n 
 
 I 
 
A MANUAL 
 
 OF 
 
 ELECTRO - METALLURGY. 
 
 BY 
 
 GEORGE SHAW. 
 
 SECOND EDITION, CONSIDERABLY ENLARGED. 
 
 LONDON : 
 
 SIMPKIN, MARSHALL, AND CO. 
 E. C. OSBOKNE, BIRMINGHAM, 
 MDCCCXIIV. 
 
iSnterett at Ittattonerfl' fJjall. 
 
 BIRMINGHAM : 
 E. C. OSBORNE, PRINTER, 30, BENNETT'S HILL. 
 
PREFACE TO THE FIRST EDITION. 
 
 The following pages contain the principal facts of the Art 
 of Electro-Metallurgy. 
 
 The author has endeavoured to introduce everything inter- 
 esting to the experimenter in this novel art ; but has at the 
 same time sought to make the work as brief as possible, by 
 the omission of some of the minute details of manipulation. 
 To the beginner this may appear discouraging, but in the 
 end he will find it to his advantage ; for although by giving 
 minute directions in the manipulatory processes, a person 
 wholly unacquainted with the principles on which those 
 processes are founded, may possibly succeed in his experi- 
 ments, yet the probability is that he would fail in the majo- 
 rity of cases, and would find himself compelled to master 
 the principles of the science of Voltaic Electricity, before he 
 could proceed to his experiments with certainty of success. 
 
 The author would not be understood to mean that the 
 subject of manipulation has been neglected ; on the contrary, 
 he has endeavoured to introduce all that is essential ; and he 
 
iv. 
 
 believes that a careful perusal of the foUowiug pages, com- 
 bined with that knowledge which experiment alone can give, 
 will enable any one to practice the Art of Electro-Metallurgy, 
 as far as it is at present developed. 
 
 As the facts stated in this work (with a few trifling excep- 
 tions,) have been experimentally verified by the author, he 
 feels little doubt of their general accuracy. 
 
 Temple Bow West, Birmingham, 
 May 16, 1842. 
 
The present edition has been considerably enlarged by the 
 introduction of recent discoveries in the art. The extent to 
 which improvements have been introduced since the publi- 
 cation of the first edition, has rendered a more systematic 
 arrangement necessary; the work has been divided into 
 chapters, and many other alterations have been made, which, 
 it is hoped, will make it more convenient and useful. 
 
 Temple Row West, Birmingham, 
 June 20, 1844. 
 
li. 
 
 f 
 
 4 
 
CONTENTS. 
 
 PAGE 
 
 Chap. I. — Introduction and Historv 1 
 
 Chap. II. — Chemistry and Electricity, as connected with 
 
 Electro-Metallurgy 16 
 
 Chap. III. — On the Voltaic Battery 34 
 
 Chap. IV. — On Magneto - Electricity and the Magneto- 
 Electric Machine 55 
 
 Chap. V. — On the production of Electricity by Heat and 
 
 Thermo-Electric Batteries .... 66 
 
 Chap. VI. — On the Salts from which Metals may be pre- 
 cipitated 69 
 
 Chap. VII. — On the preparation of Surfaces for receiving 
 
 Metallic Deposites 88 
 
 Chap. VIII. — On the production of Moulds or Surfaces to 
 
 RECEIVE Electro-Metallurgical Deposites . 101 
 
 Chap. IX. — On the various arrangements of Electro-Metal- 
 lurgical Apparatus 112 
 
 Chap. X. — On the circumstances which influence the qua- 
 lity and quantity of Electro-Metallurgical 
 Deposites 129 
 
 Chap. XI. — On Electro-Gilding, Plating, &c. and the pro- 
 duction of Works of Art by Electro-Metal- 
 lurgy 149 
 
 Chap. XII. — On the production of Printing Surfaces by 
 
 Electrical agency 152 
 
 Chap. XIII. — On various applications of Electro-Metal- 
 lurgy 168 
 
 Chap. XIV. — On colouring Metallic Surfaces . . . 183 
 
 Chap. XV. — On the value and probable results of Electro- 
 Metallurgy 189 
 
A MANUAL 
 
 OF 
 
 ELECTRO -METALLURGY. 
 
 CHAPTER I. 
 
 INTRODUCTION AND HISTORY. 
 
 1. In reviewing the early history of the physical sciences, 
 we cannot but be struck with the fact, that many discoveries, 
 which now either minister to our wants, or add to our 
 enjoyments, lay for a long time after their announcement 
 wholly neglected, or at best, served but to swell the pages 
 of the historian. It is not so, however, in modern times; 
 no sooner is a discovery now made, than its application to 
 some useful purpose is attempted ; and at this moment there 
 are, probably, hundreds anxiously watching the progress of 
 discovery, eager for the announcement of some fact, which 
 may be made available for purposes of use or ornament. 
 
 2. No department of science more strikingly exemplifies 
 these remarks, than that branch of the science of electricity 
 which the following pages are intended to illustrate, namely, 
 the precipitation of metals by voltaic agency. During the 
 short period that has elapsed since the constant battery of 
 Professor Daniell was made public, a fact presented by the 
 action of that instrument, has given rise to a new application 
 of the voltaic battery, which has already effected the most im- 
 portant changes in the production of works of art. In treating 
 of the voltaic battery, we shall fully describe the invention of 
 Professor Daniell ; it will suffice to notice in this place, that 
 
 B 
 
2 
 
 the solution of sulphate of copper used in the excitation of 
 that instrument, suffers rapid decomposition, and that the 
 metallic copper which is precipitated, attaches itself closely to 
 the copper cylinder in which the solution is contained, and 
 it is found, on detaching the precipitated metal, that it had 
 been deposited in such intimate contact with the copper 
 cylinder, that the most minute marks are faithfully copied. 
 The application of this fact constitutes the electrotype, — the 
 earliest branch of the art of electro-metallurgy. 
 
 3. From this it would appear, that the history of the art is 
 so simple as to require no comment, and so modern as to ad- 
 mit of no dispute ; such, however, is not the case. It is a 
 subject which has given rise to the most angry discussions, 
 and concerning which even now opinion is strangely divided. 
 
 4. The earliest recorded process in electro-metallurgy is 
 contained in the Philosophical Magazine.* Brugnatelli re- 
 lates, in a letter to Van Mons, that he had deposited a film 
 of gold on ten silver medals, " by bringing them into commu- 
 nication by means of a steel wire with the negative pole of a 
 voltaic pile, and keeping them, one after the other, immersed 
 in aramoniuret of gold newly made and well saturated." This 
 announcement of a process identical with those now exten- 
 sively used, attracted no attention at the time it was made, 
 and its existence has only been recently pointed out by Mr. 
 Brayley. 
 
 5. The earliest experimenters with the voltaic pile, observed 
 the precipitation of metals in the voltaic circuit. The preci- 
 pitation of copper was distinctly noticed by Mr. Nicholson in 
 a paper entitled " Account of the New Electrical Apparatus 
 of Sig. Alex. Volta, and Experiments performed with the 
 same. W. N."t The following passage is extracted from 
 this paper. " When copper wires were used for the broken 
 circuit, with muriatic acid diluted with 100 parts of water 
 
 ♦ Phil. Mag. 1805, f Nicholson's Journal, July, 1800, p. 179. 
 
3 
 
 in the tube, no gas nor the least circulation of the fluid 
 was perceived, when the distance of the wires was two 
 inches- A short tube with two copper wires very near each 
 other, in common water, was made part of the circuit, and 
 showed, by the usual phenomena, that the stream of electricity 
 was rapidly passing. The wires in the muriatic acid were 
 then slided within a third of an inch of each other. For the 
 sake of brevity, I avoid enumerating the effects which took 
 place during several hours, and simply state, that the minus 
 wire gave out some hydrogen during an hour, while the plus 
 was corroded, and exhibited no oxide, but a deposition of 
 copper was formed round the minus or lower wire, which 
 began at its lower end ; that no gas whatever appeared in this 
 tube during two hours, though the deposition was going on, 
 and the small tube showed the continuance of the electric 
 stream; and that the deposition at the end of four hours 
 formed a ramified metallic vegetation, nine or ten times the 
 bulk of the wire it surrounded. In this experiment it appeared, 
 that the influence of electricity increasing the oxidability of 
 the upper wire, and aflFording nascent hydrogen from the lower, 
 caused the latter to act as the precipitant of a solution of one 
 and the same metal." 
 
 6. Voltaic precipitation of the metals was observed about 
 the same time by Mr. Cruikshank, as the following extracts 
 from his paper, " Some Experiments and Observations on 
 Galvanic Electricity," will shew.* "The tube was filled 
 with a solution of the acetite of lead, to which an excess of 
 acid was added, to counteract the effects of the alkali. When 
 the communication was made in the usual way, no gas could 
 be perceived, but after a minute or two, some fine metallic 
 needles were perceived at the extremity of the wire connected 
 with the silver. These soon increased, and assumed the form 
 of a feather, or rather, that of the crystals of the muriate of 
 
 * Nicholson's Journal, July, 1800, p. 187. 
 
 b2 
 
4 
 
 ammonia. The lead thus precipitated was perfectly in its 
 metallic state and very brilliant ; a little gas escaped from 
 the wire connected with the zinc, and it was considerably 
 corroded as usual. A solution of the sulphate of copper was 
 next employed, and with the same result, the copper being 
 precipitated in its metallic form by the wire connected with 
 the silver. In this instance the metal did not crystallize, but 
 formed a kind of button at the end of the wire, which adhered 
 so completely to the silver, that it was found impossible to 
 separate it. The most beautiful precipitate, however, was 
 that of silver from its solution in the nitrous acid. In this 
 case, the metal shot into needle-like crystals articulated or 
 joined to each other as in the ai-hor DianasP The same phi- 
 losopher also remarks as follows, in his "Additional Remarks 
 on Galvanism :"* — " Having found that the solutions of 
 metals in acids were decomposed by this influence (voltaic 
 electricity), I next wished to ascertain if their solutions in 
 alkalies, more particularly in ammonia, could be decomposed 
 in the same way. For this purpose, I added to a dilute solu- 
 tion of the nitrate of silver some pure ammonia, until the mix- 
 ture smelled strongly of the latter substance. This mixture 
 was introduced into a glass tube secured by corks in the usual 
 way, and silver wires applied. When the tube was placed in 
 the circle of communication, a very rapid production of gas 
 took place from the wire connected with the silver extremity 
 of the machine, although but little or none escaped from the 
 zinc wire during the whole process." 
 
 7. " After some time, a quantity of greyish flakes, evidently 
 of metallic silver, were separated by the wire which gave out 
 the gas, and a dark grey powder was deposited on the zinc 
 wire ; at this period of the process much less gas was disen- 
 gaged, although a considerable quantity still appeared at the 
 silver wire. After some hours, the apparatus was removed j 
 
 * Nicholson's Journal, July, 1800, p. 254. 
 
5 
 
 at this time a very considerable quantity of metallic silver was 
 deposited, and the zinc wire was encrusted with a blueish 
 black substance. On endeavouring to remove this crust with 
 the finger, part of it exploded, although still moist." .... 
 " This experiment was repeated, and instead of a solution of 
 silver, nothing but pure ammonia was introduced into the 
 tube, which answered exceedingly well ; for the silver of the 
 zinc wire, after being corroded &c., was immediately taken 
 up by the vol. alkali and afterwards deposited in its metallic 
 form by the silver wire." " I next filled the tube with an 
 ammoniacal solution of copper, and employed copper wires. 
 In a very short time after this had been exposed to the action 
 of the machine, the upper part of the fluid in contact with the 
 silver wire became considerably paler, and copper was preci- 
 pitated. In about an hour, the whole of the fluid in this part 
 of the tube became as colourless as distilled water, so com- 
 pletely had the metal been precipitated. The precipitated 
 metal was also the purest I had ever seen. From these expe- 
 riments it would appear, that the galvanic influence might be 
 employed with success in the analysis of minerals, more par- 
 ticularly in separating lead, copper and silver, from their 
 different solutions. A very small quantity of a metal may 
 likewise be detected in this way, as I have found from direct 
 trial." 
 
 8. From the time Brugnatelli's experiment was announced, 
 till the year 1830, no experiments on the application of elec- 
 tricity to the deposition of metals for the purposes of art were 
 published. On the 2oth of November in that year, a paper 
 by Mr. Edmund Davy was read before the Royal Society, 
 in which he distinctly states that he had gilded, silvered, 
 coppered, and tinned various metals by the voltaic battery ; 
 and although he does not give the disposition of the appara- 
 tus for reducing these metals, he describes accurately the 
 means to be taken for procuring depositesof mercury, copper, 
 lead, arsenic, and those metals the salts of which constitute the 
 
6 
 
 more common poisons, and he states, that in a future commu- 
 nication he shall enter into the application of these facts to 
 the purposes of gilding, plating, &c. ; but so far as the author 
 is aware, the concluding part of his paper never appeared. 
 There is, however, sufficient evidence of Mr. Davy's familia- 
 rity with the voltaic precipitation of the metals, in the paper 
 from wdiich the subjoined extracts are made, as well as such 
 information as would have enabled any one to carry out the 
 practical application of voltaic precipitation to useful purposes, 
 had the value of such precipitations been as evident then as 
 it is now. Mr. Davy's paper will be found in the Philosophical 
 Transactions of the Royal Society for the year 1831, p. 147. 
 The following are extracts. 
 
 9. " On a Simple Electro-chemical Method of ascertaining 
 the Presence of different Metals, applied to detect minute 
 quantities of Metallic Poisons. By Edmund Davy, F.R.S., 
 ^6'." (Read Nov. 25, 1830.) — " It is now nearly a quarter of a 
 century since the late Sir Humphry Davy, by a train of masterly 
 researches, developed the general principles of electro-chemical 
 action, which subsequently led him to many fine discoveries 
 and important practical applications. Some years since, I 
 repeated most of the interesting experiments noticed in his 
 excellent Bakerian lecture, ' On the Chemical Agencies of 
 Electricity.'"* On the decomposition of metallic salts by the 
 voltaic battery. Sir Humphry is very brief. He clearly ascer- 
 tained, however, that " when metallic solutions were placed in 
 the circuit, metallic crystals or depositions were formed on 
 the negative surface," and that " the metals passed towards 
 the negative surface, like the alkalies, and collected round it." 
 ' In the course of my experiments on this subject, pheno- 
 mena occurred which led me to think that some novel results 
 might be obtained by instituting a series of experiments on 
 metallic salts, using, as a voltaic arrangement, the feeble 
 
 * Phil. Trans, of the Royal Society, 1807. 
 
7 
 
 power produced by the contact of small slips of dilFereut 
 metals with solutions of the common metallic salts. Opera- 
 ting in this manner, I could readily detect very minute quan- 
 tities of different metals, coat platina with gold, silver, copper, 
 &c., or cover gold with a surface of these metals, and tin, 
 
 copper, brass, iron, &c."" " Circumstances which it is 
 
 unnecpssary to mention have hitherto prevented me giving 
 greater publicity to these facts The fear of trespass- 
 ing too much on the time of the Society, induces me to limit 
 the present paper to one part only of the subject. At no 
 distant period I promise myself the pleasure of communicating 
 the remaining part, which will embrace the different electro- 
 chemical experiments I have made on the other metals and 
 their compounds, together with the application of the facts to 
 the processes of gilding, silvering, tinning, &c." 
 
 10. These experiments of Brugnatelli and Davy having 
 been completely lost sight of, do not affect the merit of suc- 
 ceeding experimenters ; and the art cannot be said to have 
 originated until after the origin of the constant battery. 
 
 11. It has already been remarked (2), that in Daniell's 
 battery, metallic copper is precipitated on the copper cylinder 
 containing the solution of the sulphate of that metal. This 
 precipitated copper is not very intimately attached, for, by 
 the application of a very moderate force, it may be torn off". 
 This fact was known to Mr. Dauiell, who shewed that the 
 detached metal had been deposited in such close contact with 
 the matrix, that it exhibited impressions of marks on the 
 latter with extreme fidelity ; he did not think, however, of 
 applying this fact to any useful purpose. In the course of 
 experiments made with this battery, other philosophers 
 observed the same fact. 
 
 12. Mr. Warren de la Hue makes the following remarks in 
 a paper " On the Effects of a Battery charged with Sulphate 
 of Copper," published in the London and Edinburgh Philoso- 
 phical Magazijie for 1830. " The zinc plate is always par- 
 
8 
 
 tially covered with a coating of copper, which, however, is not 
 detrimental to the power of the battery ; the copper plate is 
 also covered with a coating of metallic copper, which is 
 continually being deposited ; and so perfect is the sheet of 
 copper thus formed, that on being stripped off, it has the 
 polish, and even a counterpart of every scratch, of the plate 
 on which it is deposited." 
 
 13. In May, 1839, it was announced that Professor Jacobi, 
 of St. Petersburgh, could employ the voltaic battery in the 
 reduction of copper for various purposes ; and to his art was 
 given the name of Volta- Plastics. 
 
 14. The first account of the result of Jacobi's experiments 
 which appeared in England was contained in a paragraph in 
 the Athenaeum for May, 1839, and was as follows : — " Gal- 
 vanic Engraving in Relief. — While M. Daguerre and Mr. 
 Fox Talbot have been dipping their pencils in the solar spec- 
 trum, and astonishing us with their inventions, it appears that 
 Professor Jacobi, at St. Petersburgh, has also made a discovery 
 which promises to be of little less importance to the arts. He 
 has found a method, if we understand our informant rightly, 
 of converting any line, however fine, engraved on copper, into 
 a relief, by a galvanic process. The Emperor of Russia has 
 placed at the Professor's disposal funds to enable him to 
 perfect his discovery." Immediately after this announce- 
 ment, the following letter appeared in the Mechanics^ Maga- 
 zine."^ 
 
 15. Engraving by Galvanism. — Sir, — Observing in the 
 last page of a recent number of your Magazine a notice 
 extracted from the Athenmim, relative to a discovery of Pro- 
 fessor Jacobi, its perusal occasioned the recollection of some 
 experiments performed about the commencement of last sum- 
 mer, with the view of obtaining impressions from engraved 
 copper plates by the aid of galvanism, which led me to infer 
 
 * June 8, 1S39. 
 
9 
 
 some analogy in principle with those of the Russian Professor, 
 and may, probably, give me the right to claim priority in its 
 discovery and application. These experiments were aban- 
 doned from the want of that most important element in pursuits 
 of this nature, time ; the writer's share of the said element 
 being occupied in a manner more imperative than pleasing. 
 I regret, however, not having made it the subject of an earlier 
 communication, as this would have placed my pretensions 
 beyond doubt ; but inasmuch as the notice alluded to is given 
 from memory, and is undescriptive, while I may be enabled 
 to exhibit the modus operandi, my assertion may be at least 
 partially substantiated. 
 
 16. " It is well known to experimentalists on the chemical 
 action of voltaic electricity, that solutions of several metallic 
 salts are decomposed by its agency, and the metal procured in 
 a free state. Such results are very conspicuous with copper 
 salts, which metal may be obtained from its sulphate, (blue 
 vitriol) by simply immersing the poles of a galvanic battery in 
 its solution, the positive one becoming gradually coated with 
 copper. The phenomenon of metallic reduction is an essen- 
 tial feature in the action of sustaining batteries ; the effects, in 
 this case, taking place on more extensive surfaces. But the 
 form of voltaic apparatus which exhibits this result in the 
 most interesting manner, and relates more immediately to the 
 subject of the present communication, may be thus described : 
 — It consists of a glass tube, closed at one extremity with a 
 plug of plaster of Paris, and nearly filled with a solution of 
 sulphate of copper ; this tube and its contents are immersed 
 in a solution of common salt. A plate of copper is placed in 
 the first solution, and is connected, by means of a wire and 
 solder, with a zinc plate, which dips into the latter. A slow 
 electric action is thus established through the pores of the 
 plaster, which it is not necessary to mention here; the 
 result of which is the precipitation of minutely-crystallized 
 copper on the plate of that metal, in a state of greater or less 
 
10 
 
 malleability, according to the slowness or rapidity with which 
 it is deposited. In some experiments of this nature, ou 
 removing the copper thus formed, I remarked that the surface 
 in contact with the plate equalled the latter in smoothness 
 and polish, and mentioned this fact to some individuals of my 
 acquaintance. It occm-red to me, therefore, that if the surface 
 of the plate was engraved, an impression might be obtained. 
 This was found to be the case ; for on detaching the precipi- 
 tated metal, the most delicate and superficial mai-kings, from 
 the fine particles of powder used in polishing to the deeper 
 touches of a needle or graver, exhibited their correspondent 
 impressions in relief with great fidelity. It is therefore evi- 
 dent that this principle will admit of improvement, and that 
 casts and moulds may be obtained from any form of copper. 
 
 17. " This rendered it probable that impressions may be 
 obtained from those other metals having an electro-negative 
 relation to the zinc plate of the battery. With this view, a 
 common printing type was substituted for the copper plate 
 and treated in the same manner ; this also was successful ; 
 the reduced copper coated that portion of the type immersed 
 in the solution. This, when removed, was found to be a per- 
 fect matrix, and might be employed for the purpose of casting, 
 where time is not an object. 
 
 18. "It appears, therefore, that this discovery may be 
 turned to some practical account. It may be taken advantage 
 of in procuring casts from various metals, as above alluded 
 to ; for instance, a copper disc may be formed from a cast of 
 a coin or medal, in silver, type metal, or lead, &c., which may 
 be employed for striking impressions in soft metals. Casts 
 may probably be obtained from a plaster surface surrounding 
 a plate of copper ; tubs [tubes ?] or any small vessel may also 
 be made by precipitating the metal around a wire, or any 
 kind of surface to form the interior, which may be removed 
 mechanically, by the aid of an acid solvent, or by heat." 
 
 " May 22, 1839." "C.J. Jordan. 
 
11 
 
 19. On the 8tli of May, 1839, Mr. Thos. Spencer, of Liver- 
 pool, announced to the Polytechnic Society of that town, 
 that he had a communication to make to the society rela- 
 tive to the application of electricity to the arts, and that he 
 then gave notice of that communication, in consequence 
 of a j)aragraph having appeared in the public prints, an- 
 nouncing that Professor Jacobi had applied the voltaic bat- 
 tery to the production of works of art. 
 
 20. Mr. Spencer's first communication to the public was on 
 the 12th of September, 1839. His paper was to have been 
 read at the meeting of the British Association in Birmingham, 
 but, for some unexplained reason, it was suppressed. It was 
 subsequently read before the members of the Liverj)ool Poly- 
 technic Society on the day above mentioned. In this paper 
 (which was afterwards published) Mr. Spencer details the cir- 
 cumstances which suggested to him this application of voltaic 
 electricity. He observed, during one of his experiments, that 
 a copper plate which he had been using as a negative element 
 in a voltaic arrangement, in which a solution of sulphate of 
 copper was employed, had become covered with the precipi- 
 tated metal in every part, excepting in two or three places 
 where by accident some drops of varnish had fallen ; it imme- 
 diately occurred to him, that if a plate of varnished copper, 
 having a design made upon it by a pointed instrument so as 
 to remove the varnish, were made the negative plate of a vol- 
 taic arrangement, the copper would be precipitated on the 
 parts where the metal was exposed, so that on removing the 
 varnish the design would be left in relief j experiment con- 
 firmed the correctness of his conjecture. 
 
 12. In the same paper, Mr. Spencer relates another experi- 
 ment which suggested to him that application of voltaic elec- 
 tricity, which is at present known as the Electrotype. " The 
 members of the society," says Mr. Spencer, alluding to the 
 Liverpool Polytechnic Society, at a meeting of which the 
 paper was read, " will recollect that on the first evening it met. 
 
12 
 
 I read a paper on the ' Production of Metallic Veins in the 
 Crust of the Earth,' and that among other specimens of cupreous 
 crystallization which I produced on that occasion, I exhibited 
 three coins; one wholly covered with metalhc crystals, the 
 other on one side only. It was used under the following cir- 
 cumstances : — When about to make another experiment, and 
 being desirous of using the piece of wire used in the first 
 instance, I pulled it off from the coin to which it was attached. 
 In doing this, a piece of the deposited copper came off with 
 it; on examining the under portion of which, I found it con- 
 tained an exact mould of a part of the head and letters of the 
 coin, as smooth and sharp in every respect as the original on 
 which it was deposited." 
 
 22. We learn, by the preceding extract, that Mr. Spencer 
 was experimenting with a voltaic arrangement similar to that 
 of Professor Daniell ; and that, on detaching the precipitated 
 copper, he found, as that gentleman and others had done, 
 that every impresssion was transferred to the precipitated 
 copper. It is true, accident presented the fact to him in a 
 much more forcible form than that in which it had been pre- 
 sented to others ; the want of a proper piece of copper to 
 complete the arrangement, occasioned Mr. S. to introduce a 
 penny as a substitute, and, on detaching the precipitated 
 copper, he found the head and letters distinctly marked upon 
 it, so that a fac simile of the coin was produced ; and this new 
 application of the voltaic battery presented to him in a man- 
 ner so forcible that it was impossible to neglect it. Mr. 
 Spencer pursued the subject, and so far succeeded in his 
 experiments as to be able to furnish processes by which 
 medals and plates may be copied, and some non-conducting 
 substances coated with copper. 
 
 23. The letter of Mr. Jordan in the Mechanics' Magazine 
 attracted so little attention, that it had been overlooked ; 
 and probably would have remained unknown, had not Mr. 
 Dircks, of Manchester, called attention to it in a recent 
 
13 
 
 number* of that journal. It will be observed that Mr. Jordan 
 anticipated all the most important parts of Mr. Spencer's com- 
 munication, and must now take the position so long occupied 
 by Mr. Spencer— that of the author of the earliest successful 
 application of electricity to the arts. 
 
 24. In studying the history of the art of electro-metallurgy, 
 it should be borne in mind that the individual who will even- 
 tually be regarded as the originator of the art, cannot claim to 
 be ranked as a discoverer the art in question consists of 
 the application of facts, already matters of notoriety, to some 
 useful or ornamental purpose. The announcements of Mr. 
 Jordan and Mr. Spencer contain no discovery, so far as 
 obtaining impressions by galvanism is concerned, for the 
 announcements of De la Rue and others contain every fact 
 which those gentlemen pointed out ; but while the philosophers 
 contented themselves with noticing the exactness of the 
 impression produced by voltaic precipitation, even to the 
 "polish" and counterpart of "every scratch," the printer and 
 the carver and gilder apply themselves to the production of 
 impressions of printers' type and medals by the same action. 
 To them, then, belongs the merit, usually reserved for prac- 
 tical men ; that of applying facts which had hitherto been 
 unapplied ; of creating a new, beautiful and valuable art from 
 materials until then neglected, although within the reach of 
 all. 
 
 25. The position which Mr. Spencer has so long occupied, 
 as the earliest English experimenter in this art, and which 
 now clearly belongs to Mr. Jordan, cannot but excite the sur- 
 prise of all who are interested in this art. It is surprising 
 that the letter of Mr. Jordan to the Mechmiics' Magazine 
 should have been so long overlooked, and still more surprising 
 that Mr. Jordan should have permitted the honour with which 
 the origin of so important an art is associated to be appro- 
 
 * No. 1069, Feb. 1844. 
 
14 
 
 priatecl by anotlier. The supineness of Mr. J ordan is equalled 
 by that of his friends, for it now appears that his claim to the 
 origin of the art of electro-metallurgy was known to many 
 individuals. 
 
 26. Besides the names of Mr. Jordan and Mr. Spencer, 
 several names new to the history of electro-metallurgy are 
 introduced by Mr. DirclvS, in the paper already referred to. 
 Mr. Bessemer is mentioned as having precipitated crys- 
 talline copper on lead castings more than ten years ago. 
 Mr. John Dancer, of Manchester, also produced a design by 
 attaching paper to a metallic plate and depositing copper 
 thereon ; the deposite was formed only on those parts which 
 were not covered by paper, so that on tearing off the precipi- 
 tated copper, the design was cut out, as it were, of the preci- 
 pitated sheet of copper. Mr. Dancer also produced designs 
 by impressing his name on a copperplate, and depositing 
 copper on the indented plate. 
 
 27. There can be little doubt that the precipitation of 
 metals by voltaic agency, particularly on the large scale on 
 which this phenomenon presents itself in the constant battery, 
 has suggested to many individuals the possibility of the useful 
 application of the voltaic battery to the arts, although but 
 few have pubhshed their views respecting such application. 
 It has been demonstrated to the author of this treatise, on the 
 most conclusive evidence, both documentary and personal, 
 that the late Mr. Woolrich, of Birmingham, succeeded in 
 applying coatings of copper to various articles by means of 
 the voltaic battery ; and that, in one instance at least, he 
 succeeded in gilding an article by voltaic precipitation from 
 the ammoniacal solution of gold, before the published experi- 
 ments of Mr. Jordan and Mr. Spencer appeared. Mr. Wool- 
 rich, however, never published an account of his experiments, 
 as, from the imperfect nature of the voltaic batteries then in 
 use, the deposition of copper was considered too troublesome 
 to be valuable ; and, from the same cause, he was unable to 
 
15 
 
 repeat his experiments on gilding. There are, no doubt, many 
 individuals who similarly experimented, but the historian has 
 only to do with published experiments ; and the present 
 instances are only adduced to show that voltaic precipita- 
 tions were so strikingly brought before experimenters in 
 electrical science, that it would have been impossible for 
 them to have been much longer neglected. 
 
 28. Since the experiments of Jacobi, Jordan and Spencer, 
 many individuals have contributed to the perfection of the 
 art of electro-metallurgy. Among those whose labours have 
 advanced the art to its present state, must be particularly 
 mentioned the names of Mason, Murray, Smee, Elkington and 
 Woolrich. 
 
 29. To Mr. Mason the art is indebted for the suggestion 
 of an arrangement of the electro-metallurgical apparatus more 
 completely under controul than that of Mr. Spencer, and 
 which led to the introduction of the voltaic battery in electro- 
 metallurgical operations as a separate and independent source 
 of electricity, instead of making the surface on which the 
 deposit was taking place a part of the electrical apparatus, as 
 had been done by previous experimenters. Mr. Murray con- 
 tributed the first completely successful process for causing a 
 deposit to take place on non-metallic surfaces. Mr. Smee 
 has experimented extensively, and with much success, on 
 the circumstances under which the various metals may be 
 deposited from their solutions. Mr. Elkington discovered a 
 class of salts from which gold and silver may be precipitated 
 with much greater success than from any previously known ; 
 and Mr. Woolrich has succeeded in applying the magneto- 
 electric current to the reduction of metals, a discovery which 
 promises to be of greater importance than any with which the 
 art has hitherto been enriched. 
 
16 
 
 CHAP. 11. 
 
 CHEMISTRY AND ELECTRICITY AS CONNECTED WITH 
 ELECTRO -METALLURGY. 
 
 30. A GENERAL knowledge of the laws of chemistry and the 
 allied sciences, is essential to the successful practice of electro- 
 metallurgy ; every process in the art is a chemical or an elec- 
 trical process, determined by conditions and controuled by 
 forces, the study of which constitutes the science of chemistry. 
 
 31. Every natural object with which we are at present 
 acquainted, whatever its origin, whether animal, vegetable or 
 mineral ; whatever its physical condition, whether solid, liquid 
 or gaseous, and whatever its physical properties, consists of 
 one of the bodies enumerated in the following table, or is a 
 compound of two or more of them. These bodies are called 
 elements, because they cannot be decomposed or resolved 
 into other simpler forms of matter, and they are hence sup- 
 posed to be the ultimate bodies or elements, of which material 
 objects are composed. 
 
 (32.) TABLE OF ELEMENTS 
 
 WITH THEIR EQUIVALENT NUMBERS OR COMBINING PROPORTIONS. 
 
 Oxygen . 
 
 Hydrogen 
 
 Nitrogen 
 
 Carbon . 
 
 Sulphur 
 
 Selenium 
 
 Phosphorus 
 
 Boron . 
 
 Silicon . 
 
 Chlorine 
 
 Iodine . 
 
 Bromine 
 
 Fluorine 
 
 Potassium 
 
 8.01 
 1. 
 14.19 
 6. 
 
 16.12 
 39.63 
 31.44 
 10.91 
 22.22 
 35.47 
 126.57 
 78.39 
 18.74 
 39,26 
 
 Sodium . 
 
 I/ithium 
 
 Barium . 
 
 Strontium 
 
 Calcium 
 
 Magnesium 
 
 Aluminum 
 
 Glucinum 
 
 Zirconium 
 
 Thorium 
 
 Yttrium 
 
 Manganese 
 
 Iron 
 
 Zinc 
 
 23.31 
 6.44 
 68.66 
 43.85 
 20.52 
 12.69 
 13.72 
 26.54 
 33.67 
 59.83 
 32.25 
 27.72 
 27.18 
 32.31 
 
17 
 
 Cadmium . . . 
 
 . . 55.83 
 
 Molybdenum . , 
 
 • . 47.96 
 
 
 
 
 
 Nickel . . 
 
 . . 29.62 
 
 Columbium . . 
 
 . . 184.9 
 
 
 31.71 
 
 Tellurium ... 
 
 . . 64.25 
 
 Bismuth . . 
 
 ! . 7l!07 
 
 Titanium . . . 
 
 . . 24.33 
 
 Lead . . . 
 
 . . 103.73 
 
 Osmium . . . 
 
 . . 99.72 
 
 
 
 
 . . 101.43 
 
 
 
 
 
 
 , . 217.26 
 
 Gold .... 
 
 . . 199.21 
 
 
 
 
 
 Antimony . . 
 
 . . . 129.24 
 
 Palladium . . . 
 
 . . 53.36 
 
 
 . . 28.19 
 
 
 
 Vanadium . . 
 
 . . 68.66 
 
 
 
 33. These elementary bodies are rarely found in nature 
 uncombined. When presented to each other under certain 
 conditions, they enter into combination so as to form com- 
 pounds, which are generally possessed of physical" characters 
 very dissimilar to those of their constituent elements. The 
 force by the operation of which the elements of a compound 
 are, in the first instance, made to combine, and by which 
 they are afterwards held together, is called chemical affinity. 
 It is essentially distinct from the other attractions or affini- 
 ties, as gravitation and magnetism; these produce changes 
 only of a physical character : whereas, chemical affinity pro- 
 duces changes only in the chemical or elementary constitu- 
 tion of bodies ; and the physical changes it commonly effects, 
 are secondary or indirect consequences of its action. 
 
 34. These elements combine only in certain proportions; 
 — that is to say, on presenting together two elements which 
 have an affinity for each other, a combination is formed, in 
 which the quantities of the elements have a certain relation. 
 The proportions in which any two elements combine with 
 each other, are the same as those in which either of these 
 elements combines with a third ; and further, if any two 
 elements combine together, in two or more different pro- 
 portions, so as to form two or more different compounds, 
 the quantities in the several compounds have a very simple 
 relation to each other. 
 
 35. Suppose four elements, A, B, C, D, to be capable of 
 combining together so as to form a variety of compounds ; — ■ 
 
 c 
 
18 
 
 and suppose, further, that one part by weight of A, combines 
 with two parts of B, to form a compound, with three of C to 
 form another, and with four of D to form a third. Now, it 
 is found that these numbers not only represent the propor- 
 tions in which these bodies combine with A, but also the 
 proportions in which they combine with each other. For 
 example, if there exist a compound formed by the union of 
 B and C, the proportions of those elements will be repre- 
 sented by the numbers above associated with them,— namely, 
 two of the former and three of the latter, or some multiple of 
 those numbers. Further, the proportion of any one of these 
 elements represented by its number, is chemically equivalent 
 to the proportion of either of the other elements represented 
 by its number : thus, if a compound consisting of three parts 
 of C, and four of D, be decomposed by the addition of the 
 element A, the proportion of this last element requisite for 
 such decomposition is represented by 1, which will com- 
 bine with 3 of C, or 4 of D, and by that combination will 
 liberate 3 of the former, or 4 of the latter, as the case may 
 be. It is evident, then, that 1 of A is equal to— inasmuch 
 as it takes the place of— 4 of D or 3 of C in a chemical com- 
 pound, and vice versa. These combining numbers of the 
 various elementary bodies, are called their chemical equiva- 
 lents, and are the numbers placed opposite to them in the 
 table. 
 
 36. If we consider with chemists generally, that matter 
 exists in the form of atoms,— that is to say, minute, indi- 
 visible, unalterable particles, then the equivalent numbers of 
 the elements represent the relative weights of their atoms. 
 
 37. Many remarkable and interesting relations present 
 themselves in studying the laws of chemical combination ; 
 but it is only to those laws of combination, and those com- 
 pounds, which have immediate reference to electro-metal- 
 lurgy, that attention will be here directed. Electro-metal- 
 lurgy is an art by which metals are reduced from their 
 
19 
 
 soluble compounds, by the agency of electricity ; these com- 
 pounds are called salts, and their constitution must be briefly 
 studied. 
 
 38. There are two classes of salts. In one class the metal 
 is directly combined with an electro-negative body, and thus 
 only two elements enter into its composition. For example, 
 chlorine and copper combine to form a salt called chloride of 
 copper. In the other class each of the constituent elements 
 of the salt is a compound ; thus, sulphate of copper consists 
 of sulphuric acid and oxide of copper — the sulphuric acid is 
 a compound of sulphur and oxygen, and the oxide of copper, 
 of copper and oxygen. 
 
 39. It will be observed that, in the first named salt 
 (chloride of copper), a simple body or element is combined 
 with a simple body ; while, in the other (sulphate of copper), 
 a compound combines with a compound ; and it was formerly 
 thought by chemists that this law was general, — that is to 
 say, that elements can only combine with elements, and 
 compounds with compounds. Such an opinion is no longer 
 entertained ; for it is now known, with certainty, that in several 
 cases this law does not obtain, and the opinion that it has no 
 foundation whatever in nature, is fast gaining ground. 
 
 40. When two elements combine together in the least pro- 
 portions, the simplest state in which w^e can conceive of their 
 connection, is that of an atom of one directly associated with 
 an atom of the other (36) ; and there is no reason why we 
 should suppose any other method of combination : but when 
 one of the elements in a compound is not in its least pro- 
 portion, we may suppose the bodies to be grouped together 
 in two ways. We may either suppose that one atom (36) 
 of one of the elements is directly combined with two 
 atoms of the other ; or we may suppose that a compound is 
 first formed between the elements, consisting of one atom of 
 each, and that this compound is combined with the second 
 atom of the element in greatest quantity. On this latter 
 
 c 2 
 
20 
 
 supposition we admit the combination of an element with a 
 compound, in opposition to the view which supposes that 
 elements can only combine with elements. (39.) 
 
 41. If we adopt this view (and there are powerful reasons 
 for believng it to be the correct one) we may regard the 
 salts as all similarly constituted. Sulphatq of copper, which 
 is formed by adding sulphuric acid to oxide of copper, is 
 not to be regarded as a compound, in which the acid and 
 oxide still exist ; but we may suppose it to be a direct com- 
 pound of the metal, copper, with a radical,* composed of 
 sulphuric acid and oxygen ; — we may suppose that, on 
 adding sulphuric acid to oxide of copper, the oxide first 
 suffers decomposition, by yielding its oxygen to the sul- 
 phuric acid, to form the radical in question, and that this 
 compound immediately combines with the liberated metal. 
 This hypothetical compound radical, whose composition is 
 that of sulphuric acid with an additional equivalent of oxygen, 
 may be called sulphat-oxygen ; and the salt, instead of being 
 called sulphate of copper, should, in confonnity with this 
 view, be called sulphat-oxide of copper. 
 
 42. These considerations have an important bearing on the 
 theory of electro-metallurgical processes; for, on the latter 
 view, the deposition of a metal is owing to the resolution of 
 a salt into its compound radical and the metal ; while, in 
 the former view, the deposition of a metal must be regarded 
 as a secondary result, brought about by the decomposition of 
 the water in which the salt is dissolved. The importance 
 of these considerations will be more evident in studying the 
 decomposition of salts by the electric current. 
 
 43. Electricity is an agent intimately allied to, if not iden- 
 tical with, chemical affinity. (33.) Of its ultimate nature, 
 as of that of every other natural agent, we know literally 
 
 * A radical is a body which, though compound, acts the part of an element. 
 Thus cyanogen, a compound of carbon and nitrogen, combines with potassium, 
 sodium, &c. 
 
21 
 
 nothing; nor does our Imowledge of its effects enable us 
 even to frame a consistent theory. By some philosophers it 
 is considered as a fluid, subtle in the highest degree, — per- 
 vading every species of matter, — unrecognised when quies- 
 cent, and developing itself in the various forms before spoken 
 of, when, by the arrangement of the necessary conditions, it 
 is set in circulation. Others, again, have been led by its 
 effects to consider it as a compound fluid, which only puts 
 forth its extraordinary powers when decomposed ; that this 
 decomposition takes place in the voltaic battery, and other 
 electrical machines ; and that these fluids circulate through 
 those instruments in contrary directions. Other philosophers 
 have rejected the idea of circulation : they regard it as an 
 affection of ordinary matter, or of the hypothetical ether, 
 the vibrations of which, constitute light. Nor are these the 
 only theories that have been framed to connect together the 
 beautiful phenomena of electricity : scarcely a philosopher of 
 distinction can be pointed out who does not entertain views 
 on this subject peculiar to himself. We shall not follow 
 these speculations into detail, but content ourselves with a 
 knowledge of the facts of the science. 
 
 44. Electricity may be excited, or set in circulation, in a 
 variety of ways ; — by the friction, compression, and rupture of 
 bodies ; — by the agency of heat and chemical action ; — and 
 by the motion of metals in the vicinity of magnetic bodies. 
 
 45. By rubbing resinous and vitreous bodies on dry 
 animal or vegetable matters, they acquire the property of 
 attracting light bodies, and of exhibiting other new and 
 extraordinary properties. On presenting a rounded metallic 
 body, or the knuckle of one of the fingers, to a stick of 
 sealing wax, which has been rubbed with dry flannel, a 
 snapping noise occurs when the knuckle is brought near 
 the wax, arising from the passage between them of a 
 luminous spark, which may be seen by performing the 
 experiment a dark room. These, and the many othpv 
 
22 
 
 properties exhibited by the sealing wax, are dependent on 
 the peculiar condition into which it has been brought by 
 friction with the flannel. A body exhibiting such properties 
 is said to be electrical, and the unknown cause of these pro- 
 perties is called electricity. 
 
 46- Electricity can be transferred from the body in which 
 it is excited to a second body, and from that to a third, &c. 
 This transferrence can only take place with certain bodies, 
 which are called conductors, and through the substance of 
 which electricity passes; while another class of bodies, called 
 non-conductors, do not admit of its passage through them. 
 Metals and charcoals are the only true conductors, as it is 
 only through them that it can pass without producing change. 
 In passing through other bodies, such as salts (38), it is only 
 conducted by virtue of the decomposition of the salt, and the 
 quantity of electricity conducted is in strict relation to the 
 quantity of salt decomposed, 
 
 47. The quantity of electricity produced by the friction, 
 compression, and rupture of bodies, is too small in quantity 
 to be of any value in electro-metallurgical operations, and 
 recourse must be had, in this art, to the electricity produced 
 by chemical action, by heat, or by magnetism. Electricity 
 may be produced more copiously from these sources than 
 from any other, and they must, therefore, be treated somewhat 
 in detail. 
 
 48. If a plate of ordinary zinc be plunged in dilute sul- 
 phuric acid, violent effervescence occurs ; the oxygen of the 
 water (as will presently be shown) combines with the metal, 
 forming ozide of zinc, which, uniting with the sulphuric acid, 
 forms sulphate of that metal ; while the hydrogen, the other 
 element of the water, escaping in the gaseous form, occa- 
 sions the effervescence observed ; eventually, the zinc disap- 
 pears, and the dilute acid is replaced by a solution of the 
 sulphate of zinc. If, during the time this phenomenon 
 is taking place, a strip of copper be introduced into the 
 
23 
 
 solution, and made to touch the zinc, effervescence also 
 occurs at its surface, by the escape of hydrogen, although it 
 will be found that no chemical action takes place upon the 
 copper. The escape of hydrogen, however, will be much 
 less than at the surface of the zinc. 
 
 49. Now, inasmuch as the copper has not been chemically 
 acted on, it is evident that the hydrogen appearing at its 
 surface can only result from the decomposition of the water 
 effected by the zinc ; and its appearance in such a part of 
 the arrangement is, at first sight, calculated to excite sur- 
 prise. This circumstance, however, is satisfactorily ex- 
 plained, by the fact, that pure zinc, except when in contact 
 with another metal, is perfectly insoluble in dilute sulphuric 
 acid ; and then, although the chemical action takes place 
 entirely at the surface of the zinc, the whole of the hydro- 
 gen escapes at the surface of the metal in contact with 
 it. We shall not enquire in this place why the hydrogen 
 appears in such a part of the arrangement; it is sufficient 
 to know the fact, to enable us to understand the experiment 
 under consideration. 
 
 50. We now perceive, in relation to the preceding experi- 
 ment, that in reality not an atom of hydrogen presents itself 
 at the true surface of the zinc, but that it is evolved from the 
 particles of foreign metals and charcoal with which the zinc 
 is contaminated, and which are scattered about its surface. In 
 other words, that which takes place on the large scale, when 
 a plate of pure zinc is associated with a plate of copper, and 
 immersed in the acid solution, takes place on a small scale 
 when impure or ordinary zinc is used alone, the surface of 
 that metal presenting almost an infinity of such combina- 
 tions. 
 
 51. In making this experiment, it is not necessary to 
 place the metals in contact under the surface of the liquid ; 
 they may be brought in contact at a point external to the 
 
•24 
 
 liquid, as shown in tlie accompanying figure, or may be con- 
 nected by the interposition of a third piece of Fig. l. 
 metal. 
 
 52. This action only takes place during 
 the time that the metals are connected to- 
 gether (either immediately, or by the inter- 
 vention of a third piece of metal) ; if they 
 are removed from each other, however small 
 the distance, the evolution of gas ceases. If 
 the plates are allowed to remain in contact, 
 after a considerable time (dependent on the 
 proportions of the ingredients) the efferves- 
 cence will become less violent, and will 
 
 eventually cease. (48.) Let us now proceed to analyze the 
 experiment : the zinc weighs considerably less than when 
 introduced ; the sulphuric acid is replaced by a solution 
 of the sulphate of zinc ; the copper is wholly unatfected ; 
 and the gas evolved from the latter metal is found to be 
 hydrogen. 
 
 53. An attentive consideration of these results leads us to 
 the conclusion, that the water of the dilute acid has been 
 decomposed ; for, as the sulphate of zinc produced is a com- 
 pound of sulphuric acid and the oxide of zinc, it is evident 
 that oxygen must have been supplied to that metal by the 
 water; and this view is confirmed by the fact, that the 
 hydrogen given off by the copper is in such proportion, that, 
 if combined with the oxygen of the oxide of zinc, water 
 would be the product. 
 
 54. In this experiment the enquiry arises, — why do not 
 the oxidation and solution of the zinc take place without the 
 presence of a second metal ; and how comes it that the 
 hydrogen, resulting from the decomposition of the water, 
 does not present itself at the surface of the zinc, where it is 
 developed, but passes through the liquid, and is evolved at 
 
25 
 
 the other metal? The question suggests the answer: — the 
 facts, that the metals must be in intimate contact, and both 
 immersed in the same acid, — that the only element set free is 
 carried to a point, at a considerable distance from that at 
 which it is liberated, — demonstrate that the chemical action 
 which takes place is accompanied by the circulation of some 
 extraordinary power, or would seem rather to be dependent 
 on it ; for, when, by breaking the contact between the plates, 
 we interrupt its circulation, all chemical action ceases. 
 
 55. That some new power is thus called into action, we 
 have abundant evidence. It has already been observed that 
 the plates, instead of being in actual contact, may be con- 
 nected together by a third piece of metal ; nay, if a stout 
 copper wire, a mile long, be employed, and one end of 
 it be made to touch the zinc, and the other the copper, 
 the same phenomena will be presented. Now, the whole 
 length of this connecting wire exhibits some remarkable 
 changes in its physical characters. Before its introduction 
 between the plates of our rude voltaic apparatus, it was 
 perfectly inert with regard to magnetic bodies ; but now it 
 attracts iron filings as though it were a magnet ; and a com- 
 pass, or magnetic needle, brought near it, is powerfully 
 deflected. It exhibits, moreover, calorific and chemical phe- 
 nomena. By making the connection between the plates with 
 a short and very fine wire, a powerful calorific ejSect will be 
 developed ; the wire will glow with the most intense heat ; 
 and if the action of the apparatus be sufiiciently energetic, 
 will be fused and dissipated in minute globules, or will bum 
 with a brilliant scintillation. 
 
 56. Again, let the connection between the plates be made 
 through the solution of some chemical compound, easily 
 decomposed — iodide of potassium, for example — and the 
 elements of that compound will be separated. All these 
 facts demonstrate the operation of some subtle power, which, 
 
26 
 
 from its presence in every part of the arrangement, is be- 
 lieved to circulate through it, and, under the circumstances 
 enumerated, to develope itself in the various forms of magne- 
 tism, heat, and light. (55.) That agent is voltaic electricity. 
 
 57. The apparatus just now described differs only from the 
 pile of Volta and the other batteries enumerated elsewhere 
 in consisting of but one pan* of plates, while they are 
 formed by the assemblage of several such pairs. The pile 
 or battery is a series of arrangements similar to the one 
 just experimented with, so disposed that the zinc of one cell 
 is connected with the copper of the next, the zinc of that 
 with the copper of a third, and so on, to any extent. Such 
 a form of instrument is called an intensity arrangement, while 
 the single pair of plates is called a quantity arrangement. 
 The different properties of quantity and intensity we will 
 now illustrate. 
 
 58. A single voltaic pair, it has already been said, will 
 decompose iodide of potassium; but if the connection be- 
 tween the plates be made with other compounds, — water, for 
 example, — no decomposition of the water will take place ; 
 the voltaic current will not pass (for water can only conduct 
 it by suffering decomposition), and, consequently, the battery 
 will be as inactive as though no such connection had been 
 made. If, however, water be made the medium of communi- 
 cation between the ends of a compound battery, consisting 
 of nine or ten pairs, the water will be rapidly decomposed, 
 and the voltaic current will pass, as the escape of hydrogen 
 at the surface of each copper plate of the battery will demon- 
 strate. The single pair is called a quantity arrangement, 
 because it decomposes, with the consumption of a given 
 quantity of zinc and acid, as great an amount of any com- 
 pound which it can decompose, as the other arrangement 
 decomposes, by an equal consumption of materials, in each 
 cell of the battery ; but there are very few compounds which 
 
27 
 
 may be resolved into their constituent elements by a single 
 pair. 
 
 59. A case will, perhaps, make the matter more clear. 
 Suppose we have a battery consisting of ten cells, and that 
 water be made the medium of communication between its 
 extremes, as much water will be decomposed by this instru- 
 ment as by one of a hundred pairs, supposing them to be 
 similarly circumstanced in every respect. This, at first 
 sight, appears paradoxical ; but an examination of the nature 
 of the chemical action in the voltaic battery will remove 
 every difficulty. 
 
 60. The annexed diagram, 2, represents a single voltaic 
 
 Fig. 2. pair, consisting of a plate of 
 
 zinc, a, and another of cop- 
 per, b, immersed in a vessel 
 of dilute sulphuric acid ; a 
 wire from the zinc is con- 
 
 nected with a plate of platinum, c, in a second vessel, contain- 
 ing dilute acid ; and a wire from the copper is attached to 
 another plate of platinum, d, also in the acid solution. It 
 has already been said that a single pair will not decompose 
 water; but in this illustration we will suppose it to pos- 
 sess that power (for, by a slight modification, it may be 
 made to do so), as we prefer that, in this experiment, water 
 should be the compound decomposed. The voltaic current, 
 then, originating at the surface of the zinc, gives rise to the 
 combination of oxygen with that metal ; while hydrogen 
 escapes at the surface of the copper ; we will suppose the cur- 
 rent passing from the copper through its wire to the platinum 
 plate in the second vessel, thence through the liquid to the 
 other platinum plate, and through its wire to the zinc. 
 
 61. Now, in tracing the current through the battery, it will 
 be observed that oxygen is that element of the decomposed 
 water which occurs at the surface from which the current 
 
28 
 
 enters the liquid ; and that hydrogen, the other element of 
 water, is disengaged at the sm-face where the current leaves 
 the liquid, — namely, the copper. On examining the decom- 
 position in the second cell, precisely the same thing occurs ; — 
 oxygen is liberated at the surface of that platinum plate con- 
 nected with the copper, and at which the current enters, and 
 hydrogen at the other plate, or that surface where the current 
 leaves the liquid ; nay, further, the quantity of water decom- 
 posed in the second cell is exactly equal to the quantity 
 decomposed in the battery ; the hydrogen is equal in volume 
 to that given off in the battery, and the oxygen equal to that 
 which has combined with the zinc. 
 
 62. We must here repeat, that we have assumed, for the 
 purpose of explanation, that which is not strictly correct ; 
 inasmuch as a single cell will not decompose water, except 
 under circumstances which we have not introduced into the 
 experiment: but other substances may be decomposed by 
 such an apparatus, and the results are in perfect accordance 
 with what has been said : an amount of such compound will 
 be decomposed, chemically equivalent to the amount of water 
 decomposed in the battery. Our reason for putting the ex- 
 periment in the above form is, that no misconception may 
 arise respecting the chemical action of voltaic electricity ; 
 for the decomposition of the same compound has been 
 effected both in the battery and in the secondary cell, and 
 the amounts of such decompositions not, as they must have 
 been with dissimilar compounds, relatively, but absolutely 
 the same. 
 
 63. We will now proceed to a consideration of the com- 
 pound battery ; and in that instrument we shall have a 
 further confirmation of the view we have been endeavouring 
 to enforce, i.e., that the voltaic current, in passing through 
 any solution, effects the same amount of decomposition as is 
 effected in the battery itself. 
 
29 
 
 64. The annexed diagram, j'i'^. 3, will serve to illustrate the 
 Fig. 3. nature of the compound bat- 
 tery, — to explain the cause 
 of the intensity of such a 
 modification, — and to recon- 
 cile the apparent anomaly, 
 that such an arrangement 
 evolves a current no greater 
 in quantity than that gene- 
 rated in any one of its cells. 
 The apparatus represented 
 consists of a series of cells, 
 each containing a plate of 
 
 zinc, a, and another of copper, b, immersed in dilute sul- 
 phuric acid ; the zinc of one cell being joined to the copper 
 of the next. An apparatus, arranged as the above, would be 
 extremely active ; the evolution of hydrogen would be very 
 copious, and the zinc would rapidly dissolve, for there is no 
 obstruction to the passage of the voltaic current. 
 
 65. To begin our illustration, let the reader imagine, in the 
 first instance, that only one of the cells of this compound 
 battery is in action ; it is immaterial which is selected ; the 
 current of electricity generated in that cell has to pass through 
 each of the others ; and, as we have before shown (60), 
 in passing through the dilute acid, the water of that acid will 
 be decomposed, oxygen will be developed at the surfaces 
 where the current enters, and hydrogen at the surfaces where 
 it leaves the solution ; so that this current, supposing it 
 capable of passing through a hundred such cells, would 
 decompose in each as much water as was decomposed in 
 the battery. Now, this current meets no obstruction what- 
 ever in passing through the airangement described ; on the 
 contrary, it acquires an additional impulse at every cell, for 
 each one, being precisely similar to that from which the 
 current was supposed to originate, is equally favourable to 
 
30 
 
 the passage of a voltaic current ; and hence the current is 
 accompanied by a given amount of chemical action in its 
 passage through each cell, and acquires thereby additional 
 intensity. In other words, each cell of a compound battery 
 is a decomposition cell, in which the materials are so arranged 
 that, instead of obstructing the passage of the current, there 
 is a disposition to the generation of one. 
 
 66. The reader will now perceive the cause of the intensity 
 of the compound battery, and, recollecting that the same 
 current effects the decomposition in each cell, will no longer 
 be surprised that the quantity of electricity in a compound 
 battery is no greater than that of one of its cells. 
 
 67. If any one of the wires connecting the plates of the last 
 described apparatus be severed, and the cells be ranged in a 
 straight line instead of a circle, it will immediately be recog- 
 nised as the couronne des tasses of Volta, described in another 
 part of this treatise ; the wires which now constitute the 
 ends of the apparatus, have been very inappropriately 
 termed the poles of the battery. After what has been 
 said, it is hardly necessary to remark that, by plunging 
 them in water, the circuit being again completed, the action 
 of the battery recommences, and the water will be decom- 
 posed. 
 
 68. It was formerly believed that the decomposing power 
 of the voltaic battery was owing to an attraction existing 
 between these wires and the elements of the compound ; it 
 is evident that such a view is incompatible with the present 
 state of science ; still, however, the terminal wires of a 
 battery are called the positive and negative poles. Many 
 attempts have been made to introduce less objectionable 
 names, but they have been only partially successful. It was 
 proposed by Faraday to call them electrodes, or passages 
 for the electricity ; the one being distinguished as the anode 
 and the other as the cathode, in reference to the presumed 
 direction of the current. It has also been advised to call 
 
31 
 
 them the zincode and platinode ; and a third party has named 
 them oxode and hydrode. 
 
 69. The reader will bear in mind that the words negative 
 pole, cathode, and platinode are synonymous, and are em- 
 ployed to designate the plate or metal, which, considering 
 the decomposition cell as one of the cells of the battery, holds 
 the place of the copper, silver, or platinum ; and that the 
 positive pole, anode, zincode, or oxode is that at which 
 oxygen, acids, &c., appear, and corresponds to the zinc of 
 the battery. 
 
 70. There are other circumstances connected with the de- 
 compositions effected by electricity, which must be noticed 
 in this place. No solid can sutfer decomposition in the vol- 
 taic circuit ; nor can any liquid, excepting such as conduct ; 
 and in them conduction and decomposition are, with few 
 exceptions, inseparable. For example, chloride of silver is, 
 at ordinary temperatures, a solid ; and in that state resists 
 decomposition by the most powerful apparatus : by the appli- 
 cation of heat, this compound fuses, and in that state conducts 
 the current even of the feeblest voltaic arrangement, and, 
 at the same time, suffers decomposition. Water affords an 
 illustration still more striking. In its ordinary, or fluid, state, 
 it is decomposed by a current of moderate intensity ; but 
 when frozen the utmost intensity will not effect the separa- 
 tion of its elements ; for in such a state it does not conduct 
 the voltaic current. If one of the platinum plates in the 
 apparatus be coated with the thinnest film of ice, the current 
 will be completely arrested. 
 
 71. There are apparent exceptions to both these laws. 
 Experiments have been adduced in which compomids, in 
 the solid state, appear to have been decomposed, and in 
 which liquids have conducted without decomposition. 
 
 72. Many of the changes which occur in the voltaic circuit 
 are due to what is called secondary action. In the case of 
 aqueous solutions, many of the decompositions may be traced 
 
32 
 
 to the action of the oxygen and hydrogen, evolsxd by the 
 passage of the current through the water, and are inde- 
 I)endent of the voltaic power. The direct action of the 
 voltaic current is very limited, as only compounds of a 
 particular constitution are susceptible of such decomposi- 
 tion ; and this constitution not with relation to the elements, 
 but the proportion of those elements ; for of two compounds, 
 formed of the same elements, one may suffer, and the other 
 resist, decomposition. 
 
 73. Only those compounds consisting of one equivalent or 
 proportion of each element are affected by the voltaic current. 
 It is not, however, essential that the elements should be simple, 
 undecomposable bodies; for a body, the constituents of which 
 are compound, suffers decomposition, or is resolved into those 
 proximate elements; and these proximate elements themselves 
 may even be so constituted as not to yield up their compo- 
 nent parts in the voltaic circuit. Examples will impress this 
 law upon the memory. Water is a compound of one atom or 
 proportion of each of its elements, and, consequently, in 
 accordance with the law above stated, is decomposed by the 
 voltaic battery. But any compound of the same elements in 
 a different proportion would not suffer decomposition. If 
 there were a compound of two atoms of hydrogen and one of 
 oxygen, it would not be affected by voltaic electricity. And 
 so with those substances whose constituent parts are com- 
 pounds ; in order to suffer decomposition by the voltaic cur- 
 rent, they must consist of one equivalent, or proportion (35), of 
 each of their component elements. Sulphate of copper, for 
 example, is resolved into sulphuric acid and oxide of copper; 
 though the sulphuric acid will not, under similar circum- 
 stances, be decomposed, for it is not a binary compound ; 
 nor will oxide of copper, because it is a solid.* 
 
 * The chemical reader need not be reminded that, in this treatise, the equivalent 
 of hydrogen, and the composition of water, as given by British chemists, are 
 assumed, in opposition to the views of continental authorities. The assumption 
 
33 
 
 74. From what has been said respecting the constitution of 
 salts (40), it is evident that, if the theory which assumes the 
 direct combination of a metal with a compound radical, be 
 the true theory, their decomposition in the voltaic circuit, is a 
 direct or primary effect ; and it is equally evident, that it is a 
 secondary effect, if salts are constituted of an acid combined 
 with an oxide. 
 
 75. By adopting the new theory, the appearance of metal 
 at the negative electrode, and acid combined with an addi- 
 tional equivalent of oxygen (41) at the other, is at once 
 accounted for ; but, if the old theory be adopted, it is neces- 
 sary to assume the decomposition of water, and to attribute 
 the decomposition of the salt to the nascent hydrogen of the 
 decomposed water ; for, according to the law of voltaic de- 
 compositions (73), the direct effect of the cuiTent is to resolve 
 the salt, on this theory, into a metallic oxide and an acid. 
 Instead, therefore, of assuming the decomposition of the salt, 
 the water in which it is dissolved is believed to be decom- 
 posed ; and the decomposition of the salt is accounted for, by 
 supposing the hydrogen of the water to combine with the 
 oxygen of the metallic oxide, whereby metal is liberated 
 and acid set free ; while the oxygen of the water is liberated 
 at the other electrode. 
 
 has only been made on the ground of convenience, and no remarks in a treatise 
 like the present, can have reference to so important a question. 
 
 D 
 
34 
 
 CHAP. III. 
 
 ON THE VOLTAIC BATTERY. 
 
 76. The science of Voltaic Electricity originated in an 
 experiment made by Galvani in the year 1790. He observed 
 that, on placing a recently killed animal upon a plate of zinc, 
 and touching it with a wire or plate of copper, also in con- 
 tact with the zinc, violent contractions of the muscles of the 
 animal immediately occurred. Although it was this experi- 
 ment that determined the masterly researches of Volta, and 
 from which the science must date its origin, yet an anala- 
 gous fact was known long prior to Galvani's discovery. It 
 had been announced, in an obscure German work, entitled 
 " The General Theory of Pleasures," that if a plate of zinc 
 were placed upon the tongue, and a piece of silver under it, 
 a strange taste would be observed each time the edges of the 
 pieces of metal were brought in contact. This experiment, 
 however, attracted no attention, and cannot be said to have 
 any connection with the progress of our science. 
 
 77. In repeating the experiments of .Galvani, Volta was led 
 to the construction of an instrument, which, in honour of its 
 illustrious inventor, is called the voltaic pile. This instru- 
 ment consists of a series of plates of dissimilar metals, usually 
 copper and zinc j these, to the extent of forty or fifty, are 
 piled upon each other in regular succession, a piece of card or 
 flannel, wetted with a saline or acid solution, being interposed 
 
35 
 
 between the metals of each pah*. It is represented in j'?^/. 4, 
 Fig. 4. where a is the plate of zinc, b the plate of copper, 
 and c the moistened flannel. It was found that 
 the effects of this instrument were much more 
 powerful than those of a single pair of plates, and 
 that it exhibited a series of new and extraordinary 
 phenomena. If the moistened hands were brought 
 in contact with the ends of such a pile, a distinct 
 shock would be felt ; and the leaves of gold-leaf 
 electrometers similarly situated were observed to 
 diverge. By connecting wires to the ends of this 
 instrument, and plunging them in water, minute 
 bubbles of gaseous matter escape from them : on examina- 
 tion, these bubbles are found to consist of oxygen and 
 hydrogen, the gaseous constituents of water. The wires 
 thus connected to the ends of the pile are called its poles ; and 
 by them the effects of the instrument could be transmitted 
 to almost any distance. The cause of the phenomena ex- 
 hibited by the pile of Volta has been already explained. (54.) 
 
 78. The plates of zinc in this and other batteries, are 
 called the positive plates, because the whole of the chemical 
 action is confined to them. The copper or silver plates are 
 called the negative plates. The arrangement of the ele- 
 ments exhibited in Jig. 4 is, in many respects, inconvenient; 
 and Volta contrived another arrangement, which he called 
 
 Fig. 5. 
 
 the couronne des 
 tasses {see Jig. 5). 
 This instrument 
 consists of any 
 number of vessels 
 containing the acid solution, and an equal number of bars of 
 zinc a and silver b soldered end to end, and so bent that, while 
 the zinc bar rests in one of the vessels, the slip of silver 
 soldered to it hangs in the other. This arrangement is 
 decidedly superior to the pile ; and it is worthy of remark, 
 
 d2 
 
36 
 
 that the voltaic batteries of the present day scarcely differ 
 from this modification. 
 
 79. The next alteration in the voltaic apparatus was made 
 
 Fig. 6. 
 
 by Mr. Cruikshanks — [Jig. 6). 
 The plates in his battery were 
 square, and the copper a and 
 zinc h of each pair were sol- 
 dered together. These com- 
 pound plates were cemented in grooves cut transversely in a 
 wooden trough, and themselves formed a series of compart- 
 ments for holding the exciting liquid. In using this instru- 
 ment, the dilute sulphuric acid was poured into the trough, 
 which was so inclined that each compartment became filled 
 with an equal quantity of the liquid. This instrument pos- 
 sesses many inconveniences : if the plates are situated at a 
 great distance from each other, the action is impeded ; and 
 if, to remove this objection, the plates are placed near each 
 other, the cells are too diminutive to hold the requisite 
 quantity of acid. The impossibility of removing the zinc 
 plates for the purpose of cleaning them, is also a serious 
 Fig. 7. objection. These inconveniences 
 
 suggested the modification, called 
 Babbington's battery — [Jig. 7). 
 This consists of an earthenware 
 trough, divided into a number of 
 compartments, in each of which 
 is placed a plate of zinc a, and 
 near that, a plate of copper the zinc of one cell being 
 connected w\\h the copper of the next. The series is sus- 
 pended from a bar of wood. This battery, like the former, is 
 excited by dilute sulphuric acid : its superiority consists in 
 the facilities afforded for removing the zinc plates, and in 
 the close approximation of the metals — points of great im- 
 portance. It was by an instrument of this kind that the 
 splendid experiments of Davy were performed. 
 
 TPf 
 
37 
 
 80. The next improvement was introduced by Dr. Wol- 
 laston. He completely surrounded the zinc with the copper 
 — an alteration which was found to increase the amount of 
 available power, to nearly double that, previously obtained 
 from an equal extent of zinc surface. The improvement 
 which comes next in order is, perhaps, the most im- 
 portant one that has yet been introduced ; it is the amalga- 
 mation of the surfaces of the zinc plates by mercury. For 
 this valuable contribution we are indebted to the late Mr. 
 Kemp. 
 
 81. It has already been stated (49) that when impure zinc 
 is used in voltaic experiments, the impurities (such as minute 
 portions of charcoal and foreign metals) with which the 
 zinc is contaminated form an infinity of galvanic circles, by 
 virtue of which the metal dissolves. Hence, when ordinary 
 zinc is introduced into dilute sulphuric acid, it dissolves 
 rapidly ; and its solution is accompanied with violent effer- 
 vescence, occasioned by the escape of hydrogen. Now, the 
 voltaic electricity, with which the solution of the zinc is 
 accompanied, is, in this case, confined to such minute circles 
 that we cannot divert it into a new channel, so as to make it 
 subservient to our purpose; and, as the whole of the zinc 
 dissolved, and acid saturated, yield no curi'ent, this local 
 action, as it is called, occasions much waste in the materials 
 of the battery. The improvement in question completely 
 destroys this local action. 
 
 82. By using pure zinc in the construction of voltaic bat- 
 teries, the whole of the chemical action is turned to account ; 
 not a particle of zinc is dissolved, but it renders, in an 
 available form, that amount of voltaic electricity which is 
 necessarily associated with such solution, but which, as 
 already explained, with the ordinary metal, is evolved under 
 circumstances 'which render it useless. (79.) The use of 
 pure zinc in the construction of voltaic batteries would be 
 attended with such expense, as to completely prevent its 
 
38 
 
 introduction ; indeed, the improvement in the voltaic battery 
 now under consideration (the amalgamation of the zinc) 
 renders its use unnecessary. 
 
 83. Many experiments had been made by Sir H. Davy, and 
 others, on amalgamated zinc; but for its introduction into the 
 voltaic battery we are indebted, as before stated, to Mr. Kemp. 
 Zinc, the surface of which is amalgamated or covered with 
 quicksilver, is, like pure zinc, insoluble in dilute sulphuric 
 acid, unless in contact with another metal ; in short, plates 
 of amalgamated zinc conduct themseves in every respect like 
 plates of pure zinc ; and what has been said of the pure 
 metal applies to that which is impure, when its surface is 
 amalgamated. Many explanations have been given of the 
 action of the mercury ; but as most of these are, more or less, 
 unsatisfactory, we shall not enumerate them, but content our- 
 selves with a knowledge of the facts. 
 
 84. Zinc is very easily amalgamated. It is only necessary 
 to immerse it for a few moments in dilute sulphuric acid, in 
 order to clean its surface. If it now be plunged into mercury, 
 it will be found to acquire a perfect coating of that metal ; 
 or the mercury may be poured on the zinc, and spread about 
 by a rag or hare's foot — a more economical and equally effec- 
 tive plan. 
 
 85. The battery now commonly employed in electro-metal- 
 lurgical operations consists of rods or plates of amalgamated 
 zinc; these are surrounded with plates of copper brought 
 as near the zinc as possible, without incurring the risk of 
 touching. The compound plates are immersed in jars, con- 
 taining a mixture of one part of sulphuric acid or oil of 
 vitriol, and eight or nine parts of water. 
 
 86. The form of battery recommended by Mr. Kemp differs 
 materially from all those hitherto described ; the amalgam of 
 zinc and mercury is in a fluid form, and is contained in a 
 series of wooden troughs or trays, piled on each other like 
 the plates in Volta's pile. Dilute sulphuric acid is poured in 
 
39 
 
 each tray; and a plate of copper immersed in each, in a 
 horizontal position, is connected with the amalgam of the 
 
 cell above it, by a rod of cop- 
 per soldered to the plate, passing 
 through the bottom of the tray, 
 and entering the amalgam. The 
 battery is represented in Jig. 8 : — 
 a a are the wooden trays, and h h 
 the plates of copper ; the amalgam 
 in each tray is represented by c c ; 
 d d represent the several portions of 
 dilute acid in the trays. The cop- 
 per plates h h should be perforated, 
 in order to allow of the escape of 
 the hydrogen. 
 
 87. Theoretically considered, this battery is perfect ; but 
 in practice, the fluidity of the amalgam is objectionable, in- 
 asmuch as in moving the battery about, there is danger of its 
 contact with the copper or negative element ; besides, the 
 still greater inconvenience of the various cells being hidden, 
 and the difficulty of rectifying any derangement of the lower 
 cells, without removing the upper ones. 
 
 88. These difficulties are, however, purely mechanical, and 
 are wholly obviated by arranging the series horizontally, in- 
 stead of vertically. This battery, moreover, is very econo- 
 mical ; for whilst in all other forms of battery, the plates of 
 zinc require to be amalgamated several times before they are 
 worn out, and eventually become so brittle as to break w^hile 
 of considerable thickness, and hence, occasion the loss both 
 of the zinc and mercury ; all that is necessary in this battery, 
 is to add pieces of ordinary zinc from time to time, to the 
 fluid amalgam ; the mercury is never lost, and the zinc is 
 not wasted. 
 
 89. The battery proposed by Mr. Kemp has never come 
 into general use, as experimentalists have generally preferred 
 
40 
 
 the amalgamated plates ; but there is little doubt, that it will 
 be eventually adopted by those, who, using the voltaic battery 
 as an instrument of art, are desirous of employing the most 
 economical arrangement. 
 
 90. Long prior to the invention of Professor Daniell (which 
 comes next in order) it was known that, by increasing the 
 size of the negative plate of the battery, there was a consider- 
 able increase in the quantity of electricity generated. The 
 reader will recollect that Dr. Wollaston's improvement con- 
 sisted in surrounding the zinc with copper, and that that 
 instrument was superior to those in which a less surface of 
 negative metal was used ; but there is obviously a limit to 
 this extension of the negative plate; for, by enlarging it, its 
 distance from the zinc becomes necessarily greater, and its 
 object is thereby defeated; for with a negative plate of a 
 given size, it will be found that the evolution of hydrogen 
 rapidly diminishes as it is made to recede from the zinc, and 
 vice versa. However large the negative plate is made — when 
 in action, it is, virtually, exceedingly small ; as we have 
 already seen, the moment the action of the battery com- 
 mences, the negative plate becomes covered with bubbles of 
 hydrogen, and the parts so coated, being defended from the 
 liquid, are for the time inactive ; hence the extent of metal, 
 which is in constant contact with the liquid, is much dimi- 
 nished by this evolution of hydrogen. 
 
 91. This defect is completely remedied by the arrangement 
 of battery devised by Professor Daniell, and called by him the 
 " constant battery." The essential principle in this instrument, 
 is the placing of a solution of sulphate of copper, in contact 
 with the copper of the battery, whereby the hydrogen pre- 
 sented at that surface, is made, while in its nascent state, to 
 enter into chemical union with the oxygen of the sulphate 
 of copper ; and by the suppression of the hydrogen, a large 
 and constant extent of negative surface, is exposed to the 
 zinc. A single cell of the constant battery, is represented in 
 
41 
 
 section in Jig 9. It consists of an outer cylindrical copper 
 Fig. 9. vessel a, of about three inches diameter, 
 
 and of any convenient height ; in the axis 
 of this cylinder is placed a cylindrical 
 vessel of porous or un glazed earthenware 
 h; and in this porous vessel is suspended, 
 a rod or cylinder of amalgamated zinc c ; 
 dilute sulphuric acid, is placed in the in- 
 terior or porous vessel, and a saturated 
 solution of sulphate of copper in the ex- 
 terior, or copper vessel. Crystals of the 
 sulphate of copper, to keep the solution 
 always saturated, are laid upon a perforated shelf c?, fixed in 
 the upper part of the cylinder. 
 
 92. The action of the sulphuric acid on the zinc, has been 
 already explained (53) ; and as the use of the porous cell is 
 simply to prevent the mixture of the two solutions, by inter- 
 posing between them a substance which will not materially 
 interfere with the passage of an electric current, we may 
 altogether dismiss it in considering the phenomena which 
 take place. The hydrogen, then, passes freely to the copper 
 cylinder or negative plate, and is there liberated ; on coming 
 in contact, while in its nascent state with the metallic solu- 
 tion, it decomposes that solution ; it combines with the oxygen 
 of the metallic salt, and liberates the metal. The copper, 
 thus precipitated, attaches itself closely to the copper cylin- 
 der, in which the solution is contained ; and this cylinder 
 constantly increases in thickness during the action of the 
 battery by the accumulation of the deposited copper. 
 
 93. By the means now described, the evolution of hydrogen 
 at the surface of the negative metal, which has been shown to 
 be so disadvantageous, is completely suppressed ; and by the 
 copper or negative surface being separated from the solution of 
 sulphate of zinc formed in the interior vessel, the reduction of 
 zinc upon the negative metal, which occasions a diminution 
 of power in the ordinary battery, is completely avoided. 
 
42 
 
 94. This voltaic arrangement produces a current of greater 
 intensity than any previously invented ; added to which, it 
 possesses the valuable property of extreme uniformity of ac- 
 tion — insomuch that it yields a current of invariable intensity, 
 for many hours. We must not, however, omit to mention the 
 disadvantages which are peculiar to it. The expense of the 
 salt of copper renders it less economical than other forms of 
 battery ; the porous cells are liable to break after use by the 
 crystallization of the saline matter contained in their pores, 
 and from which repeated washings scarcely suffice to free 
 them. A very small extent of zinc surface is exposed ; and 
 as the instrument is inactive until the solutions have pene- 
 trated the porous cell, it requires longer time to bring it into 
 active operation, than most of the other forms of battery. 
 We repeat, however, that it has valuable properties not pos- 
 sessed by any other instrument. 
 
 95. Subsequent to the battery of Professor Daniell is that 
 of Mr. Grove — an instrument which far surpasses all that 
 preceded it, in point of intensity. In principle it is precisely 
 similar to that of Professor Daniell ; Mr. Grove appears, how- 
 ever, to have arrived at its construction, by considerations in- 
 dependent of those which led to the invention of the constant 
 battery ; the hydrogen is suppressed at the negative plate by 
 being presented to concentrated nitric acid ; and, in order that 
 the acid may have no action on that plate, Mr. Grove uses 
 platinum. It is hardly necessary to remark, that the hydro- 
 gen decomposes the nitric acid by combining with its oxygen. 
 
 Fig. 10. Fig, 10 is a sectional representa- 
 
 _ tion of two cells of Grove's bat- 
 T tery ; a is the outer cell of glazed 
 earthenware ; h a plate of zinc bent 
 into the form represented ; c a vessel 
 of unglazed earthenware ; d the plate 
 of platinum. The vessel a, is charged 
 with dilute sulphuric acid, in the 
 proportion of one of concentrated acid, 
 
43 
 
 to seven of water; the vessel c, is filled with concentrated nitric 
 acid. The advantages attendant on this battery, are its ex- 
 treme activity, and the intensity of the current generated ; a 
 single cell of this arrangement decomposes water, and a bat- 
 tery of three or four cells, possesses intensity enough, for all 
 ordinary purposes ; the disadvantages under which it labours 
 are, that its power is transient, and that the evolution of 
 nitrous fumes, renders it exceedingly offensive. The expense 
 of the nitric acid is also an objection. 
 
 96. From what has been previously said respecting the 
 intensity of voltaic batteries, the reader will, perhaps, be 
 somewhat surprised at the remark, that Daniell's battery pos- 
 sesses a greater intensity, than is produced by a simple acid 
 battery, and that a single pair of plates, arranged on Grove's 
 principle, will decompose water. It is nevertheless true, that 
 the intensity of a single pair of voltaic elements, is increased 
 in a surprising degree by the application, either of the solu- 
 tion of the sulphate of copper, or concentrated nitric acid, to 
 the negative plate. The following experiment will illustrate 
 this fact : — take a single cell of Grove's battery, and connect 
 the platinum and zinc with two platinum plates, immersed in 
 dilute acid, as shown in Jiff. 2. Let the battery be partly 
 filled with dilute sulphuric acid, and let a quantity of the 
 same be put in the porous cell. No action will take place ; 
 the current will not pass through the acid in the second cell, 
 and the water, consequently, will not be decomposed. With- 
 out disturbing the arrangement, introduce some concentrated 
 nitric acid into the porous cell, and the platinum plates in the 
 second cell will immediately evolve — the one oxygen, and the 
 other hydrogen — and these gases will continue to be given off, 
 until all the nitric acid in the battery, has been decomposed 
 by the hydrogen evolved in it — demonstrating, that the cur- 
 rent has, by the introduction of the nitric acid, acquired an 
 intensity, much greater than it previously had. 
 
 97. It is by no means easy to understand the cause of this 
 
44 
 
 intensity ; the most plausible theory which has been proposed 
 is, perhaps, the following : — the intensity of the current in 
 the simple acid battery may be represented by the attraction 
 of the oxygen of the water, for the zinc; in Daniell's battery, 
 the attraction of the oxygen for the zinc, plus the attraction 
 of the hydrogen for the oxygen of the oxide of copper, minus 
 the attraction of that oxygen for the metallic copper with 
 which it is combined ; and in Grove's battery, the intensity 
 will be represented, by the attraction of the oxygen of the 
 water, for the zinc ; plus, the attraction of the hydrogen at 
 the negative plate, for the oxygen of the nitric acid, minus, 
 the attraction of that oxygen, for the nitrogen with which it 
 is combined. 
 
 98. If we adopt that view of the constitution of the salts, 
 which has been referred to, in the preceding chapter (41), and 
 by which they are all regarded as similarly constituted, the 
 batteries of Mr. Daniell and Mr. Grove, must be differently 
 explained. According to this theory, the sulphate of copper 
 is the sulphat-oxide of that metal ; that is to say, a compound 
 of sulphat-oxygen (41) and copper; and its decomposition, 
 and the liberation of metallic copper, a direct, and not accord- 
 ing to the old theory, a secondary effect. The acids, too, 
 when combined with water, must be regarded, not as mere 
 solutions, but as definite compounds ; dilute sulphuric acid 
 must not be considered as a mere solution of sulphuric acid 
 in water, but as a compound, in which the oxygen of the 
 water is combined with the sulphuric acid, and that com- 
 pound with hydrogen — in other words, sulphat-oxide of 
 hydrogen. Similarly, nitric acid must be regarded as a salt of 
 hydrogen — the nitrat-oxide of hydrogen, and its decomposi- 
 tion receive a similar explanation. 
 
 99. The battery formed by the immersion of a plate of zinc, 
 and a plate of copper in dilute sulphuric acid, receives a 
 simple exj)lanation on the new theory. Instead of referring 
 it to the decomposition of water, and oxidation of the zinc. 
 
45 
 
 and subsequent combination of the oxide with sulphuric acid, 
 we have only to suppose the decomposition of the sulphat- 
 oxide of hydrogen (dilute acid) ; the zinc, combining with 
 the sulphat-oxygen, and the hydrogen being evolved. 
 
 100. The phenomena of voltaic electricity tend to prove 
 the correctness of the new theory of the constitution of salts, 
 but such considerations are too theoretical for discussion in 
 the present treatise. 
 
 101. The battery of M. de Moleyns consists of an arrange- 
 ment exactly similar to that of Mr. Grove, but is excited 
 differently. The external cell containing the zinc is filled 
 with a saturated solution of muriate of ammonia (sal ammo- 
 niac) ; and the internal porous cell in which the platinum is 
 placed, is filled with a solution prepared in the following 
 manner : — Dissolve one pound of nitrate of ammonia in a 
 pint of water ; place the vessel containing the solution in a 
 frigorific mixture, and add slowly an equal quantity of con- 
 centrated sulphuric acid. Nitric acid is liberated, and is the 
 active ingredient. 
 
 102. This battery possesses an intensity equal to that of Mr. 
 Grove's ; and the iiiventor states that its advantages are — the 
 length of time it continues in action ; the intensity which it 
 possesses ; and, as the zinc plates need not be amalgamated, 
 he claims that as one of its advantages. The last, however, is 
 not peculiar to his battery. The solution of muriate of am- 
 monia (sal-ammoniac) is commonly employed in Daniell's bat- 
 tery instead of the dilute acid, and in that case the zinc is not 
 amalgamated ; and in many experiments made by the author 
 with Grove's battery, in which a saturated solution of the 
 salt in question was employed in lieu of the dilute acid, the 
 effect was certainly not diminished by the substitution ; nay, 
 in the few comparative experiments made on the subject, 
 there appeared to be a considerable increase of power ; for, 
 with two batteries, of exactly the same size, one charged with 
 dilute sulphuric acid, in contact with the amalgamated zinc, 
 
46 
 
 and the other with the saturated sokition of muriate of am- 
 monia and unamalgamated zinc, the latter gave in eight 
 minutes a volume of the mixed gases from the decomposi- 
 tion of water equal to that produced by the former in nine 
 minutes and a half. 
 
 103. Various other modifications of Grove's battery have 
 been proposed by different experimenters. A modification 
 much used on the continent is called Bunsen's battery ; it 
 appears, however, to have originated wdth several individuals 
 about the same time. The novelty in this battery is the substi- 
 tution of carbon, or charcoal, for the platinum. The carbon 
 is formed into a vessel, which is substituted in place of the 
 porous vessel, and is filled with concentrated nitric acid. 
 The carbon thus constitutes at once the porous cell for 
 separating the liquids used, and the negative plate or element 
 of the battery. The preparation of the carbon cylinders can- 
 not be undertaken on a small scale ; and, therefore, the pro- 
 cess by which they are made need not be described. 
 
 104. M. de la Rive has substituted metallic oxides in place 
 of the nitric acid in Grove's battery. The substitution had, 
 however, been previously suggested by Mr. Grove himself. 
 Either the peroxide of manganese, or the peroxide of lead, in 
 a state of fine powder, may be used ; the latter is most effec- 
 tive. The porous vessel is filled with the oxide, the platinum 
 plate being in the middle of the vessel, and, consequently, 
 closely surrounded by the oxide. After the vessel has been 
 filled with the peroxide of lead, dilute sulphuric acid is in- 
 troduced so as to fill up the interstices between the particles. 
 It is hardly necessary to remark, that the peroxide suffers 
 decomposition by the hydrogen evolved at the surface of the 
 platinum. This battery possesses an intensity somewhat 
 greater than that of Grove's. 
 
 105. The electro-metallurgist rarely requires a current more 
 intense than that afforded by Daniell's battery ; and where 
 a greater intensity is necessary, two or three of Daniell's cells, 
 
47 
 
 arranged as a series (64), are to be preferred to the batteries 
 of Grove, Bunsen, and De la Rive. 
 
 106. The next modification of the battery we have to 
 notice is the arrangement of Mr. Smee. In order to avoid 
 the expense attendant on the removal of the hydrogen, by 
 chemical means, in the batteries just described, Mr. Smee 
 endeavours to effect the same object by mechanical means. 
 Having observed, during the evolution of gaseous matter 
 from different plates, that the bubbles of gas adhere very 
 tenaciously to smooth surfaces, but are, on the contrary, 
 quickly liberated from roughened ones, Mr. Smee precipitates 
 the metal platinum in a finely divided state on the negative 
 plate of his battery, so as to give it an infinity of points ex- 
 ceedingly favourable to the evolution of gas. The way in 
 which this is effected will be understood by a perusal of the 
 subsequent pages of this treatise. The battery of Mr. Smee 
 differs only from those used long before the inventions of 
 Daniell and Grove, in this preparation of the negative plate ; 
 and, like them, it is excited by dilute acid only. 
 
 107. It has been proposed to remove the hydrogen from 
 the negative metal of the battery by using, instead of a 
 metallic plate, a sheet of wire gauze, so inclined, that the 
 hydrogen, instead of having to pass over the face of the 
 plate opposed to the zinc, passes through the apertures to 
 the surface of the liquid. The advantage to be gained by 
 this substitution is very questionable. The hydrogen being 
 removed from the plate, the latter is rendered more effectual ; 
 but as this removal is effected in the alteration in question, 
 by the diminution of metal, the object is gained by directly 
 making the sacrifice, to avoid which the alteration is pro- 
 posed. 
 
 108. It is, indeed, doubtful if any of the plans proposed for 
 the mechanical removal of the hydrogen are of much value, 
 even when they accomplish all their inventors claim for them. 
 The adhesion of hydrogen to the surface of the metal, renders 
 
48 
 
 it, for the time being, inactive ; but the inactivity is attended 
 by no direct loss, and it is only necessary to increase the size 
 of the plates, in order to produce an instrument in which 
 there is a sufficient extent of active surface, after deducting 
 the inactive ; in other words, the only advantage that can be 
 claimed for these batteries, is, that they produce a current 
 of given power, in a somewhat less space; but beyond 
 economy in room (which in a battery is generally insigni- 
 ficant) there can be no pretence to superiority. 
 
 109. Amalgamated zinc and silver, roughened by sand- 
 paper, or by immersion in nitric acid, form as good an 
 arrangement as any at present known, excepting, perhaps, 
 those having porous diaphragms. 
 
 110. In using a voltaic battery the first thing to be attended 
 to, is the state of the zinc. If the amalgamation is perfect, 
 there is not the slightest effervescence when the zinc is 
 plunged into dilute sulphuric acid ; if there is any evolution 
 of hydrogen from its surface, it must be amalgamated again. 
 The plates of the acid battery may be immersed in a vessel 
 containing one part of concentrated sulphuric acid to nine or 
 ten parts of water ; and if, by bringing one end of a clean wire 
 against the binding screw connected with the zinc, and the 
 other end in contact with the screw of the copper or silver, 
 a violent effervescence arises at the latter metal, the battery 
 is in perfect order. In preparing Daniell's battery, the porous 
 cell should be filled with the dilute acid, and the external 
 copper vessel with a saturated solution of sulphate of copper, 
 crystals of which salt, should be placed on the perforated 
 shelf in the upper part of the copper cylinder— care being 
 taken that the surfaces to be brought in contact, in making 
 the necessary connections, are perfectly clean; — the instru- 
 ment may then be considered ready for use. 
 
 111. Instead of dilute acid, the internal or porous cell of 
 Daniell's battery, may be filled with a saturated solution of 
 sal ammoniac (hydro-chlorate of ammonia), or a solution of 
 
49 
 
 common salt (chloride of sodium). In placing the crystals of 
 sulphate of copper on the perforated shelf (91), care must be 
 taken not to let any fall into the inner or porous cell. In 
 such a case, metallic copper is precipitated on the zinc rod, 
 and innumerable local circles (81) are formed, the injurious 
 tendency of which, has been already pointed out. If any 
 effervescence is observed to arise from the zinc rod, it should 
 be removed, and the particles of copper, which, in such a 
 case, will be generally found on it, carefully wiped off. 
 
 112. The reader must bear in mind that, in using a very 
 dilute acid, a current, small in quantity, (and of an intensity 
 dependent on the nature of the battery), will be generated ; 
 and that, by using a strong acid, a more copious current will 
 be produced ; he must also bear in mind that the strength of 
 the acid employed does not in the least affect the intensity of 
 the battery; a mixture of one part sulphuric acid, with a 
 hundred parts of water, determines a current possessed of an 
 intensity, equal to that produced by acid of the strength 
 recommended, though the latter gives rise to a much more 
 copious current. P'or example, suppose a battery of a given 
 number of plates, and charged with an extremely dilute acid, 
 have its electrodes introduced into water, and that it does 
 not possess sufficient intensity to decompose that water, no 
 augmentation of the strength of that acid will enable it to effect 
 the decomposition. On the other hand, if the battery have 
 power to decompose water, when charged with strong acid, 
 the only effect produced by the most copious dilution, will 
 be a diminution of the quantity of water decomposed ; but if 
 the same number of pairs be preserved, however dilute the 
 acid be made, it will not lose its poAver to effect the decom- 
 position. 
 
 113. The quantity of electricity generated in a battery may 
 therefore be regulated in two ways — either by altering the 
 strength of the acid, or by exposing a greater or less extent 
 of surface to its action. A small battery, charged with a 
 
 E 
 
50 
 
 strong acid, is the same in effect as a large one excited by 
 weak acid, and vice versa. The temperature of the apparatus 
 has a very important influence on its action. If the battery 
 is heated artificially, its action is much more rapid than under 
 ordinary circumstances ; while, in cold weather, it is much 
 retarded. 
 
 114. It is important in using the common acid battery, 
 consisting of plates of zinc, and copper or silver, to charge all 
 the cells with acid of the same strength, and to fill each, with 
 very nearly the same quantity ; if either of these conditions 
 be neglected, it will frequently happen, that the cells in 
 which the acid is too dilute, or too small in quantity, become, 
 not merely inactive, but a source of obstruction to the current 
 generated in the other cells. When the whole of the acid 
 in a cell is saturated, that cell becomes inactive ; but as 
 the current generated must pass through all the cells (65), 
 it cannot pass through these inactive ones, without effecting 
 decomposition of the sulphate of zinc, with which they are 
 charged ; the consequence is, the deposition of zinc where 
 hydrogen was evolved, that is to say, on the copper or 
 silver plate, and when the cell is next charged, the arrange- 
 ment is inactive, owing to the presence of zinc on the copper 
 or silver. 
 
 115. The removal of zinc accumulated on the negative 
 plate of a battery, is easily effected. It is only necessary to 
 immerse the copper or silver plate so coated into dilute acid, 
 and place in contact with it, a silver or copper wire ; or if 
 there is the least portion of the silver or copper uncoated, 
 that is sufficient to cause the removal of the zinc when the 
 plate is immersed in acid. A voltaic combination is formed, 
 by virtue of which (49) the zinc dissolves. 
 
 116. Before dismissing the subject of voltaic batteries, we 
 would remark, that whatever form is given to an instrument 
 of this kind, the amount of electricity generated by the con- 
 sumption of a given amount of zinc is the same in each ; they 
 
51 
 
 differ only in the rapidity with which the developement of 
 the voltaic power takes place. In the invention of Daniell a 
 flow of electricity of extreme uniformity is produced. We have 
 a torrent of surprising intensity, but of transient duration, in 
 the battery of Mr. Grove ; and a copious flow of electricity, of 
 moderate intensity, in the common acid battery, and that of Mr. 
 Smee : but we repeat (for it cannot be too strongly urged upon 
 the reader), that in all these instruments a like amount of this 
 subtle agent is obtained by a like consumption of materials, 
 the intensity alone being affected by the arrangements of 
 Daniell and Grove. In Smee's battery this is not at all in- 
 creased ; the mechanical form of the surface of the negative 
 plate only facilitates the escape of the hydrogen therefrom. 
 
 117. The experimenter is strongly recommended to use, in 
 his early experiments, a Daniell's battery in preference to 
 every other. He is much less likely to fail in his operations 
 by its use ; and, from the extreme regularity of its action, the 
 character of the deposit is not likely to change, even during 
 a long experiment. 
 
 118. A single cell of Daniell's battery possesses in general, 
 sufficient intensity for electro-metallurgical processes. It 
 will sometimes, however, be found advisable to use a series 
 of two. In using the acid battery, one cell will be seldom 
 found to have sufficient intensity ; a series of two, three, or 
 four, must sometimes be employed. The intensity requisite 
 depends on the salt to be decomposed. 
 
 119. From what has been said of quantity a.nA intensity 
 in the voltaic battery, it will be understood, that by joining 
 a number of battery cells together, in different ways, a quan- 
 tity or intensity arrangement will be produced. If the plates 
 or rods of zinc be joined together, and the copper or silver 
 plates similarly connected, an arrangement will be produced, 
 in which the quantity will be directly as the surface of the 
 zinc, the intensity remaining the same as that of one cell. 
 If, on the other hand, the zinc of one cell be joined to the 
 
 E 2 
 
52 
 
 copper or silver of the next, and so on, through the series, a 
 battery is formed, in M'hich the quantity does not exceed that 
 of one cell ; but in which the intensity, is directly as the 
 number of cells. 
 
 120. The electro-metallurgist may sometimes have occasion, 
 in his experiments, to determine, accurately, the quantity or 
 intensity of the voltaic current he employs ; and a brief 
 description of the instruments used for that purpose may be 
 conveniently introduced here. These instruments depend for 
 their action on the decomposing and magnetic powers of the 
 electric current ; the two commonly employed, are the vol- 
 tameter and galvanometer. 
 
 121. The voltameter is a vessel in which water is decom- 
 posed by transmitting through it, a voltaic current ; the 
 oxygen and hydrogen evolved are collected either together 
 or separately ; and the volume of gas thus liberated, is an 
 accurate measure of the quantity of electricity which has 
 passed. This instrument is made of many different forms. 
 Fig. 11 represents one of the most convenient. It consists of 
 
 and hydrogen from the other. The gases are collected and mea- 
 sured by tubes suspended over the plates ; or by closing the 
 vessel a, and connecting a pipe with its top, the gases may be 
 conducted to a pneumatic trough, and collected in a gra- 
 duated jar. 
 
 122. The galvanometer is a magnetic needle stationed near, 
 
 /I 
 
 Fig. 11. 
 
 a glass vessel a, partly filled witli 
 dilute sulphuric acid ; two platinum 
 plates h h are connected with cups 
 to hold mercury, or binding screws, 
 c c on the base of the instrument. 
 When the voltaic current is trans- 
 mitted through the instrument by 
 means of the mercury cups c c, de- 
 composition takes place, and oxygen 
 is evolved from one of the plates h b, 
 
53 
 
 and parallel with, a wire, conducting the current to be mea- 
 sured. A magnetic needle brought near a wire conducting 
 a voltaic current suffers a deflection from its natural position 
 (55) ; the extent and direction of this deflection are dependent 
 on the amount of electricity passing, and the relative position 
 of the needle and. wire. A simple magnetic needle is a rude 
 galvanoscope ; but it affords no information as to the quantity 
 of electricity passing. In order to render it a galvanometer, 
 it is necessary to make the wire, intended to transmit the 
 current, pass many times over and under the needle; the 
 deflecting power of such a coil is directly proportionate to 
 the number of its convolutions. In order to increase still 
 more the sensitiveness of the galvanometer, it is usual to 
 make it astatic ; that is, to destroy, more or less, its directive 
 power. This may be done by placing a magnet near the gal- 
 vanometer ; or it may be more conveniently effected by placing 
 a second needle over the first ; the north pole of the second 
 being over the south pole of the first. Such an arrangement 
 possesses little directive power, and is hence more sensitive to 
 any deflecting force. 
 
 123. Fig. 12 represents Ritchie's galvanometer; a h are 
 the magnetic needles suspended in the pig. 12. 
 
 coil c ; the ends of this coil are con- 
 nected with the mercury cups d d on 
 the base of the instrument. The 
 needles are suspended by a fine wire, 
 or thread of glass, a:, from the arm e. 
 The wire, or thread of glass, is at- 
 tached to a moveable index, which 
 describes a circle on the graduated 
 plate /. In order to use this instru- 
 ment, the needles are allowed to as- 
 sume their position in the magnetic meridian, and the coil c 
 (which is moveable), is brought in the same plane ; on passing 
 a current from a battery through the coil, the needles are de- 
 
54 
 
 fleeted. The index, or hand, is now turned in a direction oppo- 
 site to that in which the needles have been deflected, until 
 they are brought into the same plane as that in which the 
 coil is situated. The number of degrees through which the 
 index has been turned, as indicated on the graduated circle/, 
 indicate the quantity of the current by which the deflection is 
 produced. The indications of this instrument are compara- 
 tive ; the quantities of electricity passing in any two experi- 
 ments being to each other, as the angles through w^hich 
 the wire x must be twisted, to restore the position of the 
 needles. . 
 
 124. The galvanometer measures a current having the 
 feeblest intensity; while the voltameter completely intercepts, 
 and, consequently, does not measure, a current which does 
 not possess sufficient intensity to decompose water. For 
 accuracy, the voltameter is superior to the galvanometer. 
 
 125. In using a voltameter in the voltaic circuit, it must 
 be recollected that the force, or intensity, of the current is 
 diminished by the amount necessary to efi'ect the decomposi- 
 tion of water. The obstruction, which is occasioned by the 
 introduction of a galvanometer in the circuit, is so small 
 (owing to the course of the cuiTent being through a me- 
 tallic conductor), that it may be neglected, excepting in 
 experiments of extreme delicacy. The electro-metallurgist 
 has rarely occasion to use either the voltameter or the gal- 
 vanometer. 
 
65 
 
 CHAP. IV. 
 
 ON MAGNETO-ELECTRICITY AND THE MAGNETO- 
 ELECTRIC MACHINE. 
 
 126. The identity of electricity and magnetism was sus- 
 pected by the early electricians, and many experiments were 
 instituted, in the hope of obtaining electrical indications from 
 the magnet. The proof of their identity, and the use of the 
 magnet as a source of electric power, have, however, been 
 reserved for modern times. The admirable researches of 
 Faraday have supplied nearly all the evidence and informa- 
 tion we have on this subject. 
 
 127. If a loop of wire, the ends of which are connected 
 with a galvanometer (123), be made to approach and encircle 
 one end, or pole, of a powerful magnet, the galvanometer 
 needle is powerfully deflected, demonstrating the passage 
 through the wire of an electric current. Immediately the 
 wire becomes stationary, the galvanometer needle ceases to 
 be affected; and, on withdrawing the wire, the needle is 
 
 Fig. 13. 
 
 deflected in the opposite direction, indica- 
 ting an opposite electric current. This 
 experiment is represented in Jig. 13. 
 
 128. If, instead of a single loop, the 
 wire is coiled into a helical or corkscrew 
 form, and this helix be brought on the 
 arm of the magnet, the needle is more 
 powerfully deflected ; the electric current 
 generated being proportionate to the number of coils in the 
 helix. 
 
56 
 
 129. It will also be observed that the action is more 
 powerful, as the motion of the wire is quicker. 
 
 130. Instead of making the magnet and wire approach each 
 other, a bar of annealed or soft iron may remain permanently 
 in the helix ; and a magnet, alternately touched against and 
 detached from, the bar of iron, determines the production of 
 the currents in question. 
 
 131. By coiling a long wire many times round a core of 
 soft iron, so as to form a compact helix, in which the several 
 coils are insulated from each other, by covering the wire with 
 cotton, or some non-conductor of electricity, and by placing the 
 north pole of a powerful magnet in contact wath one end, and 
 the south pole of another in contact with the other end, an 
 arrangement is formed, from which, by suddenly detaching 
 the magnets with a blow, very powerful currents may be ob- 
 tained. If the ends of the wire coil are dipped into a cup of 
 mercury, and one of them removed at the moment of detach- 
 ing the magnets, the electric current generated passes between 
 the surface of the metal and the retiring wire in the form of a 
 spark. In short, this magneto-electric current exhibits all 
 the phenomena of the voltaic current. In passing it through 
 water, that compound is decomposed ; it also gives powerful 
 shocks, and deflagrates metals. 
 
 132. In order to develope these magneto-electric currents 
 with rapidity and effect, the necessary motion is communi- 
 cated to the magnet, or coil of wire, by machinery. Various 
 arrangements have been proposed for this purpose, the most 
 convenient of which is that of Mr. Saxton. 
 
 133. Saxton's magneto-electric machine may be briefly 
 described as a powerful compound horse-shoe magnet, sup- 
 ported horizontally, and in front of which an armature of soft 
 iron, on which a long copper wire is coiled, rotates on an 
 axis situated midway between the arms or poles of the 
 magnets. The rotating armature consists of a bar of soft iron 
 bent twice at right angles. When this armature is in a 
 
57 
 
 horizontal position, its arms are in the same plane as, and 
 are opposite to, the poles of the magnet, but as it rotates, 
 they assume a vertical position, and thus alternately approach 
 and recede from, the magnetic poles. As the ends of the 
 armature approach the magnetic poles, a powerful magnetism 
 is induced in them, which arrives at a maximum when they 
 are opposite to the magnetic poles ; as they recede from 
 the magnet, they become demagnetised ; and when they are 
 at right angles to the magnetic poles, that is to say, in a 
 vertical plane, they are not at all magnetic. Hence, at every 
 semi-revolution, the armature becomes highly magnetic, and 
 is again demagnetised. The consequence of the induction of 
 magnetism in the armature, is the determination of a powerful 
 magnetic current in the wire surrounding it, and by an elegant 
 mechanical arrangement, this current is collected, and may 
 be made to exhibit all the phenomena of an electric current 
 from any other source. 
 
 134. From what has been already said (127), it will be 
 evident that two currents will be generated during every re- 
 volution of the armature, namely, one as the armature ap- 
 proaches, and another as it leaves, the magnet ; these currents 
 are in opposite directions, and if not insulated fi-om each 
 other, their effects would be completely neutralized. The 
 difficulty of directing these currents in the same direction, 
 combined with the small quantity of electricity, which it was 
 supposed could be obtained by magnetic influence, caused 
 the application of the magneto-electric machine to the art of 
 electro-metallurgy to be long neglected. 
 
 135. Mr. Sturgeon appears to be the first who deposited 
 metals by this apparatus, but his experiments were on a 
 small scale ; and it is to Mr. J. S. Woolrich, of Birmingham, 
 that the art is indebted for the perfection of the magneto- 
 electric apparatus, and the developement of its extraordinary 
 power as an electro-metallurgical instrument. 
 
 136. Mr. Woolrich constructs machines after two models ; 
 
58 
 
 one resembles, to a considerable extent, that of Mr, Saxton, 
 and is used where a moderate amount of work is to be per- 
 formed, and the other is a modification of one of the early 
 magneto-electric machines ; this latter form is employed 
 where large quantities of electric power ai'e required. 
 
 137. The small magneto-electric machine is represented in 
 plan in Jiff. 14, and in elevation vajlg. 15. a is a powerful 
 Fig. 14. Fig. 15. 
 
59 
 
 horse-shoe magnet, composed of any convenient number of 
 magnetic bars fastened together; this magnet is supported 
 horizontally on the table h ; c is the armature affixed to the 
 end of the spindle or axis d ; this axis works in bearings at 
 e e, and is made to rotate by means of a band and the pulley/; 
 a contrivance for determining a uniform direction in the cur- 
 rents (134) is attached to the axis near the pulley f ; it is 
 called the break or divider, and is composed of the following 
 parts : — g is a cylindrical piece of wood fixed on the axis ; two 
 semi-circular bars of metal k I (brass) are fitted on this 
 cylinder of wood ; these pieces of metal are carefully insulated 
 from each other by the insertion between their ends of two 
 small pieces of wood ; 7i is a spring supported on the base of 
 the instrument by a pillar ; this spring presses on the upper 
 part of the cylinder g, and a similar spring i presses on the 
 under side of the cylinder ; one end of each coil is attached 
 to one of the semi-circular pieces, and the other end of each 
 coil to the other semi-circular piece. The similar end of each 
 coil must be joined to the same semi-circle of metal ; that is 
 to say, those ends must be joined which, supposing the 
 armature to be a straight bar of iron, and the wire on each 
 end to be coiled in the direction of the motion of a watch- 
 hand, or of a screw on being driven home, constitute the 
 beginnings, and similarly those constituting the endings, of 
 the coils. The semi-circles k I represent the terminations of 
 the coils ; and the springs h i pressing on them are in elec- 
 trical communication therewith. Now, it will be observed, 
 that by the rotation of the armature and break, the springs 
 h i are alternately in connection with the beginnings and 
 endings of the coils. When the armature is vertical, there is 
 no magnetism in it, and, consequently, no current in the coil 
 of wire ; and at that moment the springs h i press on the 
 pieces of wood which separate the semi-circles k I. As the 
 armature quits its vertical position, and approaches the 
 magnetic arms, it becomes powerfully magnetic, and a current 
 
60 
 
 is determined through the coils. The springs h i now press 
 on the semi-circles k I, and receive from them the current. 
 As the armature, by a half revolution, becomes again vertical, 
 it leaves the poles by which it was magnetised, becomes 
 neutral, and again approaches the poles in an opposite direc- 
 tion ; that is to say, that end of the armature which was last 
 opposed to, and is now leaving, a north pole, is approaching 
 a south pole, and vice versa ; but at the same moment each of 
 the springs h i quits the semi-circle against which it presses, 
 and comes in contact with the other ; hence, by reversing the 
 connection at the moment the direction of the current is 
 changed, the springs h i are always in the same relation to 
 the currents produced. By rapidly rotating the armature, and 
 connecting a wire with the pillars carrying the springs h i, 
 a constant current of electricity passes through the wire. 
 
 138. The large magneto-electrical machine is represented in 
 Jig. 16. It consists of four, six, or eight compound magnets, 
 
 Fig 16. 
 
61 
 
 arranged as radii to a common centre. A drum, or wheel, 
 rotates rapidly between the arms of these magnets ; and, car- 
 rying the armatures on its periphery, conveys them rapidly 
 during its rotation between the arms of each magnet, so as to 
 induce in them a momentary magnetism. There are thus four, 
 six, or eight armatures (as the case may be) generating power- 
 ful currents at the same time ; and the combined effects of 
 these currents is proportionately great : — a a are the magnets 
 supported on the frame b ; c c are the armatures fixed in the 
 periphery of the wheel or drum d ; the break or divider is 
 shown at e ; the rotation of the drum d is effected through a 
 pulley on the axis f. 
 
 139. The intensity of the current of a magneto-electric 
 machine depends on the length and diameter of the wire of 
 which the coils on the armature are made. If the wire is 
 long and of small diameter, the current is of great intensity, 
 and small in quantity. (58.) If, on the contrary, a short 
 thick wire is used, the current is large in quantity, and of 
 small intensity. 
 
 140. The intensity of the current is altogether dependent 
 on the length of the coil, but the quantity may be affected by 
 other circumstances. The power of the magnet, and the 
 rapidity with which the armature revolves, are circumstances 
 which determine a difference in the quantity of the current 
 generated. As the power of the magnet is diminished, the 
 quantity of the current diminishes ; as it also does, in pro- 
 portion as the rapidity of the revolution of the armature 
 decreases. 
 
 141. Experiments are yet wanting, to determine accurately 
 the relation which exists between the length and diameter of 
 the wire, and the intensity and quantity of the induced cur- 
 rent; it appears, however, probable, from limited experi- 
 ments, that in using wires of different lengths and diameters 
 (all other circumstances remaining the same), the quantity in- 
 creases and diminishes inversely as the intensity; that is to 
 
62 
 
 say, by using a wire of a given length and diameter, a current 
 is obtained of a certain quantity and intensity, and by what- 
 ever alteration in the length and diameter of the wire, we 
 effect a change in either property, the other is increased or 
 diminished in the inverse ratio. 
 
 142. The direction of the current is not dependent on the 
 direction of the rotation of the armature. 
 
 143. The absolute size of the magneto-electric machine 
 may be varied to suit the purpose to which it is intended to 
 be applied ; there are, however, proportions between the 
 various parts, which must be observed, in order to obtain 
 the maximum effect. All that is said in this treatise relative 
 to the proportions of the magneto-electric machine, has refe- 
 rence only to its use as an electro-metallurgical instrument. 
 
 144. The small machine from which figs. 14 and 15 were 
 made, consists of ten magnets, 27 inches long; they are 
 made of steel 2|-in. broad, and |-in. thick. The distance 
 from centre to centre of the arms is 5 inches. The armature is 
 made of soft iron If-in. diameter, and the wire of which the 
 coils are made, is f -in. diameter, and each coil 90 feet long. 
 In making 1000 revolutions per minute, this machine de- 
 posites 120 ounces of silver per week from the sulphite solu- 
 tion described in another part of this work. 
 
 145. The large machine represented in fig. 16 consists of 
 four compound magnets, 2-ft. 3-in. long ; each magnet is com- 
 posed of ten bars. These bars are made of steel 2|-in. broad, 
 and f -in. thick. The drum or wheel carrying the armatures 
 is 2 feet in diameter. The distance between the poles of 
 the magnets is 6 inches. The armatures are cylinders of 
 iron 2|-in. diameter and 6-in. long. Each armature is 
 covered with a coil of wire f-in. diameter and 90 feet 
 long. When the drum or wheel carrying the armatures 
 makes 650 revolutions per minute, this machine deposites 
 from 300 to 400 ounces of silver per week from the sulphite 
 solution. 
 
63 
 
 146. The following remarks, relative to the magneto-electric 
 machine, are of a practical nature. The iron, of which the 
 armatures are made, should be as pure and as well annealed 
 as possible, in order that the magnetic induction may take 
 place in it with rapidity and intensity. 
 
 147. The copper wire surrounding the armatures should be 
 well annealed, and closely covered with cotton ; it is also 
 desirable to coat each layer or stratum of wire with a resin- 
 ous cement, in order to insulate it perfectly from the other 
 layers ; a cement composed of equal quantities of bees' wax 
 and resin answers very well. 
 
 148. The quantity of electricity generated by the magneto- 
 electric machine maybe adjusted to the work to be done with 
 the greatest nicety. This adjustment may be effected in two 
 ways ; — either by diminishing the rapidity of the rotation of 
 the armature (140), or by diminishing the intensity of the 
 magnetic induction. The latter is the simplest and most 
 manageable. 
 
 149. In order to diminish the current in the small machine 
 {fig- 14 & 15), the magnet is made to slide horizontally by 
 means of a screw, and it can thereby be placed at any distance 
 from the rotating armature. In the large machine {fig. 16) 
 the same effect may be produced by using keepers, or bars of 
 iron, laid across each magnet; by sliding these keepers near 
 the poles of the magnet, the magnetic circle is completed, 
 partly through them, and partly through the rotating arma- 
 tures. When the full power of the magnets is required, the 
 keepers must be wholly removed ; when they are used, they 
 should be fixed in their places by pins or cotters, so that 
 accident may not occasion any change in their position. 
 
 150. The magnets of these machines (contrary to what 
 would have been expected) do not appear to lose their power 
 during the most prolonged action to which they have been 
 subjected. 
 
64 
 
 151. The first cost of the magneto-electric machine is cer- 
 tainly greater than that of the voltaic apparatus necessary to 
 produce the same amount of power ; but the current or work- 
 ing expense is incomparably less, being limited to a trifling 
 motive power ; and the economy of the magnetic machine 
 must eventually gain for it a preference to the voltaic battery, 
 where metal is to be deposited on a business scale. The wear 
 and tear of these machines is, of course, limited to the friction 
 between the axis and its bearings, and that between the break 
 and springs. 
 
 152. The magneto -electric machine appears destined to 
 supersede every other apparatus in the deposition of metals 
 of low equivalent proportions (35), as the expense of the 
 voltaic battery in such precipitations, renders the process an 
 expensive one. Thus, in depositing zinc, as in zincing iron, 
 supposing two cells, arranged as an intensity battery, to 
 be employed, the quantity of zinc deposited would be just 
 one-half of that, consumed in the battery, and very nearly the 
 same proportion would obtain in the case of copper. Hence, 
 the expense of depositing, compared with the value of the 
 metal deposited, is very great ; in the magnetic machine, on 
 the contrary, the expense of depositing is limited to the 
 power required to produce the rotation of the armatures. 
 
 153. The uniformity of the current developed in the mag- 
 neto-electric machine is not the least of the many advantages 
 this machine possesses. In the best constant battery the 
 quantity varies during the course of several hours ; and even 
 the best operators with the battery find it necessary to give 
 close attention to the state of the instrument and the pi'ogress 
 of the deposition. With the magnetic machine the deposition 
 goes on with extreme regularity; and, when once adjusted, 
 may be left for any length of time without fear of derange- 
 ment. So accurately is the deposition by this machine pro- 
 portioned to the time of working, that, in an establishment in 
 
65 
 
 Birmingham where this process is extensively employed, the 
 quantity of metal deposited is estimated by the time during 
 which the machine works ; repeated weighings having de- 
 monstrated, that the relation between the time of working and 
 quantity of deposited metal, is sufficiently accurate.* 
 
 * The process of magneto-plating is extensively carried on by Mr. Prime, of 
 Northwood-street, Birmingham, by whose kindness the author has been enabled to 
 verify many of the statements contained in this chapter. 
 
66 
 
 CHAP. V. 
 
 ON THE PRODUCTION OF ELECTRICITY BY HEAT 
 AND THERMO-ELECTRIC BATTERIES. 
 
 154. If a circuit be formed of two metals, and heat be 
 applied at one of the points of junction, an electric current 
 will be determined through the arrangement; or if, instead of 
 applying heat, one of the junctions be cooled, the same effect 
 will be produced ; it being only necessary to produce, either 
 by heating or cooling one of the junctions, a difference of 
 temperature in them. 
 
 155. The accompanying figure {Jig. 17), represents a 
 Fig. 17. simple thermo-electric arrangement, a is a 
 
 semi-circular bar of bismuth, and h a similar 
 bar of antimony. These bars are joined 
 together, by soldei'ing, at the points c d. 
 By applying heat to one of the joinings, c d, 
 an electric current will circulate through 
 the whole arrangement, which current 
 will be increased by cooling the other joining, so as to pro- 
 duce a greater inequality of temperature. A magnetic needle 
 brought near such an arrangement, will be deflected (122) ; 
 and if the circuit be interrupted at some point, and be con- 
 nected by a saline solution, easy of decomposition (58), the 
 solution will be resolved into its constituent elements. These 
 and other phenomena, demonstrate the circulation of an electric 
 current. 
 
 156. Different combinations of metals, possess the power of 
 
67 
 
 determining thermo-electric currents, in different degrees. 
 The most effective combination is that of bismuth and anti- 
 mony ; but, owing to the brittleness of these metals, other 
 combinations are used, — as of platinum and iron, German 
 silver (an alloy of nickel) and iron, or copper. 
 
 157. The thermo-electric current is, however, possessed of 
 a very feeble intensity, and on that account, has not hitherto 
 been applied with success to the deposition of metals. 
 
 158. Attempts have been made to increase the effects of the 
 thermo-electric current by combining together a number of 
 pairs, so as to form a thermo-electric battery, as voltaic pairs 
 are combined together to form a voltaic battery. Fig. 18 
 
 Fiy- 18. represents a thermo-electric 
 
 battery. It consists of a 
 number of bars of iron, and 
 others of German silver, sol- 
 dered together end to end, 
 so as to have regular alter- 
 nations of the two metals. The bars are piled side by side, 
 but separated from each other by some non-metallic sub- 
 stance. The whole forms a compact mass, which, when in 
 use, is heated at one end, and cooled at the other. By the 
 application of heat to the lower end, the first, third, fifth, &c., 
 joinings are heated ; while, by the application of water to the 
 upper end, the second, fourth, sixth, &c., joinings, are kept 
 cool. 
 
 159. The intensity of a thermo-electric current does not 
 increase as that of the voltaic battery does, in proportion to 
 the number of elements, or pairs, in the battery ; nor is it at 
 all clear, that there is any analogy between the constitution of 
 the voltaic, and thermo-electric batteries. It has been shown 
 (65) that the electric current in the battery, in passing 
 through the different cells, must effect a decomposition in 
 each ; and that, if decomposition be prevented in one cell, 
 the whole must become inactive, as the passage of the current 
 
 F 2 
 
68 
 
 is dependent on the decomposition. Now, in passing through 
 the various colls, the current is not only not opposed, but 
 there is, as it were, a disposition to decomposition, which is 
 favourable to the passage of the current, and by which the 
 current acquires intensity. 
 
 160. The constitution of the thermo-electric, however, does 
 not at all resemble that of the voltaic batterj^. A bar, or wire 
 of metal, can transmit a hundred currents from as many bat- 
 teries, without those currents interfering with each other; and so 
 in the thermo-electric battery, if only one junction be heated, 
 a current is generated which can circulate freely through all 
 the other pairs, without impediment. On heating a second or 
 third alternate junction, a second and third current will be 
 produced, which will circulate through the whole arrange- 
 ment, independently of the current produced at the first 
 joining ; and so the current of a battery of this kind will be, 
 in quantity, the sum of the individual currents, while the in- 
 tensity will be wholly unaffected by the number of alterna- 
 tions, and dependent only on the nature of the metals asso- 
 ciated. 
 
 161. It has been many times announced that thermo-electric 
 batteries have been constructed which effect directly"^ the de- 
 composition of water. Experience has not confirmed these 
 reports ; and there is also reason to doubt the correctness 
 of those statements, in which the successful reduction of 
 metals, by thermo-electricity, is represented to have been 
 accomplished. 
 
 • By induction, cuiTents of the feeblest intensity can be made to develope others 
 of great intensity ; and in this way the intensity of a thermo-electric current may 
 be increased, so as to give sparks, shocks, &c., and eifect decompositions ; but such 
 induced currents are so inferior to those obtained with the voltaic battery, that, for 
 practical purposes, they are worthless. 
 
69 
 
 CHAP. VI. 
 
 ON THE SALTS FROM WHICH METALS MAY BE 
 PRECIPITATED. 
 
 162. Metals may be precipitated by voltaic agency from 
 any of their soluble salts (38), or from solutions of those of 
 their salts, which are insoluble in water, in any menstruum 
 capable of dissolving them. The reduction, by voltaic agency, 
 of some of the metals is effected with extreme facility ; while 
 the reduction of others is accompanied with many difficulties. 
 The precipitation of gold, silver, copper, &c., in the reguline 
 state, is easily accomplished ; while the reduction of potas- 
 sium, sodium, manganese, &c., is attended with difficulty. 
 
 163. The reduction of the same metal from its different 
 salts is attended with different degrees of difficulty ; thus, the 
 reduction of copper from the nitrate and sulphate of copper 
 takes place under the influence of a feeble voltaic current, 
 while the precipitation of the same metal from its acetate, re- 
 quires a current of considerable intensity (58). 
 
 164. The metals which are reduced by voltaic agency for 
 the purposes of art are few in number ; and it is only to those 
 metals that particular attention will be given : — they are gold, 
 silver, platinum, copper, and zinc. The other metals, which 
 may be conveniently deposited by electric agency, will after- 
 wards be briefly studied. 
 
 165. The precipitation of the noble metals received early 
 attention at the hands of those who experimented with the 
 
70 
 
 electrotype ; but the successful application of the voltaic 
 battery in their reduction, is of but recent date. Mr. Spencer 
 relates experiments he made with gold, and describes a plan 
 of effecting its reduction, which, (though the materials are in 
 connection with the voltaic battery,) is wholly unconnected 
 with electric agency. The plan alluded to consists in forming 
 an arrangement similar to that called the single cell apparatus 
 described in the following chapter. The porous cell is charged 
 as usual, and the outer vessel filled with a very dilute solution 
 of the chloride of gold, to which a few crystals of carbonate 
 soda have been added. If a battery and decomposing cell 
 be used, Mr. S. recommends that the former be charged with 
 cold water only. A film of gold is deposited on the surface 
 thus treated, but it is extremely thin ; and, however long the 
 connection with the battery is maintained, it cannot be made 
 thicker — a sufficient proof that the cause of the deposition 
 does not exist in the battery ; indeed, the effect is produced 
 without the battery, and, therefore, cannot with any propriety 
 be called a voltaic precipitation. A mode of precipitating 
 gold has been described in the " Annates de Chimie^'' by M. 
 de la Rive. It is essentially the same as that of Mr. Spencer. 
 The process is described at great length by M. de la Rive, 
 but, as it is so inferior to the methods at present adopted, it 
 is usless to describe it. Subsequent experiments have sup- 
 plied us with processes, by which works of art may be multi- 
 plied in gold and silver, with as much ease as in copper. 
 
 166. Gold may be precipitated from its chloride, bromide, 
 iodide, cyanide, sulphite, and hypo-sulphite. 
 
 167. Chloride of gold is formed by dissolving gold in nitro- 
 muriatic acid — a mixture also called aqua regia, from its 
 property of dissolving this metal. Aqua regia is formed by 
 adding together one measure of nitric acid and two measures 
 of hydro-chloric or muriatic acid. To procure chloride of 
 gold, the metal is added to about four times its weight of 
 aqua regia, and a gentle heat applied. Decomposition of 
 
71 
 
 the two acids takes place ; the hydrogen of the hydro-chloric 
 acid combines with the oxygen of the nitric acid, foraiing 
 water; while the other elements of the decomposed acids are 
 liberated ; the nitric oxide of the nitric acid escapes, and the 
 chlorine of the hydro-chloric acid remains in solution, and is 
 the real solvent of gold. 
 
 168. When the metal is dissolved, the solution should be 
 carefully evaporated. It is necessary to stop the evaporation 
 when the solution becomes of a dark red colour and emits 
 chlorine, which is readily detected by its odour. On setting 
 the solution aside, the chloride forms a dark red crystalline 
 mass. The salt thus formed is the per-chloride or sesqui- 
 chloride of gold, and consists of two equivalents (35) of 
 gold, and three equivalents of chlorine. If the evaporation 
 of the solution be carried too far, a portion of chloride of gold 
 (properly so called) will be formed. This compound consists 
 of two equivalents (35) of gold, and one equivalent of 
 chlorine ; it is insoluble in water, but when in contact with 
 that liquid suffers decomposition ; it resolves itself into the 
 per-chloride and metallic gold, the former dissolves and the 
 latter remains undissolved. The operator may, therefore, con- 
 clude, that when any metallic gold appears in the solution of 
 the chloride, the evaporation for the production of the crys- 
 talline mass has been carried too far. This salt is the first 
 from which gold was successfully precipitated ; but it has 
 now fallen into disuse, owing to its inferiority to many of the 
 solutions more recently proposed. 
 
 169. Bromide of gold may be formed by the direct union 
 of bromine with gold. Bromine is an elementary body (31), 
 existing, at ordinary temperatures, in the form of a dense liquid, 
 of a very dark red colour ; it is very volatile, and, at common 
 temperatures, gives off dense red fumes, having a pungent, 
 suffocating odour. In order to form the bromide of gold, the 
 metal, in a state of fine division, should be digested in 
 bromine. The application of a gentle heat favours the forma- 
 
72 
 
 tion of the compound, but, owing to the volatility of bromine, 
 it must be cautiously applied. The digestion should take 
 place in a well closed vessel, a stoppered glass bottle, for 
 example. In order to prevent the evaporation of bromine, it 
 is usual to pour a small quantity of water into bottles con- 
 taining that substance. Water is not miscible with bromine ; 
 and, being much lighter, floats on the surface, and forms a 
 stratum, through which the bromine evaporates with difficulty. 
 Bromine is slightly soluble in water, and the stratum of that 
 liquid speedily acquires a beautiful red colour by dissolving 
 a portion of it. A considerable quantity of bromine evapo- 
 rates from this aqueous solution, which, becoming weaker, 
 replenishes itself by dissolving more bromine, and thus, even 
 when the precaution is taken of covering the bromine with 
 water, evaporation goes on with considerable rapidity ; it is 
 hence advisable to keep the mixture of bromine and gold 
 in a stoppered bottle, even when covered with a stratum of 
 water. 
 
 170. In order to procure gold in that state of fine division 
 which is favourable to its solution in bromine and other 
 solvents, the metal should be dissolved in aqua regia (167), and 
 proto-sulphate of iron (green copperas) added to the solution. 
 The gold is precipitated as a brown powder, which has no 
 resemblance to gold, but which, nevertheless, is that metal 
 in a state of purity, and of minute division. This powder is 
 readily taken up by all the solvents of gold. 
 
 171. The bromide of gold is a salt of a rich red colour, and 
 from its aqueous solution, the metal may be precipitated by 
 voltaic agency. In its chemical relations it closely resembles 
 the chloride of gold. It is more expensive in its preparation 
 than the chloride, and possesses no equivalent advantage ; 
 indeed it is inferior, for electro-matallurgical purposes, to 
 many of the other salts of gold. Its use was first proposed by 
 Mr. Spencer ; it is, however, rarely, if ever, employed for 
 manufacturing purposes. 
 
73 
 
 172. Iodide of gold may be formed by digesting hydiiodic 
 acid, with oxide of gold ; it may also be prepared by adding a 
 solution of iodide of potassium to a solution of chloride of 
 gold (167). Iodide of gold is of a yellow colour; it is inso- 
 luble in cold water, and but slightly soluble in boiling water. 
 It is dissolved readily by a solution of iodide of potassium, 
 and from its solution in that menstruum, gold may be precipi- 
 tated by the voltaic battery. Its use was first proposed by 
 Mr. Spencer, but it possesses no advantages, and has hence 
 never been generally used. 
 
 173. Oxide of gold may be made by adding a cold solution 
 of potash to a solution of chloride of gold (167). The potash 
 must be added cautiously, as an excess redissolves a portion 
 of the precipitated oxide. It may also be obtained by adding 
 magnesia to the solution of the chloride ; and the latter 
 method is to be preferred. The precipitated oxide should be 
 washed first with pure water acidulated with nitric acid, and 
 afterwards with pure water alone. 
 
 174. Cyanide of gold may be formed by adding metallic 
 gold, in a state of fine division (170), to a solution of cyanide 
 of potassium. The metal dissolves slowly in the solution, 
 but the action may be quickened by the application of heat. 
 It may, however, be more readily prepared, by the addition 
 of oxide of gold (173) to the solution of cyanide of potassium, 
 or any of the salts of gold may be substituted for the oxide, 
 but the latter is recommended. The solution may be favoured 
 by boiling the liquid. A solution much used for electro- 
 metallurgical purposes, is formed by adding two pounds of 
 cyanide of potassium to one gallon of water, and saturating 
 the solution with oxide of gold. 
 
 175. Cyanide of potassium may be made in various ways. 
 It may be formed by the direct union of its elements. If 
 potassium be heated in cyanogen, it burns with a beautiful 
 flame ; cyanogen is absorbed, and the cyanide of potassium 
 formed. This process cannot be used for its production in 
 
74 
 
 large quantities. One of the simplest and most economical 
 modes of forming it, is to heat the salt known by the names of 
 prussiate of potash, ferro-prussiate of potash, and ferro-cyanide 
 of potassium. It is known in commerce as prussiate of potash. 
 It should be put in a close vessel, and heated to redness, and, 
 after cooling, the addition of water will dissolve away the 
 cyanide of potassium, which may be obtained in crystals 
 by evaporation. The latter, however, is not necessary, as 
 it must be used in the state of solution. The salt thus pro- 
 cured is not quite pure, as a portion of the prussiate gene- 
 rally escapes decomposition ; the impurity is, however, of 
 little consequence, and the salt thus obtained answers every 
 purpose. In order to obtain the cyanide free from impurity, 
 it should be dissolved in alcohol; the cyanide is largely 
 soluble in that menstruum, and is dissolved, while the prus- 
 siate is insoluble, and remains at the bottom of the vessel. 
 By decanting the clear solution, and evaporating or distilling 
 oflf the alcohol, the cyanide of potassium may be obtained, in 
 the form of a white crystalline mass, perfectly free from the 
 prussiate. 
 
 176. Prussiate of potash maybe considered as a compound 
 of two equivalents of cyanide of potassium, with one equivalent 
 of proto-cyanide of iron* ; the former undergoes no change on 
 exposure to a red heat, while the latter is decomposed into 
 carburet of ij-on, with evolution of nitrogen gas. The carburet 
 of iron forms a spongy mass, which absorbs the fused cyanide 
 of potassium, and from which it is afterwards separated by 
 water or alcohol. 
 
 177. By the process just described (175), a loss of one- 
 third of the cyanide contained in the prussiate is sustained ; 
 
 * Chemists are by no means agreed respecting the proximate constitution of the 
 class of salts described in this chapter as cyanides. It is, however, certain that they 
 are not simple cyanides; but being commonly called so, it has been thought better 
 to retain their common names in the present work, than to introduce others which 
 involve theoretical considerations. 
 
75 
 
 but a modification of the process has been pointed out by 
 Liebig, by which this loss is avoided. It is as follows : — 
 eight parts of the prussiate are dried on a hot plate of iron, 
 then finely powdered, and mixed well with three parts of dry 
 carbonate of potash, and thrown at once into a Hessian cru- 
 cible, previously heated to redness, and kept at that tempera- 
 ture ; the mixture fuses into a brown mass, with a lively 
 evolution of gas. After a few minutes, when the fluid mass 
 has become red-hot, its dark colour is seen to become brighter, 
 and on continued fusion, the salt becomes clear and of an 
 amber yellow tint. If, from time to time, a hot glass rod be 
 immersed in it, the adhering mass, on cooling, is at first 
 brown, afterwards yellow, and at last, towards the close of the 
 operation, clear and colourless as water, and solidifies into a 
 shining white crystalline mass. During the fusion, brown 
 flocks are seen floating in the fluid mixture, which, subse- 
 quently, unite into a spongy mass, and assume a light grey 
 colour. If the crucible be now removed from the fire, and 
 allowed to cool somewhat, the grey powder generally settles 
 entirely at the bottom ; this is facilitated by stirring once or 
 twice with the glass rod. The fused mass may now be easily 
 poured into a warm porcelain dish, without a particle of the 
 sediment accompanying it. This mass consists of two com- 
 binations, of which the cyanide of potassium forms the chief 
 portion ; the other compound is the cyanate of potash, in the 
 proportion of five of the former to one of the latter. The 
 reaction in the fusion of the yellow prussiate with carbonate 
 of potash, is as follows: — at the commencement, the proto- 
 cyanide of iron of the ferro-cyanide is decomposed, and forms 
 cyanide of potassium with the potash of the alkaline carbo- 
 nate, and the proto-carbonate of iron, which is deprived of all 
 its oxygen, at a higher temperature, by the cyanide of potas- 
 sium. In consequence of this reduction, cyanate of potash 
 and pure metallic iron are obtained. From two equivalents 
 of the ferro-cyanide of potassium we thus obtain five equiva- 
 
76 
 
 lents of the cyanide, that is, one-fourth more than by fusing 
 it alone. The cyanate of potash mixed with it has no injurious 
 influence in any one of its applications. The presence of 
 cyanate is readily detected, by the effervescence caused from 
 the escape of carbonic acid, on the addition of an excess of 
 acid, and an ammoniacal salt is afterwards found in the liquid. 
 The explanation given above of the formation of the cyanide 
 of potassium under the conditions described, is not absolutely 
 correct, as the proto-carbonate of iron, previous to its reduc- 
 tion, is decomposed into carbonic acid, carbonic oxide, and 
 the black oxide of iron, at the expense of which an undeter- 
 minable quantity of cyanate is formed, more than the formula 
 indicates. The metallic iron is precipitated, and the sides of 
 the crucible are covered by cyanide of potassium, to obtain 
 which, it is only necessary to remove with cold water all that 
 is soluble, and to warm the solution with some sulphuret of 
 iron, which easily dissolves in it. The cyanide of potassium 
 is thus obtained, on evaporation again, in the form of ferro- 
 cyanide, and sulphuret of potassium remains in the mother-ley. 
 
 178. Gold may be precipitated with great facility, from the 
 solution of its oxide in sulphite of potassa. The use of this 
 salt for electro-metallurgical purposes, M as first proposed by 
 Mr. J. S. Woolrich. In order to form this solution, oxide of 
 gold precipitated with magnesia (173) is added to a solution 
 of sulphite of potassa, until the latter is saturated. After 
 saturation, one-fifth part more of the solution of sulphite of 
 potassa must be added to the solution of gold, as it is neces- 
 sary to the proper working of the solution, that the sulphite of 
 potassa be in excess. 
 
 .179. The solution of sulphite of potassa is made as fol- 
 lows : — 28 parts of pearlash of commerce are dissolved in 30 
 parts of water, by boiling in an iron vessel. The solution is 
 filtered when cold, and diluted with 14 parts of water. Sul- 
 phurous acid gas is passed through the solution, until it is 
 saturated. The liquor is again filtered, and is then fit for use. 
 
77 
 
 The process for making this solvent is a simple one ; the only 
 precaution to be observed is, not to add the sulphurous acid 
 in excess. 
 
 180. Sulphurous acid gas, for making sulphite of potassa, 
 may be made as follows : — Concentrated sulphuric acid (oil 
 of vitriol) is poured into a retort, or flask, and filings or turn- 
 ings of zinc, iron, or copper added thereto; or mercury may 
 be used instead. Heat is carefully applied to the flask, or 
 retort, and regulated so as to cause the evolution of gas with 
 the desired rapidity. Decomposition of the sulphuric acid is 
 effected, the metals combine with a portion of its oxygen, and 
 sulphurous acid gas is liberated. The gas is conducted into 
 the alkaline solution, contained in Wolf's, or three-necked, 
 bottles, until the solution absorbs no more. 
 
 181. Gold may be precipitated from the solution of its 
 hypo-sulphite. This solution maybe readily made by adding 
 chloride of gold to a solution of hypo-sulphite of soda or 
 potassa. It is, however, inferior to the cyanide and sulphite 
 for electro-metallurgical purposes. Hypo-sulphite of soda 
 may be made in the following manner : — Sulphurous acid gas 
 (180) must be passed through a solution of soda until it ab- 
 sorbs no more. A solution of sulphite of soda is thus formed : 
 — a quantity of flowers of sulphur is introduced into the 
 solution of sulphite, and allowed to remain there twenty-four 
 hours; the solution dissolves a little sulphur, and becomes a 
 solution of hypo- sulphite of soda. It must be separated 
 from the flowers of sulphur by filtration or decantation ; and 
 carefully evaporated at a temperature below the boiling point. 
 Crystals of hypo-sulphite will form as the solution cools. It 
 is not, however, necessary to crystallize the salt, as a solu- 
 tion of hypo-sulphite of soda, made from a solution of the 
 sulphite, of the strength recommended (179), answers very 
 well. 
 
 182. A new method of making hypo-sulphite of soda has 
 recently been proposed, by which the salt may be formed 
 
78 
 
 much more economically. Carbonate of soda is carefully 
 dried, by exposure to heat, and when perfectly deprived of 
 water, is reduced to a fine powder. This powder is inti- 
 mately mixed with not less than one-fifth its weight of sul- 
 phur; an excess of sulphur is not prejudicial. The mixture 
 is gently heated in a porcelain vessel on a sand-bath, and is 
 constantly stirred during its exposure to heat. The mixture 
 assumes a dark colour, and eventually becomes almost black. 
 The change of colour indicates the decomposition of the car- 
 bonate of soda, and formation of sulphuret of sodium. The 
 mixture must now be carefully stirred, as much of the success 
 of the process depends on the proper exposure of the sulphuret 
 to the air. The colour again becomes lighter, and eventually 
 the dark-brown pasty mass is converted into a whitish 
 powder, which is principally sulphite of soda. After cooling, 
 Avater must be added to take up the sulphite formed, and the 
 splution filtered. Flowers of sulphur must now be added to 
 the solution, and allowed to digest twenty-four hours. The 
 solution should again be filtered, to separate the flowers of 
 sulphur, and cautiously evaporated at a temperature below 
 the boiling point. On setting the solution aside, crystals of 
 hypo-sulphite of soda will be deposited. This process, if 
 properly conducted, succeeds well, and nearly the whole of 
 the carbonate becomes converted into hypo-sulphite. It is 
 however, only by extreme care that so successful a result can 
 be obtained ; and usually a considerable quantity of carbonate 
 of soda will be found in the solution, from which, however, 
 it may be separated by crystallization. If the mixture of 
 the carbonate and sulphur be heated too quickly, or the 
 temperature be raised too high, a portion of the sulphur takes 
 fire, and burns away ; and, unless there be an excess, an 
 equivalent portion of the carbonate of soda escapes decom- 
 position. It is also necessary to expose the sulphuret to long 
 continued heat, and stir it well, otherwise the whole of the 
 sulphuret is not converted into sulphite. 
 
79 
 
 183. Gold may be deposited, by voltaic agency, from many 
 solutions besides those enumerated. A solution of sulpho- 
 cyanide of gold in sulpho-cyanide of potassium may be used 
 for this purpose, as well as a solution of oxide of gold in 
 chloride of potassium, or chloride of sodium ; but as these 
 solutions are inferior to those already enumerated, the modg 
 of preparing them need not be given. The solutions of cyanide 
 and sulphite of gold are superior to all others for the use of 
 the electro-metallurgist. 
 
 184. Silver may be most conveniently precipitated from its 
 cyanide, sulphite, hypo-sulphite, sulphate, acetate ; and the 
 solution of most of its salts, in ammonia. 
 
 185. Cyanide of silver may be made by adding oxide of 
 silver to a solution of cyanide of potassium. A solution com- 
 posed of three pounds of cyanide of potassium dissolved in 
 two gallons of water, and saturated with oxide of silver, 
 answers well for electro-metallurgical depositions. The true 
 nature of the salt thus formed is not well understood ; by 
 some it is regarded as a solution of cyanide of silver in 
 cyanide of potassium, while by others it is regarded as a salt 
 analagous in constitution to the ferro-cyanide of potassium, 
 and, according to which view it is called the argento-cyanide 
 of potassium. The same remarks apply to the analagous salts 
 of gold, copper, &c. The cyanide of silver is an excellent 
 salt from which to precipitate silver ; it is equalled only by 
 the sulphite ; and, but for the spontaneous decomposition 
 which it slowly undergoes, would be superior to every other. 
 
 186. Oxide of silver (185) may be prepared by the addition 
 of lime water, or a solution of caustic potash to a solution of 
 nitrate of silver. Nitrate of silver may be prepared by adding 
 pure silver to nitric acid, diluted with an equal volume of 
 water ; the action should be favoured by the application of a 
 gentle heat. When the metal has dissolved, the solution 
 should be evaporated, and the salt crystallized ; the crystals 
 must be dissolved in distilled or rain water, and lime water 
 
80 
 
 added ; a brown precipitate falls, which is the oxide of silver. 
 The lime water must be added until it ceases to produce any 
 further precipitation. The precipitated oxide should be col- 
 lected, and well washed with pure water. 
 
 187. In order to prepare a solution of silver with the sul- 
 phite of potassa, the solution of sulphite of potassa — prepared 
 as before described (179) — should be slowly poured into a 
 solution of nitrate of silver, made by adding 12 ounces of the 
 nitrate to 3 lbs. of water. A whitish precipitate falls, and the 
 sulphite must be added until it ceases to produce a precipi- 
 tate. The precipitate must be separated from the liquid, 
 either by allowing it to subside, or by filtration, and must 
 be well washed with water. It is then added to the solution 
 of sulphite of potassa, until the solution will take up no 
 more. As it is, however, desirable that the sulphite 
 of potassa should be in excess, about one-sixth part of the 
 sulphite of potassa solution should be added to the saturated 
 solution. 
 
 188. The sulphite of silver is an excellent salt from which 
 to precipitate silver ; it is not liable to spontaneous decom- 
 position like the cyanide and hypo-sulphite ; it is less costly 
 than the cyanide, and is unaccompanied by any unpleasant 
 smell. 
 
 189. Hypo-sulphite of silver, as proposed by Mr. Talbot, 
 may be made by adding chloride of silver to a solution of 
 hypo-sulphile of soda (181) or potassa; oxide of silver, or 
 any of the insoluble salts of that metal, may be substituted 
 for the chloride. The chloride, or other salt, should be added 
 till the solution will take up no more. Hypo-sulphurous acid 
 has so great an affinity for oxide of silver, that all the soluble 
 hypo-sulphites are decomposed by the salts of silver, giving 
 rise to the formation of hypo-sulphite of silver. On adding a 
 salt of silver to hypo-sulphite of soda, or potassa, a double 
 salt, hypo-sulphite of soda, or potassa, and silver is formed, 
 which is supposed to consist of one equivalent (35) of hypo- 
 
sulphite of silver to two of the alkaline hypo-sulphite. The 
 hypo-sulphite of silver itself, is insoluble in water. When 
 dilute solution of hypo-sulphite of soda is added to dilute 
 solution of nitrate of silver, a white precipitate of hypo-sul- 
 phite of silver is formed, which speedily re-dissolves from the 
 formation of the double salt. The hypo-sulphite of silver 
 may be advantageously used for the electrical precipitation 
 of silver ; it is one of the best solutions, though inferior to 
 the sulphite and cyanide, and, like the latter, suffers spon- 
 taneous decomposition. 
 
 190. Sulphate of silver may be obtained by dissolving silver, 
 by the aid of heat, in concentrated sulphuric acid. It may 
 also be formed by adding sulphuric acid, or sulphate of 
 potassa, to a solution of nitrate of silver ; from its imperfect 
 solubility in water it is precipitated as a crystalline powder, 
 if the solutions are not too dilute. The salt is soluble in 
 about 90 times its weight of water. A saturated solution 
 must be employed ; but it is inferior to many other solutions, 
 and is not recommended. 
 
 191. Acetate of silver is formed by the addition of oxide of 
 silver to acetic acid ; or a solution of acetate of potassa to a 
 solution of nitrate of silver. It is inferior, for electro -metal- 
 lurgical purposes, to the sulphite and cyanide. 
 
 192. Many of the salts of silver, which are insoluble in 
 water, dissolve in other menstrua, and may be used in 
 electro-metallurgy. Chloride of silver, which is insoluble 
 in water, is soluble in a solution of chloride of potassium, 
 or chloride of sodium (common salt) ; and silver may be 
 reduced from these solutions. Oxide of silver may also be 
 dissolved in a solution of bitartrate of potassa (cream of 
 tartar) ; but the solution possesses no advantages. Iodide 
 of silver, obtained by adding iodide of potassium to nitrate of 
 silver, may be dissolved in a solution of iodide of potassium, 
 and in this way, be used for the deposition of silver. Mr. 
 Spencer has proposed a solution of the bromide of silver in 
 
 G 
 
acetate of ammonia. For this purpose, bromide of silver, which 
 may be obtained by adding bromine to a solution of nitrate of 
 silver, is added to about 30 times its weight of a saturated solu- 
 tion of acetate of ammonia, and the solution effected by the ap- 
 plication of heat. Many other solutions of silver have been 
 proposed, some of which, however, vary but little from those 
 already described ; and as these solutions possess no advan- 
 tages which are not common to those already described, a 
 description of them is unnecessary. The sulphite and cyanide, 
 are superior to all the other salts of silver, for electric depo- 
 sitions. 
 
 193. Copper may be precipitated from a great variety of its 
 salts ; of which the most valuable are the sulphate, the nitrate, 
 the sulphite, and the cyanide. Sulphate of copper may be 
 made by dissolving copper in sulphuric acid, to which a small 
 quantity of nitric acid has been added. The copper is oxi- 
 dated at the expense of the oxygen of the «iitric acid, and the 
 sulphuric acid combines with the oxide so formed. Sulphate 
 of copper is an article of commerce, and its preparation need 
 not, therefore, be undertaken by the electro-metallurgist. 
 The solution of sulphate of copper is not readily decomposed 
 by a voltaic current of low intensity ; and it is usual to in- 
 crease its conducting power, by the addition of sulphuric or 
 nitric acid, or a mixture of the two. Two parts of a saturated 
 solution of the sulphate, and one part of dilute sulphuric acid 
 (consisting of one-eighth concentrated acid), form a mixture, 
 which practice has shown to be equal, if not superior, to every 
 other. When it is desired to effect a rapid deposition of the 
 metal, a little nitric acid should be added ; the quantity must, 
 however, be small, not exceeding one part to sixty or seventy 
 parts of the cupreous solution. 
 
 194. Nitrate of copper may be made by dissolving copper, or 
 scales of copper, in nitric acid, and crystallizing. Although a 
 more expensive salt than the sulphate, it is much more valuable 
 for electro-metallurgical operations ; it suffers decomposition 
 
83 
 
 more readily, so that a given quantity of copper may be depo- 
 sited from it in a shorter time. A saturated solution of this salt 
 may be conveniently used ; and its conducting power, and, con- 
 sequently, the rapidity with which it suffers decomposition, 
 may be increased by the addition of nitric acid. One part of 
 concentrated nitric acid to thirty parts of a saturated solution of 
 nitrate of copper, form a solution, from which copper may be 
 precipitated with greater rapidity than any other. A mixture 
 of the solutions of sulphate and nitrate of copper has been 
 proposed, and although it answers well, it has no peculiar 
 advantages. 
 
 195. A solution, from which copper may be conveniently 
 deposited, may be made with the sulphite of potassa solution 
 (179). A solution of carbonate of potassa should be added 
 to a solution of sulphate of copper, until it ceases to produce 
 a precipitate. This precipitate is well washed, and added to 
 the solution of sulphite of potassa, until it will take up no 
 more. As it is desirable that the sulphite of potassa should 
 be in excess, one-third more of its solution is added to the 
 saturated solution. 
 
 196. Cyanide of copper is formed by adding oxide of cop- 
 per to a solution of cyanide of potassium, until the solution is 
 saturated. The application of heat facilitates the solution of 
 the oxide. Oxide of copper may be prepared by exposing 
 metallic copper, at a red heat, to the action of air. It may also 
 be obtained by decomposing the nitrate by a red heat. For 
 ordinary purposes, the cyanide is very inferior to the sulphate, 
 nitrate, and sulphite ; but occasions may present themselves in 
 which it may be used with advantage. The same remark 
 applies to the acetate, which may be made by digesting ver- 
 digris in acetic acid, and crystallizing. Instead of verdigris, 
 oxide of copper may be used. 
 
 197. Oxide of copper is readily dissolved by ammonia, and 
 the solution may be used for voltaic precipitation. It pos- 
 sesses no peculiar advantages. 
 
84 
 
 198. Platinum may be deposited from a solution of its bi- 
 chloride, bromide, iodide, and the double chloride of platinum 
 and sodium. 
 
 199. Bi-chloride of platinum is formed by dissolving pla- 
 tinum in aqua regia. The latter consists of one part of nitric 
 acid and two parts of hydro-chloric (muriatic) acid. The 
 salt may be obtained by cautiously evaporating the solution. 
 When redissolved, it forms a solution of an intense and pure 
 yellow colour. It is the only salt of platinum, which is com- 
 monly used for voltaic precipitations. 
 
 200. Bromide of platinum may be obtained by digesting 
 platinum in that highly divided state, in which it is called 
 spongy platinum, in a mixture of equal parts of bromine and 
 alcohol. The conducting power of the solution of bromide of 
 platinum, may be increased by the addition of dilute sulphuric 
 acid. The use of this salt was first proposed by Mr. Spencer. 
 
 201. Iodide of platinum, precipitated by iodide of potassium 
 from chloride of platinum, and redissolved in excess of the 
 precipitant, has been proposed for electric deposition ; but it 
 is inferior to the chloride, and the chloride of platinum and 
 sodium. 
 
 202. Chloride of platinum and sodium, may be made by 
 the simple addition of chloride of platinum to chloride of 
 sodium. 
 
 203. Zinc may be reduced from its sulphate, chloride, 
 iodide, and acetate, and the solution of its oxide in potassa, 
 or muriate of ammonia (sal-ammoniac). Sulphate of zinc is 
 formed, when impure zinc is added to dilute sulphuric acid. 
 If pure zinc be used, some other metallic body must be 
 brought in contact with it, otherwise it will not dissolve in 
 the acid (50). The electro-metallurgist wdll rarely have 
 occasion to make this salt, as it is formed in considerable 
 quantity by the action of the common acid battery (110), and 
 when crystallized from the acid^ which has been used to 
 excite the battery, is in a state of great purity. A saturated 
 
85 
 
 solution of the sulphate, free from uucombined acid, may be 
 used for the reduction of zinc. 
 
 204. Chloride of zinc, is formed when zinc is dissolved in 
 hydro-chloric (muriatic) acid. 
 
 205. Iodide of zinc, may be. formed by digesting together 
 zinc, iodine, and water. 
 
 206. Acetate of zinc is formed when oxide of zinc is dis- 
 solved in acetic acid ; the solution of this salt answers well, 
 for the electrical reduction of the metal. 
 
 207. Oxide of zinc is a white powder, obtained by the 
 combustion of zinc in an earthenware crucible ; it may also 
 be prepared by precipitation, from the sulphate, or any of its 
 other salts, by the addition of potassa or soda. Oxide of zinc 
 is soluble in ammonia, potassa, soda, and muriate of ammonia 
 (sal-ammoniac), and its reduction may be effected from any of 
 these solutions. The sulphate, however, is suitable for most 
 purposes. 
 
 208. It has already been remarked (162), that all metals may 
 be reduced from their soluble compounds, by the agency of 
 voltaic electricity. There are few, hovt'ever, excepting those 
 already mentioned, which the electro-metallurgist will have 
 occasion to operate upon, and it is therefore unnecessary to 
 notice them in detail. Iron may be reduced from a solution of 
 its proto-sulphate (green copperas), made by dissolving iron in 
 dilute sulphuric acid ; or from its proto-chloride, which is pre- 
 ferable, and which is made by dissolving iron in hydro-chloric 
 (muriatic) acid. Lead may be reduced from its acetate (sugar 
 of lead) and nitrate ; and tin, from its sulphate and chloride. 
 
 209. Many of the salts used in electro-metallurgy, may be 
 made by means of the voltaic battery itself. In order to pro- 
 duce any salt, it is only necessary to arrange the metal as the 
 electrodes in a solution, from which, by voltaic decomposition, 
 the element to be combined with the metal, may be liberated. 
 Thus, in decomposing water with copper poles or electrodes, 
 the oxygen liberated combines with the copper, and forms 
 
86 
 
 oxide of copper (5) ; and if the water were acidulated with 
 sulphuric acid, the oxide so formed would combine with the 
 acid, and sulphate of copper would be the product. In this 
 way almost all the salts may be formed ; it is rarely, however, 
 that they can be made so quickly, or so economically, as by 
 the methods pointed out, and it is only where a salt cannot 
 be conveniently made in the ordinary way, that its formation 
 by the battery is recommended. 
 
 210. The cyanides of gold, silver, copper, &c., may be 
 formed by passing a voltaic current through a solution of 
 cyanide of potassium, the electrode in connection with the 
 silver or copper end of the battery being of gold, silver, 
 copper, &c., the other electrode may be of the same metal, or 
 of platinum. Mr. Spencer has proposed to make the iodide 
 and bromide of gold, and the iodide and bromide of silver, by 
 means of the voltaic battery. The following is the plan he 
 adopts : — to make the bromide of gold ; make a mixture of 
 equal parts of bromine and alcohol ; and of this mixture take 
 one part, of acetic acid one part, and four parts of water. 
 To this mixture let a few drops of sulphuric acid be added. 
 Gold may be dissolved in this mixture by attaching it to the 
 platinum, or copper end, of a voltaic battery ; while another 
 piece of gold is, in like manner, attached to the zinc end of 
 the battery. These pieces of gold must be immersed in the 
 compound containing the bromine ; and when the battery is 
 excited into action, the gold attached to the platinum end of 
 the battery will be dissolved. When the mixture is saturated 
 with gold, it should be diluted with three times its volume 
 of water, and a few drops of sulphuric acid added. Mr. 
 Spencer also describes a solution of gold, made in the way 
 just described, combined with an ammoniacal salt ; two parts 
 of a saturated solution of acetate of ammonia should be added 
 to one of the solution of bromine. When the metal required 
 to be gilt is of such a nature as to act on the solution of gold 
 and bromine by mere immersion, Mr. Spencer directs the 
 
87 
 
 addition of carbonate of soda, till the solution will take up no 
 more. 
 
 211. Silver may be dissolved in a saturated solution of 
 acetate of ammonia, by means of the voltaic battery, and this 
 solution may be used for electro-metallurgical purposes ; and 
 the same metal may be dissolved in bromine, in the following- 
 manner : — A mixture is made of bromine and alcohol ; and 
 plates of silver, connected with the poles of a galvanic bat- 
 tery, are immersed in the mixture. By the action of the 
 battery, that plate of silver connected with the platinum or 
 silver end of the battery is dissolved in, and combines with, 
 the bromine. On setting aside the solution, a yellow precipi- 
 tate of bromide of silver falls to the bottom of the vessel. 
 The fluid is decanted from the precipitate, and the latter is 
 dissolved by boiling, in thirty times its weight of a saturated 
 solution of acetate of ammonia. 
 
88 
 
 CHAP. VIL 
 
 ON THE PREPARATION OF SURFACES FOR RECEIVING 
 METALLIC DEPOSITS. 
 
 212. It is essential that the surface on which it is wished 
 to deposite a metal by electro-metallurgical agency, be a con- 
 ductor of electricity (46). 
 
 213. It has already been remarked (46), that the only con- 
 ductors are metals and charcoal ; and it is, therefore, only on 
 those bodies that metallic precipitations can be effected by 
 the agency of electricity : and when it is wished to precipi- 
 tate upon a non-metallic or non-conducting surface, it is 
 necessary to give, by some preparatory process, a film of 
 metal or charcoal, to the article intended to receive the 
 deposite. 
 
 214. These metallic or carbonaceous films may be produced 
 on non-conducting bodies by a variety of processes. The 
 earliest process is tHat of Mr. Spencer; and the following 
 account is in his own words : — " I procured two models of 
 an ornament, one made of clay, and the other of plaster of 
 Paris, soaked them for some time in linseed oil, took them 
 out, and suffered them to dry, first getting the oil cleared off 
 the surface. When dry, I gave them a thin coat of mastic 
 varnish. When the varnish was nearly dry, hut not tho- 
 roiiglily so, I sprinkled some bronze powder on that portion 
 I wished to make a mould of. This powder is principally 
 composed of sulphur and mercury, or it may be chemically 
 termed a sulphuret of mercur3^ There is a sort that acts 
 
89 
 
 much better, in which is a portion of gold. I had, however, 
 a complete metalliferous coating on the surface of the mould, 
 by which T was enabled to deposit a surface of copper on it 
 by the voltaic method I have already described. I have also 
 gilt the surface of a clay model with gold leaf, and have been 
 successful in depositing copper on its surface. There is like- 
 wise another, and, as I trust it will prove, a simpler method 
 of attaining this object ; but, as I have not yet sufficiently 
 tested it by experiment, I shall take another opportunity of 
 describing it." The method here alluded to was afterwards 
 given by Mr. Spencer, in the following words : — " To obtain 
 a copper mould, or cast from a-piece of wood, plaster, or clay, 
 or, indeed, any non-metallic material, proceed as follows: — 
 Suppose it to be an engraved wooden block which you are 
 desirous of metallizing, in order that copper maybe deposited 
 on its surface — this example holding good for any other 
 material. The first operation is, to take strong alcohol, or 
 spirits of turpentine, in a glass vessel, and add to it a piece 
 of phosphorus (a common corked phial will answer the pur- 
 pose) ; 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 three-hundredth of its bulk of phos- 
 phorus, and we thus obtain a solution of phosphorus. Next, 
 procure a weak solution of nitrate of silver, place it in a flat 
 dish or saucer ; the engraved face of the block must now be 
 dipped in this solution, and let remain for a few seconds to 
 allow capillary attraction to draw the nitrate of silver into the 
 wood. This operation being performed, a small portion of 
 the solution of phosphorus must be placed in a capsule or 
 watch glass, and this be placed on a sand-bath, that it may 
 gradually evaporate. The block must now be held with its 
 surface over the vapour, and an immediate change takes 
 place ; the nitrate of silver becomes deoxidised, and gives 
 place to metallic silver, which allows the voltaic deposit to 
 go on with as much rapidity and certainty as the purest 
 
90 
 
 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, when the 
 material to be acted on is not very large, fasten it to the top 
 of a bell-glass receiver, with a bit of pitch or cement, and 
 place it thus over the capsule on the sand-bath ; the phos- 
 phoric vapour is by this means equally diffused, and not dis- 
 sipated. A solution of phosphorus in sulphuric ether also 
 answers ; and a solution of chloride of gold may be used." 
 
 215. This elegant process, as applied to wood, and those 
 substances which can be wetted with the solution of nitrate 
 of silver, answers perfectly ; but it is obviously limited in its 
 application to such substances as will absorb an aqueous 
 solution. 
 
 216. This plan has recently been modified with advantage. 
 Instead of the vapour of phosphorus, a solution of that sub- 
 stance is now commonly used. The best solvent of phos- 
 phorus hitherto known is bi-sulphuret of carbon. 
 
 217. Bi-sulphuret of carbon may be prepared in two ways. 
 A cast-iron or porcelain tube, or vessel, is filled with small 
 pieces of charcoal, and heated to redness in a furnace. This 
 tube, or vessel, is connected at one end with a retort, or 
 second vessel, containing sulphur ; and at the other with a 
 condensing apparatus. Heat is applied to the vessel con- 
 taining the sulphur, which is thus volatilized, and, in its 
 passage over the red-hot charcoal, combines therewith, to 
 form the compound in question. The vapour is conducted 
 through a tube to the bottom of a vessel containing water, by 
 which it is condensed. 
 
 218. Bi-sulphuret of carbon may also be formed by dis- 
 tilling a mixture of four parts of bi-sulphuret of iron, or 
 pyrites, with one-part of charcoal. The ingredients should 
 be in a state of fine powder, and intimately mixed. 
 
91 
 
 •219. Bi-sulphuret of carbon is a colourless liquid of a 
 peculiar odour ; it reflects light powerfully ; it burns with a 
 beautiful blue flame ; and gives out, during combustion, in- 
 tense heat. It is very volatile, and produces intense cold by 
 its evaporation. As it is heavier than water, and is not mis- 
 cible with it, it is best preserved from wasteful evaporation, 
 by a stratum of water on its surface. This substance dis- 
 solves phosphorus in very large quantity ; it is, however, 
 advisable not to use the saturated solution, as a much thicker 
 film of phosphorus, would in that case be left, than is neces- 
 sary. A solution, commonly used, is made by dissolving 
 one part of phosphorus in twelve parts of bi-sulphuret of 
 carbon. The articles to be coated should be dipped, for a 
 moment, in this solution ; on removal, the bi-sulphuret of 
 carbon, w^hich is very volatile, quickly evaporates, and leaves 
 a film of phosphorus on the article. If the cast, or mould, be 
 now immersed in a solution of sulphate of copper, a precipi- 
 tate of copper is immediately formed on it ; it is, however, 
 preferable to use a dilute solution of nitrate of silver. From 
 this solution a film of silver is immediately precipitated ; and 
 the surface of the article being now a perfect electric con- 
 ductor, may be introduced into the solution, and treated in 
 every way as a metallic article. The surface of an article 
 before immersion in the solution of phosphorus, should be 
 perfectly free from water. By the use of this solution the 
 most delicate matters may be covered with metallic films by 
 electric deposition ; lace, feathers, insects, preserved birds, 
 fruit, and indeed, any article which will bear immersion in 
 a liquid. 
 
 220. The solution of phosphorus in bi-sulphuret of carbon 
 should be very carefully used, as any drops allowed to fall about, 
 may occasion serious accidents. This solution is, under some 
 circumstances, spontaneously inflammable ; its inflammation, 
 too, is sometimes delayed a considerable time. If a piece of 
 dry paper be dipped into a solution of phosphorus in bi-sul- 
 
 m 
 
92 
 
 phuret of carbon, and laid aside, it will, after the sulphuret 
 has evaporated, first give off a dense white vapour, and after- 
 wards inflame ; from five minutes to half an hour (depending 
 on the strength of the solution) elapse before this inflamma- 
 tion occurs. 
 
 221. An improvement in the preparation of non-metallic 
 surfaces has recently been introduced, by which much of the 
 inconvenience attending the usual methods of preparation is 
 avoided. It consists, in forming the cast, or mould, on 
 which the deposite is to take place, of a compound con- 
 taining phosphorus. A mixture of wax or tallow with phos- 
 phorus answers admirably. As phosphorus will not mix with. 
 wax or tallow by the simple addition of one to the other, the 
 following method of mixing them must be resorted to. The 
 phosphorus is dissolved in bi-sulphuvet of carbon, and the 
 solution introduced into the wax or tallow while the latter are 
 in a state of fusion. The utmost precaution must be em- 
 ployed in preparing this compound ; the extreme inflamma- 
 bility of the solution of phosphorus in bi-sulphuret of carbon, 
 at ordinary temperatures, is a source of great danger ; but 
 when, as in the preparation of this compound, its temperature 
 is considerably raised, it is necessary to conduct every part 
 of the process with extreme care. The wax or tallow should* 
 after melting, be allowed to become as cool as is compatible 
 with tolerable liquidity ; and in that state the solution of phos- 
 phorus should be introduced into it. The solution should be 
 contained in a vessel having a long spout, which can be 
 plunged under the surface of the melted wax or tallow, so as 
 to deliver it at the bottom of the vessel. The phosphoric 
 solution should be slowly poured into the liquid wax with 
 one hand, while with the other the intimate mixture of the 
 liquid is effected, by constant stirring with a glass rod. The 
 stirring must be continued until the solidification of the wax 
 or tallow has commenced. One ounce of the solution of 
 phosphorus (219) may be added to eacli pound of wax. The 
 
93 
 
 mixture smells strongly of phosphorus, and when freshly cut 
 is luminous in the dark. A cast taken with this mixture, 
 immediately becomes covered with a metallic film, on immer- 
 sion in a dilute solution of nitrate of silver, and requires no 
 other preparation, previous to its introduction into the preci- 
 pitating trough. 
 
 222. The mixture of phosphorus and wax or tallow, may 
 sometimes be conveniently substituted for the solution of 
 phosphorus, in bi-sulphuret of carbon. In order to give a 
 conducting surface to a non-conductor, the latter may be 
 dipped into the melted mixture ; on being withdrawn slowly, 
 it retains a thin film, which, by immersion in the dilute 
 solution of silver, immediately precipitates a metallic coating. 
 
 223. It is necessary in using this mixture to stir it fre- 
 quently, while in the melted state ; otherwise, the phosphorus 
 slowly separates, and collects at the bottom of the vessel. 
 
 224. For the purpose of rendering the surface of any small 
 article of wax, or plaster of Paris, an electric conductor, the 
 process of Mr. Murray may be resorted to. It consists in 
 covering the surface of the mould with plumbago, or, as it is 
 commonly called, black lead. If the mould or surface is of 
 wax, all that is necessary, is to brush the powder slightly over 
 the surface with a soft camel-hair pencil j a very small quantity 
 will adhere, and will communicate to the wax that metallic 
 appearance so characteristic of plumbago. An exceedingly 
 thin coating is attached, so thin indeed, as scarcely to be 
 visible, excepting by reflected light. This is sufficient for 
 every purpose, and is even to be preferred to the thicker 
 coating that may be given by several applications. 
 
 225. The proces of black-leading is equal to any process 
 which has yet been made known. It is applicable to every 
 substance likely to be used for the manufacture of moulds : 
 wax, wood, plaster of Paris, sealing wax, are equally suscep- 
 tible of receiving a coating of this substance. Much difference 
 of opinion has existed relative to the value of Mr. Murray's 
 
94 
 
 process ; some have highly extolled it, while others have been 
 loud in condemning it. These contradictory opinions are 
 explained by the fact, that there is a great difference between 
 one specimen of black lead and another ; one sample appears 
 a perfect conductor, while another is an equally perfect non- 
 conductor; and it is only by actual experiment that its 
 quality can be determined. 
 
 226. The treatment by phosphorus gives an actual coating 
 of metal to the article ; and hence, when an article so treated 
 is introduced into the electro-metallurgical apparatus, an 
 immediate deposition commences over the whole surface. 
 With black lead, however, it is otherwise; the deposition 
 commences at the wire, by which the article is connected to 
 the battery, and around that, as a centre, the metal spreads in 
 every direction, until the whole surface is covered. Unfortu- 
 nately, this beautiful process is limited to copper, as that is 
 the only metal in common use which will spread on a black- 
 leaded surface. Silver and gold spread to so limited an 
 extent, that the process is inapplicable with those metals. 
 
 227. The surface on which electric deposition is to take 
 place, must not only be a conductor of electricity, but it must 
 also receive such a preparation previous to use, as will deter- 
 mine the adhesion of the deposit, or its non-adhesion, as the 
 case may be. 
 
 228. In depositing on metallic bodies, from which we wish 
 the deposite to separate, as in the copying of engraved copper- 
 plates, medals, coins, and metallic moulds, the surfaces of 
 these articles must be prepared so as to prevent the adhesion 
 of the metal ; when the metal deposited is the same as that 
 on which it is thrown down, there is greater danger of adhe- 
 sion than when the metals are dissimilar. A piece of metal 
 (copper, for example) by immersion, first in an alkaline, and 
 afterwards an acid solution, becomes chemically clean ; and 
 copper deposited on such a piece of copper would adhere, 
 and form one with it. If, however, the copper so cleaned be 
 
95 
 
 left simply exposed to the air for several hours, especially in 
 a cold situation, its surface receives some change, by which 
 the copper deposited on it, by an electro-metallurgical 
 process, has so feeble an adhesion, that the application of a 
 slight force suffices to detach it. The nature of this change 
 in the character of the surface, is not well understood ; it is 
 by some supposed to be a slight oxidation, or some change 
 of a chemical nature ; while by others it is regarded as the 
 condensation of a film of air on the surface of the metal. 
 We may avail ourselves of this state of surface to prevent 
 the adhesion of the deposited metal; and to do so, we 
 must be careful not to rub it, nor expose it to acids, or 
 alkaline solutions. This state of surface is also destroyed 
 by heat; it is, therefore, absolutely necessary, if the wire 
 which connects the plate to the battery has been soldered to 
 it, or the plate otherwise heated, to allow it to remain many 
 hours exposed to the air in a cool situation ; for if it be in- 
 troduced into the apparatus immediately after having been 
 heated, the precipitated copper will adhere so as to resist all 
 attempts to remove it ; but, after the treatment above recom- 
 mended, there is much less disposition to adhesion. Still, the 
 introduction of a plate into the apparatus, under such circum- 
 stances, is not unattended with risk ; and it is advisable 
 always to adopt the simple and efficacious plan recommended 
 by Mr. Spencer, which will be found perfectly effectual in 
 preventing the adhesion of the deposite. 
 
 229. The surface on which the deposite is to take place, 
 should be heated and rubbed with bees' wax until every part 
 has received a coating ; the wax should be thoroughly melted, 
 and, after having remained a few minutes on the surface, be 
 carefully wiped off with a linen rag ; when cold, it may be 
 introduced into the electro-metallurgical apparatus without 
 fear of adhesion. In cleaning off the wax, care should 
 be taken not to leave any portion uncleaned ; in such 
 a case, no deposite will take place on the coated part. 
 
96 
 
 Where the surface to be deposited upon is not of extreme 
 delicacy, the following method may be adopted for pre- 
 venting the adhesion: — the article should be immersed in 
 some solution that will deposit upon it a thin film of a dis- 
 similar metal — the cyanide of silver, for example, which, in a 
 few seconds, will give it a thin coating of silver ; or it may be 
 connected with the battery, as hereafter described, so as to 
 obtain a thin coating of that metal ; the deposited metal, 
 being separated from the original surface by a thin film of silver, 
 will readily separate. Copper reduced in the electrotype may 
 become one with the copper on w^hich it is deposited, or 
 silver with silver ; but dissimilar metals are with difiiculty 
 made to unite firmly. 
 
 230. The electro-metallurgist sometimes wishes to effect 
 the adhesion of the precipitated metal to the surfaces on 
 which it is deposited ; as in the deposition of films of gold 
 and silver in plating articles, and in defending iron, and other 
 metals, by means of coatings of copper and zinc. In such 
 cases, the utmost attention must be paid to the cleanliness of 
 the articles which are about to receive the deposite. When 
 practicable, a slightly rough surface should be given to the 
 articles, either by the chemical process called " dipping," or 
 by the mechanical process called " scratching." It often hap- 
 pens that the nature of the articles will not admit of this 
 rough surface, and when thin films of metal are to be de- 
 posited, it is obviously impracticable ; in such cases the end 
 must be attained by carefully cleaning the surface. 
 
 2.31. The most effectual cleaning is effected by immersion 
 in an acid liquor, called " dipping liquor." The composition 
 of this liquid is as follows : — 
 
 Sulphuric Acid 64 
 
 Nitric Acid 32 
 
 Hydro-chloric (muriatic) acid .... 1 
 
 Water 64 
 
 161 
 
97 
 
 If the surface of the article to be cleaned, is covered with oily 
 or greasy matters, the process of dipping will be of little avail, 
 the metal being effectually defended from the action of the 
 acid, by the film of greasy matter. In such cases it is neces- 
 sary to remove the oil, or grease, before the process of 
 dipping. This may be done in a variety of ways ; the most 
 convenient, and a very effectual one, is that of boiling the 
 articles in a strong solution of pearlash ; after such treatment, 
 the dipping acid will take effect. 
 
 232. Metallic surfaces may be made clean by means of the 
 voltaic battery. It has been already more than once stated (6), 
 that when a metal, having an affinity for oxygen, is connected 
 with the copper or silver end of the battery, and made one of 
 the electrodes in an acid or saline solution, the oxygen evolved 
 there by the passage of the voltaic current, combines with 
 the metal, and forms an oxide; an excellent method of 
 cleaning surfaces to receive voltaic deposites, is founded 
 on this fact. In order to clean a metallic surface by means 
 of the battery, the article must be attached by a wire to the 
 copper, or negative metal, of the instrument ; and a metallic 
 surface, at least equal in area to that of the article to be 
 cleaned, must be connected with the zinc. The metals 
 must be plunged in an acid or saline solution, when 
 decomposition of the water will take place. The oxygen 
 evolved will combine with the metal of the article to be 
 cleaned; and this oxide will be dissolved by the acid, or 
 other solution employed. Articles may thus he cleaned in 
 two or three minutes. This plan possesses the advantage of 
 great uniformity; it is impossible by any process of scouring, 
 to treat every part of an article equally ; but by the foregoing 
 process a minute film is removed from the whole of the surface. 
 The solution to be employed for this process of cleaning must 
 be varied to suit the metal, or alloy, of which the article to 
 be cleaned is made. All that it is necessary to observe is, that 
 the solution should be one which has no action on the metal 
 
 H 
 
98 
 
 of which the article is composed, but which will dissolve the 
 oxide or salt formed. For copper articles, a solution of sul- 
 phate of copper, slightly acidulated with sulphuric acid, may 
 be employed ; for silver surfaces, a solution of cyanide of 
 potassium, or, by preference, of sulphite of potassa ; for iron, 
 a saturated solution of sulphate of soda has been recom- 
 mended by Mr. Spencer. A battery of two or three cells 
 "^should be used in this process. 
 
 233. Some metals, when immersed in the solutions by 
 which they are to be coated, receive a film of metal without 
 the application of the battery ; thus, when copper is 
 introduced into the cyanide of silver, a film of silver 
 is deposited immediately on immersion, the copper dissolv- 
 ing in equivalent quantity (35), and taking the place of the 
 silver in the cyanide. In such cases the difficulty of securing 
 the adhesion of the precipitated metal is increased, for the 
 quantity of metal dissolved is small, and the impurities with 
 which all metals manufactured in the ordinary way abound, are 
 left on the surface, and the adhesion of the silver prevented. 
 This difficulty may, to a considerable extent, be got rid of, 
 by scouring the articles with the solution, previous to intro- 
 ducing them into the depositing vat. For this purpose, a 
 quantity of Calais sand, wetted with the cyanide solution, 
 should be taken on a scratch brush (an instrument made 
 by binding together a great number of fine wires), and the 
 article should be well scoured in this way, until it has a coat- 
 ing of silver, when it may be put into the precipitating, or 
 depositing vat. The film of silver thus produced, adheres more 
 closely than that obtained by mere immersion. 
 
 234. The electro-metallurgist, however, finds great diffi- 
 culty in producing a perfect adhesion, even where the utmost 
 precautions are taken. The cause of this difficulty is obvious : 
 all the processes hitherto noticed, have for their object the 
 production of a perfectly clean surface ; and when that is ob- 
 tained, all that can be effected, is the deposition of the metal 
 
99 
 
 in intimate contact with that of the article to be coated. But 
 the metals are simply in contact, there is no alloy ; and, in 
 this respect, the plating by electric agency is defective. In 
 the ordinary method of plating, where an ingot of silver is 
 attached to one of copper by fusion, there is an alloy ; 
 that is to say, the silver is united to, and forms one with, the 
 copper ; but in electro-metallurgical plating, there cannot be 
 any such junction. 
 
 235. Such are the difficulties that have presented themselves 
 in obtaining, with certainty, the necessary adhesion between 
 the metals, that the most experienced operators in the art, 
 despair of ever being able to produce sufficient adhesion, by 
 any process of cleaning the surface to be plated. Nothing 
 short of an actual alloy between the two metals, suffices to 
 prevent the occasional detachment of the deposite. 
 
 236. A film of mercury is now commonly used for the pur- 
 pose of alloying the two metallic surfaces ; the liquid metal 
 is applied in the following manner : — Mercury (quicksilver) 
 is dissolved in nitric acid slightly diluted with water. The 
 solution is set aside to crystallize, and the crystals of nitrate of 
 mercury are dissolved in water. A solution, containing an 
 ounce of mercury to a gallon of water will be found very 
 convenient ; but the exact strength of the solution is not of 
 much consequence. 
 
 237. When a piece of copper, or of an alloy of copper, is 
 plunged in a solution of nitrate of mercur}"-, the former metal 
 becomes immediately covered with a film of the latter. The 
 thickness of this film is dependent on the time during which 
 the copper is immersed in the mercurial solution. The cause 
 of this precipitation of mercury, is the decomposition of the 
 nitrate by the copper ; the oxygen and nitric acid of the 
 mercurial salt have a greater affinity for the copper than for 
 the metal with which they are combined, and hence quit the 
 mercury to combine with the copper ; the liberated mercury 
 attaches itself to the metal by which it has been set free. 
 
 H 2 
 
100 
 
 •238. The film of mercury which may be thus deposited on 
 a metallic surface, is sufficient to effect the most perfect 
 adhesion between the metal of the article under experiment 
 and the film deposited on it; for the mercury amalgamating 
 with both metals, acts precisely as a stratum of solder between 
 them, completely alloying their surfaces. The quantity of 
 mercury requisite to produce this effect is exceedingly small, 
 indeed it is scarcely possible to use too small a quantity, and 
 too large a quantity should be most carefully avoided ; if too 
 much mercury accumulates on the metal, the amalgamation 
 w^hich takes place gives a roughness to it, which, in 
 most cases, it is desirable to avoid ; and the deposited film 
 is sometimes injured, by the mercury amalgamating with it to 
 such an extent, as to penetrate it and appear on the surface 
 of the plated article, so as to injure its colour. The mercury 
 may, indeed, be dissipated by the heat which is generally 
 applied to the plated articles ; but even in that case, the ex- 
 cess of mercury leaves the surface rough. In using the nitrate 
 of mercury, the articles, after having been properly cleaned, 
 should be dipped for a few seconds into the nitrate of mer- 
 cury, and on removal, passed through water to remove any 
 trace of the solution, and should be introduced into the pre- 
 cipitating vat as quickly as possible. Immediately after the 
 articles have been plated, they should be heated to a tempe- 
 rature of about 600° F., in order to dissipate the mercury. 
 
101 
 
 CHAP. VIII. 
 
 ON THE PRODUCTION OF MOULDS, OR SURFACES, TO 
 RECEIVE ELECTRO-METALLURGICAL DEPOSITES. 
 
 239. The electro-metallurgist frequently has occasion to 
 produce facsimiles, both of metallic and non-metallic articles ; 
 for this purpose, it is necessary to procure impressions or 
 moulds of the articles in question, and by depositing metal in 
 the interior, or on the exterior of such moulds, to produce the 
 desired copy. Moulds may be made either of metallic or non- 
 metallic substances ; the form of the original article, and the 
 material of which it is made, must determine which of the 
 methods hereafter described is most applicable in any parti- 
 cular case. 
 
 240. In copying coins, medals, or plates, or objects of 
 which it is wished to copy only one surface, we may intro- 
 duce them at once into the solution, and, by procuring a 
 deposite upon them, obtain a mould, which will afterwards 
 serve to receive another deposite, ihe facsimile of the medal. 
 It is necessary to remark that the bronze appearance of a 
 medal is sometimes injured by this mode of proceeding ; of 
 all methods of copying coins or medals by electricity it is 
 the worst, and should only be adopted in those cases where 
 slight injury to the coin or medal is unimportant. A much 
 better way is to take moulds of the coin or medal, and procure 
 a deposite in them. In copying engraved plates, or large 
 subjects the surfaces of which are not of so delicate a 
 
102 
 
 » nature as those of medals, the preceding process is, however, 
 exceedingly convenient. 
 
 241. For small plates and coins, moulds may be readily 
 made in lead, and there is no risk of adhesion between this 
 metal and the copper ; such moulds need no preparation. If 
 the medal, or other subject to be copied, be not very promi- 
 nent, impressions of either side (in case of a medal) may be 
 procured by simply placing it between two pieces of sheet 
 lead, the surfaces of which have previously been made clean 
 by scraping, and subjecting it to the action of a press. Mr. 
 Spencer suggests that a number of coins be placed between 
 two strips of lead, and these passed through a copper- plate 
 printer's press. A series of impressions will thus be produced, 
 and, by placing these strips in the voltaic apparatus, a sheet 
 of electrotype casts will be obtained, or, by varnishing the space 
 between the impressions, they will be separated. This plan, 
 however, will not succeed in subjects the surfaces of which 
 are prominent. Moulds from these must be obtained by east- 
 ing, either in fusible alloy, wax, plaster of Paris, &c. The 
 alloy known by the name of Newton's fusible metal, and 
 consisting of about eight parts of bismuth, four of tin, and 
 five of lead, may be used ; but the composition will be much 
 improved if one part of antimony be added ; this mixture 
 must be melted repeatedly, and poured in drops, in order to 
 effect a perfect uniformity in the composition. It fuses at a 
 low temperature, and a lamp is a very convenient means of 
 melting it in small quantities. In using this alloy, it is well 
 to melt it with the application of as little heat as possible, 
 and, after having stirred it, to pour a quantity either upon 
 paper placed upon a flat surface, or on anon-metallic surface, 
 slightly concave. It may be stirred about with cards until 
 it approaches the solidifying point, when the medal is to 
 be pressed upon it in the manner which will be hereafter 
 described. The stirring, however, is not necessary, for the 
 most perfect casts may be obtained by simply pouring out the 
 
103 
 
 metal and, after having drawn lightly over its surface the 
 smooth edge of a card, held in an inclined position, applying 
 the medal thereto just before it is about to solidify. The 
 exact point of time is essential ; if it is placed upon the fluid 
 metal while too hot, the cast wiW be deficient in that sharp- 
 ness and brilliant surface essential to perfection — and, if too 
 cold, an imperfect impression will be the result ; the moment 
 when the metal is assuming that crystalline arrangement 
 which is the first step to solidification, is the best time for the 
 application of the medal. In order to ascertain this time, we 
 have only to look closely at the surface of the liquid metal. 
 At first, a picture of the surrounding objects will be reflected 
 from it with the utmost accuracy ; in a few moments, the 
 edges of the melted mass appear less bright, and eventually 
 the whole surface partakes of the same character. A number 
 of points appear to be rising upon the surface, and thus des- 
 troy the accurate reflection of objects. It is at this stage that 
 the medal should be suddenly brought down upon it in a 
 horizontal position, and with such force as to bury half 
 its thickness in the alloy. In order to bring the medal 
 down in a horizontal position considerable care is requi- 
 site, and, even then, unless assisted by some mechanical 
 contrivance, it is exceedingly difficult. Much of the uncer- 
 tainty of the process may be removed by attaching the medal 
 to some support, which affords firm hold for the hand — a rod 
 or cylinder of wood, for example. It is unneccessary to 
 enlarge on this subject, as a variety of ways of accomplishing 
 the same object will occur to the experimenter. 
 
 242. Alloys of different degrees of fusibility may be em- 
 ployed. Either of the following may be used instead of 
 Newton's : — An alloy of fourteen parts of bismuth, sixteen of 
 mercury, and thirty-two of lead, which melts in boiling water; 
 as also does an alloy consisting of four parts of bismuth, four 
 of lead, one of tin, and one of mercury. The following 
 requires a heat somewhat higher than that of boiling water 
 
104 
 
 for its fusion : — two parts of lead and one of bismuth ; as also 
 the alloy formed of three parts of bismuth, six of lead, and 
 one of antimony. 
 
 243. In using fusible alloys in large quantities, it is most 
 convenient to heat them over a lamp or gas burner, in a 
 vessel having a tap at the bottom, so as to allow the lower 
 portion of the metal to run out, and thus avoid the scum, or 
 oxide, on the surface. 
 
 244. Moulds of extreme beauty may be made of wax and 
 other similar substances, such as stearine and tallow. Moulds 
 of wax are formed very readily. The medal should be slightly 
 smeared with olive oil, and a slip of paper fastened around 
 it. The melted wax is poured over it, and allowed to cool. 
 It is desirable to have the medal warmed, and the wax should 
 be allowed to become so cool as to set soon after it is poured 
 on. If either of these conditions be neglected, the experi- 
 ment will be unsuccessful. If the medal is not warmed, the 
 wax will be suddenly chilled, and the mould will present a 
 waved appearance ; and if the wax is used too hot, the oil 
 becomes incorporated with it before setting, and the cast 
 cannot be removed. 
 
 245. Casts of plaster medallions may be taken in wax by 
 a process of extreme simplicity. The plaster model is to be 
 placed in warm water, and allowed to remain there until it 
 ceases to absorb it. It may then be removed, and, after the 
 water has disappeared from its surface, the wax may be 
 poured over it. Immediately it has cooled, it may be 
 removed without the slightest difficulty. Moulds, if thus 
 procured, are of singular beauty ; and, if the plaster model 
 has been properly prepared, it is not in the least injured by 
 the application of the warm water. If it be made of bad 
 plaster, small portions of it will probably be detached, and 
 will be found adhering to the wax mould ; these may be 
 removed by the application of dilute sulphuric acid; after a 
 short time a camel-hair pencil will clear it away. 
 
105 
 
 246. Moulds may also be formed of plaster of Paris. The 
 manner of operating with this substance is so well known, that 
 a detailed account of it, is unnecessary. Powdered gypsum, 
 or sulphate of lime, when heated to a proper temperature, 
 possesses the remarkable and valuable property of forming 
 with water, a hard solid. The powder is mixed with water 
 so as to have the consistence of thick cream, and, after 
 having been stirred to remove the bubbles arising from the 
 air which had been lodged in the plaster, it is poured on the 
 medal, or object to be copied, which, when necessary, should 
 be slightly oiled. After the lapse of a few minutes, the 
 plaster will be so hard that it may be safely removed ; but it 
 requires a much longer time to attain its greatest hardness. 
 
 247. In those cases where it is necessary to produce copies 
 of busts, vessels, and elaborate works of art, a more complex 
 method of preparing the models or moulds to receive the 
 deposite, must be resorted to. In order to produce facsimiles 
 of such objects, the electro-metallurgist may adopt either of 
 the following methods : he may prepare a hollow mould of 
 the object, that is to say, such a mould as would completely 
 encase the object to be copied, and deposit metal therein ; or 
 he may obtain a model, by casting, exactly resembling the 
 object to be produced, and deposit a thin film of metal 
 thereon ; the internal model may be removed as soon as the 
 metallic film is sufiiciently strong, and metal deposited in the 
 interior, so as to give the object the desired strength. The 
 former method produces the most perfect results. 
 
 248. To produce a mould in which it is intended to deposite 
 internally, the following course should be pursued : — The 
 operator must first prepare a mould of the article to be 
 copied, in plaster of Paris. This mould is made in the usual 
 manner, that is to say, in parts that can be separately removed 
 from the model on which they have been cast. The model 
 being enclosed in its mould, the operator proceeds to remove 
 one of the pieces of which the mould is formed, and pours 
 
106 
 
 into the vacant space the melted fusible alloy (242), wax, or 
 other material of which he intends to construct the mould to 
 be deposited on. When the liquid metal or wax has cooled, 
 it is removed, and forms a portion of a mould, exactly resem- 
 bling the plaster portion, in whose place it has been cast. 
 This portion of the plaster mould is replaced, and a second 
 portion is removed, and the vacant space left by its removal, 
 filled up by the melted alloy or wax ; and in this way every 
 portion of the plaster mould is, in turn, removed, and a cor- 
 responding metal or wax portion cast in its place. A 
 complete mould of the article to be copied is thus produced. 
 The various parts of which the mould is composed, must be 
 securely held together by being bound with wire, or other- 
 wise. When the object to be copied is made of a material 
 that will not admit of the application of the heated metal or 
 wax, plaster of Paris may be employed. If metal be used, the 
 exterior surface must be treated in the way pointed out in 
 another part of this chapter (256), in order to prevent a 
 deposite taking place thereon ; and if wax, or plaster of 
 Paris be employed, their surfaces must be rendered con- 
 ductors of electricity, by the means pointed out in the last 
 chapter. 
 
 249. The method just described may, under some circum- 
 stances, be conveniently modified. By this process, a mould 
 is procured, in which a number of copies may be made ; 
 but where it is only desired to make one copy of an article, 
 the following method may be conveniently substituted : — the 
 mould, cast in portions on the object to be copied, should be 
 removed from the object, and melted wax, or fusible alloy, 
 poured therein. If the operator uses wax, the plaster should 
 he saturated with warm water (245), to prevent its absorption 
 and adhesion. The mould should be moved about until the 
 wax is cold, so as to produce a uniform coating on every 
 part of it. If fusible alloy be employed, a core of wood 
 or plaster, should be introduced into the hollow mould, so as 
 
107 
 
 to diminish its capacity, and the fused metal poured into the 
 space between the core and the mould. 
 
 250. By these means a model is obtained in wax or fusi- 
 ble alloy, exactly resembling the object of which a copy is 
 to be formed. The next step in the process, is the formation 
 of a mould on this model. This may be done by electric 
 deposition ; the model being connected, in the manner 
 described in another part of the treatise, with a battery and 
 precipitating trough, quickly receives a deposite of copper. 
 When the copper coating is deemed sufficiently thick, it may 
 be removed from the precipitating trough, and the wax, or 
 fusible alloy, removed from its interior by fusion. The inte- 
 rior of this mould having been properly cleaned (227), and its 
 exterior defended (256), it is ready to receive an electro- 
 metallurgical deposite. This process is peculiarly adapted 
 to the production of copies in gold and silver, as in case any 
 difficulty occurs in tearing the copper mould from the electric 
 deposite, it may be readily removed by chemical means. Per- 
 chloride of iron possesses the valuable property of dissolving 
 copper, tin, lead, &c., but is without action on gold and 
 silver; hence, when any adhesion takes place between a 
 copper, tin, or lead mould, and a gold and silver deposite 
 thereon, the copper, tin, or lead, may be dissolved, by immer- 
 sion in a solution of per-chloride of iron, and the gold or 
 silver article preserved. 
 
 251. Per-chloride of iron may be formed by dissolving per- 
 oxide of iron (colcothar) in hydro-chloric (muriatic) acid. 
 
 252. Per-oxide of iron may be procured by adding nitric 
 acid to a boiling solution of proto-sulphate of iron (green 
 copperas), and precipitating by the addition of ammonia ; or 
 more readily, by decomposing the same salt (green copperas), 
 at a high temperature. Sulphuric and sulphurous acids are 
 driven off", and per-oxide of iron remains. 
 
 253. When the solution of per-chloride of iron is saturated 
 with copper, ammonia added precipitates the per-oxide of 
 
108 
 
 iron ; and this, when separated by filtration, may again be 
 dissolved in hydro-chloric (muriatic) acid, so as to form the 
 per-chloride. 
 
 254. In obtaining copies of works of art, by depositing on 
 the external surface of a mould or model, it is only necessary 
 to obtain a model in wax, or fusible metal, exactly resembling 
 the object to be copied. This mould may be made by the 
 method already described (248), and after having rendered 
 its surface (if made of wax) a conductor of electricity, it may 
 be placed in the precipitating vat, so as to receive a deposite. 
 The action of the battery should be regulated so as to deposite 
 slowly, in order to preserve the surface of the metal, smooth. 
 When a sufficient thickness of metal has accumulated, the 
 internal model may be removed by heat, or otherwise. The 
 deposite may be strengthened to the required degree, by 
 reducing metal in the interior, the exterior having been 
 previously defended. 
 
 255. When the object to be copied has over-hanging parts, 
 it is obviously impossible to remove the mould cast on it, 
 unless it be made in so great a number of parts, as to render 
 it inconvenient in use. This difficulty has suggested the use 
 of an elastic material for the construction of moulds, which 
 will yield, so as to admit of its removal from intricate parts, 
 and afterwards regain its proper form. The most suitable 
 materials for the construction of elastic moulds, are glue, and 
 a mixture of glue and treacle. When it is intended to use 
 the mould soon after it is made, glue answers in every respect, 
 but moulds made of glue alone, soon become hard, and lose 
 their form ; in order to avoid this difficulty, treacle should 
 be mixed with the glue. To make a mould of glue, the 
 article should be surrounded with a case of any convenient 
 material, and the melted glue, as thick as it can be used, 
 should be poured on the article, so as to fill up the space 
 between it and the surrounding case. When the glue is 
 quite cold, it should be cut into as many pieces as may be 
 
109 
 
 thought desirable, and the mould thus removed. If the 
 article is of plaster of Paris, or any substance likely to 
 absorb the glue, it should be slightly oiled, previous to pour- 
 ing the glue on it. Models in plaster of Paris and wax may 
 be cast in glue moulds. In casting wax models, care should 
 be taken to have the wax as cool as is compatible with the 
 requisite degree of liquidity. 
 
 256. Moulds of plaster of Paris require a particular pre- 
 paration, before they can be rendered conductors of electri- 
 city, by the application of black lead (224), or a metallic film, 
 precipitated by phosphorus (219). The porosity of plaster 
 of Paris is such, that without such preparation, when put 
 into the solution, it will absorb the liquid, and the air, which 
 previously filled its pores, will be expelled, and the mould 
 will be covered with small bubbles, which obviously render 
 it unfit for the reception of the metallic deposite. In order 
 to prepare the plaster for experimenting in the electro- 
 metallurgical apparatus, it is necessary to fill its pores with 
 some substance insoluble in water, and capable of resisting 
 the action of the metallic solution. The various substances 
 that will answer this purpose, are wax, tallow, spermaceti, 
 linseed oil, and varnishes. As wax answers in every respect, 
 and is superior to the other substances enumerated, we shall 
 content ourselves with noticing its application. The wax 
 should be well melted, and the plaster mould (which must be 
 perfectly dry,) should be immersed in it, and allowed to 
 remain some minutes : it may then be removed, and placed, 
 with its face upward, in a warm situation, until the liquid 
 wax has disappeared from its surface ; when it may be 
 allowed to cool. The black lead should be applied, as in 
 the case of wax, with a soft brush, or the solution of phos- 
 phorus, in the way already explained (219). 
 
 257. In those cases where a metal mould is used, it will be 
 necessary to cover with wax, varnish, or some other non- 
 conducting material, those parts of the mould where the 
 
110 
 
 deposited metal is not required. This coating of the back 
 and other parts requires to be done with care : if the smallest 
 portions be exposed, they will receive a coating of metal, 
 which is so much waste. Nor is this the only inconveni- 
 ence — for if the edge of the mould is left uncoated, the 
 metal spreading on it, will render the removal difficult, inas- 
 much as that part must first be cut away ; and it rarely 
 happens that, under such circumstances, the mould escapes 
 wholly uninjured. 
 
 258. The material most commonly employed for coating 
 metallic surfaces, where it is wished to prevent a deposite of 
 metal, is caoutchouc, or India rubber ; and the most effective 
 solvent of this substance, is bi-sulphuret of carbon (217). 
 
 259. A convenient solution is made by adding one part, 
 by weight, of caoutchouc, to four parts of bi-sulphuret of 
 carbon. The solution should be kept under water. It may 
 be applied with a brush, and must be spread quickly, as, 
 from the volatihty of the sulphuret of carbon, it soon becomes 
 hard. 
 
 260. The precaution of coating, with a non-conducting 
 substance, those parts of a mould on which it is wished to 
 prevent a deposite, is obviously limited to metal moulds ; as 
 those made of wax and plaster of Paris are themselves non- 
 conductors, and only receive a deposite on those parts which 
 have received a coating of conducting material (213). 
 
 261. The first step, after the preparation of the mould, is 
 the attaching of a wire to it. If the mould is of fusible 
 alloy, the wire may be readily attached by holding it for a 
 few seconds in the flame of a candle, and melting it into the 
 substance of the metal ; or a hole may be made in the edge 
 of the mould, and the wire being bent in the form of a hook, 
 introduced in it, and the mould thus suspended in the solu- 
 tion. If the mould or design is of wax, and its surface 
 has been prepared for a deposition of copper, by black lead 
 (224), a wire should be melted into its edge, and the black- 
 
Ill 
 
 lead brush rubbed around the wire and the edge of the mould, 
 so as to make a continuity of the black-leaded surface from 
 the wire to the surface of the mould ; if of plaster of Paris, 
 the edge, as well as the surface of the mould, should be 
 black-leaded, and a thin wire twisted round it ; if the mould 
 or plate is of lead, the wire should be soldered to its back. 
 As it is desirable, in depositing copper on a black-leaded 
 surface, to cause the deposition to go on with as great rapidity 
 as possible, contact between the surface and the connecting 
 wire should be made in several places, especially if the sur- 
 face be a large one. The cases in which this can be done 
 without risk of injui'y to the mould, must be determined by 
 the operator. Whatever plan of attaching the wire is adopted, 
 it is necessary to have a perfect connection between it and 
 the surface to be deposited on. 
 
11-2 
 
 CHAP. IX. 
 
 ON THE VARIOUS ARRANGEMENTS OF ELECTRO- 
 METALLURGICAL APPARATUS. 
 
 262. The sources of electrical poAver which have been 
 made available in electro-metallurgy, namely, the voltaic 
 battery and magneto-electrical machine, have been already 
 fully discussed in their general nature ; particular modifica- 
 tions of the apparatus, the various forms in which they may 
 be applied under different circumstances, and the conditions 
 to be observed, form the subjects of the present chapter. 
 
 263. All electro-metallurgical arrangements,in which voltaic 
 electricity is the source of power, resolve themselves into two 
 classes; one in which the surface, receiving the deposite, 
 constitutes part of voltaic apparatus, by which the electi'ical 
 power is generated ; and the other, in which the voltaic 
 j)ower is obtained from a battery, of which the surface, 
 receiving the deposite, forms no part. The former is called 
 the single-cell process, and the latter, the battery process. 
 
 264. The single-cell process which was the only one used 
 in the early practice of the art, consists of an apparatus 
 resembling, in the number and disposition of its parts, a 
 Daniell's battery ; the surface corresponding to the copper in 
 that battery, being the surface or mould on which the deposi- 
 tion is to take place. This form of apparatus is still much used 
 for the production of copies of coins, medals, plates, &c. 
 
113 
 
 It is represented in Jig. 19. a is a glass or earthen vessel, 
 Fig. 19. containing a saturated solution of sulphate of 
 copper: 6 is a cylinder of glass, the bottom 
 of which is closed by brown paper, plaster of 
 Paris, or bladder ; this vessel contains a solu- 
 tion of sulphate of soda, or muriate of ammo- 
 nia (sal ammoniac), or chloride of sodium 
 (common salt) : c represents the plate or mould 
 on which the deposite of metallic copper is to 
 be received ; a wire, fixed by soldering or otherwise to this 
 mould, is connected with a piece of zinc placed in the sahne 
 solution in the glass cylinder h. To set this apparatus in 
 action, the outer vessel is filled with the cupreous solution, and 
 some crystals of sulphate of copper, to keep the solution satu- 
 rated, are suspended in the upper part of the vessel, either 
 on a perforated metallic shelf, or in a piece of muslin, as the 
 decomposition of the salt is continually going on during the 
 working of the apparatus ; the saline solution being put into 
 the glass cylinder in which the zinc is situated, completes the 
 preparation. If the metallic communication between the 
 zinc and the mould be perfect, action immediately com- 
 mences ; the mould becomes almost instantly covered with a 
 stratum of copper, which goes on increasing in thickness so 
 long as the strength of the cupreous solution is maintained. 
 The rapidity of the deposition is determined by the nature 
 of the porous material with which the bottom of the glass 
 cylinder is closed. If it is of brown paper, the deposition 
 proceeds with considerable rapidity; bladder occasions a 
 slower deposition ; and plaster of Paris retards the process 
 still more : the thickness of the various materials also influ- 
 ences the action, which is most intense when the interposed 
 diaphragm is thinnest. From what has been said respecting 
 Daniell's battery, the reader will easily understand the nature 
 of the action, and the cause of the changes which take place 
 in this apparatus. 
 
114 
 
 265. Fig. 20 represents an apparatus for manufacturing cop- 
 Fig. 20. per plates, as described by Mr. 
 
 Spencer: — a is a box, which may 
 be made either of earthenware, wood, 
 or glass, and of any size which may 
 be found convenient ; & a box of either of the above mate- 
 rials, but having a thick brown paper, or thin unglazed 
 earthenware bottom, the sides being impermeable by a liquid. 
 This must be made to go into the interior of a, and to rest on 
 the rim c c, running round the interior of the larger box, 
 taking care, at the same time, that there shall be an inch or 
 more of free space, according to the size of the apparatus, 
 between the exterior of the small box and the interior sides 
 of the larger one. The rim c c must be perforated with small 
 holes, and it must be made to support a supply of crystals of 
 sulphate of copper ; d, the plate to be deposited on, to which 
 a wire is attached, leading to the binding screw, e, fastened 
 to the top of the exterior box ; /, the plate of zinc, to which 
 a wire is attached, also leading to the binding screw. The 
 connection between the two plates is thus rendered perfect, 
 and either may be conveniently removed without disturbing 
 the other. A few projecting studs of wire on the sides of 
 the interior box, are also found useful, to keep the zinc plate 
 perfectly parallel, and to prevent it from touching the porous 
 bottom. They must be varnished, to prevent local action ; 
 or, if the vessel be made of earthenware, they mayifee attached 
 to the sides in the first instance, and be of the same material. 
 The plate to be deposited on may be kept in its place by 
 similar studs or moveable pieces of earthenware. " The ends 
 of the wires must all be brightened before they are pressed 
 together by the binding screws. When all is arranged, as 
 shown in the figure, pour into the outer box a saturated 
 solution of sulphate of copper until it is nearly full, and then 
 pour into the interior one, containing the zinc, a weak solu- 
 tion of sulphate of zinc. At this stage of the proceedings, 
 
115 
 
 let a quantity of the undissolved crystals of sulphate of 
 copper, be placed on the perforated rim. Should this be 
 neglected for any length of time, a brown powder will be 
 deposited on the plate instead of the pure metal. This 
 substance is the protoxide of copper, and will always be 
 precipitated when the liquid is not kept thoroughly saturated 
 with sulphate of copper. In summer the deposition goes on 
 much quicker than when the weather is cold, as heat very 
 much facilitates chemical decomposition." 
 
 266. A very convenient form of apparatus is represented 
 Fig. 21. mjig. 21. It consists of a trough a, made of 
 
 porcelain, glass, or varnished wood. It is di- 
 vided into two parts by a partition of unglazed 
 earthenware or plaster of Paris, b. The zinc 
 plate c, isplacedin the compartment /, containing 
 the dilute acid, or solution of muriate of ammo- 
 nia to act upon it ; and into the other compart- 
 ment e is placed the saturated solution of sulphate of copper, 
 to which a little sulphuric acid has been added ; crystals of 
 the sulphate must be suspended in the upper part of the 
 latter compartment, in order to maintain the saturation of the 
 liquid. In this compartment the plate d, to receive the deposite 
 is placed, and is connected to the zinc c, by a wire. 
 
 267. Another, and in some cases more convenient arrange- 
 ment, is shown in Jig. 22, where « is a cell of earthenware 
 
 Fig. 22. or water-tight wood, in the middle of which is 
 placed a porous or unglazed earthenware cell 
 the latter is filled with the dilute acid or saline 
 solution, and contains the zinc plate c, and the 
 former is filled with the acidulated cupreous 
 solution ; crystals being suspended in its upper 
 part, as in all other modifications of this 
 apparatus. In the outer vessel a, the plates to 
 receive the coating of copper are situated. The peculiarity 
 in this apparatus is that two surfaces, each as large as the 
 
 i2 
 
116 
 
 zinc, can be experimented upon at the same time. The con- 
 nection of the copper plates with the zinc is so evident from 
 the figure that it needs no description. When dilute sulphuric 
 acid is used in any of the instruments described, the zinc 
 immersed in it must be amalgamated ; but where solutions 
 of muriate of ammonia or sulphate of soda are used, the 
 amalgamation of the zinc is unnecessary. 
 
 268. Immediately after the publication of Mr. Spencer's 
 paper, in which these forms of apparatus were first de- 
 scribed, an important improvement was announced by Mr. 
 Mason, by which a great economy is effected. Mr. Mason 
 used an apparatus exactly similar to that of Mr. Spencer ; 
 hut, instead of connecting together the zinc and the metal on 
 which the deposite was to take place, he effected a communi- 
 cation through a second vessel, in which, by the passage of 
 the voltaic current, a quantity of copper was precipitated, 
 equal in amount to that precipitated in the primary cell. 
 The process took somewhat longer time, but on the whole, 
 was much more economical than any which preceded it. 
 
 269. In order to make this improvement intelligible, a 
 
 Fig. 2^. figure (Jig. 23^ is subjoined: — 
 
 a is the common single-cell appa- 
 ratus ; the wire from the zinc, 
 instead of communicating directly 
 with the mould, is conducted into 
 the vessel h, and is joined to the 
 mould d; the mould x in the 
 primary cell is connected with a 
 piece of copper c in the cell b. 
 Now, the current of electricity, in passing through this 
 arrangement, causes the deposition of copper to take place 
 upon the moulds, x and d ; but in order that the modus 
 operandi of this instrument may be more clear, we shall 
 again refer to the voltaic battery, and examine the nature of 
 the chemical action of that instrument. 
 
117 
 
 270. — Let us imagine, then, that we have, in the following 
 experiments, a battery of sufficient power to decompose 
 water. If the terminal wires of this battery, which we will 
 suppose to be made of the metal platinum, be introduced 
 into acidulated water, we shall observe gas escape from them, 
 and by examination, we further find that the water is decom- 
 posed, and that oxygen is evolved at one wire, and hydrogen 
 at the other. If the experiment be varied by the introduction 
 of a solution of sulphate of copper into the acidulated water, 
 a remarkable change in the products of the decomposition 
 will take place. We shall now find that only one wire evolves 
 gas, and that that gas is oxygen. On examining the other 
 wire, where the hydrogen was evolved, we shall observe it to 
 be covered with metallic copper : by continuing the experi- 
 ment, the precipitated metal will gradually accumulate, the 
 solution, will become paler, and at length colourless. When 
 this happens, the whole of the copper will have been precipi- 
 tated, and hydrogen will be again evolved from the surface 
 of the newly-deposited metal. We see, then, that by pass- 
 ing a voltaic current through a metallic solution, the hydrogen 
 evolved by the decomposition of the water, effects the reduc- 
 tion of the metal; it combines with the oxygen of the metal- 
 lic oxide, thereby forming water, while the metal with which 
 it was united is deposited, and attaches itself to the surface 
 at which the hydrogen escaped ; the acid which was com- 
 bined with the oxide to form the salt, remains in solution (75.) 
 
 271. We will now consider what takes place when the wire 
 or surface from which the oxygen is evolved is made of a 
 metal that combines readily with oxygen — we will suppose 
 copper. We shall observe that the hydrogen is evolved as 
 usual, but that, in the place of oxygen, a brown powder will 
 accumulate about the wire ; the latter rapidly diminishes in 
 size, and, by continuing the experiment a sufficient length of 
 time, the whole of that part which was immersed in the 
 water will disappear, and the action of the battery, through 
 
118 
 
 the interruption of the circuit, Avill cease. The brown powder 
 which appears is oxide of copper, and is formed by the com- 
 bination of the oxygen with the copper of the electrode. 
 
 272. We will next suppose that we immerse two copper 
 wires, or plates, connected with a voltaic battery, in a solu- 
 tion of sulphate of copper. We have already seen that a 
 plate from which hydrogen is evolved, receives a deposite of 
 copper when immersed in such a solution ; and we have also 
 seen that a copper wire, or plate, when oxygen is evolved, 
 combines with that element, forming oxide of copper. Now, 
 as the oxygen evolved at one of the wires is chemically equi- 
 valent to the hydrogen liberated at the other, the quantity 
 of oxide of copper formed by the combination of the oxygen 
 with the copper of the former electrode, is exactly equal to 
 that decomposed by the hydrogen at the latter ; hence, in 
 the experiment under consideration, there is no visible evo- 
 lution of gas at either of the wires, the only effect produced 
 being the formation of oxide of copper at one of them, and 
 its reduction on the other, and consequently, the transfer of 
 metallic copper from one wire to the other. We will now 
 observe these changes as they take place in the apparatus of 
 Mr. Mason. We may suppose that the voltaic current 
 originates at the surface of the zinc, and determines the 
 formation of oxide of that metal ; passing to the second cell, 
 it is accompanied by the evolution of hydrogen at the plate, 
 and metal is deposited thereon ; the current, travelling 
 through the liquid to the second plate, c, developes oxygen, 
 which, combining with the copper, forms oxide ; passing 
 from this cell to the first, it again occasions the evolution of 
 hydrogen, and a second deposition of metal is effected on x; 
 the current completes its course by passing again to the zinc. 
 In this arrangement of the electrotype apparatus, a double 
 quantity of the reduced metal is obtained. 
 
 273. It is necessary to explain what will otherwise appear 
 a discrepancy. We have supposed the use of a compound 
 
119 
 
 battery in our illustrative experiment, though the cell, which 
 in Mr. Mason's apparatus generates the electricity, is but a 
 single one. The following fact explains the cause of this 
 difference : — It requires considerable intensity to decompose 
 water, if platinum or gold electrodes or poles are used ; and 
 in such a case the elements of the water are delivered in a 
 pure form ; but where the arrangements are such that the 
 elements enter into combination before assuming the gaseous 
 form, the intensity required for that decomposition is less ; 
 the intensity of the current seems to be augmented by the 
 affinity between the oxygen and hydrogen, and the elements 
 with which they are combining. We have seen that a single 
 voltaic pair will determine a current through a solution of 
 sulphate of copper, if the electrodes are of copper, though a 
 series is required to decompose water with platinum elec- 
 trodes ; in the former case the evolved elements enter into 
 combination, in the latter they do not. 
 
 274. It will immediately occur to the reader that if, by the 
 voltaic current entering the solution in the second cell, copper 
 is reduced, and by its passage from that cell, an equal amount 
 of that metal is taken into the solution, by causing it to 
 pass through a series of such cells, a similar quantity of 
 copper will be reduced in each ; such is exactly the case ; 
 and it is now common to cause the completion of the voltaic 
 circuit to take place through six, or even more of such cells, 
 and thus obtain, at a given expense of zinc, six times the 
 quantity of copper that would be obtained by the single-cell 
 apparatus. The process goes on much more slowly than if a 
 single decomposition were being effected ; but the great sav- 
 ^^9 24. ing in the consumption of mate- 
 
 z rial is more than sufficient to 
 warrant the adoption of this 
 plan. This arrangement is 
 shown in Jig. 24, where a a are 
 the moulds on which the deposite 
 
120 
 
 is to take place, and h b, pieces of copper to be dissolved. It 
 is necessary to place the mould and copper plate very near 
 each other, and parallel, as represented in the figure ; and 
 they should be as nearly of a size as may be. 
 
 275. The cell a, in Mr. Mason's apparatus, is, strictly 
 speaking, a voltaic battery, and, although it map be used, as 
 represented in the sketch, as an electrotype apparatus, by its 
 negative plate being a mould on which a deposite of copper 
 is to be etfected ; yet by far the most convenient plan, and, 
 perhaps, even the most economical one, is to substitute for 
 the cell a, in the arrangement represented, an ordinary vol- 
 taic battery ; indeed, the apparatus now used for electro- 
 metallurgical purposes, to the exclusion of almost every 
 other, is that now recommended. The improvement intro- 
 duced by Mr. Mason possesses such advantages, that the 
 single-cell apparatus described by Mr. Spencer has already 
 fallen into very general disuse. By generating the voltaic 
 electricity in an apparatus distinct from that in which the 
 precipitation of the metal takes place, a much greater com- 
 mand over the process is obtained, and the flow of electricity 
 can be regulated with much greater nicety than when the 
 mould to be deposited upon constitutes one of the elements of 
 the battery. It is evident, too, that as the solution in the 
 second, or decomposing cell, is always of the same degree of 
 concentration, the experiment, when once adjusted, may be 
 suffered to proceed, without risk of failure from any change 
 in the nature of the solution. Another convenience attend- 
 ing this mode of procedure is its simplicit}^ In the single- 
 cell apparatus, the solution of sulphate of copper is suffering 
 continual loss of the salt, owing to its decomposition, and it 
 is necessary to replenish the solution by the suspension of 
 crystals of sulphate of copper in the upper part of the vessel ; 
 but in Mr. Mason's apparatus it is only necessary to use so 
 much sulphate of copper as is sufficient to form the original 
 solutions ; for, as has been shown, the solution is not at all 
 
121 
 
 affected by use, and is in precisely the same state of concen- 
 tration throughout the longest process in which it may be 
 employed. 
 
 276. The nature of the apparatus best suited for depositing 
 metals, depends on the metal to be deposited, and the extent 
 to which the process is to be carried on. For small opera- 
 tions, the single-cell apparatus answers very well ; and depo- 
 sites, of copper, silver, and gold, may be very readily effected 
 by such an apparatus, where the surface to be deposited on 
 is of small extent. For gilding coins, and such like articles, 
 one of the two compartments formed by the porous dia- 
 phragm, (h, Jig.2\J should be filled with the solution oi 
 chloride, sulphite, or cyanide of gold, and the other with a very 
 dilute acid, or if the coin or medal be very small, with pure 
 water only. The coin or medal is connected by a wire with 
 a piece of zinc ; the former is immersed in the auriferous 
 solution, and the latter in the dilute acid or water. 
 
 277. The gilding of very small articles may be effected 
 without the use of any other means than the solution of gold 
 and a small piece of zinc. Small coins may be gilded in this 
 way, by being laid in a shallow vessel containing the gold 
 solution, and touched with a slip of zinc; the zinc, liquid, and 
 metal of the coin, form a voltaic combination (48), by virtue 
 of which, the gold will be deposited on the coin. In the 
 same way, the interior of small vessels, bowls of spoons, 
 watch cases, and other articles may be gilt : the solution of 
 gold may be poured into the vessel, and the slip of zinc 
 touched against the edge of the vessel, and also partially 
 immersed in the solution. The zinc must be moved about 
 in order to equalize the deposite, as the latter is always formed 
 in greatest quantity in the vicinity of the zinc. The distance 
 to which the slip of zinc is immersed, is of importance ; if 
 too much zinc surface be exposed to the solution, the surface 
 of the article under experiment will be coated with minute 
 bubbles of hydrogen, and the gold will be deposited in the 
 
122 
 
 form of a black powder ; the remedy in such a case is 
 obvious. This process is only recommended to be used in 
 those cases where very small articles are to be coated, and 
 wdiere the number of them is so limited as not to warrant the 
 charging of a battery ; the immersion of the zinc occasions 
 much precipitation of the metal by local action (81), and 
 hence the process is not economical. 
 
 278. The single- cell process may be used for the production 
 of deposites of copper, as in making impressions of coins, 
 medals, and engraved plates; and it may also be used for mak- 
 ing similar deposites of gold and silver. The following circum- 
 stances must be attended to in using this form of apparatus : — 
 The strength of the solution being constantly diminished by 
 the reduction of the salt, it is necessary to replenish the solu- 
 tion by the addition, from time to time, of fresh quantities of 
 the salt ; or the same effect may be produced by keeping a 
 quantity of the salt in the upper part of the vessel, as repre- 
 sented vajig. 19. 
 
 279. In using the single-cell apparatus for coating articles 
 on all sides with a film of metal, as in silvering and gilding^ 
 it is necessary to turn the articles from time to time, in order 
 to present every part in its turn to the porous diaphragm, 
 fb, Jig. 21 J, as the deposition goes on with much greater 
 rapidity on the side turned towards the diaphragm, than on 
 the opposite side ; and if this precaution be neglected, the film 
 of metal will not be of uniform thickness. 
 
 280. Where the film of metal deposited is very thin, as in 
 plating with gold and silver, the form of apparatus repre- 
 sented in ^gs. 21 and 22 may be employed ; but when the 
 deposite is of considerable thickness, as in copying engraved 
 plates, the position of the matrix or mould becomes highly 
 important. If it is placed vertically, the deposited metal 
 will possess various degrees of hardness, from the different 
 degrees of concentration of the upper and lower parts of the 
 cupreous solution. The circumstances which determine the 
 
123 
 
 quality of the deposited metal, are explained in a succeeding 
 chapter ; but we will anticipate that part of our subject by 
 observing, that the metal may have an extreme hardness, — 
 may be so crystalline as to break with the slightest touch, or 
 be almost as soft as lead, and may assume every variety of 
 texture between these extremes ; and as these various cha- 
 racters are produced principally by the relation between the 
 current of electricity and the concentration of the solution, 
 the reader will appreciate the importance of attention to the 
 position of the mould. 
 
 281. When the mould is vertical, the solution in contact 
 with the bottom of it, losing a portion of its saline matter, 
 becomes specifically lighter than the surrounding solution, 
 and is, consequently, buoyed up ; and as the same action is 
 taking place at every part of the plate, an upward current is 
 established on its surface ; this current is of course greatest 
 at the upper part, and it loses more and more of the cupreous 
 salt as it approaches the top ; this gives rise to a difference 
 in the texture of the copper in different parts of the deposited 
 plate. 
 
 282. Where a considerable thickness of metal is deposited 
 in this way, the plate will exhibit a number of grooves on its 
 surface, formed by this ascending current ; the lighter liquid 
 having found the most favourable channels, continues to flow 
 therein, and, from the small amount of the salt contained in it, 
 very little deposite accumulates there ; while the intermediate 
 portions being exposed to the more concentrated sohition, 
 the deposition goes on at those parts with facility ; hence, 
 the grooved appearance of the surface. 
 
 283. These inconveniences may in some degree be remedied 
 by inclining the plate, so that the currents may rise through 
 the liquid without passing over its surface ; but with large 
 plates, it is much more convenient to lay them in a horizontal 
 position. In this case, it is necessary to place the mould or 
 plate to be deposited on, at the bottom of the vessel, and the 
 
124 
 
 copper-plate to be dissolved, over it ; the precaution of intro- 
 ducing a piece of muslin, or some such fabric between them, 
 must not be omitted, otherwise the impurities with which 
 the copper to be dissolved is contaminated, will fall down as 
 the pure metal is taken into the solution, and, lodging upon 
 the mould, will at first impair its delicacy, and afterwards its 
 solidity. 
 
 284. The reader may, perhaps, suppose that this objection 
 would be obviated by reversing the position of the mould ; 
 that is, by placing it in the upper part of the vessel, face 
 downwards, and the plate to be dissolved, under it. This 
 plan is attended with so many inconveniences that it cannot 
 be practised advantageously. There is, first, the liability of 
 minute portions of air being retained in the intricate parts of 
 the mould or surface, and from which, in its inverted position, 
 it is scarcely possible to free it ; and there is a still more 
 weighty objection in the circumstance, that there is a greater 
 irregularity in the state of the solution with this arrangement 
 than with any other. The stratum in contact with the 
 inverted mould, when deprived of a portion of its salt, being 
 lighter than that immediately below it, has no tendency to 
 give place to the more concentrated solution : when, how- 
 ever, this dilute stratum has accumulated a little, it escapes 
 at the edges of the horizontal plate ; and, by another portion 
 becoming exposed to action, the process for a time continues 
 to go on well. It is only, however, until the whole of the 
 solution above the plate is thus deprived of its cupreous salt ; 
 there is then no tendency to circulation ; the lighter fluid is 
 in the upper part of the vessel, and the heavier at the bottom ; 
 the action becomes impeded, and the small quantity of cop- 
 per deposited from such a dilute solution is of such a texture 
 as to render it perfectly useless. The copper dissolved from 
 the waste plate at the bottom of the vessel will crystallize 
 there, while the upper part of the same solution is exceed- 
 ingly dilate. These difficulties would not present themselves 
 
1-25 
 
 if a constant agitation of the liquid could be kept up ; but 
 this is obviously impracticable. The most convenient arrange- 
 ment, then, is that in which the mould or plate to be depo- 
 sited upon is at the bottom of the vessel, and the piece of 
 waste copper to be dissolved above ; in this case, as the 
 solution is deprived of its salt of copper, it rises and gives 
 place to a more concentrated portion, while the salt formed 
 by the solution of the waste copper descends to the lower 
 part of the vessel ; and with such an arrangement, the process 
 goes on with much regularity. 
 
 285. The reader must particularly bear in mind that, in 
 whatever position he may place the surface to receive the 
 deposite, the piece of metal forming the positive pole must 
 be parallel to it ; if this condition is not observed, the depo- 
 site will be of different thicknesses at different parts ; if the 
 two surfaces are inclined to each other, a much greater thick- 
 ness will be observed at the point where the two surfaces are 
 nearest; and in proportion as they become more distant from 
 each other, will the thickness of the deposite diminish. 
 
 286 In precipitating metal upon very irregular surfaces, it 
 is difficult to obtain a deposite of uniform thickness ; in such 
 a case, it is desirable to bend the positive plate so as to 
 assume the general figure of the negative surface ; and when 
 a sufficient thickness of metal has accumulated on those parts 
 nearest the positive pole, the deposite may be removed from 
 the solution, and they may be varnished or covered with 
 some non-conducting substance, such as wax; on again 
 introducing the surface thus treated, the copper will only be 
 precipitated on the more distant or unvarnished parts ; if the 
 amount of surface thus defended from the solution is consi- 
 derable, a difference in the texture of the metal will be pro- 
 duced, unless such alterations are made in the arrangement of 
 the apparatus as will be hereafter pointed out, when treating 
 of the conditions on which the nature of the deposite 
 depends. 
 
126 
 
 287. These observations relative to the proper position to 
 be observed between the surface deposited on and the opposed 
 metallic plate, are equally applicable to the single-cell and bat- 
 tery processes. For thin deposites, as in gilding and silver- 
 ing, the position of the articles is of little consequence ; they 
 are generally suspended vertically in the solutions. 
 
 288. For all precipitations on a large scale, the most con- 
 venient arrangement is that of a large vat for containing the 
 metallic solution, to two opposite edges of which strips of 
 metal are attached, for the purpose of making connection with 
 the battery, or other source of electrical power. One of these 
 strips is connected with the zinc end of the battery, and the 
 other with the copper or silver end. In order to suspend the 
 articles to be coated in the solution, and at the same time 
 connect them with the zinc end of the battery, metallic rods 
 should be laid across the vat, one end of each of such rods 
 resting on the strip of metal connected with the zinc end of 
 the battery, and the other resting on, but insulated from, the 
 strip connected with the copper or silver end of the battery. 
 In order to thus insulate it, a strip of wood, or even two or 
 three folds of paper, may be introduced between it and the 
 metal. The articles to be coated may be suspended from 
 these rods by copper wires. 
 
 289. The plates of metal to be dissolved are connected to 
 the copper or silver end of the battery by being similarly 
 suspended by wires from metallic rods, one of each of which 
 rests on the edge of the vat, connected with the copper or 
 silver end of the battery, but insulated from the zinc end, in 
 the manner already described. In this way, a great number 
 of rods may be laid across the vat, from every alternate one of 
 which, several articles may be suspended, while the inter- 
 mediate rods support the plates to be dissolved. Vats are 
 commonly used in manufactories of such a size as to admit of 
 the introduction of eighteen or twenty dozen of spoons. 
 
 290. It is scarcely necessary to remind the reader that all 
 
127 
 
 these metallic surfaces, by which connection is made with 
 the battery, must be kept perfectly clean, by frequent rubbing 
 with sand paper, or by other means ; if this precaution be 
 neglected, the passage of the current will be obstructed, and 
 imperfect results obtained. 
 
 291. The nature of the vessels for holding the solution, 
 from which the metals are to be precipitated, merits the 
 attention of the electro-metallurgist. Where the operations 
 are on a small scale, no material can be compared with glass ; 
 next to that, stoneware should be selected, or well-glazed 
 earthenware. In selecting vessels of earthenware, the great- 
 est attention must be given to the nature of the glaze used 
 in its manufacture, as the glaze of the greater part of such 
 vessels is attacked by acid and saline solutions, and in a short 
 time they become perfectly useless, the penetration of the 
 solution completely disintegrating them. 
 
 292. Vessels of lead have been recommended, and may be 
 used in those cases w^here the nature of the solution used will 
 admit of it ; but as that metal is attacked by many of the 
 solutions employed by the electro -metallurgist, its use is very 
 limited. Vats made of wood, and well varnished by resinous 
 matters, have been frequently used, but these are by no 
 means universally applicable, as they are acted on by some 
 solutions ; for example, shell lac, or sealing wax, is almost 
 immediately rendered soft and useless by the solution of 
 cyanide of silver. 
 
 293. The vessels now commonly used in large establish- 
 ments are constructed as follows : — Two wooden vessels are 
 made of such sizes, that one nearly fits inside the other, a 
 space of about a quarter of an inch being left between them 
 on every side ; into this space, melted pitch is poured, so as 
 to fill it completely : a vessel is thus formed which is per- 
 fectly impervious to liquids, and which answers admirably 
 for electro-metallurgical purposes. 
 
 294. It is not necessary to have a separate solution for each 
 
128 
 
 article, or series of articles, operated on ; that is to say, 
 any number of articles connected with different batteries may 
 be at work in the same vat, without the action of one affect- 
 ing that of the other. It is, however, better to connect all 
 the power of the batteries employed, with the whole of the 
 articles operated on, by means of the contrivance already 
 described (288), rather than confine a small power to a small 
 series of articles ; the larger the scale on which operations 
 are conducted, the more uniform will be the results. 
 
129 
 
 CHAP. X. 
 
 ON THE CIRCUMSTANCES WHICH INFLUENCE THE 
 QUALITY AND QUANTITY OF ELECTRO-METALLUR- 
 GICAL DEPOSITES. 
 
 295. It was observed, by the earliest experimenters in 
 electro-metallurgy, that the character of the deposited metal 
 was affected by the rapidity with which it was precipitated 
 (16), and by various other causes; and more recent inves- 
 tigations have determined with accuracy, the conditions on 
 which the production of the various kinds of metallic deposites, 
 depend. 
 
 296. Metals may be deposited in the form of a dark 
 powder, without cohesion, and having anon-metallic appear- 
 ance; or in continuous layers, as ductile and malleable as 
 the same metals can be produced by the common methods of 
 reduction ; as distinct crystals, or as a mass, composed of 
 crystalline grains, having little cohesion. 
 
 297. The cause of these differences in the character of the 
 deposited metal, is by no means well understood, although the 
 conditions under which they are produced are well known. 
 
 298. The circumstances which operate to produce the dif- 
 ferent kinds of deposites, are the quantity and intensity (58) 
 of the electric current ; the relative size of the surface receiv- 
 ing the deposite, and that suffering solution ; the distance of 
 these surfaces apart ; the strength of the solution ; the con- 
 ducting power of the salt under decomposition ; and the tem- 
 perature of the battery and solution. 
 
 K 
 
130 
 
 299. If the quantity (58) of the current be too great for 
 the surface to be deposited on, the metal will be precipitated 
 as a black powder, having no cohesion, and presenting none 
 of the appearances of a metal ; and the same effect will be 
 produced if the intensity of the current be too great ; if, on 
 the other hand, the quantity and intensity of the current be 
 too small, the metal will be reduced in a crystalline form. 
 
 300. If the size of the plate, or electrode, in connection 
 with the copper or silver end of the battery, be too large, 
 compared with the surface receiving the deposite, the metal 
 will be reduced in the form of a black powder ; if it be too 
 small, a crystalline deposite will be the result. 
 
 301. The distance between the plate, or electrode, in con- 
 nection with the copper or silver end of the battery, and the 
 surface on which the metal is reduced, has an important 
 influence on the nature of the deposite ; if the plate is too 
 near, a black powder will be thrown down, (supposing the 
 battery to be sufiiciently powerful) ; when removed to a 
 greater distance, the ductile metal will be reduced ; and when 
 still further removed, a crystalline deposite will be formed. 
 
 302. The strength of the metallic solution has a most 
 important influence on the character of the deposite ; with a 
 strong solution, there is a disposition to the production of the 
 crystalline metal ; by dilution, the metal becomes more 
 ductile ; and by very large dilution, a black powder will be 
 precipitated. 
 
 303. The character of the deposite produced by the same 
 voltaic power, differs with different salts of the same metal. 
 The facility with which different salts suffer decomposition 
 in the voltaic current, determines the character of the depo- 
 site which will be produced from them with the same voltaic 
 power. Thus, the battery which will produce a crystalline 
 deposite wnth a saturated solution of sulphate of copper, 
 gives a ductile metal with a saturated solution of the nitrate 
 of copper ; and similarly with salts of the other metals. 
 
131 
 
 304. The temperature of the solution in the precipitating 
 vessel, as well as that of the battery, must be constant, in 
 order to produce uniform results, for the application of heat 
 increases the conducting power of the solution under decom- 
 position, as well as the activity of the battery, both of which 
 causes determine the circulation of a more copious current ; 
 the former, by diminishing the opposition to its passage, and 
 the latter, by exalting the affinity by which the current in the 
 battery is determined. For example, the current from a single 
 cell of the acid battery, transmitted through a saturated 
 solution of sulphate of copper, by means of copper electrodes 
 of the same size as the plates of the battery, gives a small 
 deposite of crystalline metal, at a temperature of 60° F. ; but 
 when both the battery and decomposition cell are heated to a 
 temperature of 180° F., a copious deposite of ductile metal 
 is produced. 
 
 305. The whole of the circumstances which interfere with 
 the character of the deposited metal, resolve themselves into 
 two ; namely, the quantity of electricity circulating through 
 the apparatus, in relation to the size of the surface receiving 
 the deposite ; and the conducting power of the solution. 
 
 306. The intensity of the current (58) operates Only by 
 effecting a change in its quantity, for however large 
 a quantity of electricity the battery employed may be 
 capable of producing, if the current have not an intensity 
 sufficient to effect the decomposition of the solution (58), 
 it will be obstructed ; by increasing its intensity, the current 
 may be made to pass in small quantity, and thus produce a 
 certain kind of deposite ; and by still further increasing the 
 intensity, the resistance to the passage of the current is so 
 far overcome, that a very large quantity passes. In this way 
 the intensity of the current determines the quantity of elec- 
 tricity which will pass in a given time through any solution. 
 
 307. The difference in the size of the electrode, or surface 
 receiving the deposite, and that suffering solution, only affects 
 
 k2 
 
132 
 
 he character of the deposite, by determinmg the quantity of 
 electricity passing. If two electrodes be immersed in a saline 
 solution, and connected with the extremities of a battery, 
 in the circuit of which a galvanometer (122) is included, the 
 needle will show, by its greater deflection, that a more copious 
 current passes when both the electrodes are wholly im- 
 mersed, than when one of them is partially removed. 
 
 308. A greater or less distance between the electrodes also 
 determines a change in the quantity of electricity passing. 
 Two electrodes, immersed in a saline solution, and connected 
 with a battery having a galvanometer (122) in its circuit, 
 determine a much more copious current when near each 
 other, than Avhen at a distance, as the deflection of the 
 galvanometer needle will demonstrate. 
 
 309. The conducting power of the solution is affected by 
 the quantity of metallic salt contained in it, and the tem- 
 perature at which it is maintained. It has already been 
 stated (302) that with a saturated solution of a metaUic salt, 
 there is a tendency to the production of the- crystaUine 
 deposite— that moderate dilution determines the production 
 of a ductile metal ; while very copious dilution produces a 
 black powder. These effects are precisely analagous to those 
 wdiich present themselves when the conducting power is 
 altered, without altering the strength of the solution. Thus, 
 with a saturated solution of sulphate of copper, a crystalline 
 deposite is produced by a single cell of the acid battery; but 
 if, by the elevation of temperature, or the introduction of 
 acid into the solution, its conducting power be increased, 
 the character of the deposite will change ; a ductile metal 
 will be thrown down. Now, precisely the same effects present 
 themselves when the saturated solution is diluted ; that is 
 to say, the deposite assumes that character which usually 
 accompanies an increased conducting power in the solution. 
 We may, therefore, consider the conducting power of 
 any metallic solution to be impaired, in proportion as the 
 
133 
 
 quantity of metallic salt in the solution is increased ; for 
 the result of such addition is the production of a deposite 
 resembling thai produced by diminished conducting power. 
 
 310. The real cause of this apparent diminution of conduct- 
 ing power, by increasing the strength of the solution, is very 
 obvious. With a saturated solution of a salt, the electric 
 current, in its passage between the two electrodes, is con- 
 ducted by so great a number of the atoms of the salt, that 
 the quantity of the current, compared with the quantity of 
 the salt, is small ; while in a dilute solution, (the battery, 
 electrodes, and all other circumstances being equal,) the cur- 
 rent is conducted by so small a number of the atoms of the 
 salt, that its quantity, compared with the quantity of the salt, 
 is large. Hence, a current in a strong solution is virtually 
 small, while the same current in a weak solution is virtually 
 large ; and thus it is, that with a strong solution, effects 
 similar to those produced by inferior conducting power, are 
 presented; while in a weaker solution, effects are produced 
 similar to those produced by superior conducting power. 
 
 311. The application of heat is another method of increas- 
 ing the conducting powder of a solution, and changing the 
 character of the deposite. In heating a solution, a greater 
 quantity of electricity passes, the quantity of the salt remain- 
 ing the same ; in diluting a solution, the quantity of elec- 
 tricity remains the same, but the quantity of the salt is rela- 
 tively diminished. 
 
 312. The production of the metallic deposite in the form 
 of a black jjowder (296), is usually accompanied by the 
 evolution of hydrogen, and is probably occasioned by the 
 reduction of the metallic salt by that element. Although it 
 is impossible, in the present state of electrical science, to 
 determine with certainty whether the reduction of metals in 
 the voltaic circuit is a primary or secondary effect (74) ; yet 
 there is strong reason to believe that a metallic salt may be 
 decomposed primarily, being resolved into the metal and its 
 
134 
 
 associated radical (41) ; and there is demonstrative evidence 
 that the decomposition may be a secondary effect (72), for 
 hydrogen decomposes many metallic salts. It may, therefore, 
 be assumed, that the production of the crystalline and ductile 
 deposites are produced by the primary action of the current, 
 unaccompanied by any decomposition of the w^ater in which 
 the salt is dissolved ; and that the production of black metallic 
 powder is the result of the decomposition of the water, in 
 addition to that of the metallic salt. Various considerations 
 favour this view ; it is easy to conceive that a metal may 
 assume a crystalline form, when liberated from a solution so 
 slowly as to allow of the full operation of the molecular 
 attraction, by which crystalline form is produced ; and it is also 
 easy to conceive that when the metal is deposited so rapidly 
 as not to admit of this arranging of the particles, that a duc- 
 tile metal is produced ; and where, in addition to this depo- 
 sition of metal, there is a liberation of gaseous hydrogen, the 
 effect produced by the interposition of the latter between the 
 particles of the former, is the prevention of that intimate 
 relation between the particles, which is necessary to cohesion. 
 
 313. When the electro-metallurgist wishes to make any 
 change in the character of a deposite, the means to be taken 
 are obvious. If a black powder is produced, and it is wished 
 to obtain a ductile metal, the size of the battery must be 
 diminished, or its intensity reduced by diminishing the num- 
 ber of the series ; or the size of the plate suffering solution 
 may be reduced, or its distance from the article receiving the 
 deposite increased ; or the temperature of the solution may be 
 depressed, or its strength increased; the alteration in the 
 size or intensity of the battery is, however, the most conve- 
 nient plan, and the only one which can, in general, be 
 adopted. 
 
 314. If a crystalline metal is deposited, and a ductile 
 metal is desired, the quantity or intensity of the electric cur- 
 rent must be augmented, by increasing, in the former case. 
 
135 
 
 the size of the battery, and in the latter, the number of the 
 series ; or the conducting power of the sohition may be 
 improved by dilution, or the addition of acid, when the latter 
 is compatible with the salt ; by increasing the size of the 
 plate, or electrode, suffering solution, or by bringing it closer 
 to the surface receiving the deposit; by heating the solu- 
 tion, or by diluting it; in this, however, as in the former 
 case, the alteration in the character of the deposite can only 
 be conveniently effected by making the necessary alteration 
 in the battery. 
 
 315. In order to produce a black powder from a solution 
 giving a ductile metal, the quantity or intensity of the current 
 must be increased ; or the plate undergoing solution, enlarged, 
 or brought nearer the surface receiving the deposite ; or the 
 solution may be heated, or its conducting power improved 
 by the addition of acid- The necessary change may be most 
 conveniently effected by increasing the quantity or intensity 
 of the current ; or the addition of acid, when the latter is not 
 incompatible with the salt under experiment. 
 
 316. To produce a crystalline deposite, the current must be 
 diminished in quantity or intensity, or the conducting power 
 of the solution reduced, either by diminution of temperature, or 
 the addition of an extra quantity of the salt. The most con- 
 venient means of producing the crystalline deposit, is the use 
 of a strong or saturated solution of the salt. 
 
 317. In producing the various kinds of deposites with the 
 magneto electrical machine, the same relations, between the 
 current and the state of the solution, as pointed out with 
 reference to the battery, must be observed ; the quantity of 
 the magneto-electric current may be regulated in the way 
 already pointed out (149). 
 
 318. The production of these different kinds of deposites 
 has been referred to the evolution of hydrogen, in the case of 
 the black powder, and the want of a tendency to its evolution 
 in the case of a crystalline deposite ; and when the arrange- 
 
136 
 
 ment is such that a small additional intensity or quantity- 
 would devolope the black powder, the ductile metal is pro- 
 duced. As the evolution of hydrogen at the negative plate, 
 or its absence there, depends entirely on the condition of the 
 battery and decomposition cell, a reference to its production 
 is only another way of expressing the condition of the 
 apparatus. 
 
 319. The following table exhibits the results of a number 
 of experiments, made for the purpose of exhibiting the effect 
 of different relations between the size of the battery, the cha- 
 racter of the solution, and the size of the electrodes. The 
 battery employed consists of two plates of amalgamated zinc, 
 between which is placed a plate of silver of the same size ; 
 the distance of the silver from each zinc plate is half an inch ; 
 the electrodes in every experiment were l^^ inches distant from 
 each other, and the average temperature 60° F. 
 
137 
 
 320. BATTERY CHARGED WITH ONE PART OF CONCENTRATED 
 ACID TO EIGHT OF WATER. 
 
 No. 
 
 Solution Employed. < 
 
 Size of electrodes t 
 ompared with < 
 each other. { 
 
 size of electrodes, 
 the largest where 
 bere is a difference) 
 ompared with ne- 
 ;ative metal of bat- 
 ery. 
 
 RESULTS. 
 
 1 
 
 Concentrated so- 
 ution of sulphate 
 y{ copper. 
 
 equal. 
 
 twice the size. 
 
 Distinct, detached, hard, 
 crystalline grains, dull red 
 colour. 
 
 2 
 
 Ditto 
 
 positive half 
 of negative. 
 
 equal. 
 
 Distinct hard crystals, red 
 colour, small in quantity. 
 
 3 
 
 Ditto 
 
 equal. 
 
 equal. 
 
 Clusters of hard, compact, 
 crystals, brilliant red colour, 
 small quantity. 
 
 4 
 
 Ditto 
 
 equal. 
 
 half the siae. 
 
 Compact crystals, so thickly 
 clustered, as to form a con- 
 tinuous stratum, — light red 
 colour, larger in quantity 
 than above. 
 
 
 Concentrated so- 
 lution of sulphate 
 of copper and one 
 twentieth of sul- 
 phuric acid. 
 
 equal. 
 
 twice the size. 
 
 Continuous stratum of fine 
 crystalline structure, clay 
 red colour, having so little 
 cohesion as to break on at- 
 tempting to bend it. 
 
 6 
 
 Ditto. 
 
 positive half 
 of negative. 
 
 equal. 
 
 Continuous stratum, brittle 
 crystalline on surface, rather 
 lighter colour than No. 6. 
 
 7 
 
 Ditto. 
 
 equal. 
 
 equal. 
 
 Continuous stratum, slightly 
 ductile, fine crystalline sur- 
 face, bright red colour. 
 
 8 
 
 Ditto. 
 
 equal. 
 
 half the size. 
 
 Continuous stratum, ductile, 
 rather hard, very fine crys- 
 talline surface, bright red 
 colour. 
 
 9 
 
 Ditto. 
 
 negative half 
 of positive. 
 
 equal. 
 
 Continuous stratum, ductile, 
 rather hard, fine crystalline 
 surface, red colour. 
 
 10 
 
 Concentrated so- 
 lution of sulphate 
 of copper with one 
 third diluted sul- 
 phuric acid.* 
 
 equal. 
 
 twice the size 
 
 Continuous stratum, defi- 
 cient in cohesion, crystal- 
 line surface, slightly ductile, 
 rather hard, bright red co- 
 lour. 
 
 11 
 
 Ditto. 
 
 positive half 
 of negative. 
 
 equal. 
 
 Continuous stratum, ductile, 
 fine crystalline surface, 
 blight red colour. 
 
 12 
 
 Ditto. 
 
 equal. 
 
 equal. 
 
 Continuous stratum, ductile, 
 rather hard, fine crystalline 
 surface, bright red colour. 
 
 13 
 
 Ditto. 
 
 equal. 
 
 half the size. 
 
 Continuous stratum, not 
 very ductile, very fine crys- 
 talline surface. 
 
 14 
 
 Ditto. 
 
 1 
 
 negative hall 
 of positive. 
 
 equal. 
 
 Continuous stratum, ductile, 
 rather hard, fine crystalline 
 surface, large in quantity. 
 
 * Consisting of one part by measure of acid, and eight of water. 
 
138 
 
 321. By an examination of this table, the reader will 
 observe that, when the solution was neutral, and a large sur- 
 face of electrodes exposed, the formation of distinct crystals 
 was the result ; that as the size of the electrodes was 
 diminished, and their proportions made such as to determine 
 a more copious current, the character of the deposite changed ; 
 and through the whole table a gradual improvement in the 
 character of the copper may be traced, as the circumstances 
 which obstruct the passage of the current are removed. 
 These circumstances, it is hardly necessary to remark, are the 
 character of the solution, and the varying size of the electrodes. 
 
 322. The above table might have been continued to a much 
 greater extent, but such extension would have been com- 
 paratively useless ; the above shows what proportion must 
 be avoided when the crystalline deposite is not wanted ; and 
 the reader will discover from it, that in order to obtain a good 
 ductile metal from the solutions given, he must cause a more 
 copious flow of electricity than is afforded by any of the 
 arrangements there described, by increasing the size of the 
 battery, or diminishing the size of the electrodes. 
 
 323. The following tables show the result of experiments 
 made by a commission of members of the Academy of 
 Sciences of Paris. They exhibit the influence of temperature 
 in increasing the conducting power of a metallic solution, 
 and, consequently, the quantity of metal deposited in a given 
 time ; they also demonstrate that the quantity of metal depo- 
 sited is (all the circumstances remaining the same,) equal in 
 equal times. In manufacturing operations, however, where 
 the battery is employed, it is impossible to preserve that uni- 
 formity, in the various influencing circumstances, which is 
 necessary to give such uniform results ; and hence the length 
 of time during which the articles are under operation, is 
 not an accurate measure of the metal deposited ; but with the 
 magneto- electrical machine, the time and quantity of depo- 
 sited metal are, as already stated (153), in a sufficiently 
 accurate relation, even for large manufacturing purposes. 
 
139 
 
 324. In the following experiments, a solution was employed, 
 consisting of one part by weight of cyanide of gold, dis- 
 solved in one hundred parts of water. 
 
 325. TEMPERATURE OF THE SOLUTION, 60° F. 
 
 Gold deposited. 
 GR. 
 
 First immersion of two minutes .... 0.009 
 Second ditto ditto . • • • 0.013 
 
 Third ditto ditto .... 0.014 
 
 Fourth ditto ditto .... 0.014 
 
 Fifth ditto ditto .... 0.013 
 
 Mean . . . 0.0126 
 
 326. TEMPERATURE OF THE SOLUTION, OS" F. 
 
 First immersion of two minutes .... 0.028 
 
 Second ditto ditto .... 0.028 
 
 Third ditto ditto .... 0.030 
 
 Fourth ditto ditto .... 0.029 
 
 Fifth ditto ditto .... 0.027 
 
 Mean . . . 0.0284 
 
 327. TEMPERATURE OF THE SOLUTION, 140° F. 
 
 First immersion of two minutes .... 0.063 
 
 Second ditto ditto .... 0.063 
 
 Third ditto ditto .... 0.063 
 
 Fourth ditto ditto .... 0.063 
 
 Fifth ditto ditto .... 0.063 
 
 Mean . . . 0.063 
 
140 
 
 CHAP. XI. 
 
 ON ELECTRO GILDING, PLATING, &c., AND THE PRODUC 
 TION OF WORKS OF ART BY ELECTRO-METALLURGY. 
 
 328. The principles on which the reduction of metals by 
 voltaic agency depends, have been treated of in the preceding 
 chapters ; the application of these principles to the processes 
 of electro gilding, plating, coppering, &c., and the production 
 of works of art by the agency of electricity, M'ill be considered 
 in detail in this chapter. 
 
 329. All electro-metallurgical processes admit of consider- 
 able variations in their details. The production of any 
 required deposite, as already explained (322), may be brought 
 about by adapting the strength and temperature of the solu- 
 tion to the quantity and intensity of the electric current ; and 
 any alteration in one of the circumstances, renders necessary 
 a corresponding alteration in the others j hence it is that one 
 operator employs and recommends a strong or saturated solu- 
 tion,and a another dilute one. A solution of almost any strength 
 may be employed to produce any required deposite, but in 
 treating of the details of the various electro-metallurgical 
 processes, the author will confine himself to those proportions 
 between the strength of the solutions and the different parts 
 of the apparatus, which are used successfully in manufac- 
 tories, or which his own experiments have demonstrated to be 
 effective. 
 
 330. In depositing films of gold, for the purpose of infilming 
 or gilding articles, a solution of cyanide (174) or sulphite (178) 
 
141 
 
 of gold should be employed, in preference to every other. 
 The solution may be of the strength directed in chap. vi. 
 
 331. Where it is desired to work with great rapidity, a weak 
 solution of gold, containing about one ounce of gold to two gal- 
 lons of water heated to the boiling point, may be employed ; 
 such a solution, when the strength of the electric current is 
 properly regulated, deposites with surprising rapidity. 
 
 332. The battery employed may be Daniell's (91), or the 
 common acid battery (109) ; a single cell of Daniell's possesses 
 sufficient intensity, but when the acid battery is employed, a 
 series of at least two should be employed. When very rapid 
 action is required, a series possessing greater intensity must 
 be employed. The size of the battery used for gilding may 
 be less than that used for the deposition of other metals; a 
 Daniell's battery will work effectually when the surface to be 
 gilt exceeds considerably that of the battery. The vessel 
 containing the solution of gold should be of glass or earthen- 
 ware ; if of the latter substance, care must be taken to select 
 one which is not attacked by the solution. The articles to 
 be gilt must be attached to the zinc end of the battery, and a 
 plate of gold to the copper or silver end, to maintain the 
 strength of the solution. The exact size of the plate of gold 
 to be dissolved, compared with that of the surface to receive 
 the deposite, may be varied to a considerable extent without 
 inconvenience ; as it is increased, however, the size of the 
 battery must be diminished, or some equivalent alteration in 
 the arrangement of the apparatus effected (298). It is usual 
 to employ a plate of gold, exposing about the same surface as 
 the article to be coated. Its size may, however, be increased 
 with decided advantage, and some manufacturers employ a 
 surface two or three times the size of that to be gilt. The 
 advantages of using so large a plate are the following : — By 
 using a small surface, the quantity of gold dissolved does not 
 equal that deposited, and hence the solution is continually 
 deteriorating ; the thickness of the coating of deposited gold 
 
142 
 
 is irregular, when the surface exposed is small, as the current 
 from the plate is almost wholly conducted by that part of 
 the article opposed to it, and the reduction of metal is 
 consequently greater there, than on the more distant parts. 
 By using a large plate of gold in the solution, both these dif- 
 ficulties are avoided ; the quantity of gold dissolved more 
 nearly approaches that reduced, and the strength of the solu- 
 tion is more uniformly preserved ; and the deposited metal is 
 of more uniform thickness on all parts of the article. If a 
 small plate be used, it will be necessary to turn the articles 
 from time to time, in order to present all parts of their sur- 
 faces to the plate of gold in connection with the copper or 
 silver end of the battery. In gilding on the large scale, the 
 articles and plates of gold maybe suspended in the precipita- 
 ting vats, in alternate rows (288), and there is then no neces- 
 sity for changing their position. 
 
 333. The surfaces to be gilt must be cleaned by one of 
 the processes already described (230), and amalgamated by 
 immersion in the solution of nitrate of mercury (236). If 
 there is any oxide or scale on the articles, it must be removed 
 previous to dipping, by immersion in dilute sulphuric acid, 
 or, as it is commonly called, "pickle." The objects to be gilded 
 must be connected with the zinc end of the battery, and the 
 electrode, or plate of gold to be dissolved, with the copper 
 or silver end. It is desirable to make all the necessary 
 arrangements before introducing the articles into the precipi- 
 tating vat, so that the electric current may be completed by 
 their introduction ; by pursuing such a course, the local 
 action which occurs with many metals when immersed in 
 the solution of gold, is, to a great extent, prevented. 
 
 334. The operator should be particularly careful to deter- 
 mine as copious a flow of electricity as possible, immediately 
 on the immersion of the articles ; it is found that such treat- 
 ment, combined with the amalgamation with mercury, produces 
 a degree of adhesion, between the deposite and the surface of 
 
143 
 
 the article, which was believed impracticable in the early prac- 
 tice of the art. The flow of electricity may be such as to give 
 a dark colour to the surface of the metal ; this intensity 
 need not be kept up long. The most convenient way of 
 carrying this plan into effect, is to introduce each article, if 
 large, or several, if small, into the solution atone time, taking 
 care to direct the whole strength of the battery upon them ; 
 during the time they are under operation, another article, or 
 series of articles, may be prepared, and the whole battery 
 power may be directed upon them ; and so on, until the 
 whole have been thus treated, when they may all be con- 
 nected, and the deposition made to proceed regularly. 
 
 335. It is necessary to examine the apparatus from time to 
 time in order to ascertain that the deposition is going on 
 properly ; any alteration in the character of the metal may 
 be effected by the means pointed out in the preceding 
 chapter. It may be properly mentioned in this place, that 
 when the character of the deposite renders it desirable to 
 determine a greater flow of electricity, the conducting power 
 of the solution of cyanide or sulphite of silver cannot be con- 
 veniently increased by the addition of acid (314), and the 
 remedy must, therefore, be sought in an increased power in 
 the battery; the conducting power may, indeed, be increased 
 by the addition of cyanide of potassium to the cyanide, or 
 sulphite of potassa to the sulphite of gold ; but an alteration 
 in the solution is not recommended. 
 
 336. In depositing gold, so as to produce copies of works 
 of art, and where, in general a deposite of considerable thick- 
 ness is required, the size and position of the electrode con- 
 nected with the silver or copper end of the battery, require 
 considerable attention. If the deposition is to be effected in 
 the interior of the mould, the exterior must be defended from 
 the action of the solution, and the electrode of gold must be 
 in the form of a rod, suspended in the centre or axis of the 
 mould, if the latter is nearly a regular figure ; if it is other- 
 
144 
 
 wise, the electrode should be of such a form as to be nearly 
 equi-distant from every part. When a sufficient thickness 
 of gold has been deposited, an inferior metal, such, for 
 example, as copper, may be reduced in the interior, so as 
 to strengthen it. The article must be removed to a proper 
 solution of copper, and a copper electrode substituted for that 
 of gold. 
 
 337. To produce a copy of any work of art by deposition 
 on the exterior of a mould, it is necessary to proceed with 
 great caution ; and with the utmost attention, the result will 
 be inferior to that produced by internal deposition. The 
 plate of gold opposed to the mould, must surround it, as 
 nearly as possible, in every part ; this condition is indis- 
 pensable to the production of a deposite of uniform thick- 
 ness. In reducing metals upon very irregular surfaces, it is 
 difficult to obtain a deposite of uniform thickness, even where 
 the utmost care is used ; in such cases it is desirable to bend 
 the positive electrode, so as to give it the general figure of 
 the mould ; and when a sufficient thickness of metal has 
 accumulated on those parts nearest the positive electrode, they 
 may be defended from further action by removing the depo- 
 site from the solution, and varnishing them with caoutchouc, 
 or some other non-conducting substance. 
 
 338. By referring to the table of equivalents (32) it will 
 be observed that the combining proportion of gold is very 
 high, and consequently the quantity of that metal liberated 
 in the precipitating vat is much greater than that of the zinc 
 dissolved in the battery ; the proportions, theoretically, are 
 199.21 to 32.31 j in practice, the difference will not be found 
 so great, owing to local action (81) in the battery, which 
 can never be wholly prevented. If a compound battery be 
 used, 32.31 parts of zinc will be dissolved in every cell, for 
 every 199.21 parts of gold deposited. It is owing to the high 
 equivalent of gold, that a smaller battery may be used for 
 depositing on a given extent of surface, than in depositing 
 
145 
 
 most other metals (332); a fact which has been already 
 pointed out. 
 
 339. The metals which may be conveniently gilded by 
 electric agency are platinum, silver, copper, brass, and alloys 
 of copper generally; steel, iron, and pewter, cannot be 
 gilded satisfactorily, unless they be first coated with a thin 
 film of copper. 
 
 340. Electro-plating is best effected by the use of the 
 solutions of cyanide (185) or sulphite (187) of silver; the 
 latter by preference. The articles to be plated must be pro- 
 perly cleaned (230), by scouring (233), or dipping (231), and 
 if any oxide be on their surface, it must be removed by 
 " pickling," previous to " dipping." The battery employed 
 may be a single cell of the acid battery (109), or a Daniell's 
 (91) ; the latter is to be preferred. If the simple acid bat- 
 tery be used, the zinc surface should be about equal to the 
 surface to be plated, and the positive electrode should be a 
 plate of silver, exposing a surface not less than that to be 
 plated ; it may be made double or treble that size with 
 advantage (332). The remarks made on amalgamation, when 
 treating of gold (333), and the direction of an intense current 
 at the first immersion of the articles, apply in the case of 
 silver. The articles must be connected with the zinc end 
 of the battery ; and the plate of silver to be dissolved, with 
 the copper or silver end, and all the connections should be 
 made before introducing the articles into the solution. When 
 large numbers of small articles are to be operated upon, 
 they and the plates of silver to be dissolved, may be hung in 
 alternate rows, as already described (288). Any alteration 
 may be made in the character of the deposite, by observing 
 the directions given in chap. x. The remarks made relative 
 to the production of works of art in gold (336), apply to their 
 production in silver. 
 
 341. By consulting the table of equivalents, the combining 
 proportion of silver will be found to be 108.3, that of zinc 
 
146 
 
 being 32.31 ; consequently, 108.3 parts of silver will be 
 deposited for every 32.31 parts of zinc dissolved in tbe bat- 
 tery, or, in case a compound battery be used, in each cell. 
 
 342. The metals which may be most conveniently plated 
 with silver by means of electricity, are platinum, gold (should 
 occasion ever require it), copper, brass, and the alloys of cop- 
 per generally, pewter, iron, and steel. The alloy of nickel, 
 called German silver, is, however, more extensively employed 
 for electro -plating than any other metal or alloy, and the 
 admirable results produced with it, warrant the preference it 
 has obtained. 
 
 343. Platinum may be precipitated from either of the solu- 
 tions before enumerated (198), but the chloride is the only 
 salt which is commonly used. Considerable care is requisite 
 in the deposition of this metal in the ductile state. In order 
 to produce the ductile metal, a very feeble current must be 
 employed, and the positive electrode should be very small. 
 The solution must be neutral, as it is almost impossible to 
 produce a ductile deposite from an acid solution of this metal. 
 In order to ensure its perfect neutrality, it is advisable 
 to add soda to the solution, and thus form the chloride of 
 platinum and sodium. When it is desired to precipitate the 
 platinum in the form of a black powder, as in making the 
 platinized silver of Smee's battery, and platinized platinum 
 for the electrodes of voltameters (121), the solution may be 
 acid, and the current of electricity may be both large in 
 quantity, and of considerable intensity ; there is no difficulty 
 in producing this kind of deposite. 
 
 344. The equivalent of platinum is 98.84; and, conse- 
 quently, 98.84 parts of that metal will be deposited for every 
 32.31 parts of zinc dissolved in the battery, or in each cell, 
 if a compound battery be used. 
 
 345. The reduction of copper has received more attention 
 than that of any other metal. The art of electro-metallurgy 
 originated with, and was, for a long time, confined to this 
 
147 
 
 metal, and it is still more extensively reduced than any other. 
 The single-cell apparatus (264) was long used for its reduc- 
 tion, and is still extensively employed; it is, however, inferior 
 to the battery process. 
 
 346. In the choice of the salt of copper from which to 
 reduce the metal, the operator must be guided by the kind of 
 apparatus he intends employing, and the nature of the sur- 
 face to be deposited on. If the single-cell process be 
 adopted, the sulphate of copper should be used, if the nature 
 of the surface to receive the metal will admit of it. The 
 sulphate is the cheapest salt of copper, and as, in the single- 
 cell process, the salt decomposed is not replaced by a cor- 
 responding quantity formed at the positive electrode, as 
 in the battery process (275), a continual addition of the 
 metallic salt is necessary, in order to maintain the strength of 
 the solution. The continual deterioration of the solution, 
 and consequent addition of the salt, renders it desirable to 
 use the cheapest salt, and for this reason, the sulphate should 
 be chosen. 
 
 347. Where the battery process is employed, the acidu- 
 lated solution of sulphate of copper may be used, or a nearly 
 saturated solution of the nitrate ; if the surface receiving the 
 deposite decomposes the solution, as iron in sulphate, or 
 nitrate of copper, the operator must select a salt which is 
 not acted on, although such salt may be inferior in every 
 other respect. 
 
 348. The surface to be coated with copper must be treated 
 or prepai-ed by some one of the methods described in chap, 
 vii. ; if it is metallic, and it is not intended to cause the 
 deposite to adhere, the precaution of exposing the surface to 
 the air for several hours (228), or some equivalent treatment 
 (229), especially if it be of copper, must not be neglected. 
 If the adhesion of the deposite is desired, it may be effected 
 by cleaning the metallic surface (230), if of copper ; or by 
 cleaning and amalgamating it (236), when of a dissimilar 
 
 L 2 
 
148 
 
 metal, which is readily susceptible of amalgamation. If the 
 surface is non-metallic, it must be rendered a conductor of 
 electricity, by treating with plumbago (224) or phosphorus 
 (216). 
 
 349. The mould, or surface thus prepared, must be con- 
 nected with the zinc end of the battery, and a sheet of cop- 
 per, to be dissolved, with the silver end. A single cell of the 
 acid battery (109) may be used ; or w^hen greater rapidity is 
 required than can be obtained with such an instrument, a 
 Daniell's (91), or a series of two or three of the acid battery 
 may be used. The size of the plate of copper connected with 
 the copper or silver end of the battery, should exceed that of 
 the surface to be deposited on. 
 
 350. Immediately these conditions are complied with, the 
 mould, if of metal, will be covered with a stratum of copper : 
 if it be of wax, plaster of Paris, or any other black-leaded sur- 
 face, this will not take place immediately ; but the precipitated 
 metal will be observed, first to aiTange itself round the con- 
 ducting wire, and gradually to spread until it has covered the 
 whole surface of the mould. The appearance of a mould on 
 which the copper is spreading, is very beautiful : the process 
 goes on with a rapidity varying with the quality of the black 
 lead; sometimes it will require an hour, or even a much longer 
 time, to spread over the surface of a moderate sized medal ; 
 at other times it vegetates, as it were, with extreme rapidity, 
 and its progress may be observed with the assistance of a 
 lens, or even with the naked eye. 
 
 351. It frequently happens, with bad plumbago, that the 
 spreading at first commences rapidly, and declines, or ceases 
 altogether, when a moderate sized metallic surface is formed. 
 It also often occurs that the copper does not spread regularly ; 
 that is to say, a number of branches form in different 
 directions, leaving spaces between them uncovered ; it rarely 
 happens that in such cases the experiment terminates suc- 
 cessfully. If the w^hole surface does not become covered in 
 
149 
 
 the course of two or three hours, the experiment may be 
 regarded as a failure ; for when the spreading of the copper 
 goes on so slowly, a slight alteration of temperature may 
 determine the expansion or contraction of the metal, before 
 the whole surface is covered, and the copper detaching itsel^ 
 from the black-leaded surface, although the distance to which 
 it separates is small, the edge of the metal not being in actual 
 contact with the black lead, the process is completely 
 arrested. 
 
 352. In placing a black-leaded surface in the electrotype 
 apparatus, a very small plate, or even a wire, should at first 
 be placed opposite to it as a positive pole. If this precaution 
 be neglected, and a large plate at once introduced, the copper 
 deposited near the wire connecting the mould with the 
 battery will be of very bad quahty, owing to the want of that 
 proportion between the quantity of electricity passing and 
 the size of the negative surface, which is essential to the 
 production of ductile copper. As more of the surface 
 becomes covered, a larger positive surface may be exposed. 
 
 353. After the apparatus has been at work a few minutes, 
 it is advisable to examine the deposite, as its colour shews 
 whether the process is going on properly or not. The ap- 
 pearance of electrotype copper is so characteristic that, when 
 once seen, it can never be afterwards mistaken. If the 
 arrangements of the apparatus are good, the metal will be 
 tough and hard, and of a bright red colour, wholly unlike the 
 copper reduced by ordinary processes ; it may, perhaps, be 
 more correctly described as of a pure orange colour ; this, 
 however, is only when the metal has the texture described. 
 If the defective arrangement of the apparatus occasions a 
 deposite of the brittle metal, its colour clearly indicates its 
 character. Such metal has a dark, dull red appearance, 
 wholly unlike the bright hue of the ductile metal.* 
 
 * A very interesting optical phenomenon may be observed, during the preci' 
 
150 
 
 354. After the surface of the mould is completely covered 
 with the deposite, the operation will not require further atten- 
 tion, excepting, of course, renewing the acid of the battery. 
 It is necessary to be very careful in observing that no minute 
 air bubbles are attached to the deep parts of the mould ; these, 
 of course, would spoil the deposited plate, as the copper can- 
 not attach itself to those parts of the mould not in contact 
 with the liquid. Sometimes the black lead (especially if a 
 superfluous quantity be left in a deep part of the mould) will 
 attach itself to one of these bubbles, and the copper spreading 
 upon it, a perfect cast of the air bubble will be produced, and 
 the operation rendered fruitless. These precautions having 
 been observed, the experiment will proceed satisfactorily. If 
 the surface on which the deposite takes place is small, a suf- 
 ficient quantity of copper will accumulate in about six hours, 
 supposing the apparatus to be in active operation. If the 
 surface is a large one, such as a copper-plate, a much longer 
 time must be allowed for the deposite to acquire additional 
 thickness. It is only necessary to have a thickness sufficient 
 to allow of the separation of the plate from the mould without 
 
 pitation of copper in the electrotype. There are certain colours which, hy mixture 
 with other colours, produce white light; any two such are said to be comple- 
 mentary ; thus red and green are complementary, because white is the result of 
 their mixture; blue and orange are also complementary, for the same reason. 
 This formation of white light by the mixture of such colours, though exhibited in 
 the utmost perfection in some of the phenomena of polarised light, is not often 
 observed otherwise ; owing, principaUy, to the rarity with which the colours are 
 presented in a pure state. This phenomenon may, however, be observed in great 
 perfection in the electrotype; the solution of sulphate of copper is of an intense 
 and pure blue ; and the newly-precipitated ductile copper is of an equally pure 
 orange ; let the reader take a vessel containing the cupreous solution, and place it 
 in the sun in order to have an abundance of light, and immerse in it, in a 
 horizontal position, a piece of new electrotype copper— a plate or medal in the 
 course of formation, for example; immediately the metal sinks beneath the 
 surface of the blue solution the orange tint fades, and, by placing it at a proper 
 depth, altogether vanishes, and the metallic plate appears intensely white ; when 
 nicely adjusted, the plate so much resembles plaster of Paris, that a person 
 unacquainted with the nature of the experiment, would with difficulty be persuaded 
 that it was not made of that substance. 
 
151 
 
 risk of bending ; any extra rigidity may be given more econo- 
 mically by the application of soft solder to the back, and 
 by other means which will suggest themselves to every 
 experimenter. 
 
 355. In depositing copper upon iron, a solution of the 
 cyanide or acetate of copper should be employed. The only 
 value of these salts is, that a die or surface of iron may be 
 immersed in their solutions, without receiving injury by the 
 corrosion consequent on the deposition of a film of metal by 
 chemical action. They are much less convenient for ordinary 
 purposes than the sulphate and nitrate, and should only be 
 used when these salts are inadmissible. The acetate requires 
 three or four cells of the acid battery for its ready decompo- 
 sition ; and the cyanide may be used at the boiling point with 
 advantage. 
 
 356. By referring to the table of equivalents (32), it will 
 be seen that 31.71 parts of copper will be deposited for every 
 32.31 parts of zinc dissolved in the battery, or in each cell 
 when a compound battery is used. 
 
 357 Depositions of zinc may readily be obtained from either 
 of the salts already enumerated (203), but the sulphate or ace- 
 tate will be found to answer every purpose; and in consequence 
 of its economy, the sulphate should be preferred. The only 
 point to Mdiich attention need be particularly directed, is the 
 neutrality of the solution. The salt formed by the battery 
 (203) should not be used until it has been re-crystallized, as 
 it is likely to be contaminated with acid, which interferes 
 with the character of the deposite, occasioning a tendency 
 to the production of the metal in the state of a black powder. 
 A strong or nearly saturated solution may be used. The 
 quantity of zinc deposited will equal that consumed in the 
 battery, or in each cell of a compound battery, should the 
 latter be employed. 
 
152 
 
 CHAP. XIL 
 
 ON THE PRODUCTION OF PRINTING SURFACES 
 BY ELECTRICAL AGENCY. 
 
 358. The earliest impressions produced by voltaic precipi- 
 tation, were from printing surfaces (15) ; and so admirably 
 minute and faithful are the details of impressions thus 
 obtained, that their production must ever constitute one of 
 the most important branches of the art of electro-metallurgy. 
 
 359. There are two methods of producing printing surfaces 
 by means of voltaic electricity ; the design may either be 
 made in metal, or of a non-metallic substance, and an impres- 
 sion in copper taken therefrom ; or a metallic surface may be 
 partially defended, by being coated with wax or caoutchouc 
 (258), and connected to the silver or copper end of a voltaic 
 battery, so as to constitute the plate to be dissolved (272). 
 When the battery is excited, those parts of the metal which 
 are not defended from the solution are corroded, while 
 the coated parts are not affected. This process is sometimes 
 called Voltaic Etching. 
 
 360. The circumstances to be attended to in copying 
 engraved copper-plates, are sufficiently indicated in the pre- 
 ceding chapters ; it is, therefore, only necessary to point out, 
 briefly, the course to be pursued. Where practicable, a mould 
 of the plate should be used instead of the plate itself ; as time 
 is thereby saved, and the risk of injuring the original plate 
 avoided. A mould of lead may generally be made without 
 difliculty (241). A mould obtained in this way, may be at 
 
153 
 
 once introduced into the solution of copper (193), without 
 risk of adhesion. A plate of copper, to be connected with 
 the silver end of the battery, about equal in size to the mould, 
 should be placed opposite to, and parallel with it. When the 
 plate itself is deposited on, the greatest care must be taken to 
 prevent the adhesion of the deposite, either by Mr. Spencer's 
 process (229), or by exposure during several hours to the air 
 (228). The deposite obtained by reducing copper on the 
 original plate, serves as a mould or matrix on which a second 
 deposition may be made, which latter will be a fac-simile of 
 the original plate. The same care is requisite to prevent the 
 adhesion of the second deposite to the mould, as in preventing 
 the adhesion of the latter to the original plate. 
 
 361. Plates for engraving may be made by depositing the 
 metal upon a burnished piece of copper. In this case, the 
 precipitated plate will have a burnished surface like the cop- 
 per on which it is deposited ; or it may be precipitated on a 
 plate not so prepared, and be afterwards treated exactly as 
 ordinary copper is, for the use of the engraver. The an*ange- 
 ment of the apparatus necessary for the production of copper 
 of a proper quality has been so fully pointed out, that it is 
 unnecessary to repeat it here. Copper-plates intended for 
 etching, when made by the electrotype process, are so supe- 
 rior to those of ordinary copper, that there can be no doubt 
 the former will very soon completely supersede the latter. 
 The electrotype metal is absolutely pure, and hence, in all 
 chemical processes, is more uniformly acted upon than any 
 other. The electrotype itself will demonstrate this. The 
 copper forming the positive pole in the decomposition cell 
 invariably presents a black surface during its solution, and a 
 greater or less quantity of scaly matter, consisting of charcoal 
 and other impurities, is invariably left behind, where thick 
 plates are thus operated upon ; but, if a piece of electrotype 
 copper is used as a positive pole, its surface does not for a 
 moment lose the beautiful orange colour so peculiar to it ; 
 
154 
 
 and, after the largest masses have been dissolved, not a par- 
 ticle of impurity is left behind — nay, the beautiful trans- 
 parency of the liquid is not in the slightest degree impaired. 
 Hence it is that, in the process of etching, the common or 
 impure metal proves a source of anxiety, and often disappoint- 
 ment to the engraver, while he uses that precipitated by voltaic 
 agency with absolute certainty of success. When the acid 
 is applied to the former, its action is frequently intense in 
 one place and feeble in another, and the etching is of neces- 
 sity irregular ; but with the latter the utmost uniformity of 
 action prevails, and a corresponding regularity in the product 
 results. From what has been said of the action of impurities 
 in zinc, when treating of the voltaic battery, the reader will 
 at once understand that the impurities may in some instances 
 accelerate, and in others retard the action of the acid, accord- 
 ing to their nature. 
 
 362. It has been proposed to prepare copper plates for 
 etching, by means of a voltaic deposite, instead of the ordi- 
 nary "ground;" it was beheved that, by depositing an 
 extremely thin film of gold on a copper-plate, so as com- 
 pletely to defend it, an artist might trace his design through 
 this film with much greater ease and certainty than through 
 the usual " ground and it was further supposed, that by 
 exposing the plate to the action of acid in the usual way, 
 those parts of the copper from which the gold has been 
 removed by the artist's design, would be attacked and etched 
 in, while the parts defended by the gold would remain unacted 
 on. Experiment has, unfortunately, demonstrated the im- 
 practicability of this proposition, for although the gold is 
 wholly unaffected by the acid, yet the parts which it covers 
 are not secured against its action; the acid commonly 
 insinuates itself between the gold and copper, and thus strips 
 off the film of the former ; or, in the few instances where 
 this does not occur, the gold and copper form, with the acid, 
 a voltaic combination (48), by virtue of which, the latter 
 
155 
 
 metal dissolves most rapidly at those parts in contact with 
 the former ; and hence, before the lines have been corroded 
 to a sufficient depth, they spread laterally, and the beauty of 
 the design is inevitably injured. 
 
 363. A very ingenious method of producing printing sur- 
 faces by electro-metallurgical deposition, has been made by 
 Mr. Palmer, and called by him " electrotint." It consists of 
 a kind of painting, executed upon a stratum of semi-fluid 
 composition, spread on a metallic plate : the surface of the 
 composition is made a conductor of electricity ; and a depo- 
 site of copper being made upon it, a metallic surface is pro- 
 duced, exhibiting the design originally drawn upon the com- 
 position, and capable of being printed from. By this process 
 two kinds of plates can be produced : the design may be 
 prominent, as in the case of a wood engraving, and the 
 impression obtained from the surface of the design ; or, it 
 may be sunk beneath the surface of the plate, and the 
 impression obtained as from ordinary copper-plates: the 
 latter promises to be the more useful. We will describe the 
 processes in detail. 
 
 364. To produce a plate to be printed from as an ordinary 
 copper-plate, a stratum of a composition, consisting of one 
 part of wax, two of lard, and one of lamp-black, is spread 
 upon a plate of German silver, plated copper, or some other 
 white metal, either polished, or having a "dead white" sur- 
 face ; to which plate has been previously soldered a wire, to 
 connect it with a voltaic apparatus. Now, if a number of 
 lines were drawn through this composition, so as to expose 
 the white plate, and the whole surface made a conductor of 
 electricity by black lead being spread upon it, a plate of cop- 
 per can be produced from it, in which the lines drawn in the 
 composition will project. If such a plate be printed from 
 by a copper-plate printer, the impression produced will 
 exhibit the projecting parts white, and the depressed ones 
 black. In the mould, the lines drawn were white, for the 
 
156 
 
 surface of the white metal was exposed, and the untouched 
 parts were black, being the black composition ; hence, in 
 order to produce a design, it is only necessary to remove the 
 black composition, so as to expose the white plate where 
 whiteness is wanted in the printed impression, and where 
 blackness is desirable, to leave the black composition ; where 
 intermediate shades are required, the composition may be 
 partially removed, so that the white plate appearing through 
 the thin stratum of the composition, gives the desired tint. 
 To produce the effect of a picture, the artist takes the plate 
 prepared as above, and by means of brushes of various 
 degrees of hardness, removes the composition in such a man- 
 ner, that the white plate appearing more or less through dif- 
 ferent parts of it, gives the effect he desires to produce. 
 Different styles of handling may be adopted ; by means of 
 soft brushes, the smoothest tint may be produced ; and by 
 harder tools, coarser or bolder effects may be obtained. As 
 the composition never sets or becomes hard, any defect may 
 be remedied by spreading the composition over it, and work- 
 ing it again. Although the principle on which these paint- 
 ings are produced is very simple, they are by no means easy 
 of execution ; for, although the effect wished may appear on 
 the prepared plate, the impression produced from the copper- 
 plate may have a very different appearance ; for it is not only 
 on the depth which may be given to different parts of the 
 composition, but on the character of the surface that the 
 depth of colour depends. Wliere perfect blackness, for 
 example, is required, it is not enough that the composition 
 be left unremoved — that will give the effect in the plate 
 drawn on, and the electrotype plate produced from it will 
 exhibit a depression in that part — but when it is printed 
 from, the ink will be removed by the printer's hand, and the 
 part will print white. In such cases, it is indispensible to 
 produce, by means of different tools, such a texture of sur- 
 face that the ink shall be retained thereon. 
 
157 
 
 365. The other kind of plate produced by this process, 
 viz., that from the surface of which the design is to be 
 printed, is produced by a process similar to the foregoing ; 
 the principal diiference is in the preparation of the plate, 
 which is in this case black, and covered with a white com- 
 position. The reason for this difference is obvious. In the 
 former kind of printing, the projections were left white, and 
 the depressions gave the dark tints ; in the present case the 
 projecting parts print black, and the depressions correspond 
 with the lights of the picture ; hence, it is necessary to have 
 a black plate covered with a white composition, by removing 
 which, the black plate becomes exposed and forms the dark 
 parts of the design ; where white parts are required, the white 
 composition is left. A copper-plate may be blackened by 
 being washed with a solution of hydro-sulphate of ammonia 
 or chloride of platinum ; and the white composition may be 
 either a mixture of two parts of sulphate of lead, two of lard, 
 and one of wax ; or sulphate of lead and olive oil, mixed in 
 such proportions as will give a proper consistence. The draw- 
 ing may be executed with different tools, so as to produce 
 various effects. After the drawing is made, the finest black 
 lead is sifted on its surface, and any superfluity removed 
 by an exceedingly soft and dry camel-hair brush ; it is then 
 exposed in the electrotype apparatus, and a metallic plate 
 obtained from it. 
 
 366. A modification of this process has been invented by 
 Mr. Palmer, by which the most elaborate subjects can be pro- 
 duced with a degree of perfection unattainable by the electro- 
 tint process ; it is called by the inventor, " glyphography," 
 or engraved drawing. 
 
 367. In the process of glyphography, a smooth copper- 
 plate, such as is used by engravers, is blackened by being 
 washed with a solution of sulphuret of potassium, or hydro- 
 sulphate of ammonia. A white composition, made by fusing 
 together sulphate of lead, wax, and resin, is spread evenly 
 
158 
 
 on the blackened plate, so as to form a stratum of about one- 
 thirtieth of an inch in thickness. The artist proceeds to 
 operate upon this plate with tools of extreme simplicity : — 
 two or three steel points, of different degrees of sharpness, 
 curved near the end, and some of them flattened at the point, 
 constitute, with some pointed wooden tools, all that is neces- 
 sary for the glyphographic artist. With these tools the artist 
 cuts away the white composition, using the finer or broad- 
 pointed instrument, as he wants fine or coarse lines, or the 
 wooden points, if he wishes to produce free and bold lines. 
 He can at all times judge of his work as it proceeds, for the 
 removal of the white composition exposes the black plate, 
 and thus produces the effect which the line made will pro- 
 duce in printing — a black line on a white ground. 
 
 368. When the design is completed to the satisfaction of 
 the artist, a cast is taken from it ; this may be done in two 
 ways, either by plaster of Paris (246), or by precipitating cop- 
 per on it; the latter, however, is preferable. To produce 
 the cast, the surface of the composition is rendered a con- 
 ductor of electricity by black lead (224), or any other suitable 
 method, and a layer of copper deposited on it by the battery. 
 When the stratum of copper is sufficiently thick, it is removed 
 from the mould, and having been strengthened at the back, 
 by having soft solder melted on it, is attached to a block of 
 wood. The cast or impression thus obtained, is an exact 
 counterpart of the design made by the artist ; every line drawn 
 in the composition is represented in the cast, by a raised 
 line, the depth of which equals the thickness of the stratum 
 of composition, that is to say, one-thirtieth of an inch ; and 
 when this surface is printed from, an impression is obtained 
 exactly resembling, in effect, the design produced on the 
 original plate. 
 
 369. When a cast has been taken in plaster of Paris from 
 the artist's design, it is oiled, and a second cast taken ; the 
 latter is a facsimile of the original plate, and a stereotype 
 
PAUL AND VIEGINIA. 
 
 palmer's GI.TPHOGRAl'HY.] 
 
 [E. C, OSBORNE, TYP. 
 
159 
 
 impression may be taken from it by the ordinary stereo- 
 typer. 
 
 370. A glyphographic impression is printed from the sur- 
 face, or projecting parts of the design, as in printing from 
 wood blocks ; it is therefore evident that the projections 
 which print, being only one-thirtieth of an inch more promi- 
 nent than the sunken parts, which are not intended to print, 
 there is great risk of the latter printing, when there is any 
 considerable surface exposed, as in broad lights. In order 
 to avoid this, a quantity of composition is laid on those parts 
 of the artist's design where he has left large surfaces un- 
 touched, so as to form projections, which, in the reverse 
 taken, produce corresponding depressions, so deep as to 
 render it impossible that they should ever print. It may, at 
 first sight, appear difficult to lay on the composition without 
 rkk of injuring the design, but as it is unnecessary, in thus 
 building up the broad lights, to approach the edges of the 
 lines cut by the artist, there is no danger of obliterating any 
 part of the design. 
 
 371. Glyphography is likely to supersede, to a considerable 
 extent, the art of wood engraving; it possesses the advantage 
 of economy, especially in complex subjects ; and as the 
 printing surface is produced from the artist's design by a 
 series of processes, the success of which is not dependent on 
 the manual skill of the workmen, the character of the origi- 
 nal is preserved with an accuracy which cannot be attained 
 by any other method.* 
 
 372. The corrosion which takes place at the positive pole 
 of the arrangement, has been made subservient to the pro- 
 duction of printing surfaces. The art which has thus arisen 
 is called voltaic etching. 
 
 373. The process by which etching on copper is ordinarily 
 effected is so generally known, that it is only necessary to 
 
 * The author is indebted to Mr. Palmer for the accompanying beautiful speci- 
 mens of his invention. 
 
160 
 
 allude to it briefly. The plate is covered with a thin layer 
 of what is technically called " ground it is a composition, 
 the principal ingredients of which are wax and pitch. It is 
 applied by being rubbed over the copper-plate while heated. 
 The artist traces the design he wishes to etch by means of a 
 pointed instrument ; the composition is removed wherever he 
 has drawn, and the surface of the copper consequently 
 exposed ; the plate is placed in a vessel, and dilute nitric 
 acid poured on it ; the copper is dissolved wherever the acid 
 comes in contact with it ; and the lines drawn thus become 
 permanently etched upon the plate. It is necessary to 
 examine the work as it progresses, and to remove it from time 
 to time, to " stop out" those parts where the lines are not 
 required to be deep : this process consists in covering such 
 parts with varnish or composition, which will defend them 
 from the further action of the acid. This part of the work 
 requires considerable attention, as much of the beauty and 
 perfection of the result depends upon it. Notwithstanding 
 the diligence and care of the workman in the production of 
 the design, and the surprising address with which he " stops 
 out," from time to time, those parts which have been suffi- 
 ciently acted on by the acid, the operation is often more or 
 less unsuccessful. 
 
 374. When treating of the purity of the electrotype cop- 
 per, we took occasion to notice the cause of the irregular 
 action of the acid upon the metal reduced in the ordinary 
 manner, and the superiority of that produced by voltaic 
 agency. We are now about to describe a process by which 
 the etching itself may be accomplished with far more ease, 
 than by the common method, and with a certainty of success 
 unattainable by any other mode of procedure. 
 
 375. From the various experiments which have been 
 already described, the reader is familiar with the corrosion or 
 decay of the copper, of which the positive pole of a voltaic 
 arrangement is made (271) ; and he is also familiar with the 
 
161 
 
 fact, that if the negative plate in a voltaic arrangement be 
 covered with varnish, or some non-conducting substance, 
 all action will be suspended at that part (257) : accordingly, 
 wherever a deposite of metal was not wanted in any of the 
 experiments before described, we have directed such parts to be 
 treated in this way. Precisely the same holds good with respect 
 to the positive surface ; only that part of it is acted upon 
 which is in actual contact with the liquid, and the shghtest 
 film of any foreign substance effectually defends it from cor- 
 rosion. It is upon these facts that the art of voltaic etching 
 is founded. 
 
 376. The plate to be etched by the voltaic battery is pre- 
 pared in the usual way, both with regard to the laying of the 
 ground and the tracing of the design ; it is then carefully 
 varnished on the back and edges, and a wire is attached to 
 some part where the copper is exposed : this must be done 
 very carefully, as it is desirable to varnish it over after- 
 wards. The wire is connected with the copper, silver, or 
 platinum of a single voltaic battery, and a plate of copper of 
 the same size, connected with the zinc, is placed in the solu- 
 tion, opposite to, and parallel with, the plate to be etched. 
 The deposition of copper immediately commences upon the 
 negative pole, and the lines, or other exposed parts of the 
 positive plate, yield up metal to the solution. It is evident 
 that it is immaterial whether the deposite on the negative 
 plate is in the state of ductile metal or not, and the various 
 circumstances with regard to the battery, which have been 
 pointed out as essential to its production, need not in the 
 present case be regarded ; as the attention should be wholly 
 directed to the conditions requisite to secure the uniform 
 etching of the plate. The battery may be a single pair, as 
 above stated, or a series of two or three may be employed ; 
 with the former the action will be slower than with the latter. 
 The distance of the two plates in the solution will also mate- 
 rially affect the rapidity of the process ; by placing them near 
 
 M 
 
162 
 
 each other, a more rapid action will be induced, and by remo- 
 ving them to a greater distance, a corresponding retardation 
 will follow. The copper-plate serving as the positive pole 
 should be as near the size of the surface to be etched upon as 
 may be ; if it is larger, the lines near the edge of the plate 
 will be more acted upon than those nearer the centre ; and, 
 on the contrary, if it is smaller, the centre will be more deeply 
 etched than the edges. In some cases, however, such an 
 effect is desirable, and it can be produced by the voltaic pro- 
 cess far more accurately than by the ordinary method. A 
 greater or less depth of the lines is effected in the common 
 process, by stopping out portions from time to time — that is, 
 covering with a varnish those parts which have been suffici- 
 ently acted upon by the acid, so as to defend them from 
 farther action. 
 
 377. This mode of operating, however, does not enable us 
 to effect a gradual transition from faint to deep lines ; it is 
 only by the voltaic process that this beautiful effect can be 
 produced. If a plate be prepared, having a series of parallel 
 lines drawn upon it, and be submitted to the action of the 
 battery in the way already described, the lines will be etched 
 with perfect regularity of depth, if the negative plate be parallel 
 to it ; but if they be inclined to each other, the lines will be 
 made deep at that end where they are nearest, and will be faint 
 at the end where they are most distant ; an impression from 
 such a plate will exhibit at one end a very dark tint, which, 
 gradually fading, will leave the other end very nearly white. 
 It is obvious, that this effect may be varied to a very great 
 extent ; if, for example, a prepared plate, having lines of 
 uniform width ruled upon it, be experimented upon, and 
 the negative pole in the decomposition cell be a circular disc, 
 placed opposite to the centre of the plate, the lines will be 
 deepest in the centre and fainter at the edges, and a surface 
 printed from such a plate will exhibit a dark spot, the edges 
 of which melt imperceptibly into the surrounding light : or 
 
163 
 
 the reverse effect may be produced, if the negative be made 
 of the size of the positive plate, or that to be etched, and 
 have a circular hole made in its centre ; the lines on the 
 middle of the etched plate will be very faint, and those near 
 the edge very deep : an impression taken from such a plate 
 has a dark ground, with a luminous spot in its centre, the 
 light of which becomes gradually fainter from the centre, and 
 is eventually lost in the surrounding darkness. 
 
 378. The effects now described may be modified in several 
 ways ; indeed there is no limit to the varied effects of light 
 and shade which may be thus produced ; and it is scarcely 
 too much to assert that the most beautiful designs may be 
 produced by this mode of treatment, upon a plate on which 
 parallel lines only have been drawn ; for, by using a positive 
 plate of the size of the negative or prepared plate, and per- 
 forating it in different forms, the etching will go on rapidly 
 where the metal is presented to it ; and the parts where no 
 metal is opposed will be left more or less unacted upon ; 
 hence a proof from the plate will have a dark ground, and 
 this design cut out of the negative plate will be left light. 
 Or, if preferred, dark designs upon a light ground may as 
 easily be produced ; for if, instead of cutting out the pattern, 
 the negative plate be cut into the desired form, the design 
 will be deeply etched, and the impression will give a dark 
 figure upon a light ground. Where it is desired to give very 
 slight gradations of shade, or to produce in this manner com- 
 plex figures, the better way of operating, is to make the 
 surface of the negative plate to project in those parts oppo- 
 site to which deep etching is required, and to be more dis- 
 tant where light is required. In other words, the negative 
 plate should be embossed ; and as it need not be thick, there 
 is no difficulty in giving it the proper figure ; the parts most 
 prominent will give shadow, and those most depressed will leave 
 light, and in proportion as the projections and depressions are 
 more or less abrupt, will the transition from light to darkness 
 
 M 2 
 
164 
 
 be more or less gradual. 1 1 is very important, however, for the 
 experimenter to remember, that the distance between the 
 plates affects the result in a very important manner; the 
 closer they are, the more accurately will the design on the 
 negative, be etched on the positive plate, and as they are 
 gradually placed farther apart the figure on the former will 
 become indistinct on the latter; indeed a plate, however 
 embossed or cut away, will leave little or no trace of its 
 figure on the positive surface, if it be placed very distant from 
 it in the solution. The cause of this is sufficiently evident ; 
 when the embossed surface is very near the plain one, the 
 distances of the raised and depressed parts from the plain 
 surface are very disproportionate; but when placed at a 
 distance, the disproportion becomes less, and at great dis- 
 tances, altogether insignificant. Now, if we suppose the 
 action to be inversely as the distance, the effect of placing 
 the plates near each other will be to render the dispro- 
 portion between the distances of the different parts of the 
 embossed plate from the plain one very great ; and the dif- 
 ference in the amount of action on the opposed surface pro- 
 portionably great ; by placing them more distant, this differ- 
 ence vanishes, and with it the difference of action. It is 
 evident that the same applies to perforated plates, or those 
 cut in peculiar forms, and also to plain plates inclined to each 
 other. 
 
 379. The advantages which the voltaic process of etching 
 possesses over the ordinary one, are — its certainty of suc- 
 cess, — the absence of gaseous matter on the surface of the 
 plate, which in some degree interferes with the action of the 
 acid,— and the clearness of the lines produced. We may 
 also add, that the rapidity of the process can be regulated 
 at the will of the operator,— that the progress of the etching 
 may be at any time examined without inconvenience,— and 
 that, besides permitting the regulation of the action by the 
 process of stopping out parts of the plate, it affords a means 
 
165 
 
 of effecting gradations of shade wholly unattainable by any 
 other known method of etching. 
 
 380. One of the most beautiful applications of the voltaic 
 process of etching is that made by Mr. Grove. This gentle- 
 man has succeeded in etching, by the voltaic battery, those 
 beautiful pictures formed by the process of M. Daguerre. It 
 is necessary to allude to the operation by which these pictures 
 are formed, in order that the subsequent process of etching 
 may be intelligible. A plate of silver, or of copper plated 
 with pure silver, is carefully cleaned by the action of finely 
 powdered tripoli and acid, and is afterwaids exposed to the 
 vapour of iodine, until, by the condensation of that element 
 upon the silver plate, a film of iodide of silver, of a rose 
 colour, is produced. The plate thus prepared, is extremely 
 sensitive to light ; and its sensitiveness may be increased by 
 subsequent exposure to the vapour of bromine, in such a way 
 as to determine the absorption of a determinate quantity of that 
 element. The prepared plate is introduced into a camera ob- 
 scura, so as to receive upon its surface the images of objects to 
 which the camera is directed, and which are formed in the focus 
 of its lens. The sensitive surface is allowed to remain under 
 the influence of the light, for a time, varying with the season 
 of the year, the clearness and brightness of the day, &c. 
 Upon removalj it is exposed, in a close chamber, to the 
 vapour of heated mercury, by which operation, the images of 
 the objects thrown upon it while in the camera obscura, 
 become developed ; the mercury attaches itself to those parts 
 where the light had fallen, and forms an amalgam, which has 
 a crystalline texture, and a dead-white appearance. The 
 plate is washed with a solution of common salt, or a solution 
 of hyposulphite of soda ; by which the iodine is removed, 
 and the plate rendered no longer sensitive to light. 
 
 381. On examining a Daguerreotype plate, it is necessary 
 to hold it in such a position that the incident light (the light 
 by which it is illuminated,) shall not be reflected from its 
 
166 
 
 whole surface to the eye ; otherwise the objects will not be 
 visible, and the plate will only present a uniformly brilliant 
 surface ; but, if the spectator places himself in such a 
 position, with regard to the plate, that the light falling on it 
 is reflected in another direction, the picture immediately 
 becomes visible. The light parts in the objects consist of an 
 amalgam of mercury and silver, and the crystalline surface of 
 the amalgam scatters the light in different directions, and a 
 portion of it consequently reaches the eye ; hence the white- 
 ness of those parts : and the dark portions of the picture are 
 those places where the mercury has not attacked the silver, 
 and the light falling there is regularly reflected from the bril- 
 liant siuface of that metal, and none of it reaching the eye, the 
 plate presents that black appearance so peculiar to highly- 
 polished metallic bodies. The intermediate lights and shades, 
 are where the texture of the surface is more or less altered by 
 the action of a greater or less quantity of mercury. 
 
 382. The chemical constitution of such a plate is, there- 
 fore, as difi'erent in different parts as is its physical structure, 
 and it is by availing himself of this fact, that Mr. Grove has 
 effected the etching of these beautiful productions. The 
 Daguerreotype plate is varnished on the back and sides, and 
 connected with the platinum of one cell of Mr. Grove's bat- 
 tery, and to the zinc is attached a plate of platinum, on which 
 the fine powder of platinum has been deposited ; such a sur- 
 face parts with the hydrogen liberated upon it, very freely. 
 The two plates of an equal size are placed in a vessel con- 
 taining a mixture of two parts of hydro-chloric (muriatic) 
 acid, and one of water ; they are fixed at the distance 
 of about one-fifth of an inch, and, by being made to shde in 
 a grooved wooden fi-ame, are maintained perfectly parallel, 
 and at the proper distance from each other. In about thirty 
 seconds the best eff"ect is produced; if the operation be 
 continued much longer, the beauty of the picture will be 
 impaired ; the etching will be deeper, but some of the fine 
 
167 
 
 parts running into each other, the exquisite minuteness of 
 detail for which these pictures are remarkable, will be 
 destroyed. The plate, on removal from the solution, is 
 washed in distilled water, and the brown deposite formed 
 upon it removed by a dilute solution of ammonia ; for this 
 purpose it is placed in a shallow vessel containing the 
 solution, and gently rubbed by soft cotton. The process is 
 completed by a second washing and drying. These plates are 
 not etched to sufficient depth to enable a printer to take good 
 impressions from them, as the ink is not well retained in the 
 deep parts, and the beauty of the plate is destroyed by the 
 process of cleaning it. 
 
 383. Although this process is at present not sufficiently 
 perfect to affi3rd plates which can be printed from in the 
 ordinary way, yet impressions may be taken in copper from 
 Daguerreotype plates, etched by Mr. Grove's process. These 
 impressions exhibit the minutest objects depicted on the 
 original, and have altogether a pleasing effect. 
 
 384. In addition to the methods already described, by which 
 printing surfaces may be obtained by electro-metallurgical 
 agency, several modifications of these methods have been 
 proposed ; but as they have never been brought into common 
 use, and are, in general, inferior to those already treated of, it 
 is unnecessary to describe them. 
 
168 
 
 CHAP. XIII. 
 
 ON VARIOUS APPLICATIONS OF ELECTRO- METALLURGY. 
 
 385. It is impossible to point out all the purposes to which 
 the voltaic precipitation of metals is applicable ; there is 
 scarcely any manufacture to which it may not, in some degree, 
 be applied; and for decorative purposes it has already 
 been applied to an extent which even the most sanguine 
 could not have anticipated. The principles on which 
 success in this art is dependent, have been detailed in the 
 preceding chapters ; as well as those purposes to which it has 
 been applied most extensively, and the practice of which 
 constitutes a new manufacture. 
 
 386. The present chapter is devoted to a consideration of 
 some of the processes in electro-metallurgy, the objects of 
 which are less important, or less valuable, (though, perhaps, 
 not less interesting), than those which have already been 
 treated of in detail, such as the production of casts of speci- 
 mens of natural history, copies of Daguerreotype pictures, 
 and other applications, which are, in general, confined to 
 amateurs. 
 
 387. In the early practice of the art, the deposition of films 
 of copper on fruits, and specimens of natural history generally, 
 was a favorite pursuit with amateurs, and each successive 
 discovery, by which metallic depositions could be more rea- 
 dily formed on non-conducting substances, has added to the 
 number of those who pursue this interesting branch of the 
 art, as well as to the perfectioii of the specimens produced. 
 
169 
 
 388. Very beautiful ornaments may be produced by depo- 
 siting metals on fruits and flowers, and preserved specimens 
 of insects and birds. These may either be preserved apart, 
 or they may be grouped together, so as to form, by the con- 
 trast which is afforded by the difference in the metals with 
 which they are covered, or the difference in the character of 
 the same metal, the most beautiful ornaments, as well as the 
 most exact form of the perishable objects from which they 
 were produced. 
 
 389. Objects which are not of a very complex form, may 
 be most conveniently covered with copper by means of plum- 
 bago (224) ; if, however, they are too intricate to admit of 
 this treatment, the process by phosphorus (216) should be 
 resorted to. It is, perhaps, more important in covering 
 objects of natural history with metallic films to secure good 
 plumbago, than in any other process ; with medals, and casts, 
 and inorganic bodies, the impression lost may generally be 
 easily replaced, or if the object itself be introduced into the 
 metallic solution, it receives, in general, no injury ; and in 
 case of failure, it is only necessary to repeat the process by 
 which it is rendered a conductor: but with the objects in 
 question it is'otherwise ; it is rarely that they can be operated 
 on more than once ; and if the experimenter introduce a spe- 
 cimen into the metallic solution without a successful result, 
 he has generally the mortification, not only of failing to 
 preserve his specimen, but of having rendered it in every 
 respect worthless. It is for this reason that the black lead 
 used for rendering specimens in natural history electrical con- 
 ductors, should be of the best quality, and its fitness deter- 
 mined by previous experiment. The black lead should be 
 laid on with a soft camel's hair brush ; it may be spread very 
 lightly, as an exceedingly thin coating is sufficient. With 
 some objects, light coloured fruits in particular, the colour is 
 so little altered by the treatment with black lead, that young 
 experimenters in this art, despairing of the conducting power 
 
 ft 
 
170 
 
 of so thin a film, frequently injure or destroy their specimens, 
 in the fruitless endeavour to give a thicker coating. The 
 reader is cautioned against such a course. 
 
 390. It is well to use a tolerably intense battery in coating 
 a black-leaded surface with metal, as the spreading of the 
 deposite takes place with much greater rapidity, than when a 
 feeble current is employed. A single cell of Daniell's battery, 
 or a series of two or three acid batteries, will suffice. A small 
 positive electrode of copper should be used when the article 
 is first introduced into the cupreous solution. The best way 
 of operating when a single fruit, such as an apple or a pear, 
 is the subject of experiment, is to point the end of a wire and 
 force it into the stalk ; particular care must be taken to insure 
 a connection between the wire and the black-leaded surface 
 of the fruit. The specific gravity of most fruits being lower 
 than that of water, they float on the surface of the liquid, 
 unless means be taken to fix them beneath its surface. This 
 may be effected by using a short stout wire to connect it with 
 the battery ; the proper bending of the wire will suffice to 
 keep the fruit beneath the surface of the liquid. If the object 
 be not large, it may be held in the hand until a film of metal 
 has covered it, and then the precaution of using a strong wire 
 is unnecessary. 
 
 391. If the black lead is good, the spreading of the metal 
 over the black-leaded surface takes place with great rapidity ; 
 it may be seen to progress slowly by the naked eye, and with 
 the assistance of a lens, its progress may be distinctly traced. 
 It is only, however, with the best plumbago that such results 
 are obtained. A moderate sized pear or apple may be held 
 in the solution by the hand, for the purpose of becoming in- 
 filmed, as the process ought not to take longer than a quarter 
 of an hour or twenty minutes ; if the spreading proceeds so 
 slowly, as to require a much longer time for covering the 
 article, the result will be more or less unsatisfactory, for the 
 surface first covered continually augmenting in thickness 
 
171 
 
 during the time it is in the solution, a considerable quantity 
 of metal accumulates there, before other parts have received 
 any deposite. The stratum of metal is thus of unequal thick- 
 ness in different parts, and generally presents a greater or less 
 degree of roughness vrhere the greatest quantity of metal has 
 accumulated. Where the film is required to be of consider- 
 able thickness, it must be allowed to remain in the solution a 
 longer time than that before given. 
 
 392. When the object to be experimented on is of complex 
 form, the treatment by phosphorus must be resorted to. The 
 method of reducing metallic films on organic matters, first 
 proposed by Mrs. Fulhame, and applied to electro-metallurgy 
 by Mr. Spencer (214), may be resorted to when the object is 
 large ; but where its size admits of its immersion in the solu- 
 tion of phosphorus in bi-sulphuret of carbon (216), this pro- 
 cess should be preferred to the other method. By the treat- 
 ment with phosphorus, the most delicate flowers, insects, 
 preserved birds, and indeed anything which will admit of 
 immersion in a liquid, may receive a coating of metal. 
 
 393. When it is wished to preserve the form of the object 
 coated, a battery of moderate intensity and quantity must be 
 employed (314), with a solution of a good conducting power 
 (193) ; a smooth, ductile metal will thereby be produced. If 
 it is intended to produce ornamental articles, rather than 
 accurate models of the coated articles, a strong solution 
 (316), without acid, and a less powerful battery should be 
 employed. The positive electrode may also be much larger 
 than the surface to be covered (332). 
 
 394. Great variety may be given to these ornamental pro- 
 ductions, not only by varying the character of the copper 
 deposited, but by gilding or silvering the deposited metal. 
 Silver may, indeed, be directly deposited on black lead, but 
 with much less facility than copper ; and it is advisable to 
 obtain a film of copper first, and afterwards plate it with 
 
172 
 
 silver. The silvering and gilding of the copper articles has 
 been already sufficiently described. 
 
 395. No sooner had the pictures produced by M. Da- 
 guerre's process been presented to the world, than the idea 
 of multiplying them occurred to several individuals; and con- 
 sidering the interest which must ever be attached to produc- 
 tions which, from their nature, must be correct representations, 
 it is not surprising that scientific men eagerly sought the 
 means of multiplying them, by a process which does not admit 
 of inaccuracy in the copy. The process of multiplying these 
 impressions which naturally first presents itself, is that of 
 etching the metal plate on which the picture is formed, and 
 printing from the etched pictures as from an ordinary copper- 
 plate. The only process by which this can be done, with 
 any approach to certainty and success, is that of Mr. Grove 
 (382). There is no reason to expect that a more effectual or 
 correct etching can be produced by any process ; but the 
 mechanical form of the etched surface, and the depth to which 
 it is possible to corrode the metal, are so unlike the etching 
 produced by ordinary means, that there is no hope of being 
 able to produce a great number of perfect impressions from 
 these etched plates. 
 
 396. One of the earliest efforts of the art of electro-metal- 
 lurgy, was directed to the production of copies of Daguerreo- 
 type pictures by electric deposition ; but the success attained 
 was very imperfect. It almost invariably happened that the 
 impression obtained on the deposited copper film was very 
 faint ; it often occurred that no picture was produced on it, 
 and the original was generally destroyed ; and thus, when 
 the utmost success that could be expected was attained, the 
 copy was procured at the expense of the original. The 
 cause of these failures is sufficiently evident : a Daguerreotype 
 picture, as produced by the original process, is simply a 
 highly-polished plate of silver, on parts of which, mercurial 
 
173 
 
 vapour has been deposited in such quantity as to destroy, 
 more or less, the reflecting surface, and thus to produce a 
 picture by the different degrees of reflection which take place 
 at different parts. The mercury is at first very slightly 
 attached to the silver, and although, after the lapse of months, 
 it appears to amalgamate with it and become fixed, yet it 
 never adheres so firmly that it may not be detached by 
 the finger; hence, the mercury was removed from the silver, by 
 the deposited plate of copper, and constituted the picture 
 on it. 
 
 397. An admirable process of fixing Daguerreotype impres- 
 sions, so that they cannot be easily removed, has been 
 proposed by M. Fizeau. By this process the pictures are 
 not only fixed and prevented from fading, but they have a 
 greater intensity, and less metallic reflection, than previous 
 to fixing. As this process is indispensable to the production 
 of electrotype copies, it is given in detail. 
 
 398. Dissolve 15 grains of chloride of gold (167) in a pint 
 of distilled water, and 45 grains of hypo-sulphite of soda 
 in another pint of water ; pour the solution of chloride of 
 gold into the solution of hypo-sulphite of soda very slowly, 
 stirring the mixture with a glass rod. The yellow colour of 
 the mixture speedily disappears, and the solution becomes 
 quite colourless ; it is then fit for use. To fix a Daguerreo- 
 type picture, it should be placed on a stand, similar to a retort 
 stand, so that the flame of a spirit lamp may be brought 
 under every part of it. If the picture has just been taken, 
 it may be removed from the hypo-sulphite solution in which 
 it has been washed, in order to remove the iodine, to the 
 fixing stand; a small quantity of the fixing liquid is then 
 poured on the surface of the plate, and the flame of a spirit 
 lamp brought under it. The lamp is moved about so as to 
 heat all parts of the plate equally. As the temperature of 
 the plate rises, the picture loses a little of its intensity ; but, 
 by continuing the application of heat until the liquid has 
 
174 
 
 nearly arrived at the boiling point, the picture again brightens, 
 and is more vigorous than before the application of the fixing 
 solution. This stage of the process is usually accompanied 
 by the appearance of minute bubbles on the surface of the 
 picture. The solution is now poured from the surface of the 
 plate, which, after washing with distilled water, is dried in 
 the usual way. 
 
 399. If the picture has been dried between the time at 
 which it was taken and that of fixing, it is desirable to pour 
 a few drops of alcohol on it, so as to wet it all over ; it should 
 then be washed in water, until the whole of the alcohol is 
 removed. The object of this wetting with alcohol is to cause 
 the adhesion of water, and afterwards the fixing liquid, to the 
 plate. If the liquid be poured on a plate which has not been 
 so treated, it will probably not adhere to the edges, but 
 retire fi*om them as though they were greasy. By pouring on 
 a larger quantity of the liquid, such parts may be covered, 
 but they will be stained in the process of fixing ; hence the 
 necessity of wetting the plate all over by the use of alcohol. 
 
 400. After treatment by the hypo-sulphite of gold, the 
 picture becomes fixed to such an extent, that it is with diffi- 
 culty removed by rubbing with the fingers ; and the produc- 
 tion of electrotype copies is a work of extreme simplicity. 
 
 401. The plate must be allowed to remain many hours in 
 a cool place after fixing (228), otherwise there would be risk 
 of the adhesion of the deposite. It must then be attached 
 to a wire by means of a binding screw, or in any other conve- 
 nient way. The back should be carefully varnished, with 
 some resinous varnish, or a solution of caoutchouc (258). 
 The solution employed should be a saturated solution of sul- 
 phate of copper. It is of the utmost importance that the 
 solution be perfectly clear, and is, therefore, necessary, not 
 only to filter it in a situation free from dust, but carefully 
 wash the vessel in which the precipitation is to take place. 
 If any particles of dust or impurity rest on the surface of the 
 
175 
 
 liquid, they attach themselves to the plate, in the act of 
 immersing it, and no process of washing will remove them ; 
 the original and the copy are thus injured. 
 
 402. The battery used for copying Daguerreotype pictures 
 should have considerable intensity, not only on account of 
 the imperfect conducting power of the neutral solution of 
 sulphate of copper, but from the circumstance that much of 
 the beauty of the picture is dependent on the immediate 
 infilming of the plate on immersing it in the solution. A 
 single cell of Grove's battery (95), the size of the plates of 
 which equals that of the pictures to be copied, will answer 
 very well; or, in its absence, two or three cells of Daniell's 
 battery (91). The wire soldered to the plate should be 
 attached to the zinc of the battery, and the plate of copper 
 to be dissolved, to the platinum or silver. The arrangements 
 should all be completed before the introduction of the 
 Daguerreotype, so that the moment it is immersed it may 
 be coated with metal. 
 
 403. When the coating of copper is deemed sufficiently 
 thick, the picture and deposite must be removed from the 
 solution ; while still in contact, they should be carefully 
 washed in water, and dried with blotting paper. The com- 
 plete removal of the sulphate of copper, and careful drying of 
 the coated picture, are of importance, as neglect in these 
 points may occasion the loss of both the picture and the copy. 
 In order to remove the precipitated metal, it is necessary first 
 to detach it from the edges of the plate ; this may be best 
 etFected by cutting off, with a pair of scissors, a narrow strip 
 all round the plate, the deposite may then be readily separated. 
 If a drop of liquid remain on the edge of the plate, it will, on 
 separating the deposite, insinuate itself between the surfaces, 
 by capillary attraction, and stain both the original and the 
 copy. It is, therefore, necessary to be particularly cautious 
 in removing every trace of liquid before separation. The 
 electrotype copy will exhibit, with surprising fidelity, 
 
176 
 
 all the beauty of the original ; and it will differ from it only 
 in being of a fine reddish brown colour, and exhibiting all 
 the objects reversed, that is to say, the objects on the right 
 in the original being on the left in the copy, and vice versa. 
 
 404. The surface of the electrotype copy must not be 
 touched, and the impression should be removed, as quickly 
 as possible, out of contact with the air, by being covered with 
 glass. 
 
 405. Electro-metallurgy has contributed another process 
 to the art of photography. The deposition of a thin film of 
 gold on a Daguerreotype picture by electrical reduction, 
 may be made to effect the fixing of the image, and to 
 communicate a rich tone of colour, which cannot be at- 
 tained by any other means. The specimens of Daguerreo- 
 type which are now commonly exhibited, and which have 
 the appearance of being produced on a plate of gold, are 
 simply ordinary Daguerreotypes, on which a thin film of 
 gold has been deposited by the voltaic battery. When 
 a Daguerreotype plate is made to receive a very thin coat- 
 ing of gold, the picture assumes a fine golden tint, without 
 losing any of its intensity. It is scarcely necessary to 
 remark that the process is a very delicate one, and should 
 never be attempted on a fine specimen until the operator has, 
 by previous experiments, assured himself that he is master of 
 the art of electro-metallurgy. The solution used for the pur- 
 pose of gilding Daguerreotypes, is that used in M. Fizeau's 
 process, viz., a dilute solution of hypo-sulphite of gold (398). 
 When the picture has been treated according to all the usual 
 processes to which Daguerreotype impressions are subjected, 
 it should be placed, face upwards, in a shallow earthenware 
 or glass vessel. The solution of hypo-sulphite of gold (398) 
 should be poured on it, and a wire from the zinc of a feebly- 
 charged battery brought against one of its edges ; a plate of 
 gold, connected with the copper or silver of the battery, 
 being also brought into the solution, and held parallel with the 
 
177 
 
 picture. Immediately all the connections are made, the 
 operator should watch the plate closely, as its beauty 
 depends upon the thickness of the film; if it is too thin, 
 the picture has a faint, greenish colour, which is by no 
 means agreeable; and on the contrary, when the coating is 
 too thick, the picture loses intensity. By careful manipula- 
 tion, and the suspension of the process at the proper point, 
 the picture may be made to assume a fine golden colour, and 
 at the same time preserve undiminished its primitive intensity. 
 Instead of M. Fizeau's solution, the cyanide may be used, 
 but, on the whole, the former is recommended. 
 
 406. It has been proposed to apply the electrical reduction 
 of metals to the analysis of ores, and the detection of minute 
 quantities of metallic bodies. It is doubtful whether, for 
 general chemical purposes, the electrical reduction of metals 
 is preferable to the methods usually employed by chemists. 
 There are, however, particular occasions on which the che- 
 mist may conveniently employ the voltaic battery to effect 
 the reduction of metals, which are otherwise reduced with 
 difficulty. Mr. Edmund Davy has made a series of researches 
 on the detection of metallic poisons by electric precipitation, 
 in which he has demonstrated that the most conclusive evi- 
 dence of the presence of those metals, the compounds of 
 which are more commonly used as poisons, may be obtained 
 by the use of a voltaic apparatus, and often with a facility 
 and certainty that the ordinary methods of analysis do not 
 afford. 
 
 407. In the detection of metals by voltaic agency, the most 
 simple apparatus may be used : a small slip of zinc, and a 
 similar slip of platinum, being, in most cases, all that is 
 necessary. By means of this apparatus, the presence of 
 gold, silver, mercury, copper, tin, lead, &c. may be almost 
 instantly detected. If a drop of the liquid, supposed to con- 
 tain either of these metals, be laid on the end of the strip of 
 platinum, and the slip of zinc be brought in contact at the 
 
 N 
 
178 
 
 same time with the liquid and the platinum, the metal, should 
 any be contained in the solution, will be immediately reduced 
 on the platinum. 
 
 408. So delicate is this method of reduction, that if half a 
 grain of arsenious acid be laid on the platinum foil, with two 
 or three drops of hydro-chloric (muriatic) acid, and touched 
 in the manner described, with zinc, that part of the platinum 
 on which the liquid rests will immediately become coated 
 with metallic arsenic, and filaments of the metal will be 
 mixed with the liquid. On exposing the platinum to the 
 heat of a spirit lamp, the metal is readily recognised by the 
 garlic-like odour so pecuhar to it. It eventually volatilises 
 in the form of arsenious acid. 
 
 409. By the treatment described, the metal arsenic may be 
 reduced from solutions of the following of its compounds :— 
 arsenious acid, arsenite of potass, hme, &c., arsenic acid, 
 arseniate of potash, lime, &c., chloride and artificial sulphu- 
 ret of arsenic. Some compounds of arsenic, the native sul- 
 phuret, for example, are little affected by hydro -chloric 
 (muriatic) acid ; in such cases, it is only necessary to heat 
 them with nitric acid, previous to the addition of the hydro- 
 chloric acid. The nitric acid should be used sparingly, and 
 any excess expelled by heat, previously to the application of 
 the hydro-chloric acid, as in case any free nitric acid be 
 present, the precipitated metal will be re-dissolved imme- 
 diately on the removal of the zinc. 
 
 410. MetalUc arsenic thus reduced, may be obtained in 
 the form of arsenious acid, by heating the platinum foil on 
 which it is reduced, in a tube loosely closed at the end. On 
 applying the flame of a spirit lamp, the metal is volatilised, 
 and condensed on a cool part of the tube as arsenious acid. 
 
 411. The following experiment, by Mr. Davy, illustrates 
 the extreme delicacy of this method of detecting arsenic. 
 " I placed," says Mr. Davy, " on a new slip of platinum, 
 weighing 22.14 grains, five drops of an aqueous solution 
 
179 
 
 of arsenious acid, and three drops of muriatic acid; a slip of 
 zinc being applied, the arsenic was soon reduced, and much 
 of it adhered to the platina, which, after being washed in 
 pure water and dried, acquired an increase of ^^th part of a 
 grain. The platina was put into a small retort, which was 
 then exhausted, twice filled with pure carbonic acid gas, and 
 heated over ajar of the same gas, untifall the arsenic rose 
 and condensed in the upper part of the bulb of the retort as 
 an extremely delicate whiteish film, exhibiting no metallic 
 lustre, even by the aid of a magnifying glass ; nor could this 
 be expected from the minute quantity of arsenic present, and 
 the extent of surface over which it was spread by subli- 
 mation. The platina was found perfectly clear, and of pre- 
 cisely the same weight as at first. Some pure water was put 
 into the retort, and occasionally agitated in contact with the 
 sublimate, but after thirty hours, a recent solution of sul- 
 phuretted hydrogen occasioned no change in the water. The 
 actual quantity of arsenic attached to the platina in the fore- 
 going experiment was ascertained to be ^soth part of a grain. 
 But this is very far from conveying a just idea of the degree 
 to which this mode of detection may be carried, for a single 
 drop of the aqueous arsenious acid would have afforded 
 ample evidence of the arsenic, as it respected colour, inso- 
 lubility in muriatic and sulphuric acids, alliacious odour, 
 and volatility, which would give asWth part of a grain. 
 Even this very minute quantity gives us by no means the 
 extreme limits to which this truly microscopic method of 
 detecting metals may be carried." 
 
 412. A very elegant plan of experimenting on the electrical 
 reduction of arsenic, is to introduce the solution containing 
 it into a platinum crucible, with an equal volume of muriatic 
 acid; on touching the crucible and solution with zinc, the whole 
 of the metal is reduced. The crucible should now be washed 
 with pure water and dried ; by placing a piece of plate glass on 
 the top, and applying a spirit lamp to the bottom of the cru- 
 
 N 2 
 
180 
 
 cible, the whole of the metal is volatilized, and condenses on 
 the plate glass as arsenious acid. The deposition of the 
 metal may be observed more readily by using a platinum 
 crucible, gilded in the interior. The film of reduced metal 
 often assumes the most variegated colours. 
 
 413. The compounds of mercury may be readily reduced 
 by placing them on a slip of platinum, and adding a little 
 dilute nitric, or hydro-chloric (muriatic) acid. On bringing 
 the zinc in contact, the liquid metal is immediately reduced, 
 and amalgamates both with the platinum and zinc. In this 
 way mercury may be reduced from its oxides, chlorides, 
 acetate, sulphate, cyanide, &c. ; and the addition of acids 
 may, in general, be dispensed with in experimenting on those 
 compounds which are soluble in water. 
 
 414. The soluble compounds of lead may be reduced by 
 treating their aqueous solutions by platinum and zinc ; and 
 the insoluble compounds by mixture with dilute nitric or 
 hydro-chloric acid. The compounds of copper may all be 
 reduced by similar treatment. 
 
 415. This reduction of metals by electric agency, is more 
 valuable, as a means of analysis, from the circumstances that 
 it is not at all affected by the presence of organic matter ; 
 and hence it is a valuable means of detecting the metals in 
 cases of poisoning. Thus, arsenious acid mixed'with tea, 
 coffee, sugar, rice, milk, starch, potatoes, gruel, egg, isinglass, 
 bile, saliva, butter, lard, oils, &c., may almost immediately be 
 precipitated by zinc and platinum ; in case of oily and fatty 
 bodies, the mixture should be first boiled in an alkaline 
 solution, and excess of muriatic acid added. These remarks 
 apply to the metals generally. 
 
 416. Among the many subjects which have engaged the 
 attention of electro-metallurgists, the reduction of alloys is 
 one of the most prominent. From time to time it has been 
 announced that the object had been effected, but investigation 
 has, in every instance, demonstrated that the experiments 
 
181 
 
 were fallacious. In the present state of electro-metallurgy 
 there is reason to believe the reduction of alloys imprac- 
 ticable. There can be little doubt that, by directing a current 
 through a solution containing salts of different metals, these 
 different salts will be reduced, provided the quantities of the 
 different salts, their relative conducting powers, and the 
 intensity and quantity of the current be in the proper 
 relation. But these conditions are not easily realised ; there 
 are no two salts of the same, or of different metals, requiring 
 precisely the same electrical intensity for their decomposition, 
 and hence, in a mixed solution, the current will be carried 
 by the salt most readily decomposed, while the other will be 
 unaffected. Supposing the current to be of such quantity 
 and intensity as to be disproportionate to the salt of most 
 easy decomposition, part of it will be conducted by the other 
 salt, and both the metals will be deposited at the same time ; 
 but when there is much difference of conducting power, the 
 current will be wholly conducted by the best conductor, and 
 will reduce it in large quantity, or even in the state of black 
 powder, rather than pass through the less perfect conductor. 
 
 417. It appears, then, that it is only by obtaining a solu- 
 tion in which the different salts are in precisely the proper 
 ratio, by exposing such extent of surface at the electrodes 
 that the current cannot be conducted by one of the salts, by 
 using a positive electrode in which the metals are combined, — 
 not in the ratio they are intended to have in reduced alloy, — 
 but in such ratio that the same quantities will be taken into 
 solution as are reduced, a ratio having reference to the sus- 
 ceptibility of their oxidation,— it is only by securing these 
 conditions, combined with the use of salts having very nearly 
 the same conducting power, (the last condition itself scarcely 
 possible,) that the reduction of alloys can be even hoped for. 
 It is not denied that it may be effected with some metals, in 
 particular proportions; but the voltaic reduction of alloys of all 
 the metals capable of alloying under the usual treatment, and 
 
182 
 
 that in any desired proportion, is not only at present 
 impracticable, but there is strong reason to fear will ever 
 remain so. 
 
 418. It yet remains to be shown, that in those cases where 
 two metals are reduced at one time from a mixed solution, a 
 true alloy is formed ; it does not necessarily follow that such 
 is the case ; on the contrary, all experience goes to disprove 
 it. It has already been many times remarked, that one of the 
 greatest difficulties the electro-metallurgist has had to con- 
 tend with, is the want of adhesion of a reduced metallic film 
 to the metallic body on which it was deposited ; and even 
 when the utmost care has been taken to clean the surface 
 under experiment, so as to expose a pure metallic surface for 
 the reception of the reduced metal, there is frequently no 
 adhesion ; and when there is, the application of an acid solu- 
 tion separates them, and demonstrates that, although there 
 was the most intimate contact, there was no alloy. It is to 
 be feared that a similar defect would present itself in the 
 deposited mixture of metals : they may be in precisely the 
 proper proportions, they may be most intimately mixed, but 
 may yet not be alloyed ; and it is difficult to suppose that 
 anything short of that liquidity which heat alone can give, 
 will allow of that intimate union between the metals necessary 
 to constitute a true alloy. 
 
 419. Whether or not all the difficulties which present 
 themselves in attempting to precipitate alloys will be eventu- 
 ally overcome, is a question which time alone can determine. 
 It has, certainly, never yet been satisfactorily effected, and 
 as far as our present knowledge extends, there is but a 
 remote hope that it will be. It is, perhaps, fortunate that 
 there would be little value in the accomplishment of this 
 object, for however interesting it may be for science, the art 
 of electro-metallurgy has little need of it. 
 
183 
 
 CHAP. XIV. 
 
 ON THE COLOURING OF METALLIC SURFACES. 
 
 420. The films of gold and silver reduced on articles by 
 the processes described in previous chapters, do not possess 
 the colour necessary for commercial purposes. The gold is 
 frequently of a dull colour, and the surface of the silver does 
 not possess the brilliant whiteness, which, by an after pro- 
 cess, may be communicated to it. The practice of colouring 
 metallic surfaces has been long established, with regard to 
 metals reduced by the ordinary processes, and the electro- 
 metallurgist finds it necessary to treat articles in a similar 
 manner, in order to meet the taste thus created. Although 
 the colouring of the surfaces of metals is wholly unconnected 
 with electro-metallurgy, the workers in this art are compelled 
 to practise it, and it is hence deemed an essential part of 
 their business. On this account, a brief description of the 
 most successful processes is introduced in this treatise. 
 
 421. In order to give surfaces of gold the rich orange tint 
 which they are generally seen to possess in their manufac- 
 tured state, they should be treated as follows : — A mixture is 
 made of five parts nitrate of potassa (saltpetre), two parts 
 sulphate of alumina (common alum,) one part sulphate of 
 zinc (white vitriol), and one part sulphate of iron (green cop- 
 peras) ; these ingredients are mixed with water and gently 
 boiled, until the mixture has about the consistency of cream. 
 The articles are to be dipped in the semi-fluid composition 
 two or three times, and allowed to become almost drv ; thev 
 
184 
 
 are then heated in a stove, or on a hot plate of metal. The 
 time during which they are exposed to heat, varies with the 
 intensity of the heat and the colour desired to be given to 
 the articles ; the longer they are heated, the darker the colour 
 will be. The articles are finally immersed in water, to remove 
 the coating ; they should here be well washed and rubbed 
 with a brush. 
 
 422. A mixture produced by adding together acetate of 
 copper (verdigris), sulphate of alumina (common alum), and 
 bees' wax is sometimes used to colour gold red. The articles 
 are coated with the mixture, and exposed to heat until it is 
 burnt off. It is not so much used as the former. 
 
 423. Silvered articles may be coloured by various processes; 
 the simplest and most effectual is that of M. Mouray. The 
 articles are dipped in a saturated solution of bi-borate of soda 
 (borax), and allowed to dry ; a film of the salt is left on the sur- 
 face after the evaporation of the water. They are immersed a 
 second or third time, until a complete film of borax covers 
 every part of the article ; when large articles are experimented 
 on, the solution may be applied by means of a brush. The 
 articles thus treated must be exposed to heat, until the borax 
 is perfectly fused ; for this purpose, a heat nearly approaching 
 to redness is required. After cooling, they should be im- 
 mersed in dilute sulphuric acid, by which the borax is 
 removed ; they should be finally dried, by being shaken in 
 heated sawdust, and warmed, in order more effectually to drive 
 off all moisture. This process possesses the admirable pro- 
 perty of preventing the rapid tarnishing of the plated articles. 
 It was observed by those who first practised electro-plating, 
 that the silver reduced from its salts by electrical agency, tar- 
 nished more rapidly than that manufactured in the ordinary 
 way. This was ascribed to the purity of the silver, which 
 was supposed to be favourable to its combination with the 
 sulphurous and other vapours, by which it became tarnished. 
 By M. Mouray's process, however, the tarnishing of the vol- 
 
185 
 
 taic silver is prevented ; and it is now scarcely, if at all, more 
 readily tarnished, than that reduced in the common way. It 
 appears that the discolouration was not produced by any 
 external action, but that there remained in the pores of the 
 reduced metal a small quantity of undecomposed salt, which 
 suffers slow decomposition, and thus injures the colour of 
 their surface. The treatment with borax completely removes 
 this saline matter, and renders the metal unalterable from any 
 internal action. 
 
 424. The communication of a bronze colour to copper, may 
 be effected in a variety of ways. The simplest method of 
 bronzing a production of the electrotype, is to rub it with dry 
 plumbago or black lead immediately, or within a few minutes 
 after its removal from the apparatus, and, after heating it till 
 it becomes too hot to touch, rubbing it briskly with a hard 
 brush (a tooth brush answers well for small objects) until 
 cold. On afterwards removing the superfluous black lead by 
 a linen rag, the bronze colour will be observed. The black 
 lead should be applied with a brush, and care should be taken 
 to avoid wetting any part of the surface during its application, 
 as stains would be thereby occasioned. On rubbing the sur- 
 face after heating, it frequently exhibits too dark a colour ; 
 this may in general be removed by vigorous rubbing, and 
 slightly moistening the rag or brush used. If the copper has 
 been exposed some hours to the air after removal from the 
 solution, it cannot be treated in this way, until it has been 
 previously cleaned by immersion in a dilute acid. The action 
 of the black lead in producing this effect is not understood. 
 
 425. A very beautiful bronze colour, somewhat lighter than 
 that produced by black lead, may be given by covering the 
 surface with oxide of iron and heating it in a muffle. On 
 removing the oxide of iron, the surface of the copper is found 
 to have a very rich colour. 
 
 426. The application of hydrosulphate of ammonia to 
 
186 
 
 copper produces a sulphuret of that metal, which is of a 
 beautiful colour. 
 
 427. A dilute solution of chloride of platinum, on being 
 applied to brass and copper, stains them of a very beautiful 
 colour, by the deposition of a minute portion of platinum in 
 an extremely divided state ; it is wholly unlike the bronze 
 produced by age, but exceedingly beautiful. Objects thus 
 bronzed should be handled very carefully, for it is easily 
 rubbed off. 
 
 428. In addition to these methods of colouring metallic 
 surfaces, and which have come into common use, several other 
 methods of effecting the same object have been more recently 
 proposed by Mr. Talbot. It has often been remarked that gild- 
 ing upon silver has a much finer colour than gilding upon 
 an inferior metal. Mr. Talbot proposes to silver the surfaces of 
 articles to be gilt, previous to gilding. This may be effected 
 by immersing them in a solution of hypo-sulphite (189) or 
 cyanide (185) of silver. 
 
 429. Boracic acid has also been proposed by Mr. Talbot 
 for the purpose of colouring gilded articles. The acid is 
 added to the solution of chloride, or other salt of gold, pre- 
 vious to the precipitation of the metal, and the colour of the 
 gold reduced from the mixed solution, is finer than that 
 obtained from the simple salt. 
 
 430. The processes already given have for their object, 
 either the production of the colour proper to the metal under 
 experiment, by the removal of the causes which interfere with 
 its developement, or the heightening or modifying of this 
 colour to suit public taste. There is, however, a process 
 strictly electrical, which, although at present unapplied, is 
 capable of producing colours of surpassing brilliancy. There 
 can be little doubt that the fine effects which, under proper 
 management, it is capable of producing, will, eventually, 
 cause it to be extensively employed for ornamenting metallic 
 
187 
 
 articles. The process alluded to is that by which electro- or 
 metallo-chromes are produced. 
 
 431. It was first observed by M. Nobili,* that the plates 
 or electrodes used for transmitting a voltaic current through 
 a metallic solution, became very beautifully coloured, under 
 certain circumstances. If the current from a battery of four 
 or five pairs be transmitted through a metallic solution, by 
 means of a platinum wire, just immersed vertically in the 
 solution, and a plate of polished metal lying horizontally, a 
 very short distance below the surface of the liquid, the plate 
 will be found, after a few seconds, to be coloured with a 
 series of concentric rings, the centre of which is opposite to 
 the point of the platinum wire. The effects may be varied 
 in a variety of ways : the nature of the metallic solution, the 
 metals composing the electrodes, the distance of the electrodes 
 from each other, the end of the battery to which the plate is 
 attached, are all circumstances which materially affect the 
 results. The phenomenon may be presented at either pole ; 
 that is to say, the plate of metal on which these concentric 
 rings are formed, may either be connected with the zinc or 
 silver end of the battery ; in either case they are formed, 
 providing the other electrode exposes a small surface. The 
 series of rings formed at the different ends of the battery 
 are, however, essentially different. The colours obtained, 
 are, for the most part, more brilliant when the plate of metal 
 is connected with the copper or silver end of the battery. 
 By using a steel plate in connection with the battery, and a 
 solution of acetate of lead, a series of coloured rings is pro- 
 duced, which rival, in brilliancy, the Newtonian rings. In 
 order to produce these colours in the greatest perfection, the 
 steel plate, highly polished, should be placed on the bottom 
 of a shallow vessel, a solution of acetate of lead should be 
 poured into the vessel until it completely covers the surface 
 
 ♦ Annal. de Ch. et de Fbys,, t. xcir.) p. 280. 
 
188 
 
 of the steel plate, a wire from the silver or copper end of 
 the battery, must be brought against the edge of the plate, 
 and a disc of copper, connected with the other extremity of 
 the battery, placed on the surface of the liquid, over the mid- 
 dle of the steel plate ; after a few seconds, the coloured rings will 
 be observed. If devices be cut out of paper and laid on the 
 steel plate, the colours will be limited to the space undefended 
 by the paper ; and a design will thus be produced of the form 
 cut in the paper, and tinted with the richest colours. 
 
189 
 
 CHAP. XV. 
 
 ON THE VALUE AND PROBABLE RESULTS OF 
 ELECTRO-METALLURGY. 
 
 432. Few arts have progressed so rapidly as that to the 
 consideration of which these pages are devoted. A very few 
 years have elapsed since curiosity was awakened, by the 
 announcement of the first rude experiments, made for the pur- 
 pose of usefully applying the voltaic precipitation of metals ; 
 and with such rapidity discoveries have followed each other, 
 that we now possess an art so perfect, that we can scarcely 
 imagine anything more to be desired. What changes have 
 already been wrought in the metallic manufactures— what 
 unhoped-for facilities in the multiplication of works of art ! 
 
 433. In this, as in every other improvement, there are diffi- 
 culties to be encountered, which experience alone can overcome 
 — prejudices to be met, which time only can eradicate ; but 
 there are no difficulties which may not be surmounted — no 
 prejudices which will not eventually yield. The blunders of 
 the ignorant, and the failures of the inexperienced, have done 
 much to retard the application of the art ; and those who 
 have imagined it their interest to oppose its progress, or affect 
 indifference to its claims, have not failed to avail themselves 
 of the opportunity thus presented : defects have been pointed 
 out, while advantages have been overlooked ; success has 
 been hailed with but feeble praise, and failure visited with 
 unmerited censure. 
 
 434. Of the value of the art there is much difference of 
 
190 
 
 opinion ; and where commercial interests are so opposed as 
 they necessarily must be, in the advance of that which not only 
 opens new branches of manufacture, but threatens to super- 
 sede others, it is not surprising that some should be slow to 
 acknowledge real merit, and others loud in defending that, 
 which the candid confess to be imperfect. It is, perhaps, to 
 be regretted that the art was made subservient to manufac- 
 turing purposes, before all its details had been sufficiently 
 investigated ; but it is, on the other hand doubtful, if without 
 such application, there would have been sufficient inducement 
 to carry out the necessary experiments ; nay, it is certain that 
 many discoveries, by which the art has been improved, would 
 never have been made, but through operations on a large 
 scale. 
 
 435. The early practice of the art was principally confined 
 to the multiplication of engraved copper-plates, medals, and 
 coins, and the eagerness with which the novel process was 
 practised, occasioned much mischief; valuable plates were 
 entombed in masses of metalj from which they can never be 
 disengaged, and the most valuable relics of antiquity have 
 been disfigured by the rude attempts of the inexperienced. 
 And even when success seemed fully attained, disappointment 
 frequently followed; the copy of the engraved plate was 
 sometimes so soft as to be wholly unfit for use, and the model 
 of the coin so brittle that it broke under the most careful 
 treatment. But these defects have their origin in the 
 operator, not in the process ; and the most uniform results, 
 can with certainty be obtained, by the exercise of an amount 
 of skill not greater than that, required to conduct the most 
 ordinary manufacturing process. Until the other arts have 
 obtained a perfection which renders failure impossible, the 
 reproach of uncertainty, which the imperfect productions of 
 the ignorant have brought on electro-metallurgy, is an unjust 
 one. 
 
 436. The strongest prejudice with which the art has had 
 
191 
 
 to contend, is that directed against electro-plating and gilding. 
 The electro-metallurgist is constantly taunted with the want 
 of adhesion between the deposited film and the metal to which 
 it is attached. It is, unfortunately, true that many of the early 
 specimens of this branch of the art were very defective. On the 
 application of heat, the metallic film frequently rose in 
 blisters, and a cut or scratch, which perforated the deposited 
 metal, was commonly the signal for the detaching of the 
 whole coating. This was not merely an acknowledged 
 imperfection, but a defect M'hich threatened to destroy the 
 otherwise great value of the art. But investigation has fur- 
 nished a key to the solution of the difficulty ; and, by the 
 treatment described in the foregoing pages, an adhesion may 
 be effected with perfect certainty, which time has shown to 
 be more than sufficient for all purposes. The adhesion may 
 not be equal to that of ordinary plating, where the two metals 
 are fused together, but experience has shown it to be abun- 
 dantly sufficient. The art is, therefore, no longer chargeable 
 with this imperfection ; and the representations which are 
 even now made respecting the inefficiency of the process, do 
 not arise in a desire to remove an existing defect, but in an 
 endeavour to perpetuate a vulgar prejudice. 
 
 437. We cannot better form an estimate of the probable 
 results of the art, than by reviewing what it has already 
 accomplished. It has furnished us with processes by which 
 the most elaborate works may be copied in metal, with an 
 accuracy and certainty to which no previous processes have 
 any pretension; and it is applicable, in many instances, where 
 every other is ineffectual. The metals with which its ope- 
 rations are most favourably carried on, are those whose work- 
 ing, under such circumstances, would be impossible in any 
 other way. In what way could we obtain impressions in 
 copper, silver, and gold, of the various objects to which the 
 electrical precipitation of metals is applicable, from copper- 
 plates, coins, medals — the endless variety of objects from 
 
192 
 
 inanimate, as well as animated natm-e — fruits, which, in a few 
 hours, shrink from their original form — flowers, which droop 
 and wither in a few minutes, and whose delicate structure 
 can bear no ruder treatment ? In what way can we multiply 
 the productions of Daguerre's inimitable process ? — pictures 
 which are destroyed or injured by the gentlest touch of the 
 finger, but which may be faithfully copied, in all their beauty 
 and detail, by electro-metallurgy, and that, too, without injury 
 to the original. 
 
 438. But the most admirable application of the art is in 
 the processes of gilding and silvering. The process of 
 electro-plating offers extraordinary facilities in the pro- 
 duction of superior designs. In the ordinary method of 
 plating it is usual to construct a plated article as far as 
 possible from plated sheet metal, while the edges and orna- 
 mental parts generally are completed, by soldering thereto 
 parts, either stamped in plated metal, or in silver. By such a 
 method of manufacture the designs must necessarily be limited, 
 being confined to such ornamental forms as could be produced 
 by stamping or otherwise fashioning sheets of metal. In the 
 process of electro-plating no such restriction is imposed ; the 
 artist produces a design without being fettered with any diffi- 
 culties of manufacture, knowing that any form is equally 
 capable of receiving a coating of silver by the voltaic pro- 
 cess. To what an extent have manufacturers already availed 
 themselves of this great advantage ; and what an improved 
 taste must such superior designs create ! We already see the 
 most elegant shapes and the most elaborate workmanship 
 bestowed upon articles which, in the old method of manufac- 
 ture, could only assume one series of monotonous forms. The 
 plain surfaces of many plated wares, have now become 
 shapes of classic elegance, and the feebly chased ornament, 
 has given way to the boldest design. No manufacture, in 
 the whole course of its history, presents greater contrasts than 
 that presented within two or three years in the manufacture 
 
193 
 
 of plated wares. The artistic skill which is now exercised in 
 the production of designs, knows no limit but that of a refined 
 taste ; and its productions seem to acquire new beauties by 
 contrast with the frigid, unmeaning forms, to which, in many 
 instances, it was previously limited. 
 
 439. Although, in the production of gilded articles, the 
 voltaic process cannot be said to have achieved so much for 
 art, it has taken part in the production of a change incom- 
 parably more important. The pernicious process of gilding 
 by an amalgam of mercury and gold, had, to some extent, 
 been superseded by the introduction of other processes ; but 
 there was none possessing all its advantages, until the voltaic 
 reduction of gold was introduced. The object is at length 
 attained, — the voltaic precipitation of gold can be effected 
 with far greater economy than the mercurial process, and it is 
 applicable in many instances where the latter fails. It 
 is much to have introduced a process superior to any pre- 
 viously known, but it is much more to have banished an art 
 whose practice is inseparable from human suffering. 
 
 0 
 
INDEX. 
 
 *»* The numbenrefer to the paragraphs, not the pages. 
 
 Acetate of silver, 191 
 
 zinc, 206 
 
 Action of acid battery, 99 
 Daniell's and Grove's bat- 
 teries, 98 
 
 Daniell's battery, 92 
 
 Action, direct, of the voltaic current, 72 
 
 local, in voltaic batteries, 81 
 
 secondary, of the voltaic cur- 
 rent, 72 
 Adhesion of deposite, 227 
 
 eflfected, 230 
 
 by dipping, 
 
 230 
 
 mercury, 
 
 236 
 
 scratch- 
 ing, 231 
 
 prevented, 228 
 
 r-V by in- 
 terposition of a dissimilar metaJ, 229 
 
 by Mr. 
 
 Spencer's plan, 229 
 
 promoted by an 
 
 intense current, 334 
 
 Advantages and disadvantages of Da- 
 niell's battery, 94 
 
 Grove's 
 
 battery, 
 
 of battery apparatus, 275 
 
 voltaic etching, 379 
 
 Affinity, chemical, defined, 33 
 different from the other 
 
 affinities, 33 
 Alloys, reduction of, 416 
 Amalgamated zinc, 84 
 
 ^ properties of, 83 
 
 Amalgamation, adhesion promoted by, 
 
 236 
 
 Anode, defined, 60 
 
 Analysis, (chemical) application of elec- 
 tro-metallurgy to, 406 
 Apparatus, battery, 263 
 , advantages of, 275 I 
 
 Apparatus, electro -metallurgical, various 
 forms of, 262 
 
 , Mr. Spencer's, for making 
 
 copper-plates, 265 
 
 , Mr. Mason's, 268 
 
 , single-cell, circumstances to 
 
 be attended to in using it, 278 
 
 Application of electro-metallurgy to che- 
 mical analysis, 406 
 
 copy- 
 ing Daguerreotype pictures. 
 
 Applications, various, of electro-metal- 
 lurgy, 385 
 
 Arsenic, compounds of, detected, 409 
 
 Arsenious acid, detection of, by electro- 
 metallurgy, 408 
 
 Art, production of works of, 336 
 
 Atom, definition of, 36 
 
 Atoms, their arrangement in a salt, 40 
 
 relative weights, 36 
 
 Battery apparatus, 264 
 
 , advantages of, 275 
 
 , Babbington's,79 
 
 , Bunsen's, 103 
 
 commonlyused for electro-metal- 
 lurgical purposes, 85, 109 
 
 , compound, illustrated, 64 
 
 ,its action explained, 
 
 65 
 
 , cleaning of surfaces by, 232 
 
 , Cruickshank's, 79 
 
 , Daniell's, 2,91 
 
 , action of, 92 
 
 , advantages and disad- 
 vantages of, 94 
 
 , intensity of, 94 
 
 , suppression of hydro- 
 gen in, 93 
 
 , De la Rive's, 104 
 
 , directions for preparing, 110 
 
 , formation of salts by, 209 
 
 , Grove's, 95 
 
 ■ , its intensitv, 95 
 
 , Kemp's, 80, 86 
 
196 
 
 Battery, Kemp's, best form of, 88 
 
 , superiority of, 87 
 
 , Moleyn's, 101 
 
 , quantity of zinc consumed in, 
 
 116 
 
 , removal of hydrogen in, 107 
 
 , Sniee's, 106 
 
 , thermo-electric, 158 
 
 , inapplicable to 
 
 electro- metallurgy, 161 
 
 , nature of, 159 
 
 , not analagous 
 
 to the voltaic, 160 
 
 , use of wire gauze in, 107 
 
 , WoUaston's, 80 
 
 Bessemer, Mr., deposition of metals by ,26 
 
 Binary compounds only suffer voltaic 
 decomposition, 73 
 
 Bi chloride of platinum, 199 
 
 Bi-sulphuret of carbon, mode of pre- 
 paring, 217, 218 
 
 , properties of, 
 
 219 
 
 , solution of 
 
 phosphorus in, 217 
 Black lead, bronzing by, 424 
 
 , selection of, 225 
 
 , spreading of copper on, 350, 
 
 351 
 
 ,treatmentof surfaces with, 224 
 
 Black powder, deposition of metals as, 
 296 
 
 accompanied with hydrogen, 312 
 Boracic acid, used for colouring gold, 429 
 Bromide of gold, 169, 171 
 
 platinum, 200 
 
 . silver, 192 
 
 Bromine, 169 
 
 Bronzing copper, 424, 425, 426, 427 
 Calorific effect of the voltaic current, 55 
 Carbon, bi-sulphuret of, dissolves phos- 
 phorus, 221 
 
 , preparation of, 
 
 217, 218 
 
 . , properties of, 
 
 219 
 
 Casts or moulds of works of art, 247, 
 
 248, 249 
 Cathode defined, 68 
 
 Cause of the intensity of Grove's and 
 
 Daniell's batteries, 97 
 Character of deposite, circumstances 
 
 affecting, 295 
 , how changed, 
 
 313 
 
 -, table illustra- 
 ting, 320 
 
 Charging batterv, precautions to be taken 
 in, 114 
 
 Chemical affinity, definition of, 33 
 
 , different from the 
 
 other affinities, 33 
 
 Chemistry, a knowledge of, essential to 
 the electro-metallurgist, 30 
 
 Chloride of gold, 167, 168 
 
 iron, 208 
 
 — platinum and sodium, 202 
 
 tin, 208 
 
 silver, 192 
 
 zinc, 204 
 
 Circumstances which influence the cha- 
 racter of the deposite, 295, 298 
 
 Claims of Mr. Spencer and Mr, Jordan, 
 24 
 
 Cleaning surfaces by alkalies, 231 
 
 battery, 231 
 
 dipping, 230 
 
 scratching, 230 
 
 Colouring copper, 424, 425, 426,427 
 
 gold, 421,422 
 
 metallic surfaces, 420 
 
 silver, 422 
 
 Combination of batteries, 119 
 Combining proportions, table of, 32 
 Compound battery sometimes neces- 
 sary, 1 1 8 
 Compounds of arsenic detected, 409 
 
 ■ lead detected, 414 
 
 mercury detected, 413 
 
 Composition for moulds, 221 
 Conductors, metals and carbon the only, 
 213 
 
 only receive deposites, 212, 
 
 213 
 
 Conducting power, how communicated 
 to non-conductors, 213 
 
 by plumbago, 224 
 
 by solution of phosphorus, 215 
 
 Mr. Spencer's plan, 21 4 
 
 Contact, metallic, necessary in electro- 
 metallurgical operations, 290 
 
 Continuous laver, deposition of metals 
 as, 196 
 
 Conducting power of salts of same metal, 
 303 
 
 solution used, af- 
 fected by quantity of salt, 309 
 
 , effect 
 
 of, 305 
 
 wire of a voltaic pair, mag- 
 netic power of, 55 
 
 Constitution of bodies susceptible of vol- 
 taic decomposition, 73 
 
 material bodies, 31 
 
 salts, 38, 39 
 
 1 Copper, colouring, 424 
 
197 
 
 Copper, cyanide of, 196 
 
 , deposite of, on iron, 355 
 
 deposited in Daniell's battery, 1 1 
 
 , nitrate of, 194 
 
 , oxide of, 197 
 
 -plates, Spencer's apparatus for 
 
 copying, 265 
 
 , copying of, 360 
 
 , making, 361 
 
 , quantity deposited, compared 
 
 with zinc consumed, 356 
 
 , reduction of, 345 
 
 , salts from which it may be de- 
 posited, 43 
 
 , spreading of on black-leaded 
 
 surface, 350, 351, 352 
 
 , sulphate of, 193 
 
 , its theoretical con- 
 stitution, 41 
 
 , sulphite of, 195 
 
 Copying copper- plates, 360 
 
 Couronne des tasses, Volta's, 78 
 
 Cruickshank's battery, 79 
 
 experiments, 5 
 
 Crystals, metallic deposition of, 316 
 
 , how procured, 316 
 
 Current, as large in quantity in single as 
 in compound battery, 59 
 
 , effect of too great quantity in, 
 
 , electric, developed by magnetism, 
 
 in a coil, 128 
 
 in a wire, 1 27 
 
 J of a magnetic machine, 
 
 regulation of, 148, 149 
 
 uniformity of, 153 
 
 , thermo-electric, intensity of, 157 
 
 Cyanide of copper, 196 
 
 gold, 174 
 
 potassium, 175, 176 
 
 , Liebig's process 
 
 for preparing, 177 
 silver 
 
 Daguerreotype pictures, etching of, 380 
 
 , fixing of, 397, 
 
 398 
 
 — , gilding of, 405 
 
 , nature of, 381 
 
 Dancer, Mr., experiments of, 26 
 Daniell's battery, 91 
 
 , action of, 92 
 
 ■ , intensity of, 94 
 
 suppression of hydro- 
 gen in, 93 
 Davy, Mr. E., experiments on gilding, 
 
 silvering. Sec, 8, 9 
 Decomposing cell, effects in, 272 
 Decomposition, illustration of, 60 
 
 Decomposition, laws of voltaic, 70 
 , may be primary or se- 
 condary, 74 
 
 , means of transference, 46 
 
 , not produced by attrac- 
 tion, 68 
 
 of a chemical compound, 
 
 55 
 
 Defending parts of surfaces, 257 
 
 Definite proportions, illustration of the 
 law of, 35 
 
 De la Rive's remarks on deposition of 
 copper, 12 
 
 Deposite, adhesion of, 227 
 
 can only be formed on con- 
 ductors, 212, 213 
 
 , circumstances which influence 
 
 the character of, 295 
 
 , cause of grooves on, 262 
 
 , table illustrating character of, 
 
 320 
 
 Deposition on irregular surfaces, 286 
 
 of copper, 345 
 
 gold, 330 
 
 metallic films on fruits and 
 
 flowers, 387 
 
 metals as black powder, 296 
 
 continuous layers, 
 
 296 
 
 crystals, 296 
 
 platinum, 343 
 
 silver, 340 
 
 zinc, 357 
 
 Designs, superior, consequent on electro- 
 metallurgy, 437, 438 
 Difficulty of reducing alloys, 417 
 Dipping, cleaning of surfaces by, 230 
 
 liquor, composition of, 231 
 
 Dirck's, Mr., remarks on Mr. Spencer's 
 
 claims, 23 
 Direct action of voltaic current, 72 
 Directions for charging acid battery, 110 
 
 Daniell's battery, 
 
 110, 111 
 
 Distance between electrodes, effect of, 
 301 
 
 Ductile deposite, how produced, 314 
 Effect of temperature, 304 
 
 using strong acid in battery, 1 12 
 
 Electricity and magnetism identical, 126 
 
 developed by magnetism, 127, 
 
 128 
 
 excited by friction, 45 
 
 , its effects in passing through 
 
 decomposing cell, 272 
 
 , magneto-, 126 
 
 , means of exciting, 49 
 
 , methods of measuring, 120 
 
 f^roduced copiously by chemi- 
 cal action, 47 
 
198 
 
 Electricity produced by friction, &.c. defi- 
 cient in quantity, 47 
 
 , quantity regulated by inten- 
 sity, 113 
 
 , thernio-, 154, 155 
 
 , tbermo-, inapplicable to elec- 
 
 tro-raetallursy, 161 
 
 , transference of, by conduction, 
 
 46 
 
 decomposi- 
 tion, 46 
 
 , voltaic, 54, 55, 56 
 
 , theories respecting, 43 
 
 Fizeau's process for fixing Daguerreo- 
 type pictures, 397,398 
 Flowers, deposition of metals on, 387 
 Friction, excitement of electricity by, 45 
 Frictional electricity deficient in quan- 
 tity, 47 
 
 Fruits, deposition of metals on, 387 
 Fusible alloy, moulds of, 241, 242 
 Fusion in the voltaic circuit, 55 
 Galvani's discovery, 76 
 Galvanometer, 122 
 
 . . deflected with magnetic 
 
 electricity, 127 
 
 , Ritchie's, 123 
 
 Gauze (wire) proposed for use in voltaic 
 
 batteries, 107 
 Gilding small articles without battery, 
 
 277 
 
 , voltaic, metals to which it may 
 
 be applied, 339 
 
 , of Daguerreotype pic- 
 tures, 405 
 
 ^, practised by Mr. E.Davy, 
 
 8 
 
 . . Mr. Wool- 
 rich, 27 
 
 Glyphography, Palmer's, 366, 367 
 Go"ld, bromide of, 169 
 
 , chloride of, 167, 168 
 
 , colouring, 421, 422 
 
 by boracic acid, 429 
 
 , character of deposite, how affected, 
 
 335 
 
 , cyanide of, 174 
 
 deposited by Brugnatelli, 4 
 
 Mr. E. Davy, 9 
 
 — De la Rive, 165 
 
 Mr. Spencer, 165 
 
 Mr. Woolrich, 27 
 
 finely divided, 170 
 
 , hypo-sulphite of, 181 
 
 , iodide and bromide of, made by 
 
 the battery, 210 
 , oxide of, 172 
 
 , production of works of art in, 336 
 
 , quantity reduced in proportion to 
 
 zinc consumed, 338 
 
 Gold, reduction of, 330, 331, 332 
 
 , sulphite of, 178 
 
 ■ ; sulpho-cyanide of, 183 
 
 Grooves in deposite, cause of, 282 
 Grove's battery, 95 
 Hydrode, 68 
 
 Hydrogen accompanies the production of 
 
 ' metals as black powder, 312 
 appears, at the surface, con- 
 nected with zinc of battery, 48 
 
 evolved from impure zinc, 50 
 
 , value of its mechanical re- 
 moval in battery, 108 
 Hvpo-sulphite of gold, 181 
 
 — silver, 189 
 
 soda, 181, 182 
 
 Illustration of law of definite propor- 
 tions, 35 
 
 Mr. Mason's apparatus, 
 
 270 
 
 voltaic decomposition, 
 
 60 
 
 Impure zinc, action of in a battery, 81 
 
 Intense current promotes adhesion, 334 
 
 Intensity and quantity, 57, 58 
 
 of Daniell's and Grove's bat- 
 teries, cause of, 97 
 
 magneto-electric current af- 
 fected by length of coils, 139, 140 
 
 . thermo-electric current, 157 
 
 Iodide of gold, 172 
 
 platinum, 201 
 
 potassium, decomposition of, 58 
 
 silver, 192 
 
 zinc, 205 
 
 Iron, chloride of, 208 
 
 , per-chloride of, 251 
 
 — — , its use in electro- 
 metallurgy, 250 
 
 , per-oxide of, 252 
 
 , reduction of copper on, 355 
 
 , salts from which it may be reduced, 
 
 208 
 
 , sulphate of, 208 
 
 Irregular surfaces, deposition on, 285 
 Jacobi's galvanic engraving, 14 
 
 volta-plastics, 1 3 
 
 Jordan's claims in electro-metallurgy, 
 
 15, 16, 17, 18 
 Kemp's battery, 80, 86 
 
 , best form of, 88 
 
 ; superiority of, 87 
 
 Layers, deposition of metals as, 414 
 Lead, acetate of, 208 
 
 , compounds of detected, 414 
 
 , moulds of, 24 1 
 
 , nitrate of, 208 
 
 , salts from which it may be re- 
 duced, 208 
 , vessels of, 292 
 
199 
 
 Magnetism, deflection of galvanometer 
 by, 127 
 
 identical with electricity, 126 
 
 Magneto-electric machine compared with 
 voltaic battery, 151 
 
 , intensity of, 
 
 how affected, 139 
 , practical re- 
 marks relative to, 146, 147 
 
 -, quantity affec- 
 
 ted by rapidity of motion, 140 
 
 how affected, 140 
 
 of, 
 
 ofme- 
 
 tal deposited by, 144, 145 
 
 , regulation of 
 
 current from, 148, 149 
 
 , Saxton's, 
 
 -, uniformitv of 
 
 current from, 153 
 
 siting metals, 
 
 -, value in depo- 
 -, Woolrich's, 
 
 137, 138 
 
 Magneto-electricity, 126 
 
 ■ — — , spark and other elec- 
 trical indications from, 131 
 
 Mason's apparatus, 268, 269 
 
 — — , its action illustrated, 
 
 270 
 
 contributions to electro-metal- 
 lurgy, 29 
 Measuring voltaic electricity, 120 
 Mercury, adhesion effected by, 236 
 
 , compounds of detected, 413 
 
 Metal, quantity deposited in agiven time, 
 
 tables illustrative of, 325, 326, 327 
 Metallic surfaces, colouring of, 420 
 Metallo- chromes, Nobili's, 431 
 Metals and carbon the only conductors, 
 213 
 
 cleaned by battery, 232 
 
 • deposited as black powder, 296 
 
 continuous layers. 
 
 296 
 
 crystals, 296 
 
 , detection of, by electricity, 407 
 
 may be reduced from any of their 
 
 soluble salts, 162 
 
 , production of in ductilestate, 314 
 
 , quantity deposited by magneto- 
 electrical machine, 144, 145 
 
 , reduced by magneto-electricity, 
 
 135 
 
 which may be gilded by electri- 
 city, 339 
 
 - silvered by elec- 
 
 tricity, 342 
 
 which may be practically reduced 
 
 by electricity, 164 
 
 Methods of producing printing surfaces 
 
 by electrical agency, 359 
 Moleyn's battery, 101 
 Motion necessary to the production of 
 
 electricity from magnets, 129 
 Moulds containing phosphorus, 221 
 
 , elastic, 258 
 
 of works of art, 247 , 248, 249 
 
 , parts of, defended, 257 
 
 of plaster, preparation of, 256 
 
 , production of, 239 
 
 by electric preci- 
 
 pitation, 240 
 
 ■ in fusible alloy ,24 1 
 
 — ,lead, 241 
 
 — plaster of Paris, 
 
 wax, 244 
 
 Mouray's process for colouring silver, 423 
 Multiplication of Daguerreotype pictures, 
 395, 396 
 
 Natural history, deposition of metal on 
 specimens of, 389 
 
 Nicholson's experiments on metallic pre- 
 cipitations, 5 
 
 Nitrate of copper, 194 
 
 Nobili's electro-chromes, 431 
 
 Non-conductors, treatment of, 213 
 
 , Mr. Spen- 
 cer's plan, 214 
 
 •, with solu- 
 tion of phosphorus, 219 
 
 Opinions of philosophers respecting elec- 
 tricity, 43 
 
 Optical phenomenon observed in the elec- 
 trotype, 353 — note 
 Originators of electro-metallurgy, their 
 
 claims, 24 
 Oxide of copper, 197 
 
 gold, 173 
 
 silver, 186 
 
 zinc, 207 
 
 Oxode defined, 68 
 
 Pair of plates, decomposition with, 58 
 Palmer's electro-tint, 363, 364, 365 
 glyphography, 366, 367 
 
 Per-chloride of iron, how prepared, 251 
 ■, use of, in electro- 
 
 metallurgy, 250 
 Per-oxide of iron, preparation of, 252 
 Phosphorus, metallic films reduced on 
 non-conductors, by solution of, 215 
 
 , moulds containing, 221 
 
 ■, precautions necessary in 
 
 using solution of, 220 
 Pile, Volta's, 57 
 
 , voltaic, description of, 77 
 
 ■, decomposition with, 77 
 
 Plaster of Paris, moulds of, 246 
 _, J preparation of, 256 
 
200 
 
 Plaster of Paris, treatment of in taking 
 
 moulds, 245 
 Plates (copper), copying, 360 
 
 — — , making, 361 
 
 Platinode defined, 68 
 
 Platinum and sodium, chloride of, 212 
 
 , bi-chloride of, 199 
 
 Platinum, bromide of, 200 
 
 , iodide of, 201 
 
 , quantity reduced, compared 
 
 with zinc consumed, 344 
 
 , reduction of, 343 
 
 , salts from which it maybe 
 
 reduced, 198 
 Plating, electro-, 340 
 , metals to which it is 
 
 applicable, 342 
 Plumbago, treatment of surfaces with, 
 
 224 
 Poles, 67 
 
 Pole, negative, defined, 69 
 
 , positive, defined, 69 
 
 Position of surface receiving deposite, 
 importance of, 280 
 
 proper, 283 
 Positive pole, position of, 285 
 Potassium, cyanide of, 175, 176 
 — . , Liebig's process, 
 
 177 
 
 Potassa, sulphite of, 179 
 Powder, black, deposition of metals as, 
 296 
 
 Precautions to be taken in charging bat- 
 teries, 114 
 
 Precipitation of copper, noticed by Ni- 
 cholson, 5 
 
 metals, by Cruickshank, 
 
 6,7 
 
 , Davy, 9 
 
 Precipitating vat, 288 
 ; suspension of articles 
 
 in, 288 
 
 Prejudices against electro-plating,_436 
 Preparation of plaster of Paris, 256 
 
 — surfaces to receive depo- 
 
 sites, 212 
 
 Printing surfaces, production of by elec- 
 tro-metallurgy, 358 
 Production of black powder, 315 
 
 — crystalline deposite, 316 
 
 - ductile deposite, 313 
 
 Pure zinc, action of, in battery, 82 
 
 , substitute for, 83 
 
 Radicals, compound, assumed existence 
 of, 41 
 
 , definition of, 41— note 
 
 Reduction of alloys, 416 
 
 , difiiculty of, 417 
 
 • copper, 345 
 
 Reduction of copper, by battery process, 
 347 
 
 ■ single-cell pro- 
 cess, 346 
 
 gold, 330, 331, 332 
 
 , by De la Rive, 166 
 
 Mr. Spencer, 165 
 
 metals from their salts, 162 
 
 Regulation of magneto -electric current, 
 148, 149 
 
 voltaic current, 112 
 
 Remarks, introductory, 1 
 
 Removal of zinc from negative plate of 
 battery, 115 
 
 Ritchie's galvanometer, 1 23 
 
 Rive's, De la, battery, 104 
 
 , reduction of gold by, 165 
 
 Salts, arrangement of atoms in, 40 
 
 , constitution of illustrated, 38, 39 
 
 , different views respecting their con- 
 stitution, 40 
 
 from which copper may be reduced, 
 
 193 
 
 gold — 
 
 166 
 
 ■ iron 
 
 208 
 
 . lead 
 
 208 
 
 platinum ■ 
 
 198 
 
 — silver ■ 
 
 184 
 
 zinc 
 
 203 
 
 , important bearing of their consti- 
 tution on electro metallurgy, 42 
 
 of gold formed by battery, 210 
 
 same metal, different conducting 
 
 powers of, 303 
 
 silver formed by battery, 211 
 
 , production of by battery, 209 
 
 (soluble), reduction of metals from, 
 
 162 
 
 Saxton's magnetic electrical machine, 
 133 
 
 Scratching, surfaces cleaned by, 230 
 Secondary action of current, 72 
 Single-cell apparatus, 64 
 
 •, circumstances to 
 
 be attended to with, 278, 279 
 
 will not decompose water, 62 
 
 Silver, acetate of, 191 
 
 , bromide of, 192 
 
 , chloride of, 192 
 
 , colouring, 423 
 
 , cyanide of, 185 
 
 , hypo-sulphite of, 189 
 
 , iodide of, 192 
 
 , oxide of, 186 
 
201 
 
 Silver, quantity deposited compared with 
 
 zinc consumed, 341 
 , salts from whicli it may be re- 
 duced, 184 
 
 , sulphate of, 190 
 
 , sulphite of, 187, 188 
 
 Size of electrodes, importance of, 300 
 Smee, experiments of, 29 
 
 ''s battery, 106 
 
 Solids, cannot be decomposed, 70 
 Sources of electricity, 44 
 Soda, hypo-sulphite of, 181, 182 
 Solution, strength of, 302 
 Solutions, vessels to hold, 291 
 Sparks produced from magnetic electri- 
 city, 131 
 
 Spencer's apparatus for copying copper 
 
 plates, 265 
 — claim to the origin of electro 
 
 metallurgy, 19, 20,21, 22 
 
 ■, reduction of gold by, 165 
 
 Speculations respecting electricity, 43 
 Substitute for pure zinc in battery, 83 
 Sulphat-oxygen, supposed existence of, 
 
 41 
 
 Sulphate of copper, 193 
 ., — , theoretical constitu- 
 tion of, 41 
 
 iron, 208 
 
 silver, 190 
 
 tin, 208 
 
 zinc, 203 
 
 -, constitution of, 53 
 
 Sulphite of copper, 195 
 
 gold, 178 
 
 •- potassa, 179 
 
 silver, 187, 188 
 
 Sulpho-cyanide of gold, 183 
 Sulphuric acid, 180 
 
 , action of, on ordinary 
 
 zinc, 48 
 
 Sturgeon reduced metals by magnetic 
 
 electricity, 135 
 Strength of solution, 302 
 Surfaces cleaned by battery, 232 
 
 ■ (irregular), deposition on, 285 
 
 , preparation of, with black lead, 
 
 224 
 
 - for receiving de- 
 
 — with solution of 
 
 phosphorus, 219 
 
 -, position of, receiving deposite, 
 I 
 
 (printing), production of, by elec- 
 
 posite, 212 
 
 Table of elements and their equivalent 
 numbers, 32 
 
 illustrative of the formation of dif- 
 ferent deposites, 320 
 
 Tables illustrative of the influence of 
 temperature, 325, 326, 327 
 
 Talbot's process for colouring gold, 428, 
 429 
 
 Temperature, effect of, 304 
 
 tables illustra- 
 
 280 
 
 trical agency, 258 
 
 , proper position of, 283 
 
 -, vertical, effects of, 281,282 
 
 ting, 325, 326, 327 
 
 -, influence of on battery, 113 
 
 Theory of electrical reduction of metals, 
 42 
 
 electricity, 43 
 
 the constitution of salts, 4 1, 42 
 
 Thermo-electric battery, 158 
 
 current inapplicable to 
 
 electro- metallurgy, 1 6 1 
 
 intensity of, 157 
 
 Suspension of articles in precipitating 
 vat, 288 
 
 electricity, 154, 155 
 
 Time, relation of to the quantity of de- 
 posite, 325, 326, 327 
 Tin, chloride of, 208 
 , salts from which it may be re- 
 duced, 208 
 
 , sulphate of, 208 
 
 Transfer of electrodes, effect of, in de- 
 composing cell, 272 
 Treatment of non-conductors, 213 
 
 , Mr. Spen- 
 
 cer's plan, 214 
 Value of electro-metallurgy, 432 
 Vat, precipitating, 288 
 
 — , best construction of, 
 
 293 
 
 Vessels holding solutions, nature of, 291 
 , of wood, lead, 
 
 &c., 292 
 
 Volta-plastics of Jacobi, 13 
 Volta's pile or battery, nature of, 57 
 - described, 17 
 
 couronne des tasses, 78 
 
 Voltaic battery (compound), explained, 65 
 , illustrated. 
 
 64 
 
 29 
 
 ■ introduced by Mr. Mason, 
 decomposition, examination of 
 
 an instance of, 61 
 
 , illustration of, 60 
 -, laws of, 70 
 - not produced by 
 
 attraction, 68 
 
 etching, 373, 375, 376 
 
 -, advantages of, 379 
 
 pair, decomposition with, 58 
 
 Voltameter, 121 
 
 , precautions in estimating its 
 
 indications, 125 
 
202 
 
 Water not decomposed by a single cell, 
 62 
 
 Wax, moulds of, 244 
 
 Weight, relative, of atoms, 36 
 
 Wollaston's battery, 80 
 
 Woolrich's, Mr., experiments on A'oltaic 
 reduction, 27 
 
 J., contributions to elec 
 
 tro-raetallurgy, 29 
 
 , magneto-electric ma- 
 chine, 136, 137, 138 
 
 Wood, vessels of, 292 
 
 Works of art, moulds of, how made, 247 
 
 Zinc, acetate, 206 
 
 , amalgamated, 83 
 
 , chloride, 204 
 
 , deposition of, 357 
 
 , how amalgamated, 84 
 
 , impure, action of, 81 
 
 impurities of, cause of local action, 
 
 50 
 
 Zinc, iodide, 205 
 
 , ordinary, acted on by sulphuric 
 
 acid, 
 
 , oxide of, 207 
 
 , pure, 82 
 
 , quantity consumed in proportion 
 
 to electricity, 1 16 
 , compared 
 
 with copper deposited, 356 
 
 with gold deposited, 338 
 with platinum deposited, 344 
 
 silver deposited, 341 
 
 , removal of from negative plate of 
 
 battery, 115 
 
 , salts from which it may be re- 
 duced, 203 
 
 , sulphate of, 203 
 
 Zincode defined, 68 
 
 THE END. 
 
 FEINTED BV E. C. OSBOKNE, 30, HENNETt's HILL, BIRMINGHAM. 
 
TO 
 
 GILT TOY & METALLIC PEN MAKERS, 
 
 mvviage m^tm^^ ^utitttutre mmufutnxtt^, 
 
 PLATERS, SILVERSMITHS, &c. 
 
 JOHN & CHAS. RATCLIFF &; Co., 
 
 Respectfully inform the Trade, that they have purchased from Messrs, 
 Elkington, Mason, & Co. the right to use their Patent 
 for depositing Gold and Silver, designated 
 
 "ELECTRO -PLATING AND GILDING." 
 
 John & Charles Ratcliff & Co. have fitted up Premises adapted for 
 carrying out the Patent to its fullest extent, and detennined to 
 
 PLATE & GILD FOR THE TRADE ONLY, 
 
 they do not manufacture any description of articles, and thus their inte- 
 rests being closely connected with the Manufacturers', a guarantee is given 
 that every effort will he exercised to meet their wishes, especially in 
 reference to PRICES, QUALITY, and DISPATCH. 
 
 By this wonderful and beautiful discovery, an impetus is given to taste 
 and design. Every description of article, however elegant and elaborate, 
 hitherto confined to the costly materials of Gold or Silver, may be manu- 
 factured in German metal, and coated to any degree of richness with the 
 precious metals; and now, so perfect is the adhesion, that red heat will not 
 affect it. The surface also obtained by Electricity is harder than by the 
 usual mode of plating. 
 
 Every facility will be rendered to Manufacturers, by modelling or casting 
 any description of articles they may require. 
 
 Private Designs and Patterns will be faithfully preserved as the property 
 of the owner, and on no account copied or shewn for the use of others. 
 
 OLD ARTICLES RE-PLATED OR RE-GILT. 
 
 ELECTRO WORKS, SUFFOLK STREET, 
 BIRMINGHAM. 
 
CHEMICAL APPARATUS. 
 
 GALVANIC BATTERIES 
 
 OF ALL SORTS, 
 
 GLASS JARS, FUNNELS, TUBING, and STONE & EARTHEN- 
 WARE ARTICLES, 
 
 WEDGWOOD AND BERLIN WARE, 
 
 SUITED FOR 
 
 CHEMICAL EXPERIMENTS OR CHEMICAL WORKS, 
 
 NOW READY, 
 
 G. T. ROLLASON 
 
 Having made arrangements to enter fully into this 
 
 IMPORTANT DEPARTMENT OF TRADE, 
 
 SUITED TO THE PECULIAR WANTS OF THE TIMES. 
 
 MANUFACTURERS SUPPLIED ON WHOLESALE TERMS. 
 
 Orders from the Country will be attended to, if accompanied with a remittance 
 or respectable reference. 
 
 georgeI^Irollason, 
 
 CUT GLASS MANUFACTORY AND CHINA ROOMS, 
 STEELHOUSE LANE, BIRMINGHAM. 
 
 JOHN YATES & SONS, 
 ij^axtnt mtttto I^\mv9, 
 
 AND MANUFACTURERS OF 
 
 ALBATA, OR PURE BRITISH PLATE, 
 
 SPOONS, FORKS, LADLES, he. 
 
 WARRANTED OF THE 
 
 BEST MATERIALS AND WORKMANSHIP; 
 
 ALSO SUPERIOR 
 
 GERMAN SILVER SPOONS, FORKS, &c. 
 No8. 38 & 39, COLESHILL STREET, 
 
PATENT MAGNETO PLATE WORKS, 
 
 GENERAL PLATING MANUFACTORY, 
 
 NORTHWOOD STREET, 
 BIRMINGHAM. 
 
 THOMAS PRIME, 
 
 In returning thanks to his friends and numerous customers for the preference 
 given to articles of his Manufacture during 25 years, respectfully announces 
 that he has brought to practical perfection the above new and beautiful 
 process of Art. 
 
 This process, possessing all the advantages of the Electro and other modes 
 of Plating, has some valuable and important ones peculiarly its own. Its 
 superiority to the Electro consists in the following : — 
 
 The Solutions are simple, not liable to decompose, and the articles entirely 
 free from those imperfections necessarily arising from the complicated 
 nature of the Solutions used in the Electro process. 
 
 The deposition is effected by Magnetic Machinery of the most perfect 
 description, certain and uniform in operation, an eflFect that cannot be 
 obtained by the Galvanic Battery and other agencies employed in the Elec- 
 tro mode. 
 
 Consequently the Silver is deposited in a smooth and even manner, and 
 quite as hard as STEBUXSTG SII.VEB, its adhesion to the articles firm and 
 perfect, and submitted to a test that renders it impossible for the Plate to 
 peel off in wear. 
 
 The articles for Plating are made of argent bietax., manufactured 
 expressly for the purpose, in its nature hard and white throughout, and is 
 also admirably adapted for articles not Plated, being free from all impunties, 
 so as to withstand the strong test of Aqua-fortis, maintains its colour, and 
 improves by use. In these articles (aBOBNT XHETAZ.) utility and eco- 
 nomy are combined. 
 
 The Magneto Plate articles are confidently recommended as bemg more 
 durable than any before offered to the Public, and decidedly the best sub- 
 stitute for siZiVEB FI.ATE, being in appearance, weight and sound, equal 
 to SOX.ID 8XZ.VEB. 
 
 T. P.'s Establishment has been visited by gentlemen of high scientific 
 attainments, who have expressed their decided opinion of the beauty and 
 superiority of the Magneto Process and its successful application to Manu- 
 factures. 
 
 For a detailed account of the Machinery, Process, 5fc. see pages 55—63 in this 
 work. 
 
RICHARD FORD STURGES, 
 
 •25 & 26, LICHFIELD STREET, 
 
 BIRMINGHAM, 
 
 MAFUFACTURER OF FATENT FROSTED AND DAMASK 
 
 As well as every possible variety of 
 PLAIN AND FLUTED BRITANNIA METAL 
 
 TEA AND COFFEE SERVICES, 
 
 Of all sizes, and comprising every shade of quality and price. 
 
 ALSO, OF BEST 
 
 BRITISH PLATE SPOONS «c FORKS, 
 
 In every Pattern as made in Silver, and the same strongly coated by the 
 
 PATENT ELECTRO PROCESS. 
 
 COFFEE MACHINES, TEA EXTRACTORS, 
 
 CRITERION COFFEE CANISTERS, 
 
 AND A VARIETY OF 
 
 USEFUL AND NOVEL INVENTIONS 
 
 Peculiar to this Establishment. 
 
33S18 
 
 iiyiy ONIERUBRAi;