a certain quantity of water, say 

 1 kilogram (=2 -2 pounds), is raised in temperature, say 1° C. 

 That quantity of heat is called a Calorie, and so we estimate the 

 " calorific value " of the coal — that is, the quantity of heat that 

 is generated when an unit mass is burned. 



Now let the coal be burned in a steam-boiler furnace, and let 

 the steam produced work an engine. The work developed by the 

 latter can easily be estimated, and so we can find the number of 

 h.p. given per ton of coal, or per Calorie. Next, use the engine 

 to drive a dynamo, and use the current generated by the latter 

 to drive an electric motor. Suppose that we utilise the entire 

 power of the engine to drive the dynamo, and the entire current 

 given by the latter to drive the motor. Now estimate the h.p. 

 developed by the motor, and compare it with the h.p. developed 

 by the engine ; it is much less. 



