110 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



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

 could be observed gradually forming and increasing in size at h, 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. 



8 17. 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 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 (8O7.), 

 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 espe- 

 cially 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 ascer- 

 tained. This is more usually the case with lead than tin. 



82 1 . 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 them- 

 selves, but also with those obtained from other substances, the whole combining toge- 

 ther into one series of definite electro-chemical actions (505.). I do not mean to say that 

 no exceptions will appear : perhaps some may arise, especially amongst substances 

 existing only by weak affinity ; but I do not expect that any will seriously disturb 

 the result announced. If, in the well considered, well examined, and, I may surely 

 say, well ascertained doctrines of the definite nature of ordinary chemical affinity, 

 such exceptions occur, as they do in abundance, yet, without being allowed to disturb 

 our minds as to the general conclusion, they ought also to be allowed if they should 



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