J. H. Reedy — Anodic Potentials of Silver. 289 



Influence of Concentration on Reaction Potentials. — In the 

 preceding table, it is noticeable that silver shows the same 

 reaction potential (about "521 volts) with a large number of 

 anions. In such cases the reaction potential is independent of 

 the concentration of the anion (see Table II), which seems to 

 show that the role of the latter is negligible, or at least of 

 secondary importance. 



Table II. Reaction Potentials of Various Concentrations of Sulphuric Acid. 



Molar Eeaction 



concentration potential 



1-0 -521 volts 



•5 -521 



•25 -522 



•1 -521 



On the other hand, with anions which showed reaction 

 potentials lower than - 521 volts, concentration effects were 

 marked. 



Table III. Concentration Effects in Solutions of Low Reaction Potentials. 



Concentration KClin-5M KBrin -5M KI in -5M NaOH in M 

 in moles H 2 S0 4 H 2 S0 4 H 2 S0 4 NaN0 3 



1 -222 



•1 -285 



•01 -350 



•001 -413 



•0001 -467 



•00001 '510 



077 — -152 -346 volts 



139 — -087 -400 



200 — -027 -462 



259 '035 -484 



319 -099 -500 



391 -183 -508 



All of the above data were found to be definite and repro- 

 ducible within a limit of one millivolt, excepting those for the 

 •00001 molar concentration, where the experimental error is 

 necessarily relatively great, and the results are consequently 

 slightly uncertain. 



Deposition Potential. — The low reaction potentials of silver 

 with the halogen ions, the cyanide ion, the thiosulphate ion, 

 and the hydroxy! ion might be explained by the assumption 

 that these ions give up their electric charges to silver very 

 readily, and are deposited on the silver anode. From this 

 point of view, the potential necessary to deposit an ion on an 

 electrode is regarded as its deposition potential and varies with 

 the concentration of the ion and the metal of the electrode. 

 This must be distinguished from the discharge potential on 

 unattacked electrodes, where the discharged ions combine with 

 one another, or react with the solvent or other materials 



