September 15, 1892J 



NATURE 



479 



One of the wonderful things about the eleclro-deposition of 

 copper, and in fact any other metal deposited from a solution of 

 its salt in water, is, that bright, hard, solid metal, such as we 

 are accustomed to see produced by means of fusion, can, by the 

 action of the electric current, be made to separate from a liquid 

 which has no appearance of metal about it. 



The beginning of every electro- deposition process is the making 

 a solution of the metal to be deposited. I am going to dissolve a 

 piece of copper, the most elementary of all chemical operations, 

 but I want to make it quite clear where the metal to be deposited 

 comes from — to show that it is actually in the solution, and actually 

 comes out of it again ; for that is an effect so surprising, that it 

 requires both imagination and demonstration to make it evident. 

 There is projected on the screen a glass cell containing nitric acid. 

 Mr. Lennox will put into it a piece of copper. He has done so ; it 

 quickly disappears, and a blue solution of copper nitrate is formed. 

 Now, if I pass an electric current through this solution, or through 

 some solution of the same kind, which, to save time, has been 

 prepared beforehand, and immerse in it, a little apart from each 

 other — ihe positive and negative wires coming from some gene- 

 rator of electric current — this will happen : metallic copper will 

 come out of the solution, and attach itself as a coating to the 

 negative wire, and consequently that wire will grow in thickness. 

 At the other wire — the positive— exactly the reverse action will 

 take place. There, if the positive wire be copper, it will 

 gradually dissolve, and become thinner. The quantity of metal 

 deposited on the negative wire will almost exactly equal the 

 quantity dissolved from the positive, and therefore the solution 

 will contain the same quantity of metal at the end of the ex- 

 periment as at first, but it will not be the same metal ; it will be 

 fresh metal dissolved from the positive wire, and the metal 

 originally contained in the solution will have been deposited as 

 metallic copper. 



I will show on the screen thi-! process in operation. Here 

 are the two wires I spoke of. The electric circuit, which in- 

 cludes these two wires, is so arranged that on its completion the 

 thick wire will be the positive, and the thin wire the nej^ative. 

 Now please complete the circuit. One wire (the positive) is 

 carrying an electric current into the copper solution, and the 

 other (the negative) is carrying the current away. The solution 

 is conveying the current between the wires, and one of the in- 

 cidents of the transport of current from wire to wire by the solu- 

 tion, is electro-chemical decomposition, or electrolysis ; and the 

 result of that is, the deposition, out of the solution, of copper, 

 upon one wire, and the dissolving away, or entering into solu- 

 tion, of copper, from the other. Now it can be clearly seen 

 that the wire that was thick is now thin, and the wire that was 

 thin is now thick. 



Imagine the growing wire to be an electrotype mould, and 

 that the deposit of copper which formed on the wire has spread 

 over the surface and formed a nearly uniform film, and that by 

 continuing the process it has become thick, that deposit, stripped 

 from the mould, would be an electrotype. 



Or imagine the negative wire to be a thin sheet of pure copper, 

 and the positive wire to be a thick sheet of impure copper, and 

 suppose the action carried on so far that the thin sheet has be- 

 come thick by the deposition of copper upon it from the solution, 

 and the thick one thin by its copper entering into solution, that 

 case would represent the condition of things in electrolytic cop- 

 per refining. 



Allow your imagination to take one more short flight, and 

 suppose that this is not a solution of copper, but one of silver, 

 and that the growing wire is a teapot to be silvered ; and, fur- 

 ther, suppose that the dissolving electrode is silver, and you 

 will then understand the principle of electro-plating. 



It requires very little explanation to make the ordinary ar- 

 rangement of electrotyping intelligible. Mere is a trough con- 

 tainmg sulphate of copper solution. Here is a mould that, 

 through the kindness of Messrs. Elkington, has been prepared 

 for me ; this is connected with the negative pole of a battery — 

 and here is a plate of copper connected with the positive pole. 

 When I immerse the mould in the solution — at about two inches 

 from the copper plate — the electrical circuit is completed, and 

 the same electrolytic action that the experiment illustrated will 

 take place. Copper will be deposited on the mould, and will be j 

 dissolved in equal quantity from the copper plate, and the sup- 

 ply of copper in the solution will thus be kept up. As it will 

 take a little time to obtain the result I wish to show, I will put 

 this aside for ten minutes or so, and proceed to speak of different 

 applications of this principle of copper deposition. 



NO. I 194, VOL. 46] 



For the reproduction of fine works of art in metal, electrotype 

 is unapproachable. The extreme minuteness with which every 

 touch of graver or modelling-tool is copied by the deposited 

 metal film, separates electrotype by a wide space from all other 

 modes of casting. Even the Daguerreotype image is not too 

 exquisitely fine for electrotype to copy it so perfectly that the 

 picture is almost as vivid in the cast as in the original. 



It is this quality that has given to electrotype a ro/e which no 

 other process can fill, and, so far, its practical utility is not 

 greatly dependent on the cost of the current. This applies to 

 all those most beautiful things here and in the Library, lent by 

 Messrs. Elkington. These could all have been produced com- 

 mercially, even if there had been nothing better for the genera- 

 tion of the current than Smee's battery— a very good battery, 

 by the way, for small operations in copper deposition. It gives 

 a very low electro-motive force and that is a defect, but in copper 

 deposition, the half volt or so is generally sufficient to produce, 

 automatically, the required current destiny. 



One of the uses of electrotype, not greatly affected by the 

 cost of deposition, is that of the multiplication of printing sur- 

 faces. In these days of illustrated periodicals, electrotype has 

 come more and more into use for making duplicate blocks from 

 wood engravings, which would soon be worn out and useless if 

 printed from direct. It is also employed to make casts from set- 

 up type, to be used instead of ordinary stereotype casts, when 

 long numbers of a book have to be printed ; also as a means of 

 copying engraved copper-plates. Here are examples of all thtse 

 uses of the electrotype process. The electro-blocks are lent by 

 Messrs. Richardson and Co., and the copper- plates by the 

 Director-General of the Ordnance Survey Office, Southampton. 

 The plates illustrate the method employed at Southampton in 

 the map-printing department. The original plates are not printed 

 from except to take proofs. The published maps are all printed 

 from electrotypes. Here is an original plate — here the matrix, 

 or first electro, with, of course, all the lines raised which are 

 sunk in the original. The second electro is, like the original, 

 an intaglio. Here is a print from it, and here one from the 

 original plate. Practically they are indistinguishable from each 

 I other, and bear eloquent testimony to the wonderful power of 

 electrotype to transmit an exceedingly faithful copy of such a 

 surface. 



Nickel has, of late years, come into extensive use for what 

 is termed nickel-plating, as applied to coating polished steel 

 and brass with nickel. Nickel not only has the advantage over 

 silver of cheapness, but also, in some circumstances, of greater 

 resistance to the action of the air. 



Another metal, usually deposited in the form of a coating, is 

 iron. The electrolytic deposit of iron is peculiarly hard — so 

 much so, that it is commonly but erroneously spoken of as sfeei- 

 facing. The deposition of a film of iron upon engraved copper- 

 plates, as a means of preventing the wear incidental to their 

 use in being printed from, has become almost universal. Valu- 

 able etchings, mezzo- tints, and photogravure plates are thus 

 made to bear a thousand or more impressions without injury. 

 By dissolving off the iron veil with weak acid, when the first 

 signs of wear appear on the surface of the plate, and re-coating 

 it with iron, an engraved copper-plate is, for all practical pur- 

 poses, everlasting. 



In this case, of course, the film of iron is extremely thin- 

 one or two hundred-thousandths of an inch. But it is possible 

 to produce most of the metals commonly used as coatings in a 

 more massive form. Here, for example, is an iron rod half-an- 

 inch in diameter, entirely formed by electrolytic deposition. I 

 am indebted to Mr. Roberts- Austen for being able to show this, 

 and also for this other example of a solid deposit of iron, and 

 for this beautiful specimen of electrolytic coating with iron. 

 Here also are solid deposits of silver. This drinking cup is a 

 solid silver electro-deposit. 



These are all departments of electro-metallurgy which would 

 have maintained a perfectly healthy industrial existence and 

 growth without the dynamo ; but now I come to speak of a 

 branch of the subject — electrolytic copper refining — which, 

 without that source of cheap electricity, could not have existed. 

 This is the most extensive of all the applications of electro- 

 chemistry, and is rendering valuable assistance to electrical 

 engineering by the improvement it has led to in the conductivity 

 of copper wire. 



One of the results of this is seen in the raising of the com- 

 mercial standard of electrical conductivity. 



Ten years ago, contracts for copper wire for telegraphy stipu- 



