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Proceedings of the Royal Society of Edinburgh. [Sess. 
exactly similar, arranged in series. Their electrodes consequently differed 
considerably in potential. The differences of potential between the 
electrodes and the liquid in the cells immediately behind the electrodes were 
then measured, at observed times, by means of the electrometer and according 
to Fuchs’* method; and the corresponding curves were plotted for all four 
electrodes. The time was observed by means of the second-hand of an 
ordinary watch. 
Each cell consisted of two small rectangular troughs connected by an 
upturned U-tube, each U-tube being fitted, for convenience in filling, with a 
branch tube closed by a clip. The electrodes consisted of rectangular 
pieces of platinum of approximately the same area, viz. T3 square inches, 
with platinum wires welded to them at their upper edges. The electrolyte 
was connected with the electrometer by means of calomel electrodes con- 
structed according to the method described in Findlay’s Practical Physical 
Chemistry (1906), page 202. 
To enable me to connect the electrometer quickly to the various 
electrodes and the liquid in which they were placed, the opposite pairs of 
quadrants of the electrometer were connected by copper wires to a mercury- 
pool commutator, with which were also connected by copper wires the four 
platinum electrodes and the corresponding calomel electrodes. 
To make sure that the nozzles of the calomel electrodes were out of the 
lines of flow of the current, the platinum electrodes were so placed, and the 
depth of liquid in the troughs so arranged, that the electrodes almost 
completely filled the cross-section of the electrolyte in the troughs ; and the 
calomel electrodes were then placed so as to have their nozzles immediately 
behind the platinum plates, thus being in that part of the trough through 
which the current does not pass directly. 
The troughs were provided with glass covers to diminish evaporation 
and to keep out dust ; and before performing each experiment the mercury 
in the commutator pools was cleaned, and the electrodes were white-heated. 
The U-tubes of the two cells differed in length and cross-section to such 
an extent that the resistances of the liquid they contained were about 
90,000 and 2000 ohms respectively. Thus the difference of potential of 
the electrodes of the one cell would be about forty-five times as great as 
that of the other. 
The electrocute used in the two cells was the same as in the calomel 
electrodes, viz. potassium chloride, and the concentration was the same 
also. Thus there would be no electromotive force at the nozzles of the 
calomel electrodes. 
* Pogg. Ann., clvi. 158, 1875. 
