1906.] The Passage of Electricity through Liquids, 24 



WEEKLY EVENING MEETING, 



Friday, February 16, 1906. 



The Right Hon. Lord Rayleigh, O.M. M.A. D.C.L. LL.D. Sc.D., 

 President R.S., in the Chair. 



W. C. Dampier Whetham, Esq., M.A. F.R.S., Fellow of Trinity 

 College, Cambridge. 



The Passage of Electricity through Liquids. 



Our subject of this evening owes much of its early development to 

 researches carried on in the Royal Institution, Here Davy investi- 

 gated the chemical effects of electric currents, and, in 1807, discovered 

 the elements potassium and sodium by the decomposition of the 

 alkalies by the electric current. Here Faraday discovered the 

 quantitative relation between the strength of the electric current on the 

 one hand and the amount of chemical action on the other, and thus 

 raised the subject to the rank of an exact science. 



Let us pass an electric cun-ent through a solution of some salt, 

 and observe the resultant changes. To make these changes visible, 

 let us choose a coloured salt, such as copper sulphate. As soon as 

 the circuit is completed, we see that one of the copper terminals or 

 electrodes, by which connection is made with the solution, begins to 

 dissolve away, while copper is deposited on the other electrode. 

 Thus copper passes through the solution, disappearing at one end and 

 appearing at the other. The direction in which the copper passes is 

 that which is taken conventionally as the direction of the electric 

 current. 



It will be seen that the middle part of the solution is unaffected. 

 The chemical changes occur at the electrodes only ; at one copper is 

 deposited, at the other copper is dissolved as sulphate, showing the 

 presence of acid in contact with the metal. The chief facts to be 

 explained then are the appearance of the opposite constituents of the 

 salt — copper and acid — at the electrodes, and the total absence of 

 change in the body of the solution. 



We may explain these phenomena by the supposition that op- 

 positely moving streams of the two parts of the salt proceed through 

 the liquid. In the middle there will always' be equal quantities of 

 the opposite parts, and the concentration of the solution is unaltered, 



