246 PROTOPLASMIC ACTION AND NERVOUS ACTION 



and thus local circuits arise which have chemical effects. 

 Rideal and Taylor also describe cases where metallic 

 couples have a greater catalytic effect than either metal 

 singly.^ The readiness with which the metalHc phase 

 conducts electricity enables any local inequaHties in the 

 metal, or in the nature or concentration of materials (e.g., 

 salts and oxidizable and reducible compounds) present 

 in the solution, to give rise to electric currents between 

 different parts of the surface. These local currents may 

 secondarily influence chemical reactions, as in other cases 

 of electrolysis at metallic electrodes. Effects of the 

 reverse or anticatalytic kind may result when the metal- 

 lic surface is altered in such a way as to lessen the local 

 potential-differences or increase the resistance of the local 

 circuits; strongly adsorbed organic compounds may 

 have both of these effects, as already pointed out. 



Electrochemical oxidations at platinum anodes are 

 subject to variations (partly mentioned above) which 

 are possibly referable to the existence of local circuits; 

 these exercise their own influence independently of the 

 E.M.F. appHed from without, and give rise to inter- 

 ference and summation phenomena of various kinds. 

 The possibiUty that the formation of local circuits plays 

 a part in the normal catalytic activity of platinum and 

 other metals in liquid systems seems to have been 

 insufficiently considered by chemists. The essential 

 conditions of such catalysis are perhaps best illustrated 

 by the decomposition of hydrogen peroxide, which is 

 effected by a large number of finely divided metals of 

 which platinum is especially active. The striking 



^ Rideal and Taylor, Catalysis in Theory and Practice (Macmillan, 

 1919), pp. 130, 160. 



