MR. W. C. D. WHETHAM ON THE VELOCITIES OF THE IONS. o21 
and after them the velocity kept constant. It is probable that the extra value was 
due to some disturbance at the boundary introduced by the first current, which 
gradually got reversed and eliminated when the current was reversed. These three 
observations were therefore neglected. The others give a mean velocity of 0°68 centim. 
in 10 minutes. We thus get for the velocity with which ferric hydroxide is trans- 
ported in the direction of the current through a dilute solution of ferric chloride, by a 
potential gradient of 1 volt per centim., at a temperature of 16°°2, the value 
0000315 centim. per second, and at 18° 
000033 centim. per second. 
This is the same, within the limits of experimental error (which with these badly 
conducting solutions are considerable) as the value deduced by experiments with 
ferric acetate solutions of rather greater concentration, which was 
000028 centim. per second. 
It seems clear, then, that what we were measuring in that case, was not the 
velocity of the acetate group, but the velocity with which the soluble ferric hydroxide 
was transported through the solution without undergoing any decomposition. 
In order further to examine this explanation, a migration experiment was made with 
the dialysed iron solution. A current of 0°003 ampére was passed through the liquid 
for five hours, at the end of which time the red colour had become much paler round 
the anode, while a precipitate of ferric hydroxide appeared at the bottom of the vessel 
containing the kathode. 
The volume of liquid in each vessel was 30 cub. centims., and in 30 cub. centims. uf 
the original solution the weight of ferric oxide was 0:0780 gram. 
In the anode vessel the weight of oxide in solution was 0°0438 gram. 
The kathode vessel contained 0°0720 gram. in solution, and 0°0158 gram. precipi- 
tated ; total, 00878 gram. 
Thus the anode vessel contains less iron, and the kathode vessel more, than an 
equal volume of the original solution. This, also, is consistent with the hypothesis 
that unaltered ferric hydroxide is carried through the liquid in the direction of the 
current. 
A similar experiment, made with ferric acetate solution, also showed an accumulation 
of iron in solution near the kathode, both as estimated by the colour of the liquid, 
and as determined by analysis. 
Our attempt to measure directly the velocity of the acetate group (C,H,0,) in acetic 
acid solutions has therefore failed, but the migration experiment, described on p. 518, 
at any rate showed that no great change of concentration occurred in the neighbour- 
hood of the anode, towards which the acetate group travelled. Its velocity is, there- 
MDCCCXCV.— A. 3X 
