1888.] Mr W. Peddie on Effects of Electromotive Force. 411 
2. On the Variation of Transition-Resistance and Polarisa- 
tion with Electromotive Force and Current Density. 
By W. Peddie, D.Sc. (Plate XYIL) 
The equation of conduction through an electrolyte may be written 
in the form 
where E is the electromotive force of the battery used, r is the total 
true resistance in the circuit, e is the reverse electromotive force, 
and X is the current strength. The quantity in brackets is 
therefore the total opposition (expressed as a resistance) to the 
passage of the current x under electromotive force E. The present 
paper deals with variation of that quantity when E, or x, or both, 
may vary. We may regard it as being made up of three parts : 
the part — ; the part p, representing transition-resistance ; and the 
X 
part R, representing the resistance of the metallic and liquid con- 
ductors, which is constant, since the temperature is supposed to be 
kept constant. 
In a former paper, I showed that a transition-resistance of some 
hundreds of ohms, due to deposited gases, existed at the surface 
of platinum plates of about 60 square cm. area when a single 
Daniell cell was used in the circuit. A few weeks ago I placed a 
similar apparatus in circuit with a Brush dynamo, the electromotive 
force of which was nearly 50 volts. The total opposition to the 
current was equivalent to a resistance of about 10 ohms. Hence, 
quite apart from variation of — , the transition-resistance p must 
QG 
have largely diminished by the increase of E or x. 
In order to determine the cause and law of variation, Mr J. W. 
Butters, ETeil-Arnott scholar in the Physical Laboratory of the 
University, undertook and carried out for me the experiments 
described below. The battery used consisted of Bunsen cells varying 
in number from one to seven. The electrolyte was an aqueous 
solution of pure sulphuric acid, and the electrodes were platinum 
plates between 50 and 60 square cm. in area. Current strength was 
determined by a Helmholtz tangent galvanometer, and electromotive 
