J. H. Reedy — Anodic Potentials of Silver. 295 



with dilution falls off very markedly, so that their lines 

 become almost horizontal. They seem to approach the solution 

 potential of silver (represented by the dotted line) asymptotically 

 and the deviation from the simpler behavior of the other two 

 anions seems to be due in some way to the proximity of the 

 potentials to this limiting value. Presumably, the bromine 

 and iodine lines would show a similar curvature if it were 

 possible to obtain satisfactory data for the extreme dilutions 

 that would be required. 



Solubility of the Oxide and Ilalides of Silver. — Figure 

 6 represents in a comprehensive way the effects of the concen- 

 tration of five different ions upon the reaction potential of a 

 silver electrode. The line AK shows the potentials of silver 

 in contact with a solution containing Ag - -ions ; that is, when it 

 functions as an electrode of the first class. The three lower 

 lines show the behavior of AgCl, AgBr and Agl electrodes, — 

 electrodes of the second class. By extending the lines for the 

 anions according to a logarithmic formula, they cut the upper 

 line at F, G, H, and it. These intersections are the points 

 where the silver may be regarded as an electrode of either 

 class, since they lie on both loci. Farther, at these points 

 the cation and the anion have the same concentration. That 

 is, they represent saturated solutions of the silver compounds 

 in question. At the high dilutions here represented, ionization 

 may be considered to be complete. In brief, assuming that 

 the potential is a logarithmic function of the dilution, the 

 solubility of the silver compound in question may be estimated 

 by noting the ionic concentrations corresponding to these 

 intersections. In the case of the hydroxy 1 and chlorine ions, 

 these intersections were actually realized by determining the 

 cathodic reaction potentials in solutions saturated with silver 

 oxide and silver chloride, respectively. For bromine and 

 iodine ions the intersections were obtained by extrapolation. 



Below are the values of the solubilities found in this way 

 compared with those by other methods : 





Table IV. 



Solubilities of Silver Compounds. 





Silver 



comuound 



Graphic 

 method 



Nernst 

 formula 



E. M. F. 

 method 



Conductivity 

 method 



Ag,0 

 AgCl 

 AgBr 

 Agl 



•6X10- 4 

 1-4XI0-' 

 7-0 X 10-' 



i-o xio- 8 



•5X10 -" 



•9X10- 5 



5-5 X 10-' 



•6 XIO" 8 



•9X10- 4 

 1-3X10-* 



6-6 X 10-' 



l-oxio- 8 



i -o x i o- 4 



•9XH)- 5 

 7-0X10-' 

 1-5 XIO- 8 



It will be noticed that the results obtained in this way (see col- 

 umn above, headed "Graphic Method") agree very well with 

 those by the other methods. The somewhat higher values 

 may be due to the presence of the solvent sulphuric acid. 



