520 MR. W. C. D. WHETHAM ON THE VELOCITIES OF THE IONS. 
The two series of numbers correspond with each other within the limits of 
experimental error, and this indicates that the conductivity of the solution of dialysed 
iron is due, in great part, at any rate, to the presence of residual chloride. Whether 
the conductivities of these two solutions are accurately equal or not, it would need a 
thorough investigation to decide, and this was unnecessary for the immediate purposes 
of this paper. One would imagine that, if the conduction is entirely done by the 
chloride, the conductivity of the dialysed iron solution would be a iittle reduced, for 
the residual chloride, finding itself in presence of a large excess of ferric hydroxide, 
one of the products of its decomposition, would be less completely resolved into 
hydroxide and acid than in its ordinary solutions, and would, therefore, have a 
molecular conductivity more nearly equal to that of common salts than in the usual 
case. 
It is interesting to observe that the molecular conductivity, in both these cases, 
reaches a maximum as the concentration decreases, and then, as the dilution is pushed 
still further, again falls. This is a characteristic property of the solutions of free 
acids and alkalis, and confirms the hypothesis that decomposition into ferric hydroxide 
and hydrochloric acid occurs. We may take it, then, that the ferric hydroxide, into 
which solutions of iron salts are partially decomposed, is electrolytically nearly 
inactive, the conductivity being almost entirely due to the acid formed. It is the large 
quantity of this hydroxide present that gives the dark red colour to ferric acetate 
solutions, and it is the motion of the ferric hydroxide which is measured by observa- 
tions on the movement of the colour boundary in the velocity experiment. 
In order to examine this conclusion, 10 cub. centims. of a solution of ferric chloride 
were run into some dialysed iron solution, and made up to 100 cub. centims. Another 
volume of 10 cub. centims. of the same ferric chloride was made up to 100 cub. 
centims. with water. These two solutions were placed in the velocity apparatus, and 
a measurement of the velocity of the red colour boundary made. It travelled in the 
same direction as the current. 
Resistance of ferric chloride in cell, 818 ohms at 18°74. 
ie s zi + hydroxide, 607 ohms at 16°°8. 
Mean conductivity in reciprocals of legal ohms at 16°°2 = 2:12 X 107°, 
Velocity—Temperature 16°2. Mean galvanometer reading = 27°5. Current 
upwards. Upward displacement during successive intervals of 10 minutes each. 
Boundary kept quite sharp. 
(yds HH, (OH, SS) «WE 
Current downwards. Downward displacement during successive intervals of 
10 minutes. | 
HL) ete erire tte Vhs to, Th SO, Wo 
The first three measurements of the latter series are much larger than the rest, 
