101 
been obtained before, it was thought advisable to observe 
the effect of varying circumstances on their form. 
{a) Effect of resistance in circuit : 
From the three curves mentioned above it is seen that an 
increase of resistance increases the time taken by tlie polari- 
sation to sink down to a given value, the general form of 
the curve remaining the same. The time is nearly propor- 
tional to the resistance. 
(h) Effect of alteration of percentage of acid. 
The solution was made 20^ acid, and a curve (C) for 
resistance =2,500 ohms drawn. The alteration of the curve 
seems due only to the alteration of resistance of the circuit, 
it comes between the 2,000 ohms and 8,000 ohms curves of 
the 10% solution. 
(c) Effect of variation of time of polarising.^ 
The cell was polarised during different periods of time 
extending from 1 minute to 90 minutes, and the curves of 
depolarising taken. These curves are shown at T>. 
The two points of inflection are not recognisable till the 
curve for 5 minutes polarising is reached. The curves show 
that increase of time of polarising increases the time of 
depolarising down to any given value. 
(d) Effect of increase of EMF of battery. 
A battery of 12 Daniells was used to polarise the cell, the 
current being kept on for two hours. 
The depolarising curve (E) is then for the first quarter 
minute nearly parallel to the time axis, and therefore totally 
different to the curves obtained with two Daniells, which 
for the first few seconds are almost parallel to the deflection 
axis. This last effect appears to indicate ; either that none 
of the gas liberated at the poles of the voltameter exists as 
a superficial film on the Pt. foil when the polarising cur- 
rent is strong and has acted for a considerable time, or 
that the electromotive force due to such a film has vanished 
This was suggested to us by Dr. Schuster. 
