38 Dr. Faraday's Experimental Researches in Electricity, 



duce a drop of dilute sulphuric* acid, j/, between them at one 

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

 the two plates are connected somewhere else, as at P Z, by a 

 body capable of conducting electricity. If that body be a 

 metal or certain forms of carbon, then the current passes, and, 

 as it circulates through the fluid at ?/, decomposition ensues. 



890. Then remove the acid from y, 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 P Z, 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 decomposi- 

 tion (8.58.) in a certain constant order, and therefore the ap- 

 pearance of the elements in certain places shows in what di- 

 rection a current has passed when the solutions are thus em- 

 ployed. Moreover, we find that when they are used at op- 

 posite 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, sub- 

 stituting them for metallic contact, and combining both ex- 

 periments 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 ac- 

 tually reversing the tendency which the elements of the latter 

 have in relation to the zinc and platina if not thus counter- 

 acted, 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 y, but the affi- 

 nities 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 affinities of two distant 

 portions of acting fluids (916.), I will proceed to examine 

 more minutely the various circumstances under which the re- 

 action of the decomposed body is rendered evident upon the 



