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 O2 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 

 effects of various compounds on the surface-tension 

 maxima in the capillary electrometer. Usually this 

 maximum corresponds to a minimal P.D. between the 

 Hg and the H2 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 observations were made by Abl 



^ Bancroft, Journal of Physical Chemistry, XXI (191 7), 734. 



* Cf. Foerster, Elektrochemie wassriger Losungen (19 15) for further 

 details. 



3 Gouy, Ann. de Chim. et de Phys., XXIX (1903), 145; VIII (1906), 

 291, and IX, 75. 



