no 
.Mi;. r>. D. STEELE OX THE ^IEASTTEE.MEXT OF lOXIC VELOCITIES 
If, on the other hand, the following ion has the greater velocity, the velocities of 
the 2 ions are given hy 
(Ir-^ in? 
dt + 
d/’o ho 
and yf = 7-^-y , 
df + Vj) c 
where u and v are the velocities of the preceding and those of the following 
ions. 
The 2 ions no longer move with tlie same velocities, Imt a mixing takes place, with 
the result that no stable boundary is to be expected. 
Whetham {loc. cit.), avoiding altogether the use of gelatine, measured the velocity 
of the Imundary l)etween two electrolytes having a common ion, and by the device of 
selecting pairs of solutions which possessed the same, or nearly the same, specific 
resistance, olTained an approximately uniform potential fall for the whole column. 
He was thus able to convert the observed velocities into those which would he 
occasioned l)y a fidl in potential of 1 volt per ceiLtimetre. 
Although, as previously mentioned, the conditions for stability of the boundary are 
pointed out l)y Wheteiam, in his experiments the values obtained are the means of 
two sets of measurements in which the boundary moves alternately in opposite 
directions, and generally with slightly difierent velocities. 
Most of Ids figures show a very good comparison with those calcidated by 
Kohlraitsch, and the measurements as a whole form the first direct confirmation 
of the theory. Proof of the fact that the velocity is proportional to the potential 
fall is also given in tins paper. 
In a second paj^er, Whetham (‘ Phil. Trans.,’ A, vol. 186 (1895), p. 507) measured 
the velocity of a number of ions in gelatine solution : in some of these experiments the 
})osition of the boundary was indicated by means of chemical indicators. The 
results show a very good agreement with Kohle.iusch’s figures. 
Masson [Ioc. cit.), employing a gelatine solution of the salt, compares directly the 
velocity of tlie anion and the cation margins, which he shows to he dependent only on 
the nature of the ions, provided certain conditions are fulfilled; the potential fall 
although mdmown is the same for both boundaries, since between these the concentra¬ 
tion, and so also the resistance, is the same at all points. His experiments afford a 
striking confirmation of the Kohlrausch theory, since he shows tliat it is possible to 
calculate the current hy measui'ing the velocity of the two mai'gins. 
The general theory of electrolysis is briefly summed up hy the equation, 
C = A-(U + y) = A-(n+ idTT.r, 
rj ' 
since the observed velocities U = Tr.ra,, and V = Tr.rr. 
