Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/350

350 and from those I was able to select two solutions which fulfilled the necessary conditions (viz., (i.) different colours; (ii.) different specific gravities; (iii.) nearly equal specific resistances). Potassium bichromate has a specific molecular conductivity (i.e., $$k/m$$) of $$9.10 \times 10^{-12}$$, and potassium carbonate $$9.34 \times 10^{-12}$$ , 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 ’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 the yellow of that portion of the carbonate solution into which a little bichromate had passed by diffusion, and the other between this and the colourless carbonate. These kept fairly distinct and travelled upwards at equal rates. I append full particulars of the first series of observations.