THALLIUM ELECTRODE AND THALLOUS IODIDE. 



217 



below the metallic electrode at 25°C. proved to be 2.8 millivolts more 

 negative than the saturated amalgam electrode in the same solution. 

 At 0°C. the difference was 1.8 millivolts in a single measurement. 

 Since the amalgam electrode was discredited by the measurements at 

 25°C. we were content with a single measurement at 0°C. It may be 

 pointed out that these results are quite in accord with the measure- 

 ments of Richards and Daniels, who found a difference of 2.49 milli- 

 volts at 20°C. 



Our value for the potential of the two-phase thallium amalgam 

 electrode at 25°C. is 0.7762 volt, or 0.5 millivolt higher than that of 

 Lewis and von Ende. This difference may perhaps be due to a more 



Figure 3. 



Figure 4. 



complete exclusion of oxygen in our experiments, or a difference in the 

 purity of the thallium. Our metal was prepared electrolytically, 

 from carefully purified thallous nitrate, whereas Lewis and von Ende 

 used the purest metal they could buy. 



Experimental Details. — For the measurement of the potential of 

 thallium against the calomel electrode the apparatus shown in Figures 

 3 and 4 was devised. The bottle in Figure 3 was employed for the 

 preparation of a saturated solution of thallous chloride at a definite 



