The guantit,y of electricity generated in the above instances depends chiefly upon the superficial extent of the metals con cerned, and upon the activity of the li quid acting upon the generating metal ; and that it is considerable, even where small surfaces and weak acids are used, is manifest by the violence with which the magnetic needle of the galvanometer is deflected. But in the above described arrangements, the intensity of the elccr tricity is very feeble ; and in order to at, twin this, an to give the current that app parent impetus which it requires to tra verse bad conductors, and easily to effect electro-chemical decompositions, it be comes necessary to repeat the metallic al ternations ; or, in other words, to employ a properly arranged succession of gene rating, conducting, and electrolytic sub stances. This leads to the grand disco very of Volta; namely, the construction of the Voltaic Pile or Pattery.
In this arrangement, which, like the simple circles, admits of infinite varieties, the metals generally used are zinc on the one hand, and copper or silver or plati num on the other. The alternation,. )ri ginally adopted by Volta, and which are quite effectual, were zinc, silver, and flan nel or pasteboard soaked in acid ; and these were repeated according to the ef fects that were to be obtained. The in convenience of arrangement led him, however, to various modifications of it ; and, among thbm, to the use of a series of separate vessels, which he called the crown of cups (couronne des tasses,) and which, slightly modified, has since been very generally adopted. The flan nel is rejected, and in its place a cup of dilute acid, or other proper electrolyte, is substituted ; so that each silver and zinc plate are in metallic communication, though in separate vessels : the arrange ment being zinc, acid, silver; zinc, acid, silver, &c. Here the direction of the electric current is the same as in the sim ple circle, namely, from the zinc through the liquid to the silver; but in this form of the apparatus, for the mere conveni ence of carrying on the series, the con ducting wire connected with the first zinc plate has a supernumerary silver one at tached to it, and that, with the last silver plate a supernumerary zinc plate ; so that much confusion has arisen in regard to the direction of the current in these cases, in consequence of calling what is here the silver extreme the negative pole, and the zinc extreme the positive pole ; whereas it is in fact the reverse, and the circulation of the current goes on through the electrodes precisely as in the simple circle. But though the direction of the current is the same, and the absolute quantity of travelling or circulating elec tricity not increased, the case as regards , intensity is very different ; and with nu morons series arranged as above we ob tain, on removing the electrodes (which in this experiment ought to consist of pointed pieces of well-burned boxwood charcoal) a little from each other, a most brilliant and continuous current of fire, luminous, so that the eye can scarcely endure it, and capable of overcoming ob stacles and traversing conductors and electrolytes in a way essentially different from that of the simple circuit. Yet,
even with all these energetic phenomena, and with a quantity of circulating. elec tricity far beyond any thing which the most powerful frictional machines can af ford, the intensity is still insufficient to penetrate a thin layer of card or paper, or to make its way through non-conduct ing obstacles, as it does in the case of the discharge of the Leyden jar or battery. And now if the hands be well moistened with salt and water, so as to overcome the non-conducting tendency of the cu ticle, and the body be made part of the circuit, an extraordinary and unendura ble sensation is perceived, winch is in fact a continuous shock. By the same means wires may be ignited, metals burn ed, combustibles exploded, magnets made, and galvanometers affected at any distance from the pile, provided the con ducting communication is perfect. Thus it is that this power has been used to blast rocks, to explode gunpowder under water, and to communicate telegraphic signs, as in the arrangement of Professors Morse & Wheatstone, Messrs. Bain, ,House, &c.
But the most important modification of this instrument is that suggested by Mr. Daniell, and which he terms " a constant battery.". In all the preceding arrangements the electrical power is lia ble to fluctuation ; and after a time va rious causes induce such a falling off of its evolution as to render them inconve nient, or even useless, where continuous or regular action is required. In 1A'ol laston's battery, for instance, which is the best of them, several circumstances com bine to render it inconstant in its action : the adhesion of hydrogen to the copper plate, and the precipitation of zinc upon it, the saturation of the acid by oxide of zinc, and the local action which common zinc induces, are perhaps the principal sources of the above-mentioned irregu larity and inconstancy. In Mr. Daniell's arrangement those inconveniences are to a great extent obviated ; and although it is more complicated tfian the preceding, its constant and regular action, when it is properly constructed, amply repays the additional trouble and expense : there are, indeed, many investigations which can scarcely be carried on without it. (See ELacruo METALLURGY, for a view of Danicll's battery.) Under the articles ELEorno METALLVR:, er and TELEGRAPH are found descriptions of Voltaic batteries.
Not only are the ultimate elements of binary compounds evolved in obedience to certain uniform laws, but proximate elements are also similarly separated. Thus, when sulphate of soda, nitrate of potassa, and other neutral salts, are sub jected in aqueous solution to the action of the current, the respective acids travel with the oxygen to the anode, and the alkalies, oxides, or bases, with the hy drogen to the cathode. Faraday terms substances susceptible of these transfer ences ions, and those which go to the anode anions ; those to the cathode Ca thus doing away with the less de finite terms of etectro-negative and electro positive bodies.