180 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(811.) 

 Electro- 

 chemical 

 decomposi 

 tion, and 

 theory of 

 the pile. 



Definite 

 character 

 of decom- 

 position 

 electrical 

 equiva- 

 lents. 



(812.) 

 Inferences 

 as to the 

 identity of 

 electrical 

 and chemi- 

 cal forces. 



Currents and from Magnets, or the discovery of 

 Magneto-Electricity. 



III. The influence of the Magnet on all bodies, 

 and the consequent division of substances into two 

 classes, Magnetics and Diamagnetics. 



IV. Optical changes induced by Magnetism. 



I. With regard to electro-chemical decomposition 

 and the theory of the pile, the great extent and intri- 

 cacy of the subject require us to restrict our analysis 

 to a few of the leading conclusions. The most im- 

 portant of these may be summed up in the following 

 propositions : 1st, The amount of a decomposable 

 substance (or electrolyte) analysed into its elements 

 by a current of electricity depends solely on the 

 amount of electricity passing through it, and is in- 

 dependent of the form of apparatus employed, the 

 dimensions of the poles (or electrodes'), the strength 

 of the solution, or any other circumstance. It is 

 thence inferred, with respect, for instance, to water, 

 that the amount of it decomposed in a given time is 

 an exact measure of the quantity of electricity set in 

 motion in that time. 2d, When a substance is thus 

 decomposed, it is a necessary, or at least a highly 

 probable, consequence of Dal ton's laws, that the 

 elements separated are in atomic proportions to one 

 another. But Mr Faraday also found that when 

 several decompositions are effected at the same time 

 by interposing different electrolytes in intervals of 

 the same circuit, the whole of the series of elements 

 separated bear the atomic relations to one another. 

 Thus, to take a single case ; an electric current de- 

 composes in the same time 0*497 grain of water 

 and 3*2 grains of protochloride of tin. Now, these 

 are exactly the proportions of the atomic weights of 

 those bodies. From this and numerous other cases 

 Mr Faraday infers, that universally the amount of 

 electrical action required to dissolve a combination is 

 in a constant proportion to the force of chemical affi- 

 nity by which its elements are united. The corollary 

 seems therefore highly probable that it is one and the 

 same force which is exerted in either case. But the 

 conclusion as to their identity becomes almost irre- 

 sistible when we add to these propositions the follow- 

 ing: 3dly, That the oxidation of one atom of zinc by 

 the acid of the battery generates precisely so much 

 electricity as would resolve one atom of water into 

 its elements. Thus, 8'45 grains of zinc dissolved 

 occasioned the analysis of 2'35 grains of water ; but 

 these numbers are in the ratio of 32-5 to 9 ; the 

 equivalents or atomic weights of zinc and water. 



From these strictly experimental laws, Dr Fara- 

 day considers that he is entitled to draw these im- 

 portant inferences : First, that the source of voltaic 

 electricity in the pile is chemical action solely; 

 Secondly, that "the forces termed chemical affinity 

 and electricity are one and the same." 1 Itis needless to 

 add that these conclusions, involving the very essence 



of the science of voltaic electricity, are supported by 

 Mr Faraday by a great variety of collateral proofs ; 

 and, on the whole, I cannot see that they admit of any 

 reasonable doubt. The contact theory of Volta still, 

 however, holds its ground in Germany, where the 

 number of influential writers on electricity is con- 

 siderable ; and so perseveringly is it maintained, that 

 it is difficult to perceive how it is ever to be dis- 

 lodged. But on this wide and not very profitable 

 controversy we cannot here enter. 



There are a great many other considerations (813.) 

 connected with the action of the voltaic battery 

 which are independent of these primary ones, an 

 which are scarcely less important. Dr Faraday and Con- 

 has entered into a most elaborate experimental duction. 

 argument to show that induction always precedes 

 both conduction and decomposition, and that de- 

 composable bodies or electrolytes must be all more 

 or less perfect conductors. His views may be thus 

 concisely summed up in his own words : " The first 

 effect" of the electrifying influence, whether of fric- 

 tional electricity or of voltaic electricity, upon bodies, 

 is " the production of a polarized state of their par- 

 ticles which constitutes induction /^and this arises 

 from its action upon the particles in immediate con- 

 tact with" the excited body, " which again act upon 

 those contiguous to them, and thus forces are trans- 

 ferred to a distance. If the induction remain un- 

 diminished, perfect insulation is the consequence ; 

 if the contiguous particles" thus polarized " have 

 the power to communicate their forces, then con- 

 duction occurs, conduction being a distinct act of 

 discharge between neighbouring particles." " In the 

 inductive condition assumed by water" when about 

 to be decomposed, " the discharge between particle 

 and particle is not, as before, a mere interchange of 

 their powers and forces, but an actual separation of 

 them, the oxygen travelling in one direction and 

 carrying with it its amount of force acquired during 

 polarization, and the hydrogen doing the same thing 

 in the other direction, until they each meet the next 

 approaching particle, which is in the same electrical 

 state with that they have left, and by association of 

 their forces with it produce discharge. This action 

 may be regarded as a carrying one performed by the 

 constituent particles of the dielectric." 2 Again, 

 " the current is an indivisible thing ; an axis of 

 power, in every part of which both electric forces are 

 present in equal amount." 3 



These views respecting the molecular progress of (814.) 

 conduction and decomposition, though perhaps never 

 so categorically stated as by Dr Faraday, have been, 

 I imagine, substantially held by a majority of those 

 who have considered the subject since the time 

 of Davy, who first gave them a partial expression. 

 And when Davy and others speak of the electric 

 forces in decomposition as if they emanated from the 



1 Researches, Art. 918. 



Ib., Arts. 1338, 1347. 



Ib., Art. 1642. 



