DEFINITE CHEMICAL ACTION OF ELECTRICITY. 105 



794. Chloride of lead was experimented upon in a manner exactly similar, except 

 that a change was made in the nature of the positive electrode ; for as the chlorine 

 evolved at the anode forms no perchloride of lead, but acts directly upon the platina, 

 if that metal be used, it produces a solution of chloride of platina in the chloride of 

 lead ; in consequence of which a portion of platina can pass to the cathode, and will 

 produce a vitiated result. I therefore sought for, and found in plumbago, another 

 substance, which could be used safely as the positive electrode in such bodies as 

 chlorides, iodides, &c. The chlorine or iodine does not act upon it, but is evolved in 

 the free state ; and the plumbago has no reaction, under the circumstances, upon the 

 fused chloride or iodide in which it is plunged. Even if a few particles of plumbago 

 should separate by the heat or the mechanical action of the evolved gas, they can do 

 no harm in the chloride. 



795. The mean of three experiments gave the number of 1 00*85 as the equivalent 

 for lead. The chemical equivalent is 103*5. The deficiency in my experiments I 

 attribute to the solution of part of the gas (716.) in the volta-electrometer ; but the 

 results leave no doubt on my mind that both the lead and the chlorine are, in this case, 

 evolved in dejinite quantities by the action of a given quantity of electricity (814. &c.). 



796. Chloride of antimony. — It was in endeavouring to obtain the electro-chemical 

 equivalent of antimony from the chloride that I found reasons for the statement I 

 have made respecting the presence of water in it in an earlier part of these Researches 

 (690. 693. &c.). 



797. I endeavoured to experiment upon the oxide of lead obtained by fusion and 

 ignition of the nitrate in a platina crucible, but found great difficulty, from the high 

 temperature required for perfect fusion, and the powerful fluxing qualities of the 

 substance. Green glass tubes repeatedly failed. I at last fused the oxide in a small 

 porcelain crucible, heated fully in a charcoal 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. 15.), 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 

 fig. 16. 



798. 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 

 endeavoured 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. 



MDCCCXXXIV. p 



