769 
anode potential, hence the concentration of the silver ions at the 
anode, keeps a detinite value, or varies in a definite way. 
Vv 
When during the electrolysis the concentration of the chlorine 
| | ‚le Ei 
ions at the anode is kept at a constant value ci,, the ratio — is 
C 
1 
constant during the electrolysis, and equal to: 
ds tA iol 
ee eee eee. We: feet re “at yee 
d, DP: c? 
la 
For silver “chloride Z is, about 10-1". If cig is kept at 10-4, a 
a, 
will be about 0.01, D, and D, differing little. Hence 1°/, of the 
total quantity of chlorine will precipitate in the liquid as AgCl. 
This quantity is lost for the analysis. The error made in the analysis, 
is, however, greater than 1°/,, for the increase in weight of the 
anode is determined. This is 1°/, too small, because AgCl precipitates 
in the liquid, but this causes a quantity of Ag of the anode to go 
into solution, which is equivalent to 1°/, chlorine, hence about three 
times the quantity. The total error amounts, therefore, to about 4°/,. 
This error would be smaller, if the analysis was carried out for, 
d : 
Ciq = 10-3. In this ease would be = 10-4. But now there remains 
C 
1 
in the solution a quantity of chlorine ions equal to 10~-*; to reach, 
therefore, an accuracy of 1°/, we should have to start from a; 
solution which is 0.1 normal. The total quantity of AgCl that must 
separate from this solution, is pretty large, for which a large silver 
surface is necessary, as the quantity of AgCl that can be deposited 
on a given anode surface, is comparatively small. It appears, therefore, 
that an accurate determination of Cl presents. difficulties.. More 
favourable are the circumstances for Br and I, as the solubility 
products of AgBr and Agl are 10~-' and 106. We can, therefore, 
work for AgBr with ¢;,—=10~-+, and for Agl with, 10~-°,: withott 
an appreciable loss taking place. 
The loss of silver chloride becomes slightly smaller when ci, is 
not kept at a constant value from the beginning, but allowed to 
diminish during the electrolysis, so that cj, bas a greater value at 
the beginning of the experiment than at the end. 
Let. us suppose the intensity of the current to be so regulated 
that ci, always remains equal to nl,» being a contant smaller 
than 1. 
Now: 
4y* 
