Eighth series of experimental researches in electricity

Abstract

This series is devoted to an investigation of the source, character and conditions of the electricity of the voltaic instrument, and is divided into five parts. In the first part, simple voltaic circles are considered; and at the outset, the great question of “whether the electricity is due to contact or chemical action ?” is investigated and decided by apparently very conclusive evidence in favour of the latter. One principal experiment in favour of this decision is the following: A plate of zinc and a plate of piatina were prepared; one end of each of these was put into a vessel containing a little dilute sulphuric acid or sulpho-nitric acid, and between the other ends was placed a piece of bibulous paper moistened in a solution of iodide of potassium: the two plates did not touch each other anywhere, but still the action of the end at the one extremity was able to induce the electro-chemica. decomposition of the iodide of potassium at the other. That this decomposition was due to the chemical action of the acid was proved by removing the latter; for then the decomposition ceased. It was also farther proved by the appearance of the iodine against the platina ; for it went there in consequence of the passage of a current (induced by the action of the acid) having the opposite direction to that which the solution of iodide would have produced had it been the only exciting body, and metallic contact had been allowed. The opposition of the chemical affinities at the two places where the acid and the solution of the iodide are placed, is shown when the metal plates are allowed to touch each other in the middle; for then two opposite electric currents are produced, but that occasioned by the acid is the stronger. This opposition is farther shown in the manner in which the weaker set of affinities are overcome by the stronger (that is, those of the iodide and zinc by those of the acid and zinc); and this dependence and relation of the two explains at once the value of metallic contact; for if the solution of iodide of potassium be placed between platina and platina, one of those pieces of metal touching the zinc which is immersed in the acid, then the solution of iodide does not tend to throw an electric current into circulation, because it exerts no chemical action in either direction and therefore the powers active in the acid are more free to act, produce a stronger current, and effect decomposition more freely.