Elements of electro-metallurgy, or, The art of working in metals by the galvanic fluid ...

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Preface

I SHOULD not have presumed, in the first instance, to have composed the present volume, had I not been earnestly soli* cited to undertake that important office, especially as I foresaw the difficulties which would arise in such an attenipt. A similar apprehension of inability thoroughly to investigate the subject has also deterred me, during the long time that this volume has been out of print, from re- writing it. At length, however, having determined to revise my pre* vious labours, I commenced the task of writing the Second Edition with an unwillingness exceeded only by that with which I began the first. The cordial reception, however, of the former, made me the more anxious to render the present deserving that favour, which I am afraid was too liberally bestowed upon my first attempt.

In prosecuting my labours such extensive alterations, cor* rections, but more especially additions, have occurred, that this volume has rather become a new Treatise than a Second Edition. Notwithstanding that the work has been doubled in bulk, and partly re-written, it has afibrded me great pleasure to discover that the new matter has arisen either from an addition or substitution of new inventions, or an extension of those before known, and not from errors in the former experiments. In fact, the more the subject is examined, the more ftilly do the principles regulating the

h

VI PREFACE.

various branches of the science then developed appear to be confirmed.

It may not be too much to hope that the addition of the proximate and intimate rationale of the production, or rather the motion of electricity, may be useful beyond their immediate and important bearing on Electro- Metallurgical operations. The detail of the electro-chemical decomposition of a large number of metallic salts, together with the laws regulating the nature of the metallic deposit from simple and complex solutions, may also afford an instructive source of inquiry to all interested in the study of electricity.

It is almost needless to add, that what is noyeL in this work is given for public utility, and whatever has arisen from my experiments at any time has also been similarly thrown open. The former edition was issued to the public on th« 26th December, 1840, and the present edition, although bear^ ing the date of 1843, according to the custom of the trade, was published as follows : the first 40 pages on the 1st Aprils 1842 ; 40 pages more were ready on the 1st of May ; the third 40 on the Ist of July ; the succeeding 40 on the 1st of August ; the fifth part, containing 44 pages, was published 1st September ; the sixth part, to the 236th page, on the 1st of October; the next 40 pages on the 1st of November, and the remainder on the Ist of December.

Nothing is more difficult than to appreciate with accura<iy the exact effect which-^he discoveries of each individuid have on any particular science, and as far as regards electro-metallurgy, I feel utterly unable to undertake such a task. The principal names of those, however, whose various writings and inventions have been most useful to me in prosecuting my electro-metallurgical experiments, I have thought right to insert in the title page without reference to the relative benefit of their labours. If there is one philosopher to whom I am more indebted than another, I should without hesitation name Faraday, to whom my hearty thanks 9b the most enlightened

PREFACE. vli electrician that the world has ever produced are justly due. There may be many others at home and abroad, who doubtless have materially aided electro-metallurgy, besides those before-mentioned ; but as they hare had but little or no influence on my proceedings, it would be improper to place them in the title-page of my work.

Were I to call public attention to all who have directly or indirectly afforded me assistance in the collateral branches of electro-metallurgy, a list of names would surprise my readers, frota its length; for I regret to state that I have been utterly unable to rely alone upon my own labours, and, therefore, have be^i compelled to cull information from the studios of artists, the galleries of sculptors, the laboratories of chemists, the workshops of artisans, and of various manu- &cturers, and frequently even from the books of merchants, and the productions of other electro-metallurgists. In a few words, arts, science, and commerce, have lent their aid to fiirther the progress of electro-metallurgy, and I can call to mind no instance of a request to see any particular manufacture having been denied ; but on the contrary, a free invitation to examine any subject that might help the application of electricity for the purposes of mankind.

As in the former edition I had to record my obligation to my friend, Mr. John Beadnell, for lessening the errors by correcting the proof sheets, so am I indebted, in a great part of this work, to my neighbour. Dr. Munk, for a similar exercise of kind offices. To my brother-in-law, Mr. Hutchison, my readers are again indebted for a most voluminous index.

The design of the medal in the title-page was kindly made for this work by the learned Mr, Thomson, of the London Institution. It affords me great pleasure to be enabled to draw the attention of my readers to its execution, for by a newly-invented machine 200 lines are ruled to the inch ; and, therefore, if the lines forming the design were crossed, eight millions of spaces would be contained in a cubic inch. To

YlU PREFACE.

form any idea of the minuteness and beauty of the workmanship the use of a magnifying glass is required, and it will be found most amply to repay such an examination.

With all my assistance from others, superadded to the ardour with which the extraordinary character of the subject must necessarily inspire every person entering upon it, the variety of subjects comprised in the present work is so great, and so far removed from my daily professional avocations, that it will doubtless not appear strange for those who entirely devote their time to particular arts, to discover errors and imperfections. As these subjects, however, are only appendages', or extraneous matter, to electro-metallurgy, of which this work professes alone to treat, I trust the indulgence of the public will be extended to their criticism ; but let the purely electro-metallurgical details be thoroughly examined, minutely sifted, and purged of their errors and imperfections, that at length truth may be exalted and electro-metallurgy triumph.

No. 7, Finsbury Circus^ London, Nov. 17th, 1842.

Contents

History of Metallurgy xvii

Chapter I. On Oalvanio 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, WoUaston, &c.^ 24 — 31. Adhesion of the hydrogen to the negative plate ; amalgamation of the positive, 34. Daniell's Battery, 37 41 . Grove's Battery, &c., 45— 47. Smee's Battery, 48 — 66. Comparison of the three batteries, 66 — 68

CHAPTER 11.

ON THE PROPERTIES OF GALVANIC BATTERIES.

Signs of a Battery in action, 69. Harris's galvanometer, 60. Spark, 61. Voltaic electricity charges in Leyden jar, 62. Physiological effects, 63. Magnetism, 64 — 68. Galvanometers, 68^70. Horseshoe temporary magnet, 71 — 73. Decomposition cell, voltameters, poles, 74 — 84. Laws of voltaic decomposition, 86, 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. Daniell's theory, 99. State of the fluid during decomposition, 101. Effect of heat upon fluids, 102. Curious induction, 103 ... 32

CONTENTS.

Book The Second. On Electro-metallurgy

CHAPTER I.

ON THE APPARATUS TO BE EMPLOYED FOR THE REDUCTION OF THE METALS.

PAGE

Electro-metallurgy requires a knowledge of galvanism, 104. The idea of electro-metallurgy suggested by Darnell's battery, 105. 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 56

CHAPTER n.

ON SUBSTANCES CAPABLE OF RECEIVING THE METALLIC DEPOSIT.

Substances on which the deposit may take place, 130^-131. Metals, 132 — 136* Non-conducting substances ; Sealing Wax, White Wax, 136 — 139. Absorbent substances, as Paper and Plaster of Paris, 139 — 141. Means of rendering them non-absorbent, 141 — 142. Means of copying non-conducting substances by metals, by plumbago, 143 — 145. Comparison between the methods, 145 . . 85

Chapter 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 this state, 151. Mode of producing them, 153 — 159. Mode of obtaining the black powder, 159. 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, 167 112

CONTENTS. XI

Chapter IV. On The Reduction Of The Metals

PAQK

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, 183. Bismuth, 184. Uranium, 185. Arsenic, 186. Tungstic acid, 187. Cobalt, 188. Manganese, 189. Reduction of alloys, 190. General remarks, 191 «...'. 128

Chapter I

General directions, 192. Electro-gilding, 193. The auro-cyanide of potassium, 194. Apparatus, 195. Copper-gilding, 196. Water-gilding, 197. Gilding by amalgamation, 198. Electro-platinating ; Electroplatinizing, 199. Electro-palladiating, 200. Electro-plating, 201. Plating by other means than Electro-Metallurgy, 202. On coating metals with nickel, 203. On eoppering metallic substances, 204. On coppering non-metallic substances, 205. On coppering medallions, 206. — Fruit, vegetables, &c., 207. — Baskets, 208. — Earthenware, 209. On coating metals with iron, zinc, &c., 210. Conclusion, 211 . 205

Book The Fourth. On Various Applications Of The Reduction Of Metals

BY GALVANISM.

CHAPTER I.

ON THE MULTIPLICATION OP COINS AND MEDALS.

Value of electro-metallurgy to 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.

3i^ii CONTENTS.

PAGB

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. Thickness of the metal, 224. Removal of the cast from the mould, 226. Zinc Medals, Iron Medals, 226. Value of electro-metallurgy for medalists, 227. On the modes of making perfect medals, 228 227

CHAPTER 11.

ON COPYING SEALS, PLASTER OASTS, ETC.

Value of a seal, 229. Process for copying a seal, 230. Copper moulds from plaster medallions, 231. Quality of the reduced copper, 232 241

Chapter III. On The Multiplication Of Brasses

Procecib for obtaining Duplicate Brasses, 233 .... 245

Chapter IV. On Making Dies From Embossed Surfaced

On metallic reverses from raised surfaces by galvanic agency, 234. Peculiarities of dies made from paper, 235 .... 247

Chapter V. On The Manufacture Of Moulds From Fruits, Vegetables, Etc

On making moulds from vegetable substances, 236. Chantrey's method, 237 • . . . 248

CHAPTER VL

ON THE APPLICATION OF ELECTRO-METALLURGY TO SCULPTURE 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 goldsmiths, 242. For surgeons, &c., 243 . 249

CONTENTS. Xlll

Chapter I. On Thb Multiplication Op Type

PAGB

The mode of printing books^ 244. On stereotyping, 245, On Electrotyping the type, 246 267

Chapter II. 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, 261. Temperature, 262. Positive pole, 263. Regulation of the texture of the copper, 254. Single-cell apparatus, 265. Time required for the process, 266. Removal of the plate, 267. Mode of preparing the plate for engravers, 268. Economy in the manu£GU!tory, 269. Expense of the plate, 260 . • 269

Book The Sixth. On Oalyanic 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, 282 286

Conclusion 292

APPENDIX, No. I.

On Electro-Metallurgical Patents 301

APPENDIX, No. II.

On the intimate rationale of the voltaic force, comprising the unities of the properties of matter and, probably, of its composition . 306

Analytical Index 328

LIST OF WOOD-CUTS AND ILLUSTRATIONS.

Fig.

Specimen of medal ruling medal, designed by Thomson. — Title,

Specimen of Electrotype from Plaster — Royal Arms.

1. Daniell's Battery .....

2. Grove's Battery .....

3. Smee's Battery, compomid six cells

4. Ditto ditto, for Electrotype

5. Ditto ditto, Odds-and-Ends' .

6. Faraday's Voltameter ....

7. Diaphragm Apparatus ....

8. Battery Voltameter ....

9. Single-cell Electrotype Apparatus .

10. Ditto ditto, another form

11. Ditto ditto .....

12. Single Battery Apparatus, with vertical trough

13. Compound Trough Apparatus

14. Mason's Apparatus ....

15. Single Battery, with horizontal precipitating trough

16. Clich^e machine .....

17. Mode of making proof seals

18. Mode of making wax moulds

19. Mode of filling plaster casts

20. Apparatus for forming electro salts

21. Apparatus for making the red ferro-cyanate of potash

22. Process for forming the cyanide of potassium

23. Reduction of platinum by compound odds-and-ends' battery

24. Reduction of gold ....

25. Apparatus for reduction of silver .

26. Metallo-chrome apparatus

PAQB

XVl Llflrr OF WOOD-CUTS AND ILLUSTRATIONS.

FIO. PAOB

27. Marsh's apparatus for the reduction of arsenic . . . 180

28. Diagram of single voltaic circuit ..... 191

29. Diagram of compound ditto . . . • . 198

30. Diagram^ showing an incomplete ditto .... 200

31. Process for electro-gilding ..... 207

32. Burnishers for gilt articles . . . . .212

33. Process for electro-plating ..... 217

34. Process for electro-coppering ..... 222

35. Medal Precipitating Trough ..... 233

36. Mode of removing the cast from the Mould . . . 234

37. Apparatus for hlasting in mines ..... 298 Coat of Arms of His R. H. the Prince Alhert, Clich^e from Electrotype ....... 277

Dog's Head, Electrotyped from Clich^e .... 277 Specimen of Electro-glyphography, a view of Highgate Church . 282

HISTORY

OP

ELECTEO-METALLURGY.

We have not to extend our enquiry into remote periods, to trace the history of the arts of working in metals by the galyanic 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 this 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 &ct after another, till the comprehensive 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 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.

It was but a short time after the discovery of this battery, that Mr. De la Bue 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

XTlll HISTORY OF

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 thought of 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 elec-. trotypes or voltatypes, or, what is better, electro-medallions.

Now what is the precise value of the discovery of these productions over the facts already 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;

ELECTRO-METALLURGY. XlX

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 behind-hand, 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 working zealously and ardently for the sake 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. Lafdner, 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 publication 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 unthank-

XX HI8T0BY OF

fill, 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 men to the fact, that persons are actually employed by great Continental Powers to find out everything new that is discovered 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 thenrto 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 useftil must afford, whilst the foreigner receives pecuniary emolument which singularly increases his desire of being acquainted with the inventions of other countries.

I may farther 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 Wheat-

ELBCTRO-METALLURGy. XXI

stone'^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 begiimings.

The next discovery, which is fiilly equal in value to the idea of the electrotype itself, was made by Mr. Murray. He found out that non-conducting substances might have 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 enquiries, in order to ascertain who really first used plumbago for this purpose, and I have the testimony of several authorities that it Was Mr. 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

d

XXll HISTORY OP

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 of hydrogen to it is so great that it would rather reduce a metallic 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 subsequently given by Mr.* Solly and Mr. Spencer, though, doubtless, had we not Mr. Murray'*s process, they would have formed valuable additions to electro-metallurgy.

Up to April, 1840, the single-cell apparatus was invariably used, but then Mr. Mason very ingeniously devised another 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", pr, in other words, obtained two equivalents of copper for one of zinc.

In 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 different 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 all other metals in three states, namely, as a black powder, as a 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 auxiliary 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 formulse for ascertaining the work that would be performed by a galvanic battery, under different circumstances, cannot £ail to be of great utility to the workman, if he 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.

The number of experiments, I may even 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 ftiUy aware that some may disagree with me BS to the superiority of my battery over all others for experimental and manu&cturing 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

XXIV HISTORY OF 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 conununicates 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; I have 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.