Ae PROCEEDINGS OF SECTION B. 
tween y and 4, and K, Cr O, between 6 and «. Each curve is’ 
shown extended slightly beyond the crossing point. By drawing 
a tangent to each curve at this point the following simul- 
taneous velocities are found (centimetres per minute) :— 
(a) Cl or Cr O, passing K = .0366 
(8) K or Ni passing Cl = .0375 
(y) Cl or Cr O, passing Ni = .0909 
(6) K or Ni passing Cr O, = .0492 
Hence the following relative velocities, each ratio being neces- 
sarily independent of ionisation or potential slope :— 
From (a) and (8), Cl: K = .976; 
From (a) and (6), Cr O,: K = .744; 
From (8) and (y), Cl: Ni = 2.424; 
From (y) and (6), Cr O, ; Ni = 1.847; 
or, referring all to the K value as in previous tables, we have 
the following relative values :— 
K= 00,00 976. -Gri0 4 744 Ni = 2408: 
Consideration of the total velocity (i.e., the sum of the 
cationic and anionic velocities) of each salt leads further to a 
knowledge of the concentration, which, as already noticed, 
differs in each case. The total velocities are :— 
For K Cl, .0375 + .0366 = .0741 
For K, Cr Og, .0492 + .0366 = .0858 
For Ni Ch, .0375 + .0909 = .1284 
For Ni Cr O4, .0492 + .0909 — .1401 
These inequalities of velocity must be compensated for by differ- 
ences of concentration, since the product of the velocity and 
concentration must, like the current, have the same value in 
each case. Since also the concentration of the K Cl is neces- 
sarily half-normal, is it was at the start, all concentrations be- 
come known. They are as follows :— 
For the K Cl, = 500 
S741 
For the Kz Cr Og .5 » Sar ia 432 
ForthacNieChwes 1 a _ 289 
"Al 
For the Ni Cr QO; .5 x —2= = .264 
F LO Tah 
Apart from any value which such experiments may have in 
connection with the exact measurements of relative velocities, 
they have some interest as affording a striking demonstration 
of the truth of that general theory of the migration of ions 
which we owe in the first instance to the classical work of 
Hittorf. 
*In my previous paper (loc. cit.), the theory of the moving boundary and ofthese 
inter-relations of velocity and concentration are more fully discussed. On p. 341 one of 
the equations was misprinted. It should read— 
a ui U + Vv iz il= pt 
n a vu! +y! U 1- p 
