84 Mr. F. S. Spiers on Contact Electricity. 



hydrogen at a not unduly high temperature. There is another 

 property possessed by iron which is of peculiar interest in 

 connexion with these experiments, namely, its transparency 

 to hydrogen at a red heat*. Owing to this remarkable and 

 interesting property (which is likewise shared by platinum), it 

 seemed probable in the highest degree that after the continued 

 heating of such a platinum-iron couple in an atmosphere of 

 hydrogen, the gas would freely permeate both metals and 

 eventually combine with every trace of oxygen present, 

 either directly or by reducing any iron oxide that has been 

 formed, and the product of the combustion (water) would be 

 driven off by the heat and absorbed in drying-tubes of 

 phosphorus pentoxide. Of course I did not expect that all 

 the oxygen would be removed in one operation ; but that if 

 the metals were brought to a red heat and then allowed to 

 cool (both iron and platinum absorb hydrogen on cooling) 

 and the operation repeated say half-a-dozen times, that little by 

 little the whole or at least the greater part of the oxygen films 

 condensed on the surface-layers of the metals would be driven 

 off and replaced by hydrogen. Thus it would be possible to 

 measure the contact P.D. between iron and platinum in an 

 atmosphere of hydrogen and of hydrogen only. As has 

 already been pointed out, it is useless to displace the outer 

 atmosphere of hydrogen and to leave the inner layers of gas 

 whose particles are within the range of molecular action of 

 the metals unchanged (see § 1). From what follows (§ 14), 

 I venture to think that as far as my experiments go they seem 

 to confirm on the whole and within certain limits the series 

 of phenomena that were suggested above as being likely to 

 take place. 



§ 14. The iron used was a piece of commercial sheet-iron. 

 I should have preferred to use pure iron, but it would have 

 had to be specially rolled, and as I was greatly pressed for 

 time that operation would have taken longer than I could 

 afford to wait. 



In order to work with as large a P.D. as I could possibly 

 get, I thoroughly cleaned and burnished the surface of the 

 iron t; the P.D. between the burnished iron and platinum 

 was 



0-50 volt. 



The next day it had fallen to 



0-37 volt 



* Discovered by Graham : see his ' Collected Papers/ p. 279. 

 t See Dr. J. Erskine-Murray, " On Contact Electricity of Metals, 

 Proc. Eoy. Soc. vol. lxiii. pp. 117-122. 



