A complete Treatise on the Electro-deposition of Metals ... Translated from the German of Dr. G. Langbein ... with additions by William T. Brannt ... Illustrated, etc

Front matter

A COMPLETE TREATISE ON THE ELECTRO-DEPOSITION OF METALS. A COMPLETE TREATISE ON THE ELECTRO-DEPOSITION OF METALS. COMPRISING ELECTRO-PLATING AND GALVANOPLASTIC OPERATIONS, THE DEPOSITION OF METALS BY THE CONTACT AND IMMERSION PROCESSES, THE COLORING OF METALS, THE METHODS OF GRINDING AND POLISHING, AS WELL AS DESCRIPTIONS OF THE ELECTRIC ELEMENTS, DYNAMO-ELECTRIC MACHINES, THERMO-PILES, AND OF THE MATERIALS AND PROCESSES USED IN EVERY DEPARTMENT OF THE ART. TRANSLATED FROM THE GERMAN OF De. GEOKGE LANGBEENT, PROPRIETOR OF A MANUFACTORY FOR CHEMICAL PRODUCTS, MACHINES, APPARATUS AND UTENSILS FOR ELECTROPLATERS AND OF AN ELECTRO-PLATTNG ESTABLISHMENT, IN LEIPZIG. WITH ADDITIONS BT WILLIAM T. BRAINTNT, EDITOR OF " THE TECHN O-CHEMICAL RECEIPT BOOK." ILLUSTRATED B Y ONE HUNDRED AND TWENTY-FIVE ENGRA TINGS.

PHILADELPHIA : HENRY CAREY BAIRD & CO., INDUSTRIAL PUBLISHERS, BOOKSELLERS, AND IMPORTERS, 810 WALNUT STREET. LONDON : SAMPj-ON LOW, MARSTON & CO., Limited, ST. DUNSTAN'S HOUSE, FETTER LANE, FLEET STREET. 1891. Copyright bt HENRY CAREY' BAIRD & CO. 1891. Printed at the COLLINS PRINTING HOUSE, 705 Jayne Street, Philadelphia, U. S. A.

Preface

. 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 further ance of this object, a translation of Dr. George Langbein's work, Vollstaendiges 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 satisfactory, 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 instru ments, 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.

. an empirical manner, by time-consuming experiments, to-day, by duly observing the determined conditions and provided with well working measuring instruments, he can at once produce beautiful and suitable deposits of the various metals. The data referring to these current-conditions, according to mea surements 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 suita ble for his special purpose. To the few formulæ, 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 w-ork as useful as possible, the most suitable for mulæ 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 pre paration of the chemicals has been omitted, since they can be pro cured 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 trans lator, as well as the chapter on " Apparatus and Instruments," and that of " Useful Tables," added by him, may contribute to the use fulness 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. i. GENERAL 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 . . . . . .17 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 Nicholson and Carlisle, 1800; WoUaston' s observation, 1801 IS Cruikshank's investigations, 1803 ; Brugnatelli's experiments in electro-gilding, 1805 ; Sir Humphry Davy's discovery of the metals potassium and sodium, 1807 ; Prof. Oersted's discovery, 1820 ; Ohm's discovery, in 1827, of the law named after him ..... 19 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 ofthe amalgams of potassium and sodium, in 1835, by Bird; Discovery ofthe galvano-plastic process, in 1838, by Prof. Jacob! ; Claims of priority of invention by Mr. T. Spencer and Mr. C. J. Jordan 20 Labors of the Elkingtons and of de Buolz ; 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; Origination ofthe term "electro-metallurgy" by Mr. Alfred Smee, 1841 ; Prof. Boettger's discovery, in 1842, of depositions of nickel from its double salt 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 ; Attempts, since 1854, by Christofle & Co., to replace their batteries by magneto-electrical machines ; The Alliance machine ; Objections to Wilde's machine ; Dr. Antonie Pacinotti's invention, in 1860, of the ring named after him .... 22 Siemens's dynamo-machine, 1866; Wheatstone's dynamo-machine, 1867; Introduction of Zenobe Gramme's machine, in 1871 ; Hefner- Alteneck's machine, 1872; Siemens & Halske' s machine, 1874; S. Schuckert's machine, 1874; Various dynamo-electrical machines; Investigators and practitioners who have contributed to the improvement of the electro-chemical process and the perfection of galvanoplasty ............ 23 II. THEORETICAL PART.

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 ........ "24 Magnetic meridian ; North and south poles ; Phenomena of attraction and repulsion ; Ampfere's theory ....... 25 Definition of the magnetic field ........ 26 2. Electricity. Definition of idioelectries and of non-electrics ; Gray's discovery, 1727; Good and bad conductors ; The electroscope and its use ; Existence of two kinds of electricity 26 Vitreous or positive, and resinous or negative electricity ; Symer's theory of the electric agent ; Franklin's one-fluid theory ; Coulomb's law ; Contact-electricity . . . . . . . . 27 Series of tension ; Production of electricity by the contact of metals and fluids ; Galvanic or hydroelectric current ; Galvanic element or galvanic chain ; Electrical potential ...... 28 Electro-motive force ; Resistance ; Conductivity of metals according to Lazere Wreiler ..........

CONTENTS. IX PAGE Quantity of current — Ohm's law ; Essential or internal resistance, and non-essential or external resistance ...... 30 Coupling of the elements . . . . . . . . .31 Coupling of the elements for tension and for quantity of current . . 32 Mixed coupling ; Proposition deduced from Ohm's law ; Effects of the electric current . . . . . . . . . .33 Electro-Magnetism. Pule for determining the direction which the magnetic needle will assume when placed in any particular position to the conducting wire . 33 Galvanoscopes, galvanometers, or multipliers ; Astatic galvanometer ; Tangent galvanometer ; Sine galvanometer ..... 34 Electro-magnets ; Solenoid ; Law of the action of two electrified wires on each other .......... 35 Induction. What is understood by induction ....... 35 Primary or inductive current ; Secondary or induced current . . 36 Alternate currents ; Extra currents . . . . . . .37 Chemical Actions of 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 current . . . . . . . . . .37 Electrolysis; Electrolyte; Electrodes; Anode; Cathode; Ions; Anions ; Cations ; Atoms ; Claussius's theory of molecular charges . 38 Counter or polarizing current; Faraday's electrolytic laws; Experiment with the voltameter ........ 39 Electrical equivalent ; Definition of local action ; Electro-chemical equivalents ........... 40 Joule's law; Consumption of power in the electrolysis; Electric units adopted by the International Congress of 1881 .... 41 Fundamental or C. G. S. (centimetre-gramme-second) system ; Force or power ; Work ; Quantity ; Potential or electromotive force ; Resistance ; The ohm ; The ampe-re ; The volt ; The farad ; The coulomb ............ 42 The watt ; Definition of the English and of the French horse-power . X CONTENTS. III. SOURCES OF CURRENT.

Chapter III. Galvanic Elements

— THERMO-PILES MAGNETO- AND DYNAMO-ELECTRIC MACHINES. A. Galvanic Elements page Voltaic pile ; Trough battery ........ 44 Reduction of local action in elements by amalgamating the zinc ; Various methods of amalgamating ; Bouant's recommendation ... 45 Definition and cause of polarization ; Smee's element ... 46 Constant elements ; Daniell' s element ...... 47 Meidinger element ; Grove element ....... 48 Bunsen elements .......... 49 Location of elements ......... 50 A. Dupne's substitutes for sulphuric and nitric acids for filling elements; Manipulation of Bunsen elements ....... 51 Advisability of having a duplicate set of porous clay cells ; Renewal of the acids ........... 52 Leclanehe element ; Lallande and Chaperon element .... 53 Various elements ; Dun's potash element ...... 54 Dipping or bichromate batteries; Fein's bichromate battery; Keiser & Schmidt's bichromate battery ....... 55 Bichromate element for gilding or silvering small articles ... 56 Stoehrer's battery .......... 57 B. Thermo-piles.

Seebeck's discovery, 1823 ; Noe'spile; Clamond's thermo-pile . . 58 C. Magnetoand Dynamo-Electric Machines. Faraday's discovery in 1831 ........ 59 Magnetic field or the region of the lines of force ; What a magneto-electric or dynamo-electric machine actually is ; Pixii's electrical machine, 1832; Saxton and Clarke's improvements . . . .60 Dr. W. Siemens's improvement, 1857; Pacinotti's ring conductor; Dr. W. Siemens' and Sir C. Wheatstone's discovery; Transition of the magneto-electric machine to the dynamo machine . . .61 Continuous current machine and alternate current machine ; Gramme machine and armature ......... CONTENTS. XI page Modern Gramme dynamo for galvanoplastic purposes .... 64 Disadvantage of the Gramme machine; S. Schuckert's flat ring machine ............ 65 Fein's dynamo machine; Brush's dynamo and armature . . . 6G Siemens & Halske's magneto-electric machine ..... 68 Siemens & Halske's dynamo-electric machine; Weston's dynamo machine 69 Kroettlinger's dynamo machine ........ 70 Lahme.yer dynamo .......... 71 Other dynamo machines ; Value of the dynamo and its effect upon the electro-plating industry ......... 73 IV. PRACTICAL PART.

Chapter IV. Arrangement Of Electro-plating Establishments In General

Necessity of sufficient light and thorough ventilation . . . .75 Location of Bunsen elements ; Provision for heating . . . .76 Great importance of a good supply of water ; Best material for floors ; Size of the operating room ........ 77 Grinding and polishing rooms ; Prevention of dust in the polishing rooms ; Location of the transmission carrying the belt pulleys . 78 Electro-Plating Arrangements in Particular. What the actual electro-plating plant consists of; Arrangement with elements ; Choice of coupling of the elements .... 79 Proportion of the effective zinc surface of the elements to that of the anodes and articles ; Coupling of elements for solid and thin deposits 80 Auxiliary apparatuses ......... 81 Current regulator, resistance board or switch board ; Conditions upon which the action of the resistance board is based . . . .82 Galvanometers ........... 83 Location of the resistance board and galvanometer ; Indications by the galvanometer .......... 84 Counter current .......... 86 Rules to be observed in conducting the current ; Positive or anode wire ; Negative or object wire ; Vats for baths ; Wooden vats. . .

CONTENTS. PAGE Vats of bricks, enamelled iron, and stoneware ; Conducting rods ; Anodes and their arrangements ....••• °-> Various forms of binding screws ; Mode of suspending the anodes in the bath 89 Mode of suspending the objects in the bath ; Protection of the rods ; Cleansing and rinsing apparatuses ; Dipping or pickling . . 90 Sawdust ; Arrangement with dynamo-electric machines ; Rules for setting up and running dynamo-electric machines . . . .91 Insulation of the object and anode wires ; Wire carriers ; Resistance boards or current regulators ........ 92 Resistance board of the dynamo ; Amperemeter or ammetre ; Voltmeter ............ 93 Coupling of the main object wire and the main anode wire with the resistance boards, the voltmeter, the shunt, and the baths . . 95 Feeding the baths ; Ground plan of an electroplating establishment . 97 Lye kettle ; Various means of removing grease and dirt ... 99 Table for freeing articles from grease ...... 100 Mode of calculating the thickness of the conducting wires for dynamos 101

Chapter V. Treatment Of The Metallic Articles

A. Mechanical Treatment. Treatment before electro-plating ; Scratch-brushing; Various forms of scratch-brushes . . . . . . . . . .102 Treatment of scrateh-bru9h.es ........ 103 Circular scratch-brushes and their construction . . . . .104 Cleansing by the sand blast ..... .105 Tumbling drum or box . . . . . . . . .106 Grinding; Grinding disks ......... 107 Treatment of the grinding disks . . . . . . .108 Vienna lime ; Grinding lathes ........ 109 Execution of grinding ; Fibres and fibre brushes .... 110 Grinding of iron and steel articles, brass and copper castings, sheets of brass, German silver, and copper-zinc castings . . . .111 Polishing sheet zinc ; Polishing ; Foot lathe for polishing ; American double polishing lathes . . . . . . . . .112 Polishing materials ; Rouge composition ; Burnishing ; Mechanical treatment during and after the electro-plating process ; Scratch-brushing the depositions . . . . . . . .114 Effect of scratch-brushing ; Decoctions used in scratch-brushing; Manner of executing scratch-brushing by hand 115 Lathe brush CONTENTS.

XIII PAGE Cleansing and drying the polished objects ; Sawdust for drying the objects ; Drying of iron and steel objects ; Removal of moisture from the pores of nickeled iron objects ; Polishing of deposits of nickel, copper and brass, tin . . . . . . . .117 Polishing deposits of gold, silver, and platinum ; Operation of burnishing ; Various shapes of burnishes . . . . . . .118 B. Chemical Treatment. Pickling; Mixture for pickling cast-iron and wrought-iron objects; Excellent pickle for iron ; To cleanse badly rusted iron objects . 119 Duration of pickling ; Pickling zinc objects ; Cleaning and brightening copper, brass, bronze, tombac and German silver ; Preliminary pickle ; Bright-dipping bath . . . . . . . .120 Use of potassium cyanide for pickling ; Storing of pickles ; Manipulation of pickled objects ; Dead dip . .

A . . . .121 Main points in pickling . . . . . . . . .122 Absorbing plant for escaping acid vapors . . . . . .123 Regaining of acid and metal from exhausted dipping baths ; Mixture for the production of a grained surface by pickling . . 1 24 Removal of grease ; Preparation of lime mixture; Cleansing with benzine . . . . . . . . . . . .125. Tying the objects to metallic wires ; Removal of oxide from the metallic objects . . . . . . . . . . .126

Chapter VI. Processes Of Electro-deposition

Importance of the constitution of the water used as a solvent ; Spring and well water; River water; Distilled water; Rain water; Importance of the purity of the chemicals used . . . . .127 Examples of the importance of the purity of the chemicals used ; Concentration of the baths . . . . . . . . .128 Effect of baths too poor in metal and too concentrated ; Stirring up the baths 129 Constant agitation of the baths ........ 130 Temperature of the baths ; Boiling of the baths ; Working the bath with the electric current ; Dissolution of nickel salts dissolving with difficulty 131 Filtration of the boiled solutions ; Securing lasting qualities to the baths; Choice of anodes . . . . . . . .132 Alloying of the deposit with the basis-metal ; Conditions for an electrolytic bath 133 Reduction of metals without a battery (electro-deposition by contact) CONTENTS.

Chapter VII. Deposition Of Nickel And Cobalt

1. Nickeling.

PAGE Growth and popularity of nickel plating ; Properties of nickel . . 135 Nickel baths; General rules for preparing nickel baths; Prepared nickeling salts; Conducting salts ....... 136 Additions to nickel baths recommended by various experts ; Boric acid as an addition to nickel baths, and its effect 137 Determination of the acidity, alkalinity and neutrality of nickel baths ; Formulæ, preparation, characteristic properties and treatment of nickel baths 139 Nickel baths containing boric acid; Weston's formula ; Kaselowsky's formula . . . . . . . . . . .141 Nickel baths for certain purposes ; Nickel bath for rapid nickeling of polished slightly coppered zinc articles ...... 142 Nickel bath for iron, brass, copper, sheet zinc and zinc castings; Recent formulæ for nickel baths ; English formula for a nickel bath ; Brace's recommendation of the addition of bisulphide of carbon 143 Nickel bath without nickel salt ; Nickel anodes .... 144 Objections to insoluble anodes ........ 145 Use of rolled and cast anodes together in one bath .... 146 Reddish tinge of the anodes ; Suspension of the anodes ; The process of electro-nickeling ......... 147 Coppering or brassing articles previous to nickeling ; Suspension of the objects in the bath ; Suitable current-strength for nickeling . . 148 Burning or over-nickeling ; Criteria for judging whether nickeling progresses with a correct current ....... 149 Most suitable density for nickeling metallic objects ; Solid nickeling . 150 Test for sufficiently heavy nickeling; Arrangement of the anodes; Nickeling of flat objects, round, or half-round surfaces, smooth articles, objects with depressions and hollows, and lamp feet of cast zinc ............ 151, General rules for nickeling and other electroplating processes; Mode of suspending the objects in the bath ; Polarizing phenomena ; Counter or polarizing current ....... 152 Nickeling en masse of small and cheap objects ..... 153 Warren's solutions of nickel and of cobalt . . . . .154 Removal of defective and old nickeling ; Remedy against the yellowish tone of nickeling . . . . . . . . . .155 Principal phenomena which may occur in nickeling and the means of avoiding them ••■•■..... 156 Refreshing nickel baths CONTENTS.

XV PAGE Polishing and cleansing nickel deposits ; Treatment of nickled objects which are to be left dead ; Nickeling sheet zinc ; Mystery surrounding the nickeling of sheet zinc . . . . . . .158 Required conditions for, and the execution of nickeling sheet-zinc ; Grinding and polishing the sheets ; Construction of cloth bobs . 159 Manner of polishing or grinding the sheets . . . . .160 Self-acting sheet polishing machines; F. Rauber's sheet grinding and polishing machine . . . . . . . . . .161 Freeing the sheets from grease ........ 163 Nickeling the sheets; Advantage of previous coppering or brassing; Great care required in the treatment of the brass bath . . .164 Coppering of the sheets ; Current-strength for nickeling zinc sheets . 165 Proportion of anode surface to that of the zinc surface ; Cause of black streaks and stains . . . . . . . . . .166 Augmentation of the metallic content of the bath ; Polishing the nickeled sheets ; Nickeling of tin plate and of copper and brass sheets 167 Nickeling of sheet iron and sheet steel . . . . . . .168 Nickeling of wire; Apparatus for nickeling wire . . . .169 Nickeling wire gauze ; Nickeling of knife blades, sharp surgical instruments, etc. . . . . . . . . . .171 Nickeling of electrotypes, clich.s, etc. ; Hard nickeling . . .172 Formulæ for baths for hard nickeling ; Process of hard nickeling ; Treatment of the nickeled plates . . . . . . .173 Recovery of nickel from old baths; Urquhart's plan for recovering nickel from old solutions . . . . . . . .174 To improve defective nickeling ; Arrangement of the " doctor ;" Nickeling by contact and boiling; Franz Stolba's process of nickeling by contact . . . . . . . . . . . .175 Deposition of an alloy containing nickel, according to R. Kaiser; Deposits of nickel alloys, and baths suitable for the purpose ; Nickel bronze ... ........ 177 French process for the deposition of German silver ; Watt's method . 178 2.

Cobalting. Properties of cobalt ; Baths for cobalting ; Cobalting of copper plates for printing ; Removal of the cobalt coating . . . . .179 Experiment in stripping the cobalt deposit from cobalted copper plates ; Warren's cobalt solution ; Cobalt solution recommended by Mr. G. W. Beardslee, of Brooklyn, N. Y 180 Cobalting by contact . . . . . . . . . .181 CONTENTS.

Chapter VIII. Deposition Of Copper, Brass And Bronze

1 . Coppering. PAGE Properties of copper . • • .181 Copper baths, their composition, preparation, properties, and treatment; Hassauer's copper bath; Copper baths for iron and steel articles . . . . . . ■ • • • • .182 Formation of slime on the anodes in a copper bath . . . .183 Phenomena appearing in copper baths containing cyanide ; Baths for coppering zinc articles, recommended by Roseleur . . . . 1 84 Copper baths without potassium cyanide ...... 185 Weil's copper baths and methods of coppering ; Copper bath recommended by Walenn ; Gauduin's copper bath 186 Execution of coppering ; Anodes used ; Scratch-brushing and treatment of defective places ; Solid and heavy coppering . . . 187 Prevention of the formation of small dark round stains ; O. Schulz's patent to prevent the formation of stains ; Polishing the deposit of copper ....... 188 Treatment of coppered objects to be coated with another metal ; Coppering small articles en masse ; Coppering by contact and dipping . 189 Bacco's copper bath ; Brush-coppering . . . . . .190 Coppering steel pens, needles, eyes, etc. ; Inlaying of depressions of copper art-castings with black ....... 191 2.

Brassing (Cuivre poli Deposit). Constitution and varieties of brass . . . . . . .191 Brass baths, their composition, preparation, properties, and treatment ; Rule for all baths containing more than one metal in solution ; Brass bath according to Roseleur . 192 Irregular working of fresh brass baths ; Effect of the addition of arsenious acid to brass baths . . . . . . . .193 On what the color of the brass deposit depends . . . . .194 Anodes for brass baths ; Formation of slime on the anodes ; Remedy against defective deposition ........ 195 Bath for brassing zinc exclusively . . . . . . .196 Bath for brassing cast-iron, wrought-iron, and steel ; Norris and Johnson's brass bath; Solution for transferring any copper-zinc alloy serving as anode ; Execution of brassing ; Distance ofthe objects to be brassed from the anodes . . . . . . . .197 Brassing of unground iron castings ; Brassing by contact and dipping ; Inlaying with black of brassed articles . . . . . .198 CONTENTS.

XVII 3. Bronzing. PAGE Gountier's solution for coating wroughtand cast-iron with bronze . 198 Other bronze baths and their composition, preparation, and treatment ; Anodes used . . . . . . . . . . .199 Baths for deposits of tombac ; Execution of bronzing . . . 200

Chapter IX. Deposition Of Silver

Properties of silver; Silver baths, their composition, preparation and treatment ; Silver bath for a heavy electro-deposit of silver (silvering by weight) 200 Preparation of the bath with silver chloride and of the bath with silver cyanide ............ 201 Silver bath for ordinary electro-silvering; Vats for silver baths ; Treatment of the silver baths ; Anodes ....... 2.02 Most suitable current-strength for silver baths ; Coupling of the elements 203 Objections to insoluble anodes ; The behavior and appearance of the anodes as a criterion of the content of potassium cyanide in the bath ; Remedy against two large a content of potassium cyanide ; Keeping the bath constant 204 Proper treatment of baths made with chloride of silver; Gradual thickening of the bath .......... 205 Method of determining whether the bath contains silver and excess of potassium cyanide in proper proportions ...... 206 Determination of the actual content of silver in the bath ; Contrivances for keeping the objects to be silvered in gentle motion while in the bath 207 Singular phenomenon in silvering ; Remedy against a yellow tone of silvering ........... 208 Execution of silvering ; Silvering by weight ; Mechanical and chemical preparation of the objects ; Treatment of copper and its alloys ; German silver and brass ; Freeing from grease ; Pickling ; Rubbing . 209 Pickling in the preliminary pickle ; Amalgamating (quicking) ; Slinging wires ; Treatment of the objects while being silvered . .210 Amount of silver deposited upon the several grades of plated table ware manufactured by the William Rogers Manufacturing Co., of Hartford, Conn.; Method of controlling the weight of the deposit . . .211 Roseleur's plating balance . . . . . . . . .212 Treatment of objects which are to retain the crystalline dead white with which they come from the bath ; Polishing the silvered articles ; Mode of executing the operation of burnishing ; Burnishing machines . 215 B CONTENTS.

PAGE Ordinary silvering; Practice of the Meriden Britannia Co.'s works of Meriden, Conn. ; With Britannia or white metal .... 216 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 ; Britannia ware (hollow ware) . . • .217 Rogers' striking solution ; Meriden Company's striking solution ; Extra heavy coating of silver on the convex surfaces of spoons and forks ; Stopping off; Stopping off varnish ....... 218 Varnish that will resist the solvent power of the hot alkaline gilding ; Silvering by contact, by immersion, and cold silvering with paste ; Bath for silvering by contact; Baths for silvering by immersion . 219 Preparation of solution of sodium sulphide ...... 22n Dr. Ebermayer's bath for immersion ; Process of coating hooks and eyes, pins, etc., with a thin film of silver ..... 222 Cold silvering with paste ; Composition of argentiferous pastes ; Graining ............ 223 Preparations used for graining ; Mode of obtaining silver powder . 224 Execution of graining ; Resist and its composition .... 225 Silvering of fine copper wire ; Incrustations with silver, gold, and other metals 226 Niel or nielled silvering ......... 227 Imitation of niel by electro-deposition ; Old (antique) silvering ; Oxidized silver ........... 228 Yellow color on silvered articles ; Dissolving silver from silvered articles (stripping) .......... 229 Determination of electro-deposited silvering; Process for the determination of genuine silvering used by custom-house officers in Germany ; Recovery of silver from old silver baths, etc. ..... 23n AVet method for the recovery of silver from old silver baths . . 231

Chapter X. Deposition Of Gold

Properties of gold ; Gold baths, their composition, preparation, and properties ........... 232 Baths for cold gilding 233 Bath prepared with yellow prussiate of potash ; Gold baths for hot gilding 234 Preparation ofthe gold baths with the assistance ofthe electric-current 235 Management of gold baths ; Anodes ; Employment of anodes of platinum strips or platinum wire for coloring the deposit . . . 23(1 Vats for gold baths ; Heating gold baths CONTENTS.

XIX PAGE Execution of gilding ; Gilding without a battery and apparatus used for the purpose ; Preparation of the articles for gilding . . . 238 Current-strength for gilding; Gilding of hollow-ware . . . 239 Gilding in the cold bath ; Gilding in the hot bath .... 240 Red gilding; Determination of the content of copper required for obtaining a beautiful red gold ; Green gilding ..... 241 Rose color gilding ; Method of gilding which is a combination of fire-gilding with electro-deposition ; Dead gilding .... 242 Methods for deadening the surface ; Deadening zinc objects ; Coloring of the gilding .......... 243 Formulæ for gilding wax for reddish and greenish gilding ; Preparation of gilder's wax ; Application of gilder's wax ; To give gilded articles a beautiful rich appearance ; French receipt for the same object . 244 Improvement of bad tones of gilding ; Incrustations with gold ; Gilding of metallic wire and gauze, and J. W. Spaeth's machine for the purpose ............. 245 Gold bath for gilding metallic wire and gauze ; Gilding by contact, by immersion, and by friction ; Formulæ for baths for gilding by dipping ............ 247 Gilding by friction or gilding with the rag, with the thumb, with the cork ; Martin and Peyraud's method of gilding by friction . . 248 Removing gold from gilded articles — "Stripping" .... 249 Determination of genuine gilding ; Recovery of gold from gold baths ; The wet process .......... 250 Recovery of gold from acid mixtures ...... 251