ELECTROLYTE 



2854 



ELECTRO-METALLURGY 



arrangement indicated in the dia- 

 gram, which represents the original 

 voltameter. A and B are inverted 

 glass test tubes, each having intro- 

 duced into it at the bottom one of 

 the electrodes. The tubes are first 

 filled with the electrolyte the 

 water, which is usually slightly 

 acidulated to facilitate the action 

 and when the current passes, the 

 gases which are released at the 

 surfaces of the electrodes rise to 

 the top of the tubes and displace 

 the liquid. Two notable points are 

 to be observed here : the gases 

 collect separately, and no action 

 whatever is apparent in the body 

 of the bath between the two tubes. 

 But, obviously, when oxygen in 

 the one tube is set free, hydrogen 

 must be liberated at the same in- 

 stant ; the latter does not, how- 

 ever, collect side by side with the 

 oxygen in the tube where it is 

 separated, but by some invisible 

 action passes out of that tube 

 across the bath and appears in the 

 other tube. Similarly, there must 

 be a migration of the oxygen from 

 the hydrogen collecting tube back 

 to the oxygen tube. Thus one of 

 the elements separated travels 

 with the electric current and the 

 other against it ; to the former 

 Faraday gave the name cation, 

 meaning that which goes down, 

 and to the latter the term anion, 

 or that which goes up. No theory 

 yet propounded fully explains the 

 phenomenon indicated. 



The phenomenon of electrolysis 

 is not only profoundly interesting 

 from the purely scientific point 

 of view, but it has received in- 

 dustrial applications of the first 

 importance. Electro-metallurgy 

 depends largely upon it, and 

 electro-chemistry wholly. The 

 phenomenon may not, however, be 

 always beneficial. In industrial 

 practice the electric current is 

 generated and caused to flow 

 through the cells by means of a 

 dynamo ; but a current may be 

 induced in the cell itself, as in the 

 ordinary voltaic or galvanic bat- 

 teries, by the employment of two 

 dissimilar metals immersed in a 

 suitable electrolyte. A current 

 may even be set up between two 

 metals of the same kind, provided 

 there be a slight difference in their 

 molecular or chemical structure. 

 Such a current may be very slight, 

 but still sufficient to set up elec- 

 trolysis if other conditions are 

 favourable. Hence, in the case of 

 machinery or metal structures 

 immersed in water, or hi solutions, 

 we may have all the conditions 

 necessary to set up electrolytic 

 action and decomposition. See 

 Cell; Electro-Chemistry; Electro- 

 Metallurgy; Voltameter. 



Electrolysis. A and B arc inverted 



test-tubes collecting the oxygen 



and hydrogen set free from water 



by electrolytic action 



Electrolyte. Term given by 

 Faraday to a substance capable of 

 being electrolysed. It is thus the 

 term by which the bath of an 

 electrolytic cell is known ; it may 

 be either a solution such as a 

 dilute acid, or of a metallic salt 

 such as sulphate of copper, or it 

 may be a mass of molten metallic 

 compound. See Electrolysis. 



Electro-Magnetism. Term 

 used for the branch of science 

 which deals with the connexion 

 between electrical and magnetic 

 phenomena. In 1819 Hans Chris- 

 tian Oersted (q.v.) discovered that 

 a wire conveying an electric current 

 is surrounded by a magnetic field, 

 and that a freely moving magnetic 

 needle sets itself at right angles to 

 the wire carrying the current. 

 Oersted's discovery was followed 

 by the researches of D. F. J. Arago 

 and A. M. Ampere and others, but 

 it remained to Michael Faraday 

 (q.v.) to show how to obtain elec- 

 tricity from magnetism, and there- 

 by lay the foundations of the 

 modern dynamo and the extensive 

 electrical industry of the present 

 day. See Dynamo ; Electricity ; 

 Magnetism. 



Electro-Metallurgy. The most 

 important advance in metallurgy 

 since the development of the Bes- 

 semer and Thomas-Gilchrist pro- 

 cesses is represented by the appli- 

 cation of electricity to the extrac- 

 tion of metals from their ores, and 

 to metal refining. In its broad 

 sense the term electro-metallurgy 

 covers the entire field of the 

 electrical treatment of metalliferous 

 ores and the working of metals 

 by electricity, and thus includes 

 electro -plating, the use of the elec- 

 tric furnace, and electric welding, 

 all of which subjects are treated 

 under their respective headings. 



Electro-metallurgy is an entirely 

 modern art which sprang into life 

 after the discovery by Volta of the 

 galvanic cell in the first year of 

 the 19th century. Three different 

 types of processes occur in this 

 branch of metallurgy ; first, those 



in which the action is purely elec- 

 trolytic, i.e. does not depend on 

 any heating effect of the electric 

 current ; secondly, those in which 

 electrolytic action and heating are 

 combined ; and thirdly, those in 

 which the effect desired is brought 

 about solely by the heat developed 

 by the electric current. 



The first class of these processes 

 is well represented by the electro- 

 lytic refining of copper, by which 

 the larger portion of the metallic 

 copper of the world is now pro- 

 duced, nearly the whole of the 

 production of the U.S.A. being so 

 treated. The principle of the pro- 

 cess has been explained in the 

 article electrolysis ; in practice the 

 material operated upon is either 

 " blister " copper or converter 



Electro-Metallurgy. Diagrammatic 

 view of copper-refining vat. See text 



copper (see Copper). Both contain 

 considerable impurities, including 

 gold or silver, and usually some of 

 each, and the treatment may be 

 either chiefly a pure refining opera- 

 tion or a process for the recovery 

 of the precious metals, which are 

 frequently present in sufficient 

 quantities to pay for the cost of 

 the entire treatment. 



The operation is carried out in 

 large wooden vats" as indicated in 

 the accompanying illustration, - 

 where A represents a plate of the 

 crude copper to be refined (the 

 anode), and B, a very thin plate of 

 the purest copper available, usu- 

 ally electrotype copper (the cath- 

 ode). The bath in which the plates 

 are suspended (the electrolyte) is 

 a solution of copper sulphate in 

 water acidulated with sulphuric 

 acid, the whole forming an electro- 

 lytic cell. The electric current from 

 a dynamo enters the cell at +, 

 passes through the plate A, across 

 the bath, up the plate B, and out 

 at . The current decomposes the 

 solution, throwing out the copper 

 which is deposited in a practically 

 pure condition on the cathode, the 

 thin copper plate. At the same 

 time the plate of crude copper 

 begins to be broken down ; the 

 copper goes into solution taking 

 the place of that removed from the 

 solution and deposited on the 

 cathode ; any iron and zinc present 

 in the crude metal will also be dis- 

 solved; but the gold, silver, and fre- 

 quently other metals present, while 



