COMPACT IRON PREPARED AT HIGH TEMPERATURE. 



25 



dull knife and measured as usual in a cell shown in figure 3, page 10. The 

 potential of these cells began at very low value, and gradually rose to a con- 

 stancy at about 0.76 volt. It was evident that the end-point is reached only 

 after a long time ; and accordingly six wires were sealed up in ferrous 

 sulphate solution. Three of these had been scraped as before to clean them 

 and the other three were rubbed with fine emery cloth, all of them being 

 carefully wiped with a cloth before immersion. Below are given the final 

 constant values attained by these samples : 



Table 6. The electromotive force of commercial iron of moderate purity. 



Thus all these samples yield a result lower than the most compact of the 

 sintered samples. The results show excellent agreement, and the number 

 0.765 volt may be taken as the true electromotive force of the cell made 

 from this wire. The Swedish iron gave a slightly higher value, about 0.770. 

 A third sample of commercial iron, the softest and purest wire obtainable, 

 was next examined. It was cleaned with fine emery cloth and wiped with a 

 clean cotton cloth. Two specimens after two days gave respectively 0.760 

 and 0.771 volt, or in mean 0.766, essentially the same as before. 



Thus all the commercial compact samples of iron showed a distinctly lower 

 solution tension than any of the spongy pure samples. Before this differ- 

 ence could be certainly ascribed to any peculiarity in the freshly reduced 

 spongy iron, proof must be afforded that it was not due to impurities in the 

 commercial samples. This possibility was most conveniently subjected to 

 trial by fusing a sample of pure reduced iron, and comparing the product 

 with the commercial sample. At first an attempt was made to prepare pure 

 fused iron by fusing a small quantity in a small lime crucible in an oxyhy- 

 drogen flame. The hydrogen used was very pure, having been made by 

 electrolysis, for impurities would be taken from the gas by the fused iron. 

 The flame was so directed as to cover the iron completely and was provided 

 with excess of hydrogen, but nevertheless all the iron oxidized. The oxide 

 unfortunately did not act as a protection to the iron underneath, because it 

 fused and was absorbed by the porous lime. No acceptable variatu 



