756 REPORT—1885. 
Let the slope of potential be one volt per centimetre, 7.e. let 2a = 105, 
x 
then w= 001; and this agrees exactly with Kohlrausch’s value ; only 
he apportions it ‘00049 to Am, and *00053 to Cl, upon Hittorfian 
grounds, instead of half to each. 
Ignoring this last mere migration question, what is there hypothetical 
about the arithmetical problem? Plainly the nature of the substance 
conveying the current; 7.e. the value of N. 
If what I have said under head ‘ migration’ has any weight, the: 
current is really conveyed partly by the dissolved substance and partly by 
the solvent, in the proportion of \ to 1 — d. Let us reconsider the above 
investigation from this point of view. 
Very little change need be made; we shall have 7? and n,° for the 
number of dissociated molecules of the two substances per c.c., and w, 
and w, for their respective ionic velocities. The ratio in which the two- 
substances conduct the current will be n,3w, : .3v.; and corresponding 
to n,* and 7°, there will be N, and N, to represent the amount of dis- 
sociated substance present, reckoned in gramme-equivalents per cubic: 
centimetre of solution; but g remains of the same value as before, and 
N, 2 
nny To> 
So the equation between two expressions for intensity of current 
becomes Y 
or 
equal to 3 
dV 
kh = q (n,2u, + 23g) =t N,>Uy 5 
or ant AR. dV 
be Tig ot eld 
and 
wa Gaye av 
2 No dz” 
The value of \ is determined by migration experiments, in the way 
already explained, and & of course is known; but, since there exists no 
known means of ascertaining the value of N, and N,, there remains com- 
plete uncertainty as to the absolute values of w, and w,; all that one can 
determine, from conduction and migration data combined, are the values 
of N,u, and of Now. 
On Kohlrausch’s hypothesis, taking the suffix 1 as applicable to dis- 
solved salt, A is supposed to be 1, and w, accordingly 0; moreover, since 
every molecule of the salt is supposed by him to be dissociated sufficiently 
to take part in the conduction, N, is considered known from concentra-. 
tion data, 7.e. from the percentage of salt contained in the water, and 
thus 2, is calculable. 
Permitting ourselves to doubt all this, we come to the conclusion that 
we do not yet know the absolute velocity of any ion, and cannot know it 
without further information regarding the dissociation ratio (that is,. 
N,/N’, or N,/N’) of each substance present. 
On the unlikely supposition that this criticism be in any sense 
accepted, what is the meaning of the striking agreement between Kohl- 
rausch’s theory and experiment ? 
His view leads to the equation 
ky a = Nu, 
