THALLIUM ELECTRODE AND THALLOUS IODIDE. 



231 



TABLE XIV. 



Summary of Potential . Measurements on Iodine Cells. 



Cells Measured: Pt, | oL N | .^^urated with iodine, 0.1 N KCl, Hg.Cl. Hg. 



25°; E = 

 0°;E = 



0.3406 

 0.3399 



Mean value for cell; 



Pt, I2 molal, I~ normal, N. E. at 



Or, if we consider cells saturated with solid iodine, we have : 



P+ T oof T- r.r. oi XT 1? / at25°;E = -0.2555 

 Pt, I2 sat., I normal, N. E. | ^^ qo! j. ^ _ q 2525 



The normal potential of the iodine electrode shown in table XIV was 

 computed from the observed results by applying three corrections: 



(1) The correction for the potential at the junction of the potassium 

 iodide and the potassium chloride solution calculated by the Hender- 

 son formula, 



(2) the correction for the influence of varying concentration of the 



iodide ion ^'^ and of the free iodine (I2) according to the Nernst equa- 



TJT (J~)- 



tion: + ^— In , thus giving the hypothetical potential which 



2F I2 



57 W. C. Bray and G. M. J. MacKay, Jour. Amer. Chem. Soc, 32, 914 

 (1910) and W. C. Bray, 32, 932 (1910). A small correction has been apphed 

 to these results (see Jones' and Hartmann's Table IV, page 251, which gives 

 the figures actually used). 



