202 Domestic Science 



a lower temperature, and when heat has been distri- 

 buted in this way, it is no longer available for the 

 performance of work. All other forms of energy tend 

 to be transformed finally into heat, and thus a continual 

 disappearance of energy apparently takes place, the 

 heat thus produced being readily dissipated. Some 

 simple examples of this may be quoted. Coal possesses 

 a store of energy by virtue of which it is able to unite 

 with one of the gases of the atmosphere oxygen 

 to form as the chief product another gas, called carbon 

 dioxide. In so doing it produces much heat, for 

 this union with oxygen is what we usually call the 

 burning of the coal. The heat is soon shared with 

 the air and other bodies in the neighbourhood of the 

 burning coal, and the carbon dioxide is found to possess 

 a much smaller store of chemical energy than the coal 

 from which it was formed. Again, when an electrical 

 current passes along a wire, part of the electrical energy 

 is used up in raising the temperature of the wire. 

 An example of this is to be found in the incandescent 

 filament lamp. This heat also soon becomes unavail- 

 able for the execution of work. Another interesting 

 example of the " degradation " of other forms of energy 

 into heat is afforded by the recently discovered element, 

 radium. This substance, whether free or combined, is 

 found to be always slightly warmer about 1'5 C. 

 than its surroundings. This continuous production of 

 heat energy on the part of the radium is accompanied by 

 the formation of simpler and less active substances, the 

 radium being said to be "degraded" during this process. 

 135. The next point to be considered is the form 

 in which heat energy exists in hot bodies. We will 

 first recapitulate briefly our previous statements con- 

 cerning the Kinetic Molecular Hypothesis. According 



