1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



16T 



cured, even with powerful sparks, and almost none with the mere current ; 

 yet the quantity of electricity in a given time was the same in all these cases." 

 " I believe at present that common electricity can decompose water in a 

 manner analogous to that of tlie voltaic pile. Cut when I consider the trite 

 effect only was obtained, tlie quantity of gas given off was so small, that I 

 could not ascertain whether it was, as it ought to be, oxygen at one wire and 

 hydrogen at the other. On substituting soUition of sulphate of soda for pure 

 water, these minute streams were still observed ; but the quantities were so 

 small, that on working the machine for half an hour, I could not obtain at 

 either pole a bubble of gas larger than a small grain of sand ; and if the che- 

 mical power be in direct proportion to the absolute quantity of electricity which 

 passes, this ought to be the case.' In paragraph 359 he says, ' It is doubtful 

 whether any common electrical machine has yet been able to supply elec- 

 tricity sufficient in a reasonable time to cause true electro-chemical decom- 

 position of water.' 



" Mr. Goodman, of Salford, near Manchester, who has published a very 

 ingenious essay ou the ' Modifications of the Electric Fluid," has, however, 

 succeeded in decomposing water by current alone, and with imr/uarded poles." 



We think it will be interesting here to give Faraday's views of induction 

 and conduction. " According to this philosopher, both induction and con- 

 duction ought to be considered the same in principle and action — every body 

 appearing to discharge in a greater or less degree, which makes them better 

 or worse conductors — worse or better insulators. He considers the first 

 effect of an e.\cited body upon neighbouring matters, to be the production 

 of a polarized state of their particles, which constitute induction ; and this 

 arises from its action on the particles immediately in contact with it, which 

 again act upon those contiguous to them; and thus the forces are transferred 

 to a distance. If the particles can maintain this polarised state, then insula- 

 tion is the consequence ; and the higher the polarised condition, the better 

 the insulation ; but if the particles cannot maintain their polarized state, if 

 they possess the power to communicate their forces, then conduction occurs ; 

 and the tension is lowered, conduction being a distinct act of discharge be- 

 tween neighbouring particles. Thus, as the higher the polarized condition 

 which the particles of the body can assume, the better insulator is that 

 body ; so is a body a better conductor in proportion to the inappetency of 

 its particles to retain a state of polarity. The discharge which takes place 

 between two conducting surfaces is termed disruptive ; it is the limit of the 

 influence which the intervening air or dielectric exerts in resisting discharge ; 

 all the effects prior to it are inductive, and it consequently measures the con- 

 servative power of the dielectric. It occurs not when all the particles have 

 attained to a certain degree of tension ; but when that particle which is most 

 affected has been exalted to the subverting or turning point, all must then 

 give way, since they are linked together, as it were, by the influence of the 

 constraining force, and the breaking down of one particle must, of necessity, 

 cause the whole barrier to be overturned. In every case, the particles 

 amongst and across which the discharge suddenly breaks, are displaced — the 

 path of the spark depending upon the degree of tension acquired by the 

 particles in the line of discharge. The spark may be considered then, as a 

 discharge, or lowering of the polarized inductive state of many dielectric 

 particles by a particular action of a few of the particles occupying a very 

 small and limited space : all the previously polarized particles returning to 

 their first or normal condition in the inverse order in which they left it, and 

 uniting their powers, meanwhile to produce, or rather to continue the dis- 

 charge effect in the place where the subverssou of force first occurred." 



Mr. Noad also says : — 



" It was with an apparatus constructed on the 

 principles of the Leyden phial, that Faraday suc- 

 ceeded in proving by the most decisive experiment 

 that induction has a particular relation to the diffe- 

 rent kinds of matter throuyh which it is everted. A 

 section of this ingenious contrivance is shown in 

 Fig. 7. a, a, are the two halves of a brass sphere, 

 with an air-tight joint at 4, like that of the Magde- 

 burgh hemispheres, made perfectly flush and smooth 

 inside, so as to present no irregularity ; c is a con- 

 necting piece, by which the apparatus is joined to a 

 good stop-cock d, which is itself attached either to 

 the metallic foot e, or to an air pump. The aperture 

 within the hemisphere / is very small : jf is a brass 

 collar fitted to the upper hemisphere, through which 

 the shell-lac support of the inner ball and its stem 

 passes; A is the inner ball, also of brass: it screws 

 on to the brass stem i, terminating above by a brass 

 ball B ; I, l,is Sl mass of shell-lac, moulded carefully 

 on to i, and serving both to support and insulate it 

 and its balls h, B. The shell lac stem / is fitted into 

 the socket p by a little ordinary resinous cement 

 more fusible than shell-lac applied at m, m, in such 

 a way as to give sufficient strength and render the 

 apparatus air-tight there, yet leave as much .is pos- 

 sible of the lower part of the shell-lac stem un- 

 touched as an insulation between the ball h, and the 

 surrounding sphere a a. The ball h has a small aperture at n, so that when 

 the apparatus is exhausted of one gas and filled with another, the ball h may 



also itself be exhausted and filled, that no variation of the gas in the interval 

 may occur during the course of an experiment. 



" The first substance submitted to examination was shell-lac, as compared 

 with air. 



" On making the experiment with all the care and attention that could be 

 bestowed, an extraordinajy and unexpected difference appeared, and the con- 

 clusion was drawn that the specific inductive capacity of shell-lac as com- 

 pared with air is as 2 to 1. With glass a result came out, showing its capa- 

 city compared with air to be as r76 to 1 ; and with sulphur a result showing 

 its capacity to be as 224 to 1. With this latter substance the result was 

 considered by Faraday as unexceptionable, it being, when fused, perfectly 

 clear, pellucid, and free from particles of dirt, and being moreover an excel- 

 lent insulator. 



" During the experiments with shell lac, Faraday first observed the sin- 

 gular phenomenon of the return charge. He found, that, if, after the ap- 

 paratus had been charged for some time, it was suddenly and perfectly dis- 

 charged, even the stem having all electricity removed from it, it gradually 

 recovered a charge which in nine or ten minutes would rise up to 50'' or 60°. 

 He charged the apparatus with the hemispherical cap of shell lac in it, for 

 about forty-five minutes, to above 600° with positive electricity at the balls 

 h and B, Fig. 7, above and within. It was then discharged, opened, the 

 shell lac taken out, and its state examined by bringing the carrier ball of 

 Coulomb's electrometer near it, uninsulating the ball, insulating it, and then 

 observing what change it had acquired. At first the lae appeared quite free 

 from anv charge, but gradually its two surfaces assumed opposite states of 

 electricity, the concave surface, which had been next the inner and positive 

 ball, assuming a positive state, and the convex surface, which bad been in 

 contact with the negative coating, acquiring a negative state ; these states 

 gradually increasing in intensity for some time. 



" Faraday was at first inclined to refer these effects to a peculiar masked 

 condition of a certain portion of the forces, but he afterwards traced them 

 to the known principles of electrical action. He took two plates of sper- 

 maceti and put them together, so as to form a compound plate, the opposite 

 sides of which were coated with metal. The system was charged, then dis- 

 charged, insulated, and examined, and found to give no indication to the 

 carrier ball : the plates were then separated, when the metallic linings were 

 found in opposite electrical states. Hence, it is clear that an actual penetra- 

 tion of the charge to some distance within the dielectric, at each of its two 

 surfaces, took place by conduction : so that to use the ordinary phrase, the 

 electric forces sustaining the induction, are not upon the metallic surfaces 

 only, but upon and within the dielectric ; also extending to a greater or 

 smaller depth from the metal linings." 



Mr. Noad in discussing the subject of chemical phenomena, page 196, says, 



" Chemical Phenomena. — Before entering upon this interesting branch of 

 our subject, it will be necessary that we describe the new terms introduced 

 by Faraday, and state his reasons for adopting them. According to the 

 views of this celebrated philosopher, electro-chemical decomposition is occa- 

 sioned by an internal corpuscular action, exerted according to the direction 

 of the electric current, and is due to a force either superadded to, or giving a 

 direction to the ordinary chemical affinity of the bodies present. He con- 

 ceives the effects to arise from forces which are internal, relative to the 

 matter under decomposition, and not erternal as they might be considered 

 if directly dependent upon the poles. He supposes that the effects are due 

 to a modification, by the electric current, of the chemical affinity of the par- 

 tides through or by which that current is passing, giving them the power of 

 acting more forcibly in one direction than m another, and consequently 

 making them travel by a series of successive decompositions and recomposi- 

 tions in opposite directions, and finally causing their expulsion or exclusion 

 at the boundaries of the body under decomposition, in the direction of the 

 current, and that in larger or smaller quantities according as the current is 

 more or less powerful. 



" What are called the poles of the voltaic battery are merely the surfaces 

 or doors by which the electricity enters into, or passes out of, the substance 

 suffering decomposition ; Faraday hence proposes for them the term electrodes 

 from riAfKTpov and o5os a way, meaning thereby, the substance, or surface, 

 whether of air, water, metaU or any other substance which serves to convey 

 an electric current into, and from the decomposing matter, and which bounds 

 its extent in that direction. 



" The surfaces at which the electric current enters, and leaves a decom- 

 posing body, he calls the oHOcfe, and the cathode ; from oro upwajds, and 

 o5os a wiiy,' — the way which the sun rises ; and Kara downwards, and o5os a 

 way, — the way xchich the sun sets. 



'•' Compounds directly decomposable by the electric current are called 

 electrolytes, from 7j\6KTpoi' and Auw to set free, — to electrolyze a body is to 

 decompose it electro-chemically ; the elements of an electrolyte are termed 

 iiins, from mv, participle of the verb fi^i to go ; anions are the iiins which 

 make their appearance at the anode, and were formerly termed the electro- 

 negative elements of the compound, and cations are the ions which make 

 their appearanc at the cathode, and were termed the electro-positive elements. 

 Thus chloride of lead is an electrotyte, and when electrolysed evolves two 

 ions, chlorine and lead, the former being an anion, and the latter a cation: 

 water is an electrolyte, evolving likewise two iiins, of which oxygen is the 

 anion, and hydrogen the cation : muriatic acid is likewise electrolytical, 

 boracic acid on the other hand is not." 



Another of Faraday's grand discoveries is that of definite electro-chemical 

 action. In the experiments on this subject he proved that water, when Bub- 



