29 S J. H. Reedy — Anodic Potentials of Silver. 



by the presence of very small amounts of the baser metals in 

 the form of solid solutions. 



Outside of such cases as copper and mercury, the cations of 

 metals less noble than silver seem to have no effect upon the 

 reaction potentials of silver. Finally, it was found that the 

 presence of the nobler metals, as platinum and palladium, in 

 contact with the silver anode exerted no perceptible influence 

 on the potential. 



Summary. 



1. The term " reaction potential " is used to designate the 

 potential difference that must exist between a metal and a 

 solution for a definite action to begin. This potential is best 

 determined by the third electrode method. 



2. For polarizable silver electrodes, where the products of 

 the reaction are soluble, the point of greatest curvature on the 

 current-potential graph may be taken as the reaction potential. 



3. A large number of electrolytes show the same reaction 

 potential ("521 volts) with silver anodes, regardless of their 

 concentration. This value is interpreted as the " solution (or 

 ionization) potential" of silver. 



4. Reaction potentials below "521 volts appear in cases 

 where the silver compound formed is insoluble or contains the 

 silver largely in the form of complex ions. These "deposition 

 potentials," except in the neighborhood of the solution poten- 

 tial of silver, are logarithmic functions of the dilutions, as 

 would he expected from the JSTernst formula for electromotive 

 force. However, the increase in the reaction potential with 

 dilution was found to be somewhat greater than would be ex- 

 pected from theoretical considerations. 



5. Certain electrolytes were made to show two reaction 

 potentials, the lower one due to the deposition of the anion, 

 the other (-521 volts) due to the solution of the silver. 



6. Electrodes coated with the insoluble silver compound 

 corresponding to the anion of the solution show higher deposi- 

 tion potentials than do electrodes of bright silver. 



7. As a rule, the presence of cations of other metals was 

 found to have no effect on the reaction potentials of silver. In 

 the case of the cations of copper and mercury, however, silver 

 shows abnormally high solution potentials. It is suggested 

 that these metals may form solid solutions with silver, with a 

 resultant lowering of its electrolytic solution pressure. 



