Page:The fundamental laws of electrolytic conduction.djvu/42

 fire; and, as it was essential that the evolution of the lead at the cathode should take place beneath the surface, the negative electrode was guarded by a green-glass tube, fused around it in such a manner as to expose only the knob of platina at the lower end (Fig. 11), so that it could be plunged beneath the surface, and thus exclude contact of air or oxygen with the lead reduced there. A platina wire was employed for the positive electrode, that metal not being subject to any action from the oxygen evolved against it. The arrangement is given in Fig. 12.

In an experiment of this kind the equivalent for the lead came out 93.17, which is very much too small. This, I believe, was because of the small interval between the positive and negative electrodes in the oxide of lead; so that it was not unlikely that some of the froth and bubbles formed by the oxygen at the anode should occasionally even touch the lead reduced at the cathode, and re-oxidize it. When I endeavored to correct this by having more litharge, the greater heat required to keep it all fluid caused a quicker action on the crucible, which was soon eaten through and the experiment stopped.

In one experiment of this kind I used borate of lead. It evolves lead, under the influence of the electric current, at the anode, and oxygen at the cathode; and as the boracic acid is not either directly or incidentally decomposed during the operation, I expected a result dependent on the oxide of lead. The borate is not so violent a flux as the oxide, but it requires a higher temperature to make it quite liquid; and if not very hot, the bubbles of oxygen cling to the positive electrode, and retard the transfer of electricity. The number for lead came out 101.29, which is so near to 103.5 as to show that the action of the current had been definite.

Oxide of bismuth.—I found this substance required too high