298 Rev. Dr. Irving — On Dynamic Metamorphism. 



exceeds that ot x (or x -\- x'), 6 is positive, and the phenomenon is 

 exothermic} The subsequent, or even simultaneous absorption of 

 heat by a diluent (such as nitrogen, in all cases of bodies burning 

 in air) makes no difference, for this belongs to the distribution of the 

 heat, and makes no difference in the quantity of heat generated, 

 which is the same for the same weight of the same materials con- 

 cerned in the same reaction.^ 



We know, for instance, that heat is used up (endothermic) in the 

 reaction C + COg = 2C0, for the simple reason that more heat is 

 required to effect the dissociation CO2 = CO + 0, than is evolved 

 in the subsequent combination (molecule for molecule) expressed by 

 the equation C + = CO ; and we are pretty sure that this is the 

 true explanation of the observed phenomena, because we know from 

 independent evidence that the heat of combustion of C into CO is 

 less than one-half of that of the combustion of the same amount of 

 carbon in the reaction CO + O = COj. These facts have found 

 their way for years past into such well-known text-books of chemis- 

 try as Williamson's " Chemistry for Students" (see § 60, 2nd ed.). 



Again, in the case of NO we require the high temperature of the 

 electric spark-discharge to effect the antecedent dissociation of the 

 N2 and O2 molecules before we get NO formed ; but in this case I 

 am not at all sure that the phenomenon is endothermic, though the 

 rapid distribution of the heat of combination may deceive us, if we 

 lose sight of the all-important distinction between quantity and 

 intensity of heat (absolute temperature).^ The absence of explosive 

 phenomena proves nothing as to this point. All this and a good 

 deal more of like import has been discussed by myself and others iu 

 published papers during recent years. 



The question raised practically resolves itself into this : Does 

 pressure promote the dissociation of previously stable molecules, so 

 as to render the intra-molecular energy of their atoms available 

 for entry into new combinations ? When this is answered in the 

 affirmative on the strength of cogent evidence, I will gladly admit 

 the ' storage of energy ' (qud potential enei'gy of chemical affinity) 

 in the crust of the Earth as the result of mere pressure. The latest 

 grand conception of Mendeleeff as to the nature of chemical affinity 

 points however exactly in the opposite direction. 



In the cases of change of volume to which Mr. Fisher's authority 

 refers, I suppose diminution of volume is meant. But I am not 

 sure that the very molecular strain involved in surface-tension may 

 not in these cases initiate chemical action ; and a suspicion remains 

 that the gases of the supernatant atmosphere may have something 

 to do with it. I am not, however, acquainted with the details of 

 the experiments referred to, nor do I think that for purposes of 

 dynamical geology they are much to the point. 



1 For a clear exposition of these principles see a paper by Spencer U. Pickering, 

 F.R.S., on "Chemical Action and the Conservation of Energy," Nature, vol. 

 xliii. pp. 165-167. 



2 Very well illustrated in the case of ammonia, which will burn continuously in 

 pure oxygen, but not in common air. 



^ See my " Chem. and Phys. Studies, etc." p. 54. 



