816.  Immediately upon the completion of the communication with the voltaic battery, the current passed, and decomposition 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 and gain were very nearly the equivalents of the water decomposed in the volta-electrometer, giving for lead the number 101.5.  It is therefore evident, in this instance, that causing 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 precisely 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 contain 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 mass of evidence, proving the truth of the important proposition which I at first laid down, namely, that the chemical power of a current of electricity is in direct proportion to the absolute quantity of electricity which passes (377. 783.).  They prove, too, that this is not merely true with one substance, as water, but generally with all electrolytic bodies; and, further, that the results obtained with any one substance do not merely agree amongst themselves, but also with those obtained from other substances, the whole combining together into one series of definite electro-chemical actions (505.).