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by the coarseness or fineness of the material.

Mr. Cooper states, "I made three similar experiments, altering the texture and thickness of the plaster each time, by which I ascertained that if the plaster partitions were thin and coarse, the metallic deposition proceeded with great rapidity, but the crystals were friable and easily separated; on the other hand, if I made the partition thicker, and of a little finer material, the action was much slower, and the metallic deposition was as solid and ductile as copper formed by the usual methods; indeed the action was exceedingly slow. I have made a metallic deposition apparently much harder than common sheet copper; but more brittle."

A friend of mine used a common garden pot, with a cork in the perforation through the bottom, which answered very well, the copper deposited being fine and tough. I think a wine cooler would be a good vessel for that purpose, being porous; and either may be at hand, when there is not a suitable glass, or any plaster of Paris.

Mr. Crosse has stated, in the account of his experiments on the crystallization of metals, that he succeeded best when the solutions were kept at a boiling temperature; and Mr. Spencer informs us, that by keeping the solutions he employed at a temperature of from one hundred and twenty to one hundred and eighty degrees of Fahrenheit, he was able to abridge the time otherwise required, three or four fold.

In all scientific experiments, care and attention are requisite for a successful result in this instance, let an uninterrupted circuit be maintained for the electricity, and let the wire have a perfect metallic contact with the plates which it connects; when it is an engraving on wood, bore a hole in the side of the block, and insert the wire in it. The zinc may be with advantage occasionally taken out of the saline solution during the operation, and cleaned in water. In the choice and application of the plates, it is better that they should be, as nearly as possible, of the same size, and it is of importance that the zinc should be as thick as the required deposition of copper, but it is easy when necessary to renew the zinc again and again. That the solution of the sulphate of copper may be continued in the necessary state, crystals of that substance should be occasionally added. When the process is long continued, the solution should be changed, for the sulphuric acid, which is set free by the deposition of the metallic copper, prevents the further action.

This was the first method; the plan now practised, to prevent any stoppage of the galvanic action by an excess of sulphuric acid occasioned by the decomposition of the sulphate of copper and the deposition of its copper in a metallic state, is to put into the acid a piece of copper in connexion with the positive pole, and thus, as the acid is set free by the galvanic action, it forms a new combination with the copper, and continues the supply of the sulphate without the necessity of changing the contents of the vessel.

In obtaining casts by this process, it must be borne in mind, that no metallic deposition can be made by voltaic electricity without the presence of a metallic surface or nucleus upon which to deposit: but this metallic surface should be given only to the part which is to be copied; the sides and bottom of the block may be covered with a varnish composed of shell lac dissolved in spirit of wine, which will prevent any metallic deposition from taking place upon those parts, as also the moisture from penetrating into the wood, and the deposition will in consequence be confined to the engraved surface.

In the management of the simple apparatus which is employed in electrotype, it is necessary to have the binding-screws, wires, and all

the metallic surfaces, quite clean and bright, as also to avoid touching with the fingers that part on which the metal is to be deposited.

With regard to the first application of galvanism to the production of facsimiles of engravings on wood, Mr. Spencer states, after the publication of his pamphlet, "The wood engraving being given, take a piece of lead the required size; let its superfice be about one-eighth of an inch larger all round than that of the wood block. The lead must now be planed, just as a piece of soft wood; (the tool termed by a joiner a try plane does best ;) a clear bright surface is thus obtained, such as I have been unable to get by any other means. The engraved surface of the wood must now be laid on the planed surface of the lead, and both put carefully in a press; should the engraving have more than two inches of superfices, a copying press is not powerful enough. Whatever press is used, the subject to be copied must be cautiously laid in the centre of the pressure, as a very slight lateral force will in some degree injure the process; the pressure to be applied regularly, and not with a jerk. When the pressure is deemed complete, they may be taken out, and if, on examination, the lead is not found to be completely up, the wood engraving may be neatly relaid on the lead, and again submitted to the press, using the same precaution as before. When the lead is taken out, a wire should be soldered to it immediately, and it should then be put into the apparatus without loss of time, as the less it is subjected to the action of the atmosphere the better: care should also be taken not to touch the surface with the fingers."

Mr. Spencer also states that plumbers, who have handled lead for the greater portion of their lives, are astonished to find it so susceptible of pressure. On the contrary, wood engravers did not, until now, imagine that their blocks would stand the pressure of a screw press on a lead surface without injury; but such is the fact in both instances. In the manner in which box wood is used for wood engravings, being in horizontal sections, it will sustain a pressure of 8,000 lbs. without injury, provided the pressure is perfectly perpendicular.

Mr. Spencer has omitted to mention the size of the engraving; if it were one inch square, it would have a pressure of 8,000 lbs. on that inch; if it were nine inches square, it would only have a pressure of 100 lbs. on the square inch: with my experience of printing engravings on wood, I would not venture to submit one to a pressure of 8,000 lbs. to the inch for fear of crushing the lines. I mention this as a caution; it may prevent an accident.

This appears to have been the first method tried to produce a facsimile of an engraving on wood by means of galvanism, with a metallic mould obtained by impressing the engraved block upon a piece of lead. This not appearing to be perfectly satisfactory, other persons were induced to endeavour to make the discovery available for letterpress printing without the risk of injury to the engraving, to which this plan seemed liable; and the next advance towards the perfection of the process was an important one, being the introduction of the real object intended to be copied in the stead of the substituted mould, and obtaining a matrix from it at once by means of the galvanic process without resorting to any intermediate measures. This improvement was made by Mr. Robert Murray, who proposed "in January last to cover the surface of the wood with plumbago [black lead], so as to render it a conductor; and then to proceed in the usual manner for obtaining an electrotype copy," as he informed me in a communication of the 21st of July, 1840. It is but fair to state, that this use of black lead has been

objected to by some engravers on wood, as having a tendency to fill up the lines of a delicate engraving, and so to deteriorate the impressions taken from it; but I am now furnishing the public with the means of deciding on this question, by presenting an impression from an electrotype copy, executed by Mr. Murray according to his own ingenious plan, by the side of one from the original wood engraving, and I leave it to bear witness for itself. I cannot perceive any deterioration in the copy, nor any difference between the two impressions: in fact they appear as if they were duplicate impressions from the same engraving.

The following letter, addressed to the editor of the Athenæum, by Mr. Spencer, which appeared in that publication on the 4th of July, 1840, details another method of obtaining a metallic surface for an engraving on wood, &c. for the purpose of inducing the galvanic deposition of copper upon it and obtaining a copper mould, which appears to be free from the objections that have been raised to gilding, bronzing,

and to black lead.

"In my pamphlet, printed last September, I there stated I considered the process comparatively incomplete, unless we were able to apply it to the multiplication of models in clay or wood, castings in plaster, wood engravings, &c., as the fact, that galvanic deposition always requires a metallic surface to act on, seemed to set bounds to those branches of its application. I then resorted to various expedients to surmount the difficulty; among others, that of gilding and bronzing the surfaces of such materials to a limited extent: this was successful, but still troublesome and expensive, and, more than all, the sharpness and beauty of the original was necessarily injured. I have since attempted to metallize surfaces by the use of plumbago (suggested to me many months ago by Mr. Parry of Manchester).

"Should I be desirous of obtaining a copper mould or cast from a piece of wood, plaster, or clay, or, indeed, any non-metallic material, I proceed as follows:- Suppose it is an engraved wooden block, and I am desirous of metallizing it, in order that I may be able to deposit copper on its surface (this example will hold good for any other material), the first operation is to take strong alcohol in a corked glass vessel, and add to it a piece of phosphorus (a common phial corked will answer the purpose); the vessel must now be placed in hot water for a few minutes, and occasionally shaken. By this means the alcohol will take up about a 300th of its bulk of phosphorus, and we thus obtain what I would term an alcoholic solution of phosphorus. The next operation is to procure a weak solution of nitrate of silver; place it in a flat dish or a saucer; the engraved face of the block must now be dipped in this solution, and let remain for a few seconds, to allow capillary action to draw it into the wood.

"This operation being performed, a small portion of the alcoholic solution of phosphorus must now be poured in a capsule or watch-glass, and this placed on a sand-bath, that it may be suffered to evaporate. The block must now be held with its surface over the vapour, and an immediate change takes place; the nitrate of silver becomes deoxidized and gives place to a metallic phosphoret of silver, which allows the voltaic deposit to go on with as much rapidity and certainty as the purest silver or copper.

"The whole process may be performed in a few minutes, and with absolute certainty of success. The interior or exterior surface of a plaster or clay mould of a statue, no matter what size, may be thus metallized with equal facility. For the process of vaporizing, and should

the material to be acted on not be very large, I prefer fastening it to the top of a bell glass receiver with a bit of pitch or cement, and thus placing it over the capsule on the sand-bath; the phosphoric vapour is by this means equally diffused and not dissipated. An ethereal solution of phosphorus also answers; and a solution of either of the chlorides of gold or platinum may be used. I am inclined to think this process, independent of its uses in galvanic precipitation, may be applicable to other branches of art. I would recommend those curious of testing its effects, to try a small and sharp plaster of Paris medallion: dip its surface in a weak solution of nitrate of silver and take it out immediately; fasten it to the bottom of a glass tumbler, and at the same time have a little hot sand ready in a dish; lay the watch glass containing a few drops of the phosphoric solution on it; now place the mouth of the tumbler over all, and the medallion will be observed almost instantly to change colour. The operation is now completed. A piece of pottery ware in the state of biscuit may be acted on in a similar manner. THOMAS SPENCER." Apparatus and process. The annexed figure and explanation will afford an example of the action of a voltaic apparatus, and will be sufficient to render the subsequent details intelligible. A is a vessel filled with a solution of common salt, which is a compound of chlorine and

"Liverpool, June 27.

B

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sodium; B is a tube immersed therein, closed at the lower end with a piece of bladder stretched over it and firmly tied; this tube is filled with a solution of blue vitriol, that is, a compound of sulphuric acid and oxide of copper. A plate of copper c, and one of zinc z, connected by means of the wire w, are immersed in those fluids. zine decomposes the salt, with the chlorine of which it unites, forming chloride of zinc, while the sodium of the salt is repelled, and passing through the bladder, enters the solution of sulphate of copper, which it decomposes, uniting with the sulphuric acid and oxygen to form sulphate of soda, and setting free pure copper in the form of beautiful crystals, which are deposited on the plate c. The connecting wire w serves to convey electricity from c to z, and thus the action is maintained so long as any common salt and sulphate of copper remain undecomposed.

Mr. Spencer's first attempt was made with a piece of thin copper plate, which he covered with a cement of beeswax, resin, and Indian or Calcutta red. The plate received its coating while hot, and on becoming cool, the experimenter scratched the initials of his name upon the plate, being careful to clear away all the cement from the scratches, so as to expose the copper below. A piece of zinc was attached to this plate by a copper wire, and the voltaic current was set in action by means of the simple apparatus shown in the adjoining figure.

A may be supposed to represent a glass vessel of convenient form. в a gas glass stopped at the lower end P, by a piece of plaster of Paris, to the depth of three quarters of an inch. z a plate of zinc, and c a similar piece of copper, a coin or any other metallic substance to be acted upon; and these two are connected by a copper wire, w. The inner vessel may be kept in its place by a cork, or any other means that may happen to be more convenient. A solution of sulphate of soda is poured into the gas glass, and the wire connecting the zinc and copper plates

W

B

being bent, as shown in the figure, the zinc plate is immersed into the solution of sulphate of soda, and the copper plate into the solution of sulphate of copper.

In a few hours Mr. Spencer, in his experiments, found that the portion of the copper rendered bare by the scratches was coated with the pure bright deposited metal, while those portions which were still covered with cement were not acted on. It now became an important inquiry whether the deposition would retain its hold on the plate, and whether it would be of sufficient solidity to bear working from; that is, supposing an etching or engraving to be made, and the lines to be afterwards filled up with copper by the voltaic process, whether such lines could be printed from.

In order to answer this last question, Mr. Spencer coated with cement a piece of copper, and with a steel point endeavoured to draw lines in the form of network, so as to penetrate the cement and expose the copper. After this plate had been exposed to voltaic action, and then heated, so as to get off the covering of cement, the copper net-work came off with it. This happened many times; but by an accident it occurred to the experimenter to employ nitric acid to the plate, after it had been cemented and engraved on as before. It was then subjected to the voltaic process for forty-eight hours, when the lines were found to be entirely filled with copper. On applying heat, and then turpentine to get off the cement, it was found that the voltaic copper had completely combined with the plate on which it was deposited.

A plate was then coated with cement, and lines worked upon it by an engraver; but these lines were of a wedge-shaped form, leaving only a hair line of the copper exposed at the bottom, and a broad space near the surface; and where the turn of the letters took place, the top edges of the lines were galled and rendered rugged by the action of the graver. All this was objectionable; but another plate, similarly prepared, and engraved on with a sharp point, had the copper deposited on the lines; and this was printed from successfully.

This was an attempt to deposit lines upon a plate of copper by the galvanic action, and thus form an engraving in relief, which I have doubts of being successfully practised with finished subjects.

The application of heat separates the two metals, in consequence of their different expansibility when subjected to its influence.

Mr. Spencer gives the form of another apparatus on a more extended scale, which he recommends, as it may be employed in large works.

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