of Electrodes in Electrolytic Cells. 



251 



galvanometer was very largely increased by substituting for 

 the suspending and connecting wires of silver above and 

 below the movable coil, fibres of silk, and making the connec- 

 tions with the coil by means of spirals 3*0 millim. diameter, 

 of platinum wire of about *064 millim. thickness, enclosing 

 the fibres. The instrument was then much more sensitive than 

 an ordinary astatic galvanometer of 100 ohms resistance.) 



To test for any difference of " surface-resistance " at the 

 two metals, an electrode of nickel 2*0 x 1*0 centim. was placed 

 in the electrolyte at exactly mid distance between the end 

 plates, and the following arrangement employed : — 



A. Battery of six pairs of zinc and platinum in dilute sul- 

 phuric acid. B. Regulator of current (see Proc. Birm. Phil. 

 Soc. vol. iv. p. 422 ; the < Electrician,' 1885, vol. xv. p. 196). 

 C. D'Arsonval galvanometer. D. Electrolytic trough. E. Box 

 of resistance-coils = 2000 ohms. F. Astatic galvanometer, 

 resistance = 2 ohms. Gr, H. Two resistance-coils of 5 ohms 

 each. 



The cyanide solution was at 9° C, and the total strength of 

 current employed was ='00058 ampere, or -00029 to each end 

 plate. The middle electrode was of nickel. The total current 

 was passed in either direction according to whether the two 

 metals were used as anodes or as cathodes, the bridge galva- 

 nometer F being brought to zero by varying the resistance 

 in E. 



When the two end plates were used as anodes, 43 ohms 

 required to be added on the side of the gold plate to restore 

 the balance ; and when they were employed as cathodes, 280 

 ohms had to be added on that side to restore it. The amounts, 

 therefore, of total " surface-resistance " at the gold and nickel 

 plates were in each case very unequal, that of the nickel one 

 being the largest. 



