158 SMITH'S INTERMEDIATE CHEMISTRY 



maintain the motion. These experiences lead us to believe that 

 we have here a set of things which are fundamentally of the 

 same kind, for each form can be made from any of the others. 

 We have, therefore, invented the conception of a single thing, of 

 which heat, light, electricity, and motion are forms, and to it we 

 give the name energy: energy is work and every other thing 

 which can arise from work and be converted into work. 



Closer study shows that equal amounts of electrical or mechani- 

 cal energy always produce equal amounts of heat. No loss is 

 ever observed in the transformations of energy, any more than 

 in the transformations of matter. Hence we have been led to 

 the conclusion that in a limited system no gain or loss of energy 

 is ever observed. This brief statement of the results of many 

 experiments is called the law of the conservation of energy. 



Application of the Conception of Energy in Chemistry. 



At first sight it looks as if the statement that energy is conserved 

 is not applicable in chemistry. Heat and electricity, for example, 

 seem to be produced and consumed, in connection with changes 

 in composition, in a mysterious manner. We trace light in an in- 

 candescent lamp back to the electricity, and this in turn to the 

 mechanical energy, and this again to the heat in the engine. But 

 what form of energy gave the heat developed by the combustion 

 of the coal under the boiler, or by the union of iron and sulphur 

 in our first experiment? Since we do not perceive any electricity, 

 light, heat, or motion, in the original materials, and yet wish to 

 create an harmonious system, we are bound to conceive of the 

 iron and the sulphur, and the coal and the air, as containing an- 

 other form of energy, which we call internal energy. Similarly, 

 when heat is used up in decomposing mercuric oxide, or light in 

 decomposing silver chloride, we regard the energy as passing into, 

 and being stored in the products of decomposition in the form of 

 internal energy. 

 These conclusions compel us, for the sake of consistency, to 



