THE ELECTROMOTIVE FORCE OF OCCLUDED HYDROGEN. 37 



The discovery that in this case nascent hydrogen may be absorbed more 

 freely than the gaseous material by iron at once reminded us of the well- 

 known absorption of the light element by metals used as a cathode in acid 

 solutions. Cailletet 88 and Johnson 37 showed in 1875 that iron will take up 

 at ordinary temperatures electrolytic hydrogen deposited upon it, while 

 ordinary gaseous hydrogen has no effect. Johnson's work was particularly 

 interesting. His iron was in the form of soft wire and his simple method of 

 testing for hydrogen was to bend the wire to test its brittleness, since he had 

 discovered the interesting fact that hydrogen imparted this property to iron 

 previously tough. Immersing the wire in acids which react on it to form 

 hydrogen uniformly made it brittle. Also when the fractured surface was 

 wetted with water it was seen to froth. Making the wire the cathode in 

 neutral, acid, or alkaline solutions had the same effect, but iron anodes were 

 unaffected even in the acid solution. Other wires were placed in a bottle 

 full of water and hydrogen was made to bubble violently through the water, 

 without any trace of absorption. 



Another interesting research yielding similar results was conducted by 

 Bellati and Lussana. 38 A barometer was closed at the top by an iron plate, 

 and by cementing a glass ring on this an electrolytic cell was made in which 

 hydrogen was generated at the iron plate ; the mercury at once fell by dif- 

 fusion of the hydrogen through the plate into the barometric vacuum. This 

 work was later confirmed and amplified by Shields. 89 



In view of these phenomena, it became a very interesting point to dis- 

 cover if the active hydrogen introduced into cathode iron from solution is 

 capable of raising the potential of a normal cell to the value of 0.93, that 

 observed with spongy iron quenched from i,ioo in nitrogen. Shields had 

 already observed that this occluded hydrogen raised the electromotive force 

 of the iron above the normal value, but the maximum had not been 

 determined. 



This point was easily tested. In order to obtain satisfactory evidence it 

 is of course necessary that iron alone should be immersed as cathode ; the 

 platinum wire supporting it must be above the liquid. Preliminary experi- 

 ments showed that a large excess of potential is as a matter of fact attained, 

 but that it falls off with very great rapidity. Spongy iron which had been 



38 Comptes rendus, 80, 319 (1875). 



" Proc. Roy Soc. (London), 23, 168 (1875). 



38 Bellati and Lussana, Z. Phys. Chem., 7, 229 (1891). 



39 Shields, Chem. News, 65, 195 (1892). Further discussion of this matter will be 

 found in papers mentioned later; see also Hoitsema, Z. Phys. Chem., 17, 1 (1895) ; 

 Winkelmann, Drude's Ann., 8, 388 (1902) ; Richardson, Nicholl and Parnell, Phil. 

 Mag. (6), 8, 1 (1904). St. Schmidt considers the assumption of a split of the hydro- 

 gen molecule to be unnecessary and unwarranted. (Drude's Ann., 13, 747 (1904).) 



