428 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



effect of the electric current under investigation (1000.) ; an influence also which, 

 when present, tends only to confuse the results. 



889. Let two plates, one of amalgamated zinc and the other of platina, be placed 

 parallel to each other (fig. 2.), and introduce a drop of dilute sulphuric acid, y, be- 

 tween them at one end : there will be no sensible chemical action at that spot unless 

 the two plates are connected somewhere else, as at |^Z, by a body capable of con- 

 ducting electricity. If that body be a metal or certain forms of carbon, then the 

 current passes, and, as it circulates through the fluid at y, decomposition ensues. 



890. Then remove the acid from 3/, and introduce a drop of the solution of iodide 

 of potassium at x (fig. 3.). Exactly the same set of effects occur, except that when 

 the metallic communication is made at PZ, the electric current is in the opposite 

 direction to what it was before, as is indicated by the arrows, which show the courses 

 of the currents (667.) • 



891. Now both the solutions used are conductors, but the conduction in them is 

 essentially connected with decomposition (858.) in a certain constant order, and 

 therefore the appearance of the elements in certain places shows in what direction a 

 current has passed when the solutions are thus employed. Moreover, we find that 

 when they are used at opposite ends of the plates, as in the last two experiments 

 (889. 890.), metallic contact being allowed at the other extremities, the currents 

 are in opposite directions. We have evidently, therefore, the power of opposing the 

 actions of the two fluids simultaneously to each other at the opposite ends of the 

 plates, using each one as a conductor for the discharge of the current of electricity, 

 which the other tends to generate ; in fact, substituting them for metallic contact, and 

 combining both experiments into one (fig. 4.). Under these circumstances there is 

 an opposition of forces : the fluid, which brings into play the stronger set of chemical 

 affinities for the zinc, (being the dilute acid,) overcomes the force of the other, and 

 determines the formation and direction of the electric current ; not merely making 

 that current pass through the weaker liquid, but actually reversing the tendency 

 which the elements of the latter have in relation to the zinc and platina if not thus 

 counteracted, and forcing them in the contrary direction to that they are inclined to 

 follow, that its own current may have free course. If the dominant action at y be 

 removed by making metallic contact there, then the liquid at x resumes its power ; 

 or if the metals be not brought into contact at 3/, but the aflfinities of the solution 

 there weakened, whilst those active at x are strengthened, then the latter gains the 

 ascendancy, and the decompositions are produced in a contrary order. 



892. Before drawing ^ final conclusion from this mutual dependence and state of 

 the chemical aflSnities of two distant portions of acting fluids (916.), I will proceed to 

 examine more minutely the various circumstances under which the reaction of the 

 decomposed body is rendered evident upon the action of that body, also in the act of 

 decomposition, which produces the voltaic current. 



893. The use of metallic contact in a single pair of plates, and the cause of its great 



