Potential of Electrodes in Stationary Liquids. 31 



For the purpose of determining the current-strength and 

 the cathode-potential, the voltage between the ends 7 : and y 2 

 of the known resistance C, and between y 2 and the standard 

 auxiliary electrode, were measured on the same potentiometer 

 circuit. The latter was composed primarily of a slidewire 

 with a variable back resistance. As several points of the 

 potentiometer had to be tapped simultaneously during an 

 experiment, a system of wires along which mercury cups 

 could be moved was arranged in parallel with the slidewire, 

 and the required potentials tapped off from these mercury 

 cups, the electrical position of the latter relative to points of 

 the slidewire being arranged by separate determinations 

 before an experiment. 



The following manipulations and measurements were car- 

 ried out during an experiment. The current was kept constant 

 at a known value, the potentiometer regulated by occasional 

 comparison with a Clark cell, and the resistance between the 

 cathode and T measured now and again as explained on p. 27. 

 At the same time the cathode-potential had to be determined 

 by measurement of the E.M.F. between y 2 and. the standard 

 auxiliary electrode, and the time had to be read. In order 

 to facilitate the last two determinations a chronograph was 

 designed, which contained a slidewire that was shunted 

 parallel to part of the potentiometer circuit. The slider on 

 the latter was moved by hand so as to balance the difference 

 of potential to be measured ; its position, however, was 

 automatically recorded on curve-paper moved past it by means 

 of a drum rotated by clockwork. 



With regard to the already explained measurement of the 

 resistance from the cathode to T by means of the condenser- 

 bridge-circuit, it must be pointed out firstly that a false 

 connexion is introduced unless the galvanometer Gx for 

 measuring the current is thrown out of circuit during a 

 determination, and secondly that the rough resistance F is 

 required in the main circuit on account of this measurement 

 in order to prevent the greater part of the current from the 

 induction-coil from finding its way through the battery 

 instead of through the electrolytic cell. The resistance taken 

 from the dial re-istance-box must be so small, that its effect 

 on the current during the fraction of a minute it is in circuit 

 need not be considered. 



All the points of the various circuits that were ever inter- 

 changed were connected by special wires to a central switch- 

 board of mercury cnpa on which all the connexions were 

 conveniently and rapidly made. All such points are indicated 

 in the figure by ,/•,/•. other switches being indicated by S. 



