11 



Kl.lXTUO-CHEMIS; 



ELECTRO-DYNAMIC3. 



au 



odium at lh negative one. The chloride* of aluminium, inagneiium, 

 barium, calcium, etc., yield up their metal t the negative pole. In 

 MOO electrolyai*, special precaution* utuit l taken to prevent the 

 BMUl from becoming ro-oxidiwd, (or the detail* of reduction by such 

 mean*, aw An MI.MI M, CALCIUM, lUaxuiUM, 4o. It may be here 

 mentioned, that fur this purpoae it i* usual to employ mixed chloride*, 

 the rotting point* of auch mixture* being lower than those of the 

 simple chloride*, and the purity of th reduced metal not being 

 impaired by the preeenoe of other metal* in the electrolyte, became 

 the more loctro-uoaitive ia wparmted in preference to the lea electro- 

 poaitiT*. 



Anwumple of the importance of the light which may be thrown upon 

 the constitution of a compound substance by the electrolytic separa- 

 tion of iu part* into the moat electro-poaitive and electro-negative of 

 it* oooctituenti, U furnished by the behaviour of the salt* of the fatty 

 acid* toward* the electric current If valerianate of potash, whose 

 empirical formula ia KG C IO H,O,, be electrolysed by mean* of plati- 

 num electrode* aeparatad by a porous diaphragm, polonium (that in, 

 potaah and hydrogen), appear at the negative pole, while carbonic acid 

 and butyl appear at the positive. 



KOC,,H,0, + BHO = H + KO + C.H, + SCO, + (n 1) HO 



Yilrriuutc of potaih. Butyl. 



Whence the formula expressing the electro-chemical constitution of 

 valerianic acid is derived. 



H, C.H,, SCO,. 



If a piece of zino be immersed in a solution of dilute sulphuric 

 acid, ao that a part of it is above the liquid, an inactive metal, such as 

 platinum (that is, one which is not attacked by the acid), which con- 

 nect* the part of the zinc attacked with the part above the liquid, is 

 found to be traversed by an electric current. This is the type of the 

 formation of all electrical currents by chemical change. And if we 

 aasume arbitrarily that the current passes only in one direction, 

 namely, from the part of the zinc attacked to the part unattacked, 

 then the direction of the current in this example gives us the direction 

 of the current in all other cases where metals are attacked by acids. 

 Hence when, in the same acid, two metals are placed, of which the 

 one is attacked, the other unattacked, by the acid, a current passes 

 through the liquid from the attacked to the unattacked metal, if 

 metallic contact be established between them above the liquid. But if 

 such metallic connector be broken, and the ends plunged into a liquid 

 containing an electrolyte (Jig. 1), then such an arrangement of active 

 and passive metal constitutes a battery. The most simple method of 

 interpreting such an arrangement with regard to the " signs " of its 

 part* electrically considered, is by remembering that the port of the 

 zinc immersed is positive ; the part out of the acid, together with the 

 connecting wire and attacked electrode, is negative ; thivoppositc elec- 

 trode, where the chlorous element is eliminated, together with the 

 whole of its platinum connection, as far as the surface of the liquid in 

 the battery, is positive. The port immersed in the liquid of the 

 battery is negative. Thi* comes to the same thing as saving that the 

 positive ion is liberated at the electrode in connection with the positive 

 element of the battery, the negative ion at that connected with t In- 

 negative element It must be borne in mind, that the ions appearing 

 at the two electrodes are not altsulutely positive and negative towards 

 one another. All that is known is that they are in the some relation 

 with regard to sign, as are the elements of the battery by whose action 

 they are separated ; and that thus, with regard to sign, all we know on 

 decomposing chloride of silver by means of a Grove's battery is that 



Ag : Cl : : Zn : Pt. 



That electric currents are established between the active and passive 

 point* of a metal, and that the positive current pastes from the active 

 to the passive part, is seen in the example of so-called passive iron. If 

 clean iron be dipped into strong nitric acid, no evolution of gas occurs, 

 and the iron is not acted on. If another piece of iron be first plunged 

 into dilute nitric acid, and then into the strong nitric acid, the decom- 

 position set up in the dilute acid is carried on in the strong acid. It 

 is possible thus in one and the same acid to have two pieces of the 

 name metal, the one of which is active and the other jKuwive. On con- 

 necting the two, a current passes through the connector, just as if 

 platinum had been employed instead of the passive iron. Nickel may 

 by the same means be brought into the passive state, and a battery 

 formed of element* of active and passive nickel. It is beyond the 



of iron i* destroyed or preserved. 



The power poaseoed by high tension or frictional electricity of 

 dfcoifag chemical change is very small in comparison with that of low 

 tension or galvanic electricity; and in many case* where chemical 

 change accompanies frictional electricity, it may be traced to the accom- 

 panying forces of light and heat 



If an electric spark be made to pass through an atmosphere of mixed 

 oxygen, nitrogen, and water, the nitrogen combines with the oxygen in 

 part and in part with the hydrogen, the two products so formed 

 combining together. 



If a spark be made to iass through water by means of exceedingly 



fine platinum poiuU, minute bubble of hydrogen and oxygen collect 

 at the pole*. 



Mixtures of oxygen and hydrogen, or hydrogen and chlorine, are 

 exploded on liaising a ipark through them. 



The following are example* of the formation of high tension elec- 

 tricity by chemical change : 



The insulated grate of a stove in which coal is burning is found to 

 be negatively electrical. If hydrogen ramm through a metal tube, and 

 is then burned, the tube is found to be negatively electrical. If dry 

 air and chlorine be passed through a thin copper tube, the latter 

 becomes negatively electrical ; if the product be then passed through a 

 platinum tube, the latter becomes positively electrical. 



With regard to the relative powers of low and high tension elec- 

 tricity to effect chemical change, it has been found that " A wire of 

 platinum and a wire of sine, each Ath of an inch in diameter, placed 

 , s thi) of an inch apart, and immersed to a depth of }th of an in. h iu 

 an acid consisting of one drop of oil of vitriol in four ounce* of distilled 

 water, at a temperature of 60 Fahr., and connected at their other 

 extremities by a copper wire 18 feet long and Ath of an inch thick, 

 yield as much electricity in about three seconds of time a* a I. 

 battery exposing a surface of 3500 square inches, charged by 80 turns 

 of a plate-glass machine 60 inches in diameter in full action. 



ELECTRODE. [ELKCTRO-CIUUUSTHY.] 



ELECTRO-DYNAMICS. In ordinary electricity, that fluid when 

 developed takes a position of equilibrium, dependent on the conducting 

 power of the medium on which it is disposed, on the non-conducting 

 power of the medium by which it is enveloped, and on the law of force, 

 whether of attraction or repulsion, between the elementary portions of 

 electricity. The motions of electrised bodies are only results of the 

 statical equilibrium of this fluid, and do not therefore belong to electro- 

 dynamics. The mode of calculating such effects may be found under 

 the head ELECTRICITY, COMMON. These effects are, moreover, of the 

 same nature, whether the source of electricity be by means of friction, 

 or by chemical action, as in the voltaic pile, the nature of the elec- 

 tricities in these cases differing from each other only in the modi' of 

 their production [ELECTRICITY] ; but when the contrary electricities 

 are no sooner produced than re- combined, again re-produced, and again 

 re-combined, a new class of phenomena arises belonging to electricity as 

 it were in motion. Suppose, for example, that the plate A is a constant 



ft 



1 



source of positive electricity, the plate B in like manner a constant 

 source of negative electricity of equal intensity ; that A c, B c, are two 

 conducting rods communicating with each ; the electricities immediately 

 combine when the conductors are made to touch at c, and for an instant 

 the whole may be conceived to be in the neutral state, but A being the 

 next instant replenished with positive and B with negative electricity, 

 the same combination takes place over again, the some neutrality suc- 

 ceeds, and so on indefinitely. The rod A o B is in a different condition 

 from one in its natural state, since electrical charges are continually 

 pouring through it from A and B ; and again it is in a different con- 

 dition from on electrised rod, since we cannot at any moment say 

 that it is charged positively rather than negatively. Hence we cannot 

 infer that it should attract rather than repel an electrised ball n, since 

 there is as much reason for one event as the other, and in point of fact 

 we find that it neither will attract nor repel D. We have here a posi- 

 tive current of electricity issuing from A and a negative from B, and no 

 effect of attraction or repulsion is produced on an electrised point as in 

 statical electricity. How then is its state recognised ? First by touch ; 

 for if we touch the rod ACS, a series of shocks is felt, the inter- 

 val between two succeeding ones being inappreciable ; and secondly, 

 powerful chemical decomposition may be effected. [GALVANISM ; 

 ELECTRO-CIIEMISTIIV.] But, thirdly, we may recognise it mechanically 

 by presenting to A B another rod A' B' under exactly similar circum- 

 A B 



A'- 



stances, when the effects of the currents in A B, A'B', will be recognised 

 by the visible motions of the rods, provided they be free to move while 

 their communication with the proper sources of electricity remains 

 unbroken : for example, if their extremities be immersed in cups of 

 mercury communicating with the constant sources of the positive an. I 

 negative electricities. The laws of the mutual action of el 

 currents constitute the science of electro-dynamics ; and previous to its 

 study it would be desirable that the reader should be acquainted with 

 the construction and applications of the galvanic apparatus, the oppo- 

 site poles of which afford the two constant sources (A B) of electricity 

 which we haw supposed. These will be found under the head 

 GALVANISM. 



To discover the laws of the mutual actions of electrical current* we 

 must have recourse to experiment The apparatus required for the 

 purpose is figured in books on physics, together with a description of 

 the mode of performing the various experiments by which these laws 

 have become known. [ELKCTRO-MAauKTlSH.J The term direcli" / 

 a current is convenient when speaking of more than one ; for instance, 



