THALLIUIM ELECTRODE AND THALLOUS IODIDE. 



221 



milliampere was employed and the process allowed to run all night, 

 with a stream of nitrogen passing through the apparatus. When the 

 desired coating had been obtained, the electrolysis was stopped, and 

 stopcock, D, turned so as to shut off communication between chambers 

 B and C. If desired, the anode chamber, B, with its stopper and 

 tubes, could be detached from the rest of the apparatus at this point; 

 but this was not essential. 



The rinsing of the thallium electrode chamber was effected by 

 alternately running out the liquid in C through siphon, S, and refilling 

 from the saturation bottle. This necessitated the proper manipula- 

 tion of the stopcocks, G and L (Fig. 3), and D and F (Fig. 4). When 

 the chamber, C, had been rinsed sufficiently (about six or seven times), it 

 was finally filled almost completely full, together with the side-arm and! 

 the bore of the stopcock, M. The cell was now ready for measurement. 

 The test applied to determine whether chamber C had been sufficiently 

 rinsed was to note whether successive rinsings caused any change in. 

 the e. m. f. of the cell. An indication of the completeness of removal 

 of oxygen from the chamber was the constancy of e. m. f. after nitro- 

 gen had been permitted to bubble through the cell for a short time. 

 The difference between any two thallium electrodes in the same cell 

 rarely exceeded a tenth of a millivolt, and usually was not greater than 

 a few hundredths. This indicates that, when carefully 

 prepared, the metallic thallium electrode is both con- 

 stant and reproducible. 



The amalgam electrodes were of two designs, one 

 of which was described by Sucheni.^^ This consisted 

 of a long glass tube, drawn down to a point and 

 sealed at the lower end, and partly filled with a satu- 

 rated thallium amalgam under water (or paraffin e). 

 A long platinum wire was embedded in the amalgam 

 at one end, and sealed tlirough the top of the glass 

 tube at the other. When the electrode was ready for 

 measurement, the tip was broken off and the amalgam 

 exposed. The other form consisted of a J-shaped 

 tube with a small cup at its lower end, containing the 

 amalgam (Fig. 5). This form of electrode permitted 

 more thorough rinsing of the surface of the amalgam. 

 A short platinum wire was sealed through the bot- 

 tom of the cup in order to make electrical connection 

 between the amalgam and the mercury in the longer 



[^ 



Figure 5. 



39 A. Sucheni, Zeit. f. Elektrochemie, 12, 726 (1906). 



