286 



J. R. Beedy — Anodic Potentials of Silver. 



ture, and the corresponding potential taken as the reaction 

 potential. 



This method was justified by the following experiment : 

 A silver anode in - 5 molar H 3 S0 4 was given a definite poten- 

 tial — say, '500 volts — which was kept constant by adjusting 

 from time to time. Oxidation by the air was prevented by 

 stirring the solution vigorously with a jet of hydrogen. At 

 the end of several hours the solution was tested for silver with 

 hydrochloric acid, and it was found that no silver had dis- 



Fig. 3. 



30 















































20 















































10 







































































300 400 SOO 



Potential In Volts 



Fig. 3. Reaction potentials of silver with dilute KI in 0'5 molar H 2 S0 4 . 



solved. The anode potential was then raised, and after several 

 hours the test for silver in the solution was again made. Fol- 

 lowing this method silver was found to dissolve between - 515 

 and "525 volts. More careful experimentation fixed "521 volts 

 as the reaction potential. The probable error in this deter- 

 mination is believed not to exceed 2 millivolts. 



Since the current-potential curves for all solutions of this 

 class with silver anodes are very similar — in fact, almost super- 

 posable — it has been assumed that the above method may be 

 used in all cases. 



No hypothesis is offered as to the nature of the residual 

 current which passes below the reaction potential as above de- 

 termined. So far as could be determined by means of chemical 

 tests, no solution of silver takes place during its passage. 



Stirring. — The reaction potentials of silver seem to be indif- 

 ferent to the stirring agent. No appreciable differences were 

 found when the solution was stirred (a) mechanically by means 

 of a rotating anode, and (b) by means of a jet of gas, such as 

 hydrogen, carbon dioxide, or filtered air, issuing close to the 

 anode. Air, however, is not suitable for stirring acidified 

 iodide solutions, on account of oxidation effects. 



