Potential of Electrodes in Stationary Liquids, 37 



by Russ* Luther and Brislee f,and others. As a rule they 

 tend to make cathodes more efficient, i. e., they enable them 

 to accomplish reduction with the expenditure o£ a smaller 

 amount of energy. The eleetrodes are also certainly per- 

 manently changed under certain conditions in such a manner 

 that they become less efficient. This is very notable with 

 the cathode of smooth platinum when small current-densities 

 are employed, If an electrode is used which has been freshly 

 cleaned with ligro'in, boiling strong nitric acid and boiling 

 caustic-soda solution, the potential of the standard electrode 

 shows a comparatively low value throughout the experiment, 

 the results beino- similar to those obtained with a cathode of 

 platinum coated with platinum black. On repetition (p. 29) 

 the cathode is, however, found to have become less efficient, 

 the potential being considerably higher than in the first 

 experiment. Further repetitions yield curves almost identical 

 with the second, the potential, however, still becoming 

 slio-htlv higher. When the cathode is cleaned after this, as 

 before the first experiment, it again yields a curve similar to 

 the lirst. In fig. 10 the first curve and one of its repetitions 

 are shown. 



Fig. 7 illustrates results obtained with a copper and a 

 platinum cathode respectively. The experiments with the 

 copper cathode were stopped after the first retrogression of 

 potential. It will be seen that the latter occurs approxi- 

 mately at the same time in the experiments with the copper 

 as in those with the platinum electrode. The difference 

 between the actual values of the potentials is, however, very 

 marked, the standard electrode at the beginning of the 

 copper experiments showing a lower value than at the 

 beginning of the platinum experiments. This corresponds 

 to a greater efficiency, i. <?., a smaller expenditure of energy 

 in the case of the copper than in that of the platinum 

 electrode. In accordance, however, with the greater E.M.F. 

 required for the liberation of hydrogen on a copper cathode 

 than on one of platinum 1. the copper curves attain higher 

 values of potential than the platinum curves at the end of 

 the experiment. 



Fig. 9 represents experiments with a copper cathode carried 

 out until evolution of hydrogen takes place. 



In tig. 8 results are shown obtained with an electrode of 

 platinum thickly coated with platinum black, the current- 

 density being the same as in the experiments of fio. 7. The 



* Rus.*, Ztschft. Phy*. Chem. xliv. p. (541 (1903). 



t Luther and Brislee, Ztschft. Phys. Chem. xlv. p. 216 (1903). 



I Caspari, Ztschft. Phy*. Chem. xxx. p. 89 ( L899). 



