Electrolysis : Migration Of The Ions

Expt. 4. - The U-tube is half-filled with a solution containing 0.3 gm. of KNO₃ in a litre of water. By connecting a funnel with the capillary tap below the U-tube, a solution containing 0.5 gm. of KMnO₄ per litre of water, to each 100 c.c. of which 5 gm. of urea have been added to increase its density, is slowly admitted. The surface of separation between the colourless liquid above and the purple permanganate solution below should be quite sharp. A current of 0.3 - 0.4 amp. Is now passed between the platinum electrodes, from the D.C. mains. The purple MnO₄'-ions at once begin to move towards the anode, and the levels alter in the directions shown. If the former levels are marked by thin strips of gummed label, the change is quite apparent after 10-15 minutes.