Definite Chemical Action of Electricity, 343 



duced; after which the metal, at its extremity, soon melted. 

 In this state of things the tube was filled up to c with melted 

 chloride of lead ; the end of the electrode to be rendered 

 negative was in the basin b, and the electrode of melted lead 

 was retained in the basin a, and, by connexion with the 

 proper conducting wire of a voltaic battery, was rendered 

 positive. A volta-electrometer was included in the circuit. 



816. Immediately upon the completion of the communica- 

 tion with the voltaic battery, the current passed, and decom- 

 position proceeded. No chlorine was evolved at the positive 

 electrode ; but as the fused chloride was transparent, a button 

 of alloy could be observed gradually forming and increasing 

 in size at b, whilst the lead at a could also be seen gradually 

 to diminish. After a time, the experiment was stopped; the 

 tube allowed to cool, and broken open ; the wires, with their 

 buttons, cleaned and weighed ; and their change in weight 

 compared with the indication of the volta-electrometer, 



817. In this experiment the positive electrode had lost just 

 as much lead as the negative one had gained (795.), and the 

 loss or gain was very nearly the equivalent of the water de- 

 composed in the volta-electrometer, giving for lead the num- 

 ber 101*5. It is therefore evident, in this instance, that caus- 

 ing a strong affinity, or no affinity, for the substance evolved at 

 the anode, to be active during the experiment (807.), produces 

 no variation in the definite action of the electric current. 



818. A similar experiment was then made with iodide of 

 lead, and in this manner all confusion from the formation of 

 a periodide avoided (803.). No iodine was evolved during the 

 whole action, and finally the loss of lead at the anode was the 

 same as the gain at the cathode, the equivalent number, by 

 comparison with the result in the volta-electrometer, being 

 103-5. 



819. Then protochloride of tin was subjected to the electric 

 current in the same manner, using, of course, a tin positive 

 electrode. No bichloride of tin was now formed (779. 790.). 

 On examining the two electrodes, the positive had lost pre- 

 cisely as much as the negative had gained; and by comparison 

 with the volta-electrometer, the number for tin came out 59. 



820. It is quite necessary in these and similar experiments 

 to examine the interior of the bulbs of alloy at the ends of 

 the conducting wires; for occasionally, and especially with 

 those which have been positive, they are cavernous, and con- 

 tain portions of the chloride or iodide used, which must be 

 removed before the final weight is ascertained. This is more 

 usually the case with lead than tin. 



821. All these facts combine into, I think, an irresistible 



