GALVANISM. 



of this science remains, even at the pre- 

 sent day, involved in considerable un- 

 certainty and obscurity. No very dis- 

 tinct or satisfactory account has yet 

 been given of the nature of that force, 

 which originally disturbs the electrical 

 condition of the different parts of the 

 voltaic apparatus, and constitutes the 

 primary source of galvanic power. It 

 was long the prevailing hypothesis, that 

 this force was the same with that which 

 gives rise to the developement of elec- 

 tricity during the contact of dissimilar 

 metals; a fact, the principal circum- 

 stances attending which have been 

 stated in the treatise on Electricity. 

 ( 203.) But in proportion as a more 

 extensive acquaintance with the pheno- 

 mena afforded the means of a more ac- 

 curate analysis, the insufficiency of this, 

 which was termed the Electrical Theory, 

 became more apparent ; and it is now 

 fully established, that the primary agent 

 in the evolution of electricity, is the force 

 of chemical attraction. This latter view 

 of the subject, has led to what may be 

 called the Chemical Theory of Gal- 

 vanism. 



(66.) Every scientific theory must 

 have for its basis some general fact, 

 comprehending a multitude of subordi- 

 nate phenomena, which are its more or 

 less direct consequences. The chemical 

 theory of galvanism assumes the fol- 

 lowing as the most general fact in that 

 science : namely, that chemical action, 

 occurring between a fluid and a solid 

 body, is always accompanied by the dis- 

 turbance of electric equilibrium ; in con- 

 sequence of which a certain quantity of 

 electricity is developed, or, in other 

 words, converted from a latent into an 

 active state. So intimate, indeed, is the 

 connection between the electrical and 

 the chemical changes, that the chemical 

 action can proceed only to a certain ex- 

 tent, unless the electrical equilibrium 

 which has been disturbed be again re- 

 stored. The oxidation of metallic bo- 

 dies (that is, their combination with 

 oxygen) is more especially accompanied 

 by the developement of large quantities 

 of electricity. r ihus it has been ascer- 

 tained, that when a plate of zinc is 

 chemically acted upon by dilute sul- 

 phuric acid, which produces first oxide, 

 and then sulphate of zinc, the metal 

 becomes negatively electrified, while the 

 liquid is in the same degree positively 

 electrified. This fact, when stated con- 

 formably to the hypothesis of Franklin, 

 implies the abstraction of the electric 



fluid from the zinc, and its transference 

 to the liquid product of the combina- 

 tion : but, when translated into the lan- 

 guage of the hypothesis of a double 

 fluid, must be understood as the separa- 

 tion of the two electricities by the che- 

 mical action, and the determination of 

 the resinous or negative electricity in 

 the direction of the zinc, and of the 

 vitreous or positive electricity in the 

 direction of the oxidating liquid. In 

 order to avoid perplexity, however, we 

 shall continue to adhere to the simpler 

 of these hypotheses ; and advert only to 

 the conditions and movements of posi- 

 tive electricity. ($ 4.) 



(67.) That two conducting bodies, 

 such as zinc and acid, thus remain, the 

 one in a negative, and the other in a 

 positive electrical state, notwithstanding 

 their being in contact, is known to us 

 as a matter of fact ; but it is a fact 

 which is not explicable by any of the 

 laws of ordinary electrical phenomena, 

 or, in other words, it is not reducible to 

 any other more general fact. We must 

 for the present, therefore, be content to 

 leave it as a subject of future inquiry, 

 to determine to what peculiarity in the 

 circumstances attending the changes of 

 chemical composition it is owing, that 

 the electric equilibrium is permanently 

 disturbed, and what is the unknown ob- 

 stacle that prevents its restoration. A 

 similar difficulty occurring in the case 

 of the electricity produced by contact, 

 has been noticed in the treatise on .Elec- 

 tricity. ($204.) 



(68.) As long as the chemical action 

 proceeds, the transfer of electricity from 

 the metal to the fluid continues ; but the 

 rapidity of the process is checked by the 

 circumstance, that as soon as the quan- 

 tity transferred has accumulated so as 

 to reach a certain degree of intensity, 

 which is generally exceedingly low, all 

 action ceases, the chemical affinities be- 

 ing balanced by an opposing electrical 

 force. But in consequence of the gra- 

 dual absorption of electricity by the 

 metal from surrounding bodies, and the 

 gradual dissipation of the superabun- 

 dant electricity of the fluid, this state is 

 never reached ; or, if attained, does not 

 long subsist : and the chemical affini- 

 ties continue to produce their effects, 

 though more slowly than if their opera- 

 tion were uncontrolled by the electrical 

 force. But if, on the other hand, by 

 the interposition of good conductors, a 

 ready passage be afforded for the elec- 

 tricity from the fluid, where it is accu- 



