Potential of Electrodes in Stationary Liquids. 35 



before, according to slight differences in the nature of the 

 electrode, the results were somewhat irregular, and have 

 therefore not been reproduced as curves. The values ob- 

 tained for the diffusion coefficient of zinc sulphate varied 



cm 

 between 3 5 x 10 -6 and 4'5 X 10" 6 '-. They point to an 



sec. J r 



increase of the diffusion coefficient of zinc sulphate at great 

 dilutions ; the value obtained by Weber * for solutions of 



* „ -, , • rv «/» mo.-equiv. , . _ _ ,_ .cm. 2 



2-114 per cent., i. e., 0*26 — — ^ , being 2'78 x 10" b . 



1 c.c. ° sec. 



In agreement with this we should expect the diffusion co- 

 efficient of zinc sulphate not to differ greatly from that of 

 copper sulphate at great dilution, owing to the fact that the 

 mobilities of the zinc and the copper ion are nearly equal at 

 great dilution. 



Alcoholic Solutions of Cuprous Chloride, 



The next series of determinations was carried out with the 

 object of testing whether the method was suitable for alco- 

 holic solutions. The solution chosen was one of cuprous 

 chloride in a mixture of hydrochloric acid, alcohol, and water, 

 its composition being 1 g. Cu 2 Cl 2 , 25 c.c. strong hydrochloric 

 acid, 45 c.c. 95 per cent, alcohol, 30 c.c. water. Owing to 

 contact with the air, part of the cuprous chloride became 

 oxidized to cupric chloride. The carves on fig. 6 show the 

 degree of coincidence obtained in successive experiments, 

 three determinations having been carried out with the current- 

 density 1*054 — |— , and two with the current-density 



1'318 — J—-' • The curves obtained are of interest inas- 



cm. 



much as they show plainly that two successive processes take 

 place : firstly, the reduction of the cupric chloride to cuprous 

 chloride, which begins at potentials lower than those regis- 

 tered in the figure, and goes on to about 45 centivolts ; and 

 secondly, the deposition of copper from the cuprous chloride 

 beginning at about 45 centivolts and going on until the 

 break in the curve is completed, when the potential becomes 

 fairly eon-tant at about 65 to 70 centivolts, and hvdroo-en 

 comes off. 



Acid Solutions of Nitrobenzene. 



We now come to the discussion of curves obtained when 

 lution of an organic sabstance, namely, nitrobenzene,, 



* Wied. Ann. vii. p. 536 (187ft.. 

 D 2 



