SECTION III. 1883. PT 994 Trans. Roy. Soc. CANADA. 
On the Transition Resistance to the Electric Current at the bounding surface between 
amalgamated Zinc electrodes and solution of Zine Sulphate. By Prof. J. G. 
MACGREGOR, M.A., D.Sc., F.R.S.E. 
[Abstract.] 
After giving a sketch of former experiments on the same subject, the author describes 
his own method and results. His method was a modified form of that of Beetz.* As 
electrolytic cell he used a glass box, in which he could insert parallel to the amalgamated 
zinc electrodes four thin plates, also of amalgamated zine. When the plates were inserted 
the current had to cross ten surfaces of contact; when they were not, it had to cross only 
two. The box was so arranged that the insertion of the thin plates diminished the 
resistance by an amount not greater than 3 of the resistance of the cell. The solutions 
used were boiled before each set of observations, and the electrodes and plates were kept 
for some time before use in a boiling solution of the same constitution. The condensation 
of dissolved gases on the metallic surfaces was thus, as much as possible, prevented. The 
author found great difficulty in getting his electrodes and plates into a state in which 
they would neither originate a current themselves, when dipped in the solution, nor 
become polarized when a current was sent through the cell. In some cases, however, he 
succeeded in making them electrically similar, and in keeping them so during the time of 
observation. In these cases, he measured the resistance of the cell with and without the 
plates, and found either no difference of resistance or differences very slight in amount 
and of variable sign. Eight transitions, therefore, produced no appreciable change of 
resistance. The apparatus used would easily indicate a difference of resistance of 0.1 ohm. 
Hence the transition resistance at one surface of contact of the area of the plates used (100 
sq. cm.) could not be greater than 0.0125 ohm. For the purpose for which the experiments 
were made, this result was sufficient. It agrees with that of Beetz. The author had 
made these experiments, notwithstanding Beetz’s published result, for reasons stated in a 
paper previously published. 
* Pogg. Ann., Bd. exyii., 1862, p. 1. 
+ Proc. R. S. Edin., 1874-5, p. 555. 
