Elements Of Electro Metallurgy
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Elements
Of
Electro-Metallurgy.
By Alfhed Smeb, P.H.S.
OaES. AOAl>. KATUR OURIOSORUM IION. fiOC. SBKXORSURCUGBOir TO THE BOYAL OBNBRAt. DI9PBESARY, AUDKRaOATB 8TRBBT ;
SUROBOB TO THB BANK OF ENOi:JI.ND, TO THE CBRTUAL OPHTHALMIC HOSPITAL.;
I4Atb Lboturer Oh Suroery,
Btc. Btc.
THOU} XDinOV,
Revissp, Oorrkoted, Ard Comsipsrably Enpabgep.
lUMtaraM witfli StBetetype* abA Bsauvmis WooA<€mt.
London:
LOHGRAK.JBaOfmr, GBBBN, AHR LONGMANS.
To
His Royal Highness
The Prince Albert, K.G. F.R.S.
President Of The Society Of Arts,
Etc. Etc. Etc.
DESIGNED TO EXTEND TUB KNOWLEDOB OP SOME OF TIIOSM NUMEROUS ADAl'TATIONS OP
The Vast Forces Of Electricity To The Wants Of Man,
THE FIRST SUCCESSFUL APPLICATIONS OF WUIClI MUST EVER DISTINGUISH THE REIGN OF
Her Majesty Queen Victoria
As An Important Era In Scientific History,
And Which Have Bestowed Upon The Arts And Manufactures
A Kew Power Of Ofebatiok,
Is,
BY PERMISSION OF HIS ROYAL HIGHNESS, GRATEFULLY DEDICATED BY HIS ROYAL highness's
Most Obedient And Dutiful Servant,
Alfred 8Mee,
Preface.
This little work now appears before the public for the third time, and on each occasion the circumstances have materially differed. In the first instance, I should not have presumed to have undertaken the task, but for the pressing solicitations of many who were interested in the extension of those processes which have been here grouped together and described under the general term of Electro-Metallurgy. When writing the first volume, I had barely entered the profession which it has fallen to my lot to follow, and consequently I had ample time at my disposal. By an intense application to the study of the precipitation of metals by means of experiments, this volume, however incomplete, was produced.
The public, however, looked with so favourable an eye upon my earnest endeavours, that speedily a large impression of the work was sold, and the work was translated into the French, where it had even a more rapid sale. Upon this I extended my former experi-
A 3
Preface.
ments and the second edition was issued. In the prosecution of both these editions, I did not rely upon my own experiments alone, but every manufactory was visited which I thought could fumiab me with any facts which might aid me in composing the work ; and I cannot refrain from bearing testimony to the very kind manner in which I have been universally received by every person whom I have had occasion to consult.
Throughout this work my readers cannot fail to observe that very many processes are detailed which are but very little described in other works. Perhaps it is only fair to mention, that many of these I have learnt during the exercise of my profession ; and, being perfectly independent of the subject, many processes have been freely shown to me for publication, which would not be communicated to an individual only seeking to extend his own business.
Of the second edition, so large a number was printed that I did not anticipate any further calL But the purchasers of the first were also found to be buyers of the second, and thus this edition had also a very large sale with the public. After a time, from causes to which I need not advert, the publisher sold the residue, with my concurrence, by auction. From being pressed upon the market, some of the copies published at ten shillings fetched but an inadequate amount. After a further time, however, the wants of the manufacturer increased; those copies, and the very same books which bad been sold at a low rate, readily fetched sixteen shillings, one guinea, and, in some instances, two guineas; very curiously showing the
PREFACE. Vli
importance of adapting the supply of any commodity to the demand.
At length it was determined to publish a third edition. In reviewing my former experiments, I saw that in many directions there was abundant scope for investigation. From my present occupations, however,
I did not feel justified in following those alluring paths, and I have been compelled to content myself with adding to this edition some account of the processes and experiments which have been carried on by others : from this source alone this work has been increased about one sixth in bulk. Throughout all the editions, it has been my aim to write from my own knowledge, and therefore, unless the text expresses to the contrary, I have act aally witnessed the processes which have been detailed.
The first and second editions held but prospective advantages to the manufacturer; the present enables us to take a review of that which Electro-Metallurgy has absolutely effected. In the former editions, the economical relations of the subject were so carefully considered, that it has given me great pleasure to find that the stimulus of remuneration has been so effective that Electro-Metallurgy in no way falls short of the sanguine expectations then formed of it, but, on the contrary, has actually advanced in more extended spheres of operation.
In presenting this third edition to the public, I can only regret that it is not more complete ; and I can assure the ardent investigator that much remains to be done ; that there are untrodden paths of great probe to be explored, both as rards the production of elec-
Preface.
tricity, the source of power, and the application of that force to various processes. Electricity is but yet a new agent for the arts and manufactures, and, doubtless, generations unborn will regard with interest this century, in which it has been first applied to the wants of mankind.
7. Jinsbury Circus,
Feb. 18th, 1851.
Contents
Book The First.
On Galvanism.
Chap. I.
On Galvanic Batteries.
Electricity; various kinds, 1 — 8. Voltaic Batteries; circumstances advantageous or disadvantageous to, 5 — 13. Proximate cause of Galvanism, 14 — 18. Resistance, Ohm's Formula, 18 — 24. Different
forms of Batteries, Couronne des Tasses, Wollaston, &c., 24 — 31. Adhesion of the hydrogen to the negative plate; amalgamation of the positive, 34. Daiiiell's Battery, 37 — 44. Grove's Battery, &c., 45 — 47. Smee's Battery, Odds and Ends Battery, 48—65. Comparison between the three batteries, 56 — 58. - - - Page 1
CHAP. n.
On The Bropebties Of Galvanic Batteries.
Signs of a battery in action, 59. Harrb's galvanometer, 60. Spark, 61. Voltaic electricity charges in Leyden jar, 62. Physiological effects, 63. Magnetism, 64—68. Galvanometers, 68 — 70. Horse-shoe temporary magnet, 71 — 73. Decomposition cell, voltameters, poles, 74 — 84. Iaws of voltaic decomposition, 85, 86. Table of chemical equivalents, 87. Fluidity necessary to decomposition, 88. Conduction of fluids associated with decomposition, 88 — 90. Intensity necessary for decompositions, 91. Electrolysis; electro-diemical decomposition, 92 — 98. Daniell's tiieoiy, 99. State of the fluid during decompositkm, 100. Eflect of heat upon fluids, 101. Curious induction, 102. AhUkrs thecny of voltaac electricity, 103. - *34
Contents.
CHAP. IlL
On Additional Soubces Op Voltaic 'Powek.
On hydro, animal, and lightning-electricity considered, as a source of power, 104. Magneto-electricity, 105. - - - Page 80
Book The Second.
On Electro-Metallougy.
Chap. L
On The Apparatus To Be Employed ¥Ob The Reduction Op The Metals.
The idea of electro-metallurgy, suggested by Danieirs battery, 106. The porous tube or single-cell apparatus. 106 — 112. Capillaiy tube apparatus, 113. Plaster apparatus, zinc, iron, and tin positive poles, 114. Compound battery apparatus, 1 16, 1 1 6. Single battery apparatus, 117, 118. Precipitating trough, 119. Single-cell and battery conjoined, 120. Mason's arrangement, 121. Management of the apparatus, 122, 123. Linos on the reduced metal, how to be avoided. 124. Adhesion and non-adhesion of the reduced metal to its mould, 125 — 128. Apparent adhesion, 128. Lateral growth of the reduced metal, 129. Bela* tive expense of various modes of the redaction of metals. - 86
Chap. Il
On Substances Capable Op Receiving The Metallic Deposit.
Substances on which the deposit may take place, 130 — 131. Metals, 132 — 136. Non-conducting substances ; sealing wax, white wax, IdC — 139. Absorbent substances, as paper and plaster of Paris ; means of rendering them non-absorbent, 139 — 141. "Gutta percha, 141, Means of copying non-conducting substances by metals ; plumbago,
143145. Comparison between the methods, 145. - -117
CHAP. m.
On The Laws Bsgulatiko The &Educt10H Of The Metals.
Metals capable of being reduced by the voltaic fluid, 146. States in which they exist, 146—148. Law for the rednetioa of the metals as
a black powder, 148. Law for the reduction of the metals in crystals, 149. Law for the reduction of the metals in the reguline state, 150. Cause of the reduction in these states, 151. Mode of producing them, 153 — 159. Mode of obtaining the black powder, 169. The crystalline state, 160. The reguline state, 161. The same results obtainable by the single-cell apparatus, 165. Time required for the deposition of the metals, 167. - - - - - Page 147
Chap. Iv.
os THB BEDUCTION OF TH£ 21£TAL8.
Introduction. Formation of salts, &c., 168. Reduction of Platinum, 169. Gold, 170. Palladium, 171. Iridium, 172. Rhodium, 173. Osmium, 174. Silver, 175. Nickel, 176. Copper, 177. Zinc, 178. Cadmium, 179. Iron, 180. Tin, 181. Lead, 182. Antimony, 188. Bismuth, 184. Uranium, 185. Arsenic, 186. Tungstic acid, 167. Cobalt, 188. Manganese, 189. - - - - - 165
Chap. V.
On Tiie Redfotion And Analysis Of Alloys.
Law for the completion of the voltaic circuit through various solutions, 190. Table of relative facility of decomposition, 191. - - 224
Book The Thied.
On Electro-Gelding, Silver-Plating, Etc.
General directions, 192. Electro-gilding, 193. The auro-cyanide of potassium, 194. Apparatus, 195. Copper-gilding, 196. Watergilding, 197. Gilding by amalgamation, 198. Electro-platinating, electro-platinizing, 199. Electro-palladiating, 200. Electro-plating, 201. Plating by other means than Electro-Metallurgy, 202. On coating metals with nickel, 203. On coppering metallic substances, 20 t. On coppering non-metaUic substances, 205. On coppering medal - lions, 206 ; fruit, vegetables, &c., 207 ; baskets, 208 ; earthenware, 209. On coating metals mth iron, zinc, &c., 210. Conclusion, 211. 221
Contents.
Book The Fourth.
On Various Applications Of The Reduction Of Metals By Galvanism.
Chap. I.
On The Multiplication Of Coins And Medals.
Value of Electro- Metallurgy for the numismatist, 212. Mode of obtaining the mould, 213. Directly by the voltaic current, 214. By lead, fusible metal, &c., 215. By non-conducting substances, 216. Metallic . duplicates of gold, 217. Silver medals, 218. Medals of platinum, 219. Copper medals, 220. Precautions to be taken to prevent air-bubbles, 221. Apparatus to be employed, 222. Single-cell apparatus, 223. Thickneiw of the metal, 224. Removal of the cast from the mould, 225. Zinc medals, iron medals, 226. Value of Electro- Metallurgy for medallists. 227. On the modes of making perfect medals, 228. Page 253
Chap. El
On Copying Beals, Plaster Casts, Btc.
Value of a seal, 229. Process for copying a seal, 230. Copper moulds from plaster medallions, 231. Quality of the reduced copper, 232. 269
Chap. Ih
On The Multiplication Of Brasses.
Process for obtaining duplicate brasses, 233. ... 274
Chap Iv.
On Maxing Dies Vbom Embossed Surfaces.
On metallic reverses from raised surfaces by galvanic agency, 234. Peculiarities of dies made from paper, 235. 276
Chap. V.
ON THE MANUTAOTUBE OF MOULDS FROM FRUITS, VEOBTABLES, XTa
Ob making moulds from vegetable subeUmoes, 236. Chantrej*8 method,
Contents.
Chap. Vl
ON THE APPLICATION OP ELBCTRO-METALLURGT TO SCULPTURE, BAS- RELIEFS, AND OTHER PURPOSES.
The mode the sculptor adopts to obtain a metallic cast, 238. On making a metallic cast by Electro-Metallurgy, 239. The texture of the copper, 240. General remarks, 241. Ou the application of Electro-Metallurgy for goldsmiths, 242 ; for surgeons, &c., 243. - - Page 279
Book The Fifth.
On The Electrotype.
Chap. I.
On The Multiplication Op Ttpe.
The mode of printing books, 244. On stereotyping, 245. On Electrotyping the type, 246. 289
CHAP. n.
On The Multiplication Of Plain Copper Plates.
The preparation of plain copper plates, 247. The electrotype plates, 248. Process for their manufacture, 249. Manipulation of the battery, 250. Precipitating trough, 251. Temperature, 252. Positive pole, 253. Begnlation of the texture of the copper, 254. Single-cell apparatus, 255. Time required for the process, 256. Bemoval of the plate, 257. Mode of preparing the plate for engravers, 258. Economy in the manufactory, 259. Expiate of the plate, 260. ... 292
CHAP. m.
On Ooftino Xnobatxd Oopper-Platxs.
Engraved copper-plates, 261. Design on the plates, 262. Varioni kinds of engraving, 263. Uses of engraved plat 264 ; Ibr the potteries, 265 for calico printers, 266. ano
Contents.
Chap. Iv.
Os The Multiplication Of Steel Plates.
Process for making a copper-plate from a steel one, 267. Perkins* apparatus, 268. Comparison between the two processes, 269. Page 310
Chap. V.
On Multiplication Of Wood-Cuts.
Design on wood-cuts, 270. Process, 271. Conclusion 272. - 314
Chap. Vi.
On Multiplication Op The Daguerrbottpe.
Value of the Electro- Metallurgy for the Daguerreotype, 273. Process for obtaining the duplicate, 274. - - - - 327
Book The Sixth.
On Galvanic Etching.
Action on the positive pole, 275. Etching by nitric acid, 276. Faults in the biting, 277. Galvanic etching, 278. Accelerating circumstances, 279. Advantages of galvanic etching, 280. Gradations of tint, 281. General remarks, 282. - - - . 330
Book The Seventh.
On Electro-Disruptivk Etching,
Process and practical application of the disruptive discharge of the etching of steel, 281. - - 337
Book The Eighth.
On Voltaic Blaj3T1Ng.
On Wasting rocks or sunken vessels under water, 282. Electrical clocks, 283. Improper uses of electricity 339
List Of Wood.Cuts And Illustrations,
1, Daniell's Battery
Page
2. Grove's Battery
3. Smee's Battery, compound six cells
4. Ditto ditto, for Electrotype
5. Ditto ditto, Odds-and-Ends'
6. Galvanometer
7. V shaied decomposition Tube -
S. Faraday's Voltameter
9. Faraday's Voltameter
10. Diaphragm Apparatus
11. Diaphragm Apparatus
12. Battery Voltameter -
13. Induced Voltaic Current
14. Diagram of single ditto
15. Thermo- Voltaic Circuit
16. Compound Voltaic Current
17. Incomplete ditto
18. Hydro-Electric Machine
19. Electro-Galvanic ditto
20. Magneto-Electric ditto
21. Single-cell Electrotype Apparatus
22. Ditto ditto, another form -
23. Ditto ditto
24. Single Battery Apparatus, with Vertical Trough
25. Compound Trough Apparatus
26. Mason's Apparatus -
27. Single Battery, with Horizontal Precipitating Trough
28. Mode of making wax moulds -
29. Apparatus for forming electro salts
List Of Wooo-Cuts And Illustrations.
Page
30. Apparatus for makiug the red ferro-cyanate of potash - 170
31. Artificial Electric Eel - - - - 171
32. Beduction of platinum by Compound Odds-and-Ends' Battery - 177
33. Apparatus for the reduction of silver - - - 191
34. Metallo-chrome apparatus - - - - 217
35. Burnishers for gilt articles 236
36. Process for electro-coppering . . - 248
Specimen of Electrotyped Type - - - 29 1
37. Dog's Head, Electrotyped from Clichee - - - 315
38. Electrotype from Thomson's Seasons - - - 321
39. Glyphograph for Bankers' Cheques ... 324
40. Glirphographic Map, from Messrs. Blackie's Gazetteer - 325
41. Apparatus for blasting in mines ... 340
History
Electro-Metallurgy.
We have not to extend our inquiry into remote periods, to trace the history of the arts of working in metals by the galvanic fluid, for truly it may be said that this art belongs to our own time, and is a characteristic of the present age. Whilst, however, we pursue our investigations into the history of the subject, we find that it has had by no means a sudden origin ; for, at different periods, various persons have, by degrees, worked out one fact after another, till the comprehensive branch of science has been developed, of which this volume is but a brief epitome. Electro-Metallurgy may be said to have had its origin in the discovery of the constant battery by the late Professor Daniell, for in that instrument the copper is continually reduced upon the negative plate. In his first experiment, this distinguished author observed, on removing a piece of the reduced copper from a platina electrode, that scratches on the latter were copied with accuracy on the copper. In this experiment we have the electrotype ; but the author, in the first paper detailing his experiments, had devoted all his attention and centred all his energies to the construction of the battery itself, and this valuable fact attracted but little of his notice. My muchrespected teacher lives indeed no more, to his pupils, his
History Of
friends, or his family; but he lives to all time, from the profound researches which led to the construction of his battery. It may be true that the particular form of battery itself is now but very seldom used ; but if that battery had not been invented, Electro-Metallurgy would doubtless not have been added even now to our range of sciences. The name of Daniell is always, in my mind, intimately connected with Electro-Metallurgy ; and probably the professor himself little thought of the important results which would accrue from the invention of the battery, when he first made it known to the public.
It was but a short time after the discovery of this battery, that Mr. De la Rue experimented on its properties. In a paper printed in the Philosophical Magazine for 1836, after describing a peculiar form of battery which he adopts, the following remarkable passage is found : '' 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, being stripped off, it has the counterpart of every scratch of the plate on which it is deposited." This paper seems to have attracted very little attention ; and, what seems still more singular, the author, although well qualified from his scientific attainments to have applied these facts, never indicated any practical benefit to which this experiment might lead.
In this state the subject remained till October, 1838, when Professor Jacobi first announced that he could employ the reduction of copper, by galvanic agency, for the purposes of the arts. His process was called galvano-plastic. Immediately upon his discovery being announced in this country in 1839, Mr. Spencer stated that he had executed some medals in copper, to which the public afterwards gave the name of electrotypes or voltatypes, or, what is better, electromedallions.
Now what is the precise value of the discovery of these
Electro-Mktallubgy.
productions over the facts alreadj described? — for we have seen that the reduction of the copper as a perfect plate, taking the exact form of the negative metal on which it was deposited, had been already noticed. Why, it is simply the idea of the application of these facts ; but that idea has been everything for Electro-Metallurgy. The only apparatus which Mr. Spencer employed was, in fact, a simple Danielfs battery. He employed various metals for the reception of the precipitated metal, which, however, was nothing new ; but he does not seem to have succeeded with any non-conducting substances. He executed medals, and perhaps duplicate copper plates ; but he does not give any details, as to the different methods for the reduction of the copper in different states, neither did he succeed with the reduction of any other metal. However, to Mr. Spencer the British public are principally indebted for the idea of the electrotype ; and perhaps the idea, as far as relates to its application in Great Britain, originated entirely with himself.
Mr. Spencer's first paper was printed in the Journal of the Polytechnic Institution of Liverpool, in 1839 ; but the author complains that, by mismanagement, it was prevented from being read at the British Association. Any discouragement of science in the present time is greatly to be lamented, and the more especially when we see that the Germans are already taking the lead, not only in chemistry, but also in physiology. Every well-wisher of science must hope that an over-anxiety to prevent the publication of what is old, will not cause the referees of our learned societies to omit what is new. However, we are not so much behindhand, but that a little zeal on the part of those who have an established reputation for scientific acquirements, joined to the effect which encouragement would have on the junior members of the country, will enable the British to keep the foremost rank in science among the European nations. There are many now workii zealously and ardently for the
Histobt Of
fake of obtaining truth, struggling against the most disheartening opposition: let that opposition be changed to assistance, and great indeed will be the results.
It is improper to throw the whole blame of the rejection of that paper upon Dr. Lardner, for this is by no means the only essay of importance which has been consigned to oblivion. The rejection of valuable papers is a fault of the system not of the man. At all the learned societies a paper submitted to the society is referred to persons to report upon its merits, and upon that report the committees act with regard to its pubh'cation or suppression, which, in some cases, is facetiously termed a careful deposition in the archives of the society, which expression literally means, that it is placed in some large box from which it will be excluded from the cheering influence of the sun's rays for ever. The examination into the merits of any particular paper is, however, a most unthankful, disagreeable, and troublesome office. And it is not, therefore, surprising that the referees should sometimes exercise their characters as men, in supporting their own or the opinions of their friends and those to whom they are under obligations, and occasionally forget their situation as judges. Their services being gratuitous, entitle the referees to the heartiest thanks of the public; but an important office like that they occupy, in which the prosperity of the whole country is interested, should decidedly not be held without remuneration, and when remunerated, the officers should be held responsible for their decisions. We perceive that had Jacobi not also been a discoverer of the electrotype, Electro-Metallurgy would not have added its valuable processes to the variety of arts which it comprises. Ponder this important matter, ye referees, carefully in your minds ! for you never can tell to what great end a single new fact or application, though in an ill- drawn up paper, may not ultimately tend.
Perhaps in this place I may call the attention of scientific
ELECTBO-METALIUltGT.
men to the fact, that persons are actually employed by great Continental Powers to find out everything new that is dis covered in this country, which, in a very few hours, can be conveyed to any part of Europe. This hint is thrown out, not to deter Englishmen from generously giving their discoveries to all countries, but to cause them to be cautious not to mention their processes till they have appeared in some British publication, and thus vindicate the scientific character of our own country. This is the more necessary, as the English receive only the pleasure which the consciousness of being useful must afford, whilst the foreigner receives pecuniary emolument which singularly increases his desire of being acquainted with the inventions of other countries.
I may further notice, in order to confirm what I have already stated, that the galvano-plastics of Jacobi, and the electrotype of Spencer, are not inventions the result of inductive reasoning and laborious research, like Professor Wheatstone's electro- telegraph or certain elaborate machines; but merely an application of a fact, formerly known to Daniell, recorded particularly by De la Rue, and observed by hundreds of others; that both Spencer and Jacobi could work only in copper, and in no other metal; whilst, had they prosecuted their subject as a science, they would have seen that the same laws regulate the reduction of all the metals.
Electro-Metallurgy, as first made known to the] world by Jacobi and Spencer, was the simplest of all inventions — the application of a fact known and recorded previously; and it forms another instance of an invention of the greatest magnitude and utility to mankind, arising from most simple beginnings.
The next discovery, which is fully equal in value to the idea of the electrotype itself, was made by Mr. Murray. He found out that non-conducting substances might have
Histokt Op
metallic copper thrown down upon them by previously applying black lead. Mr. Murray's process is extremely simple, and absolutely perfect. The first application of this invention was made in January, 1840; but it is to be lamented that he did not further extend its application and publish his researches, for his method was communicated orally, in the conversaziones of the Royal Institution, and not by any paper. I lay particular stress upon the value and perfection of plumbago, because some have denied its applicability : and the reader will find, throughout the whole of the work, that I have extended the use of this substance, to the benefit of the public and to the fame of the inventor. I have made very extensive inquiries, in order to ascertain who really first used plumbago for this purpose, and I have the testimony of several authorities that it was Afr. Murray, whose claim, therefore, to this invention is rendered quite indisputable.
Since the above was written, I am happy to inform my readers that the Society of Arts thought fit to record their sense of the value of plumbago to Electro-Metallurgy by presenting Mr. Murray with a silver medal; and perhaps the merit of Mr. Murray's discovery is much enhanced by black-lead not only answering its purpose most fully, but from being so simple that very few were likely to have thought of its application. I cannot conceive a more perfect substance than black-lead for this purpose, for the adhesion pf hydrogen to it is so great that it would rather reduce a melic salt than be evolved ; and this is the very property desirable for Electro-Metallurgy, and in this respect forms a striking contrast with the processes which had been previously given by Mr. Solly, though, doubtless, had we not Mr. Murray's process, this would have formed a valuable Addition to Electro-Metallurgy and have been universally adopted.
Up to April, 1840, the single-cell apparatus was invariably nsed, but then Mr. Mason very ingeniously devised another
Electro-Metallurgy.
mode by which the reduction might be effected. He used the single-cell apparatus as a Daniell's battery, which he connected with another cell to reduce another metal. In the second cell he used a copper positive electrode, which was dissolved during the action. By this means he made two metals by one pound of zinc, or, in other words, obtained two equivalents of copper for one of zinc.
Jn the London Journal for April, 1840, as far as I know, is contained the first specimen of printing from an electrotype, by Newton. It is a small, rough sketch, but as the first of the kind is peculiarly interesting.
The laws regulating the reduction of all metals in diffident, states were first given in this work, as the result of my own discoveries. By these we can throw down gold, silver, platinum, palladium, copper, iron, and almost ell otlier metals in three stotes, nanny, as a black powder, as h crystalline deposit, or as a flexible plate. These laws appear to me at once to raise the isolated facts known as the electrotype into a science, and to add Electro-Metallurgy as an auxilifury to the noble arts of this country.
The regulation of the power of the battery to the strength of the metallic solution, also required an investigation of the principles which regulated the diffusion of the newly-formed salt, which is of great importance to the operator. In this work I have also appended data, whereby the manufacturer may calculate the expense of particular processes before he adopts them. The formulae for ascertaining the work that would be performed by a galvanic battery, under different circumstances, cannot fail to be of great utility to the work man, if jhe rightly employ them ; and the intimate rationale of the motion of electricity in the battery must be a subject, at least, of great interest to all. The principle regulating the adhesion of the reduced metal is also one of paramount importance in all cases where it has to be removed from the plates on which it is deposited.
Bistort Op
The number of experiments, I may eren say the thousands, that have been tried to elucidate these laws (for this book is not a detail of experiments, but rather a digest of them), could never have been executed had I not first discovered my galvanic battery ; for its simplicity alone enabled me, without any assistance, to undergo the laborious undertaking. I am fully aware that some may disagree with me as to the superiority of my battery over all others for experimental and manufacturing purposes. I shall not flinch upon this account from stating its advantages, especially as they appear to me likely to contribute to general benefit.
The value of the battery process over all others, is its applicability to all cases; moreover, when we use a single cell of the battery, the quantity of zinc dissolved to do any amount of work, is the same, or even less, than attends the use of the other apparatus; because the local action in a battery of this construction is less than in the single-cell apparatus ; and, lastly, the quality of the precipitated metal can be regulated with the utmost nicety; and I have no hesitation in stating, that the battery process is the only one that ever can be employed by the manufacturer with advantage.
The platinized silver battery is peculiarly suitable for the operator, for when it is in action it communicates to him the degree of work that it is doing ; in fact, it completely talks to its possessor. If the current is very feeble, a faint murmur is heard ; if a little stronger, the battery whispers ; if a moderate current is passing, it hisses ; but if a violent one, it roars. At this present moment I have nineteen batteries at work in the same room where I am writing, and they are each telling me the work they are performing. This very instant the fall of a heavy ledger in a neighbouring office has jarred two wires into contact, and the roar of that one battery has immediately informed me of the fact notwithstanding the action of the eighteen others; 1 have
Electro-Metallurgy,
separated the wires, and the universal singing communicates to me that all are now working satisfactorily. Any local action on the zinc in the same way is immediately notified by its different and peculiar voice, and I have been surprised how quickly the experimenter catches the characteristic peculiarity of each noise, which is learnt more readily than the sound of different bells in a strange house.
With regard to the constancy of this battery, I may be expected to say a few words ; for, although theoretically it is not absolutely constant, yet, practically, for the purposes of the electro-metallurgist, its constancy remains for two or three days, or, in other words, until the battery is nearly exhausted ; and then, to replenish the solution of zinc with a fresh supply of dilute acid will not occupy more than half a minute. In recording my own experience of its practical, though not of its absolute, constancy, I can at the same time conjoin the testimony of some of the most extensive manufacturers in this country. By the practical manufacturer this instrument is re-charged with acid, at intervals, varying from three days to a fortnight, or even a twelvemonth, according to the size of the vessel containing the acid. Whilst upon the use of the battery, I may state, that the platinum, with proper care, never wears off the silver, and that the platinized silver never undergoes the slightest cliange, or is affected by the slightest local action.
The departments of Electro-Metallurgy comprising electrogilding and plating, received great impulses from Elkington ; some of his processes being most admirable. As far as gilding is concerned, he was anticipated by Brugnatelli nearly forty years ago; the following passage has been pointed out to me by Mr. Brayley, then one of the editors of the Phil. Mag. " I have lately," adds he (Brugnatelli in a letter to Van Mons), ''gilt in a complete manner two large silver medals, by bringing them into communication by means of a steel wire, with the negative pole of a voltaic
a
mSTOBY OF
xxti
pile, and keeping them one after the other immersed in ammoniuret of gold, newly made and well saturated." This account is 'contained in the Phil. Mag. for 1805, but the same passage is also found in the '' Archives of Philosophical Knowledge;" but it is to be regretted that neither journal gave the letter or stated where it was published. This process differs in nothing from the ones now employed, and doubtless ought to be considered as the introduction of Electro-Metallurgy, being the first instance in which any metal was ever reduced by galvanism for the purposes of the arts.
Since my last edition, the discovery of the use of the bisulphuret of carbon, for the deposition of bright silver and gold, is a very remarkable and important improvement of certain elcctro-metallurgic processes. In this discovery is contained the germ of other discoveries, which talented experimenters will not fail to turn to account.
The processes for platinating, palladiating, &c., rest upon the authority of this work; for hitherto the reduction of these metals, in any other state than that of the black powder, has been always considered impossible. The electrometallurgist will be enabled, by the processes which he will find here fully described, to execute reliefs and intaglios in gold, and, in fact, in nearly every other metal ; facts altogether new in science. The working of all other metals, as in zinc, silver, &c. &c., except copper, is also due to the discovery of the laws regulating the precipitation of the metals.
Every author has given directions for making moulds on plaster casts in metal ; but it is singular, that by no process hitherto known can a perfect reverse of plaster be obtained. In investigating the cause of this, I soon discovered that the extreme porosity of the plaster was the block over which they had all stumbled, and the difficulty was overcome by rendering the plaster non-absorbent In this work the
Electbo-Mbtallurgy.
reader will find that the copying of reliefs in plaster is brought to the utmost possible perfection, and by very simple means.
The success of this department of my experiments has amply repaid me for my labours and expense ; for there is not a town in England that I have happened to visit, and scarcely a street of this metropolis, where prepared plasters are not exposed to view for the purpose of alluring persons to follow the delightful recreation afforded by the practice of Electro-Metallurgy.
The extended use of white-wax, bees*-wax, rosin, &c., for the electro-metallurgist, I trust will be found acceptable. Their manipulation 1 have given as the result of my own experience, and therefore, doubtless, those who make a trade of working these substances will find the account not 80 full as might have been expected or wished ; yet I believe practice alone is required to make the operator perfect in these arts.
Since my last edition gutta percha has been added to the materials of the electro-metallurgist. I hardly know how 1 can adequately convey my sense of the immense importance of this new substance. Its plastic properties and its power of resisting acid and alkaline solutions render it of incalculable value. For moulds it has already nearly superseded every other substance, so in like manner it has been employed for troughs and other vessels ; and Dr. Montgomerie, who first brought it into use in Great Britain, has earned for himself a lasting name amongst the benefactors of his country. Surely it would not be inconsistent to bestow a public reward upon those who render such important public services I
The application of Electro-Metallurgy to the copying of leaves, fruit, &c., is for the first time described in this work. The new mode of etching here detailed, I confidently trust, will be also found a valuable adjunct to the knowledge of
History Of
the engraver. The principle which regulates the adhesion and non-adhesion of the plates will enable the operator to conduct his operations with certainty — a circumstance of no small importance to the engraver, ignorance on this score having already produced untoward results.
In this history, a sketch only has been given of the leading discoveries ; but undoubtedly the person who carries out a new branch of science is deserving of considerable praise, for frequently he has to incur great expense without any immediate prospect of a return for his capital.
The electrotype department of Electro-Metallurgy was, I believe, first undertaken as a business by Mr. Palmer ; who was speedily followed by De la Rue, and afterwards by Lockett, Mabley, and several others: though, not having seen the productions of the latter, I have been unable to report more minutely of their works.
The laws which I have given in this work, and the universality of their application, will doubtless influence importantly the attainment of the grand object of using the galvanic fluid commonly among our manufacturers ; and having thus, as I believe, raising the isolated facts called the Electrotype into a vast and comprehensive branch of science, a new name is required which may be suitable to its importance, and embrace its various applications. The term which I have ventured to apply to the science is Electro-Metallurgy, which comprises the principles regulating all the arts of Working in Metals by the Galvanic force ; and the value of the new nomenclature is evident, when we consider that it takes in every mode by which it is possible to work metals, either by dissolving or precipitating them by the agency of the voltaic current.
As a surgeon, I feel bound to pass my opinion upon the effect which an extensive application of Electro-Metallurgy would have on the health of the workman ; and in one word I may state, that I believe the mode of working in metals by
Electro-Metallurgy.
the galvanic fluid is more wholesome, and attended with far less deleterious properties, than the methods now practised. The use of the salts of gold, silver, and platinum, is liable to discolour the fingers ; but the other salts have no particular eflect. However, in passing the above decided opinion, strengthened as it is by watching the eflects of the experiments on myself, and also from paying attention to the health of some who have reduced electrotype copper by the hundredweight, I feel but little doubt, that, if the electro-metallurgist were several times in a day to leave his work with his fingers covered with metallic solutions, and take his meals without any ablution, and repeat this for a long time, the quantity of metal which he would thus draw insensibly into his system might be attended with inconvenience. Several of the processes here detailed, as those of gilding, &c., are likely most materially to benefit the health of the workman, as they supersede the use of pernicious mercurial fumes.
Those conducting electro-metallurgical operations generally fatten with their oceupatiou, the minute quantities of sulphate of zinc and sulphuric acid which they imbibe improving the tone of their stomach, helping digestion, and strengthening the whole frame. The salts of copper have the same eflects as those of zinc, but perhaps, upon the whole, must not be made quite so free with. I would warn my reader against too free and careless a use of the cyanides, believing that the simple inhalation of the vapour which they emit is very pernicious ; but with proper care no fear peed be entertained, and, doubtless, upon the whole, Electro- Metallurgy is a great blessing to the workman.
The Electro-Metallurgist who requires further information on galvanism, should consult the original papers of the various authors who have most contributed to a knowledge of the subject; but I would especially urge every person interested in any department of Electro-Metallurgy to buy and keep ready for reference Braude's Manual of Chemistry,
History Of
one of the most extensive and general collections of chemical facts in the English language. The operator will find it indispensable if he attempt to leave the beaten track and follow new paths. He may also possess Gmelin's Chemistry, which is an excellent compilation from the transactions of learned societies, and scientific and philosophical journals. It is, however,'most deficient in processes published in monographs.
Since my last edition, Electricity is employed not only for the voltaic battery, but also for the magneto-electric machine. Now, when this work was first written many of my scientific friends thought that the title would have been better had it been termed Voltaic-Metallurgy ; and, in fact, the processes were described abroad as galvano-plastics. I dissented from this nomenclature, because it appeared to me that although at that time we could only carry on the processes by voltaic electricity, yet the time would arrive when electricity from other sources would also be employed. That time has arrived ; and the magneto-electric machine is now being extensively applied for electro-metallurgy, and thus my term has been fully justified.
No person can now plead ignorance of Electro-Metallurgy as an excuse for not following it. There are such a variety of works upon the subject to suit every class of persons, from a penny up to three or four shillings, that certainly he must be enabled to purchase one according to his means* The best of them are generally written by workmen, who detail in their own language, the processes they are in the habit of using. Those works which are made up by abstracting a part from one author and part from another, generally lose force from the inconsistent whole that they present ; though, doubtless, there is not a single treatise upon the subject that might not be useful to the incipient operator, and from which some good might not fee drawn.
It has often been mentioned to me, and considered strange
Electro-Metallurgy.
that the Societies whose business it is to superintend and cherish the rising arts and infant sciences, should not contain any single paper on the new science of Electro-Metallurgy, and that the student is compelled to obtain his knowledge from other sources. For the electrotype, he may possess Spencer's treatise on that subject, although the mode of proceeding detailed by him is very different from those wliich the laws I have developed require me to recommend. Jacobi has written a treatise, in German, on Galvano-Plastics, which has been translated by Sturgeon. These two books, from respect to their authors, every electro-metallurgist should not only possess, but value and carefully preserve, as the first dawn of this delightful science. The manufacturer would do well to consult the various electro-metallurgic patents, the titles of which are given in the Appendix of this work, and an abstract of many of wliich are printed in various magazines. The original papers upon electro-metallurgy have now become so numerous, that every periodical contains notices, of various degrees of value and novelty, in some portions of this extensive subject. The value of these excellent periodicals in making public new discoveries and fostering talent, which would otherwise be frequently crushed by the overwhelming weight of interested opinion, is here evident, and to their spirited editors this country is daily owing increase of knowledge, power, and wealth.
Elements
ov
Electeo-Mbtalluegy.
Book The First.
On Galvanism.
Chapter L
On Galvanic Batteries.
Electricity; various kinds, 1 — S. Vcdtaic Batteries; circumstances advantageous or disadvantageous to, 5 — 13. Proximate cause of Galvanism, 14 — 18. Resistance, Ohm's Formula, 18 — 24. Different forms of Batteries, Couronne des Passes, Wollaston, &c., 24 — 31. Adhesion of the hydrogen to the negative plate; amalgamation of the positive, 34. Daniell's Battery, 37 — 44. Grove's Battery, &c., 45 — 47. Smee's Batteiy, Odds and Ends Battery, 48—55. Comparison between the three batteries, 56 — 58.
(1.) As phycists have arranged an extensive series of effects under the general term of Heat, so they have named another series Light, and a third they have called Electricity. We find, if we examine organised bodies, that all these principles are capable of being produced through the medium of living bodies, for nearly all animals have the power of evolving heat; many insects, moreover, can voluntarily emit light ; and the property of producing electricity is well
Toltaic Batteet.
evinced in the terrible shock of the electric eel, as well as in that of some other creatures. We are indeed in the habit of talking of the Electric fluid, or the Gtilvanic fluid, but this in reality is nothing but a licence of expression suitable to our finite and material notions.
(2.) In my sources of Physics I have more particularly considered the mutual relation of these forces, and they all appear to be so singularly and intimately connected with each other, that from any one the others may be eliminated. As a high generalisation we may assume that any new attraction will produce force, and that this force may act upon attracted matter, and produce, according to circumstances, heat, light, galvanism or electricity.
(3.) Electricity is the only force of which we have particularly to treat in this work, and this subject is subdivided into several departments : as electricity of tension, or frictional electricity, where the efiects of electricity derived from the electrifying machine are considered ; thermo- or stereo-electricity, where it is derived from solid bodies through the agency of heat; animal electricity, from organised bodies; magnetic electricity, from the natural or artificial magnet; and voltaic or galvanic, where it is obtained from the voltaic pile.
(4.) Although these names, from their multiplicity, may tend to confuse, be it remembered, there is but one electricity which thus manifests itself in such diflerent ways, either under varying circumstances, or from differences from whence it is derived. Our inquiry will not extend into all these details, but principally into its effects when obtained from the voltaic battery.
(5.) The phenomena, to which the name of voltaic or galvanic electricity has been given, are those which arise from the voltaic or galvanic battery, so named from its discoverers, Volta and Galvani. They found that two lieoes of metal, possessing different facilities for combination
Conductors Of Electricity.
with oxygen, produced, when properly united, singular convulsions in a dead frog ; and, following out this experiment they constructed the battery, which has now, from the improvements of later discoverers, become so powerful and valuable an instrument.
(6.) Without pursuing in detail the interesting experiments of subsequent authors, it must always be borne in mind, that, to make a galvanic battery with advantage, two conducting substances must be employed, and a compound conducting fluid must intervene, capable of being decomposed, and the resulting compound formed should be removed as rapidly as possible out of the sphere of its production by the solvent powers of the fluid. The first substance should have the strongest possible affinity for one element of the fluid, and the second substance the least possible affinity. Thus, in a simple circuit, composed of zinc, silver, and water (the water being rendered a good conductor by the addition of acid), zinc has a very strong attraction for 'the oxygen of the fluid, whilst silver has a very slight attraction ; and therefore a powerful current is generated. As a gal vanic curiosity Becquerel has described a battery made by an acid and alkali, separated from each other by a porous diaphragm, and simply connected by a platinum wire. Mr. Grove has also described an interesting arrangement of nitric acid and muriatic acid, separated by a diaphragm and connected together by gold leaf immersed in both fluids In this case oxygen is transferred over to the muriatic acid, chlorine is set free, and one piece of gold becomes dissolved. The older electricians considered that galvanic batteries might be made of muscle and brain, beet-root, and various other non-conducting substances, but probably their observations were inaccurate.
(7.) With regard to the rebtive conducting powers of
The Yoltidc currents in the living animal I have described in the Elements of Electro-Biology.
4 ELBOTRO-POSntVB — BLECTBO-MaATIVB PLATES.
bodies, the metals, and att the varieties of carbon excepting the diamond, hold the foremost rank among solids. The fluids are generally imperfect conductors ; none more so than pure water ; though in combination with the acids, pure alkalies, or any of the salts, it forms a good conductor. Fused chlorides and iodides are also good conductors. The metals are conductors in the following order ; silver, copper, lead, gold, brass, zinc, tin, platinum, palladium, and iron.
(8.) If we except the earthy and alkaline metals, as potassium, sodium, &c., zinc has by far the strongest affinity for oxygen ; and on this account is invariably used as the electro-positive metal (the term applied to the metal which acted upon by the solution, or which in reality acts on the fluid). All other metals, in any acid solution, are electro-negative to them ; the term used to imply the opposite state to electro-positive. The following table shows the state of electricity in which the metals stand with regard to each other in acid solutions, where every metal is positive to all below it and negative to all above it. This series relates only to a dilute sulphuric acid solution, for it varies with almost every other solution used : —
Potassium, Iron, Silver,
Barium, Bismuth, Palladium,
Zinc, Antimony, Gold,
Cadmium, Lead, Charcoal,
Tin, Copper, Platinum.
This order appears to me to require to be again made the subject of experiment; I would suggest that, for this investigation, every metal should be used in a finely divided state, similar to the finely divided platinum of my battery.
(9.) When a metal which acts slightly upon a fluid (as for instance, copper) is brought into contact with another tnetal, which has a stronger affinity for the oxygen of the Ituid, the latter, or electro-positive, is dissolved, and gives a
Elbgtbo-Neqative Plates. S ,
negative tendency to the former, which in that state does not act at all upon the duid, but is preserved bj the latter. Of this singular property Sir H. Davy took advantage, for the protection of the copper sheathing of vessels, which was effectually preserved from decay by pieces of zinc or iron placed in contact with it under the water ; but then unfortunately the copper, ceasing to be deleterious, did not prevent the adhesion of marine animals and vegetables, which accumulated to such an extent as materially to impede the ships* progress through the water. In this way zinc protects all the less oxidable metals, when pure ; but if the electro-negative metals be contaminated with charcoal, or with a metal having less affinity for oxygen, they will still be acted upon. This doctrine of negative tendencies appears to be much overrated, for a metal can only be protected by the negative tendency, when hydrogen Las to be evolved from the metal to be protected; thus, zinc will protect copper when placed in dilute sulphuric or other saline solutions, but no voltaic force will protect the copper when placed in the salts of silver, gold, platinum, or/ palladium, or in nitrous acid, because the hydrogen in these cases is immediately absorbed, and the copper is acted upon by the liquid, or rather itself decomposes the fluid, by seizing upon the oxygen of the metallic salt. For the same reasons it is impossible to give a negative tendency to iron or tin, in a solution of sulphate of copper, because there is no hydrogen to protect the iron. There are a thousand other similar instances ; therefore let the electro-metallurgist place no reliance on giving a negative tendency to a metal, but take care in all his operations not to place one metal in a metallic solution which it is enabled to decompose.
(10.) The converse of this observation applies to the electro-positive metal, as the zinc ; for, when pure, it is not acted upon by the sulphuric acid till contact be made with some other metal having less affinity for oxygen ; if it con*
f
tilbk fladtronegatiye metal however, it will Hot only he bj the fluid for the generation of the galvanic current, but independently of this a great waste and expense will be incurred. This additional wasting is termed local action, and should be avoided in every possible way.
(11.) Local action, arising as it does from either the zinc or the negative metal being contaminated with some other metal, is to be considered as an infinity of small batteries, the action of which is quite independent of the great battery ; where the hydrogen is entirely transferred to the negative plate, and where consequently no apparent action is visible at the positive plate.
(12.) It is for this reason that the pure metals are exceedingly difficult to dissolve, particularly if the acids be also pure ; as, for instance, pure silver in pure diluted nitric acid, or pure zinc in dilute sulphuric acid ; because there is no local battery of different metals established to favour the solution.
(13.) A battery, in an acid solution, when put into action, exhibits apparently no change at the electro-positive metu(, or zinc, if the local action be destroyed ; although in fact it is the zinc which is being dissolved. On the contrary, the electro-negative metal, which is in reality undergoing no change, exhibits a copious disengagement of gas, which arises from the transference of the hydrogen to that plate, while the oxygen is all absorbed by the zinc.
(14.) This leads us at once to the proximate cause of the voltaic current, for it is found that the amount of action on the zinc is exactly proportionate to the quantity of electricity produced ; hence zinc appears to be the fuel of the battery, holding the same place as coals in a fire. From these and various other facts. Dr. Wollaston, Dr. Faraday, and with them most of the present experimenters in this country, believe that the chemical action of the add solution on the zinc, or rather of the zinc on the water of Ihe add solution
ift.tlie ioiifca of the dectno current in the battayi end thie is termed the Chemical Theory of the pile* The Germane again, and others, following Volta, believe that the chemical action is the effect of the electric current, and that the power is produced by the contact of two dissimilar metals ; and this latter has received the name of the Contact Theory.
(15.) In opposition to the Contact Theory, Dr. Faraday has described, in the Philosophical Transactions, curious instances, where the connection of a single battery, excited by dilute sulphuric acid, was not made through any metal whatever, but through a liquid capable of being decomposed by the stronger energies of the dilute sulphuric acid. He found that a solution of iodide of potassium was best adapted to show this interesting fact
(16.) Whichever theory be adopted, the use of the negative metal is by no means apparent; for the quantity of electricity developed, cceteris paribus is exactly as the surface of negative metal exposed ; thus, provided there be no obstacle to overcome, if the surfijpe of this, be doubled, the quantity of electricity will be likewise doubled. The extent of surface of the positive metal, within certain limits, is not of so much consequence, although too great a deficiency of this is attended with detriment. The importance of the surface of positive metal differs with every metal, and perhaps depends more on the attributes of the salt formed luring the action of the battery. In a dilute acid solution, when zinc is used for the positive metal, the extent of surface is not very material ; but when other metals, as copper or iron, are employed in a decomposition apparatus, the size is of the utmost consequence, as we shall hereafter have particularly to notice.
(17.) One circumstance must be noticed, that every point of the negative offers a radiating point to the positive metal ; for every point not so situated is much less active, and some*
8 sxnrma vLxm of oalyanic battebxss.
times eveii perfectly inactive. In different cases this property is shown more or less strikingly ; for if the hydrogen be removed in its nascent state, it will, under the combined action of its adhesion and elasticity, manifest itself at a great distance from the positive metal, and even quite without the sphere of its radiation, as is the case where the back of a piece of metal is active, while the front alone is opposite to the fluid. When very smooth metals are used, it will also pass to a great distance ; but when a metal is prepared in the manner I have hereafter to point out, by platinum, the gas will only be given off from a small extent, though very violently, when touched by the point of a fine zinc wire. In fact, the stratum of fluid interposed between the pieces of metals affords a great resistance to the galvanic fluid, and this is proportionate to the thickness of the stratum and its conducting power,
(18.) A relation exists between the power, and the distance interposed between the electro-positive and negative metals ; for, the nearer these can be brought together, the greater the quantity electricity developed ; though the intensity is not influenced by the difference of arrangement.
(19.) The function of the acid solution has already been partially explained ; for we have before mentioned that the water is decomposed, the hydrogen is transferred to the negative metal, and the oxygen combines with the zinc, and forms oxide of zinc. The acid now comes into play, and, in addition to its adding considerable conducting power to the solution, it removes the oxide to form the sulphate of zinc. The water which now remains undecomposed is required to dissolve the sulphate of zinc, for, as soon as the liquid becomes saturated with that salt, no farther galvanic action can take place, although the liquid may still remain intensely sour. This property is of great importance, because it shows us that the acid and water must be so regulated that the sulphate of zinc which results the action may saturate
the water and leave little or no excess of acid. Whatever add is left beyond the saturation of the fluid by the sulphate of zinc, must of necessity be wasted, unless we dilute the solution with more water. It is a most striking .experiment to add water to a battery charged with a saturated and acid solution of sulphate of zinc, as immediately activity and power are exhibited by that which appeared before to be inert and inoperative. The function of the water has been very much overlooked, or even altogether neglected ; but for electrometallurgical operations the fact must be continually borne in mind, and a sufficiency of fluid always added to the metallic salt, in order that when the salt is formed it may be freely dissolved. If the rivers had been filled with anhydrous sulphuric acid, and water had been manufactured in the laboratory, then we should have come to the conclusion that the water excited the battery, and the acid was of secondary importance ; but, as it has been the reverse, we have decided too carelessly that the acid excited the battery, and the water played a secondary part ; whereas the one is as necessary as the other, the acid to render soluble the metal the water to dissolve the newly formed metallic salt. Different salts vary very much in the rapidity with which they are dissolved by fluids ; thus sulphate of zinc is very rapidly dissolved, ferrocyanate of potash and sulphate of copper very slowly, and this does not depend upon the quantity of salt the water will take up ; and there is no doubt that this property is of considerable importance, not only in the galvanic battery, but also in the precipitating trough. After these observations, we must not be deceived by imagining we can have a battery which will do much work, and at the same time take up but little space ; for any person may at once calculate the capabilities ci a battery ftma its size, by first ascertaining the nature of the salt fonned the galvanic action, then its Boltibitity in water, by which ineans we can learn to a nicety Hm nlmesl amount of galvanic power that can be attained
10 Quantitt Of Electricitt In Different Cases.
from any battery. The only chance we have of lessening the size of a galvanic battery, and at the same time performing the same work, is to take care that the salt made during the action of the battery should be soluble in but little water.
(20.) Whatever exciting fluid is employed to charge the battery, its efficacy depends upon the same principles, but the intensity varies with each variation in the foreign body placed in the water ; thus dilute nitric acid, dilute sulphuric acid, or a solution of salt, all impart different powers to the battery : an increase, however, or diminution in the proportion of these, does not interfere in the intensity, though the quantity is materially altered ; for, if but ten drops of dilute sulphuric acid are placed in a gallon of water, the intensity would be the same as if a pint of acid were employed ; but the quantity in one case would be infinitely less than in the other.
(21.) The nature of the exciting fluid also materially affects the resistance which is afforded to the galvanic current, for no two fluids, or no two strengths of fluids, conduct the galvanic power with equal facility. From the above considerations we arrive at the proper manner to make a galvanic battery ; first, we must have two good conducting substances, separated by a good conducting intervening liquid. The amount of action which it will produce will be proportionate to the ready action of the liquid on one substance, and its inaction on the other ; and will depend on the size of the terminal plates. This amount of action may be fairly called the power of the battery, but it is always lessened ; first, by a slight resistance which the metals afford to the passage of the current ; and, secondly, by the resistance which the intervening liquid is sure to afford, which is proportionate to its thickness. If, instead of a good conducting metal, the connection between the terminal plates is made by any imperfecUy conducting substance, or any great lengtili of wire.
Resisting Hebiitms. — Ohm'S Formula. 11
then will also the power be still further materially lessened. A single ceD, composed of two metals and an intervening fluid, provided it be large, is sufficient to produce any amount of action where no resistance is afforded to the passage of the voltaic current. These will remain inactive while they do not touch ; but as soon as contact takes place, either in the exciting fluid, at a distance, or through a fluid of more easy decomposition than the exciting fluid of the battery, the action immediately commences. The contact may be made through a great length of wire with the same result. In this case, however, if the wire be either long, of small diameter, or of a metal of no great conducting power, it will be seen that the hydrogen evolved from the negative metal will be materially lessened, showing that an obstacle is presented to the electric fluid.
(22.) To overcome this obstacle we must have recourse to a number of galvanic batteries, arranged as a series ; that is, the zinc of one battery connected with the silver of the next, and this in regular continuation, leaving the extreme zinc and silver free. In this way a hundred batteries may be conjoined, but no more electricity is obtained 5 for only the same amount of electricity passes as when one cell is used. Now, however, this same amount can pass through a much greater resistance, for it would seem as if, at every alternation of the battery, the electric fluid obtained a push to overcome any obstacle afforded to its passage. The amount of electricity will have a power of overcoming obstacles in a compound battery, equal to its power in a single cell, multiplied by the number of cells. By this arrangement the amount of electricity actually passing will not be increased beyond what it would have been, had there been no resistance to ovOTCome.
Ohm, in an elaborate and obscurely worded paper, has given a mathematical formula for the galvanic current. His general formula may be thus expressed. The action (A) is
ohm's formula.
equal to (the electromotive force (E) multiplied by the number of batteries) (n) divided bjr the resistance the current has to overcome, external to the liquid of each battery (B) plus (the resistance encountered by the peculiar arrangement of each cell r multiplied by the number of cells
It would be thus : —
n E n R-f r
In this formula he has discarded the terms quantity and intensity, and unfortunately has adopted the contact instead of the chemical theory of the pile, which is now universally held in England.
(23.) There is no advantage, but even a loss, in using a battery with a series more than sufficient to nearly overcome a resistance, whether produced by a fluid to be decomposed, or by any other means ; for if ten cells arranged as a compound battery be sufficient to overcome the obstacle, the effect of sixty cells, arranged as six tens, would be nearly six times as much as if a single ten were used, because they would then form a battery of six times the size ; but if the whole were used as one compound series, the resulting decomposition would be enormously less than six times the quantity, being but a trifle more than before ; and, to use a battery with advantage, this fact must be borne in mind. If, again, the surfaces be increased before sufficient series be obtained, in like manner it will not add a proportionate amount of power. The subjoined plans will illustrate the two modes of arranging a number of batteries, first, as one large battery, by connecting all the zincs and silvers together.
""z z z z z z z
8 S 8 S 8 8 S
COURONNE DBS TAS8ES. — DB LUC's COLUMN, ETC. 13
Or, secondly, into a compound battery by alternately connecting the zinc of one battery with the silver of the second.
— Z — S 2— S 2 — S 2 — S-— .
(24.) A compound galvanic battery, or one of many cells, has the same quantity of electricity passing in each cell, and therefore the same quantity of zinc dissolved. On this account, the fewer the cells that can be employed to overcome the obstacle, the greater will be the economy. It is obvious, therefore, that as soon as, by increasing the series or number of the cells, sufficient intensity has been attained to overcome partially the resistance, quantity should be sought by increasing the surface or size of the plates in each cell ; for when one cell, as a single series, requires one pound of zinc to do a given amount of work, when that same work is done more quickly by twelve cells, twelve pounds are dissolved — one pound in each cell ; and of whatever size the cells may be, still the result will be the same, for no more zinc will be dissolved.
(25.) The simplest form of compound battery is the Couronne des Tasses, which is composed of alternate slips of zinc and platinum soldered together ; the zinc is to be placed in one glass, the platinum in the next ; and the series, thus arranged, may be charged with dilute sulphuric acid : care must be taken that the metal of the alternate pairs do not touch in the fluid.
(26.) When intensity alone is required, a large number of small plates should be used, as in De Luc's column, which is constructed of pairs of plates of dissimilar metals, separated by paper. There are several methods by which it may be ixiade ; the most common of which is to place alternate discs of silvered paper on similar discs of zinc, taking care that the series (i. e. the relative position of zinc) has always the same direction. It may be also made of discs of silvered or gilt paper, the uncovered side having been first spread
Compound Battbbt, Etc.
am with the black oxide of manganese and honey. Howcare most be taken that the manganese be not exposed tO snn as ih that case it is rendered inert ; and also that Ikesliver or gilt paper be not covered with any varnish as Hiit is usvudly add in the shops : 500 to 1000 iscs ita be employed to make an efficient instrument.
(27.) The larger batteries, which were in use for a number of years, consisted generally of copper and zinc, arranged in different forms, according to the fancy of the operator. Thus, the copper of each cell surrounded the zinc, and both were united to fit into a porcelain trough, with eight, ten, or more cells. Here each cell is to be considered as a distinct battery, although the copper and zinc of the whole trough are united ; an arrangement contrived to remove the series of batteries from the trough at one time.
(28.) In this compound battery a porcelain diaphragm separates each simple battery ; but Dr. Hare discovered that a series of batteries might be placed in one vessel, provided that the metals of each battery did not touch in the fiuid, and that neither the electro-positive metal afforded a radiator point to the electro-negative metal of any other but its own pair, nor that any electro-negative metal radiated in a similar manner to any electro-positive metal. This form of battery is very little known in this country, and I believe but seldom used anywhere.
(29.) There is another form, which was devised by Cruikshank, and which consists merely of square pieces of zinc and copper, soldered together, and fixed at regular intervals in a wooden trough ; the zinc always being in one direction. In this battery the metals themselves divide the cells.
(30.) There are many other forms of compound batteries, which do not require particular mention, as the principles which have been already explained affect them alL
(81.) Provided the metals be sufficient to carry the current their thickness does not influence the quantity of electricity,
THICKNESS OP HETAL REQinBBI) POK A BATTERY,' 15
that depending upon the surface exposed to the fluid $ bul if the metals be so thin that thej cannot carry the electricity a dimtnutioa in the quantity of the current produced will jmOar to that which aHses from thin wires imply because a resistance is aflTorded to gairhnie Wm
this reason, earthenware coated with platinum was to answer for the native plate id ah acid the
platinum surface not being of sniletent thiclniesS Ydy however thin a metallic or good conducting surface be employed, the current will gradually traverse it ; a property of no small importance for the electrotype.
(82.) As the metals are good conductors, and the metallic oxides non-conductors, it is important that the negative metal should expose a clean metallic surface, or else it will be perfectly inert ; therefore, when the old forms of batteries are employed, the copper should be thoroughly cleansed from oxide before the battery is put in action.
(33.) When the metal is thoroughly cleaned before it is employed, it still very speedily, in fact, almost instantaneously, loses its power. Now this depends principally, if not entirely, in a single battery, upon the hydrogen's adhering to the negative metal, which thereby becomes coated with a non-conducting surface of hydrogen, and is therefore rendered inoperative. The state of surface influences this adhesive quality.
The reader may readily convince himself of the truth of this. Let him immerse in a tumbler of dilute sulphuric acid a polished plate of copper, and then place a piece of zinc in contact with the copper below the surface of the fluid. Bubbles of hydrogen will speedily appear upon the surface of the copper, and will soon cover its entire surface. It will be seen that these hubbies, instead of rising to the surface, and escaping as soon as formed, (or in other words being evolved,) will continue adhering to the metal. This upon the principle called heterogeneous adhesion,
16 Adhesion Of Hydrogen To Metallic Plates.
can only operate when the surfaces of bodies are brought into very close contact. A smooth surface of metal favours the adhesion of the gas to such an extent as to counterbalance the force with which it tends upwards to the surface of the fluid. This, considering the difference of specific gravity between hydrogen and water, can by no maus be a trifling force. Mechanical roughening by aimdps0t obviates in some degree this annoyance, but is no Ontii a remedy. The mode of overConung tills when we describe mybattey. T'glve an 4diea of the amount of hydrogen which will adhere to' imiooth metals, 1 have frequently seen platinum, the heaviest of all substances, rise, by the force of the hydrogen, to the top of the water, after it had been in contact with shic,
(84.) The same observations apply to the positive metal ; for, it even impure zinc be polished, the hydrogen will yet adhere to such an extent, that scarcely any action will take place till the surface is corroded, when it will immediately become violent. There is another mode, however, of overcoming this local action, which has been adverted to in this place, instead of mentioning it before, because I believe its action depends upon the facilitating the adhesion of hydrogen ; this mode is the amalgamation of the zinc by mercury4 In making a battery this should never be neglected, from its economy, as but a small quantity of mercury is required. It Is effected by acting upon the surface of the zinc, either by acid, or by planing the oxidized surface and timn Tublnng it with metallic mercury. Practically, plates of Idnc are placed for a short period in dilute sulphuric acid, when metallic mercury is well rubbed over them. In conducting this operation the workmen should be taught to endeavour to make the zinc absorb as much the quicksilver as possible, and in the long run that will be found be tile .most economicaL Xet us never forget to whom we
AHiXGAMATIOX OF THE POSITIVE METiX.
owe this discovery, which of itself enables galvanic batteries to be used extensively in the arts. Ages to come will perhaps have to thank the inventor, whom we are too apt to forget because he was neither on the council of the Royal Society nor a London Professor, yet still the obligation from the public to Mr. Kemp is the same.
The explanation which 1 have ventured to give of this valuable improvement is the following : the mercury envelopes the sma ll pmtions q £ charcoal and fmren metali and therefore the first gas evolved adheres so tenlj to tiiese that every finreign point of metal becomes coated so as to prevent farther action ; for, of all the metals known, ere is none to which the hydrcen sticks so firmly as to merenry* A very instructive experiment proves that the absence of action depends on the adhesion of the hydrogen; for, if mercury with zinc dissolved in it, be placed in dilute sulphuric acid, it will give off no gas, but will be covered with large bubbles ; but if a little sulphate of copper, nitrate of silver, or nitro-muriate of platinum be placed in the amdl,' an instantaneous change ensues, for the hydrogen has not now to be evolved, but is absorbed in the nascent stato, to reduce the oxides of these metals. The protective influence which mercury exerts upon zinc is only operative when the hydrogen has to be evolved and not absorbed ; thus it is but little protection to zinc when placed in dilute nitrie acid, because the nascent hydrogen is absorbed by the nitrous acid, and does not infilm the zinc. This fact may be readily observed if two pieces of amalgamated zinc be taken of similar size ; when one is placed in dilute sulphuric add, and the other in the dilute nitric, the degree of action upon the zinc will be found to be far greater in the latter than in the
Time only oonSnns the strong opinion which I entertain of the value of die diflcoveiy of the nee of amwgamated zinc, and it wae with eatieikc* tion I read the above paragraph, popped into the obitu of Mr. Kemp, in the Gentleman's Magae, as a proof that hie biopher held the same minion as myself
vAJMALGAMATION OP THE POSITIVE METAL.
former case. In fact, in dilute sulphuric acid, zinc well amalgamated will last for days, or even weeks, without suffering any important loss. These observations clearly indicate the necessity of abstaining altogether from the use of nitric acid, when we are desirous of obtaining the galvanic power at the lowest cost
(35.) In an elementary treatise it is unnecessary to enlarge upon these views, but those desirous of entering into them can consult the Philosophical Magazine for April 1840, or the Transactions of the Society of Arts for that year. An observation of these facts led me to construct the Chemico-mechanical battery, of which we shall speak after we have described the other forms. Before, however, entering upon that subject, there is still another property of metals which has not been adverted to : viz. that the least oxidable metals, as platinum, in common with the metals which have most affinity for oxygen, become coated, or so infilmed with air, that they are rendered useless, because they expose a film of badly conducting substance to the fluid instead of a metallic one. The film may be instantly destroyed by heat, or by strong nitric acid. This fact has been long known, and the familiar experiment of causing iron filings to swim, while magnesia, which is an impalpable powder, sinks, is an example. But I believe it had not been noticed as influencing galvanic effects till mentioned in the paper before quoted.
(36.) The mode in which the hydrogen is evolved, is supposed to influence the power of the battery ; for, if removed from the negative metal in the nascent state by any substance which readily yields oxygen to combine with it this power is greater than when it is evolved. The cause of this is not exactly known ; some supposing that it arises from chemical action at both poles of the battery, whilst others explain it by supposing that the hydrogen carries off a certain portion of electricity of tension, jas ey find that a
daniell's battery.
gold leaf [electrometer is affected when brought near the evolved hydrogen.
(37.) No farther improvement was made in the galvanic battery hitherto described ; all previous alterations being as to size or form, as flat cells, round cells ; or as to the arrangement of the metals, as to which should be innermost : but these can scarcely be called improvements. At length Professor Daniell turned his attention to the subject, and produced a battery on a principle altogether new.
(38.) The form of battery which he recommended was from eight inches to two feet in height, and four inches in diameter. The outer vessel is to be made of copper, of which the external part may be painted, as it plays no part in generating electricity ; while the inner remains uncoated. Into this cylinder a solution of sulphate of copper is to be poured, inbead of the dilute acid used in previous batteries ; but now, if a zinc plate were put into this solution, and contact were made, the copper of the solution would be reduced upon the zinc as well as on the outer cylinder, and thus great waste would ensue. It therefore became necessary to enclose the zinc in a porous vessel, in order to separate it from the sulphate of copper. This was effected by a piece of the gullet of the ox ; and into this, which forms an inner vessel, the zinc, with dilute sulphuric acid, is to be placed.
Thus we have an outer copper cylinder (c) with a solution of sulphate of copper (s), and an inner porous vessel (f) containing zinc (z) and dilute acid (a). As soon as contact is made, the zinc is dissolved, and sulphate of zinc is retained in the inner part of the vessel ; whilst, instead of the hydrogen being evolved at the negative metal, it reduces the copper from the sulphate of copper. The inner vessel mast be looked upon as a disadvantage, because
20 YABIOtJS AREiLNGBMENTS OP DAKIELL's BATTERY.
there is no doubt that it lessens the power of the battery by materially increasing the resistance. The more porous this vessel is, the greater is the quantity of electricity developed ; and so common brown paper, coarse canvass, and porous earthenware tubes are employed, instead of the bladder, or the lining membrane of the gullet or intestines, as formerly. Professor Daniell used for his positive metal cast zinc rods, which he amalgamated ; and, as a little copper always passes through the porous vessel, this should be repeated every time it is employed. The earthenware tubes immediately after use should be plunged into water, and there kept till all the sulphate of copper is dissolved out ; or else, by crystallization, it will sometimes disintegrate the vessel.
(39.) Many have thought that the zinc being two inches apart from the copper is too far, and they have used cylinders which approached a great deal closer; but although there is no doubt that by these means increase of power is obtained by lessening the resistance, yet many more inconveniences attend their application than the employment of the form originally suggested by Professor Daniell. In the use of porous tubes of every soi% whenever the reduction of a metal takes place, care must be taken that neither of the plates of the battery touch the porous vessel ; for otherwise the reduction of the metal will take place upon it, and at length a line of continuity will extend from one to the other. Candidates, ever anxious to obtain the fame of a new invention, made this battery square, oblong, parallelepiped, and even in many other forms, without any real advantage ; for all the alterations, attended with benefits one way, have counterbalancing disadvantages.
(40.) This battery has been thought to be principally valuable for its constant effects ; that is, for the power which it possesses of generating exactly the same amount of eleotricity for a bug time together.
(41.) To obtain its constant effects kowev, obtain
CONSTANT EFFECTS OF DANIELL's BATTERT. 2t
cautions are required ; for if we alter the resistance of any part of the voltaic circuit, whether in the cell of the battery or without it, the amount of electricity passing will vary ; thus, if the size of the wires used for the communication be altered, or their length either materially increased or diminished, then will the quantity of electricity vary. The distance between the poles, and also their size, must remain the same, and great care must be taken that the porous tubes be of the same texture ; for it is to be remembered, that if but one bad earthenware tube be used in a battery of large series, the quantity of electricity will be influenced throughout.
(42.) Much misunderstanding has arisen from the use of the term constancy ; it is often thought to signify long-continued action, whereas these properties are really difierent ; for a battery may be constant, but only remain in action for a short period ; and again, a battery might continue in action for years, and not be constant in its action : the property of long continuation, however, is by far the more valuable.
(43.) The principal disadvantages of this battery are, , the labour required to set it in action ; secondly, the trouble and expense attending the use of the porous tubes; and further, the necessity of continually re-amalgamating the plates; and, lastly, the small quantity of fluid which the porous pots contain to dissolve the sulphate of zinc.
(44.) The essential advantage which this excellent battery possessed over all which preceded it, is the removal of the hydrogen, whilst in the nascent state, by its decomposing the sulphate of copper, instead of its evolution at the negative vesseL It is owing to this, also, that this battery gives off no fumes. To employ its decomposing eflects on acidulated water, with platina poles, with the greatest advantage, a series of ten or twelve is required.
(45.) Another battery, upon precisely the same princes, although applied in a very difTereni way, was invented by
grove's battery.
Mr. Grove. He uses, for his negative metal plati- 2 . num (p), and in the inner porous cells he puts strong nitric acid (n), and in the outer vessel, with the zinc (z), dilute sulphuric or muriatic acid (a). The form which Mr. Grove prefers is a many- celled trough, like the Wollaston's, with flat parallelopiped porous tubes in the interior ; and, as platinum is an expensive metal, he takes care that the whole surface is brought into full operation, by completely surrounding it with zinc. In this battery the nitric acid is decomposed by the hydrogen and deutoxide of nitrogen is evolved ; which, coming in contact with the atmospheric air, is converted into nitrous acid.
(46.) This battery is remarkable for the intensity of its power ; a series of four being sufficient for most decompo sitions. A large series exhibits the arc of light in a very brilliant manner ; for showing this phenomenon it exceeds all other batteries. This battery, however, with its great intensity, is not without some serious disadvantages ; for the nitrous fumes which are evolved during its action are extremely pernicious to the animal economy, so much so that it is highly dangerous to be exposed to them without a free access of air. Many cases have come before myself of injury to the lungs, and even constitutional effects, from exposure to nitrous fumes; and, therefore, in using this excellent battery, due precautions should be taken. These nitrous fumes will attack almost every metallic surface with which they come in contact, and therefore it should not be employed in a room where there are polished stoves or metallic apparatus. The nitrous acid moreover passes through the porous tubes, and attacks the zinc to a considerable extent, independently of that zinc which is dissolved to generate electricity ; and lastly, this battery has the objection of requiring porous tubes.
(47.) We have thus seen that Mr. Grove's intense battery
grove's battery.
is, in its principle, similar to that proposed by Professor Daniell, for in both the hydrogen is removed by chemical means ; in the first instance by nitric acid, and in the second by sulphate of copper. It possesses a great advantage by having one of the best fluid conductors we are acquainted with ; for the nitrous acid formed during the action of the battery, has been found by Dr. Faraday to possess this valuable property in a most eminent degree. It is a curious fact that the use of nitric acid had long been known ; for in all the old forms of batteries, a certain proportion of this acid was employed in the charge. Of course there are many other modes by which the same results may be obtained ; as, for instance, by using nitrate of silver, or the salts of gold, palladium, and platinum, or by other oxygenated acids, as the iodic, chloric, and bromic. I have tried many other substances upon this principle, but have not arrived at any new result, nor have found any arrangement superior for its power to the nitric acid battery.
A new substance, to be used in a similar manner, has lately been brought before the Chemical Society, a society which promises to give a great impetus to chemistry in this country. It is the dichromate of potassa, a solution of which is placed on the negative side of the battery, whilst dilute sulphuric acid is used on the zinc side. Now the zinc is dissolved on the outer side of the battery by the dilute sulphuric acid, and the dichromate is decomposed at the negative end ; by which means, as. in all diaphragm batteries, you incur a double expense without any advantage as to power, but with a slight sacrifice of space, and, in fact, by burning your candles at both ends. The ingenious application of this salt was first made known by Dr. Leeson.* Mr. Grove's battery, charged
♦ A Daniell's battery, charged with dichromate of potassa, instead of sulphate of copper, forms a Leeson's battery; bat it has never come into general ose.
THE OHEmCO-MECHAKICAL BATTERY.
with potash, instead of nitric acid, also forms a powerful instrument.
A battery has been occasionally employed with iron for the negative pole. Sbonbein showed that it might even he used as a Grove's battery ; but although means have been used to bring it into notoriety under a new name, it is not particularly employed, because the iron is liable to be acted upon. A platinized iron battery I have occasionally employed, but it is liable to the same objection.
(48.) In conducting a series of experiments on the ferrocyanuret of potassium, having had frequent occasion for the use of a galvanic battery, I found that although the two last were admirably contrived instruments, yet that it was very desirable to possess one that could be set in action at a moment's notice, and with comparatively little trouble. It became thenceforth my endeavour to construct one that should require little or no labour in its employment, and this was followed by devising the Chemico-mechanical battery.
(49.) This battery, after I had minutely investigated every property which belongs to the metals of which batteries are constructed, was made upon noticing the property which rough surfaces possess, of evolving the hydrogen, and smooth surfaces, of favouring its adhesion. Thus, whatever metal we use for our negative plate, we take care that it be roughened, either by a corrosive acid, as iron by sulphuric acid, copper and silver by nitric acid, or mechanically, by rubbing the surface with sand-paper. Even by these means the metals are rendered much more efficient ; but, to take advantage of this principle to the fullest extent, I cover platinum with finely divided black powder of platinum, by galvanic means ; that is, I place the platinum as the copper is placed in a Daniell's battery, but, instead of emplo 3 ring sulphate of copper in the outer vessel, I use a small quantity of nitro-muriate of platinum, so that the finely divided metal is thrown down on the sheet platinum previously roughened by sand-paper.
PRlNOrPLB OF SMEE's BATTERr.
In this way it was also placed on palladium, silver (roughened by nitric acid), plated copper, iron of every sort, and on charcoal, with the same good result ; but no other metal was found to answer for its reception. The metal generally employed is silver, because of its cheapness and its not undergoing any alteration. But whatever metal be used, the principle is the same, viz. the affording a surface to which the hydrogen shall not adhere, but from which it shall be evolved ; and the infinity of the points which are presented by such a surface as above described, appears to be the cause of this excellent result. The preparation of the silver is now made a separate branch of a trade, and perhaps it is the first application of the decomposing power of the galvanic battery which was publicly sold. The platinized metal can now be bought ready for use ; but, for those who desire to perform this operation, a brief description is here added.
(50.) The metal to be prepared should be of a thickness sufficient to carry the current of electricity, and should be roughened, either by sand-paper, as in the case of platinum or palladium, or, when silver is employed, by brushing it over with a little strong nitric acid, so tliat a frosted appearance is obtained. The silver is then washed, and placed in a vessel with dilute sulphuric acid, to which a few drops of nitro-muriate of platinum are added. A porous tube is then placed in this vessel, with a few drops of diluted sulphuric acid; into this the zinc is put. Contact being made, the platinum will in a few seconds be thrown down upon the surface of the silver, as a black metallic powder. The operation is now completed, and the platinized metal ready for use. However, iron, when thus prepared, is as effectual as silver, and may be sometimes employed with advantage. With this metal, all that is required is to rub a little nitromuriate of platinum over it, and an immediate deposit of the black powder takes place. Palladium and iridium are found nearly as effectual as platinum to coat other metals with, and.
this kticar metaL Wiifai ihe hs $m wa iilea bat prevailed in the minds of tonie 41mt wife game might be used with advantage ; but it is diffiet to eonemve where the benefit would lie, for the eost of the material would be greater, the surface for the same weight of metal would be less, and neither space nor power gained bj its adoption.
(51.) The liquid generally adopted to excite this battery is a mixture of one part by measure of sulphuric acid, and seven of water, which will be found amply strong for all purposes. Where we desire greater intensity, we can obtain it by the addition of a few drops of nitric acid ; but, if too much be used, it might attack the silver. When, however, platinized platina is employed, the nitric acid in very small quantities may be used with impunity. The electro-metallurgist will frequently find it advisable to use dilute sulphuric acid, only containing from 1-lOth to l-16th of the pure acid, and adding some acid when the first is exhausted ; taking care, however, that the quantity of acid never exceed the l-4th of the original water, for any excess above that quantity will be useless, as the liquid will then become saturated with the sulphate of zinc (19). The zinc, acid, and water being severally required to excite the battery, it is possible to regulate them that they should all be exhausted at once, so that the zinc should neutralize the acid, and the resulting sulphate of zinc exactly saturate the water. This, however, is very interesting in principle, but practically it would be impossible to act with such precision ; yet we must never forget this fact whenever we charge our batteries.
(52.) Numerous inquiries have been made as to what arrangement is best suited to this battery; but this must depend upon the purpose for which it is employed* Far the student's laboratory the porcdain or gutta percha trough of many celb appears to be best adapted ; and it is some-
of em bd of Hie oth ms Hiej m&j be reqmixed. le sihrer ling the most expenslTe meti the me should oompletdij surround it, so that the whole of the silver may be brought into action. Where a battery is
required to continue in action for a very long time, as for days or even weeks, a larger vessel, to contain more dilute acid, must be used ; for electro-metallurgical purposes it has been hitherto found most economical to use a vessel of a size sufficient to hold liquid to last for seven or ten days. The form of battery now most universally employed for these purposes, consists of a piece of silver (s), on the top of which is fixed a beam of wood (w) to prevent contact with the silver. A binding screw is soldered on to the silver to connect it to any required object. A strip of zinc, varying at the fancy of the operator (z) from one half to the entire width of the silver, is placed on each side of the wood, and both are held in their place by a binding screw (b) sufficiently wide to embrace the zincs and wood. These batteries vary from the size of a tumbler to a ten or twelve gallon vessel. In the very extensive application of this battery to the arts, the little pieces of zinc which remain undissolved in the battery form an im-
Fobms Of Smee'S Batteht*
portant consideration to the manufacturer. Some distil the mercury from them, others sell them to the zinc works, whilst others have never turned them to any account at all, waiting patiently, in the hope that some more beneficial application of them might be discovered. These latter have hundred-weights of odds and ends in hand which they are desirous to employ. After considering the matter carefully, I have to propose the following use for them; in fact, I make them the positive pole of a battery, by placing them at the bottom of a vessel and covering them with mercury. A silver wire is then placed down a glass or gutta percha tube into the quicksilver, so that the wire may nowhere touch the dilute sulphuric acid, with which the vessel is filled, but simply make a good metallic communication with the mercury. At the other end of the wire a binding screw may* be tached for the convenience of the operator. The platinized silver plate (s) is then to be immersed in the fluid, and placed as near to the mercury as possible, without actually being in contact, whilst no part of it should be more than three inches from it, as a considerable reduction of power would then ensue. This form of battery may be fairly called the Odds and Ends Battery, and though not so philosophical an instrument in its construction as the form last described, yet no manufacturer should be without one to use up the scraps from his other batteries ; and 1 must say this instru* ment requires less trouble jn its manipulation than any oer form 1 have ever seen. An odds and ends compound battery, which will only require a binding screw at each end, may be made by placing the mercury and zinc at the bottom of a many-ceUed porcelain trough; the platinized mlver should be cut into suitable squares, leaving a narrow slip to
Forms Of Smees Battery. 2&
connect it with the next cell. The strip must be placed in a glass tube, or covered with any nonconducting substance, as gutta percha, leaving the end only to dip in the mercury of the next cell. A series of little glasses may be used instead of the many celled trough for some purposes. The only objection which I have found in this form of compound battery, is the possibility of the zinc in one cell being completely exhausted, when the silver wire will begin to dissolve ; in all other respects it is a delightful instrument when you do not care about obtaining the maximum of power, and you can obtain the galvanic principle by this means at a lower cost than by any other way. The odds and ends battery is admirably adapted for gilding and plating, or it may be employed for any operation that requires much time for its performance. The charge for this battery might contain one-third by measure of strong sulphuric acid, as the local action is very trifling ; but it is found more advisable not to employ the solution so strong, as, when nearly exhausted, the sulphate of zinc will sometimes envelope the zinc and mercury, and prevent farther action before the top part of the liquid is fully saturated. Some contrivance should be adopted to carry off the saturated liquid as soon as formed. An advantage of this instrument is, that spelter, or raw zinc, may be used instead of manufactured zinc, and that no mercury is wasted, as the whole is left after the solution of the zinc.
(53.) When we desire to employ a battery for manufacturing purposes, it might be as well in some cases to remove the sulphate of zinc as soon as formed, by means of a syphon tube passing to the bottom of the vessel, while fresh acid is continually supplied at the top; but this is not generally necessary. For these purposes the battery should be so constructed, that any of the zinc plates, when worn out, can be readily replaced. There are many other forms which
Fobms Of 8M££*S Battebt.
may be adopted ; as the circular, with the zinc outside ; or ft may be used as a tumbler battery.
(54.) The characteristic of this battery is the great quantity of electricity produced, and its simplicity ; moreover, it requires but very little trouble in its manipulation. The zinc seldom demands but one amalmagation, as that will generally last till the metal is all dissolved. It is very important to use for batteries zinc as pure as possible, for by that means the chance of local action is materially lessened. The manufacturers of zinc plates have a trick which is very fatal to this metal, for they buy up the refuse or waste pieces which frequently contain solder, a composition of lead and tin, and melt them with the raw zinc. This mixture always tells its tale during the action of the battery, as a light spongy flocculent precipitate rises to the top of the liquid which is metallic tin, and when any particle touches the zinc a little local battery is formed, which causes great waste of metal. If the zinc or acid contains much tin it is almost hopeless to attempt any operation.
(55.) In using this battery it is important that no salt of copper, lead, or other base metal be dropped into the exciting fluid, as by that means the silver would become coated therewith ; the plain consequence being, that a surface of copper, instead of that of the finely divided platinum, is presented to the fluid. From a want of knowledge of this fact, in some who have used the battery, I have seen the negative metal covered with copper, which finally becoming oxidated rendered the platinum useless. When this takes place, it is best removed by immersing the plate in dilute sulphuric acid, to which a few drops of nitro-muriate of platinum should be previously added ; by this process the baser metals are dissolved and metallic platinum tlurown down. Some manufacturers prefer dipping the silver into a sdution of this sort every week. In this battery the ehm is never reduced upon the negative metal, from sulpimte of zinc
Compabison Between The Three Batteries. 31
formed during the action of the battery, so long as the ex* citing fluid contains any acid at all. Other interesting matter connected with this subject will be detailed when treating of the reduction of zinc.
(56.) Such is a brief view of the three batteries now in use: Professor Daniell's excellent invention being distinguished by its constancy ; Mr. Grove's powerful battery, by its intensity ; and my own by the cheapness with which the quantity of electricity may be developed, and by its simplicity. Neither of these can be regarded as a perfect galvanic battery, for each wants some of the properties of the others ; it is to be hoped, therefore, that every attention will be given to the further improvement of these valuable instruments, until the good properties of each are combined in one. Which of the three is at present to be preferred, must depend upon the purpose for which it is required ; and the choice must of course be left to the operator. For my own part, it affords me much pleasure to see that the platinized silver battery has fully answered the / expectations which I formed of it ; or even, I may say, in its extensive application very far exceeded it, as the amount of work already actually performed by this instrument is much greater than the total amount done by all other batteries ever since their first invention. By some it has been too much extolled, by others too much blamed. Notwithstanding the mis-statements on both sides, it has fully stood the test of time, and has been employed by the public in a manner which I had not even hoped. The reason they prefer it for general and especially for heavy manufacturing purposes appears to be, that it does not require the use of porous tubes, nor of the strong acids, and that it does not give off poisonous fumes. It usually continues in active operation for six, eight, ten, or more days, when a sufiOLciency of acid is supplied to it. The zinc, as a rule, demands but one amalgamation after that operation has been thoroughly
82 Comfabisok Betweek The Thheb Batteries
Bibeted ; and tlie time required either for siting it in action or for maintaining its operation, is comparatively not worth a thought ; and, lastly, the expense of working it is reduced to the lowest possible amount, being exactly proportionate to the power obtained. With regard to the choice of the battery, it appears to me that he must be a clumsy operator who obtains the galvanic principle and cannot apply it J therefore the whole subject under consideration may be summed up by ascertaining with what battery the greatest amount of the galvanic fluid can be obtained at the smallest cost, the least labour, and the greatest convenience. These three batteries agree by being each excited by the action of 2 inc upon water, the formation of oxide of zinc, and its subsequent removal by the sulphuric acid forming a sulphate of zinc ; now, as this same salt is formed in each battery, the same quantity of water to dissolve the sulphate of zinc will be required to produce any amount of work, and therefore, whether Grove's, Daniell's, or my own battery be employed, the same sized vessel must be employed ; proving the fallacy of attempting to obtain a battery in a small compass where sulphate of zinc is formed. In Grove's and Daniell's battery, however, if the diaphragm be of a nature that precludes the free passage of the zinc to the side of the platinum or copper, then will the amount of action depend upon the capacity of the vessel in which the zinc is immediately placed, and in that case a much larger vessel will be required for theirs than for mine.
(57.) Perhaps I may be expected to give an approximation to the relative cost of working the three batteries. In mine it is the cost of the zinc dissolved by the acid : zinc 4 - acid+a local action. In the constant battery it is zinc+ acid. + sulphate of copper -f much local action. Each cell of this, to do any given amount of work, would cost about twice as much as mine. In Grove's battery it is zinc + acid 4 "Bitric acid reduced by the hydrogen + nitric acid combined
The Theme Inexhaustible.
with ammonia formed during the action of the battery + extensive waste of the zinc about three times as much as mine.
(58.) The construction of all the various forms of galvanic batteries has now been considered, and the principles also on which the peculiarities of each are founded have been briefly explained ; though, if this important branch of our subject were to be alone discussed at a length proportionate to its value, this volume would not be suflScient for the interesting and important matter relating to it.
Chap- Il
ON THB IBOPSBTIES OF OALYANIO AittNSiSB-
if Hi In fMibU, 59. HfinETs galtaubmete, 6b. Staa il.
ildctiy charges in teydenjar, 62; PliTsiological offsets, 63. Magnetism, 34 — 68. Galvanometers, 68 — 70. Horse-tiioe temporary magnet, 71—78. Decomposition cell, voltameters, poles, 74 — 84. Laws of voltaic decomposition, 85, 86. Table of chemical equivalents, 87. Fluidity necessary to decomposition, 88. Conduction of fluids associated with decomposition, 88 — 90. Intensity necessary for decompositions, 91. Electrolysis'; electro-chemical decomposition, 92 — 98. Danieirs theory, 99. State of the fluid during decomposition, 100. Effect of heat upon fluids, 101. Curions induction, 102. Author's theory of voltaic electricity, 103.
( 59 .) After describing the various forms of the galvanic battery, we are led to consider the effects which they prodace ; for these are called the galvanic effects, and the theoretical principle which causes them is termed galvanism.
The sign of a battery in action, is the change going on in each cell of the battery itself. In Daniell's battery it is evinced by a deposit of copper on the negative metal; in Grove's battery, by the evolution of nitrous fumes ; and in mine, by an evolution of hydrogen. These several actions mark exactly the quantity of current passing ; but in the two former batteries no accurate measure can be readily made, although in the latter the hydrogen may be collected in one of the cells by means of a glass jar, and the quantity thus exactly ascertained.
In my battery, as the hydrogen passes off from the silver it causes various sounds. When the current is feeble it makes
HAREIS'S galvanometer.
a gentle singing sound; when more electricity passes, it hisses ; but when it is giving off its gas at the utmost power, it roars, the liquid bubbling and boiling from the astonishing quantity of gas evolved. Formerly, when I resided in the Bank, 1 had a long room, and, when tr 3 ring the experiments necessary for my former editions, there were fluently not less than or sixty batteries at work. From habit and custom the sound which ought to be elicited was so familiar, that in the middle of the night 1 could enter that apartment in the dark, and detect any battery which was following its own course instead of complying with mine.
(GO.) The next phenomenon which a battery displays is the power of heating conducting substances according to the amount of current which is actually passing, and the resistance which they afford to its passage ; and by this the most infusible metals, as platinum, palladium, gold, copper, iron, and steel, may be instantaneously melted. The size of the wires melted will depend upon the quantity of electricity developed, while the length will depend upon the intensity of the current. Mr. Snow Harris has ingeniously taken advantage of this property to make an instrument for measuring the voltaic current. It consists of a fine wire passed through a delicate air thermometer, and the expansion of air shows the degree to which the wire is heated. This instrument is a valueless test, unless both thick and thin wires be used in two experiments, for otherwise but one property of the battery is estimated.
Conducting liquids may be heated in a similar manner. This fact may be seen in a great variety of ways ; dilute sulphuric acid may be made to boil in a syphon connecting two vessels in which the poles of an extensive series of batteries are placed. Another mode of showing the same fact is to take a piece of string and moisten it with acid, and connect the extremities with the poles of a series of gvanie batteries, when it will begin to smoke and become
61.) The next property which a battery displays, is it
.|e#6lr ef igiiitii!ig metalUc or charcoal points, when joined io tkk twb ende of the battery, and held so that they barely ) a light is then exhibited equal in brilliancy to that of a little sun. This has been called the spark, and much controversy has taken place among the learned as to the distance at which the spark will pass. Some have asserted that it will pass through some distance; Jacobi, however, considered the distance to be extremely small; but Mr. Gassiot fitted up 100 series of Professor Danielles largest batteries, but with them by the most delicate micrometer he could not discover that the spark would pass at any appreciable distance; on the contrary, this large battery would remain quite inert if the poles were separated by the distance of the thinnest film of paper. In a late number of the Philosophical Magazine, Mr. Crosse has revived the inquiry by stating that by a very extensive series of water batteries in his own possession he hat succeeded in obtaining the spark at a short distance. He proposes to enlarge his Jbattery to 1000 cells, in order fully to determine this point. Since that period the experiment has been tried with 100 cells of Grove's battery, belonging to Mr. Gassiot; but the spark was only found to pass through the smallest interval, and a most brilliant arc of fiame was obtained after the poles were connected and then withdrawn.
The spark seems principally to depend upon a combustion nf fine particles of metal, and, when chaicoal or hard gas
{62.) The next property evinced by the galvanic battery is its power of charging a Leyden jar ; but this is a prcerty of little importance, and requires an extensive series ef teries to be used to effect this object.
(63.) Depending upon the same causes as the last m .Uie shock, which is a convulsive twitching in the muscle from the intensity of the battery. This singular effect. requires generally a series. It is felt only when contact k either made or broken ; but if a cut exists in the finger, a series will illustrate this property.
When we desire to exhibit the effect of the shook upon a dead animal, a pin ought to be pn through the skin at the head, and another at its hind leg ; every time the poles of a battery are connected or disconnected with these, strong convulsions will take place. If the upper lip be touched with a piece of zinc, and the under part of the tongue with a piece of platinum, or tnce versa, a flash of light will be perceived when they are connected, whether the eyelids he open or closed. All these phenomena are termed the physiological effects, and I have amply considered their importance in my Llements of Electro-Biology."
(6i.) A galvanic battery has the power of producing certain effects which are called magnetic effects, and the supposed principle of magnetism. To describe the term magnetism would be impossible, like galvanism, or electricity, because we are only cognizant of it by its properties. There are but two metals capable of being magnetic, and these are nickel and iron. The identity of magnetism and electricity has, like all other branches of philosophy, received many important additions from the indefatigable Faraday; but, although magnetism is fraught with interest, it will be foreign to the purpose of this work to enter farther into its important details than to illustrate the effects of galvanism.
(65.) The voltaic current, passing at right angles to a piece of iron, from which it is separated by any non-conducting substance, induces in it the properties which are termed magnetic ; for, if another piece of iron be now held to it, it will be attracted. The more frequently the same current passes round the iron, the greater will be the power ; and for this purpose it is usual to twist wire covered either with silk or cotton round the iron, in order that the same current may pass at right angles a great number of times. When the current ceases, from the connection with the battery being broken, a difference according to the nature of the iron is observed ; for, if it be the pure malleable soft iron, all magnetism immediately ceases ; hence iron so situated is termed a temporary magnet: but if hard steel is used for the experiment, the magnetism indeed is not so powerful, but it continues for a very long period ; hence in this state it is called a permanent magnet.
(66.) A permanent magnet, if suspended in such a way that it can vibrate, has one of its poles turned to the north pole of the earth, the other to the south pole ; but, if a galvanic current be passed round this permanent magnet in the direction of its axis, the magnet will be instantly deflected at right angles the current mid upon
HAGKETIC OiXVANOMETEHS. 89
principle an instrument has been constructed called the galvanometer.
(67.) The direction in which the needle is deflected is best remembered bj a little device which Professor Daniell described in his lectures ; for by supposing that we ourselves are the conducting wires, and the electric current passes from our head to our heels while we are looking at the magnet, the north pole will be turned to our right band. This ingenious device is applicable to every position, provided we are either above or underneath the plane of the needle.
(68.) Galvanometers are differently constructed, according to the delicacy of the experiments for which they are required. In general it is suflicient to use a needle centred as if it were to be used 6.
for a mariner's compass, and a long covered wire is to be passed alternately over and under it in the direction of the long axis. The two ends of the wire may be connected to mercury cups (p, n), to afford a ready means to unite them with the poles of the battery (, 6.).
(69.) A much more delicate form of galvanometer is constructed by using two needles, so suspended that the north pole of one is over the south pole of the other.
The polarities are thus neutralised, and no longer under the influence of the earth's magnetism. In this state they are called astatic, and are generally suspended by the finest fibre of silk, so that the slightest voltaic current will act upon them.
It is advisable to allow one needle to have a slight prepon derance, in order that the long vibration may not be trouble* some. An instrument like this is only necessary fosr tiie most minute experiments.
40 MAGOTTISM A TBSOf OF THB QUANTITT OF ELECTRICIXY,
(70 Another form is termed the torsion galFanometer because a resistance is afforded by the twisting of an elastic substance. By this we are enabled to appreciate differences in slight currents*
(71.) However useful the instrument may be for all small currents, large quantities of electricity are seldom measured by magnetic effects ; but I believe that the right use of the magnet is a very important addition to our instruments for measuring galvanic currents. To estimate the quantity of electricity in any voltaic current, a piece of soft iron is to be bent in the form of a horseshoe, and a good sized covered copper wire is to be wound round it, the two ends being left free for connection with the battery. A piece of soft iron with a hook attached to it is to be used for the keeper, and the weight which this sustains indicates the amount of electricity.
This instrument is only valuable for comparative experiments, as different results will always be obtained by different magnets, because the quality of iron is found materially to influence the results ; but if the same magnet be used, and the wire of sufficient dimensions and of moderate length, there will be scarcely any appreciable resistance offered to the curi'ent ; and the relative quantity of electricity evolved, independently of its intensity, can be accurately ascertained.
(72.) Temporary magnets are too frequently made with very thin covered wire, and even great lengths employed. Now, in this case, the amount of magnetism induced by any current ceases to be an exact measure of the quantity of electricity passing, because intensity is required to overcome the resistance afforded to the passage of the current from the wires ; and it is from this cause that electro-magnetic engines, possessing, as they do, several magnets, and very often thin wires, require several cells before the current freely passes.
(73.) To give a comparative estimate of the value of this test of the quantity of electricity evolved, and of that where-
Toltahbtebs*
afforded by the evolution of the oxygen at the positive pole, this effect is not manifest ; but even in that case, if it be reduced to a fine wire, I have seen a battery, capable of evolving 80 cubic inches of gas in five minutes, not able to evolve from the diminished surface scarcely one cubic inch in the same period. When a metal is used capable of combining with the oxygen, as silver or copper, then the size of the poles makes important alterations, even if large plates- are employed. We shall hereafter see, that in the reduction of every metal these properties must not only be remembered, but acted upon, if we wish to perform our operations with success.
(76.) There are many forms of the decomposition cell which are useful, according to the purpose for which it is wanted. The simplest is the V-shaped tube, which is nothing but a glass tube bent in the shape of the letter from which it derives its name. A little strip of platinum is to be placed in either part with the fluid, and these are to be connected, one with the negative, the other vrith the opposite pole of the battery.
(77.) The next form was devised by Professor Faraday, and is adapted to measure the quantity of gas given off when water is decomposed. To this he gave the name of voltameter, as indicating the amount of electricity passing. Of this form there are many varieties, differing as a small or large quantity of gas is required to be measured. In the former case, two pieces of platinum are fixed about a quarter of an inch apart, and a tube, graduated to cubic inches, is supported over these poles so that the gas may be collected. Sometimes two tubes are employed, one over each pole, the object of which is to collect separately whatever may be evolved. In other cases, where large quantities have to be estimated a bent tube passes from the top of the apparatus
4
to a graduated jar placed in a pneumatic trough. Where great accuracy is required in the measure of the gas or gases
Fig. 8 .
evolved, they must be corrected bygrometrically, thermometrically, and barometrically ; but this nicety would only be required for most delicate experiments. This instrument is made more complicated when the operator is desirous of investigating the changes which take place in the solution ; for then porous tubes of earthenware, bladder, &c. are used to separate the poles, and to prevent the solution on one side passing freely to the other. Substances requiring heat to bring them into a state fit for decomposition are generally placed in a tube containing two fine platinum wires, which serve as poles when connected to the battery*
A very useful form of decompositicm apparatus is a vessel with a diaphn {fig. 10.) or a glass tumbler {fig. 11.) (t) cut in half, and the edges ground smooth : between thm
Fig. 10 .
I !i'
'Ei
h
Blbcte0De8, Anode, Cathode, Etc.
any diaphragm (d) can be placed, as the two halves are kept firmly together and water-tight, by a brass band surrounding them (b).
(78.) Having described the usual apparatus to effect decomposition, we have seen that in every case they have in common two pieces of metal, separated from each other, but capable of being connected to either extremity of the battery. These pieces of metal have the mysterious and incomprehensible names of poles ; one of which may be considered as holding the place of the negative metal, and is called the electro-negative pole ; and the other, the electropositive pole.
(79.) However, Dr. Faraday, disapproving of the name of poles, has called the electro-negative the cathode ; and Professor Daniell, disapproving of both, has called it the platinode. These three terms, the electro- negative, cathode, and platinode are synonymous, and are given to that pole which would have been the metal unacted upon, had it been in an ordinary cell of the battery. The opposite pole holds the same place in the decomposition cell as zinc in the ordinary battery, and technically has the name of the electro-positive, anode, zincode, or oxide of the battery.
Dr. Faraday has described the poles as the passages or doors by which the electricity enters into, or passes out of, the solution suffering decomposition. On this account he has given the term of electrodes. Gnod conductors are the best adapted for poles, and for this reason metals are generally employed ; but poles of water, and even of air, have served this office.
(80.) The metal employed for Faraday's voltameters should undergo no change either from the solution in which it is placed, or from the elements which may be evolved at its surface ; and in this respect platinum answers above every olh&t substance, for almost all other metals are liable to be oxidized, or even dissolved.
Mc0Mp081Ti0N Cell.
(81.) The greatest confusion has arisen by not considering the decomposition cell as one of the cells of the battery, but referring the effects to the plate of the battery to which the pole is connected. The reason of this itf obvious ; for, when the terminal plates of a battery are connected with a wire, the circuit is completed, and the platinum of the battery is the platinode, electro-negative, cathode, or hydrogode of the battery. When the circuit is completed by a liquid to be decomposed, the effect is no longer to be attributed to the terminal plates of the battery, but to the plates in the decomposition cell with which they alternate ; so that, as the free zinc of the battery is connected with the platinum of the decomposition cell, the name must not be given from the zinc of the battery, but from the platinum of the decomposition cell ; and, therefore, it is the platinode of the battery. The converse of this applies to the extreme platinum of the battery ; for, as the platinum in the decomposition cell with which it is connected holds the place of the zinc in the other cells, the platiiMim being substituted for zinc, to cause the evolution of the oxygen and to prevent its combination, the name must be given to the platinum in the decomposition cell, which is there holding the place of the zinc, and not to the terminal plate of the battery ; it therefore is the zincode, electro-positive, anode, or oxide of the battery. Some have given a different explanation of this alteration of the poles, when the circuit is completed by a solution to be decomposed, instead of metallic wires ; they suppose that the two terminal plates in a compound battery hold no farther place than that of carrying the current ; but this will not bear the test of inquiry.
(82.) We have now seen that the decomposition cell or decomposing apparatus, is nothing but one of the cells of the battery varied for the purpose of experiment ; it necessarily follows the law, that in every cell there is a similar amount of chemical action. The mure of electric! by the chemical
Vaj.Tte Of The Toltameter.
action may be made in any other cell in a great variety of other ways, such as by ascertaining the amount of the reduction of any metal at the negative pole, or the solution of a metal at the positive pole ; for, wherever it is made, it will indicate exactly the action taking place. To Faraday these important facts are due, which, perhaps, have given us a greater insight into the properties of the galvanic fluid than any other series of inquiries.
(83.) Of the value of the decomposition apparatus, or voltameter, it is necessary particularly to take notice. As far as the amount of chemical action actually passing is concerned, the voltameter is a most valuable test, being in all ordinary circumstances infallible. But if we are desirous of comparing the amount of electricity capable of being generated by combinations of different metals, or the effects which are produced by differences of arrangement, or the resistance which various substances offer to the passage of the current, then it must be recollected that, if two platinum poles are employed, a strong resistance is offered to the passage of the current by the positive platinum pole, which would materially interfere with the accuracy of the result, unless that be overcome. In fact, the voltameter is an accurate test of that electricity which actually passes in a galvanic circuit, but it does not at all indicate what might pass. A want of application of these facts has led many distinguished scientific chemists into singular blunders, and many circumstances have not been appreciated which would otherwise have been noticed.
(84.) A far better voltameter can be constructed by using one of the cells of the platinised silver battery, and collecting the gas evolved from the negative plate. This apparatus would offer but little resistance to the passage of the elec tricity, and would thus give more accurate results ; but it has the disadvantage of itself generating dectricity, thereby Increasing the power. Practically, it iseeedingly diiBcuU
Talus Op The Voltameter. 47
to compare exactly the power of any two batteries or combinations ; for there are such a number of resistances in the galvanic circuit, and these vary with every battery, that it becomes quite a complicated mathematical problem to analyse the precise relative power of galvanic batteries. My battery voltameter is constructed in the following way : — a bell-glass is procured with a bent glass tube ground into the upper part to allow the gas to pass off to the pneumatic trough to be collected (a). In the bell- Fig. 12. glass a piece of platinised silver
is placed, which is connected by means of a piece of silver wire running through the glass to a binding screw outside the glass. The whole of the apparatus is plunged into another glass filled with dilute sulphuric acid, at the bottom of which is mercury and pieces of waste zinp; a silver wire connects this to another binding screw, to finish the connection, when the apparatus is ready for use. This instrument is extremely valuable when we desire to measure the work done with a single battery, for it makes not only a voltameter, but the battery itself. When we are compelled to make an experiment with extreme accuracy, we might vary the apparatus a little, so that the hydrogen arising from any trifling action on the zinc may not be collected along with that obtained from the voltaic decomposition. The zinc in that case should be placed exterior to the inner vesseL
(85.) When we state that the action in each cell is alike, it is not meant that the same weight of metal or salt would be decomposed in each cell, but that one equivident of some
C5Hbmicai- Equivalents.
substance is decomposed in each cell : thus for one grain of hydrogen liberated in one cell, 36 grains of chlorine would be liberated in a second, 96 grains of platinum in a third, and 200 of gold in a fourth, because these are the chemical equivalents, or combining numbers, of each of these separate substances.
(86.) The very term chemical equivalent seems to mark that it relates to something not very intelligible, and unfortunately that is found to be too correct, for this doctrine is found by all beginners to be exceedingly difficult. However by granting one supposition, the whole mystery is cleared up ; for let us fancy that every elementary body is capable of being subdivided into ultimate atoms, and that the atoms of these are of different sizes and different weights, it will then be apparent that, if we group these atoms together to form any compound, we shall require different weights. Thus, if we combine gold with hydrogen, 200 grains of the first would take only one grain of the last, and yet there would be but one atom of each ; or if one grain of hydrogen is liberated in the battery, 200 grains of gold would be deposited in the decomposition cell.
(87.) The following is a table of the equivalents of many of the substances which we shall have to speak of in this work ; for our present purpose we may consider them as the weight of the primitive atoms. Thus, if we are able to ascertain the weight of zinc dissolved, of hydrogen evolved, or of the metal reduced, we shall be enabled to ascertain either of the other cases, or how much, either in weight or bulk, of any other substance would have been under the same circumstances thrown down : —
Equivalent, by weight Equivalent, by weight
Hydrogen Potassium - - 40
Oxygen ... 8 Sulphur - - - 16
Chlorine - - - 36 Zinc - - 32
Ohemioal Or Yoltaio Rquivalents. 49
Equivalent, bj weight
Lead
Tin-
Iron
Copper -
Gold
Platinum -
Palladium
Silver
Nickel
Chloride platinum
Equivalent, by weight
Chloride gold - - 308
Sulphate copper - 125
Nitrate copper, anhydrous 94 Sulphate zinc - -143
Sulphate iron - - 139
Nitrate silver - - 170
Sulphuric acid - - 40
Nitric acid - - 54
Muriatic acid - - 37
Ammonia - - - 17
As 100 cubic inches of hydrogen weigh 2 grains and 1-lOth, it follows that, for every 47 cubic inches of gas evolved from my battery, 32 grains of copper, 96 of platinum, and 200 of gold, would be reduced ; and the equivalent of every other substance would show in grains the quantity thrown down. I shall frequently use the term " an equivalent of galvanic power," by which is meant that amount of power which is necessary to cause the evolution of one grain of hydrogen, 200 of gold, &c . ; therefore, whenever I use that expression, the grain will be taken as the standard, and it will be assumed that 47 cubic inches of hydrogen are evolved from my battery.
(88.) Next to the form of apparatus for decomposition, a description of the laws by which they are influenced follows as a natural sequence, and these have been fully investigated by the labours of Dr. Faraday. All bodies must be in a peculiar state to suffer decomposition, for no solids can be thus acted upon. When fused by heat, however, they very readily give up these elements ; as, for example, chloride of silver, which is decomposed by a single cell of zinc and platinum, excited by dilute sulphuric acid, though no voUmo power will separate them in the solid form.
There are apparent exceptions to this law, as the decom-
irf lime and baryta with the additiim ef yet the drat of these k undoubtedly moderately Vcduble. The same may perhaps even be said of the lattmri though probably a little dissolves which is decomposed, and thus the fluid not being saturated dissolves more, and this is repeated till the whole is dissolved.
(89.) No fluid will be decomposed unless it be a conductor : thus pure water, which is a very bad conductor, does not peld up its elements ; whilst if acids or alkalies be added to it, then it becomes a very excellent conductor, and IS easily decomposed. Water may also be made a good conductor by the neutral salts.
As a general rule, fluids will not conduct an electric current without suffering decomposition ; and for this cause, as soon as water is made a good conductor, it is decomposed, and the water does not conduct more electricity than is to be accounted for by the decomposition.
(90.) Some fluids, however, of good conducting power, may have a current of less intensity than that which is required for the decomposition passed through them ; therefore these two laws, both developed by Faraday, are not exactly the converse of each other. Examples of the exception to the second are to be found in chloride of lead or fused nitre, which conduct feeble currents without decomposition.
(91.) A certain intensity is necessary to effect all decompositions, and this differs with different substances, according to the resistance they offer to the passage of the galvanic fluid; thus, a solution of iodide of potassium, or fused chloride of silver, yields to a single battery, whilst dilute sulphuric acid and other substances require more intensity to eflbct the same object.
The following, upon the authority of Faraday, k a short list of substances in the order in which they most readily give up their elements : —
Iodide potaiiiiia iduMofi.
Chloride of silvery fused*
Froto-diloride of do.
Chloride of lead, do.
Iodide of lead, do.
MuriaUc add,
Water, acidulated with sulphuric acid.
(92.) Some bodies suffer decomposition directly, as the consequence of the voltaic force passing; as water, which gives up its elements, hydrogen and oxygen, solely from the electric currents. To this Dr. Faraday has given the term electrolysis, because the elements appear to be rent from their combination directly by the voltaic force, in contradistinction to another important property, which will be hereafter mentioned. The elements which are decomposed he has called ions ; they are not both evolved at one pole, but one at the electro-positive, anode, zincode, or oxide, while the other is given off at the electro- negative, cathode, platinode, or hydrogode of the battery. Tliose which pass to the first pole are called anions; those to the second, cathions.
(93.) The poles, or electrodes, have no attraction for elementary bodies as long as they are in a simple state, for bodies must be in combination to be affected by the voltaic current. Upon this account, a simple solution of chlorine, bromine, &c. does not give up these substances to either electrode.
(94.) Those bodies capable of suffering decomposition must contain one equivalent of each element, that is, they must be composed of one of the hypothetical atoms, which have been previously mentioned (87) ; and to this general law but a single exception can be found in the periodide of mercury, however is so unstable a oompoundy that the idightest e 3 0 ure to light will cause its decomposition,
Antons, Cathions, Etc.
which alone would be calculated to throw doubt on the validity of the experiment.
Sulphuric acid and phosphoric acids are not themselves electrolytes, that is, they do not directly yield their elements to the force of the battery, because they consist of one equivalent of phosphorus or sulphur to three of oxygen.
(95.) It is not necessary that a substance should be directly composed of elements to enable it to pass to the electrodes or poles ; or, in other words, bodies composed of compoundub-f stances are ions, as well as those composed of simple substances: thus, sulphuric acid, phosphoric acid, arsenic add, and other acids are ions to the electro-positive pole, or anode; while protoxides generally, ammonia, potassa, and many other substances, are supposed to be ions to the opposite pole. The following is a list of simple and compound
ions given by Dr. Faraday : —
Oxygen,
Anions ;
Fluorine,
Selenium,
Chlorine,
Cyanogen,
Sulphocyanogen,
Iodine,
Sulphur,
Acids.
Bromine,
Cathions
Hydrogen,
Alkalies,
All the metals, Yegeto alkalies, as
Metallic oxides, morphia, &c.
The earths,
(96.) The same substance, under different circumstances, will be evolved at different electrodes ; as at one time it may take the part of a base, at another it will perform the function of an acid. A familiar example of this is afforded in the oxide of copper ; for when combined with sulphuric, nitric,
Electeo-Chemical Action*
mariatic, or any other acid, it is evolved at the negative polcf or cathode ; whilst, when in combination with ammonia, it has been supposed to act the part of an acid, and is evolved at the anode or positive pole.
(97.) The opinions of philosophers upon the cause of metals being reduced when solutions of their salts are jected to the voltaic circuit, from the period when electricity first lent its mighty aid to chemists, are various. Some have supposed that hydrogen evolved by the decomposition of water reduces the metals, others that the poles directly attract the metals to their surfaces, and lately a paper has been printed in the Transactions of the Boys Society, whereby a new constitution of the salts is inferred ; the acid and oxygen being supposed by electrolysis to pass in one direction, the metal in the other. The first opinion was put forward by Hisinger and Berzelius, and may be found in the Annalei de Chimie voL li. p. 174. ''II rdsulte de tous ces faits, que Ton a une id4e fausse de la reduction op4r6e par Tlectricit, puis qu'on Tattribue au degagement de I'hydrogen, comment expliqueroit-on la reduction du fer et du zinc, qui ont la propriety de decomposer I'eau sans eiectricite."
A similar opinion has been advocated by Faraday in the Philosophical Transactions, and he applied a new name to this kind of action, giving it the term electro -chemical action. The second hypothesis was promulgated by Sir Humphrey Davy, who states, " that hydrogen, the alkaline substances, the metals, and certain metallic oxides are attracted by negatively electrified metallic surfaces, and repelled by posi* tively electrified metallic surfaces ; and contrariwise, that oxygen and acid substances are attracted by positively electrified metallic surfaces, and these attractive and repulsive forces are sufficiently energetic to destroy or suspend th usual operations of chemical affinity.
♦ Phil Trans, 1807.
Electro-Chemical Decomposition.
If we then find a body at the pole of the battery, it is by no means certain that it has passed by direct decomposition of the voltaic current ; because, if the compound of which it formed a part, was dissolved in water, the elements of the latter being set free, often act in an important way to form new combinations, which result from the secondary effects ; thus an aqueous solution of a metallic salt, for instance, copper being subjected to a voltaic current, has hydrogen presented at the cathode, and oxygen at the anode. But at the same time this [change is taking place, oxide of copper is passing to the cathode, and sulphuric acid to the anode. The hydrogen seizes upon the oxygen of the oxide of copper, and forms water, whilst the metallic copper is thrown down on the electrode or pole, not by direct voltaic action, but as a secondary effect, attributable to the hydrogen Sometimes the elements will combine with the poles or elec* trodes, forming new combinations ; thus, if the poles be easily ozydated, the oxygen will form an oxyde, and, in the same way, if any other substance be presented to the gases for which they have strong affinity, a similar combination will take place. Hence this class of effects, which are far more numerous than electrolytical effects, are called secondary, or electro-chemical decompositions. Sometimes these secondary results are most complicated, and perhaps none more so than the extraordinary one which I have described to take place with the oxygen, on the common yellow ferrocyanate of potash ; as this, by combining with a portion of the potassium of the ferrocyanate, gives rise to a totally new definite salt*, whilst the potash so formed is carried away from the sphere of action.
(98.) The secondary effects of oxygen and hydrogen have been proved by numerous well-devised experiments, but still no positive demonstration was obtained, that the hydrogen
♦ Philosophical Magaadne for September, IWO.
daniell's theory. '
evolved from the decomposition of water, would reduce the metals without the voltaic current. However, whilst experimenting on the non-metallic elementary bodies, the porous cokes and charcoal were observed to retain a portion of gas, after they had formed either the negative or positive pole of the battery.* When those which had been made the negative pole were afterwards plunged into a solution of sulphate of copper, they became immediately coated with the metal, adding positive confirmation to inductive reasoning. Coke charged with hydrogen retains this curious property for many days.f This very interesting experiment has been followed by Mr. Grove by the construction of his gas battery.
(99.) Professer Daniell, in a paper read before the Royal Society last spring, has given an entirely new view, as to the mode in which the metallic salts are sometimes decomposedL The Professor found if a solution of a metallic salt was placed in a vessel, over which a piece of membrane was tied, and that inserted into another containing a solution of caustic potash or soda, so that the membrane formed a sort of diaphragm between the two solutions, and then if the poles of a compound galvanic battery were placed into the two solutions, the positive into the metallic solution and the negative into the alkaline solution, that the metal of the first solution was deposited on the bladder. This is an experiment easy to repeat with several solutions, especially silver, mercury, and copper, though with gold and platinum the same result does not appear to take place. If acids or neutral salts be employed, instead of the alkaline solutions, 1 have never seen metal deposited on the bladder. When the alkaline solutions are used and the metal is precipitated, gas is always evolved from the membrane. In these cases a question might be raised whether the membrane between the
Philosophical Magazine for May, 1840.
f Philosophical Marine for Decker, 1840.
Electbo-Ohemical Deoompositiok.
two solutions might not become polar similar to interposed Professor Daniell supposes that in this experiment liwi mM and oxygen pass one way and the metal the other. FiNnh these considerations he has given a new view of the ebmpositicm of the salts : thus, sulphate of copper, instead of consisting of sulphuric acid oxide of copper is supposed to be constituted of (sulphuric acid -f oxygen) -f copper. The first two elements, as they are considered to be in combination, are called oxysulphion, and the salt oxysulphion of copper. In the same way, the radicle of the nitrates he called oxy nitro of the carbonates, oxy carbon — of the oxalates, oxalion — of sulphovi nates, sulphovinion.
In the same paper, another fact is detailed ; which is, the property the electric current possesses of decomposing two substances in the same solution; thus, both a metallic salt and acidulated water may be decomposed at the same time, the current dividing itself between them.
(100.) We have now seen that substances may be decomposed in two ways, either from directly yielding their elements to the voltaic current, when the compound consists of single equivalents, which is termed electrolysis, or, by a secondary action which occurs oftentimes, as a result of a new decomposition by or combination of the elements of the first substance decomposed, upon a second substance within the sphere, which secondary action is termed by Dr. Faraday electro-chemical decomposition.
The fluid between the electrodes, whilst decomposition is taking place, apparently undergoes no change ; that is, the effects of the decomposition are only manifested at the poles ; thus, if sulphate of copper be electrolysed, sulphuric acid passes one way, oxide of copper another ; yet neither acid nor oxide can be found in any part intervening. These experiments are best conducted in a long flat vessel with two porous plates, which divide it into three departments of which the two exterior receive the electrodes.
Cubious Induction.
(101.) The temperature at which the solution to be decomposed is kept, materially interferes with its conducting power; a fluid which is a good conductor at ordlnarj temperatures, will scarcely admit the passage of the galvanic fluid at the freezing point, whilst at the boiling point a passage will be aflbrded with the greatest readiness. It beijpmes, therefore, a very important matter to keep solutions at a high temperature, when we are desirous of effecting much decomposition in a short time, and at a slight expense.
(102.) The galvanic fluid, when it has the choice of a passage through various conducting substances, prefers that which affords the least resistance to the exclusion of the rest ; thus, if a galvanic battery of large series is connected to a decomposition apparatus, and is capable of giving off 20 or 30 cubic inches of gas in five minutes, yet the finest platinum wire on being placed across the poles, will cause the whole of the power to pass by the wire during the short time that it remains unmelted.
A curious property of induction is observed, under certain circumstances, in the voltaic circuit: thus, if a wire or a series of copper wires is suspended in a liquid which is Buffering decomposition, whether that be in one of the cells of a battery or in the decomposition apparatus, one part of each wire will be seen to become positive and be dissolved, whilst another part will be negative and reduce any metallic salt. This phenomenon will be seen to be taking place differently in each of the wires. If a platinum wire be interposed in the circuit the resistance which the evolution of oxygen affords is so great, that the polarity of the wire is only to be seen in certain cases. However, feeling assured that platinum could be made polar, I set to work with determination to effect it. I tried large plates of platinum in sulphate of copper, between two copper electrodes, connected wi a powerful battery, but could not succeed ; however, not to be he&ien I tried the experiment in a different way. A
Curious Induction.
piece of fine platinum wire was fixed in a small tube, one part remaining in the inside, the other on the outer part of the vessel, a small hole was then left in the tube, of such a size that water could freely run out. The tube was filled with dilute acid, and placed in a glass full of the same liquid, whenthe pole of a series of batteries (not less than 8 cells) was inserted into the tube, taking care that it did not touch the wire fastened in the tube : the other pole of the battery was placed in the glass of dilute acid, when immediately gas was evolved from the two poles, and also from the platinum wire. It was then thought desirable to ascertain whether as much gas was evolved from the intermediate platinum wire, in which the gas was given off by induced electricity, as from the original poles. This point was determined upon the principles which regulate electro-metallurgical operations, for upon the addition of a small quantity of sulphate of copper to the acid, the pole connected with the zinc of the battery was coated with spongy copper, whilst the part of the intermediate platinum wire which became negative had the bright reguline copper reduced on its surface. The rest of the intermediate wire was positive, and evolved oxygen gas. It is a matter of great interest to ascertain whether non-conducting substances could be made polar in a similar way, but all the evidence with me has varied sometimes one way and sometimes another ; and I am quite uncertain whether they may be made polar or not Of course the smallest portion of any solid conducting substance, as the smallest atom of charcoal or plumbago, will instantly become polar and give off gas. This kind of induction is interesting as explaining the action which takes place on a binding screw or piece of copper dropped into a galvanic battery, or into a metallic solution, which is being decomposed.
These experiments have obtained additional importance from their having enabled me to determine the course of the
Theory Of The Voltaic Current.
voltaic currents in the human body, which have since been detailed in the Elements of Electro Biology Upon the principle which may be inferred from these experiments, the electro-voltaic test for voltaic currents passing though fluids was obtained. The following apparatus well illustrates the principle.
The diagram consists of two gutta percha tubes, containing dilute sulphuric acid, and two series of plates of zinc (z) and platinized silver (s). By the introduction of two copper wires into one of the tubes the presence of the current will be indicated by a galvanometer.
(103.) In this place perhaps it may be advisable to give my own theory of the voltaic circuit. I claim for this theory no infallibility, and I ofler it merely as an epitome of the results which have been obtained during the experiments necessary for writing this volume. I ask, however, my reader to adopt it whilst studying the experiments hereafter to be detailed ; but as soon as the theory has been used to help him to obtain the facts, I beg him to discard the theory and hold to the facts as he himself observes them, that, in his own mind, he may hold that theory which expresses the facts with which he has been made cognizant.
In performing my electro-metallurgical experiments 1 noticed that in various mixed solutions the quantity of voltaic force passing was not at all dependent on the nature of 'the negative element, but upon the ease with which the hydrogen was removed from it Thus, in a solution of sulphate of zinc very slightly acidulated, the hydrogen could not be evolved from smooth copper, but would rather reduce
Fig, 13.
tbe Isulpliate of zinc when connected with a small battery. The substitution of smooth platinum in no way added to the power, but the employment of platinized platinum caused an abundant evolution of gas, even to the removal of the zinc already reduced on the smooth platinum. Any metal having but little affinity for hydrogen caused a similar result ; thus, iron caused gas to be evolved and increased the force passing, when smooth platinum would not have the effect, and even zinc itself caused a little gas to be evolved, because the adhesion of the gas to it is slighter than the adhesion to smooth platinum.
In the same way I observed that nitric acid allowed far more electricity to pass than sulphate of copper ; and that again, than dilute sulphuric acid, simply from the facility with which hydrogen reduces these substances being greater than the facility of its evolution. I moreover noticed in other cases that the hydrogen would rather be evolved than reduce a metallic salt, — as sulphate of zinc ; — and in every case that the facility of its removal affected the amount of power passing, quite independently of the nature of the negative plate.
Now these facts appeared to me a positive proof of there being no such thing as a negative plate contributing to the production of power, and that this latter is of no value, further than as a means for the removal of the second element of the intervening compound fluid. On the other hand, the multitude of experiments by Faraday all show that the che mical action between one element of a compound fluid and some conducting body appears to be the source of the power, or rather that the power is always dependent on and proportionate 10 this chemical action. Putting these two series of facts together, an idea presented itself to my mind explanav tory of the nature of the voltaic force, for if the force from the experiments of Faraday is proved to depend on chemical action, and the negative pole from my own experiments is
ICETALS METALS OF LIKE KATXTBfi. 61
proved to be useless, except as affording the means for the removal of the second element of the compound fluid, then it follows as a natural consequence, that if the chemical affinity of any 'substance for one element of a compound fluid is greater than the resistance offered to the evolution of the second force is produced. Now it immediately occurred to me that some metals might be made to reduce from a solution of one of their own salts, metal of the same description, by placing the metal partly in a solution for one element of which it has great affinity, and partly in a solution of one of its salts. This was actually found to take place in various cases, by following the facts that were made out respecting the ease with which hydrogen reduces various salts.
Zinc reduces zinc by taking a piece of the metal and doubling it, one half is then to be amalgamated and placed in dilute muriatic acid, and the unamalgamated into a strong solution of chloride of zinc, made as neutral as possible, when the affinity of the chlorine for the muriatic acid is sufficiently great to cause zinc to be reduced at the other end of the same piece of metal. The use of platinum, palladium, silver, copper, or any other metal appears not to increase the action in the least, which experiment shows most powerfully the utter fallacy of the contact theory, or in other words that the voltaic force is in any degree dependent on the opposition of one substance to another. In this experiment according to the advocates of this now untenable doctrine, the force should have set from the amalgamated zinc to the mercury, the two metals, according to these theorizers, having from simply looking at each other the property of evolving power, but we find that the chemical affinity determined the course of the current.
Copper may by very simple means be made to reduce copper with truly great rapidity ; for if a test tube be half filled with sulphate of copper, and then muriatic acid be poured gently at the top, so that the two fluids do not mix to any
62 MXTAts ' xetjjls or mss katube.
gmit ertenl, and a copper wire be then placed throughont the whole length of the tube, it will speedily show signs of action. The copper in the acid will rapidly dissolve, whilst copper will be as freely deposited at the lower part of the vessel. Now copper will undergo no action alone, either in muriatic acid or sulphate of copper. This experiment may be varied by the use of different acids or even some salts at the upper part of the vessel, for although muriatic acid shows this experiment most strongly, dilute sulphuric acid or muriate of ammonia will produce the same result.
Silver reduces silver by placing one end of a silver wire in a porous tube containing nitrate of silver, the other in dilute sulphuric acid, though the metal placed in either separately is not affected.
Lead reduces lead by immersing one end of a piece of lead in a solution of the tris-nitrate of lead, the other in dilute nitric acid.
Tin reduces tin by placing one portion of a piece of metal in muriate of tin, the other in muriatic acid.
Gold even reduces gold by immersing one end of a gold wire in the chloride, the other in dilute muriatic acid, the two solutions being separated as in all the former cases by a porous diaphragm.
There is a beautiful experiment detailed [by Mr. Grove which is analogous to those last described, though he attributed the results to a different cause. His experiment is to place two pieces of gold wire in muriatic or nitric acid, separated by a porous diaphragm, when no action will take place on either, but on being connected, that in muriatic acid will rapidly be dissolved, and the nitric acid will at the same time be decomposed by the hydrogen transferred to the other part of the wire.
From the various experiments which 1 have examined, added to the extensive researches of Faraday on the chemical portion of the voltaic pile, voltaic effects may be defined to be
oertidn effects produced by the chemical action of a body on one element of a compound and manifested between this point of action and the evolution of the second element. Voltaic actions might in other words also be defined to be the peculiar actions evinced between the chemical action of a body on one element of a compound* and the evolution of the second element, the point of abstraction and subsequent combination of the first element being called the positive pole ; the point of evolution or removal of the second element of the compound body, the negative pole. Hence it might be called circular chemical action, because the phenomenon always evinces itself as a circle.
These definitions suit equally every possible case, and there is but one point included in those definitions which is uncertain, though as they now stand, whichever way that doubtful case be taken, they equally apply. The difficulty, and the only one, that I know concerning the production of the voltaic force, is an uncertainty whether the force is produced by the analysis of the compound body,' or the synthesis of the newly-formed salt. This is a point concerning which? perhaps, we shall ever be ignorant, yet analogy would rather lead us to suppose that the combination rather than the analysis is the source of the voltaic force. These definitions show why we cannot obtain the force from the union of two elements ; indeed, we can never hope to obtain voltaic power directly from ordinary combustion, for though the energy of the combination of oxygen with carbon is immense, there is no second element, and therefore no intermediate point at which the effects can be manifested. For the same reason no force oan be obtained from the union of liquid sulphur jor bromine with metals.
The intensity of voltaic power being always proportionate to the chemical action, and being the only source of power in the pile, it follows, that (i) the intensity or the power which
PiJRTS OP THE VOLTAIC CIRCLE
the voltaic fluid possesses of overcoming obstacles is equal to (f) the affinity which regulates the chemical action. But as we find that this power is lessened under different circumstances, 0. O standing for the amount which F is
lessened by the obstacles aflbrded to the chemical charge.
Let us take at once a circle and examine its properties. We find that the intensity of the action (i) is equal to the affinity (f) of the body used to separate one element of the compound fluid (in the galvanic battery this is produced by the zinc and oxygen) lessened by the mechanical resistances afforded by the removal of the newly-formed compound (a), by the obstruction offered to the passage of the force by the compound solution (r), by the imperfection of the conducting power of the solid parts of the circuit (c), and lastly, by the obstacle which is afforded to the removal of the second element of the compound fluid (c); thus we have algebraically I—F—ac~\-r-€, This circle is suppo5ed to consist of but a series of single atoms of fluid, exposed at one time to the action of the body combining with one of its elements, and all the resistances are supposed to be constant.
Svme times this circle is exceedingly small, the (r) consisting of but one atom of the compound, and the (c) but of a single atom of the body combining with one element. This might be called properly an atomic circle, a good specimen of which has heretofore been called local action.
.W e must now consider the different parts of the circle in detaiL F the chemical affinity of a body for one element of a compound is immensely strong where zinc is employed, the attraction of that metal for oxygen being most power-
Fip, 14.
Formula Op The Voltaic Force.
ful ; but if we substitute iron, tin, lead, copper, or gold, for the zinc, the attraction being feeble the value of (f) would be reduced in various proportions, in some cases almost to zero.
(a) the removal of the newly-formed compound affords but little resistance when the new salt is soluble in the fluid and a sufficiency is supplied for that purpose. In batteries generally the removal of sulphate of zinc affords but little obstacle, being quickly dissolved by water,
(r) vanes very much f'om the extent of the interposed flui and its conducting power being very different in each case. It vaiies much in different batteries. Sometimes r is a very complex quantity, as when two or more fluids are used oetween the combination of one element of a compound and the evolution of the eond. In Danielfs battery, for instance, it is ma le up of three parts, not only the resistance offered by dilute sulphuric acid and solution of sulphate of copper, but a' so a resistance offered by the interposed diaphragm. It might be made up ol* a far greater number of parts, for different may be of different temperature, which alone (if the temperature interferes with the conducting power) would cause r to be complex.
(c) the resistances of the connecting part of the arrangeat is generally in batteries very slight because we select metals which conduct pretty freely (c) may be very complex, by being made of a variety of conducting substances, thus, if the conn.lions are made of wires of different kinds of metal, a dffereat resistance is offered by each, (c) in every battery, is generally made up of three parts, the conducting power of the positive and negative plates, and the intervening connecting wires.
(e) the resistance to the removal of the second' element is generally very great, affording a considerable obstacle in all cases, but the differences in this respect are very remarkable. Ordinarily (e) is a simple quantity, but becomes com-
Parts Op The Voltaic Circle.
plex when the hydrogen is removed in a variety of ways at the same moment. It becomes a curious question to ascertain whether (e) might ever be made a plus quantity. If the force proceeds from analysis, then the use of any body having great affinity for the second element might cause the current to be increased. If from synthesis, and this is most probable, if not absolutely certain, (e) can never be a plus quantity, but always a minus. In the removal of the second element by decomposition of another compound body, it is by no means uncommon for a voltaic circuit to be formed. In Grove's battery the hydrogen acts upon nitric acid, forming water, and setting deutoxide of nitrogen, &c., free but in this case the intermediate part between the combination of the first element and the removal of the second is only the atom of hydrogen ; it therefore follows, that this action must be regarded as nothing but a series of little local batteries, or atomic circles, having nothing to do with the great battery which we make available for our purposes.
It is absolutely essential, according to our definition of the voltaic force, that to be enabled to apply this principle for any purpose, however small a quantity of the force may be required, that either (c) or (r) should possess a capability of being so far prolonged as to enable us, with the imperfect powers that nature has furnished us, to handle or eal with these intervening portions of the circuit.
In the principal batteries now in use, their relative powers and attributes may be fully understood by considering each of the above properties in their construction.
F
a
e
r.
Grove
large
small
small
little
medium.
Daniell
large
small
small
much
most.
Smee
large
small
small
considerable
small
Smooth platinum
large
small
small
enormous
small.
Thus the four batteries may be considered equal in the properties of the r, a, c, the differences being only in (r) and
PARTS OP THE VOLTAIC aRCLE.
(e). In Grove's the {e) is so small as not only to compensate a slight increase in the (r) over mine, as usually constructed, but to give a great advantage to his form of battery. In Danieirs the {e) is rather smaller than in mine, but that in practice is more than counterbalanced by the use of the diaphragm. The effect of these properties is that p in Grove's is diminished but little, f in mine more, in DanielFs more still ; and in the smooth platinum battery by far the most. Thus is explained the decomposition of dilute sulphuric acid between platinum plates, by one cell of Grove's battery, and the same result not being obtained by the others. This equation is not only valuable for batteries, but applies to every single case where any substance acts upon a compound fluid in such a way as first to decompose it, then to combine with one of its elements, and set free in some way the other. Thus, if potassium be cast into dilute muriatic acid, (f) is immensely large, potassium having a violent affinity for oxygen ; (a) is exceedingly small, potash being readily soluble in water ; (r) is almost nothing, onlyone atom of fluid being traversed by the force ; (c) is practically nothing from the same cause ; (e) is very small. The result of such a state of things necessarily causes a vast intensity of action, and an explosion is the result.
Good specimens of contrasts in the magnitude in the several parts of the circuit are to be seen in the relative power of (p), as obtained by zinc and silver ; in the relative resistance of (a) in the solubility of sulphate of lead and sulphate of zinc ; in the resistance of (r) in the conducting power of pure water and muriatic acid ; of the resistance of (c) in a leaden wire a hundred miles long, and a short silver one ; in the resistance of (e) in the evolution of hydrogen from smooth platinum, and its removal by nitric acid.
The relative degrees of action evinced by zinc, tin, iron, and lead upon sulphate of copper are easily explained ; (f)
CTIBIOUS VOLTAIC CiaCLBS.
differs from being larger, (a) in being smaller when zinc is emplojed, whilst (c) (r) (c), in each case remain nearly the same ; (a) indeed is so large when lead is employed as soon to put a stop to the action.
How intelligible is the want of action of dilute sulphuric acid on amalgamated zinc, if examined by our equation for (e) ; the adhesion of the second element, hydrogen, being increased enormously, counterbalances (f), the affinity of zinc for the first element, or oxygen, and no action takes place* Amalgamated zinc is rapidly dissolved if placed in a solution of salts of copper or silver, for (c) in that case is depressed, the hydrogen'rapidly reducing the copper. Nitric acid in the same way does not respect the amalgamation of the zinc, for (e) in that case'is also diminished by the removal of hydrogen from the decomposition of the acid. As the adhesion of hydrogen to plumbago is very great, it occurred to me that the simple application of black-lead to zinc would, by preventing the evolution of hydrogen, increase (e), and therefore stop the local action; but although the experiment fully succeeded, the plumbago so quickly came off, that I have not at present made any practical application of the experiment. If the zinc be brightly polished, the adhesion of hydrogen is so great that it is protected as well as though it had been amalgamated.
The above cases, with all their analogies, are not the only ones to which the equation applies, for it will account for the action of bodies on each other.
In cases of single elective affinity, as the action of sulphuric acid on nitrate of barytes, a compound is decomposed, one element enters into another combination, the other is set free; a voltaic circuit is therefore produced, the parts of which are thus made.
(c) Sulphuric acid 1 (p) M f Barytes t (a)
' \Nitric acid (e)
CTTEIOtrS TCKLTAIO CIBOLE8.
In cases of double electric affinity, "as the action of sulphate of ammonia on nitrate of barytes, a similar circuit is formed thus ; —
(f) C Sulphuric acid Ammonia 7 v (a) ( Ba ines Nitric ac id 3 '
In both these cases, however, we have not the means of increasing the (r) and (e) to a tangible size (at least I have never been able to do it), and at present these actions have been restricted to the formation of atomic circles.
There are some cases where we can extend the intermediate parts (c) and (r), and then our definition of the voltaic force with the formula arising from it enables us to form most extraordinary voltaic circles, which indeed we never could have formed before, unless we happened to light upon them by chance ; thus proto-sulphate of iron, placed on one side of a diaphragm, and nitrate of silver on the other, will give a current when connected with the platinum wire, and a beautiful deposit of silver will be reduced on the platinum wire, on the nitrate of silver side of the circuit.
In the same manner circuits may be formed of protosulphate of iron and chloride of gold — of proto-nitrate of mercury and chloride of gold — of oxalic acid and chloride of gold, &c. In all of which cases the metal is freely reduced on that part of the platinum wire inserted in the metallic salt. The reason why a galvanic circuit is formed in these cases is sufficiently obvious ; water is the electrolyte or compound decomposed, proto-sulphate of iron is the substance combining with one element, and the metallic salt affords a means for the removal of the second element or hydrogen, and, as we have the power of extending the compound (r) and connecting parts (c), not only an atomic circuit, but a working battery may be made* At the diaphragm or the
Applications Of The Equation.
point of juncture of the two liquids, indeed, an atomic or local battery is formed independently of the general or working battery. The following are the parts of the circuit in the above cases.
(c)
(f) f Proto- Sulphate of Iron Platinum Wire "(a) Oxygen Hydrogen (c)*
(0
It would be extremely interesting to find every case of decomposition of a compound fluid obedient to the equation, and, indeed, there is every appearance of that being the fact.
To form a voltaic battery or to extend the decomposition of the fluid electrolyte to a tangible length, it is necessary that some obstruction be afforded to the evolution of the second element at the point where the affinity acts, and that a place should exist where the resistance to that evolution is lessened. In other words at (f), it is requisite that (c) be large, and by lessening (e) at one distant point we extend the line between (f) and (e), and thus make a voltaic battery. Upon attending to this law I have constructed the thermo and photovoltaic circuits t, in which light and heat set in motion the voltaic force.
Under different circumstances the part heated is either a negative or a positive pole. Under the same law I found smooth zinc positive to rough zinc, and amalgamated zinc to smooth zinc.
The impossibility of giving a negative tendency to a metal when hydrogen is removed from its surface is also perfectly accounted for by [our equation ; for the non-evolution of
(a) IB the removal of the per-sulphate of iron by solution ; (e) is the
removsJ of the hydrogen by the decomposition the metaUic salt
f See Elements of Electro-Biology.
Applications Op The Equation.
lijdrogen, as has been already shown, protects the metal ; so when a facility is offered for its removal not only is the direct protection removed by diminishing the value of (c), and (f) the natural affinity of the metal for one element of the fluid, having but little resistance opposed to it, begins to act, and the metal is therefore dissolved.
The superior action of a rough metal in contrast with a smooth one is explainable on the equation most satisfactorily, for in the first case the affinity (f) is opposed by the resistance to the evolution of the hydrogen (c), whilst in the latter case (f) is so strongly opposed by {e) that no action can take place. Zinc shavings, which always have one side bright and the other rough, show this phenomenon clearly.
Hitherto we have considered (f, a, c, e) in every case to be constant, but in many instances they are subjected to continual variation. I do not, indeed, happen to recollect an instance of (f) varying to any amount, but (a) varies frequently ; in the gradual saturation of a fluid it progressively increases, so much so, as at last to equal (f). This accounts for zinc ceasing to be dissolved on the saturation of the fluid by sulphate of zinc, although still intensely acid, (c) generally remains constant, (r) is very unsteady, for as in all voltaic arrangements the fluid is always undergoing change it is therefore sure to be altered in its conducting power, (c) is subject to great variations from alteration of the liquid and other causes.
In every case of a single battery we have seen that the intensity is equal to chemical affinity, minus deductions for the resistances to that affinity. In a compound battery the expression is equally simple, for the intensity is equal to the sum of the affinities, minus the sum of the deductions for the resistances. In a series of batteries all of the same nature, w. Sometimes is very complex. For example, if a compound battery be made up of a
72 Applications Op The Equation.
Grove's, a Daniell's, and my own, the values of (i) must be considered separately, and their sum taken.
Fig, 16 .
The diagram exhibits well the arrangement and properties of the compound battery.
A good example of the affinity of (n) is seen in the water battery, where (i) is exceedingly small from the deduction for resistances of (a) and (r) being large, but becomes amplified to such a degree by as to possess prodigious force ; indeed as it possesses a capability of being amplified infinitely by an infinite series completely insulated, a battery might be constructed powerful enough for the force to pass from one electrode, placed in the Thames at London Bridge, and the other in some river in Australia, though the resistances of (r) and (c) in this case, from their extreme length, would be very great. In every water battery, as (a) instead of being constant gradually increases, the power gradually declines, at length to nothing, The curious and wonderfully-multiplying powers of whereby the intensity can be increased, precludes our saying that the galvanic power is unable to efiect any particular object ; for, after all, it might turn out that (n) was not magnified sufficiently to attain that end.
When we are turning our power to some application it is very convenient to consider the purpose for which it is applied as a resistance, and call the deduction necessary for it b. If we have a series of them alike it would be b x If,
Compound Voltaic Batter!.
however, the series is not alike, it would be R+R'-fR". The intensity of the current here would be also equal to the sum of the intensities, or the intensity of the whole battery i"', with the obstacles inherent on its construction deducted, minus the sum of the deductions for the resistances. The R is frequently very complex, as in the reduction of metals in a decomposition trough, where it is made up of as many parts as a voltaic battery.
Having amply discussed the power of the force to overcome obstacles, we are led to determine the time in which any given number of equivalents of voltaic power can be obtained. Hitherto we have considered the circuit to be made up of a single atom of the body combining with one element of the compound, and if the affinity exceeds but ever such a trifle the deductions for its obstacles, then in time any amount of work would be performed provided the current remained constant. A current can easily be conceived so feeble as to take millions of years to reduce a pound of copper. If the entire circuit of single atoms be increased at every part, in fact if the mathematical voltaic circles be placed side by side till they reach the size of a tunnel, then (w), the amount of work performed in a given time, would be equal to the intensity of the battery, minus the deduction for the resistance of our working apparatus, multiplied by the number of parts of the tunnel (a) thus ; w=i'-— b. x a.
This equation, however, gives us the sum of chemical actions in the whole series of batteries and decomposition troughs, or, in other words, the sum of the actions evinced in each ; we generally, however, are desirous of estimating the amount done in one particular cell, in which case we divide our equation by the number of cells and troughs thus,
— B X A n
It is at this point where our theory of the pile joins Ohm's
Thb Amount Op Work
law, for virtually, hie electromotive' power e is equal to our I A, or intensity and quantity combined. According to Ohm, w, or the work in any battery, is equal to e divided by its resistances, and according to our formula w is equal to e— the deductions for these resistances, both of which expressions amount to the same thing. The theory here propounded, therefore, amounts rather to an analysis of Ohm's formula in the battery itself than to an opposition to it, as has been supposed by some of my mathematics-electrical friends. The formulas which are here detailed, appertain to the quality of the force produced, and its mode of production, whilst Ohm's equation refers to the application when produced.
Sometimes this equation is rendered extremely complex by an increase of the circuit at one side but not at another ; in fact, the tunnel is cut away on one side, and this is a case that is perpetually occurring in practice. In this case it is not impossible but that the force is only derived from those parts of the circuit which are complete ; in that case the equation would
p standing for the incomplete parts.
In this view of the question we are supported by the analogy of water running through a pipe of given dimensions from a cistern, for however large this cistern be, provided there be no more pressure, the water running through the pipe would be the same. So far as the voltaic fluid is concerned 1 feel certain, from numerous observations, that beyond a certain point the increase of a battery does not cause a greater amount of electricity to pass through a given resistance ; and, perhaps, in those cases, where the enlargement of a battery increases the voltaio force, battery in the former
In A Given Time.
instance was deficient in size in relation to the size of the resisting part n, the tunnel, in fact, having been defective originally in that part. It is possible that the expression for this condition might be altered ; for r, the deduction for resistance to the single voltaic circle, might possibly vary in some new manner, for which further experiments are wanted.
-/ . lO
In that case it would be w The old English IR
n
standing for the deductions for the new resistance afforded to the whole current. The tunnel might be cut away at any other part besides (r) ; thus it might be deficient at (f), (a), (c), (r), or (e) ; but the student will readily perceive the expressions for these cases. Whilst experimenting upon large masses of water or rivers, I have been much astonished at the small resistance oflfered from great lengths of the interposed fluid, which favours the above supposition. It may possibly turn out that (c) and (r) in conducting bodies does not affect the (i) but only the (a), but my own opinion inclines to the opposite belief.
Sometimes w is very small, as in De Luc's columns, where the total amount of chemical action, although (w) is frequently 500 to 1000, is so small that the experimenters have even denied its existence ; but when we consider that these veiy persons assert, that as soon as chemical action does become decidedly manifest, the action ceases, how strongly do they favour our views, for, according to our equation, we expect (a) to be gradually increased till all action would be stopped, w indeed, according to our equation, might be so small, as not to be cognizable to our senses for weeks, months, years, or centuries ; and yet multiplied by a very large would show enormous intensity or power of overcoming resistances.
The present modifications of the theory of galvanism are perfectly consonant with every practical direction given in the following pages, and the only difference in the theory will be found in the uncertainty expressed upon the contact
Voltaic And Other Electricities.
and chemical action theories. By removing the slight difficulties which appeared to envelope the latter theory, by showing the necessity for a negative pole to cause power is unfounded, the beautiful doctrine of Faraday is placed on the surest foundation, and the extraordinary and dogmatical paradox of a power without a cause is proved to be a fanciful chimera.
With regard to the connexion of the voltaic power with that of electricity produced from other sources, perhaps it might be expected I should say a few words. In the voltaic battery (i) is small, but may be increased to any size by (w), and as we have the power of increasing (a) also unlimitedly, we can perform any amount of work per second, indeed we might throw down hundreds of tons of copper per second, if we were disposed to make our circuit large enough. In frictional electricity (i) is enormous, but (a) is depressed to its utmost limit, so that not having a perfect command over (a) to increase it indefinitely, we cannot at present obtain what work we please in a given time. In animal electricity (i) is great, (a) is moderately large. In thermo-electricity (i) is depressed, perhaps increasingly, so that although (a) and (n) may be multiplied indefinitely, yet, practically, we ehould never be able thoroughly to overcome the smallness of (i). Ill that mighty operation of Nature which has just occurred, where the noise accompanying the discharge of the electricity over the metropolis was so awful as to alarm not only delicate females but the stoutest hearts of men, and even the heretofore unterrified nervous system of infants — in that terrific storm, when every living creature trembled, and Nature seemed almost alarmed at her own operations, how vast was (i) 1 how large (a) ! O I therefore that I could
A violent thunder-storm which visited the metropolis in the year 1842, at about five o'clock in the morning, and during which a numb of trees, buildings, churches, Ac., over an area of many nes were apparently struck at the same instant.
Resistances Of The Voltaic Force.
but have imprisoned that collection of force which in discharging itself committed such devastation on houses, churches, and trees, and, having encased it, been able to have let it loose as it might have been required ; then indeed would all batteries be henceforth discarded as playthings for children — philosophical toys to be admired, still despised, for (ia) being unlimitedly great, we could obtain what work we pleased in any given time, at no expense.
The estimate of the parts of (i) in other cases where force is produced, i. c. an electricity not proved to be derived from chemical action, I do not deem it my business now to consider, but great difficulties would attend its accurate investigation, as it is almost impossible to magnify the size of the circle in these cases, in such a way as to make the action in each part cognizable by our senses. It is however quite evident that as in the voltaic and thermo circuits (i) may be magnified to any extent by (n), that the power of (i) in every case might be brought to the same standard in the power overcoming the resistances ii' k" &c.
The obstacles to the completion of the voltaic circuit (o), are made up as we have seen of several parts, a, r, c, but, although they differ in kind, still if they have similar resisting properties, a perfect table might be made, referring them to one given standard, showing the separate value of each. The principle on which it should be constructed is the law of the completion of the voltaic current, which will be detailed when treating of the reduction of alloys ; and as soon as we have this table accurately and numerically drawn up, the principles of the passage of the voltaic circuit, which formerly puzzled the most enlightened experimenters, will be rendered certain, and the difficulties will be also reduced te the facility and certainty of common arithmetic. Having obtained perfect tables of (o) and its several parts, we can readily obtain the relative value of (i), derived from variotis sources, by finding out what extent of (o) neutralizes each
Resistances To The Voltaic Force.
individual (i), and the value of (i), or the force of any battery, will be determined with equal facility. Complete tables of (o) and (i) now become the greatest desiderata not only to Electro-metallurgists, but to all who use the voltaic battery. In attempting to construct tables of (o) as the relative power of (o) varies with different amounts of (i), that fact must be carefully considered, but probably in many of these cases Ohm's law may come to our assistance.
I now bid adieu to my theory of galvanism and my formulae ; and to those who have neither time nor inclination to dive into these mysteries, remember, in all operations that the sum of the deductions for resistance does not exceed the sum of the intensities ; and that in increasing 'the circuit, every part is equally enlarged. To those who have devoted themselves to these properties, remember, they will be useless if not brought into active operation ; thus, if any difficulty occurs in your voltaic circuit, refer it at once to its proper head, and the operator may be sure that a continual practice and habit of using these expressions will enable him to conduct his proceedings with a certainty never obtainable by blind experiment.
Let us now recapitulate every circumstance which, by affording a resistance to the passage of the galvanic fluid, will lessen the amount of the action. In the first place, in the battery itself, the current of electricity might be diminished by the metallic plates being too thin to carry the current readily. It may also be lessened by the plates being far apart, or the interposed liquid being an imperfect conductor. The negative metal may be covered with hydrogen and rendered nearly inert, or the positive may be rendered inoperative, by the saturation of the acid by the zinc, or the liquid by the metallic salt. External to the battery resistance may be afforded by small wires, or by connexions of imperfect conducting power, or by attaching it to a decomposition ap-
Application Of Voltaic Power To The Arts. 79
paratus, every part of the construction of which obeys the same laws as the galvanic battery itself.
The application of voltaic poiver to the arts is one of the greatest improvements of modern times, and although much has been done in this important and extensive field of inquiry, yet this alone suffices to show, that as we progress the path to be pursued widens and enlarges, exposing to view an immense tract, fertile exactly in proportion to the labour and ability employed in its cultivation.
E 4
CHAP. ni.
On Additional Sources Of Voltaic Power,
On hydro, animal, and lightning-electricity considered, as a source of power, 104. Magneto-electricity, 105.
(104.) Whenever electricity, from whatever source it is derived, acts upon, or passes through a fluid, the eflfects which are observed are obedient to the same laws. Practically, the electricity developed in a voltaic battery is, as a general rule, alone applicable to electro-metallurgy ; yet the very lightning from the clouds, the electricity from the hydroelectric machine, or magneto-electricity, might be, at times, applied to the same results.
With regard to hydro-electricity, a very powerful current may be produced by high-pressure steam.
For this purpose a high-pressure boiler is used, and the steam, with aqueous particles, passes through a tube, and by their friction against a piece of hard wood the electric force is generated. At present it has not been employed for electrometallurgy, and is probably vastly inferior to the voltaic battery.
Fig, 18.
Electro-Magnktic Currents
Gassiot, by way perhaps of a humorous experiment, made an electric eel form one of Nobile's rings ; but it is liardly necessary to state, that, for electro-metallurgic operarations, we cannot ordinarily press these curious creatures into our service.
There is something truly poetical in tlie idea of making lightning our servant instead of our master ; but as it has decomposed water, it could also be made to perform some cdectro-metallurgic process : and thus we may safely say that the matter of fact of the present day exceeds, in poetical idea, the wildest imaginations of former ages. That which ill a former age would be so far beyond the sublime ns to constitute the ridiculous, now becomes an ordinary matter of fact, not even presenting a subject for observation.
By the electro-magnetic contrivances, we have the power of obtaining a current of intensity from a current of quantity. It was first discovered by Faraday, that, upon making or breaking the contact of a galvanic battery by a long wire, another current was developed in a second wire, isolated from the first by some non-conducting material. Thus, if we take a copper wire, say 60 feet long and one eighth of an inch thick, and form it into a helix by winding it regularly round a hollow tube, and superimpose upon that a great length (say 1200 feet) of a very thin wire, covered with silk, cotton, or any such non-conducting material, and wound round the first wire in a similar direction, we form an apparatus that at once shows the experiment on making contact with the two ends of the thick wire with the plates of a galvanic battery. A current of electricity is generated in the second wire ; and though the first current may be derived from only a single pair of plates, the second current may have amazing intensity, in fact, sufficient to give the most powerful shocks ; a secondary current is produced on again breaking contact, but no second current is formed whilst the circuit is completed. These efiects are far more exalted
£ 5
mamwchuxommc afbkbultxjb.
if we place a piece of soft iron, or a bundle of soft iron wires, into the tube round which the primary wire is wound, because we then add the powers of magnetic induction to that derived directly from the galvanic battery. A machine upon this principle is constructed in the manner above detailed, one end of the primary wire being connected to a metallic- toothed wheel, the other joining a flexible piece of brass capable of pressing the teeth. By revolving the wheel the contact is made and broken, according to the rapidity of the revolution, and thus hundreds of shocks may be transmitted in a minute.
The induced current so produced is a to and fro current ; but the current should always be cut off (fig. 19.). Messrs. Horne and Thornthwaite have devised a self-acting machine, which they call an electro-magnetic machine in which the secondary current is cut off, from the peculiarity of its con-
Fiff. 19 .
struction. In these cases the magnetic induction is added to the galvanic induction, and the result may be beneficially used in <me or two instances for the purposes of the arts.
(105.) Fifteen years ago my much respected master, Pro* feasor Daniell, used to show in his lectures a magnet, from which Faraday first obtained an electric spait by induction. When, with darkened windows he used to demonstrate this little spark, nothing could exceed his animation and delight that his magnet was that on which the discovery was made. He little thought then, that that little philosopher's spark, in a few short years, would find its way into the arts, and constitute a source of wealth to the manufacturers, and a source of honour to the inventor. The philosopher's spark has been converted into a working electric current, by using very powerful magnets, and revolving before them pieces of soft iron wound round with numerous layers of silk; according to the power of the magnet, the closeness of the approximation of the armatures, and the length and sizes of the wires, so do we obtain a greater or less intensity or quantity of electricity by the revolution of the armatures (fig. 19). The magnetoelectric apparatus gives a to and fro current ; but for electrometallurgic processes, it may be readily contrived that every alternate current may be cut off. It is a curious fact, that, although this machine gives an intermittent current, it causes a constant deflection of a magnetic needle, so that, in its chemical effects, it is equivalent to a constant current.
Throwing out of consideration the first cost of a magnetoelectric machine, we may consider whether it be preferable to the battery as a source of power. It is a primary law of physics that to produce any change of matter a corresponding change of matter must take place, and in the battery the change of matter takes place in the battery cell, where the power arises from the action of the zinc on the water. In the magneto-electric machine, the power arises for the combustion of the coals which generates the steam which moves the wheels of the steam-engine and turns the armatures. As wherever there is a steam engine, the power usually exceeds the demand, it may be thought that magneto-
Magneto-Electric Telegraph.
electricity is obtained for nothing. Nevertheless, although magneto-electricity has been beneficially applied to the reduction of gold and silver, both of which, from their high equivalents, require but a low amount of electricity to effect any required reduction, I am of opinion that the battery must, for the present, supersede the magneto-electric power.
Mr. Henley has patented a magneto-electric telegraph, which certainly appears to be the most elegant and perfect instrument of that kind which has yet been devised.
The American papers have lately contained an account of the manufacture of gas by this machine ; but the published statements contain internal evidence of the whole paragraph being an attempt at a circumstantial hoax, such as the Americans alone can produce.
The magneto-electric machine, however, deserves grave
Magneto-Electric Machines.
consideration , and attention; for if ever its construction should be so improved, that water could be rapidly decomposed in large quantities by its agency, then indeed it would be one of the most important engines of modern invention.
When electricity has been obtained from the magnetoelectric machine it differs not from electricity derived from battery ; and when it acts upon any metallic or other solution or fluid, the effects produced depend upon the intensity or quantity of the electricity actually passing through the fluid. The principal disadvantage of these machines is the production of a power having but feeble quantity, although it exhibits a very high intensity. As a consequence of the high intensity we are enabled by its means to overcome great resistance. Hence in its economical application the compound trough hereafter to be described may be employed.
Book The Second.
On Electro-Metallurgy.
Chapter I.
On The Apparatus To Be Employed For The Reduction Of The Metals.
The idea of electro-nictalliirgjr, suggested by Daniell's battery, 106. The porous tube or single cell apparatus. 106 — 112. Capillary tube apparatus, 113. Plaster apparatus, zinc, iron, and tin positive poles, 114. Compound battery apparatus, 115, 116. Single battery apparatus, 117, 118. Precipitating trough, 119. Single cell and battery conjoined, 120. Mason's arrangement, 121. Management of the apparatus, 122, 123. Lines on the reduced metal, how to be avoided. 124. Adhesion and non-adhesion of the reduced metal to its mould, 125 — 128. Apparent adhesion, 128. Lateral growth of the reduced metal, 129. Relative expense of various modes of the reduction of metals.
(106.) Electro-metallurgy, depending essentially on electric agency is subject to the operation of the same principles, and governed by the same laws which have already been laid down in the book which treats of galvanism and galvanic batteries. The successful reduction, therefore, of the metals must depend entirely upon a thorough knowledge of galvanism and galvanic apparatus. We should recommend our readers, then, before they enter upon this department, to make themselves thoroughly conversant with the contents of the first book ; for what operation can be successfully performed without a complete knowledge of the nature of the implements with which that operation is to be effected.
8
fi!ir€LB OSXX
of value for the electro-metallurgist, an4 t£ey laitfot a considerable period without renewal. Of late, rfchenware tubes have been very extensively employed. The kind of most value are made absorbent, similar to the vessels employed for wine-coolers, and are made of different shapes, to suit various purposes. The best are generally made with care and of superior clay ; but the common earthenware garden-pots answer in some cases where porous vessels are required. In selecting a porous vessel we have to guard against two extremes ; for, either it may be over fired, or baked at too great a heat, when it will not be sufficiently permeable by liquids, or it may not be sufficiently baked when any metallic solution will act upon and partly dissolve its substance. We should, furthermore, always ascertain whether water will pass slowly, but entirely, through every part of its texture, in order that universal porosity may be proved. But the practised electro-metallurgist can always judge of the fact by touching it with his tongue, when the degree of dryness produced on that organ by tlie absorption of its moisture will indicate the freedom with which liquids will pass. A clayey appearance, and peculiar odour when placed in water, are the only test of an imperfect baking. A common tobacco pipe, with the hole blocked up with a little plug of wood is very useful for small experiments. Wooden porous tubes have been used by some persons ; Jacobi makes mention of having employed them. They should always be boiled in acid before they are first used, to render them more porous ; but no particular advantage attends their application. Plaster of Paris is sometimes employed, but it speedily becomes acted upon by the fluids, and upon the whole is not a useful diaphragm. Any vessel with a small fissure, or fine crack, in it may be used as a porous pot, for any vessel which will let fluid run out will allow the galvanic current to pass. We have already mentioned, in a former part of the work, that the more porous this veswl is, the greater the quantity of
SmatB €9BtL APPABATUS*
eleoctty developed* greater, therefore*
tity of metal depcwrit aa the amoiiJt of depowlt iM idwaya in relation to the qumitity of eleetrioity generated. 'Rie following is the order in which different snbstanees stand: with regard to their capabilities of admitting the passage of electricity ; —
Brown paper,
Thin plaster of Paris, '
Porous earthenware, ,
Gold beaters' skin,
Bladders of various thickness,
Thick plaster of Paris,
Capillary tube,
( 108 .) Of the various forms of apparatus, which may be used for the precipitation of the metals, the most simple is Daniell's battery, having a porous earthenware tube, to oontain the acid and zinc, whilst the negative metal, which is usually a mould, is placed externally to this, and connected by a piece of wire to the zinc. Thus, for instance, take a pound pot, and half fill it with a solution of sulphate of copper (s) ; in this, place the earthen vessel (p), with the dilute acid (a) and zinc (z), and this constitutes the whole of the present form of apparatus ; for, when we desire to make an electromedallion, it is only necessary to place one or more casts in the outer vessel (m m) connected by a wire with the zinc, and then action will immediately commence. Any number of moulds may be placed in the outer vessel, provided they can radiate to the zinc. Saturation of the liquid may be preserved by suspending some of the salt in a linen bag over the mould. This form is objectionable, because
lomuE mLL,
die ikU of sine speedily passes through to the outer yessel ; hm it has the advantage of allowii the mould to be placed TerticaUy, in which position it is much less liable to have particles of dust settling upon it. There is no limit to the size of this outer vessel : for a water-butt, a tank, or even a lake naturally impregnated with sulphate of copper, would would form glorious apparatus for the electro-metallurgist.
(109.) There is another form where bladder takes the place of the earthen vessel, and where the position of the cast is horizontaL Here, the outer vessel, which is square, is made of wood, coated internally with cement ; on one part of the edge of which, a piece of brass is fixed, in which are two holes, one for connection with the wire of the cast, the other with that of the zinc. In the interior of the trough, a moveable shelf of mahogany is placed, on which is supported a glass containing a zinc plate, and crystals of sulphate of copper to be dissolved. The glass has a piece of bladder tied over the rim, and this forms an outer vessel similar to the porous tube in the former apparatus. It, in like manner, contains the acid and zinc; the latter being connected by a screw to a wire, in such a way that it can be readily removed. This apparatus is preferable in many respects to that first described ; because the sulphate of zinc cannot pass through the membrane readily to the copper, and facilities are ofiered for changing the zinc and acids, &c. In this apparatus, care must be taken that the mouth of the glass be wide enough to afford a radiating point from the zinc to every part of the cast, as it has been already noticed, that want of attention to this would be attended with inconvenience, (17.)
(110.) In every single cell apparatus, the solution of me-
Fig. 22 .
, ' ▲FPjfcSA.TITS.
tallic salt should be maintained in the rented 4e§p?ee/ concentration, by keeping some crystals of madiasolved in the solution. If these crystals ane allowai to to the bottom of the vessel, they will not answearioi ataod od purpose of maintaining a saturated solution ; to fiio jKWliSM of the fluid which have been deprived of thmi metals Mil rise to the surface, whilst the saturated parto rental in contact with the crystals at the bottom, thus preventiiig their solution. This difficulty may, however, be reay overcome, by placing the crystals to be dissolved in a hUie bag, on a shelf at the top of the liquid, by which means the saturation of the fluid will be ensured.
(111.) Another form might be made by dividing a box into two compartments, by a flat porous slab of earthenware, similar in composition to the porous tubes of a DanieU's h&t- tery. Into one compartment the solution of sulphate of copper is to be put, together with the negative metal, which in the cut is represented by two moulds (m m), and into the other dilute sulphuric acid (a) and the zinc (z). The advantage of this apparatus would consist in the facility gained in the manipulation ; and in the arrangement of the positive and negative metals, so that they may be at every place equidistant
from each other — a circumstance of great importance. The porous diaphragm, however, cannot be made of any large size, so, perhaps, it might be exchanged for a more ready, but less durable one of plaster of Paris, paper, or bladder. The decomposition apparatus (fig. 11.) made of a cut tumbler answers well for numerous experiments.
(112.) Other forms may suggest themselves to the operator, for in whatever way a Daniell's battery may be constructed, a similar form will equally answer to the
, Fig. 23.
Capillaby Tube Apparatus.
electro-metallurgist. (38.) The only circumstance to be observed is, that the zinc be equidistant at every place from the metal on which the reduction of the new metal is to be effected, so that the deposit may be everywhere equally thick. If the distance varies, the reduced metal will be found to be of unequal thickness ; that part nearest the positive metal will be very thick, whilst the substance will diminish as it recedes from that point: in some cases the effect is more apparent than in others, but occasionally, where a mere rod of positive metal is placed opposite a large surface of negative, a complete convex mass is formed, gradually diminishing in thickness in every direction. In some cases these effects of radiation present some complex phenomena ; but generally they may be referred to the fact, that the galvanic principle is not so essentially radiant, but that it wMl pass round a corner: thus, if a flat piece of copper is placed opposite to another mould in a solution of sulphate of copper, a portion of current is generated at every part of the back of the positive pole, which, turning round the corner, causes a far greater mass of metal to be reduced at the circumference of the mould. At other times the effects of radiation are farther complicated by the imperfect uniformity of the strength of the solution during the action of the apparatus, in which case, every part not being of equal conducting power will admit a different quantity of electricity, and, therefore, a different thickness of metal will be reduced.
(113.) An apparatus for very weak currents, I sometimes use with great advantage, when the change takes place at the cathode of the battery. It is made in a very simple manner ; the solution to be decomposed, is placed in a tumbler ; a piece of glass tube is then drawn at one extremity to a capillary bore. This fulfils the oflBice of the porous tube, and contains the zinc (which in this arrangement is merely a piece of amalgamated zinc wire) and a very dilute acid solution. The quantity of electricity generated by such
Zinc Positive Pole,
an arrangement as this, is necessarily very small indeed, for the construction is in every way unfavourable to its development ; first, the dilutencss of the acid solution materially lessens the quantity ; then, the hole through which the current has to pass is so small that much force is required to blow any liquid through the aperture, even by drops, and therefore a great impediment is offered to the passage of the current. Moreover, a very fine platinum wire is employed to effect communication ; and, lastly, the substance, which is the subject of experiment, is not placed opposite to the capillary hole. The mode in which the capillary tube acts in lessening the current, seems to be by interrupting or breaking the continuity of the fluids, so that but a feeble amount of the current can pass. The regulation of the quantity of electricity can be perfectly effected by regulating the bore of the tube.
(114.) Sometimes, when a very feeble current is required, a glass is filled up at one end with a thick piece of plaster, which fulfils the office of a porous tube. Where we only require to lessen slightly the quantity of electricity, we content ourselves with extending the distance between the electro-positive and negative metals. In other cases we use a thick bladder or thin communicating wires, and we conjoin the whole or a part of these contrivances for lessening the power.
In the single cell apparatus up to the present time, zinc has been invariably used for the positive metal, and varioua solutions may be employed with the zinc : common salt has been much used, &c. The various sulphates and other neutral salts can be also employed without the amalgamation of the zinc ; but if we go to the expense of this amalgams* tion, we may employ dilute sulphuric acid, or dilute muriatic wid, both of which, from their superior conducting power, enable us to reduce far more metal in a given time. Zinc ia
Ikon Single Cell Apparatus.
a single cell will reduce nearly all the metals, and, as it forms soluble salts with nitric, muriatic, sulphuric, acetic, tartaric acids, it may, therefore, be employed for all salts which contain these acids, for we must never forget that it is essential that the new salt formed should be soluble in water, and that a sufficiency of water be supplied for its solution.
Now having discussed the arrangements principally suitable to those cases where zinc is employed, as the positive metal, or metal used to generate the current, I have to impart the great secret, that it is not always necessary to use zinc as the generator of the voltaic power, for, practically, it is possible in a great many cases, especially in the reduction of copper, to make iron take the place of zinc, thereby superseding the use of that expensive metal, and substituting one of but trifling value. But iron is not capable of imparting the same electro-motive power, intensity or primitive force of the galvanic principle that zinc is so eminently endowed with ; for this reason we are compelled to use a greater extent of surface when iron is employed, and from this cause up to the present day has been but little or never employed. Moreover, we have still other difficulties to contend with ; iron cannot be amalgamated like zinc to stop local action, and, therefore, can only be used profitably with saline or other solutions that do not themselves act upon the iron when not forming a galvanic current. The apparatus the most suitable to the application of this metal is that which most favours an increase of the positive metal A very simple form is a common cast-iron supply cistern, into which a parallelepiped porous tube, one inch smaller each way, might be placed, separated by two pieces of wood inserted at the bottom of the tank. The inner vessel contains the saturated solution of sulphate of copper with crystals suspended at the upper part to maintain the saturation of the fluid, and its cmiducting power should be increased as mueh as possibid
Ibon Single Cell Apparatus.
by tbe addition of dilute acid. Before we determine wbat is the best exciting fluid to be used in the iron cell, we must determine what salt of iron is most desirable to be formed during the action of our apparatus. Iron forms soluble salts, with a considerable variety of acids, with muriatic, nitric, and sulphuric, &c. ; but I am inclined to believe, from my experiments, that the sulphate is the most convenient salt to be generated ; therefore, we must employ a solution of some sulphate, of which the sulphate of zinc, sulphate of soda, or what is, perhaps, best, sulphate of magnesia, or Epsom salts. This salt is retailed by chemists for about one penny an ounce ; but the electro-metallurgist will And that he will be enabled to buy a pound for about two pence. I have tried a great variety of other saline substances in the outer cell, as nitrates, chlorides ; but, upon the whole, the sulphates appear to be entitled to the preference. The low combining number of iron adds much to its advantage, for twenty-eight grains would be be as effective, that is, would generate as much power, as thirty -two grains of zinc. By using an iron positive pole, I feel no doubt that many who have never succeeded in making electro-medallions heretofore, will be enabled to carry on their operations although slowly, yet with perfect success. A box, divided by a porous diaphragm, and every other single cell apparatus in which we can place a large surface of metal, is suitable for the application of iron as the positive metal. It is really very pretty to pick up a few old rusty nails, and from them generate a sufficiency of the extraordinary and mysterious power of galvanism to make a copy, by a few minutes* labour and a few hours' patience, of the most elaborate work of art that the exalted imagination and the untiring patience of the ancient Ghrecian could possibly execute. When we can obtain an accurate cast of a Syracusan coin, worth upwards of one hundred pounds, hy two or three old rusty nails, and the solution of a penny**
Lead Positive Pole.
piece, let no one henceforward throw away or despise an old rusty nail.*
There are other metals besides zinc and iron that might be used to generate electricity ; thus, lead will reduce copper, silver, gold, and various other metals. When it is employed for electro-metallurgical experiments we must form a soluble salt, of which the acetate and nitrate are most conspicuous. If we use nitrate of potash, in the outer side with the lead, and a solution of metallic salt, say of copper, in the inner side, with the negative plate, the reduction will take place. It is vain to attempt to reduce a sulphate by this salt, for the sulphate of lead is absolutely insoluble. Its equivalent number is very high, one hundred and four of lead being equal to thirty-two of zinc, which is one serious objection to its use. The only chance of its ever being employed for the reduction of any metal, especially copper, is the possibility of the nitrate of lead, formed during the galvanic action, being a valuable product ; for were this the case, we should obtain our power for nothing, and the cost to the electro-metallurgist would be only the value of the weight of metal produced, plus the cost of the previous process, for converting it into a metallic salt. The sulphate of iron and sulphate of zinc produced in the former cases are now thrown away i but, as in many chemical manufactures the cost depends on the value of the products, it would be desirable for the elect
Since writing the above, I perceived the following paragraph in "The Chemist" for this month, by Mr. Z. J. Rockline, which I subjoin entire In all my electrotype experiments I have employed, and with the greatest success, ordinary eet-iron instead of zinc for the positive metal, —than which it is much cheaper. The difference must, I think, be palpable in lai electro-castings, where extensive surfaces of sine wod be necessarily requisite. Iron, in the form of cyUndrical rods, which are extensively manufactured, would, if cut into suitable lengths, fiwta most excellent and cheap substitutes for the zinc bars hitherto used m cir cular constant batteries. To electrotypists, this metal, in whatever torm it may be used, must prove a (heap substitute for
Tin Positive Pole.
&7
tro-metallurgist to form a salt which is of value. I throw out this hint for trial, as I have reduced copper from its nitrate, hy lead, so if the nitrate of lead could be converted into the carbonate with advantage, we should obtain our power comparatively for notliing ; lead gives a feeble electromotive power ; therefore, it requires a large plate, and a thin porous tube. I hear of no instance where lead has ever been practically used in the arts for this purpose.
Tin may be used to generate electricity, it being soluble in muriatic, sulphuric, acetic, oxalic acids, &c. It has a feeble force, requires a large plate, and a thin tube. It is best used with dilute sul])huric acid on one side, and the metallic salt, which should be a sulphate, on the other. It reduces several metals, but, unfortunately, has a high combining number, requiring fifty-eight grains to generate as much power as thirty-two grains of zinc. Some alloys of tin and zinc might come into use for the single cell apparatus, did not the high equivalent and price of tin prohibit its adoption.
Other metals might be used, under certain circumstances, as the positive metal to generate power ; for instance, copper to reduce palladium, gold, or platinum ; silver to reduce gold and platinum ; but, as they will probably never be employed by the electro-metallurgist as a positive pole, there can be no occasion to consider them farther : always remembering, however, that whatever metal is employed as the positive element, it is requisite that such an exciting fluid be employed that a soluble salt may be generated during the action of the apparatus, and that sufficiency of water be supplied to dissolve it as soon as formed.
(115.) In all these cases the metals are precipitated at the negative metal of a single battery. In like manner, bywhatever other method we can render a plate negative, there will the metal be precipitated ; thus, if a battery, sufficient to decompose acidulated water, be connected with two platinum
Battery Apparatus.
poles, at one pole oxygen, at the other hydrogen, will be evolved ; therefore at the latter the metal would be precipitated. It has been mentioned before, that one cell of Grove's, two or three of Daniell's, or of my form of battery, will decompose acidulated water between platinum poles ; but still, with that series only, a feeble quantity of gas is given off* Now where we wish to employ feeble currents, the series just mentioned may be used with great advantage.
(116.) Where we have considerable resistance to overcome, and require but very feeble quantity, we may use a number of cells, exciting the battery either by simple water, or water acidulated with a single drop of acid in each cell. The oxygen in tin's method of reducing the metals is always evolved at the positive pole, and the acid in combination with the metal set free, so that the solution gradually becomes more acid. In most cases, however, we require to precipitate a large quantity of metal, and then it becomes a matter of importance to effect that object by the smallest series, as by this compound battery apparatus the cost is multiplied by a number of cells employed.
(117.) For most purposes the last method is very seldom adopted ; but advantage is taken of the affinity which most metals have for the oxygen ; and instead of using a platinum pole at the oxygen end of the batter}% which affords great resistance to the passage of the galvanic fluid, we employ a piece of metal of the same nature as that which we wish to precipitate, which performs the functions of the positive plate or zincode in the trough. As the solution of metallic salt is continually depositing its metal, the piece which constitutes the positive pole is dissolved by the acid and oxygen which held the reduced metal in solution, and the liquid is thus kept nearly at the same point of saturation. One battery is amply efficient for this mode, as there is but little resistance to ovoome.
( 116 .) To illtistrate this method, let us suppose that we
Battery Apparatus.
have to take a cast in copper. A solution of a salt of copper is to be placed in a convenient vessel (b), and the object on which the precipitation is to take place (n), is to be connected with the zinc (z) of the battery (a), whilst a piece of sheet copper (p) is connected with the silver (s). As soon as action commences, water is decomposed, oxygen passes to the copper pole and oxydizes it, and the hydrogen passes to the negative plate. Whilst the decomposition is taking place, oxide of copper is supposed to be passing to the negative pole, and the acid to the positive pole ; the hydrogen reduces the oxide of copper at the negative plate, whilst the acid combines with oxide of copper at the positive end, and thus the saturation is continued. Practically we never find that all the acid passes to the positive pole, but on the contrary, the proper diffusion of the metallic salt occasions us much inconvenience.*
A series of precipitating troughs, arranged like a compound battery, may be employed occasionally with only one battery. In this case, we should have one generating cell in the battery, and six, eight, or ten decomposition cells ; therefore, by the fundamental laws to which the action of the galvanic fluid is obedient, we should have six, eight, or ten equivalents of metal reduced for one equivalent of zinc. Tlieoretically, thia apparatus exceeds every other in economy practically, it has not been so much employed as it ought
It has been mentioned before (99.), that Professor Daniell has given a different theoretical explanation of ese decompositions, though, prac* ticaBy, the change taking place is the same as here ghren.
Fig, 24.
wo
PRECIPITATINa TROUGH.
to be, particularly in the reduction of plain copper-plates. The galvanic series is made by alternating the metal to be dissolved (c) with the ©tect to receive the precipitate the last mould being joined to the zinc (z) of the battery, and the last copper with the silver (s) ; the positive plates should be large, and the liquid rendered as conducting as possible to lessen resistance. It is important in 'this apparatus that every positive and negative plate should possess nearly the same surface, and the solution the same strength, in order that metal of the same quality should be reduced in each cell.
(119.) The apparatus used as a precipitating trough, must vary in shape, — round, flat, square, according to the form of the object to be copied ; its dimensions may vary from a single drop to the largest reservoir filled with metallic solution instead of water, and the solution must be altered according to the metal to be thrown down. These will demand a particular description ; but here we must say a few words as to the materials best adapted for this vessel, viz., the precipitating trough, and, certainly, glass is preferable in all respects, excepting its brittleness and its expense ; these two qualities rendering it much less generally applicable than it would otherwise be. For some metallic solutions it is absolutely necessary to employ glass, as other vessels are more or less acted upon by them. The removal of the excise duty from this commodity will ultimately prove a great boon to the chemist ; as he will be enabled to obtain vessels which he could never otherwise reasonably hope for. Porcelain of
PllECIPITATINa TEOUGH.
some kinds, such as Wedgewood's, &c., is found to be occasionally useful. However, even this is too expensive, and we have recourse sometimes to the common earthenware. Doubtless, many will be astonished at being informed that most metallic substances, in a state of solution, will penetrate through the glazing, into the very heart or biscuit of the jar and freely pass to the exterior of every kind of earthen vessel. This can be only thoroughly prevented by coating the interior with pitch. The best ironstone ware was thought to be invaluable to the electro-metallurgist, as, if well glazed, it was supposed to last for any length of time. A refiner showed me some that he had used for parting gold during twenty years, as good as new. Whenever round vessels can be employed, the electro- metallurgist will be enabled to find them ready-made, at the large earthenware houses, as they are frequently used as salting vessels. If they could be manufactured similar to a trough, tliey would be of extensive application ; but the makers complain of their warping in the oven. Even with this form of ware, in process of time, the metallic salt intrudes and disintegrates them. Wooden vessels are more frequently employed than these, because they admit of great variety of form, and can be rendered completely water-tight, by a cement composed of bees' wax one pound, rosin five pounds, red ochre one pound, and two table- spoonfuls of plaster of Paris. A common tin trough, or especially a leaden vessel, will answer, but the interior must, in like manner, be coated either with cement or pitch. Leaden vessels are particularly applicable when the metal is to be reduced from its sulphate. One advantage of the pitch is, that the salt in solution has but little tendency to crystallize upon it, which, with other substances, is a very troublesome property ; as, occasionally, the whole of the salt from a solution will pass to the outer part of the vessel, thus covering it with crystab. Slate troughs have also been frequently used ; they ought always to be painted or pitched.
m
to ffowmt tine absorption of the liquid, which is apt to pene* state into the slates, and crystallize and disintegrate the substance, which is always made up of numerous layers. The sides are generally bolted together with copper ties ; but slate vessels should altogether be discarded, as they are not found to last above a twelvemonth.
Troughs of a peculiar construction have been employed by my friend Mr. Terry ; he obtains two boxes, one so much smaller than the other that a space of half an inch is everywhere left when one is inserted in the other. The interval is filled with melted pitch, and the inner one is lined also with the same material. He finds that troughs made in this way are admirably adapted for the intended purpose, and, doubtless they might be employed in some cases.
Within the last few years a new substance of the highest possible importance has been introduced into Europe, called gutta-percha. It is very similar to Indian-rubber in most of its properties, but wants its extensibility. It has the power of resisting, at moderate temperatures, the action of acids and alkalies, if they be not too strong. It is impervious to moisture, and pieces can be readily joined together by moderate heat and pressure. From these invaluable qualities, gutta-percha is now extensively used by electrometallurgists to line wooden tanks, and these troughs are the best which can be employed for these purposes, and are now superseding every other form of trough. I have seen troughs in use for two or three years which were as perfect at the end as they were in the beginning of their use ; and, in fact, gutta-percha should in future be the sheet-anchor of electro-metallurgists.
The galvanic battery and precipitating trough is the process almost universally adopted for all large objects, and there are many reasons why it should be employed. In the first place, we are enabled to regulate the quantity of electricity to the strength of the solution far better than by any other
method ; secoiadly, we are enabled to keep up nearly a unistrength of solution, and, letly, the process is frequently cheaper. In fact we have two or three manufacturing processes going on at the same time ; we are not only generating our electricity and reducing our metal into the form we require it, but we are actually forming, by the same operation, our sulphate of copper or other salts. To reduce metallic copper from crystals of blue vitriol, or silver from lunar caustic, may appear to the unlearned to be a sort of alchemical operation, whereby copper or silver is actually made ; but this is by no means the case, for we only re*obtain that metal which we had formerly made into the salt, and we have to pay, occasionally, at a most exorbitant rate for that change. All this cost we save by making the battery our manufacturer, and the trough our laboratory, for by using a certain portion of metallic salt in the first instance, the metal, during the action of the battery, is reduced, and the acid combines with another portion of metal, so that, in this way, the acid contained in a few ounces of metallic salt may be employed over and over again, as tliere is no limit to the amount vf metal that might pass through it.
The galvanic battery and precipitating trough need not be joined together like Siamese twins. They may be separated to any distance, provided the conducting wires afford no resistance to the passage of the fluid; therefore, when we separate them to any amount we should make our connecting rods of copper, which is a good conductor, and take care to employ thick rods instead of wire. Sometimes it has been found convenient to have our batteries in one room, and our troughs in the other. In the first room, everything necessary for the galvanic batteries should be kept, such as zinc, acid, mercury, connecting wires, &c. /kc. In the other room, everything should be methodically arranged for the electrometallurgists. If operations were carried on in a very extensive scale, and a great variety of metals were being
mason's apparatus.
reduced, then would the manufacturer do well to devote a separate apartment to each separate metal. I can see in my mind's eye a large electro-metallurgical manufactory, with the batteries in a room in the centre, surrounded by rooms on every side, in each of which a different metal is being deposited.
(120.) Another form of apparatus may be employed occasionally with advantage ; when we require a considerable intensity, or power to overcome obstacles, and do not wish to incur the expense of a large series. It is a union of the single apparatus and the battery. In the decomposition cell we have a porous tube, containing the acid and zinc, and in the outer part we have the solution to be decomposed. The zinc is to be connected with the silver of the battery, and the zinc of the battery with the negative plate in the decomposition cell, and thus the circuit is completed. It is manifest that this apparatus increases the power, by adding one more to the series, and thus, by using zinc at the positive pole of the decomposition cell, the impediment offered to the electric current is prevented.
(121.) There is yet another mode by which we can precipitate the metals with the utmost cheapness, though the length of time required is very much increased by the process. We use here the Daniell's 26.
battery apparatus, or single cell for the reduction of the metal; but instead of connecting the zinc with the negative metal at once, we make that zinc and medal a battery to be connected to another decomposition cell.
In this we have a second medal as a negative plate, and a piece of copper as the positive plate. The second
rRECIPITATION OF METALS.
lOo
medal is connected with the zinc of the first cell, and the copper with its medal. In this way, with one pound of zinc we obtain two pounds of copper. The application, however, of the second cell affords an impediment, and, therefore, the porous tube in the first cell should be as thin as possible. This very ingenious apparatus was devised by Mr. Mason, but has not been much used, because it has not been sufficiently known.
(122.) The whole management of the precipitation of metals, depends for its success on a right knowledge of the principles of quantity and intensity, or, more correctly speaking, of resistance and electrical power. The latter property does not influence the result, as we shall hereafter see, so much as the former, but in most cases this should be rather abundant than deficient. The intensity, so far as regards electrometallurgy, may be increased in two ways; by adding to the series, or by using exciting liquids, capable of giving greater intensity, or primitive force to the galvanic current. The quantity of the current may be increase4 by enlarging the size of the negative plates of the battery, by increasing the strength of the acid solution, by using a larger anode, zincode, oxide, or positive pole in the decomposition cell, by diminishing the distance between this and the negative plate, or, by that which is by far the best, by using the fluid in the decomposition cell in that state which most favours the convexion of the current, or, in other words, diminishes the resistance to its passage. Each of these, separately, is quite sufficient to regulate the quantity of electricity passing.
(123.) To ascertain the exact quantity of electricity passing* a galvanometer must be employed, especially for very feeble currents; but, if my form of battery be used, the operator can judge with sufficient accuracy of the quantity of electricity passing, from the evolution of hydrogen from the negative plate. All instruments are incumbrances to the practical mechanic, and I believe that no workman would
Position Of The Negative Plate.
require anything farther, if my battery be used, than the ocular or aural test which the evolution of hydrogen affords.
(124.) The position of the substance upon which the metal is precipitated, causes, in certain cases, a very singular phenomenon in the deposit ; for if it be placed vertically in the apparatus, or especially if the upper part overhang the lower part of the plate, a series of lines will be produced, amounting, in some cases, to grooves of an inch in depth. The cause of this is easily discovered, if the solution be watched whilst the battery is in active operation ; it will then be seen that as the hydrogen reduces the metal from the fluid, it directly becomes colourless, and lighter than the surrounding solution. It, consequently, rises and causes a current, which, like a stream, is reflected in various ways, at every elevation or obstacle. Having once made for itself a channel, it keeps to it, and increases till the lines become of the depth which I have mentioned. This prevents the deposit being of uniform thickness, and makes the plate valueless. It may, however, in a great measure, be obviated, by giving the plate a slight inclination, or this tendency may be entirely destroyed by placing it horizontally. If the metallic solution is used stronger, the lighter solution instantly mixes with the denser, and, also, when the deposition is very slow, these lines are not seen.
In conducting our electro- metallurgical experiments, we must recollect that, in every solution of a salt, the heavier parts are apt to subside to the bottom, so that, in reality, at the bottom of the vessel, the solution is saturated, whilst at the top the solution contains but little metallic salt. This property is far more evident when the new salt is formed in the liquid ; thus, in every instance, where a metal is being dissolved, it should never be placed at the bottom of the solution, or else the salt will not be able to diffuse itself over the liquid, but will crystallize upon the metallic plate, com* pletdy encasing it On the contrary, if it is placed at the
Horizontal Decomposition Apparatus. 107
upper part of the solution, the salt newly formed will be spread more evenly over the fluid, which is a circumstance of great importance for almost all operations. These facts would point out the horizontal decomposition apparatus to be the most philosophical, for in that vessel the metal removed by decomposition of the salt on the negative plate from the lower part of the solution has its place immediately supplied with a new portion of salt derived from the action on the positive pole, and thus the fluid next the negative plate is always maintained about the same point of saturation. Practically, however, the horizontal apparatus has some disadvantages which affect its universal application, for in this apparatus the objects to be copied cannot so readily be immersed in the liquid or removed from the trough. If the relative position of tlie poles be reversed, the positive being placed at the bottom of the vessel, crystals of metallic salt will encase it, and, at last, stop farther action, whilst the negative pole will be surrounded with a liquid containing little or no metallic salt, and spongy metal will be reduced. I rather dwell on these phenomena, from having heard that one of the first practical electricians that this country can boast, has inadvertently recommended the positive pole to be placed at the bottom, clearly, however, without having tried by experiment the effect of such position.
In conducting the series of experiments for my first edition which led me to recommend the horizontal apparatus for many purposes,
1 found that some metals could not actually be reduced without it from an imperfect distribution of the salt. The use of the horizontal apparatus (b), then, by placing the posi-
i r 6
103 Horizontal Decomposition Apparatus
tive pole (c), or metal to be dissolved, above the negative, or pole to receive the deposit (p), is only to afford this equable distribution, and, therefore, is to be superseded whenever we can effect that object more readily. The solution must be filtered occasionally when this apparatus is employed, to separate any particle of dust, and the positive pole must be kept very clean.
Mr. De la Rue, for the purpose of keeping up the same strength in his metallic solution, fixed up an extensive apparatus for ensuring that object by the circulation of fluid. He fixed a large tank at the upper part of the room, and another at the bottom. The upper one was filled with the metallic solution, and the liquid was suffered to run to the lower vessel, from whence it was again pumped up to the higher. Now this appeared to be the most direct and philosophical manner of overcoming the imperfect diffusion of the salt, but it caused on the negative metal such curious circular lines, and the process of the deposition of the metal was so much interfered with, that the apparatus was obliged to be abandoned. This experiment is extremely interesting, as showing that an idea most excellent and philosophical in principle, may fail in its application, through the interference of some new influential circumstance, which it would be impossible to have foreseen. At the present time some electro-metallurgists agitate the solution to insure a proper diffusion of the metallic salt, which answers in many instances.
(125.) The new deposit of metal may, sometimes, be removed with the greatest facility ; at others, it adheres with such firmness as to form one metallic mass, with its mould, from which it cannot be separated by any means whatever. Now we require both these properties for different purposes, and though, heretofore, the results have been too much the effect of chance, doubtless it is a matter of the utmost consequence to have such a control over the process, as
Abhesion Of The Eepuced Plate.
to obtain, with certainty, either, as we may happen to require them.
(126.) The adhesion of the original to the duplicate is termed, technically, buttoning down; the non -adhesion has not been, as yet, vulgarly christened. Both depend on two facts, the enfilming of metals by air, and the possibility of that becoming a pole. (35.) These properties have been fully entered into in the first book, but here we have to notice their practical application. If a of smooth metal be plunged into water, it will resist wetting, and in that state is to be used, when we do not wish the deposit to adhere to its mould. In order to take advantage of this property, the plate is to be dipped into the solution, and the circuit immediately completed. The air would now appear to be the pole, and to afford a separation between the original and duplicate. Of course the plate should be neither heated nor rubbed with potash or nitric acid, previously to its submersion ; and, above all, should not remain in an acid solution for a single moment before the galvanic circuit is completed. Sometimes one or more of these circumstances will take place partially, and then a partial adhesion or buttoning will ensue. After any plate has been soldered, it should be allowed to remain in a cold place for at least twenty-four hours, it will then regain its film of air.
The metals are not singular in their afiinity for air, nearly every substance in contact with it becomes coated with it. Paper, although having a strong affinity for water, has also a similar affinity for air. Thus, when large quantities have to be damped for printing, the air becomes a serious obstacle. By the machinery introduced into the Bank of England, as well as in the Bank of Ireland, by the late Mr. Oldham, the paper on which Bank notes are printed is placed in a vessel connected with an air-pump, and the air is pumped out, which causes a vacuum. Into this water rises, and a million of notes, if necessary, are in a very few minutes
no
Adhesion Op The Reduced Plate.
wetted thoroughly. It is usual to pass the paper through rollers to deprive it of excess of fluid, and thus, by a simple application of a chemical fact, a saving of much labour is effected. The same principle is brought into operation in the process of Kyanising timber, where the air is first pumped from the wood, and then a solution of corrosive sublimate rushes into the pores of its structure ns soon as the pressure of the air is again admitted.
The non-adhesion of metals is not, in all cases, dependent on the adhesion of air ; sometimes a film of oxide, at other times a thin film of sulphuret, or a thin film of grease will prevent this property. I have at this moment before me a wire, the reduced metal covering which is in several distinct layers, caused by simply withdrawing it as many times from the solution, and allowing it to dry before it was again immersed. Eeduced copper plates will, occasionally, have this imperfection, being in a series of layers from a similar cause.
(127.) When we are desirous to employ the opposite property, or to cause the new deposit to adhere, we pursue a contrary course ; we either heat the metal and plunge it into water, or rub it with a solution of caustic potash, with nitric acid, or else we make it the positive pole of the battery, and in that state place it in the solution : for then the surface, being quite clean, allows the deposit to take place on the metal itself, and not on the pole of air. It will then adhere so firmly, that no mechanical separation can be effected, as some can testify, who, ignorant of these facts, have entrusted valuable copper-plates in acid solutions, and entombed their device in a mass of copper, from which it could never be disinterred.
The observations on the enfilming of the metals after having been exposed to the air for a short period, applies to many cases besides electro-metallurgy. The application of heat to the Daguerreotype plate, it is exposed to the
Lateral Growth Of Reduced Metal.
vapour of iodine, is, perhaps, on the same principle, and doubtless any of the other modes which I have described for cleaning the plate will answer as well.
(128.) The adhesion, or buttoning of one metallic plate to another, must not be confounded with apparent adhesions of the duplicate to the original, arising from the copper growing round the edge, and firmly embracing it. This is to be remedied in a great measure, in the first instance, by coating the edge with a layer of lac varnish or grease, which prevents the deposit taking place at that part. After a considerable lapse of time, the plate increases laterally, and covers the coating.
(129.) The lateral growth of the metal of a plate is a property of considerable importance, for if a particle of nonconducting substance be placed upon a metal, it will be covered. This lateral growth, or the diffusion of electricity over a large surface, differs with every metal, nay with every salt of the same metal. In this way drawings made on copper, with varnishes, may be multiplied. If a nonconducting substance is to be copied, by means of a thin film of conducting substance, a break in the continuity of the latter will not prevent tlie formation of a perfect plate. For the same reasons, care must be taken that no air or gasbubbles adhere to the plate, for, in like manner, they will be enfilmed, and leave a little flaw or gap in the duplicate plate. To cast metals upon an air bubble, seems, at first, too wonderful to be believed, and, in former times, would, doubtless, have subjected the discoverer to destruction, on the supposition that he was in communication with an evil spirit ; but in these latter days we find it even more difficult to efifect than to prevent.
He who desires to make electro-metallurgy bis business, must well consider the relative expense of the materials absolutely essential to his processes. An undue attention to this very important consideration has caused experimenters
Expense Of Electro-Metallurgy.
to take out patents and incur great expense, for modes of working in metals by the voltaic fluid, when the object could be obtained in the ordinary mode of proceeding, at one half the trouble, one half the cost, one sixth the time, and, even then, nearly as well as by the galvanic current. To estimate the expense of working in metals by the voltaic fluid, we may divide the processes into several departments, — the single cell, the battery, the compound battery apparatus, in which manufactured zinc is employed ; the odds and ends' battery which is applicable to raw zinc ; the compound decomposition apparatus ; Mason's apparatus ; iron single cell apparatus ; tin single cell apparatus, &c.
An equivalent of power (87.) may be obtained in the single cell, by the solution of 32 grains of zinc ; now as 7000 grains of that material in a manufactured state, that is, rolled, are .vorth nearly 7(/., the equivalent of zinc in round numbers would cost of a penny. To this must be added waste of zinc not used, destruction of porous tubes, and cost of saline excitant, which would probably bring the charge up to the of a penny.
In the single battery, provided it be of my construction, the equivalent of power would cost about the same or rather less. In this case it would be the zinc (the same as in the single cell) plus the acid, plus the waste of zinc from local action, plus the difference of value between the manufactured zinc and the remnants that necessarily occur (52.), say, collectively, yV of a penny. If the constant battery were employed, the cost would be raised from one and a half to twice that sum, making allowance for the value of the copper reduced. The application of the nitric acid batteries for electro-metallurgy, would entail more than treble this cost, raising the sum to 4- of a penny for the same equivalent of power. The expense of the power derived from a compound battery would be the same as that of the single battery, of
Expense Of Electro-Metallurgy.
a penny, multiplied by the number of cells, so that if twenty cells were employed, the equivalent would cost (jyX20) Id.
By the use of spelter in the odds and ends* battery, we lower the price to nearly one-half or the because spelter is much cheaper than rolled zinc, on account of the difficulty of rolling, and because there is but little local action, and no remnant of undissolved metal to cause waste.
The compound decomposition apparatus is the reverse of the compound battery apparatus, for the equivalent of power, as obtained from a single battery, must be divided by the number of decomposition troughs : thus if we have twenty cells it would cost 'ihu penny for each
trough.
Iron, to give an equivalent of power, must lose 28 grains, that being its equivalent ; therefoie, as 7000 grains in the manufactured state are worth from Id. to 2d. it would cost about 7 V penny, making allowance for waste and exciting liquid.
The equivalent of power, if obtained by the agency of tin, of which 58 grains would be dissolved, costs, making allowance for waste, exciting fluid, &c., 7 of a penny, reckoning tin at 9d. a pound.
From the above considerations, we form the following table of the bare cost of the materials to produce an equivalent of galvanic power, under different circumstances ; it is assumed that the salt of zinc, of iron, or of tin, is of no value : —
Zinc Single Cell - - of a penny
Iron Single Cell - "73 —
Tin Single Cell - - —
Smee's Battery - - —
Daniell's Battery - ji —
Grove's Batteiy - - —
Odds and Ends' Battery - —
Compound Battery - - x by the number of cells.
Compound Trough - - by the number of troughs.
EXPENSE OF ELECTBO'METALLUBaY.
Having obtained this table, an important clue to the expense is arrived at ; for, if we are desirous of ascertaining the cost of the reduction of a metal from its particular salt, we ascertain its equivalent number (87.), then the value of that quantity, and lastly, by adding this cost to that of the power, we arrive at the bare value of materials for that equivalent. Having ascertained the value of the number of grains corresponding to the equivalent number of a single proportion, we learn the cost of 7000 grains or one pound avoirdupois.
Let us suppose, for instance, that we are anxious to know the cost of the reduction of copper from its sulphate, we find that the equivalent of this salt is 125, which at 4c?. for 7000 grains, or one pound, would amount to 7000 : 4 : : 125 :
of a penny. This we add to the number appended to the particular process against the above table, which would make the cost for one equivalent of copper, or 32 grains, as reduced by the single cell, nearly J of a penny + of a
penny). Then to ascertain the cost per pound, as 32 the equivalent of copper : of a penny : : 7000 to about
2s. 3d. a pound. On the negative side, we have in addition, a certain waste of materials ; there is more metal reduced upon the edges than we require, and some copper left in the exhausted solution, of which it is impossible to give exact estimates.
So much for the cost of the materials in a single cell, and to put them in the form of an equation, C, the cost=(e) value of an equivalent of power + (s) the cost of an equivalent of metallic salt —
To ascertain the cost of our materials in a battery apparatus, the equation would be altered, C, the cost=e, value of equivalent of power -fm, the price of an equivent of rolled metal suitable for our positive pole. To this we must
add a loss for the imparities in the metil, ti nants, and the occaaimmi cost o( renew** ' solution.
C=eH-iii.
Let us take an example of the precipitation of copper from the single battery apparatus. C=e-3. + in, with a little loss about I, for thirty* two grains of metal reduced. In this case, rolled copper is estimated to be worth one shilling per pound.
Although every person ought to make the calculation for himself, before he enters into any large operation, I subjoin, as a rough guide for the electro-metallurgist, another table, showing the price of the reduction of copper from its sulphate by each of the methods detailed above ; —
per equivalent.
8. d.
Single cell zinc -
- id -
2 3 per lb.
iron -
tin, nearly -
- id
Single battery
- id -
Paniell's - - -
- id -
Grove's . -
Odds and ends' -
Ten cell compound battery
. lid. .
Ten cell compound trough
Mason-8 plan
. id
Besides the elementary
cost, we have
to pay for the
negative metal, or moulds
on
which our metal is reduced.
we have the time requisite to keep the apparatus in action, we have the rent of the room in which the operations are conducted, and a hundred other circumstances, for which no general computation could possibly be given, as they vary with every case. All these things will be considered in the description of the processes. The preceding equations show clearly that electro-metallurgy shines conspicuously forth for utility, where the value of the metal is great and its equiva
Expense Of Electro-Metallurgy.
lent high : thus, by applying our equations to gold, we find that the equivalent of power is nothing compared with the value of the metal, for we reduce two hundred grains of gold for srV of a penny, whilst the metal is worth nearly 2/. For this same cost of penny, we can obtain only
thirty-two grains of copper, that being its equivalent ; but if we desire to make hydrogen, we can only get one grain for our money. This simple principle prevents the employment of the galvanic power for the production of gas for illuminating purposes, as, if we make our calculations, we shall find that the cost of materials for this purpose would be about 11 . 10. per 1000 cubic feet, whilst the gas companies supply us at four shillings for the same quantity. Had the equivalent of hydrogen been 200, the cost of its production would have been only nine-pence, which would have been the means of converting every coal-gas company in the country into a galvanic gas company, and with the gas, such an abundant supply of galvanic power would have been available for electro-metallurgy, that all other modes of working many metals would have been entirely superseded.
We know for certainty that zinc and other metals are not employed for the voltaic currents which exist in animal bodies, and we have reason to infer that hydrogen and carbon arc the materials used by nature. The equivalents of these elements only being 1 and 6 respectively, it is proved that for economy they should alone be employed for the positive pole of the battery. For hours I have sought to obtain a working battery from ordinary hydrocarbons, but hitherto have totally failed. The value of the steam engine over electrical contrivances, depends upon the cheapness of coals as compared with zinc ; for if ever the philosopher should discover an effective carbon battery, then will the steam engine cease, then will gas companies be compelled to stop their works, and a total revolution'will be produced in all the physical forces employed by man.
Char Ii.
On Substances Capable Of Receiving The Metallic Deposit.
Substances on which the deposit may take place, 130 — 131. Metals, 132 — 136. Non-conducting substances ; Scaling Wax, White Wax, 136 — 139. Absorbent substances, as Paper and Plaster of Paris ; means of rendering them non-absorbent, 139 — 141. Gutta percha, 141. Means of copying non-conducting substances by metals ; by Plumbago, 143 — 145. Comparison between the methods, 145.
(130.) The voltaic deposit of raetal may take place upon any conducting substance, which is capable of a'ting the part of the negative metal, in the arrangement. The laws which relate to this, are the same which regulate, in a similar manner, the plates of the battery. The deposit may be effected upon most metals, except the earthy and alkaline, and upon any alloy or compound of them. It may, likewise, take place upon charcoal and plumbago. When the metals are employed, the effect is evident enough, for the arrangement differs in nothing from that of a Daniell's battery.
(131.) Where we desire the duplicate to possess a surface and form exactly like those of the original, it is of the utmost importance that the metal on which the deposit is to take place, should not of itself decompose the fluid, because, in that case, the duplicate is sure to be more or less impaired. To illustrate this, zinc, lead, tin, or iron, in sulphate of copper, precipitate the copper immediately from its solution, but the former metals are dissolved exactly in equivalent proportion with the reduction of the latter. The solution of this metal impairs the surface, and renders the duplicate less
List Of Substances For Moulds.
perfect. This may be prevented, in a great measure, by taking care that the voltaic current is passing at the moment when the metal is plunged into the fluid ; and this mode of proceeding is supposed, by many, entirely to supersede the elective afiinity, as it is termed, or the spontaneous action of the metal on the fluid. But I can decidedly affirm, that no battery, even of large series, will entirely prevent the solution of the more oxidizable, and the reduction of the less oxidizable metals, because it is impossible to protect by a negative tendency a metal where the hydrogen is in a condition to be absorbed.
The metals which can be employed with advantage to receive a deposit of any other metal, are, therefore, those which are not acted upon by the particular fluid in which they are immersed ; those, however, which are but slightly acted upon, may still, in some cases, be employed. The same thing may be said of the non-metallic bodies when coated with a thin* film of conducting substance, for it is essential, in order to make an accurate cast of any body, that it should not be decomposed by the fluid in which it is inserted, but remain entire during the time requisite for its immersion. The following is a short list of substances which may be used to receive the deposit of metal : —
Carbon - Platinum Palladium Silver -
Copper
Lead -
Bismuth
Antimony
Tin -
Iron
IBnc
In all metallic solutions, acid, neutral, or alkaline.
Ditto
ditto ditto
Ditto
ditto
Ditto
ditto
In all alkaline, in all but the preceding, saline acid.
Ditto
Ditto
ditto
Ditto
ditto
Ditto
ditto
Ditto
ditto
Ditto
ditto
In some alkaline
ditto
List Of Substances For Moulds.
Non-Metallxo Substances.
Gutta percha
Sealing wax - White wax -
In all saline or acid solutions. Ditto, not in alkaline.
Ditto
ditto
Bees* wax and rosin
Ditto
ditto
Stearine
Ditto
ditto
Spermaceti -
Ditto
ditto
Plaster of Paris, prepared
Ditto
ditto
Some animal substances
Ditto
ditto
Most vegetable substances
Ditto
ditto
Now by the preceding table we perceive that some substances may be immersed in one solution with impunity, while others would be destroyed by its action on them. It is, therefore, important to know, when we have a substance which is acted upon by any metallic solution, how to make a reverse from it that shall not be injured. For convenience a table is appended, showing at one view the modes of preparing moulds of different substances. The perpendicular row is a list of the objects to be copied, the horizontal the means of multiplying them. Suppose the operator had a valuable silver medal, of which he was desirous of making a fac-simile, he would look in the table against silver, and would there find that he could make a mould, or reverse, in copper, by electro-metallurgy ; but to this he would doubtless object. He would then see by what other methods he could also make a mould, and he would find that he could would prefer plaster of Paris, as least likely to be injurious to his medal. Having made the mould in plaster, he succeed with each of the processes given, and perhaps he would see from the former table, that, when prepared, it might be placed in any saline, or acid solution of copper, to form the fac-simile.
list of the principal mod of making moulds or reverses of various objects.
PLAXmCM, GOLD.
(132.) Carbon, from its cheapness, from its indestructible nature, and from its being unaltered in all metallic solutions, is invaluable for electro-metallurgy. One variety of it, graphite, or plumbago, usually called black-lead, has a most extensive application, which we shall hereafter have occasion more especially to describe.
Platinum, from its being unaltered by any solution, holds an important place for the reception of every metal ; its great price, however, must always be an impediment to its general use.
(133.) Gold is equally valuable with platinum, but is still more expensive ; yet when extended to that state in which it exists as gold-leaf, it may be applied over the surface of any soft substance, and thus a metallic surface is presented. This plan may be employed with other metals, such as silver or tin; but we have other methods which render all these modes unnecessary.
(134.) Silver only reduces gold, platinum, palladium, and two or three more metals from these acid solutions, and therefore may be employed as a negative one for the reduction of metals. Silver-leaf, of a thickness of about one square foot to the ounce, and made of pure metal, is much used by foreign forgers. The process they adopt is, to place the coin to be copied on a piece of wood, and upon the coin they place a piece of this thin silver. They beat it gently with a wooden mallet, till a perfect impression is taken on the metal, a result soon obtained. They then copy the opposite side of the coin in the same way. The two impressions are then soldered together, and the manufacturer sallies forth nd risks his neck for the illicit shilling which has cost him this labour. The reader will doubtless have no inclination to practise this fraud, and, therefore, it is unnecessary to enter farther into the process; but it should be borne in mind, that the same means may be employed with a better intention by the electro-metallurgist to obtain a moul(|,
Q
Ullots Of Lead, Tin, Etc,
Copper may be used for the reception of many metals, but unless the object to be coppered happens to be a mould, we cannot easily make a reverse in this metal, except by electrometallurgy.
(135.) We have now to treat of the alloys of lead, tin, bismuth, antimony, and zinc, which demand especial attention, because there are means of casting these alloys, and of making reverses, moulds, and medals, by more ready methods than we possess for any other metals. It has been remarked that these alloys have melting properties, not only below the mean of the melting points of the respective metals which compose them, but even some of them considerably below the fusing point of the most fusible metal that enters into their composition. To some of these alloys we owe the manufacture of type, to others the process of stereotyping, to others that of polytyping or cliche. The composition of the typemetal is stated to be 1 part of lead to 16 of antimony, and sometimes a portion of copper is added; this proportion probably varies at each foundry ; as they generally consider that part of the business a secret. Other compositions are given as 6 to 2, 4 to 5, or 4 to 1 of antimony to lead. In the foundry there are a number of crucibles, each heated by a charcoal fire, one being allowed to each workman. To make a type, the operator takes a little of the melted alloy in a small ladle each time, and pours it into the mould which has the counterpart of the letter he wishes to make. The moment it is in the mould, he cames it suddenly upwards with a jerk above his head, by which means the metal is forced into all the fine parts of the work, and a good impression is insured. Now we might expect that those Who day by day work at this occupation, would attain to certainty in their proceedings; but this is by no means found to be the case, for they form a very large number of imperfect types which are obliged to be re-mted. I give this process to show that with those about to be detailed a
Allots Of Lead, Tin, Etc.
Strong analogy to coining is presented. In the first case, it is with a fluid, or semi-fluid, metal; in the last with a solid mass. The alloys which may be used for these purposes are very various, according to the object from which we desire to obtain a reverse, for as a great latitude is allowed in the fusing point, so at one time we prefer the more fusible, at another that which melts at a higher temperature.
The following is a list of alloys which are employed by various authors, to which should be added all the compositions of type-metal, last described, and as antimony possesses the property of expanding in the act of cooling its alloys are well adapted for casting.
Tin.
Lead. Bismuth. Zinc.
fuses about 212® Falit. said to fuse at Faht 200.
ditto 200. ditto 200.
The alloy No. 5 is called the fusible metal of 9ir Isaac Newton. No. 6 is the fusible alloy of Rose. The two last are after the French. Sometimes a little mercury is added by the instrument-makers to render the alloy more fusible, but this ought always to be discarded in electro-metallurgy. All these compounds are used at a point between the fluid and the solid state, for at that heat they assume a pasty appearance, which is probably caused by the alloy consisting of two parts, one more fusible than the other. In fact, we examine the mass veiy attentively, it appears to be composed of a quantity of perfectly solid metal in a flne state of division suspended in another portion of alloy perfectly fluid* Having obtained our alloy in this state, it is ready for the
}24
Clichee.
process of making our reverse, and this process is termed the cliche. The alloys marked 1, 2, 3, 4, as well as the compositions for type-metal, will answer for iron, brass, copper, or other hard substances ; perhaps No. 2 and No. 3 will be found, after type-metal, entitled to the preference. When we desire to clichee from wood, sulphur, or from another clichee, we must employ those alloys which fuse more readily, and Nos. 5, 6, 7, and 8 come into use. If hard metals are used from which to clichee, we should take care to clean them thoroughly before using, and always employ them in a cool state. In using one clichee for making a second, we must take care to employ a less fusible alloy for the first than for the second ; thus the type-metal and Nos. 1, 2, 3, 4, answer as a primary mould to make casts in 5, 6, 7, 8. To clichde from Plaster of Paris, the material must be prepared either by linseed oil, gum, or gelatine, which processes will be described when treating of those substances, and sulphur moulds must be employed within a few hours of their manufacture.
The simplest mode of making a clichee is to pour a little of the fused alloy on any flat surface, then to skim it clear with the edge of a card that the surface may be most perfectly bright, after which we should wait till it is nearly at the point of cooling, when with a considerable jerk the matrix is to be brought down upon the alloy, by which operation the fluid part will be forced out in all directions, and a reverse equal in polish, sharpness, and beauty to the original, will be instantly obtained. If the alloy is used too hot, the surface is apt to present a crystalline appearance ; it is, therefore, very important that the object should be cool enough to make the alloy perfectly hard, as soon as the blow has driven the metal into all the finest lines. When taking a clich4e from an intaglio the air has not always time to get away, in which case little holes or bubbles are very apt to be caused. The surplus metal round the edges of the mould
Cliches. 125
80 formed, is then trimmed off in a lathe, but this operation is generally unnecessary for electro-metallurgy.
The Italians have a method of taking very perfect moulds with these alloys. They take a portion of the melted mass, and place it on a piece of paper; upon this they lay the medal, and under both a piece of carpet ; upon the medal they place a log of wood, and then a shai*p blow on the wood will ensure the sharpness of the cast. The worth of a cast thus made, is from sixpence to half-a-crown. I have before mentioned, the clicliee is nothing but a process of coining, and sometimes a sort of coining press is used for these purposes ; the medal or other object is fixed either by mastic or by screws on a piece of metal, which descends with force on the semifluid alloy. Previously to the operation of striking, the object is suspended by a cord passing through a ring, and attached to the rod of iron connected with the piece of metal. When every thing is ready, the doors are shut and the cord let loose, which allows the object to fall with great force on the metal.
An impression may be given to a perfectly clean bright surface of sheet lead, by placing upon it the object to be copied, and then with a steady hand dealing a heavy blow. By this mode even a sealing-wax impression may be copied, although this, at first sight, would appear hardly credible. By pressure alone, it would be difficult to obtain the result which can be given by the blow. Rolled lead, first scraped, in order to remove any oxide from the surface, and then flattened by running it through a press upon a polished iron plate, will readily take the impression of the most delicate work or engraving. The object to be copied is simply to be placed upon the lead, and then the two are to be sent once, and once only, through the printing-press, as in the ordinary operation for taking a print. The pressure in rolling is far greater than can be given by direct pressure, though there are instruments used by embossers capable of exerting great
Sealing-Wax.
power. The disadvantage of forming moulds by rolling is a liability of distortion of the image from imperfect stretching of the metal.
The stereotype is not of much value for electro-metallurgy; moulds made of stereotype metal may, however, be employed should there appear to be any occasion to use them*. Stereotype-casts are only made practically from plaster of Paris reverses: thus to stereotype this page a plaster-cast would be taken of the type when set up, and this would then be thoroughly baked in an oven to expel all moisture. The plaster-mould is next placed face downwards in a box, and confined in that situation by a plate of iron, when the whole apparatus is lowered into a caldron of melted alloy kept over a fire. It is suffered to remain in that situation a few moments, when it is withdrawn, and the vacuity caused by the contraction of the metal during the process of cooling is supplied by the workman. All the metal moulds will doubtless soon be discarded from electro-metallurgy for gutta percha.
(136.) Non-conducting substances are of three kinds: — substances having no affinity either for the metal or the solution ; substances acted upon by the solution ; and, lastly, substances capable of combining with the metal thrown down. Those of the first class are by far the most valuable, but are not very numerous. The best of these is sealingwax — a composition of shell-lac, Venice turpentine, and colouring matter. Dr. Ure gives, as the proportion in which these are used, four, one, and three. The manu* facturers have several varieties, the most expensive of which is the best for making seals. Some of them are extremely hard, as for example, a black wax which is used for filling up the letters in the engraved plates of shop-windows, but 1 do not know how a difference of composition can affect the properties of the wax in this important manner. The use of sealing-wax is attended with considerable 'expense, as
good wax cannot be purchased under tiiree and sixpence or £onr [fillings a pound, but it takes impressions of objects of the greatest delicacy with the utmost accuracy. Every one uses this substance, and sealing is one of those operations in which every one thinks that he excels his neighbour in the manner m which he performs it ; but, however well satisfied he may be with his skill in the small way, yet the management of large seals is attended with great difficulty and uncertainty. Proof-seals are made by engravers, by holding a piece of card over a flame, and rubbing, gradually, a stick of wax, previously softened by heat, upon the heated card, till a sufficiency is obtained, when the coin is to be pressed upon it. Very large seals are made by taking a good-sized stick of wax, and holding it in a flame, not only till the point, but even three or four inches of its length are lighted. It is then to be held over a piece of paper or card, when large drops of melted wax will keep falling, and in a short period a considerable quantity will be melted. The flame of the stick is to be blown out, and tlie fluid mass well stirred round and round, till all the air-bubbles are dispersed, and a clear surface of semi-fluid wax is exposed. It is now ready to receive the impression of the object of which we are desirous of obtaining a copy. This is to be laid upon the wax, and pressed with considerable force, and lastly, plunged into cold water, so as to cool it suddenly. Much less difficulty attends the use of a metallic die, for that abstracts the heat, and does not adhere. The accuracy with which sealing-wax takes impressions with care, is shown by its copying the lines on mother-of-pearl, and analogous substances, which naturally possess the property of decomposiDg the rays of light, and the same colours which exist in the original are also to be observed in the copy.
When we are desirous to obtain an impression in wax from wood or similar substances, they should be previously
.White Wax.
brushed over with a little salad oil. In these cases, by plunging the wax into cold water, its surface is apt to sink in places, and thus becomes uneven. Very large seals have been made of sealing-wax, by means of placing the mould on the semi-fluid composition, and subjecting it to hydrostatic pressure. In this way operators have succeeded in making perfect casts of six or more inches in diameter.
(137.) White wax may be used for taking casts, and can be procured with least expense by buying the waste ends of wax candles, which may be readily melted over a lamp. The object to be copied is to be very lightly oiled with a hog's -bristle brush previously dipped in that fluid. A moment's exposure of the medal to a current of steam, or even to the breath, will answer the same purpose, because a film of water, for which wax has no affinity, covers the medal, and, therefore, causes a separation between the wax and the metal. A narrow strip of paper should then be procured which is to be wound round the object to be copied, and kept in its position by a piece of twine tied around it. The ends of the paper may be even still better kept together by a little bit of melted sealing-wax. If the object to be moulded happens to be a medal, this is easily accomplished, and in other cases the same thing may be, with but little more difficulty, effected. By this proceeding we form a kind of rim to the medal. The fluid wax is then to be poured into the cup thus formed, care being taken that no bubbles of air adhere to the medal. The heat at which the melted wax is used influences the success of our operation. If the object to be copied be small, it need not be so warm as if it were of considerable size. The conducting poer of the body requires a similar regulation of temperature, for if it be a good conductor, a metal for
white wax.
instance, it has the power of abstracting the heat from the melted wax so rapidly that a higher temperature must be employed. As a general rule, the surface of the object should be entirely covered with fluid wax a second or two before hardening commences at any one point, and in the same way the wax should not be so warm as to remain long before it begins to set firm. It is then suffered to remain not only until it becomes solid, but even quite cold, which will not take place in less time than two or three hours, on account of the wax being a bad conductor of heat. It may then be taken off by gently pulling the wax-cast from the medal.
Plaster-casts may be even copied in wax, by simply oiling the plaster with a little sweet oil, previously to pouring in the fluid, and thus a perfectly sharp reverse of the plaster will be obtained. A still better method of taking a reverse from plaster, is to let it absorb as much hot water as it will take up without any remaining on the surface. For this purpose the cast is placed in water not above half its height, and as the water penetrates by capillary action, the surface begins to assume round the edge a slightly dark colour, and the eye can accurately trace its progress till the action is finished. It is then to be enclosed in paper, and melted wax poured upon it while it is warm ; after which the whole is to be allowed to cool, when the wax will separate from the plaster with the greatest facility. In this process much of the success of our labour depends on the quantity of water employed, a very nice adaptation of that being requisite. If there is too much water it will then be drawn up between the wax and the plaster, after the former has been poured upon the cast, and a wavy hollow surface will be given to the mould which completely unfits it for electro-metallurgy. If too little water be used, the wax will penetrate into the pores of the plaster of Paris and adhere to it. The plaster must not be soaked in water one minute longer than necessary, for
J30
Spermaceti.
that will soften the structure, and render the surface indniteljr more liable to tear up and be destroyed upon the separation of the wax reverse. Should the slightest adhesion exist, it shows that the plaster has not absorbed sufficient water, a circumstance which the operator must avoid another time ; if, however, a very slight adhesion should exist, it may, generally, be overcome by soaking the mould and cast for a few minutes in water, when frequently a spontaneous separation will ensue. Those engaged in making moulds do not esteem wax as the best substance for taking casts, and, perhaps, with justice, from the reverses made by this substance not entirely possessing the sharpness of the original, the edges of the sharp parts frequently being rounded and dull.
The substance called stearine makes, also, excellent moulds, for which purpose, I believe, it has been much used by Jacobi. Stearine is made from common tallow, by pressing it with an hydraulic machine and squeezing out the fluid parts. This process is however imperfect, a portion of the oily matter being always left. The metallic-wick candles are jaid to be an example of this mode of proceeding. A &r better operation of preparing this substance is to saponify the tallow by potash, soda, or, what is more used, lime, and then decompose the salt thus formed with dilute sulphuric acid. In this way excellent stearine candles are made, which in illuminating powers and cleanliness are inferior to none. The observations applied to wax are suitable also to stearine, the proceeding in both cases being alike. The price of raw stearine in London, at the present time, is about one shilling a pound. Spermaceti is perfectly analogous to stearine in its properties. It is the solid part of the ml of certain whales, particularly of the physeter maeroctphaluii or sperm whale ; the best is to be obtained from the head of tibe animaL It is to be used in the same manner as wax and
Papsb.
(138.) A mixture of equal parts of bees*-wax and rosin may be employed for taking casts and may be used in a similar manner to wax ; sometimes they add a little turpentine, and increase the quantity of rosin. This composition is used a great deal by the Italians, but care must be taken not to use the fused mixture too hot. The composition should be melted, and then allowed to remain till the bubbles have dispersed, and till it becomes nearly as thick as treacle, when it is to be poured over the object, in the same way as wax.
(139.) Of the second kind of non-conducting substances, there are several varieties : paper, plaster of Paris, &c., which are acted upon by the fluid. Paper is of no great value for obtaining a reverse from any object ; by the embossing machines, however, we can obtain from metals and hard substances, a cast like the ordinary stamps, and we can effect the same result by placing two pieces of paper over the object and rubbing the upper one with a black-lead pencil, by which means the paper is forced into every depression. Paper rapidly absorbs the fluid of the solution, and becomes rough, and therefore, must be treated with various substances, in order to give it a perfectly uniform surface. It may be brushed over with a little drying oil, such as linseed or nut oil, to the former of which I give the preference. The oil should be thoroughly boiled, that it may dry as quickly as- possible, after its application to the paper. The substance to which the oil is to be applied, should be clean. It is then to be brushed lightly over with a cameFs hair brush till all absorption ceases, and the surface is left shining, owing to the small quantity of oil still remaining upon it. Great care must be taken that the plaster, or paper, be just saturated, and no more, as the superfluous oil, by drying on the surface, will All up the space between the fine lines. The paper most then be left to dry for about twenty-four hours, and, if possible, exposed to sunshme ss
o 6
Tarnishes.
tb rays of light favour the absorption of oxygen, a circumstance absolutely essential to the drying of linseed oil. It is then ready to receive some conducting substance, of which I shall hereafter speak. This mode of treating paper appears, for most purposes, to be superior to every other.
Varnishes may be applied for the same purpose, and as some of them dry more quickly than the oils, their use is attended in some cases with advantage. The principal of these is the white hard, copal, mastic, and carriage varnish. The first dries in a few minutes, and should be applied until a small quantity bears out from the surface. It is best adapted for highly-glazed papers, where the quantity of size prevents the absorption of the more viscid varnishes. The mastic fulfils its purpose very well, but no particular advantages attend its application. The carriage varnish may be sometimes used, but great care must be taken that it does not clog up the fine lines, otherwise it is a most valuable varnish for this purpose, and leaves a very smooth surface. It would be in vain to describe all the modes which may be adopted to render paper non-absorbent and smooth, — it is the principle to which I wish to direct particular attention. Sometimes a mixture of bees** wax and rosin previously fused, may be applied, particularly to the absorbent papers. The paper should be held over a flame so that it does not burn, and the composition rubbed upon the opposite side to that on which we desire to make the copy, till the paper is thoroughly infiltrated, when it will be found not to pass beyond the surface. The paper is hard in a few minutes, and ready for the solution. This is an excellent process and one which may be frequently adopted. Sometimes rosin itself may be used, but it is apt to be brittle. Other substances may be employed in a similar manner, as balsam of Canada, &c.
(140.) The preparation of plaster of Paris is of the tost impprtauce, and the destruction of Tts absorbent pripiy is.
Plaster Op Paris.
to be effected by means similar to those employed in the preparation of paper. Plaster of Paris is sulphate of lime, or gypsum, deprived of its water of crystallization by heat. In this state it has such an affinity for water, and is capable of taking up so much, that when the powder is mixed with water till it becomes of the consistence of cream, it sets after a few seconds into a hard mass. In the manufacture of plaster-casts, we must pay attention to several little niceties, in order to get rid of all the air-bubbles. These arise from two causes, either from the adhesion of the air to the plaster, or from the plaster carrying down air with it, when added to the water. The first is to be remedied by using fresh burnt plaster, which is always adopted by the cunning stereo, types, for they state that if it simply stands a fortnight, the casts will not be so good. The workman cannot explain this, but the rationale was well known to Mr. Wyatt, our celebrated sculptor, who told me he attributed it to the adhesion of the air ; and that thus many delicate casts were injured. He places the dry plaster in a saucepan over the fire, and heats it, when it heaves from the discharge of the gas, and is then ready for use. When we desire to make a plaster cast, a sufficient quantity of plaster should be placed in a basin, and water poured upon it till it is completely covered. The bubbles having ceased to rise, the plaster and water are to be thoroughly mixed by rubbing them together. Mr. Williams, in an interesting lecture delivered before the Royal Institution, recommended that a basin of water should be taken, and the plaster gently shaken into it, and allowed to stand for half a minute, when the superfluous water was to be poured offi, and the semi-fiuid mass remaining being stirred up is then in a state ready for use. Now these two processes are somewhat the reverse of each other, but both agree in principle : that is, by both methods the operator endeavours to get rid of adherent air as much as possible, ome excellent mechanics decide that the first method is
Preparation Op Plaster Moulds.
the best, others that the last is the only one that can be adopted with success, but as both sets of workmen turn out equally good impressions, we need not be very particular which V follow ; in either case, however, we must take care not to over-saturate the plaster with water, for although the plaster will still set, it does not sufficiently harden. For all electro-metallurgic purposes it is preferable to have plasters as hard as possible ; therefore, we must take care to use rather more plaster of Paris in our mixture than that which is ordinarily employed.
The surface to which it is to be applied, should be slightly brushed over with a very small quantity of salad oil. A little fluid plaster may then be poured on the cast, and with a hv g s- bristle painting brush, thoroughly rubbed into all the fine parts, which will prevent the adhesion of any air-bubbles in the plaster which might prevent a perfect impression. Another portion of plaster, sufficient to give the desired thickness, is now to be added, and time must be given for the whole to set, when it should be removed from the mould, and gently heated over a fire to drive off excess of moisture. It is then found to be exceedingly hard, and ready to receive substances to destroy its absorption.
The great advantage of plaster of Paris is its applicability to nearly all cases, for it may be employed with all metallic substances. Casts can also be made with the utmost sharpiss from sulphur, and it delivers so admirably from moulds of that substance, that the Italians use for their medallions almost exclusively sulphur-moulds. It is even possible to take a plaster-cast from a plaster-mould by previously saturating the mould with boiled linseed oil, but, however, the Italians do not consider these moulds form such sharp casts as those of sulphur. Rough and large objects are occasionally copied from plaster-moulds by simply soaking them previously to the operation. Thare is no difficulty in taking moulds ikom wax, bees'-wax, and rosin, stearin iqermaceti.
PBEPAaATION OF PLASTER MOULDS.
animal, vegetable, or, indeed, almost any organic substance* Plaster of Paris is frequently coloured in various ways to suit the fancy of the operator, and a pretty effect is sometimes produced by using two colours of plaster, one being first employed for the sunk parts of the mould, the other being applied over that to the fiat parts, so that when the cast is removed from the mould, all the rilievo is of one colour, all the flat portion of another.
There are various modes of filling plaster-casts to render them incapable of absorbing fluid. These may, however, be divided into two classes, the application of solid substances, as stearine, wax, &c., by the employment of heat, and of substances in solution, as varnishes, &c. It may seem unnecessary to detail such a variety of modes for obtaining the same object, but as we do not always have the best at our command, we are glad to avail ourselves of some other material which will answer nearly equally well. The application of solid substances, rendered fluid through the agency of heat, is effected in every case in precisely the same way ; a minute description of one will, therefore, sufilpe for all. This mode of treating plaster-casts is to place them in a flat dish with the material, which should not exceed half the height of the cast, and the heat employed should be sufficient to render the composition perfectly fluid. The heat may be applied by means of a lamp, or gas-furnace, the top of a stoVe, or the hob of a fire, and the temperature should be raised a few degrees above the melting-point of the substance. The plaster previously to this operation, although well dried, will part with more water, which, passing off in the form of steam, gives an appearance of boiling. After it has remained in this state for a short period the cast is to be removed from the fluid. The temperature at which this operation is performed, influences the success of the process, for if taken out at too low a heat, a pordon of the substance, be it wax, tallow, or stearine, will oongeal on the surface of our mould, and. much
Preparation Op Plaster Moulds.
impair its sharpness. If removed at too high a heat the fluid remaining upon the surface, will rush into the pores of the plaster, and not sufficiently fill its texture. I like to see the surplus fluid on the surface of the mould gradually and quietly entering, taking its own time, being first absorbed at the circumference, and gradually lessening till the whole has penetrated into the mould. For different processes we require a more or less perfect filling. When we are only desirous of using our mould for simply making a metallic reverse, a less perfect preparation will suffice, and fifteen minutes* exposure to heat will be found ample enough ; if, however, we want most thoroughly to protect the plaster, the cast must be left for nearly an hour, and boiled at a higher heat, till the steam ceases to rise from the mould. If the plaster is thus thoroughly saturated, it will become semitransparent, and the light of a candle may be distinctly seen through it. When the plaster is cool, a uniformly smooth, polished appearance will be given, and nothing will be left on the surface, if the operation has been properly performed. My experiments on plaster have been more extended than may at first sight seem necessary, because from the first it appeared to me obvious that this was the substance on which electro-metallurgy must be dependent for a very extensive application. Its mode of moulding is comparatively so simple, so economical, and so effectual, that it is applicable from the smallest medallion that the genius of a Wyon can produce, to the most gigantic statue ever constructed by the ingenuity of man.
The substances used to fill plaster need not be lost, for after the mould has been used, by throwing it into hot water acidulated with dilute sulphuric acid, the substance will leave the plaster, and float at the top of the liquid, whilst the water will combine with the plaster, and remain at the bottom of the vessel. My attention was first directed to the use of the add by Mr. De La Bue. During the immersion of the pre-
Preparation Op Plaster.
pared plaster in the solution, a soap of copper is formed which the acid decomposes and sets free, and thus by this chemical trick we employ our preparing substances over and over again.
There are several analogous materials which may be employed without difficulty for filling plaster ; I generally give the preference to stearine, because it is cheaper and more cleanly than the other substances. From the best stearine we pass by every grade to stearine prepared by pressure, to hard mutton fat and at length to ordinary tallow. This is well adapted for filling plaster. It is readily melted, and from its fluidity passes into the numerous pores of its texture. It is as well to boil the cast for some considerable time in the tallow, then drain off the superfluity, and, afterwards, leave it in a cool place to harden. By boiling, I dc not mean that the tallow should boil, but that the vapour from the plaster should give an appearance of boiling ; in general the hardest tallow should be selected, but good candles answer every purpose. The elaine in the tallow perhaps helps importantly to protect the plaster, and, therefore, in very large casts is valuable.
Spermaceti also renders plaster non-absorbent, and is to be applied in the same way as the tallow. Spermaceti, as sold for candles, answers the purpose admirably.
White wax, such as that obtained from wax candles, suffices very well to prevent the absorption of plaster, and is very easy to apply.
Equal parts of bees'-wax and rosin previously fused, may also be employed with advantage to fill the plaster. The more rosin contained in the above composition the higher will be the heat required for its perfect fusion, and although rosin will answer by itself, yet it cannot be made to penetrate more than a very short distance into the texture of the plaster, though a hard, clean, non-absorbent surface, can by this means be produced. A solution of rosin in oil of
Ibs
FBXPAEAiTlOK OF FLASTEB.
turpentine majr be used, but it is difficult to drive offi all the turpentine. A miEture of rosin and grease maj be also emplojed.
Fluid substances, and substances in solution are to be applied in the same way as solid materials in a state of fusion the greatest care, however, being required to prevent any of the preparation remaining on the surface.
The application of boiled linseed oil is another mode which may be practised. It should be applied to the cast until a very minute quantity remains unabsorbed on the surface ; it is then to be dried, and this is best accomplished by free exposure to sunshine. The mere hardening of the exterior film does not indicate a sufficient dryness for the object to be placed in the solution, it being necessary that the oil should be somewhat dry throughout. If the object be placed in the solution previously to its being dry, the oil will separate from the plaster, the solution will act upon the cast, and both cast and solution will be materially impaired, if not utterly destroyed. Piaster requires a large quantity of oil for its saturation, perhaps as much as half of its bulk. The casts should not be overdried when the oil is applied, as the oil does not then so readily harden.
The same observations which apply to varnishes, balsam of Canada, Venice turpentine, &c., with respect to their application to paper, apply also to plaster articles. Of varnishes, the mastic and white hard are the best, but the methods described above are superior to those in which any of the varnishes are used. Experiments have been tried upon every other substance likely to be useful, but these it is needless to describe.
I am tempted to give a table of the substances which may be applied to plaster, as a summary of the results of my experiments, taking into consideration their relative efficiency as well as cheapness ; —
Tallow,
Stearine.
Spermaceti,
White wax. Bees'-wax and rosin. Bosin. linseed oil.
Ntit oil.
Solution of rosm in turpentine. Balsam of Canada.
Mastic varnish.
White hard varnish.
Lac varnish, &;c.
Sometimes we are desirous of hardening plaster, which we effect in two ways, either by filling it with a solution of gum arabic, or strong size melted. Tlie French authors state that by these processes we are enabled even to take a clich4e from plaster.
(141.) At the present time, by far the most important substance which electro-metallurgists can employ for their casts is gutta percha. This material is quite of modern introduction, and to Dr. Montgomerie is due the honour of having made Europeans acquainted tilth its existence, as heretofore it was only known to certain inhabitants of Malayan forests. It is procured by cutting notches in the bark of the tree, from which a milky juice exudes, which very soon curdles. The tree attains the diameter of three or four feet, or even, in Sarawak, is occasionally said to be six feet across. The material is imported into this country in large square blocks, which contain many impurities. These blocks are cut up by machinery into very small shreds, and then soaked and boiled in water. They are then torn to pieces by other machines to get every foreign particle out of them, and afterwards the material is thoroughly kneaded together in another machine, at a temperature nearly of boiling water. The gutta percha, after this preparation, is in a state ready for use ; and it is only necessary slightly to cover the mould with soft soap, to enable a most perfect fac-simile to be produced under proper pressure. For small objects, the pressure of the thumb is sufficient, for large objects a coining-press must be employed, and when large surfaces are desired to be
GOTTA tEBOHA*
copied an hydriiulic press capable of exerting a force of many tons, is required to be used.
The material was brought before my own notice, in 1844, by Mr. NichoUs, the original patentee ; I immediately desired to try it for electro-metalhirgic purposes, in which it perfectly succeeded ; and forthwith I also tried it for splints and other surgical appliances.
Gutta percha, at ordinary temperatures, is hard, but on being heated to the temperature of boiling water, can be moulded into any form. For the purpose of heating it, we may either soak it in boiling water, or place it in a glue-pot, so as to have the yielding mass free from water. In taking casts in it, the principal difficulty which is experienced is, to prevent, at times, small air-bubbles from interfering with the impression.
For moulds, it is the most perfect material which possibly can be desired, and already is practically to supersede very generally all other substances which have been employed for electro-metallurgy. It not only takes the most exact impression, but can be used over and over again without in any way being injured, or altered in its qualities.
The Gutta Percha Company use gutta percha very extensively for the purpose of forming electro moulds, and these electro moulds are again extensively employed for making embossed articles of gutta percha for sale, such as ink-stands, watch-stands, trays, vases, baskets, &c. &c.
Gutta percha is so admirably adapted for electro-metallurgy, that I am not aware of one single 'metallic solution in which it may not be plunged with perfect impunity.
This material is a very imperfect conductor of heat and electricity. On account of the former property, it retains its heat a long time, and on account of the latter it is used to envelope wires to convey electrical currents under water, and 4n this way the experiment was made to convey the electric telegraph between Dover and the French coast by insulating
;i4i
a copper wire hj placing it in about half an inch of gutta percha.
It would be very desirable if the trustees of the British Museum would issue gutta percha casts or moulds of the various coins and medals in their possession. Whilst locked up in the strong room, they are only seen by the curious and dilettante antiquarians, who delight rather in the marvellous than the beautiful, the rare than the useful. If the collection of those exquisite productions has any meaning at all, it must be to improve the taste of the people ; and I must submit that the issue of casts of them at a reasonable price would tend to improve the taste of artisans, who have now no mode of cultivating it.
(142.) The third class of substances, which comprises those which are acted upon by the metal reduced from the Uuid, are few in number ; yet, unfortunately, this class contains one substance which takes finer ists than any other, and that is sulphur. The newly-precipitated metal no sooner comes in contact with the sulphur than it combines with it, forming a sulphuret, and the cast swelling enormously, is quite disinf tegrated. The only mode of remedyihg this is to coat the sulphur-mould with a varnish, such, for instance, as white hard and mastic, of which a very thin layer should be applied. Sulphur-casts, however, have not in my own experiments answered well under any treatment, and as we have so many other modes of taking casts, there appears to be no inducement to follow the subject farther.
Jacobi, indeed, mentions that sulphur may be employed for the reception of copper, but probably it was an inadvertent assertion made by classing it generally with all other non-metallic bodies.
Although sulphur cannot be thus employed directly in the metallic solution, it makes most admirable moulds from which to take plasterrcasts. For this purpose a stick of sulphur is melted in a pipkin over a lamp or fire when it is ready for
use. The heat should be applied gradually, for being bad conductor, one part is apt actually to sublime and be on fire before another is in fusion. It is always as well to have a piece of old carpet at hand to place over the vessel should the sulphur catch fire. It may be used for most metallic surfaces, taking care previously either to moisten them with vapour, or to oil them. It may be employed for plastercasts either wetted with water or oiled, and it may be used to make a oast from a sulphur-mould. This is rather a nice process, but it is done as follows: — The sulphur-mould is oiled, and the melted sulphur is allowed to remain till very near the point of cooling, when a little is poured into the mould, and immediately poured out again, so that the smallest possible quantity is left. This is allowed to cool, when a little more sulphur is poured in, and again poured out, and these processes of pouring in, and pouring out, are respectively repeated till a sufficient thickness is produced to give strength to the medal. Sulphur is a bad conductor of heat, and is apt to crack to pieces from a very slight exposure to that agent. Sometimes the heat of the hand will make the mould fly to pieces, and even, occasionally, the warmth generated during the solidification of the plaster. It is stated by French authors, that this brittleness is not to be seen for two or three hours after it has been melted, and in that state it may be used for the cliche. Where appearance is an object to the modeller, the sulphur is coloured, either with vermilion, charcoal, red chalk, Prussian blue, or plumbago, all of which tend probably, but especially the latter, to render it less brittle. A very general belief exists among chemists that sulphur, when employed for taking moulds, is used in the peculiar thick state which it assumes after it has been heated to a considerable degree, via., between 400® or 600® Faht., and plunged into water. Thus treated, it remains for some time in a soft condition, and of a red colour, but aa fiur I can kanv there is im fimimbitiiinior tl
BSEAD-CRUMBft. — GLUE.
Sometimes bread-crumbs are used for moulding. The inner part of the loaf of bread is moistened with water, and thoroughly kneaded in the hand, like paste used for catching roach. The substances should neither be so moist as to adhere to the object, nor so dry as not to mould properly. It is, then, to be pressed upon the cast about to be copied. This is not a very valuable mode of proceeding, but some years ago it was extensively used for what were called breadseals.
Glue is also, occasionally, employed for moulding. It is melted in the usual way by soaking it in water for twentyfour hours, and then boiling it at a moderate temperature — the glue-pot, in fact, forming a water-bath. The especial purpose for which it is used is to overcome the difficulty which presents itself in moulding any object much undercut, for then the elasticity, flexibility, and general yielding nature of this substance is so great theat the most irregular objects may be copied by it. Glue and whiting are much used for picture frames, and other similar ornaments, but this composition will not prove of much benefit in electro-metallurgy. The last substances cannot be used as the negative pole in metallic solutions, but, perhaps, in some few cases they may be useful to the operator for taking other casts which may be used to receive the metallic deposit.
(143.) Non-conducting substances may be copied or multiplied by depositing a thin film of any conducting substance upon this ; and gold, silver, bronze, or copper powder, might be employed for this purpose.
There is another process by which non-conducting substances, such as animal matter, vegetables or minerals, may be coated with the finely-divided metal. The object is to be brushed over with a small quantity of the solution of any salt of gold, silver, or platinum, and in that state is to be exposed to the vaponr of phosphorus olained from the evaporation of either an alcoholic or etfaerial solution, when unmediate
m
$, deposit of finely divided metal will take place on tbe luffaoe* It has been supposed that this is a phosphuret of the metal, but if a little piece of phosphorus be placed in a solution of gold, silver, platinum, or copper, the phenomenon will be explained, as the respective metals will coat the phosphorus. The deposit of copper is particularly beautiful, and it is strange that I cannot find any notice of it.
The substance to be copied may be also brushed over with a solution of any of the metals last mentioned, and exposed either to sunshine or to heat, when reduction will take place : but the process is tedious, and is, therefore, very rarely employed. Any other mode by which the metals may be reduced, would suffice ; as, for instance, their reduction by proto -sulphate of iron, or hydrogen gas.
Gilding, silvering, or coppering objects by means of their respective leaves may be employed; yet all these modes are imperfect, and we have no need of any metallic covering whatever, as other means answer the purpose better, and are even more simple and cheaper.
(144.) One of the best methods of giving a non-conducting substance a thin conducting layer, is by the application of carbon, either by charcoal or powdered black-lead. It is only necessary to brush these substances over the object till the thinnest film is obtained, as that will be amply sufficient for the purpose for which it is wanted. The black-lead is the best, on account of its peculiarly unctuous nature, which enables its application to be made with the greatest ease, either by a camel's hair, or hog's bristle brush, according to the nature of the substance to be covered ; care must, however, be taken, that the interstices between the fine lines are not blocked up, as this would of course render the duplicate imperfect. Occasionally, there is some difficulty in making a thin film adhere to the surface, but if it an object where perfect sharpness is not indispensable, a small quantity
of varnish maj be applied ; a proceeding which is suitable to earthenware. Sometimes a little spirit of wine may be nsed when a cast is capable of being acted upon by that fluids as sealing-waX) but great care must be taken not to render the surface rough. Upon many substances the blacklead may be made to adhere by simply breathing upon the object In whatever manner we cause its adhesion, it ia important always to bear in mind, that it is of more consequence that a smooth polished surface of black-lead be exposed, than a thick and rougher coating.
The different opinions which are entertained, as to the applicability of black-lead for this purpose, are owing entirely to the fact, that great difference exists between samples of that article ; for if it be not really carbon, it is absolutely a non-conductor, and I have found a number of pieces totally inactive, while others were most excellent conductors. The action or inaction of different pieces, before grinding, is not at all dependent on their hardness, for I possessed a piece of that variety, called by the pencil-makers rock, which completely annihilated the teeth of three of the saws with which I attempted to cut it. 1 then sent it to a celebrated mechanic, for the purpose of having it sawed, but he succeeded no better than myself ; in fact, nothing but a diamond would have made any impression upon it, and yet it was one of the best pieces for voltaic purposes which I ever possessed. Sometimes, on the contrary, hard pieces are of no value, whilst soft ones are excellently adapted for galvanic purposes. There is no method but direct experiment, by which the conducting quality of any particular sample of black-lead can be ascertained. There are not two shops where it can be bought alike, so much being either naturally bad, adulterated, or ill -prepared. Perhaps the best test of good blacklead is to take a pinch between the finger and thumb, and press it, when, if good, it will cake together and adhere. If charcoal be employed, it should be well burnt, and in the
Char Iii.
On The Laws Regulating The Reduction Of The Metals.
Metals capable of being reduced by the voltaic fluid, 146. States in which they exist, 146 — 148. Law for the reduction of the metals as a black powder, 148. Law for the reduction of the metals in crystals, 149. Law for the reduction of the metals in the reguline state, 150. Cause of the reduction in the states, 151. Mode of producing them, 153 — 159. Mode of obtaining the black powder, 159. The crystalline state, 160. The reguline state, 161. The same rets obtainable by the single-cell apparatus, 165. Time required for the deposition of the metals, 167.
(146.) When we subject any metallic solution to tbe action of the voltaic current, the metal itself will he reduced, although not always in the saihe state. Thus, if we dip a knife into a strong solution of sulphate of copper, bright metallic copper will be deposited; but if we use a piece of zinc, a black mass of copper will be thrown down. Again, introduce a piece of zinc into an ammoniacal solution of sulphate of copper, and the reduced copper will be bright, whilst, if we dip iron into a very dilute and acid solution of the sulphate, black metal will be reduced. The learned are divided in their opinions as to whether the metal, in these cases, is reduced by jingle elective affinity, as they term it, or whether a galvanic action causes the deposit. Perhaps, in the first instance, the iron or zinc having a greater affinity for the acid and oxygen of the salt than the copper, combines with it, forming a sulphate, whilst the copper is thrown down, but as soon as the first portion of copper is deposited,
H 2
On The Laws Beottlating The
ft galvftBic battery is formed, which increases the action still faer. Be this, however, as it may, the fact I wish to impress in this place is, that the same metal may, under different circumstances, be reduced in different states.
Having shown that the same metal may be reduced in different states, we are next led to ascertain experimentally, what are the circumstances which tend to vary these conditions. We, accordingly, procure a galvanic battery and connect it with two platinum poles, which we place in a vessel to serve as the precipitating trough. In this trough we place a saturated solution of a metallic salt, for instance, copper, when on examination, if the battery possesses but feeble power, we shall find that crystalline copper will be deposited ; if, however, we dilute this solution with twice, thrice, or four times its bulk of water, the metallic deposit will assume a very different aspect. It will then be aggregated in a flexible state, which, to prevent circumlocution, I shall term the reguline deposit. If we now dilute this same solution to an infinitely greater extent, the metal will still be reduced, but in the form of a black powder ; a deposit so fine that the highest power which the skill of a Powell, or a Ross, can impart to the microscope, will not enable the eye to discover the form of the minute particles of which it is composed. Almost all metallic solutions may be substituted for that of the sulphate of copper, and the experiment will show nearly the same result, namely, that the strength of the metallic solution very materially influences the nature of the deposit. If this fact is really correct, we ought to be enabled to obtain on one negative pole several kinds of deposit, were h but possible to make a solution of unequal strength. Now we can make a solution of unequal strength by placing the crystals of metallic salt at the bottom of a tall glass vessel, and pouring upon it some conducting fluid, for, after a little time, if the liquid be examined, the lower part will be found to be of the most intense colour, and contain most metallic
REDTTOTXOK OF METiLLS.
14d
salt, whilst the shade will yarj to the top from that portion containing scarcely any- For this experiment a solution of sulphate of copper will answer perfectly well. In it we place our electrodes, which may be of copper, and connect them with a single galvanic battery. At the pole joined with the zinc of the battery, copper will presently begin to be deposited; black powder at the top, reguline metal a little below the centre, and crystalline copper at the bottom. If we stir the solution up and thoroughly incorporate it, a uniform metal will be deposited at every point. This experiment confirms our previous view, that the power being equal, the condition of the metal will depend upon the strength of the solution. If we examine the converse of the experiment, and take a solution of sulphate of copper (which should be acidulated to make it a better conductor), and use successively, first one very small battery, then two or three batteries arranged in a series, and, lastly, a very intense battery, we shall find that with this self-same solution we can obtain by these means, first a crystalline, then a reguline, and, subsequently, a black deposit. This experiment shows that the amount of electricity passing in any given metallic solution also influences the state of the deposit. From variation of the strength of the metallic solution causing reduction of metals in diflferent states, and from variation in the amount of the power also influencing the state of the metal, we are forced irresistibly to the conclusion, tAat to obtain with certainty any particular metallic deposit, we must regulate the galvanic power actually passing to the strength of the metallic solution* This is the fundamental principle — the very essence, in fact, of electro-metallurgy; and when we consider from how many causes the one, the other, or both may be interfered with,;we begin at once to obtain an insight into the difllculties which the operator must incur in conducting his operations. This grand principle applies to all mals, and even to all the salts of each
Reduction Op Metals As A Powder.
metal; but as every metallic salt varies in its conducting power, and in the facility with which it yields its elements, great choice is given to the workman to select the salt most applicable to the particular process which he is desirous of performing.
(147.) The laws which regulate the deposit of every metal appear to be the same, and although very simple, yet they have cost me much labour for their development. The properties of which I have here to speak are strictly those which relate to the quality of the metal, which is so materially influenced by various circumstances. The reduced metal may be precipitated in three different ways ; as a black powder, as a reguline metal, (or, in other words, a metal having the properties of ductility and malleability,) and, lastly, as a crystalline deposit. Between these there are, indeed, other intermediate states, or mixtures of two different states, of which we shall hereafter take notice.
(148.) Law L — The metals are invariably thrown down as a black powder, when the current of electricity is so strong in relation to the strength of the solution, that hydrogen is freely evolved from the negative plate of the decomposition cell.
The different states which reduced metals assume, as well as the different varieties of each state, appear to be nothing but a difference of aggregation of the minute metallic particles of which they are composed : metals deposited in a black powder are, probably, in an infinite state of division ; then, as a variety of this amorphous mass, we have a spongy material, resembling, more or less, the colour of the metal, but the particles of which are still so fine, that it may be moulded with the fingers into any shape we desire. As another variety of this deposit, the spongy mass may be aggregated here and there into hardish lumps, interspersed
Reduction Op Metals As A Powder.
in the sponge, and this condition may be so far increased as to give rise to the form which is termed the sandy deposit. Such are the varieties of the pulverulent deposit, the first class of metallic reductions, comprising black powder, sponge, and sand.
The cause of these varieties appears perfectly obvious, for hydrogen and copper are deposited at the same time. In a former part of the work we had to treat at great length upon the power of adhesion which this gas possesses, and if in this place we apply the same fact, we shall see that it will sufficiently account for every variety of the pulverulent deposit. If the hydrogen is evolved in very large quantities, we can easily imagine that it would envelope each ultimate particle of the reduced metal, and prevent the cohesion of tlie neighbouring atoms. In confirmation of this rationale, the metal in this state, notwithstanding its usual colour, is uniformly black, a fact perfectly in accordance with the properties of light. Any substance in infinite division must of necessity be black, from its not having breadth enough to reflect a ray of light, which requires certain definite dimension, which philosophers have measured. If the hydrogen is evolved in smaller quantities, we can easily conceive that some of the atoms of the metal would be aggregated together, forming the spongy deposit ; if, on the contrary, the quantity of metal deposited far exceeds the quantity of hydrogen produced, we can easily see that more metallic particles would be in conjunction, and, therefore, the deposit would be much firmer. If, lastly, the hydrogen is almost nothing, we can also understand that the particles of sand would be still farther increased in size. Metals of all colours and properties exhibit the same phenomenon ; even silver, platinum, &c., which are usually white, gold, which is yellow, and copper, which is red, together with other metals, obey this law, all being easily reduced as a black powder.
H 4
Reduction Of Metals In Crystals.
( 149 .) Law II. — Every metal is thrown down in a crystaUine state, when there is no evolution of gas from the negative plate, or no tendency thereto.
When I speak of no tendency to the evolution of the hydrogen, I mean, that the strength of the metallic solution is so great that either electricity of a much greater tension must pass, or the solution must be rendered of more easy decomposition, before gas would be evolved from the electrical power employed.
This is, in fact, in strict accordance with the generally known properties of bodies, for we find, universally, where bodies are deposited quite at their ease, and very slowly, that they have a tendency to assume each for itself some peculiar and definite form. In the deposition of a salt, for instance, if it is suddenly precipitated, it always presents itself as a fine powder, which would appear to be almost in the ultimate state of division ; but if the deposit takes place very slowly, it will assume some peculiar form. Nothing can be more complete than the analogy between the crystallization of a salt and the crystallization of a metal, for both agree in their atoms requiring sufficient time to arrange themselves in their own peculiar way. The crystalline condition is not very generally adapted for the purposes of the arts, because the sides of each separate crystal do not firmly adhere to its neighbour, but it is most admirably suitable for coating a reguline deposit, adding a beauty and lustre which it is impossible to give in any other way. If, indeed, the crystals are very slowly formed, each one will have so slight an adhesion to its neighbour, that a piece held by its edge will break from its own weight ; and we may even increase this property to such an extent that only solitary crystals may, here and there, be deposited. In the crystalline state, the brittleness of the metal would appear to be caused by the liquid wetting each separate crystal, and the interval caused
Reduction Op Reguline Meta.L. 153
by the film of water in the mass of copper, would account for the very slight adhesion that is found to exist.
(150.) Law III. — Metals are reduced in the reguline state when the quantity of electricity in relation to the strength of the solution is insuflScient to cause the production of hydrogen on the negative plate in the decomposition trough, and yet the quantity of electricity very nearly suffices to induce that phenomenon.
In fact, the reguline state is obtained in the greatest perfection when hydrogen is not far from the point of evolution, but yet none is really given oflT from the negative metal.
(151.) The reguline metal, possessed of the properties of flexibility, malleability, and elasticity, seems to be produced by such an arrangement of the ultimate particles of the deposited metal, that, being thrown down in exact apposition, they form a regular mass, presenting frequently, at the back of the object, a similar uniform surface to that seen at the front. When we perceive in ordinary metallurgic operations that the same metal may vary much in its properties, that at one time it may be flexible, at another elastic, and at a third brittle ; and when we farther perceive that the density of the same metal may vary, that a cubic inch at various times may even differ in weight, we must not be surprised to find that reguline metal formed by electro-metallurgical processes may vary in the same way ; and, indeed, we do find that differences of the same nature really occur. To attempt the explanation of these things, would lead us far beyond human knowledge, and carry us to the properties of the ultimate atoms of substances, for, doubtless, these differences are produced by variations in the arrangement of these partides ; how otherwise can we account for the compression caused by hammering a solid body, or the increase of volume from
Beduotion Op Eeoulinb Metal.
jinnealing it. To obtain, however, the reguline metal in great perfection, we should carry on our process with such celerity in relation to the strength of the solution, that at every point of the negative surface, or that at which the metal is deposited, the action should be uniform, and atom by atom of the metal should be so quickly thrown down, that no time is allowed for the particles to follow their own fancies and arrange themselves in crystals. There are, indeed, many little circumstances which interfere with the apparent density of the reguline metal ; thus the ultimate particles appear to be thrown down closer together at a low than at a high temperature.
(152.) Dismissing theories, however, we must remember these facts : that the electric power in any solution, when barely sufficient for the production of hydrogen, causes the reduction of the metal in a malleable and ductile state ; that the electric power, when not nearly sufficient to cause the appearance of the gas, throws down the metal in crystals ; and, lastly, that the pulverulent deposit is produced when there is evolution of the gas.
(153.) A very brief examination of our laws will show that the two properties of galvanic batteries must operate in an important manner in regulating these results, and, accordingly, we find that they are materially modified by the size and power of the battery. The regulation of intensity is, perhaps, of the greatest importance ; for, on the one hand, economy requires as few cells as possible, and, on the other hand, other circumstances require more. Whenever it is possible, the fluid to be decomposed should act on the positive pole of the fluid. Thus, in the decomposition of salts of gold silver, iron, lead, tin, and copper, we use in the decomposition apparatus, positive poles of these respective metals. This enables us to conduct our precipitations with a single cell, which, with my battery, enables us to obtain any given amount of work at the smallest possible cost. During the
Effect Of Inten81Tt On The Decomposition. 155
decomposition, the metals mentioned above are dissolved precisely to the same amount as that to which the new deposit is obtained if no interference takes place. The solution is, in the same way, always of the same strength.
(154.) The degree of action of the fluid on the positive poles, or rather of the oxygen and acid transferred to the positive pole, varies with every salt of the same metal. To regulate the action equally in different cases, acids, either of more or less oxydizing power, or in greater or less quantity, are added to the metallic solution to be decomposed. An increase or decrease of the temperature influences, materially, the intensity required for different salts, because at a higher temperature the current passes with more facility, and the action on the positive pole is more energetic. These minutia; have hereafter to be fully discussed but here I wish to point out, that, when possible, one cell only of the battery is to be used, and where this is rather deficient in intensity, a compensation should be obtained by adding to the metallic solutions acids of more or less affinity for the positive pole, according as that may be required, so, that, instead of increasing intensity, we lessen resistance.
(155.) For those cases where we use a positive pole or anode made of platinum, we are compelled to obtain increased intensity by employing a more extensive series of batteries. In these cases, we must use as many cells as will decompose water ; and three or four will in general be amply sufficient. Beyond the mere capability of decomposing water,
I cannot perceive that increment or decrease of intensity, as a general use, is of material importance, and the regulation of the quantity must then be made the subject of attention.
(156.) The quantity of electricity passing in any fluid will depend, caeteris paribus, upon the distance between the electrodes, the extent of surface they expose to the fluid, or their relative size one to another. These properties have been
Mode Of Obtaining Various Deposits.
Decomposition Tkouoh.
Gaxtanic Battery.
Unifonn strength of metallic solution.
Tenaperatore of ditto.
Conducting power of ditto.
Size of positive pole.
negative pole.
Badiatlon between the poles. Approidmation of the poles. Faality of removal of the newly formed salt.
Primitive force of battery.
Size of plates of ditto. Approximation of the plates. Conducting power of exciting fluid.
Ditto, of connecting wires, facility of removal of the iMwly formed salt.
Mode Of Obtaining Various Deposits.
solution the deposit is influenced by the amount of electricity passing, according as these conditions in the trough or battery are varied. The more these conditions are exalted, the greater the quantity of electricity which will pass : the more they are depressed the less the amount of the voltaic force that will traverse the solution.
In those instances in which the electro-magnetic ahd magneto-electric power are substituted for the power derived from the galvanic battery, the deposition of metal is obedient to similar laws, and is influenced in the same manner in the decomposition trough. When we desire to lessen the power from the machine, we may most conveniently efiect it by causing the keeper to revolve more slowly, and in some cases by lowering the magnetical power.
(159.) In any given solution we may increase the disengagement of the hydrogen so as to cause a black deposit, by increasing the intensity and quantity of the battery ; by a series ; by diminishing the size of the negative pole and enlarging the positive electrode in the decomposition trough ; by approximating the electrodes or poles ; or, lastly, by increasing the heat. All these conjointly, or any of them separate} , will favour the increase of electricity, as they will increase the quantity of hydrogen evolved.
For any given size of the negative plate we can obtain a black deposit, by increasing the intensity and quantity of the battery; by increasing the positive electrode in the precipitating trough ; by diminishing the quantity of metallic salt in solution, at the same time adding to its acid ; and by approximating the poles.
With any given battery (provided it will decompose water) we can obtain a black deposit, by diminishing the size of the negative pole in the precipitating trough ; by increasing the size of the positive ; by approximating them, and by rendering the metallic solution very weak with dilute acid.
. (160.) To obtain a crystalline deposit with any given solu-
Reguline Deposit.
fluid passes to a much greater degree at a high than at a low heat.
The converse of all these procedures is equally applicable to those cases where the hydrogen is deficient. By regulating the strength of the metallic solution, and adding more or less dilute acid, the evolution of the hydrogen, in any battery (provided it be sufficiently intense to decompose water), will be perfectly under control.
The student in electro-metallurgy will at once perceive that these three last voluminous directions are perfectly unnecessary to any person thoroughly conversant with the properties of galvanic batteries and the doctrine of resistances, for they are but a recapitulation of what has been already so fully considered in the book on Galvanism. To recapitulate, therefore, in a few words : when we desire to cause the powdery deposit, we diminish all resistances to the passage of the electric fluid ; when we desire to cause the crystalline deposit, we increase all the resistances ; and, lastly, to cause the reguline metal, we must cautiously regulate the resistances according to the strength of the metallic solution.
(162.) Thus, with any amount of salts in solution, with any- sized negative plate, with any-sized battery, and at all temperatures, we can obtain the reduction of any metal in any state we please. It is true that this excessive refinement has hardly been carried to each salt of every metal, yet the principles have been so far accurately demonstrated with such a number of them, as to leave no doubt of their general truth and value.
It has accidentally been discovered that when a few drops of bi-sulphuret of carbon are dropped into a large quantity of certain solutions, the metal deposited has a particularly brilliant appearance. This property has been patented and has been found by various electro-metallurgists to be of great value to the arts. The theory of its action is totally unknown ; but doubtless, when worked out, may lead to im-
Regulation Of Galvanic Power.
portant discoveries, and is therefore well worthy the attention of the experimenter.
In detailing my observations upon the deposition of metals, I have assumed that we are working with pure salts ; for if two or more salts are mixed together, the deposition obeys the laws which will hereafter be detailed when speaking of *'lloyd.
(163.) To regulate the galvanic power to the strength of the solution will henceforward be my constant theme throughout the concluding part of this volume. Having once begun I shall continue and end with it, that this important point may be so firmly impressed upon the minds of those who practise electro-metallurgy, that they may conduct their processes — not by chance, nor blind experience, but — by unerring ana never-failing principles ; that when the operator desires to make alterations in his battery, his trough, or his solution, he wdl at once be possessed of the secret of adapting every other circumstance to attain the end he requires. To regulate also the uniform strength of the solution by the proper diffusion of the newly-formed metallic salt, must also be my continued advice ; that success may crown the labours, pleasure the success, and profit the pleasure derived from the practice of electro-metallurgy. The want of an uniformity of strength in the metallic solution perplexes the tyro in electro-metallurgy more, perhaps, than any other circumstance , for after having mixed a solution of definite strength, and Laving taken me greatest pains that the positive and negative surfaces should be under the same conditions in every part, he is surprised that frequently, in the same solution, he has every variety of deposit. He, perhaps, in his disappointment, declares that electro-metallurgy depends on chance ; but let him only particularly examine the state of the solution, and he will find that, from various causes, the uniformity has been destroyed. At one place the acid will be in excess, and in another the metallic salt. Bays from
162 &Inglb-Cell Apparatus.
the ftuxi may have heated the upper part of the solution, which would still remain at the top, as the hotter part being lighter would not cause that circulation which is necessary for the heating of fluids. Sometimes, indeed, the metallic salt would seem to subside to the lower part of the decomposition vessel, leaving the upper part comparatively unsaturated. In the description of electro-metallurgical apparatus, the best methods of regulating the uniformity of the strength of the solution has been already considered ; we need not, therefore, further allude to it in this place.
(164.) In detailing the above laws, the battery has been more especially alluded to, because we can, by its means, regulate most exactly the quantity and intensity of the current. The same principles apply to the cases in which the metal on which the reduction is to take place is made the negative plate to a piece of zinc enclosed in a porous tube, but we cannot adapt this with that nicety which the battery admits.
(165.) The quantity of electricity in a single-cell apparatus may be increased by enlarging the zinc plate ; by approximating it to the negative ; by diminishing, as much as possible, any resistance offered ; by the use of diaphragms, and by adding to the acid of the solution which acts upon the zinc. The quantity of electricity may, in like manner, be diminished by adopting an opposite course of proceeding. In the use of the single-cell apparatus, as in that of the battery, the strength of the metallic solution to be decomposed will materially influence the quantity of electricity required for its reduction. The neutrality of the solution, the acidity, or the nature of acidity, will operate in a similar manner. The different conditions have been sufficiently adverted to, when speaking of the effects of those circumstances in the use of the battery. The above facts alone are sufficient to make forcibly apparent the imperfection of the single-cell apparatus, and the superiority of the process
Effect Of Time On The Deposit.
lead, this formation of crystals is one of the greatest difficulties with which we have to contend. As we find this tendency of the crystals to start from the negative to the positive pole, where the current of electricity manifests much intensity, it would be as well to have, in such cases, batteries of the lowest possible intensity, or divide that intensity amongst a series of precipitating troughs.
(166.) There are certain peculiarities appertaining to each metal, and even to each salt of the same metal. !Each demands somewhat different management, depending upon the circumstances under which the reduction of the metal takes place. The necessary variation in the modes of operating will be considered in the next chapter.
(167.) And now let us consider the influence which time exerts over these processes. Is it necessary, as all authors have asserted, that the voltaic precipitation should go on slowly ? The fundamental laws which regulate the precipitation of metals exclaim at once, by no means ! For if the electric power be regulated to the strength of the solution, precipitation may take place at a rapid rate. In fact, we shall hereafter show that the reduction of the metals may be more speedily effected than at first sight appears possible, because the deposition is amenable to the same laws, whether it takes place slowly or rapidly, because the quality of the metal depends on the regulation of the quantity of electricity to the strength of the metallic solution.
Chap. Iv.
On The Keduction Op The Metals.
Introduction. Formation of salts, &c., 168. Eeduction of Platinum, 169. Gold, 170. Palladium, 171. Iridium, 172. Rhodium, 173. Osmium, 174. Silver, 175. Nickel, 176. Copper, 177. Zinc, 178. Cadmium, 179. Iron, 180. Tin, 181. Lead, 182. Antimony, 183. Bismuth, 184. Uranium, 185. Arsenic, 186. Tungstic acid, 187. Cobalt, 188. Manganese, 189.
( 168 .) To what part of electrical science are we not indebted to Faraday ? He lias increased our knowledge of the hidden and unknown to such an extent, that all subsequent writers are compelled so frequently to mention his name and quote his papers, that the very repetition becomes monotonous. However humiliating it may be to acknowledge so great a share of successful investigation to one man, yet when we come to describe the electro- chemical decomposition of metallic salts, we are forced to render our feeble tribute for his communications on the extended subject of voltaic decompositions. He has shown that we can only reduce metals on the negative pole of a galvanic battery from a solution which contains them in combination with some other substance : for if we galvanize a metal in the elementary state for ever, the voltaic power would have no property to move it to either electrode. He has also proved that not only must the metal be combined in the definite chemical proportion to form a metallic salt, but, in order that it may be decomposed, it must be in that peculiar physical state called liquidity, or fluidity. It is not indeed, necessary that the salts themselves should be liquid, for if dissolved in any other fluid they will still yield up their
ttm jHysxAiov of salt
elements to the electric principle. From these considerations it is manifest, that, whenever we are desirous of working in any particular metal by the galvanic fluid, it is necessary first to form some compound of that metal which is soluble in some fluid. The substances [with which metals most readily combine are oxygen, chlorine, bromine, iodine, sulphur, cyanogen, and, in some cases, even hydrogen. The compounds of chlorine and bromine are generally soluble in water, giving rise to that class of salts called muriates, or hydrobromates, and are then at once fit for use. The compounds of iodine are, as a class, insoluble themselves, though with hydriodate of potash they frequently form soluble compounds.
Of the metallic fluorides I have had but little experience, and, probably, they will not be much employed for electrometallurgy.
Most of the compounds of metals with oxygen, or oxydes, are insoluble themselves in water, but become soluble when further combined with acids, alkalies, and certain neutral salts. Thus, oxyde of copper, which is absolutely insoluble, readily dissolves in sulphuric acid, in ammonia, or cyanuret of potassium, &c. Were I to enter fully into these matters, the reader would find himself troubled with an extensive work on chemistry, instead of an epitome of electro -metallurgy, and, therefore, I can only add a very short list of substances which, combining with oxydes, render them soluble in water : —
Bromine.
Chlorine.
Fluorine.
Sulphuric acid.
Nitric acid.
Aceric add.
Tartaric add, — indeed nearly all the other 200 adda
Ammonia.
Potash.
Soda.
Bitartrate of potash.
Muriate of ammonia. Hypo-sulphite of soda. Sulpho-cyaxmret of potasdum. Cyanuiet of potasdum.
FOBMiLTION OV BT MjLGKETISM.
Metallic salts are generally formed in three ways. The first, where the metal itself is added to the acid and water ; when the latter is decomposed hj the metal, the hydrogen being evolved, and the corresponding equivalent of oxygen combining with the metal produces an oxyde which again unites with the acid to form the metallic salt. The second mode of forming metallic salts, when the metal cannot decompose water, is, to add the oxyde already prepared to the acid, and, if necessary, digest it at a moderate temperature. The last mode of making metallic salts is, to take a solution of the acid which we desire to be the radicle of our salt, and place a very large positive pole of the metal desired to form the base at the lower part of the fluid, and connect it with the terminal silver (s) of a series of batteries (two, three, or four, according to circumstances). For the negative pole we use a small piece of metal, and connect it with the terminal zinc of the battery (z).
In this way we very readily and conveniently make our saline solution ; for the metal being dissolved is retained principally at the lower part of the vessel, whilst the hydrogen is evolved from the negative pole.
After a short time, some black powder appears at the negative pole, but as the saturation of the acid progresses, sponge seeds the black deposit, and sand succeeds sponge ; when, if the solution is for electrometallurgy, the process may be stopped, for we may be perfectly sure, considering the large size of our positive pole as opposed to the negative, that the solutionis" sufficiently strong.
Sometimes we vary the arrangement by using a in the decomposition trough, placing the acid and fiitive pole on the one side, and on the other, with our negame pole,
Compounds Op Oxtdes With Alkalies.
some acid to render the fluid a conductor. The cut tumbler (figured No. 11.) answers well for these purposes. Occasionally, instead of an acid, we substitute an element dissolved in the water, as iodine, chlorine, bromine, and, occasionally, we employ a neutral salt, the acid of which unites with the metal, whilst the alkali is transferred over to the negative side. Wherever we can use an element or an acid dissolved in water, it is to be preferred to a neutral salt, as in my battery I have found a difficulty in causing the alkali to travel.
The manufacture of salts by the voltaic fluid is generally more expensive than the processes usually adopted, and is, therefore, to be avoided for large commercial operations, especially where the metal is but of little value ; yet when we desire a very pure salt, a salt of a very valuable metal, or a salt difficult to form by the ordinary processes, then does the galvanic battery come into play, and, under these circumstances, economy, facility, excellence, and despatch, are insured by the use of this wonderful engine, and in very many cases has been found to be a really useful process.
The solution of oxydes in alkalies is to be performed in the same way as the corresponding solution in acids ; thus it may be efiected by simply digesting the metal in the alkali — a process, however, which should always be discarded in practice from its slow and tedious character. These solutions may be formed by adding the oxydes recently precipitated to the alkalies ; or, lastly, they may be very conveniently produced by making the metal the positive pole in the alkali, connecting it with a galvanic battery. The second process is generally to be preferred, but the latter will frequently be found convenient.
The compounds of the oxydes of metal with salts are generally made by digesting them in a solution of the salt, or by making the metal the positive pole in their solution. The compounds of oxydes of metals with bitartrate of potash
Metallo-Ctanides.
and muriate of ammonia, are familiar examples of this class of compounds.
Allied to this last division of metallic compounds is a peculiar class, in which the metal, in combination with the bicarburet of nitrogen, or cyanogen, forms an acid which, when uniting with an alkali, produces a true salt. The union of iron, cyanogen, and potassium has been the longest known under the name of ferrocyanuret of potassium. Some philosophers, indeed, consider this salt as a double cyanuret of iron and potassium, but probably the iron and cyanogen form a distinct proximate element, analogous in the general properties with cyanogen, which again is perfectly analogous to the primitive elements, chlorine, iodine, or bromine.
Almost any othei metal may be substituted for iron, and an analogous compound will be formed. Thus, with silver an argento-cyanide, with gold an auro-cyanide, with nickel a nickel-cyanide, may be made. The electro-chemical decomposition of all these substances is peculiar, for under different circumstances different results may be obtained. If placed on the positive side of a diaphragm apparatus, potash will be carried over to the negative pole, where hydrogen is also evolved ; whilst at the positive, oxygen is absorbed, and a peculiar compound is left which presently decomposes into a cyanuret of the metal contained in the liquid. To take, as an example, the decomposition of the zin co-cyan uret of potassium, a solution placed at the positive side of a diaphragm apparatus has the potash carried over to the negative pole, while a compound, perhaps zinco-cyanogen, is left at the positive electrode, which speedily resolves itself into the cyanuret of zinc. The electro-chemical decomposition of ferrocyanate of potash is the same as that of the above metals.
The formation of the ferro-sesquicyanuret of potassium has been alluded to in treating of electro-chemical decompomtions ; but Sir John Herschel having lately brought it into
Metalixhsesquicyanides.
use by one of the most elegant and refined chemical processes in the whole range of photography, a more detailed account is here added. The solution of the yellow salt, which may be either completely or nearly saturated, is placed in a large porous tube, and into this is inserted as large a positive platinum pole as possible. I generally use all the odds-and-ends of platinum I can collect, and jrg 30
string them together with a platinum wire, the object being to bring the pole in contact with as much fluid as possible. The porous tube is placed in a jar containing plain water and a large copper negative elect when on the platinum being connected with the silver of a compound-battery of not less than four cells, and the copper with the zinc, half an equivalent of potash is carried over to the outer vessel, and hydrogen is evolved, whilst oxygen is absorbed nt the platinum side, and ferrocyanogeu is apparently liberated, which, combining with the yellow salt, forms ferro-sesquicyanuret of potassium. Whether oilier analogous metallo-sesquicyanurets may be formed in the same way I have not been able satisfactorily to determine ; the great difijculty being the uncertainty attached to the formation of a hitherto undiscovered salt, for we might moke it and still be ignorant of the fact.
When the metal lo-cyanide is placed on the negative side of a diaphragm ap[)aratus the metal itself is reduced ; thus, in one case we actually make the metal pass to the positive platinum electrode, in the other to the negative platinum electrode.
When the yellow ferrocyanate of potash is galvanised in a porous cell, one part becomes the red prussiate, the other remains as the yellow prussiate. If a piece of platinum be inserted into each side, the yellow salt becomes positive to the red salt, an arrangement which 1 believe to be analogous to
The Formation Of Mstallootanioe8.
the arrangement of the cells of the electric eel, with the substitution of arterial blood for the pmssiates of potash.
When the metallo-cyanide is simply galvanised between platinum electrodes, the metal is reduced, and, as the result varies with different metals, we shall enter into these circumstances when treating of each respectively, confining our attention, however, to such facts as more especially relate to the electro-metallurgist.
When the raetallo- cyanide is galvanised, the positive pole being the same as the metal in the cyanide, the metal, in most cases, is reduced from the salt, and its place supplied from the solution of the [>positive pole ; in some cases, however, the metal is not reduced, but a salt is formed with the metallo-cyanide and the metal dissolved, the potash being transferred to the positive pole.
Such is a rough sketch of the general properties of the metallo-cynnides. We have next to consider the mode of preparing this important set of salts, and numerous are the methods by which they may be obtained. They are formed most easily and usually by boiling the oxyde of the metal with the cyanide of potassium j but they inay also be procured by adding a solution of the cyanide of potassium to a solution of a salt of the desired netal, but in this case a foreign salt always contaminates the solution. One of the best processes for making metallo-cyanides is to arrange the metal as the positive pole in the solution of cyanuret of potassium. They may even be made by simply placing the metal itself in the solution of the cyanuret of potassium, when it will slowly dissolve in this truly remarkable salt ; even gold and palladium are readily taken up in this manner especially at tlt part of the solution in contact with the
Ctanide Of Potassium.
air, which contact seems to favour the action — perhaps by causing a galvanic current, and thereby materially assisting the solution of the metal. Some metallo-cyanides may be even formed by boiling the oxyde of the metal with ferrocyanate of potash, but it is not a very good process. Metallocyanides may also be formed by heating together potash, dry animal matter and the metal ; when the animal matter affords carbon and nitrogen to form the cyanogen, which then lays hold of the potash and metal to form the metallocyanide. This process, with slight modifications, is generally adopted in the arts to form ferrocyanate of potash, which is used upon a most extensive scale. Whether the same process may be adopted for other metals, I am unable to state from direct experience; but, in all probability, many other metallo-cyanides of potassium, or sodium, might be made in the same manner.
When metallo-cyanides are subjected to the voltaic force, curiously enough they appear, in many instances, to form a positive pole and take oxygen ; thus, if we use a solution of auro-cyanide of potassium with a gold pole, more gold is reduced at the negative pole than that which is dissolved at the positive. At different times I suppose that I must have received nearly a dozen letters from experimenters, who, noting this fact, and being ignorant of its cause, thought that they had actually found out a process for making gold.
The cyanide of potassium so often alluded to while treating of the metallo-cyanides may be formed in several ways. It may be obtained by heating to a dull redness, the yellow ferrocyanate of potash in a covered iron vessel, filtering and rapidly evaporating it. The objection to this method, however, is, that without great care, the whole of the ferrocyanate is not decomposed, a circumstance which much reduces its value for electro-metallurgy. By boiling, however, the ignited residue with spirits of wine, this difficulty is said to be overcome, as the ferrocyanate is absolutely
insoluble in that menstruum, while the cyanuret at that heat freely dissolves, and is as easily redeposited on cooling.
There is, however, a much better process by which this salt may be formed, namely, by simply transmitting hydrocyanic acid through potassium. Although the modes of making this acid are very numerous, there is but one which is likely to be employed on a very large scale, and that is its formation from the yellow ferrocyanate by means of sulphuric acid. This process is performed as follows : any given weight of the yellow salt is taken and dissolved in about live times its weight of water : this is placed in a retort, or some such analogous vessel, to which is then added a quantity of strong sulphuric acid, twice the weight of the salt, and diluted with three or four times its quantity of water. A pipe is carried from the neck of the retort to the receivingbottle, which should be kept as cool ns possible. For small operations those invaluable vessels, Florence flasks, answer well : a bent tube being connected at one end to its mouth, the other passing into the second vessel ; heat should be cautiously applied by means of an Argand lamp, a little vessel of sand being placed under the flask, which helps the acid to decompose the salt. Prussic acid is then generated and passes through the tube to the recipient vessel, which is to be charged with liquor potossae. When the potash is saturated the operation is completed. The Germans recommend a strong alcoholic solution of potassa to be used in the second vessel, for in this case, the hydrocyanic or prussic acid combines with the potassa, forming a hydrocyanate of potassa, or, the water being abstracted, the cyanuret of potassium, which spontaneously precipitates on the saturation of the fluid, the cyanuret being insoluble in strong alcohoL The fernxanate of potash may be considered as containing 3 equivalents of hydrocyanic acid, 2 of potash and I of iron j but, unfortunately, we can only obtain half the acid from the salt, owing to the formation of a compound during its decom-
PRBPABATION OF PEU88IO ACnx
position which resists the action of the acid. The decomposition of this salt taking 2 equivalents or 426 grains to avoid fractions, would afford 3 equivalents or 81 grains of hydrocyanic, or prussic acid, capable of forming 198 grains of cyanuret of potassium, whilst in the retort there would remain 384 grains or 3 equivalents of bi-sulphate of potash, and 1 equivalent or 174 grains of a peculiar compound, said to contain 3 equivalents of cyanogen, 1 of potassium, and 1 of iron. (Pereira.) It is manifest that, but for this latter compound, we might double the quantity of hydrocyanic acid from the yellow salt. The decomposition just described is the one usually received ; but too much reliance must not be placed on its accuracy, for the analysis of the several compounds is too difficult for the results to be fully admitted. The residue left in the retort speedily turns to one of the blues, identical with, or allied to, Prussian blue. This is at best a disagreeable process to conduct, for the hydrocyanic acid formed adheres so strongly to the glass that, instead of being freely given off, bubbles are evolved suddenly with such explosive violence as occasionally to crack the vessel. This may be remedied as far as is possible by the insertion of plenty of waste pieces of platinum— if platinized so much the better, as that facilitates the escape of the gas. The heat should be applied to every part of the vessel, and the flame should not be allowed to play upon one single part alone. Large commercial operations are performed in green glass or stone-ware retorts.
Now for one word of advice to the tyro. Remember that you are working with prussic acid, therefore, never the process in a room, the fumes being quite as poisonous as the solution of the acid itself; moreover, have always a bottle of ammonia, or chlorine, by your side, that should you have chanced to inhale more than is pleasant, it will be instantly at hand to counteract any bad effects. It is stated by Pereira, that a little sulphuric acid or hydroferrocyanic
PREPARiLTlON OF.PRUSfilC ACID.
in
acid passes to the outer vessel, but probably the amount would be of no consequence for electro-metallurgy, otlierwise, it might be as well to use a Woulfe's apparatus, and discard the salt formed in the first vessel. To the largo manufacturer it may be worth considering whether some other metallo-cyanuret, formed in a similar manner to the ferrocyanuret, might not be more advantageously employed, because the residue of the process last-described contains a large quantity of cyanogen which the acid is unable to set free.
There are other modes of procuring prussic acid, besides the one which has been so tediously described ; but these are found to be more expensive. The only one which I shall now notice is the process by which it is obtained from bicyanide of mercury. The bicyanide of mercury itself is formed when peroxyde of mercury is digested with Prussian blue, the peroxyde of mercury abstracting the whole of the cyanogen from the blue, and leaving the oxydes of iron at the bottom of the vessel. The solution may be evaporated to dryness, and one part of the salt dissolved in six of water ; one part of muriatic acid, sp. gr. PI 5, is then added, and the solution distilled, when the whole of the hydrocyanic acid passes over, and by being conducted into a solution of potassa, as in the former process, forms cyanuret of potassium. This process, though easier than the first described, is rather given as a resource under peculiar circumstances than as one to be adopted by the large manufacturer. The expense is the only objection, but in a small quantity this cannot be a eonsideratioD.
In giving this very rough outline of the general mode of forming salts, the minutias necessary for chemical work have altogether been avoided ; and those parts alone are entered upon, which are more immediately necessary for the electrometallurgist to know and practise for himself. This will account for the long description of the cyanuret of potassium,
REDUCTION OF IfETALLIC COMPOUNDS.
whilst the preparation of the equally important and even more used acids, the sulphuric, muriatic, drc., commonly found in commerce, are altogether neglected.
In using solutions of cyanide of potassium, the workman should not immerse his arms into them, otherwise it occasionally happens that the solution produces very troublesome eruptions over the skin.
(169.) Having now described the kind of compounds necessary to be employed for the reduction of the metals, and their general preparation, and having already treated of the laws regulating the reduction of the metals in various states, the substances on which they may be reduced, the various apparatus in which the processes may be conducted, and, moreover, described the various forms of galvanic batteries, their properties and manipulations, we are, at length, in a condition to consider the precise manner in which each respective metal may be reduced from its soluble compounds.
Platinum is the first metal of which we have to consider the reduction. There are not many compounds of this metal : the principal being the chloride, the sulphate, and the compounds of chloride of platinum with alkalies. The chloride of platinum is formed by digesting platinum in nitro-muriatic acid, consisting of one part of strong nitric to two of muriatic acid. If evaporated to dryness, at a moderate heat, it forms the chloride of platinum. This salt is a most ready conductor of the galvanic fluid, and, therefore, might be employed great advantage, were it cheap enough, for a Daniell's battery, instead of sulphate of copper. When we desire to obtain the black powder of platinum, this is the salt to be selected ; if acid, it requires great skill to obtain any other deposit from it. To obtain the black deposit, the xinc single-ceU apparatus is generally to be preferred. The same deposit may also be obtained by the compound battery decomposition apparatus, by using five or six cells of the battery, charged with the usual strength of add, and by
EEDUCTION OP PLATIiqUM,
using a large positive platinum pole in the trough. Unfortunately, the oxygen has always to be evolved on the positive pole, as the platinum does not dissolve, except to a very trifling amount, and fresh chloride of platinum must continually bo added to maintain the strength of the metallic solution. This applies to all salts of platinum, as in no case is the positive pole acted upon sufficiently to supply the place of the metal reduced from the fluid. To obtain the reguline deposit of platinum from this solution, we must of course overcome resistances at all points of the circuit ; wo must begin by employing a very small battery, feebly charged, and use a fine positive wire in the trough, combined with a very strong solution of the chloride of platinum. A compound odds-and-ends' battery is well adapted to obtain the reguline deposit ; the little glasses, of which the battery figured below is composed, need not contain more than an ounce of fluid, and four arranged as a scries will be amply sufficient.
At the bottom of each glass a little mercury is placed, containing a piece of zinc ; a piece of silver wire, either amalgamated or coated with some non-conducting substance, except at the end, is immersed in the mercury, and passes to a small piece of platinized silver in the next vessel ; the
first piece of silver and the last zinc of the series being attached to a binding-fcre, or mercury cup, for the convenience of making metallic connections. In the battery figured, the ends are left free. The batteries are charged tiith dilute sulphuric acid, and a fine platinum wire is connected with the extreme silyer of the battery, and the object to receive
JHLORIDE of FLATINUaf.
the reduced platinum with the terminal zinc. This solution of platinum will bear but a very feeble current when we desire the reguline deposit. Oxygen and chlorine are evolved abundantly from the positive platinum wire, which must not be immersed more than half an inch in the solution, and frequently the insertion of one-eighth or even one-sixteenth of an inch will amply suffice. If the solution of the chloride of platinum be strong, the fumes of the chlorine will, at length, fill the whole room in which the operation is conducted.
Chloride of platinum forms double salts with several alkalies. The amraonio-muriate and potassio-chloride are very insoluble, but the sodio-chloride of platinum, or, perhaps, more correctly, the platino-chloride of soda, is very soluble in water. This forms an excellent compound, and perhaps the best for the reduction of the metal in the reguline state, the mode of proceeding being precisely similar to that of the last-described salt. In fact this is, perhaps, the best salt for these purposes ; and as scarcely any metal reduces the platinum spontaneously from the solution, they may be indifferently employed os a negative pole in it.
With the electro-chemical decomposition of the sulphate of platinum, I am practically unacquainted ; but it is said to form a soluble salt.
If hydriodate of potash be added to a solution of chloride of platinum, a precipitation ensues, winch is soluble in excess of the precipitate. It forms a very dark-coloured solution from the presence of iodine ; to counteract which, a little free potash is required. It is an unfavourable salt for electro-metallurgy, especially for the reduction of reguline metal.
A platino-cyanide of potassium has been described by some authors, but it appears a difficult salt to manufacture. It can neither be made by galvanism, nor by allowing the metal to stand in the cyanide. If chloride of platiniua be
Cost Of The Reduction Of Platinum.
added to cyanide of potassium, some change takes place, bnt I have not succeeded in making any advantageous use of it for electro-metallurgy.
A hyposulphite of platinum may be formed by adding the hyposulphite of soda, or potash, to the chloride of platinum ; but this, likewise, forms a very indifferent solution for electro-metallurgy.
The equivalent of platinum being ninety-nine, we obtain three times more in weight for our equivalent of power, than we should of copper, or three times more than the zinc dissolved in each cell of the battery; but inasmuch as we know no method of dissolving regulino platinum at the positive pole, at least, to any useful amount, we cannot employ a single battery, but require a scries of three or four to effect that object. If we our etpiation to ascertain the cost of I'educing platinum, we find that, as platinum in solution is wortli about 201, per lb., the value of the power to be added to this would barely exceed , ; but if the single cell could be adopted advaritugeously, the galvanic power sufficient to effect that object would not exceed Ad, This aspect of affairs is so exceedingly promising that, doubtless, some manufacturer of platinum will enter into the galvanic process on a large scale to ascertain whether electro-metallurgy might not triumph over the Woolastonian method of working in this metaL The one mode, we have seen, requires a battery of almost nominal value, the other apparatus is of the most complicated and expensive nature; so that by ascertaining the labour required for each respective process, the relative time occupied by them, and the quality of the metal reduced being once learnt on the large scale, the question w ould be satisfactorily determined.
(170.) Grold is rendered solvent by combination with several substances, and its chloride, bromide, iodide, cyanide, and other compounds, all merit separate attention.
Rbdikjtion Of Gold,
31ie chloride of gold may be formed in various ways ; by ptsriag a stream of chlorine through water containing gold that fine state of division termed by assayrs brown gold. For obtaining a solution of this salt, however, such a method is but seldom adopted, as the metal is more commonly subjected to the solvent powers of aqua regia — a composition of one part nitric to two muriatic acids. The gold is placed in three or four times its weight of this acid, and a moderate heat is applied to favour the action. In this case the nitric acid being a highly oxygenated compound, and the muriatic containing hydrogen, mutually re-act on each other. Nitrous gas is evolved, water is formed, and chlorine set free, which then combines with the gold to form the chloride. By this mode of proceeding the compound is always acid, which is best removed by very carefully evaporating it, when, on cooling, crystals will be deposited. If the operator conducts his process at too great a heat, he will find that a part, or the whole, of the gold will be deposited in the metallic state, and he will be compelled to re-dissolve it. Having avoided this difficulty, and obtained a choride of the metal, he will find it to be a very soluble salt and an excellent conductor. This salt may be reduced by the single-cell process, which, however, for gold should always be discarded, or by the battery apparatus. In either case the hydrogen appears to have a great tendency to be evolved, and, therefore, the deposit of black powder is easily accomplished. For its reduction in the bright reguline state we must increase resistances. By using a very fine platinum pole, which affords the greatest resistance to the voltaic current, I have worked a solution of this salt quite colourless, and still obtained a ruling deposit. Some better salts are now known, however, for obtaining this object more readily. If the battery apparatus be employed, then we may use a series of three or more batteries, with a fine platinum wire. If we use a gold positive pole in this solution, a little is dissolved; but it affds
Bbohide Of Gold.
nearly as violent a resistance to the passage of the voltaic current as platinum, the oxygen seeming rather to prefer to be evolved than to combine with the metal. This solution of gold is decomposed by nearly all metals, and is, therefore, objectionable on that account ; carbon and platinum alone having no effect on it.
The bromide of gold is readily prepared by adding a little bromide to the brown gold of the assayers, and allowing it to remain some time under water, or assisting its action by a gentle heat. It forms a salt of a lovely bright crimson colour, but in its general properties is precisely similar to the chloride, except, that a gold positive pole is rather more quickly acted upon in it.
Chloride of gold is soluble in and in this state has long been used for gilding penknives, and other steel articles, by simple immersion. It may be used, but possesses no peculiar advantages for electro-metallurgy. Copper and silver rapidly reduce the metal from this solution. I have endeavoured to dissolve the chloride in naphtha, oil of turpentine, essential oils, and other fluids, thinking that by these menstrua its conducting power might be lessened, but, unfortunately, the gold is slowly reduced simply from contact with these substances.
The hyposulphite of gold may be formed by adding the hyposulphite of soda or potassa to the chloride of gold. The solution, though not decomposed by copper or silver, does not answer well, as the reduced gold is apt to peel off from the object, and it seems os if some other substance was reduced coiointly with it. Gold will dissolve when made the positive pole in this solution.
Chloride of gold forms double salts with certain alkalies, especially soda and potash. They are made by simply adding the alkali to the metallic salt. These compounds might be used for electro-metallurgy, as they are not very readily decomposed by silver or coppet, which may, therefore, be
AUBO-CrANn>£ OF FOTASSnJH.
used as negative poles. These compounds, however, are very inferior to the auro*cyanuret of potassium, and the gold reduced from them has frequently the appearance of the brown gold of the assayers. Sometimes magnesia or lime may be added to a solution of the chloride of gold with advantage.
If a solution of iodide of potassium be added to a solution of gold, a precipitate of iodide of gold takes place, soluble in excess of the precipitate. It requires the addition of free potash to combine with any iodide that may chance to be set free by the acid in the chloride of gold. A gold positive pole is slightly dissolved in this solution, but it has the disadvantage of yielding up its metal to silver by elective affinity, or else it might, perhaps, be employed, though it is by no means the best solution for this purpose.
The striphocyanide of gold is insoluble in water, but dissolves pretty freely in sulphocyanide of potassium. It has the advantage of not being decomposed by silver or copper. A plate of gold dissolves with moderate rapidity when arranged as a positive pole in the liquid. It may be decomposed in all the various ways that have been so frequently alluded to.
We have now to treat of the most important salt of gedd for electro-metallurgy, the nuro-cyanide of potassium. It was first employed by Elkington, whose discoveries we have fully considered in our history of electro-metallurgy. It is a salt somewhat analogous to the ferrocyanate of potash, and is easily prepared in a variety of ways. It may be made by simply placing a piece of pure gold in a solution of cyanuret of potassium, but this process requires some little time. It may be formed by arranging a piece of pure gold as the posi-
Tha sulphocyanide of potossiam is a troublesome salt to pnpaie ; but Hr. Low, the patentee of the celebrated Prince's or Naphtha Gas, informs me that large quantities arc thrown away in the rose of the gas
works.
AURO-CTiLNIDE OF POTASSIUM,
live pole in a solution of cyanuret of potassium, using, at the same time, a small negative pole. It may be also formed, and this is the process that many prefer in the large way, by boiling the oxyde of gold for half an hour in a solution of cyanuret of potassium ; the fluid may then be poured otF, and is ready for use, whilst the remaining oxyde of gold is to be carefully preserved. Of these three processes, to the second I should unhesitatingly give the prefertiiice ; for, by using a strong battery, a large quantity may be made in a few minutes, and it only requires the metal itself, and not the oxyde, in the production of which alone more trouble and time is incurred than is consumed in the entire manufacture of the salt by galvanism. The galvanic process of making salts has been already so fully described that no further detail is here required, only remembering to have a strong battery, a large positive, * a small negative pole. There are still other modes by which this salt may be made; it is, for instance, produced by simjdy adding the soluble salts of gold as the chloride to the solution of tin*, cyanuret of potassium, or by digesting insoluble compounds of gold, as the sulphuret, in the same solution. It may also be formed by digesting the oxyde of gold in a solution of ferrocyanate of potash, and in this case the presence of a little of the latter salt is not very material, but on the w hole we had better, perhaps, employ the pure metallic salt.
The auro-cyanide of potassium having been formed is at once ready for the electro-metallurgist, and it is quite a matter of indifference whether it contains a little free potash, or a little cyanuret of potassium. The solution may be of any strength ; the stronger, liowever, is to be preferred, as this salt is by far the best adapted for reguline metal. The metal may be reduced from it by the single-cell process, for which a large zinc plate would be required. However, no one should ever think of employing this process, as by its means we should reduce our gold from the solution, and our
AUB0-CTA2m>£ OF POTASSIUM.
C7aziiir6t of potassium, would be wasted. Of the battery processes, the compound battery, with a platinum positiTC pole, may be employed, but, unless under very peculiar circumstances, it is better discarded. The battery-process with a gold positive pole is, therefore, our resource for this salt As a general rule the gold positive pole should be about the size of the negative pole, or that in which the reduced gold is being deposited. A single battery will in general suffice, the gold being attached to the platinized silver, and the object to receive the deposit to the zinc. A very small battery will be required, a platinized silver wire for small objects being almost sufficient. I have even used a battery formed with a glass tube drawn to a point, with a hne platinum wire melted into the glass, so that a little piece is left inside, and the rest on the outer part of the tube ; some mercury with fragments of zinc are placdft in the vessel sufficiently high to cover the wire : the tube is filled with dilute sulphuric acid: and, last of all, the apparatu*' h completed by the insertion of a second platinized silver wire.
The process, when a gold positive pole is employed, is materially influenced by the quantity of free cyanuret of potassium in the solution, as a deficiency of that salt causes the action to take place very slowly, whilst an abundance so much increases the action, by dissolving the positive gold pole with great rapidity, that the deposition is very speedily eflfected. Any other form of battery may be employed instead of the small one mentioned, taking care to adjust it according to the three laws already detailed. One of the little batteries figured above for the reduction of platinum may be very conveniently used.
It is a high penal offence to tamper with the coinage, and only a few years ago the offence was punished with death. Under these circumstances, the electro-metallurgist should not be invited to try experiments with his coins,
EEDUCTION OF PALLADltJlL
wliich, always being at hand, are very tempting to the manipulator.
The reduction of gold by galvanism is accomplished at a low rate, for as the equivalent of gold is very high and its value great, we find the galvanic process a most advantageous mode of proceeding. We obtain for one equivalent of power, costing of a penny, 200 grains of pure gold, worth about 2L ; and, therefore, 11b. avoirdupois of gold would be reduced for less than 2cf., and the gold so reduced would be worth nearly 70/. The power from the magneto-electric machine is also well adapted for the deposition of gold.
(171.) Palladium is a noble metal, but has the singular defect of being brittle when hot. It would be extremely valuable were there to be found any great consumption for it, but the supply happens to exceed the demand ; and, therefore, it is fnoderately cheap, considering that its usual mode of manufacture is similar to that in use for platinum. There are various salts from which it may be reduced : its nitrate, its animonio-chloride, and its palladio-cyanide, arc the principal 1 shall notice.
The nitrate of palladium is formed by digesting the metal in nitric acid, and the process is facilitated by the addition of a few drops of muriatic acid. It is a ready conductor, and in its general electro-metallurgical characters is precisely similar to the chloride of gold or platinum. It is better adapted for the reduction of the black powder than the reguline metal. The palladium is reduced from this solution by man} metals, and perhaps only carbon, gold, platinum, and palladium can be used as a negative pole.
The ammonio' muriate of palladium is very soluble in ammonia, and is the best salt for obtaining the reduction of
' I have aMumed the oaual chemical equivalent of gold, 200, to be its voltaic equivalent, but have no authority for that asramptUm, as Faraday, the only authority this subject, has uot determined it.
1&6 BEDUOTION Olf IRIDIUM AND RHODIUM.
palladium in the reguline state. The compound battery apparatus is to be preferred for this purpose, two or three cells being required. In the decomposition trough, the positive pole should consist of a very fine platinum wire, which should be immersed only to a moderate extent in the fluid. This salt is not readily decomposed by other metals, and on that account nearly all may be used as a negative pole to receive the palladium. During the decomposition the positive pole has a bright yellow powder deposited upon it, giving it the appearance of being converted into gold.
The iodide of palladium is formed by adding iodine of potassium to a solution of palladium. It may be dissolved in excess of the precipitant. It is by no means a valuable salt for electro-metallurgy.
The palladio-cyanide of potassium may be formed by simply immersing palladium in a solution of cyanide of |>otassium, when it will be gradually dissolved ; or it may be made by galvanism, or even by boiling the oxyde in the cyanuret of potassium. It may be employed with a palladium positive pole, or with a platinum positive pole, but the former is to be preferred.
The reduction of palladium is accomplished at a low cost, as far as thu materials are concerned, for palladium being a valuable metal and a high equivalent, requires but a small amount as the cost of galvanic power to be added to the value of its solution.
(172.) Iridium has but few soluble salts ; of these however the chloride may be mentioned. The black deposit of iridium is easily reduced from its solution, and is very frequently found on the platinized silver of commerce, which is, perhaps, the only fact concerning the metal worth recording, 1 have reduced this metal in the bright reguline state, but only on a small scale.
(173.) Rhodium forms soluble salts, of which the only one I have subjected to the voltaic fluid is the sodio-muriate.
Reduction Of Osmium And Silver. 1S7
It was decomposed with a compound battery of ten cells with platinum electrodes, the positive consisting of a very slender wire, — at the negative a depositor rhodium took place. It was of a whitish colour, and might be strip}>ed off from the platinum in small pieces, but was very brittle. A black powder was deposited by a more powerful voltaic current
(174.) Osmium has a soluble oxyde, but subjected to the voltaic fluid between platinum poles it did not yield reguline metal, but a black deposit, which appeared to be the metal in a lower state of oxydation than the volatile soluble oxyde, and not the black powdery metallic deposit.
(175.) Silver, on account of its universal importance, demands our most serious attention. The nitrate, sulphate, acetate, hypo-sulphite, ammoniurct, and several others, must be separately considered, though the argcnto-cyanide of potassium is most decidedly entitled to the preference.
As a solution, from which the silver is to be reduced, the nitrate is for all purposes the most unfavourable. When this salt is used, the hydrogen has a great tendency to bo evolved from it, and therefore a relatively feeble current must be employed. The decomposition cell may contain a positive pole of platinum, or even of silver, as the latter will, by being dissolved, always maintain the same state of saturation of the fluid. When we use a positive pole pf silver, there is a risk of materially increasing the quantity of electricity, and therefore only a silver wire should be employed ; and then the distance at which the operator places them in the fluid, will accurately regulate the amount of current. The negative pole to be placed in tliis solution, for the purpose of receiving the precipitated metal, may consist of either gold, platinum, charcoal, or silver ; but the other metals are not at all fit for the purpose, owing to the energy with which they decompose the solution. The strength of the solution of this salt may be from 10 to 420
Salts Of Silver.
grains to the ounce of water, taking care that the electricity is regulated in its quantity, according to the strength of the solution, in the manner already directed.
The sulphate of silver is easily formed by adding sulphuric acid to a saturated solution of nitrate of silver, as, by its being far less soluble than the nitrate, it is very quickly deposited. The supematent liquor is to be poured off and well washed with a little distilled water, when it is ready for the operator. It is not so easily decomposed as the nitrate, nor so ready a conductor, but it is a very inferior salt for electrometallurgy, as the silver, under the most favourable circumstances, is very brittle.
The acetate of silver is formed in an analogous manner to the sulphate, and in its conducting power and facility of decomposition much resembles it. In both these cases, a silver positive pole may be employed in the decomposition apparatus, and a single battery of small power for the source of electricity.
The hypo-sulphite of silver may be readily made, by adding any hypo-sulphite, such as that of potash, to the nitrate, chloride, or any other salt of this metal. There appears to be a strong attraction between silver and this acid, as the hypo -sulphite decomposes the most insoluble salts of silver. The hypo-sulphites of the alkalies may be prepared by adding sulphurous acid to their sulphurets ; as, for instance, to the sulphuret of potassium or sodium. This salt of silver is pretty soluble, and will bear a larger quantity of electricity for its decomposition than the nitrate, sulphate, or acetate, but generally the hypo-sulphites are not well adapted for electro-metallurgy, and in this case the metal is apt to be brittle. A silver positive pole dissolves in this salt
The ammonio-nitrate and ammonio-chloride of silver are very soluble salts. Great care is required in the nse of these salts ; for if the solution, by being kept for some time, be
Salts Of Silver.
allowed to evaporate, so as to leave dried portions adhering to the sides of the vessel, it can no longer be even touched with safety ; for a fulminating salt is thus formed, which, if merely touched with the finger, in order to remove it from the sides of the vessel, will explode with mischievous and awful violence. I take particular notice of this fact, as I nearly lost my right eye in learning it. Tliese salts are good conductors, and their solutions may be used of any strength. They should invariably be alkaline, from excess of ammonia. A negative pole, suitable for the reception of the silver, may be made of platinum, gold, palladium, carbon, or silver itself; all of which are unaffected by the solution, and thus whenever we desire a duplicate of silver, the original should always consist of those metals.
A very fair solution for the reduction of silver is the ammonio-carbonate. It is formed by adding carbonate of ammonia in large excess to nitrate of silver. Carbonic acid is disengaged with effervescence, and a white powder is deposited, which, on further excess of the ammoniacal salt, becomes soluble. It may be used with a silver positive pole, a mere wire sufficing, and a single battery.
The iodide of silver produced by adding iodide of potassium to the solution of nitrate of silver, and dissolved with excess of the precipitant, may be employed for electro-metallurgy. It is not decomposed by copper, and may be used with a silver positive pole and single battery.
The sulpho-cyanide of silver formed by adding sulpho-cyanide of potassium to the nitrate of silver, and then dissolving the precipitate with excess of the sulpho-cyanide, may be employed like the iodide. A positive pole of silver dissolves in this solution.
A potassio-tartrate of silver is formed by boiling oxyde of silver in bitartrate of potash. It is easily decomposed by light, and possesses no advantage for electro-metallurgy.
Of Potassium.
The spongy mass can be obtained fVom any of these salts, with the utmost readiness, by increasing the quantity of electricity.
In the electro-chemical decomposition of nearly aU the above salts of silver, where the positive pole consists of the same metal, a black crust is very frequently observed on the silver, which very probably is a peroxyde of silver analogous to the peroxyde of lead, &c.
We have, at last, to treat of by far the best solution of silver for electro-metallurgy, which is the argento-cyanide of potassium. This may be formed by digesting the oxyde of silver with ferrocyanuret of potassium, but this constitutes a very imperfect process. It may even be prepared by adding any soluble salt of silver to a solution of the cyanuret, or even by digesting the insoluble salts in the same solution, but in these cases, a new salt is formed between the radicle of the salt of silver, and a part of the potassium besides the part required for the formation of the argento-cyanuret of potassium ; thus chloride of silver and cyanuret of potassium form chloride of and argento-cyanide of potassium. It is far better to prepare it by boiling a portion of the oxyde of silver for a few minutes in a solution of the cyanuret of potassium, and pouring off the supernatent liquor; the undissolved oxyde is to be washed and carefully prc8er\'ed for subsequent operations. The best mode, however of preparing this salt is, to make a large silver plate the positive pole in a solution of cyanuret of potassium, using, at the same time, a very small negative pole in connection with a strong battery, and continuing the process till reguline silver begins to be deposited at the small negative pole, when the operator may be perfectly well-assured that for all larger negative surfaces his solution is sufficiently strong : the little superfluity of cyanide of potassium, by favouring the conducting power of the solution, facilitates the reduction of the metal. The argento-cyanide of potassium, if suflered to crystallize,
▲BGENTO-CTANIDS OF POTASSIUaff.
Id!
forms clear, colourless crystals, and the solution should also be colourless* If it is at all yellow, it shows the presence of ferrocyanate of potash, which it sometimes contains in commerce*
However formed, this salt, first used and patented by Elkington, is by far the best adapted for electro-metallurgy. It may be employed of any strength, the nearly saturated solution being preferable, and it should always be placed in a glass or stone-ware vessel. It may be reduced by the single-cell process, taking care to use on the positive side of the diaphragm apparatus a very large plate of zinc, with a solution containing a little muriate of ammonia, or common salt ; but no electrician would ever think of employing this apparatus for the reduction of silver, for the cyanuret of potassium in combination with the silver would bo wasted. The compound battery apparatus with a platinum pole may be used, but should, as a general rule, be discarded, and the single battery apparatus invariably be employed. The positive pole may be the same size as the negative, and should consist of a piece of thick silver sheet, one-third of an inch or more in thickness. The battery need not be very large, for the conducting power of the metallic solution being low, only a moderate quantity of electricity passes. For small drawing-room operations, a tumbler battery with a glass precipitating-trough forms a most elegant instrument for amusement, and the largest manufacturer has only to increase the size of his trough, which should be glass or stoneware, and regulate the size of the battery to it. The plate of silver must be connected with the silver of the battery, and the object to receive the deposit with the zinc. The
192 Reduction Of Silver*
presence of even a large portion of ferrocyanate of potash in a solution of the argento-cyanide is of little consequence in strong solutions but in very dilute ones the positive pole becomes covered with a white deposit of ferrocyanate of silver, which materially retards the action. The presence of free cyanuret of potassium adds to the conducting power of this salt, and much facilitates the quickness of the deposition of the metal, and therefore as much should be contained in the solution as can be added without causing the metal to be thrown down in the various states of spongy deposit. The metal reduced from the salt, especially if reduced with the utmost speed that tlie strength of the solution will allow, is as perfect in its physical properties as the best rolled metal, combining elasticity softness and flexibility, and the decomposition may take place to any extent.
It was accidentally discovered that a few drops of bisulphate of carbon confers peculiar qualities upon the silver solution. The metal, instead of being thrown down with a matted appearance, is deposited as brilliantly as though it were burnished. The discovery of this fact is very important to the manufacturer, inasmuch as it saves a vast amount of labour in burnishing and polishing. The discovery is patented, and is now generally adopted at Birmingham.
The magneto-electric force is well adapted for silver. I have been informed by Mr. Elkington, that he is constructing a magneto-electric machine, which is supposed to have sufficient force to reduce fifty ounces of silver per hour.
The reduction of silver metal is very easily performed, and is economical The equivalent of the metal is 108 ; therefore, for one equivalent of power, costing of a penny, we obtain that quantity of silver ; or the reduction of lib. avoirdupois of silver, worth £4 4 m woum by the simple battery process cost less than 4d. For further particulars of the
BEDUCTION OF NlCKSL. 193
cost of the reduction of this metal, the student is referred to the equations and data given in a former chapter.
(176.) Nickel is the last in the list of noble metals, being the most ignoble of that class. The nitrate of nickel, the sulphate of nickel, the ammonio* nitrate and sulphate of nickel, the nikclo- cyanide of potassium, but especially the chloride of nickel, require consideration. The nitrate of nickel is very soluble, but the metal has no great inclination to be precipitated, for the hydrogen appears rather to prefer being evolved than to reduce the metal. If the compoundbattery process be used, the positive pole should consist of a fine platinum wire, and should only be immersed for a short distance in the solution. The sulphate of nickel is also a soluble salt, and the metal is reduced more readily from it than from the nitrate. It is best reduced by the compoundbattery process, with a platinum positive pole, though a nickel positive pole may be employed. When we employ either the nitrate or sulphate of nickel for electro-metallurgy, it is preferable to use the solution ns strong as possible. Of the compounds of these salts with the alkalies, those of ammonia the preference, and the ammonio-nitrate, and the ammonio-sulphate may be used for the reduction of this rather troublesome metal.
Nickel forms a compound with the cyanide of potassium by boiling the oxyde in a solution of that salt, which takes up a considerable quantity. The solid salt is of a yellow colour, though the solution generally is of an orange tint. Even in this solution, the hydrogen seems much rather to be evolved than to reduce the metal, and for this reason we must have a very feeble power in relation to the strength of the solution.
The acetate of nickel is easily formed, by adding pyroligneous acid to the oxyie of nickel. It forms a green salt, and may be decomposed either by the compound-battery with a platinum pole, or even by using a nickel positive pole ; but
K
SEDUOnOK OF COPPEB.
it is a bad solution for obtaining reguline metal, though the black powder can be obtained with ease.
The chloride of nickel is formed bj digesting the metal in muriatic acid. It forms a fine green-coloured salt, and a ▼ery excellent one for our purposes, as hydrogen in this case luis not nearly so great a tendency to be evolved. It may be used with a nickel positive pole with one or two batteries, or with a series of two, three, or four little odds-andends' batteries, and a platinum positive pole. The nickel so deposited has a peculiar white brilliant lustre, looking almost like glass, — this deposit is so very beautiful, though brittle when removed from the negative pole, that its examination would amply repay any person taking tlie trouble to precipitate it. It is such a contrast to the nickel of the shops, that no person would ever suppose that there was any similarity of composition between the substances, still less identity. For practical purposes this salt is perhaps to be preferred to all the others which have been mentioned, and, next to the chloride, the sulphate is the best for the reguline deposit.
Any of the above solutions will yield readily the pulverulent deposit by using a very strong galvanic current.
Nickel possesses but a low equivalent, only 28 grains being deposited for one equivalent of power worth penny. The voltaic reduction, therefore, of an avoirdupois pound, worth 7s, would amount to about
(177.) Copper requires more than ordinary examination, because the purposes for which its reduction by voltaic electricity has been applied are far more numerous than those of any other metal. Its reduction may take place from several of its salts, of which the sulphate, muriate, nitrate, and acetate, are the most worthy of attention. The sulphate is most commonly used, because it is the cheapest It deports thirty-two grains of pure metallic copper, for erej hundred and twenty-five grains of the sulphate, decomposed
RSDUOnOK OF COPPEB FBOM ITS SULPHATK. 195
bj the Toltaio carrent, and thirty- tiro grains of zinc are dissolved for every thirty-two grains of copper which arc reduced. In the use of all the salts of copper we must call to mind the function of water in voltaic arrangements to dissolve the newly-formed metallic salt ; and, therefore, we must take care never to employ solutions of the salts of copper at the utmost degree of saturation, but have n superfluity of that very important agent in our arrangements. Copper may bo very readily reduced from a dilute neutral solution of the sulphate, and, in fact, from a solution of any strength, according to the laws given for the reduction of metals. It is however, a salt of rather difficult decomposition, and offers considerable resistance to the passage of the electric current. Its conducting power, and, therefore, its facility of decomposition, may be increased by adding acid to the solution, which may be either dilute sulphuric, or dilute; nitric. A solution, made by dissolving one pound of the salt in four pounds of water, and by afterwards adding from one-third to one-half of its bulk of dilute sulphuric acid, is best adapted for many purposes. The dilute atud should consist of one part sulphuric acid to eight of water, well mixed together. This solution answers extremely well, when we have to cover non-conducting substances, to which a metallic or black lead covering has been given ; because the hydrogen, with a sufficient battery, has not such tendency to be evolved.
It is very desirable that the solution of copper should be as pure as possible, as that which is sold generally contains some salts of iron. Perhaps it would be well worth the attention of any electro-metallurgist to make his own sulphate of copper, by using distilled sulphuric acid, and a positive pole of the best copper which he can purchase. The positive pole should be very large, the negative very small ; the acid should be diluted to the strength which he desires
196 BEDUCnOK OF COPPER FROM ITS STTLPHATR.
his solution, and the whole should be connected jrith an active battery.
A variation may be made in this fluid, bj employing rather less dilute sulphuric acid, and at the same time adding a little nitric acid, by which the conducting power of the solution is materially increased. A solution formed by a saturated solution of sulphate of copper, diluted with onethird its bulk of dilute sulphuric acid as before, and to which two drachms of strong nitric acid are added, in the pint of fluid, forms a most unexceptionable solution for general purposes. The lateral growth of the copper in this solution takes place to a great extent, — a property which always enhances the value of the process. The nitric acid attacks the positive pole, so that the metallic solution is apt to become stronger. When this takes place, the solution must be diluted. The positive pole is more apt to be attacked after the action has continued some little time, for nitrous acid is formed, which assists the solution. In both these cases, ther reduction takes place with considerable rapidity. Tlie effect of the acids is to diminish the resistance offered to the passage of the electric current, which is virtually equivalent to increasing the intensity ; and we find that the quality of the copper obtained by either of these methods is the same, being soft, flexible, malleable, and ductile, but not very elastic. To obtain these qualities in the most eminent degree, the voltaic power should be so regulated to the strength of the solution, that a little more would cause the evolution of a few bubbles of hydrogen. We generally require the copper to be somewhat harder, and more elastic than this; to accomplish which we slightly increase the strength of the solution.
The acid solution must not be employed when the negative plate or mould, to be copied consists of a more ozydable metal than copper ; for the acid would act upon it, and perhaps even entirely dissolve it. In this case, a central
Coffer Of Yab10U8 Quautiss*
solution most be used. If in these cases the copper is required to possess the qualities which I haye before described, a series of two, three, four, or more batteries must be used if a strong solution be employed, by which means intensity is obtained, and the tendency to the evolution of the gas is increased. The cost would be, at the same time, double, treble, or quadruple that attending the application of one battery. A flexible state can be also obtained by using a dilute neutral solution, with a single battery, or even by employing a stronger solution kept at an elevated temperature. The student will now begin to perceive the value oi the grand principle — the regulation of the amount of electricity to the strength of the metallic solution.
We can obtain the copper of the utmost possible hardness, though slightly brittle, if we are desirous of employing it in that state, by adopting a somewhat different arrangement ; we employ a saturated solution of sulphate of copper, without any acid, a very large positive pole, and we use a cell of such a size that n considerable quantity of electricity is generated. In this case the copper will be found extremely hard, and somewhat crystalline in its appearance. This state may be termed the greater crystalline, and the brittleness depends upon the crystals which form its structure, as a mechanical dissection will show ; for if a piece of this copper be broken, a slight adhesion only will exist between the different particles of the copper. When we throw down the copper, however, in this state, it is apt sometimes to play curious freaks ; for the reduced metal, appearing to be abundant, passes to the back of the plate, causing nearly as much deposit behind as before. Sometimes it will pass to the comer, producing efflorescences apparently from a similar cause.
From the preceding statement it is apparent, that it is quite a vulgar error to suppose that the brittlexiess or
198 Time Requibed Fob The Behcction Of Coppeb.
flexibility, the hardness or softness of the copper, depends alone upon the greater or less quantity of electricity passing, or, in other words, upon the rapidity of the process, for a plate may be a fortnight in its precipitation, and yet so brittle as to break with the slightest touch ; and again, when the process has been performed in two days, or even twentyfour hours, the metal has exhibited great flexibility. We may reverse these results by altering the circumstances ; thus, a plate may be a fortnight in the making, and by using a weak solution and a slight current, be yet flexible ; or it may be made in two days, and still brittle, by using too small a quantity in a very strong solution. The flexibility depends upon the quantity of electricity being suited to the facility with which the reduction of the metal from any solution is eflected, and upon the quantity of salt contained in the solution ; thus, with a neutral solution of sulphate of copper alone, in order to obtain a flexible and soft plate, a small quantity of electricity must be employed, and that with a weak solution, if it be attached to only one cell of the battery ; a stronger solution may be used with a series of batteries with the same result. If the solution be very acid, a more considerable quantity of electricity of a single cell will pass, therefore more sulphate of copper may be employed with the same result, agreeably to the laws regulating the precipitation.
Extreme brittleness may be produced by using a deficient quantity of electricity in a strong solution. In fact, the plate looks as if it were nothing but an agglomeration of bright metallic sand, the particles having no greater cohesion than those of common sand-stone. This state may be called the lesser crystalline.
The copper may be always thrown down as w black powder, a spongy or sandy deposit, by employing a Y&ry powerful battery, or by the other general methods stated in the description of the laws. The sandy deposit, arising
Nitrate Op Copper.
from too much electricity, must not be confounded with that from too little. They are, indeed, easily distinguished ; the former always containing more or less traces of the darker spongy deposit; while the latter possesses a metallic brilliancy ; either of them are equally brittle.
The nitrate of copper is a salt far more easily decomposed than the sulphate. It is an expensive salt, out of all proportion to the trouble of preparing it. In the form of apparatus, however, where the solution is kept at the same strength by the aid of a copper positive plate, the first expense is the only one incurred. The electro-metallurgist may readily prepare this salt for himself by dissolving metallic copper in nitric acid. The operator must be careful not to expose himself to the nitrous fumes which are then generated, as, by inhaling them, the pulse would be lowered, and other disagreeable consequences produced. It may be acidulated with nitric acid, which will increase its conducting power 'materially, so much so that scarcely any im[>ediment will be offered to the current of a single of plates when a positive copper pole is employed.
There is one objection to the use of nitrate of copper, for the hydrogen not only reduces the copper, but is enabled to decompose the nitric acid. This does not indeed occur when the acid remains as nitric acid to any great extent, but as soon as a little of it is decomposed and nitrous acid set free, it is apt to form little bubbles of deutoxyde of nitrogen on the negative plate, which remain adherent to it, and finally become encased with copper. A plate of copper will sometimes be completely cellular from this cause, appearing like a sieve when held between the eye and the source of light.
When this solution is employed, a pound of the salt may be dissolved in a pint and a half of water, and acidulated with half an ounce of strong nitric acid. From a saturated and acidulated solution of this salt, we can obtain a copper
lOTRIATE OF COPPER.
plate ia the most rapid manner possible. The positive copper pole should be of the same size as that of the negative plate, and the two poles should be placed within half an inch of each other. A series of from' four to six batteries must be employed at ordinary temperatures, though at high temperatures less would suffice. A plate of copper should never be made by the compound battery process, however, unless it be wanted in a great hurry, for although the copper is the same in quality, or even slightly superior to that obtained by one battery cell, yet the expense attending its precipitation is greater.
For all the ordinary purposes for which the reduction of copper is required, there is no objection to the use of a small quantity of the nitrate in the solution, and indeed such should always be employed. There is no solution from which good copper may be obtained more readily than the sulphate to which a little of the nitrate has been added. For this reason I have mentioned the use of the nitric acid in the solution, when treating of the sulphate, and be it remembered that if the nitrate of copper is small in quantity relatively to that of the sulphate in any solution, the bubbles of deutoxyde of nitrogen, which alone prevent the universal adoption of that salt, never occur.
The muriate of copper may be employed, but I do not know that any advantage attends its application. It is not so readily decomposed as the nitrate, but more readily than the sulphate. From my own experience it is one of the worst, if not the very worst solution, for the reduction of copper, as the metal is apt to assume a very peculiar appearance. From this peculiar deposition of copper the presence of muriatic acid had better be prohibited, and therefore, we should be very careful never to add it to our solutions of copper. In the employment of the single-cell apparatus muriatic acid should never for the same cause be employed even at the outer or zinc side, for we must re-
AMMONlO-KlXaikTB OF COPPEB, BTC. 201
collect that almost all diaphragms allow a tolerably easy passage of the liquid from one vessel to the other.
Other salts may be used, as the ammoniuret, acetate, and hypo-sulphite; these salts offer no advantage, when copper or any other metal of less affinity for oxygen is used for the negative plate ; yet, with metals having a greater affinity for oxygen, they may be employed with advantage, for it is important that the negative metal of itself should exert no action upon the saline solution, otherwise the duplicate will be impaired.
Acetate of copper is formed by digesting common verdigris in acetic acid, and evaporating the product till crystals are obtained. It is a salt difficult to decompose, requiring the intensity of several cells. It is not decomposed by iron whilst neutral.
The com{)ounds which ammonia forms with the salts of copper, are the lunmoniuret of the oxyde, the ammonio-nitrate, and ammonio- sulphate of that metal ; the reduction of the metal from these is attended with difficulties, and it is requisite that the solution be alkaline from the presence of free ammonia. Iron and steel do not spontaneously decompose these compounds, but I am afraid that this, the only benefit attending their application, will not compensate for the trouble and difficulty attendant on the process. The last salts require a series of batteries to effect their decomposition, although a positive copper pole be used.
The oxyde of copper is very soluble in the muriate of ammonia, but it forms a very bad solution for the precipitation of the reguline metal, as hydrogen seems to have a great tendency to be evolved in it. Cupreous sponge is best obtained from this salt.
We cannot employ a solution of iodide of copper in hydriodate of potash, for iodine is continually being set free if iodide of potassium be added to a soluble salt of copper. Repeated washings of the precipitate will not help us.
a 5
or oomsst, rm
m
The jndplio-cjranide of copper 1 have tried, but do not like it for eleotrometallurgj. The solation in aulphoHniik) of potassium does not contain much metal. A copper positive pole is but feebly acted upon in it
The cupro-cyanuret of potassium is another salt, which has yet to be described. It may be formed by boiling the oxyde in cyanuret of potassium, or by making a sheet of copper a positive pole in a solution of the cyanuret of potassium. The salt when evaporated forms small white crystals; the solution is not a very ready conductor, but may be improved by the addition of free cyanuret of potassium. The only possible advantage it possesses for electrometallurgy is its non -decomposition by iron, though very fair reguline metal may be reduced from it by either of the battery processes.
Sulphate of copper forms a great many double salts ; thus, we have a sulphate of copper and potash, sulphate of copper and magnesia ; and there are a great variety of other double salts, as it forms compounds with almost all the alkalies, earths, and even some of the metallic oxydes. From the electro -chemical decomposition of these, nothing has turned up beneficial to the electro-metallurgist, and a great number of them when submitted to experiment were decomposed by iron.
The compounds of oxyde of copper with vegetable acids offer no advantage. The citrate might be used, as it is soluble, and a copper pole dissolves in the liquid ; but iron reduces it, so that, being but an imperfect conductor, although otherwise an excellent solution for the reduction of copper in the reguline state, it is never likely to be employed.
The tartrate of copper forms rather an insoluble salt, and the potassio-tartrate cannot be turned to any good account, from the very slight action that the copper pole undergoes in the solution.
There are even many other salts of copper, as the com-
OOPFtX POaiTIYB FOLK.
pounds of the ojtydes with the acids of fat but they are insoluUe; and there exist, moreover, a great variety of other salts of this metal which water does not dissolve.
As a summary of the modes of proceeding with various solutions of different strengths, it is to be observed, that the more readily any particular salt can bo decomposed, the stronger may be the solution ; the more diiBcult of decomposition, the weaker. A more concentrated solution of a salt requires more intensity and quantity than a weak solution, whilst a weaker solution may have the current of a single battery passed through it. These comprise the whole of the practical secrets for regulating the quality of the copper, and they have materially assisted in the discovery of the general laws which have been already laid down, for, in every case, the hydrogen is near its evolution when the texture of the copper is at its utmost degree of tenacity.
It has been mentioned that rolled copper may be used as the positive plate of the decomposition cell, os, during the action of the battery, the metal is dissolved to the same extent as it is reduced at the negative plate. It is curious to notice bow regularly that part of the plate which is opposite to the negative pole is thinned, until the whole is removed. From the amount of action being greater opposite to the surface receiving the metallic deposit, it happens that when a medal is allowed to remain for some time opposite a piece of copper, during the process, that a circular hole is formed in the positive plate. For this reason, it is advisable so to vary the arrangement of the negative and positive surfa43e8, that every part of the plate of copper to be dissolved should bo equally acted upon ; but during this process a considerable quantity of black matter, apparently charcoal, is left, arising from impurities in the manufacture of the copper. The ordinary sheet copper of the shops appears a compound of copper and carbon, more analogous to steel than to pure copper* This carbon it acquires in the very curious process called polling,
204 Tabxous Keoatits Poles.
which is performed by allowing willow' sticks to be charred by the melted copper when the metal absorbs a certain portion of the charcoaL The black matter is not always attributable to charcoal, for it appears to a much greater extent in a neutral than in an acid solution ; in which case it appears to be partly owing to the formation of an oxyde of the metal. If an electrotype plate be made the positive pole of the apparatus, no remains will be left, but every particle will be dissolved. The piece of copper forming the positive pole of the trough may be partially dissolved by coating the rest with any varnish or substance which can resist the action of the fluid, a property of which hereafter we shall have more particularly to speak.
The negative pole to receive the reduced copper may consist of a solution of sulphate of copper, plumbago, charcoal, gold, silver, platinum, palladium, nickel, or copper itself, all of these being suitable for the reception of copper. All other metals are, more or less, acted upon by the solution, though lead and its alloys may be used with the sulphate, especially if it be diluted. Tin is much inferior to lead for the reception of this metal, as it acts more readily upon its salts.
The same observations apply to the nitrate of copper, except that lead, tin, and their alloys, much more readily act upon them than upon the sulphate, and that iron does not quite 60 readily decompose this solution as it does the sulphate. Almost all metals may be employed as the negative pole in the ammoniurets of copper, and also in the cuprocyanuret of potassium, for they so feebly act upon these solutions as to make it scarcely vrorth consideration. Iron and even dne produce but little change upon them.
Toe copper thus reduced, assumes the form and appearance of the cast on which it is deposited. If the snriaoe of the original be polished, the duplicate will be so likewise, and the colour will, in many cases, be slightly influenced,
BSDUCTIOK OF PPliR BY SIKOLE-CBBL PBOOBSS*
especially where copper has been used as the original. The surface is not quite so brilliant, where lead, tin, and such metals are employed, but when black lead is applied on smooth surfaces, as sealing wax or white wax, the surface of the duplicates is perfectly bright.
When we desire to clean the surface we can easily effect our object by brushing it over with charcoal and water, or with emery and water, which speedily removes any extraneous matter from the surface. It is by no means a good plan, ordinarily, to plunge the metal in acid and water to effect this object, as it acts upon the surface and injures the brilliancy of the metal.
Copper may be reduced by the single-cell process, from a great variety of salta by means of zinc, tin, lead or iron ; the first and last, however, being the only metals likely to be employed. The advantages and disadvantages of the single-cell in comparison with the battery apparatus, have been fully discussed in the first chapter of the second book ; but if there is one metal to which the single-cell process is more particularly applicable, it is copper, especially its reduction from the more ordinary salts : where tlie acid in conjunction with the metal is not worth preserving, the employment of the zinc single-cell apparatus, unless under particular circumstances, is better dispensed with. The reduction of the metal by iron is, for its economy, to be preferred to all other methods in those cases where it is applicable. Yet upon the whole, as the single battery process is suitable to every possible case, for which the reduction of copper can be required, it as a general rule must still supersede the other modes of working in copper. The expense of each process has already been noticed when treating of the general means by which the expense of working in metals is calculated, and as the reduction of copper is there taken as an example, it would be but a vain repetition again to detail it.
Black Lead Bbonze. — Grease Bronze.
For copies of medals, and other works of art, a copper surface is not always desirable, bronze having a much better appearance, and this may be communicated in various ways. The one most generally adopted is the following: — The medal is covered over with oxyde of iron, and placed in a muffle, and in this state exposed to heat; when removed from the fire, it simply requires to be brushed, and is then fit for the cabinet.
Generally, however, we adopt more ready methods of producing the bronze ; one of which is to brush the medal over with black lead, immediately upon its removal from the solution. It is then placed on the fire till moderately heated, when it may be smartly brushed with a hog's-bristle painting-brush, the slightest moisture being used at the same time, in order to remove the black lead. An uniform shining bronze is thus obtained. There is no method of bronzing to be preferred to this for beauty, as a medal not two hours old displays the fine colour of antiquity so much prized by numismatists. In these operations, I believe an oxyde of copper is produced, to which the effect is mainly to be attributed. If the metal has been allowed to remain out of the solution for some time before the bronze is given, it is not found to take so readily. In that case it is better most thoroughly to clean the surface, and then to proceed as before.
The application of a very minute quantity of grease, or wax, much improves the bronze. This is, however, unnecessary when the copper has been deposited on a mould consisting in part, or entirely, of these substances ; but in otlier cases, the application is very advantageous. Grease or wax alone, when applied in an infinitesimal quantity over the surface of a medal, enables it to take a fine bronae when simply heated to a proper temperature. We cannot readily give the precise temperature at which the best efiect is produced, but, as a general rule, the heat should be applied
Icethod Of Bronzino Coffer.'
just so high, and for such a length of time, that smoke from the incipient decomposition of the grease begins to appear. A greater heat causes the copper to blister, but if removed at that precise moment the surface will be beautifully oxydated. The perfection of this kind of bronzing, as well as that of the black-lead, depends in great measure on the skill of the operator, and the efl'ect may be mucli enhanced by rubbing the medal with a nail-brusli containing plenty of bristles, and finishing it with a little whiting, placed on a piece of wash-leather.
The French have a method of bronzing clicht'e8, which is very effective. They arc sometimes so readily mistaken for copper, that a gentleman placed what he conceived to be a copper medal into a trough to obtain a reverse, when to his astonishment, on the removal of the mould, instead of a copper medal he found he had a leaden one. The mode by which this bronze appearance is given, is to moisten the surface with a little spirits of wine, and at the moment of drying, dusting it with a little red chalk, modified in colour with a portion of black-lead, and then with a good puff dispersing any superfluity that may have been employed. This process might also be employed for copper medals, but the colour is, perhaps, not so fine as by the process already detailed. There are other modes of bronzing clichdes which are not applicable to such as dipping them in a solution of the binacetate of copper, acidulated with acetic acid, by which means the medal reduces a small portion of copper, and therefore has all the appearance of a copper medaL
Instrument-makers have a mode of bronzing the copper which is used for binding-screws and other parts of their apparatus. It is simple and effectual, for the metal is simply to be rubbed over with a little weak solution of platinuin, when the copper, or a portion of it, is dissolved, and an equivalent proportion of platinum u thrown down. Th
Sulphuret Bronze.
generally protect this from change by Tarnish, but this should never be applied to delicate impressions. A solution of gold would answer the same purpose, did not its value prohibit its application.
Another valuable method of bronzing is the application to the metal of a very weak solution of the hydro-sulphate of ammonia, or the sulphuret of potassium, when a sulpburet of the metal is obtained, which is of a very beautiful colour If the solutions are used too strong, a thick layer of sulphuret is produced, which much detracts from the beauty of the medal as a work of art.
A new mode of bronzing has lately been introduced by Mr. De la Rue, for which he has obtained a patent. The metal to be bronzed is first of all blackleaded, and then placed in a basin of water. Upon the water a few drops of white hard varnish, to whicli had been previously added a little oil of lavender, are then placed. The varnish is gently skimmed till it is very thin, when, upon the principle of Newton's rings, it exhibits its colours. The blackleaded object is then raised from the water and draws with it the iridescent film, and finally the object is very slowly dried, when a very beautiful bronze is exhibited. When this film is fixed upon paper it is called opaline, and when brought before the public, will doubtless be much employed.
The object of all these methods is to throw up the fine workmanship — a result which is efficiently obtained in the colour given by the methods which have been detailed ; the choice of these is left to the operator, but perhaps none excels, or even equals, the mode of bronzing by black lead, or grease, when those operations are perform with care, and in the manner which has been described.
(178.) Zinc may be reduced in the bright metallic state from a variety of solutions, as the oxyde of zinc is soluble in a great number of acids. The sulphate of zinc, however, is by far the most common salt of tl metal, and it is fonned
Chlobide Of Zinc.
tolerably pure and in large quantities during the employment of galvanic batteries. The solution of the sulphate of zinc may be of any strength, but perhaps the stronger is to be preferred. It should be as neutral as possible, and it is a good plan to add a little oxyde of zinc to the sulphate, but this salt always reddens litmus paper. Sulphate of zinc is best formed for electro-metallurgy in a series of my galvanic batteries, gradually decreasing the rapidity of the process towards the termination until zinc begins to be deposited. Zinc can only be reduced practically by the battery process. In the trough it is as well to use a very large zinc positive pole, and take especial care to cause a proper diffusion of the new sulphate of zinc, and the compound trough apparatus is particularly commendable for this process. Hydrogen has a considerable tendency to be evolved from the solution. The battery should be small, as the galvanic power should be feeble, and the resistance in this case should be rutiier in the battery or the connections than in the positive pole. In some cases the positive pole of zinc might be platinized, so that any free acid may be immediately neutralised. Reduced zinc may be thrown down in a very flexible state, and is for more slowly acted upon in dilute sulphuric acid than common zinc.
The ammonio-sulpbate of zinc may be made by adding liquor ammonia to a solution of sulphate of zinc. It is a good conductor, and may be used with a zinc positive pole. It is a tolerably good solution of the metal to obtain the regnline deposit.
Potash added to a solution of sulphate of zinc throws down a precipitate which is soluble in excess. The zinc is not so readily reduced from it os from the sulphate, and it requires a series to effect that object. Tlie zinc positive pole does not freely dissolve in it.
The chloride of zinc is usually formed by dissolyiiig the metal in muriatic acid, when hydrogen is most abundantly
Kitratb Op Zinc, Etc.
evolved. It is now occasionally used in surgery as an escharotic, and it may be employed for electro-metallurgy in the same way as the sulphate of zinc. It is a good solution, but possesses no particular advantages. If chloride of zinc is formed by the galvanic battery, it is better adapted for electro-metallurgy. This, perhaps, is the best solution for obtaining crystals of zinc.
The nitrate of zinc formed by the action of nitric acid on zinc is the very worst salt I have tried for the reduction of the metal in the reguline state.
The oxyde of zinc is very soluble in muriate of ammonia. There is a great tendency to the evolution of hydrogen in this solution, and therefore it is not a good compound for the reduction of the reguline metal, though it is well adapted for obtaining zinc sponge in large quantities.
The acetate of zinc may be formed by digesting oxyde of zinc in pyroligneous acid, or by making zinc the positive pole in that fluid. It is a very good solution for obtaining reguline metal by the single battery process.
The tartrate of zinc formed as the acetate, possesses no peculiar advantage for electro- metallurgy.
The potassio-tnrtrate of zinc may be made by boiling the oxyde in cream of tartar, or by making a plate of zinc the positive pole in a solution of bitartrate of potash. The zinc positive pole does not freely dissolve in it.
The hydriodate of zinc is a good solution for electrometallurgy. It is best formed by galvanism, by using a zinc positive pole in a solution containing a very minute quantity of iodide of potassium and a very large quantity of undis* solved iodine at the bottom of the vesseL The iodine will at last be entirely taken up and a corresponding quantity of iodide of zinc formed.
The zinoo-cyanuret of potassium may be formed by either digesting the oxyde in the cyanuret of potassium, or galvanizing a plate of zinc in a solution of the cyanuret. It
Reduction Of Zinc.
forms octohedral crystals, but it is a difficult salt to decompose, requiring a series of batteries for its reduction, and it is difficult to obtain even a small amount of zinc from it.
The reduction of the zinc is not of much importance in itself, although very interesting when considered in reference to the plates of galvanic batteries ; for if one battery in a compound series, from any cause, has the whole of its exciting fluid neutralized, then will that cell be in the same condition as the apparatus employed for the reduction of the zinc, and zinc will immediately be deposited on its negative pole. This will occur with all the forms of batteries now employed, although it is a property of no consequence, as the action of the battery ought to be stopped before it has so thoroughly exhausted itself. When this deposit takes place, it can readily be removed by placing the plate in contact with any metal which can act (is a negative plate to it. The necessity of this arises from the diflieiilty with which pure zinc is dissolved in acid. As soon us a dozen or more batteries, arranged as a series, have the acid of their exciting fluid saturated with zinc, the zinc will be deposited on the negative plate, if a single battery only out of the whole number contain any acid ; thus eleven batteries out of twelve may have their negative metal thickly coated with a very beautiful and perfect deposit of zinc, whilst the last will not have the smallest trace upon it. Zinc is never found in all the batteries of a series. There will be some curious matter to be discussed when we Lave to describe the reduction of alloys.
In the reduction of zinc from any salt there is a difficulty to be encountered which will be explained when treating of the reduction of alloys, for reguline zinc of the best quality may go down at first, but afterwards one of the varieties of the spongy deposits will take place. This alone forms a great impediment to the reduction of zinc'oii a large scale.
The reduction of zinc is generally a disadvantageous pro-
REDUCTION OF CADMIUli.
cess, as the cost of its deposition is the same as that of copper, from their voltaic equivalents being alike. Zinc, however, is worth but threepence a pound, whilst the value of copper is a shilling.
The material which is sold under the name of galvanised iron, is not iron coated with zinc by the voltaic process ; in fact galvanism has nothing to do with it. The iron is very thoroughly cleansed by acid, and then dipped into a bath of melted zinc, and moved about till a coating is effected. There is another variety called galvanised tinned iron, in which the iron is first coated with zinc, and then dipped into melted tin. Tlie use of the word "galvanised** is highly improper in both these cases, because people are prone to think that the process has been effected by galvanism. These processes for zincing iron are extremely valuable, and should be extensively employed as a substitute for paint.
(179.) Cadmium has a variety of soluble salts, of which the sulphate, ammonio-sulphate, and chloride, are the only ones I shall notice. The sulphate may be employed with a cadmium positive pole and a small battery. For small nega* tive surfaces, one of the odds-and-ends* little glass batteries, described when treating of the reduction of platinum, is well adapted. Cadmium of good quality does not readily go down from the sulphate.
The chloride of cadmium may be made by galvanism, by arranging a piece of cadmium as the positive pole in dilute muriatic acid. The chloride of cadmium behaves much in the same way as the sulphate. Cadmium, however, has a tendency to be thrown down in a peculiar state between the sponge and crystalline deposits, and hydrogen has a considerable tendency to be evolved from both this and the last solution.
The ammonio-sulphate of cadmium may be formed by adding ammonia to a solution of the sulphate as the pre-
Reduction Of Iron.
cipitate is soluble in very small excess of the precipitant. It may be employed with a cadmium positive pole in conjunction with a small odds-and-ends* battery. This is the best solution for obtaining the reguline deposit, which may be easily thrown down in a flexible state from it.
The reduction of cadmium might be followed with advantage as an equivalent of power ; value of a penny would reduce about 56 grains of the metal ; so that a pound of cadmium obtained by the voltaic force would only require about sixpence to be added to the cost of the metal, which, being scarce, is considerable.
(180.) Tlie salts of iron have a strong tendency to be peroxydised, in which state they cannot be reduced by the voltaic current. We must use, therefore, the proto-salts, of which the proto-sulphate of iron is a good example ; this is prepared very carefully for the use of chemists, and the reduction of metallic iron may take place from a solution of the proto-sulphate. The metal upon which the deposit is to be effected, is connected with the zinc of the battery, whilst an iron nail is connected with the silver ; as the source of power, a relatively small single battery will suffice, and the silver need not be larger than the negative pole in the trough. The nail is to be just so far dipped into the solution, that the minutest quantity of hydrogen, or none at all, is evolved from the metal to receive the iron ; and after the lapse of a short time, the negative metal will become coated with metallic iron. The reduced metal is brighter, and rather whiter than polished steel, but it soon tarnishes in the air.
Proto-chloride of iron may be formed by dissolving iron in muriatic acid; it forms a perfectly neutral salt, and is well adapted for the reduction of the metaL It may be reduced by either battery process, of which the single battery will always suffice. The hydrogen has not so great a tendency to be evolved as in the sulphate, and the
Citrate Of Iron, Etc.
metal goes down freely from it. This is an excellent solution, perhaps the best for the reduction of this metaL If the iron is removed from 'the plate on which it is deposited, the surface next to the negative pole is polished if the original is so also ; and very thin layers of this metal have a very fair cohesion, inferior, however, to the rolled iron of commerce.
Iron may be reduced, but only in the minutest quantity, from the ferro-cyanate of potash, which is, therefore, useless for electro-metallurgy.
The compounds of iron with the vegetable acids may be employed for electro metallurgy. The citrate may be made by arranging a plate of iron ns the positive pole in a solution of citric acid ; but it is difficult of decomposition, requiring a series of batteries.
The proto-ioduret of iron, as used in medicine, may be employed for electro-metallurgy. It is not, however, so good a compound as the chloride for these purposes.
Iron reduced by electricity has not yet been examined as to its magnetic properties, and, doubtless, pure iron obtained in this manner must possess peculiar properties still undi8Covor'd.
The reduction of iron, in a pecuniary point of view, is the very worst process in the whole range of electro-metallurgy ; for the metal is worth scarcely anything in comparison with others we have had to treat of. The ironmasters, doubtless, will sleep in perfect security when they ore told, that for one equivalent of galvanic power derived from my battery costing of a penny, but 28 grains of iron are reduced ; so that the reduction of lib. of iron, worth about one penny, would cost more than one shilling for the bare materials used in its reduction, to be added to the value of the metal. Under this aspect of affairs, not only the blast, but even the puddling and melting furnaces, are Hkely to continue to send forth their pestiferous fumes by
Reduction Of Tin.
2U
daj, and their pandemonium -looking dames by night, corrupting the atmosphere, to the injury of vegetation, as weli as to the detriment of the health of all living beings.
(181.) Tin is a difRcult metal to manage, because the transition from the decidedly spongy state to the crystalline is so rapid, that we can scarcely hope to obtain any amount of reguline metal. The salts which I have tried are numerou8> but they all liave the same general charactiTs. The muriate is the most common of the salts of tin. It yields very fine crystals when by a small odds-aud ends* battery, with a tin positive pole. If the battery is very active, the tin positive pole large, and the solution strong, the growth is marvellous; a little point will present itself on the negative metal, which rapidly increases, and in a few seconds will grow to the positive pole. If during this rapid growth the })ositivc* pole be moved, the crystal will follow it.
The finest crystals are obtained, however, by the strongest neutral metallic solution, and a very low action in the battery. The deposit is certainly very beautiful. The spongy deposit of tin is very peculiar, and the ciectro-inctallurgist is apt to see it much oftener than he wishes ; for that light, fiocculent spongy deposit, which is frequently observed during. the action of the battery, is nothing but metallic tin, arising fk*om zinc clippings mixed with solder Ixiing melted with the rough spelter ; if a little of this mass be squeezed between the fingers into a mass, and then struck and rubbed against anything hard, a bright metallic surface will be exposed.
The sulphate of tin may be formed by digesting the protooxyde in dilute sulphuric acid ; it is rather a better salt than the other ; and might be used for some purposes to coat iron. A kind of lesser crystalline deposit may be obtained from it, but not sufficiently good to form a tin medaL
The oxalate of tin and acetate of tin are made in the same
Reduction Of Leid.
way as the sulphate. They are not quite such good conductors as the sulphate and do not yield good reguline tin to any extent.
The potassa solution of the oxyde of tin is a bad con ductor, requiring an intense battery for its decomposition. A good thin layer may be deposited from the solution, but I have never made a medal with it.
The oxyde of tin dissolved in cyanide of potassium is difficult of decomposition, and does not yield any amount of tin.
I have tried a great variety of other mixtures of these salts, as oxyde of tin with cream of tartar, sulphate of alumina, chloride of sodium, hydriodate of potash, &c., Ac., without any satisfactory result.
The reduction of tin by galvanism cannot be considered an advantageous process, from the low value of the metal. One equivalent of power, costing of a penny, will reduce about 58 grains of tin, making the cost of the power, about sixpence a pound, to be added to the value of the tin.
(182.) Lead has but few soluble salts, of which the acetate, the nitrate, and plurabo-cyauide are the principal which deserve attention.
The acetate is abundantly soluble, and may be employed for the reduction of the metal. It may be used with a lead positive pole, connected with a small battery. Lead has such a tendency to be deposited in crystals from this solution and the crystals grow so rapidly, and to such a size, that it is in vain to attempt to obtain the reguline deposit from it, especially as the gradation from the spongy to the reguline deposit is very dose. The crystals of lead as reduced by zinc form what is termed the lead tree. To produce it a small piece of zinc is suspended in a bottle, containing a dear solution of acetate of lead, when speedily the metal begins to be thrown down, and continues to be deposited in the beautiful forms to which the name of the lead tree is given. The
Mstallo-Chbome8.
experiment may be varied by using a copper wire round the zinc, and passing it to the bottom of the vessel, when the lead will also be deposited on the copper wire ; in a solution of acetate of lead, the positive pole becomes encrusted with a deposit, which is the peroxyde of that metal. I have observed a similar deposit in the decomposition of other metallic salts, but as none have been turned to any account but this, the fact need not be more particularly alluded to. The production of this oxyde has been used by Mr. Gassiot to form metallo-chromes, which, for striking effect and beauty of colours, are unecualled by any other work of art. They are formed by throwing down a deposit of this compound of various thicknesses, on a plate of polished metal (burnished steel answering best). Tlie difference in the thickness of this deposit is accomplished by placing the plate of steel at unequal distances from the negative The negative pole should consist of a copper disc made slightly convex, which at once very effectually causes a variation in the distances. The exact modu$ operandi, which Mr. Gassiot recommends, is to place the polished steel plate in
a solution of ace- Fiy- 34.
fate of lead, and over that a piece of card with some regular device cut out (c). A Small rim of wood (tr) should be placed over the card, and the circular copper disc (d) (which is represented in the wooden on one side) over alL On contact being made from d to 20% with 2 or 3 of a small battery — the steel plate being connected with the silver, the copper disc with the zinc, the deposit will be effected, and a series of those
Xetallo-Chbomes.
exquisite colours will delight the operator, which arise from the decomposition of light, bj a layer of different thicknesses of peroxyde. By reflected light every prismatic colour is seen, and by transmitting light a series of prismatic colours, complimentary to the first series, will appear occupying the place of the former series.
The best way of viewing these beautiful fairy forms is to place the plate before a window, and incline a sheet of white paper at an angle of 4/>® over the plate, when if the plate be viewed at a considerable angle the colours appear to stand boldly forth on a white ground.'*
Tlie tris-nitrate of lead forms rather a better salt for the reduction of reguline metal. It may be used in the same way as the acetate, but I have only reduced small portions of reguline lead that I could strip from the negative pole from it.
From the pi umbo-cyanide of potassium I have reduced reguline lead of good quality, which could be stripped from the negative plate, still only in small quantities ; probably, from the insolubility of the oxyde of that metal at the positive pole.
The reduction of lead by galvanism is not, independently of the difficulties attending it, a good process, because the value of the metal is low, yet inasmuch as we obtain for one equivalent of power 104 grains of lead, that would rather lessen the cost of the process.
(183.) Antimony is one of those metals by rfo means deserving more than a cursory glance. The only solution
♦ I have formed metallo-chromcs analogous to those described in the text, in a very different war, jet dependent on the same principle. A plate of polished copper phu over a card device, and thra exposed to iodine. Incomes coat with a thin film of apparently iodide of copper, which shows the prismatic colours very beaatifnlly ; yet fu* inferior to those formed by peroxyde of lead. This experinsent may be varied in many waji.
Seduction Of Antimony, Bismuth, Etc. 219
which I shall notice is that of the potaasio- tartrate. It ia tolerably well adapted for the reduction of the raetal in the reguline state. It is not very readily decomposed, requiring a couple of batteries with an antimony positive pole. The metal is then thrown down slowly, but forms a brilliant deposit, which may be stripped from the negative pole. Antimony, instead of being deposited at the negative plate, in some cases combines with the hydrogen, and is evolved ns antimoniuretted-hydrogen gas.
(184.) Bismuth is another metal, to the characters of which, in an electro-metallurgical view, very little interest can be attached. Its super-nitrate is a soluble salt, and may be employed with a positive pole of the same metal attached to a single battery. The deposit, however, from this has a tendency to assume a mixture of the sponge and crystalline deposits.
The tris-nitrate, or medicinal salt of bismuth, is nn insoluble salt, and thenjforc inapplicable for our purpose.
The iodide of bismuth is soluble in excess of iodide of potassium, but I have not turned it to any good account.
The potassio-tartrate of bismuth may be soluble by making a piece of bismuth the positive pole in bi-tartrate of potash. It may be employed with two batteries arranged as a series, It is not a ready conductor. The metal is reduced but slowly from it. A white powder forms upon the positive electrode, which at length stops the action. So little importance is attached to the reduction of this raetal in the reguline state, that I have not bestowed much time upon it.
(183.) Uranium is another metal which I have endeavoured to deposit from its nitrate, but without success ; in fact, being a per salt it was not likely to be reduced, I have not succeeded in procuring any proto salts of uranium on which to experiment.
(186.) Arsenic is a metal not likely to be of much value for electro-metallurgy, yet there are some important clrcum-
xoTsonoK OF ABssma
Itaioes to be noticed in its characters when anbjeoted to the Fidtaic dnidf which require some notice in this place.
The oade of arsenic or arsenious acid is frequently em ployed as a means of destroying animal life, and though its means of detection when improperly administered, are more simple and certain than that of any other poison whatever, the minds of chemists are continually being directed to some new mode of effecting that object As far as the voltaic power may be brought to bear in the detection of this metal, 1 shall briefly notice the subject, but no further.
Arsenious acid is not very soluble in water, and is but a bad conductor of the voltaic force. It may be decomposed by a series of batteries with platinum electrodes, oxygen being evolved at the positive, and the metal reduced at the negative electrode. The hydrogen, however, in this case, not only reduces a part of the metal, but combines with another part, forming arseniuretted- hydrogen gas. This gas has a peculiar alliaceous or garlicky smell, which is a good characteristic of its presence. If a small jet is inflamed and a cold object placed over it, arsenious acid is deposited, but, however, if the cold object be depressed so as to cut a portion of the flame, metallic arsenic will be reduced.
The phenomena appertaining to this gas were first applied ingeniously by Marsh to the detection of arsenic. He employed ainc, dilute sulphuric acid, and the suspected liquor, and then tested the hydrogen when inflamed, in the manner just pointed out. He describes a considerable number of pretty contrivances for effecting that object ; sometimes he uses a tube simply bent upon itself into one end of which a st<>-cock and jet is fixed, the other being left free ; sometimes he dilates his tubes into a . A great variety of afqMwatuses are described for the prodnetion of the gas. All these forms are well adapted for the deteotion of arsei when they are not wanted for organic mixtures, bat when the contents of the stomadi have to be examined, they are
Bxd0Ct1< Op Ar8Bnxc*
m
generally but ill adapted from the firoth that generally ensues. When aracmio is taken into the stomach, that organ not liking its new customer endeavours to remove it out of contact by pouring out a large quantity of mucus which envelopes the poison and protects the stomach in some degree from its in* fluence. The cunning chemist should mechanically dissect from this secretion the white powder, and subject that to experiment, for it is only in those cases where poisoning is effected by very minute quantities, that the poison is not at once seen as a white powder. Having separated it, it is to be dried at a gentle heat, and distilled from the bottom to the upper part of a test tube by means of a spirit lamp when it is ready for the various experiments to which the operator is inclined to submit it. If we choose the arseniurettedhydrogen test the vessel should bo capacious, a phial with a piece of glass tube drawn to a point and inserted in the cork, is well adapted.
Zinc is apt to contain arsenic itself, therefore it would be better always in judicial coses to employ that reduced by the voltaic agent ; the sulphuric acid is also apt to be intermixed with small portions of this metal, for which reason both should be tested before they are used. We should never be satisfied with this test alone, unless we can obtain arsenioiis acid sufficient to test with the ammonio*nitrat6 of silver, ammonio-sulphate of copper, and sulphuretted-hydrogen, for not only may a little black crust of antimony be mistaken for arsenic, but even a little animal matter may give a similar deposit.
Morton, in order to overcome the errors from impurities in the acid and zinc, proposed to subject the suspected fluid to an intense galvanic battery, and then examine the hydrogen. The only difficulty in this proceeding is the imperfect conducting character of the compound to be operated on. This difficulty might be overcome by the addition of pure potash.
L a
Of Arsenic.
I have now to call attention to the following mode of taking advantage of the opportunity afforded to us of subjecting the suspected fluid to a long continued galvanic curipeni of but feeble quantity ; for by that means we should be enabled to determine the presence of arsenic, by heating the Amative pole in a test tube when arsenious add would be formed* This would be deposited at the upper part of the tube, and being tested would give the most unequivocal signs of the presence of that metal This, although by no means the most delicate is by far the most satisfactory proceeding we can adopt, for we need not introduce into the suspected solution, any new substance, so that not a shadow of doubt could be thrown on the accuracy of the result if arsenic be obtained: if, however, we do not succeed in obtaining arsenic, it is not an infallible proof of its absence. By this plan the following characteristics are shown :
(a.) The reduction of the metallic arsenic on platinum.
(b,) Its volatility and conversion into arsenious acid, leaving the platinum clear.
(c.) The yellow precipitate of arsenite of silver with ammonio-nitrate of silver.
(d.) The green precipitate of arsenite of copper with ammonio-sulphate of copper.
(c.) The yellow, sulphuret of arsenic with sulphurettedhydrogen.
In conducting the process, a series of not less than a dozen batteries should be used, and the process should be continued till the negative platinum pole (a wire will suffice) becomes coated with metallic arsenic which presents a somewhat bright black appearance. The wire is then simply to be coiled up, placed in a test tube, and heated over a spirit-lamp when the arsenious acid will be seen at the upper part of the tube, as small white crystals, which are to be dissolved and subjected to the other solutions. By continuing this process sufficiently long, the whole or the greater part of the arsenie will
Reduction Op Cobalt.
be reduced, and tben would the medical man be enabled to go into court armed not only with the reasons in his breast, but the arsenic in his hand.
If a copper or a silver positive pole be used in a solution containing arsenious acid, the yellow or green precipitate will be formed ; but they are not satisfaotoiy modes of detecting the presence of that metal.
(187.) 1 have endeavoured to reduce tungsten flrom tungstie add by using a small platinum wire as a positive pole in solution of the acid. It is but an imperfect conductor, and requires a series of nine or ten batteries. 1 have not, however, succeeded in obtaining any metal from the acid.
(188.) Cobalt may be reduced from its chloride, to which excess of ammonia has been added, by using a cobalt positive pole connected with a series of batteries, when the deposition will take place upon the negative plate, which may consist of copper. The reduced metal is white, but it is not thrown down freely. The chloride of cobalt alone, seems only to yield an oxyde at the negative pole. The cobalto-cyanuret of potassium formed by digesting oxyde of cobalt in the cyanuret, yields, by decomposition with a compound battery, some metal, but hydrogen has a great tendency to be evolved from this solution.
(189.) Manganese has been attempted to be reduced from the sulphate or chloride with signal failure, for the hydrogen has a decided preference to be evolved, even from a polished surface, rather than to reduce the metal. At the positive pole an iridescent deposit, apparently a peroxide, is abundantly thrown down.
Chap. V.
On The Reduction And Analysis Of Alloys.
Law for the completion of the Toltaic circuit through varioufl solutions, 190. Table of relative facility of decompositions,
(190.) Hitherto we have only considered the formation of ingle salts, and the reduction of simple metals. We have now to discuss the important question, whether two or more metals can be reduced at the same time ; and whether the metals can* be thrown down coiyointly with other bodies. This conudering the ama 2 ing number of solutions, becomes a very complex question ; and only a general outline of the principles regulating these phenomena can, in the present* state of our knowledge, be attempted. In entering upon this subject I began by selecting metals far apart in the facility of their reduction by hydrogen ; thus, solutions of the salts of dnc and copper, being mixed, only copper was reduced at the negative pole. Without detailing a mass of similar experiments, I shall at once state, as a fundamental principle, an absolute law derived from a most extensive examination of the voltaic force, that, the voltaic circuit is
INVARIABLY COMPLETED IN THAT MODE WHICH OFFERS LEAST RESISTANCE TO THE PASSAGE OF THE FORCE. That is tO say, that if a great variety of roads are offered by which that object may be effect that the force, provided the road be large enough, would pass exclusively through the one offering the least resistance. To take an example of this, add to strong nitric acid, chloride of gold, chloride of platinum, diloride of palladium, and any other metallic salt
Keduction Op Alloys.
you have at hand that will remain soluble in the acid,-and then decompose the mixture between platinum poles, you will find that the circuit will be completed alone through the nitric acid. You may analyze your experiment by placing each salt in a separate vessel, with precisely the same result, as the current will alone traverse the fluid easiest of decomposition, provided that the electrodes exposed to that fluid be sufliciently large. By acting upon this principle the student will perceive that one body might be separated from another, or even from a variety of others : thus, if brass is dissolved in dilate sulphuric acid by the aid of the voltaic force, the precipitate at the negative pole will by management be pure copper only. A person who accidentally stumbled upon this result, bought a large quantity of that alloy in the vain hope of amassing a fortune by what he conceived to be a transmutation of metal, though he doubtless must have discovered at last that he only obtained the copper originally contained in the alloy.
Whatever experiments are detailed relative to the reduction of the alloys, the converse of them applies exactly to the separation of one metal from another. Before we proceed farther in our inquiries we should form a list of the fluid roads by which the voltaic circuit may be completed, and place them in the order of the facility with which the passage is made by the voltaic force. As it has been shown that the decomposition of various salts is attributable to the secondary action of hydrogen, termed electro-chemical decomposition, the first thing that we have to determine is the point, in various cases, at which hydrogen would rather be evolved tbn decompose the metallic salt. But the very construction of my battery depends upon the primitive fact that different meti and even the same metals under different circumstances, evolve hydrogen from the same solution with various facilities. It is natural to suppose then, if our law for the passage of the fluid be correct, that there are some cases
evolved. This experiment may be varied a hundred analogous ways, with results at one time in favour of the evolution of the gas, at another of the removal of the gas by the decomposition of some compound. This at once introduces a new element into our reasonings, for we should form a table showing the relative ease with which hydrogen is evolved from various bodies ; the top of this table is either platinum, palladium, or silver, in the infinitely divided state used for my battery : but the exact relation which the perfectly divided metals bear to each other, or even to themselves in other states, in different solutions, or even in the same solution, at different temperatures, 1 am unable at the present time to give ; indeed it would be a work of such mechanical labour, that 1 should not with my present avocations feel warranted in undertaking it
The evolution of hydigen gas from any given solution being taken at unity, as soon as the ease of its evolution is less than any other mode by which the circuit may be oom-- pleted, the evolution of the hydrogen is ceded to that mode : generally, the hydrogen if not evolved, reduces some oxygenated body or some metallic salt, and then the analogy is kept up by its reducing that salt, which yields its metal most readily to the gas. The gas is perhaps easiest evolved from muriatic or dilate sulphuric acid.
(191.) We here require another extensive table showiBg
Keduction Op Axloy8.
the relative ease with which bodies are reduced by hydrogen; perhaps nitric acid is at the top of the list; then follow the salts of some of the nobler metals, whilst salts of zinc and numerous other metals are below the evolution of hydrogen from sulphuric acid : —
Nitric acid.
Gold chloride. Palladiam nitrate. Platinum chloride. Silver nitrate. Copper sulpliatc. Tin sulphate.
Hydrogen dilute sulphuric acid. ' Cadmium sulphate.
Zinc sulphate.
Nickel sulphate.
Iron suljdiatc.
Manganese sul]>hnte.
Salts of alkalies, generally.
Hydrogen easily reduces the per salts of iron into proto salts, — a fact of considerable importance in many electrometallurgic operations.
The above is given as a rough specimen of a tabic showing the relative facility by which the removal of gas may be effected ; therefore, supposing our electrodes were sufficiently large, and an ample supply of solutions of the vaiioua salts were afforded, but one compound would be decomposed at one time.
However, suppose by using an intense voltaic current, we compel such a quantity of the force to pass from a small electrode, that any one compound body in its vicinity is insufficient to complete the circuit, it would then be completed through two, three, four, or more bodies, and it would reduce them all at once ; thus, our mixture of metallic salts with nitric acid, decomposed by on intense current with small electrodes, had a great variety of metals reduced, whilst on the increase of the poles the circuit was entirely completed through the nitric acid. In the same way 1 have decomposed twenty different solutions arranged not as a series but as one decomporidon cell.
As a general princip to obtain a deposit of two or more bodies on any negadve pole, we must nse a quantity of the
Reduction Of Allots.
voltaic force, more than sufficient to reduce the elementary substance from the compounds most readily decomposed. By the first law regulating the quality of metal reduced by the voltaic current, the metal is always reduced as a sponge when hydrogen is evolved from the negative plate ; therefore, it would he impossible to obtain a reguline alloy in a solution of any two metals, one of which is above, the other below, the evolution of hydrogen, from the particular negative pole we employ in these solutions.
Such is a rough sketch of the principles to be pursued for the reduction of alloys, but at present practically 1 have not reduced a perfect reguline alloy of any metal, though I feel no doubt, by following out the above principles, a person might succeed in attaining his object with some metals, by a careful examination of their various salts.
Electro depositions of brass have occasionaUy been stated to he pjQpduced, but in these cases the zinc and copper have been reduced contemporaneously, and their union has been afterwards effected by heat.
The general principle which regulates the reduction of alloys is far more important than for the specific object for which it is given ; for the experimenter will find that the current will invariably pass through the road which presents the least obstacle, be that obstacle solid, fluid, elementary, compound, small, or great.
Book The Third.
Pn Electro-Gilding, Silver-Plating, Etc.
General directions, 192. Electro-gilding, 193. The auro-ejanide of potassium, 194. Apparatus, 195. 196. Watergilding, 197. Gilding by amalgamation, 198. Electro-plalinaling, Electro-platinizing, 199. Elcctro-polladiating, Electro-plating, 201. Plating by other means than Electro-Metallurgy, 202. On coating metals with nickel, 203. On coppering metallic substances, 204. On coppering non-mctallic substances, 205. On coppering medallions, 206 ; fruit, vegetables, &c., 207 ; baskets, 208 ; earthenware, 209. On coating metals with iron, zinc, &c., 210. Conclusion, 211.
(192.) The infilming of one metal by another, is a subject of much interest, and the process has received, different names according to the metal employed for that purpose. Thus, when gold is used, it is termed gilding ; when copper, coppering ; silver, silvering, or silver-plating, &c. In every one of these cases we have to be careful that the two metals adhere, and for this purpose we take means to prevent any film of air, oxyde, or any non-conducting substance, from remaining on the first plate, as that would cause a separation between the metals. We apply heat, we scour the plate, or where it is possible, we slightly act upon the surface of the metal to receive the new deposit, taking care thoroughly to wash the metal after this operation.
(193.) Electro-gilding is, in most cases, remarkably easy,
Mr. Brayley, librarian to the London Institution, has been so kind as to call my attention to a process for elcctro-jdlding practised Bmgnatelli, an Italian c h e m ist, and noticed in the Fkilog, Mag, (First SerieiX 1S05, voL xxi, p. 187. It is nngnlar that one of Uie supposed novelties of oar own petiar time should be dtsoorered to be upwards of forty years old, a ctrcumsuiice which we most more fully notice whm treating of the histoty of electro-metaUmgy.
Electbo-Oilding.
for if care be taken to follow the laws which have been already detailed, it will be attended with very little trouble. The metal to receive the gold, may be either platinum, palladium, silver, copper, carbon, gold itself, or indeed almost any other metal, when the auro-cyanide of gold is employed. The surface should be chemically clean, and freed from adherent air, either by plunging it into nitric acid or a solution of potash, or by heating it and then quenching it in acid. The smoother the surface, the more favourably the deposit will take place upon it, for a very rough surface is not quite so well adapted for these operations, the hydrogen having a greater tendency to be evolved from it. When the metal to be gilt does not decompose the solution of gold, the solution may be stronger. When, on the contrary, the metal acts upon the solution, it must be weaker. The electrical current must be suited to these varying circumstances, aqd in general but a feeble current is required.
Pursuant to the plan I have already laid down, the best process in each respective department of electro-metallurgy will alone be detailed; and those who desire to use other solutions or other processes, are referred to the second book of this work, in the four chapters of which he will find such information as will enable him to make the alterations he desires with profit and success.
(194.) For all cases of electro-gilding the auro-cyanide of potassium makes by far the best solution. It is scarcely decomposed by any metal. It may be prepared by digesting oxyde of gold in a strong solution of cyanide of potassium, but its mode of preparation has been amply detailed when treating of the redaction of gold. For our present purpose, a strong solution of the salt is to be preferred, and, from the corrosive nature of the cyanide of potassium, it should always be placed in a glass vessel. For gilding, it would be folly, nay, almost madness, to use any other process than tiic
Electko-Gildikq.
battery, of which the single-battery process will answer every purpose where time is not an object, and is indeed as a general rule to be much preferred ; but if great is required, the compound battery made of two, three, or four batteries must be employed, or more cyanide of potassium must be added to the solution of gold. The size of the battery need never exceed the size of the object to be gilded, though if it be larger, it will not be of any material consequence, as a strong obstacle to the passage of the current is situated at the positive gold pole. The positive pole, os a general rule, should consist of a piece of pure gold flattened, and the part exposed to the solution should not exceed the size of the object to receive the deposit.
Every portion of the object on which we are desirous to have no layer of gold, must be coated with tallow, wax, or any other non-conducting substance, the presence of which will prevent any deposit from taking place on those parts. In this way, an object may be coated to any desired limit, or upon any circumscribed parts of its surface, as, for example, drawing or writing thereon. The rapidity of the process may be regulated to the greatest nicety by placing more or less of the positive plate of gold in the solution, by which means, as in other cases, the quantity of electricity passing may be regulated with the utmost precision.
The time occupied for the process must vary according to the amount of electricity passing, and the quantity of gold required to be deposited ; but the thickness of the deposit can at any time be learnt, either by ascertaining the additional weight it has received, or by the reduction which the positive gold pole has suffered.
To conduct tliis elegant process with the greatest economy of time, the quantity of electricity should be so regulated to the strength of the metallic solution, tliat the hydrogen is kept below its point of evolution from the negative plate i for we must always bear in mind, that evolution of
Silveb Oe Coppeb-Gildino.
hydrogen is attended with evil, as the precipitate will then be in one of the finely-divided states or even as a black powder.
During the process, particularly if the object have a rough surface, it is a good plan to remove it from the solution before the completion of the process, and rub it with a hard brush and a small quantity of whiting or rotten-stone, and well wash it ; by these means, any finely-divided metal will be removed, and the gold will be precipitated in a very even manner. This cleansing is not required when the deposition takes place very slowly from the auro-cyanide of potassium. The colour of the gold, if the precipitated layer be very thin, will be a greenish yellow, but when thicker it will be the natural colour of the pure metal.
The state of the surface of the reduced gold varies with the rapidity of the process, in relation to the strength of the metallic solution. If reduced very slowly it will assume the beautiful frosted appearance of dead gold. If deposited more rapidly the surface will have a brighter appearance. If still more rapidly the surface will again begin to be brown, and quicker than this the operator must not conduct his process ; for then the spongy deposit begins, which the electro-gilder should shun as the very bane of his art.
All objects of silver may be readily gilt in this way, and objects of copper as great facility as those of silver. Some suppose, and, perhaps, with good truth, that copper articles require less gold than silver ones ; the silver when heated having the property of taking into itself a certain portion of gold. However, copper is more difficult to bring into a thoroughly clean state than silver, especially in deep crevices. For those cases it is better to plunge the copper article into some acid solution of a metal which it can spon taneously reduce; for instance, into dilute sulphuric acid, containing a trace of either nitrate of silver, chloride of platinum, palladium, or gold, the object of which immersion
An imperfect layer of gold betokens imperfection in the cleansing of the object before immersion. Electro-gilding is applicable from the finest platinum wire, to any object, however large ; and no doubt the dome of St. Paul's could be gilt as readily as a silver tliimble, if any person could place it in a proper apparatus.
Whatever be the object to be gilt, it is highly important that every part should be entirely immersed in the liquid, or else, that part at the junction of the air and water might be liable to be rapidly dissolved.
The extent to which gold is applied to silver and copper articles is very great, and no variation is required in the process, except in those cases where the object itself may form s decomposition-trough — as silver vases, the bowls of large ladles or spoons, where it is only necessary to fill them with the solution of the auro-cyanide, which in this case, should contain no free cyanide of potassium; connecting them by means of a wire with the zinc of a battery, and
Steel-Oildiko, Etc.
inserting a plate of gold in connection with the silver of the battery in the interior of the solution taking care not to allow the gold and vessel to form a metallic contact; but even in these cases it is far better to immerse them entirely in the liquid for reasons before stated. All these cases of gilding appear to be rather for appearance and beauty than utility ; but sodietimes metals are coated for the protection which the coat of gold affords : thus the hair-springs of chronometers have lately been gilt by this process, and patents have been taken out for its application — a circumstance to be more fully considered when treating of the history of electro-metallurgy. The gilding of iron and steel only differs from gilding silver and copper in the necessity to be careful to overcome the difRculty which occurs in most thoroughly cleansing the iron. It should be plunged into dilute sulphuric acid, and allowed to remain for a short time in that fluid before being immersed in the auro-cyanide ; and if we wish most thoroughly to protect the metal from the action of extraneous causes, a tolerably thick layer of gold should be used. I am informed that the application of heat to the auro-cyanide favours the adhesion of the metals.
Some years ago the attention of engravers and etchers was directed to the application of gilt copper-plates for their art, instead of plates prepared with the biting ground, 08 now employed ; but a difficulty arose in coating the surface so thoroughly as to* resist nitric acid in every place, except where, by the aid of his etching instrument, he cut through the gilt. It is not improbable but that electro-gilding might be now employed for this object, and, indeed, I recollect seeing the fact mentioned in one of the Journals, but I am unaware whether it is at present practically carried into effect.
Cliches and objects of lead, tin, and pewter, are rather difficult to gild in the same way, because their surfaces, although scraped very clean, seem to become coated with
Gold Colouring.
23
an insoluble cyanide which prevents a good cohesion. It might, perhaps, be a good plan to coat the surface with Uie slightest layer of copper by immersing it in verdigris dissolved in vinegar.
The electro-gilder will occasionally find that his salt will get into a very inactive state, apparently without any cause. The subject is deserving further inquiry, but I would venture to assert, from facts that have come to my knowledge, that it is owing to the absorption of oxygen, either from the atmosphere or at the positive pole of the trough. This circumstance, therefore, should at any rate be avoided, by leaving the solution when not in use as short a time as possible in contact with the air, and by increasing the size of the positive gold pole when we desire a large current of electricity to pass, rather than increase the series of batteries. The same observations apply to all the mctallo-eyanides, for even the yellow ferrocyanatc of will become partially changed into the ferrosesquicyanurct by long exposure of its solution to the air.
After any object is gilt, it is usual to colour it, by which much is added to its richness. If we wish simply to give the gold a darker colour, the following process is said to be well adapted : two ounces of alum, tw'o of saltpetre, and half an ounce of sal enixum are well powdered together, and placed in a pipkin with four or six ounces of water, and warmed over a fire ; into this, one ounce of what is termed gilders'-wax is placed, which is to be dissolved and gently simmered. The mixture must be allowed nearly to cool, when the object is to be plunged into it two or three times, and then withdrawn ; the oftener the process is repeated the deeper the colour of the gold. It is then to be well rinsed in cold water and brushed with a nail brush. A green colour is said to be given by soft soap and alum. By the electric current alone, the colour of the gold may be varied considerably by variations in the quantity of electricity
286 Bukkishin6.
in reladon to the strength of the metallic solution. In fact I haye observed gold of every colour reduced from the aurocyanide and even other solutions.
In many cases the object as soon as removed from the precipitating trough, has only to be well washed in soap and water, when it is quite fit for use; and in this state presents the appearance called dead gold. Sometimes the operator is desirous of having his object bright, either entirely or partially, so that the bright and dead parts may form a contrast with each other. In this case the object is dipped into a solution of soft soap, to which a little prussic acid is added, thoroughly to cleanse It, when an instrument called a burnisher (b), which is nothing but a bright piece of steel, the shape of which is suitable to the object to be burnished, is rubbed over it two or three times, and finally the process is completed by a bloodstone fixed upon a handle. The operation of burnishing, is generally performed by women ; and it is indeed remarkable that they should have learnt the use of prussic acid for cleansing gold, which has been employed for many years, especially when we consider that the fact was not known to chemists at the time. It is worthy of remark, that the solution of soft soap and prussic acid is admirably adapted for cleansing trinkets and all articles of gold when they have become dirty.
(197.) The process of gilding by galvanic precipitation from a solution of gold, is very different in its effects from the method formerly patented by Elkington, termed watergilding ; by the latter process the metal which is to be gilt is dissolved in an equivalent proportion to the gold deposited* and therefore as soon as a mere surface of gold is obtained, it has been supposed that no further deposition can take place; but when the gilding is effected by the galvanic
Fig. 35,
Hr. Cooper, howerer, in an admiraUe lecture delivered at tlie Bojal lutitatioii, itated that this optnkm is nnlbonded, and that anjr Infer of gold might be deposited bjr this procem. His assciticKi shows that thia mode of gilding most be more or less imperfect, otherwise the oopper or ailrer wo be pierented, hf the coating of gold, from ftuther aetton.
ELECTRO-PIATINATma.
itself from this powerful agent. It is a sad matter of notoriety, that as soon as the workman becomes the prey of the disease caused by following his business, the master dismisses him as an unprofitable servant, and casts him off as worthless dross.
A comparison between the durability of gilding by the galvanic process, with that by the other methods, can only be made after the lapse of a considerable period ; I find, however, that some spoons and other articles which I gilt by the battery, wear extremely well. The thickness of the deposit can be regulated with the utmost accuracy, from the thinnest possible layer to a coating of an inch in thickness.
Electro-gilding appears not to be generally applicable for non-conducting substances, for I have not at present succeeded in applying the gold to any extensive surface, although I have seen it grow, for a short distance, over blackleaded sealing-wax. Perhaps by using the strongest solution of gold, it may be possible to gild surfaces in that way.
Electro-gilding is generally an advantageous process ; for the value of the materials used is trifling. It can be, however, repeated at pleasure ; and probably an article could be nearly twice as thickly gilt by electro-metallurgy, at the same cost, as once by amalgamation, on account of the waste of gold and mercury, which always ensues in the latter operation.
(199.) Platinating metals by the galvanic current, is anew feature in science. The process is similar in all respects to gilding, but is more difficult. The best solution to be employed is the nitro-muriate of platinum, to which sufficient soda is added to render it neutral. The object to be coated should be smooth, and thoroughly cleansed by potash before the process is commenced. Having proceeded thus far, and the solution of platinum being ready, a fine platinum wire, in connection with the silver of a compound battery, must be placed so as to dip into the solution, but must not be immersed beyond a very short distance. The olyect to be pU-
Sxectbo-Platinizino.
tinated is now ready for connection with the zinc of the battery ; after this is effected, it is to be dipped in the solution. {Fig. 23.) Immediately, oxygen gas will be given off from the platinum wire, in connection with the silver. From the copper or other metal to be platinated, no gas will be evolved, provided too much electricity be not generated. In a few minutes the object will bo coated with platinum.
This process must not be confounded with that by which negative metals are prepared for my battery ; for, in this case, the platinum is precipitated of the colour and appearance of platinum but in the latter case it is thrown down as a black powder. The first process I propose to name platinating in contra-distinction to platinizing. To platinize metals, wo use a strong current to throw down the metal in the black powder; to platinate, we may employ solutions of any strength, but we must use more moderate currents, so that the electricity is insufficient for the production of hydrogen.
An attempt has lately been made to form my battery of platinized lead* as a substitute for platinized silver, but with only partial success. Before publishing an account of the battery, I tried lead, and even all it alloys, as solder, pewter, type-metal, fusible metal, &c., together with most other metals and alloys usually met with in commerce, but was very ill satisfied with the result; for many parts of the surface soon become imperfect from a deposition of sulphate of lead, independently of the imperfectly-conducting nature of the lead itself. I tried to obtain lead plated with silver, but did not succeed, being informed that the two metals would not roll together. Now, however, that we can silver
Perhaps platinised lead scarce possenes more than ludf the effeettre smiace platinised silver does ; but it is a fact very difficult to ascortain, being the (lA) of my equation, which is by no means equal to Uie work performed when the battery is connected with a voltasneter, becaoie
Electro-Platinatiko*
lead by voltaic electricity, it perhaps might be employed ; or we may palladiate the metal by simply immersing it in a dilute solution of the nitrate of palladium, and then platinize it. Upon the whole, perhaps, platinized lead is better discarded, unless silvered or palladiated, especially as we can always make a cheap battery of platinized iron if we want a battery of large surface to last a short period, and platinized plumbago, charcoal, or even cinders are preferable to platinized lead. To sura up in a few words my experience in the construction of the battery : — it is preferable that the finely-divided metal should be either platinum, palladium, or iridium, the first being beat ; and the metal to receive the deposit platinum, palladium, gold, silver, carbon, or iron, which are preferable ; then follow tin, lead, and their several alloys, together with those of antimony and bismuth ; whilst zinc, cadmium, copper, are the worst of all the metals.
A cheap metal or alloy for the reception of the finelydivided metals, that would not undergo the slightest change in dilute sulphuric acid, would be hailed by electro-metallurgists as a great boon ; perhaps some compounds of silver, zinc, and nickel might be discovered applicable for this purpose.
Specimens of electro-platinating which I have prepared by this method, will not resist the action of nitric acid, because there are generally some little fissures uncovered, some little crack which, admitting the nitric acid, tears oft the platinum in thin scales. It is not applicable to rough surfaces, as it is preferable that the surface for its tception should be smooth. The colour of the metal thus reduced is so similar to polished steel, that it would be difficult to distinguish the one from the other. It is needless to say that it has a beautiful appearance. It would be of great value as a sMbg for telescopes, microscopes, quadrants, and a hunmiier artides which most be exposed to the action of
Elkctro-Silver Plating.
(200.) To palladiate articles> wc adopt methods similar in all respects to those used in platinating them. We employ the ammonio' muriate of palladium dissolved in liquid am> monia, and employ the compound battery process with a small positive platinum pole. The palludio-cyanide of po* tassium with a palladium pole may also be employed. This metal is whiter than platinum, but not so bright as silver. It might be used in the same cases, and with the same advantages, as platinum ; and we have, besides, twice the bulk of metal in the same weight.
Palladium adheres w'ith such firmness to copper, when reduced by voltaic electricity, that it is almost impossible to remove it when once deposited. It might be worth while for caeperimenters to ascertain how far it might be employed for the protection of iron or steel.
(201.) There is no process at the present time more readily conducted than electro-silver plating. The best solution which cun be used is the nrgento.cyanide of potassium. It is generally by boiling the oxyde of silver in a strong solution of cyanuret of potassium. The process which is most fu\ durable is the single battery. The solution should be placed in a gla.ss vessel, and used with a silver positive about the same size as the object to be silvered. The same precautions should be taken, and the same measures observed with regard to plating as gilding. The object should be clean, in order that a most |>erfect adhesion may be effected between the object to be silvered and the reduced metal. The silver will be thrown down in somewhat difierent states, according to circumstances. If thrown down very slowly, it will assume a beautiful dead appearance ; if still more rapidly, it will be brighter. It is, perhaps, as well to use the solution as strong as possible, and take care to stir the liquid occasionally, in order tbi a proper difiusion of the metallic salt may take place. As a precipitating trough, either the vertical or horizontal may be
H
Electro- Silver Plating.
employed according to circumstances ; the latter is to be preferred for large surfaces, as waiters, and similar objects ; in which case a corresponding large plate of silver should be used as the positive pole, and placed over the object to be silvered. Sometimes a large circular silver positive pole may be made to surround the object. The silver positive pole is to be connected with the silver plate of a battery, exposing nearly as much surface as the object to be plated, whilst the object to be plated is to be connected with the zinc. A little free cyanuret of potassium, added to the argento-cyanide of potassium, hastens the process by increasing the solubility of the positive pole. The quantity of metal reduced can be readily ascertained, either by finding the additional weight of the object receiving the deposited silver, or by ascertaining the deficiency of the positive pole.
At the present time all electro-silver platers take advantage of the peculiar qualities of bisulphuret of carbon, for causing the metal to be deposited quite bright, as described when treating of the reduction of silver ; and so perfect is the method now adopted, that they are enabled to perfect articles for sale, without polishing, scratch-brushing, or other operation.
Electro-plating is now most extensively carried out, not only for every legitimate kind of business to which plating can be possibly applied, but also, I regret to state, for the bad purposes of false coining. The forgers purchase the britannia metal spoons and melt them to form a fac simile of tlie coin. But the greasy feeling of lead would lead to instant detection, and hence they cover the surface with a very thin film of silver. The cheat may be detected by the coin being about one third lighter ; also, on being rubbed between the fingers, they give ofl* the peculiar smell of the cyanide of potassium, and if touched with a drop of strong nitric acid, the silver comes off, and a black mark is produced. A vast number of these coins are in circulation, made so well that.
ELECTRO* SI LVEn rLATINO.
ringing as perfectly as the ill-struck coins of the Mint, they may readily deceive the casual observer. Tlio coiners are continually convicted and transported, but new ones arise to carry on the illegal process. If these men would but make medals by the same process, to sell at a cheap rate, they would earn good wages, and be valuable members of society.
Plated articles may be either partially or entirely burnished in tlie same way ns gilt objects, according to the fancy of the operator ; and the contrast of di'ad silver with the bright polished metal much increases the beauty of the object.
Copper and its alloy are most readily silvered by this process, but lend do<!8 not take the metal so freely ; it does indeed become coated, but the two metals have not generally n firm adliesion, because the lead, although made perfectly clean, becomes in part coated with an insoluble cyanide immediately it is irninersed in the solution. Perhaps the best mode of remedying that would to reduce a thin film of copper upon the object by immersing it in verdigris disftoUed in vinegar, or by touching it with a solution of the nitrate of palladium, by which a slight film of metal would be reduced.
Now conducting substances can be silvered by first blackleading them, then attaching a wire in such a way as to come in contact with the plumbago. In this case we siiould be careful to use rather a larger plate of silver than the object, as that favours the growth of the metal, but as a general rule it would be preferable to coat the object first with copper and then silver it.
(202.) The mode in which articles are plated independently of electro-metallurgy, is very difierent from the one now used. It is customary to take an alloy of silver and copper, about the standard used for coining, and to solder it on a bar of copper. This bar is then rolled out thin, by
Electbo-Silver Plating.
which means, as the two metals extend equally, the silver forms an exceedingly thin covering. This plated metal is then, by hammering, formed into the required shape, and soldered to other parts. The handles and edges are made of thin silver rolled to about a square foot to the ounce which is first embossed with a die, and then the hollow parts are filled up with solder. These steel dies at some manufactories have* cost alone many thousand pounds. Now, although the silver on plated articles is so exceedingly thin, it is astonishing, if the goods are well made, as Sheffield goods usually are, how long the thin coat lasts. Tliis excellent result is owing to the compression and hardening that the metal undergoes during the process of rolling. In this respect it is superior to electro-plating, but the process can never be repeated, whilst electro-plating may be performed any number of times.
Electro-plating is of considerable advantage to the operator, for articles may be made entirely of copper, and even finished with laborious minuteness, and then silvered. The probability is, however, that electro-plated articles will not wear quite so well, in proportion to the thickness of the metal, as ordinary plating, for all metals reduced by electricity are found not to resist attrition so well as rolled metals. Electro-silver plating is a cheap process, independently of the intrinsic value of the silver used. Electrosilver plating is now most extensively employed to cover spoons and various other objects, even such os formerly I should hardly have considered adapted to be the subjects of the process ; and it now forms an important branch of manufacture.
(203.) Metals may be covered with nickel, by proceeding as in the former cases. The solntion to be used is the chloride of nic||6l, with a nickel positive pole. The singlebattery process is to be preferred, bat pure nickel though very brilliant, is apt to be rather brittle.
Electko-Coppkring.
24o
(204.) Various substances, both metallic and non.metallic, maj be coated with copper by the agency of the galvanic current. The various solutions to be employed, and the apparatus to be used, have been already fully described, when treating respectively of electro-metallurgic apparatus, and the reduction of copper. As a general rule, the single battery apparatus is to be preferred, and an acidulated solution of sulphate of copper, as the salt from whence the reduction of copper should be effected. The solution given before is well adapted for a smooth deposition of metal, but it must contain more metallic salt when we desire the crystalline deposits. The advantage of its application relates principally to non-metallic substances, which may, in this way, receive a metallic surface of pure copper. Not the slightest difficulty would attend the coppering of almost any metal ; and it is a process which is frequently used in the arts.
(205,) Coppering non-conducting substances may be divided into two departments ; the first of which contains those which require the deposit to assume, as nearly as possible, the form of the original substance ; the second comprises those cases where the deposit is desired to be in a crystalline state.
A somewhat different arrangement is required in each instance; for in the first, the battery and solution must be so arranged that the hydrogen is near the point of evolution ; but in the second, the solution may be much stronger, and the quantity of electricity may be increased by increasing the size of the battery, and the surface of the positive copper pole in the decomposition apparatus.
(206.) In the first division we have delicate substances, such as medallions, &c. The substances of which the cast is made should be rendered most thoroughly non -absorbent by the processes already described. For this purpose the medal must be boiled for such a time in wax, stearine sper* M 3
Electro-Coppering.
maceti, or tallow, till it becomes translucent, or semi-transparent. It is then to be brushed over with black-lead, and at the edge a very fine copper wire is to be once twisted, in order that perfect contact may exist between the battery and black dead. It is now ready to be placed in the solution of acidulated sulphate of copper, the end of the wire having been first connected with the zinc of the battery. After this has been done, the last thing is to place a piece of waste copper in the solution, rather larger than the cast, and to connect it, by means of a wire, with the silver of the battery. Action will immediately take place, the copper will be dissolved, and the metal precipitated on the black-lead of tlie object, over the surface till the wliolc is covered. It is as well, perhaps, to use a large positive pole of copper and a small battery, so that the decomposition may take place very slowly, which causes the surface to assume a delicate matted appearance. In some cases we may use two batteries arranged as a series for this purpose, as that will ensure more rapidly the uniform spreading of the copper over the medal. The medial must not be left in long after it has been coated, as that will detract much from its sharpness and beauty ; after it has been taken out, it may be rubbed over with coarse paper to remove any little asperity that the copper may have thrown up. To the numismatist this process will appear barbaric, as he would consider that it would detract from the beauty of the medal ; but though decidedly detrimental, it is not so injurious as might at first sight appear; because as the copper is of nearly uniform thickness all over, the effect is to increase in size the whole design. By the sculptor and architect, perhaps, it might be used with advantage to coat statues or other ornaments. In all these cases it is advisable to coat not only the front but the back of the object with tlie metal.
Small statuettes of plaster or wax are now frequently covered with C([>er, and are nearly as beautiful as bronze.
Electro-Coppered Fruit, Etc.
In these cases the whole success of the process depends upon so thoroughly boiling the plaster of Paris cast, that it shall totally lose its power of absorbing water, or otherwise some of the metallic solution will enter into its pores, and in process of time will surely crystallise and thrust off the coating of copper. Many of the most lovely electro-coppered medallions which I formerly made are now totally destroyed from this cause.
At the present time gutta percha has come to our aid, and already electro-coppered gutta percha inkstands and other articles arc sold. This alone opens a wide field of extending art into the ordinary manufactures; and the time must come when the manufacturer will only succeed when he adds the taste of the artist to the knowledge of the chemist. Chemists occasionally protect their retorts and glass vessels by covering them with copper. For this purjiose the glass is varnished and covered with gold leaf or plumbago. This vessel is then attached, by a wire, to the zinc of my battery, and a large positive pole surrounds the object to be coated. This positive pole is converted to the platinized silver, when, after a certain tiioo, a sufficient deposit ensues.
(207.) A pretty application of the art of coppering is suitable to horticulturists, as by its means, fruit, vegetables, leaves, seeds, and various other sfiecimens may be coated with copper, either for ornament, or for the purpose of illustrating the size, form, and other peculiarities of the object. Apfiles and pears may be very readily coppered ; tliey are to be brushed over with black-lead, and then a small pin is to be thrust in at the stalk ; to this a wire should be attached which is connected with the zinc of the battery. It may then be placed in the solution, and the whole arrangement completed by the insertion of a piece of copper, which is to be connected with the silver of the battery. In a similar manner, cucumbers, gourds, potatoes, carrots, and a hundred other vegetable seeds and roots can be covered* The wood*
iStECTRO-COPPEREl) LEAVES.
cut esihibits a bunch of Portugal grapes submitted to the action of the duid to be electro-coppered. The form, after the process, is characteristic, and marks so strongly the individual character of each variety, that the horticulturist is at no loss to distinguish the specimens at once. The condition in which the copper is thrown down, can of course be varied according to the laws set forth in the last chapter. For ornamental purposes, the crystalline copper is the most beautiful i but for a specimen intended to illustrate the form of the object, the smooth copper is best adapted. After the objects are completely covered, the pin is to be withdrawn, which will leave a little hole, and that enables the evaporating juices of the vegetable to pass freely out, and thus promotes the complete drying of the encased object. A cucumber which I coated during the past summer, appears now to contain scarcely anything inside the copper, and the pears, apples, &c., consist of little else but the metallic coat. The botanist will readily perceive in what way this process may be employed for his advantage.
The beauty of electro-coppered leaves, branches, and similar objects, is surprising. I have a case of these specimens placed on a black ground, which no one would take to be productions of art. In the same room with them are a couple of those cases, in which Ward has taught us to grow in this smoky metropolis some of the most interesting botanical specimens. In these cases are contained varieties of fairy-formed adiantums, verdant lycopodiums, brilliant orchidess, rigid cacti, and creeping lygodiums, all growing in their natural luxuriance. The electro-coppered leaves, however, are beautiful when placed by the side of the productions of this miniature paradise ; and when I state that the numerous hairs covering the leaves of a melostoma, and even the
Electro-Coppered Baskets,
delicate hairs of the salvia are all perfectly covered, the botanist must at once admit that these specimens have rather the minuteness of nature than the imperfections of art (208.) A beautiful effect of metallic surfaces may be obtained by the deposition of crystallised metal on baskets. The wicker-work must be black-leaded, and connected by means of a wire to the zinc of a galvanic battery ; when on being immersed in the metallic solution, and the circuit completed, it will be covered with the most beautiful crystals of copper, spai'kling in the light from the facets of thousands of little crystals. It is as well to puss a very fine copper wire round several parts of the basket, so that it may toucli the blacklead in several places, for this will insure the coating being more ra[)idly complete. Any other mode of giving a conducting surface will answer equally as well as black-lead. The pole for these objects should be very large, and a scries of two or three batteries employed. The solution of sulphate of copper should be perfectly concentrated, for all these circumstances will tend to render the copper crystalline. Baskets thus prepared, and filled with metallic fruit, leaves, insects, &c., might be used as ornaments for the drawingroom, and would greatly exceed in interest the usual appendages; for if these objects were made by the individual who possessed them, it would show his interest in the noble science of galvanism ; and if they were purchased, it would be the means of encouraging the application of this powerful agent, to the arts and manufactures. It is now, indeed, but a small germ, but will doubtless become a vast tree, which by bearing fruit will cause a mighty revolution in many manufactures. Let the attention of the wealthy be directed to the subject ; let them patronise ornaments made by these means, and then speedily will the artizan become more perfect in his work, and the galvanic fiuid will be as commonly used as steam or gas. 1 particularly dwell upon these circumstances in this plac because most coppered objects are exceedingly beau*
The foregoing electro-coppered objects are trifling compared to the purposes to which electro-coppering has been tried ; for actually, experiments have been made to cover the bottoms of ships with that metal. There are two or three experimenters who lay claim to the first idea of the invention ; one of them is Mr. Hays, a distinguished practical chemist of Portsmouth, and experiments have been tried at the dock-yard at Portsmouth upon the subject ; Mr. Hays, first coats tlie bottom of the vessel with pitch, thoroughly black-leads it, and then attaches wires as a medium of communication with the plumbago, and the zinc of a very large battery. The vessel is laden with ballast till it sinks as low in the solution of acidulated sulphate of copper as it is desirable that the copper should extend. The solution of the metallic salt is placed in a suitable reservoir, and a large positive pole, composed of sheets of copper, is attached to the silver of the battery, which completes the arrangements. In this mode of proceeding the negative pole being above the positive, a proper diffusion of the newly-formed metallic salt cannot take place as readily as could be desired, and it would be attended with much trouble to turn the boat over, so that the positive pole might be arranged over the bottom of the boat ; especially, if it were a first-rate man of war. In all large commercial operations, the expense becomes the most important consideration, and I am afraid that in this case, the cost of the reduction of copper when added to the labour required for the process, will not at all compensate for the additional time that the reduced copper would last over the copper sheathing as usually employed.
. (209.) Earthenware, or any other similar substance can be
Electbo-Tinnino Eincing, Etc.
coated in like manner with the metallic copper ; but when these smooth surfaces are to be covered, some difficulty arises, which may be overcome by the previous application of a very little varnish. In this way, by coating a jar or gutta percha cell with copper, copper batteries are frequently made.
Electro-coppered objects may be gilt, silvered, or coated with other metals. Crystalline objects, however, are more beautiful in their cupreous chai*acter j though smooth objects, as leaves and fruit, are very beautiful when gilt. Electro-coppered objects, when silvered, are not so striking as either of the other two, and this on account of the dull whiteness of the silver.
(210). Metals may bo coated with nearly every other metal besides those I have so fully described. Some of these metals are found to be much more troublesome than others, and some will only give an irregular coating ; yet, by following the principles explained in a former book, any metal may be thrown down in the reguline state, with more or less success.
(211.) Electro-tinning is a process which, whether considered in its difficulty, inefficiency, inutility, or expense, is equally disadvantageous. To obtain a thick layer of tin directly by electricity, would be extremely difficult ; and although a thick layer may be readily obtained by depositing either crystalline or spongy tin, and then fusing it, 1 cannot see that any advantage is likely to accrue from such a proceeding. Perhaps the sulphate of tin is the best solution that can be used for this purpose, conjoined with the single battery process.
Electro-leading is a process equally unfavourable in its results, as electro-tinning. The iris-nitrate of lead makes perhaps as good a solution as can be employed for this purpose.
Hectro-zincing is not attended with any great difficulty ;
Electro-Ironing, Etc.
the metal may be readily reduced from the sulphate, made as neutral as possible. The single battery apparatus should be employed with a zinc positive pole ; any metal may be used to receive the deposit, taking care to employ it very clean, and the smoother it is, the more favourable will be the result.
Metals may be readily coated with a beautiful deposit of iron, by using the proto-sulphate, or neutral chloride of iron Tlie single battery process with an iron positive pole is best adapted for this object.
The facts in this book are generally new, and their application is extremely interesting ; for to those who follow galvanic science as an amusement, the exercise of the arts of gilding, plating, and coppering, will not only be interesting but useful ; in the arts doubtless they will assume a higher importance, and add new branches for the successful application of electricity. Those who are desirous of following these processes as a business, will find that practice alone will make them perfect ; and as the scientific man details the principles to be pursued, so the mechanic must follow these laws, and regulate the details as his extended experience may dictate.
Book The Fourth.
On Vauious Applications Of The Reduction Of Metals By Galvanism.
Chapter 1.
On Tue Multiplication Of Coins And Medals.
Value of Eleotro-Mctallurpy for the numismatist, 212. Mode of obtaining the mould, 213. Directly by the voltaic current, 214. By lead, fusible metal, &c., 2 1 5. By non-conducting substances, 2 1 6. Metallic duplicates of gold, 217. Silver medals, 218. Medals of platinum, 219. Copper medals, 220. I'rccautions to be token to prevent air-bubbles, 221. Apparatus to <ycd, 222. Single-cell a{>paratuH, 223. Thickness of the metal, 224. Removal of the cast from the mould, 225. Zinc medals, iron medals, 226. Value of Electro-Metallurgy for medalists, 227. On the modes of making ]>erfoct medals, 228.
(212.) To the numismatist, the reduction of the metals by galvanism is of the highest importance ; for, on the one hand, it presents him with the means of having casts of coins or medals, which on account of their great rarity he could never otherwise possess, and, on the other hand, it orders to the coin-manufacturer the means of forging the more scarce coins, so that the collector must be doubly careful in making his purchases. At present, I am afraid that our art, in unskilful hands, has been the means of destroying so many medals, that no benefit which has yet accrued has been able to compensate for their loss.
(213.) There are three methods of taking the duplicate of a emo or medal By the first, a primary cast or an intaglio
Modes Of Making The Moulds.
is made in metal, directly by the galvanic precipitation ; by the second, a metallic cast of the medal is first obtained, either in fusible, type, or analogous metals ; and by the third, we make the intaglio cast in some non-conducting substance, as white wax, sealing-wax, &c.
(214.) To take a primary cast at once from the medal or coin should not be attempted by an inexperienced hand, and never by any one from an unique specimen, for fear of any mischance. The process, however, is and very valuable, when we desire an absolutely perfect intaglio impression of any coin or medal. The object to be is to be coated, on the side where we do not require action to take place, with grease, wax, varnish, or other non-conducting substance. A fine wire is to be round the rim, and then it is ready to be placed in the metallic solution. The adhesion of the air to the metal is of considerable importance in this case, and the metal should not be allowed to remain a single instant in the solution before the galvanic circuit is completed.
The obverse and reverse can be copied by two operations, or even both by one, taking care to grease the rim, so that the whole medal may not be confined by the new deposit. This operation gives us two moulds, one of either side of the coin or medal, in intaglio. By this process a copper medal or coin is liable to hove its bronze removed, and, perhaps, it is a good plan always to remove the bronze of the medal before immersion, by cleansing it with oil of turpentine ; but a gold or silver one will not suffer the slightest injury. This mould may be used for making plaster-casts, sealing-wax impressions, or it may itself be again used as a mould to receive the galvanic precipitate, and we may thus obtain a very perfect relievo copy of the original
(215.) Intaglios may be taken off coins or medals in lead, pewter, fusible metal, tin foil, or silver-leaf in the manner pointed out in the preceding hooks, and these intaglios are
Moulds For Coins.
then to have a wire either soldered or placed in connection with them, when they will be ready for the reception of the metallic precipitation. (134, 135.)
(216.) The third method, however, is the one which should generally be adopted ; for by non-conducting substances we can obtain most excellent moulds for receiving the precipitation. For coins, very small medals, and cameos, impressions in good sealing-wax are to be preferred by tlie amateur. (131>.) These must have a fine wire melted into the wax, and be black-leaded, and then they are ready to be copied. (144.) At the present time on gutta percha we most chiefly place reliance, as for all these purposes its properties are invaluable.
Larger medals may be copied in wax, stearine, bees'-wax, and rosin, or plaster of Far is. Tlie plaster of I'aris must be rendered non-absorbent by any of the processes given in a former book ; tallow or spermaceti are best adapted, and from their being always at hand, are to be preferred ; they are then to be blackleaded, when they may be placed in the solution. By cither mode, perfectly sharp medals may be taken. To the workman who requires to make a large number of metallic impressions of coins, I would recommend the use of a square piece of plaster or gutta percha of any convenient size, say six inches each way, with impressions of medals as thick as he can put them. This might be easily managed by joining separate plaster moulds together till the size is obtained; this piece must be filled by the processes given before, black-leaded, and lastly, the metal is to be thrown down upon it. By this means he will obtain a sheet of coins, which he may either retain in that form, or by cutting them out may have each separately. The copper thrown down upon plaster or gutta percha is quite as perfect as the original cast.
(217.) Having determined upon the process to be adopted, the operator has next to decide of what metal he will make
SILVER 'feLECTRO-MEDALLIONS.
his duplicate. To make a gold medal, perhaps the best solution on the whole would be the auro-cyanide ; because it allows the use of a great many kinds of metals as the negative pole. The modus operandi is similar in all respects to that of gilding ; the only difference would be, that the deposit should be allowed to be a great deal thicker. I am doubtful whether non-conducting substances could be employed in this way.
A very useful mode of the application of gold would be, first, to throw down only a moderately thick layer, and then to fill up the deficiency by throwing down copper upon it. This, to the false coiner, might form a valuable piece of information ; but is here mentioned to put people on their guard.
(218.) Silver electro-medallions require a more attentive description than gold ones, because the silver is of less value, and the process is easy to conduct. Silver electromedallions may be made from every variety of mould — metallic (even iron) and non-metallic — that can be employed for electro-metallurgy generally.
For all metallic moulds but little difficulty occurs, except that adhesion must carefully be prevented. There is but little fear of adhesion of the new metal to iron, steel, or lead ; but to copper, silver, and some other metals, there is some risk, from the corrosive nature of the solution of silver ; perhaps an infinitesimal layer of some greasy compound might with advantage be employed over the mould : that is, the smallest quantity of that substance might be rubbed over the mould, and then rubbed over as far os possible. The best solution of silver for these purposes is a strong solution of the argento-cyanide, though I have made medals from several other solutions. The single battery process is the best adapted, conjoined with a silver positive pole about twice the size of the object to be copied.
Moulds made of non-conducting substances are also well
Silver Electro-Medallions*
adapted for the formation of silver electro-medallions. The object has only to be black-leaded and connected by a wire to a battery about its own size, when the silver will gradually grow over the object, cover it, and become of any thickness the operator may require.
The quality of the metal thus reduced, if thrown down in the best reguline state, is very strong and elastic ; so much so that but a thin deposit w'ill suffice. Sometimes we are desirous of having the medal somewhat thicker, wliich may be accomplished in some cases (where we are desirous of being economical with our silver), by giving it a layer of copper at its back ; the only circumstance of which we have to be careful is, to cause a proper adhesion between the two metals by making the surface of the silver chemically clean before immersion.
Silver medals are made as readily as copper ones, the only extra difficulty being first to get the pure silver ; for every electro-metallurgist will not like to pay six shillings an ounce for this substance to make medals, independently of the cost of the mould and galvanic power derived from the battery ; the latter, howe\ cr, in this case, would not amount to a penny an ounce.
The surface of the silver is quite bright when it is removed from bright moulds ; when removed from non-mctallic moulds it is apt to be discoloured with plumbago: in which case the surface should be rubbed with emery or fine charcoal powder and a hard brush, and finally polished with a soft brush and rouge.
(219.) Medals may be made with great difficulty of platinum or palladium entirely, as in the cases just mentioned : or a duplicate cast of the medals may have an exterior of either of these metals, whilst the interior may consist of copper. Tlie mould for these metals should consist of either gold, platinum, palladium, or silver. The solutions may be of any strength, although the operator will
Coppee Electb0-Meda.Ll10Ns.
find the strongest the best adapted. See the general remarks on platinum, palladium, &c. (169 — 171.)
(220.) is tlje metal of most importance to numismatists, and it will answer like silver both for metallic and non-metallic surfaces. The salt which may be employed for ordinary purposes is the sulphate; and when used for this purpose the solution should be more concentrated than when the reduced metal is required for the electrotype. A saturated solution of sulphate of copper, mixed with one-third of its measure of dilute sulphuric acid will answer admirably for general purposes.
(221.) In making electro-medallions, we must be cautious that no bubbles of air adhere to the mould, or are carried down into the solution when the mould is immersed. This is very apt to occur when the mould is very deep, ns sometimes a series of air-bubbles may be observed adhering in the hair, the beard, or even the top of the nose ; a circumstance which would not a little impair the features of the copy. To prevent any occurrence of this nature, the medal should be inspected after it has been in the solution a short time, and any bubble dispersed. If this be not attended to, the bubbles would become quite encased with copper, and a little hole be left.
(222.) The battery process is without doubt the best for making medals, especially if large ; but the form of the precipitating trough must vary according to the size and form of the medals to be made. For very large medals, say six inches in diameter, a common earthernware basin is the best. The medal is to be connected with a wire, and placed fat at the bottom of the vessel, and this wire is to be connected with the zinc of the battery. A piece of copper is now to be procured, which must be somewhat larger than the medal above which it is to be placed in the basin. The peculiar form of the basin will of course prevent the copper from descending upon the medal, a result which is carefully
Various Processes.
to be avoided. This copper is to be connected with the silver of the battery. The solution is then to be poured into the basin, when action will immediately commence; the copper will be reduced upon the mould from the solution, and copper will be dissolved from the positive pole to keep up the saturation of the fluid. It is always necessary to employ a battery sufficiently large; twice the surface of negative metal is most favourable for precipitation, though by following the principles already given, any sized battery may be employed. For many medals the battery process is greatly to be preferred. In this case the vertical precipitating trough may be used. A piece of copper, connected with the silver of the battery, is placed in the middle of the trough ; and on either side, as many medals may be suspended as can be arranged opposite to the copper ; and these are all to be connected with the zinc of the battery. The advantage of this mode of proceeding above all others, is the facility given to the operator, either to remove or add one or more medals without any injury to the others; and eight, ten, twelve, twenty, or even a million, if he pleases, may be made at once.
(223.) Although the battery process is generally to be preferred, yet it does not follow that it is the only mode capable of being adopted. Electro-coins and medallions may be made by any process described in the first chapter of the second book; as the zinc single-cell apparatus, the iron single-cell, the tin or lead single-cell apparatus will answer for this purpose, and if the objects happen not to be very large, the operator will not find it material what process he adopts. The only general rule to be followed, in any case, is to take care tliat the sulphate of copper be concentrated, the positive metal sufficiently large, and the distance of the positive metal from the mould not too great. A Ihtle add added to the sulphate of copper, will generally improve the quality of the reduced metaL (107 — 113.)
Removal Of The Medal.
(224.) By any of these processes we can obtain a perfect cast from our mould ; yet if the device on the mould be very deep, the deposit will not always take place favourably on the deepest parts. In these cases, when the medal is nearly completed, we may remove it from the solution, wipe it dry, and coat the parts most thickly covered with any non-con* ducting substance. The medal is then again to be placed in the solution, when the deficiencies will be soon filled up.
Great thickness of copper is not required for medals ; for if it be as thick as a wafer, and of good quality, it will amply suffice. For most purposes it is of no advantage to have it thicker, and when we are desirous of strengthening the deposit, the back may be coated with sealing-wax. All these details must be regulated by the fancy of the operator, but by proper management the deposit obtained in twenty-four hours is quite sufficient for many purposes.
(225.) The last operation is the removal of the cast from the mould, which is attended with no great difficulty. We must be careful to remove any copper which embraces the mould at the edges, by placing the medal and mould in a vice, for which purpose a common wooden one answers admirably; then by filing the surplus metal from the edges, and pulling one from the other with moderate force, a separation will be effected. When the duplicate has taken place upon the original medal itself, the adhesion will be very slight, if the precautions are taken w'hich 1 have before detailed. Casta made from most non-conducting substances come off sometimes so readily that the mould is not the least injured. The adhesion, indeed, is greater when leaden moulds are used, yet, with care, the duplicate may be removed without much detriment to the mould, although it is generally slightly impaired. In every case some judgment is required to regulate 'the direction in which we make the pulling force, according to the manner in which the prominent parte are arranged ; for generally there is one way where the cast can
ZINC AND IRON ELECTRO-aiEDALLIONS.
be removed more easily than any other. To copper, &c., there need be no adhesion. (125.)
(226.) Copper electro-medallions may be gilt, plated, platinized, or coated with other metals, so that tliey may exactly resemble the original. The coating of* foreign metal in this case ought to be very thin for fear of injuring the sharpness of the cast.
Electro-mcdnllions may be readily made of zinc, by using a solution of sulphate of zinc, as neutral as possible, with a zinc positive pole, and connected with a battery of about the same size. Zinc electro-medallions possess no peculiar beauty. A metallic mould appears to be necessary in this case.
Electro-medallions might be formed of iron, by using a solution of chloride of iron, an iron positive pole, and a battery about the size of the negative metal.
Before we can understand the value of electro* metallurgy to the medallist, we must consider the processes he now uses to effect his object. Medals divide themselves naturally into two great classes : the first, which are cast and chased, that is, touched iij> afterwards, and the second division, which are made by a piece of metal being impressed with a steel die by a heavy blow given by an apparatus called a coining-press.
The first division of medals are first modelled in wax by the artist, from that wax impression a mould is made, and from that mould a cast in metal is procured. This cast is then touched up by the artist ; but, as each individual medal has to be touched up, absolute identity is destroyetL
For this class of medals electro-metallurgy will undoubtedly supersede the old method ; for the artist may take a plaster-cast from his original design, and make by electrometallurgy a perfect fac-simile. The metal-cast he may then touch up and bring to great perfection ; and be will be enabled to obtain any number perfectly identical with the first which he has so laboriously perfected*
The second division of medals are those coined or made
262 Vaxue Of Electro-Metallurgy To The Medallist.
with a punch. The mode of proceeding in this case is more complex ; but let us trace the processes necessary to make the current coin. In the first place a likeness of the reigning sovereign is modelled by the artist in wax, which being approved of is finished as highly as possible in that material. The coins of the present reign are made by Mr. Wyon, and the beauty and high finish of the present five-pound pieces are a theme of universal admiration. As the workmanship of the coins during a whole reign depend entirely upon the skill of the artist, and as in centuries hence the state of the arts in our time will be inferred from the workmanship on our coins, how important is it to secure the first talents for that object ; and having secured them to cherish them with a fostering care, and place within their reach every possible means that in any way, however remote, may contribute to the super-excellence of the work. The original sketch of the artist should always be copied in metal, either silver or copper, and carefully preserved ; one copy being sent to the British Museum, another to Oxford, and a third kept at the Mint. By these means posterity would be enabled to have the identical likeness of each sovereign, that served ns a model for the artist from which to make all his other works. A copy of such a sketch should always be placed under the foundation-stone of large buildings. To return to our subject — a plaster-cast is then taken from the wax mould, and a cast is generally made from it in iron, which is placed in a lathe, first employed in the French Mint : a blunt point passes from the centre of the object spirally over its entire surface, and is forced into all the depressions. This point communicates a similar motion to a cutting instrument, which cuts out an analogous impression on a piece of steel. This is repeated many times, by which at last a die is formed. This is required to be highly finished by the artist who made the original model, so that the proper feeling and expression may be given to the die. This die is then hardened and used as a punch, by which another steel relievo is made by
The Mint.
a very powerful press. After this second punch is formed, it is hardened and used to form the dies employed for coining. Pieces of metal of the exact size and weiglit of the coin are then prepared by a series of operations, arnl made very clean previous to coining. In the Mint, tlie pieces of metal are placed in a hopper, and one by one is let loose by mechanical contrivances and conveyed directly under the die, which is connected with a piston communicating with a vacuum. The pressure of air on the piston causes the die to descend with great force upon the object, and the piece of money is immediately thrown out coined. Such is the rapidity of the operation, that notwithstanding the immense outlay in the first instance for the apparatus, and the expense of making dies, the cost of each coin is very far short of what would be incurred by electro-metallurgy, even if we were able to make perfect medals by that process.
I have seen another method used fur coining. A punch is taken, on which one side of the coin is engraved. Over tliis an iron collar is placed. A second die is then made with the opposite side of the coin, to fit into the collar. A piece of metal is then placed between botli, and a smart blow, or a series of blows makes the impression.
However, the success of mechanics over electricity has its limit, for as soon as the medals begin to be larger, one blow will not suffice to bring up an impression ; two or three are required, and between each blow the medal has to be placed in a furnace and annealed, as tlic compression of the first blow would incapacitate it for receiving a second with any advantage. The largest medal ever struck was the medal of Boulton, of which some impressions it is said had 300 blows. The beautiful medals now being engraved by Mr. Wyon and Mr. Leonard Wyon, as prizes for the Exhibition, will probably require nearly 200 blows to obtain their full perfection. Here electricity begins to show its utility, and for all larger medals will for ever totally supersede every mode of casting. Fine medallions of the Duke of Wellington and
tomes's carving apparatus.
Sir Robert Peel have lately been modelled by Palmer, and multiplied by his brother.
' A machine, differing somewhat from that used at the Mint for copying dies, has been invented by Mr. Tomes, for cutting those parts of artificial teeth which rest upon the gums, to which they require to be adapted with great accuracy. Mr. Tomes's carving apparatus consists of three slides, two of which are placed in the vertical plane at right angles to each other, while the third occupies the horizontal plane, with its motion at right angles to the motions of the other two slides. The model to be copied, and the material in which the copy is required, are fixed side by side on a plate of metal operated on by the slides situated in the vertical plane, while a tracer and a drill are fixed on a plate of metal which moves in the horizontal slide. The various slides are set in motion by mechanical arrangements, and in such a manner that every part of the model is passed over by the tracer, which accurately governs the motion of the drill, so that a perfect copy of the model is produced during the operation.
This machine, though invented by Mr. Tomes for the purposes of his own profession, is equally suitable for producing copies of medals. But, like all machines which produce the copy by means of a rapidly revolving drill, it leaves a little work to be finished by hand where acute angles are required. In artificial teeth all the surfaces are curvilinear, hence the machine finishes the work with an accuracy of detail which the hand cannot equal; but in copying a coin, all sharp angles, such as those about the letters in the inscription, require to be picked out with an engraver's tool.
Hitherto we have been speaking of the comparative value of different modes of making original medals; but let us compare electro-medals with other casts used by numismatists. Now there are only two substances much used for this purpose, and these are sulphur, and plaster of Paris. For
Casts Of Coins.
mcrly the obverse and reverse were arranged side by side on one piece of sulphur, wound round with paper gilt at the edge ; latterly, however, it has been the fashion to make the cast exactly like the original, the obverse being on one side and the reverse on tlie other. Now the obverse and reverse of electro-medallions, after having been filed flat, can very readily be joined together with a little glue in such a way as to render it almost impossible to distinguisli the point of junction; and it must be a matter of taste, whether the two sides should be kept separate or joined together. The great superiority of electro over other casts must be apparent to all, especially when we eomsider that the duplicate may be made exactly to resemble the original, not only in workmanship, but also in the nature of tJic metal of which it is composed. If the medals are gilt, or of gold, they will show to greatest advantage it* arranged on a green ground ; if silver, or plated, on a light blue ; if bright copper, on a black; but if bronze, on a pale yellow ground.
Casts of entire coins may be made in sulphur, britannia metal, or plaster of Paris, by making a mould of either side of the coin, and so adjusting the two moulds, which should be twice or three limes the width of the coins, that the obverse and reverse are separated to the same amount us that of the thickness of the coin. A little channel is then cut, into which tlic sulphur, fusible or britannia metal may be poured out ; in that way a cast of the coin is accurately made. Now, if any man should look into this book for a bad purpose, he will probably peep into this chapter; and let me DOW' warn him of the consequences which must inevitably ensue from carrying out improper proceedings. Sooner or later he will be inevitably banished the country. There is an organised staff always watching for dedinquents, and no expense is spared in their prosecution. I can assure the man who can successfully turn a knowledge of casting or plating to a bad account, that he possesses abilities and know*
List Of Coins.
ledge which would enable him successfully to obtain an honourable livelihood. If the advancement of science has placed within his means processes which may be turned to bad account, a corresponding advancement of science will render his detection not only more necessary but more easy.
As to the coins the electro-medallist should select for his operations; he should begin with the Jewish shekel from its historical associations ; he should then copy the exquisite specimens of Macedonian coins, in which series those of the renowned Alexander and Philip of Macedon are contained. He should then select the extraordinary productions of the Syrian empire, the race of the Seleucidm being much esteemed for their beauty. He may continue with Alexander's other generals, the Ptolemys, &c. In his road the electrometallurgist must not neglect tiie Syracusan coins — the honest the world has ever produced — nor pass unnoticed the (Carthaginian series, nor forget the relics of the former grandeur of the Crreek Islands. The Roman empire next demands consideration, and the Cmsars must be copied. The medallist may copy a few more Roman medallions and coins, after our Saviour's time, and then pass to the early British, of which the Saxon should be the beginning of the series ; after which, he should continue through the various reigns to modern times. Having completed such a series, the electro-medallist should arrange them in chronological and geographical order, and he will find that he has made an epitome of history, in which the progress of the arts may be traced through upwards of two thousand years. The high state of the arts in Greece, with their subsequent fall to the degradation into which the world had sunk under monkish dominion is striking, and their rise to the reign of the unfortunate Charles, about which period the Symons executed their splendid works, is remarkable. The slight vacillation of the numismatic art from that period to the present time may also be traced.
List Of Coins, Medals, Etc.
Those who prefer medals to coins may select the finely cast and chaste medals of France and Italy, the medals of William and Mary, the Napoleon medals, we should not forgot the medal struck by the Pope to commemorate the to him" glorious massacre of St. Bartholomew, those of the kings of France, and Wyon's latest productions, of which to my taste the medal executed for Prince Albert is the most exquisite.
The finest collection of coins and medals at the present time in the whole world, is at the British Museum, and when tliat establishment has an electro-cast of every other coin or medal that is known, either in copper-gilt, silver, or bronze, so ns to resemble the original, tlien indeed may Englishmen be proud of their national collection. It would not be dirticult to arrange3 casts of every known medal in a room open to the public.
Where we desire electro-medallions to have a very perfect rim, it may be accomplished by winding round the mould a thin piece of sheet l('ad, or such metal, and allowing it to project about one eighth of an inch beyond the edge, when it will be found, that on the completion of the process the electro-medallion will have a rim of that depth.
(227.) There are many eminent persons distinguished for their learning, their abilities, their public station, or, their private virtues, a medallion of whom would be greatly esteemed by their friends. Now the engraving a steel die in a first-rate manner, is such, that it altogether precludes the idea in ordinary cases ; but as soft substances can be copied by the galvanic process, the expense of obtaining a medallion in wax, when divided among thirty or forty persons, would surely not be a material object, and they would be thus enabled to possess a likeness of the person so much endeared to them. What a contrast would there be between the distribution of the portrait of a deceased and
PEnFECT ELECTKO-MEDALLIONS.
esteemed friend, and the unmeaning custom of giving a black and gold ring, simply bearing an inscription ! How much better would tlie remembrance be perpetuated ! for the ring is valued more frequently for its size and intrinsic worth, than for the remembrance it is intended to convey ; and after having been worn for a year, is too frequently cast without remorse into the melting-pot. A copper or silver medal, on the contrary, no matter how beautiful its execution, would intrinsically be worth only a few pence, and frequently would be far more prized and taken care of by the possessor.
(228.) It is a great desideratum to be enabled to take a perfect coin or medal by electro-metallurgy, that is, one having both obverse and reverse ; ns yet this has not been obtained, and from my experiments it appears to me to be very difficult. The manner in which I have attempted to attain this object has been, to procure casts of both sides of a medal, and to place the.se in contact at the part of the plaster external to the impression, in such a manner that a distance intervened equal to the width of the coin ; the inner surface of the plaster-casts were then black -leaded, and connected with the zinc of the battery, wdiilst the piece of copper to be dissolved was placed above a little hole left in the rim of the plaster-mould. In this position the moulds w'ere connected with the silver of the battery ; but the process with me did not succeed. I conceive, however, that it is possible, by this method, to make a thick medal with both obverse and
reverse.
Chap. Ii.
On Seai.S, Plaster Oasts, Etc.
Value of a seal, 229. Process for copiiig a seal, 230. Copper moulds from plaster medallions, 231. Quality of the reduced copper, 232.
(229.) In former times, when the art of writing was an extremely rare accomplishment, a seal was an instrument of great importance : it fulfilled the same purpose at the end of a conveyanceor deed that is now accomplished by the written names of the parties ; which even now, in reference to the ancient custom, are termed .signatures. No business was performed without the seal, no corporation existed without this The extraordinary seal of Southwick, which required three separate dies to form one impression, is a good instance of tlie important functions of the seal; for the three parts being in the respective hands of three trustees, it required the concurrence of all, before a perfect impression could be made ; and consequently, before any land or other property under the trust could be disposed of. Now the value of the seal is nearly lost, and in the great establishment where I lately resided, thousands of pounds hourly change hands without any such ceremony ; a faint representation only of the seal being made by a black wafer, a bare relic of former customs.
(230.) Now that seals arc nearly valueless, there can be no harm in describing the process for copying them. This is very simple; we first give them the thinnest film of blacklead, with a hard brush. If necessary, this may be aided by cautiously applying the most minute drop of spirits of wine, but it should be avoided if possible ; for the wax being soluble
w 3
Process Of Mounting Seals.
in alcohol, the seal is liable to more or less injury. A fine metallic wire is now to be heated over a candle, and the hot end placed in contact with the rim of the seal so that it may adhere. Care must be taken to apply a little plumbago round the point of insertion, that it may be continuous with the wire. It is then ready to be placed in the solution. This part of the operation is similar in all respects to that required for the moulds of coins. (220, 221, 222.)
After the seal is removed from the wax, it is usual to mount it by soldering it on to a piece of metal, and then to fix it on a turned handle for convenience of using.
Considerable care is required to effect this purpose, the seal must be first cleaned at the back with charcoal and water, and then dried. A little powdered rosin is sprinkled on the back, and the medal is then held in the flame of a spirit-lamp till the rosin begins to smoke, when a stick of soft solder is rubbed over it, and as soon as the solder adheres all over and fills up the hollows it is allowed to cool. The seal is then placed face downward on a oork, and with a file carefully reduced in thickness till the edge of the copper is apparent all round, but care must be taken to keep the two surfaces quite parallel. If the seal is very thick, the filling with solder may be dispensed with, as the copper in that case may safely itself be filed flat. A piece of metal, either Copper or the alloy known as red gun metal (an alloy of copper and tin), is then prepared with a flat surface at one end sufficient to cover the seal, and with a socket at the otlier, to wdiich a handle of either agate, ivory, ebony, or other hard wood, may be fixed. The flat part of the handle must be coated with a thin layer of solder, and that, together with the prepared surface of the seal, sprinkled with a little rosin, when the two surfaces are placed in accurate contact, and then held in the flame of a spirit-lamp until the solder melts and unites the two, the edge is then to be carefully filed and polished, and the face of the seal cleaned by char-
Process For Copyrsig Plasters.
coal and water. In those cases where the device is very deep it will not admit of being reduced perfectly flat, and in that case, the rim is filed to the same extent all round, and an indentation must be cut in the handle corresponding to the elevation at the back of the seal.
The largest seal, as the great seal of England, or the large seals of the bishops, may, in this way, be copied with ease ; and the smallest are attended with no more dillieulty. The operator must remember, that although he is at perfect liberty to copy the Chancellor's seal of the lust reign, yet he would be liable to the utmost penalty of the law if he were to curry on his scientific proceedings upon the great seal of Her present Majesty. A letter received in the morning may be answered the next day, or even the same night, by a letter sealed with an electrotype impression of your friend's seal. If a relievo be reijuired from u sealing-wax relievo, it may be obtained by a double electrotype operation, or by first making a plaster intaglio, and proceeding with that as for plaster generally. Seals may be made either in silver or copper, the {processes hr which arc similar, in all respects, to that described for making electro-medallions.
(231.) Copper or silver moulds may be obtained of tlio utmost perfection, from plaster medallions. If we desire to take a copper mould or intaglio from u plaster relievo, we simply prepare the plaster by tallow, wax, or any otlntr similar substance. We then carefully apply the black-lead, and twist round the rim line wire to connect it with the battery, after which it is ready to be placed in tlie metallic solution. The copper or silver copy is by these means as perfect as the plaster. When a relievo of a plaster medallion is desired, we may either electrotype the copper mould obtained as before, or we may make a mould of white wax, having first filled the plaster with water. The wax mould is to be blackleaded, and must bare a wire attached to it, before it is put into the solution. The compound of bees**wax and rosin may be
From a plaster cast we can obtain a stereotype moulJ, and from this a medallion in copper, silver, &c. ; but few now would be inclined to follow this method when others are so well adapted. The apparatus and fnodns operandi are similar, in all respects, to that employed for the multiplication of coins and medals. (220 — 222.)
(232.) The reduced metal, be it silver or copper, for the foregoing objects, can be made of any texture that may suit it best. It may be either produced of the greatest flexibility, or of the most extreme hardness, by following the laws which we have laid down. A very hard medal, cameo, or seal, is best obtained by using a very strong solution, a single battery, a large positive copper pole. It might be very useful for Bate's Anaglyptograph, an ingenious instrument, by which a correct engraving of any raised object can be executed. A point is passed over the medal at an angle of 45°, this communicating a motion to a diamond point. As the point passing over the medal is raised or depressed, the diamond point takes a corresponding curve, so that the lines ruled on the plate form certain curves, the effect of which is to give a correct drawing of the medal. When a thin layer of black-
Hard Copper Hedal8.
lead is used, the deposited copper will not in the slightest degree be discoloured bj it> as the plumbago will always be taken into it, leaTing none on the prepared plaster. If a very thick layer of black lead is employed the copper will be discoloured.
The hard copper is of great use to the metallurgist, as he is in the habit of using it for his macliinc, by which he mechanically forms the dies.
Char Hi.
On The Multiplication Op Brasses.
Process for obtaining Duplicate Brasses, 233.
(233.) There is scarcely a church in the country which has not some curious old monument where characteristic likenesses of a whole family are engraved on a brass plate. To the Town Council of Yarmouth these relics were of so little interest that they condemned the whole collection from one church to be applied to the manufacture of standard weights for the use of the town. By some clergymen and churchwardens they have been regarded as legitimate mines of wealth, as they have been frequently sold as old metal, either to enrich themselves or to benefit the parish. By antiquaries, however, these monuments are highly prized, and many would be delighted to possess a fac-simile of many of these obje<*t8. This may be accomplished by comparatively simple means. It is only necessary to take a cast of the brass in gutta percha or plaster of Paris, having previously oiled the brass ; if plaster is used, it is to be well dried, and then soaked in tallow. A wire must now be passed round it, and black-lead applied with a soft brush, when it is ready to be connected with the battery. Only moderately-sized brasses can be copied in this manner, for some are so large, as that of the Archbishop of York in Chigwell church, in Bssex, or those in Westminster Abbey, that they would require such large vessels as virtually to render the manufacture of a duplicate almost impossible.
The battery process is best suited for these purposes. A
On The Kultiplication Of Brasses.
large piece of refuse copper must be employed for the positive pole, and it should be placed as near the plaster as possible. As a large surface of plaster is generally required to be copied, a large battery will be required, otherwise the strength of the metallic solution must be regulated to the power, and rendered much more dilute and acid.
A great taste has lately arisen for studying monumental brasses. The lover of those objects prowls over the country with a roll of lining paper in his band, and a packet of heelball ♦ in liis pocket ; and wherever lie finds one of these much-prized brasses, he places the paper over it, and rubs the surface of the paper with heel-ball, which blackens it, except at those parts immediately over the incised lines. This mode decidedly gives the clearest impression, but some antiquarians prefer a mixture of linseed oil and black-lead, about the consistence of mustard, which they apply to tissue paper with a leathern rubber. For further particulars relating to these curious matters, the student must refer to works peculiarly devoted these remains, but especially to those exquisitely beautiful and accurate illustrations of monumental brasses by the Wallers ; a work in the library of eve'y person having the slightest pretensions to a knowledge of the antiquities of Great Britain.
A composition used by shoemakers to rub over heels and sides of the boots and shoes.
Chap. Iv.
On Making Dies From Embossed Surfaces.
On metallic reverses from raised smfaccs by galvanic agency, 234.
Peculiarities of dies made from pajKjr, 235.
(234.) All embossed surfaces may be copied with facility, whether they consist of paper or any other substance. They must be first rendered non-absorbent by oil, varnisli, or wax, according to tlie thickness of tlie texture ; linseed oil, perhaps, is to be preferred for paper. It must be allowed to dry before the black-lead is applied to make it ready for the solution.
(235.) Dies made from paper generally exhibit a slightly dented appearance in the smooth parts, from the little projecting points of the paper having been copied. This, it is said, disappears after many impressions have been printed.
A hard copper die formed from sealing-wax or other impression would in all probability be applicable to the formation of stamped wafers now so much in use. Since my last edition the use of these dies has been much extended by !Mr. Barclay ; and, at the present time, a book of coins is published, in which a hundred different coins are illustrated by fac-similes in tin-foil or paper, the impressions of which have been struck from these copjHjr dies. Colonel Leake has also a book illustrating his rare and curious Greek coins in a similar way.
Chap. V.
ON THE MANUFACTURE OF MOULDS FKOaM FRUITS, VEGETABLES, ETC.
On making moulds from vegetable substances, 23G. Cliantri 7*8 method, 237.
(236.) In a former book, means were adverted to for coating various kinds of fruit, vegetables, and leaves wdtli metallic copper, having first black-leaded them. (207.) By simply carrying on the process until a tliick deposit be obtained, instead of merely coating the object, a mould will be obtained for any purpose required. A cast thus taken of a leaf, for instance, that of a Morel cherry, baffles all description. The copy is absolutely perftict ; every fibre and nerve, in fact the minutest part, is cast in copjKir with the utmost fidelity; and in the same way the surface of fruit may be correctly copied, so that every excrescence or depression, however minute, will be as apparent as in the original.
(237.) Sir Francis Chantrey had a very ingenious, though a troublesome and complicated, method of obtaining a cast of leaves or sprigs of trees; he takes the finest river sift, ground up, and encloses the leaves and sprigs in it ; the whole is then dried and thoroughly Imkcd, by which process the wood is carbonised ; a strong blast of air is then sent through the apertures, which removes, the carbon and leaves a cast of the object, and that serves as a mould, into which he pours his melted copper. The same end might be attained in some cases far more readily by the galvanic current.
Metallic Moulds.
Evciy vegetable and animal substance whatever, which will remain undecomposed in the solution of copper for a few hours, can have a metallic mould made from it. For nearly all these cases the battery apparatus, similar to that used for medals, is the best.
Chap. Vi.
ON THE APPLICATION OF ELECTRO-METALLURGY TO SCULP- TURE, BAS-RELIEFS, AND OTHER PURPOSES.
The mode the sculptor adopts to obtain a metallic cast, 238. On making a metallic cast by Electro-Metallurgy, 239. The texture of the copper, 240. General remarks, 241. On the application of Electro- Metallurgy for goldsmitlis, 242 ; for surgeons, &c., 243.
(238.) Unfortunately the British public have nearly ceasetl to patronise British sculpture, otherwise electro-metallurgy would be a valuable assistant to that art. The sculptor first makes his model in clay, from which he takes a east in plaster, and this again servos as a mould, into which he pours his fused metal. This latter proceeding is attended with much trouble, and not unfrequently with great danger from a risk of explosion. The metallic cast when made is by no means perfect, as it requires much labour to finish it.
The electro-metallurgi.st could obtain a far more perfect cast at once, by preparing his plaster, black-leading it, and placing it in the solution of sulphate of copper. A wire in contact with the black lead must communicate with the ssinc of the battery, whilst the sheet of copper to be dissolved should communicate with the silver.
(239.) For very large designs, an inconveniently large vessel would be required; to obviate this difficulty, the mould, provided it be hollow, might have the separate pieces of which it is made so joined together by war or grease that itself should form the vessel to contain the liquid. Very le batteries ought to be employed by the sculptor, and
Cost Of The Pbocess.
rather a dilute solution ; because, in all probability, the size of the battery will not be proportionate to the immense surface exposed in even a moderately-sized design. The piece of copper forming the positive plate should be as large and as close to the plaster mould as it can be placed, in order that as little impediment as possible may be afforded to the passage of the current.
(240.) Tiie copper may be of any thickness ; and its strength and thickness may be regulated, as required in different parts, by increasing or diminishing the distance between the various parts of the plaster and the positive ])late of copper. Tlie relative cost of this method of making a bronze figure, to that of the plan now in use, is, perhaps, difficult to estimate accurately. By the old plan a bronze figure costs the value of the copper and the coals required for its fusion, besides the labour requisite to render the metal cast perfect afterwards. By the galvanic method it would cost the value of the copper, -f the value of an equal weight of amalgamated zinc, -h the cost of the labour required to work the batteries — the value of the sulphate of zinc formed. From the above statements, a rough idea only can be formed of the relative cost of these two methods in practice, and it can only be determined with certainty by very large operations.
I do not know that I can give any more accurate notion of the power of electro-metallurgy, than to notice that it can copy a Barton's button with most perfect accuracy. I liave an electro cast of a Barton's button in copper, which was given to me by Mr. Poulton, one of our preparers of microscopic objects, of whom, I believe, they can be purchased. The specimen is now upon my paper, and the dazzling brilliancy of the colours is so great, that it painfully distresses the eye to observe it at the reflecting angle. Perhaps it is hardly necessary to remind my readers, that the lovely colours which it presents are due to lines ruled exceedingly
Copying Colours Of Mother* Of-Pkarl.
close together. These electro casts might doubtless be used for ornamental purposes.
In Mr. Timbs* valuable Year Book of Facts for 1847, a record is made of certain experiments performed by Professor Silliman in America, in which he most successfully copied the iridescent colours of mother-of-pearl, and the process of which appears to be of sufficient importance to transcribe : —
" A few months ago, while engaged upon some experiments in electrotyping, I was led to think that by this process the hues of the pearl might be readily transferred to those metals which, from their hardness, are incapable of receiving impressions in mass ; but yet on account of their freedom from oxidation retain for a long time a surface comparatively pure. 1 therefore took a Smee's battery which I had just constructed, and after several experiments succeeded in obtaining small sheets of silver radiant with the hues of the shell. When seen by a single light as that of a lamp, the play of colours is surpassingly beautiful, scarcely inferior to that of the pearl, and where equal care was employed, the plate of silver which was formed eight months ago rivals in brilliancy that which came fresh from the battery a few hours since.
" The process by which this result is obtained is as follows : — The first thing required is to prepare the shell. This is effected by grinding and polishing it upon the back in such a manner as to cut through the numerous concentric strata that compose its substance. When this is done, by the aid of a microscope the surface will be seen covered with delicate grooves, some thousand in an inch, formed by the sections of the concentric laminae, and this configuration gives rise to the glowing tints of the shell. The next step is to obtain an exact impression of this surface upon some good conductor of electricity. This we are enabled to do by means of fusible metals, if proper precautions are em-
fusing the metal I pour it upon oiled paper, and when the air bubbles cease to rise through the metal, the oxide is skimmed from its surface with a card, and as soon as it presents the appearance of a perfect mirror the shell is forced down upon it by a sudden pressure. When the metal has cooled, I remove it from the shell, and having ascertained the accuracy of the impression, immediately plunge it before any change of the surface can occur, thereby completing the circuit between the poles of the battery. In a few moments the surface of the metal is frosted with silver, and tlie configuration of the shell exactly copied. A sheet of silver of sufficient thickness to be easily removed with a penknife will be deposited in the course of five or six hours under favourable circumstances."
Electro-metallurgy is now found of the utmost value to the model maker. I have lately seen some parts of a most beautiful model which is being manufactured by Mr. James, the eminent model engineer, for the Great Exhibition. It is a perfect representation of the Menai Bridge, showing its construction, and made to scale. The tubes were deposited in parts which were after wards soldered together and electro-silver-plated. Another model of the great suspension bridge over the Dniester has the abutments electrosilvered so correctly to imitate stone that the eye may be easily deceived on inspecting it.
Mr. Chaterton, who executes exquisite carvings of ivory by means of a peculiar machine, exhibited last winter at the various scientific soir a skull bust prepared by electrometallurgy. His modus operandi was to form a cast of the head, and coat it with copper, and then to remove the interior cast. In the copper mould thus obtained, he deposited a copper reverse ; but the whole operation is subject necessarily to considerable difficulties requiring continual watching. The
bust he exhibited was very perfect, but the exact means he used have not been published. As far as regards the electrometallurgical process, the solution, positive pole, &c., must be regulated by the principles so fully detailed in former parts of the work.
(241.) Before bringing this book to a conclusion, I may mention that the application of electro-metallurgy, or the art of working in metals by the galvanic fluid, is not confined to the foregoing subjects ; for every kind of object which can possibly be made in copper by any other method, can also be made by electricity. With regard to the use of other metals for the like purpose, they can in some instances be employed ; but still, the application of the galvanic fluid to the working of these must be limited, because the intrinsic value of many is so great ns to preclude their general use ; wliilst the value of others is so trifling as to render their application of little value.
As a general rule, all articles of tin, lead, iron, and zinc are infinitely better and far more cheaply made by the present mechanical processes than they be by electrometallurgy. I do not pretend to my that there may not be some particular cases in which the pure metal obtained by the latter process might be preferred to the impure metal. Pure iron might be valuable, pure zinc might be useful, but, for all manufacturing purposes, there is but little doubt that the cheapness, ease, and, above all, the capability which mechanics possess of an unlimited production of articles by the steam-engine gives a vast preponderance in its favour, especially when we consider the mind continually required to superintend and direct voltaic processes.
For articles of copper, the benefits of electro-mctallnrgy do not manifest themselves whenever the cost of the workmanship is not to the cost of the voltaic reduction, and whenever the object can be made by pure mechanical means,
Attei>'*pts have indeed been made to make copper tubes by electro -metallurgy, and also saucepans and similar vessels, but there is no doubt that those who practised this mode must have been ignorant of the relative expense of the processes. However, in this case, as in others, it is possible that tubes of peculiar curves might sometimes be made profitably by electro-metallurgy, and that the absence of soldering might be turned occasionally to advantage.
Amongst the extraordinary applications of electro-metallurgy which have come under my notice, I may state that it has been applied to coat the tops of wine bottles to endeavour to close them effectually from the atmosphere.
Electro-metallurgy offers means for the multiplication of polished surfaces, but its benefit is confined to particular
Oekerax Bemabks.
2S5
cases, as highly burnished surfaces cannot be so perfectly multiplied, because if those siarfaces are absolutely clear adhesion would take place, and if the air adler to tte originals a slight spotted ipearance termed '*a is noticed, which would seem to be an irregulanty thickness of the film of air. Although burnished surfaces cannot be absolutely and perfectly multiplied, yet for my practical purposes the process may be effected# The formation of duplicates of specula must be regulated by the preceding observations, for it would be requisite always to finish the duplicate by burnishing. All such delicate processes should never be attempted till experience has taught the operator how to overcome the difficulties likely to occur.
With regard to the manufacture of silver articles by electro-metallurgy, the preceding observations equally apply# The manufacture of silver spoons and forks by the present process is effected so cheaply as to leave no shadow of doubt that it is infinitely to be preferred to electro-metallurgy# Very elaborate articles of which duplicates are required, miglit be advantageously made by electricity, and it is almost needless again to mention that the silver might be strengthened with layers of copper, should ever such process be required. One objection to electro-metallurgy for these purposes is the necessity for the employment of pure silver.
(242.) To workers of gold electro-mctallurgy promises to be occasionally of value ; for, after having once procured a mould, he can obtain the most elaborate devices ; but still, in buying manufactured articles of gold, the intrinsic value of this metal is so great that the workmanship forms frequently but a small part, — or otherwise electro-metallurgy might be of importance to the goldsmith.
The dentist requires for artificial teeth an exact cast of the mouth in gold, platinum, or palladium. Now the cost of the
APPLICATIONS or ELECTRO-METALLtJROT.
manufacture of this is so expensive, that many are prevented from availing themselves of these valuable appendages. It is absolutely necessary that the gold should fit very accurately, or else the possessor is not able to use them. Electro-metallurgy might, perhaps, be brought to aid the mechanic in this matter, but the operator must recollect that notwithstanding the scientific principles detailed in this work, considerable skill in the manipulation would be required, especially as it is necessary that the metal should be of the utmost tenacity and firmness.
(243.) Even to the surgeon, electro-metallurgy appears likely in some cases to be useful ; for when he is desirous of exerting constant pressure on any part, or of confining any part in a particular position, he can make a copper instrument exactly to suit any individual case by first taking a cast in gutta percha, plaster of Paris, or, in some cases, by a piece of gummed sheeting. At present no case has occurred in my own practice where such an application of electrometallurgy has been required ; but I have seen cases of club-foot, where, doubtless, a metallic mould might have been applied with great benefit to the patient. With regard to metallic splints, perhaps in some cases they might be used with great advantage, but as a general rule those made of the moulding tablets or of gutta percha (such ns I have described in the Medical Gazette) are more applicable. By a proper use of splints made of these moulding tablets many cases of broken limbs have occurred where the patients have been enabled to leave their beds and enjoy the comforts of the external air within three or four days of the accident. For these purposes splints made of gutta percha or of my moulding tablets would, from their lightness, be much preferable to metallic splints, for though they may be made to take a perfect cast of the face, they yet set so firm and hard as to bear a very severe blow without accident.
To the geologist electro-metallurgy is not without its in-
Value Of Electro-Metallurgy To The Geologist. 287
terest, for, independently of the rationale which it affords of the veins of metals embosomed in the earth, it gives the means of obtaining in copper casts of any fossil which will remain unacted upon in the metallic solution. If the solution is acid, of course it will be unsuitable for any strata containing carbonate of lime ; but then, by first taking an impression in plaster, a metallic reverse can be taken from it which will be a perfect fac-simile in metal of the original. These metallic casts arc preferable to any other kind of duplicate, because they occupy less bulk, are lighUT, less destructible and fragile than any other material.
Electro-metallurgy is now brought to such perfection, that a copper east of tenacious metal can be made of any size or form ; and it may he even painted to resemble tlie object it is intended to imitate. All other muterialH, ns far ns should be discarded from our museums, as for nearly all purposes the copper is entitled to a decided preference.
Mr. Poulton has lately sent me an eh'ctro cast of the eye of a dragon tly, which umler the microscope exhibits perfectly all the facets common to a compound eye. This must be regarded as a very remarkable, application of this ingenious manipulation.
The architect should always bear in mind tin* powers with which electro-metallurgy furnishes him. liy it he will be enabled to introduce at but moderate* expense, relievos, ornaments, statues, friezes, &c. &c., into tin* composition of his building. In the construction of churches electro- metallurgy, if used rightly, is capable of adding great effect. If electro-metallurgy, only in a slight gree, should cause us to return to the splendour with which Solomon considered that buildings dedicated to worship should be constructed, then, indeed, will all who have assisted in developing its laws and facilitating its practical application be proud ; for there is no national disgrace more to be deplored, than that
288 Value Of Electro-Metallurgt To The Architect.
buildings erected for dancing, feasting, or debauchery, should be fitted with all the embellishments which modern science has so abundantly supplied, whilst, too frequently, buildings not sufficiently excellent to be used as kennels for the hounds of the nobility are thought amply splendid for consecration to the worship of the Almiglity !
S89
Book The Fifth.
On The Electbottpk.
Chapter L
On The Multiplication Of Type.
The mode of printing hooka, 244. On stereotyping, 245. On Electrotyping the type, 246.
(244.) The ordinary type, such as this work is printed with, has each letter separately cast of a particular alloy ; these letters when combined together form words ; again, a number of words form a paragraph — a scries of paragraphs a chapter — a number of chapters a book — and lastly, several books form this volume. Most works are printed in parts ; thus, w'hilst I am writing this chapter, the second book is completely printed, and the types distributeil, whilst the proof of the third is lying on my desk to receive such alterations as may occur to iiic. Now the electrotype would be of no value to the printer in this case, for the same type which is used for the first part of this work, will bo again used for the last, and even after the whole is printed, will be very little impaired.
(245.) With books which have a very large circulation, as the Bible or Prayer-book, and where no changes are required in the matter for a series of years, it is usual, after the work is completely set up in type to take a stereotype copy of it A plaster mould of the type is first obtained, which is thoroughly baked in an oven, and from this a metallic cast in stereotype metal is made, which is a copy of the original. The duplicate thus obtained is slightly impaired by the injury which the plaster cast receives in the furnace, otherwise it has advan-
o
O! The Multiplication Op Type.
tagee over the type ; for every stereotype page is in one piece, ivhilst the type is made up of as many different pieces as there are letters, besides numerous pieces termed leads, &c. The process of stereotyping is cheaply effected, but the electrotype may be made more perfect. An attempt is now being made to introduce a new material, apparently a composition of shell-lac nd other matters, for the purpose of forming the cast. The mould is made of plaster of Paris, and the material is fixed unto a cast block to keep it perfectly steady. The material is said to be brittle, but nevertheless to print satisfactorily. I have seen a very beautiful cast made in this manner, but it has not yet sufficiently come into use to tell how far it will answer its intended purposes. The process of casting has yet materially to be improved, as a more rapid mode of conducting the process is required.
(246.) To procure an electrotype copy from a page of type, we have to take an intaglio impression from the type, which is most conveniently effected by making a cast in gutta percha : it may also be effected by taking a cast in sealing-wax, or in plaster of Paris, which must afterwards be rendered non-absorbent, or we may take it in white wax; the intaglio impression must be black-leaded and placed in the solution to receive the deposit of copper. Great care must be taken to disperse air-bubbles. A moderately thin layer of copper would suffice, if it were backed with solder, type metal, or some such analogous alloy. This process is only likely to be useful for the Bible, Shakspeare, Pilgrim's Progress, or works that have a large circulation ; and, probably, might be found to wear longer and print better than the usual stereotype metal : but at present we have no experience on that matter; though there is but little doubt that for these purposes' electrometallurgy will eventually be preferred. Up to the present time this has not been brought extensively into use from its difficulty and expense, but now, doubtless, it spill be sometimes employed, as gutta percha materially diminishes
Anastatic Process.
the cost. A Frenchman has attempted the mechanical manufacture of type in copper ; the specimens I saw appeared to be good, and register truly, but up to this time it has not become an article of commerce.
A very useful process has been added to printing since my last edition was written : it is called tiie anastatic process. If a page of print be washed over phosphatic acid, an acid which is formed by the spontaneous combustion of phosphorus in contact air and w'ater, it appears to have the effect of starting the ink, and when the paper is then subjected to great pressure against a zinc plate, a copy of the impression is made upon the zinc, which, on being rolled as by the ordinary mode of lithographic printing, may be used in a similar way. Tlie anastatic printing is now continually being used for reproducing any sheet which happens to be defective when nn impression of a work is nearly sold.
[Sjtecimen of Electrotype. 'I MORNING FRAYER.
Midi Book : after tery LfMoon. Here the First, or the Second Lceaon.
Ty E pralee thee, O God ; we acktiowledge thee to be the Lord.
All tlte earth doth womhip thee : the Father everlasting.
Tothoe all AngeU cry aloud : the HeavcsuMUidall the Fowem therdn.
To thee Cherubln, and Bera> phin : conUnoally do cry. Holy. Holy, Holy : Lord God ofSabaotlii Heaven and earth are of the Mokety i of thy Glory.
The glorioiu eompany bf the Apoetlea : pralae tne.
The goodly feUowabJp of the Proph : praise thee.
TIM noble araqr 01 :
nralac tliaa.
The holy Ctibwii tindoghoct
We therefore pray tliee, livlp thy servant : wlumi heat redeemed with thy jireclotw blood.
Make them to be numbered with thy BaJnU : In glory everlasting.
O Ird, aavc thy people and blean Uiim* heritage.
Govern them : and Lift them up fc.>r ever.
Lay by day : we magnify tliee ;
And we worship thy Name ever world wHhoot end.
Vouebaafe. O Lord : to keep oa tliia day without ain.
O Lord, have mercy upon Ui; have mercy ua.
O Ixird. lei thy mercy llghG en upon tw : aa our tnist la In thee.
O Lord, in thae have I tmated : let me nerer be con*
o 2
CHAP. n.
On The Multiplication Op Plain Copper Plates.
The preparation of plain copper plates, 247. The electrotype plates, 248. Process for their manufacture, 249. Manipulation of the battery, 250. Precipitating trough, 251. Temperature, 252. Positive pole, 253. Regulation of the texture of the copper, 254. Single-cell apparatus, 255. Tune required for the process, 256. Removal of the plate, 257. Mode of preparing the plate for engravers, 258. Economy in the manufactory, 259. Expense of the plate, 260.
(247.) The application of the electrotype to the various dedepartments of engraving is of the greatest importance, and the new field open to this branch alone is very extensive. Engravings generally are made upon copper-plates which have undergone a tedious preparation. The copper which is to be employed for this purpose should be as pure as possible ; it has first to be rolled to a certain thickness, after which it passes into the hands of the copper-plate maker. He carefully examines the plate, and picks out any little piece of foreign metal he may chance to perceive, and then fills up the gap by dexterously hammering around it, so that he draws the neighbouring copper over the hollow. The plate is then well hammered, and receives a rough polish by charcoal. The price of a plate so manufactured, is worth from two shillings and sixpence to three shillings and sixpenoe per pound.
(248.) This copper-plate is by no means pure, as it generally contains tin and other metals which render the engraving sometimes difficult, and the etching very uncertain. To obviate these faults we make an electrotype plate on one of the prepared copper-plates and as the metal of this is
Electbotype Coppeb Plates For Engraving. 293
absolutely pure it is found to be far better adapted for the purposes of the engraver. This duplicate plate possesses a similar surface to the original, and may therefore be at once used ; but it is found better to hammer the duplicate, and prepare it with charcoal, as that greatly improves it by making it more elastic.
On one of these electrotype plates hammered and prepared as plates ordinarily are for engraving, Mr. Palmer had various specimens of art executed. First, the plate-maker's, opinion was taken of it, and he decided that it was vastly superior to the common copper ; here we may remark, that many persons have doubted whether the electrotype copper would bear hammering ; now this plate was thus prepared. The plate was then sent to a le tter- writer, to receive a 8{>ccimen of this sjKJcies of engraving, os well as to have his opinion of it ; he stated, that the quality of the copper was such that much less labour was required for the process which it had to undergo. It was then sent to an etcher, and he found it greatly superior to ordinary copper.plate ; for the nitric acid bit with the utmost uniformity on account of the purity of the copper. A specimen of machine-ruling, rose-engine turning, and medal-ruling by Bate's patent anaglyptograph was then executed, and the opinion of all the artists concerned in the work was similar ; for the superiority of using pure copper over the ordinary copper, which is usually contaminated with other metals and charcoal, was apparent to alL
(249.) The exact process by which these electrotype plates may be prepared is very simple. The plain plate on which the deposit is to take place, is to have a flat band soldered on its back, in order that sufficient connexion may be made with the zinc of the battery. The heat necessary to effect this, drives off the air which infllms the meial, so that if it were placed at once in the solution of sulphate of copper the two plates would stand a very fair chance of adhering to each
Battery, Troughs, Etc.
Other. To prevent this serious evil, the plate which has been soldered ought to be placed in a cold place for twenty-four or more hours, which will enable it to regain a second time its film of air. Those who are not skilful in soldering metals, may simply place a wire or piece of metal in contact with the back of the plate, as that connection will be amply sufficient Every part of the plate which is not intended to receive the deposit, must be covered with tallow, wax, or any other non-conducting substance.
(250.) Having thus prepared the plate, a platinized silver battery, which exposes about twice the surface of negative metal, is to be charged with dilute sulphuric acid, consisting of about one pint of strong sulphuric acid in two gallons of water. By using the acid thus diluted, the risk of much local action is materially lessened, and for the same reason the acid should never be poured into the battery till it is quite cold. The best form of battery for these purposes is fig. 4. The silver has a binding screw soldered to it, and a piece of wood is fixed on its upper part. The zinc is placed on each side of the silver, and consists simply of two strips which have no solder attached to them, but are connected to each otlier, and to a binding screw by a large screw, which embraces at once the two zinc plates and intervening piece of wood fastened on to the silver. This very ingenious arrangement appears to have been devised by the instrument-maker, from a necessity which the manufacturer experienced of repeatedly adding a new zinc as soon as the former was dissolved.
(251.) The precipitating trough may be either the horizontal or vertical. The vertical trough is an oblong wooden vessel cemented in the interior ; on one side the plate to be multiplied is placed, on the other a piece of copper to be dissolved 12.). Hie horizontal trough is a shallow, square vessel, on the bottom of which the plate to be copied is placed, and half an inch above it, the copper to be diseolTed
Different Qualities Of Metal. 296
{Jig- 1.). It is necessary to place the negative plate underneath, or else the uniform strength of the solution would not be preserved, but a mass of crystals deposited at the bottom of the vessel ; or if it is placed in the reverse manner, some mechanical means of agitating the solution must be employed. The first apparatus is best adapted for a slow precipitation and small plates, but the last for a rapid deposition of the metal and large plates.
Whichever process be employed, the trough must bo filled with a solution of sulphate of copper of a strength suitable to the power of the battery. If one battery be used, it should consist of a saturated solution of sulphate of copper, diluted with rather more than one third of dilute sulphuric acid. A solution of nitrate of may be employed of about one pound to the pint and a half, which will allow the deposit to take place more quickly. A nearly saturated solution of sulphate of copper may be used, if a series of four or five butteries be employed, or the solution be kept at a high temperature. It is advisable to place the plate in a neutral solution at first, and afterwards, when it is slightly covered, in the acidulated solution, in order tliat the film of air may not be removed.
(252.) Where practicable, the solution should always be kept at a moderately high temperature ; as by that means the deposit will take place far more rapidly, and the copper will be more elastic. The reader must not confound the property of elasticity with flexibility, although this is an error very commonly made. Flexibility is the property which bodies possess of being easily bent ; elasticity is the power which bodies have, of returning to their former shape after they have been bent. The flexibility of any metal is a property very readily obtained by the laws pointed out; elasticity, on the other band, is a property more difilcult for the electro-metallurgist to obtain than any other.
(253.) Having filled the trough with the liquid, we take
296 REGULATION OP THE QUANTITT OP ELEtlTRlCITT.
a pieoe (f copper tbe same size as the plate, and connect it by a wire to the silver of the battery. We have now the battery charged, the precipitating trough filled with its solution, and the piece of copper to be dissolved placed in the precipitating trough, and connected with the silver. Having proceeded thus far, the wire, soldered on to the copper plate on which the new deposit is to take place, must be connected with the zinc of the battery, and the operator must be particularly careful that dropping the copper plate into the precipitating trough is the last operation for completing the galvanic circuit, as immediately a precipitate of pure copper commences. This does not adhere to the copper plate, because it is not in contact with it, for a thin layer of atmospheric air is interposed between the two.
(254.) Having put the apparatus in action, the operator must regulate the quantity of electricity passing, by approximating or increasing the distance between the two poles in the precipitating trough, according as he may require differences of texture in his copper ; for the reduced metal may be obtained soft or hard ; the copper should neither be too crystalline nor too flexible, but should be of a texture intermediate between both extremes. The laws regulating these points have been sufficiently dwelt above. The apparatus will require no material alteration for two or three days, and then the acid in the battery should be changed, and the zincs, if necessary, renewed. The piece of copper forming the positive pole should always be examined, and removed if necessary. A plate should not be allowed to remain inactive in a neutral solution for any considerable time whilst it is being made, as in that case the reduced copper is apt to be in layers.
(255.) The single-cell apparatus is not at all well adapted for taking copper plates, because it is impossible to regulate with accuracy the quantity of electricity to the strength
Ecokoky To Be Pursued By The Manupa.Cturer. 297
of the solution. In fact, all the largest and most perfect plates hitherto made have been produced by the battery apparatus.
(256.) The time necessary for the complete formation of a plate, varies according to the thickness of the copper required, the ease with which the solution suffers decomposition, the power of the battery, and the distance between the plates in the decomposition cell, or precipitating trough. The shortest time in which it could possibly be made, is from twenty-four to thirty-six hours ; but with a single cell and dilute acid it ordinarily takes a week, or even more ; the texture of the copper, however, in both cases, may be made similar. The only limit which is afforded to the rapidity of the process, is the cu 2 )reou 8 salt. As the nitrate is the most soluble salt of copper, we never can obtain a plate more rapidly than the strength of its solution will allow.
(257.) Having made the plate, we have now to take it off ; and for this purpose, any cop|)cr embracing the edge of the original plate is to be removed; after which, the operator without uiiy difficulty may separate the two plates, for provided he has followed exactly tlie directions which I have before given for insuring a film of air on the plate, not the slightest adhesion will exist.
(258.) A plain copper plate is thus made, which can be used at once by the engraver, or it may be hammered and rubbed with charcoal, as copper plates ordinarily are. Duplicate copper plates have been made from another similar plate, but we can obtain a copper plate from smooth substances, which are not capable of being acted upon by the duid ; thus, smooth white wax, sealing wax, or smooth plaster of Paris, will receive the deposit after they have been -leaded.
(259.) The manufacturer who makes electrotype plates in an extensive way, must endeavour to lessen the expense of
298 USB OP thB sulphate op ibon, copper clippings.
the process by every possible means. In the first place, he must recollect that the mercury used for the amalgamation of the zinc is not at all acted upon, but that when all the zinc is dissolved, it remains upon the fine particles of foreign metals which the zinc contained. He should carefully preserve this mass, as well as all the fragments which have been left; the mercury may in great part be separated from this, by enclosing the mass in wash-leather and squeezing it ; the rest may then be obtained by distilling the residue. Theoretically, the operator ought to regain as much mercury as he originally employed ; but practically, he will always 8ufi*er a certain loss.
The sulphate of zinc left in the battery after it has been exhausted is absolutely pure ; and therefore the solution may be evaporated and the crystals of the sulphate of zinc obtained ; or the metal may be converted into a carbonate, for which there is great demand in the arts. The deposited copper in the same manner is also pure, and, therefore, all the clippings should be preserved for the purpose of alloying gold, as it is necessary to have a perfectly pure metal for that purpose ; but strangely enough a refiner told me that he did not approve of electrotype copper for his purposes.
Those who manufacture a great number of plates and to whom time is not an object in their proceedings, can adopt a peculiar form of battery. The battery should be large, and should be connected, not to one precipitating trough alone, but to a series arranged exactly as a compound battery ; thus, if twenty troughs were arranged and connected with the battery, they would obtain twenty pounds of copper for one pound of zinc dissolved. The solution of sulphate of copper in each cell should be rather more dilute, and be much more acid, than when a single trough is employed, and the positive copper-plate and negative plate of each cell should be of the same size. The huge battery, in this case, is not attended with more expmisa
Expemsb Op The Pbogess.
than a small one ; for to do any given amount of work, as much zinc would be dissolved in a battery made of a silver thimble, as in one exposing a surface of negative metal equal to the surface of the whole of Europe I The rationale of this apparent paradox is explicable by the important law, that "In every cell the amount of chemical action is the same one battery will therefore, for every pound of zinc dissolved, precipitate one pound of copper in each precipitating trough, so that the number of precipitating troughs, arranged as a compound series, will give the number of pounds of copper thrown down for each pound of zinc dissolved. If we consult the equations given in a former part of this work, we shall find that it is of no use increasing our batteries above a certain size, and therefore we must take care to lessen the resistances in all our troughs.
(260.) In this great commercial city it is useless to mention the excellence of the process, unless, at the same time, some idea be given of the expense attending its adoption. This, with a single battery and precipitating trough, will be, first, the intrinsic value of the copper, say one shilling and twopence for each pound, plus an equivalent of amalgamated zinc one shilling, plus some zinc lost by local action, plus sulphuric acid, say fourpence, equal to two shillings and sixpence a pound for the bore cost of the materials. To this, labour, time, house rent, and profit are to be added, which will increase, at present, the price to one sovereign per pound of copper ; though doubtless the expense will be diminished as the demand increases. For plain plates persons would hardly like to give this price, unless an engraver were about to execute a very splendid sulgect, and dien perhaps it would be fully worth his while to go to the extra expense, from the superiority of his materiaL
CHAP. m.
On Copying Engraved Copper-Plates.
Engraved copper-plates, 261. Design on the plates, 262. Various kinds engraving, 263. Uses of engraved plates, 264 for the potteries,
265 ; for calico printers, 266.
Engraved copper-plates are not more difficult to copy than plain oues. A plate possessing the most elaborate design, the most brilliant conception, the finest execution, the most delicate workmanship, in fact everything calculated to render a plate valuable, can be copied with the same readiness, the same fidelity, the same ease, as the plate without any workmanship at all ; because the deposit of new metal takes place in such a way that an exact cast is made in both instances.
(262.) The design of all engraved copper-plates is in intaglio ur depressed below the surface, and the problem is to obtain a duplicate in a similar state. To effect this, a reverse of the plate must first be taken in relief. This may be done in various ways. In the first place, a relievo may be 6 tained in copper, precisely in the same way as a duplicate plain plate. (249 — 257.) This is the most perfect process, and should always be adopted for very delicate designs.
An impression of a plate may be made on perfectly clean lead, by placing the lead on a printing-press with an iron bottom, and then placing the engraved plate upon the top of it The two are then to be run through the press, exactly in the same way as an ordinary print is taken off In this operation, if the lead be placed underneath, a very perfect
Relievo Mould Op Enoraved Plate. 80
impression may be effected ; but the upper plate is sure to become bent, which is a disadvantage. K the copper-plate is placed underneath, that will receive no injury, but the lead will be curled in a similar manner. Now', on considering these facts it occurred to me, that if a third plate above the other two were employed, there would be no curling, and upon the experiment being tried two or three times, my expectations were realised, for neither lead nor copper were curled to any amount. The mode in which I directed the experiments to be performed, was to place smooth lead at the bottom, then the copper-plate upon this, and lastly a third metallic plate at the top, which became curled by the process. A great disadvantage, however, in the use of lead for these purposes is, that the metal is liable to stretch unequally.
A perfect mould may be taken from an engraved plate in white wax, but it requires some practice to copy a large plate. The white wax must be black leaded, and then placed in the solution. Plaster of Paris may also be used to take a relievo impression, and the stereotypes are very excellent hands at using this substance ; but although I have made duplicate copper-plates from plaster, I am afraid that it will scarcely be thought sufficient! v perfect to be used for the electrotype in all cases. The plaster must be very carefully filled by the methods I have elsewhere detailed, and after the application of the black-lead it may be placed in the solution.
A tolerably perfect matrix may be made with gutta pereba, and I have reason to believe some operators have a secret process for forming it, which at present they decline to put me in possession of.
Having by any one of these methods taken a relievo impression, a reverse is again to be taken, in a manner similar to that pointed out for copying a plain plate. The film of iur, which substance acquire by exposure to the atmosphere,
Different Kinds Op Engraved Plates.
must be obtained before a metallic matrix is placed in the solution. (249 — 257.)
(263.) The back of the reduced plate will be always more or less rough, which is to be filed smooth before a print is taken from it. Sometimes, when the plate is thin, a second plate of tin or iron is soldered into the back ; but the unequal expansion of the metals, when heated, is liable to be attended with inconvenience. By the use of this artificial back, how ever, we can employ the crystalline copper, which is so in tensely hard, in all probability the plate would last much longer.
The front of the plate is liable to exhibit over its otherwise polished surface an appearance in copper, as if the slightest breath, or film, covered the surface. This has been technically termed the curd," and is instantly removed by the copper-plate maker by a few slight touches with his charcoal. To account for this curd will not require much thought when we mention, that if the operator simply places his finger on a polished plate the copper reduced upon it would Imve precisely similar marks ; and I have seen it exhibit every line of the finger, and even the opening of each perspiratory duct.
(264.) Those not much acquainted with engraving will perhaps be astonished at the various means which artists employ to execute an engraving. They may however be divided generally into three heads. The first contains those cases where the design is made by instruments of various kinds, as gravers, dry points, In the second, the device is obtained by acting partially on the plate by acids capable of dissolving it, or in fact by biting out the lines or figure of which the engraving is constituted. The third kind, where the surface of a plate is uniformly raised up by an instrument, in such a way that it prints all over perfectly hlack, in which state it is ready for the engraver. By burnishing the plate all the asperities are rubbed and that portioa thus treated
Use Of Engraveu Plates.
prints whiter : so that by regulating the degree of burnishing the different effects of light and shade are produced, which constitute the engraving. This is called mezzotinto. It is far cheaper than the line engraving, and is now much in vogue. Each of these three classes of engraving has been copied by Mr. Palmer and others, with the utmost fidelity, so that the application of the eleetroiype may be said to meet every case for which it is likely to be required.
The Art Union of London have used ekotro-metallurgy for their pmrpoees. Ten different original plates were multiplied in this manner. In answer to an application on my behalf, the secretary ted that the impressions taken from each electrotype plate varied from 400 to 1000, depmiding chiefly on the character of the engraving, the average being about 720. They found that repairing was required to some extent in the earlier plates, but latterly it was only necessary where the plates were much undercut or burnished. The council of the society consider that for large numbers of impressions more dependence can be placed on steel plates if carefa% watched while at press, than on plates produced by the electrotype.
(265.) Engraved plates were not employed till the fourteenth century, but now their uses are manifold. To hand down to posterity, and to diffuse among the multitude, copies of the choicest pictures and other works of art, are their most prominent applications. To perpetuate the resem* blance, and to distribute the portraits of the great, the good, and the beloved, are other important uses. With these the public are most acquainted, but they do not constitute a tithe of the purposes for which engraved plates are required. The great consumption now for these plates is at the potteries ; for almost every common dinner-service, or every piece of pottery, has its design given by a copp&r plate. The device is deeply cut in the copper, and then it is printed on a piece of thin pap ; but tbe impression is print with
Use Op Engraved Plates.
a composition of arsenite of cobalt instead of the ordinary ink. The paper is then pressed upon the pottery plate before it is glazed, in order that the ink may adhere to it ; after which the paper is carefully washed off. The pottery plate is next glazed, and is then ready for use.
The most unmeaning devices are printed on the plates, and the willow and other similar patterns certainly exhibit no great beauty of design. Our common pottery- ware, however, is the envy of every foreign country, for nowhere but in Britain have they ever been able to make common earthenware with any degree of perfection. The electrotype promises to materially improve the patterns of our otherwise unrivalled pottery, for the expense of engraving valuable plates has been hitherto sucli, that on account of the small number of copies th'ty will afterwards print their application has been necessary prevented. Now if a plate cost originally a thousand guineas, an infinite number of duplicates could be taken from it by the electrotype, and in this way the expense of every common dinner plate would be the same, whether the ordinary blue-and-white service were used, or plates and and dishes were embellished copies of our finest works of art, the most exquisite scenes of nature, the most elaborate machinations of fancy, or the most intricate specimens of execution. Before long I trust that the silly devices we have at present in use, will be changed for more elegant and highly finished drawings.
(266.) A second extensive application of copper plates, is to be found in the manufactories of the calico-printers. They employ copper plates for printing their calicoes. In these instances, the copper plate is first engraved, and bent round so as to form a cylindrical roller, and then the two edges are soldered. By contrivances the die is placed by other rollers into the hollow of the engraving, when the calico to be printed passes under the roller by the force which the roUer itself exerts from the revolution imparted to it by a steam-;
Multiplication Of Engraved Plates. 305
engine. In tliis way twenty or thirty yards of calico can be printed in a few minutes. These copper plates might be either multiplied before they are bent, or afterwards, upon the same principles that plain electrotype copper plates are made. There would be no great difficulty to make a perfect copper roller without any solder, should that be a desideratum to the manufacturer.
By tlie kindness and courtesy of Captain Yalland, R. N., I was enabled to examine the mode in which the multiplication of engraved plates is usefully carried out at the Ordnance Map Department, at Southampton. The plans of the maps are first drawn ipon paper, from w'hich the engravers work. There are many curious plans by which labour is saved by mechanical contrivances ; as some effects are produced by fine lines, others by dots. Again the representations of words are engraved mechanically, and the altitudes of different places arc punched into the copper plate. These copper plates are of large size, and are technically called double elephant plates, and when finished are transferred to the electrotype department, where Mr. Geddes has arranged and conducts the process in a masterly manner. The batteries are of platinized plated copper, the back and edges being very thoroughly varnished to prevent any action from the liquor. The pieces of plated copper are carefully screwed on to a frame, so that one piece of zinc can radiate to each surface of negative metal. In a former part of this work I have recommended large troughs, but what will my readers say to troughs of such depth and magnitude that the dilute sulphuric acid will last for nearly two years before it becomes exhausted with zinc; and there can be no doubt but that these large troughs are practically economical and convenient. The zincs are large cast plates, which are thoroughly amalgamated; and they inform me that since they have commenced operations they have used about 320 pounds of mercury, some of which, however, is still reclaimable by distilling the frag-.
l£DI-TIPLlCi.TION OP ENGRAVED PLATES.
ments of zinc* remaining undissolved. The precipitating troughs are horizontal, and each is placed upon four wheels for convenience of moving it about The positive pole is made of a verj thick plate of copper which is placed at the bottom of the vessel and the plate to be copied is fixed firmly to a piece of wood, which comes within a short distance in contact with the positive plate. The solution is rather diluted, inasmuch as this form of apparatus demands a somewhat slow deposit.
The object in placing the negative plate at top is to prevent any foreign body from falling upon the plate, and thus injuring the duplicate; but this course would insure a bad deposit of metal, if some contrivance were not used to circulate the fluid and cause a proper difl'usion of the metallic salt continually formed at the positive pole. To effect this result, the whole trough is alternately raised up on one side and then on the opposite, which causes a little splash each time. This effect is produced by mechanical contrivances attached to the steam engine and appears to answer admirably.
Great care is taken to have a pure solution of sulphate of copper, wiUi dilute acid and water, and the positive pole is frequently cleansed of that black powder which is always lefl upon it.
The rate of deposit in this horizontal apparatus where the negative plate is uppermost, must be necessarily slow, but it is stated that from one and a half to two pounds of copper were deposited upon a double elephant plate every day.
Captain Yalland informed me that by making connection the instant the negative plate was inserted in the liquid they
♦ According to Mr. Warren De U Rue, 1000 parts of zinc plate reaidaes uBoally give the following results, on ajrsis : —zinc, 673, moroarj 43, kias S84. From the distilled residBe a imnarkalile crystalline compound was obtained of the form of right rhombic priami, and appeared to obey the following formula : — 240 zinc, 8 iron, 5 lead, and 4 other.
Multiplication Of Coppeb Plates. 307
had never encountered a single mishap by the adhesion of the new plate.
Electro-metallurgy has, in this case, been of the utmost importance, by enabling the ordnance maps to be published at a moderate price ; but, this is by no means the only benefit which it confers on the public. The Ordnance maps represent the entire surface of England, and every spot on these maps represents some definite spot in existence. But the objects in each spot in a series of years change ; a church is built upon the site of a tree ; railroads are made over rivers and through woods. Now, to accomplish these changes, the electrotype is of great value, for it is only necessary to form a matrix from the original plate when the engraved parts appear in relief. Wherever any alteration is desired these projections are scraped off. A duplicate plate is again made, when the parts to be altered are flat and suitable to go into the hands of the engraver to have the alteration inserted in the plate. In this manner three sets of plates have been produced from each original, each being different from the other.
Notwithstanding all this perfection of detail, it appears to me that ultimately it will be found preferable to make a complete series of blocks for surface printing in addition to those plates which have been already prepared, as that course will reduce the price of printed maps to at least one fourth their cost ; a matter of no small desideratum to the multitude to whom the cost is a great object.
The unlimited multiplication of copper plates by electrometallurgy opens a question of curious interest ; for however beautiful the design of any work may be, however perfect its execution, if it is always before our eyes it ceases to have a pleasing effect. Who ever saw a ploughman ad* miring the brilliant petals of a buttercup, and yet what woric of art is equal to it ? In this case, however, the object is far more common than any work of art posaibly could be-
m
REPBODtJCnON OP OLD ENQEA.VIKGS.
con and, therefore, probably but little analogy exists between the two cases. Those print-sellers who allow but a limited number of any engraving to enter the market act foolishly ; for, if the design is really excellent, it would be impossible to render it so common that every individual in the whole range of civilised nations should cease to admire it. The more perfect the work the greater extension will it bear ; therefore, let those who engage in these arts seek rather to produce a perfect work and an extended circulation, than several imperfect engravings with but limited circulation. Engravers who are desirous of obtaining not only the necessary means for present subsistence, but also a laudable and permanent reputation, should cause a relievo of their work to be executed and deposited in some national collection, as with but moderate care such a cast would last from generation to generation.
Mr. Russell has discovered a process by which a steel plate can be prepared from a single impression. He keeps this process at present secret ; he tells me that he has worked it out with little or no knowledge of chemistry. After the plate is prepared, he states that it generally requires to be touched up by the graver in some parts, and that the total charge is about five shilling per square inch. He himself considers that his method will enable fine old engravings to be brought witliin the range of the means of the middle classes, and he entirely repudiates the vending of these duplicate plates as originals, although there is too much reason to fear that such a course is extensively practised. I recently purchased a proof engraving of the Village Politicians for eighteen shillings, whilst the original is worth fifteen or more guineas. Although critical judges must determine that the duplicate is vastly inferior to the original, yet the impression gives a pleasing picture. According to ordinary notions of trade profits, my picture should not have exceeded five or six shillings.
METHOD OF OBTAININa IMPRBSIXONS FROM EMORATHmflU
Poitevin has described a method hf which we maj obtain on plates raised or sunk impressions, from drawings or engravings ; these plates, in their turn, majr be used for multiplying the impressions. The engraving is exposed to iodine vapours, which only adhere to the black parts ; tiie sheet is then attached to a silver plate, polished according to Daguerre's method, by means of slight pressure ; the iodine is transferred to the silver, so that layers of iodide of silver a7e formed corresponding to the shadows of the engraving. The plate is then immersed into a concentrated solution of sulphate of copper, and used as the negative pole of a weak battery ; it is removed before the iodized portions are coated with copper. The plate is at once washed, and the iodide removed by hyposulphite of soda; the copper surfaces are then oxydized by heat until they become dark brown, the exposed silver surfaces are amalgamated after cooling, and the plate being covered with two or three layers of gold leaf the mercury is volatilized by heat The gold is brushed off from those parts which arc covered with oxyde of copper, and to which it does not adhere. The oxyde of copper is then dissolved by a solution of nitrate of silver, and the silver, as well as the subjacent copper, exposed to the action of dilute nitric acid. The parts covered with gold are not affected, so that the etching may be carried to any depth ; the plate which is thus obtained, may be employed for taking impressions, in the manner in which wood-blocks are used.
In order to obtain plates engraved as deeply as the plates used for ordinaiyr copper-plate engravings, a plate of gilt copper is employed. By proceeding as above, the light parts are covered with copper, and the shaded parts being deprived of the iodine, the gold amalgamated is removed from the shaded, and the oxide of copper from the light parts by acid. The latter will then be protected against the further action of the acid by the gold, and we obtain a deep engraving.
Chap. Iv.
ON THE MCLTrPLTCATION OF STEEL PLATES.
Process for making a copper plate from a steel one, 267. Perkins's appa* lotus, 26S. Comparison between the two processes, 269.
(267.) Steel plates can only be copied in a peculiar man* ner. They must not be placed either in the sulphate, nitrate, or muriate of copper, as certain destruction would ensue. I have heard of steel plates being thus destroyed, and therefore I particularly dwell on the fact to prevent its repetition. The crystallized acetate of copper is not decomposed by steel, though after the galvanic current has been pas8ing*for some time free acid is left, which is apt to attack the steel. A steel plate, however, undergoes no change in an alkaline ammoniuret of copper, ammonio-sulphate, or ammonio-nitrate of copper. From these salt therefore, the copper may be thrown down upon the steel, but I am afraid that no advantage can be taken of the fact, as the reduction of copper by these means is attended with considerable difficulty. Under these circumstances, we must have recourse to other methods of making a relievo duplicate from a primary plate of steel. This may be done in either lead, gutta percha, wax, plaster, or any other substance on which we can obtain a perfect cast, and from this a copper plate can be again made in the same way.
Besides these modes of making a reKevo from a sted engraved plate, I have yet another plan to propose, whiek is even far superior to any yet detailed, and which on that account, must supersede every other mode. This process of multiplication, which is so excellent, consists in first making
Vultiplication Op Steel Plates.
a reverse in silver, and lastly, a second reverse in copper, which is used at once for printing. To effect this object, the steel plate must be carefully cleaned from any adherent grease, and allowed to remain in a cold place twenty-four hours before using it. A strong solution of argento-cyanide of potassium must then be procured and placed in a stoneware or glass vessel. A piece of silver connected with the platinized silver of a battery should be next placed in the solution, and the size should be about the same as that of the steel plate. The last operation is to immerse the steel plate itself, which must not be elected before it is connected with the zinc of the buttery. The process should be continued tiy the silver is sufficiently thick for removal, which opera-* tion must be performed in the usual manner. There are, perhaps, no processes in the whole range of electro-metallurgy more easy than this ; for the silver may be obtained of excellent quality, and not the slightest adhesion will be found to exist between the original and duplicate ; even the absolute polish of a highly burnished surface will not suffer any injury from such a proceeding.
It is hardly necessary to mention that this process is applicable to steel dies, punches, and every other kind of article, as no greater difficulty would ensue in conducting the operation.
The only detriment to the formation of a silver relievo, is the expense of the metal, which in large plates would be considerable ; perhaps, in some cases, that might be diminished by giving a layer of copper ; otherwise we must be careful, as soon as we have formed a second reverse of copper, to re-melt our silver, and take especial care to suffer as little waste of metal as possible. The process except in the great value of the silver, is profitable from the equivalent of silver being high.
(268.) Before 1 bring to a conclusion a description of method by which duplicate copper plates can be obtained
F£Rk1Ks*S Pbockss.
from primary plates either of steel or copper, I think it necessary to mention, that metallic plates may be multiplied not only by voltaic, hut also by mechanical means. This latter method has been in use for some years, and was devised by that original mechanic, Mr. Perkins, who obtained a patent for his invention. The apparatus he employed may be described generally in a few words : he first engraves on soft steel plates, and then hardens them. From the intaglio impression of the device he obtains a relievo impression on a circular roller of soft steel, by employing an immense pressure on the roller as it revolves. The circular roller which has the drawing in relievo is then hardened, when any given number of printing plates can be made from it, in a very short space of time, by placing a plain plate under the roller, and causing the roller to revolve whilst under an immense pressure.
Some difficulty arises in performing the operation, for if it is continued too long, the fine work is injured; if too short a time, the deep portions are not sufficiently indented.
(269.) The duplicates by Mr. Perkins's process are never such perfect copies of the original but that engravers can tell one from the other, on account of an apparent imperfection in the plate, which requires the plate to be touched up. It is needless to add, that this immediately destroys absolute identity. The duplicate obtained by electricity is perfectly identical with the original plate, and no engraver can tell the original when both are placed before him. However, there is one circumstance which is very singular, namely, that the duplicate or second plate gives a more beautiful impression than the original. This variation does not arise from any difference of tint, for this depends more on the printer than the plate, and is technically termed the pull. In fact, a oopper-plate printer can print the same plate of several de-* grees of shade, depending upon the quantity of ink which he leaves in the work. The beauty of the dujdicate over the
Durability Of 8Tebl Plates.
origrinaly perhaps, is to be attributed to the superior quality of the copper, which gives a better tone to the impression, for certain it is that every electrotype is slightly superior to the original plate. To give an idea of the durability of steel plates for printing, 1 may mention that Mr. Oldham, the Bank Engineer, informs me that a steel plate, with occasional reparation, will print about 60,000 impressions.
Some years ago an attempt was made to print from stereotype copies of engraved plates. A plaster cast was made from the original, when a stereotype copy was formed in the usual manner ; but the process failed, not from a want of accuracy in the duplicate, but from the circumstance that the alloy of lead was found not to print clear like the copper or steel originals.
Since this edition has at press, it has occurred to me that for all multiplications of plates it would be preferable to use a copper pole made like a Venetian blind, each blade being about three inches in depth, and inclined at an angle of 45® to the perpendicular, and the blades being separated from each other by an interval of half an inch. By this plan the deposit may be more rapidly carried on ; but at present 1 have not had time to ascertain, on an extensive scale, its superiority over the present plan.
Char V.
On The Multiplication Of Wood-Cuts.
on wood-cuts, 270. Process, 271. Conclusion, 272.
(270.) Civilised nations ought to regard the first application of wood-cuts with peculiar veneration, as they seem to have suggested the idea of printing. At the present time, however, wood-cuts deserve especial notice, on account of the beauty of their execution ; for they have now been brought to such perfection, that in minuteness and sharpness of drawing, I have seen specimens which fairly equal steel engravings. They might appear not often to require multiplication, because it is almost impossible to wear them out; 10,000, 20,000, 50,000, nay, even 500,000 or more impressions have been taken from one wood block. Still, however, a duplicate in copper is frequently required for various purposes. Wood-cuts are somewhat the reverse of copperplates ; for in the latter, the print is obtained from the ink left in the hollows of the plate, but in the former the design is the most elevated part, and the impression is printed from the ridges.
(271.) Surface printing seems to have been very little employed till the fifteenth century, at the conclusion of which, it reached a high style of perfection, the cuts of Albert Durer, as well as those of his contemporaries, being much esteemed for the beauty of their design and execution. After that period the art ban, strange to say, again gradually to decline, and was nearly lost, when the genius of Bewick, at the conclusion of the eighteenth century, gave a fresh stimulus to this important branch of art, and from that period it tom to its present unrivalled excellence. The
SrRFACK PRINTING.
dl/l
superiority . of surface over other kinds of printing depends upon the facility with which the former operation of printing is performed, and the comparative indestructibility of tlie design.
For the multiplication of wood-cuts and other analogous designs for printing surface blocks, electro-metallurgy is useful in many ways. For cuts that are used for a variety of purposes, as the arms of the sovereign, where many persons design a separate block to [rint, the type-founder usually lias the design cut in wood. This is coated at the back and edges with wax or grease, black-leaded, and immersed in the solution of copper in the usual way, so that an intaglio mould is produced. This mould may be used to make reverses, which are at once ready for the printer ; or it may be used ns n die to form clich(;e easts.
In many instances, especially from moderate* sized woodcuts, a cliche reverse is at once taken from the cut. At present there are few in England that are trusted with the perfonnunce of this operation, and I believe that only
Branston practises it as a profession. Prom the annexed cut, designed by the younger Landseer, then a lad twelve
Multipucation Of Wood-Cuts.
years of age, whose rising genius will doubtless some day place him at the top of his profession, a cliche mould was first taken, and then, from the clichde, an electrotype duplicate, which, as in every case where an electrotype is wanted for surface-printing, required the back to be coated with solder, or fastened to a block of wood to render it thick enough for fixing with the other type. The above cut I am enabled to give through the kindness of Mr. Longman ; the clicbe was executed by Branston, and the electrotype by De la Rue. Valuable wood-cuts, however, are but seldom permitted to have cliches taken from them, for fear any mischance or injury should ensue to the original. In these cases, a reverse of the original is formed in gutta percha, plaster, white wax, &c. ; the former, however, being much to be preferred. Mr. De la Rue has discovered and recorded that electrotypes will not long print vermilion inks, although ordinary copper is well adapted for that object. The electrotype after some time decomposes the vermilion and turns white, showing that it has reduced the mercury. This fact he attributes with great probability to a difference of aggregation of the two metals.
The multiplication of wood-cuts has been far more extensively carried on by Messrs, De la Rue than by any other firm. Their manufactory is reckoned, by those most competent to form an opinion, one of the most complete specimens of the union of art and science in mechanics, physics, and chemistry, that this metropolis, or perhaps even the entire world, can boast The electrotype department occupies but a trifling nook in their vast establishment, and is used for the multiplication of the surfaces they employ for printing. Engaged extensively in the printing of every kind of ornamental and fancy stationery, they have a vast number of designs they find convenient to multiply by the electrotype, and perhaps at their establishment the value of ekctio-
SURrACE PRINTING FROM COPPER. 317
metallurgy in the department of surface-printing is bettor seen than at any other manufactory.
for surface-printing are found to be even preferable to the wood itself, os not only is the copper far more durable than the wood, but even the cupreous surface is found to print more beautifully.
Our friend Punch finds a copper face is suitable for his purposes, inasmuch as his title-page is clectrotyped. Every body reads Punch, and likes to see every person's follies shown up in a humourous point of view except his own ; but his turn coming but seldom he is perfectly satisfied to enjoy laugh at other people, notwithstanding the occasional sacrifice* of himself. From the artistic and literary talent employed upon this periodical a very large sale is secured, and I am informed that between four and five millions of impressions have been taken from their frontispiece, which well shows how far a coppered face will serve, at any rate for surfaceprinting. As Punch has amused his readers at my expense, he cannot complain at my endeavour to instruct mine at his.
I am also informed that the vignette at the top of the Illustrated London News is engraved on copper to print as a wood engraving. This wonderful periodical, which has done so much for the public in wood-engraving, has also an enormous sale ; for nobody is satisfied without seeing the representation of every occurrence which takes place, and it is said that some copies of this vignette have printed at least three millions of impressions. Doubtless this journal would find the electrotype suit their purposes as well as the copper die. It is a curious fact that at the present time the great difficulty which is experienced by the large periodicals is, tliat of getting them printed to supply the public. The Times newspaper has been so much inconvenienced that a new printing press has been devised to meet the difficulty, and
APPLBOAKTh's PBINTIKO MACHINE.
even the weekly journals experience great trouble on this score, and can only supply to the venders the few quires as they come from the press. The demand for newspapers continually increases with improved intelligence, so much so that the aid of the mechanic is perpetually being worked to meet the increasing wants of the public, and in some cases the printer is compelled to work with two sets of type.
The present machine for printing the Times newspaper, devised by Applegarth, is an astounding example of human ingenuity. It is a great object to be able to print one side of the paper as rapidly as possible, so that the public may be supplied with intelligence up to the latest possible moment. The type is set up in columns as for any other newspaper, but, instead of lying flat, is fixed on a cylinder with a wedgeshaped rule between each column to adapt the series of flat surfaces to the circular form of the cylinder. As the cylinder is placed vertically the type requires to be screwed very tightly, otherwise it might be disarranged by centrifugal force, or other causes during the action of the machine. By elaborate contrivances of wheels and tapes it is so arranged that during one revolution of the cylinder the type is inked by machinery, and supplied by eight men with eight sheets of paper, which are printed, and removed by eight other men. By this mechanism 10,000 impressions are printed per hour, forming a strong contrast with the old mode of printing by hand-presses in vogue at the beginning of this century.
During the action of the machine every paper must be supplied precisely at the right time, otherwise it would not be printed at the right place ; and much of the nicety of the machine is given by care movements, which regulate the speed of different parts of the operation. It is perfectly bewildering to see the machine in motion, the rapidity with which tile sheets traverse is extraordinary, and whether we consider the machine for the effort of mind required in its
Baxter's colour priktwq.
construction, or whether we consider it for the social and moral results wliich it produces in the community, wo must admit that it is a far more noble testimony to the power and ingenuity of this country, than the pyramids were to Egypt, or St Peter's to Rome.
A process devised by Baxter is now much in vogue, lie is said to employ a copper or steel plate to give the general outline. Subsequently he engraves one or more wood blocks, which he dabs with diiferent coloured varnishes instead of printing-ink, and in some cases he is said to apply one colour over the other ; and then the print is taken from a press as from an ordinary wood-cut. By the combination ot about eight colours all the beautiful artistic effects can be produced. By Mr. Baxter's processes the various tints blend into each other in succession, and thus character is given to the figures, and a degree of tone and shading is given to the land8ca[>e. The appreciation of these pictures by the public is interesting; and 1 have authority for stating that some have reached a sale of 300,000 copies ; and thus, by placing elaborate and beautiful paintings within the means of the industrial classes, the taste of the community cannot fail to be improved. From the incredible sale, the first cost of getting up is of no object, and 1 am informed the actual working of the smaller subjects is slightly under half a farthing each. The coronation of her Majesty is the most elaborate work which ho has executed ; but a holy family after a picture in the possession of Lord Brougham, a portrait of Jetty Treffz, and other specimens now lying before me, are very beautiful examples of this style of art. Doubtless the electrotype, by allowing us to vary the details of an original block in any number of duplicates, might be brought to great use for Baxter's process. In my visitations in more humble dwellings I like to see these pictures. They enliven the homes of those whose duties have occupied the day. The beautiful forms and harmonious colours gladden the
Glyphogkapht.
heart of the owner, and thus we find that science contributes to morality and happiness. The English, as a nation, are remarkable for their non-appreciation of the harmony of colours ; and doubtless printed pictures, if extensively circulated, cannot fail to tend to remedy this defect.
Electro-metallurgy promises to lend an important aid for printing surfaces generally, as an unlimited production will allow of the use of illuminated letters similar to those which graced the works of former years. There is but one obstacle to a great improvement in this department of the arts by electro-metallurgy, and that is the insecurity which the founder experiences in the absolute right to his productions ; for if he incurs a great expense and executes a splendid design, as soon as he sells a duplicate he is liable to have the design pirated, when perhaps his original outlay will not be sufficiently covered. As soon, however, as more stringent laws are made to protect particular designs every printed book will doubtless show the benefit of electrometallurgy.
One of the most beautiful series of specimens of printing from electrotypes is to be found in an illustrated edition of Thomson's Seasons, all the woodcuts of which were carefully preserved, and the actual printing performed from electrotype copies. (Jig, 38.)
In no application of electro-metallurgy is the value of the science more conspicuously shown than in a mode of producing surfaces for printing lately patented and called by the patentee Glyphography. This branch of art was invented by Mr. E. Palmer, of Newgate Street, and forms an important feature for the general illustration of printed works, and on that account demands particular consideration. The term Glyphography has been given by Palmer to this invmition, to signify that the original drawing itself is at once engraved, requiring no copying, and in fact scarce) any instruments, exot those with which the artist mak
Ui& design. The mode in which so extraordinary an end lb acoompHshedf appears ridiculously simple when it is detailed. The most essential part of the process is to make all the surfaces for printing as flat as possible, and for this purpose a plate of copper as used for engraving is first procured. This is blackened with the sulphuret of potassinm, in order that the draftsman may be enabled to judge of the effect which his drawing would produce as he proceeds with his work. This blackened plate is warmed and then coated with a compound of Burgundy pitch, white wax, rosin, spermaceti, and sulphate of lead, preriously fused together. This composition, which is nearly white, must be uniformly
<}tTPfiOGIUPHIO PBOOESSES.
spread over the plate, and the thickness should be about the one'thirtieth of an inch. The plate is now ready for the artist, who cuts through the white composition completely down to the blackened copper, and in fact with the exception of that precaution makes his drawing in the usual manner. In the selection of tools the artist should be guided by the manner in which they can completely and clearly cut out the composition ; for it is important to make a clear indentation and not to turn aside the coating and leave a burr. A simple hook fixed in a wooden handle, a hook filed away on one side which most effectually cuts away the composition, or a piece of wood tapering to a fine point, are the forms particularly recommended by Palmer. The former instrument is best adapted for very fine lines, the second for larger lines, and the last for foliage and other free drawings and designs.
When the artist has finished his drawing, the parts of the composition wliich are removed leave black lines, which have precisely the same relation to the white ground as the black lines in the subsequent print have to the white paper ; so that a most important feature in Palmer's operations, is the exact similarity between the design and the print.
Many improvements have been made in the process since the former edition of tliis work was published ; such, for instance, as giving a greater depth to the ; for the ground through which the drawing is made being necessarily very thin, printers found great difficulty in keeping their work clean. To alleviate this the plate is now submitted to the following process.
A roller being made of glue and treacle, such as is used by printers for inking their work, is charged with a compositioii of gum thus, turpentine, litharge, and red lead, and then passed light j over the drawing, taking care that the roller is very lightly charged in the first instance, that it may not stop np the work. When this coat has become dry, which
OLTrHOGRU*HIC PROCESSES.
it will in a very short time if put on thin, the operation must be repeated again and again, until a considerable depth has been given to the work.
The required depth having been obtained for the general work, broad lights should be built up by means of brushes with the same composition containing more litharge and sulphate of lead, or any other composition which will tend to aid the drying, and is not acted upon by the copper solution in the subsequent process. This part is very essential, or in printing the paper is pressed to the bottom of what is intended to be a light, and the effect destroyed.
The operator must now allow tlie whole to get hard, and then with a magnifying glass go carefully over it, and remove anything which may have accidentally got into the lines, lie must also then carefully brush it over with the best plumbago, taking great care to brush all out of the lines, or the block, after it is formed, prints rotten by the lines not being sound and firm.
The drawing is now ready to receive a deposit of copper, and the power of the battery must be carefully regulated to prevent too rapid a deposition, or the copper is apt to grow over some parts if the line is not well cleaned out, and disappoint the artist by work not being copied, which he imagined be had put in.
Having obtained a sufficient thickness in the electrotypt trough, and this must vary according to the size of drawing, the deposited plate is separated, and the back trimmed to receive a layer of type metal, and then, having made the face perfectly flat, the back is turned off and mounted upon a block of wood similar to a stereotype. Many touches to relieve different parts may then be readily put in by a person accustomed to use the graver ; indeed much time is saved by removing the composition altogeth in some parts, and potting in any little touches afterwards to give relief to the dark.
GLYPHOQRil*BlC PROCESSES.
This deepening of the work by the rolling process was a great improvement by giving to the artist a plate with a much thinner ground than was at first used ; but it was subsequently found by Mr. Hawkins, who now carries on the process, that he could likewise form a block upon a common etching ground, which had been so much desired by those accustomed to etching; indeed practice has now enabled him to form a surface block from almost any engraved plate.
Many very beautiful subjects have been done by this process. Some of the most successful are those well known prints of the ''Bottle," by Cruikshank ; but the subjects best adapted, are maps, or writing of every description, and here it stands unrivalled both for price and quality. Messrs. Chapman and Hall, the publishers, are at this time bringing out a series of electro-glyphographic maps at one penny each. A series of very excellent copy-books have also been done by this art, and it has also been employed for bankers'
Bankers
cheques. Messrs. Blackie and Son, of Glasgow, are novr publishing a very valuable work entitled the Imperial Gazetteer, the maps of which, executed by this process, appeared to me so excellent, that 1 wrote to those gentlemen, and they kindly lent me one of Bordeaux, which I am enabled to give as an example of the value of this kind of printing.
Such are the prindpal features of Palmas glyphography ; and although it did not answer the patentee's expectatioiis by a speedy return for his labour and capital, it is now being very generally adopted for the purposes which ha?e just been described.
Electro-Tint.
Fig. 40 .
We have yet another branch of art to describe, which is an invention called the electro-tint, and which may be dismissed in a very few words. A plain copper-plate is procured, upon which the artist makes a painting with some substance insoluble in the solution of sulphate of copper. The plate is placed in the solution and a reverse made, which is at once ready for the printer.
A great many specimens of the cleclro-tint have been published at different times, and 5f various degrees of excellence, but the best that I have seen is a small portrait of Lance, by himself. There is something very pleasing in this print, and it shows at what perfection the art might eventually arrive. Sometimes the electro-tint cast is used to print from the hollows, at others from the elevations : thus, in one ease it forms a kind of engraving, at another a
Applications Op Electbotipb.
surface similar to that of a wood-cut. The first idea of the electro-tint was published in the Phil. Mag., June, 1840.
(272.) The different cases in which electro-metallurgy is serviceable for the various departments of printing have been now described, and extensive as are their present application, doubtless still there is much to be effected in this department alone. It appears to me that the general name of electrotype ought to be restricted to these cases ; for although the propriety of the term when thus employed cannot be doubted, yet an extension of its use for dissimilar purposes is certainly inaccurate. The electrotype, therefore, I consider as one of the subordinate branches of the general science of electro-metallurgy; though, doubtless, as the importance of the art of electrotyping for our manufactures is extremely great, so also its interest is increased from its being the first department in which the electric fluid has ever been used extensively to further the manufactures of the country.
Chap. Vi.
On Multiplication Of The Daouebrkotype.
Value of the Electro- Mctalluiy for the daguerreotype, 273. ProceM for obtaining the duplicate, 274.
(273.) Papers and periodicals from time to time have contained accounts of the multiplication* in copper, of these splendid works. The success, however, which at first ottended these ojierations, 1 am afraid was not so great as has been reported. The image on the copper duplicate was sometimes moderately distinct ; but it did not become visible till it had been exposed to the sun*8 rays. Sometimes nothing was left on the original plate, nor was anything visible on either till exposed to the light. On the original, however, the image never returned ; but the plate was uninjured and therefore might be employed again. The copper deposited upon a great number of plates had not the faintest trace of any view upon it. In some of these cases, the image was transferred from one plate to another rather than multiplied, because there was no increase of images, the image on the silver being only removed to the reduced copper, leaving the original plate quite plain and polished. In other original plates, however, a faint image was left. The daguerreotype processes have been much improved of late years : the faint images first produced have given way to the most lively and distinct impressions. These impressions may very readily be multiplied, and the copper duplicate is in no way inferior to the original, although it requires to be very carefully protected from the action of the air. It
PBOCBSS worn XCLTXPUCATXOK.
(mai to iMmror beit for oMouaioaoing the depodtiott ; but u mm m iSk plmta it weQ covered then it majrbe removed to lilt adfd eolittioiH and the deposit carried on by means of a battery.
Take a saturated solution of sulphate of copper, and having filtered it, as before describe and placed a porous tube containing the proper acid and water in the same vessel, unite the daguerreotype at the corner to a ainc plate by means of a wire having a binding screw at each end. The wire must be long enough to allow both zinc and picture to go at the same moment into their respective solutions, by which means galvanic action is instantly set up, and a deposition immediately takes place over the whole of the surface, without allowing time for the plate in any way to be acted on.
Care must be taken not to remove the plate too soon from the solution, but any air bubbles are best removed by allowing a stream of water for an instant to flow over the surface.
As soon as the required thickness has been obtained, the zinc plates must be separated, and the original daguerreotype plunged into clean water to remove all traces of copper, and finally dried off in the usual manner, whilst the deposited copper should be protected as much as possible from the air.
With respect to the above account, I am of opinion that the battery process may be safely used throughout, if ample power is supplied at first by using two batteries in series.
It is necessary here to call the attention of my reader to the fact that, notwithstanding Monsieur Daguerr was liberally rewarded for his invention in his own country, and France proudly vaunted her liberality in giving his discovery to other nations, yet a patent is taken out in England, which renders it illegal to apply it for sale without the especial license of the patentee !
Book The Sixth.
On Galvanic Etching.
Action on the positive pole, 275. Etching by nitric acid, 276. Faults in the biting, 277. Galvanic etching, 278. Accelerating circumstances, 279. Advantages of galvanic ctclung, 280. Gradations of tint, 281. General remarks, 282.
(275.) All our previous operations have been conducted at the negative pult* of the battery ; but at the positive pole certain effects take place which may be taken advantage of in the arts. Let us call to mind the fact, that gold, silver, and all metals with a greater affinity for oxygen, are dissolved when made the positive pole of a cell charged with a solution of the same metal. Now the relative distance which is maintained between the positive and negative poles affects the degree of solution which takes place. This property may be easily shown by attaching a wire by one of its ends to the silver of the battery, and placing the other in a solution of sulphate of copper in the bottom of which a piece of copper connected with the zinc of the battery is immersed. After a short time the wire will begin visibly to be dissolved, and the part nearest the negative metal will be affected ; this will go on till the wire is dissolved, in such a manner that the part nearest the negative metal will diminish to the sharpest point, and the different amount of action will produce a perfect taper.
(276.) Although this property is of no value in its application, yet 1 have introduced it to show the facility with which the copper in every place is dissolved exactly in propmrtloii
ETCHING BY NlTlllC ACID.
33 !
to the electricity passiDg : and this is likely to be extremely valuable for engravers in their etchings. The term etching, is given to those engravings where the lines are not cut by instrument, but are dissolved out by an acid. In order to make an etching, a copper plate is first to be prepared by covering it with a substance which protects it from the action of the acid in which it has to be immersed. The substance used for this purpose is composed of asphalte and wax in equal proportions, combined with a fourtii part of both black pitch and Burgundy pitch. This mixture is placed in a piece of silk, and rubbed over the copper plate which is kept at a moderate heat, by holding it over a lamp or chafing-dish. Tliis operation is technically called laying a ground ; this at first is colourless, but it is afterwards blackened by holding it over the fiame of a candle, and depressing it till a copious supply of smoke covers the surface*
The engraver, with an instrument like a needle, called an etching point, executes his drawing, and in so doing removes tlie ground, and exposes a clean surface of metallic copper. The plate is then placed in a dish, and dilute nitric acid poured upon it, till the copper is dissolved out from the exposed lines to a sufficient depth. The plate is not allowed to remain in the acid a sufficient length of time to bite deeply, as this would cause the engraving to be of one degree of blackness ; but after it has been in the acid a short time, those parts which are required to be of a light shade are stopped out, that is, they are covered with Brunswick black, or a coat of varnish capable of resisting the action of the acid ; the plate is then replaced in the dilute acid, and after a time It is again removed, and a farther portion is stopped out ; and these operations are repeated as many times as their are differences of shade required in the engraving* The degree of perfection that the professed engraver obtains by practice is truly extraordinary, considering the uncertainty which must
Process Op Oaxvanic Etchikg.
attend the operation ; for the action of nitric acid is not subject to any regular laws, and moreover is never alike over all parts of the same plate. This is owing to the copper plate itself being never pure ; but always containing tip, dispersed here and there throughout its texture, which resists the action of the acid. After a splendid plate is bitten in, some portions are sometimes left which cannot be acted upon by the nitric acid, but absolutely require the graver to bring up the fine lines.
(277.) No engraver that I have conversed with, can explain the cause of these faults in their work, but to the chemist they are perfectly intelligible ; the nitric acid attacks the copper, forming a soluble nitrate of that metal which is dissolved in the fluid ; but the action of nitric acid on tin is altogether different, for it converts the metal into a peroxyde, which being insoluble, protects the copper from the acid. The engravers have always noticed this white powder (the peroxyde of tin), so fatal to the success of their operations.
(278.) Etching by galvanism is a far more certain operation than the foregoing, because it can be reduced to known principles. In this case, the plate to be bitten in has the device first drawn upon the same ground that is used in the ordinary process ; the back and edges of the plate are then coated with wax, and it is to be connected, by means of a wire, with the silver plate of one or two of my batteries
The siae of the negative pole of copper, I stated in my former edition, should be as large as the positive or etching plate ; but subsequent experiments have proved that to bite with greater regularity and sharpness, the relative size of the two plates should be as dissimilar as possible ; for that purpose, a fine wire should be preferred, and when an equal depth is required, should be eqoi-distant from every part of the plate.
The piece of copper to form the negative pole should then be connected to the sine, when both the copper-plate and
Advantages Of Galvanic Etching.
the piece of copper are to be placed in a solution of sulphate of copper. Immediately copper will be reduced from the the solution on the negative plate, and copper from the etching plate will be dissolved to keep up the strength of the solution.
Whatever is favourable to the increase of electricity, causes the copper to be more quickly acted upon, and whatever diminishes the galvanic current, retards the solution of the metal; the nearer the etching plate forming the positive pole and the piece of copper forming the negative are approximated, the more rapid will be the action. In the
same way, the intensity of the battery also affects the
rate at which the plate is bitten in. The negative plate of copper, however, should not exceed in size the copper-plate on which the etching is executed, or else there is a risk of some of the lines being more deeply bitten in ; and, in like
manner, if any considerable part of the plate has a great
deficiency of lines compared with other parts, that part must be stopped out rather before the other, to insure a uniformity of depth, or else the negative copper opposite this part must be bent in such a ay os to increase the distance.
(279.) The advantages of galvanism for etching, ore, the absence of poisonous nitrous fumes, which are evolved in the ordinary process ; the greater uniformity of action which takes place than when the acids are used; and the rapidity of biting, which may be regulated to the greatest nicety ; the lines may be made of any depth, and are sharper and cleaner than when acid is used ; and lastly, no bubbles are evolved, which the engraver well knows are apt to tear up the ground, or to cause unequal action.
The exact quantity of copper dissolved from the plate can be ascertained by weighing the metal reduced on the sheet of copper which forms the negative pole, or by measuring the quantity of hydrogen evidved from the silver plate of tme of the platinized silver batteries ; for thirty-two
834 On Executing Gradations Of Shade.
grains of copper will be dissolved for every forty- eight cubic inches of gas evolved.
Etching by galvanism can be executed with any desired degree of rapidity, according to the series of batteries to which the plate is connected ; but 1 believe that the practical man will find that the action should neither be too slow nor too quick, and perhaps two or three batteries, arranged as a series, will be found best adapted, though a single cell would sufilce.
(280.) Galvanism would be valuable to the engraver for executing gradations of shade, such as, for instance, the effect of a strong light illuminating a whole room. The most simple manner in which this can be shown, is to take a copper plate and draw a number of lines on the ground with a ruling-machine. The plate, after having its back and edges coated with any non-conducting substance, should be then connected with the silver of the battery, and copper wire. These two should be then arranged in the solution of sulphate of copper, that at one end they nearly touch, while at the other they are widely apart. By this position, the greatest quantity of electricity would pass at that part of the plate where it is nearly in contact with the negative pole, whilst the least would pass at the opposite extremity. The action on the etched plate being exactly in proportion to the quantity of electricity passing, is unequal over the whole length of the plate, being greater where the metals are nearest, and gradually diminishing to the other end. This is the most perfect mode by which it is possible to obtain a gradation of shade. Many variations in the arrangements might be made by using, as a negative plate, a wire or a rod of copper, placed over the centre of a prepared plate for then a perfect gradation would be obtained, extending in all directions from the dark centre. In the same way, two or more radiating shades may be obtained, by using two or more negative wires. An insensible gra-
(Jalvanic Ktchino.
m
datiot) might be made from the darkest shade at the external edge of the plate, to the lightest point at its centre, by cutting out a hole in the negative piece of copper, opposite the part where the transition into light is required.
*The professed engraver who once practically masters the galvanic method of etching by the theoretical principles which I have here detailed, is sure to obtain great results. He could easily execute the most extraordinary transition of light into darkness, with fidelity, and with the utmost certainty. However, I trust that the value of electric etching will not be confined to the artist ; for, by removing the disagreeable consequences attending the use of nitric acid in the present of etching, more persons may be induced to enter into it, and, by this means, numbers studying the sciences will be enabled U) execute an etching of those subjects which are curious and rare, to send to their brethren who are studying the same subject. Thovse travelling in foreign countries, or in picturesque situations, might transmit to their distant friends an idea of the sublimity and grandeur of the scenery which they are enjoying, or of the appearance of the towns and villages through which they are passing. In fact, there is not a person who might not be benefited by receiving etchings from others, and who might not, in return, circulate engravings of those objects which he may see. Pictorial representations are avowedly better than any verbal descriptions, so that there is ample scope for any one to exercise his talents usefully ; and certainly many cannot be aware that etchings are not more difficult to execute than common pencil drawings. The process is as suitable for ladies to practise in their drawing- Tooros, as are any of their usual amusements ; the operation being attended with as little trouble. It is necessary at first to have the plate prepared, or have a ground laid (which might be done by a workman), and at the conclusion of the drawing it has to be bitten in. The objection to this,
MB. grove's process.
hitherto, has been the disagreeable properties of the acid, as it is likely to spoil clothes or injure furniture ; but now that these objections are removed, I trust that numbers will enter into this amusing and useful branch of art.
Mr Grove has lately extended this process of galvahic etching, to the etching of daguerreotype plates. He arranges the silver plate as the positive pole in a trough, by connecting it to the negative plate of a battery. He employs the silver plate about the same size as the daguerreotype; but, I believe, he would find that he would be able to bite much deeper by following the improvements in galvanic etching described in a former part of this chapter. It is stated that these etchings, when printed, showed extraordinary minuteness of detail. Up to the present time I have been unable myself to conduct experiments upon the matter ; but it appears to me that the process should be conducted upon the principle of the current taking the easiest road, to the exclusion of the rest.
Book The Seventh.
ON ELECTRO-DISntrrTIVE ETCiriNO.
ProccJis and practical applicitton of tlic dibniptivo diHchargfj to the etdting of steel, 3S1.
(281.) It is well known tliat when the [connecting wires of a battery arc brouglit together, a spark ensues, and portions of that piece of metal communicating with the silver, are transferred to that metal communicating with the zinc. To Dr. Bring is due the merit of having first brought this fact into practical use for the purpose of engraving the hardest steel. This gentleman fixes the plate to be engraved in a small hand-vice, such as is used by watchmakers ; this [)late is then connected with un electro-magnetic coil, which is again connected with the zinc of about half a dozen of moderatesized platinized silver batteries. To another wire, attaclied to the platinized silver, is joined a wire of platinum or of gold, which it is found convenient to fix in a crochet needle holder. When this wire is brought into contact with the steel plate a portion of the latter is thrown bodily off and transferred to the etching tool, and thus by electro-mechanical skill a perfect device can be made upon the liardest steel.
If the plate and graver be attached to the reverse plates of the battery, then the wire is transferred and a gold or platinum design is effected ; but this result only takes place well in the purest steel, and the steel around the deposit is charred and burnt.
electro-disruptive etching.
Dr. Pring's process is at present a scientific curiosity of high interest ; it bears the same relation to the arts now as the first electro copies of penny pieces did many years ago ; in it is involved, however, a new application of a scientific fact, and on being thoroughly worked out may be, for aught we can tell, applicable to the die sinker and other branches of the arts, and is now applicable to imprint the most beautiful designs on swords and steel instruments of every description made of hardened steel, which would, by any other process, be diificult to engrave.
The electro-disruptive etching is totally distinct from voltaic etching. In the latter, the voltaic force assists chemical affinity, and the metal is dissolved. In the former, the aggregation of the particles of metal is interfered with, and portions are throivn out. In the one case we act, therefore, by interfering with the attraction of chemical affinity ; in the latter, by interfering with the attraction of cohesion. This process was submitted to the Royal Society in 1846, and with the peculiar wisdom for which that greatest association of philosophers in Europe are particularly notorious in their corporate character, it was allowed to slumber ; and from the mrcumstance of the inventor living in the country, it is even up to the present time but imperfectly known. The specimens which I have seen are extremely beautiful, and I hear that very interesting examples will be shown at the Great Exhibition.
Book The Eighth.
On Voltaic Blasting.
On blasting rocks or sunken vessels nnder water, 282. Electrical clocks, 283. IinprojM'r of electricity.
(282.) There aro purposes besides electro-metallurgy for which the galvanic force is applicable to the wants of mankind, and of the most con8picuou.s of the.se i.s the mode of blasting by voltaic-electricity. This beautiful idea was first adopted by Mr. Martyn Roberts, who used it for blasting in mines; but for bla.sting under water was first put in practice by Major-Gen. Pasley, who I Indieve was the first who adopted this system of blowing up sunken vessels. Whilst engaged in operations on the River Thames, he was written to by Mr. Palmer, wh(. recommended him to employ the galvanic battery instead of the long fuse then in use. After having been shown in what manner the voltaic battery was applible to bis wants, he instantly adopted it, and has since turned it to good account in the removal of the wreck of the Royal George. He at first used Danieirs battery, but when 1 visited the lighter, he had abandoned the professor's battery, and simply used an ordinary sulphuric acid battery. Captain Fisher, the Harbour-Master of the River Thames, has used extensively this process for the removal of wrecks. This gentleman has also found voltaic blasting of great value in removing hard shoals of concrete, which continually form in the bed of the river, and which could not be removed by any other method. The nature of the proceedings which Captain Fiaher adopted I am enabled to give with more
a 2
l&LASTING BY VOLTAIC ELECTRICITr,
minuteness, which will serve as a guide for others requiring similar proceedings. The barrel in which the powder is placed had a hole bored in it, 'so that it might admit a copper tube (t). This copper tube had a plate soldered to it at the upper part by which it might be fastened by copper nails to
the cask ; a plug (//) was fixed in the tube, through which two copper wires were inserted, and round the end of the wires was wound a fine piece of platinum wire (/?;, so that but a single filament extended from w4re to wire ; the rest of the tube was filled with fine powder, and a piece of cork (r) was placed an the other end. This copper tube was then* carefully secured water-tight by smearing pitch round the copper. For securing the tube and wires in their place, the ends of the two copper wires were bent and nailed to the tub- The next thing was to fill the tub with blasting-powder by another hole, and then secure the aperture water-tight with a wooden plug, which was afterwards smeared over with pitch. The cask was then lowered to the bottom of the vessel, and placed in the situation where it was destined to act A rope, previously made by procuring two wires first covered with cotton and varnished, and twisting them with the texture of which the rope is made, was then lowered tor
Advantages Of Galvanic Blasting.
S4l
the bottom of the sea, and the ends of the two wires communicating with the tube were tightly lashed to the two wires in the ro[>c. All the wires should be now insulated by gutta percha, as that material effects the object in the most perfect manner. All these things being ready, the ends of two wires at the other extremity of the rope were connected the two extremities of a small com|)Ound platinized silver battery, wlien immediately on contact being made the explosion took place.
The galvanic force is also now employed for telegrajdiic and other purposes, of which a description would here be given if it did not re<|uire a too great extension of the work, I have been compelled, howtner, to introduce the mode of blasting, iVom the inquiries made about it, and the great benefit which the process allbrds to the operator, by diminishing materially the risk of accident to those engaged in mining operations. The great advantage of galvanic blasting is dependent on the source of heat not till the moment it is wanted, and then being instantaneous; whereas, in tlie forintjr inodes of proceeding, it frequently take? place aft- r it is expected, wh<;n the workman imprudently a[)proaching to see the cause of the delay is instantaneously mutilated or destroyed. The employment of galvanic batteries in mines, ought to be peremptorily enforced ; for but a few batteries would suilice for the largest mine, and as the immerstoii in the li(|uid need not be longer than half a minute for each explosion, the charge of acid 'would scarcely require to be changed once a month, and consequently but little destruction of zinc would ensue. Tle battery might be fixed to some secure situation, and the workman would then only have to move the rope to the spot desired.
When Sir Harry Smith desired to astonish the natives of Africa, having previously arranged the contrivances required for voltaic blasting, he told them that, as an example of
Electrical Clocks.
power, he would show that he could at any definite moment command the waggon to go to pieces. The word of command was given, the circuit was completed, and, to the astonishment of the Africans, the whole was blown into the air. '
Electricity has been brought to bear to give the motion to clocks. Messrs. Shepherd, of Ieadenhall Street, have constructed electric clocks worked by four or five of my batteries, which have attracted much attention amongst the scientific. These ingenious mechanical inventors have constructed a very interesting electrical clock for the Crystal Palace, which, doubtless, will much interest foreigners.
Besides the useful purposes of electricity, it might sometimes be made to play the part of the marvellous ; and doubtless Wiseman, Faber, and such others, who seek to rule mankind by acting upon their credulity, rather than their reason, when they have caught a victim and safely concealed him in a religious house, away from his friends, might, in addition to their present indus operand manufacture apparitions of good and evil spirits, the better to assist their ordinary mental processes. Electrical appaidtions might prodttce mai'vellous effects, if used in a solitary chamber upon either a fatuous female, or a youth bewildered by theological dogmas ; but 1 feel sure that there is no electrician who would lend bis aid for such a purpose, but would rather seek to destroy the heathenish darkness of priestcraft by the illumination afiforded by the light of science.
Conclusion.
I HAVE now dctailicl briefly, but I trust usefully, the properties of bodies wliich are called galvanic, and the effects which galvanic batteries produce, m far as relates to the interesting subject of electro-metallurgy. Our science, even in itself, is essentially upon galvanism, and the precipitating apparatus employed is nothing but a battery cell. With regard to the laws regulating the metallic deposit and the metals capable of being deposited by the voltaic current, these are derived from my own observations. The importance of these laws to the operator, will be to enable him to proceed with certainty. The reason which has induced me to devote so much labour and thought to these laws, has arisen from a conviction that the electrotype must have been abandoned unless the operator could proceed upon certain fixed principles. The extension of the few isolated facts formerly known, and their enlargement into a general science will, I trust, be found useful to those engaged in prosecuting these operations.
The influence which this new branch of science will liave on the arts, manufactures, and commerce of our great country, it is scarcely to foresee. The extended use of galvanism for manufactures requires the utmost encouragement, and the improvements must not be shackled by patents, if we desire the scheme to succeed ; for the ingenuity and the talent of the whole country is required to place it upon a firm footing.
The multiplication of copper-plates will cause a far gteater demand for them than has ever existed heretofore, and the engraver need be under no apprehension ; for not only will
344 Effect Of The Electeottfe On Matofactdbes.
bis talents be more required, but he will be called upon to execute more splendid specimens of art ; for as these can be multiplied ad infinitum a large circulation will render it worth while for any publisher to pay a very high price for an original which he conceives will meet with great publiS approbation. The publisher, in the same way, could lessen the price of engravings from our finest works of art, so as to bring them within the means of every person ; and there is no doubt that he who first engages in a business upon the above liberal and well known principles, will realise for himself a large fortune, and contribute greatly to the benefit of society.
For our potteries, the multiplication of plates assumes a higher importance even than the last-described valuable applications ; for it enables the manufacturer to improve the designs upon our otherwise perfect earthenware, and then all countries will indeed be jealous of what they are already otherwise inclined to look upon with envy.
Our calico-printers will also now be enabled to use far more costly plates than they have hitherto employed.
There are many other applications of this science besides those which I have already detailed ; such as the capability of adding copper to copper, and other similar purposes, which cannot be effected by any other process. Another important application of galvanism is, the means which it is likely to afford of separating one metal from another, or from its ore.
A great variety of the applications of electro-metallurgy may appear to many to be trifling, as they contribute only to embellish the drawing-room and gratify the eye ; but let them remember, that as private persons engage in the manufacture of these little trifles, it leads to a knowledge, and a practical knowledge, too, of the effects of one of the most important and universal agents operating in nature. As manufacturers engage in it, it leads to a more general use the galvanic
ELECTRO-METALLURaT FOR BAD PURPOSES.
battery, which, doubtless, will eventually hold an important place in our manufactures.
It is true that electro-metallurgy oflfers many opportunities for fraudulent proceedings, as by it the forger can copy, with e&e and unfailing accuracy, any embossed surfaces or stamps, and therefore no embossed work whatever should be used where there is likely to bo any inducement for copying. By it seals may be forged, and an impression may be taken off a copper plate if it only remain in the possession of the party for a few seconds ; besides, our new science gives the false coiner many opportunities to further his fraudulent practices. Those things are particularly pointed out to put people on their guard against the designs of bad men.
Science, however, must not stop because some of its applications are liable to be turned to bad account by the evildesigned ; and we must recollect that those things which can be forged by the electro-metallurgist, can also be forged by other processes before known. It was a favourite maxim of our great countryman, Wollaston, that, " whatever man can cxecut(*, man can also copy," and therefore the very idea of any device being ininiitable is absurd.
Of the value of electro-metallurgy to the arts and manufactures, even in the present state of the science, there can be no doubt. It is not now a question of probability whether this science is practically applicable or not, for we have detailed wbat has been done by its agency ; we have given full descriptions of all the various processes for obtaining with certainty many results ; and finally, we have arranged all the facts into a tangible and systematic form, and, by laying down laws by which all its operations are governed, reduced the whole into a vast comprehensive science.
It may be, indeed, a matter of conjecture, to what extent this science may be ultimately carried out, or to what other purposes it may be applied in years to come ; bnt were it never to be applied otherwise than it has already been,-—
346 Electeo-Mbtallurgy Dependent On Electricity.
were it to stop for ever at the point to which we have now brought it, — no one can deny that it is a most valuable acquisition ; in short, we may safely assert, tliat no other single discovery ever presented capabilities at once so many, so various, so interesting, or so valuable.
This science depends for its very existence on electricity ; and among the indirect benefits which it may surely be hoped will arise from it, we may mention the study of electricity generally, of which gigantic power so little is known, and which plays so important a part throughout nature ; for though all of us recognise its operation in the thunder-storm, and view with terror and amazement the devastating violence with which, at such times, it makes known its power, yet, at present, how little do we know of the effects which it is at all times producing around us by its silent and continued operation.
The science of electricity is perhaps one of the most sublime examples of the might of human intellect, for by its agency man has made obedient to his will a power capable of producing such vast and terrible effects. "iVt/ mortaUbus arduum est, says Horace, when speaking of Prometheus, who was fabled to have stolen fire from heaven ; and modern science has proved again and again the truth of this assertion, though little could he have thought, when writing the passage, how nearly the fable of Prometheus would in after ages become verified.
To the young chemist, we would particularly recommend the study of this science, and should he be tempted to turn hk attention to it in a systematic manner, he will be amply rewarded for his trouble. The results of his experiments are lasting, and will be contemplated by him in after years with pleasure; whereas chemistry, being too olen used as u source of amusement, brings forth very different results. The experiments tend to notlung, and end in nodding, hejoad the present gratification ; they iUostrate facts which
SYSTEMATIC PJftOCEEDINGS NECESSARY.
have been illustrated exactly in the same way a thousand times before, and are usually selected to be gone over and over again, purely because they possess some incidental character which is calculated greatly to astonish the uninitiated though not to enhance the scientific acquirements of the o[>erator. By such a course of proceeding (for undoubtedly such it very commonly is) nothing is done, either directly by the operation, or by increasing the knowledge of the o[)erator, and there remains noticing to show for the labour and money expended, except, perhaf8, the trouble of clearing away the remains, or, what is not so easily accomplished, tlie rectifying of the mischief done to furniture generally. We have no hesitation in saying, that electro-metallurgy will afford as much or more gratification as an intellectual pursuit, and infinitely greater satisfaction in its results.
In conclusion, we cannot too often impress upon our readers the advantage of making themselves thoroughly conversant with the principles upon which tlic operations of electro-metallurgy depend, and the laws by which these arc in all cases governed. By hurrying at once into the performance of the various processes without thus qualifying themselves, what can he expected hut failure and its consequences, — and mortification P Proceeding in ignorance of the rationale of the process, untoward circumstances are for ever marring the designs of the operator ; experiment follows experiment, and failure follows failure ; materials are expended in vain, and, after the loss of much time, the student (if such he can be called) becomes tired of a science which lias yielded him so little satisfaction, and throws it aside in disgust, persia|>8 attributing its uncertainty to that which is the pore and absolute result of his own idleness, and consequent Ignorance. But if the student proceed in orderly and philosophic manner, making himself first acquainted with the nature and
Prospective Advantages.
modus operandi of the materials with which he is about to work, he cannot by any possibility fail in his results. With such preparation no casualty can occur which cannot be readily referred to its true source, and consequently as readily remedied. Those who are comparatively unacquainted with electricity and galvanic apparatus may meet with some little trouble in entering upon the science of electro-metallurgy ; but commencing upon a right method, their first trouble will be their last; and let them always bear in mind, that without trouble no great good was ever accomplished.
Doubtless the galvanic fluid will, before long, be as important to the manufacturer as the heat of a furnace. At present a person may enter a room by a door having fingerplates of the most costly device made by the agency of the electric fluid ; the walls of the room may be covered with engravings, printed from plates originally etched by galvanism, and multiplied by the same force ; the chimneypiece may be covered with ornaments made in a similar manner. At dinner the plates may have devices given by electrotype engravings, the salt spoons gilt by the galvanic fluid, and bis table covered by costly electro-silver-plated ornaments. All these, and many other applications, we may liave at present, — but we must still look forward to the most important properties of the electric current derived from the galvanic battery ; for although great and glorious are the triumphs of science detailed in this work, yet the prospect of obtaining a power which shall supersede steam, exceeds in value all these applications. For to cross the seas, to traverse the roads, and to work machinery by galvanism, or rather electro- magnetism, will certainly, if executed, be the most noble achievement ever performed by mam
Appendix.
ON KLECTKO-METALLrucaCAL I'ATENTS.
The statute of Monopolies, (21 J. 1, c. 3), declares the conferring on any per.ton the exclusive privilege of carrying on a particular or manufacture, to be altogether contrary to the laws of this realm, and a species of offence, called monopoly. The statute, however, excepts Letters Patent for the term of fourteen years and under, for the working or making of any manner of new manufactures within this realm, which others at the time of making such Letters Patent shall not use,
A new manufacture may be the prcaluction of a new article for the first time, or a new mode of producing the same article either by an addition or omisHton of any part of the process, or. with regard to chemical }>tents, of some new specific process. A new manufacture may also consist of a new application and adaptation of some known agent or thing.
It is essential that any of the above manufactures or processes should be a new invention as to the public use and exercise thereof in other words, no patent is valid that is taken out for an invention in public use, although the practice in secret of any process, by a manufacturer, will not prevent another manufacturer from taking out a patent for the same process and forbidding the first. The prior publication of a process in a printed bk in this country, under certain ctr. cumstauces, will vitiate a patent, though a process well known and freely practised abro may be patented in this country. The new manufacture, in any case, must be useful to entitle it to a patent ; therefore, the slightest novelty attended with great good will justify a patent.
For the inventor to secure to himself the exclusive right
Appendix.
of a new manufacture it is essential that he should disclose his process in such a way that persons may use the same at the expiration of his patent ; and the spirit of the English law seems to suppress monopoly, but to allow advantages for a limited period, to those who benefit their country by adding or introducing any new and useful manufactures.
The principle which guided our forefathers upon patents deserves the highest commendation, though the practice of their successors upon this subject cannot well be worse ; for, as now constituted, Letters Patent cause great expense to inventors who really deserve them, great injury and trouble to manufacturers from their being frequently granted where not deserved, and endless expense and litigation from their insecurity when obtained. If the principle of patents according to the English constitution were strictly adhered to in practice, nothing could more tend to improve and enlarge our manufactures.
By reducing the expense of the patent, affording greater facility for procuring it when deserved, preventing the possibility of its being granted improperly, and rendering it, when obtained, an absolute protection, the inventors would be directly benefited, the manufacturers protected, and the prosperity of the whole country would be enhanced by the monopoly, in the manner that the wisdom of our forefathers contempmted.
From the preceding observations, the Electro-Metallurgist will perceive that it is not only essential that a patentee should have a patent to secure the monopoly of any manu facture, but that he should have acquired it properly. For this reason it is by no means certain that the following patents are rightfully possessed, and therefore it would be wise in a person interested in any process to examine carefully how far any patent interfering with his business is valid. The following list 1 have principally compiled from the
Repertory of Patent Inventions and Kewtons London Journal,'* — particularly valuable sources of reference for these matters ; and in these journals tolerably full extracts of a great number of electro-metallurgical patents have been given-
There is a curious point of law emmected with some of
Ap1'End1X.
these patents, and that is, particular processes have come into public use between the granting of a patent and its specihcation ; and which processes could not even be inferred in the slightest degree from the title o|' the patent. In these cases, common sense, doubtless, says that the patent *ought not to prohibit the manufacture in common use ; but what the law says lawyers alone can decide. Persons requiring information on this subject may consult a cliapter dedicated to these matters in Stephen's Commentaries on the Laws of England, book ii. part ii. chap. 3, or a very interesting little treatise by Webster, "On the Subjectmatter of Letters Patent by Invention," the author being a great authority on these points.
If a true and valid patent is infringed, the inventor has his remedy by an action of trespass for injury sustained, and be may also obtain an injunction to restrain the continuation of the manufacture, and can compel the aggressor to deliver an account of the profit he has derived from the sale of the article. Moi'cover, any person using the name or mark of the tmtentee is subject to a penalty of 50/. The action may be resisted by showing that the patent is void in the manner already pointed out, or the patent may be formally impeached (if improperly obtained) in the Queen's name by the Attorney-General, or even by any other person with his consent.
The first strictly electro-metallurgical patent was granted to James Shore, of Birmingham, merchant, for improvements in prest.rving and covering certain metals and alloys of metals. Sealed March 3, 1840. Enrolled in the Enrolment Office, Sept. 1840. The patentee claims the coating of manufactured articles of wrought or cast iron, lead and copper, and its alloys, with copper or nickel ; soch coating being effected by galvanic-electricity.
The next patent was granted to George R. Elkington and Henry Elkington, of Birmingham, for improvements in coating, covering, or plating certain metals. Sealed March 25, Enrolled in the Enrolment Office, Sept. 1840. The patent is for numerous processes of gilding, plating, Ac., Ac.
The next patent was granted to Thomas foeneer, of Liverpool, carver, and gilder, and John Wilson, of the same phme, lecturer on chemistry, for certain improvements in
Appendix.
the process of engraving on metals by means of voltaic-eleotricity. Sealed Oct. 7, 1840. Enrolled in the Petty Bag Office, April, 1841.
A patent was granted to Joseph Lockett, of Manchester, in the county of Lancaster, for certain improvements in manufacturing, preparing, and engraving cylinders, rollers, and other surfaces for printing and embosing calicoes or other fabrics. Sealed August 27, 1840. Enrolled in the Petty Bag Office, February, 1841. This appears to be an important patent connected with the cotton printing manufactures.
A patent was granted to William Tudor Mabley, of Wellington Street North in the parish of St. Paul, Coventgarden, in the county of Middlesex, mechanical draftsman, for certain improvements in producing surfaces to bo used for printing, embossing, or impressing. Sealed Dec. 17, 1840. Enrolled in the Rolls' Chapel Office, 1841. This patent seems to contain numerous applications of electrometallurgy to printing surfaces, but to what perfection he carries out his processes I am unable to state.
A patent was granted to Alexander Jones, engineer, for improvements in the manufacture of copper tanks and vessels. Sealed June 14, 1841. Enrolled in the Enrolment Office, May, 1841.
To George R. Elkington and H. Elkington, of Birmingham, for improvements in coating, covering, or plating certain metala. Sealed June 22, 1841.
To Edward Palmer, of Newgate Street, gentleman, for improvements in producing printing-surfaces, and in the printing of china, pottery, vases, music, and maps. Sealed June 12, 1841. This patent is briefly noticed under the head Electro-tint in the text, and a little work dedicated to this subject has been written by Sampson.
Specification of the patent grant to Islam Baggs, of Cheltenham, gentleman, for improvements in printing. Sealed Jan. 1841 ; enrolled 23rd, 1841. This is a very Ingenious patent, whereby colours are given by means of the gfljvanic battery.
To Ogilthorpe Barratt, of Birmingham, metal gilder, for certain inrovements in the precipitation or deposition of metals. Sed 8, 1841.
To W. H. Fox Talbot, of Laycock Abbey, Wilts, Esq., for
Appendix.
improvements in coating or covering metals with other metals, and in colouring metallic surfaces. Sealed Dec. 9, 1841. '
To Edward Palmer, of Newgate Street, iHiilosophieal instrument maker, for improvements in producing printing, and embossing surfaces. Scaled Jan. 15, 1842. This important patent has been described under Glypliography " in the text, and an illustration is given.
To H. B. Leeson, of Greenwich, Doctor of Medicine, for improvements in the arts of depositing and manufacturing articles by electro-galvanic agency, and in the apparatus connected therewith. Sealed June 1, 1842.
To Edmund Tuck, of the Ilayinarkct, silversmith, for improvement in the covering or plating with silver various metals and metallic alloys. Sealed June 4, 1842.
To J. S. Woulrich, of Birmingliarn, chemist, for ments in coating with metal the surface of articles formed of nickel, or metallic alloys. Sealed August 1, 1842.
To Alexander Parkes, of Biriiuiighum, lor certain improvements in the production of works of art in metal by electric March 29, 1841.
To Alexander Parkes, of Birmingham, artist, for improvements in the manufacture of certain alloys or combination of inetaL, and in depositing certain metals, October 29,
To James Napier, of Hoxton, for improvements in treating mineral waters to obtain products therefrom, and for separating metals from other matters, October 22, 1844.
To Arthur Wall, of Poplar, for certain improvements in the manufacture of steel, and other metals, December 18, 1844.
To Louis Ilypolitc Piaget and Philip Henry du Bois, of Wynyatt Street, Clerkenwell, Middlesex, November 12,
To Thomas Lyon and William Milhvard, of the county of Warwick, for certain improved alloys of metals, and improvements in the deposition of metals, March 23, 1847.
To Cyprien Maire Tessie du Motay, of Paris, for improvements in inlaying and coating metals with various substances, November 1847.
To Sidney Edwards Nurse, of Ajnpton Ilace, Gray's Inn
Appendix.
Road, for improvements in the manufacture of plates or surfaces for printing and embossing. Sealed in Scotland, July 10, 1848.
To Alexanr Parkes, of Harborne, in the county of Stafford, chemist, for improvements in the deposition a;id manufacture of certain metals and alloys of metals, and improved modes of treating and working certain metals and alloys of metals, and in the application of the same to various useful purposes.
To Thomas Henry Russell, of Wedncsbury, and John Stephen Woolrichj of Birmingham, for improvements in coating iron and certain other metals and alloys of metals. Sealed March 19, 1849.
To Stanho[>e Baynes Smith, of Birmingham, in the county of Warwick, electro- plater and gilder, for improvements in depositing metals. Sealed June 7, 1849.
Such is the list of those electro-metallurgic patents which I have succeeded in finding, but there may be many more which have escaped my diligent search ; and, besides these, we must remember that there are innumerable paragraphs slipped into other patents which refer to electro-metallurgic processes. When some men take out a patent, they contrive to slip in as much as they can find of other processes, so that the most opposite things are sometimes contained in the same patent At the present time the whole practice of the patent law is exceedingly bad. It neither rewards inventor'8 nor benefits the public, but it appears that with this, as with other matters, it is easier to perceive the defects, than to point out a satisfactory remedy.
Analytical Index
Abmorption, by phuiter of Paris, prevented, 13JS.
Acetate ul sihur, reduction of silver from, IMH.
,, of copper, reduction of copper fnirn. 'iOl .
,, of nickel, reduction of nickel, tVom, l*)3.
Acid soiutiuu ol K'dvauic batteries, its use,
„ of DauielPs battorj , to.
„ of Grove's iMttcry,
,, of bincu's iMtttcry,
Artion, local, 0.
AUhcsiuu of hydrogen to platus of Imttery, Id. 17.
,, of original and dutd irate plates in eltvtro-mctallurgy, loy.
,, cause of, Ihl).
„ ohiaiiuHl or Avoided, IW, 1 10. i
„ of air to tiietals, 1 lU.
,, of air bubbles to the moulds. 111.
Air, blm ot, on metals, IH lU!t. Alr-bubbles. reduction of metal* on. 1 1 1. Alkalies, compounds of, with oxides, Alloys usshI for making moulds, &c. 122.
„ tuhlo . f. 12.1.
„ reduction of, 224.
Amalgamation of metal in batteries. 16. 17. lys.
„ gilding by 4 237.
Ammonia, chemical equivalent, 4!l. Ammonio-nitrate. chloride, and carbonate of silver, reduction of silver from, IHN,
Anaglyptngranb, Date's, 272.
.\QimaJ electricity. 61.
Anions, table of, 62.
.Anode with zincude, &c. 41. Antimony, reduction of, 218.
.Apfiaratus, single cell, for precipitation of metals, 87. V7.
„ capillary tube, 93.
e ster, 93. tery, 104.
„ unimtof battery and single cell,
103. 104.
„ Mason's, lOO.
„ Marsh's, for detecting arsenic,
„ for reduction of gold, 184.
Applegarth*s machine, 318.
Anastatic printing. 291 .
Arseuie, detectiim of, by Morton's plan,
M „ by Marsh's appa-
ratus, 220.
Arsenic, detection of, by galvanic precipitation, 2'iS.
Astatic needles, 39.
„ galvanometer, 39.
Atuinic tiieory. 4H.
Aurocyantdc of potassium, formation of,
reduction of gold from. 145, 146. 183, 184.
Batk's annglyptograph, 272.
Biiitcry, galvanic, discovery of. 2.
„ ,, requisites for, 8.
„ „ acid solution, 3. 8. 10,
„ electro-negative plate, 4,
„ ,, clet'tro-positive plute, 4.
,, local action In, 6.
ni)|>oarnnce In attlon, 6. chemical thcoi y of, 7 . contact tiieory, 7. quantity, 9. intvnsily, 10. amount of action In, 10. 'p4fwer of, 1 1 . compound, 13. various forms : —
,, „ Conronne des tasscs,
„ „ Luc's column, 13.
,, ,. Hare's, 13.
„ „ Crulckshank's, 14.
,, „ otiier old forms, 13,
,. .. Danlell's. 19. 21.
„ „ Grove's, 22.
„ „ Leeson's, 23.
,, „ fiimee's, 24.
,, „ odds and ends', 28.
„ ,, its premerties : —
„ „ heating wires, 36.
„ ,, igniting charcoal
points, 36.
M „ giving a spark. 86.
charging Leyden Jar,
„ ,, shock, 87.
,, „ maijinetlc eflbcts, 88.
„ decomposition efllscUi,
41,42.
Battery apparatus for reduction of metals,
„ „ for redwetko of platl-
n, 176-
fbr multiying copper-plates, 296. 296
Analytica.L Index.
Baskets, electro-coppered, 249.
Baxter's process, 319.
Bees' 'Wax and rosin for making moulds,
„ „ for preparing plaster
casts, 137.
Bicyanlde of mercury, 175,
Bismuth, reduction from nitrate, 210.
„ „ from tris-nitrate,
,, ,, from iodide, 219.
„ „ from pntassio-tar-
trate, 219.
Blsulphuret of carbon, 242.
Black-lead, used for coating n-metallic 144.
„ first applied by Mr. Murray,
„ application of, 144.
„ test of quality, 145.
„ for browsing copper. 20fi.
Black powder of platinum for bmeo s bat. teries 24 . 25.
„ of metals, reduction of, 1.51.
Bladder for porous tubes in UunicU's teries, 19.
" ,, for single-rell apparatus, 87. Blasting, galvanic, 339.
BrKjks to be consultiHl by electro-metallurgists, xxix.
Brasses, monumental, multiplication of,
,, mode of copying or " rubbing,"
Bread moulds. 143.
Britannia Bridge, model of, 282.
Bromide of gold, 1 81.
Bronsing of cop|>er by iron, 206.
„ „ by black lead, 206.
„ „ De la Hue's, 208.
„ by grease, 20fJ.
„ „ by solution of plati-
num, 207.
,. „ by sulpluiret of potas-
tiura,
„ ofcliches, 207.
BrugnatelU first invents electro-gilding,
Burnishing mid, 236.
Busts made by electro-metallurgr, 282. Buttoning down of duplicate and original plates, 109.
„ cause of. 109.
„ avoided, 109.
Caduivm, reduction of, from sulphate, 212. „ „ from chloride,
„ „ from ammonio-
sulphate, 212. expense of, 213. Calico printing, process of, 304.
„ application of electro-
meUllui to, 305.
Capillary tube, apparatus .lor reduction of metals, 93.
Carbon, a conductor, 4.
„ receives the metallic deposit, 121.
.. for coating non-cooductlog sub-
stances, 144.
Casts, modes of obtatadng, Ac. (See Mould.)
Cathtons, 62.
Cathodes, 44.
Cell of battery, 11, 12.
„ single, apparatus, for reduction of metals, 87. 91 .
Chantrey, Sir Francis, his mode of making moulds from leaves, &c., 277.
Charcoal points, ignition of, by battery,
,, used for coating non-conductors,
Chemical theory of the pile, 7,
„ circular, action, 63.
„ equivalents, theory, and table of,
electro, decomposition, 51. 56. Chemico-raechanical battery. (See Smec's battery.)
Chloride of platinum, 177, 178. of gold, 180. of iridium, 186. of cobalt, 223. of tine, 208. of cadmium, 212. of nickel, 193
Chlorine chemical equivalent, 49. t'homes, metallic, 217.
Clichees, jirocens of making, 123. 126.
„ from wood, 124
„ fiom plaster of Paris, 124.
,, Italian mode of making, 125.
,, bv the press, 125.
„ bronzing of, 207.
„ from womlcuts, 215.
Clocks, electric, 342.
Coating, metallic, for non -conductors, 144. Cubuli, reduction of, from chloride, 223.
„ „ from cobalto-cya-
nuret of potassium,
„ arsenite of, used in the potteries,
Coiners, practices of, 121.
Coining at ibe Mint, 263.)
Coins, list of, for electro-metallurgists,
„ moulds from, 255.
„ nuihipiication of. 256. 260.
„ old mode of making, 261. 263. Column, De l.uc's, 13.
CoinUustion of metals hy the battery, 35. Composition for making wooden vessels water-tight, 101.
Compound battery, 13.
precipitating trough, 99. Conductors of electricity, 4.
Conducting power of water Increased, 4.
„ „ of solutions vary with
temperature, 51 .
„ substances capable of receiving meuUic deposit, llfi,
Constancy, meaning of tbe term. 21.
„ of Danin's battery, 20.
„ practical, of ttmee's battery,
Contact, theory of the pile, 7.
Copper, reduction of :
„ from sulphate oi; 194.
„ from fdin, IM.
from acetate, 101.
Aialttical Index
Copper, reduction of:
„ from its compounds
with ammonia, 201. „ from its oxyde, 201.
from Its iodide, 162.
„ from its sulpho-cya-
nide, 202.
f, from cupro-cyanuret
of potassium, 202. „ from its citrate, 202.
„ from its tartrate, 202.
„ from tlie double salts,
„ in flexible state, 196,
„ in greater rrystallino
state, 197.
„ In state of extreme
brittleness, I9i.
„ in black powder, 198
,. time required fur,
„ positive polo of de-
compoaition cell,
„ negative poles,
„ by siiigle-cetl pro-
cess, wa
„ by battery apparatus.
summary of various I modes, 1
„ expense of, 1 15.
„ reduced metal assumes the form of negative pile.
„ sheathing of ves*ei preserved, 5 „ positive inetal of Datiicirs battery, 2ti.
.. chemical eq 111 vai .ft, 49.
t, used for receiving metallic deposit. 122.
,. bruntlng of. 206
,. reduces copper, 61 .
„ of. 2, Vi.
„ multiplication of articles in, 283.
., plates for engravers. 292.
„ present preparation of, 292.
„ M value of these,
292,
„ disadvantages
of. 292.
„ proved by electrotype, 260.
„ form of bsdtery, adapted,
M plates, form cf preciplutingtrough, 294.
M solutkm, beat adapted, 2f.5.
„ diflbrent qualities of metal ,
„ engraved plates. ( See En-
graved elrctrotytie )
medals. (See Meliotis.)
Coppering efoctro-medalUons. 258.
fru leaves, Ac. 247. 248.
prboets, 947.
M ,949.
n sbipetSO.
M e l e ctr o earthenware, 290.
Cooronne des taseee, 18.
Crosse, Mr., on the galvanic spark, 36. Cruickshank's battery, 14.
Crystalline deposit or metals, 148, 149.
- „ obtained with given so-
lution, battery or negative plate, 158. Current, voltaic. (See Voltaic.)
„ measure of. (See Voltameter and Galvanometer.)
Cyanide of potassium, formation of, 172,
Cyanuret of imtassium, formation of, 173.
Daouerrbotype plates, multiplication of,
„ patenttHl in this coun-
try, 329.
,, etcheil by galvanism,
3;)6
Daniell's observations on copper reduced in his battery, . view of the decomposition of metallic salts, 55, 56.
„ battery :
„ construction of, 19.
„ attempts to improve, 20
,, constant efforts of, 20,
.. „ most constant form of,
.. „ disadvantages of, 21.
.. advantages of, 21 ,
., removal of hydrogen, 21 .
Decoiiiposltiun a property of the battery.
laws of, 49. 50.
Faraday on the laws of, 49, electrolytlcal, 51. eUVtro-chemical or seettndary, M, 54. of rnetallle suits, Professor Daiilell on, 55, 56. effects of, only maiilfcstetl at the poles, 56, affectetl by temperature of olutltm, 57.
„ apparatus, 41.
Decomposition apparatus, various forms,
„ V-shaped tube,
„ Faraday's vol-
ta meter. 42.
., new form. 48.
poles of, 44.
„ „ norlxofital, com-
pared with vertical, 107.
Definition of voltaic force, 62,
Deflection of permanent magnet from voltaic current, 38,
De U Hue's observations on copper re.
duced in Daniell's battery,
„ brooke, 908.
De Lise's oolumn, 18.
Dentbt, value of eiectro-mcUtllurgy to,
DIchromate of potash to Leeson's battery.
Dies for coins and medals, 261 . 968.
„ from e m boaaed surCaces, 378.
ANATTnCAl INDEX.
Dies from paper, 276.
Dip of the magnetic needle neutralised,
EARTHENnAKB, porouB tubes, 19. (See Porous.)
„ precipitating troughs, 100.
Elective atBinity of original plate for solution, 118.
Electricity, various forms of, 2.
„ voltaic, 2.
Electric clocks. Shepherd's, 842.
„ light, 87.
Electro-disruptive etching, 887.
Electro-magnetic machine, 82.
„ telegraph, 84.
Electro, Barton's, battery, 280.
Electro-chcnslcal decompositions, !V3, 54.
Electrodes, name given to the poles by Faraday, 44.
Elcctro-glyphography, 321 .
Electrolysis, 61.
Electrolytes, 62.
Electrometers, Harris's, 3.5,
Electro, negative. (See Negative.)
„ positive. (Sec Positive.)
„ coppering, 246. Coppering.) „ gilding, 229. (See Gilding.)
„ ironing, 2.52.
„ leading, 2.51.
„ nickeling, 240.
„ platinatlng, 238.
„ platinising, 2.39.
„ palladiating, 241.
„ plating, 242.
„ lining, 261.
„ singing, 251.
„ magnetic apparatus, 82.
„ „ shock, 82.
,, medallions, 266.
„ roetalluBgy requires a of galvanism, 343. apparatus. 87- 168. expense of, by various batteries, 112. 116.
„ „ applied multiplying
medals, 263.
Electro-metallurgy applied to multiplying seals, 269.
„ to multiplying brasses, 274.
„ to multiplying embossi surfaces, 276.
„ to coppering
fruit, Ac. 277. „ to sculpture,
manufacture of silver articles by, 236. manufacture of copper articles by. 284. various ottw applications oC 267. etehtiif by.fSea Etchtog.)
tts eflbct on angrav. togs, 343.
prosporttoa advaa* tagmor,S46-
Electro models, 282.
Electrotype, origin of, xvii.
„ Daniell's observations on the,
„ De la Rue's observations,
Xv Ih.
„ Jacobi's idea of its applica-
tion, xviii.
„ Spencer's idea of its applica-
tion, xviii.
„ multiplication of type, 280.
„ multiplication of plain copper-
plates, 293, 294.
„ form of battery for, 294.
„ economy in, 297, 298.
„ expense of, 299.
„ multiplication of engraved
copper plates, 300.
„ multiplication of copper
plates for the potteries,, and for tlie calico-printers,
„ multiplication of steel plates
in copper, 310.
„ multlplk'dtion of wood-cuts,
Rlectro-tmt, Palmer's patent. 325. Elkington's water-gilding, 2.36 Kinbosseil surfaces, muitiplirntlon of, 276. Engraved copper plates, multiplication of.
300.
„ „ relievos in cop-
per, 300.
„ „ relievos in lead,
,, „ relievos In white
wax, 301 .
„ „ reli VOS in plaster
of Paris, 301 .
„ „ relievos in gutta
perrha, 301.
,, „ formation of re-
verse, 301.
„ „ bark of reducevl
plate, 302.
„ „ the " eurti," 802.
„ steel plates, multiplication of.
In copper, 310. ,, „ multiplication of.
In relievo, 310.
„ „ in silver, 811.
Engraving, various kinds of. 302.
„ uses and application of, 303.
„ line, 302.
„ mesxottoto, 808.
Equivalents, chemical theory of, 48, 49.
„ table of, 48.
„ voltaic, 49.
„ of galvanic power. 48, 49.
„ expense of, 112. 114. Etching, prepanUion of plate, or laying the ground for, 831.
„ cxecuBon of the design, 381.
ax OALVAiifaii', tit.
of,
Analytical Index,
Etching, BT G4LVAN1SM, for executing gradations ot shade, 334.
„ useful to ama-
teurs, 335.
,. applied to etch-
ing Daguer. rdotypes, 336.
Extiting fluids have various intonslties, 10. II have various conducting
powers, 10.
I, used in Danieli's battery,
II used in Grove's battery, 22.
.1 used in Smee's battery, 26.
Expense of equivalent of power, 1 12, 1 13.
II relative, of tlie three bate erio*, 32.
II of making copper plates, 202.
I. of electro-metallurgy, 112. 116"
FAaAD.iY's Toitameter, 42.
II on the chemical theory of the pile, 7. I
.1 on the poles of decomposition apparatus, 44.
„ on the laws ofileromposition, 40. or electrolysis, ft).
II on tito ions, anions, rations, 52.
„ electriwhemical decomposition . IM. '
Ferro sesquicyanurot of potassium, made by galvanism, 169, 170.
Film of air, 100.
Fisher, Captain, hli iiukIc of removing wret ks by galvanic blasting, :i3y, Formulaj, Ohm's, II, 12.
I, resulfi of. 12.
.. for ayrertaining cost of electro-
nietallitrgy, t t.l H.'V.
,1 of voltaic forrr 66.
for intensity hi compound battery (Hmee's), 71.
,1 foranumnt of work (Smee's),
Fruits, elerlrn-coppered, 24,
metallic moulds of, 277.
Fumes, nitrons, of Grove's batten deleterious, 22,
I, absence of, In galvanic etching,
Fusible metals, table of, 123.
Galtaxic BATTgar. (See Battery )
blasting in mines and under water. 330. 341.
afiplled by Lieut. Gen.
Paisi, 339. pt. Flahcr's mode
etching, 237.
Galvanised irtm, 212.
Oalvaoomeler, Snow Harris's. S3.
H magnetic, 36, 37.
asutic, 39.
n tortioo, 40.
It borsesboe, 40.
(Bee Voliameter.)
to for aaagiMtie electrtchy, 04. Gaasiot tbe of the battmy.SO. on flMCantc chromes, 217.
Capt. Ffi of, 330.
Geddes, Mr., 305.
Gilding, electro : — preparation of plate to be gilt, 229.
„ positive pole, 231.
„ coating of parts not to be
gilt, 231.
„ quantity of electricity re-
quired for, 231.
„ whiting used In, 232.
„ colour of gold reduced by,
„ copper articles, 233.
I, silver, 233.
iron and steel, 234.
I. copper plates, 234.
„ clich6es, 234.
' lead, tin, and pewter, 234.
„ colouring (*f gold, 235,
burnishing, 236.
„ water. Elkington's method of, 236, snltitlon, 2f6, 237.
„ process, 237.
by amalgamation, 237.
I „ compared ulth electro-
gilding, 2.36.
dotrlmeiital to
,,, ,, ... heami, 237.
Glue used for moulding. 14.I.
Glyphogruphy, Palmers patent, 320.
M preparation ol the plate,
I, execution of the design, 8'22,
„ formation of electro.gly.
phographic caat, 323.
.. furmgiioii of stereo giy.
nut. 323.
Gold, ehcmlcal equivalent of, 4S.
., n relies the metallic deposit, 121 .
„ redm et gold, 62,
„ elect ro-medaltions of, 266.
„ chloride of, 1 HO.
„ bromide of, I HI,
„ of, 181,
„ IfHlide ol, IH2.
,, suipbo-cyanide, 182.
„ redualon of ; —
„ from chloride, 180.
from bromide, INI.
„ from iodide. 1N2.
„ from sulpho-cysnfde.
182. '
„ from auro-cyanide of
potassium, 183.
„ expense of, 1N6.
„ apparatus. 184.
Ground for eichlng. all .
.. fur glypbography, 321 .
Grove's bslteiy, construction of, 22.
H principle, 82.
„ acivantages and disadvan-
tages of, 22.
„ signs of action fn. 34.
„ compared with Danieli's
and Bmee's, 31. 33, Gutta percha for roouldi. 140.
„ troughs, 102.
Analytical Index-
Gutta perch a fur tatucttea, 247.
„ matrice* of woodcuu,
11 aaKa' battery, 14. ,
Harrtt't galvanometer, 33. :
Ilaya, Mr., electro-coptx'red thipo, 2.V). '
Health, effect of metallic ohition* on, '
„ effect of nitrniu fumes on, 22. i
,, effect gilding by amalgamation
on, 237. !
Heating wires by galvanic battery, 3.S, !
History of eleciro-meUllurgy, . Horizontal dacompositlon apparatus, 107. ' llydro-electrlclty, HO.
Hydrogen, chemical, (luivalent of, 4S.
„ adhesion of, to negative plate. '
„ adhesion of, to positive plate.
If*. I
,, facilitated by nmatgamation. 1(>, '
evolution of, affects the power,
„ removal of, in Duniell's bat- !
lery, l;. 21. !
,, removal of, in Grove's battery, i 21 . 22 .
„ removal of, in Sinec's battery, 2f !
„ evolution of. in batter) . I I test of quantity, 47. 105. Hydriodatfl of zinc, 210.
HypO'iulphite of silver, IRR.
of platmun ,
, of gold, 181. i
loNiTioM of charcoal iKilnts. 37. I
Illustrated London Newt, 317. ImtKiudernbIr agents, 2. '
Intaglio. (See linuld.)
Intensity a property of the battery. 10, II,
„ effects of, 11, H. j
„ battery remarkable for, 22. 23. j
,, required for electro-magnet. 40, „ required for decom|>ositian, 50. i „ modes of regulating, I '
„ effet of, on decomposition, 155.
.. formula for, 77.
Iodide of gold. 182.
„ of palladium, 186.
of silver, 189.
„ of copper, 261.
Ions, simple and compound. 52.
„ FanMlay on, 52.
Iridium, reduction of, 186.
M from chloride, 186.
Iron tingle-cell apparatus, 94, 95.
„ of equivalent of power ob> tained by, 113.
„ eleciro-medallioos, 261 .
„ gilding of, 234.
„ mubliicatioo of article* in, 283. reduction of : —
proto-sulphate,
fhoro citrate, 214. from ferro-cyaoite of potash, 214.
Iron, reduction of, from proCo-loduret,
„ ,, expense of, 214.
Ironing, electro, 2-52.
Italian mode of making cUch6es. 12'.
.Iacobi's Idea of the electrotype, xvili.
.lames's electro models, 282
Jar, Leyden, charged by battery, 37. ♦
. Inventor of amalgamation of zinc of the battery, 16.
Laws of decomposition, 49, 50.
„ of precipitation of metals, 1.50.
.. for their reduction in black powder.
„ for their reduction in crystalline state. 152.
„ for their reduction in reguUno state.
Lc.ad, cluMnical equivalent of, 49.
relievos in, from engraved plates,
,, single-cell apparatus, 90. tree, 216.
reduction of : — from acetate, 216.
„ ,, from oxyde. 217.
„ „ from tris-nitrate. 2I.
„ ,, from plumtK>-cyanide
.. ex|)ens of, 215.
. ' lead, 62.
.. oxyde of, for metallo-chromes, 217. Leading, electro,
Leaves, electro-coppered, 247, 248.
„ inemllic moulds 277. Isnn's Irattery, 23.
Leyden j.ir chargtHl by batter), 37.
I.lne engraving. 302.
l.insect oil, preparation of plaster .
l.ocal action, 6.
„ „ overcome, 16.
MAnNmsM, Identical with electricttv, 88. ,, but two metals capable ot,
„ a test of quantity, 40.
Magnetic efft*cts of battery, 38. 41.
electro machines, 81. 8.5.
Magneto electricity, 84,
Magnets, gslvanometers. 38, 89.
„ temporary, 38.
,, permanent, 38.
„ deflection of, 38.
,. soft iron horse-aboe, 40.
„ electro, require lutmsity, 41. Manganese, black oxide of, in De Luc's column, 14.
„ reduction of, 223.
Marsh's apparatus for detecting artenlr,
Mason's decomposition apparatus, 10ft, Measures of quantity. (SeeGalvanometor.) Medals, chased, 261
process of. 261. struck or coined, 262.
processor.
Mint,
Analytical Index,
multiplication of, MS.
„ moulds from, 12). 354.
boat suited for multiplication,
ModalUoos, electro, of gold, 356.
„ „ of silver, 256.
„ „ of platinum, 257.
„ n of palladium, 257.
„ „ of copper, 258.
„ „ of sine, 261.
„ „ oflrtin, 261.
„ „ of hard copper, 244.
„ n thickness of, 260.
„ „ removal of, from
moulds, 260.
.. Rildingof, 261.
„ „ Dattery process, 258,
25P.
„ „ other prot'cites. 250.
„ „ with perfect rim, 267.
„ „ with obverse and re-
verse, 26H.
Mercury, used for amalgamating sine of batteries, 16.
„ to be preserved alter reduction of sine, 2'8. gilding by, 2.17. bicyanide of, 175.
Meta), type. rnmfKisitiuu of, 122, 123.
„ fusible, 123.
Metals, relative condticting powers of, 3.
„ clortro-negatlvc, 4,
„ electro. positive. 4.
„ become iiifilmed with air. IH
„ reduction of, various forms for,
„ „ laws regarding, 1.50.
„ „ in black powder, 150.
„ „ in crystalline state,
„ „ ill reguline state, 153.
„ effects of intensity on, l.'>4. 1.55.
„ effects of quantity on, 156.
reduce like metals, 60.
Metallic solutions, variations in strength of, 161. 162.
Metallic salts, formation of, 167.
Metal lo-cbromes, 217.
Metallo.yaoides, electro.rhemical de* compositions, 169. r, preparation of, 171.
Mesaotinto engravings, 303,
Moulds ill silver loaf, I2I.
„ la alloys, 122.
„ in fbsibie metals, 123.
„ 124.
„ by the press, 125.
„ in lead from engraved plates, 135.
by stereotyping, 126.'
in sealing.wax. 126,
in white wax. 138.
in white wax, from plaster casts,
m.
in stearine, 130.
In spermac, 180. in bees*-wax and rosin, 131.
In paper, 131.
In plaster of Paris, 133. 134 in salphur, 141.
In ffu proba, 140.
Moulds in bread, 143.
„ in glue and whiting. 143.
„ meialllc coatings for, 144.
„ from medals uud coins, 121. 354,
„ from monumental brasses. 274.
„ Hrom embossed surfaces, 276.
„ from fruit, loav*s, Ac., 277.
„ from engravcHi plates, 301.
Muriate of copper, 300.
„ of tin, 215.
Murray first applied black-lead to nonconductors, 22.
Kbkdi.b, astatic, 39.
Negative-electro metal. 4.
,, surface of, 7.
„ cleanness Import-
ant, 15.
„ ,, adhesion of hy-
drogen to, 15.
„ of Danleirs bat-
tery, 10.
„ „ of flri*ve*s bat-
tery, 22.
„ ,, of .Sinee's buttery,
„ pole, 44.
Newton's. Mr I., fusible racstal, 133. Nickel, reduction of: —
from nitrnti*. 19.1. from sulphate, 103. from acetate, 193. from chloride, 194. of, 194. Nickeling, elm tro. 240.
„ of silver, 1 h|.
„ of nickel, 193.
,. of palladium, 185.
Nitric acid used In etching, 231. Non-conductmg substances : —
first clsii,
12a
second class ,
third class,
metallic coatings for. 143.
Numismatist, value of electro- metallurgy to, 253.
Ohm's formula for the galvanic current,
n. 12 .
„ results of, 12.
Oil, iinsecd, preparation of plaster by,
.. nut. preparation of plaster by. 139. Ordnance map office, 530.
Osmium, reduction of, from oxyde, 187. Oxygen, chemical equivalent, 48.
Oxydes , compounds of, with alkalies, T68.
with satu, 168.
Oxyde of copper, 301.
Oxalkm, 5a Oxycarbion, 56.
Oxynltrkm, 56.
QoAMTmr of idaotrktty infloenetd bf tiie of nogatire plate,
„ „ Tarieawithitrength
of exciting fluid,
H measured by rolta-
meter, 46.
H mode of regulating,
10&. 162.
„ „ effect! of, in reduc>
tion of medal!,
Reduction of ailoyt, 225.
„ antimony, 218.
„ artenic, 220. ,
„ biimuth, 219.
„ cadmium, 212.
„ cobalt, 223.
„ copper, 194.
„ gold, 180.
„ iridium, 186.
„ iron, 213.
„ lead, 176. 21G.
„ manganese, 223.
„ nickel, 193.
„ osmium, 187.
,, palladium, 185.
„ platinum, 17G.
,, rhodium, 186.
„ silver. 187.
„ tin, 215.
„ tungsten, 223.
„ uranium, 219.
sine, 208.
Reguilne state, roductlon of metals in, 148. ,, with any given solution,
negative plate or battery,
Rhodium, reduction of, from ate. 186.
Rose's fusible metal, 123.
Rosin and bees'. wax, moulds in, 131. 2.55. „ „ preparation of plas-
ter by, 137.
,, and turpentine, preparation of plas> ter bv, 137.
„ and grease, preparation of piaster by. 138.
Ruisdl's process, 308.
Salts, metallic, formation of, 167.
ft by gal van.
ism, IC7.
Sculpture, application of elcctro-meial> lurgy to. 279.
„ casting, present method of. 279. „ casting, by electro-meuilargy,
„ casting, from large designs, 279. expense. 'MQ,
M texture ' of reduced metal for casting. 280.
Sealing-wax, composltioa of. 126.
„ impressions, 127. 250.
Seeds, moceas for copying. 269.
Seoosioary effects of decorotHMition, 53, 54. Ships, electro-coppered. -60.
„ copper fbeatbing preserved, 5. Sboefc of galvanic batter, 37.
n electro-magoettc apparatus, 92.
SllUnum*! eoplM of part, 981 . surer, chemical equivalent, 49.
„ used to receive the metallic deposit, 121.
„ reduction of : — .
,, H from acetate, 188.
„ „ flrom argento-cyanide
of potassium, 190.
t, „ from
trate, 188.
„ „ from ammonto-chlo-
ride, 188.
„ „ from ammonlo-car-
bonate, 189.
„ „ from hypo-sulphite,
„ „ from Iodide, 189.
„ „ from nitrate, 187.
„ „ from potasso.tartrate,
„ „ from sulpho-cyanide,
„ „ expense of, 192.
„ electro-medallions in, 256.
„ quality of reduced metal, 257.
„ on the multiplication of surticles In, 285.
Silvering, electro. (See Plating.) Single-cell apparatus, 87.
„ diaphragms for, 87.
„ porous tubes for, 88.
„ various forms of, 92,
yo.
If zinc for poBitlve
pole, 93.
M ' Iron for positive
pole, 94, 96. lead for rHisltivo
polo, fiO.
„ tin for positive polo,
„ union with battery apparatus, 102, 103.
Smee's battery, principle of, 24.
„ platinizing of negative
metal, 24. 2.5.
„ platinized silver, liest fur
negative tnetiti, 25.
„ exciting fluid of, 26.
„ various arrungeiiionts of,
„ form best siiiteil for elec*
(ro-rnetailiirglst. 27.
,, odds and end*' battery. 28.
„ constriirtiori and use, 28.
„ advantages and disadvan-
tages of, 29.
„ exciting fluid, strength of,
„ compared with Panieirs
ami drove's, 31, 3'i.
„ voltameter, 46.
Sodio-muriaie of rhodium, 186.
Spark of blurry, 36.
„ fiasslot on, 36.
„ CrosM on, 36.
Specula, multiplkatbm of. 2H.5,
Spelter, cheajprr than rolled zinc, |i3. Spencer, his Mea of the electrotype, 6. Speimaceti, moulds In, 130.
Anajlttical Index.
Spermaceti renders plaster non-absorbent, 137.
Stearlne, manufacture of, 130.
„ moulds In, 130.
preparation of plaster bjr, 135, 13C. Steel plates, multiplication of :
,, „ by eJoctro-
metallurgy,
„ „ by Perkins*
process, 312.
„ „ by Btereo>
Stereotype-printing, 289.
Htercotyping, proceM of, 91. Stereo-.glypnogriiphy, 323.
iitg out in etching. 331 .
Sulphate of sine in exhausted battery, Its use, 208.
„ of tine, 208.
,, of silver, 188.
„ of nickel, 193.
., of copper, 195, 190.
„ of cadmium, 2i2.
Sulpho-cyanide of copper, 202. Sulpho-vinton, 30.
Sulphur, casts in, from plaster, 141.
„ „ sulphur, 142.
Sulphuret of potassium, fur bronzing, 208.
Table of chemical equivalents, 48, 49.
„ of fusible metals and alloys, 123.
„ of cost ofequi valent of power under various circumstances, 115.
„ of expense of reduction of copper by various methods, 1 15.
„ of substances w hich render oxydes soluble, IGG.
„ of substances for making moulds.
„ of principal modes of making moulds, I'iO.
Tallow reiKlera.* plaster non*abiorbent,
Theory, chemical, 7.
„ contact, 7.
of the r<*duction of alloys. 224.
" I'' Year-Book of Facts,*' 281.
Tlmea machine. 318.
„ neaspnper, 318.
Tin, reduction of ;
„ from muriate, SI 5.
„ from sulphate, 215.
„ from acetate, 215.
„ from oxalate, S15.
„ from other salts, 316.
expense of. 316. positive pole In slnglecell apparatus, 97. expense of equivalent of powi by,
tu.
Tinlng, electro, 251 Tortkm galvanometers. 4a Trough, precipiUting, 99. lOI. Tungst remicUon oi; 229.
Turpentine and rosin render plaster nonabsorbent, 137.
Type, metal. Its, 123.
,, manufacture of, 122. !
multiplication of : —
„ by electrotype, 390.
„ by stereotype, 290.
Ubaniom, reduction of, 219.
V-SHAPBD tube, 42.
Varnishes render plaster non-absorbent,
render paper non-absorbat,
Vegetables, electro-coppering of, 247, 248.
.. metallic moulds nrom, 277. Voltaic battery, 2. (See Battery.)
„ current, proximate cause of, 6.
„ ,. theory of, *9.
„ equivalents. 48, 49.
„ circles, curious instances, 67--69.
Voltameter, Faraday's. 42.
„ a test or quantity, 46.
„ Smee's battery, 47.
Watbe, an exciting Buid, its use, 9.
„ gilding, Elklogton's mode of, 236, 237.
Wax, white, moulds in, 128. 265.
„ preparation of plaster by,
Whiting used in electro-gilding, 238. Wlros, healed by battery, 35.
„ thin, bad conductors, 11.
Wood -cuts, durabllUy of, 314.
„ priming from, 314.
„ mulUplicatlon of, 315.
,, ciichMS from, 316.
„ electrotypes from, 316.
Yalland, Captain, 305.
ZlMc, chemical equivalent, 49.
„ amalgamation of, with mercury, 16.
„ ptwiiive to nearly all metals, 4.
„ positive metal in siotle.eil ejqparetus, 93.
reduction of: —
negative plates of battery. 211. by tine, 61. hrom suifdiide, 206. from ammoaio-tnlphate, 900. from chloride, 200. from acetate. 210. ftoni hydiiodate. 2f0. from other salts, Sll. expense. SIS.
.. electro-medallions, 961.
Ztneed iron, 129.
Zlncing-electro. 951 .
Ziocode, synonymous with anode, wsciroda,44.
The End.
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TO Misses. LONGMAN Aiili Co.*i CATALOGUE.
New Woeks And New Editions
rOBMiHIS BT
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Xotott Oookerp ter Private
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NEW WORKS AKl> NEW EDITIONS
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Conversations on Botany. Kew
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Oonybeare.—Rssays, Ecclesiastical and Social t Ilrprlnted, with additions, from the SdleAwrA Rerlem. By the Rev. W. 3. CoNrasAKB. M.A., latr Fellow of Trinity CoUeife, Csmbridge. 8vo. it*
Oonybeare and Howson.—The
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Rr. Copland's Riotionary of
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Oreay's Encyclopedia of Civil [
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The Criehet-rield) cr,the Sei-
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Xduiy Oast's Invalid's Book.—
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Relabeohe.-'The Geological Ob-
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Rennistoun. — Memoirs of Sir
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Riscipllnc. By the Author of
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Eastlake.— Materials for s Bls-
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The Eclipse of ) or, a
Visit to a RcBgiotts Bpeie, Beveath KdiUoa. Pcap.Svo. price ts.
A Refenoe of The Eclipse of
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The Englishman's Gre Omi*
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The Rafliihinana Hebrew and
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Ephemera. A Handbook of
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Ephemera. —The Book of the
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Fcp. 8yo. with coloured
W. Erskine, Esq.—Hiftory of
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Faraday (Profcaaor).— The Subject-Matter of Hlx Lettarea on th NoitlletalUc Elrwcati, deUrered before ibc Members of the Royal Institatfou by Professor FAHAoar, U.C.L., F.R.H, ele. Arratwed br permlaalon from the ' Imctdrer'a Nutrs W J. eMormnw, M.U Fcp. Hr o. price bf.s/.
Franeia. — Annalf , Aneedotea,
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Eilbart.-'lsOgie for the mUions
A Familiar RxpoaUlou of the An of Reasan> iu. By J. W. Oii.nAT F.ll.B. EofHawt Portmlt of the Antbur.
13am. paBa.d.
CKlbart;-LM for the Tottngs
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GtldamHha Poetioal Worka.
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Goaae.~A KaturaliaVa Sojourn
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Saaaya on PoUtioal and Social
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Oumey. Historical Sketches
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Garney.—St. Louie and Henri
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I Hamilton.— Diaoaasiona in Philosophy and f.ltaralure, Kduratlon and Unlrcrslty Rsform. Cbicdy from the Adlri* RrHrw/ rorrreird, rindicatad, enlarged, ill Notes and Appaudlces, By Mir WtLLtAM IlAWiLroR, Bart. Breond Kdltinn, with Addltluos. gro, price Sis.
Hare (Archdeacon) s— The Life
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f In tk$ pr*9U.
Harriaon. — The Light of the
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Harry Hieover.-e Honting-
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Harry Hie over. — Practical
Horsemsoshlp. By llAWfiv fitaovaa. WUb 3 nate. Fep. Sm. 4s. baiL bound .
Han Hieotrer.-The Study for
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Harry Hlcorere— The Poekat
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Nkw Works New Editions
Ham Hieom. — stable Talb
ml Talk I or SfocuelM for Bparinoen. Bf Bakov HtaoroK. Ntw BdlUoik, S volt. tro. irltk Fortndt, t4.
. irltk Fortndt, t4.
Haatally (Dv.HTood and its
I CrmiprUlnf tk tUpvrta of tk Analytkol SMiSUrT CoaralMleo uf Tkr Lmmet for tko IBSl to WM IocImIt*, nrrUioil ood extondod. Bf Abthoa Hux HamaiXi otc.| Ckfof Analjrit of tb* CommoImIob t Author of Thr Iflcforoiool 4 of tht Bmm*n Body. 8ro. irltk 169 WoodcoU* pole* lit.
OoL Hawker's Xastriietieiis to
YottM Bporttflito hi oU that rolairt toGtuit ad fiaootlRf. Tooth Edltloojrorkod aad biim)(kt dowa to tko frcoaat 'niM* ky tk Author*! Soa, Major P. W, L. UAWasa. With a New Portrait of the Author, from a Boat ky VF.Bokaot Bao.i aad OMaoroot explanatory Flaiot aad woodcau. §vo. lie.
HasrdB's Bo of Bbniitiest
CooUtnlof Unlit of Ike OBclal Fartoaacwt of the Brltlidi Riaplro. CWU, KcctoalaatlcaJ. Jadidid. Mlllury, Naral, and Maalclpal, from the SarlfoM Foriodt to the Froaeat
Ttoeot coatallcd eklcdy from tko lloeordt of the Pabile Otieot. Ifmko r the 8o<
Mkr with the 8o.
t Mow ICdttioa Im-
Iirorod and eoatlaaoof BMottoat Political I ladox. By ioeara Bavin*. Fro. pricoSit.
HardeB.— The Ulii ef BeJaakin
Ito b o t t Raydoa, HbKorlcal Fatatar. foom hit oAd looraalt. KdiMd adcoaipUod by Tom Tarhoa, M.A.,or the labor Toatalo. Bta.i Uto FeUow of TrlaHp Cottofo, Ca wi iii rtdfot aad toto Fro* fooaoltho FMoHok Imbmmm and Utoro-
eoad BdlMoa, i fwatBea. ptfoo tl.dd.
Sir John HeneheL-'OatUiieB
of Attro n oa i y. BrSlrJaatfrF. W.Raao* a%_Bart. etc. Near MMoai wtob Flaiot aad Wood Safiartaft. tea. prlco I8t.
HiUaHraTels In Siberia. By
S. 8. Miia. Aatkor of fVarrCi oa Mr Adoroo V BolUo. Wkk a lara
eoloaradl Jbungtnm Ailaflc
Hinti BUqBette and the
Oatfae at Bw fo tt t WBk a Blaaca at Bad Maa larlood (Mtk 4M.
ilJUdjaflSuM. rcp.ra.fa
HeUaad'ii
Fartp daitaf My
HoUand.'-pterB en Hesfeal
ntyttology. Bf Sir Hawav Bouaxo, Bart.* F. 11.8., to tko Qaeea. Pottoded cklody oa Cfcopl*** tolnod in Jfedfiwf ATotea aad Aecffoae. price I8t.] by the taato Aatkor. 8va* prlet lOt. id.
Hook. — The Xast Baya of Dor
Lord'Maltt t A Courte of Loetaroton tht prmclpal Krcnta of Paotloa Week. By W. F. Uoox, D.D., Chaplain In Ordinary to the Qaotn. Naur Bdltloa. f cp. 8vo . ft.
I Hooker and Amott'a BrlUsb
Flora; Compritinf the Pbrnaopaakoot or Plnwcrino Plonta, and th Fcma. The Strronth 8ditlonnth Additlona aad Corroc* tiont, and ouawront Fifarot, Ulaatratlrt of the UmbtlUferout Plnata, the Cotapo* tlto FUntt, the Orattot, and the Ferae. ISmo. with 11 Flatoe, price Ide., with tkc FUUe coloarod, price Sic.
SirW. J. Hooker'BPopnlar Guide
to the Roynl Sotaalc OA8DKNS of Bow. Kcir Rdltloai with ooworona Wood Bafraeloft. Idmo. ptlca Slxpaaeo.
Hooker.— Mnsenm of Eeonomle
Botany ; or, a Poralar Gaide to the UeefoJ and ftamaibablc Veiretable Frodacte of tko MUSBUM In the Boyal Oaidtna of Kov. By Sir W. i. Hooaaa, K.H.. DX.L. Oxoa. V R.A. and L.S.etc., DIroetor. Whk I Woodcote. tftiao. price le.
Home's Introdoetlon to the
CrHlcal Stadr aad Kaowledc* of tka Holy Script**' A titw RdMon, ml t od, oor.
B. PatwBAvx iStaoBixsa. d rota.
Btoie's OompeiidioiiBXatrodBB*
t to the Btndy of the Bible.
to Mr tvirioal Btadp aad X mmf 4 i0 Mo Hoff doriptwreo. Mow BdMiaa i orlia Mope aad otkoc Bafiarlafa, llhM.yeloo ie.
Horne.— The OoimBWitBBBt's
Cotapaaloa t Conprtataf aa maioefool Beaay oa tk iaed* ModiUtloae aad Ihwfore for eke Uea of C oma uto foieafet
aad Prayore for eke Uea of C oatai aoif an f ei aad tka Ordar of tko Adad ul a traOn a of Mo Loed'e ffoppor or ffoJp C ema raafa a. Br tko Bor. T. Haavwaaa B oa aw. BBu Bayal tino. le. td. t morocowt daJdd*
How to Horse Siek OhlldrsBt
latoadad aapeclatly aaaBabMtktBli la tka Hoapltal for Sick CkUdraat kal taMw IMraciloaa of oarrlco eoall vko kao of tka Yoaar. Boo. la. Of.
.-(S. BU> An AH Sl-
dR la Wecoick. Ifo Wa MaAt SUmr. taola.poat8ro.pcfea Ida.
PUBLUUBD BY LONGMAN, UHOWN, akp Co.
Howitl-*Tl;ie Ohildren'i Tear.
Bf Mabv Howrrr. WUh Four lUuttratloM, htm peslfM b? Akna IIaav Hovm.
Rowitt.~Laud, Labeiir, and
Gold; or. Two Ver. in VlctorU. WUh 4 ' VUU* to RjrdBej .nd Van '. Ind. Bj Wiluam Howitt. StuU. pott
i WUUaiii HowittHi Boy's Ooun-
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I with 40 Woouta. Vrp. 8vo. price
j Howitt.— The Rural Life of £ng*
UihI. By WilxiAM UowiTT. New fCdltlon, corrected and rcviacdi with Woodcut, by Bewich and Wllltami. Medlun Ovo 31r.
HowiU.~inBits to Remarkable
Plnreat Old Halle, Battle-Helde, and Beeuea iUnatratire of HtHhing Paaugea in KttiriUh Ntatwryaud Poetry. Bt Wiaaiam I lowirr. New Rditioa j with prHrda of 00 Woodeuta. Plrat and Kecond tferlea, me* dtnaa Svo. price 31a. eai-h.
Huo.~~The Ghlnese Empire t a
tiraael to Hoc oud tinWAOKrnrp i Thihrf. fly the AnW Moo. many year. Miaaionary ApoatoHc In China. Copyright Traaelalloa. with the Antbor'e eancUon. 8*tmid Edititm, with coiuured Map and indem. S eeb. Vro. Mr.
HadMu's Plain Bireetions for
Hafctef Wilia in confonnitr with the Lav i with* deor aeseelllMiof the low reUting Mtbe Platrlbni of Peraonal Eaiata In the eaae of Inicatacy. two Form, of WtIU. aud much uaefet Iwuirmattnn. New and eniaiged BrittiMi liMrIediag the proriaiow* td the WnU Act Amaadmeut At. Fep eu.ptleeSi.W.
Hadson's Sxeeotor's Guide.
If eur mmI enlarged Kdirion i with the Addi> tfeu Mreetioaa for paying tturceaaleR Untlaa on Beal P roue r tr muir WlUa aud luteaUcIce, and a Table for indlag the Valuea pi Aonltiea and tbe Aaaount of l yi weceeaalon Ihity thereon. Fcp.
Huahdldfs CotaoB. Traas-
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HWbaldt'B AspseU of Ratore*.
Trnnlatadwlth tha Author'a authoeitf . by Mab. . Maw Wittou. IMao. price la.! oolsSeola.ic. M. esefc cloAf Sa.Bf. aaehaourgd.
Humphrey Sa—SentimentB and
Kimilea of Bbahaneare. With as elaborately Uiumlnated border la the characiarlatic style uf the Kilaabcthan Period, maative carved covers, and other KmbeliUhnieata, drained and eaecnted hy U N. Hum* psaava. Square, poet Hvo. price 3l.
Hunt. — Researches on Light in
Us Chemical Relalton.i Imbractiiy a Con. i alderatiun of all the Pholrimnhte Prutee> ace. By RoaanT Hoirr. F.B Frofeeeor of Pbyilce In the Metropolitan School of BHruce. Hecimd KdUioa i with Plate and Woodente, #vo. price lOr.iaf.
ldle.--Bints on Shooting, Pish-
log, etc. both OB Am aad Lead, aad In the Freahwatcr Loche of Scotland i bring tbe Reperieacea of CaavwoiifBhA lut4i, Ba. hep mo. 6$,
I Mrs. Jameson's Legends of the
I SaUite aad Martyra. Forming iba PIrti I harlre of Smettd mod Lrgendmrp Art. Second SdUlnn i with aameroaa WtHid* cate, end miitchlngahy tbe Aathar. Squere crows Sro. price Mr.
Mrs. Jameson's XrOgends of the
Munaatlc CUdera, aa rcpreaauted la tbe hlar Arte. Korming the Seeotid Sariae of Bmerfd mud Art, Neiond SdL tlni>. eorrrcicd ainl enlarged , with 11 Steb* Inga by tba Antbov, and M Woodeata. Bqaare crows Bro. priea We.
Mrs. Jameson's Legends of the
hfadonne.aa reprceeated to the Fine Arte. Forming the Third Sovlea of Aaeved aad Art. WUh U Utiawlsga by tbe Autbor, aad Ui Wood Kaftaflsfe, Square crowa Sve. priea SB.
Mrs. Jaineson.-8liters of Oha*
rtty. Caibulk and Protestant, Abroad aad at Home. Sy Mra. iAMaaoa, Aatbur of MmmrmdmmdLmgtmdmggAH. SccuadSdltloa, witb a new Praface. Fep.Sre.4.
JaxBoson.— A Oonunonplaoe Book
of Thoaghta, Memoriee, aad Faaelos, final aad Selected. Part 1. Btklra and Cbaracteri Part I f . Lltorainrc aad Alt. Sr Un.JjM—om, WUh Kuhlaga aad Wood Bttgrsriage. S<|Osra crowa Svo, print fib.
JBQuemet.~A Oonpendium of
Chronoioffyt Coalalafng the piaet impa rt aa t Itetee of Ueoeral History, PelUkal, Keck' starticai, and Utarary, from the Cremioa of the World to the aW of tho Yaar ISbd- By P.fl. jAucaMov. Bd tba Bof. doss Aacoaa.MA. Port Sea. 7c. Sri.
Lord Jei&ey's Oontrihntions to
the Bdlnbaifb Review. A New Sdliloa. complete to OweTolama I wMh portrait aai Tirt Sdsage evowp Seo. Yta. afrtSt
a LmSASr EOITION, Is S vola. Bro. price 430.
New Wobk8 Amd New Editions
BUhop Jeremy Taylor's Entire Eirby k. Spence's Xntrodoction
Workas With kl* lAfe* bir Blahop . to SiUOtaolof jr i or, BlMirau of tbt Nb> Mevlaod and corrtiSodbjtMllev. CsAHLsa tool Hlatorjr of Inaoctai eowprlaiof wi
Mevlaod and corrtiSodbjtMaev.
Fmb Edkm, Folloar of Ortol CoUeoa, Oxford. Cooiplet* in lOvola.Sro.lOa.dd. each.
Johns and Kioolas.— The Oalen-
dxr of Victory t Sohif x Record of BrltUh Vxionrxnd Conqueat bp Mcx xud Lend, on every Dp hi the Yew. from the Serlleat Period to the Settle of Inkermuin. Pro-
i end comaetterd bp the late loflMat R.M. i completed bp Lieut. P. H. NicuiAa,R.M. Fcp.Svo. price 12a. 64.
Johnston.'-AKew Dietlonary of
Geoffrephv. Deacrtpclve, Phpalcel, 8tesla> tlcel, end Hiatorlcelt Forming e complete Gcnerel (leketteerAf the World. Bp A. KetTH JoMHaTon.P.R.b.X. Stevnd Editimn. brought down to Mep. 185A t in I vol. of 1360 Pegee* oomptialng about 60,000 Namea of Placea. Svo. Ma. cloth i or helf-bound Itt rmaele, 4la.
Jones (Owen).'— Flowers and
their Kindred Tfaoughta : A Herlea of Bteiiaaa. Bjr Haht Amnk Bacon. With beautiful Illuatratlona of Flo were, deaifrned and ctecuted in Illuminated Prmiluir bp Owen 4onca. A New Uditlon Impl. svo.
[iVanr/p .
Kalisoh.— BUsiorical andOriti-
cel Coinmentenr the Old Teatement. Bp Dr. It. KaLtaen, M.A. Flrat Portlun— Bxoduat In Hebrew end BuKUah, with coploua Notea. Critical, Pbllolofloel, and axplenetorp. vro. 16a.
An KdlUon of tbe JLrodwa. ea above ffor the uae of KnflUh reederaj, rompHaing Enfllab Traneletlon, aid an abridged Coetwenterp. 8vo. price IBl
BLexnble.'-Ths Saxons in Eng*
land I A Nlatovy of the Kegliab Comnaonwealth till tbe period of tbe Norouan ConeuoM. Sf Joan MtToneaA KnatuLn, iC.A., F.C.P.tl.,ete dvota.gvo.pviee Wa.
Kemp.'he Fhasis of Xatters
Being an Outline of tbe Dlacoveriee and Application of Modem Chcualetrp. Bp T. LiJur Xnaar, M.D., Author of Tk, Hitfvrp gf tVaollen. laiBIcefiena fiMtimet, etc. With IM Woodeuta. f voib. Clown 3*0. tla.
EMtoTen.-'A Kannal of Bo-
aeaetlc Pmrtlce of Medtetao, etc. Bp W. B. , P.a.C.B. faiaaropoet 3vo.
tha prew.
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1. MACAULAVS E8BAYB oo WARREN HASTINGS and LORD CLIVE
9, ESSAYS oa PITT CHATHAM, RANKE M GLADSTONE ..
I. LAING'B RESIDENCE to NORWAY
4. IDA PFEIFFER'S LADY'S VOYAGE ROUND the WORLD
I. EOTHEN t or, TRACES of TRAVEL from the EAST
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If. The Rav. O. R. OLKIO'S LRIP8IC CAMPAIGN
18. Hughes'S Australian Colonies
14. Sir Edward Seaward'S Shipwreck
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18. OUR COAL-FIELDS aad OUR C0.4L PITS
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t ESSAYS on SWIFT and RICHARDSON /
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