314 TENTH ANNUAL REPORT OF 



as the electric tension occasions chemical decomposition, in conse- 

 quence of which the current circulates. Even Faraday, who is prom- 

 inent in maintaining chemical decomposition as the source of the elec- 

 trical current, concedes that decomposition is preceded by a state of 

 tension of the liquid; for he says, in the case where he applies his 

 theory of induction to, electrolytic decomposition : 



"The theory assumes that the particles of the dielectric (now an 

 electrolyte) are, in the first instance, brought, by ordinary inductive 

 action, into a polarized state, and raised to a certain degree of tension 

 or intensity before discharge commences; the inductive state being, 

 in fa.ct, a, 7iecessary preliminary to discharge. By taking advantage 

 of these circumstances, which bear upon the point, it is not difficult to 

 increase the tension indicative of this state of induction, and so make 

 the state itself more evident. Thus, if distilled water be employed, 

 and a long, narrow portion of it placed between the electrodes of a 

 powerful voltaic battery, we have at once indications of the intensity 

 which can be sustained at these electrodes, * * * for sparks may 

 be obtained, gold leaves diverged, and Ley den bottles charged." — 

 Twelfth Series of Experimental Besearches on Electricity, 1345. 



Thus Faraday himself concedes that a polarized state precedes de- 

 composition of the electrolyte in the separate cells of the battery, con- 

 sequently it precedes the formation of the current. The difference 

 between Faraday's theory of the pile, and the contact theory, is not to 

 be found in the fact of deriving the circulation of the current from 

 chemical decomposition in the cells. The contact theory supposes, 

 with Faraday, that in the water-battery (hydro-kette) the formation 

 of the current is the consequence of chemical decomposition in the 

 cells. It also supposes, with Faraday, that this decomposition must be 

 preceded by a state of tension ; and it is only in reference to the cause 

 of this tension, which is nothing else than the electro-motive force, 

 that there can be any difference of opinion. 



§ 2. Schonhein's chemical theory. — Schonbein has attempted so to 

 modify the propositions of the two theories as to bring them more in 

 harmony. The following are the principal features of his theory, ex- 

 tracted from his own paper: 



" AVhatever maybe the cause or force by which elementary sub- 

 stances are enabled to unite together into an apparently homogeneous 

 body, and to continue in their new combination, this much is cer- 

 tain — that a change must always take place in their condition if a. third 

 element is brought into contact with one of the substances, which 

 exercises a perceptible chemical attractive force upon the other 

 components of the compound. To illustrate our idea, let us select 

 water as an example. Oxygen and hydrogen are held together in 

 this compound with a given force ; or, to express the same thing in 

 other words, the chemical attractive forces of the elements of water 

 are in a state of equilibrium. An oxidable substance, as zinc, being 

 now brought into contact with water, it will have a chemical attrac- 

 tion of a certain intensity for the oxygen of the water. But in conse- 

 quence of this attraction, tlie chemical relation which subsisted between 

 the oxygen and hydrogen before the presence of the zinc must be 

 changed, or the state of the original chemical equilibrium of these 



