A complete treatise on the electro-deposition of metals

Front matter

A COMPLETE TREATISE

ELECTRO-DEPOSITION OF METALS.

COMPRISING

Preface To The Second American Edition

The rapid sale of the first American edition of Dr. George Langbein's work, "Handbuch der Galvanischen Metall-Niederschlaege" and the constant demand for it, are the best proofs of the value and usefulness of the book.

In the second edition, which is now presented to the public, a few changes have been made in the arrangement of the text, and it has been endeavored to include all practical methods of plating metals which have become known since the publication of the first edition, as well as the most recent machinery and apparatus, so as to make the work still more acceptable and useful to the reader.

The editor is under obligations for information and electrotypes to the Hanson & Yan Winkle Co., of Newark, N. J., and the Zucker & Levett Chemical Co., of New York, two well-known firms dealing in electro-platers' supplies.

The publishers have spared no expense in the proper illustration and the mechanical production of the work, and, like the first edition, it has been provided with a copious table of contents and a very full index, so as to render reference to any subject prompt and easy.

W. T. B.

Philadelphia, November 14, 1893.

Preface To The First American Edition

The art of the electro-deposition of metals has during recent years attained such a high degree of development, that it was felt that a comprehensive and complete treatise was needed to represent the present advanced state of this important industry. In furtherance of this object, a translation of Dr. George Langbein's work, Volhtaendiges Handbuch der Galvanischen Metall-Niederschlaege, is presented to the English reading public with the full confidence that it will not only fill a useful place in technical literature, but will also prove a ready book of reference and a practical guide for the workshop. In fact, it is especially intended for the practical workman, wherein he can find advice and information regarding the treatment of the objects while in the bath, as well as before and after electro-plating. The author, Dr. George Langbein, is himself a master of the art, being the proprietor of an extensive electro-plating establishment combined with a manufactory of chemical products, machinery and apparatus used in the industry.

The results yielded by the modern dynamo-electric machines, to which the great advance in the electro-plating art is largely due, are in every respect satisfactoiy, and the more so since the need of accurate, and at the same time handy, measuring instruments has also been supplied. With the assistance of such measuring instruments, the establishment of fixed rules regarding the current-conditions for a galvanic bath has become possible, so that good results are guaranteed from the start. While formerly the electro-plater had to determine the proper current-strength for the depositions in

VI . PREFACE TO THE FIRST AMERICAN EDITION.

an empirical manner, by time-consuming experiments, to-day, by duly observing the determined conditions and provided with wellworking measuring instruments, he can at once produce beautiful and suitable deposits of the various metals.

The data referring to these current-conditions, according to measurements by Dr. Langbein, are given as completely as possible, while for the various baths, only formula? yielding entirely reliable results have been selected. To most of the baths a brief review of their mode of action and of their advantages for certain uses is added, thus enabling the operator to select the bath most suitable for his special purpose. To the few formulae which have not been tested, a note to that effect is in each case appended, and they are only given with due reserve.

To render the work as useful as possible, the most suitable formula? for plating by contact and immersion, as well as the best methods for coloring the metals, and the characteristic properties of the chemicals used in the industry, are given. However, the preparation of the chemicals has been omitted, since they can be procured at much less expense from chemical works than it would be possible for the electro-plater to make them in small quantities, even if he possessed the necessary apparatus and the required knowledge of chemistry and skill in experimenting.

It is hoped that the additions made here and there by the translator, as well as the chapter on " Apparatus and Instruments," and that of " Useful Tables," added by him, may contribute to the usefulness of the treatise.

Finally, it remains only to be stated that the publishers have spared no expense in the proper illustration and the mechanical production of the book; and, as is their universal practice, have caused it to be provided with a copious table of contents, and a very full index, which will add additional value by rendering any subject in it easy and prompt of reference.

W. T. B.

Philadelphia, July 1, 1891.

Contents

HISTORICAL PART.

Chapter I. Historical Review Of Electro-metallurgy

PAGE

The method of coating metals by simple immersion known to Zozimus and Paracelsus; Luigi Galvani's discovery of the electric contact-current, in 1789; Alexander Volta's discovery, in 1799, of the true causes of the electric contact-current ...... 1

Erroneous inference drawn by Galvani from his experiments ; General ignorance in regard to the nature of the electric current ; Construction of the pile of Volta or the voltaic pile ; Cruikshank's trough battery ; Decomposition of water by electrolysis by Nicholson and Carlisle, 1800; Wollaston's observation, 1801 2

Cruikshank's investigations, 1803 ; Brugnatelli's experiments in electro-gilding, 1805; Sir Humphrey Davy's discovery of the metals potassium and sodium, 1807 ; Prof. Oersted's discovery of the deflection of the magnetic needle, 1820; Ohm's discovery, in 1827, of the law named after him ............ 3

Faraday's discovery, in 1831, of electric induction; First electro-magnetic induction machine constructed by Pixii ; Faraday's electrolytic law laid down and proved in 1833; Production of iridescent colors, in 1826, by Nobili ; Production of amalgams of potassium and sodium, in 1835, by Bird ; Discovery of the galvanoplastic process, in 1838, by Prof. Jacobi ; Claims of priority of invention by Mr. T. Spencer and Mr. C. J. Jordan ....... 4

Labors of the Elkingtons and de Ruolz ; Murray's discovery, in 1840, of black-leading ; Introduction of gutta-percha by Dr. Montgomery, in 1843 ; First employment, in 1840, of alkaline cyanides by Wright; Patent for the deposition of nickel, 1840 ; Origin of the term " electro-metallurgy" by Mr. Alfred Smee, 1841 ; Prof. Boettger's discovery, in 1842, of deposition of nickel from its double salt .... 5

VI 11 CONTENTS.

PAGE

First deposition in 1842, of metallic alloys by de Ruolz ; First use of thermo-electricity, in 1843, by Moses Poole; Advances in the Art of electro-deposition ; The first magnetic machine that ever deposited silver on a practical scale constructed, in 1844, by Woolrych ; Attempts since 1854 by Christofie & Co., to replace their batteries by magneto-electrical machines; The Alliance machine; Objections to Wilde's machine ............ 6

Dr. Antonie Pacinotti's invention, in I860, of the ring named after him ; Siemens's dynamo-machine, 1866 ; Wheatstone's dynamo-machine, 1867 7

Introduction, in 1871, of Zenobe Gramme's machine; The Hefner- Alteneck's machine, 1872; Siemens & Halske's machine, 1884; S. Schuckert's machine, 1884; Various dynamo-electrical machines; Investigators and practitioners who have contributed to the improvement of the electro-chemical process and the perfection of galvanoplasty . . . . . . . . . . .8

Chapter II. Magnetism And Electricity

1. Magnetism.

Loadstone or magnetic iron ore ; Natural and artificial magnets ; Definitions of the magnetic poles and of the neutral line or neutral zone, and their positions .......... 9

Magnetic meridian ; North and south poles; Phenomena of attraction and repulsion ; Ampere's theory ; The solenoid . . . .10

Rejection of Ampere's theory by many scientific men ; Definition of the magnetic field . . . . . . . . . .11

2. Electricity.

Definition of idio-electrics and of non-electrics ; Gray's discovery, 1727; Good and bad conductors ; The electroscope . . . . .11

Existence of two kinds of electricity ; Vitreous or positive and resinous or negative electricity ; Double-fluid hypothesis of electricity . . 12

Single-fluid hypothesis of electricity ; Coulomb's law ; Series of electromotive force or tension . . . ... . . .13

CONTENTS. IX

PAGE

Production of electricity by the contact of metals and fluids ; Galvanic or hydro-electric current ; Galvanic element or galvanic chain ; Electrical potential ; Electro-motive force . . . . . .14

Resistance ; Conductivity of metals according to Lazere Weiler ; Quantity of current — Ohm's law ........ 15

Essential or internal resistance ; Non-essential or external resistance . 16

Union or coupling of the elements for electro-motive force or tension, and for quantity of current ; Mixed coupling . . . . .18

Proposition deduced from Ohm's law ; Effects of the electric cmrent . 19

Electro-Magnetism.

Pule for determining the direction which the magnetic needle will assume when placed in any particular position to the conducting wire . 19

Galvanoscopes, galvanometers, and multipliers ; Astatic galvanometer ; Tangent galvanometer ; Sine galvanometer ; Electro-magnets . . 20

The solenoid; Law of the action of two electrified wires on each other 21

Induction.

What is understood by induction . . . . . . .21

Primary or inductive current ; Secondary or induced current ; Alternating currents ; Extra currents ....... 22

Chemical Actions op the Electrical Current — Electrolysis.

Reduction of the constituents of a fluid by the electric current ; Pure water a bad conductor ; Faraday's discovery of the chemical actions of the electric current ; Electrolysis ; Electrolyte ; Electrodes . 23

Anode; Cathode; Ions; Anions; Cations; Atoms; Clausius's theory of the molecules . , . . . . . . . .24

Counter or polarizing current; Faraday's electrolytic laws; Experiments with the voltameter ........ 25

Definition of local action ; Electro-chemical equivalents ... 26

Joule's law; Consumption of power in electrolysis; Electric units adopted by the International Congress of 1881 ; Fundamental or C. G. S. (centimetre-gramme-second) system; Force or power — dyne 27

Work — erg. ; Quantity; Potential or electro-motive force; Resistance; The ohm ; The ampere ; The volt ; The farad ; The coulomb ; The watt ; Definition of the English and of the French horse-power . 28

CONTENTS.

Chapter III

GALVANIC ELEMENTS — THERMO-PILES — MAGNETO- AND DYNAMO-ELECTRIC MACHINES.

A. Galvanic Elements.

Voltaic pile ; Trough battery ........

Reduction of local action by amalgamating the zinc ; Various methods

of amalgamating ; Bouant's recommendation . Definition and cause of polarization; Smee's element Constant elements ; Daniell's element Meidinger element ; Grove element ....

Bunsen elements .......

Improved Bunsen cell ......

Composition of electropoion ......

Location of elements; A. Dupre's substitute for sulphuric

acids for filling elements .....

Manipulation of Bunsen elements ; Advisability of having

set of porous clay cells ......

Renewal of the acids ; Leclancl.e element ; Lallande and Chaperon

element . .

Various elements ; Dun's potash element .

A new element patented in Germany Plunge or bichromate batteries ; Bunsen plunge battery Fein's bichromate battery ; Keiser & Schmidt's bichromate Bichromate element for gilding or silvering small articles Stoehrer's battery .......

and nitric a duplicate battery

PAGE

'-'9

30 31 32 33 34 35 36

40 41 42 43 44 45

B. Thermo-Electric Piles.

Professor Seebeck's discovery, in 1822, of a new source of electricity ; Definition of a thermo-electric couple ; Definition of thermo-electricity ; Noe's thermo-electric pile ....... 46

Clamond's thermo-electric pile . . . . . . . .47

Hauck's thermo-electric pile . . . . . . . .48

Gulcher's thermo-electric pile . . . . . . . .49

Superiority of dynamo-electric machines over thermo-electric piles . 50

CONTENTS. XI

C. Magneto- and Dynamo-Electric Machines.

page

Faraday's discovery in 1831 ; Magnetic field or the region of the lines of force . . . . . . . . . . .51

What a magneto-electric or dynamo-electric machine actually is ; Professor S. P. Thompson's definition of a dynamo-electric machine ; Constituent parts of a dynamo-generator, or a dynamo-electric machine proper ........... 52

Pixii's electrical machine, 1832; Saxton and Clarke's improvements ; Dr. W. Siemens's improvement, 1857; Pacinotti's ring conductor; Dr. W. Siemens's and Sir C. Wheatstone's discovery ... 53 Classes of electric generators ; Continuous current machine and alternating current machine ; Gramme machine and armature . . 54 Modern Gramme dynamo for galvanoplastic purposes .... 56

Disadvantage of the Gramme machine ; S. Schuckert's flat-ring machine ............ 57

Fein's dynamo-machine; Brush dynamo and armature . . .58 Siemens & Halske dynamo-electric machines ..... 60

Kroettlinger's dynamo-machine . . . . . . . .61

Lahmeyer dynamo . . . . . . . . v . .62

Weston dynamo-machine ......... 64

Hanson & Van Winkle Co.'s new dynamo electro-plating machine . 65 Hanson & Van Winkle Co.'s bicycle-power plating dynamo; Zucker &

Levett Chemical Co.'s improved " American Giant" dynamo . . 68 Various dynamo-machines ; Value of the dynamo and its effect upon the electro-plating industry ........ 70

Chapter IV. Arrangement Of Electro-plating Establishments In General

Necessity of sufficient light and thorough ventilation .... 72

Location of Bunsen elements ; Provision for heating .... 73 Importance of a good supply of water; Best materials for floors ; Size

of the operating-room ......... 74

Grinding- and polishing-rooms ; Prevention of dust in the polishing-

room ; Location of the transmission carrying the belt pulleys . 75

Xll CONTENTS.

Electro-plating Arrangements in Particular.

page What the actual electro-plating plant consists of; Arrangement with elements ; Choice of coupling the elements ..... 76

Proportion of the effective zinc surface of the elements to that of the anodes and articles . . . . . . . . .77

Coupling of elements for solid and thin deposits ; Auxiliary apparatuses 78 Rheostat, current-regulator, resistance-board or switch-board ; Conditions upon which the action of the resistance-board is based . . 79 Horizontal and vertical galvanometers ...... 80

Location of the resistance-board and galvanometer ; Rheostats patented

by the Hanson & Van Winkle Company, of Newark, N. J. . . 81 Indications by the galvanometer ....... 85

Counter-current ; Rules to be observed in conducting the current; Positive or anode-wire ; Negative or object-wire ..... 87

Vats or tanks ; Wooden vats ........ 88

Enamelled iron tank ; Agate vessel for gold and other solutions ■ . 89

Conducting rods .......... 90

Binding-posts and screws ; Anodes and their arrangement . . .91 Slinging wires ; Protection of the rods ; Cleansing and rinsing apparatuses ........... 92

Dipping or pickling ; Sawdust ; Arrangements with dynamo-electric

machines ; Rules for setting up and running dynamo-electric machines 93 Insulation of the object- and anode-wires ......' 94

Wire-carriers ; Resistance-boards or current-regulators ; Resistance-board of the dynamo ; Amperemeter or ammeter ; Voltmeter . . 95 Coupling of the main object- wire and the main anode- wire with the resistance-boards, the voltmeter, the shunt, and the baths ... 98 Feeding the baths . . . . , . . , . .100

Ground plan of an electro-plating establishment 101

Lye-kettle; Table for freeing the articles from grease . . .102

Mode of calculating the thickness of conducting wires for dynamos . 103

Chapter V

treatment of metallic articles.

A. Mechanical Treatment.

Treatment before electro-plating ; Scratch-brushing ; Various forms of scratch- brushes . . . . . . . . . .104

Treatment of scratch-brushes ; Circular scratch-brushes and their construction . . . ... . . . . . .106

Cleansing by the sand-blast . . • . . . . . 108

CONTENTS. xiii

PAGE

Tumbling box or drum ......... 109

Polishing articles in the tumbling-drum . . . . . .110

Grinding ; Grinding disks and their construction . . . .112

Treatment of the grinding disks ; Vienna lime ; Grinding lathes . . 113 Execution of grinding . . . . . • . . .114

Fibres and fibre- brushes; Grinding iron and steel articles . . .115 Grinding brass and copper castings, sheets of brass, German silver, and copper zinc castings, and sheet zinc ; Polishing ; Foot lathes for polishing 116

American double polishing lathe; Lathe manufactured by the Hanson & Van Winkle Co., of Newark, N. J. . . '. . . .117

Belt strapping attachment . . . . . . . . .110

Polishing materials ; Rouge composition ...... 120

Burnishing ; Mechanical treatment during and after the electro-plating

process; Scratch-brushing the deposits ; Effect of scratch-brushing . 121 Scratch-brushes used for different metals ; Decoctions used in scratch-brushing; Scratch-brushing by hand ; Lathe brush . . . . 122

Cleansing and drying the finished electro- plated objects . . .123 Sawdust for drying the objects ; Drying plated objects of iron and steel ; Removal of moisture from the pores of nickelled iron objects ; Polishing deposits of nickel, copper and brass, tin, gold and silver, and platinum; Operation of burnishing . . . . ■ . . .124

Various forms of burnishers . . . . . . . .125

B. Chemical Treatment.

Pickling ; Mixture for pickling east-iron and wrought-iron objects ; Excellent pickle for iron ; To cleanse badly rusted iron objects ; Duration of pickling . . . . . . . . . .126

Pickling zinc objects; Cleansing and brightening copper, brass, bronze, tombac, and German silver ; Preliminary pickle ; Bright dipping bath; Use of potassium cyanide for pickling ..... 127

Manipulation of pickled objects ; Dead dip . . . . .128

Main points in pickling ; Absorbing plant for escaping acid vapors . 129 Regaining of acid and metal from exhausted dipping baths . . . 130 Mixture for the production of a grained surface by pickling ; Removal of grease ........... 131

Preparation of lime mixture ; Cleansing with benzine ; Tying the objects to metallic wires . . . . . . . . .132

Removal of oxide from the metallic objects . . . . .133

Carboy stand 134

XIV CONTENTS.

Chapter VI. Processes Of Electro-deposition

PAGE

Importance of the constitution of the water used as a solvent ; Spring and well water . . . . . . . . . .134

River water ; Distilled water ; Rain water ; Importance of the purity of the chemicals used ......... 135

Concentration of the baths ; Effects of baths too poor in metal and too concentrated . . . . . . . . . . .136

Stirring up the baths . . . . . . . . .137

Constant agitation of the baths by mechanical means ; Temperature of the baths ; Boiling of baths ; Kettles and boiling pans . . ./ 138

Working the bath with the electric current in place of boiling; Dissolution of nickel salts dissolving with difficulty ; Filtration of the boiled solutions ........... 139

To secure lasting qualities to the baths ; Choice of anodes ; Alloying of the deposit with the basis-metal ; Gore's experiments . . . 140

Conditions for the good performance of an electrolytic bath ; Reduction of metals without a battery (electro-deposition by contact) . . 141

Dipping baskets . . . . . . . . . .143

Chapter VII. Deposition Of Nickel And Cobalt

1. NlCKELLING.

Growth and popularity of nickel-plating . . . . . . 143

Properties of nickel ; Nickel baths ; General rules for preparing nickel

baths 144

Prepared nickelling salts ; Conducting salts ; Additions to the nickelling

bath recommended by various experts ; Effect of the presence of

small quantities of a free acid ....... 145

JBoric acid as an addition to nickelling and all other baths, and its effects ;

Determination of the acidity, alkalinity, and neutrality of nickel baths 146 Formula?, preparation, characteristics, and treatment of nickel baths . 14 7 Burning or over-nickelling . . . . . . . .148

Nickel baths containing boric acid; Weston's formula . . .149

Kaselowsky's formula . . . . . . . . .150

Nickel baths for certain purposes; Nickel bath for rapid nickelling of

polished slightly coppered zinc articles ; Nickel bath for iron, brass,

and copper and sheet zinc and zinc castings . . . . .151 Recent formulas for nickel baths ; An English formula ; Addition of

bisulphide of carbon to nickel baths ; Bath for nickelling small articles 152 Nickel baths without nickel salt ; Nickel anodes ; Objections to the use

of insoluble anodes . . . . . . . . .153

CONTENTS. XV

PAGE

Use of rolled and cast anodes together in one bath . . . .155

Cause of the reddish tinge of the anodes ; Suspension of the anodes ;

Process of electro-nickelling . . . . . . . .156

Coppering or brassing articles previous to nickelling ; Suspension of the

objects in the bath ; Suitable current-strength for nickelling . . 157 Burning or over-nickelling ; Criteria for judging whether nickelling progresses with a correct current-strength . . . . .158

Most suitable current-density for nickelling ; Solid nickelling ; Test for

sufficiently heavy nickelling ; Arrangement of the anodes . . 159 Nickelling of flat objects, round or half-round surfaces, smooth articles, objects with depressions and hollows, and lamp-feet of cast zinc ; General rules for nickelling and other electro-plating processes ; Mode of suspending the objects in the bath . . . . .160

Polarizing phenomena ; Counter or polarizing current . . .161

Nickelling en masse of small and cheap objects . . . . .162

Warren's solutions of nickel and of cobalt; Stripping nickelled articles 163 Remedy against the yellowish tone of the nickelling; Principal phenomena which may occur in nickelling and the means of avoiding them . . . . . . . . . . .165

Refreshing nickel baths . . . . . . . . .167

Polishing nickel deposits ; Treatment of nickelled objects which are to be left dead ; Nickelling sheet zinc ; Mystery surrounding the nickelling of sheet-zinc . . . . . . . . ' . .168

Required conditions for, and the execution of, nickelling sheet-zinc ;

Grinding and polishing the sheets ; Construction of cloth bobs . 169

Manner of polishing or grinding the sheets ; Self-acting sheet-polishing

machines; F. Rauber's sheet grinding and polishing machine . .170 Freeing the sheets from grease ; Nickelling the sheets . . .173

Advantage of previous coppering or brassing; Great care required in the treatment of the brass bath . . . . . . .174

Coppering the sheets; Dimensions of the vats for nickelling the sheets 175 Proportion of anode surface to that of the zinc surface ; Cause of black

streaks and stains; Augmentation of the metallic content of the bath 176 Polishing the nickelled sheets ; Nickelling of tin plate, copper and brass sheets, and of sheet-iron and sheet -steel . . . . . .177

Nickelling of wire . . . . . . . . . .178

Apparatus for nickelling wire . . . . . . . .179

Nickelling wire gauze ......... 180

Nickelling of knife-blades, sharp surgical instruments, etc. . . .181

Nickelling of electrotypes, cliches, etc. ; Baths for hard nickelling . 182 Process of hard nickelling . . . . . . . . .183

Treatment of the nickelled plates ; Recovery of nickel from old baths ; Urquhart's plan for recovering nickel from old solutions ; To improve defective nickelling ; Arrangement of the " doctor" . . .184

XVI CONTENTS.

PAGE

Niekelling by contact and boiling ; Franz Stolba's process of nickeiling by contact ........... 185

Deposition of an alloy containing nickel according to R. Kaiser . .186

Deposits of nickel alloys, and baths suitable for the purpose ; Nickel bronze; French process for the deposition of German silver . .187

Watt's method for the deposition of German silver .... 188

2. COBALTING.

Properties of cobalt . . . . . . . . . .188

Baths for cobalting ; Cobalting of copper plates for printing ; Determination of the quantity of copper dissolved in stripping the cobalt deposit from cobalted copper plates ....... 189

Warren's cobalt solution ; Cobalt solution recommended by Mr. G. W. Beardslee, of Brooklyn, N. Y. ; R. Daub's bath for cobalting small fancy articles of copper, brass, or steel . . . . . .190

Cobalting by contact . . . . . . . . . . . 191

Chapter VIII

deposition of copper, brass, and bronze. 1. Coppering.

192 193

194 195

196 197

Properties of copper; Copper baths, their composition, preparation properties, and treatment .......

Hassauer's copper bath ; Copper bath for iron and steel articles .

Formation of slime on the anodes in a copper bath ; Phenomena ap pearing in copper baths containing cyanide . . .

Baths for coppering zinc articles recommended by Roseleur

Copper baths -without potassium cyanide ; Weil's copper bath and method of coppering . . . . .

Copper bath recommended by Walenn ; Copper bath according to Pfan hauser ; Gauduin's copper bath ......

Execution of coppering ; Anodes used ; Scratch-brushing and treatment of defective places ; Solid and heavy coppering . . . .198

Prevention of small, dark, round stains ; O. Schultz's patent to prevent the formation of stains ; Polishing the deposit of copper . . 199

Treatment of coppered objects to be coated with another metal ; Coppering small articles en masse . . . ... . . 200

Coppering by contact and dipping ; To coat zinc plates with a very thin but hard layer of copper ; Bacco's copper bath; Brush-coppering . 201

Application of a thin film of copper to iron and steel objects ; Coppering steel pens, needles, eyes, etc. ; Inlaying of depressions of coppered art castings with black ...... . 202

CONTENTS. X\ T ii

2. Brassing (Cuivre-poli Deposit).

PAGE

Constitution and varieties of brass ; Brass baths, their composition, preparation, properties, and treatment ....... 203

Rules for baths containing more than one metal in solution ; Brass bath according to Roseleur ; Irregular working of fresh brass baths . . 204

Effect of the addition of arsenious acid to brass baths ; Bath for brassing iron ............ 205

On what the color of the brass deposit depends ; Anodes for brass baths ............ 206

Formation of slime on the anodes ; Remedy against defective deposition 207

Bath for brassing zinc exclusively ; Bath for brassing cast iron, wrought iron, and steel ; N orris and Johnson's brass bath ; Solution for transferring any copper-zinc alloy serving as anode .... 208

Pfanhauser's bath for brassing all kinds of metals ; Execution of brassing 209

Distance of the objects, to be brassed, from the anodes ; Brassing of unground iron castings ; Brassing by contact and dipping . . 210

Inlaying, with black, of brassed articles . . . . , .211

3. Bronzing.

Gountier's solution for coating wrought and cast iron with bronze;

Other bronze baths, and their composition, preparation, and treatment 21 1 Hess's bath for deposits of tombac ; Execution of brassing . . . 212

Chapter IX. Deposition Of Silver

Properties of silver . . . . . . . . . .212

Silver baths, their composition, preparation, and treatment ; Silver bath for a heavy electro-deposit of silver (silvering by weight) ; Preparation of the bath with silver chloride . .• . . . .213

Preparation of the bath with silver cyanide ; Silver bath for ordinary electro-silvering . . . . . . . . . 214

Vats for silver baths ; Treatment of silver baths ; Silver anodes ; Most suitable current-strength for silver baths . . . . . .215

Coupling of the elements ; Indication of the presence of too much or not enough potassium cyanide ; Objections to insoluble anodes ; The behavior and appearance of the anodes as criteria of the content of potassium cyanide in the bath. ....... 216

Keeping the bath constant by silver anodes ; Proper treatment of baths made with chloride of silver . . . . . . . .217

Gradual thickening of the bath ; Augmentation of the content of silver

B

CONTENTS.

Determination of the actual content of silver in the bath ; Contrivances

to keep the objects to be silvered in gentle motion while in the bath 219 Singular phenomenon in silvering ....... 220

Remedy against a yellow tone of the silvering ; Execution of silvering ; Silvering by weight ; Mechanical and chemical preparation of the

objects 221

Treatment of copper and its alloys, German silver and brass ; Freeing from grease ; Pickling ; Rubbing ; Pickling in the preliminary pickle ; Amalgamating (quicking) ; Slinging wires. . . . 222

Treatment of the objects while being silvered ; Amount of silver deposited upon several grades of plated-ware manufactured by the William Rogers Manufacturing Co., of Hartford, Conn. ; Method of controlling the weight of the deposit ...... 223 ,

Roseleur's plating balance ......... 225

Plating balance with resistance-board, voltmeter, and silver bath ; Treatment of articles which are to retain the crystalline dead white with which they come from the bath ....... 226

Polishing the silvered articles ; Mode of executing the operation of burnishing . . . . . . . . . . .227

Burnishing machines ; Ordinary silvering ; Practice of the Meriden Britannia Co.'s works at Meriden, Conn., with Britannia or white metal ............ 228

With German silver or nickel articles ; Steel articles ; Methods in use in the William Rogers Manufacturing Co., Hartford, Conn., for preparing work for plating ; For cleansing steel cutlery ; Nickel silver (German silver) for spoons ........ 229

Britannia metal (hollow ware) ; Rogers's striking solution ; Meriden Company's striking solution ; extra heavy coating of silver on the convex surfaces of spoons and forks ; Sectional plating . . . 230 Stopping- off; Stopping-oflf varnish ; Silvering of iron ; Silvering by contact, by immersion, and cold silvering with paste ; Bath for silvering by contact with zinc . . . . . . . .231