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



free halogens gave exactly the same potentials as those coated 

 by electrolysis. 



Curves with More than One Flexure. — Some of the curves 

 obtained showed two flexures, as in fig. 3, which gives the 

 curve for a very dilute solution of potassium iodide in - 5 

 molar sulphuric acid. The first reaction potential is at "136 

 volts, and a second at "521 volts. These two different poten- 

 tials are best explained by assuming that the first one repre- 

 sents the deposition potential for I'— ions of that particular con- 

 centration ; but as a higher anodic potential is impressed, the 

 current density reaches a limit on account of the reduction of 

 the I'-ion concentration close to the anode, and with increasing 

 potential remains approximately constant until the potential is 

 reached at which silver begins to dissolve. A similar explana- 

 tion holds for the JBr0 3 '-ion curve (tig. 4). 



Reaction Potentials with Yarious Electrolytes. — The above 

 method was used for the determination of the reaction poten- 

 tials of a large number of solutions. The following is a partial 

 list of the results obtained : 



Table I. Reaction Potentials. 



Molar 

 Electrolyte used concentration 



Sulphuric acid '5 



Sodium sulphate "5 



Potassium sulphate *25 



Zinc sulphate.. "5 



Magnesium sulphate '5 



* Copper sulphate. *5 



* Mercurous sulphate # 0016 



Nitric acid 1 



Potassium nitrate _ 1 



Sodium nitrate 1 



Phosphoric acid "333 



Disodium phosphate.. '333 



Oxalic acid # 5 



Ammonium oxalate *5 



Acetic acid 1 



KC1 in 5M. H 2 S0 4 1 



KBrin oM. H,S0 4 1 



KI in -5M. H 2 S0 4 1 



Sodium hydroxide .i 1 



Potassium hydroxide 1 



Sodium thiosulphate _ "5 — 



Potassium cyanide.. 1 (about) — 



Eeaction 

 potential 



521 volts 



523 



521 



521 



522 



550 



660 



520 

 521 

 520 



521 

 523 



520 

 521 



522 



222 

 077 

 152 



346 



348 



147 

 611 



* The anomalous behavior of solutions of copper and mercury will be dis- 

 cussed later. 



