ELECTRICAL AND OTHER FACTORS 237 



viscosity and on adsorption entering in addition to that 

 on contact-potentials. 



In a recent review of the facts and theories of contact- 

 catalysis Bancroft^ cites various instances where electrol- 

 ysis and electrode-potentials are altered by foreign 

 substances. Thus the P.D. at which O, is freed at a 

 platinum surface is found to be influenced by the electro- 

 lytes present. With platinum electrodes oxidations 

 occur more readily at platinized than at smooth surfaces, 

 apparently because of the '^ catalytic" action of the 

 finely divided platinum. The presence of cyanide and 

 other compounds reduces the rate of oxidation occurring 

 at an electrode under a given P.D.; for example, a 

 neutral solution of Na2S203 is oxidized to tetrathionate 

 at a platinized anode with a P.D. of 0.44 volts and a 

 current-density of 3X10"'* amperes per square centime- 

 ter. If a trace of Hg(CN)2 is added, the anode P.D. for 

 the same current rises to 0.48 volts. Various salts have 

 marked influence on the electrochemical processes at 

 smooth anodes.^ Gouy^ made an extensive study of the 

 eflfects of various compounds on the surface-tension 

 maxima in the capiflary electrometer. Usually this 

 maximum corresponds to a minimal P.D. between the 

 Hg and the U, SO4; but the P.D. and the surface-tension 

 are both changed by the substance added, so that the 

 position of the maximum is shifted, and this influence 

 was found to be greatest with highly surface-active 

 substances. Similar observ-ations were made by Abl 



" Bancroft, Journal of Physical Chemistry, XXI (191 7), 734- 



'Cf. Foerster, Elektrochemie wassrigcr Losungcn (19 15) for further 



details. 



3 Gouy, Ann. de Chim. el de Phys., XXIX (1903), US', VIII (1906), 



291, and IX, 75. 



