THE SOURCE OF THE OCCLUDED HYDROGEN. 



35 



The results, together with those of the previously described quenched iron, 

 are given in the following table : 



Table 8. The effect of reheating quenched iron. 



It is clear at once that samples 45 and 46 had once more acquired the 

 same condition they possessed before they were quenched as was to be 

 expected. Thus there can be no doubt that the reheated iron returns essen- 

 tially to its normal condition. 



From these experiments it was clear that something, either chemical or 

 physical, had happened to the iron during its heating and plunge into water 

 which caused it to assume an excessive potential. Two possible causes 

 might underlie these interesting results. Either the sudden cooling might 

 have preserved the iron in an unstable allotropic form yielding a higher 

 electromotive force, or else occluded hydrogen might in some way be respon- 

 sible for the differences. The former of these explanations was disproved 

 by the already described experiments on cooling iron in a vacuum on a cold 

 iron plate. Hence only the latter explanation remained, and the phenomenon 

 was obviously to be classed with the occlusion of hydrogen from the hot gas. 



It now became an interesting matter to find whether this hydrogen came 

 from the hydrogen gas or from the water during the instant of quenching. 

 This was easily decided by an experiment in which the metal was heated in 

 and quenched from an atmosphere of nitrogen. The quenching apparatus 

 was exactly the same as that used in all the previous experiments. The 

 nitrogen was prepared by Wanklyn's method of blowing air through aqua 

 ammonia, passing this ammoniacal air over hot copper gauze, and purifying 

 the resulting nitrogen in the usual way. All rubber used in the apparatus 

 had been boiled in caustic solution and was thickly coated on the inside with 

 the semi-solid paraffin. In this apparatus a typical sample of porous iron 

 was heated for twelve minutes in nitrogen at a temperature of 1,040 and 

 was then quenched in ice-water. Of the two pieces thus quenched, one was 







7 



