754 REPORT—1885. 
Specific Velocity of different ions in centimetres per second when urged in a 
very watery solution (i.e. one whose viscosity differs very little from 
water, no matter what acid or salt is being electrolysed in it) when urged 
by an E.M.F. of one volt per centimetre: according to Kohlrausch. 
Cations: H K Am Na Li Ba Sr 
0029 -00051 00049 -00032 -00020 -00033 -00030 
Ca Meg 
‘00025 -00022 
Anions: I Br Cl F N,O, Cl,03; C,H;0, 
00058 -00056 -00053 -00031 -00050 -00038 -00023 
It is only with much misgiving that I venture to criticise so admirable 
a theory supported by close agreement with experiment; but it seems 
less dangerous to hesitate unduly over a true theory, than to accept 
too hastily a false one. 
In the expectation that the objections I urge against the entire and 
comprehensive truth of this doctrine of specific atomic velocity will be 
speedily met and shattered I proceed to state them. 
In the first place I proceed to draw a radical distinction between the 
sum of the velocities of opposite ions and their individual velocities. 
Even if we admit provisionally that the sum of anion and cation velocities 
can be calculated from conductivity data, I demur at the partitioning of 
this velocity u into two unequal portions and affixing a definite velocity to 
either ion. The only data existing for such apportionment of wu, into 
nu and (1 — n)u, are the migration data of Hittorf; and I have 
shown at some length that all the observed facts may be otherwise ex- 
plained: I even venture to think, must be otherwise (or to some extent 
otherwise) explained. 
But, passing over this point, there are doubts about the sufficiency of 
our present data for u itself. The Kohlrausch theory considers the dis- 
solved salt as the sole electrolyte; it neglects the conductivity of the 
water.1 Let us therefore start de novo and independently. 
Attempt at calculation of absolute ionic velocity. 
Let 7 equal the number of dissociated molecules of the substance 
undergoing decomposition in a liquid, per unit length. Let g equal the 
total charge (reckoning + and — together numerically), and m the mass 
of each molecule; and let w be the relative velocity of opposite ions with 
respect to each other, under the influence of a propelling force te 
Ai 
Consider an element dzdydz. The number of active molecules in its 
face is n7dydz, the number leaving it per second is n?dydz.nu = n3u dydz. 
The quantity of electricity thus conveyed is qn?udydz per second, and 
1 In the January (1886) number of Wiedemann’s Annalen, Professor Kohlrausch 
gives a long account of his present standpoint. In § 20 he discusses this question 
of the conductivity of water, and sees reason fur modifying his original view, and 
for admitting that in very dilute solutions water does share in the electrolysis. 
He mentions, what I did not know, that part-conduction by water had been sug- 
gested by Prof. Ciausius as accounting for migration; but Prof. Kohlrausch himself 
adheres to his old Hittorfian view of it. 
