34 Dr. H. J. S. Sand on the Measurement of the 



point to the break in the curve occurring before complete 

 depletion of the silver at the electrode has taken place. The 

 matter is, however, undergoing further investigation. See 

 also remarks below regarding deposition- potential of copper. 

 The numbers given in Table II. may be taken as typical 

 results for the determination of the resistance of the copper 

 sulphate solution between the cathode and the junction T 

 described on p. 27. The experiments 1, «, I, c, d, were carried 

 out before the current passed through the solution ; experi- 

 ments 2, a and b, after the break in the potential of the 

 cathode had taken place. 



Table II. 



No. of 



Experiment. ! Condensers. 



Ratio of | Resistance in Resistance calculated by 



Dial-box. 



Formula 



on p. 



2 a 



b 



500 



500 



20 



05 



40 



207 



50 



278 



70 



425 



50 



122 



100 



462 



From 1 a and 1 b 77 ohms. 



From la and 1 c 77 ohms. 

 From 1 a and 1 d 79 ohms. 



From 2a and 2 b 218 ohms 



The potential of the cathode, after allowance had been made 

 for the drop according to Ohm's law between the cathode 

 and the junction T, was, in the majority of experiments on 

 copper sulphate solutions, found to lie about 10 to 20 milli- 

 volts below the potential of equilibrium. This matter, as 

 well as the slight retrogression of potential at the beginning 

 of the experiments which is visible in the copper sulphate 

 curves (fig. 5, PI. I.), similarly the conditions on which the 

 crystallization of the silver depends, is undergoing further 

 investigation. Some of the results referred to, if cor- 

 roborated, would lead to the conclusion that the deposition 

 of metals from solutions like copper sulphate is not an 

 absolutely reversible process, and this again would prove of 

 importance in its bearing on the different nature of metal 

 deposits obtained from different solutions. In a series of 

 experiments on a decinormal zinc-sulphate solution with an 

 amalgamated copper electrode, similar curves resulted to 

 those obtained with the copper sulphate. Owing, no doubt, 

 to the fact that hydrogen is evolved sometimes alter all the 

 zinc has been removed from the solution, and sometimes 



