24 



ELECTROMOTIVE FORCE OF IRON AND OCCLUDED HYDROGEN. 



reduced at the lowest possible temperature. Accordingly two samples were 

 prepared, the first being very slowly reduced at a temperature well below 

 8oo. In the second of these reductions the temperature was measured by a 

 Le Chatelier thermopile laid under the boat containing the iron, and the 

 highest temperature it indicated through a reduction lasting three days was 

 615 . The iron in boat No. 1 was of a clear gray color in those parts where 

 the temperature became highest and dark blackish gray on the surface. All 

 the iron in boat No. 2 was like the top of boat No. 1. Even the firmest iron 

 in boat No. 1 could easily be crushed between the fingers. 



Two samples of the light-gray material from boat No. 1 gave the follow- 

 ing measurements : 



Table 5. The electromotive force of porous iron reduced at low temperature. 



These values are somewhat higher (0.002 and 0.006 volt) than any ob- 

 tained in previous work, and are further evidence in favor of believing that 

 the low temperature of reduction really causes a product having a higher 

 potential. The contents of boat No. 2 were found to contain much hydrogen, 

 and will be discussed later. 



Having thus shown that iron reduced at low temperature may give in 

 combination with the decinormal electrode a potential as high as 0.800 volt, 

 and that increasing temperature of reduction causes a steady decrease in this 

 value until the metal prepared at perhaps 1,200 gives a value as low as 0.776, 

 it became a matter of interest to discover if iron subjected to a still higher 

 temperature might not give a still lower value. The obvious subsequent 

 step was therefore to test iron which had been fused, and accordingly several 

 specimens of the purest commercial iron (Swedish bar iron and pure piano 

 wire) were tested in preliminary experiments. The Swedish bar iron was 

 very pure, and soon reached a constant value. The piano wire was less 

 regular, and hence was examined more thoroughly. The wire was " hard 

 drawn," and its purity was indicated by the fact that when heated to i,ooo 

 in hydrogen and quenched in ice-water it was as soft and pliable as the 

 purest iron. Two pieces of this wire were scraped bright and clean with a 



