436 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



922. It might at first be supposed that a conducting body, not electrolytic, might 

 answer as the third substance between the zinc and the platina ; and it is true that 

 we have some such capable of exerting chemical action upon the metals. They must, 

 however, be chosen from the metals themselves, for there are no bodies of this kind 

 except those substances and charcoal. To decide the matter by experiment, I made 

 the following arrangement. Melted tin was put into a glass tube bent into the form 

 of the letter V, fig. 6, so as to fill the half of each limb, and two pieces of thick platina 

 wire, /?, w, inserted, so as to have their ends immersed some depth in the tin ; the 

 whole was then allowed to cool, and the ends p and w connected with a delicate gal- 

 vanometer. The part of the tube at x was now reheated, whilst the portion y was 

 retained cool. The galvanometer was immediately influenced by the thermo-electric 

 current produced. The heat was steadily increased at x, until at last the tin and platina 

 combined there ; an effect which is known to take place with strong chemical action 

 and high ignition ; but not the slightest additional effect occurred at the galvanome- 

 ter. No other deflection than that due to the thermo-electric current was observable 

 the whole time. Hence, though a conductor, and one capable of exerting chemical 

 action on the tin, was used, yet, not being an electrolyte, not the slightest effect of an 

 electrical current could be observed (947.). 



923. From this it seems apparent that the peculiar character and condition of an 

 electrolyte is essential in one part of the voltaic circuit ; and its nature being con- 

 sidered, good reasons appear why it and it alone should be effectual. An electrolyte 

 is always a compound body : it can conduct, but only whilst decomposing. Its con- 

 duction depends upon its decomposition and the transmission of its particles in direc- 

 tions parallel to the current ; and so intimate is this connexion, that if their transition 

 be stopped, the current is stopped also ; if their course be changed, its course and 

 direction changes with them ; if they proceed in one direction, it has no power to 

 proceed in any other than a direction invariably dependent on them. The particles 

 of an electrolytic body are all so nmtually connected, are in such relation with each 

 other through their whole extent in the direction of the current, that if the last is 

 not disposed of, the first is not at liberty to take up its place in the new combination 

 which the powerful affinity of the most active metal tends to produce ; and then the 

 current itself is stopped ; for the dependencies of the current and the decomposition 

 are so mutual, that whichever be originally determined, i. e. the motion of the par- 

 ticles or the motion of the current, the other is invariable in its concomitant produc- 

 tion and its relation to it. 



924. Consider, then, water as an electrolyte and also as an oxidizing body. The 

 attraction of the zinc for the oxygen is greater, under the circumstances, than that of 

 the oxygen for the hydrogen ; but in combining with it, it tends to throw into circu- 

 lation a current of electricity in a certain direction. This direction is consistent (as 

 is found by innumerable experiments) with the transfer of the hydrogen from the zinc 

 towards the platina, and the transfer in the opposite direction of fresh oxygen from 



