40 



ELECTROMOTIVE FORCE OF IRON AND OCCLUDED HYDROGEN. 



would effect the adjustment of equilibrium as quickly as the ferrous sul- 

 phate. In an easily carried out variation on the preceding series, a normal 

 solution of potassic suphate was used as a typical electrolyte. Brief im- 

 mersion in this solution seemed to show no more effect in discharging the 

 hydrogen than in water, but long immersion showed a slight difference in 

 favor of the electrolyte. The rate was nevertheless so much slower than 

 that observed in the case of ferrous sulphate as to indicate entirely another 

 mechanism of reaction. 



0.9, 



0.8 



0.7 



0.6 



0.5 



' 2 3 4 9 6 7 8 9 10 II 12 19 14 15 IG 17 18 19 20 

 Fig. 6. The Changing Potential of the Iron Electrode. 



In the direction of ordinates are plotted the potentials of the iron electrodes in normal sulphate, in 

 combination with a decinormal calomel electrode. Time in hours is plotted in the direction of 

 abscissae. The curves are typical, No. 7 of porous iron which has been exposed to air, No. 33 of 

 pure fused iron, No. 48 of porous iron which has been made a cathode, No. 51 of porous iron 

 quenched in water, and No. 53 of the same after exposure to air for 2% hours. 



The progress of the evolution of the gas in ferrous sulphate may be sup- 

 posed to be as follows : The active hydrogen, having a higher potential than 

 the iron, causes metal to deposit from the ferrous sulphate, and the acid 

 thus formed immediately attacks the deposit, or a neighboring portion of 

 metal. Without the interposition of the iron as carrier, the hydrogen seems 

 to find it difficult to go from its occluded to its gaseous state. When an 

 electrolyte which contains no easily deionized cation is substituted for the 

 ferrous sulphate, the reaction involving deposition can not take place, and the 

 hydrogen remains in its occluded condition. 



