14 



ELECTROMOTIVE FORCE OF IRON AND OCCLUDED HYDROGEN. 



compress the iron. In order to resist such enormous pressures they were 

 made of the very finest tool steel, and after the lathe-work was finished they 

 were quenched to a condition of maximum hardness. They were frustra 

 of cones, the diameters of the bases being about 16 cm. and those of the 

 tops, between which the iron was compressed, about 3 cm. Their heights 

 were about 8 cm. The pressures exerted were 500,000 pounds and 700,000 

 pounds. Exactly how much of this pressure bore on the iron test-piece it 

 is impossible to say, for the soft iron was pressed so deeply into the hard 

 steel that there was some possibility of the whole top surface (7 sq. cm.) 

 receiving part of the pressure. On the other hand, if, as is probable, the 

 test-piece alone bore the stress, the maximum pressure was at least 350,000 

 kilograms per sq. cm., for the surface of the soft iron was never 1 sq. cm. 



In order to make more striking any differences which might result from 

 these pressures, samples 13 and 14 had each been broken in two, and one 

 piece of each was kept in a spongy condition, in order to compare with the 

 other compressed one. Thus it was certain that all treatment previous to 

 measurement" had been precisely the same, except for this one matter of 

 compression. Other pieces of porous iron gave essentially the same results. 



As in the previous experiments, the edges of the compressed iron were 

 protected with paraffin, so that the exposed surface should be that alone 

 which had been compressed. 



Table 3. The effect of previous compression on the electromotive force 

 Iron electrode against decinormal electrode. 



The results with samples 13 to 15, inclusive, lead to the conclusion that no 

 permanent change in free energy had resulted from the compression. They 

 are exactly similar to those obtained with the lower pressures. The appar- 

 ently contradictory result of sample 16 will be shortly explained. 



As a step toward this explanation, it is necessary to call attention once 



15 Including the temperature to which it had been exposed, the importance of which 

 will shortly be pointed out. 



