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ELECTRO-METALLURGY 



Imperial Academy of Sciences. But, on the other hand, neither Mr. Jordan nor Mr. 

 Spencer appears, as far as wo are aware, to have been so sensible of the importance 

 of the results to which they had arrivrd as to have taken any steps to secure them 

 as an invention or to publish them, until their attention was roused by the previous 

 publication of the successes of Jacobi. 



.lacohi's ' Galvano-plastik,' Smee's and also Shaw's ' Electro-metallurgy,' Walker's 

 * Electrotype Manipulation,' four well-known works on the subject before us, present 

 the different names under which the art is known ; and from which it is gathered 

 that metals may become, as it were, plastic under the agency of galvanic electricity, 

 and may be worked and moulded into form. Voltaic pairs are described in general 

 terms in the article on ELECTRO-TELEGRAPHY. The particular voltaic pair which led 

 to the discoveries now before us, hero requires special notice ; because, on the one 

 hand, while in use for other purposes, it was the instrument which 

 first directed attention forcibly to the behaviour of metals under 

 certain conditions of electric current ; and, on the other hand, it 

 has been itself extensively used in electrotype operations. Pro- 

 fessor Daniell first described his mode of arranging a voltaic pair, 

 in the ' Philosophical Transactions,' for 1836. Fig. 792 shows one 

 cell complete of Daniell's combination, which from its behaviour 

 is called a constant battery. A is a copper yessel ; B a rod of 

 zinc, contained in a tube c of porous earthenware. The liquid 

 within the tube c is salt and water, in which case the zinc is in 

 its natural state ; or, sulphuric acid and water, in which case the 

 zinc is amalgamated ; the latter arrangement being the more active 

 of the two. The liquid in the outer vessel A, consists of crystals 

 of sulphate of copper, dissolved in water. At c is a perforated 

 shelf of copper below the surface of the liquid, upon which are 

 placed spare crystals of sulphate of copper, which dissolve as re- 

 quired, and serve to keep up the strength of the solution in pro- 

 portion as the copper already there is extracted by the voltaic 

 action hereafter to be described, a and b are screws, to which 

 wires may be attached, in order to connect up the cell and con- 

 vey the current from it into any desired apparatus. Certain chemical changes take 

 place when this instrument is in action : oxygen, from the water within the porous 

 tube, combines with zinc, making oxide of zinc, which enters into combination with 

 sulphuric acid, producing as a final result sulphate of zinc ; hydrogen is liberated 

 from water in the outer cell, and itself liberates oxygen from oxide' of copper, and 

 combines with it producing water, and leaving copper free. As far as the metals 

 are concerned, zinc is consumed from the rod B, at the one end, and 

 copper is liberated upon the plate A, at the other end. These 

 actions are slow and continuous ; and the copper, as it is liberated 

 atom by atom, appears upon the inner surface of the cell ; and 

 after a sufficient quantity has been accumulated, may be peeled 

 off or removed ; when it will be found to present the marks and 

 features of the surface from which it has been taken, and which, 

 as we have already said, arrested the attention of many into whoso 

 hands this instrument fell. A slight modification of the above 

 c arrangement gives us a regular electrotype apparatus. Tho cell 

 c in this arrangement (fig. 793), is of glass or porcelain, or gutta- 

 percha, filled as before with a saturated solution of sulphate of 

 copper, to which a little free acid is generally added ; it is provided 

 with a shelf or other means of suspending crystals of sulphate of 

 copper. A zinc rod z is placed in a porous tube p, as already do- 

 scriU-d ; and m, the other metal of the voltaic, pair, is suspended in 

 the copper solution and connected with the zinc z by the wire w. 

 Tho electric current now passes; zinc is consumed, as in Jiff. 792, but copper is now 

 deposited on the metal m front and back, and on as much of the wire w as may be in 

 the liquid ; or, if Mr. Spencer's precaution is taken of varnishing the wire and (lie 

 back of the metal m t all the copper that is liberated will !>< accumulated on the face 

 of m. If salt and water, or very weak acid water, is contained in the porous lube, p, 

 and the zinc z does not considerably exceed in si/e the met.-il //?, the conditions will l>e 

 complied with for depositing copper in a compact regnlino form. 



It is obvious that, with this arrangement, m maybe a mould or other form in 

 metal, and that a copy of it may be obtained in copper. Fusible metal, consisting 

 of 8 parts of bismuth, 4 of tin, 5 of lead, and 1 of antimony ; or <S parts bismuth, 

 3 tin, and 5 lead, is much used for taking moulds of medals. Tho ingredients aro 

 well melted together and mixed ; a quantity sufficient for tho object in view is 



