THE ELECTROMOTIVE FORCE OF IRON UNDER VARYING 



CONDITIONS, AND THE EFFECT OF 



OCCLUDED HYDROGEN. 



The topics named in the title of this paper are of great practical import- 

 ance, as well as of great interest from the theoretical point of view. The 

 rate of rusting and the change of properties caused by the occlusion of 

 hydrogen are essential factors in determining the permanence and strength 

 of most modern buildings, bridges, and underground pipes. For this reason 

 the literature which has already accumulated upon the subject has grown 

 almost to the dimensions of a library in itself. The theoretical side of 

 the matter also is of great interest. The cause of the sudden diminution 

 of activity produced in iron under certain well-known circumstances has not 

 yet found its definitive explanation, and the mechanism of the occlusion of 

 hydrogen by a solid so tenacious and compact as iron is a theoretical ques- 

 tion of no small interest. 



Phenomena relating to these topics are considered together in this paper, 

 because the method of investigation furnished evidence with regard to both. 

 The matter was considered rather from the theoretical than the practical 

 standpoint. The method was the determination of the electromotive force 

 of iron, after subjection to a great variety of changing conditions, on immer- 

 sion in a solution of one of its salts, in order by comparison of these different 

 values of electromotive force to draw inference concerning the state of the 

 metal and its occluded gas. 



The object of the research, as originally planned, was to add to the experi- 

 mental evidence concerning the significance of changing atomic volume, and 

 it was proposed to discover whether or not changes in free energy were 

 associated with changes of density and of other properties of the solid. 

 During the progress of the work it was found that this matter could not be 

 satisfactorily studied without studying the properties of occluded hydrogen, 

 because, in spite of the great volume of literature upon the subject, certain 

 important questions seemed to have remained hitherto almost untouched. 

 Lack of time has as yet prevented the completion of the program ; but the 



3 





