Definite Chemical Action of Electricity. 337 



merit that the equivalent of chlorine had been evolved at the 

 anode, and having formed bichloride of tin as a secondary re- 

 sult, had passed away. 



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 chlo- 

 ride 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 

 100*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 definite quantities 

 by the action of a given quantity of electricity (814. &c). 



796. Chloride of Antimony. — It was in endeavouring to ob- 

 tain 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 cru- 

 cible, 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 sur- 

 face, 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 sub- 



Third Scries. Vol. 5. No. 29. Nov. 1834. 2 X 



