350 
MR. W. C. D. WHETHAM ON IONIC VELOCITIES. 
and from those I was able to select two solutions which fulfilled the necessary con¬ 
ditions (viz., (i.) different colours; (ii.) different specific gravities : (iii.) nearly equal 
specific resistances). Potassium bichromate has a specific molecular conductivity 
(i.e., him) of 9d0 X (Lenz), and potassium carbonate 9'34 X 10”^^ (Kohl- 
rausch), a difference of less than 3 per cent. 
I thought it better to use solutions of slightly different strengths and exactly equal 
conductivities to get rid of even this small variation, and therefore adjusted the 
strength of the carbonate till its resistance just equalled that of the bichromate. 
Thus, in the resistance cell which I used, the bichromate gave 1485 ohms and 
1490 ohms at 17'^‘4, and the carbonate 1475 ohms and 1480 ohms at 17‘^'5. 
The first point I investigated with these solutions was the influence of change of 
potential gradient on the velocity. These should, on Kohlrausch’s theory, obviously 
be proportional to each other. 
When the current was passed downwards, so that the junction travelled up the 
tube, two distinct surfaces of separation appeared, one between the orange of the 
strong bichromate and tlie yellow of that portion of the carbonate solution into which 
a little bichromate had passed by diffusion, and the other between this and the colour¬ 
less carbonate. These kept fairly distinct and travelled upwards at equal rates. I 
append full particulars of the first series of observations. 
Velocities. —Potassium Bichromate and Carbonate. Current Downwai’ds, Move¬ 
ment Upwards. 
Velocity 
Galvanometer. 
Time. 
Rosition. 
in centims. 
per hour. 
Orange .... 
35-0 
11.45 
24-70 
.46 
•65 
.47 
•60 
Yellow .... 
354 
11.48 
23-03 
.49 
•22-92 
.50 
•85 
Orange .... 
354 
12.0 
23-80 
1 i 
.1 
•74 
> 3-63 [ 
o 
•69 
J 1 
Yellow .... 
354 
12,3 
22-18 
1 
1 
.4 
•08 
^ 3-39 
.5 
•00 
/ 
Orange .... 
35'4 
12.15 
22.89 
1 
.16 
•83 
3-65 
.17 
•77 
/ 
Yellow .... 
35-6 
12. IS 
21-32 
1 
.19 
•28 
> 3-24 
.20 
•23 
i 
! 
