31-0 Dr. Faraday's Experimental Researches in Electricity. 



805. Iodide of potassium was subjected to electrolytic action 

 in a tube, fig. 13. (789.). The negative electrode was a 

 globule of lead, and I hoped in this way to retain the potas- 

 sium, and obtain results that could be weighed and compared 

 with the volta-electrometer indication ; but the difficulties de- 

 pendent upon the high temperature required, the action upon 

 the glass, the fusibility of the platina induced by the presence 

 of the lead, and other circumstances, prevented me from ob- 

 taining such results. The iodide was decomposed with the 

 evolution of iodine at the anode, and of potassium at the cat- 

 hode, as in former cases. 



806. In some of these experiments several substances were 

 placed in succession, and decomposed simultaneously by the 

 same electric current; thus, protochloride of tin, chloride of 

 lead, and water, were thus acted on at once. It is needless 

 to say that the results were comparable, the tin, lead, chlo- 

 rine, oxygen, and hydrogen evolved being definite in quantity 

 and electro-chemical equivalents to each other. 



807. Let us turn to another kind of proof of the definite 

 chemical action of electricity. If any circumstances could be 

 supposed to exert an influence over the quantity of the matters 

 evolved during electrolytic action, one would expect them 

 to be present when electrodes of different substances, and 

 possessing very different chemical affinities for the evolving 

 bodies, were used. Platina has no power in dilute sulphuric 

 acid of combining with the oxygen at the anode, though the 

 latter be evolved in the nascent state against it. Copper, on 

 the other hand, immediately unites to the oxygen, as the elec- 

 tric current sets it free from the hydrogen ; and zinc is not 

 only able to combine with it, but can, without any help from 

 the electricity, abstract it directly from the water, at the same 

 time setting torrents of hydrogen free. Yet in cases where 

 these three substances were used as the positive electrodes in 

 three similar portions of the same dilute sulphuric acid, spe- 

 cific gravity 1*336, precisely the same quantity of water was 

 decomposed by the electric current, and precisely the same 

 quantity of hydrogen set free at the cathodes of the three so- 

 lutions. 



808. The experiment was made thus. Portions of the di- 

 lute sulphuric acid were put into three basins. Three volta- 

 electrometer tubes, of the form figg. 5, 7. were filled with the 

 same acid, and one inverted in each basin (707.). A zinc 

 plate, connected with the positive end of a voltaic battery, 

 was dipped into the first basin, forming the positive electrode 

 there, the hydrogen, which was abundantly evolved from it 

 by the direct action of the acid, being allowed to escape. A 



