34 ELECTROMOTIVE FORCE OF IRON AND OCCLUDED HYDROGEN. 



ficially oxidized sample was immersed in ferrous sulphate and half an hour 

 later it gave the value 0.89 volt against the decinormal electrode, instead of 

 only 0.79 as before. This extraordinary value was only temporary, the 

 electromotive force falling rapidly, at the end of one hour being 0.825 volt 

 and of five hours, 0.803. Three other pieces quenched at the same time gave 

 similar results. Because the electromotive force fell rapidly it appeared pos- 

 sible that an immediate reading might have given even higher results. A 

 repetition of the experiment with frequent readings was evidently very 

 desirable. 



The second quenching was a repetition of the first. To remove the 

 adhering water after the operation, the samples of iron were rinsed for a 

 minute or two in ferrous sulphate solution before putting into the cells, thus 

 preventing dilution of the normal solution in which they were measured. 

 The results verified those of the first quenching, but added to them, in that 

 the later ones showed the speed of decrease in potential to be much less in 

 the first half hour than afterwards. The potential started at about 0.9 volt, 

 and after remaining almost constant for thirty minutes began to fall off 

 rapidly. A number of other similar quenchings were made, most of which 

 gave similar results, only a few showing no excess of potential. Typical 

 examples are given in the following table, under the heading, Sample 44. 



Further experiments were made to determine if the temperature before 

 quenching caused any considerable effect on the results. 



The apparatus used was the same as the one which served in the previous 

 experiments. One sample was quenched from 695 and another from 6oo. 

 In both cases the quenched iron rose to a maximum electromotive force less 

 strikingly above the normal value, the former attaining 0.87 volt and the 

 latter 0.82 volt, which potentials, as usual, settled down to the normal values 

 of 0.795 m tne course of half a day. These experiments showed that the 

 excessive value of the electromotive force was directly dependent upon the 

 temperature before quenching, a higher temperature giving a greater excess. 

 They added to the evidence already given that the " gamma " or high-tem- 

 perature phase of iron could have nothing to do with the excessive values, 

 because the latest quenching occurred from a temperature below the recog- 

 nized transition point. It will be remembered in this connection that pure 

 iron quenched from i,ioo on a cold iron plate gave normal values for its 

 electromotive force. 



The experiment was next made of reheating the quenched iron in hydro- 

 gen in order to discover whether or not it would return to its normal condi- 

 tion. Two pieces of this same quenched iron were thoroughly dried in 

 alcohol and ether and three days later were reheated in hydrogen for one 

 hour (the highest temperature being faint redness) and then slowly cooled. 



