PURE IRON HEATED IN VACUUM. 



27 



This iron must have been wholly free 

 from carbon, from any other metal, and 

 indeed even from all but the merest 

 trace of hydrogen. It is hence clear that 

 the impurities in the commercial iron 

 could not have been enough to affect its 

 electromotive force, and that pure, com- 

 pact iron really gives a lower value than 

 the same iron reduced by hydrogen. To 

 what cause, then, is this difference to be 

 ascribed ? Is the higher solution tension 

 of the spongy iron due to the traces of 

 hydrogen within it, or to difference of 

 internal structure, or to the disposal of its 

 external surface? 



The first of these three possible causes 

 of an extraordinarily high potential does 

 not seem to be a very probable one ; 

 nevertheless, it seemed worthy of test, 

 especially in view of the results on oc- 

 cluded hydrogen to be recorded later. 

 Accordingly, several samples of spongy 

 iron were ignited for varying lengths of 

 time at varying temperatures in a 

 vacuum, while inclosed in a stout porce- 

 lain tube. It was thus found that while 

 short ignition or ignition at a low tem- 

 perature left much of the gas in the 

 metal, treatment at a higher temperature 

 for a longer time seemed to remove 

 nearly all of it, while causing the iron to 

 sinter into a compact mass. Iron thus 

 treated at 1,160 gave in conjunction 

 with the decinormal electrode the usual 

 potential 0.787 in a few hours, a value 

 which remained unchanged 

 even in the last decimal place 

 after ninety hours. Even this 

 iron, however, undoubtedly 

 contained traces of hydrogen, although 

 much less than at first. 



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