On the Concentration at the Electrodes in a Solution. 45- 



the spectrum as sufficiently accurate to make this point certain. 

 The work in this region will have to be repeated under more 

 favourable conditions. 



It was our intention to apply the results of the work to a 

 proof of the Ketteler-Helmholtz dispersion formula, but the 

 discovery of the second absorption-band makes this impossi- 

 ble until the extent of the band has been determined, and the 

 extinction coefficient measured, a matter of considerable 

 difficulty. Some of the discrepancies found by Pfluger 

 between his calculated and observed curves, he thought 

 might be explained by the possible presence of an absorption- 

 band in the remote ultra-violet. 



University of Wisconsin, 

 Madison. 



III. On the Concentration at the Electrodes in a Solution, with 

 special reference to the Liberation of Hydrogen by Electro- 

 lysis of a Mixture of Copper Sulphate and Sulphuric Acid. 

 By Henry J. S. Sand, Ph.D., Bowen Research Scholar at 

 Mason University College, Birmingham *. 



Contents : — Historical introduction. — Theoretical consideration of 

 the Liberation of Two Constituents at an Electrode. — Calculation of the- 

 Concentration in a Solution contained in a cylindrical vessel, across one 

 end of which a constant flow of salt is taking place. — Application of 

 results to obtain Values for the Concentration at the Electrode of the 

 Solution of a single Salt and of a Mixture. — Experimental determination 

 of the Time required till Hydrogen appears during Electrolysis of an. 

 Acid solution of Copper Sulphate. — A new method for determining 

 the Diffusion-Coefficient of Copper Sulphate. — Experiments to show the 

 great influence of Convection-Currents on the quantity of Hydrogen, 

 given off in the Electrolysis of an Acid Solution of Copper Sulphate. — 

 Summary of results. 



SINCE the electrolysis of mixtures first attracted the^ 

 attention of scientists, three distinct views have been 

 held about the processes which take place at the electrodes. 



In 1857 Magnus t put forward the theory that in the 

 solution of a mixture of two salts, only one is decomposed 

 if a current of small density be employed ; if, however, the 

 current- density exceeds a certain definite value, the second, 

 salt also suffers from decomposition. He attempted to find- 

 this definite value in the case of a mixture of copper sulphate 

 and sulphuric acid, ascribing it to a current-density which 

 produced a visible amount of hydrogen at a vertical cathode 

 within fifteen seconds. The result obtained was ; that the 



* Communicated by the Physical Society : read Oct. 26, 1900. 

 t Pogg. Ann. cii. p. 17. 



