Mr. M. M. P. Muir on Chemical Notation. 19 



in accord with the molecular theory to suppose that there is 

 taking place so rapid an atomic interchange among the mole- 

 cules both of hydrogen and of chlorine that when these two sub- 

 stances are brought together, under suitable conditions, it is easy 

 for the momentarily dissociated atoms to combine together so 

 as to form the new molecules of hydrochloric acid, and that 

 when these are formed there is not so rapid an atomic ex- 

 change taking place among them as there is among the mole- 

 cules of the generating substances. The general result of 

 such an action, so far as change of energy is concerned, would 

 therefore be an evolution of heat. Indeed the fact that it is 

 possible to completely carry out the reaction symbolized above, 

 appears to me to be in perfect keeping with the fact of the 

 evolution of heat which is noticed during the the reaction ; for 

 if the number of atomic exchanges between the products 

 HC1 HC1 were as great as those between the generating mole- 

 cules H 2 Cl 2 in equal times, the decomposition would cease 

 before the equation was completely realized. But the actual 

 result points to the conclusion (on the assumption that the 

 molecular theory is true) that there are less rapid intramole- 

 cular movements occurring in the case of the molecules HC1 

 HC1 than in the case of the molecules H 2 Cl 2 — in other words, 

 that some portion of the initial molecular motion has disap- 

 peared. But inasmuch as the total energy of the system is 

 supposed the same, the energy which has disappeared in one 

 form must have reappeared in another ; it has reappeared as 

 heat. 



42. Lastly, as to isomerism. So called isomeric bodies un- 

 dergo different reactions; they are produced by different 

 reactions, &c. : these facts may be expressed irrespective of 

 any theory as to their cause, by means of structural or dissected 

 formulae. It has been supposed that isomerism is to be ex- 

 plained by imagining that the atoms are differently arranged 

 in isomeric molecules. Again, it has been supposed that 

 isomerism is to be explained by granting that isomeric bodies 

 are endowed with varying amounts of energy, that in the for- 

 mation of these bodies different quantities of energy change 

 form, and that, conversely, the various reactions noticed with 

 isomeric substances are to be traced to different degrees of 

 conversion of one form of energy into another. Dr. Milk 

 (loc. cit.) says, " to measure, both in quality and in quantity, 

 the energy associated with each isomeric substance, is to give 

 a complete account of the phenomenon of isomerism." Not, it 

 seems to me, to give a complete dynamical account of the phe- 

 nomenon of isomerism ; for it is only when we explain a 

 phenomenon as a " change in the configuration and motion of 



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