Speyers — Heat of a Change. 61 



Art. yi. — The Heat of a Change in Connection loith 

 Changes in Dielectric Constants and in Yolunies ', by 

 C. L. Speyees. 



When carbon and oxygen react to form carbon dioxide 

 many of us say that chemical energy brings this about ; that 

 carbon and oxygen containing more chemical energy than the 

 quantity of carbon dioxide produced, the difference escapes as 

 heat and light. But when asked to define chemical energy we 

 become extremely perplexed. We can measure heat energy as 

 such in water units but we cannot measure chemical energy as 

 snch in any units. We can measure heat energy as such by 

 the increase in volume produced by it, but we do not know of 

 any effect by which we can measure chemical energy as such. 

 Invariably do these attempts result in producing heat energy, 

 or light energy, or electric energy, or mechanical energy, or 

 some other energy. But because we do not find these energies 

 previously in the reacting system, we say they come from the 

 chemical energy, which must have been previously in the sys- 

 tem. How account otherwise for the energy evolved ? 



That is, many of us say this, not all of us. Yet all of us 

 agree that water does not contain chemical energy although it 

 gives out heat and changes into ice when placed in an atmos- 

 phere below 0°. We all of us agree to this because we agree 

 to call this change into ice a physical change and not a chemical 

 one. Eo other real reason. On careful investigation and 

 thought we come to the conclusion that the term " chemical " 

 is one for convenience only, that we cannot distinguish chem- 

 ical changes from physical ones by any definition that can be 

 experimentally sustained at all points. So if we wish to 

 express things as they are, all we can say is that the term 

 chemical energy is an abbreviation for the statement that some 

 energy is involved in chemical change, hut not that there is 

 snch an energy as chemical energy. Abbreviations are very 

 good and necessary, but unless extremely simple and clear, 

 their proper meaning is likely to be forgotten, and this is what 

 has happened with the term chemical energy. It has come to 

 mean a real thing in the minds of writers. A real thing in an 

 elementary text-book"^ as well as in the last work by Ostwald, 

 a philosophic work too.f Still Ostwald writes in another 

 place:}; " Jeder, der die Beseitigung einer unhaltbar gewordenen 

 allgemeinen Auffassung und ihren Ersatz durch eine neue sich 



*Eemsen; Inorganic Chemistry, p. 38 (1889). 

 f Vorlesungen u. NaturpMlosophie, p. 232 (1901). 

 tlb.,p. 166. 



