SUMMARY AND CONCLUSION. 43 



(5) Iron reduced at a low temperature was found to have an electro- 

 motive force higher by at least 0.02 volt than iron which had been fused. 

 If the normal calomel electrode is taken as having a single potential differ- 

 ence of 0.56, pure compact iron has a single potential difference of 0.15, 

 and spongy or porous iron about 0.17 to 0.18 volt. The former is to be 

 chosen as the normal value. It is pointed out that the much lower results 

 of others are probably to be referred to the acidity of their solutions and 

 to insufficient waiting for equilibrium. 



(6) No important change in these values was caused by sudden cooling 

 from a high temperature. 



(7) Speculations concerning the relations of these facts to the structure 

 and internal pressure and solubility of iron are tentatively recorded. The 

 difference of potential of the different forms of iron is probably but not 

 certainly to be referred to the different sizes of their separate particles. 



SUMMARY OF PART SECOND. 



(8) It was found that hydrogen could be taken up by finely powdered 

 iron reduced at low temperatures without affecting the metal's electromotive 

 force. When the metal is wholly coated with hydrogen the electromotive 

 force is diminished. It is probable that hydrogen thus held is merely 

 adsorbed or held as molecular hydrogen. 



(9) It was found further that by quenching in water, whether from 

 hydrogen or from nitrogen gas, that iron takes up hydrogen in an active 

 form, raising the single potential by as much as 0.15 volt. This hydrogen is 

 quickly expelled in ferrous sulphate solution, and very slowly in water or 

 potassic sulphate solution, the potential returning to the normal value. The 

 gas thus evolved was proved to be hydrogen gas. 



(10) A small amount of hydrogen in the same active form may be taken 

 in from hot hydrogen gas. 



(11) Active hydrogen thus occluded by iron seems to be in every way 

 similar to that occluded by iron in the presence of nascent hydrogen, whether 

 this is chemically or electrolytically produced. 



(12) It is pointed out that the most reasonable explanation of these facts 

 is to suppose that the active dissolved hydrogen is dissociated but not ionized. 



The investigation will be continued in the near future. 



