532 Proceedings of Royal Society of Edinburgh. [sess. 
Note on Polarisation Phenomena observed in Quantitative 
Electrolytic Determinations. By Hugh Marshall, D.Sc. 
(Read March 6, 1899.) 
The phenomena to which it is desired to call attention were first 
observed in the course of an investigation into the electrolytic 
methods of determining nickel, carried out in connection with the 
work of the British Association Committee on the Electrolytic 
Methods of Quantitative Analysis. The results of the investigation 
are given in the Beport of last year’s meeting (Bristol, 1898, 
p. 300), but the present matter is not referred to there, as it was 
first noticed only during the preparation of the report. 
The apparatus employed for most of the determinations con- 
sisted of the usual Classen form of cathode basins, with disc anodes. 1 
The current was drawn from storage batteries at 12 volts, variable 
resistances being used in the circuits. A Davies’ ammeter could be 
introduced easily into any circuit at will, and a Davies’ voltmeter 
was also used to indicate the difference of potential at the 
electrodes. These measuring instruments were so arranged and con- 
nected that the operation which introduced the ammeter into a 
circuit simultaneously brought the voltmeter into action ; hence it 
happened that voltmeter readings were always taken conjointly 
with ammeter ones, although attention was paid almost entirely to 
the effects of varying the current density, and to any changes which 
might occur during the course of the experiment, with no special 
consideration of the potential involved. 
For the determination of quantities of nickel varying between 
0T and 0‘5 gram, the conditions adopted as most generally suitable 
when employing the usual method were those given below : — 
Volume of solution, about 135 c.c. (giving about 100 sq. cm. 
of cathode area), containing 5 grams each of ammonium sulphate 
and of ammonia ; current density at cathode (amp. per sq. decim.), 
O'G-O'T ; ordinary temperature ; time necessary, about 4 hours. 
As it was found that the method of testing for complete 
deposition of the metal by withdrawing a portion of the liquid and 
