Bev. Dr. Irving — On Dynamic Mefamorphism. 297 



instances " (loc. cit.), are very well known to students of 

 chemistry ; but they are not to the point. There is the error 

 which mistakes the algebraic sum of the results of a chemical 

 reaction (as expressed in thermal units) for pure chemical com- 

 bination, qiid entry into atomic union. I thought that ' chemical 

 combination ' was a phrase sufficiently guarded, if taken in its 

 technical and literal sense ; and I still think so. All that Mr. 

 Fisher's ' authority ' has urged, and a good deal more, was before 

 my mind when I penned the sentence : " It is something much 

 more complex than that" (p. 563).^ Mr. Fisher's authority thus 

 takes a different ground altogether from mine, when he enunciates 

 the doctrine that " many chemical changes are attended with the 

 disappearance of heat." Of course they are. Why, every case of 

 dissociation (which is a 'chemical change') is attended with the 

 disappearance of heat or of an equivalent amount of electrical energy 

 (in electrolysis). But all such cases will at once be seen to be 

 rigidly excluded from the term " chemical combination." The fact 

 is the term chemical change, as illustrated by the authority who 

 uses it, covers the whole process of the reaction in each case ; it 

 includes the antecedent dissociation (or partial dissociation), bringing 

 on what I have elsewhere called the " quasi-nascent state," ^ which 

 must precede the recombination of the atoms or radicles to form 

 new molecules. It is of the latter only that I speak in my December 

 letter ; and it must be quite obvious that pressure is antagonistic to 

 the former. We may put it thus : — If 6 = the amount of kinetic 

 energy manifested {qua heat) as the result of a reaction of two 

 bodies on one another ; further, if we take x = the amount of heat 

 used up in the preliminary dissociation (or partial dissociation) of 

 the antecedent molecules ; and if y = the amount of heat evolved 

 in the recombination of the atoms thus rendered available ; the very 

 simple equation 



seems to me to cover the facts of the case, in the simplest form in 

 which the problem can be presented to us ; as (e.g.) in the com- 

 bination of two volumes of hydrogen and one volume of oxygen to 

 produce steam. And if, as in a comparatively small number of 

 cases, there follows a secondary dissociation into proximate con- 

 stituents different from those which formed the antecedents of the 

 reaction, calling the heat expended in this x', we get the equation 



e ■= y — (x -\- x'). 



All that Mr. Fisher's authority has contributed then to the 

 discussion is to inform us that in the cases he has cited (and there 

 are plenty of others) the value of x (or in some cases of a; + x') 

 exceeds the value of y, in which case 6 is negative, and the phe- 

 nomenon is endoihermic. On the other hand, if the value of y 



^ Those who wish for real information on the subject may he referred to Pattison, 

 Muir's "Thermal Chemistry" (1885), and the English edition of Ostwald's 

 " Outlines of General Chemistry" (1890), both published by Macmillan. 



2 See Chemical News, Nos. 1402 and 1505, "OnDissociationand Contact Action." 



