THE DISCHARGE OF THE EXCESSIVE POTENTIAL. 39 



said that the hydrogen taken in by iron from an acid solution is in equilibrium 

 with nascent hydrogen, and therefore possesses a high chemical potential. 



In the course of the quenching experiments it was found that iron 

 charged with active hydrogen lost its impurity much more quickly when 

 immersed in ferrous sulphate than when immersed in water or kept in air. 

 This interesting fact seemed worthy of more careful study, because it might 

 be capable of throwing light on the singular occlusion. Accordingly the 

 following series of experiments was instituted upon six pieces of iron, all 

 quenched at once under such conditions that all were exactly alike : 



Piece No. 51 was immersed in ferrous sulphate and measured immediately 

 after quenching. Its electromotive force began at about 0.8 volt, gave the 

 maximum value 0.91 volt after a few minutes, and then fell off as before, 

 reaching 0.90 volt in half an hour and 0.793 volt in four hours. 



No. 52 was left in the water in which it was quenched for an hour and 

 twenty minutes before measurement. When the electromotive force had 

 reached its maximum of 0.90 volt after 26 minutes subsequent immersion 

 in ferrous sulphate, No. 51 had passed that point over an hour and a half 

 before. 



No. 53 was also left in water and was first measured after two hours and 

 forty minutes had elapsed. By the time it gave its highest electromotive 

 force, 0.91 volt, No. 1 had dropped to 0.803 volt. 



No. 54 was left in water for 26 hours and then immersed in ferrous 

 sulphate. It behaved but little differently from No. 53, but its maximum was 

 lower, being only 0.85 volt. Before its immersion all the preceding had 

 reached their constant values 0.795. 



No. 55 was thoroughly dried in alcohol and ether immediately after 

 quenching and kept in a desiccator an equal length of time (26 hours) 

 before measurement. This specimen began at 0.79 volt, rose regularly to 

 0.88 volt in two hours, and reached 0.80 volt again in twenty-four hours. 



No. 56 also was immediately thoroughly dried and was measured after 

 73 hours, giving a similar but less marked maximum (0.85 volt). 



The whole series of experiments was then repeated with essentially identi- 

 cal results. 



The comparison of the results of these series of experiments shows that 

 mere exposure to dry air slowly lowers the high electromotive force due to 

 quenching, that pure water hastens this lowering a very little more than 

 exposure to the air, but that immersion in ferrous sulphate quickly estab- 

 lishes equilibrium. The more typical of these experiments, with some of the 

 previous ones, are plotted in figure 6. 



It became now an interesting matter to discover if any other electrolyte 



