Page:The New International Encyclopædia 1st ed. v. 06.djvu/896

* ELECTRO-CHEMISTRY. 780 ELECTRO-CHEMISTBY. place without producing electrical energy. Tims. the reaction of a Daniell cell can be produced b.v simply immersing a bar of zinc into a solution of copper sulphate. In that case the change is accompanicil by the evolution of a detinite anioiuil of licat. The question therefore arises, Can all that "heat of the reaction" be transformed into electrical energy or not? At one time this question was answered in the allirmalive (Thom- son's law"). But Wilhird tiibbs and Jlelmhollz have proved thermodynamically. and it has since been demonstrated experimentally, that the elec- trical energy of a cell need not by any means equal the heat of the reaction: that, on the con- trary, the latter is generally greater than the former, so that even in perfect cells (producing a maximum of electrical energy) a rise of tem- perature might generally be observed. See TilEKJlO-CllEMISTBY. lliSTOUy. The earliest electrochemical ob- servation on record was made by Deimanu and I'aets van Troostwyk, of Haarlem, in 1789. The experiment was carried out as follows: a glass tube with one end closed and the other open, and with a metal wire sealed into the closed end, was filled with water and inverted over a dish of water; a second metal wire was passed through the open end of the tube, up to within some distance of the end of the upper wire; and electric sparks were caused to pass between the ends of the two wires. The result was that water was decomposed into its constituents, oxygen :ind hydrogen, a mixture of which collected in the upper part of the tube. As long as the end of the uppej' electrode remained innnersed in water, nothing further happened; but the instant the end of the electrode became exposed to the mix- ture, a violent exiilosion took place, owing to the recombination of the two elements. In a similar manner, Kitter afterwards carried out the first true electrolysis, using silver wires as electrodes and a solution of a silver salt as the electrolyte. Then came Volta's celebrated experiments, which resulted in his invention of voltaic batteries (see Voi.T.ic Kattery) ; and in 1705 Volta was able to prepare the first electro-chemical series. An a])preciation of the work of Davy and Berzelius, and of the sway of Berzelius's ideas exercised for many years in the science of chemistry, may be found in the article Chemi.stry (historical sec- tion). Faraday's discovery, in 1S:U. of the true laws of electrolysis marked a great step forward both in I'liemistry and in the science of electricity. The conception of energy, of its several forms, and of their mutual transformations, was devel- oped in course of the fifth and sixth decades of the nineteenth century, and in 1847 llclmholtz first advanced the belief that the heat of the chemical reactions of a cell may he entirely transformed into electrical energy. Having been again brought forward by Thomson in 18.51, the belief became known in science as 'Thomson's law.' The researches establishing the true relation were carried out by Gilibs in 1878 and by Helniholtz in 1882, and were completed by the exiKrimental investigations of Czapski and Jahn. In 1880 Van't Holl' introduced the modem theory of osmotic pressure (see Sonrxiox), and in 1887 .Arrhenius advanced the theory of elec- trolytic dissociation (see Dissociation), which is at the basis of the most importjint chapters of modern electrocliemislry. The idea that electrolytes must be more or less broken up in their solutions originated with Clausius; but .rrlienius was the first to give to it its present (pianlitative form, to connect it with the theory of solutions, ami to demonstrate its great ini- jiortance for theoretical chemistry. The re- searches of Hittorf on the relative rates of trans- portation of the ions during electrolysis were carried out as early as 18.5;{ to IS.")'.', but gained great scientific importance only after Arrhenius established his theury of dissociation. Other important names connected with the progress of general electro-chemistry are those of Ustwahl, Xernst, Planck, l.e Blanc, and Ivohlrausch. The concept of electrons originated in Helnduiltz's lectures on Faraday's ideas of electricity, deliv- ered in London in 1881. Among those who liave contributed to the recent development of this promising ide;i are Xernst, .begg. and Bodliinder. B:blio(hai'11v. .lalin, dndnliiKu tl); Loeb, <!ruiid::uge der Eleklrocheiiiie (Leipzig, 1897); Haber, (Jriind^iige dcr tcchnischt'ii EleKlrochcmie auf thearetischer Orundliiye (l.*ipzig, 1898): Liipke, (Jriindziige der Eleklrochemie (Berlin, 1899) ; Jones, The Theory of Eleetrolytie Oixso- rintion and Nome of Its Applicatioiin (Xew York, 1900) ; Jones, Oiitliiiis of Elrrlro-Chemifitry (Xew York, 1901); Arrhenius, l.chrbuch der Elektrochemie (Leijizig, 1901); Xernst and Bor- chers (editors), jiihrbiieh der Elektrochemie (Halle). See Chemistry ; Electkk'ITY; Voltaic- Cells: Dissociation; Solutiox; Ax.ly.sis, ClIE.MU'AL. ELECTRO - CHEMISTRY, Lnihstrial.' Electro-chemical processes are now employed in extracting metals from their ores and in ])arling them from their alloys ; in the deposition of certain of the finer metals upon the surfaces of baser metals, and other materials; in the manu- facture of various chemical products employed in the arts, and for various mi'-cellaneous pur- poses. The processes of electrometallurgy, by which metals are extracted from these ores or parted from these alloys, can be best considered in the articles describing those metals and their production. See ALr.Mixust; Copper: Gold; XicKEL; Silver; Zixc; etc. . The electro-deposition of certain metals upon the surfaces of other substances is called electro- plating. When electro]il;iting is employed as a means of copying printing-type, medals, seals, woodcuts, etc., it is called elect rotyjiing. The metals commonly used for electroplating other metals are aluminium, copper, nickel, silver, and gold, which are in each case made the anode or positive pole of a voltaic current, while the metal to be coated is made the cathode or nega- tive |)ole. The electrolyte or immersing bath is dill'erently composed, according to the metal which is to be deposited. The electro-deposition of aluminium was em- ployed on a very large scale in constructing the tower of the Piiiladelphia City Hall, in which the iron columns and plates were electroplali'd with this metal. .Some of the largest eolunms which were plated were 2 feet long and 3 feet in diameter at the largest end. The various operations were as follows: (1) Preparation of the iron coluuuis by boiling in caustic soila. l)ickling in acid, and scouring; (2) plating with