81* 



vu.rmiv. 



I'HO-MKTALLURaY. 



could have 1 <il by a cast made with the copper in a state of 



fusion. Perhaps few fact* conmvted with the laws of aggregation of 

 < more striking than tin- on< under oongidera- 

 fuels iudirtvtly afford a more remarkable instance of the 

 chemi.-i! divNiliility of matter. The infinite gradations of tint pro- 

 duced on a silvered surface coated with v.i]vnir of iodine, ainl I 

 by light, in the proceaa of the IViguerreotypc. eon IK- copied with the 

 mot perfect accuracy by electm-mrtallurgy ; and it must be remem- 

 bered that thaw gradation* depend solely on variation* in tin- mole- 

 cular arrangement of a coating of mercury, with which the silver lias 

 \wn amalgamated, by exnoxing it to the vapour of that metal, too 

 thin to be manured, and defying microscopic power to detect. 



In order to admit of the copper during its deposition arranging itaelf 

 no M to assume a iiullc.iMc or true metallic texture, it is necessary 

 that the electrolytic action be not too rapid, accordingly the battery 

 should be weak in its action. Among other precautions which should 

 be mentioned is that of not reversing the connections, if at any time 

 during the process they should be broken, to allow of the progress of 

 the work being ascertained ; for if this should be done, the current 

 being reversed, the copper previously deposited on the mould will be 

 re-absorbed. And in order to keep up the equable and constant de- 

 posit which is necessary to ensure homogeneity in the metallic deposit, 

 the liquid solution, both in the vessel containing the mould and in the 

 lattery, must be kept constantly saturated by the addition of fresh 

 solid crystals of sulphate of copper: but in putting these into the 

 former vessel, care must be taken not to let the crystals touch the 

 mould ; and indeed the fluid in this vessel should not be disturbed if 

 possible during the process, which is easily insured by placing a suffi- 

 cient quantity of the salt in the vessel before the commencement of 

 the operation. 



The electrotype, as the above process was called, was first indicated 

 by Professor Daniell, of King's College, shortly after the invention of 

 the constant battery. He observed that copper deposited upon a plate 

 of platinum produced a coherent sheet, in which the lines and irregu- 

 larities on the platinum were correctly reproduced by the copper. In 

 1839, Mr. Spencer, and Mr. Jordan in this country, and M. Jacobi, of 

 St. Petersburg, announced their invention of that process, at least in 

 its main features, as above described. The electrotype at once became 

 a popular pursuit Thousands of amateurs occupied themselves in 

 copying medals, seals, plaster casts of medallions, vegetable objects, 

 such as twigs, fruit, leaves, seeds, and even insects ; but the subject 

 was too suggestive to be neglected by manufacturers, and accordingly, 

 in the following year, Mr. Elkington, in England, and M. Ituolz, in 

 France, began to apply the voltaic battery on an extensive scale to the 

 arts of plating and gilding. Innumerable patents have been granted 

 for new processes, or variations of old ones, and the electric current 

 came to be used not only for depositing copper, gold, and silver from 

 their solutions, but also zinc, tin, lead, platinum, and nickel. Many 

 other metals have also been reduced from their salts by its means 

 when required for special purposes. Original inquirers at home and 

 abroad, have lent their aid in investigating the subject, and the 

 result has been a wide extension of electro-metallurgy to other arts, 

 irach as stereotyping and nature-printing; it has been used for 

 making moulds for the foundry, for reproducing printed characters, 

 copper-plates, wood engravings, rollers for the calico printer, copper- 

 plate engravings, daguerreotype pictures, &c. Such are a few of the 

 varied applications of the art, and we will now give an example of 

 one of its important applications, and connect it with some general 



an . :- 



The electrotype has been used for multiplying large copper-plates, 

 such as those engraved for the Art Union, for which purpose a matrix 

 is first produced, in which all the sunk lines of the original plate are 

 represented in relief in the copy or matrix, and this is used as the 

 parent of succeeding copies. In forming the matrix, a slip of copper 

 is soldered to the original plate, the back of which is covered with 

 a resinous varnish to prevent it from receiving a deposit of the reduced 

 metal, and thus prepared, the plate is lowered vertically into a 

 saturated solution of sulphate of copper, and connected with the 

 negative pole of a voltaic battery, which may consist of three or four 

 of Smee's or Darnell's cells. Connected with the positive pole of the 

 battery is a sheet of copper, equal in size to the one to be copied, and 

 placed parallel to it. The solution immediately begins to be decom- 

 posed; metallic copper is deposited on the surface of the negative 

 plate, while an equivalent quantity of copper is dissolved from the 

 positive plate, by which means the solution always retains an equal 

 quantity of sulphate of copper. The process requires watching at the 

 commencement, to gee that the deposit is uniform, for should the 

 negative surface be soiled with grease or resin, no deposit will tike 

 place in those parts. The solution also requires to lie frequently 

 agitated, to prevent it from In-coining ini|>vcrisl)i>d about the negative 

 pUte.and too much Maturated about the positive plate, for should such 

 occur, the unequal density of the solution will cause current 

 in, whereby vertical groove* ami Kt.ru- will ! formed on the I Kick of the 

 sheet of deposited metal. To prevent these ell'ucts, the | ilatc.s ;ire some- 

 supported horizontally in the Irnth, the negative plate being 

 undarmott, bat in such caw the positive plato must b wrapped in 

 flannel to pit-vent tin- wmll particles of mctil, which are constantly 

 leaving it, from falling upon the lo.vcr pint.-. Win n the deposit is 



sufficiently thick, it is detached at the edges, and can be easily 

 removed. 



Tin- text it I" the deposited plate depends upon four circumstances : 



. : 2, the degree of concentration of the 



solution ; :i. it* temperature ; 4, the relative size and position of the 

 two electrodes. As these conditions vary, the deposit may be as hard 

 and brittle as steel, as soft and flexible as lead ; of a crystalline texture. 

 and even pulverulent. M. Boquillon has found, other things being 

 equal, that if the positive electrode be of larger sine than the negative, 

 the deposit will be crystalline, and if the ilill'erenci- between tin- 

 two plates be considerable, the deposit may be pulverulent. The 

 contrary effect takes place, if the positive electrode be the smaller of 

 the two. Similar results may arise from an increase in temjicrature. 

 In the case of the solution, if it be completely saturated, the deposit 

 will be hard and brittle ; if less saturated, it will be more flexible, 

 and if weak, it will be spongy, crystalline and even pulverulent. 

 :-oneralisations. however, do not apply to all the metals, for 

 many of them are thrown down from their solutions in a cry- 

 form, whether the deposition be made quickly or slowly, 

 behaves in this way when separated from its nitrate, and lead 

 from its acetate and nitrate. Gold and platinum do not form coherent 

 plates from solutions of their chlorides, but it sometimes happens 

 that where the solution of a simple salt fails, good results may be 

 obt-uned by the use of certain double salts of the same met.-il. with 

 potash or soda: thus, the double cyanide of gold and potassium is 

 used for gilding, and a similar salt of silver for silvering. 



Steel plates do not admit of being copied in the same mair 

 ''I 'pei plates, since the steel and the sulphate of copper solution act 

 chemically on each other, but by first electrotypine the steel plates in 

 silver, which can be deposited without injury to them, and using the 

 silver as a matrix, a copper fac-simile of the original plate can be 

 obtained. 



In copying objects which would be injured by immersion in the 

 metallic solution, we have seen that the early electrotypists to< il 

 in wax, and made the surface conducting, by rubbing it over with 

 finely divided black-lead. Casts are now made in fusible metal. 

 stearine, or gutta-percha; in the last case, two parts of gutta-percha, 

 and one part of marine glue should be used, the glue to be melted at a 

 gentle heat and incorporated with the fragments of gutta-percha. In 

 taking a cast, the paste is to be applied soft, and with a gradually 

 increasing pressure. In some cases, an impression of the object to be 

 copied is obtained in sheet lead, by the application of a strong pressure, 

 as for example, in what is called nature-printing ; suppose a frond of 

 fern is the object to be copied, this is placed between a plate of steel 

 and one of sheet lead and so passed between a couple of steel rollers 

 in a press. The soft lead receives the markings of the plant, so as to 

 indicate its structure very minutely, and from this leaden impression 

 a copper deposit or matrix can be formed, from which other i i 

 type plates are procured, well adapted for printing. When natural 

 objects, such as leaves, flowers, insects, &c., have to be coated with 

 metal, they are made conducting by being immersed in a weak solution 

 of phosphorus, in bi-sulphide of carbon, or in ether, allowing the 

 solvent to evaporate, and then plunging the object into a solution of 

 nitrate of silver : the phosphorus 'reduces upon the object a very thin 

 film of silver, which enables it to receive the deposit from the battery 

 when placed in a metallic bath. 



In copying small objects, a separate voltaic battery is not required, 

 since the depositing cell may itself be converted into a voltaic couple : 

 for example, an arrangement may be extemporised by means of the 

 chimney of an Argand gas-burner, closed below by means of plaster of 

 Paris, and supported in a vessel containing the sulphate of copper 

 solution. The lamp-glass is to contain dilute sulphuric acid, and also 

 an amalgamated zinc rod. From this rod proceeds a wire, which 

 supports at its other end in the copper solution the mould or medal 

 which is to be electrotyped. Crystals of sulphate of copper should be 

 suspended in the upper part of the solution to keep it saturated. 



Surface-Deposit, in Electro-Plating. In the common manufacture of 

 table-plate the articles are either made of standard gold or si I 

 have a surface of these costly materials laid upon a foundation of 

 cheaper metal ; and it is as an improved mode of applying the gold 

 or silver that the electro process has been chiefly introduced. Messrs. 

 Elkington, of Birmingham, have obtained considerable celebri 

 their electro-plated and gilt articles. The metal employed by them as 

 the basis is a hard, white alloy of copper, nickel, and zinc, and fusible 

 only at a high temperature; but silver can be readily deposited on brans, 

 copper, bronze, and German silver. If the article is to i- pvodii 



'in;?, the alloy is rolled into thin sheets, which are 

 worked up into form by the stamping-press or the hammer. [CIIASIM; 

 OP METALS.] But when the article is to be cast (which the more 

 i e patterns generally ai i, from which 



is made a brass cast, or " pattern," and this is carefully worked up by 

 chasing-tools to the proper fineness and delicacy of detail. From this 

 brass pattern is made- a sand-m.mld : and in this nod-mould the ai 

 itself is cast in the alloy or white metal. Thin is made chemically 

 clean by boiliug in an alkaline solution, or heating to redness in a 

 muffle, washing, and brushing with sand, and dipping in nitric acid, in 

 i prepare it for tl ! i of the silver; for it is an impor- 



tant object in electro-gilding, silvering, and zinking, to obtain 



