Rev. Dr. Irving — On Dynamic Meiamorphism, 301 



interaction of hydrocliloric acid and calcspar, and upon the com- 

 bination of water with dehydrated calcium sulphate, they all tell 

 against the notion of pressure helping chemical action. Pfaff draws 

 this general conclusion from them : " It follows quite decisively 

 from these experiments, that high pressure intercepts chemical 

 affinity, when for its activity an increase of volume is necessary." ^ 

 All this seems to have been clear enough to Mr. Harker some six 

 years ago, when he wrote : ^ " The effect of increased pressui'e is 

 to facilitate such physical and chemical changes as involve con- 

 traction of volume in the substances acted upon, and to retard 

 changes which are accompanied by expansion." If he will furnish 

 references to later work of Pfaff in which his conclusion cited above 

 is superseded, he will confer a favour upon all who are interested 

 in this fundamental question of petrology. 



As to the work of Dr. W. Spring, assuming that the alleged 

 crystalline copper sulphide was proved to be a definitely crystal- 

 lized chemical compound, we have to consider whether such alleged 

 combination is accompanied by increase of density. "We may 

 attack the question I think fairly in this way : — 

 Assuming the following constants : — 



At. Wt. Sp. Gr. 



Metallic copper Cu = 63-5 8-9 



Elementary sulphur ... S = 32 2-07 



and dividing each at. wt. by the sp. gr., multiplied into the molecular 

 weight of water, we have for our present purpose, 



63-5 ~ (8-9 X IB) = -39 (vol. ratio of Cu atom): 

 32 -^ (2-07 X 18) = -86 (vol. ratio of S atom). 

 If the combination were merely 'additive,' we should have •39 + '86 

 (=: 1-25) for the vol. ratio of the fundamental Cu S molecule. 

 But the sp. gr. of Cu S (crystalline) being 4-6, we get 

 (63-5 + 32) -f- (4-6 x 18) = 1-14 

 for the actual vol. ratio of the same molecule. This tells us plainly 

 enough that the union of atoms is accompanied by an increase of 

 density. 



Mr. Harker is careful to point out the necessity for keeping the 

 apparatus cool in the experimental work of Dr. Spring, as cited by 

 him. Where, one may ask, would be the necessity for this, if 

 (i.) there were no heat generated by friction during compression; 

 (ii.) the process of chemical combination (as alleged) were endo- 

 thermic ? We have no right even here to say that any portion of 

 the mechanical energy is transformed into chemical energy. The 

 chemical energy was potentially already in the atoms of Cu and S 

 respectively, as a function of their atomic weights (according to 

 one of the latest generalizations of chemical science) ; all that the 

 pressure did in the experiment in question was to coerce them 



^ See Allgem. iind Chem. Geol. pp. 308-310: "Es geht also aiis diesen Ver- 

 suchen ganz entschieden hervor, dass starker Druck die chemisclie Verwandtschaft 

 dann aufhebt, wenn zu der Eutfaltung ihrer Wirksamkeit eine Volumvermehrung 

 esforderlicli ist." 



2 Erit. Assoc. Eeporb, Aberdeen Meeting (1885), p. 846. 



