42 ELECTROMOTIVE FORCE OF IRON AND OCCLUDED HYDROGEN. 



other way. In one respect only does Ramsay's opinion appear question- 

 able, namely, in his assumption that the dissociated gas is ionized. 43 In 

 recent years the word ion has been used in so many senses that an unfortu- 

 nate vagueness has crept into its definition ; but the idea of ionization seems 

 always at least to be associated with electric charges. Now, in this case 

 there seems to be no need of assumption of an electric charge on the 

 occluded hydrogen atom ; indeed it is hard to see how much a charge could 

 be held in the midst of so good a conductor as iron. To the writers it 

 appears much more probable that the hydrogen is rather in the condition of 

 nascent hydrogen, set free from the positive charges which had caused it to 

 ionize in the aqueous solution, but not yet consolidated into the form of 

 hydrogen gas. It would appear that iron is permeated with minute cavities 

 into which only this dissociated form of hydrogen is able to enter, and that 

 upon all occasions when the nascent element is liberated in the presence of 

 the iron, the opportunity of entrance is at once seized. In the wording of 

 the atomic hypothesis, the active hydrogen occluded by iron seems to be 

 atomic but not ionized hydrogen, very different in its properties from the 

 molecular hydrogen which is adsorbed by the fine powder reduuced at low 

 temperatures. 



In conclusion, it is a pleasure to express our gratitude to the Carnegie 

 Institution of Washington for generous pecuniary assistance in this 

 investigation. 



SUMMARY OF PART FIRST. 



( i ) A method, both rapid and convenient, is given for the preparation of 

 iron containing no impurity but hydrogen. 



(2) The potential of this spongy iron in ferrous sulphate was measured 

 and found to be at first greatly affected by previous exposure to the air. 

 After long immersion in ferrous sulphate solution a constant and trustworthy 

 value was reached. 



(3) Even the enormous pressure of about 350,000 kilograms per square 

 centimeter did not produce any appreciable permanent change in this value, 

 although the masses were effectively cold-welded. Taken in conjunction 

 with the results of Spring, this fact is shown to be consistent with the 

 hypothesis of compressible atoms. 



(4) Measurements of the free-energy change in iron during a pull upon 

 a wire great enough to cause rupture gave results showing that this change 

 must be very small, and called attention to regrettable errors in previous 

 work on this subject. 



41 Ramsay, "Modern Chemistry," II, 31 (London, Dent, 1904)- 



