THALLIUM ELECTRODE AND THALLOUS IODIDE. 



233 



■^- (1) Tl, Til sat., TlCl sat., Tl 



(2) Tl, TlCl, sat., 0.1 N KCl, HgjCla, Hg 



(3) Hg, Hg.CU, 0.1 N KCl, x N KI, I2 sat., Pt 



(4) Pt, I2 sat., X N KI, Til sat., I2 sat., Pt 



Adding: Tl, Til sat., I2 sat., Pt 



The potential (1) is calculated by the Nernst equation from the 

 measured concentration of the thallous ion in thallous chloride and in 

 thallous iodide. 



The potentials (2) and (3) are the directly measured values after 

 applying the liquid junction corrections. The potential (4) is calcu- 

 lated by the Nernst equation from the known concentration of the 

 iodide ion in saturated thallous iodide and in the potassium iodide 

 solutions saturated with iodine. 



The free energy of the reaction Tl (solid) + 1/2 I2 (solid) = Til 

 (solid) is evidently F (= 96,500 coulombs) multiplied by the sum of 

 these four potentials. 



TABLE XV. 



2.5°C. 



