II 
 
 

 
 
 
 
 
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 in 2011 with funding from 
 The Library of Congress 
 
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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 VOLTAIC CELLS, DYNAMO-ELECTRIC MACHINES, 
 
 THERMO-PILES, AND OF THE MATERIALS AND PROCESSES 
 
 USED IN EVERY DEPARTMENT OF THE ART. 
 
 TRANSLATED FROM THE SIXTH GERMAN EDITION OF 
 DR. GEORGE LANGBEIN, 
 
 PKOPKIETOE OF A MANUFACTORY FOR CHEMICAL PRODUCTS, MACHINES, APPARATUS, 
 
 AND UTENSILS FOR ELECTRO-PLATERS AND OF AN ELECTRO-PLATING 
 
 ESTABLISHMENT IN LEIPZIG. 
 
 WITH ADDITIONS BY 
 WILLIAM T. BRANNT, 
 
 EDITOR OF THE " TECHNO-CHEMICAL RECEIPT BOOK." 
 
 SIXTH EDITION, REVISED AND ENLARGED, 
 ILLUSTRATED BY ONE HUNDRED AND SIXTY-TWO ENGRAVINGS. 
 
 PHILADELPHIA : 
 HENRY CAREY BAIRD & CO., 
 
 INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS, 
 
 810 Walnut Street. 
 
 1909. 
 

 \ 
 
 
 Copyright, by 
 HENRY CAREY BAIRD & CO. 
 
 1909 
 
 
 PRINTED AT THE 
 
 WlCKERSHAM PRINTING HOUSE, 
 
 111-117 EAST CHESTNUT STREET, 
 
 LANCASTER, PA., VI. 8. A. 
 
 LIBRARY of CONGRESS 
 
 Two Codes Received 
 
 APR 22 \\m 
 
 CLA3S O^ AXo. No, 
 
 2-37313 
 
 COPY B 
 
PREFACE TO THE SIXTH AMERICAN EDITION. 
 
 The sale within a few years of the fifth American edition oi 
 
 Dr. Georye Langbein's work, Ifandbuch der elektrolytischen 
 Metallniedcrschlage ', and the continued demand for it, may be 
 accepted as evidence that the book has been found to fulfill 
 the purpose for which it is primarily intended, namely, to serve 
 as a ready book of reference and a practical ;yjide for the 
 workshop. 
 
 In this, the sixth American edition, now presented to the 
 public, the general scheme and scope of the fifth edition have 
 been retained, but a thorough revision has been made, and a 
 good deal of new matter has been inserted. 
 
 Due attention has been paid to all important innovations, 
 particularly to the electrolysis of zinc, in which considerable 
 progress has been made during the past few years, and it has 
 been endeavored to include all practical methods of plating 
 which have become known since the publication of the fifth 
 edition, as well as the most recent machinery and apparatus. 
 
 The editor is under obligations to The Hanson & Van 
 Winkle Co., of Newark, X. J., and Zucker & Levett & Lees 
 Co., of New York, the well-known manufacturers of, and dealers 
 in, electro-platers' supplies, as well as to The Egyptian Lac- 
 quer Manufacturing Co., of New York, for valuable information 
 and engravings. 
 
 The publishers have spared no expense in the proper illus- 
 tration and the mechanical production of the work, and, like the 
 previous editions, it has been provided with such a copious 
 table of contents and very full index as to render reference to 
 any subject prompt and easy. \V. T. B. 
 
 Philadelphia, Afkil io. [909, 
 
 (iii 
 
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 Lang- 
 bein's work, Vollstandiges Handbuch der Galvanischen Metall- 
 Niederschldge, 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 establish- 
 ment 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 in- 
 struments has also been supplied. With the assistance of such 
 measuring instruments, the establishment of fixed rules regard- 
 ing the current-conditions for an electro-plating 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 an empirical 
 manner, by time-consuming experiments, to-day, by duly ob- 
 
 (v) 
 
vi PREFACE TO THE FIRST AMERICAN EDITION. 
 
 serving the determined conditions, and provided with well- 
 working measuring instruments, he can at once produce beau- 
 tiful 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 pos- 
 sible, while for the various baths, only formulae 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 
 formulae 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 chemi- 
 cal works than it would be possible for the electro-plater to 
 make them in small quantities, even if he possessed the neces- 
 sary 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 Instru- 
 ments," and that of " Useful Tables," added by him, may con- 
 tribute 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. 
 
 VV. T. B. 
 Philadelphia, July i, 1891. 
 
CONTENTS. 
 I. 
 
 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, in 1789, of the electric 
 contact-current; Alexander Volta's discovery, in 1799, of the true 
 causes of the electric contact-current; Galvani's experiments . . 1 
 
 Erroneous inference drawn by Galvani from his experiments; General 
 
 • ignorance in regard to the electric current; Discovery which led to 
 the construction of the pile of Volta, or the voltaic pile; Cruik- 
 shank's trough battery 2 
 
 Decomposition of water by electrolysis by Nicholson and Carlisle, 1800; 
 Wollaston's observations, 1801; 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 . 3 
 
 Construction of the galvanoscope or galvanometer; Ohm's discovery, 
 in 1827, of the law named after him; Faraday's discovery, in 1831, of 
 electric induction; First electro-magnetic induction machine con- 
 structed by Pixii; Faraday's electrolytic law laid down and proved 
 in 1833; Production of iridescent colors, in 1826, by Nobili; Produc- 
 tion of the amalgams of potassium and sodium, in 1853, by Bird; 
 Discovery of the actual galvanoplastic process, in 1838, by Prof. 
 Jacoby 4 
 
 Claims of priority of invention byT. Spencer and C. J. Jordan; Labors 
 of the Elkingtons, and of De Ruolz; Murray's discovery, in 1840, of 
 black-leading; Introduction, in 1843, of gutta-percha by Dr. Mont- 
 gomery; First employment, in 1840, of alkaline cyanides by Wright. 5 
 
 Patent for the deposition of nickel, 1840; Origination of the term 
 " electro-metallurgy" by Mr. Alfred Smee, 1841 ; Prof. Boettarer's 
 
 (vii) 
 
Vlll CONTENTS. 
 
 discovery, in 1842, of the deposition of nickel, from its double salt ; 
 First deposition of metallic alloys by De Ruolz; First use of thermo- 
 electricity, in 1843, by Moses Poole; Advances in the art of electro- 
 deposition ............ 6 
 
 First magnetic machine that deposited silver on a practical scale con- 
 structed, in 1844, by Woolwych; Attempts, since 1854, by Christoffle 
 & Co. to replace their batteries by magneto-electrical machines; The 
 Alliance machine; Objections to Wilde's machine; Dr. Antonio 
 Pacinotti's invention, in i860, of the ring named after him; Siemens' 
 dynamo-machine, 1866; Wheatstone's dynamo-machine, 1867; In- 
 troduction, in 1871, of Zenobe Gramme's machine; Hefner-Alte- 
 neck's machine ........... 7 
 
 Siemens' & Halske machine, 1874; S. Schuckert's machine; European 
 and American constructions of dynamo-electrical machines; Investi- 
 gators and practitioners that have contributed to the improvement 
 of the electro-chemical processes and the perfection of galvanoplasty. 8 
 
 II. 
 
 THEORETICAL PART. 
 
 CHAPTER II. 
 
 Magnetism and Electricity. 
 
 Magnetism. 
 
 Loadstone or magnetic iron ore; Natural and artificial magnets; Defi- 
 nition of the magnetic poles 9 
 
 Neutral line or neutral zone; Magnetic meridian; North and south 
 poles; Phenomena of attraction and repulsion; Ampere's theory . 10 
 
 Magnetic field 11 
 
 Electro-Magnetism . 
 
 Direction of the deflection of a magnetic needle; Galvanoscope or gal- 
 vanometer; Astatic galvanometer . . . . . . .11 
 
 Tangent galvanometer; Sine galvanometer; Magnetizing effect of the 
 current; Electro-magnets; Ampere-turn number . . . .12 
 
 Remanent or residual magnetism; Properties of the electro-magnet; 
 Flow of the magnetic lines of force; Magnetic field; Direction and 
 magnitude of the field-force 13 
 
 Effect of the electro-magnet upon soft iron; Permeability; Magnitude 
 of the magnetic induction 14 
 
 The solenoid 15 
 
CONTENTS. ix 
 
 Definition of induction . . • . . . . ... . .15 
 
 Primary, inducing or main current; Secondary or induction-current; 
 Direction of the induced currents ..*.... 16 
 
 Electro-magnetic alternating actions; Hand-rule for following the di- 
 rection of the induced current 18 
 
 Fundamental Principles of Electro-Technics . 
 
 Electric units; Comparison of the electric current with a current of 
 water 18 
 
 Unit of the quantity of electricity (coulomb); Unit of current-strength 
 (ampere); Electro-motive force or tension; Unit of electro-motive 
 force (volt) ............ 20 
 
 Difference of electro-motive force or difference of potential; Volt- 
 ampere or watt; Unit of electrical work; Electric resistance; Propor- 
 tion of current-strength to electro-motive force; Electric resistance 
 of the circuit .21 
 
 Unit of electric resistance (ohm) ; Law of Ohm; Equations; Examples 
 to equations ............ 22 
 
 Internal and external resistances; Decrease in electro-motive force; 
 Proportion of the current-strength to the resistance of the circuit . 23 
 
 Equation for calculating the decreasing electro-motive force; Impressed 
 electro-motive force; Specific resistances 24 
 
 Specific resistances and coefficients of temperature of the metals; Co- 
 efficient of temperature ......... 25 
 
 Law of Kirchhoff; Branching or distributing the current; Main wire 
 and branch wires 26 
 
 Law of Joule 27 
 
 Fractional Electricity . 
 Idio-electrics and non-electrics; Good and bad conductors; Electroscope. 28 
 Kinds of electricity; Vitreous or positive electricity; Resinous or nega- 
 tive electricity 29 
 
 Contact-Electricity . 
 
 Generation of a current of electricity by the contact of various metals; 
 Potential 29 
 
 Difference of potential; Series of electro-motive force of the metals; 
 Galvanic current or hydro-electric current; Galvanic element or 
 voltaic cell ............ 30 
 
 Chemical processes; Action of moist air upon bright iron or steel; Ac- 
 tion of heat upon red oxide of mercury or red precipitate . . 31 
 
 Synthetic and analytical chemical processes; Law of the conservation 
 of matter .32 
 
 Chemical elements; Molecules; Atoms; Atomic weights; Symbols 
 and their formation; Table of the most important chemical elements, 
 together with their symbols and atomic weights; Chemical formulas. 34 
 
X CONTENTS. 
 
 PAGE 
 
 Expression of the chemical processes by equations; Valence of the 
 
 elements 35 
 
 Equivalent weights or combining weights; Arrangement of the most 
 important elements according to their valence .' . . . -37 
 
 Metals, metalloids, and their classification 38 
 
 Acids, bases, salts; Great affinity of the elements for oxygen; Oxida- 
 tion; Reduction; Formation of oxides ...... 39 
 
 Acids and their properties; Haloid acids; Oxy-acids; Bases; Hydroxyl 
 
 groups; Salts and their properties 40 
 
 Neutralization; Reagent papers 41 
 
 New products formed by the neutralization between acids and bases . 42 
 Formation of salts from the acids; Neutral and acid salts . . -43 
 
 Nomenclature of salts '. ........ 44 
 
 Fundamental Principles of Electro-Chemistry. 
 
 Electrolytes; Conductors and non-conductors; Conductors of the first, 
 
 and of the second, class 45 
 
 Electrolysis; Electrodes; Positive electrode or anode; Negative elec- 
 trode or cathode; Ions; Kathions; Anions; Properties of the ions . 46 
 Theory of solutions; A solution not a mere mechanical mixture; Ex- 
 periment with cupric sulphate solution ...... 47 
 
 Law followed by the gases; Osmotic pressure 48 
 
 Electrolytic dissociation; Clausius' theory; Raoult's method of deter- 
 mining the molecular weights of dissolved bodies . . . .49 
 
 Discovery of Arrhenius 50 
 
 Migration of the ions; Processes on the electrodes; Energy; Defini- 
 tion of energy; Mechanical work; Force and counter-force . . 51 
 Law of the conservation of force and work ...... 52 
 
 Processes on the electrodes; Electrolysis of a solution of potassium 
 
 disulphate 53 
 
 Electrolysis of sodium hydroxide 54 
 
 Electrolysis of a silver bath containing potassium-silver cyanide; Laws 
 
 of Faraday 56 
 
 Proportion of the quantity of substances, which is separated on the 
 
 electrodes, to the strength oi the electric-current . . . . 57 
 Second law of Faraday as expressed by v. Helmholz . . . .58 
 Electro-chemical equivalent, and its definition . . . . -59 
 
 Table of electro-chemical equivalents; Solution-pressure of metals . 60 
 
 Osmotic theory of the generation of the current, according to Nernst. 61 
 
 Process which takes place in a cell 62 
 
 Determination of the electro-motive force of a cell; Additional chem- 
 ical processes which take place in a cell . . . . . .63 
 
 Polarization; Occurrence of polarization 64 
 
 Counter-current or polarization current; Origin of the electro-motive 
 
 force of the polarization-current ........ 65 
 
CONTENTS. XI 
 
 PAGE 
 
 Decomposition-pressure; Decomposition-values of solutions; Velocity 
 
 of ions . . . 66 
 
 Transfer-members of the ions . . .67 
 
 III. 
 
 SOURCES OF CURRENT. 
 
 CHAPTER III. 
 
 Voltaic Cells, Thermo-Piles, Dynamo-Electric Machines, 
 Accumulators. 
 Voltaic cells; Conversion of chemical energy into electrical energy; 
 
 Inconstant and constant cells . 68 
 
 Voltaic pile; Trough battery; Local action; Amalgamation . . 69 
 
 Smee cell 7° 
 
 Avoidance of polarization; Daniell cell 7 1 
 
 Meidinger cell 7 2 
 
 Grove cell; Bunsen cell; Artificial carbon 73 
 
 Depolarization; Processes in the Bunsen cell . . . . . 74 
 
 Forms of Bunsen cells 75 
 
 Improved Bunsen cell 76 
 
 Good plan of amalgamating zinc; Electropoion 77 
 
 Dupre's substitute for sulphuric and nitric acids for filling cells; Solu- 
 ble chromium combination 78 
 
 Treatment of Bunsen cells 79 
 
 Advisability of having a duplicate set of porous clay cups; Renewal of 
 
 the acid; Leclanche cell; Cupric oxide cell 80 
 
 Cupron cell ............ 82 
 
 Plunge batteries; Fein's plunge battery 83 
 
 Keiser & Schmidt's plunge battery 84 
 
 Bottle-form of the bichromate cell; Stoehrer's plunge battery ' . .85 
 
 Dr. G. Langbein & Co.'s plunge battery 86 
 
 Coupling cells 87 
 
 Coupling in series for electro-motive force 88 
 
 Coupling for quantity of current, or parallel coupling; Mixed coupling 
 
 or group coupling 89 
 
 Thermo-electric piles; Discovery by Prof. Seebeck; Definition of a 
 thermo-electric couple, and of thermo-electricity; Noe's thermo- 
 electric pile 9° 
 
 Clamond's thermo-electric pile 9 2 
 
 Hauck's thermo-electric pile; Gulcher's thermo-electric pile . . 93 
 Dynamo-electric machines; Fundamental principles of dynamo-electric 
 
 machines . -95 
 
Xll CONTENTS. 
 
 PAGE 
 
 Windings; Armature . . . 96 
 
 Separate parts of the dynamo-electric machine; The frame; Magnet 
 
 winding or field winding 97 
 
 Two-polar and four-polar types of dynamo; Remanent magnetism; 
 Self-excitation; Foreign or separate excitation; Armature or induc- 
 tor; Ring armature; Drum armature 98 
 
 Ring wiring 99 
 
 Alternating currents; Drum armature windings 100 
 
 Chief difference between the modes of winding ..... 101 
 
 Slotted armature; Commutator; Brushes; Choice of the material for 
 the brushes ............ 102 
 
 Copper and brass gauze brushes; Brushes of thin metal plates; Brush- 
 holders: Brush-rocker 103 
 
 Continuous-current wound dynamos; Series-wound machines; Shunt- 
 wound and compound-wound machines 104 
 
 Two-pole shunt-wound dynamos 105 
 
 Dynamos of the shunt-wound type manufactured by Zucker & Levett 
 
 & Loeb Co., New York . . 107 
 
 Separately excited dynamo of the multipolar type, manufactured by 
 
 The Hanson & Van Winkle Co., Newark, N.J 109 
 
 Motor generator sets manufactured by the same firm . . . .111 
 Types of directly connected motor and generator manufactured by 
 
 Zucker & Levett & Loeb Co., New York 112 
 
 Secondary cells (accumulators); Plante's practical application of 
 
 accumulators, and his accumulator 114 
 
 Use of lead grids by Faure; Formation; Chemical processes in the 
 
 accumulator; Elb's theory 115 
 
 Liebenow's theory 118 
 
 Common form of an accumulator 119 
 
 Maintenance of accumulators; Mode of charging a cell . . . 120 
 
 Coupling accumulators; Ampere hours capacity .,'".'. . . 121 
 
 IV. 
 
 PRACTICAL PART. 
 
 CHAPTER IV. 
 
 Arrangement of Electro-Plating Establishments in General. 
 Light in plating rooms; Ventilation . . . . . . 122 
 
 123 
 124 
 
 125 
 126 
 
 Heating the plating rooms ..... 
 Renewal of water; Floors of the plating rooms 
 Size of plating rooms; Grinding and polishing rooms 
 Distance between machines; Transmission . 
 
CONTENTS. 
 
 ELECTRO-PLATING ARRANGEMENTS IN PARTICULAR. 
 
 Parts of the actual electro-plating plant; Electric conditions in the 
 
 electrolyte; Current-density 127 
 
 Electro-chemical equivalent of the ampere-hour; Determination of the 
 quantity of deposit and the time required; Calculation of the current- 
 strength 128 
 
 Examples of calculation . . . . . . . . . 129 
 
 Determination of the current-output, with examples .... 130 
 
 Electro-motive force in the bath; Determination of the resistance of 
 
 the electrolyte, with examples 131 
 
 Electro-motive counter-force of polarization 133 
 
 Determination of this force; Scattering of the current-lines . . 134 
 
 A. Installation with Cells. 
 
 135 
 137 
 
 Coupling of cells; Examples of coupling ..... 
 
 Current-regulation 
 
 Current-regulator, resistance board; or rheostat; Conditions upon 
 which the action of the rheostat is based 
 
 Location of the resistance-boards; Various modes of coupling the re 
 sistance-board .......... 
 
 Parallel coupling of the resistance-board with the bath; Current-indi 
 cator; Galvanometer . . . 
 
 Horizontal galvanometer; Vertical galvanometer 
 
 The Hanson & Van Winkle Patent Underwriter's rheostat; Specia 
 rheostat constructed by The Hanson & Van Winkle Co. . 
 
 Indications made by the galvanometer; Validity of the deductions 
 drawn from the position of the needle ..... 
 
 Means of recognizing the polarity of the current .... 
 
 Measuring instruments; Ampere-meter or ammeter; Volt-meter 
 
 Instruments constructed according to Hummel' s patent 
 
 Voltmeter manufactured by The Hanson & Van Winkle Co. 
 
 The Weston ammeter; Arrangement of the switch-board and ammeter 
 with a bath operated by a battery: Voltmeter switch . . .150 
 
 Scheme showing the coupling of the main object-wire and the main 
 anode-wire with the resistance-boards, the voltmeter, switch, and 
 two baths . • • • • • J5 1 
 
 Dependence of the current-density on the electro-motive force . .154 
 
 Conductors; Most suitable material for conducting the current; Loss 
 of electro-motive force in the conductors; Proper mounting of con- 
 ductors; Contacts; Main conductors and branch conductors . . 155 
 
 Connection of main conductors and branch conductors . . .156 
 
 Tanks; Construction of wooden tanks; Lead-lined tanks . . .157 
 
 Cement-lined tanks; Stoneware tanks; Conducting fixtures; Binding 
 posts and screws; Conducting rods . . . . . . • 159 
 
 Arrangement of objects and anodes in the bath ..... 160 
 
 138 
 
 140 
 
 141 
 142 
 
 143 
 
 M4 
 146 
 147 
 148 
 149 
 
XIV CONTENTS. 
 
 PAGE 
 
 Anode hooks; Slinging wires ........ 162 
 
 Apparatus for cleansing and rinsing; Freeing the objects from grease. 163 
 Special table for this purpose . . 164 
 
 B. Installation with Dynamo-Electric Machines. 
 
 Setting up and running a dynamo; Cause of most of the troubles with 
 plating dynamos ........... 165 
 
 Considerations which should govern the choice of location; Founda- 
 tions; Mode of ascertaining the direction of rotation; Belting . . 166 
 
 Starting up; Proper position for the tips of the brushes; Adjustment 
 of the brushes; Lubrication; Treatment of the commutator . . 167 
 
 Choice of a dynamo ...'....... 168 
 
 Impressed electro-motive force of the dynamo; Explanation by an ex- 
 ample of the choice of a suitable dynamo 169 
 
 Destruction of an excess of electro-motive force; Advisability of using 
 several dynamos with different impressed electro-motive forces . 171 
 
 Principle of series-coupling of baths illustrated; Connection of the 
 baths, resistant-boards and measuring instruments to a shunt-wound 
 dynamo .172 
 
 Parallel coupling and series coupling of dynamo machines; Rules to 
 be observed in coupling several dynamos in parallel .... 173 
 
 When the coupling of dynamos in series may become necessary; Three 
 conductor system . . . . . . . . . . -175 
 
 Ground plan of an electro-plating plant with dynamo .... 176 
 
 Plating room fitted up by The Hanson & Van Winkle Co., Newark, N.J. 180 
 
 Switch boards 181 
 
 C. Installation with Accumulators. 
 Use of an accumulator .......... 182 
 
 Dynamos for supplying the accumulator; On what the magnitude of 
 the performance of an accumulator depends; Ampere-hour capacity 
 
 of an accumulator; Explanatory example 183 
 
 Diagram showing the connection of a plant as installed by The Electro- 
 Chemical Storage Battery Co . 184 
 
 CHAPTER V. 
 
 Preparation of Metallic Objects. 
 
 a. mechanical treatment previous to electro-plating. 
 
 Nature of the mechanical treatment; Formation of the deposit in cor- 
 respondence with the surface of the basis-metal 186 
 
 Scratch-brushing; Various forms of brushes ...... 187 
 
 Treatment of scratch-brushes 188 
 
 Circular scratch-brushes . 189 
 
 Various kinds of brushes suitable to the different operations . . 190 
 
CONTENTS. XV 
 
 PAGE 
 
 Use of the sand blast for cleaning; Different types of sand blasts . 191 
 
 Portable sand-blast outfit . 192 
 
 Uses to which a sand-blast can be put 193 
 
 Cleaning metallic articles in the tumbling barrel or drum . . . 194 
 Adjustable, oblique tumbling barrel; Grinding; Grinding wheels and 
 their construction .......... 196 
 
 Grinding wheels of paste-board and of cork waste; Elastic wheel; Re- 
 form wheel . . . . . . . . . . . . 197 
 
 Emery for gluing; Treatment of the grinding wheels .... 198 
 
 Vienna lime 199 
 
 Grinding lathes 200 
 
 Belt attachment combined with a double grinding lathe; Types of 
 
 electrically-driven grinding motors 201 
 
 Execution of grinding and brushing ' . . 202 
 
 Fiber brushes 203 
 
 Grinding iron and steel articles, brass and copper castings, sheets of 
 
 brass, German silver, and copper 204 
 
 Grinding zinc castings, and sheet zinc; Polishing; Foot lathe for pol- 
 ishing; Patented triplex buff, manufactured by Zucker & Levett & 
 
 Loeb Co 205 
 
 Union canvas wheel 206 
 
 Walrine wheel 207 
 
 Types of grinding and polishing lathes 208 
 
 Electrically-driven polishing and buffing lathes; Belt strapping attach- 
 ment or endless belt machine 211 
 
 Flexible shafts for grinding, polishing and buffing 212 
 
 Polishing materials; Polishing with Vienna lime; Burnishing . . 214 
 
 B. Mechanical Treatment During and After Electro-Plating. 
 
 Scratch-brushing the deposits; Porosity of the deposit; Effects of 
 scratch-brushing; Scratch-brushes for various purposes . . .215 
 
 Mode of operating with the hand scratch-brush; Lathe-brushes . . 216 
 
 Drying the finished plated objects; Saw-dust; Centrifugal driers; 
 Freeing nickel objects from moisture 217 
 
 Production of high luster; Polishing deposits of nickel, copper and 
 
 brass, gold, silver and platinum; Operation of burnishing . . 218 
 
 Forms of burnishers; Cleansing the polished objects .... 219 
 I 
 
 Chemical Treatment. 
 
 Pickling and dipping; Pickle for cast iron and wrought-iron articles; 
 
 Cleansing badly rusted iron articles; Excellent pickle for iron; 
 
 Pickling in the electrolytic way 220 
 
 Bath for electrolytic pickling; Removal in the electrolytic way of the 
 
 layer of hard solder remaining after soldering bicycle frames . . 221 
 Duration of pickling 222 
 
XVI CONTENTS. 
 
 PAGE 
 
 Pickling zinc objects; Cleansing and brightening copper and its 
 
 alloys; Preliminary pickle; Bright dipping bath .... 223 
 
 Use of potassium cyanide as a pickle; Matt-dipping .... 224 
 Preparation of a good matt dip; Mixture for the production of a matt- 
 grained surface by pickling; Main points to be observed in pickling. 225 
 
 Absorbing plant for escaping acid vapors 226 
 
 Recovery of acid 227 
 
 Removal of grease and cleansing; Materials used for the purpose . 228 
 Preparation of lime mixture or paste; Electro-chemical cleaning . 229 
 Electro-chemical cleaning baths and their application .... 230 
 Cleansing objects of iron and steel, of copper, brass, bronze, German 
 silver, and tombac. Treatment of lead and Britannia; The Hanson & 
 Van Winkle acid pump 232 
 
 Electro-Plating Solutions (Elfxtrolytes, Baths). 
 Solvents; Spring and well water; Distilled water, Rain water; Purity 
 
 of chemicals ■ . .233 
 
 Examples of difference in chemicals 234 
 
 Concentration of baths: Conclusions which can be drawn from the 
 
 specific gravity; Cause of dark or spotted nickeling .... 235 
 Difference in concentration in summer and in winter; Agitation of 
 
 the baths 236 
 
 Uneven wearing of the anodes; Advantage of constant agitation . 237 
 
 Cause of changes in concentration of the baths 238 
 
 Temperature of the baths 239 
 
 Boiling the baths; Use of nickeled kettles; Dissolving nickel salts sol- 
 uble with difficulty 240 
 
 Working the bath with the current; Objections to this process; Filter- 
 ing the baths 241 
 
 Prevention of impurities; Choice of anodes ...... 242 
 
 Absorption of the deposit; Effect of the current-density . . . 243 
 
 Current-output 244 
 
 Reaction of the baths; General cpialifications an electro-plating bath 
 should possess 245 
 
 CHAPTER VI. 
 
 Deposition of Nickel and Cobalt. 
 
 i. deposition of nickel. 
 
 Growth and popularity of nickel plating; Properties of nickel . . 246 
 
 Nickel salts 247 
 
 Conducting salts 248 
 
 Other additions to nickel baths; Boric acid 249 
 
 Substitution of glycerine for water in the preparation of nickel baths . 250 
 Effect of current-density; Electro-motive force; Reaction of nickel 
 baths 251 
 
CONTENTS. xvii 
 
 PAGE 
 
 Formulas for nickel baths; Most simple nickel bath .... 252 
 Baths with the addition of chlorides; Nickel baths containing boric 
 
 acid; Weston's bath . 254 
 
 Kaselowsky's formula . . . .' . . . . . 255 
 
 Nickel baths for special purposes 257 
 
 For copper and its alloys; Bath yielding a very fine dark nickeling 
 upon iron, brass, and copper; Black nickel bath .... 258 
 
 Bath for platers having but a feeble current at their disposal; Composi- 
 tion of a few nickel baths which have been highly recommended . 259 
 An English formula for a nickel bath; Bath for the production of very 
 thick deposits ........... 260 
 
 Addition of carbon disulphide to nickel baths; Action of freshly pre- 
 pared nickel baths; Nickel bath without nickel salt .... 261 
 
 Prepared nickel salts; Correction of the reaction of nickel baths . . 262 
 Thick deposits in hot nickel baths; Foerster's experiments; Dr. 
 George Langbein's experiments; Quick nickeling .... 263 
 
 Thick deposits in cold nickel baths . 264 
 
 Coehn and Siemens' experiments with electrolytes containing nickel 
 salts and magnesium salts; Nickel anodes ...... 265 
 
 Elliptic anodes patented by The Hanson and Van Winkle Co., New- 
 ark, N. J 266 
 
 Silverite anode manufactured by Zucker & Levett & Loeb Co., New 
 
 York; Objections to the use of insoluble anodes .... 268 
 
 Proportion of cast to rolled anodes; Properties of cast anodes . . 270 
 Rolled nickel anodes; Cause of a reddish tinge on the anodes . . 271 
 Mode of suspending the anodes; Uneven solution of the anodes; Scat- 
 tering of current lines; Process of nickeling; Removal of grease 
 
 from the objects 272 
 
 Previous coppering or brassing of the objects; Security against rust; 
 Double nickeling ........... 273 
 
 Nickeling parts of bicycles; Variation in the porosity of the nickel 
 
 deposit; Means for preventing the rusting of the basis-metal . . 274 
 Over-nickeling, and means of avoiding it ..... 275 
 
 Normal deposition, and criteria for judging it; Most suitable current- 
 density for nickeling 276 
 
 Advisability of the use of a voltmeter and ammeter, as well as of a 
 
 rheostat; Production of a very thick deposit; Solid nickeling . . 277 
 Faulty arrangement of anodes; Suspension of flat objects; Nickeling 
 
 of cavities and profiled objects . 278 
 
 Use of the hand-anode; Experiments in nickeling the inside of brass 
 
 tubes 279 
 
 Polarization; Reason why iron requires a stronger current for nickel- 
 ing than copper alloys, and zinc a stronger one than iron . . 281 
 
 Stripping defective nickeling; Stripping acid 282 
 
 Removal of the nickel coating by mechanical means; Stripping by 
 electrolysis; Remedy against the yellowish tone of nickeling . . 283 
 
XVlil CONTENTS. 
 
 PAGE 
 
 Defective nickeling; Resume of the principal defects which may occur 
 
 in nickeling, and remedies 284 
 
 Refreshing nickel baths; Treatment of the articles after nickeling; 
 Polishing nickel deposits ......... 286 
 
 Cleansing polished articles; Calculation of the nickeling operation . 287 
 Nickeling small and cheap articles in large quantities; Stoneware dip- 
 ping baskets ............ 288 
 
 Brass wire baskets for suspending the objects ..... 289 
 
 Warren's solutions of nickel and of cobalt which can be decomposed 
 in a simple cell apparatus; Contrivances for electro-plating small 
 articles in large quantities ......... 290 
 
 Mechanical electro-plating apparatus manufactured by The Hanson & 
 
 Van Winkle Co., Newark. N.J 291 
 
 Mechanical plating apparatus manufactured by Zucker & Levett & 
 
 Loeb Co., New York; Nickeling sheet zinc 293 
 
 Preliminary grinding and polishing; Construction of cloth bobs . . 294 
 Mode of polishing the sheets ......... 295 
 
 Automatic sheet-polishing machines 296 
 
 Freeing zinc sheets from grease; Nickeling the sheets . . . 297 
 
 Advantages of previous coppering or brassing; Prevention of the peel- 
 
 ing-off of the nickel deposit ........ 298 
 
 Coppering the sheets; Dimensions of tanks for nickeling the sheets . 299 
 Anodes for nickeling sheet-zinc; Alkalinity of the baths . . . 300 
 Polishing the nickeled sheets; Nickeling tin-plate; Nickeling copper 
 
 and brass sheets 301 
 
 Nickeling sheet-iron and sheet-steel 302 
 
 Nickeling wire, and apparatus for that purpose 303 
 
 Nickeling knife blades, sharp surgical instruments, etc. . . . 305 
 Nickeling skates; Nickeling of soft alloys of lead and tin . . . 306 
 Nickeling printing plates (stereotypes, cliches, etc.); Hard nickeling 
 
 and baths for that purpose 307 
 
 Treatment of the baths 308 
 
 Previous coppering of stereotypes of type metal, and of zinc etchings; 
 Recovery of nickel from old baths ....... 309 
 
 Depositions of nickel alloys; Nickel bronze; Deposits of German silver. 310 
 Examination of nickel baths: Determination of the content of acid . 311 
 Methods for the examination of baths; Gravimetric analysis; Volu- 
 metric analysis 313 
 
 Klectrolytic method of analysis, and apparatus for that purpose . . 314 
 
 2. DEPOSITION OF COBALT. 
 
 Properties of cobalt; Baths for plating with cobalt; Cobalting copper 
 plates for printing 318 
 
 Determination of the quantity of copper dissolved in stripping the 
 cobalt deposit from cobalted copperplates; Warren's cobalt solution. 319 
 
CONTENTS. xix 
 
 PAGE 
 
 CHAPTER VII. 
 
 Deposition of Copper. Brass, and Bronze, 
 i. deposition of copper. 
 
 Properties of copper; Copper baths; On what the composition of these 
 baths depends . . ... . . . . . . . 321 
 
 Copper cyanide baths, and their preparation; Formation of cupric 
 cyanide; Stockmeier's experiments ....... 322 
 
 Hossauer's copper bath; Copper baths for iron and steel articles; Bath 
 to be used at the ordinary temperature ...... 323 
 
 Bath for hot coppering; Copper bath which has been highly recom- 
 mended ............. 324 
 
 Stockmeier's copper bath ......... 325 
 
 Copper bath with sulphate of copper (blue vitriol) .... 326 
 
 Use of cupro-cupric sulphite for the preparation of copper baths; 
 Copper bath recommended by Pfanhauser; Copper bath for small 
 zinc objects ............ 327 
 
 Prepared copper salts; Ruby oxide ...... 
 
 Copper baths without potassium cyanide; Bath for coppering zinc ob 
 
 jects; Weil's copper bath ........ 
 
 Gauduin's copper bath; Tanks for potassium-copper cyanide baths 
 Copper anodes; Formation of slime on the anodes; Execution o 
 
 copper plating . 
 
 Causes of copper baths yielding no deposit at all or only a slight one 
 
 and their remedies ......... 
 
 Scouring and pickling the articles to be coppered; Treatment of de 
 
 fective places of the deposit; Washing the coppered objects 
 Prevention of stains; O. Schultz's method for removing hydrochloric 
 
 acid from the pores of the objects; Polishing the coppered objects 
 
 Penetration of the deposit into the basis-metal .... 
 Coppering sheet-iron or sheet-zinc; Treatment of copper baths when 
 
 they become inactive ......... 
 
 Coppering small articles in quantities; Inla3'ing of depressions of cop 
 
 pered art-castings with black . 
 
 Examination of copper baths containing potassium cyanide . 
 Determination of potassium cyanide ...... 
 
 Determination of copper by electrolysis 
 
 Volumetric determination of copper ...... 
 
 328 
 
 320 
 
 330 
 
 331 
 332 
 333 
 
 334 
 335 
 
 336 
 337 
 338 
 339 
 34i 
 
 2. DEPOSITION OF BRASS. 
 
 Constitution and varieties of brass; Behavior of brass towards acids; 
 
 Brass baths, their composition, preparation, and treatment . . 343 
 Rules for baths containing more than one metal in solution . . 344 
 
 Brass bath according to Roseleur ........ 345 
 
 Other brass baths; Brassing iron; Use of cupro-cupric sulphite and 
 
 cuprous oxide for the preparation of brass baths .... 346 
 
XX CONTENTS. 
 
 PAGE 
 
 Bath for brassing zinc; Bath for brassing cast-iron, wrought iron and 
 steel; Solution for transferring any copper-zinc alloy which serves as 
 anode ............. 348 
 
 Irregular working of fresh brass baths; Prepared brass salts; Tanks 
 for brass baths; Brass anodes ........ 349 
 
 Execution of brassing; On what the color of the deposit depends . 350 
 
 Formation of slime on the anodes, and what it indicates; Remedies 
 for the sluggish formation of the deposit 351 
 
 Effect of too great an excess of potassium cyanide .... 352 
 
 Treatment of a brass bath that has not been used for some time; Pro- 
 duction of brass deposits which are to show a tone resembling gold. 353 
 
 Importance of the distance of the objects to be brassed from the 
 anodes; Brassing of unground iron castings ..... 354 
 
 Examination of brass baths; Determination of free potassium cyanide 
 and the content of copper . 355 
 
 Volumetric determination of the zinc ....... 356 
 
 Deposits of tombac; Deposits of bronze; Solution for coating wrought 
 iron and cast iron with bronze; Other bronze baths, and their 
 preparation 357 
 
 CHAPTER VIII. 
 
 Deposition of Silver. 
 
 Properties of silver ........... 359 
 
 Silver baths, their composition, preparation and treatment . . . 360 
 
 Advantage of baths prepared with silver chloride; Refreshing the baths 
 
 with silver cyanide 361 
 
 Silver baths for a heavy deposit (silvering by weight); Preparation of 
 of a bath with silver chloride; Preparation of silver chloride . . 362 
 
 Preparation of a bath with silver cyanide; Preparation of silver cyanide. 363 
 
 Silver-bath for ordinary electro-silvering; Tanks for silver baths; 
 Treatment of the silver baths; Silver anodes; Potassium cyanide re- 
 quired for the baths .......... 364 
 
 Indication of the presence of too much or not enough potassium 
 cyanide in the bath 365 
 
 The behavior and appearance of the anodes as criteria of the content of 
 potassium cyanide in the bath; Regulating the content of potassium 
 cyanide 366 
 
 Keeping the bath constant by silver anodes; Proper treatment of baths 
 made with silver chloride 367 
 
 Gradual thickening of the baths; Determination of the content in 
 proper proportions of excess of potassium cyanide and silver . . 368 
 
 Agitation of silver baths; Contrivances for keeping the objects to be 
 plated in gentle motion 369 
 
CONTENTS. XXI 
 
 PAGE 
 
 Addition of certain substances to silver baths; Preparation for bright 
 
 plating , 370 
 
 Yellow tone of silvering .......... 372 
 
 Silver alloys; Areas silver-plating ........ t>72> 
 
 Experiments in areas silver-plating ....... 374 
 
 Execution of. silver-plating; Silver-plating by weight; Mechanical and 
 chemical preparation of the objects; Treatment of copper and its 
 alloys; Freeing from grease; Pickling; Rubbing .... 375 
 
 Pickling in the preliminary pickle; Amalgamating (quicking) ; Sling- 
 ing wires 376 
 
 Methods of depositing an extra heavy coating of silver on the convex 
 
 surfaces of spoons and forks t,77 
 
 Determination of weight of deposit 378 
 
 Roseleur's plating balance 380 
 
 Plating balance, together with rheostat, voltmeter, and silver bath; 
 
 Voltametric balance; Copper voltameter 383 
 
 Advantages and disadvantages of the voltametric balance . . . 384 
 
 Neubeck's balance 386 
 
 Volumetric controlling apparatus ........ 387 
 
 Calculation of the weight of the silver deposit from the current- 
 strength used . . . 390 
 
 Matt silver; Polishing the deposits 391 
 
 Ordinary silver-plating; Quicking solution; Direct silvering of Britan- 
 nia, tin, German silver . . . . . . . . 392 
 
 Australian patent for directly silver-plating iron and steel; Stopping- 
 off, and varnish for that purpose; Special applications of electro- 
 silvering; Silvering of fine copper wire 393 
 
 Incrustations with silver (and gold and other metals); Imitation of 
 
 niel or nielled silvering . . . 394 
 
 Nielling upon brass; Old (antique) silvering 395 
 
 Oxidized silver 396 
 
 Yellow color on silvered articles; Stripping silvered articles . . 397 
 
 Determination of silver-plating; Process for the determination of gen- 
 uine silvering used by German custom-house officers; Examination 
 of silver baths . . . . . . . . . . . 398 
 
 Determination of free potassium cyanide, and of potassium carbonate . 399 
 Calculation of the quantity of barium cyanide required for the conver- 
 sion of the quantity of potassium carbonate found; Table for the use 
 of a 20^2 per cent, barium cyanide solution . . . . . 400 
 
 Determination of the silver by the electrolytic method . . . 401 
 
 Recovery of silver from old silver baths; The wet method . . . 402 
 Recovery of silver from acid mixtures used for stripping . . . 403 
 
XXI 1 CONTENTS. 
 
 PAGE 
 
 CHAPTER IX. 
 Deposition of Gold. 
 
 Occurrence of gold; Properties of gold; Mode of expressing the fine- 
 ness of gold; Testing gold by means of the touch-stone . . . 404 
 Shell-gold or painters' gold; Gold baths, their composition, prepara- 
 tion and treatment 405 
 
 Baths for cold gilding; Effect of too large an excess of potassium 
 
 cyanide 406 
 
 Bath with yellow prussiate of potash for cold gilding .... 407 
 
 Bath for hot gilding 408 
 
 Preparation of gold baths with the assistance of the electric current . 409 
 Gold anodes; Management of gold baths; Use of insoluble platinum 
 
 anodes; Use of steel anodes, and experiments with them . . . 410 
 Advantages claimed for steel anodes; Use of carbon anodes; Platinum 
 
 anodes for coloring the deposit 412 
 
 Cause of unsightly and spotted deposits; Tanks for gold baths . . 413 
 
 Heating the baths 414 
 
 Execution of gold-plating; Gilding without a battery; Preparation of 
 
 the articles for gilding 415. 
 
 Current-strength for gilding; Agitation of the objects in the bath; 
 Gilding the inner surfaces of hollow ware ...... 416 
 
 Process of gold-plating in the cold, and in the hot, bath . . .417 
 
 Polishing the gold deposits; Red gilding 418 
 
 Determination of the content of copper required for obtaining a beau- 
 tiful red gold; Plating rings, watch chains and other objects of base 
 
 metal with red gold 419 
 
 Green gilding; Rose-color gilding; Method of gilding which is a com- 
 bination of fire-gilding with electro-deposition 420- 
 
 Matt-gilding; Matting with the sand-blast and by chemical, or electro- 
 chemical means 421 
 
 Coloring of the gilding 422 
 
 Gilder's wax; Process to give gilded articles a beautiful, rich appear- 
 ance; Preparation of gilder's wax 423 
 
 Method of improving bad tones of gilding; Incrustations with gold; 
 
 Gilding of metallic wire and gauze 424 
 
 J. W. Spaeth's machine for gilding wire and gauze .... 425 
 
 Use of Bessemer steel anodes for wire gilding 426 
 
 Removing gold from gilded articles — Stripping; Electrolytic smooth- 
 ing and polishing scratched or rubbed rings 427 
 
 Determination of genuine gilding; Examination of gold baths; De- 
 termination of the gold by the electrolytic method .... 428 
 Recovery of gold from gold baths, etc.; The wet process . . . 429 
 Recovery of gold from acid mixtures 430 
 
CONTENTS. xxiii 
 
 PAGE 
 
 CHAPTER X. 
 
 Deposition of Platinum and Palladium. 
 I. DEPOSITION of platinum. 
 
 Properties of platinum; Platinum baths, their composition, preparation 
 and treatment 431 
 
 Boettger's bath; Preparation of platoso-ammonium chloride; Platinum 
 bath patented by the Bright Platinum Plating Co.; Platinum lactate 
 bath 432 
 
 Dr. W. H. Wahl's directions for preparing platinum bath; Alkaline 
 platinate bath 
 
 Preparation of an oxalate solution; Preparation of the phosphate bath 
 
 Management of platinum baths 
 
 Execution of platinum plating; Production of heavy deposits 
 
 Recovery of platinum from platinum solutions .... 
 
 433 
 434 
 435 
 436 
 437 
 
 2. DEPOSITION OF PALLADIUM. 
 
 Properties of palladium; Bertrand's palladium bath .... 437 
 Pilet's bath for plating watch movements ...... 438 
 
 CHAPTER XI. 
 
 Deposition of Tin, Zinc, Lead, and Iron. 
 
 1. deposition of tin. 
 
 Properties of tin; Moire metallique on tin; Tin baths, their composi- 
 tion, preparation and treatment 439 
 
 Tinning of objects of zinc, copper, and brass, iron and steel; Experi- 
 ments with Salzede's bronze bath 440 
 
 Neubeck's bath; Management of tin baths; Effect of too strong a cur- 
 rent; Process of tin-plating ........ 441 
 
 2. deposition of zinc. 
 Properties of zinc ........... 442 
 
 Value of electro-zincking ......... 443 
 
 Comparative experiments regarding zincking by the hot process and 
 by electro-deposition; Disadvantages of hot galvanizing; Loss of 
 zinc in electro-zincking; Drawbacks of both processes . . . 444 
 Preece's test for judging the thickness of the coating of zinc ob- 
 tained by hot galvanizing; Burgess's method of testing the power of 
 resistance of coatings obtained by electro-zincking .... 445 
 
 Zinc baths, their composition, preparation, and treatment . . . 446 
 Dr. Alexander's patented zinc bath; Decision of the Circuit Court of 
 the United States for the District of New Jersey in regard to the 
 Alexander patents .,,,.,..,. 447 
 
xxiv CONTENTS. 
 
 PAGE 
 
 Recent investigations regarding the electrolysis of zinc; Electrolyte 
 
 used by Cowper-Coles 448 
 
 " Sherardizing;" Addition of aluminium-magnesium alloy, and of 
 
 dextrose to zinc baths 449 
 
 Addition of pyridine to zinc baths; Addition of glucosides; Formula 
 
 for an alkaline zinc bath 450 
 
 Formulas for zinc baths; Importance of using zinc salts free from 
 
 other metals . . . 451 
 
 Zinc anodes — Treatment of zinc baths; Loss of zinc by the formation 
 
 of basic zinc salts 452 
 
 Heating the baths for strongly profiled objects 453 
 
 Tanks for zinc baths; Execution of zincking ..... 454 
 
 Zincking sheet-iron 455 
 
 Zincking of pipes 456 
 
 Zincking of wrought-iron girders, "f"-h"on, U -iroia, L-hon, etc.; Free- 
 ing the objects from scale; Profiled anodes; Zincking of wire, steel 
 
 tapes, cords, etc 457 
 
 Zincking of screws, nuts, rivets, nails, tacks, etc. .... 459 
 Deposition of zinc alloys 460 
 
 3. DEPOSITION OF LEAD. 
 
 Properties of lead; Lead baths, their composition, preparation, and 
 treatment; Anodes for lead baths; To coat gun-barrels and other 
 articles with peroxide of lead; Metallo-chromes (Nobili's rings, 
 iridescent colors; electrochromy) 461 
 
 4. DEPOSITION OF IRON (STEELING). 
 
 Principal practical use of the deposition of iron; Iron (steel) baths, 
 
 their composition, preparation and treatment 464 
 
 Management of iron baths 465 
 
 Execution of steeling 466 
 
 CHAPTER XII. 
 
 Deposition of Antimony, Arsenic, Aluminium. 
 
 i. deposition of antimony. 
 
 Properties of antimony; Antimony baths, their composition, prepara- 
 tion and treatment; Explosive power of antimony deposits . . 467 
 
 Non-explosive deposit of antimony; Antimony bath which yields good 
 results ...... 468 
 
 2. DEPOSITION OF ARSENIC. 
 
 Properties of arsenic; Arsenic baths, their composition, preparation 
 and treatment 468 
 
CONTENTS. 
 
 3. DEPOSITION OF ALUMINIUM. 
 
 Depositions of aluminium from aqueous solutions of its salts have thus 
 far not been feasible; Aluminium baths offered by unscrupulous deal- 
 ers and the results of testing them 470 
 
 4. DEPOSITIONS UPON ALUMINIUM. 
 
 Difficulties met with in the electro-deposition of other metals upon 
 aluminium; Behavior of aluminium towards the usual cleansing 
 agents 471 
 
 Coppering aluminium previous to plating; Copper bath recommended 
 by Deval; Villon's process; Prof. Nees' process .... 472 
 
 Burgess and Hambuechen's process; Gottig's method; Electro-deposits 
 upon aluminium produced by the Mannesmann Pipe Works, Germany. 473 
 
 CHAPTER XIII. 
 
 Deposition by Contact, by Boiling, and by Friction. 
 Theory of contact-depositions; Deposits by immersion or boiling; 
 
 Plating by means of a brush or by friction 475 
 
 Extent of the application of the contact-process; Drawbacks of the 
 
 process 476 
 
 Contact-metals; Properties of the electrolytes for the contact-process. 477 
 Means of increasing the conductivity of the electrolytes containing 
 potassium cyanide; Promotion of the attack on the contact-metal; 
 Plating small objects in quantities; Useless reduction of metal in 
 
 contact-depositions 478 
 
 Methods to avoid the metal being reduced on the wrong place; De- 
 fects of the contact-process; Nickeling by contact and boiling; 
 Stolba's process of nickeling ........ 479 
 
 Nickeling of steel objects ......... 481 
 
 Use of an aluminium-contact in place of zinc-contact; Darlay's pat- 
 ented process of nickeling; Autovolt baths 482 
 
 Composition of the electrolyte to be used; Chemical process of Dar- 
 lay's electrolyte; Cobalting by contact and boiling . . . ■ . 483 
 Coppering by contact and dipping; Liiderdorff's solution . . . 484 
 Bacco's copper bath; Darlay's patented bath . . . . . . 485 
 
 Chemical process of Darlay's formula; Brush-coppering . . . 486 
 Coppering iron and steel objects, steel pens, needles' eyes; Brassing 
 
 by contact; Darlay's bath 487 
 
 Silvering by contact, immersion, and friction ..... 488 
 Darlay's patented bath; Silvering by immersion; Solution for this 
 
 purpose 489 
 
 Preparation of solution of sodium sulphite 491 
 
 Ebermayer's silver immersion bath; Process of coating with a thin 
 
 film of silver small articles, such as hooks and eyes, pins, etc. . 492 
 Cold silvering with paste; Composition of the argentiferous paste . 493 
 
XXVI CONTENTS. 
 
 PAGE 
 
 Graining; Graining parts of watches 494 
 
 Preparations for graining; Preparation of silver powder; Paste for 
 
 graining 495 
 
 Composition of resist .......... 496 
 
 Gilding by contact, by immersion, and by friction; Formulas for con- 
 tact gold baths ........... 497 
 
 Gilding by immersion (without battery or contact); Formulas for this 
 purpose; Gilding by friction, or gilding with the rag, with the 
 
 thumb, with the cork 498 
 
 Reddish gilding by friction: Martin and Peyraud's process . . . 499 
 Platinizing by contact; Tinning by contact and boiling; Bath for 
 tinning by immersion .......... 500 
 
 Zilken's bath for tinning by contact in a cold way; Darlay's bath with 
 
 aluminium contact; Tinning solution for iron and steel articles . 501 
 Characteristic method of tinning by Stolba ...... 502 
 
 Zincking by contact; Darlay's bath with aluminium contact; Process 
 for coating brass and copper with a bright layer of zinc; Depositions 
 of antimony, and of arsenic by immersion ...... 503 
 
 CHAPTER XIV. 
 
 Coloring, Patinizing, Oxidizing, etc., of Metals — Lacquering. 
 
 Definitions of patina and patinizing; Requirements for the practice of 
 coloring 504 
 
 Coloring of copper; Shades from the pale red of copper to a dark 
 chestnut brown; Brown color upon copper; Brown layer of cuprous 
 oxide upon copper .......... 505 
 
 Method for the production of a brown color upon copper used in the 
 Paris mint; Beautiful and uniform brown tone on copper; Manduit's 
 process; Red-brown copper-tone ........ 506 
 
 Coloring copper blue-black; Blue-gray shades on copper; Cuivre fume; 
 Black color on copper; Matt black on copper; Deep black color on 
 copper 507 
 
 Artificial patina; Processes of patinizing; Donath's process . . . 508 
 
 Imitation of genuine green patina ........ 509 
 
 Steel gray on copper; Various colors upon massive copper, and upon 
 brass, and nickel 510 
 
 Coloring of brass and bronzes; Lustrous black on brass; Black pickling 
 in the hot way; Black of a beautiful luster; Steel-gray on brass . 511 
 
 Silver color on brass; Gray color with a bluish tint on brass; Pale gold 
 color on brass; Straw color, to brown, through golden yellow, and 
 tombac color on brass; Color resembling gold on brass . . . 512 
 
 Brown color, called bronze Barbedienne on brass 513 
 
 Coloring bronze articles dead-yellow or clay-yellow to dark brown; 
 Dark red-brown color upon brass; Coloring brass articles in large 
 quantities brown; Violet and cornflower blue upon brass . . . 514 
 
CONTENTS. xxvii 
 
 PAGE 
 
 Spurious gilding of small brass and tombac articles; Ebermayer's ex- 
 periments in coloring brass 515 
 
 Coloring zinc ............ 516 
 
 Gray, yellow, brown to black colors upon zinc; Brown patina upon 
 zinc; Gray coating on zinc . . . . . . . . .517 
 
 Bronzing on zinc; Red-brown shades on zinc; Yellow-brown shades 
 on zinc; Coloring of iron; Browning gun-barrels; Patina which pro- 
 tects metals from rust: Lustrous black on iron 518 
 
 Meriten's process for obtaining a bright black color on iron . . 519 
 
 Matt black coating upon watch cases of iron and steel, the so-called 
 Swiss black; Brown-black coating with bronze luster on iron; To 
 
 give iron a silvery appearance with high luster 520 
 
 Coloring of tin; Bronze-like patina on tin; Durable and very warm 
 sepia-brown tone upon tin and its alloys; Dark coloration on tin . 521 
 
 Lacquering; Application of lacquer . 521 
 
 Drying the lacquered objects; Development in the art of lacquer-mak- 
 ing; Most noted irriprovements in lacquers ..... 522 
 
 Pyroxyline lacquers and their properties 523 
 
 Preparation of pyroxyline lacquer; Lacquering by dipping; Appearance 
 
 of rainbow colors upon object lacquered with pyroxyline lacquer . 524 
 Production of various shades of color; Special invisible lacquer for grille 
 work; Satin finish lacquer; Dip lacquer for pickled castings to be 
 copper-plated and oxidized ......... 525 
 
 Helios dip lacquer, special; Dead black lacquers ..... 526 
 
 Dead-black lacquer as a substitute for Bower-Barff .... 527 
 
 Spraying of lacquers .......... 528 
 
 Spraying black lacquers .......... 520. 
 
 Water-dip lacquers and their use ........ 530 
 
 Points to follow when using water-dip lacquers ..... 531 
 
 CHAPTER XV. 
 Hygienic Rules for the Workshop. 
 
 Neutralization of the action of acid upon the enamel of the teeth and 
 the mucous membranes of the mouth and throat; Protection against 
 the corrosive effect of lime and caustic lye ..... 533 
 
 Vessels used in the establishment not to be used for drinking purposes; 
 Precautions in handling potassium cyanide and its solutions; Sensi- 
 tiveness of many persons to nickel solutions; Poisoning by hydro- 
 cyanic (prussic) acid, potassium cyanide, or cyanides, and antidotes. 534 
 
 Poisoning by copper salts, lead salts, arsenic, alkalies, mercury salts, 
 and sulphuretted hydrogen, and antidotes 535 
 
 Poisoning by chlorine, sulphurous acid, nitrous and hyponitric gases, 
 and antidotes 536 
 
CONTENTS. 
 
 CHAPTER XVI. 
 
 Galvanoplasty (Reproduction). 
 Definition of galvanoplasty proper; Applications of galvanoplasty; In- 
 vention of the process .......... 537 
 
 I. GALVANOPLASTY IN COPPER. 
 
 Properties of copper deposited by electrolysis; Constitution of the bath 
 
 for depositing copper; Hiibl and Forster's investigations . . . 538 
 Formation of spongy and sandy deposits; Galvanoplastic reproductions 
 for graphic purposes (electrotypy) ; Classification of the process used 
 
 in galvanoplasty . 539 
 
 Galvanoplastic deposition in the cell-apparatus; Component parts of 
 the cell-apparatus; Form of cells ....... 540 
 
 Simple apparatus frequently used; French form of cell-apparatus . 541 
 
 German form of cell-apparatus 542 
 
 Copper bath for the cell-apparatus; Freeing the bath from an excess of 
 
 sulphuric acid 543 
 
 Decrease of the content of copper in the bath; Table of the content of 
 blue vitriol at different degrees of Be.; Electro-motive force in the 
 
 cell-apparatus and its regulation 544 
 
 Galvanoplastic deposition by the battery and dynamo; Arrangement 
 
 required for the employment of an external source of current . . 545 
 Regulation of the current; Depositions with the battery; Cells . . 546 
 Depositions with the dynamo; Dynamos; Electro-motive force for the 
 
 slow process 547 
 
 Double aggregate; Coupling the baths 548 
 
 Coupling in series; Mixed coupling or coupling in groups . . . 549 
 Electro-motive force with baths coupled in parallel and with baths 
 
 coupled in groups 550 
 
 Combined operation with dynamo and accumulators . . . . 551 
 Disadvantage of interrupting the galvanoplastic deposition of copper; 
 Copper baths for galvanoplastic depositions with a separate source of 
 
 current 552 
 
 Functions of the sulphuric acid; Bath for the reproduction of shallow, 
 
 as well as deep, moulds 553 
 
 Properties of the deposited copper; Bath for copper printing plates; 
 Influence of the temperature of the electrolyte on the mechanical 
 properties of the copper; Current conditions ..... 554 
 Color of the deposit as a criterion of its quality; Table showing the 
 
 results of Hubl's experiments 555 
 
 Coupling of cells 556 
 
 Causes of brittle copper deposits; Forster's investigations; Hubl's in- 
 vestigations 557 
 
 E. Miiller and P. Behntje's investigations on the effects of organic 
 additions; Duration of deposition 558 
 
CONTENTS. xxix 
 
 PAGE 
 
 Table of the duration of deposition for electrotypes 0.18 millimeter 
 thick with different current densities; Nitrate baths .... 559 
 
 Agitation of the baths . 560 
 
 Sand's experiments; Stirring contrivances ...... 561 
 
 Agitation of the bath by blowing-in air; Agitation by flux and reflux 
 
 of the solutions; Arrangement of the baths for this purpose . . 562 
 Necessity of keeping agitated baths clean; Filtering .... 563 
 
 Anodes; Effect of impurities in the anodes; Forster's experiments . 564 
 
 Tanks for the baths; Rapid galvanoplasty 565 
 
 Principles upon which the process of rapid galvanoplasty is based . 567 
 Bath for shallow impressions of autotypes, woodcuts, etc.; Heating 
 the bath; Danger of the crystallization of blue vitriol; Agitation of 
 
 the bath 568 
 
 Current-density for this bath; Knight's process of coppering . . 569 
 Bath for deep depressions; Rudholzer's process ..... 570 
 
 Quality of the copper deposit; Treatment of the rapid galvanoplastic 
 baths; Examination of the acid copper baths ..... 571 
 
 Determination of free acid; Volumetric determination of the content 
 of copper according to Haen's method ...... 572 
 
 Electrolytic determination of the copper ...... 573 
 
 Mode of calculating the additions which have to be made to the bath; 
 Operations in galvanoplasty for graphic purposes; Preparation of 
 
 the moulds (matrices) in plastic material 574 
 
 Moulding in gutta-percha; Softening gutta-percha; Moulding in wax. 575 
 Mixtures for this purpose; Wax-melting kettles; Preparing the wax 
 for receiving the impression; Mould-box ...... 576 
 
 Modern method of operation ......... 577 
 
 Presses; Toggle press . 578 
 
 Hydraulic press ........... 579 
 
 Metal matrices; Dr. E. Albert on the rational preparation of metal 
 matrices . . . . . . . . . . . . 580 
 
 Basis for the solution of the problem . 582 
 
 Explanation of the process . 583 
 
 Fischer's process ........... 586 
 
 Kunze's method; Further manipulation of the moulds; Removal of 
 inequalities and elevations ......... 587 
 
 Making the moulds conductive; Black-leading the moulds, and ma- 
 chines for this purpose ......... 588 
 
 Knight's process of black-leading; Electrical contact; Wiring gutta- 
 percha moulds; Feelers ......... 590 
 
 Preparation of the black-leaded mould for suspension in the bath; 
 Hook for suspending the mould; Preventing the copper deposit from 
 spreading . . . . . . . . . . . . 591 
 
 Treatment of very deep forms; Suspending the moulds in the bath . 592 
 Detaching the deposit or shell from the moulds 593 
 
CONTENTS. 
 
 Moulding and melting table for wax moulds; Detaching the shell 
 from metal matrices .......... 594 
 
 Finishing; The saw table; Planing or shaving machines . . . 595 
 Testing and mounting the plates ........ 596 
 
 Copper deposits from metallic surfaces; Process of making a copy 
 directly from a metallic surface without the interposition of wax or 
 gutta-percha ............ 597 
 
 Coppering stereotypes, and zinc plates; Preparation of type matrices . 599 
 Suspension originals of hard lead or similar alloys; Electro-etching . 600 
 Covering or etching ground; Work of the engraver .... 601 
 
 Photo-engraving and processes used 602 
 
 Photo-galvanography; Collographic printing; Properties of chrome- 
 gelatine .... 603 
 
 Zincography; Mode of reprinting . . . . . . . . 604 
 
 Another process of transferring by reprinting; Autotypy . . . 605 
 Etching with the assistance of the electric current .... 606 
 
 Heliography 607 
 
 Electro-engraving; Rieder's patented process ..... 608 
 
 Apparatus for electro-engraving 609 
 
 Galvanoplastic reproduction of plastic objects; Reproduction of busts, 
 vases, etc.; Materials for the moulds; Moulding surfaces in relief 
 and not undercut; Dissection of the objects . . . . . 61 r 
 Moulding with oil gutta-percha; Preparation of oil gutta-percha . . 612 
 Moulding with gutta-percha; Metallic moulds, and metallic alloys for 
 
 this purpose 613 
 
 Plaster of Paris moulds and their preparation; Moulding large objects. 614 
 Rendering plaster of Paris moulds impervious . . . . -615. 
 Gutta-percha lacquer, and its preparation; Rendering impervious por- 
 ous, non-metallic moulds upon which copper is later on to be de- 
 posited 616 
 
 Rendering the moulds conductive, or metallization by the dry way; 
 Black-leading; Metallization by metallic powders; Metallization by 
 
 the wet way 617 
 
 Parkes' method of metallization 618 
 
 Another method of metallization 619 
 
 Lenoir's process — Galvanoplastic method for originals in high relief; 
 
 Gelatine moulds . 620 
 
 Directions for making gelatine moulds ....... 621 
 
 Special applications of galvanoplasty; Nature printing; Production of 
 copper tubes ............ 622 
 
 Corvin's niello; Plates for the production of imitations of leather . 623 
 
 Incrusting galvanoplasty 624 
 
 Copper bath and current-conditions for incrusting galvanoplasty ; Neu- 
 
 beck's investigations of the work in the cell-apparatus . . . 625 
 Additional manipulation of the deposits; Philip's process of coating 
 
CONTENTS. xxxi 
 
 PAGE 
 
 laces and tissues with copper; Coating grasses, leaves, flowers, etc.; 
 Providing wooden handles of surgical instruments with a galvano- 
 plastic deposit of copper; Coppering busts and other objects of terra- 
 cotta, stoneware, clay, etc. ......... 626 
 
 Copper deposit for the mercury vessels of thermometers; Coppering 
 mirrors; Galvanoplastic decorations in copper or silver on glass and 
 porcelain ware ........... 627 
 
 Decorating umbrella and cane handles of celluloid with a metallic de- 
 posit; Coppering baby-shoes for a keep-sake; Coating carbon pins 
 and carbon blocks with copper; Coppering rolls of steel and cast-iron, 
 pump pistons, etc. .......... 628 
 
 Coppering steel gun barrels for marine purposes 629 
 
 II. GALVANOPLASTY IN IRON (STEEL) • 
 
 First production of serviceable iron electrotypes 629 
 
 Klein's bath; Lenz's investigations; Dr. Geo. Langbein's examina- 
 tions 630 
 
 Precautionary measures to counteract the spoiling of the deposits; Con- 
 trivance for mechanically interrupting the current .... 631 
 
 Neubeck's experiments; Properties of electrolytically deposited iron; 
 advantages of steeled copper electrotypes ...... 632 
 
 III. GALVANOPLASTY IN NICKEL. 
 
 Production of nickel electrotypes in an indirect way .... 633 
 Cold nickel bath for the direct method; Requirements for working with 
 
 the direct process of deposition ........ 634 
 
 Most suitable electro-motive force; Devices for preventing the nickel 
 
 deposit from rolling off 635 
 
 Nickel matrices 636 
 
 Mode of effecting an intimate union of the copper casing with the 
 
 nickel 637 
 
 Matrices of massive nickel and cobalt . . . . . . 638 
 
 IV. GALVANOPLASTY IN SILVER AND GOLD. 
 
 Difficulties in the preparation of reproductions in silver and gold; 
 Moulding of the originals ......... 639 
 
 Bath for galvanoplasty in silver; Bath for galvanoplasty in gold . . 640 
 
 CHAPTER XVII. 
 
 Chemicals Used in Electro-Plating and Galvanoplasty. 
 
 I. Acids. 
 
 Sulphuric acid (oil of vitriol) 641 
 
 Recognition of sulphuric acid; Nitric acid (aqua fortis, spirits of nitre) 
 and its recognition; Hydrochloric acid; (muriatic acid) and its recog- 
 nition; Hydrocyanic acid (prussic acid) . . . . . . 642 
 
xxxii CONTENTS. 
 
 PAGE 
 
 Recognition of hydrocyanic acid; Citric acid and its recognition; Boric 
 
 acid (boracic acid) and its recognition 643 
 
 Arsenions acid (white arsenic, arsenic, ratsbane) and its recognition; 
 Chromic acid and its recognition; Hydrofluoric acid .... 644 
 Recognition of hydrofluoric acid 645 
 
 II. Alkalies and Alkali >ie Earths. 
 
 Potassium hydrate (caustic potash); Sodium hydrate (caustic soda); 
 Ammonium hydrate (ammonia or spirits of hartshorn) . . . 645 
 
 Recognition of ammonium hydrate; Calcium hydrate (burnt or quick- 
 lime) 646 
 
 III. Sulphur Combinations. 
 
 Sulphuretted hydrogen (sulphydric acid, hydrosulphuric acid) and its 
 recognition; Potassium sulphide (liver of sulphur) .... 646 
 
 Recognition of potassium sulphide; Ammonium sulphide (sulphydrate 
 or hydrosulphate of ammonium); Carbon disulphide or bisulphide; 
 Antimony sulphide; Black sulphide of antimony {stibium sulfuratum 
 nigrum); Red sulphide of antimony {stibium sulfuratum aurantia- 
 cum) ; Arsenic trisulphide or arsenious sulphide (orpiment) . . 647 
 
 Ferric sulphide . . . . . . . . . . . . 648 
 
 IV. Chlorine Combinations. 
 
 Sodium chloride (common salt, rock salt) and its recognition; Am- 
 monium chloride (sal ammoniac) and its recognition; Antimony 
 trichloride (butter of antimony) ; Arsenious chloride . . . . 648 
 
 Copper chloride; Tin chloride and its recognition; Stannous chloride 
 or tin-salt; Stannic chloride; Zinc chloride (hydrochlorate or muri- 
 ate of zinc, butter of zinc) and its recognition; Chloride of zinc and 
 ammonia ............ 649 
 
 Nickel chloride and its recognition; Cobaltous chloride and its recog- 
 nition; Silver chloride and its recognition 650 
 
 Gold chloride (terchloride of gold, auric chloride), and its recognition; 
 Platinic chloride, and its recognition ....... 651 
 
 V. Cyanides. 
 
 Potassium cyanide (white prussiate of potash) 652 
 
 Comparative table of potassium cyanide with different content; Copper 
 cyanide, and its recognition; Zinc cyanide (hydrocyanate of zinc, 
 prussiate of zinc) ........... 654 
 
 Recognition of zinc cyanide; Silver cyanide (prussiate or hydrocyanate 
 of silver); Potassium ferro-cyanide (yellow prussiate of potash), and 
 its recognition 655 
 
 VI. Carbonates. 
 Potassium carbonate (potash) 655 
 
CONTENTS. xxxiii 
 
 Recognition of potassium carbonate; Acid potassium carbonate or 
 mono-potassic carbonate, commonly called bicarbonate of potash; 
 Sodium carbonate (washing soda); Sodium bicarbonate (baking 
 powder); Calcium carbonate (marble, chalk) 656 
 
 Copper carbonate, and its recognition; Zinc carbonate and its recogni- 
 tion; Nickel carbonate and its recognition; Cobaltous carbonate . 657 
 
 VII. Sulphates and Sulphites. 
 
 Ammonium sulphate, and its recognition; Potassium-aluminium sul- 
 phate (potash alum) and its recognition; Ammonium alum, and its 
 recognition 658 
 
 Ferrous sulphate (sulphate of iron, proto-sulphate of iron, copperas, 
 green vitriol) , and its recognition; Iron-ammonium sulphate; Cop- 
 per sulphate (cupric sulphate, blue vitriol, or blue copperas) and its 
 recognition; Zinc sulphate (white vitriol) ...... 659 
 
 Recognition of zinc sulphate; Nickel sulphate, and its recognition; 
 Nickel-ammonium sulphate; Cobaltous sulphate .... 660 
 
 Cobalt-ammonium sulphate; Sodium sulphite, and its recognition; 
 Sodium bisulphite; Cuprous sulphite 661 
 
 VIII. Nitrates. 
 Potassium nitrate (saltpetre, nitre), and its recognition; (Sodium 
 
 nitrate (cubic nitre or Chile saltpetre) ; Mercurous nitrate . . 662 
 
 Mercuric nitrate (nitrate of mercury), and its recognition; Silver 
 
 nitrate (lunar caustic), and its recognition ..... 663 
 
 IX. Phosphates and Pyrophosphates . 
 
 Sodium phosphate 663 
 
 Recognition of sodium phosphate; Sodium pyrophosphate and its 
 recognition; Ammonium phosphate ....... 664 
 
 X. Salts of Organic Acids. 
 Potassium bitartrate (cream of tartar); Potassium-sodium tartrate 
 
 (Rochelle or Seignette salt) ........ 665 
 
 Recognition of potassium-sodium tartrate; Copper acetate (verdigris), 
 
 and its recognition; Lead acetate (sugar of lead), and its recognition. 665 
 Sodium citrate 666 
 
 APPENDIX. 
 Contents of vessels; To find the number of gallons a tank or other 
 vessel will hold; Avoirdupois weight; Troy weight .... 667 
 
 Imperial fluid measure; Table of useful numerical data .... 668 
 
 Table for the conversion of certain standard weights and measures . 669 
 Table of solubilities of chemical compounds commonly used in electro- 
 technics ............ 670 
 
 Content of metal in most commonly used metallic salts . . . 672 
 
XXXIV CONTENTS. 
 
 PAGE 
 
 Table showing the electrical resistance of pure copper wire of various 
 diameters; Resistance and conductivity of pure copper at different 
 temperatures 673 
 
 Weight of iron, copper, and brass wire, and plates .... 674 
 
 Table of hydrometer degrees according to Baume, at 63. 5 F., and 
 their weights by volume; Comparison of the scales of the Fahren- 
 heit, Centigrade, and Reaumur thermometers, and rules for con- 
 verting one scale into another ........ 675 
 
 Index 677 
 
ELECTRO-DEPOSITION OP METALS. 
 
 i. 
 
 HISTORICAL PART. 
 
 CHAPTER I. 
 
 HISTORICAL REVIEW OF ELECTRO-METALLURGY. 
 
 In reviewing the history of the development of electrolysis, 
 i. e., the reduction of a metal or a metallic alloy from the solu- 
 tion of its salts by the electric current, the simple reduction 
 which takes place by the immersion of one metal in the solu- 
 tion of another, may be omitted. This mode of reduction was 
 well known to the alchemist Zozimus, who described the re- 
 duction of copper from its solutions by means of iron, while 
 Paracelsus speaks of coating copper and iron with silver by 
 simple immersion in a silver solution. 
 
 Before the discovery, in 1789, of contact-electricity by Luigi 
 Galvani, there was nothing like a scientific reduction of metals 
 by electricity; and only in 1799 did Alexander Volta, of Pavia, 
 succeed in finding the true causes of Galvani's discovery. 
 Galvani observed while dissecting a frog on a table, whereon 
 stood an electric machine, that the limbs suddenly became con- 
 vulsed by one of his pupils touching the crural nerve with the 
 dissecting-knife at the instant of taking a spark from the con- 
 ductor of the machine. The experiment was several times re- 
 peated, and it was found to answer in all cases when a metallic 
 conductor was connected with the nerve, but not otherwise. He 
 
2 ELECTRO-DEPOSITION OF METALS. 
 
 observed that muscular contractions were produced by forming 
 a connection between two different metals, one of which was 
 applied to the nerve, and the other to the muscles of the leg. 
 Similar phenomena having been found to arise when the leg of 
 the frog was connected with the electric machine, it could 
 scarcely be doubted that in both cases the muscular contrac- 
 tions were produced by the same agent. From a course of 
 experiments, Galvani drew the erroneous inference that these 
 muscular contractions were caused by a fluid having its seat in 
 the nerves, which through the metallic connections flowed over 
 upon the muscles. Everywhere, in Germany, England and 
 France, eminent scientists hastened to repeat Galvani's experi- 
 ments, in the hope of discovering in the organism a fluid which 
 they considered the vital principle ; but it was reserved to Volta 
 to throw light upon the prevailing darkness. In his repeated 
 experiments this eminent philosopher observed that one cir- 
 cumstance had been entirely overlooked, namely, that in order 
 to produce strong muscular contractions in the frog-leg experi- 
 ment, it was absolutely necessary'for the metallic connection to 
 consist of two different metals coming in contact with each 
 other. From this he drew the inference that the agent pro- 
 ducing the muscular contractions was not a nerve-fluid, but was 
 developed by the contact of dissimilar metals, and identical 
 with the electricity of the electric machine. 
 
 This discovery led to the construction of what is known as 
 the pile of Volta, or the voltaic pile. The same philosopher 
 found that the development of electricity could be produced by 
 building up in regular order a pile of pairs of plates of dissimi- 
 lar metals, each pair being separated on either side from the 
 adjacent pairs by pieces of moistened card-board or felt. On 
 account of various defects of the voltaic pile, Cruikshank soon 
 afterwards devised his well-known trough battery, which con- 
 sisted of square plates of copper and zinc soldered together, 
 and so arranged and fastened in parallel order in a wooden box 
 that between each pair of plates a sort of trough was formed, 
 which was filled with acidulated water. 
 
HISTORICAL REVIEW OF ELECTRO-METALLURGY. 3 
 
 Nicholson and Carlisle, on May 2, 1800, first decomposed 
 water into hydrogen and oxygen by electrolysis ; and, in 1801, 
 Wollaston found that if a piece of silver in connection with a 
 more positive metal, for instance, zinc, be put into copper 
 solution, the silver will be coated over with copper, which 
 coating will stand the operation of burnishing. 
 
 Cruikshank, in 1803, investigated the behavior of solutions 
 of nitrate of silver, sulphate of copper, acetate of lead, and sev- 
 eral other metallic salts, towards the galvanic current, and found 
 that the metals were so completely reduced from their solutions 
 by the current as to suggest to him the analysis of minerals by 
 means of the electric current. 
 
 To Brugnatelli we owe the first practical results in electro- 
 gilding. In 1805, he gilded two silver medals by connecting 
 them by means of copper wire with the negative pole of the 
 pile, and allowing them to dip in a solution of fulminating gold 
 in potassium cyanide, while a piece of metal was suspended in 
 the solution from the positive pole. He also observed that the 
 positive plate, if it consisted of an oxidizable metal, was dis- 
 solved. 
 
 One of the greatest discoveries connected with the subject, 
 however, is that of Sir Humphry Davy, made October 6, 1807, 
 when, by the decomposition of the alkalies by means of the 
 electric current, he discovered the metals potassium and sodium. 
 
 Prof. Oersted, of Copenhagen, in 1820, found that the mag- 
 netic needle is deflected from its direction by the electric cur- 
 rent. It was known long before this that powerful electric dis- 
 charges affect the magnetic needle. It had, for instance, been 
 observed that the needle of a ship's compass struck by light- 
 ning had lost its property of indicating the North Pole, and 
 several physicists, among them Franklin, had succeeded in pro- 
 ducing the same phenomena by heavy discharges of the elec- 
 trical machine, but they were satisfied with the supposition that 
 the electric current acted mechanically, like the blow of a 
 hammer. Oersted first perceived that electricity must be in a 
 state of motion in order to act upon magnetism. This led to 
 
4 ELECTRO-DEPOSITION OF METALS. 
 
 the construction of the galvanoscope or galvanometer, an in- 
 strument which indicates whether the cells or other source of 
 current furnish a current or not, and by which the intensity of 
 the source of current may also to a certain degree be recognized. 
 
 Ohm, in 1827, discovered the law named after him, that the 
 strength of a continuous current is directly proportional to the 
 difference of potential or electro -motive force in the circuit, and 
 inversely proportional to the resistance of the circuit. This law 
 will be more fully discussed in the theoretical part. 
 
 Ohm's discovery was succeeded, in 1831, by the important 
 discovery of electric induction by Faraday. By induction is 
 understood the production of an electric current in a closed 
 circuit which is in the immediate proximity of a current- 
 carrying wire. Faraday further found that the current induced 
 in the contiguous wire is not constant, because after a few 
 oscillations the magnetic needle returned to the position occu- 
 pied by it before a current was passed through the current- 
 carrying wire ; whilst, when the current was broken, the needle 
 deflected in the opposite direction. 
 
 In the year following the discovery of Faraday, Pixii, of 
 Paris, constructed the first electro-magnetic induction machine. 
 
 Faraday's electrolytic law of the proportionality of the cur- 
 rent strength and its chemical action, and that the quantities of 
 the various substances which are reduced from their combina- 
 tions by the same current are proportional to their chemical 
 equivalents, was laid down and proved in 1833, and upon this 
 Faraday based the measurement of the current-strength by 
 chemical deposition, as, for instance, that of water, in the 
 voltmeter. 
 
 Of the practical electro-chemical discoveries there remain to 
 be mentioned the production of iridescent colors, in 1826, by 
 Nobili, and the production of the amalgams of potassium and 
 sodium, in 1853, by Bird. 
 
 The actual galvanoplastic process, however, dates from 1838. 
 In the spring of that year Prof. Jacoby announced to the 
 Academy of Sciences of St. Petersburg, a description of his 
 
HISTORICAL REVIEW OF ELECTRO-METALLURGY. 5 
 
 discovery of the utility of galvanic electricity as a means of re- 
 producing objects of metal. Hence Jacoby must be considered 
 the father of galvanoplasty in as far as he was the first to utilize 
 and give practical form to the discoveries made up to that time. 
 Though Jacoby's process was published in the English periodi- 
 cal, "The Athenaeum," of May 4, 1839, Mr. T. Spencer, who 
 read a paper on the same subject, September 13, 1839, before 
 the Liverpool Polytechnic Society, claimed priority of inven- 
 tion, as was also done by Mr. C. J. Jordan, who, on May 22, 
 1839, sent a letter to the "London Mechanical Magazine," 
 which was published on June 8, 1839. 
 
 From this time forward the galvanoplastic art made rapid 
 progress, and by the skill and enterprise of such men as the 
 Elkingtons, of Birmingham, and De Ruolz, of Paris, it was 
 speedily added to the industrial arts. 
 
 Though copies of a metallic object by means of galvanoplasty 
 could now be made, the employment of the process was re- 
 stricted to metallic objects of a form suitable for the purpose, 
 until, in 1840, Murray succeeded in making non-metallic sur- 
 faces conductive by the application of graphite (black lead, 
 plumbago), which rendered the production of galvanoplastic 
 copies of wood-cuts, plaster-of-Paris casts, etc., possible. 
 
 Dr. Montgomery, in 1843, sent to England samples of gutta- 
 percha, which was soon found to be a suitable material for the 
 production of negatives of the original models to be reproduced 
 by galvanoplasty. 
 
 Though it was now understood how to produce heavy de- 
 posits of copper, those of gold and silver could only be obtained 
 in very thin layers. Scheele's observations on the solubility of 
 the cyanide combinations of gold and silver in potassium 
 cyanide, led Wright, a co-worker of the Elkingtons, to employ, 
 in 1840, such solutions for the deposition of gold and silver, 
 and it was found that deposits produced from these solutions 
 could be developed to any desired thickness. The use of solu- 
 tions of metallic cyanides in potassium cyanide prevails at the 
 present time, and the results obtained thereby have not been 
 surpassed by any other practice. 
 
6 ELECTRO-DEPOSITION OF METALS. 
 
 From the same year also dates the patent for the deposition 
 of nickel from solution of nitrate of nickel, which, however, did 
 not attract any special attention. This may have been chiefly 
 due to the fact that the deposition of nickel from its nitrate 
 solution is the most imperfect and the least suitable for the 
 practice. 
 
 To Mr. Alfred Smee we owe many discoveries in the deposi- 
 tion of antimony, platinum, gold, silver, iron, lead, copper, and 
 zinc. In publishing his experiments, in 1841, he originated 
 the very appropriate term " electro-metallurgy" for the process 
 of working in metals by means of electrolysis. 
 
 Prof. Bcettger, in 1842, pointed out that dense and lustrous 
 depositions of nickel could be obtained from its double salt, 
 sulphate of nickel with sulphate of ammonium, as well as from 
 ammoniacal solution of sulphate of nickel ; and that such de- 
 posits, on account of their slight oxidability, great hardness, 
 and elegant appearance, were capable of many applications. 
 However, Bcettger's statements fell into oblivion, and only in 
 later years, when the execution of nickeling was practically 
 taken up in the United States, his labors in this department 
 were remembered in Germany. To Bcettger we are also in- 
 debted for directions for coating metals with iron, cobalt, 
 platinum, and various patinas. 
 
 In the same year, De Ruolz first succeeded in depositing 
 metallic alloys — for instance, brass — from the solutions of the 
 mixed metallic salts. In 1843, the first use of thermo-electricity 
 appears to have been made by Moses Poole, who took out a 
 patent for the use of a thermo-electric pile instead of a voltaic 
 battery for depositing purposes. 
 
 From this time forward innumerable improvements in exist- 
 ing processes were made ; and also the first endeavors to apply 
 Faraday's discoveries to practical purposes. 
 
 The invention of depositing metals by means of a permanent 
 current of electricity obtained from steel magnets was perfected 
 and first successfully worked by Messrs. Prime & Son, at their 
 large silverware works, Birmingham, England, and the original 
 
HISTORICAL REVIEW OF ELECTRO-METALLURGY. 7 
 
 machine constructed by Woolrych in 1844— -the first magnetic 
 machine that ever deposited silver on a practical scale — is still 
 preserved. It .is now owned by the Corporation of Birming- 
 ham, England. The Woolrych machine stands 5 feet high, 5 
 feet long, and 2^ feet wide. 
 
 As early as 1854, Christofle & Co. endeavored to replace 
 their batteries by magnetc-electrical machines, and used the 
 Holmes type, better known as the Alliance machine, which, 
 however, did not prove satisfactory; and besides, the prices of 
 these machines were, in comparison with their efficiency, exor- 
 bitant. The machine constructed by Wilde proved objectiona- 
 ble on account of its heating while working, and the consequent 
 frequent interruptions in the operations. 
 
 In i860 Dr. Antonie Pacinotti, of Pisa, suggested the use of 
 an iron ring wound around with insulated wire, in place of the 
 cylinder. This ring, named after its inventor, has, with more or 
 less modifications, become typical of many machines of modern 
 construction. In the construction of all older machines, steel 
 magnets had been used, and their magnetism not being con- 
 stant, the effect of the machine was consequently also not 
 constant. Furthermore, they generated alternately negative 
 and positive currents, which, by means of commutators, had to 
 be converted into currents of the same direction ; and this, in 
 consequence of the vigorous formation of sparks, caused the 
 rapid wearing-out of the commutators. 
 
 These defects led to the employment of continuous mag- 
 netism in the iron cores of the electro-magnets, the first 
 machine based upon this principle being introduced in 1866, 
 by Siemens, which, in 1867, was succeeded by Wheatstone's. 
 
 However, the first useful machine was introduced in 1871, 
 by Zenobe Gramme, who in its construction made use of Paci- 
 notti's ring. This machine was, in 1872, succeeded by Hefner- 
 Alteneck's, of Berlin. In both machines the poles of the elec- 
 tro-magnet exert an inducing action only upon the outer wire 
 wrappings of the revolving ring, the other portions being 
 scarcely utilized, which increases the resistance and causes a 
 
8 ELECTRO -DEPOSITION OF METALS. 
 
 useless production of heat. This defect led to the construction 
 of flat-ring machines, in which the cylindrical ring is replaced 
 by one of a flat shape, and of a larger diameter, thus permitting 
 the induction of both flat sides. Such a machine was, in 1874, 
 built by Siemens & Halske, of Berlin ; and in the same year by 
 S. Schuckert, of Nuremberg. In Schuckert's machines nearly 
 three-quarters of all the wire wrappings were under the induc- 
 ing influence of both of the large pole shoes of the electro-mag- 
 nets.. The flat-ring armature was later on replaced by the 
 drum armature, and the more modern machines are almost 
 without exception of the drum-armature type. 
 
 Of European constructions of dynamo-electrical machines 
 may be mentioned Mather's, Elmore's, Fein's, Krottlinger's 
 Nagle's, Reutlinger's, Lahmeyer's, Poschmann & Co.'s, and Dr. 
 G. Langbein & Co.'s. In this country Weston's machine and 
 the dynamos manufactured by the Hanson & Van Winkle Co., 
 of Newark, N. J., the Zucker & Levett & Loeb Co., of New 
 York, and others are largely used for electro-plating purposes. 
 
 For the sake of completeness, there may be mentioned the 
 investigators and practitioners who have contributed much to 
 the improvement of the electro-chemical processes and the 
 perfection of galvanoplasty. Besides those already named, 
 they are: Elkington, Becquerel, Heeren, Roseleur, Eisner, 
 von Leuchtenberg, Meidinger, Weil, Goode, Christofle, Klein, 
 von Kress, Thompson, Adams, Gaiffe, and others. 
 
II. 
 
 THEORETICAL PART. 
 
 CHAPTER II. 
 
 MAGNETISM AND ELECTRICITY. 
 
 Magnetism. 
 
 FOR the better understanding of the electrolytic laws it will 
 be necessary to commence with the phenomena presented by 
 magnetism, and to consider them somewhat more closely. 
 
 A particular species of iron ore is remarkable for its property 
 of attracting small pieces of iron and causing them to adhere to 
 its surface. This iron ore is a combination of ferric oxide with 
 ferrous oxide (Fe 3 04),and is called loadstone or magnetic iron 
 ore. Its properties were known to the ancients, who called it 
 magnesian stone, after Magnesia, a city in Thessaly, in the 
 neighborhood of which it was found. If a natural loadstone be 
 rubbed over a bar of steel, its characteristic properties will be 
 communicated to the bar, which will then be found to attract 
 iron filings like the loadstone itself. The bar of steel thus 
 treated is said to be magnetized, or to constitute an artificial 
 magnet. The artificial magnets thus produced may be straight, 
 in the shape of a horse-shoe, or annular; but no matter what 
 their form may be, there will always be two regions where the 
 attractive force reaches its maximum, while between these two 
 points there is a region which has no attractive effect whatever 
 upon iron filings. The two ends of the magnet, especially, show 
 the greatest attractive force, and they are called the magnetic 
 poles, whilst the line running around the magnet, which pos- 
 
 (9) 
 
IO ELECTRO-DEPOSITION OF METALS. 
 
 sesses no attractive force, is termed the neutral line or Jientral 
 zone. In a closed magnet the poles are situated on the ends of 
 one and the same diameter, while the neutral zones are located 
 on the ends of a diameter standing perpendicular to the first. 
 
 When a magnetized bar or natural magnet is suspended at 
 its center in any convenient manner, so as to be free to move 
 in a horizontal plane, it is always found to assume a particular 
 direction with regard to the earth, one end pointing nearly 
 north and the other nearly south. If the bar be removed from 
 this position it will tend to reassume it, and after a few oscilla- 
 tions, settle at rest as before. The direction of the magnetic 
 bar, i. e., that of its longitudinal axis, is called the magnetic 
 meridian, while the pole pointing toward the north is usually 
 distinguished as the north pole of the bar, and that which points 
 southward as the south pole. 
 
 A magnet, either natural or artificial, of symmetrical form, 
 suspended in the presence of a second magnet, serves to ex- 
 hibit certain phenomena of attraction and repulsion, which 
 deserve particular attention. When a north pole is presented to 
 a south pole, or a south pole to a north pole, attraction ensues 
 between them, the ends of the bar approaching each other, and, 
 if permitted, adhering with considerable force. When, on the 
 other hand, a north pole is brought near a second north pole, 
 or a south pole near another south pole, mutual repulsion is 
 observed, and the ends of the bar recede from each other as 
 far as possible. Poles of an opposite name attract, and poles 
 of a similar name repel each other. 
 
 According to Ampere's theory, each molecule of iron or steel 
 has a current of electricity circulating round it; previous to 
 magnetization these molecules — and hence the currents — are 
 arranged irregularly ; during magnetization they are made to 
 move parallel to one another, and as the magnetization becomes 
 more perfect they gradually assume greater parallelism. 
 
 If an iron or steel needle be suspended free in proximity to 
 a magnet it assumes a fixed direction according to its greater 
 or smaller distance from the poles or from the neutral zone. 
 
MAGNETISM AND ELECTRICITY. I I 
 
 However, before the needle assumes this direction, it swings 
 rapidly with a shorter stroke, or slowly with a longer stroke, 
 according to the greater or smaller attractive force exerted 
 upon it. The space within which the magnetic action of a 
 magnet is exercised is called the magnetic field, and the mag- 
 netic, as well as the electric, attractions and repulsions are, 
 according to Coulomb, as the densities of the fluids acting upon 
 each other, and inversely as the square of their distance. 
 
 As electro-magnets act in exactly the same manner as mag- 
 nets, their further properties will be discussed in the next 
 section. 
 
 Electro- Magnetism . 
 
 When a wire through which a current is passing is brought 
 near, and parallel, to a magnetic needle, the latter is deflected 
 from its ordinary position, no matter whether the current- 
 carrying wire be placed alongside, above, or beneath it. The 
 deflection of the needle is always in the same direction, i. e., 
 its north pole is always deflected in one and the same direction. 
 
 The direction of the deflection is determined by what is 
 known as Ampere's rule, which is as follows : Suppose an ob- 
 server swimming in the direction of the current, so that it 
 enters by his feet and emerges by his head : if the observer 
 has his face turned towards the needle, the north pole is always 
 deflected to his left. 
 
 When the current-carrying wire is coiled in many windings 
 around the needle, the action of the current is increased, be- 
 cause every separate winding deflects the north pole in the 
 same direction. Such instruments are known as multipliers, or 
 galvanoscopes, or galvanometers, and are used for recognizing 
 feeble currents. These instruments have been improved by 
 Nobili through the use of a very long coil of wire, and by the 
 addition of a second needle. This instrument is known as the 
 astatic galvanometer. The two needles are of equal size and 
 magnetized as nearly as possible to the same extent. They 
 are then immovably fixed together parallel and with their poles 
 
12 ELECTRO-DEPOSITION OF METALS. 
 
 opposed, and hung by a long fiber of twisted silk, with the 
 lower needle in the coil and the upper one above it. The ad- 
 vantage thus gained is twofold : The system is astatic, unaf- 
 fected, or nearly so, by the magnetism of the earth ; and the 
 needles being both acted upon in the same manner by the cur- 
 rent, are urged with much greater force than one alone would 
 be, all the actions of every part of the coil being strictly con- 
 current. A divided circle is placed below the upper needle, 
 by which the angular motion can be measured, and the whole 
 is inclosed in glass, to shield the needles from the agitation of 
 the air. 
 
 The deflection of the magnetic needle by the electric current 
 has led to the construction of instruments which allow of the 
 intensity of the current being measured by the magnitude of 
 the deflection. Such instruments are, for instance, the tangent 
 galvanometer, the sine galvanometer, etc., but they are almost 
 exclusively used for scientific measurements, while for the de- 
 termination of the intensity of current for electro-plating pur- 
 poses other instruments are employed, which will be described 
 later on. However, the electric current exerts not only a re- 
 flecting action on magnetic needles, but is also capable of pro- 
 ducing a magnetizing effect on iron and steel. If a bar of iron 
 be surrounded by a coil of wire, covered with silk or cotton for 
 the purpose of insulation, it becomes magnetic so long as the 
 current is conducted through the coil. Such iron bars con- 
 verted into temporary magnets by the action of the current are 
 called electro-magnets, and they will be the more highly mag- 
 netic, the greater the number of turns of the coil, and the more 
 intense the current passing through the turns. 
 
 The magnitude of the magnetizing force of the current is 
 expressed by the product from the number of turns and cur- 
 rent-strength passing through the turns, and is called ampere- 
 turn number. 
 
 By interrupting the current passing through the wire-turns, 
 the magnetism of the iron bar disappears to within a very 
 small quantity, its magnitude depending on the quality of the 
 
MAGNETISM AND ELECTRICITY. 
 
 13 
 
 iron. This remaining magnetism is called remanent or residual 
 magnetism. 
 
 An electro-magnet possesses the same properties as an 
 ordinary magnet, and, like it, has a north pole and a south pole, 
 as well as a magnetic field, through which its influence extends. 
 Place a piece of paper above an electro-magnet and sift uni- 
 formly iron filings over it. On giving the paper slight taps, 
 the filings arrange themselves in regular groups and lines. 
 Most of the filings collect on the two poles, while, in fixed 
 decreasing proportions, lines of filings are formed from the 
 north pole to the south pole. This experiment demonstrates 
 
 Fig. i. 
 
 that the action is strongest on the poles, and decreases towards 
 the center. The entire space in which the magnetic action — 
 the flow of the magnetic lines of force — exerts its influence, is 
 called the magnetic field. The lines of force flow from the 
 north pole to the south pole, where they combine, and flow 
 back through the iron bar to the north pole, as shown in the 
 accompanying illustration, Fig. 1. 
 
 The dotted lines actually take also their course from one 
 pole to the other, but by a more circuitous way. The direc- 
 tion, as well as the magnitude, of the field-force (see later on) 
 varies on all points of the magnet or electro-magnet, with the 
 sole exception of the symmetrical plane between the two poles, 
 
14 ELECTRO-DEPOSITION OE METALS. 
 
 the latter being on all points struck at a right angle by the 
 lines of force. 
 
 By placing a bar of soft iron, a b, in the proximity of a mag- 
 net or electro-magnet N S, covering both with a sheet of paper 
 and sifting iron filings upon the latter, delineations, as shown 
 in Fig. 2, are obtained. 
 
 The lines of force gravitate in large numbers towards the 
 side where the iron bar is, traverse the iron quite compactly, 
 and while, without the bar, the center of the magnet showed a 
 feeble magnetic field, the field-force in that place "has now 
 become greater. Upon the opposite side the density of the 
 lines of force which pass through the air is less. The prop- 
 
 N I ■ ' ' - " .- - - - - v x I .' ' 
 
 / 
 
 / I I "I | ■ ' ' I ' V - _ . '/.'/'/ ,111 1 \ \ \\ ^" ,v . 
 
 
 erty of a material to be traversed by the lines of force is called 
 
 its permeability . 
 
 The number of lines of force which traverses through I 
 square centimeter of cross-section of a material, is called the 
 magnitude of the magnetic induction of the material in question. 
 
 Every material opposes a certain fixed resistance to the 
 electrical current, as well as to the magnetic lines of force. 
 Soft iron opposing the least resistance to the lines of force ; it is 
 most compactly traversed by them. Air, on the otherjjjhand, 
 opposes far greater resistance, and, hence, the density of the 
 
MAGNETISM AND ELECTRICITY. I 5 
 
 lines of force, in Fig. 2, where they pass through the air is 
 much less. 
 
 A conducting wire through which passes a powerful current 
 also becomes itself magnetic. If a circular conducting wire, 
 through which a current passes, be suspended so as to move 
 free around its vertical axis, its direction is influenced by the 
 terrestrial magnetism, and it assumes such a position that its 
 plane stands at a right angle upon the plane of the magnetic 
 meridian. By now conducting the current through a spiral 
 wire suspended free — a so-called solenoid — the plane of each 
 separate turn will also place itself at a right angle upon the 
 plane of the magnetic meridian, or in other words, the axis of 
 the solenoid will be brought to lie in the magnetic meridian. 
 
 In a manner similar to the action upon a magnet by a con- 
 ducting wire through which a current passes, two conducting 
 wires, through which currents pass, exert attracting and repel- 
 ling influences one upon the other. Two currents running 
 parallel alongside each other in the same direction attract; but 
 repel, each other, when running in opposite directions. 
 
 Induction. 
 
 By induction is understood the production of an electric 
 current in a closed conductor which is in the immediate 
 proximity of a current-carrying wire. 
 
 Suppose we have two insulated copper-wire coils, A and B, 
 Fig. 3, B being of a smaller diameter and inserted in A. When 
 the two ends of B are connected with the poles of a battery, a 
 current is formed in A the moment the current of B is closed. 
 This current is recorded by the deflection of the magnetic 
 needle of a multiplier, M, which is connected with the ends of 
 A, the deflection of the needle showing that the current pro- 
 duced in A by the current in B moves in an opposite direction. 
 The current in A, however, is not lasting, because, after a few 
 oscillations, the magnetic needle of the multiplier returns to its 
 previous position and remains there, no matter how long the 
 current may pass through B. If, however, the current in B be 
 
i6 
 
 ELECTRO- DEPOSITION OF METALS. 
 
 interrupted, the magnetic needle swings to the opposite direc- 
 tion, thus indicating the formation of a current in A, which 
 passes through it in the same direction as the interrupted 
 current in B. 
 
 The current causing this phenomenon is called the primary, 
 inducing or main current, and that produced by it in the closed 
 circuit the secondary, induced or induction- current. From what 
 has been above said, it is clear that an electric current at the 
 moment of its formation induces in a contiguous closed circuit 
 
 Fig. 
 
 a current of opposite direction, but when interrupted, a current 
 of the same direction. 
 
 In the same manner as closing and opening the main 
 current, its sudden augmentation also effects the induction of a 
 current of opposite direction in a contiguous wire, while its 
 sudden weakening induces a current of the same direction. 
 The same effect is also produced by bringing the main current- 
 carrying wire closer to, or removing it further from, the contig- 
 uous wire. 
 
 It is supposed that by closing the current a magnetic field is 
 formed in the coil B, which sends forth its lines of force radially 
 
MAGNETISM AND ELECTRICITY. 1 7 
 
 in an undulating motion. The lines of force cut the turns of 
 the coil, A, which is without current, and thereby induces a 
 current. This current disappears again when the primary 
 current flows in equal force, and re-appears when by the 
 strengthening of the inducing current a change in the number 
 of lines of force takes place by reason of the strengthening of 
 the magnetic field. In the same manner induced currents are 
 also produced by a decrease in the number of lines of force, 
 and hence it follows that the production of induction-currents 
 is always conditional on the change of proportion between the 
 conductor and the magnetic field. 
 
 When a magnet or electro-magnet is pushed into a wire coil, 
 
 Fig. 4. 
 
 AtOTfOM 
 
 an electric current is produced in the turns of the coil so long 
 as the motion of the magnet is continued ; when the motion is 
 interrupted, the production of current ceases. If the magnet 
 be now withdrawn from the coil, a current is again formed, 
 which, however, flows in an opposite direction to that formed 
 by pushing the magnet into the coil. The currents produced 
 in the above-mentioned manner are also induction-currents, and 
 their formation is again explained by the fact that the lines of 
 force cut the turns of the conducting wire, and excite thereby 
 a current, the electro-motive force of which increases or de- 
 creases with the magnitude of the number of lines of force. 
 2 
 
1 8 ELECTRO-DEPOSITION OF METALS. 
 
 The induced currents follow the law of Ohm (see later on) 
 in precisely the same manner as the inducing currents. A 
 long induction-wire with a small cross-section offers greater 
 resistance than a short wire with a larger cross-section, and 
 consequently, in the first case, the current will be of slighter 
 intensity and higher electro-motive force, and, in the other, of 
 greater intensity and less electro-motive force. 
 
 Electro-magnetic alternating actions are the relations which 
 exist between the magnetic field, the conductor, and the 
 motion. The direction of the induced current can readily be 
 followed by the hand rule which is as follows : Place the right 
 hand in the position shown in Fig. 4, so that the thumb, index 
 finger and middle finger form right angles to each other. 
 When the index finger of the right hand is placed in the direc- 
 tion of the lines of force and the thumb in the direction of the 
 motion, the middle finger indicates the direction of the induced 
 current. 
 
 The mechanism of the formation of the electric current will 
 be fully discussed later on, but it will be necessary to here give 
 the values in which the performances of the current are ex- 
 pressed in order to shape the succeeding chapters more uni- 
 formly. 
 
 Fundamental Principles of Electro-Technics. 
 
 Electric Units. For the better comprehension of the prop- 
 erties, effects, and value of the electric current, it has become 
 customary to compare it with a current of water, and this cus- 
 tom will here be followed. 
 
 Fig. 5 shows a funnel A secured in the stand D, and con- 
 nected by a tube with the horizontal discharge pipe B. 
 Underneath B stands the vessel C, which serves for catching 
 the water. If the funnel be placed in a higher position and 
 filled with water, the latter runs off more rapidly from the pipe 
 B, than when the funnel occupies a lower position. If the 
 force of the current of water is expressed according to the 
 quantity of water which runs out in the time-unit, it follows 
 
MAGNETISM AND ELECTRICITY. 
 
 19 
 
 that in a certain pipe conduit, the quantity of water which runs 
 out in the time-unit, increases if there be an increase in the 
 height of fall. 
 
 Suppose it has been determined how many seconds are re- 
 quired for the water in the funnel to run through the pipe B. 
 If the pipe be now lengthened by joining to it several pipes of 
 the same cross-section, it will be found that a greater number 
 
 Fig. 5. 
 
 of seconds are required for emptying the funnel than with the 
 use of only one pipe. From this we learn that with a deter- 
 mined height of fall, the quantity of water which flows in the 
 time-unit through a pipe of determined cross-section decreases 
 when the pipe is lengthened. 
 
 If now the discharge pipes used in the last experiment be 
 replaced by pipes of the same length but of smaller cross- 
 sections, it will be found that a greater number of seconds are 
 also required for emptying the funnel than with the use of pipes 
 
20 ELECTRO-DEPOSITION 01' METALS. 
 
 of larger cross-sections. Hence, at a determined height of fall, 
 the quantity of water which flows through a pipe of fixed 
 length in the time-unit, decreases if the cross-section of the 
 pipe be increased. 
 
 The height of fall has to be considered as the motive power 
 which effects the flow of water. The pipe opposes a resistance 
 to the flowing water, this resistance increasing with the length 
 of the pipe and the reduction of the cross-section, and decreas- 
 ing as the cross-section becomes larger. 
 
 If now these principles be applied to the electric current, by 
 current- strength has to be understood the quantity of electricity 
 which passes in the time-unit through a conductor. 
 
 The unit of the quantity of electricity is called the coulomb. 
 Its magnitude results from the fact that for the I gramme 
 hydrogen 96,540 coulombs must migrate through the elec- 
 trolyte. 
 
 The unit of current- strength is called the umpire, i. e., a cur- 
 rent which every second canies one coulomb through the con- 
 ductor. The magnitude of an ampere is the current-strength 
 which is capable of separating in one minute 0.01973 gramme 
 of copper, or in one hour 1.184 grammes, from a cupric sul- 
 phate solution. In order to separate from an electrolyte 1 
 gramme of hydrogen, a current of I ampere must accordingly 
 pass 96,540 seconds, or 26 hours 49 minutes, through the 
 electrolyte. 
 
 The electro -motive force or tension of the electric current 
 corresponds to the height of fall of water. The work an electric 
 current is capable of performing does not only depend on the 
 current-strength, i. e., the quantity of current, which passes in 
 the time-unit through a cross-section of the conductor, but also 
 on the electro-motive force. The unit of electro-motive force is 
 called the volt. The material value of a volt is about the 
 electro-motive force of a Daniell's cell (zinc-copper). 
 
 In a water conduit the difference in pressure between two 
 points in the pipe is measured according to the difference in 
 the height of the column of water. To this difference in pres- 
 
MAGNETISM AND ELECTRICITY. 2 1 
 
 sure corresponds the difference of electro-motive force, also called 
 difference of potential, which is expressed by the number of 
 volts. 
 
 The product of current-strength in amperes and electro- 
 motive force in volts, which, in so far as an ampere is an 
 electric unit in one second, represents work performed in one 
 second, is called the volt-ampere or watt, and hence is the unit 
 of electrical work. 
 
 The electric resistance is similar to the resistance offered by 
 a water-pipe to the flowing water. As previously stated, the 
 quantity of water running out in the time-unit decreases when 
 the pipe is lengthened, as well as when the cross-section is 
 smaller, and, in both cases, the resistance opposed to the water 
 by friction increases. On the other hand, the quantity of 
 water flowing out in the time-unit increases, when the length 
 of pipe is shortened and the cross-section increased, because 
 there is less resistance. The same takes place with the electric 
 current. The quantity of current which can pass through a 
 conductor becomes smaller when the length of the conductor 
 is increased and its cross-section reduced, because the resist- 
 ance becomes thereby correspondingly greater. It has further 
 been seen that the quantity of flowing water in a certain con- 
 duit increases as the height of fall becomes greater. If now 
 the electro-motive force of the electric current be substituted 
 for the height of fall, the current-strength which passes through 
 a conductor will be increased in keeping with the changing 
 electro-motive force. From this results the following propo- 
 sition : 
 
 In a determined circuit the current-strength increases at the 
 same ratio as the electro-motive force which acts upon the circuit. 
 
 If now the current-strength increases proportionally to the 
 electro-motive force, the expression, 
 
 E(= electro-motive force in the circuit) 
 J (= current-strength in the circuit), 
 must be a fixed value dependent on the magnitude of the 
 electro-motive force and the current-strength, and this value is 
 called the electric resistance of the circuit. 
 
22 ELECTRO-DEPOSITION OF METALS. 
 
 The unit of electric resistance is called the ohm, it having thus 
 been named after the physicist Ohm, who laid down the rules 
 known as the laws of Ohm. The value of the ohm is equal to 
 the resistance at 0° C. of a column of mercury of one square 
 millimeter section and one meter long. A volt is the electro- 
 motive force which is capable of sending a current-strength of 
 one ampere through the resistance of one ohm. 
 
 Law of Ohm. It has above been seen that the fraction 
 
 E 
 
 (i) <v = resistance (W), 
 
 whereby under E is understood the electro-motive force which 
 is at disposal in the entire circuit. The current- strength J is 
 throughout in all places of the same magnitude, and Vindi- 
 cates the total resistance of the circuit. 
 
 From the preceding equation are deduced the following 
 further equations : 
 
 ( 2 ) W. J=E, 
 that is, the electro-motive force is equal to the product of 
 current-strength and resistance ; 
 
 (3) w=y, 
 
 that is, the current-strength is equal to the electro-motive force 
 
 divided by the resistance. 
 
 Example to equation I. If through a circuit closed by a long 
 
 wire and a current-meter, a current of 4 volts and 2 amperes is 
 
 conducted, the resistance of the circuit is 
 
 4 volts 
 
 = 2 ohms. 
 2 amperes 
 
 Example to equation 2. 5 amperes are to be conducted 
 through a circuit of I ohm resistance, what electro-motive force 
 is required for the purpose? 
 
 1 ohm X 5 amperes = 1 volt. 
 
 Example to equation 3. A current of 10 volts electro- motive 
 force is to be conducted through a circuit with 2 ohms resist- 
 ance ; what current-strength may be looked for? 
 
 10 volts 
 
 — ; — = ; amperes. 
 2 ohms J r 
 
MAGNETISM AND ELECTRICITY. 23 
 
 The total resistance, W, is composed of the internal resist- 
 ance of the current-source and the external resistance which the 
 current in its progression has to overcome. This external re- 
 sistance is composed of the resistance of the conducting wire, 
 the electrolyte, etc. If the internal resistance be designated W 
 and the external resistances wi and w2, equation 3 assumes 
 the following aspect : 
 
 < 4 > w , E L — = J" 
 
 W -f WI + W2 
 
 Hence, the current-strength is equal to the total electro- 
 motive force divided by the sum of the internal and external 
 resistances. 
 
 Example to equation 4. A cell possesses an internal resistance 
 of 0.3 ohm and an electro-motive force of 1 .8 volts, and the resist- 
 ance of the conducting wire, wi, is 1 ohm and that of the electro- 
 lyte 0.5 ohm. The current-strength then amounts to 1 ampere 
 
 ( !*_ __,) 
 
 V0.3 + I 4- O.K J 
 
 ,0.3 + 1 + 0.5 
 
 If a determined current-strength flows through a resistance, 
 a decrease of electro-motive force results in the resistance, 
 exactly as in a water-conduit the pressure of the column of 
 water is decreased with the length of the pipe, a decrease in 
 pressuie taking place. It might be said that the resistance 
 consumes the pressure, and the greater the resistance of a con- 
 ductor is, the less the current-strength will be, since, if in the 
 equation 3 the divisor grows, the current-strength, J, must be- 
 come less. According to the law of Ohm, the following prop- 
 osition here holds good : 
 
 The current-strength is inversely proportional to the sum of 
 the resistance of the circuit, or, in other words, the current- 
 strength decreases in the proportion as, with the same electro- 
 motive force, the resistances increase. 
 
 The resistance of a wire or of a body increases in proportion 
 to its increase in length, and decreases in proportion to the in- 
 crease of its cross-section. If the resistance of a conductor be 
 designated W, its length L, and its cross-section Q, then 
 
24 ELECTRO-DEPOSITION OF METALS. 
 
 (5) W= L 
 
 Q 
 
 The decreasing electro-motive force, according to the law of 
 Ohm, is calculated by the following equation, in which a de- 
 notes the decrease in electro-motive force, J the current- 
 strength, Wi the internal resistance. 
 
 (6) a=J X Wi. 
 
 In the example to equation 4, the current-strength amounted 
 to 1, and the internal resistance of the element to 0.3 ohm; 
 this gives a decrease of electro-motive force of 1 x 0.3 = 0.3 
 volt; hence the actual electro-motive force of the current flow- 
 ing from the cell will only be : E — a = 1 .8 — 0.3 = 1.5 volts, 
 and this effective electro-motive force is called the impressed 
 electro-motive force of the cell or other source of current. 
 
 If now the preceding separate propositions of the law of Ohm 
 be collected, the latter reads as follows: 
 
 The current-strength is directly proportio)ia I to the sum of the 
 electro-motive forces, and inversely proportional to the resistance 
 of the circuit ; however, the resistance of each part of the circuit 
 is proportional to its length, and inversely proportional to its 
 cross-section . 
 
 Specific resistances. The resistance of a wire of the same 
 material is consequently proportional to its length and in- 
 versely proportional to its cross-section. If now, one after the 
 other, wires of equal length and equal cross-section, but of 
 different materials, be placed between the binding posts of a 
 source of current, different current-strengths are obtained in 
 the wires. From this it follows that every material possesses 
 a definite capacity of its own to conduct the current. Hence, 
 if the resistance is to be calculated from the length of the wire 
 and its cross-section, the magnitude, called the specific resist- 
 ance of the material, has to be taken into consideration. By 
 the specific resistance is to be understood for conductors of 
 the first class, the resistance of a material 1 meter in length 
 and 1 square millimeter cross-section, and for conductors of 
 the second class, the resistance of a cube of fluid of 10 centi- 
 meters = 1 decimeter side length. 
 
MAGNETISM AND ELECTRICITY. 
 
 25 
 
 If the specific resistance be denoted c, the resistance of a 
 wire of L meters length and a cross-section of Q square milli- 
 meters cross-section is found from the equation : 
 
 (7) W = —. c. 
 WJ Q 
 
 The specific resistance c of the metals at 59 F. and the co- 
 efficient of temperature a (see later on) amount for: 
 
 Aluminium . . , 
 Antimony 
 
 Bismuth 
 
 Brass 
 
 Copper 
 
 German silver. 
 
 Gold 
 
 Iron 
 
 Lead 
 
 Manganin . . . 
 
 Mercury 
 
 Nickel 
 
 Nickelin 
 
 Platinum 
 
 Silver 
 
 Steel 
 
 Tin 
 
 Zinc 
 
 From the above table it will be seen that silver is the best 
 conductor, then copper, the specific resistance of which is 
 slightly greater, next gold, aluminium, and so on. The great- 
 est specific resistance in descending series have mercury, man- 
 ganin, nickelin, German silver, these metals or metallic alloys 
 showing at the same time the slightest change in resistance at 
 a higher temperature. 
 
 Coefficient of temperature. One and the same material has 
 the same specific resistance only at the same temperature. In 
 conductors of the first class — the metals — the resistance in- 
 creases, though even only in a slight degree, as the tempera- 
 ture increases. The formula for this is : 
 
 (8) Wt 2 = Wt 1 »+ a (t 2 — to], 
 
 0.029 
 
 0.0039 
 
 0475 
 
 0.0041 
 
 1.250 
 
 0.0037 
 
 0.10 to 0.071 
 
 0.0016 
 
 0.017 
 
 0.0041 
 
 0.30 to 0.18 
 
 0.0003 
 
 0.024 
 
 0.0040 
 
 0.120 to O.IO 
 
 0.C048 
 
 0.207 
 
 0.0039 
 
 °-455 
 
 0.00002 
 
 o-953 
 
 0.0009 
 
 0.15 
 
 0.0036 
 
 0.435 to °-340 
 
 0.000025 
 
 0.15 to 0.094 
 
 0.0024 
 
 0.016 
 
 0.0038 
 
 0.50 to 0.168 
 
 0.0040 
 
 O.IO 
 
 0.0042 
 
 0.065 
 
 0.0040 
 
26 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 in which Wt 2 is the resistance at the higher temperature U, and 
 Wt x , the resistance at the lower temperature ti, and the magni- 
 tude a, the number of ohms the resistance increases by a rise 
 of i° C. in the temperature. 
 
 In the conductors of the second class — the electrolytes — the 
 resistance decreases, as a rule quite considerably with a rise 
 in the temperature, and is calculated from the following 
 equation : 
 
 ( 9 , Wt^WtxO— a(t 2 — iO]. 
 
 The magnitude a is called the coefficient of temperature of 
 a material, and these coefficients are given in the second 
 column of the above table. 
 
 Fig. 6. 
 
 Law of Kirchhoff. From a water- conduit, the water may 
 by means of branch-pipes be conducted to different points. 
 In the same manner, the electric current may be conducted 
 from the main wire by means of different wires to different 
 places. This is called branching or distributing the current. 
 The wire from the source of current up to the point of branch- 
 ing is known as the main wire and the wires branching off as 
 branch wires. 
 
 The heavy lines in Fig. 6 represent the main wires ; a is the 
 junction from which three wires, I, 2, and 3, branch off, and b, 
 the junction at which they meet. If a current-meter (see later 
 on) be placed in the main wire, and one in each of the branch 
 
MAGNETISM AND ELECTRICITY. 27 
 
 wires, it will be found that the sum of the current-quantities 
 flowing through the separate branch wires is equal to the cur- 
 rent-quantity in the main wire. If, however, the current- 
 quantities which flow through the separate branch wires of the 
 same cross-section, 1, 2, 3, are examined, it will be seen that 
 these current-quantities are not the same, but vary one from 
 the other, the current-quantity flowing in the branch wire 1 
 being greater than that in 2 or 3, while that in 2 is greater than 
 that in 3. These variations are due to the fact that the branch 
 wire 1 is shorter than 2 or 3, and hence possesses less resist- 
 ance. Suppose that the longest branch-wire, 3, had a much 
 larger cross-section than the branch-wires 1 and 2. By reason 
 of its slighter resistance more current would flow through it, 
 notwithstanding its length, than through 1 and 2. 
 
 Hence the law of Kirchhoff may be summed up as follows : 
 
 1. When the current is branched, the sum of the, current- 
 strengths in the separate branch-wires is exactly as great 
 as the current- strength before and after branching off. 
 
 2. The current- strengths in the separate branch-wires dis- 
 tribute themselves in inverse proportion to their resist- 
 ances. 
 
 In the practical part of this work the further conclusions re- 
 sulting from the law of Kirchhoff will be referred to. 
 
 Law of Joule. If a current flows through a conductor which 
 possesses not too slight a resistance, the latter becomes heated, 
 and, hence, electric energy is converted into heat. It has been 
 shown by experiments that the quantity of heat, which is pro- 
 duced by the passage of a determined current-strength through 
 a determined resistance, increases in the same ratio as the dur- 
 ation of the passage of the current. It has also been shown 
 that by the passage of a determined current-strength through a 
 resistance, the heat produced in the latter in a determined time 
 is proportional to the magnitude of the resistance, and, hence, 
 that the quantity of heat becomes larger as the resistance in- 
 creases. It has further been established that the quantity of 
 heat produced in a determined resistance during a determined 
 
28 ELECTRO-DEPOSITION OF METALS. 
 
 space of time by the current flowing through it, is proportional 
 to the square of the current strength. 
 
 From these propositions determined by experiments, the law 
 of Joule may be brought into the formula: 
 
 (10) Q = C. p. W. t. 
 
 If O is the quantity of heat developed in calories, J is the 
 current-strength in amperes which flows through the resistance, 
 W the resistance through which J flows, and t the space of time 
 in seconds of the passage of the current; C is a constant which 
 by experiments has been ascertained as 0.0002392. In words, 
 Joule's law, therefore, reads : The quantity of heat produced in 
 t seconds by the passage of a current-strength J through the 
 resistance W is proportional to the expression J 2 Wt. 
 
 Friction al Electricity . 
 In an ordinary state solid bodies exhibit no attractive effect 
 upon such light particles as strips of paper, balls of elderpith, 
 etc., but by being rubbed with a dry cloth or fur, many solid 
 bodies acquire the property of attracting such light bodies as 
 mentioned above. The cause of this phenomenon is called 
 electricity, and the bodies which possess this property of be- 
 coming electric by friction are termed idio- electrics, and those 
 which do not appear to possess it, non-electrics. Gray, in 1727, 
 found that all non-electric bodies conduct electricity, and hence 
 are conductors, while those which become electric by friction 
 are non-conductors of electricity. Strictly speaking, there are 
 no non-conductors, because the resins, silk, glass, etc., conduct 
 electricity, though only very badly. It is therefore better to 
 distinguish good and bad conductors. To test whether a body 
 belongs to the idio-electrics, the so-called electroscope is used, 
 which in its simplest form consists of a glass rod mounted on a 
 stand, and bent at the top into a hook, fro.m which hangs by a 
 silken thread or hair a pitch ball. If, on bringing the rubbed 
 body near the pith ball, the latter is attracted, the body is 
 electric; whilst if the ball is not attracted, the body is either 
 non-electric, or its electricity is too slight to produce an attrac- 
 tive effect. 
 
MAGNETISM AND ELECTRICITY. 29 
 
 From the following experiments it was found that there exist 
 two kinds of electricity : When a rubbed rod of glass or shellac 
 is brought near the ball of elder-pith suspended to a silk thread, 
 the ball is attracted, touches the rod, adheres for a few moments, 
 and is then repelled. This repulsion is due to the fact that the 
 ball by coming in contact with the rod becomes itself electric, 
 and its electricity must first be withdrawn by touching with the 
 hand before it can again be attracted by the rod. By now 
 taking two such balls, one of which has been made electric by 
 touching with a glass rod, which had been rubbed with silk, 
 and the other by touching with a shellac rod rubbed with cloth, 
 it will be observed that the ball, which is repelled by the glass 
 rod, is attracted by the shellac rod, and vice versa. These two 
 kinds of electricity are called vitreous ox positive, and resinous 
 or negative electricity, and it has been found that electricities of 
 a similar name attract, and electricities of an opposite name re- 
 pel each other. 
 
 Co n ta ct- Electricity . 
 
 However, a current of electricity is generated not only by 
 friction, but also by the contact of various metals. In the same 
 manner as the copper and iron in Galvani's experiments with 
 the frog-leg, other metals and conductors of electricity also be- 
 come electric by contact, the electric charges, being, however, 
 stronger or weaker, according to the nature of the metals. If 
 zinc be brought in contact with platinum, it becomes more 
 strongly positively electric than when in contact with copper ; 
 whilst, however, copper in contact with zinc is negatively ex- 
 cited, in contact with platinum it becomes positively electric. 
 
 The metal which has become positively electric is said to 
 have the higher potential, i. c, it possesses a larger measure of 
 electricity than the metal which has become negatively electric, 
 and as the flow of water from higher to lower points takes place 
 in a larger degree the greater the difference in altitude is, the 
 electric current flows also the more rapidly from a positively 
 charged body — the positive pole — to the negatively charged 
 body — the negative pole — the greater the difference in their 
 
30 ELECTRO-DEPOSITION OF METALS. 
 
 charges is, and this difference in the charges of two bodies is 
 called difference of pole?itial. 
 
 If now the metals be arranged in a series so that each pre- 
 ceding metal becomes positively electric in contact with the 
 succeeding one, a series of electro-motive force is obtained in 
 which the metals or conductors of electricity stand as follows : 
 Potassium, sodium, magnesium, aluminium, zinc, cadmium, 
 iron, nickel, lead, tin, copper, silver, mercury, gold, platinum, 
 antimony, graphite. 
 
 While two metals of the series of electro-motive force touch- 
 ing each other become electrically excited in such a manner 
 that one becomes positively and the other negatively electric, an 
 exchange of the opposite electricities takes place by introducing 
 a conducting fluid between the metals. Thus, if a plate of zinc 
 and a plate of copper connected by a metallic wire are immersed 
 in a conducting fluid, for instance, dilute sulphuric acid, the 
 electricity of the positive zinc passes through the fluid to the 
 negative copper, and returns through the wire — the closed circuit 
 — to the zinc. However, in the same degree with which the 
 electricities equalize themselves, new quantities of them are 
 constantly formed on the points of contact of the metals with 
 the conducting fluid ; and, hence, the flow of electricity is con- 
 tinuous. This electric current generated by the contact of 
 metals and fluids is called the galvanic current ; or, since it is 
 generated by the intervention of fluid conductors, hydro-electric 
 current. 
 
 A combination of conductors which yield such a galvanic 
 current is called a galvanic or voltaic cell or battery, and the 
 production of current from the above-mentioned differences of 
 potential of the metals was formerly explained by the supposi- 
 tion that chemical processes take place in the solutions in 
 which the metal plate is immersed. However, as will be seen 
 later on, the production of the current is at present reduced, 
 according to Nernst's theory, to the solution-pressure and the 
 osmotic pressure. It is first of all necessary to explain the 
 fundamental principles of chemistry, since without a knowledge 
 of them, the subsequent sections could not be understood. 
 
MAGNETISM AND ELECTRICITY. 3 I 
 
 Fundamental Principles of Chemistry. 
 
 The phenomena presented by magnetism and electricity 
 have, so far as required for our purposes, been briefly discussed 
 in the preceding sections. All these phenomena, no matter 
 how much they may vary in their nature, have this in com- 
 mon, that the bodies in which they appear undergo no change 
 in substance and weight, notwithstanding that they acquire the 
 most diverse properties. If, for instance, steel by being rubbed 
 with a magnet has acquired the power of attracting iron articles, 
 and hence has become a magnet itself, no other changes can 
 be noticed in it, even by the most minute examination ; it re- 
 mains the same steel which had been originally used, it having 
 solely acquired the property of being capable of acting as a 
 magnet. 
 
 The phenomena to be treated of in this section devoted to 
 the fundamental principles of chemistry, are of an entirely 
 different nature, we having constantly to deal with changes in 
 substance, as may be shown by the following examples. 
 
 When bright iron or steel is exposed to the action of moist 
 air, it becomes gradually coated with a brown-red powder 
 known as rust, which is formed by the iron combining with 
 the oxygen of the air. On examining this brown-red sub- 
 stance it will be found to possess entirely different properties 
 from iron, and that the latter has undergone a material change. 
 By the absorption of oxygen the iron has been converted into 
 an oxide of iron, and a process known as a chemical process 
 has taken place, whereby from two different substances a third 
 one is formed which possesses other properties, and is of a 
 different composition. 
 
 The phenomena which appear in subjecting the well-known 
 red oxide of mercury or red precipitate to the action of heat, 
 furnish another example of a chemical process. If red oxide 
 of mercury be heated in a test-tube, its red color soon dis- 
 appears, its bulk decreases, and, if heating be for some time 
 continued, it disappears entirely. On the other hand, there 
 will be found deposited upon the upper, cooler portions of the 
 
32 ELECTRO-DEPOSITION OF METALS. 
 
 tube, metallic mercury in its characteristic form of globules. 
 If the gaseous products evolved during the process be also 
 caught, a gas, different in its nature from air, is obtained, which 
 will inflame a mere spark on wood. This gas is the well-known 
 oxygen, which plays such an important part in the respiratory 
 process of human beings and animals. 
 
 While by the formation of a new body in consequence of 
 the combination of different substances, the first example 
 presents a chemical process of a synthetic, i. e., building-up, 
 nature, the second one, shows a process of an analytical, i. e., 
 resolving, nature. We have thus learned the nature of the 
 chemical processes in general, which, no matter how diverse 
 the separate processes may be, consist in that an alteration in 
 the material nature of the bodies takes place. If the quantities 
 by weight of a substance entering into a chemical change be 
 determined, it will be noticed that in all transpositions, in the 
 decomposition of a compound into its constituents, and in the 
 union of the elements to form compound bodies, loss in weight 
 never occurs. The weight of the resulting compoujid is in- 
 variably equal to the sum of the weight of the bodies entering into 
 the reaction. This furnishes proof that the most important law 
 of the indestructibility and non-creation of weighable substance 
 in nature, which is known as the law of the conservation of 
 matter, is also valid as regards chemical processes. 
 
 Moreover, we find the further conformity to law that the 
 quantities by weight of the substances formed by their mutual 
 action in a chemical process, stand one to the other in a fixed, 
 unchangeable proportion. Thus, for instance, a given quantity 
 by weight of iron can only combine, under the co-operation of 
 water, with an unchangeable quantity of oxygen, to ferric 
 hydroxide (rust) ; and the quantities by weight of mercury 
 and oxygen formed from red oxide of mercury, must always 
 stand one to the other in an unchangeable proportion. 
 
 If now in a similar manner as in the second example, all the 
 bodies offered by nature be decomposed by means of the 
 auxiliary agents at our command, into such constituents as do 
 
■ MAGNETISM AND ELECTRICITY. 35 
 
 not allow of a division into further substances, it will be found 
 that there are altogether comparatively few substances which 
 compose the bodies of nature. Such substances are called 
 chemical elements ; they cannot be converted into each other, 
 but constitute, as it were, the limit of chemical change. At 
 present 79 such elements are known. 
 
 The smallest portion of an element, or of a chemical com- 
 pound, which can exist in a free state, is called a molecule. If, 
 for instance, common salt be triturated to such a fine powder 
 that further reduction by mechanical means is impossible, such 
 finest particle represents the molecule. However, common 
 salt consists of two elements, namely, sodium and chlorine. 
 Consequently both these elements must be present in the mole- 
 cule, and these smallest particles of the elements, which are 
 contained in the molecule, are called atoms. Hence the atom 
 of an element is the smallest quantity of it which takes part in 
 chemical combinations. As a rule, the atom is equal to half 
 the molecule. Hence, for the formation of a molecule at least 
 two atoms of an element are required. 
 
 The atoms of the elements aggregate according to fixed pro- 
 portions by weight, and the smallest quantities by weight of 
 the elements which enter into combinations with each other 
 are called their atomic weights, the weight of hydrogen, which 
 is the lightest of all the elements, being taken as the unit. It 
 must, however, be stated that a series of elements may unite 
 not only in a single proportion of weight, but also in several 
 different ones, forming thereby combinations of entirely dif- 
 ferent properties. If, however, these different proportions by 
 weight are more closely compared, they will be found to stand 
 in quite simple relations to each other, the higher being always 
 a simple multiple of the lowest. 
 
 In the table below are given the most important chemical 
 elements, together' with their atomic weights. In addition the 
 table contains the symbols used for designating the elements. 
 These symbols are formed from the first letters of their names, 
 derived either from the Latin or Greek. Hydrogen is, for in- 
 3 
 
34 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 stance, represented by the letter H, from the word hydrogenium ; 
 Oxygen by O, from oxygenium ; Silver by Ag, from argentum. 
 If Latin or Greek names of several elements have the same first 
 letters, the latter serves only for the designation of one of these 
 elements, while for the other elements, the first letter is fur- 
 nished with an additional characteristic letter. Thus, for in- 
 stance, boron is represented by the letter B ; barium by Ba ; 
 bismuth by Bi ; bromine by Br. 
 
 Name of Element. 
 
 Sym- 
 bol. 
 
 Aluminium Al 
 
 Antimony Sb 
 
 Arsenic As 
 
 Barium ' Ba 
 
 Bismuth i Bi 
 
 Boron B 
 
 Bromine Br 
 
 Cadmium Cd 
 
 Calcium Ca 
 
 Carbon C 
 
 Chlorine CI 
 
 Chromium Cr 
 
 Cobalt Co 
 
 Copper Cu 
 
 Fluorine F 
 
 Gold I Au 
 
 Hydrogen i H 
 
 Iodine I 
 
 Iron Fe 
 
 I 
 
 Atomic 
 Weight. 
 
 27.04 
 119.6 
 
 74-9 
 
 136.9 
 
 207.5 
 10.9 
 79.76 
 
 in. 7 
 
 39-9 
 11.97 
 
 35-4 
 
 5 2 -4 
 
 58.6 
 
 63.18 
 
 19.06 
 
 196.2 
 1. 000 
 
 126.54 
 55.88 
 
 Name of Element. 
 
 Lead Pb 
 
 Magnesium Mg 
 
 Manganese Mn 
 
 Mercury i Hg 
 
 Sym- 
 bol. 
 
 Nickel 
 Nitrogen . . . 
 Osmium 
 Oxygen 
 Phosphorus 
 Platinum . . . 
 Potassium . . 
 Selenium . . . 
 Silicium . . . 
 
 Silver 
 
 Sodium 
 Sulphur . . . 
 
 Tin 
 
 Zinc 
 
 Ni 
 
 N 
 
 Os 
 
 O 
 
 P 
 
 Pt 
 
 K 
 
 Se 
 
 Si 
 
 Ag 
 
 Na 
 
 S 
 
 Sn 
 
 Zn 
 
 Atomic 
 Weight. 
 
 206.4 
 23-94 
 54-8 
 
 199.8 
 58.6 
 14.01 
 
 191.0 
 I5-96 
 30.96 
 
 I94-3I 
 39-03 
 78.87 
 28.0 
 
 107.66 
 23.00 
 31.98 
 
 "7-35 
 
 64.88 
 
 The symbols not only represent the elementary bodies, but 
 also their fixed quantities by weight, namely, their atomic 
 weights, so that, for instance, the symbol Ni means 58.6 parts 
 by weight of nickel. 
 
 Compounds produced by the union of the elements are 
 represented by placing their corresponding symbols together, 
 and designating them chemical formulas. As previously men- 
 tioned, common salt consists of one atom sodium (Na) and 
 one atom chlorine (CI), and hence its formula has to be 
 written NaCl. The latter shows that one molecule of common 
 
MAGNETISM AND ELECTRICITY. 35 
 
 salt consists of 23 parts by weight of sodium and 35.4 parts by- 
 weight of chlorine, which together form 58.4 parts by weight of 
 common salt. If several atoms of an element are present in a 
 compound, this is denoted by numbers which are attached 
 to the symbol of the atom. Water consists of 2 atoms hydro- 
 gen (H) and one atom oxygen (O), and hence its formula is 
 H 2 0, which shows that 2 parts by weight of hydrogen, together 
 with 15.96 parts by weight of oxygen form 17.96 parts by 
 weight of water. 
 
 By means of the symbols and formulas it is also made pos- 
 sible to express in the most simple manner, the chemical pro- 
 cesses by equations, which not only denote the manner of the 
 chemical transposition, but also allow of the calculation of the 
 quantities by weight which have entered into reaction in the 
 transposition of the different substances. If, according to this, 
 our former examples, by means of which it has been en- 
 deavored to explain the nature of a chemical process, be trans- 
 lated into this chemical language, the equations read as 
 follows : 
 
 1. 2Fe 2 +30 2 + 6H. i O=4Fe 8 (OH) s . 
 
 Iron. Oxygen. Water. Ferric hydroxide. 
 
 2. 2HgO = Hg. 2 + 2 . 
 
 Mercuric oxide. Mercury. Oxygen. 
 
 Valence of the elements. If the combinations into which the 
 elements enter one with the other are more closely examined, 
 and their formulas compared, it will be seen that entire groups 
 of combinations are composed in an analogous manner. This 
 analogy of composition appears very plainly in the compounds 
 into which a series of elements enters with hydrogen, and we 
 thus come across four different groups of compounds. The 
 elements of the first group, namely, of the halogens, chlorine, 
 bromine, iodine and fluorine, combine with one atom of hydro- 
 gen ; those of the second group, to which belong oxygen and 
 sulphur, are capable of saturating two atoms of hydrogen ; 
 those of the third group, which embraces nitrogen, phosphorus, 
 
36 ELECTRO-DEPOSITION OF METALS. 
 
 arsenic and antimony, fix three atoms of hydrogen, and finally, 
 the elements of the fourth group, carbon and silicium, may com- 
 bine with four atoms of hydrogen. Hence, we must ascribe a 
 particular function of affinity to each element in its relation to 
 hydrogen, and this property is called valence. 
 
 Now, according as the elements are capable of combining 
 with one, two, three or four atoms of hydrogen, they are 
 designated as univalent, bivalent, trivalent, or quadrivalent; and 
 all elements, which possess the same valence, are called chemi- 
 cally equivalent. In chemical compounds, such equivalent 
 elements may replace each other atom for atom, such substitu- 
 tion being also possible in elements of dissimilar valence, but 
 it must take place in such a manner that a bivalent atom re- 
 places two hydrogen atoms, a trivalent atom three hydrogen 
 atoms, so that an equal number of valences is always ex- 
 changed. Thus, in accordance with this, one atom of chlorine 
 is equivalent to one atom of hydrogen and hence, when a 
 substitution of hydrogen by chlorine results, it can only be 
 by one atom of chlorine taking the place of one atom of 
 hydrogen. Hence it follows that 35.4 parts by weight of 
 chlorine are equivalent to one part by weight of hydrogen. On 
 the other hand, one atom of oxygen is equivalent to two atoms 
 of hydrogen, or 15.96 parts by weight of the former are 
 equivalent to 2 parts by weight of the latter. A mutual sub- 
 stitution of these two elements must, therefore, always take 
 place in the proportion of 15.96 to 2. Since the elements, 
 nitrogen, phosphorus, etc., are capable of fixing 3 hydrogen 
 atoms, mutual substitution must also take place in such a man- 
 ner that 1 nitrogen-atom replaces 3 hydrogen-atoms or that 
 
 -Zl = 4.67 parts by weight of nitrogen are substituted for I 
 
 3 
 part by weight of hydrogen. Finally, one atom of carbon or 
 of silicium is equivalent to 4 parts by weight of hydrogen, or 
 I part by weight of hydrogen is replaced by 3 parts by weight 
 of carbon. These quantities by weight determined for some 
 of the elements, which are equivalent to one part by weight of 
 
MAGNETISM AND ELECTRICITY. 37 
 
 hydrogen, or, in general, to one part by weight of a univalent 
 element, are called equivalent weights or combining weights, and 
 are in a similar manner deduced for all the other elements. 
 
 While the elements preserve a constant valence towards 
 hydrogen, many of them show a varying valence, which differs 
 also from the hydrogen-valence towards other elements, so that, 
 for instance, the same element may appear opposite to a second 
 one, trivalerit in one combination and quinquivalent in another. 
 Combinations of phosphorus with chlorine may serve as an 
 example. Together they form a combination, PCL, as well as 
 one PC1 5 ; in the first case 3 atoms of chlorine or 3 X 35.4 parts 
 by weight are equivalent to I atom of phosphorus or 30.96 
 parts by weight. This capacity of different elements of being 
 endowed with totally unequal valence, forces us to the assump- 
 tion that valence is not a characteristic property of the 
 elements, but is dependent on the nature of the elements com- 
 bining with each other, and is also influenced by the conditions 
 under which the formation of the chemical combination takes 
 place. 
 
 By arranging the most important elements according to their 
 valence, we obtain the following groups: 
 
 Univalent elements : Hydrogen, chlorine, bromine, iodine, 
 
 fluorine, potassium, sodium, silver. 
 Bivalent elements : Oxygen, sulphur, barium, strontium, 
 calcium, magnesium, cadmium, zinc, lead, copper, mer- 
 cury. 
 Bivalent and trivalent elements : Iron, cobalt, nickel, man- 
 ganese. 
 Trivalent elements : Boron, aluminium, gold. 
 Trivalent and quinquivalent elements : Oxygen, phos- 
 phorus, arsenic, antimony, bismuth. 
 Quadrivalent elements : Carbon, silicium, tin, platinum. 
 Later on, in the section on the fundamental principles of 
 electro-chemistry, in speaking of the development of the laws 
 of Faraday, we will have to refer to these groups, and their im- 
 portance will then become evident. 
 
38 ELECTRO-DEPOSITION OF METALS. 
 
 Metals, metalloids. In accordance with the greater or less 
 conformity of their physical properties, the elements have, for 
 the sake of expediency, been for a long time divided into two 
 classes, namely, metals and non-metals, the latter being also 
 called metalloids. In the first class are placed the elements of 
 the known metallic luster, which are opaque or at the utmost 
 translucent in thin laminae, and are good conductors of heat 
 and electricity. All the other elements which have not such 
 physical properties in common are classed as metalloids. The 
 two groups of bodies obtained by this mode of division also 
 show in a chemical respect such similarities as to justify this 
 classification, the metalloids forming with hydrogen readily 
 volatile, mostly gaseous, combinations, while the metals unite 
 more rarely with hydrogen, and, at any rate, do not form 
 volatile combinations with it. The combinations which the 
 metalloids form with oxygen also show, in their behavior 
 towards water, very characteristic phenomena, entirely different 
 from those presented by compounds of the metals with oxygen. 
 These differences will later on be referred to in detail. A very 
 remarkable difference, of the utmost importance, especially for 
 our purpose, is in the action of the electric current upon the 
 combinations between metals and metalloids, the metals being 
 always deposited on the electro-negative pole, and the metal- 
 loids on the electro-positive pole. 
 
 However, notwithstanding these properties, differing on the 
 one hand and corresponding on the other, a sharp separation 
 of the elements based upon the above-mentioned considerations 
 cannot be reached, and the classification as regards some ele- 
 ments turns out different according to whether one or the other 
 behavior is first taken into cunsideration. 
 
 On the other hand, a classification free from ambiguity re- 
 sults from adhering, as is now also done in science, to the be- 
 havior of the elements towards salts as the distinctive principle. 
 In this manner two sharply defined groups are obtainable, one 
 comprising the elements — the metals — capable of evolving 
 hydrogen with the acids, while the elements of the other group 
 
MAGNETISM AND ELECTRICITY. 39 
 
 do not possess this power, and are classed among the metal- 
 loids. From this results the following classification : 
 
 Metalloids : Chlorine, bromine, iodine, fluorine, oxygen, 
 sulphur, nitrogen, phosphorus, boron, carbon, silicium. 
 Metals: Potassium, sodium, lithium, magnesium, calcium, 
 barium, strontium, aluminium, zinc, iron, manganese, 
 chromium, nickel, cobalt, copper, cadmium, arsenic, 
 antimony, tin, lead, bismuth, mercury, silver, gold, 
 platinum. 
 Acids, bases, salts. Attention has previously been drawn to 
 the difference in behavior towards water of combinations of the 
 metalloids, and of the metals with oxygen, and this behavior 
 will have to be somewhat more closely considered, because we 
 are thereby directed to extremely important classes of chemi- 
 cal combinations. 
 
 Oxygen is the most widely distributed element, it forming, 
 together with nitrogen, air, and with hydrogen, water. All the 
 elements, with the exception of fluorine and a few more rare 
 ones, show great affinity for it and enter readily into reaction 
 with it. In the processes enacted thereby, the large class of 
 oxides is formed, and the chemical process in which an absorp- 
 tion of oxygen takes place is generally called oxidation, while 
 the term redaction is applied to the opposite process by which 
 a withdrawal of oxygen from a substance is effected. 
 
 If these oxides, with the exception of a few so-called indif- 
 ferent oxides, be brought together with water, they impart to 
 it either an acid taste, as well as the power to redden blue 
 litmus and to evolve hydrogen with metals, or they give to the 
 water a lye-like taste and the power of restoring the blue color 
 to the previously reddened litmus. The oxides of the first kind 
 are chiefly formed with the co-operation of the elements be- 
 longing to the metalloids, while those of the second class con- 
 tain exclusively metals in addition to oxygen. 
 
 These two classes of bodies, which possess entirely different, 
 even directly opposite, properties, are the acids and bases, and 
 will have to be separately discussed. 
 
4-0 ELECTRO-DEPOSITION OF METALS. 
 
 Acids. As characteristic properties of the acids have been 
 mentioned, their acid taste, their power of reddening blue 
 litmus, and to evolve hydrogen with metals, magnesium being 
 especially suitable for the latter purpose. If now the chemical 
 compositions of all the compounds which possess the above- 
 mentioned properties be more closely examined, they will be 
 found to contain, without exception and without regard to 
 their own constituents, hydrogen which can be displaced by 
 metals. This hydrogen may be present in the combinations 
 in one or more atoms, and according to the number of the 
 hydrogen-atoms present, a distinction is made between mono- 
 basic, dibasic, tribasic, etc., acids. 
 
 A further distinction is made between acids containing no 
 oxygen, to which belong the haloid acids, for instance, hydro- 
 chloric acid, and acids containing oxygen, which are therefore 
 called oxy acids. The latter group comprises the majority of 
 acids, the well-known sulphuric and nitric acids belonging to 
 it. However, the characteristic feature of the acids consists 
 solely in that they contain hydrogen which can be displaced by 
 metals. 
 
 Bases. The second group of oxides imparts to water, as 
 previously mentioned, a lye-like taste and the power to restore 
 the blue color of litmus reddened by acid, and these properties 
 are utilized as valuable agents for the characterization of the 
 substances as bases. Nevertheless, by the above-mentioned 
 definitions the meaning of bases is not unequivocally estab- 
 lished, and for a thorough investigation of their material nature, 
 their exact composition has to be determined with the assist- 
 ance of analysis, as was done with the acids. From this it results 
 that, in addition to metals or metal-like groups of atoms, all 
 basic compounds contain oxygen and hydrogen, the latter 
 elements being always present in the same number of atoms, 
 namely, in the form of hydroxyl groups, OH. According to 
 their valence the metals combine with one or more hydroxyl 
 groups to bases. 
 
 Salts. The groups of chemical combinations above referred 
 
MAGNETISM AND ELECTRICITY. 4 1 
 
 to, show a very remarkable behavior in so far that by their 
 mutual action they are capable of equalizing or saturating their 
 characteristic features, so that by means of a basic combination 
 the specific properties of an acid can be removed, and by means 
 of an acid the specific properties of a base. 
 
 An example will explain this process. If to a certain quan- 
 tity of hydrochloric acid a few drops of blue litmus be added, 
 the fluid in consequence of its acid properties will change the 
 blue coloring matter, the latter acquiring a red color. By now 
 adding drop by drop dilute soda lye, which is a basic combi- 
 nation, it will be noticed that on the spot where the lye falls 
 upon the acid, the red color disappears momentarily, and gives 
 way to a blue one. If the addition of lye be carefully continued 
 and the fluid constantly stirred, a point is suddenly reached 
 when by a single drop of the lye the red color of the entire 
 fluid is removed and converted into pale blue. If no more lye 
 than exactly necessary for the sudden change in color has been 
 brought into the fluid, the latter now possesses neither the 
 properties of an acid nor of a base, but has become what is 
 called neutral. A process of the kind above described, by 
 which the acid character of a combination is equalized by the 
 basic character of another, or vice versa, is in chemistry called 
 neutralization. 
 
 This example shows, that it is frequently of importance to 
 know whether a fluid possesses acid, basic or neutral prop- 
 erties, or as it also expressed, whether it shows an acid, basic, 
 or neutral reaction. For the determination of these properties 
 so-called reagent-papers are used. They consist of unsized 
 paper dyed with various organic coloring matters, preferably 
 blue litmus tincture, or the latter slightly reddened by acids. 
 When small strips of such papers are dipped in the fluid to be 
 examined, blue litmus paper will be colored red if the fluid has 
 an acid reaction, and red litmus paper, blue, if it shows an 
 alkaline or basic reaction. Finally, fluids which change neither 
 blue nor red litmus paper react neutral, or they show a neutral 
 reaction. If we now return to our example by which the pro- 
 
42 ELECTRO-DEPOSITION OF METALS. 
 
 cess of neutralization between acid and base has been described, 
 it will above all be of interest to learn whether this equalization 
 of the mutual properties runs its course according to fixed laws, 
 and what the nature of the latter is. It will be further desir- 
 able to gain an insight into the chemical transformations which 
 have taken place in the process, and to learn the products 
 which have been newly formed. 
 
 For the elucidation of these questions, let us take a deter- 
 mined quantity of acid and, in the same manner as in the above- 
 described example, add to it lye until the acid is just neutral, 
 this being shown by the sudden change in color of the litmus. 
 If we now take another quantity of the same acid and proceed 
 with it in the same manner, it will be found that the consumed 
 quantities of bases stand in the same proportion to each' other 
 as the quantities of acid used, so that if, in one case, for 50 
 ccm. of acid 30 ccm. of lye were used for neutralization, in the 
 other, with the use of the same acid and the same lye, for 75 
 ccm. of acid 45 ccm. of lye were required to obtain a neutral 
 solution. By repeating these experiments with any other acids 
 and bases, the same conformity to law will always be found, 
 and it will thus be seen that neutralization between acids and 
 bases runs its course in positively fixed quantities, and that for 
 the neutralization of a certain quantity of an acid, a positively 
 fixed quantity of a base is required, and vice versa. 
 
 Of this conformity to law much use is made in analytical 
 chemistry by volumetric methods for the determination of the 
 content of an acid by means of a base of known content, and 
 vice versa. 
 
 In order to learn what new products are formed by the 
 neutralization between acids and bases, the neutral solution 
 obtained, according to our example, is concentrated by evapo- 
 ration, and it will be found that from the fluid separates a white 
 substance in small crystals which, according to analysis, con- 
 sists of sodium (Na) and chlorine (CI), and hence constitutes 
 the well-known common salt (NaCl). However, in addition to 
 the common salt, water (H-.O) has also been formed by the 
 chemical process, as shown by analysis. 
 
MAGNETISM AND ELECTRICITV. 43 
 
 If now, as another example, we take as an acid, sulphuric 
 acid (H 2 S0 4 ), neutralize it with caustic soda (KOH), and 
 again determine the products formed, we arrive at a substance, 
 the composition of which, according to analysis, is K 3 S0 4 , 
 hence represents potassium sulphate, water being again formed 
 as an additional product. The process of neutralization takes 
 its course in an analogous manner with any kinds of acids and 
 bases, and it will be seen that every neutralization of an acid 
 and a base is accompanied by the formation of water, and 
 further, that after the withdrawal of the hydrogen from the 
 acid, the metal of the bases forms with the remainder a new 
 neutral combination, which is called a salt. 
 
 These processes are more distinctly presented by bringing 
 them into chemical formulas, and for our example we have to 
 write 
 
 HC1 + NaOH = H 2 + NaCl. 
 
 Hydrochloric acid. Sodium hydrate. Water. Sodium chloride (common salt). 
 
 H 2 SO, + 2KOH = H 2 + K.SO,. 
 
 Sulphuric acid. Potassium hydrate. Water. Neutral potassium sulphate. 
 
 These formulas show plainly the connection which exists be- 
 tween the acids, bases and salts. 
 
 The formation of salts from the acids is, therefore, as we 
 have seen, brought about by the replacement of the hydrogen- 
 atoms of the acids by metals. However, this replacement of 
 the hydrogen can only take place in accordance with the va- 
 lence of the metal, so that a univalent metal can take the place 
 of only one hydrogen-atom, a bivalent metal of only two 
 hydrogen-atoms, and so on. With the use of a monobasic 
 acid, i. e., one in which only one hydrogen- atom is contained 
 in the molecule, salts can only be prepared which, besides 
 metal, contain no free hydrogen-atoms, and salts of the above 
 mentioned kind, namely neutral salts, are exclusively obtained. 
 By taking, on the other hand, an acid with several bases, its 
 hydrogen-atoms can be either partly or entirely replaced by 
 metals. In the first case, salts result which still possess an 
 
44 ELECTRO-DEPOSITION OF METALS. 
 
 acid character, they containing hydrogen besides a metal, and 
 are called acid salts, while in the latter case neutral salts are 
 formed, with which we are already acquainted. Sulphuric acid 
 is a dibasic acid and, hence, contains two hydrogen-atoms in 
 the molecule. Let us take, as an example, the salts which 
 sulphuric acid is capable of forming, and first saturate in it 
 only one hydrogen-atom by a univalent metal, for instance, 
 sodium, by adding just enough soda lye to the soda to half 
 saturate it. This solution still shows a strong acid reaction, 
 and by sufficiently concentrating it, a salt is separated which 
 throughout possesses acid properties and, as shown by analysis, 
 has the chemical formula NaHS0 4 . It is different from the 
 neutral sodium sulphate, which is obtained by completely satu- 
 rating the sulphuric acid with caustic soda, i. <?., by compound- 
 ing the sulphuric acid with caustic soda up to the neutral re- 
 action. The two processes just described are explained by the 
 following equations, which also show distinctly the difference 
 between neutral and acid salts : 
 
 i . H,S0 4 + NaOH = NaHSO, + H,C>. 
 
 Sulphuric acid. Sodium Acid sodium Water. 
 hydrate. sulphate. 
 
 2. H 2 SO* + 2NaOH = Na 2 S0 4 + H,0. 
 
 Sulphuric acid. Sodium Neutral sodium Water, 
 hydrate. sulphate. 
 
 In an analogous manner, as a dibasic acid is capable of form- 
 ing two series of salts, three series of salts may be derived from 
 a tribasic acid, for instance, phosphoric acid, so that in general 
 an acid of several bases can form as many series of acids as it 
 contains hydrogen-atoms in the molecule. 
 
 Nomenclature of salts. In conformity with the definition of 
 salts given above, according to which they are derived from the 
 acids by the replacement of the hydrogen by metals, they are 
 classified according to the acids they have in common, the 
 salts derived from sulphuric acid being thus designated sul- 
 phates. For the sake of distinguishing the various metallic 
 
MAGNETISM AND ELECTRICITY. 45 
 
 salts of the same acid, the names of the metals are added. 
 Thus, for instance, the scientific term for white vitriol, formed 
 by the action of sulphuric acid upon zinc, is zinc sulphate. 
 The designations for the salts of the other acids are formed in 
 the same manner;, those derived from nitric acid being called 
 nitrates, from phosphoric acid, phosphates, etc. Salts in which 
 all the hydrogen-atoms of the acids from which they are de- 
 rived, have been replaced by metal-atoms are called neutral, 
 normal, or primary salts in contradistinction to the acid or 
 secondary salts which, besides metal-atoms, also contain 
 hydrogen-atoms in the molecule. Finally, the salts are also 
 designated by indicating with the assistance of the Greek 
 numerals, mono-, di-, etc., the number of metal-atoms con- 
 tained in one acid- molecule. With the use of the latter mode 
 of designation, the scientific term for the acid sodium sulphate 
 is sodium mono-sulphate, and for the neutral sodium sulphate, 
 sodium disulphate. 
 
 Fundamental Principles of Electro- Chemistry. 
 
 Electrolytes. Solutions of chemical compounds which can 
 be decomposed by the current, are called electrolytes. 
 
 A distinction is made between conductors and non-conductors 
 of electricity, and, as previously mentioned, the metals are con- 
 ductors, while most of the metalloids, for instance, sulphur, do 
 not transmit the electric current. 
 
 The conductors are divided into conductors of the first class, 
 to which belong the metals, and conductors of the secojtd class, 
 the latter being chiefly the aqueous solutions of metallic salts 
 and certain other substances. 
 
 The conductors of the first class do not experience a per- 
 ceptible material change by the passage of the current, they 
 being at the utmost heated thereby. On the other hand, the 
 conductors of the second class undergo, by the passage of the, 
 current, a chemical change in so far as that on the places where 
 the current-carrying metallic conductor enters the solution, the 
 constituents of the latter are decomposed and separated. 
 
46 ELECTRO-DEPOSITION OF METALS. 
 
 This phenomenon of the chemical decomposition of sub- 
 stances or compounds by means of an electric current is called 
 electrolysis, and the conductors of the second class which 
 undergo such decomposition, are termed electrolytes. 
 
 The metal plates through which the current passes in and 
 out of the solution are called electrodes, the positive electrode 
 through which the current enters being termed anode, and the 
 negative electrode through which it leaves the electrolyte, 
 cathode. 
 
 Ions. This term is applied to the constituents into which the 
 combinations present in the solution are decomposed by the 
 current, and carried to the cathodes and anodes. 
 
 If a sodium chloride solution be subjected to electrolysis, 
 the sodium chloride is decomposed, chlorine being separated 
 on the positive electrode, and sodium on the negative electrode. 
 Thus chlorine and sodium are the ions of sodium chloride. If 
 an acid be decomposed by the electric current, hydrogen is 
 always separated on the negative electrode, and the other con- 
 stituent of the acid on the positive electrode. 
 
 The ions separated on the negative electrodes are called 
 katJiions and, hence, in the above-mentioned examples, sodium 
 and hydrogen are the kathions of sodium chloride, or of the 
 acid. The kathions migrate from the positive to the negative 
 electrode. 
 
 The remaining ions of the combinations migrate from the 
 negative to the positive electrode (anode), and are there sep- 
 arated. These ions separated on the anode are called anions. 
 Thus, chlorine is the anion of sodium chloride, as well as of 
 hydrochloric acid and of other chlorine compounds. 
 
 The ions exhibit, partly, properties entirely different from the 
 elements the names of which they bear. The hydrogen-ion of 
 the acids, for instance, is not known as a gas, but only in solu- 
 tion, while the element hydrogen is gaseous and but very 
 slightly soluble in water. Further, while the hydrogen-ion de- 
 termines the characteristic properties of the acids, hydrogen 
 gas exhibits none of these properties, and the hydrogen-ion 
 
MAGNETISM AND ELECTRICITY. 47 
 
 can only be met with in aqueous solutions of acids in which 
 are at the same time present the other constituents of the acids 
 possessing ion-properties. 
 
 If in hydrochloric acid, hydrogen exists as ion, chlorine must 
 be the other ion, because this acid contains no other constitu- 
 ents, and this chlorine-ion possesses the same properties ex- 
 hibited by the chlorine-ions of other combinations in which it 
 is contained, hence, in all soluble metallic chlorides. These 
 properties of the chlorine-ion, however, differ entirely from 
 those of chlorine in the ordinary elementary state, it possessing 
 neither its odor nor color ; it exists only in solution and has 
 not the bleaching effect of chlorine gas. 
 
 These totally different properties thus clearly indicate that 
 the ions have to be considered as modifications of the elements 
 designated by the same name, or that the ions have to be 
 thought of as existing in a condition different from the elemen- 
 tary one; and the reason for these different conditions and 
 properties will be more accurately known after we have to 
 some extent become acquainted w T ith the 
 
 Theory of solutions. A solution is not a mere mechanical 
 mixture of an invisible, finely divided solid body with the 
 solvent, but by solution in a solvent a body partially loses its 
 characteristic properties and acquires new ones, and the dis- 
 solving process may be viewed as a chemical pr< c . s in so far 
 as changes of energy (see later on;, for instance, fixation or 
 disengagement of heat, are connected with it. 
 
 There are not only solutions of solid substances in liquids, 
 but also solutions of liquids in liquids, of gases in liquids, and 
 of gases in gases. However, the last-mentioned solutions are 
 of interest to us only in so far as it has been shown that the 
 a which they follow are also valid for solutions of solid 
 bodies in liquids. For the proof of this we are indebted to 
 van't Hoff. 
 
 If a layer of a dilute, pale blue cupric sulphate solution be 
 carefully brought, so as to avoid mixing, upon a concentrated 
 cupric sulphate solution of a vivid blue color, and the v 
 
48 ELECTRO-DEPOSITION OF METALS. 
 
 containing the solutions be allowed to stand quietly, it will be 
 noticed that the pale blue solution gradually acquires a more 
 intense blue color, while the concentrated solution becomes 
 paler. The molecules of the cupric sulphate diffuse from the 
 stronger, into the weaker, solution until the liquid has acquired 
 a uniform concentration. 
 
 This phenomenon is based upon the same law followed by 
 the gases. A gas endeavors, when occasion is offered, to 
 occupy a larger space; the energy of motion (kinetic energy) 
 inherent in the individual gas molecules propels them until 
 their motion is stopped by the walls of the enlarged space. 
 The molecules in the cupric sulphate solution possess a similar 
 energy of motion and by it, as we have seen, are forced from 
 the concentrated, into the weak, solution. This force, which 
 corresponds to the gas pressure, is called 
 
 Osmotic pressure. Its presence can readily be demonstrated 
 by the following experiment. Fill a glass-cylinder with satur- 
 ated sugar solution, close the cylinder air-tight with a semi- 
 permeable bladder, and place it upright in a vessel rilled with 
 water so that the latter stands a few centimeters above the 
 bladder; the bladder bulges up in a short time. This pheno- 
 menon is caused by the effort of the sugar molecules to diffuse 
 into the surrounding water, being, however, prevented from 
 doing so by the bladder, while water molecules penetrate through 
 the bladder into the cylinder. If the cylinder be removed from 
 the water and the bladder be punctured with a pin, the pressure 
 which had existed becomes plainly perceptible by a jet of fluid 
 being forced upward. By exact investigations of the magnitude 
 of osmotic pressure it has been ascertained that it is propor- 
 tioned to the number of molecules dissolved in the unit volume, 
 and that the temperature has the same effect upon osmotic 
 pressure as upon gases, conformity with the laws valid for gases 
 being thus proved. According to Avogadro equal volumes of 
 gaseous substances have under the same conditions of tempera- 
 ture the same number of molecules, and the weights of equal 
 volumes of gaseous substances, i. e., their vapor densities, have 
 the same ratio to each other as their molecular weights. 
 
MAGNETISM AND ELECTRICITY. 49 
 
 Solutions, as has been proved by van't Hoff, follow the same 
 law and, according to van't Hoff, the law applied to them is 
 expressed as follows : Solutions which contain an equal number 
 of dissolved molecules in the same volume of solvent (equimol- 
 ecular solutions) exert, under the same conditions of tempera- 
 ture, the same osmotic pressure which has the same value as the 
 gas-pressure these bodies, if in a gaseous state, would under the 
 same conditions of temperature exert in a volume of gas equal 
 to the volume of solvent. 
 
 It should, however, be borne in mind that the osmotic laws 
 are valid only for dilute solutions, just as the gas-laws hold 
 good only for dilute gases. 
 
 Electrolytic dissociation. Clausius originated the idea that 
 the molecules of an electrolyte are dissociated to molecular 
 particles corresponding to our ions. He supposed that the 
 molecules are in constant motion whereby they are partially 
 decomposed, and that molecular particles formed again attract 
 the molecular particles of opposite names of the non-decom- 
 posed aggregate molecules, and thus effect the dissociation 
 of the latter. On the other hand molecular particles of op- 
 posite names will again form, under favorable conditions, 
 aggregate molecules. However, as soon as a current passes 
 through the electrolyte, the irregular and changing movements 
 of the molecular particles will cease, and they will take the 
 direction presented by the action of the current, i. e., the posi- 
 tive molecular particles will wander with the direction of the 
 current to the cathode, and the negative ones to the anode. 
 
 The method, discovered by Raoult, of determining the mole- 
 cular weights of dissolved bodies from the elevation of the 
 boiling point and the depression of the freezing point, caused, 
 in connection with van't Hoff's osmotic laws, a further investi- 
 gation of the dissociation of electrolytes. It was known that 
 salt solutions possess a higher boiling point than the pure 
 solvent. Further investigations proved the elevation of the 
 boiling point to be proportional to the number of the dissolved 
 molecules, and that equimolecular solutions, i. c, solutions 
 4 
 
50 ELECTRO-DEPOSITION OF METALS. 
 
 which contain an equal number of dissolved molecules in the 
 same volume of solvent, show the same elevation of the boiling 
 point. On the other hand, the freezing point of solutions is 
 lowered in proportion to the dissolved molecules, and equi- 
 molecular solutions show the same depression of the freezing 
 point. 
 
 However, not all substances furnished, in equimolecular solu- 
 tions at the same temperature, the same osmotic pressure as 
 sugar solutions or solutions of other organic bodies. Thus, 
 solutions of acids, bases, and salts yielded too high an osmotic 
 pressure, and also showed deviations in so far that, as compared 
 with equimolecular solutions of many organic substances, they 
 caused under entirely equal conditions, a higher elevation of 
 the boiling point or of the freezing point. Since, as regards 
 gas-pressure, some gases also do not follow Avogadro's law, 
 and these exceptions were explained by assuming that the 
 molecules decompose to molecular particles, the same assump- 
 tion was made for solutions of acids, bases, and salts. 
 
 S. Arrhenius, in 1887, found that all the solutions which 
 formed exceptions to the osmotic law and showed deviating re- 
 sults as regards elevation of the boiling point and depression 
 of the freezing point, possessed the common property of con- 
 ducting the electric current, while solutions of organic bodies 
 which, as above mentioned, followed the laws referred to, were 
 non-conductors of the electric current. Arrhenius ascertained 
 that very considerable exceptions appear for water as solvent, 
 since the pressure is greater than van't Hoff's law requires, and 
 it would therefore be but natural to suppose that substances 
 which give too large pressures in aqueous solutions are dis- 
 sociated. He further found that dissociation increases with 
 increasing dilution, and he established the law that for every 
 dilute solution the ratio of dissociation is equal to the ratio of 
 molecular conductivity present to the conductivity of infinite 
 dilution, i.e. to the maximum of molecular conductivity. The 
 independent particles of the molecules formed are the ions. 
 
 Tt further follows that it is the ions which take charge of the 
 
MAGNETISM AND ELECTRICITY. 5 I 
 
 progressive motion of the current because only ion-forming 
 solutions are capable of conducting the current. The ions are 
 supposed to be charged with a certain quantity of electricity — 
 the kathions with positive, the anions with negative, electricity 
 — and so long as no current passes through the electrolyte, 
 they move free in the latter. However, when a current is con- 
 ducted through the electrolyte, the ions are attracted by the 
 electrodes, the positively charged kathions by the negatively 
 charged cathode, and the negatively charged anions by the 
 positively charged anode. By reason of the movements of the 
 ions to the electrodes this phenomenon is called migration of 
 the ions. 
 
 The ions on reaching the electrodes are freed of their charge, 
 i. e., they yield their electricity to the electrodes, but they lose 
 thereby their ion-nature and are changed into their respective 
 elementary atoms ; they show no longer the properties of ions 
 but those of the ordinary elements. As is well-known the var- 
 ious modifications of carbon (diamond, graphite) are chem- 
 ically alike, namely in all cases carbon, but they have entirely 
 different properties, the latter being conditional on an entirely 
 different content of energy. 
 
 Energy. By energy is understood the work and everything 
 which can be the result from work, and be again converted into 
 work. A distinction is made between various kinds of work. 
 The effect of mechanical work expresses itself through the pro- 
 duct of force and motion, i. e., the force required to convey a 
 body a certain distance. If we push a wagon, the force with 
 which we push against the wagon multiplied by the motion, 
 i. e., the distance the wagon has been pushed, is the value of 
 the work. 
 
 Now a distinction has to be made between, the force with 
 which a man in pushing presses against the wagon, and that 
 with which the wagon presses against the man, who does the 
 pushing. In comparison we speak of both forces as force and 
 counter- force, and physics teaches us that force and counter- 
 force are, in all cases, of the same magnitude, but exerted in 
 
52 ELECTRO-DEPOSITION OF METALS. 
 
 opposite directions. Both these propositions may be com- 
 bined to the proposition of the conservation of force and work, 
 which reads : No quantity of force and no quantity of work are 
 lost ; the force and work consumed are always again met with 
 in another definite form . 
 
 When a wagon has been pushed to a higher point of an 
 oblique plane, it has taken up a certain quantity of work cor- 
 responding to the value from force multiplied by motion in the 
 direction of the force. It possesses a certain energy which it 
 can and does give up when it is released ; the wagon runs 
 down the oblique plane, and the velocity with which it runs 
 down is also a form of energy. 
 
 If an article be ground upon an emery wheel, a certain fric- 
 tional work is performed ; the article becomes warm by friction. 
 Hence the heat which is developed is another form of energy 
 of the frictional work, since according to the law of the conser- 
 vation of work no quantity of work is lost in nature. 
 
 If carbon (C) be burnt in the air, carbonic oxide (C0 2 ) is 
 formed. The law of the conservation of matter teaches us that 
 no substance is lost, and hence the quantity of carbonic acid 
 which has been formed by combustion must be exactly as large 
 as the quantities of carbon and oxygen of the air which existed 
 previous to combustion. The carbon and oxygen of the air 
 prior to their union to carbonic acid possess a quantity of work 
 or energy differing from that after union, the heat generated by 
 the combustion being a manifestation of energy produced in a 
 chemical way. 
 
 Every element has to be thought of as possessing a definite, 
 inherent content of energy which, when the element enters into 
 combination with other elements, may, and generally does, 
 undergo a change. Thus in entering into a combination the 
 elements yield a portion of their content of energy, generally 
 in the form of heat, though sometimes also with luminous 
 phenomena, so that the content of energy in the combination 
 is less than the content of energy of the elements before their 
 union. If now a solution of the combination in water be pre- 
 
MAGNETISM AND ELECTRICITY. 53 
 
 pared, a change in the content of energy again takes place by 
 dissociation, the content of energy present in the combination 
 being partially converted into electrical energy. The ions 
 appearing thereby receive electrical charges — the metal-ions 
 positive charges and the other ions negative charges — and the 
 nature of ions may be characterized by saying, they differ from 
 the elementary atoms of similar names in having a different 
 content of energy. 
 
 Processes on the electrodes. As previously mentioned in the 
 salts all the metal-ions are positive and the other ions of the 
 metal combination — the acid residue — negative. 
 
 The ions arriving at the electrodes possess the power of en- 
 tering into chemical processes with the constituents of the 
 electrolyte or with the electrodes, as may be shown by the fol- 
 lowing examples : 
 
 When a solution of potassium disulphate (K 2 S0 4 ). is electro- 
 lyzed between unassailable platinum electrodes, the following 
 event takes place. The potassium-ions migrate to the cathode 
 and separate metallic potassium, 
 
 Potassium disulphate. 
 
 which, however, as is well known, cannot exist in water, but 
 immediately forms with the solvent potassium hydroxide 
 (caustic potash) according to the following equation: 
 
 2K + 2H 2 = 2KOH + H 2 
 
 Potassium. Water. Caustic potash. Hydrogen. 
 
 That this transposition takes place in the manner described, 
 is shown by the abundance of hydrogen * which escapes in the 
 electrolysis of the potassium disulphate. On the other hand, 
 the acid residue SOi migrates to the anode, which, as it con- 
 sists of insoluble platinum, cannot saturate the acid residue, 
 
 * This explanation is here retained, though based upon potential measurements, it 
 may, according to Le Blanc, be supposed that the hydrogen separates primarily and 
 originates from the hydrogen-ions of the dissociated water of the solution. 
 
54 ELECTRO-DEPOSITION OF METALS. 
 
 and the latter is also transposed with water according to the 
 following equation: 
 
 SO, + H 2 = H 2 S0 4 + O 
 
 Sulphuric acid residue. Water. Sulphuric acid. Oxygen. 
 
 The oxygen escapes, and the sulphuric acid formed combines 
 again to potassium disulphate with the caustic soda formed on 
 the cathode. 
 
 A like liberation of oxygen takes place when very dilute 
 hydrochloric acid * is electrolyzed with platinum anodes. 
 Hydrogen escapes on the cathode, but no chlorine appears on 
 the anode, an equivalent quantity of oxygen being, however, 
 liberated. The water is decomposed by the chlorine, hydrogen 
 chloride and oxygen being formed according to the following 
 equation : 
 
 Cl 2 + 2H„ = 4 HC1 + 2 
 
 Chlorine. Water. Hydrogen chloride. Oxygen. 
 
 The oxygen appearing in both cases, as well as the hydrogen 
 appearing in the first-mentioned example, are called secondary 
 products of electrolysis, because the products first separated 
 under the given conditions could not exist and, in being de- 
 composed or transposed, formed together with the solvent the 
 above-mentioned products. 
 
 When sodium hydroxide (caustic soda) is electrolyzed, 
 hydrogen appears on the cathode, because sodium, like potas- 
 sium in the former example, cannot exist with water, and 
 sodium hydroxide is again formed, hydrogen being at the same 
 time liberated. The hydrogen-ion which also cannot exist by 
 itself, is discharged on the anode, water and oxygen being 
 formed according to the following equation : 
 
 4OH = 2H,0 + 2 
 
 Hydroxide. Water. Oxygen. 
 
 * The process does not pass off as smoothly as represented by the formula, but 
 the example is given as an illustration according to Ostwald's " Grundlinien der 
 ( hemie," I. p. 203. 
 
MAGNETISM AND ELECTRICITY. 55 
 
 Let us now turn to the other cases in which the ions, sepa- 
 rated on the electrodes, enter with the latter into chemical 
 processes. 
 
 A solution of cupric sulphate Cblue vitriol) CuS0 4 is to be 
 electrolyzed. The copper ions migrate to the cathode 
 
 <-Cu 1 so*-> 
 
 Cupric sulphate. 
 
 + 
 
 and deposit their copper in the form of a galvanic deposit, the 
 acid residue — the anion — migrating to the anode. If the latter 
 consists of a soluble metal, for instance, copper, the acid resi- 
 due becomes saturated with copper, dissolving approximately 
 the same quantity of it as has been deposited upon the cathode. 
 Theoretically the quantity dissolved from the anode by the 
 acid residue should exactly correspond to the quantity of metal 
 separated on the cathode. However, in practice, such is not 
 the case, because the acid residue is partly subject to other 
 decompositions, especially the formation of H2SO4, oxygen 
 being at the same time separated. 
 
 All other processes in which metallic anodes capable of solu- 
 tion by the acid residue are used, run their course in a manner 
 similar to the electrolysis of blue vitriol. 
 
 As previously mentioned, secondary products may be liber- 
 ated by electrolysis. The separation of metal on the cathode 
 may also be effected in a secondary manner, and in galvanic 
 processes this is mostly brought about on purpose. Referring 
 to the previously-mentioned example of the electrolysis of blue 
 vitriol, the copper could only be separated in a primary man- 
 ner; by adding, however, a small quantity of sulphuric acid to 
 the blue vitriol solution, separation of copper in a secondary 
 manner takes place. The sulphuric acid being in a diluted 
 state is more strongly dissociated than the blue vitriol solution, 
 the ions of sulphuric acid — hydrogen and acid residue S0 4 — 
 first of all taking charge of the conduction of the current, and 
 the hydrogen-ions separate the copper on the cathode accord- 
 ing to the following equation : 
 
56 ELECTRO-DEPOSITION OF METALS. 
 
 CuSO, + H 2 = Cu + H 2 S0 4 
 
 Cupric sulphate. Hydrogen. Copper. Sulphuric^acid. 
 
 In the electrolysis of a silver bath containing potassium-sil- 
 ver cyanide (KAgCN..,), potassium-ions and silver cyanide-ions 
 (AgCN 2 *) appear: 
 
 (a) — | <£-K | AgCN,-^- | + 
 
 From the solution of potassium-silver cyanide, the potas- 
 sium-ions separate secondarily metallic silver on the cathode, 
 potassium cyanide being formed according to the following 
 equation : 
 
 (b) K + KAgCN 2 Ag + 2KCN. 
 
 Potassium-ion. Potassium stiver cyanide. Silver potassium cyanide. 
 
 The anions AgCN 2 migrate to the anode, are there decom- 
 posed to silver cyanide (AgCN) and cyanogen (CN), the 
 cyanogen ions dissolve from the anode silver, silver cyanide- 
 being formed, and 2 silver cyanide atoms combine with the 
 above (in b~) liberated 2 potassium cyanide, to 2 potassium 
 silver cyanide, atoms: 
 
 (O Ag CN = AgCN 
 
 Silver. Cyanogen. Silver cyanide. 
 
 (d) 2 AgCN + 2KCN 2KAgCN 2 
 
 Silver cyanide. Potassium cyanide. Potassium silver cyanide. 
 
 The quantities of substances separated from the electrolytes 
 by the electric current are subject to fixed laws, which, after 
 their discoverer, are named 
 
 Laws of Faraday. These laws are followed by both the 
 primary, as well as secondary s products of electrolysis, because 
 the latter are produced by primary separations, the secondary 
 being proportional and chemically equivalent to them. The 
 first of these laws is as follows : 
 
 * llittorf, Ostwald's Klassiker, 23, § 45. 
 
MAGNETISM AND ELECTRICITY. 
 
 57 
 
 Fig. 7. 
 
 ' 1 
 
 H 
 
 I 
 
 I 
 
 1 
 
 7$£ quantity of substances which is separated on the electrodes 
 is directly proportional to the strength of the electric current which 
 has been conducted through the electrolytes, and the time. 
 
 By conducting the current through a closed decomposing 
 cell, Fig. 7, filled with acidulated water and furnished with two 
 platinum electrodes which are con- 
 nected with the poles of a source of 
 current, oxygen is evolved on the 
 positive electrode, and hydrogen on 
 the negative electrode. If the gas- 
 mixture (oxyhydrogen gas) which 
 is evolved be caught under water in 
 a graduated tube, the quantity of 
 oxyhydrogen gas produced by a 
 current of fixed strength within a 
 determined time can be readily ascer- 
 tained. If now a current of double 
 the strength be for the same length 
 of time passed through the decom- 
 posing cell, the quantity of oxy- 
 hydrogen gas produced will be found 
 twice as large as in the first case. 
 
 Faraday allowed the same quantity of current to pass through 
 a series of decomposing cells, coupled one after another, which 
 contained electrolytes of different compositions, and determined 
 quantitatively the separations of kathions effected in the various 
 cells by an equal quantity of current. Suppose the first cell to 
 be a water-decomposing cell like Fig. 7, let the second cell 
 contain potassium silver cyanide solution with a slight excess 
 of potassium cyanide, the third cell an acidulated solution of 
 cupric sulphate, and the fourth cell a solution of cuprous 
 chloride in hydrochloric acid. 
 
 When electrolysis has been carried on for half an hour, the 
 current is interrupted, and the quantity of hydrogen calculated 
 from the measured quantity of oxyhydrogen gas produced. 
 The platinum cathodes, the weight of which has been deter- 
 
 
 
s> 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 mined previous to electrolysis, are rinsed in water, next in alco- 
 hol, and finally in ether. They are then thoroughly dried and 
 again weighed to determine the quantities of metal separated 
 in the individual cells. The following quantities were found : 
 
 Electrolyte. 
 
 Quantity of sepa- f 
 rated kathions. . \ 
 
 For i mg. H are 
 separated 
 
 I. 
 
 Dilute 
 
 sulphuric acid 
 
 i: I 5 . 
 
 67 ccm. H = 
 6.00 mg. H 
 
 1 mg. H 
 
 Atomic weights 
 
 II. 
 
 Potassium 
 
 silver cyanide 
 
 KAgCy 2 . 
 
 650 mg. Ag. 
 
 108.33 ni g- Ag. 
 108 
 
 III. 
 
 Cupric 
 sulphate 
 CuS0 4 . 
 
 IV. 
 
 Cuprous 
 
 chloride 
 
 CuCl. 
 
 190 mg. Cu 1 380 mg. Cu 
 
 31.66 mg. Cu 63.3 mg. Cu 
 63-3 63.3 
 
 From this it follows that the separated quantities of kathions, 
 referred to one part by weight of hydrogen, represent almost 
 exactly the quantities of metals which correspond to a single 
 valence of their atomic weights. In the electrolytes II and IV, 
 the silver atoms and copper atoms are univalent, and in elec- 
 trolyte III, bivalent. Hence, in II and IV were separated the 
 quantities of metal, 108.33 m g- silver (error in per cent. 0.33) 
 and 63.3 mg. copper, which corresponds to the univalence of 
 the atoms, and in III only a valence amounting to 31.56 mg. 
 copper which corresponds to the bivalence of the copper atoms 
 in cupric sulphate. 
 
 Hence the second law of Faraday, as expressed by v. Helm- 
 holtz, reads as follows: The same quantity of current liberates 
 in the different electrolytes an equal number of valences or con- 
 verts them into other combinations. 
 
 It has previously been mentioned that for the development 
 of 1 g. hydrogen, 96540 coulombs must pass through the elec- 
 trolyte. According to determinations by F. and W. Kohl- 
 rausch, 0.3290 mg. copper is liberated from cupric salts by a 
 quantity of 1 coulomb, or 31.65 g. by 96540 coulombs. This 
 quantity of current is the 
 
MAGNETISM AND ELECTRICITY. 59 
 
 Electro-chemical equivalent, i. e., the number of coulombs 
 which split off in one second the portion of atomic weights of 
 the kathions (metals) or of the anions referred to a valence 
 and expressed in grammes, i. e., the gramme-equivalent. 
 Hence, for the separation of I gramme-equivalent of copper = 
 31.65, or of 1 gramme-equivalent of silver = 108, 96540 coul- 
 ombs are always required. 
 
 From the laws of Faraday results the view previously re- 
 ferred to, that the passage of the current through the electro- 
 lyte is confined to the simultaneous movement of the ions, and 
 that no current can pass through the electrolyte if the ions be 
 wanting. Hence the ions of the electrolyte are charged or 
 combined with specified quantities of electricity, and one por- 
 tion of Faraday's law may, according to Ostwald, be thus 
 expressed : The quantities of the different ions combined with 
 equal quantities of electricity are proportional to the combining 
 weights of these ions, and the entire law may be summed up as 
 follows : In the electrolytes the electricity moves only simulta- 
 neously with the constituents of the electrolytes which are the 
 ions. The moved quantities of electricity are proportional to the 
 quantities of ions, and amount to 96540 coulombs, or a multiple 
 of them, for one molecule of any one ion. 
 
 Below is given a table of the electro-chemical equivalents, 
 and from them will be calculated, in the practical part of the 
 work, the time required for the formation of deposits of a cer- 
 tain specified weight, the current-strength required for the 
 purpose, etc. The specific gravities of metals, which are also 
 required for the above-mentioned calculations, have been added 
 to the table. 
 
oo 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Hydrogen 
 
 Antimony 
 
 Arsenic • 
 
 Cobalt 
 
 Copper from cupric salts 
 Copper from cuprous salts 
 
 Gold from auric salts 
 
 Gold from aurous salts . . 
 Iron from ferric salts. 
 Iron from ferrous salts . . 
 
 Lead 
 
 Nickel 
 
 Platinum, 
 
 Silver 
 
 Tin from stannic salts.. 
 Tin from stannous salts. . . 
 Zinc 
 
 Electro-chemical 
 Equivalent. 
 
 0.104 
 0.415 
 0.258 
 0.305 
 0.329 
 0.658 
 0.681 
 2.043 
 0.193 
 0.289 
 I.071 
 0.304 
 0.504 
 1.1 iS 
 0.308 
 0.616 
 °-339 
 
 Deposit in 
 1 Ampere-hour. 
 
 °-°375 
 1.4940 
 0.9322 
 1 . 1 co 1 
 1.1858 
 2 -37 '7 
 2 -45 x 3 
 
 7-35 6 ° 
 0.6950 
 1.0423 
 3.8580 
 1.0945 
 1.8160 
 4.0248 
 1.1004 
 2.2180 
 1.2200 
 
 Specific 
 Gravity. 
 
 0.COC09 
 6.8 
 
 5-7 
 
 8.7 
 
 8.8 
 
 8.8 
 19.2 
 19.2 
 
 7.8 
 
 7.8 
 
 "•3 
 
 86 
 21.4 
 10.5 
 
 7-3 
 
 7-3 
 
 7.2 
 
 Solution-pressure of metals. A fluid evaporates on its surface 
 until the vapor-pressure produced is equal to the evaporation- 
 pressure of the fluid. Analogous to this process a salt dissolves 
 in water until the osmotic pressure of the solution balances the 
 effort of the salt to pass into solution, i. e., its solution-pressure. 
 According to Nernst, every metal, when immersed in an elec- 
 trolyte, also possesses the power conditional to its chemical 
 nature to send metal atoms as ions (kathions) into solution, 
 and this power is called solution-pressure. 
 
 The solution-pressure is the greater the smaller the number 
 of kathions which are already present in the electrolyte ; if, on 
 the other hand, the electrolyte contains a great number of 
 kathions derived from the dissociation of the salt, the osmotic 
 pressure may overbalance the solution-pressure, or the osmotic 
 pressure may be equal to the solution pressure. 
 
 In the first case, when the solution-pressure preponderates, 
 the metal will send into solution kathions charged with positive 
 electricity, while an equally large quantity of negative electricity 
 remains in the metal. Suppose zinc dipping in water, then the 
 zinc-ions passing into solution will be charged with positive 
 
MAGNETISM AND ELECTRICITY. 6 1 
 
 electricity, while the metal is charged with an equally large 
 quantity of negative electricity. 
 
 If the water be replaced by a solution of zinc sulphate (white 
 vitriol) which, in consequence of dissociation, already contains 
 a larger number of positive zinc-ions and negative acid-residue- 
 ions, additional positive zinc-ions will be sent into solution by 
 the zinc so long as the solution-pressure of the zinc over- 
 balances the osmotic pressure of the dissolved zinc-ions. When 
 an equilibrium between osmotic pressure and solution-pressure 
 is reached, the further formation of zinc-ions ceases. 
 
 If the more electro-negative copper be dipped in water it 
 also makes an effort to ionize, i. e., to send into solution copper- 
 ions charged with positive electricity. If, however, the water 
 be replaced by cupric sulphate solution, it happens that the 
 osmotic pressure of copper-ions formed by dissociation of the 
 electrolyte is greater than the solution-pressure of the copper, 
 and hence not only counteracts the formation of new copper- 
 ions, but carries positive copper-ions from the electrolyte to 
 the copper, the latter receiving thereby a positive charge, while 
 the fluid surrounding the copper becomes negative. 
 
 However, no matter whether the solution-pressure may 
 considerably overbalance the osmotic pressure, by the mere 
 dipping of the metal in the electrolyte the quantity of ions 
 which are newly formed will always be small, because by rea- 
 son of the electrostatic attraction of the kathions by the nega- 
 tively-charged metal, there will take place on the contact- 
 surface between the metal and the electrolyte an accumulation 
 of kathions, the osmotic pressure of which will consequently be 
 increased, and counteract the solution-pressure. The latter 
 can only become again active, when the free electricities are 
 conducted away by a closed circuit, as will be explained in the 
 next section. 
 
 Osmotic theory of the production of the current, according to 
 Nernst. The behavior of zinc in a zinc sulphate solution, and 
 that of copper in a cupric sulphate solution, has above been 
 referred to. If a cell be put together of zinc dipping in zinc 
 
62 ELECTRO-DEPOSITION OF METALS. 
 
 sulphate solution, and copper in cupric sulphate solution, such 
 as a Daniel cell, in which the two solutions are separated by 
 a porous partition, called a diaphragm, the following processes 
 take place : 
 
 From the zinc, positive zinc-ions pass into solution so long 
 as the, at first, slighter osmotic, pressure of the electrolyte 
 balances the solution-pressure ; the zinc becomes negatively 
 electric and the electrolyte positively electric on the contact- 
 surface. By the preponderance of the osmotic pressure of the 
 copper sulphate solution over the solution-pressure of the 
 copper, positive copper-ions are separated on the copper, and 
 yield their positive charges to the latter. They themselves are 
 transformed from the ion state into the molecular state, thus 
 becoming non-electric, while on the contact-surface the cupric 
 sulphate solution becomes negatively electric. Hence a state 
 of rest supervenes, in which the zinc is charged with negative, 
 and the copper with positive, electricity, while the zinc solution 
 is charged positively and the copper solution negatively. If 
 now by means of a metallic wire the zinc be outside of the solu- 
 tions Connected with the copper, thus, establishing a closed cir- 
 cuit, the following process takes place : The positive electricity 
 in the copper migrates through the wire to the zinc, and neu- 
 tralizes the quantity of negative electricity present in the latter. 
 By the flow of positive electricity from the copper the state of 
 equilibrium, which existed between copper and cupric sulphate, 
 is disturbed, and the osmotic power being now predominant, 
 the solution again sends copper-ions to the copper, whereby 
 the latter is again charged with positive electricity. On the 
 other hand, after the exchange of electricities in the zinc by the 
 solution-pressure, fresh zinc-ions can be brought into solution. 
 Thus a current flows continuously from copper to zinc until 
 either no more copper-ions are conveyed from the cupric sul- 
 phate solution to the copper, or until all the zinc is ionized, 
 i. e., dissolved. 
 
 Nernst's conception of the solution-pressure of the metals is 
 analogous to that of the osmotic pressure, the impelling force 
 
MAGNETISM AND ELECTRICITY. 63 
 
 of a Daniell battery having the character of a pressure, and for 
 that reason Ostvvald designates a galvanic battery as a machine 
 driven by osmotic pressure, eventually by electrolytic solu- 
 tion-pressure. 
 
 The electro-motive force of such a cell is mainly determined 
 by the magnitude of the solution-pressure of the metals. In 
 the closed cell the metal sends with greater solution-pres- 
 sure its atoms as ions into the electrolyte in which it is con- 
 fined, while the kathions of the other electrolyte are discharged 
 on the metal contiguous to it and pass into the molecule state. 
 By this, the dissolving metal, to which the anions of the other 
 electrolyte — the acid residue — migrate, becomes the anode, 
 and the other metal on which the kathions of its electrolyte 
 separate non-electrically, the cathode. Since the kathions are 
 discharged on the cathode, the latter is also called the conduct- 
 ing electrode, and the anode which dissolves, the dissolving 
 electrode. 
 
 From what has been said, it might appear that the current 
 in a Daniell cell owes its existence to purely physical forces. 
 The solution-pressure of the metals depends, however, on their 
 chemical affinity, and the current is actually electric energy 
 which has been formed from chemical energy. The solution 
 of the anode-metal is a chemical process, whereby the kathions 
 are forced from the electrolyte surrounding the anode; the 
 anode-metal endeavors to expand, and hence the mode of 
 action of chemical affinity in converting chemical into electric 
 energy may be designated as the effect of pressure. 
 
 However, additional chemical processes take place in the 
 Daniell cell; the zinc dissolves to zinc sulphate because the 
 anions of the cupric sulphate solution migrate to the zinc, while 
 from this solution a quantity of copper equivalent to the dis- 
 solved zinc is deposited on the cathode. By the anion SO* of 
 the cupric sulphate solution an oxidation of the zinc takes 
 place, the latter acting therefore as a reducing agent. The 
 cupric sulphate solution, on the other hand, is reduced to 
 copper, and the acid-residue S0 4 being liberated thereby acts 
 
64 ELECTRO-DEPOSITION OF METALS. 
 
 as an oxidizing agent, while the copper of the cathode remains 
 chemically unchanged. Since, according to Ostwald, in every 
 chemical process which takes place between an oxidizing and 
 a reducing agent, variations appear in the ion charges by 
 reason of the varying capacities of the ions to absorb or dis- 
 charge more quantities of electricity, such cells are also called 
 oxidising and reducing cells. Concentration cells will later on 
 be referred to. 
 
 Polarization. By polarization is understood the appearance 
 of a counter-current passing in a direction opposite that of the 
 current conducted into an electrolyte ; the main current is 
 therefore weakened by this counter- current. Polarization takes 
 place when the current produces substantial changes in the 
 electrolytes or on the electrodes, no matter whether such 
 changes consist in a difference of the nascent concentrations 
 of the electrolyte, or in the formation of gas cells by the separa- 
 tion of layers of gas on the electrodes, etc. 
 
 If a weak current be conducted into a cell filled with stand- 
 ard cupric sulphate solution, both electrodes of which consist 
 of copper, and a galvanometer be placed in the circuit, it will 
 be noticed that an electrolytic decomposition takes place. The 
 copper-ions discharged from the copper solution on the elec- 
 trode connected with the negative pole of the source of current, 
 pass into the molecular state, and metallic copper separates 
 upon this electrode, while the anions of the acid-residue S0 4 
 migrate to the electrode connected with the positive pole, 
 where they dissolve copper, thus sending fresh copper-ions 
 into the solution. Hence the concentration of the electrolyte 
 remains constant, provided electrolysis lasts not too long, and 
 the current introduced is not stronger than just necessary for 
 the decomposition of the cupric sulphate solution; the nature 
 of the electrodes themselves remains unchanged. The needle 
 of the galvanometer makes one deflection and when the cur- 
 rent is interrupted returns to the O point, thus indicating the 
 absence of a counter-current ; the electrodes have proved them- 
 selves as non-polarizable. 
 
MAGNETISM AND ELECTRICITY. 65 
 
 However, the case is different when an electrolyte is electro- 
 lyzed between insoluble electrodes. If a powerful current be 
 conducted through a platinum anode into standard sulphuric 
 acid (H 2 S0 4 ), the latter is decomposed into hydrogen-ions 
 which go to the platinum cathode while the SCVions migrate 
 to the anode. As previously mentioned, the S0 4 -ions cannot 
 exist in a free state, neither can they dissolve platinum and, 
 while water is decomposed, sulphuric acid and oxygen-gas are 
 again formed, the latter being separated on the platinum anode. 
 The hydrogen separated on the cathode is electro-positive 
 towards the oxygen separated on the anode, the consequence 
 being that from the hydrogen of the cathode a counter-current 
 flows to the oxygen of the anode, which is indicated when the 
 primary current is interrupted by the needle of the galvano- 
 meter, instead of merely returning to the O point, deflecting in 
 a direction opposite to that of the previous deflection, and re- 
 turning to the O point only after the equalization of the charges 
 in the electrodes. 
 
 The counter-current or polarization-current appears also 
 when two different metals dip in one electrolyte. In a Volta 
 cup cell, a zinc plate and a copper plate connected by a metal- 
 lic wire dip in dilute sulphuric acid. A current flows from the 
 copper through the wire to the zinc, and returns from the zinc 
 through the acid to the copper, decomposing thereby the acid 
 into hydrogen and S0 4 . The hydrogen separates on the cop- 
 per, the acid-residue S0 4 on the zinc, and dissolves the latter, 
 zinc sulphate being formed. The separated hydrogen being 
 electro-positive towards the separated acid-residue, a current 
 in the direction from the copper to the zinc is generated, and 
 consequently flows in a direction opposite to that of the main 
 current, which passes from the zinc to the copper. The elec- 
 tro-motive force of the main current is thus decreased by the 
 magnitude corresponding to the electro-motive force of this 
 counter current. 
 
 If a zinc chloride solution be electrolyzed between two plati- 
 num electrodes, zinc separates on the cathode while chlorine 
 5 
 
66 ELECTRO-DEPOSITION OF METALS. 
 
 appears on the anode. If the current be interrupted, a galvano- 
 scope placed on the electrodes indicates a vigorous counter- 
 current which turns from the zinc deposit — hence the cathode 
 —to the anode, therefore opposite to the current at first sup- 
 plied. This counter-current originates from the tendency of 
 the substances separated on the electrodes to return, in conse- 
 quence of the solution-pressure, to the ion state, and this ten- 
 dency exists during the entire process of the electrolysis. 
 
 The farther the metals in the series of electro-motive force 
 are distant from each other, the greater the electro-motive 
 force which the polarization- current possesses, as will be more 
 particularly shown in the practical part of this work. 
 
 Decomposition-pressure. An electric current can only pass 
 through an electrolyte and decompose it, when its electro- 
 motive force possesses a certain minimum magnitude. The 
 characteristic values at which the electrolytes are perma- 
 nently decomposed are designated, according to Le Blanc, 
 as their decomposition-values ; the decomposition-pressure being 
 the electro-motive force required for the separation of the 
 electric charge of the ions. The decomposition-values of solu- 
 tions which separate metals vary. Le Blanc found as decom- 
 position-values of solutions which contained per liter one com- 
 bining weight of the metallic salts, for 
 
 Zinc sulphate, 2.35 volt; Cadmium sulphate, 2.03 volt. 
 
 Nickel sulphate, 2.09 volt; Cadmium chloride, 1.88 volt. 
 "Nickel chloride, 1.85 volt; Cobaltous sulphate, 1.92 volt. 
 
 Silver nitrate, 0.70 volt; Cobaltous chloride, 1.78 volt. 
 
 The difference in the decomposing values of metallic salt 
 solutions explains the feasibility of separating from a solution 
 which contains different metals, the individual metals, one after 
 the other, free from other admixtures. 
 
 Velocity of ions. It has previously been shown that no 
 polarization-current is generated when a cupric sulphate solu-^ 
 tion is for a short time electrolyzed between copper-electrodes. 
 If, however, not too strong a current be for a longer time 
 passed through the solution, a polarization-current appears, 
 
MAGNETISM AND ELECTRICITY. 67 
 
 the origin of which must be due to another cause than the 
 formation of a gas cell, because no gases are separated with 
 not too strong a current. It has been shown that changes of 
 concentration take place in the solution, concentration becom- 
 ing greater on the cathode and less on the anode. These 
 changes in concentration have been subjected to a thorough 
 investigation by Hittorf, and it was found that the former view, 
 according to which the number of positive and negative ions 
 which migrate in opposite directions through an electrolyte, 
 must be equal, was an erroneous one. The mobility of the 
 ions varies, and depends on their nature. If, for instance, 
 hydrochloric acid be electrolyzed, the hydrogen-ion migrates 
 about five times as rapidly to the cathode as the chlorine-ion 
 to the anode. The kathions and anions of the metallic salts 
 act in a similar manner, and consequently a greater concen- 
 tration will take place on the cathode and a reduction in the 
 content of metal on the anode, when the anions migrate more 
 slowly than the kathions ; and vice versa, concentration will 
 increase on the anode when the anions migrate more rapidly 
 than the kathions. 
 
 The middle layer of the electrolyte always remains un- 
 changed and of the same concentration, the changes in concen- 
 tration being shown in the layers of fluid surrounding the 
 electrodes, and these differences in concentration also effect 
 the formation of a current, which, according to the nature of 
 the electrodes may flow in the sense of the main current or in 
 that of the counter-current. 
 
 The quotients obtained by dividing the distances, which the 
 kathions and anions perform in the same time, by the total dis- 
 tance of the road traveled by the two ions, Hittorf designates 
 as the transport-values of the respective ions. 
 
 We herewith conclude the theoretical considerations, and 
 will later on have occasion to touch upon other fundamental 
 electrolytical principles of less importance. 
 
III. 
 
 SOURCES OF CURRENT. 
 
 CHAPTER III. 
 
 VOLTAIC CELLS, THERMO- PILES, DYNAMO-ELECTRIC 
 MACHINES, ACCUMULATORS. 
 
 The sources of current which are used for the electro- 
 deposition of metals are : Voltaic cells, thermo-piles, dynamo- 
 electric machines, and accumulators. 
 
 A. Voltaic Cells. 
 
 It is not within the province of this work to enter into a de- 
 tailed description of all the forms of voltaic cells, because the 
 number of such constructions is very large, and the number of 
 those which have been successfully and permanently intro- 
 duced for practical work is comparatively small. 
 
 In the theoretical part, we have learned the origin of the 
 current and the explanation of its origin by the solution-pres- 
 sure of the metals or the osmotic pressure of the solutions, and 
 we know further that in a voltaic cell chemical energy is con- 
 verted into electrical energy. In speaking of polarization which 
 is formed when two different metals dip in one fluid, we have 
 seen that the hydrogen separated on the copper in a Volta cup 
 cell generates a counter-current which weakens the principal 
 current. This hydrogen appearing on the positive pole is the 
 cause of a rapid decrease in the efficiency of the cell, and all cells 
 in which the hydrogen on the cathode is not neutralized by 
 suitable means, are called inconstant cells, while cells in which 
 the hydrogen is removed in a physical way or by chemical 
 agents which oxidize it, are called constant cells. 
 
 (68) 
 
SOURCES OF CURRENT. 69 
 
 The original form of voltaic cells, the voltaic pile, consisting 
 of zinc and copper plates separated from one another by moist 
 pieces of cloth, has already been mentioned on p. 2, as well as 
 its disadvantages, which led to the construction of the so-called 
 trozigh battery. The separate elements of this battery are 
 square plates of copper and zinc, soldered together, and 
 parallel, fixed into water-tight grooves in the sides of a wooden 
 trough so as to constitute water-tight partitions, which are filled 
 with acidulated water. The layer of water serves here as a 
 substitute for the moist pieces of cloth in the voltaic pile. 
 
 In other constructions the fluid is in different vessels, each 
 vessel containing a zinc and a copper plate which do not touch 
 one another, the copper plate of the one vessel being con- 
 nected with the zinc plate of the next, and so on. 
 
 In all cells with one exciting fluid, the current is quite strong 
 at first, but decreases rapidly for the reasons given above. On 
 the one hand, during the interruption of the current a change 
 takes place in the fluid by the local effect in the cell, and, on 
 the other, the zinc forms with the impurities contained in it, 
 small voltaic piles with a closed circuit, in consequence of which 
 the cell performs a certain chemical work even when the current 
 is interrupted. The local action can be reduced to a minimum 
 by amalgamating the zinc. Such amalgamation is also a pro- 
 tection against the above-mentioned chemical work of the cell, 
 the hydrogen bubbles adhering so firmly during the interrup- 
 tion of the current to the amalgamated homogeneous surface 
 as to form a layer of gas around the zinc surface by which its 
 contact with the fluid is prevented. 
 
 Amalgamation may be effected in various ways. The zinc is 
 either scoured with coarse sand moistened with dilute sulphuric 
 or hydrochloric acid, or pickled in a vessel containing either of 
 the dilute acids. The mercury may be either mixed with moist 
 sand and a few drops of dilute sulphuric acid, and the zinc be 
 amalgamated by applying the mixture by means of a wisp of 
 straw or a piece of cloth ; or the mercury may be applied by 
 itself by means of a steel wire brush, the brush being dipped in 
 
11 EC rRO-DEPOSI riON OF META1 s. 
 
 the mercury, and what adheres is quickly distributed upon the 
 zinc by brushing until the entire surface acquires a mirror-like 
 appearance. The most convenient mode of amalgamation is 
 to dip the zinc in .1 suitable solution of mercury salt and rub 
 with a woolen rag. A suitable solution is prepared by dissolv- 
 ing 10 parts by weight of mereurous nitrate in [00 parts of 
 warm water, to which pure nitric acid is added until the milky 
 turbidity disappears. Another solution, which is also highly 
 recommended, is obtained by dissolving 10 parts by weight of 
 mercuric chloride (corrosive sublimate) in i_ parts of hydro- 
 chloric aeid and 100 of water, or by dissolving 10 parts by 
 weight of potassium mercuric cyanide and 2 parts potassium 
 cyanide in [00 parts of water. In order to preserve as much 
 as possible the coating of mercury upon the zinc, sulphuric 
 aeid saturated with neutral mercuric sulphate is used for the 
 cells. For this purpose frequent!}' shake the concentrated 
 sulphuric aeid (before diluting with water) with the mercury 
 salt. As much mercuric sulphate or mercuric chloride as will 
 lie upon the point of a knife may also be added in the cells to 
 the zinc. 
 
 Instead ot the addition of mercuric sulphate, Bouant recom- 
 mends to compound the dilute sulphuric aeid with J per cent. 
 ot a solution obtained as follows: Boil .1 solution ot ; ( _- ozs. of 
 nitrate of mercury in 1 quart of water, together with an excess 
 ot a mixture of equal parts of mercuric sulphate and mercuric 
 chloride, and, after cooling, filter and use the clear solution. 
 
 S ... ell. Proceeding from the conviction that rough surfaces 
 allow the bubbles of hydrogen to pass off much more freely than 
 smooth surfaces, Smee constructed the cell named after him. It 
 sts of a zinc plate and a platinized silver plate dipping into 
 dilute acid. It may be formed of two zinc plates mounted with 
 the platinized silver between them in a wooden frame, which 
 being a very feeble conductor may carry away a minute fraction 
 of the current, but serves to hold the metals in position, so that 
 quite a thin sheet ot silver may be employed without fear of its 
 bending out of shape and making a short circuit. The platiniz- 
 
SOURCES OF CURRENT 
 
 71 
 
 ing is effected by suspending the silver plates in a vessel filled 
 with acidulated water, adding some chloride of platinum, and 
 placing the vessel in a porous clay cell filled with acidulated 
 water and containing a piece of zinc, the latter being connected 
 with the silver plates by copper wire. The platinum coating 
 obtained in this manner is a black powder which roughens the 
 surfaces, in consequence of which the bubbles of hydrogen 
 become readily detached, and polarization is less than with 
 silver plates not platinized. The use of electrolytically-pre- 
 pared copper plates, which are first strongly silvered and then 
 platinized, is still more advantageous on account of their 
 greater roughness. To increase the constancy of the cell, it is 
 advisable to add some chloride of platinum to the dilute acid 
 of the element. 
 
 The Smee cell is still frequently used in England and in the 
 United States, especially in processes for which at first a higher 
 current-strength is required, whilst later one of less inten- 
 sity suffices, or is even necessary, as, for instance, in silvering. 
 Its electro-motive force is about 0.48 volt. 
 
 As previously mentioned, polarization can 
 be entirely avoided only by allowing the 
 electro-negative pole-plate to dip in a fluid 
 which, by combustion, reduces the hydro- 
 gen evolved to water, or, in other words, 
 which immediately oxidizes the hydrogen 
 to water. From this conviction originated 
 the so-called constant cells with two fluids, 
 the first of these cells being, in 1829, con- 
 structed by Becquerel, which, in 1836, was 
 succeeded by the more effective one of Daniell. 
 
 Daniell cell. In its most usual form Daniell's cell (Fig. 8) 
 consists of a glass vessel, a copper cylinder, a porous clay cup 
 and a zinc rod suspended in the latter. The glass vessel is filled 
 with concentrated blue vitriol solution, a small piece of blue 
 vitriol being added, and the porous clay cup with dilute 
 sulphuric acid. The acid residue SO* migrates to the electro- 
 
 Fig. X. 
 
.-•• ION N : :'M S, 
 
 .'.• . . \ .• •. -. .- w hile the h\ dh ogen, 
 
 which ■ ■ es on the electro ■- . •■. \ i ■ > .• ■ -. > . noes from 
 
 . ■ . \ c>l solution an ,-.- , \ - . - . . ■ • . \ . . opper, \> 
 
 ..-.'.. »on the eleetro-neg . . . c« . -.; to the 
 
 I "^ 
 
 • - the h\ - : -• ;-• • •• e no\ -•. >\ •• - • .; v\ th the 
 
 ... . -^ N to - . i . . V drawback o the D i . 
 
 he >'. e * . -■' ••-- ..-•-. . ■ .■ • • ..- : te >e i ■• 
 • where i •■ . e\ o " »oset h\ the u i>n eoro •.; t eon ict 
 heeop -• - --■ • - . • • he tc, thee de icj 
 
 .- o ee ot the ' ■ • - ee - q ■ .-' exact ly n \ oh 
 '. ' • - ■■ t\ ><£ ..-■-.. .v ■■.'. . . Dani< 
 
 lake the t . - • . has to 
 
 oats partition* the w \ ture . the ' . •• 
 
 •. ■.; . . . •• the . ..-.-•.. . 
 ties Che sb •.- .- . '.- Men .. 
 - ••.--. .;-• ■. seeL is shown 
 
 p 
 [ ■■■.-.' •-.-■.- a glass , esse] . I 
 ..-..-. . ■ - . stands j 
 
 - •■ • .. ss e> • itch contains th< 
 
 ... . . e copper e; 
 
 . • . ig . - to t '. 
 
 . \ . - Cpon the she .te . ests 
 
 *c e> icta itch is also pre 
 
 ^ to the ex 
 Che v .--■ • r closes the 
 ■ • . fhe balloon is eel ■ q . ces o 
 .- e Kps - - ■ -• • fhe entire ce 
 
 Kpsom s - ' ■ som s ..... 
 
 n>n O concent - mi of blue vttrie -.-■-:.- 
 
SOURCES Of '.'.J-)-;. /: 
 
 dosed, th< concentrated copper solution remains quietly 
 ing in £, its greatei specific gravity preventing il from 
 higher and reaching the /inc. if, however, tin i irrent be 
 closed, /-ii)'. ■ ■ clved, while metallic coppei eparated 
 from the blu< vitriol solution, and concentrate! -- I o 
 from the balloon £ to the sam< extenf as the bl u •■ trio 
 tion in 2? becomes dilute by th< separation of coppei H 
 the action of the cell remain co foi q to • long 
 
 and of all the modified forms of Danieirs cell co 
 
 , - vitriol for a determined quantity of currcnf How 
 ever, in consequ< nc< of if greal info ■ I n ce'(3 to 5 
 
 ohms, according to its size) its currcnf strength The 
 
 electro motive for< 1 of - cell is 95 
 
 Grove cell. Grov< in 1839 . d plai - foi coj 1 
 
 The platinum dips in concentrate* trie acu c the zin< 
 
 ds in dilute sulph c acid 'J he :.>•■ 
 
 • on the p ; oxidki d to 
 
 ous acid escaping the form of gas '1 h< 1 
 motive for'.': of the Grove cell do >le that < 
 
 Daniel) cell, but it soon abafo s on ac< of 1 d tioi 
 nitric acid by m ter 'J prevenf I con* 
 
 sulphuric a< d, rhich absorbs the ei -. - 
 
 tion of the hydrogen, may be added to 1 caci< 1 
 
 the resistance of tin G . re a 11 (0,5 c 
 
 electro-motive force j.70 to 1.90 volf >r< ;; to I - coj 
 
 centration of th< sol tions, it is b I • don '■ accc 
 * costliness. 
 
 Bunsen cell. Hansen, in j^4', ■" ■.■■/■■■ ■ 
 num by prisms cut from gas carboi hicl 5 still Jess el< trc 
 
 live than platinum an< am ol - thaf 
 
 rectly resists the a< 01 of the nitric acid. Jn plaa 
 gas-carbon an artificial carbon may-,- prepared by leneat g 
 a mixture of pulverized cos and cola ■.'■■. gat 1 en or 
 syrup, bringing the mass under pressure itc i iron 
 
 moulds and heating it red-hot, tin • r . ngexc 
 cooling the carboi a© ; ate< ths grarsolutioi 
 
74 ELECTRO-DEPOSITION OF METALS. 
 
 use tar, or a mixture of tar and glycerine) and again heated, 
 the air being excluded. These operations are, if necessary, 
 repeated once more, especially when great demands are made 
 on the electro-motive force and solidity of the artificial carbons. 
 In the Bunsen cell the zinc electrode dips in dilute sulphuric 
 acid and the carbon in concentrated nitric acid. Independent 
 of the fact that by reason of its rough surface, the carbon has 
 by itself the tendency to repel the hydrogen-bubbles and thus 
 acts to a certain degree as a depolarizer, depolarization, i. e. v 
 the removal of the hydrogen-bubbles which produce polariza- 
 tion's most effectively assisted by the nitric acid, the hydrogen 
 being oxidized to water according to the following equation, 
 while the nitric acid is reduced to nitric oxide : 
 
 2HNO3 + 6H 2NO + . 4TLO 
 
 Nitric acid. Hydrogen. Nitric oxide. Water. 
 
 The processes which take place in the Bunsen cell are as 
 follows : From the positive carbon a current passes through the 
 wire to the zinc and returns from the latter through the dilute 
 sulphuric acid to the carbon. The sulphuric acid (H 2 S0 4 ) 
 is thereby decomposed to hydrogen and sulphuric acid residue 
 S0 4 . the hydrogen migrating to the carbon and is oxidized to 
 water by the nitric acid, while the sulphuric acid residue mi- 
 grates to the zinc and combines with it to zinc sulphate (ZnS0 4 ) 
 as illustrated by the following scheme : 
 
 Sulphuric acid | Nitric acid 
 -> 
 
 H,S0 4 I 2HN0 3 
 
 Carbon 
 
 ( + )C 
 
 /.n SO, (Zinc sulphate) 2H NO s (Nitric acid) H 2 (Hydrogen) 
 
 \ 
 
 NA +2H a 
 
 Nitrogen tetroxide Water. 
 
SOURCES OF CURRENT. 
 
 75 
 
 To prevent the two fluids from mixing, the use of a porous 
 partition is required, the same as in Daniell's cell. 
 
 Figs. 10, ii and 12 show three forms of Bunsen's cell gen- 
 erally used. 
 
 Fig. 11 is the most convenient and practical form. It con- 
 sists of an outer vessel of glass or earthenware. In this is 
 placed a cylinder of zinc in which stands a porous clay cup, 
 and in the latter the prism of gas-carbon. This substance is 
 the graphite of the gas retorts. It is not coke. It is easily 
 procurable in lump at a small price, but costs much more when 
 cut into plates, as, when the material is good, it is exceedingly 
 
 Fig. 10. 
 
 Fig. 11. 
 
 Fig. 12. 
 
 difficult to work. It is generally cut with a thin strip of iron 
 and watered silver-sand. Blocks for Bunsen cells cost less be- 
 cause they are more easily produced. Rods for Bunsen cells 
 should be a few inches longer than the pots to protect the top 
 from contact with the acid. A good carbon is of a clear gray 
 appearance, has a finely granulated surface, and is very hard. 
 A band of copper is soldered or secured by means of a binding- 
 screw to the zinc cylinder, while the prism of gas carbon carries 
 the binding- screw (armature), as seen in Fig. 10 in the upper 
 part of which a copper sheet or wire is fixed for the transmis- 
 sion of the current. The other vessel is filled with dilute sul- 
 phuric acid (1 part by weight of sulphuric acid of 66° Be. — 
 
7 6 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 free from arsenic — and 15 parts by weight of water), and the 
 porous cup with concentrated nitric acid of at least 36 Be., or 
 still better 40 Be., care being had that both fluids have the 
 same level. 
 
 In Fig. 1 1 the cylinder of artificial carbon is in the glass 
 vessel, while the zinc, which, in order to increase its surface, 
 has a star-shaped cross-section, is placed in the porous clay cup. 
 In this case the outer vessel is filled with concentrated nitric 
 acid, and the clay cell with dilute sulphuric acid. 
 
 The form of the Bunsen cell shown in Fig. 10 is more ad- 
 vantageous, because its effective zinc surface can be kept larger. 
 
 Fig. 12 shows a plate cell such as is chiefly used for plunge 
 batteries. 
 
 Fig. 13 shows an improved Bunsen cell of great power for 
 
 Fig. i ;. 
 
 rj:,'.'Vi iu/ ' "T^^-- .- _.,> g ^ - rrr: 
 
 nickel and electro-plating, electro-motors, etc. It has an elec- 
 tro-motive force of 1.8 volts. When the absence of power pre- 
 vents the use of a dynamo, a battery of these cells is very suit- 
 able for nickel plating. It is an easy battery to set up and 
 keep in working order. The batteries are set up by well 
 amalgamating, inside and outside, the zinc, and placing it in 
 the jar. Inside the zinc, place the porous cup, and within the 
 
SOURCES OF CURRENT. JJ 
 
 porous cup the carbon, and then pour nitric acid in the porous 
 cup. In the outer jar pour a mixture of I part sulphuric acid 
 to 12 of water (previously mixed and allowed to cool).* This 
 acid mixture should cover the zinc or be on a level with the 
 liquid in the porous cup. When the liquid in the outer jar 
 becomes milky, withdraw it with a syringe or siphon, and refill, 
 adding occasionally small quantities of nitric acid to the porous 
 cup, and keeping the zinc thoroughly amalgamated by one of 
 the methods given on page 69. A very good plan of amal- 
 gamating zinc is as follows : Dip in lye to remove grease, 
 rinse, next dip in the dilute acid in the glass jar, and then brush 
 over with about 2 ozs. of mercury contained in a little flannel 
 bag. 
 
 Electropoion may be substituted for the nitric acid in the por- 
 ous cup. This battery liquid consists of 1 lh. of bichromate of 
 potash dissolved in 10 lbs. of water, to which 2)/ 2 lbs. of com- 
 mercial sulphuric acid have been gradually added. 
 
 The Bunsen cells are much used for electro-deposition, since 
 they possess a high electro- motive force (1.88 volts), and, on 
 account of slight resistance (05 to 0.25 ohm, according to 
 their size), develop considerable current-strength. Like the 
 Grove cells, they have the inconvenience of evolving vapors of 
 nitrogen tetroxide, which are not only injurious to health, but 
 also attack the metallic articles in the workshop. Wherever 
 possible they should be placed in a box at such a height that 
 they may be readily manipulated. This box should have 
 means of ventilation in such a way that the air coming in at 
 the lower part will escape at the top through a flue, and carry 
 away with it the acid fumes disengaged. It is still better to 
 keep the cells in a room separate from that where the baths 
 and metals are located. Furthermore, as the nitric acid be- 
 comes diluted by the oxidation of the hydrogen, and the sul- 
 phuric acid is consumed in the formation of sulphate of zinc, 
 the acids have to be frequently renewed. 
 
 * The sulphuric acid should be poured into the water; not the water into the acid. 
 
78 ELECTRO- DEPOSITION OF METALS. 
 
 To get rid of the acid vapors, as well as to render the cells 
 more constant, A Dupre has proposed the use of a 30 per cent, 
 solution of bisulphate of potash in water, in place of the dilute 
 sulphuric acid, and a mixture of water 600 parts, concentrated 
 sulphuric acid 400, sodium nitrate 500, and bichromate of 
 potash 60, in place of the nitric acid. 
 
 The following method can be recommended : The outer 
 vessel which contains the zinc cylinder is filled with a mode- 
 rately concentrated (about 30 per cent.) solution of bisulphate 
 of potash or soda, and the clay cup with solution of chromic 
 acid — 1 part chromic acid to 5 parts water. As soon as the 
 electro-motive force of the cell abates, it is strengthened by 
 the addition of a few spoonfuls of pulverized chromic acid to 
 the chromic acid solution. It is preferable to use the chromic 
 acid in the form of a powder especially prepared for this pur- 
 pose than a chromic acid solution produced by mixing potas- 
 sium dichromate solution with sulphuric acid, such a solution 
 having a great tendency to form crystals which exerts a dis- 
 turbing effect. Solution of sodium dichromate compounded 
 with sulphuric acid does not show this drawback. 
 
 The efficiency of the chromic acid solution rapidly abates in 
 a comparatively short time, the electro-motive force of the cell 
 decreasing in a few hours and chromic acid has frequently to 
 be added, or the cell eventually refilled. 
 
 Dr. Langbein has succeeded in preparing a soluble chromium 
 combination which depolarizes rapidly and for a longer time 
 maintains the efficiency of the cell constant. With a single 
 filling of this solution, the battery has been kept working for six 
 days, from morning to evening, without refilling being required. 
 During the night the battery remained filled, but inactive. The 
 solution is obtained by treating Langbein's chromic iron pow- 
 der with concentrated sulphuric acid and carefully diluting with 
 water. 
 
 The electro-motive force of a cell filled with this solution is 
 1.8 volts. Considering the lasting quality and great constancy, 
 and consequent cheapness, as well as freedom from odor of 
 this solution, it would appear to be the most suitable. 
 
SOURCES OF CURRENT. 79 
 
 If nitric acid is used for filling the cells it is advisable in 
 order to decrease the vapors, to cover the acid with a layer of 
 oil y to y inch deep. 
 
 The binding-screws which effect the metallic contacts must 
 of course be frequently inspected and cleaned, the latter being 
 best done by means of a file or emery paper. It is advisable to 
 place a piece of platinum sheet between the binding surface of 
 the carbon armature and the carbon, in order to prevent the 
 acid, rising through the capillarity of the carbon, from acting 
 directly upon the armature (generally brass or copper). To 
 prevent the acid from rising, the upper portions of the carbons 
 may be impregnated with paraffine. For this purpose the car- 
 bons are placed y to 1 inch deep in melted paraffine and 
 allowed to remain 10 minutes. On the sides where the arma- 
 ture comes in contact with the carbon, an excess of paraffine 
 is removed by scraping with a knife-blade or rasp. 
 
 Treatment of Bunsen cells. Before use the zincs should be 
 carefully amalgamated according to one of the methods given 
 on page 69. The nitric acid need not be pure, the crude com- 
 mercial article answering very well, but it should be as concen- 
 trated as possible and show at least 30 B6. Carbons of hard 
 retort-carbon are to be preferred, although those cut from 
 carbon produced in gas-houses, gasifying coal without an 
 addition of lignite, may also be used. Artificial carbon, if 
 employed, should be examined as to its suitability, the non- 
 success of the plating process being frequently attributed to the 
 composition of the bath, when in fact it is due to the defective 
 carbons of the cells. In order to avoid an unnecessary con- 
 sumption of zinc and acid, the cells are taken apart when not 
 in use, for instance, over night. Detach the brass armature 
 of the carbon and lay it in water to which some chalk has 
 been added. Lift the carbon from the clay cylinder and place 
 it in a porcelain dish or earthenware pot; empty the nitric acid 
 of the clay cup into a bottle provided with a glass stopper ; 
 place the clay cup in a vessel of water, and finally take the 
 zinc from the dilute sulphuric acid and place it upon two 
 
80 ELECTRO-DEPOSITION OF METALS. 
 
 sticks of wood hid across the glass vessel to drain oft". In put- 
 ting the cell together the reverse order is followed, the zinc 
 being first placed in the glass vessel and then the carbon in the 
 porous clay cup. The latter is then filled about three-quarters 
 full with used nitric acid, and fresh acid is added until the fluid 
 in the clay cup stands at a level with that in the outer vessel. 
 The cleansed brass armature is then screwed upon the carbon. 
 Finally, add to the dilute sulphuric acid in the outer vessel a 
 small quantity of concentrated sulphuric acid saturated with 
 mercury salt. 
 
 It is advisable to have at least a duplicate set of porous clay 
 cups, and, in putting the cells together, to use only cups which 
 have been thoroughly soaked in water. The reason for this 
 is as follows : The nitric acid fills the pores of the cup, and, 
 finally reaching the zinc of the outer vessel, causes strong local 
 action and a correspondingly rapid destruction of the zinc. It 
 is, therefore, best to change the clay cups every day, allowing 
 those which have been in use to lie in water the next day with 
 frequent renewal of the water. For the same reason the nitric 
 acid in the clay cup should not be at a higher level than the 
 sulphuric acid in the outer vessel. 
 
 When the Bunsen cells are in steady use from morning 
 till night, the acids will have to be entirely renewed every third 
 or fourth day. The solution of sulphate of zinc in the outer 
 Vessel, bemg of no value, is thrown away, while the acid of the 
 clay cells may be mixed with an equal volume of concentrated 
 sulphuric acid, and this mixture can be used as a preliminary 
 pickle for brass and other copper alloys. 
 
 The Leclanchi cell (zinc and carbon in sal ammoniac solu- 
 tion with manganese peroxide as a depolarizer) need not be 
 further described, it not being adapted for regular use in electro- 
 plating. It is in very general use for electric bells, its great 
 recommendation being that, when once charged, it retains its 
 power without attention for a long time. 
 
 Cupric oxide cell. Lallande and Chaperon have introduced 
 a cupric oxide cell shown in Fig. iq which possesses certain 
 
SOURCES OF CURRENT. 1 
 
 advantages. It consists of the outer vessel G, of cast-iron or 
 copper, which forms the negative pole-surface, and to which the 
 wire leading to the anodes is attached, and a strip of zinc, Z T 
 coiled in the form of a spiral, which is suspended from an 
 ebonite cover carrying a terminal connected with the zinc. The 
 hermetical closing of the vessel G by the ebonite cover is 
 effected by means of three screws and an intermediate rubber 
 plate. Upon the bottom of the vessel G is placed a 3 to 4 inch 
 deep layer of cupric oxide, 0, and the vessel is filled with a 
 solution of 50 parts of caustic potash in 100 of water. When 
 
 Fig. 14. 
 
 pliP 
 
 the cell is closed, decomposition of water takes place, the oxy- 
 gen which appears on the zinc forming with the latter zinc 
 oxide, which readily dissolves in the caustic potash solution, 
 while the hydrogen is oxidized, and cupric oxide at the same 
 time reduced to copper. When the cell is open, i. e., the 
 circuit not closed, neither the zinc nor the cupric oxide is 
 attacked, and hence no local action nor any consumption of 
 material takes place. The electro-motive force of this cell 
 is 0.98 volt, and its internal resistance very low. It is remark - 
 6 
 
82 ELECTRO-DEPOSITION OF METALS. 
 
 ably constant, and is well adapted for electro-plating purposes 
 by using two of them for one Bunsen cell. The following 
 rules have to be observed in its use : It is absolutely necessary 
 that the ebonite cover should hermetically close the vessel G, 
 as otherwise the caustic potash solution would absorb carbonic 
 acid from the air, whereby carbonate of potash would be 
 formed, which would weaken the exciting action of the solu- 
 tion. Further, the vessels G which form one of the poles must 
 be insulated one from the other as well as from the ground, as 
 otherwise a loss of current or defective working would be the 
 consequence. 
 
 The regeneration of the cuprous oxide or metallic copper 
 formed by reduction from the cupric oxide to cuprous oxide, 
 requires it to be subjected to calcination in a special furnace. 
 The expense connected with this operation is, however, about 
 the same as that of procuring a fresh supply of cupric oxide. 
 Lallande himself, as well as Edison, endeavored to bring the 
 pulverulent cupric oxide into compact plates, but the regenera- 
 tion of these plates was still more troublesome. By treatment 
 with various chemical agents, Dr. Bottcher, of Leipsic, has suc- 
 ceeded in producing porous plates of cupric oxide which, after 
 subsequent reduction by absorption of oxygen from the air, 
 can be readily re-oxidized to cupric oxide, but as far as we 
 know of, cells with these plates have not been introduced into 
 commerce. 
 
 Ctipron cell. The cell brought into commerce under this 
 name by Umbreit & Matthes is a modification of the Lallande 
 and Chaperon cell, it being furnished with a cuprous oxide 
 plate. A square glass vessel or vat, furnished with a hard 
 rubber cover, contains two zinc plates and between them the 
 porous cuprous oxide plate. The glass vessel is filled with 20 
 per cent, caustic soda solution, and the current is delivered by 
 means of two binding screws on the outside of the cover. The 
 zinc dissolves, zinc-oxide-soda being formed according to the 
 following scheme, while the cuprous oxide is reduced to copper : 
 
SOURCES OF CURRENT. 83 
 
 Cuprous oxide 
 
 Cud(+) 
 
 Zn{ONa) i 
 Zinc oxide soda. 
 
 The reduced positive pole plates are regenerated by rinsing 
 in water and keeping them in a warm place for 20 to 24 hours, 
 it being only necessary to replace the caustic soda solution 
 which has become saturated with zinc oxide. The electro- 
 motive force of the cell is 0.8 volt; the standard current- 
 strength, according to the size of the cells, 1, 2, 4, and 8 am- 
 peres. Like the Lallande and Chaperon cell, this cell works 
 without giving off any odor and the remarks regarding hermeti- 
 oal closing of the former also apply to the latter. An addition 
 of sodium hyposulphite to the caustic soda solution is recom- 
 mended as being productive of uniform wear and greater 
 durability of the zinc plates. 
 
 According to Jordis' investigations * the use of potash lye 
 with 15 per cent, potassium hydrate is more advantageous, as 
 well to heat the plates for the purpose of regeneration to 302 F. 
 
 The elements of Marie, Davy, Naudet, Duchemin, Sturgeon, 
 Trouville, and others, being of little practical value may be 
 passed over. 
 
 Plunge batteries. For constructive reasons only one fluid is 
 used into which the zinc plates as well as the carbon plates 
 dip, a solution of chromic acid prepared by dissolving 10 parts 
 of potassium dichromate, or better sodium dichromate, and - B V 
 part of mercuric sulphate in 100 parts of water, and adding 38 
 parts of pure concentrated sulphuric acid, being. employed. 
 
 Fig. 15 shows a plunge battery as constructed by Fein. 
 The wooden box M contains in two rows six vessels into which 
 
 * Zeitschrift fur Elektrochemie, vii, 469. 
 
8 4 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 dip the zinc and carbon plates. The latter are secured to 
 wooden cross-pieces furnished with handles, and may be main- 
 tained at any height desired by the notches c in the standard 
 G. According to the current-strength required, the plates are 
 allowed to dip in more or less deeply. 
 
 Fig. 15. 
 
 Fig. 16 shows a plunge battery as constructed by Keiser & 
 
 Schmidt. 
 
 In using the above-mentioned chromic acid solution origin- 
 ally recommended by Bunsen, the cells first develop a very 
 strong current, which, however, in a comparatively short time 
 becomes weaker and weaker. The current-strength can be in- 
 creased by adding at intervals a few spoonfuls of pulverized 
 chromic acid to the chromic acid solution, which, however, 
 finally remains without effect, when the battery has to be freshly 
 filled. Hence these batteries are not suitable for electro- 
 plating operations requiring a constant current for some time, 
 but they may be employed for temporary use. 
 
SOURCES OF CURRENT. 
 
 *5 
 
 For temporary use, for instance by gold-workers and others, 
 for gilding or silvering small articles, the bottle-form of the 
 bichromate cell (Fig. 17) may be advantageously employed. 
 In the bottle A two long strips of carbon united above 
 by a metallic connection are fastened, parallel to one another, 
 to a vulcanite stopper, and are there connected with the bind- 
 ing-screw ; these form the negative element, and pass to the 
 bottom of the bottle. Between them is a short, thick strip of 
 
 Fig. 16. 
 
 zinc attached to a brass rod passing stiffly through the center 
 of the vulcanite cork, and connected with the binding-screw. 
 The zinc is entirely insulated from the carbon by the vulcanite, 
 and may be drawn out of the solution by means of the brass 
 rod as soon as the services of the cell are no longer required. 
 
 If plunge batteries are to be used for constant work in electro- 
 plating, it is preferable to use batteries with two acids, namely, 
 dilute sulphuric acid and concentrated nitric acid, or chromic 
 acid. 
 
 In Stoehrer's construction (Fig. 18) the porous clay cup is 
 omitted, the massive carbon cylinders K, K, etc., being each 
 
86 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 provided with a cavity reaching almost to the bottom, which is 
 filled with sand and nitric acid. The contact of the carbon and 
 zinc cylinders is prevented by glass beads imbedded in the 
 carbon cylinders. 
 
 Fig. 19 shows a plunge battery manufactured by Dr. G. 
 Langbein & Co., the details of which will be readily understood 
 
 Fig. 18. 
 
 Fig. 19. 
 
 "^WKaHOraEE^feSi 
 
 without further description. The zinc plates dip in the dia- 
 phragms, which are filled with a mixture of 26 lbs. of water and 
 2 lbs. of sulphuric acid free from arsenic in which 2% ozs. of 
 amalgamating salt have previously been dissolved. The car- 
 bon plates dip into the glass vessels, which contain a solution 
 of commercial crystallized chromic acid in water in the propor- 
 tion of 1 part acid to 5 water. In place of this pure chromic 
 acid solution the following mixture may also be used : 
 
SOURCES OF CURRENT. 87 
 
 Water 10 parts by weight, sodium dichromate 1.5 parts by 
 weight, pure sulphuric acid of 66° Be. 5 parts by weight. 
 
 This solution shows no inclination towards crystallization. 
 In the illustration only two cells are combined to a battery, 
 but in the same manner a plunge battery of four or eight 
 cells may be constructed, the separate cells of which may 
 all be coupled parallel, as well as one after the other, and in 
 mixed groups. 
 
 Coupling cells. According to the laws of Ohm, previously 
 discussed, the current-strength J of a cell is equal to its electro- 
 motive force E divided by the sum of the internal resistance W 
 and the external resistance Wl : 
 
 W + WI 
 
 By now combining several such cells, say n cells, to a battery, 
 the electro-motive force of the latter will become n.E, but the 
 internal resistance n.W, and with the same closed circuit as the 
 single cell had, the external resistance Wl will not increase. 
 Hence the current-strength of these n elements has to be 
 written 
 
 T _ n 'E 
 
 n.w + wi. 
 
 Now it is evident that, if a definite closed circuit with a 
 resistance of wi be given, the current-strength cannot be 
 indefinitely raised by increasing the number of n elements. 
 While with an increase in the number of n elements, the electro- 
 motive force to be sure grows as many n times, the internal 
 resistance, w, also grows, so that finally the value wi which 
 remains the same disappears for the resistance nw which 
 increases n-times. Thus the current-strength approaches more 
 and more the limit of value 
 
 nE E 
 
 nw w 
 
 On the other hand, the effect can neither be increased at will 
 by enlarging the surface of the pair of plates or decreasing the 
 
88 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 conducting resistance of the fluid in a given number of cells. 
 Because if wi — the external resistance — is large enough so that 
 the internal resistance nw may be disregarded, the current- 
 strength approaches more and more the value 
 
 w I 
 
 Hence, it follows that the enlargement of the surface of the ex- 
 citing pair of plates produces an increase i)i the current-strength 
 only when the external resistance in the closed circuit is small 
 in proportion to the internal resistance of the battery. 
 
 If we now apply the results of the above explanations to 
 practice, we find that the cells may be coupled in various ways 
 according to requirement. 
 
 i. If, for instance, four Bunsen cells (carbon-zinc) are 
 coupled one after another in such a manner that the zinc of one 
 cell is connected with the carbon of the next, and so on (Fig. 
 20), the current passes four times in succession through an 
 
 Fig. 20. 
 
 equally large iaycr of fluid, in consequence of which the in- 
 ternal resistance (4w), is four times greater than that of a 
 single cell, while the resistance of the closed circuit (wi), re- 
 mains the same. Hence, while the current-strength is thereby 
 not increased, the electro-motive force is, and for this reason 
 this mode of coupling is called the union or coupling of the 
 elements for electro-motive force or tension. 
 
 Fig. 21. 
 
 2. By connecting four cells alongside of each other, i. e., all 
 
SOURCES OF CURRENT. 
 
 89 
 
 Fig. 22. 
 
 the zinc plates and all the carbon plates one with another 
 (Fig. 21), the current simultaneously passes through the same- 
 layer of fluid in four places ; the internal 
 resistance of the battery is therefore the 
 same as that of a single cell, and since 
 the surface of the plates is four times 
 as large as that of a single cell, the 
 quantity of current is increased by this 
 mode of coupling. This is called coup- 
 ling for quantity of current, or parallel 
 coupling. 
 
 3. Two cells may, however, be con- 
 nected for electro-motive force or ten- 
 sion, and several such groups coupled 
 
 alongside of each other, as shown in Fig. 22, whereby, accord- 
 ing to what has above -been said, the electro motive force, as 
 well as the current-strength, is increased. This mode of con- 
 nection is called mixed coupling, or group coupling. 
 
 According to the resistance of the bath as the exterior closed 
 circuit, and according to the surfaces to be plated, the electro- 
 plater may couple his cells in either way. We will here only 
 mention the proposition deduced from Ohm's law, that a number 
 of voltaic cells yield the maximum of current-quantity when they 
 are so arranged that the internal resistance of tJie battery is 
 equal to the resistance in the closed circuit. Hence, when oper- 
 ating with baths of good conductivity and slight resistance, for 
 instance, acid copper baths, silver cyanide baths, etc., with a 
 slight distance between the anodes and the objects, and with a 
 large anode-surface, it will be advantageous to couple the ele- 
 ments alongside of each other for quantity. However, for baths 
 with greater resistance and with a greater distance of the anodes 
 from the objects, and with a smaller anode surface, it is best to 
 couple the elements one after the other for electro-motive force 
 or tension . 
 
90 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 B. Thermo-Electric Piles. 
 
 Though thermo-electric piles are only used in isolated cases 
 for electro-plating operations, for the sake of completeness 
 their nature and best-known forms will be briefly mentioned. 
 
 In the year 1822, Professor Seebeck, of Berlin, discovered a 
 new source of electricity, namely, inequality of temperature 
 and conducting power in different metals, or in the same metal 
 in different states of compression and density. When two 
 pieces of different metals, connected together at each end, have 
 one of their joints more heated than the other, an electric cur- 
 rent is immediately set up. Of all the metals tried, bismuth 
 and antimony form the most powerful combination. 
 
 In Fig. 23 Bm represents a bar of bismuth, and mS a bar of 
 antimony soldered to the bismuth bar. By carrying wires from 
 B and 5 to a galvanometer, G, and heating the point of junc- 
 tion m, the needle of the galvanometer is deflected. From this 
 it may be concluded that an electric current circulates in the 
 closed circuit GBmSG. By a closer examination the direction 
 of the current may be recognized, it flowing on the heated 
 point of junction from the bismuth to the an- 
 timony, and in the connecting wire of the 
 ends of the rods which remain cold, from the 
 antimony to the bismuth. The current is the 
 stronger the greater the difference in the 
 temperature of the point of junction and the 
 free ends of the bars. Hence the electric 
 current will be especially strong when the 
 place of junction is heated and the ends B and 
 5 are at the same time cooled off. A combi- 
 nation as above described is called a thermo- 
 electric couple, and the electricity obtained in 
 this manner thermo-electricity. By a suitable 
 combination of several or many of such couples, a thermo- 
 electric pile is obtained. 
 
 Noe's thermo-electric pile (Fig. 24) consists of a series of 
 
 Fig. 23. 
 
SOURCES OF CURRENT. 
 
 91 
 
 small cylinders, composed of an alloy of 36^ parts of zinc and 
 62T/2 parts of antimony for the positive element, and stout 
 German silver as the negative element. The junctions of the 
 
 Fig. 24. 
 
 elements are heated by small gas-jets, and the alternate junc- 
 tions are cooled by the heat being conducted away by large 
 
 Fig. 25. 
 
 blackened sheets of thin copper. A pile of twenty pairs has 
 an electro-motive force of 1.9 volts. 
 
92 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Clamond's thermo-electric pile (Fig. 25) consists of an alloy 
 of 2 parts antimony and I of zinc for the negative metal, while 
 for the positive element ordinarily tinned sheet-iron is em- 
 ployed, the current flowing through the hot junction from the 
 iron to the alloy. To insure a good contact between the two 
 metals, a strip of tin-plate is bent into a narrow loop at one end. 
 This portion is then placed in a mould and the melted alloy 
 poured around it, so that it is actually imbedded in the casting. 
 The pile shown in the illustration consists of five series, one 
 placed above the other. Each series has ten elements grouped 
 in a circle, and is insulated from the succeeding series by a 
 layer of cement, composed of powdered asbestos moistened 
 with a solution of potassium silicate. With the consumption 
 
 Fig. 26. 
 
 of about 6]/ 2 cubic feet of gas per hour, such a pile precipitates 
 0.7 oz. of copper, which corresponds to an electro-motive force 
 of about 17 amperes. 
 
SOURCES OF CURRENT. 
 
 93 
 
 Hauck' s thermo-electric pile. — An essential defect of Cl?mond's 
 thermo-electric pile consists in that the junctions of the dissimilar 
 metals are subjected to ready destruction by being exposed to 
 the direct action of the flame. Further, it is very difficult, or 
 at least inconvenient, to make repairs, since in such a case it 
 may become necessary to take the entire pile apart. Hauck 
 has successfully overcome these defects by adopting the princi- 
 ple of indirect heating, as well as by giving the couples a more 
 suitable form and by improving the alloy. The couples form 
 four-sided wedges, to which are attached cast-iron pieces that 
 transfer the heat of the gas burner to the couples. The electro- 
 motive force of a single couple is ^ that of a Daniell cell. 
 Fig. 26 shows a combination of two piles standing upon a com- 
 mon plate, one of the piles being given in cross-section. The 
 glass vessel, H, with the tube, B, G, R, /, serves as a regulator 
 for the gas-pressure. The pile shown in the illustration serves 
 for the production of metallic deposits an a small scale, especi- 
 ally for analytical examinations. Hauck, however, also fur- 
 nishes combinations of three larger piles. 
 
 Gulcker's thermo-electric pile, invented in 1890, is shown in 
 
 Fig. 27. 
 
 Fig. 27. It is arranged for gas-heating, and with a constant 
 supply of gas requires a pressure-regulator. The negative 
 electrodes consist of nickel, and the positive electrodes of an 
 antimony alloy, the composition of which is kept secret. The 
 negative nickel electrodes have the form of thin tubes and are 
 
94 ELECTRO-DEPOSITION . OF METALS. 
 
 secured in two rows in a slate plate, which forms the termina- 
 tion of a gas conduit with a U-shaped cross-section beneath it. 
 Corresponding openings in the slate plate connect the nickel 
 tubes with the gas conduit, the latter being connected by means 
 of a rubber tube with the pipe supplying the gas. Thus the 
 gas first passes into the conduits, next into the nickel tubes, and 
 leaves the latter through six small holes in a soapstone socket 
 screwed in the end of each tube. On leaving these sockets the 
 gas is ignited and the small blue flames heat the connecting 
 piece of the two electrodes. This connecting piece consists of 
 a circular brass plate placed directly over the soapstone socket. 
 One end of it is soldered to the nickel tube, while the other 
 end, towards the top, is in a socket in which are cast the posi- 
 tive electrodes. The latter have the form of cylindrical rods with 
 lateral angular prolongations. To the ends of these prolonga- 
 tions are soldered long copper strips secured in notches in the 
 slate plate. The}' serve partially for cooling off and partially 
 for connecting the couples. For the latter purpose each cop- 
 per strip is connected by a short wire with the lower end of the 
 nickel tube belonging to the next couple. When the pile is to 
 be used, the gas is ignited in one place, the ignition spreading 
 rapidly through the entire series of couples. In about io min- 
 utes the junctions of the metals have attained their highest 
 temperature and the pile its greatest power, which, with a con- 
 stant supply of gas, remains unchanged for days or weeks. 
 
 In view of the conversion of the heat produced by the com- 
 bustion of the gas into electricity, the useful effect of the 
 thermo-electric pile can be considered only a very slight one. 
 One cubic meter of ordinary coal-gas produces on an average 
 5200 heat-units, hence 200 litres per hour referred to one 
 second J-.-gV-e-. 5200=0.20 heat-unit. These correspond to 
 1208 volt-amperes, 1 volt-ampere being equal to 0.00024 heat- 
 unit. Hence, in Gulcher's thermo-electric pile, which of all 
 known thermo-piles produces the greatest useful effect, not 
 much more than 1 per cent, of heat is utilized in the entire 
 circuit, and about y 2 per cent, in the outer circuit. 
 
SOURCES OF CURRENT. 
 
 95 
 
 Although thermo-electric piles may be, and are occasionally, 
 used for electro-plating operations, they cannot compete with 
 dynamo-electric machines driven by steam, which as regards 
 the consumption of heat are at least five times more effective. 
 They can only be used in place of voltaic batteries, having the 
 advantage of being more convenient to put in operation, more 
 simple, cleanly, odorless, and requiring less time for attendance. 
 But, on the other hand, their original cost is comparatively large, 
 it being ten to twenty times that of Bunsen cells. 
 
 C. Dynamo-Electric Machines. 
 While in the voltaic cells, chemical energy is converted into 
 electric energy, and in the thermo-piles, heat into electricity, in 
 the dynamo-electric machine a conversion of mechanical energy 
 into electrical energy takes place. 
 
 Fig. 28. 
 
 Fundamental principle of dynamo-electric machines. In the 
 dynamo-electric machines the generation of the current results 
 from induction, and the fundamental principle of such a 
 machine is as follows : 
 
96 ELECTRO-DEPOSITION OF METALS. 
 
 Suppose an iron magnet frame M, formed of a powerful 
 horse-shoe magnet, which is provided with two cylindrically- 
 turned planes, and concentrically fixed to these planes, a 
 cylinder, A, built up of discs of soft iron as shown in Fig. 28. 
 
 Lines of force running in the direction from the north pole to 
 the south pole permeate the soft-iron cylinder. If in the air- 
 space between the north pole of the magnet and the cylinder, a 
 copper wire, indicated in the illustration by a small circle, be 
 introduced, and moved in such a manner that it cuts the lines 
 of force flowing from the north pole through the air-space to 
 the cylinder, a current is induced, and a certain electro-motive 
 force appears at the ends of the wire. By moving the left- 
 hand wire in the direction indicated by the arrow, the current, 
 according to the hand rule illustrated by Fig. 4 will flow away 
 from the observer into the plane of the illustration, and by 
 moving the right-hand wire in the direction of the arrow, out 
 from the plane of the illustration towards the observer. 
 
 Instead of moving the wire in the air-space, it may also be 
 insulated from the soft- iron cylinder and secured to it. If now 
 the cylinder be moved around its axis, the wire cuts the lines 
 of force in exactly the same manner as in its motion in the air- 
 space, the effect remaining the same. If several wires, one 
 alongside the other, be secured upon the cylinder, a corre- 
 sponding electro-motive force will be produced on the ends of 
 each wire, the positive poles of the wires being then on one side, 
 say the front, of the pole pieces, while the negative poles of all 
 the wires lie upon the other, the rear, side. If now the wires 
 be connected one with the other, so that, when the cylinder 
 is revolved, a positive pole is always attached to a negative 
 pole, the electro- motive force is raised in the same degree as 
 the number of wires coupled one after the other (in series) 
 increases. 
 
 These wires fastened upon the iron body are called windings, 
 and the term armature is applied to an iron body furnished 
 with such windings. 
 
 The electro-motive force generated in the windings is the 
 
SOURCES OF CURRENT. 
 
 97 
 
 greater, the greater the velocity with which the wires, or con- 
 ductor forming the windings, are moved through the magnetic; 
 field. If the length of the conductors be increased by enlarg- 
 ing the windings, and the velocity with which the armature 
 moves remains the same, the electro-motive force generated in 
 the conductor is proportional to the length of the latter. If, 
 on the other hand, the magnetic field be strengthened, thus 
 increasing the lines of force cut by the conductor during its 
 motion, and the velocity with which the conductor moves, as 
 well as its length, remains the same, the electro- motive force 
 is proportional to the number of lines of force, reaching its 
 greatest value when the lines of force are perpendicularly cut 
 by the conductor. 
 
 Separate parts of the dynamo-electric machine. The frame. 
 The production of the magnetic field has for a long time been 
 
 Fig. 29. 
 
 Fig. 30. 
 
 effected by electro- magnets. The field magnets of gray cast- 
 iron or cast-steel are cast in one piece with the gray cast-iron 
 or cast-steel frame, or screwed to it. These field magnets are 
 wrapped with wire through which the current, by which they 
 are magnetically excited, is conducted. This winding is called 
 magnet winding or field winding. According to the number 
 of field magnets, a distinction is made between two-polar, four- 
 polar, six-polar and multipolar machines. 
 7 
 
c,8 ELECTRO-DEPOSITION OF METALS. 
 
 Fig. 29 shows a two- polar, and Fig. 30 a four-polar type of 
 dynamo of the firm of Dr. G. Langbein & Co., Leipsic, Ger- 
 many. The frame and foundation plate of soft cast-iron are 
 cast in one single casting ; only in larger types is the frame 
 secured to the foundation-plates by screws. 
 
 For the production of the magnetic field, the current was 
 formerly conducted from another source of electricity into the 
 magnet windings, but since the discovery of the dynamo- 
 electric principle by \V. v. Siemens, the electric current gener- 
 ated in the armature is utilized for the excitation of the mag- 
 netic field. The basis of the dynamo-electric principle is as 
 follows : In every frame of a magnet there is present, from a 
 previous excitation, a small number of lines of force, and this 
 is called remanent magnetism (see p. 13). In revolving the 
 armature, the existence of this small quantity of lines of force 
 suffices for the induction of a weak current, which is partly 
 conducted through the magnet-winding, the magnetic field be- 
 ing thereby intensified. The effect of this is the generation of 
 currents of considerably greater power in the armature, which 
 again bring about an increase in the current-strength in the 
 magnet-winding, until the frame is saturated with lines of force. 
 This process is called self-excitation, while the term foreign or 
 separate excitation has been applied to it, when the magnetic 
 field is excited by another source of electricity. 
 
 Armature or inductor. It has already been mentioned that 
 the armature consists of a cylindrical iron body and the wind- 
 ing- wrapped around it. The iron body cannot be made of one 
 piece because rotator}- currents would be formed in it, which 
 heat the iron very much, and cause a loss of current. Hence 
 the body of the armature is built up of thin, soft sheet-iron discs 
 insulated one from the other by. discs of paper. The discs are 
 firmly pressed upon the core of the armature and secured by 
 screws, while the core of the armature itself is wedged upon 
 the shaft by means of a wedge. 
 
 According to the manner in which the wire windings are laid 
 around the armature- core, a distinction is made between a ring 
 armature and a drum anna tare. 
 
SOURCES OF CURRENT. 
 
 99 
 
 In the ring armature the wire windings are wrapped in a 
 continuous spiral around the armature-core, it being necessary 
 for the latter to have a wide bore in the center through which, 
 in wrapping, the conducting wire may be carried. Fig. 31 
 represents a scheme of such ring-winding. N and 5 are the 
 two field magnets of the frame. Every two of the continuous 
 
 Fig. 3j. 
 
 ISO. 
 
 wire windings represent a coil, and from the point where the 
 end of one coil is connected with the commencement of the 
 next coil a conducting wire branches off to the collector. 
 According to what has above been said, induction is greatest 
 when the windings of the wire cut the lines of force at a right 
 angle, this being the case when the windings are directly under 
 the poles. In revolving the armature from o° to 90 , the 
 
IOO 
 
 t 1 EC rRO-DEPOSl HON OF META1 S. 
 
 generation of current increases, from 90 to 180 it decreases, 
 from [So to 270 it increases in a contrar) sense, and from 
 ■ to 360 it again decreases Thus, currents flowing 
 alternately in opposite directions, the so-called alternating cur- 
 i 1 e generated, and theii conversion into constant currents 
 of uniform direction is effected by the commutator. At o v and 
 at 180 , the generator of current is equal to 0, and at these 
 points the current changes its direction ; the line o to [80 is 
 called the neutral zone. 
 
 Fig. 32. 
 
 In the drum armature the conducting wires are wound upon 
 the armature-core parallel to its axis, carried on the face- of 
 the core around the core-shaft, and the ends of every two coils 
 lying alongside each other on a taee are connected, one with 
 the other, and with a segment of the commutator. 
 
SOURCES <)V CURRENT 
 
 J 1 
 
 Wig. 32 shows the drum winding viewed from the side of the 
 commutator. Each coil is only indicated by a single wire 
 winding, and therefore 8 coils are shown. The full lines indi- 
 cate the connection of the coils upon the commutator-side and 
 with the commutator, and the dotted lines, the coil-connections 
 upon the opposite face. 
 
 What has been said in regard to the intensity of induction in 
 ring-armatures applies also to drum-armatures. 
 
 The chief difference between the modes of winding consists 
 in more wire being required for ring winding, because wires 
 run on the faces as well as in the interior of the the bore, which 
 are of no importance as regards the generation of the current 
 
 Fig. 33- 
 
 by induction, but, on the one hand, materially increase the 
 weight of the armature, and, on the other, enlarge the resist- 
 ance. As regards these points, drum-winding has much in its 
 favor, and it has the further advantage that the armature- core 
 can be provided, parallel to its axis, with grooves or slots for 
 the reception of the windings, they being thus better protected 
 from injury, and the effect of centrifugal force can in a suitable 
 manner be prevented by bands. In such armatures, even 
 when equipped with thick copper wires or flat copper bands, 
 scarcely any rotatory currents are generated, because the slots 
 are but slightly permeated with lines of force, the latter running 
 rather around the copper wires through the iron. However, 
 the chief advantage of such an armature consists in that the 
 air-space between armature and magnet-pole can be less than 
 in armatures with windings not placed in slots, because the 
 space occupied by the winding of such so-called smooth arma- 
 
T02 ELECTRO-DEPOSITION OF METALS. 
 
 tures has to be considered as an air-space and offers the 
 greater magnetic resistance. Hence for armatures furnished 
 with slots, the number of ampere-windings may be less than 
 for smooth armatures. Fig. 33 shows a slotted armature of a 
 dynamo constructed by the firm of Dr. G. Langbein & Co., in 
 which the conductors consist of flat copper rods, connected on 
 the faces by bent copper bands called evolvents. 
 
 Commutator. This is a cylindrical body built up of segments 
 and fastened to the armature-shaft. It is insulated with mica. 
 The segments consist of copper, tombac, or brass, and are in- 
 sulated from each other as well as from the commutator frame, 
 i. e., the iron body. The commutator has as many segments 
 as the armature has coils, and every point of junction of two 
 coils is intimately connected by means of copper with a seg- 
 ment. The function of the commutator consists in converting 
 the alternating currents of the windings generated by induc- 
 tion, into constant currents of uniform direction. As seen 
 from Fig. 31, currents of opposite directions flow in each half 
 of the windings of the ring-armature. If now sliding contacts 
 be placed on the commutator on the points of the neutral zone, 
 the current of one-half of the windings is carried along as posi- 
 tive current by one of the sliding contacts, and the negative 
 current of the other half by the other sliding contact. The 
 armature winding is divided into two halves by the brushes 
 which are coupled parallel to each other. The induction of 
 each separate coil corresponds to its position for the time 
 being in the magnetic field, the sum of the induction of all the 
 coils in one-half of the armature being equal to that of all the 
 coils in the other half, but as previously shown, the direction 
 of the current in both halves is different. 
 
 finishes. The function of the brushes is to take off the cur- 
 rent from the commutator. For such dynamo-electric machines 
 as here come into question, the brushes are of fine copper or 
 brass wire-gauze, or of very thin metal-plate. Carbon brushes 
 are often used for dynamo-electric motors. 
 
 The choice of material for the brushes depends on the prop- 
 
SOURCES OF CURRENT. 103 
 
 erties of the material of the commutator. As there should be 
 as little wear as possible of the commutator by the brushes, 
 the material used for the latter should be somewhat softer than 
 that for the former. Copper and brass gauze brushes produce 
 by their wear considerable metallic dust, which settles on all 
 parts of the machine, as well as on the armature and, if not re- 
 moved by frequent blowing out with a pair of bellows, or a 
 similar instrument, may readily cause short-circuiting. Brushes 
 of twisted, thin metal-plates (Boudreaux brushes) do not show 
 this disagreeable formation of dust, and cause but little wear 
 of the commutator, rather polishing it. They have, however, 
 the drawback of the portions bearing on the commutator oxi- 
 dizing readily, in consequence of becoming heated by the large 
 quantities of current. This oxidation is not removed by the 
 friction, and greater resistance is thereby opposed to the pas- 
 sage of the current from the commutator to the brushes. This, 
 on the one hand, results in the commutator and brushes be- 
 coming strongly heated and, on the other, causes a decrease in 
 taking off the current. 
 
 The bearing surfaces of the brushes should be so large that 
 no heating is caused by the passage of the current, which 
 would increase to a considerable extent the quantity of heat 
 unavoidably formed by the friction, and be a disadvantage as 
 regards the useful effect of the dynamo. 
 
 Brush-holders. These serve for securing the brushes and 
 should hold them so as to bear with an even pressure upon the 
 commutator. This is effected by metal springs by means of 
 which the brush- frame, which carries the brush, is elastically 
 connected with the portion of the brush-holder screwed to the 
 bolt of the brush-rocker. 
 
 Brush-rocker. This serves for carrying the brush-holder, and 
 for this purpose is furnished with two thick copper bolts having 
 a cross-section corresponding in size to the quantity of current 
 to be conducted. In multi-polar dynamos, the rockers are 
 equipped with as many bolts as there are poles. These bolts 
 are insulated from the rocker by cases of a good insulating 
 material, and secured to the rocker by insulated nuts. 
 
104 ELECTRO-DEPOSITION OF METALS. 
 
 The rocker is mounted upon the turned end of a bearing, 
 and is concentrically movable to its axis, so that by turning it, 
 the brushes may be shifted into a position at which the dynamo 
 runs with the least sparking. In this position the brush holder 
 is kept by means of an adjusting screw. 
 
 The rocker should also be kept free from metal dust, other- 
 wise short-circuiting may readily result. 
 
 The other parts of a dynamo, such as bearings, cable, etc., 
 need not be especially referred to, and it only remains to dis- 
 cuss the various types of 
 
 Continuous- current wound dynamos. If the whole of the cur- 
 rent traverses the coil of the field magnet, the dynamo is said to 
 be series-wound ; or if a portion of the current be shunted we 
 have a shunt-wound dynamo, or finally there may be a com- 
 bination of the two, in which case the machine is a compound 
 dynamo. Whatever be the arrangement, provided the volume 
 of the copper and the density of the current are the same, the 
 same field is always produced. 
 
 Nearly all the early types of electric dynamos were what is 
 known as "series-wound" machines, where the full current of 
 the armature passed through the field coils. These machines 
 had the very serious disadvantage of possessing poor regula- 
 tion and being subject to frequent reversal of current direction. 
 The plating dynamos on the market to-day are what is tech- 
 nically known as " shunt-wound " machines and " compound 
 wound " machines. 
 
 In a shunt-wound dynamo the field magnet coils are placed 
 in a shunt to the armature circuit so that only a portion of the 
 current generated passes through the field magnet coils, but all 
 the difference of potential of the armature acts at the terminals 
 of the field circuit. 
 
 In a shunt-wound dynamo, an increase in the resistance of 
 the external circuit increases the electro-motive force, and a 
 decrease in the resistance of the external circuit decreases the 
 electro-motive force. This is just the reverse of the series- 
 wound dynamo. 
 
SOURCES OF CURRENT. 105 
 
 In a shunt-wound dynamo a continuous balancing of the 
 current occurs. The current dividing at the brushes between 
 the field and the external circuit in the inverse proportion to 
 the resistance of these circuits, if the resistance of the external 
 circuit becomes greater, a proportionately greater current 
 passes through the field magnets, and so causes the electro- 
 motive force to become greater. If, on the contrary, the re- 
 sistance of the external circuit decreases, less current passes 
 through the field, and the electro-motive force is proportion- 
 ately decreased. Thus, up to a certain degree, a shunt-wound 
 dynamo regulates itself. 
 
 A compound wound dynamo has two distinct windings on 
 its field magnet — one of the very many turns of fine wire, 
 called the shunt winding, and another known as the series 
 winding, which latter consists of a number of turns of heavier 
 gauge wire. The series winding is in series with the vats or 
 external circuit. The current that is used in the vats, passing 
 through this winding, increases the magnetism of the field as 
 the load increases, and thus the drop in voltage, which would 
 otherwise occur by reason of the increased drop in the arma- 
 ture winding and increased magnetic reaction caused by the 
 armature current is provided for. 
 
 Fig. 34 illustrates a two-pole shunt-wound dynamo, and Fig. 
 35 a two-pole shunt-wound dynamo for high current- strengths. 
 
 In Fig. 34 the frame is of cast-steel and the bearing plates 
 are screwed to it. In Fig. 35 the pillow-blocks and frame are 
 mounted upon a common cast-iron plate. 
 
 The armature is of the slotted drum type described on 
 p. 102. It is encompassed by two strong field magnets 
 arranged in vertical position, radially opposite one to the other. 
 The ends of the field magnets are concentrically turned to the 
 armature and their oblique tapering shape prevents the jerky 
 formation or interruption of the current, thus rendering possi- 
 ble a sparkless taking-off of current on the commutator. The 
 ends of the armature coils are soldered to the copper segments 
 of the commutator, loosening of the connecting points being 
 
id6 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 thus excluded, as is invariably the case with wires secured by 
 means of screws to the commutator. An abundance of copper 
 cross sections being used, the degree of efficiency of the 
 
 Jbio. 34. 
 
 dynamo is an excellent one. To decrease friction the portions 
 of the steel armature shaft which run in the journal boxes of 
 phosphor-bronze, as well as the latter themselves, are highly 
 
 Fir,. 
 
 polished. The bearings are furnished with automatic ring- 
 lubrication. By reason of the use of large cross sections of 
 copper upon the armature and magnet winding, the number of 
 
SOURCES OF CURRENT. 
 
 IO7 
 
 revolutions is a moderate one, and consequently the consump- 
 tion of power and wear of the bearings are slight. 
 
 Dynamos which yield high current strengths are furnished 
 with two commutators to avoid overloading and consequent 
 excessive heating of a single commutator. Customers fre- 
 
 Fig. 36. 
 
 quently demand that dynamos for slight current-strengths 
 should also be furnished with two commutators. This is, how- 
 ever, entirely unwarranted, as it makes the machine unneces- 
 sarily more expensive and no advantage is gained. Of course 
 the single commutator must be of such dimensions that the 
 maximum current-strength which can be generated by the 
 dynamo, is taken off by the brushes without excessive heating. 
 Fig. 36 shows a dynamo of the shunt-wound type manu- 
 factured by Zucker & Levett & Loeb Co., New York. It is a 
 225-ampere machine, which is designed for smaller size plat- 
 ing rooms. 
 
io8 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 The armature wires of this dynamo as well as of all the other 
 machines manufactured by this firm are soldered directly to the 
 commutator, thus insuring a perfect electrical contact, which 
 cannot be obtained by means of screws. Though this may 
 necessitate the return of the armature for putting on a new 
 commutator, this is more than offset by the increased efficiency 
 obtained through the prevention of poor contact in a part of a 
 dynamo where good contact is absolutely necessary. 
 
 Fig. 37. 
 
 I 
 
 Among the changes made in the new type plating dynamos, 
 manufactured by the above mentioned firm, to produce a 
 machine that would give the largest output with the least ex- 
 penditure in first cost, costs of repairs and power, the following 
 ma}' be noted : 
 
 Increase in the size of bearings. Substitution of steel for 
 cast-iron in the magnet circuit, with the result that a more 
 powerful field is obtained, and better regulation secured. 
 
SOURCES OF CURRENT. 
 
 109 
 
 Adoption of the toothed form of armature as being superior 
 for plating dynamos to the smooth core, thus obtaining a field 
 practically free from distortion and insuring sparkless com- 
 mutation. Increase in the brush surface and the size of the 
 commutators — ample brush surface being of prime importance 
 on plating machines, as it not only increases the output of the 
 machine, but also insures cooler running, longer life for both 
 commutator and brushes, and consequently less expense for 
 repairs. 
 
 Fig- 37 shows a somewhat different design of a 500-ampere 
 machine with double commutator and brushes on each end, 
 manufactured by Zucker & Levett & Loeb Co. This machine 
 is more symmetrical in shape and better balanced, and renders 
 possible the use of a very large brush surface. 
 
 Fig. 38. 
 
 ^*^ 
 
 Fig. 38 shows a separately excited dynamo of the multipolar 
 type manufactured by The Hanson & Van Winkle' Co., Newark, 
 N. J. It is a very popular form of generator, the field being 
 
I 10 ELECTRO-DEPOSITION OF METALS. 
 
 excited from an external circuit, usually I 10 or 220 volts D. C. 
 The capacity is 4000 amperes at 6 volts. The commercial effi- 
 ciency is high, 86 per cent. — the electrical efficiency averages 
 93 per cent. This form of dynamo is furnished for both two 
 and three wire system of current distribution. The frame and 
 pole pieces are of steel. For the frame a special, soft grade is 
 used, having a high magnetic permeability. The field coils 
 are made of insulated copper wire wound compactly by 
 machinery, insuring the maximum ampere-turns without great 
 bulk. The whole coil is properly insulated and protected from 
 mechanical injury. 
 
 The great advance which has in modern times been made in 
 the art of electro-plating is largely due to the important im- 
 provements that have been made in the construction of 
 dynamo-electric machines, by which mechanical energy gener- 
 ated by the steam-engine or other convenient source of power 
 may be directly converted into electrical energy. Without 
 dynamos it would be impossible to electro-plate large parts of 
 machines, architectural ornaments, etc., which are thus pro- 
 tected from the influence of the weather. They may safely be 
 credited with having called into existence an important branch 
 of the electro-plating art, viz., nickel-plating, and especially the 
 nickel-plating of zinc sheets, as well as sheets of copper, brass, 
 steel, and tin, which would have been impossible if the manu- 
 facturer had to rely upon the generation of the electric current 
 by batteries. The latter, at the very best, are troublesome to 
 manage: they only give out their full power when freshly 
 charged, and as the chemical actions upon which they rely for 
 their power progress, they deteriorate in strength and require 
 frequent additions of acids and salts to be freshly charged, and 
 their use demands constant vigilance and attention. Even 
 when working on a small scale, it is cheapest to procure a small 
 gas or other motor for driving a small dynamo, the lathes, and 
 grinding and polishing machines. 
 
 M'>st cities and towns are now supplied with electric light 
 
SOURCES OF CURRENT. 
 
 1 i 1 
 
 from central stations, and thus the means are furnished to 
 smaller plants to avail themselves of the use of electricity with- 
 out the necessity of installing their own source of power. From 
 such central stations the conductors are fed with currents of 
 1 10 or 220 volts. Hence the wires from the power circuit can 
 be directly connected with a motor-generator, which is con- 
 structed for the respective voltage and converts the supply of 
 current into power, driving, for instance, a connecting gear, 
 from which the grinding and polishing machines, as well as a 
 dynamo of low voltage, are impelled. The dynamo may be 
 directly connected by means of a flexible or rigid coupling to 
 
 *IG. 39. 
 
 the motor-generator. The armature of the latter may also be 
 directly placed upon the grinding and polishing shafts, and the 
 magnets arranged around it, so that every working machine 
 becomes a motor-generator. 
 
 Fig- 39 shows a 150-ampere motor generator set, and Fig. 
 40, a 4000-ampere motor generator set, manufactured by The 
 Hanson & Van Winkle Co., Newark, N. J. A low voltage 
 dynamo is directly connected to a motor of suitable size, the 
 whole outfit being mounted on a substantial iron base. There 
 is no loss of power as in the case when belts are used, so the 
 full capacity of the generator is available. In many instances 
 
i I 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 the plating dynamo is installed some distance from the tank, 
 and conductors of large cross-sections must be used in order 
 that there may be no drop in voltage at the tanks. This, of 
 course, increases the cost of installation. With the motor- 
 
 FlG. 40. 
 
 generator set, wires from the power- circuit can be brought to 
 the plating room and the outfit can be set up near the tanks. 
 These outfits are made in all sizes, both bipolar generators, as 
 shown in the illustration, or generators of the multipolar type 
 being used. 
 
 Figs. 41 and 42 show types of directly connected motor and 
 generator manufactured by Zucker & Levett & Loeb Co. 
 These machines are designated to be put in places where 
 factories are electrically driven and are made with both self 
 and separate excitation. They are manufactured in sizes from 
 60 to 6500 amperes. Fig. 41 shows a 60-ampere directly con- 
 nected motor and generator, and Fig. 42 a 600-ampere machine. 
 
 To enable the manufacturer of dynamos to suggest the most 
 suitable machine, the following data should be submitted to 
 him : 
 
SOURCES OF CURRENT, 
 
 113 
 
 I. Variety, size, and number of the baths which are to be 
 
 fed by the machine. 
 
 Fig. 4.1. 
 
 2. The average surface of the articles in the bath, or their 
 maximum surface, and the metals of which they consist. 
 
 3. Whether at one time many, and at another time few, arti- 
 cles are suspended in the bath. 
 
 Fig. 42. 
 
 4. The distance at which the machine can be placed from 
 the baths. 
 
 5. The power at disposal. 
 
 If the establishment is to be electrically driven by a motor- 
 
114 ELECTRO-DEPOSITION OF METALS. 
 
 generator, the machines which in addition to the dynamo, are 
 to be driven by the motor-generator should be mentioned, as 
 well as the voltage of the power circuit which is to be used as 
 a supply of electricity. 
 
 D. Secondary Cells (Accumulators). 
 
 In the theoretical part of this treatise, the polarization- current 
 has been referred to. Although the polarization of metal plates 
 for the production of secondary currents had previously been 
 employed by Ritter, the construction of practically useful 
 accumulators was first accomplished by Plante. He found 
 that lead plates dipping in dilute sulphuric acid were specially 
 well adapted for the production of secondary currents, and he 
 arranged the accumulators as follows: In a square glass vessel 
 filled with 10 per cent, sulphuric acid solution, a large number 
 of lead plates were suspended in such a way that all plates 
 with even numbers, 2, 4, 6, and so on, were electrically con- 
 nected one with the other, while the plates with uneven num- 
 bers, hence, 1, 3, 5, and so on, were also in contact with each 
 other. Between the separate plates dipping in the acid was 
 sufficient space to prevent them from touching one another. 
 One series of the plates served as positive, and the other as 
 negative, electrodes. Now by conducting an electric current 
 through the plates, lead peroxide is formed upon the positive 
 electrodes, and by interrupting the current and combining the 
 series of electrodes with each other, the peroxide is reduced to 
 metallic lead, and the negative lead plates are oxidized, whereby 
 an electric discharge takes place, the secondary or accumulator- 
 current passing through the metallic connection of the series of 
 plates from the peroxide to the lead plates. 
 
 Hence, in charging, a conversion of electrical energy into 
 chemical energy takes place and, in discharging, a reconversion 
 of the chemical energy into electric energy. A large quantity 
 of the latter can therefore accumulate in the cells, whence the 
 term accumulator is derived. 
 
 For the production, in the above-described manner, of cur- 
 
SOURCES OF CURRENT. I I 5 
 
 rents of high power and longer duration, the plates have to be 
 suspended as closely together as possible without danger of 
 contact, in order to decrease the internal resistance of the 
 element as far as practicable, and also to increase the quantity 
 of lead peroxide. 
 
 However, the formation of the layer of lead peroxide upon 
 the lead plates of Plante's accumulator was a slow process, and 
 for this reason Faure used lead grids. The square openings in 
 the negative plates are filled with a paste of litharge and sul- 
 phuric acid, and the positive plates with one of minium and 
 sulphuric acid. The current reduces the litharge and peroxi- 
 dizes the minium. 
 
 Plante showed that accumulators form by usage — that is to 
 say, that up to a certain point their capacity is greater the 
 more frequently they have been charged and discharged. By 
 repeated oxidation and deoxidation the lead acquires a spongy 
 structure, and gradually a large mass of metal takes part in the 
 reaction. The formation is accelerated by immersing the fresh 
 plate for a day or two in nitric acid diluted with its own 
 volume of water. 
 
 Chemical processes in the accumulator. Regarding these pro- 
 cesses, several theories have been advanced, for instance, by 
 Elbs, Liebenow, and others, but it has not yet been definitely 
 settled which of these views is correct. There can, however, 
 be no doubt that the lead sulphate which is formed by the 
 action of the sulphuric acid upon the lead, plays the principal 
 role, in so far as the charging and discharging of the accumu- 
 lator are effected only by the decomposition and subsequent 
 reformation of the lead sulphate. 
 
 Elb's theory is as follows : As lead is bivalent and quadri- 
 valent, after the decomposition of the lead sulphate to lead and 
 sulphuric acid, the latter combines with the lead sulphate, which 
 remains undecomposed, to lead disulphate. This formation of 
 lead disulphate must chiefly take place on the positive elec- 
 trodes, since the anion (the sulphuric acid residue) migrates to 
 the positive pole, and by the action of the water the lead disul- 
 phate is decomposed to lead peroxide and free sulphuric acid. 
 
Il6 ELECTRO-DEPOSITION OF METALS. 
 
 If, therefore, the current taken from a dynamo be conducted 
 into the electrodes of an accumulator, so that the positive plates 
 are connected with the -f pole of the dynamo and the negative 
 plate with the — pole, decomposition of sulphuric acid takes 
 place, the hydrogen migrating to the negative electrode, and 
 the sulphuric acid residue to the positive electrode. On the 
 latter, the sulphuric acid residue forms first of all with the lead, 
 lead sulphate according to the following equation : 
 
 S0 4 + Pb = PbS0 4 
 
 Sulphuric acid residue. Lead. Lead sulphate. 
 
 By the influx of additional S0 4 -ions, this lead sulphate is 
 converted into lead disulphate : 
 
 S0 4 + PbS0 4 Pb(S0 4 ), 
 
 Sulphuric acid residue. Lead sulphate. Lead disulphate. 
 
 However, since the formation of the lead disulphate does 
 not take place quantitatively, S0 4 -ions are simultaneously con- 
 verted into sulphuric acid, H,S0 4 , oxygen being separated in 
 the form of gas. 
 
 According to Elbs, lead disulphate decomposes with water 
 to lead peroxide and sulphuric acid according to the following 
 equation : 
 
 Pb(S0 4 ) 2 + 2H 2 = PbO a 2 + H 2 S0 4 
 
 Lead disulphate. Water. Lead peroxide. Sulphuric acid. 
 
 Thus, if the current be interrupted, we have lead peroxide 
 on the positive electrode, and spongy lead reduced by hydro- 
 gen, on the negative electrode. If now the positive electrodes 
 be connected with the negative electrodes by a closed wire, a 
 current passes through this wire from the positive lead peroxide 
 electrodes to the negative lead electrodes, and from the latter, 
 through the electrolyte, back to the positive electrodes. 
 
 Thus during the discharge, the spongy lead plate becomes 
 the positive electrode and the lead peroxide plate, the negative 
 electrode, in consequence of which, by the decomposition of 
 
SOURCES OF CURRENT. 117 
 
 the sulphuric acid, the anion S0 4 migrates to the positive lead 
 electrode, and forms lead sulphate, while the hydrogen sep- 
 arated on the negative electrode reduces the lead peroxide to 
 lead oxide or to metallic lead. 
 
 These processes take place according to the following equa- 
 tions : 
 
 On the — electrode 
 
 On the -f electrode 
 
 Pb + SO, = PbSO, 
 
 Lead. Sulphuric acid residue. Lead sulphate. 
 
 Pb0 2 + 2H = PbO -f H 2 
 
 Lead peroxide. Hydrogen. Lead oxide. Water. 
 
 This lead oxide formed on the + electrode also forms lead 
 sulphate with sulphuric acid, and when all the lead peroxide is 
 reduced, the generation of current ceases, the accumulator is 
 exhausted, and has to be recharged, whereby a repetition of 
 the processes above described takes place. On the spongy 
 lead plate which has now again become the negative electrode, 
 the lead sulphate formed is reduced by the hydrogen to spongy 
 lead and sulphuric acid : 
 
 PbS0 4 + 2H = Pb + H 2 SO, 
 
 Lead sulphate. Hydrogen. Lead. Sulphuric acid, 
 
 whilst on the positive electrode lead peroxide is formed accord- 
 ing to the above-described transpositions. 
 
 From these processes it follows that by the discharge of the 
 accumulator, sulphuric acid for the formation of lead sulphate 
 is fixed on the negative, as well as on the positive, electrode. 
 The electrolyte must therefore contain less free sulphuric acid 
 than at the time of charging, during which the lead sulphate at 
 the negative electrode is reduced to lead, and oxidized to lead 
 peroxide on the positive electrode, the sulphuric acid of the 
 sulphate being thus again present in the electrolyte in the form 
 of free sulphuric acid. The specific gravity of the electrolyte 
 will be the higher, the more free sulphuric acid is present, and 
 by determining it by means of a hydrometer, it can be seen 
 when charging is finished, the latter being the case when no 
 
I I 8 ELECTRO-DEPOSITION OF METALS. 
 
 further increase in the specific gravity is noticed. The com- 
 pletion of charging is further indicated by a copious escape of 
 oxygen on the positive pole plates, which is due to the sul- 
 phuric acid residue finding no more material for the formation 
 of lead sulphate, therefore forms sulphuric acid, water being 
 decomposed, while oxygen in the form of gas is liberated. 
 
 Liebenow assumes that in charging there are formed by the 
 decomposition of the lead sulphate, sulphuric-acid-ions, lead- 
 ions, and, by the co-operation of water, lead-peroxide-ions and 
 hydrogen-ions, according to the following equation: 
 
 + + + 
 
 2PSO, + 2H,0 == Pb + 4 H + PbO, + 2S0 4 . 
 
 The anions sulphuric acid and lead peroxide migrate to the 
 positive pole and the kathions lead and hydrogen to the nega- 
 tive pole. However, on both the poles only those ions are 
 separated for the precipitation of which the least work is re- 
 quired, or, in other words, whose decomposition-point is low- 
 est, which in this case are lead peroxide and lead. Since, 
 however, on account of the slight solubility and dissociation of 
 lead salts, the ions in the immediate proximity of the electrodes 
 would soon be exhausted, further charging can only take place 
 when from the lead sulphate formed on the electrodes, fresh 
 molecules are brought into solution, by the dissociation of 
 which the precipitated ions are replaced, and charging is only 
 finished when all the lead sulphate is dissolved and separated 
 as lead peroxide and lead-sponge. With a further passage 
 hydrogen-ions, which possess the next highest decomposition- 
 point, are separated. The above-described process which in 
 charging takes place by the action of the current, progresses in 
 a reverse sense when, by connecting the positive and negative 
 electrodes, the discharge is rendered possible, whereby the 
 accumulator-current becomes available for exterior work. The 
 lead peroxide is reduced and lead and lead sulphate are formed, 
 while on the negative electrode the lead-sponge is oxidized, 
 sulphate of lead being also formed at the same time. 
 
SOURCES OF CURRENT. 
 
 119 
 
 According to Liebenovv's theory the electrolytic process is 
 reversible without loss of energy, while, according to Elbs's, the 
 process is irreversible and connected with a loss of energy. In 
 most recent times, Dolezalek, Nernst, Loeb, and others have 
 expressed themselves in favor of Liebenow's view, while Le 
 Blanc has discussed the possibility of the formation of lead 
 peroxide-ions alongside of quadrivalent lead-ions. He assumes 
 that at the moment of discharge, the latter are converted into 
 bivalent lead-ions, the dissolving lead peroxide furnishing ad- 
 ditional quadrivalent lead-ions, while at the moment of charg- 
 ing the bivalent lead-ions are converted into quadrivalent ones, 
 
 Fig. 43. 
 
 and form lead peroxide. The view, that instead of one process 
 in the accumulator, several processes are jointly enacted, may- 
 prove to be the correct one. 
 
 Fig. 43 shows a common form of an accumulator. The 
 separate electrodes are insulated from each other by glass 
 tubes, the entire system being secured by lead springs which 
 press the electrodes against the glass tubes. Small accumu- 
 lator cells are of glass, hard rubber or celluloid, and larger ones 
 of wood lined with lead. 
 
120 ELECTRO-DEPOSITION OF METALS. 
 
 The sulphuric acid used for filling should be free from 
 chlorine and metallic impurities, and have a specific gravity of 
 1.18. In a charged state of the accumulator, the specific 
 gravity rises to about 1.2 1. 
 
 Maintenance of accumulators. An accumulator should never 
 be allowed to stand without being charged, since, in such a case, 
 crystals of lead sulphate are formed upon the electrodes, which 
 can only be removed with difficulty, and by this formation of 
 crystals the accumulator acquires a very great resistance. 
 When not in use an accumulator should be freshly charged 
 every two weeks, because it gradually discharges itself. 
 
 The acid should be put in the cells to such a height that the 
 electrodes are covered about 5 millimeters deep and, since by 
 the evaporation of water and, especially by the so-called " boil- 
 ing " of the accumulator, i. e., by the escaping gases of oxygen 
 and hydrogen, sulphuric acid is carried along, the fluid has to 
 be brought to its original level by the addition of dilute sul- 
 phuric acid of 1.05 specific gravity. 
 
 By the formation of lead peroxide and its subsequent reduc- 
 tion, the positive electrodes readily undergo changes in volume, 
 they being liable to buckling and the scaling off of active mass ; 
 lead-crystals of considerable length may deposit on the nega- 
 tive electrodes, both these occurrences giving rise to short- 
 circuiting. Hence, the accumulator should be frequently in- 
 spected, and the mass collecting on the bottom, as well as the 
 lead-crystals, be removed. 
 
 Charging of a cell should always be effected with a higher 
 voltage than that of the cell, and the dynamo should only be 
 coupled with the accumulator when it furnishes a current of 
 sufficiently good electro-motive force. For a single cell, charg- 
 ing is commenced with an electro-motive force of 2 volts. 
 Towards the completion of charging, the electro-motive force 
 of the charging current should be 2.6 to 2.7 volts. After in- 
 terrupting the charging current the electro-motive force of each 
 cell falls off to about 2.25 volts. 
 
 During the discharge, the electro-motive force of the cells 
 
SOURCES OF CURRENT. 12 [ 
 
 rapidly falls to about 2 volts each, remaining constant at this 
 value for quite a long time, when it falls slowly to 1.8 volts, and 
 rapidly from that point on. The appearance of the last-men- 
 tioned occurrence should by all means be avoided and, when 
 the electro-motive force falls to 1.8 volts, discharge of current 
 should be discontinued, as otherwise the electrodes would be 
 subject to rapid destruction. 
 
 Coupling accumulators. Like the voltaic cells, the individ- 
 ual accumulators may, according to requirement, be coupled 
 alongside one another (in parallel), or one after the other (in 
 series). 
 
 For the production of electrolytic depositions, cells of great 
 capacity have to be taken exclusively into account, that is, 
 cells capable of yielding a great strength of current for a cer- 
 tain number of hours. This value, current-strength X time, is 
 called ampere hours capacity. 
 
 If for an electrolytic process a maximum electro-motive force 
 of 1.8 volts is required, one cell may be coupled to the bath, or 
 if its capacity be insufficient, several such cells in parallel. If, 
 on the other hand, the bath requires a greater electro-motive 
 force, two or three cells will have to be coupled one after the 
 other, and an excess of electro-motive force has to be destroyed 
 by a resistance. The cells may be charged and discharged in 
 parallel, or they may be discharged in series by means of a 
 transformer, and vice versa, they may be charged in series and 
 discharged in parallel, further details of which will be given in 
 the Practical Part. 
 
IV. 
 PRACTICAL PART. 
 
 CHAPTER IV. 
 
 ARRANGEMENT OF ELECTRO-PLATING ESTABLISHMENTS IN 
 
 GENERAL. 
 
 Although rules valid for all cases cannot be given, because 
 modifications will be necessary according to the size and extent 
 of the establishment, the nature of the articles to be electro- 
 plated, and the method of the process itself, there are, never- 
 theless, certain main features which must be taken into consid- 
 eration in arranging every establishment, be it large or small. 
 
 Light in plating rooms. Only rooms with sufficient light 
 should be used, since the eye of the operator is severely taxed 
 in judging whether the articles have been thoroughly freed from 
 fat, in recognizing the different tones of color, etc. A northern 
 exposure is especially suitable, since otherwise the reflection 
 caused by the rays of the sun may exert a disturbing influence. 
 For larger establishments the room containing the baths should, 
 in addition to side-lights, be provided with a sky-light, which, 
 according to the location, is to be protected by curtains from 
 the rays of the sun. 
 
 Ventilation. Due consideration must be given to the fre- 
 quent renewal of the air in the rooms. Often it cannot be 
 avoided that the operations of pickling, etc., must be carried 
 on in the same room in which the baths are located. Espe- 
 cially unfavorable in this respect are smaller establishments 
 working with batteries, in which the vapors evolved from the 
 
 (122) 
 
ELECTRO-PLATING ESTABLISHMENTS. I 23 
 
 latter are added to the other vapors, and render the atmos- 
 phere injurious to health. Hence, if possible, rooms should be 
 selected having windows on both sides, so that by opening 
 them the air can at any time be renewed, or the baths and bat- 
 teries should be placed in rooms provided with chimneys. By 
 cutting holes of sufficient size in the chimneys near the ceilings 
 of the rooms, the discharge of injurious vapors will in most 
 cases be satisfactorily effected. 
 
 To those working with Bunsen cells, it is recommended to 
 place them in a closet varnished with asphalt or ebonite lac- 
 quer, and provided with lock and key. The upper portion of 
 the closet should communicate by means of a tight wooden 
 flue with a chimney or the open air. 
 
 Heating the plating rooms. Since the baths work with 
 greater difficulty, more slowly and more irregularly below a 
 certain temperature, provision for the sufficient heating of the 
 plating rooms must be made. Except baths for hot gilding, 
 platinizing, etc., the average temperature of the plating solu- 
 tions should be from 64.5 ° to 68° F., at which they work best; 
 it should never be below 59 F., for reasons to be explained 
 later on. Hence, for large operating rooms such heating 
 arrangements must be made that the temperature of the baths 
 cannot fall below the minimum even during the night, other- 
 wise provision for the ready restoration of the normal tempera- 
 ture at the commencement of the work in the morning has to 
 be made. Rooms heated during the day with waste steam from 
 the engine, generally so keep the baths during the winter — the 
 only season of the year under consideration — that they show in 
 the evening a temperature of 64. 5 to 68° F., and if the room 
 is not too much exposed, the temperature, especially of large 
 baths, will only in rare cases fall below 59 F. For greater 
 security the heating pipes may be placed in the vicinity of the 
 baths, but if this should not suffice to protect the baths from 
 cooling off too much, it is advisable to locate in the plating 
 room a steam conduit of small cross-section fed from the boiler, 
 and to pass steam for a few minutes through a coil of a metal 
 
124 ELECTRO-DEPOSITION OF METALS. 
 
 indifferent to the plating solution suspended in the bath. In 
 this manner baths of iooo quarts, which on account of several 
 days' interruption in the operation, had cooled to 36 F., were 
 in 10 minutes heated to 68° F. 
 
 It has also been tried to heat large baths, for instance, nickel 
 baths, by electrically heated boilers. The consumption of cur- 
 rent is, however, very great, and the boilers of nickel sheet 
 thus far do not answer all rational demands, especially as re- 
 gards durability. 
 
 For smaller baths it is advisable to bring a small portion of 
 them in a suitable vessel to the boiling-point over a gas flame, 
 and add it to the cold bath. If, after mixing, the temperature 
 is still too low, repeat the operation. 
 
 Renewal of water. Another important factor for the rooms, 
 is the convenient renewal of the waters required for rinsing and 
 cleansing. Without water the electro-deposition of metals is 
 impossible ; the success of the process depending in the first 
 place on the careful cleansing of the metallic articles to be 
 electro-plated, and for that purpose water, nay, much water, 
 hot and cold, is required, as will be seen in the section treating 
 on the " Preparation of the Articles." Large establishments 
 should, therefore, be provided with pipes for the admission and 
 discharge of water, one conduit terminating as a rose over the 
 table where the articles are freed from grease. In smaller 
 establishments, where the introduction of a system of water- 
 pipes would be too expensive, provision must be made for the 
 frequent renewal of the cleansing water in the various vats. 
 
 Floors of the plating rooms. In consequence of rinsing and 
 transporting the wet articles to the baths much moisture col- 
 lects upon the floors of the plating rooms. The best material 
 for floors of large rooms is asphalt, it being, when moist, less 
 slippery than cement. A pavement of brick or mosaic laid in 
 cement is also suitable, but has the disadvantage of cooling 
 very much. The pavement of asphalt or cement should have 
 a slight inclination, a collecting basin being located at the low- 
 est point, which also serves for the reception of the rinsing 
 
ELECTRO-PLATING ESTABLISHMENTS. 1 25 
 
 water. Wood floors cannot be recommended, at least for large 
 establishments, since the constant moisture causes the wood to 
 rot. However, where their use cannot be avoided, the places 
 where water is most likely to collect should be strewn with sand 
 or sawdust, frequently renewed, or the articles when taken from 
 the rinsing water or bath be conveyed to the next operation in 
 small wooden buckets or other suitable vessels. 
 
 Size of plating room. The plating room should be of such a 
 size as to permit the convenient execution of the necessary 
 manipulations. Of course, no general rule can be laid down in 
 this respect, as the size of the room required depends on the 
 number of the processes to be executed in it, the size and num- 
 ber of articles to be electroplated daily or within a certain time, 
 etc. However, there must be sufficient room for the batteries 
 or dynamo, for the various baths, between which there should 
 be a passageway at least twenty inches wide for the table where 
 the articles are freed from grease, for the lye kettle, hot-water 
 reservoir, sawdust receptacle, tables for tying the articles to 
 hooks, etc. 
 
 Grinding and polishing rooms. The rooms used for grinding, 
 polishing, etc., also require a good light in order to enable the 
 grinder to see whether the article is ground perfectly clean, 
 and all the scratches from the first grinding are removed. 
 Where iron or other hard metals are ground with emery it is 
 advisable to do the polishing in a room separated from the 
 grinding shop by a close board partition ; because in the pre- 
 paratory grinding with emery, which is done dry, without the 
 use of oil or tallow, the air is impregnated with fine particles of 
 emery, which settle upon the polishing wheels and materials, and 
 in polishing soft metals cause fine scratches and fissures which 
 spoil the appearance of the articles, and can be removed only 
 with difficulty by polishing. Hence all operations requiring 
 the use of emery, or coarse grinding powders, should be per- 
 formed in the actual grinding room, as well as the grinding 
 upon stones and scratch-brushing by means of rapidly revolv- 
 ing steel scratch-brushes. Articles already plated are, of 
 
126 ELECTRO-DEPOSITION OF METALS. 
 
 course, scratch-brushed in the plating room itself, either on the 
 table used for freeing the articles from grease, or on a bench 
 especially provided for the purpose. In the polishing room 
 are only placed the actual polishing machines, which by means 
 of rapidly revolving wheels of felt, flannel, etc., and the use of 
 polishing powders, or polishing compositions, impart to the 
 articles the final luster before and after electro-plating. The 
 formation of dust in the polishing rooms is generally overesti- 
 mated ; it is, however, sufficiently serious to render necessary 
 the separation by a close partition of the polishing rooms from 
 the electro-plating room, otherwise the polishing dust might 
 settle upon the baths and give rise to various disturbing phe- 
 nomena. In rooms in which large surfaces are polished with 
 Vienna lime, as, for instance, nickeled sheets, the dust often 
 seriously affects the health of the polishers, especially in badly 
 ventilated rooms, and in such cases it is advisable to provide 
 an effective ventilator. If this cannot be done, wooden frames 
 covered with packing-cloth, placed opposite the polishing 
 wheels, render good service ; the packing-cloth, by being fre- 
 quently moistened, retaining a large portion of the polishing 
 dust. 
 
 Distance between machines. Care should be taken to have 
 sufficient room between the separate machines to prevent the 
 grinders and polishers, when manipulating larger pieces of 
 metal, from inconveniencing each other. Tables for putting 
 down the articles should also be provided. 
 
 Transmission. For grinding lathes requiring the belt to be 
 thrown off in order to change the grinding, it is best to place 
 the transmission carrying the belt pulleys at a distance of about 
 three feet from the floor, while for lathes with spindles outside 
 the bearings the transmission may be on the ceiling or wall. 
 The revolving direction of the principal transmission should be 
 such as to render the crossing of the belts to the grinding and 
 polishing machines unnecessary, otherwise the belts on account 
 of the great speed will rapidly wear out. 
 
 The more modern electrically-driven grinding and polishing 
 
ELECTRO-PLATING ESTABLISHMENTS. 1 27 
 
 machines are briefly called grinding and polishing motors, and 
 have decided advantages over machines driven by belts. They 
 will be referred to later on in the section " Mechanical Treat- 
 ment." 
 
 Electro-plating Arrangements in Particular. 
 
 The actual electro-plating plant consists of the following 
 parts: 1. The sources of current (batteries or dynamo-electric 
 machines) with auxiliary apparatus. 2. The current-conductors. 
 
 3. The baths, consisting of the vats, the plating solution, the 
 anodes, and the conducting rods with their binding-screws. 
 
 4. The apparatus for cleansing, rinsing, and drying. 
 
 Before entering into the discussion of these separate parts of 
 an electro-plating plant, it will first be necessary to speak of 
 the electric conditions in the electrolyte, since what will here 
 be said applies to all electro-plating processes, and will serve 
 for a better comprehension of the succeeding sections. 
 
 Current-density. For the result of the electrolytic process, 
 the requisite to be taken first of all into consideration is, that a 
 sufficient quantity of current acts upon the surfaces of the ob- 
 jects to be electro-plated, and next that the current possesses 
 sufficient electro-motive force for the decomposition of the 
 bath. The quantity of current which is necessary for the nor- 
 mal formation of an electro-deposit upon 1 square decimeter 
 = 10 x 10 centimeters (100 square centimeters) is now desig- 
 nated as the current-density . In the electro-plating processes 
 to be described later on, the suitable current-density is always 
 given. If, for instance, this normal current-density is for a 
 nickel bath, 0.4 ampere per square decimeter, the electro-motive 
 force 2.5 volts, and the largest object-surface to be nickeled in 
 the bath, 50 cm. x 20 cm. == 1000 square centimeters, a cur- 
 rent strength of at least 0.4 x 10 = 4 amperes is required. A 
 Bunsen cell, which furnishes 4 amperes, would therefore suffice 
 if the electro-motive force required for the decomposition of 
 the electrolyte did not amount to 2.5 volts. As previously 
 mentioned, a Bunsen cell furnishes about 1.8 volts, and to 
 
128 ELECTRO-DEPOSITION OF METALS. 
 
 attain the greater electro-motive force two cells have to be 
 coupled one after the other. The performance of the battery- 
 would then amount to 4 amperes and 3.6 volts, and the excess 
 of electro-motive force, which would be an impediment to 
 deposition proceeding in a normal manner, has to be destroyed 
 by a current-regulator to be described later on, in case it is not 
 preferred to increase the object-surface in the bath. 
 
 For silvering the current-density amounts to 0.25, and a 
 silver bath with a slight excess of potassium cyanide requires 
 1 volt. If now, for instance, an object-surface of 55 square 
 decimeters, about equal to 50 large soup spoons, is to be 
 silvered, 55 x 0.25 = 13.75 amperes and 1 volt are required. 
 Hence three cells of 5 amperes each have to be coupled along- 
 side each other to obtain 15-amperes current-quantity. 
 
 The abbreviation of ND 100 is used to designate the normal 
 current-density. By multiplying it with the number of square 
 decimeters which the object-surface represents, the current- 
 strength required for the object-surface is found. 
 
 When the current- density with which deposition is made is 
 known, the quantity by weight of the deposit effected in a 
 definite time can be readily calculated. The electro-chemical 
 equivalent has been referred to on p. 59, and it has been 
 established that it represents the number of coulombs which 
 separate 1 gramme-equivalent of metal per second. When by 
 1 coulomb, i. c, by 1 ampere, 0.3290 mg. copper per second is 
 separated from cupric oxide salts, 1.184 gr. copper are sepa- 
 rated in the ampere-hour (3600 seconds). 
 
 For practical purposes the quantities of a metal separated in 
 1 ampere-hour are designated as the electro-chemical equivalent 
 of the ampere-hour, and the quantities of metal separated with 
 a known current-strength in a definite time are obtained by 
 multiplying the electro-chemical equivalent with the current- 
 strength in amperes and the number of hours. 
 
 For calculating the time in which with a known current- 
 strength, a certain quantity by weight is obtained, the latter is 
 simply divided by the weight of the ampere-hours deposit X 
 the current-sfrength. 
 
ELECTRO-PLATING ESTABLISHMENTS. 1 29 
 
 Another problem may be to calculate the current-strength 
 which is required for furnishing in a certain time a definite 
 quantity by weight of deposit. For this purpose, divide the 
 quantity by weight by the product of ampere-hours deposit 
 and number of hours. 
 
 We will first of all illustrate these calculations by two ex- 
 amples without regard to the current-output. Suppose the 
 time is to be determined during which a square decimeter of 
 surface has to remain in the nickel bath in order to acquire a 
 deposit of ^0 millimeter thickness with a current-density of 0.4 
 ampere. First calculate the weight of the deposit by multiply- 
 ing the surface in square millimeters with the thickness and 
 specific gravity. One square decimeter is equal to 10,000 
 square millimeters, which, multiplied by -~w millimeter, gives as 
 a product 1000, which multiplied by the specific gravity of 
 nickel — 8.6 — gives 8600 milligrammes = 8.6 grammes. Hence 
 a deposit of yL milligramme thickness upon a surface of 1 
 square decimeter represents a weight of 8.6 grammes. Since, 
 for the normal deposit per square decimeter, a current-density 
 of 0.4 ampere is required, and 1 ampere deposits, according 
 to the table given on p. 60, 1.1094 grammes in 1 hour, yd 
 ampere deposits 0.4437 gramme in 1 hour, and, therefore, 
 about 19^ hours will be required for the deposition of 8.6 
 grammes. 
 
 For calculating the time which one, two or more dozen of 
 knives and forks or spoons, which are to have a deposit of silver 
 of a determined weight, must remain in the bath when the 
 current-density is known, proceed as follows: Suppose 50 
 grammes of silver are to be deposited upon 1 dozen of spoons, 
 and the most suitable current-density is 0.2 ampere per square 
 decimeter; if the surface of 1 spoon represents lio square 
 decimeters, the surface of 1 dozen spoons of equal size is 13.2 
 square decimeters. Hence, they require 13.2 X 0.2 = 2.64 
 amperes; now, since 1 ampere deposits in 1 hour 4.025 
 grammes of silver, 2.64 amperes deposit in the same time 10.62 
 grammes of silver, and with this current, the dozen spoons must 
 9 
 
130 ELECTRO-DEPOSITION OF METALS. 
 
 remain about 4% hours in the bath for the deposition of 50 
 grammes of silver upon this surface. 
 
 However, the figures obtained are correct or approximately 
 correct only when the current-output amounts to 100 per cent., 
 or to approximately this value, as in the case with acid copper 
 baths, silver, gold, zinc and tin baths ; with a smaller current- 
 output as yielded by potassium cyanide copper and brass 
 baths, and nickel baths, a suitable correction has to be made. 
 
 The current-output of a bath is best determined as follows : 
 Deposit upon an accurately weighed plate (sheet) of metal for 
 several hours with the normal current-density, and note the 
 exact time of deposition and the quantity of current measured 
 by a voltmeter inserted in the circuit. Rinse the plate first 
 with water and then with alcohol and ether, and dry thoroughly. 
 Weigh it and by deducting the previous weight, the weight of 
 the deposit is found. Now calculate from the table of electro- 
 chemical equivalents (p. 60) how much metal should have 
 been precipitated in the time consumed by the current- strength 
 used, the result being the theoretical current-output. The 
 practical current-output in per cent, is found by multiplying 
 the weight of the deposit found by 100 and dividing by the 
 calculated weight of the theoretical current-output. 
 
 Suppose the plate weighs 12.00 grammes and after having 
 deposited upon it nickel for 3 hours with 1.5 ampere, it 
 weighs 16.45 grammes, which corresponds to a deposit of nickel 
 of 16.45 — 12.00=4.45 grammes. Theoretically, 1.5 ampere 
 should separate in 3 hours ( 1.1094X 1-5 X 3) 4-923 grammes 
 of nickel. Hence, the practical current-output attained is 
 
 4.925 14.45 = 100: x 
 x = 90.35 per cent. 
 
 In calculating the quantity by weight, the product obtained 
 from electro-chemical equivalent X current-strength X num- 
 ber of hours, would have to be multiplied by the fraction 
 Current-output in per cent. . jn cakulating the time , the re _ 
 100 
 
ELECTRO-PLATING ESTABLISHMENTS. 131 
 
 suit obtained above would have to be multiplied by the fraction 
 100 
 
 , and for calculating the current- 
 current-output in per cent. 
 
 strength the quotient is likewise to be multiplied by the fraction 
 
 100 
 
 current-output in per cent. 
 
 Electro-motive force in the bath. It has previously been seen 
 that for the permanent decomposition of an electrolyte, an 
 electro-motive force is required which must be large enough 
 to overcome the resistance of the electrolyte, as well as the 
 polarization-current flowing counter to the main current. 
 
 The resistance of the electrolyte is found by multiplying its 
 specific resistance, i. e., the resistance of a fluid cube of 1 deci- 
 meter side-length by the electrode distance in decimeters, and 
 dividing by the object-surface expressed in square decimeters, 
 thus, 
 
 Resistance of the electrolyte - Specific resistance X dm . e lectrode-distance 
 
 dm. object-surface. 
 
 According to p. 20^ the electro-motive force required for 
 sending a certain current- strength through a conductor is equal 
 to the product of current-strength and resistance. To calculate 
 this electro-motive force, the resistance of the electrolyte, i. e., 
 of the bath, as found above, has to be multiplied by the current- 
 density. 
 
 For the better understanding, an example may here] be given, 
 the problem being to copper in an acid copper-bath an object- 
 surface of 100 square decimeters. 
 
 Let the specific resistance of the acid copper-bath of a given 
 composition be 0.92 ohm, the electrode-distance 1.2 decimeters, 
 the normal current-density 1.25 amperes. The required current- 
 strength, J, is found by multiplying the normal density by the 
 object-surface in square decimeters, thus, 
 
 J = 100 X 1.25 = 125 amperes. 
 
 From what has above been said, the resistance, ', W, of the 
 
132 ELECTRO-DEPOSITION OF METALS. 
 
 electrolyte is obtained by multiplying the specific resistance by 
 the electrode-distance in decimeters, and dividing the product 
 by the object-surface in square decimeters : 
 
 „ 7 O.Q2 X 1.2 , 
 
 W = - =0.01104 ohm. 
 
 100 
 
 From this the electro-motive force, E, required to send the 
 current-strength, J, through the bath is calculated. 
 
 E = JX W=i25 X 0.01 104 == 1.38 volt. 
 
 However, this is valid only for the normal temperature of 
 1 8° C. (64. 40 F.). If the electro- motive force has to be 
 calculated, which is required at a higher temperature, for send- 
 ing the current-strength of 125 amperes through the bath, we 
 have to fall back upon the temperature- coefficients and the 
 formulas given for them on p. 25, whereby, if the temperature 
 of the bath is 24 C. (75. 2° F.), the equation assumes the fol- 
 lowing form : 
 
 Specific resistance — 0.92 (1 — 0.01 13X6) = 0.858 ohm. 
 
 Hence the temperature-coefficient 0.0113 has to be multi- 
 plied by the number of degrees C, the bath is warmer than 
 1 8° C, the product subtracted from I, and the remainder 
 multiplied by the specific resistance at 18 C, 0.92 ohm. It 
 will be seen that the specific resistance (Sp. R.), which amounts 
 at 1 8° C. to 0.92 ohm, amounts at 24 C. only to 0.858 ohm. 
 The resistance, W, of the electrolyte at 24 C. is therefore 
 
 W 
 
 0.858 X 1.2 „ , 
 
 _ = 0.0103 ohm. 
 
 100 
 
 and the electro -motive force, E, which is capable of forcing 125 
 amperes through the resistance of 0.0103 ohm: 
 
 E = JxW= 125 X 0.0103 = 1.287 volt- 
 
 If the electrolyte is 6° C. colder than 18 C, the formula is 
 
ELECTRO-PLATING ESTABLISHMENTS. I 33 
 
 so changed that the temperature-coefficient 0.0113 has to be 
 multiplied by 6, the product added to 1, and the sum multi- 
 plied by the specific resistance (Sp. R.). 
 
 Sp. R. = 0.92 (1 + 0.01 13X6) = 0.9824 ohm ; 
 
 the resistance of the bath is then : 
 
 ,, f 0.9824 X 1.2 ~ , 
 
 W = — - 5— : = 0.0 1 178 ohm, 
 
 100 
 
 the electro-motive force required being therefore : 
 
 E = J X W == 125 X 0.01178= 1 .472 volt. 
 
 Electro-motive counterforce of polarization. In addition to 
 this resistance of the electrolyte, the electro-motive counter- 
 force of the polarization-current has to be taken into considera- 
 tion. The causes of polarization have been explained on p. 
 64 ; it being partly due to the formation of gas-cells during 
 electrolysis with insoluble electrodes, especially anodes, partly 
 to changes in concentration in the vicinity of the electrodes, or 
 to oxidizing or reducing processes in the electrolyte. In most 
 cases of electrolysis coming here in question, the dilution 
 formed on the cathodes by the separation of metal will send a 
 polarization-current towards the more concentrated layers of 
 fluid formed by the solution of the anode-metal, to which is 
 added the counter-current formed by the contiguity of fluids 
 with salts of a lower degree of oxidation to fluids with salts of 
 a higher degree of oxidation. The magnitude of polarization 
 is materially influenced by the nature of the metals of which 
 the electrodes consist; the more electro-positive the cathode- 
 metal and the more electro-negative the anode-metal, the 
 greater the electro-motive force of the polarization-current 
 which flows from the more positive cathode to the negative 
 anode, hence in an opposite direction to the main current, 
 which enters at the anode and passes out at the cathode. This 
 explains why in nickeling iron less electro-motive force is re- 
 
134 ELECTRO-DEPOSITION OF METALS. 
 
 quired than in nickeling zinc, iron being only to a slight degree 
 more positive than the nickel-metal of the anode, and hence 
 less electro-motive counterforce appears. Zinc, on the other 
 hand, is far more positive than iron, and the electro-motive 
 force of the polarization-current is consequently essentially 
 stronger. 
 
 The determination of this electro-motive counterforce is in 
 the most simple manner effected by experiment. If a volt- 
 meter of great resistance be placed at the bath, and the main 
 current which had been passed into the bath be suddenly in- 
 terrupted by means of a switch, the needle of the voltmeter 
 does not at once return to the O-point, but remains for some 
 time in a position above that point, and then gradually returns 
 to it. The electro-motive force indicated by the needle for the 
 short time after the interruption of the current gives the electro- 
 motive force of the polarization-current. 
 
 The electro-motive counterforce is influenced by the magni- 
 tude of the current-density, growing and falling with the latter. 
 When the magnitude of the counterforce has been determined 
 by experiment as above described, the electro-motive force of 
 he main current required for the electrolytic process is made 
 up of the electro- motive force found by multiplying the current- 
 strength by the resistance of the electrolyte plus the electro- 
 motive counterforce of polarization found by experiment. 
 
 Proceeding from the opinion that the electric current-lines 
 are subject to scattering similar to the magnetic lines of force, 
 Pfanhauser has taken into account the magnitude of this scatter- 
 ing of the current-lines for the calculation of the resistance of 
 the electrolyte. When such scattering takes place, the current- 
 lines will not collectively migrate by the shortest road from the 
 anode to the cathode, but describe greater or smaller curves, 
 the cross-section of the fluid which takes part in the conduc- 
 tion of the current, becoming thereby greater than if the cur- 
 rent would pass, without deviation whatever, between the elec- 
 trodes, and the resistance of the electrolyte consequently be- 
 comes smaller. The least scattering was found with electrodes 
 
ELECTRO-PLATING ESTABLISHMENTS. 135 
 
 of the same size, it increasing with the greater distance of the 
 electrodes from each other. In electro-plating processes run- 
 ning a normal course, the decrease in the resistance of the bath 
 by the scattering of current-lines may practically be disre- 
 garded, and it will later on only be referred to in so far as 
 various phenomena which appear in electro-plating have been 
 explained by this scattering. 
 
 We will now turn to the discussion of electro-plating installa- 
 tions with the different sources of current, and the arrangement 
 with cells will first be described. It will be necessary to specify 
 in this section all the laws and rules which are also valid for 
 installations with other sources of current, and the reader is 
 requested thoroughly to study this section as repetition in sub- 
 sequent sections is not feasible. 
 
 A. Installations with Cells. 
 
 Coupling of cells. Prior to the time when it became possible 
 to calculate the normal current-strength for a definite object - 
 surface, because the magnitude to which the term current- 
 density has been applied was not known, the transmission of the 
 quantity of current required for the electro-plating processes 
 was effected in a purely empirical manner. The effective zinc 
 surface of the cells was taken as the basis, and it was held that 
 with baths of medium resistance a good deposit is generally 
 effected when the effective zinc-surface of the cells is of the 
 same size as the object-surface which is to be plated, and as 
 large as the anode-surfaces. The electro-motive force required 
 was obtained by coupling a larger or smaller number of cells 
 one after the other. Suppose we have a nickel bath which re- 
 quires for its decomposition a current of 2.5 volts of electro- 
 motive force. Now since, according to p. 77, a Bunsen cell 
 develops a current of 1.88 volts, the reduction of the nickel 
 cannot be effected with one such cell alone, but two cells will 
 have to be coupled for electro-motive force one after the other, 
 whereby, leaving the conducting resistance of the wires out of 
 consideration, an electro-motive force of 2 X 1.88 — 3.76 volts 
 
136 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 is obtained, with which the decomposition of the solution can 
 be effected. 
 
 If, on the other hand, we have a silver bath which requires 
 only i volt for its decomposition, we do not couple two cells 
 one after the other, because the electro-motive force of a single 
 cell suffices for the reduction of the silver. On p. 87 it has 
 been seen that by coupling the elements one after the other 
 (coupling for electro-motive force) the electro-motive force of 
 the battery is increased, but the quantity of current is not in- 
 creased, and that to attain the latter, the cells must be coupled 
 alongside of one another (coupled for quantity). Hence in a 
 group of, for instance, three cells coupled one after another, 
 only one single zinc surface of the cells can be considered 
 effective in regard to the quantity of current. Now, the larger 
 the area of articles at the same time suspended in the bath is, 
 the greater the number of such effective zinc surfaces of the 
 
 Fig. 44. 
 
 group of cells to be brought into action must be; and, if for 
 baths with medium resistance, it may be laid down as a rule 
 that the effective zinc surface must be at least as large as the 
 surface of the articles, provided the surface of the anodes is at 
 least equal to the latter, the approximate number of cells and 
 their coupling for a bath can be readily found. 
 
 Let us take the nickel bath of medium resistance which, as 
 above mentioned, requires a current of 2.5 volts, and for the 
 decomposition of which two cells must, therefore, be coupled 
 
ELECTRO-PLATING ESTABLISHMENTS. I 37 
 
 one after the other, and suppose that the zinc surface of the 
 Bunsen cells is 500 square centimeters, then the effective zinc 
 surface of the two cells coupled one after the other will also be 
 500 square centimeters; hence a brass sheet 20 X 25 = 500 
 centimeters can be conveniently nickeled on one side with 
 these two cells, or a sheet 10 X 25 = 250 centimeters on both 
 sides. Now suppose the surface to be nickeled were twice as 
 large, then the two cells would not suffice, and a second group 
 of two cells, coupled one after the other, would have to be 
 joined to the first group for quantity, as shown in Fig. 22, or 
 perspectively in Fig. 44. Three times the object-surface would 
 require three groups of elements, and so on. 
 
 In giving these illustrations it is supposed the objects are to 
 have a thick, solid plating. For rapid plating and a thin deposit 
 a different course has to be followed. Only a slight excess of 
 electro-motive force in proportion to the resistance of the bath 
 being in the above-mentioned case present, reduction takes 
 place slowly and uniformly without violent evolution of gas on 
 the objects, and by the process thus conducted, the deposit 
 formed is sure to be homogeneous and dense, since it absorbs 
 but slight quantities of hydrogen, and in most cases it can be 
 obtained of such thickness as to be thoroughly resistant. 
 
 For rapid plating, without regard to great solidity and thick- 
 ness of the deposit, the cells, however, have to be coupled so 
 that the electro-motive force is large as compared with the 
 resistance of the bath, so that the current can readily overcome 
 the resistance. This is accomplished by coupling three, four, 
 or more cells one after the other, as shown in the scheme, Fig. 
 20. However, special attention has to be drawn to the fact 
 that deposits produced with a large excess of electro-motive 
 force can neither be dense nor homogeneous, because, in 
 accordance with the generally-accepted view, the deposits con- 
 dense and retain relatively large quantities of hydrogen gas, the 
 term occlusion being applied to this property. 
 
 Current regulation. Only in very rare cases will it be possi- 
 ble to always charge a bath or several baths with the same 
 
138 ELECTRO-DEPOSITION OF METALS. 
 
 object-surface ; and according to the amount of business, or the 
 preparation of the objects by grinding, polishing and pickling, 
 at one time large and at another small, surfaces will be sus- 
 pended in the bath. Now, suppose a battery suitable for a 
 correct deposit upon a surface of, say five square feet, has been 
 grouped together ; and, after taking the articles from the bath, 
 a charge of objects only half as large as before is introduced, 
 the current of the battery will, of course, be too strong for this 
 reduced surface, and there will be danger of the deposit not 
 being homogeneous and dense, but forming with a crystalline 
 structure, the consequence of which, in most cases, will be 
 slight adhesiveness, if not absolute uselessness. With sufficient 
 attention the total spoiling of the articles might be prevented 
 by removing the objects more quickly from the bath. But this 
 is groping in the dark, the objects being either taken too soon 
 from the bath, when not sufficiently plated, or too late, when 
 the deposit already shows the consequences of too strong a 
 current. 
 
 For the control of the current an instrument called a current- 
 regulator, resistance board or rheostat has been devised, which 
 allows of the current-strength of a battery being reduced with- 
 out the necessity of uncoupling cells. It is obvious that the 
 current of a battery, if too strong, can be weakened by decreas- 
 ing the number of cells forming the battery, and also by de- 
 creasing the surface of the anodes, because the external resist- 
 ance is thereby increased. This coupling and uncoupling of 
 cells is, however, not only a time-consuming, but also a dis- 
 agreeable, labor ; and it is best to use a resistance board with 
 which, by the turn of a lever, the desired end is attained. Figs. 
 45 and 46 show this instrument. 
 
 Its action is based upon the following conditions: As previ- 
 ously explained, the maximum performance of a battery takes 
 place when the external resistance is equal to the internal re- 
 sistance of the battery. By increasing the external resistance, 
 the performance is decreased, and a current of less intensity 
 will pass into the bath when resistances are placed in the 
 
ELECTRO-PLATING , ESTABLISHMENTS. 
 
 139 
 
 circuit. The longer and thinner the conducting wire is, and 
 the less conducting power it possesses, the greater will be the 
 resistance which it opposes to the current. Hence, the resist- 
 ance board consists of metallic spirals which lengthen the 
 circuit, contract it by a smaller cross-section, and by the nature 
 of the metallic wire, has a resistance-producing effect. For a 
 slight reduction of the current, copper spirals of various cross- 
 sections are taken, which are succeeded by brass spirals, and 
 finally by German-silver spirals, whose resistance is eleven 
 times greater than that of copper spirals of the same length 
 and cross-section. In Fig. 45 the conducting wire coming 
 
 Fig. 45- 
 
 Fig. 46. 
 
 til. 
 
 To the Both 
 
 from the battery goes to the screw on the left side of the re- 
 sistance board, which is connected by stout copper wire with 
 the first contact-button on the left; hence by placing the 
 metallic lever upon the button furthest to the left, the current 
 passes the lever without being reduced, and flows off through 
 the conducting wire secured to the setting-screw of the lever. 
 By placing the lever upon the next contact button to the right, 
 two copper spirals are brought into the circuit; by turning the 
 lever to the next button, four spirals are brought into the 
 circuit, and so on. By a proper choice of the cross-sections of 
 
140 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 the spirals, their length, and the metal of which they are made, 
 the current may be more or less reduced as desired. 
 
 In case great current-strengths must flow through the resist- 
 ance board, it is more advantageous to couple the spirals in 
 parallel, and not one after the other, as in Figs. 47 and 48. 
 
 The resisting boards may be placed in the circuit itself in two 
 different ways. If the resistance board is to maintain the 
 electro-motive force of the current at the bath constant at a 
 certain height, it is coupled in series. In this case the same 
 current-strength which is consumed at the bath flows through 
 the resistance. This coupling in series, or one after the other, 
 of the resistance board is shown in Fig. 47. 
 
 Fig. 47. 
 
 3 ATM 
 
 BATTERY 
 
 In the other mode of coupling, Fig. 48, the resistance lies in 
 shunt to the circuit, it being coupled parallel to it. According 
 to Kirchoff's law, if there be a branching-off of the current, 
 the sum of the current-strengths in the separate branches is 
 just as great as the current-strength prior to and after branch- 
 ing off, and the current-strengths in the separate branches are 
 inversely proportional to the resistances of the separate 
 branches. 
 
 In the case in question the coupling of the resistance-board 
 (Fig. 48) represents such a branching-off of the current; the 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 141 
 
 greater the resistance of the resistance-board, the less the 
 current-strength will be which flows through it ; otherwise, a 
 greater resistance in the main circuit, hence in this case in the 
 bath, will cause a portion of the current-strength to flow through 
 the resistance board, where it is destroyed. 
 
 This parallel coupling of the resistance board with the bath 
 is utilized to remove differences in the operating electro-motive 
 force of baths coupled in series, which may appear by electrode- 
 
 Fig. 48. 
 
 MU 
 
 / 
 
 BATTERY 
 
 surfaces of uneven size, or by changes in the resistances of the 
 electrolytes. 
 
 Current indicator. In order to be able to control the change 
 in the current conditions which is effected in a circuit by the 
 resistance board, a galvanometer is coupled behind the latter. 
 This instrument consists of a magnetic needle oscillating upon 
 a pin, below which the current is conducted through a strip of 
 copper, or, with weaker currents, through several coils of wire. 
 The electric current deflects the magnetic needle from its north- 
 pole position, and the more so the stronger the current is; 
 hence the current-strength of the battery can be determined by 
 the greater or smaller deflection. 
 
 For a weak current, such as, for instance, that yielded by 
 
142 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Fig. 49. 
 
 two cells, it is of advantage to use a horizontal galvanometer 
 (Fig. 49). It is screwed to a table by 
 means of a few brass screws in such a po- 
 sition that the needle in the north position, 
 which it occupies, points to o° when no 
 current passes through the instrument. 
 Articles of iron and steel must, of course, 
 be kept away from the instrument. For 
 stronger currents it is better to combine a vertical galvanometer 
 with the switch-board and fasten it to the same frame, as shown 
 in Fig. 46. The screw of the lever of the switch-board is con- 
 nected with one end of the copper strip of the vertical galvanom- 
 eter, while the other is connected with the screw on the right 
 side of the switch-board, in which is secured the wire leading 
 
 Fig. 50. 
 
 OCT 
 
 to the bath. The switch-board and galvanometer are placed 
 in one conducting wire only, either in that of the anodes or of 
 the objects ; one of these wires being simply cut, and the end 
 connected to the battery, is secured in the binding-screw on 
 the side of the resistance board marked " strong," while the 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 143 
 
 other end, which is in connection with the bath, is secured in 
 the binding-screw on the opposite side marked " weak." The 
 entire arrangement will be perfectly understood from Figs. 50 
 and 51. 
 
 Fig. 51. 
 
 Fig. 52 shows the Hanson & Van Winkle Patent Under- 
 writer's Rheostat. It has twice the carrying capacity of any 
 resistance board ever made for this purpose, it having sufficient 
 length of wire to allow of turning down the highest electro- 
 motive force used in plating, to the lowest figure called for, 
 without showing heat or any unfavorable symptoms. By the 
 use of this rheostat the output from a plating room using two 
 or more tanks can be doubled, providing the dynamo has the 
 current capacity. 
 
 Fig. 53 shows a special rheostat constructed by the Hanson 
 & Van Winkle Co. for use on nickel, copper or brass solutions 
 requiring heavy ampereage. For the reason that so large an 
 ampere current is used the instrument is especially constructed 
 to withstand any excessive heating to which it may be sub- 
 jected. This rheostat may also be used in the main line to 
 control the voltage of several tanks. It is suitable for solutions 
 
144 ELECTRO-DEPOSITION OF METALS. 
 
 containing 175 to 200 square feet of nickel work, or on copper 
 or brass baths of 100 to 125 square feet, or for zinc solution 
 containing 75 feet of work surface. 
 
 The advantages derived from the use of a resistance board 
 having been referred to, it remains to add a few words regard- 
 ing the indications made by the galvanometer. Since the 
 greater deflection of the needle depends, on the one hand, on 
 the greater current-strength, and on the other, on the slighter 
 
 Fig, 52. 
 
 V \ \ Wit 
 
 resistance of the exterior closed circuit (conducting-wires, 
 baths and anodes), it is evident that a bath with slighter resist- 
 ance, when worked with the same battery and containing the 
 same surface of anodes and objects, will cause the needle to 
 deflect more than a bath of greater resistance under otherwise 
 equal conditions. 
 
 Hence, the deductions drawn from the position of the needle 
 for the electro-plating process are valid only for definite baths 
 and definite equal conditions, but, with due consideration of 
 these coditions, are of great value. 
 
 Suppose a nickel bath to work always with the same surfaces 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 '45 
 
 of objects and anodes, and experiments have shown that the 
 suitable current-strength for this surface of objects is that at 
 which the needle stands at 15 ; and suppose, further, that the 
 battery has been freshly filled and causes the needle to deflect 
 to 2 5 , then the lever of the resistance board will have to be 
 turned so far to the right that the needle in consequence of the 
 interposed resistances returns to 15 . Now if, after working 
 
 Fig. 53. 
 
 for some time, the battery yields a weaker current, the needle, 
 by reason of the resistance remaining the same, will constantly 
 retrograde, and has to be brought back to 15 by turning the 
 lever to the left, when a current of equal strength to the former 
 will again flow into the bath. This manipulation is repeated 
 until finally the lever rests upon the button furthest to the left, 
 at which position the current flows directly into the bath with- 
 10 
 
140 ELECTRO-DEPOSITION OF METALS. 
 
 out being influenced by the resistances of the resistance board. 
 If now the needle retrogrades below 15 , it is an indication to 
 the operator that he must renew the filling of the battery if he 
 does not prefer suspending fewer objects in the bath. For this 
 reduced object-surface it is no longer required for the needle 
 to stand at 15 in order to warrant a correct progress of the 
 electric process, since the resistance toeing in this case greater, 
 a deflection to io°, or still less, may suffice. This example 
 will make it sufficiently clear that the current-indication by the 
 galvanometer is not and cannot be absolute, but that the de- 
 ductions must always be drawn with due consideration to the 
 conditions, namely, surfaces of objects and anodes, and dis- 
 tance between them. 
 
 It frequently happens that in consequence of defective con- 
 tracts with the binding-screws of the battery, or by the conduc- 
 tors of the objects and of the anodes touching one another 
 (short circuit with non-insulated conducting wires), no current 
 whatever flows into the bath. Such an occurrence is immedi- 
 ately indicated by the galvanometer, the needle being not at all 
 deflected in the first case, while in the latter the deflection will 
 be much greater than the usual one. 
 
 The needle of the galvanometer also furnishes a means of 
 recognizing the polarity of the current. If the galvanometer 
 be placed in the positive (anode) conductor by securing the 
 wire coming from the battery in the binding-screw on the 
 south pole of the galvanometer, and the wire leading to the 
 bath in the binding-screw on the north pole of the needle, the 
 needle, according to Ampere's law, will be deflected in the 
 direction of the hands of a watch, i. <?., to the right if the ob- 
 server stands so in front of the galvanometer as to look from 
 the south pole towards the north pole, because the battery- 
 current flows out from the positive pole through the conducting 
 wire, anodes, and fluid to the objects, and from these back 
 through the object wire to the negative pole of the battery. If 
 now in consequence of the counter-current formed in the bath 
 by the metallic surfaces of dissimilar nature or other causes, and 
 
ELECTRO-PLATING ESTABLISHMENTS. 1 47 
 
 flowing in an opposite direction to that of the battery-current, 
 the latter is weakened, the needle will constantly further retro- 
 grade from the zero point, and when the counter- or polariza- 
 tion-current becomes stronger than the battery-current, it will 1 
 be deflected in an opposite direction as before. Hence, by 
 observing the galvanometer, the operator can avoid the annoy- 
 ing consequences of polarization, which will be further discussed] 
 under nickeling. 
 
 Measuring instruments. It may here be stated that the use 
 of the galvanometer has been to a great extent abandoned, and 
 measuring instruments are at present generally employed. 
 
 For measuring the current-strength, the ampere-meter or am- 
 meter is employed, and for measuring the electro-motive force of 
 the current, the volt-meter, these instruments allowing of the 
 direct reading off of the current-strength in amperes and of the 
 electro-motive force in volts. 
 
 Space will not permit us to enter into the different con- 
 structions of these measuring instruments, and only the principle 
 of their construction will here in a few words be explained. 
 
 It has previously been seen that with a given object- and 
 anode-surface, the deposit in the plating bath depends chiefly 
 on the current-strength and electro-motive force of the current. 
 The deposit will turn out most beautiful and most homogeneous 
 only with a definite current-strength, and though the skilled 
 operator may succeed by empirical experiments in obtaining a 
 beautiful deposit without a knowledge of the current-conditions, 
 this mode of working requires far more attention than when by 
 simply reading off" the deflection of the needle on the measur- 
 ing instruments, it can be ascertained that the bath works in 
 the most rational manner, without having first to inspect the 
 objects and the bath itself. Such instruments are a great con- 
 venience, especially with a varying size of the object-surface, 
 particularly if each bath is provided with one, because the 
 electro-motive force at the bath changes every time the object- 
 surface is changed. Hence, as previously stated, the current 
 has every time to be regulated before it is allowed to pass into 
 the bath, if the deposit is to be always of the same quality. 
 
*4'8 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Fig. 54. 
 
 While voltmeters allow of a reliable control of the electro- 
 motive force in the bath, ammeters serve the purpose of recog- 
 nizing, on the one hand, whether the current-strength required 
 for a certain object-surface passes into the bath, if the calcula- 
 tion of the total current-strength is based upon the normal 
 current-density. On the other hand, they allow of the deter- 
 mination of the quantities by weight of metal deposited, the 
 weight of the deposit depending solely on the current-strength. 
 Although it is not always necessary to know this, yet it is fre- 
 quently desirable to ascertain how great the current-strength is, 
 in order to determine what demands are made on the battery 
 or the dynamo. 
 
 Notwithstanding their extraordinary simplicity, the instru- 
 ments constructed according to 
 Hummel's patent, are very sen- 
 sitive, and do not change in the 
 course of time as is the case with 
 many other constructions. Their 
 mode of action is based upon the 
 phenomenon that soft iron is at- 
 tracted by a current-conductor. 
 In the scheme, Fig. 54, 5 is a cir- 
 cular current-conductor, consist- 
 ing of a greater or smaller number 
 of copper-wire coils. In the in- 
 terior is a piece of thin sheet-iron. 
 E, connected with an axis of rev- 
 olution, a. G is a weight which 
 is to be lifted by the attractive 
 foice of the current S upon the iron E. The stronger the 
 current, the greater the attraction of the coils lying next to 
 'the sheet-iron, and, hence, the greater the elevation of the 
 weight, G, will be, and the further the indicator, Z, connected 
 with the axis of revolution, and below which a scale is fixed, 
 will deflect. 
 
 As regards construction, the voltmeter and ammeter are 
 
 7 
 
 / 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 149 
 
 alike, with the exception of the coil S. In the voltmeter, it 
 consists of many windings of thin copper wire, and in the am- 
 
 Fig. 55. 
 
 meter of but a few windings of stout copper wire, or in instru- 
 ments for great current-strength, of a massive, bent piece of 
 copper. 
 
 Fig. 56. 
 
 The voltmeter, Fig. 55, manufactured by the Hanson & Van 
 Winkle Co., is arranged with fifteen negative points. By its 
 
150 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 use the current generated by the dynamo can be determined, 
 and by moving the lever to the point corresponding to the 
 tank number, the voltage of any one of the fifteen tanks can be 
 instantly determined. 
 
 Fig. 56 shows the Weston ammeter. The ammeter is placed 
 in one conductor only, either in that of the objects or the 
 anode, and thus the whole of the current must pass through it. 
 The voltmeter, however, is connected with both conductors. 
 
 Fig. 57. 
 
 On the points where the electro-motive force is to be measured, 
 one of the binding screws of the voltmeter is connected by 
 means of a copper wire with the object-conductor, and the 
 other, with the anode-conductor. 
 
 Fig. $7 illustrates the arrangement of the switch-board and 
 ammeter with a bath operated by means of a battery. 
 
 Voltmeter switch. If many baths are in operation in an 
 electro-plating plant, it would be quite a task to furnish each 
 
ELECTRO-PLATING ESTABLISHMENTS. 151 
 
 bath with a special voltmeter. However, this is unnecessary, 
 one voltmeter being sufficient for three or four baths. In 
 order to be able to read off conveniently on the voltmeter the 
 electro-motive force passing into one of these baths, a switch is 
 required, the construction of which will be seen from Figs. 58 
 and 59. 
 
 Now, if there are a number of baths in operation, the expense 
 of providing a special voltmeter for each bath would be quite 
 considerable. However, this is not necessary, one voltmeter 
 for three or four baths being sufficient. To conveniently read 
 off at any time on the voltmeter the voltage of the current 
 passing into one of these baths, a switch is required, the con- 
 struction of which is seen in Figs. 58 and 59. 
 
 Fig. 58 shows the coupling of the main object-wire ( — ) and 
 of the main anode-wire ( + ), which will be referred to later on, 
 together with the resistance boards Ri and Ro, the volt-meter 
 V, switch U, and the two baths. In Fig. 59 the coupling is 
 enlarged, and upon this illustration the following description is 
 based : Suppose the main object-wire and anode-wire to be 
 connected with the corresponding poles of a dynamo-machine 
 or a battery, which for the sake of a clearer view is omitted in 
 the illustration. The switch ^/consists of a brass lever, mounted 
 with a brass foot, upon a board. In the foot is a screw, with 
 which is connected by a 0.039-inch thick copper wire one of 
 the pole-screws of the volt-meter. The brass handle slides with 
 spring pressure upon contact buttons connected by copper wire 
 with the binding-screws, 1, 2, 3, 4, 5 (upon the switch), which 
 serve for the reception of the 0.039 mc h thick insulated wires 
 1, 2, 3, 4, for measuring the electro-motive force, which branch 
 off from the various tanks or resistance boards. The other 
 pole-screw of the volt-meter is directly connected with the main 
 anode-wire. From the main object-wire, a wire, whose cross- 
 section depends on the strength of the working current, passes 
 to the screw marked " strong" of the resistance board v^i ; the 
 screw marked "weak" of the resistance board R x is connected 
 by a wire of corresponding thickness with the object-wire of 
 
*52 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 bath I, and at the same time with the binding-screw i of the 
 switch. The resistance board R 2 , of the bath II, is in the same 
 manner connected with the main object-wire, the bath, and the 
 
 Fig. 58. 
 
 binding-screw 2 of the switch ; also the resistance boards R, and 
 R, of the baths III and IV, which are not shown in the illustra- 
 tion. With the main anode-wire each bath is directly con- 
 nected by conducting the current to an anode-rod of the bath 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 153 
 
 by means of binding-screws and a stout copper wire, and estab- 
 lishing a metallic connection between this anode-rod and the 
 next one. However, instead of connecting both, the current 
 may also be conducted from the main anode-wire to each 
 anode-rod. 
 
 In the illustration, the handle of the switch rests upon the 
 second contact-button to the left, which is connected with the 
 binding-screw 2 of the switch. In the latter is secured the wire 
 for measuring the electro-motive force which leads from the 
 resistance board R,\ hence the voltmeter V will indicate the 
 
 Fig. 59. 
 
 electro-motive force of the current at bath II. Suppose that 
 bath II is full of objects and, with the position of the lever of 
 the resistance board at "weak," as shown in the illustration, the 
 voltmeter indicates 1.5 volts, while the most suitable electro- 
 motive force for the bath is 2.5 volts, the handle of the switch 
 is turned to the left until the needle of the voltmeter indicates 
 the desired 2.5 volts. 
 
 If the handle of the switch U be turned to the left so that it 
 rests upon the contact-button 1, the measuring wire of bath II 
 
154 ELECTRO-DEPOSITION OF METALS. 
 
 is thrown out, and the voltmeter indicates the electro-motive 
 force on bath I; if the lever rests upon contact-button 3, the 
 electro-motive force in bath III is indicated, and so on. 
 
 Dependence of the current-density on the electro-motive force. 
 If a current of known strength be at the outset conducted 
 through electrodes of a certain size into a bath of determined 
 resistance, and the electrode-surfaces be then doubled, the 
 current-strength must also be doubled in order to maintain the 
 same current-density as before. By increasing the electrode- 
 surfaces to twice their size, the resistance of the bath is, how- 
 ever, reduced one-half the value it amounted to with electrodes 
 of half the size, the increased electrode-surfaces corresponding 
 to a cross-section of the bath-fluid enlarged in the same pro- 
 portion. 
 
 Suppose the resistance of the bath with an electrode-surface 
 of 1 square decimeter amounted to 2.4 ohms, and the current- 
 strength, which in this case also represents the current-density, 
 had been 0.4 ampere, an increase of the electrode-surface to 2 
 square decimeters will require a current-strenth of 0.8 ampere, 
 in order to maintain a current-density of 0.4 ampere per square 
 decimeter. The resistance of the bath then declines from 2.4 
 ohms to 1.2 ohm. According to the laws of Ohm, the resist- 
 ance of 2.4 ohms required an electro-motive force of current- 
 strength X resistance, hence of 0.4 X 2.4 = 0.96 volt. After 
 increasing the electrode-surfaces to 2 square decimeters and 
 raising the current-strength to 0.8 ampere, the resistance de- 
 clined to 1.2 ohm. The electro-motive force then amounts to, 
 0.8 X 1.2 = 0.96 volt, hence to exactly the same as in the first 
 case. 
 
 From this it follows, that with an unaltered electrode- 
 distance, the current-density remains unchanged with varying 
 electrode-surfaces, if the electro-motive force at the bath be 
 kept constant at the same height. 
 
 It is also obvious that with an increasing electro-motive force 
 at the bath, the current-density must also increase, because, 
 according to the law of Ohm, the current-strength is equal to 
 
ELECTRO-PLATING ESTABLISHMENTS. I 55 
 
 the electro-motive force divided by the resistance. Since the 
 latter is not changed when the electrode-distance remains the 
 same, the quotient will be adequately larger if the divisor re- 
 mains the same and the dividend be increased. Hence the 
 current-density becomes greater. 
 
 Now, as for the production of a useful deposit, a certain cur- 
 rent-density should not be exceeded, the voltmeter furnishes 
 us the means to insure against failure by keeping the electro- 
 motive force at the bath constant with a varying charge of the 
 latter, and such an instrument should not be wanting in an 
 electro-plating establishment. 
 
 Conductors. The most suitable material for conducting the 
 current is chemically pure copper, its conducting power being 
 next to that of silver, but the use of the latter noble metal for 
 this purpose is of course excluded by reason of its costliness. 
 
 The laws of Ohm have shown us that the current-strength 
 depends on the magnitude of the electro-motive force and the 
 resistance in the circuit; the greater the resistance, the less the 
 current-strength which can flow through the conductor. From 
 this it follows that in order to reduce losses of electro-motive 
 force to a minimum, conductors of adequate cross-sections 
 should be selected. 
 
 Conductors which cause a loss of more than 10 per cent, of 
 the electro-motive force have to be considered insufficient as 
 regards dimensions, and it is recommended to entrust the in- 
 stallation of such constructions only to competent hands capa- 
 ble of making the calculations required for the purpose. 
 
 In addition to the correct dimensions of the conductors, the 
 mode of mounting them also deserves the greatest attention. 
 All the connections of the conductors, which are called contacts, 
 must be made in the most careful manner, since bad contacts 
 cause a transition-resistance, and, in such a case, a large de- 
 crease in electro-motive force could not be prevented even by 
 conductors of ample dimensions. 
 
 A distinction is made between main conductors and branch 
 conductors, the former effecting the transmission of the current 
 
i 5 6 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 from the source of current to the baths, while the latter branch 1 
 off from them to the separate baths. 
 
 The positive main conductor or anode conductor is con- 
 nected with the -f- pole of the source of current, and the nega- 
 tive main conductor or object-conductor with the — pole. 
 
 Both bare and insulated conductors are used. For con- 
 ductors of larger cross-sections, bright electrolytic copper in 
 the form of round bars or flat rails is employed, while for 
 conductors of smaller cross-sections, copper wire covered with 
 an insulating material, such as hemp or jute coated with 
 asphalt or varnish, suffices. For connecting certain movable 
 parts with the rigid main conductor, flexible cables of copper 
 wire, either bare or insulated, are very convenient. 
 
 Bare conductors must be fixed in such a manner that they 
 do not touch each other, which would cause short-circuiting,, 
 and possibly danger of fire, nor come in contact with damp 
 brick-work. This is effected by placing the conductors upon- 
 porcelain insulators, to which they are secured by wire. 
 
 It is also advisable not to allow even thoroughly insulated' 
 conductors to lie directly one upon the other, as the insulation, 
 may happen to be damaged, and short-circuiting would result. 
 
 Fig. 60. 
 
 Fig. 6i. 
 
 Fig. 62. 
 
 As regards the dimensions of the conductors, it should, in 
 view of the slight electro-motive force of the current used for 
 electrolysis, be made a rule to calculate for every ampere cur- 
 rent-strength one square millimeter of copper cross-section, if 
 the entire circuit is not over 20 meters long. 
 
 Connection of main conductors and branch conductors is 
 effected by inserting the ends of two round conductors in coup- 
 
ELECTRO-PLATING ESTABLISHMENTS. 157 
 
 lings, Fig. 60, securing them by means of screws, and filling 
 any intermediate space with solder. If the round main con- 
 ductors are to be run at an angle, the coupling, Fig. 61, is used, 
 and the "T-coupling, Fig. 62, is employed on the points from 
 which branches are to be run at a right angle from the main 
 conductor. 
 
 Flat copper rails are connected in the most simple manner 
 foy means of a piece of copper-sheet and screws, the contact 
 ■surfaces having been first tinned to prevent oxidation. 
 
 Tanks. The choice of material for the construction of tanks 
 to hold the plating solutions depends on the nature and prop- 
 erties of the latter. 
 
 Solutions containing potassium cyanide require tanks of 
 stoneware, enameled cast-iron or impregnated wood. Nickel 
 baths and other baths which do not attack pitch and wood may 
 be kept in wooden tanks lined with pitch. The best material 
 for wooden tanks without pitch lining is pitch-pine, it containing 
 least tannic acid. Larch may also be used, but is inferior to 
 pitch-pine. Wood which contains tannic acid spoils every 
 nickel bath, causing dark nickeling, so that, for instance, an 
 oak tank cannot be used. For smaller baths, up to 300 quarts, 
 the most advantageous tank is one of stoneware or enameled 
 iron. 
 
 Wooden tanks must be carefully constructed, and should be 
 securely clamped together with strong iron bars, riveted and 
 bolted, as shown in Fig. 63. The tank is then coated with a 
 mixture of equal parts of pitch and rosin boiled with a small 
 quantity of linseed oil. Another mixture, which has been 
 found to afford a good protective covering to wood, consists of 
 10 parts of gutta-percha, 3 of pitch, and iyi each of stearine 
 and linseed oil, melted together and incorporated. 
 
 For large acid copper and nickel baths wooden tanks lined 
 with chemically pure sheet-lead about 0.1 18-inch thick, and the 
 seams soldered with pure lead, are quite suitable. Care must, 
 of course, be taken that neither the conducting rods nor the 
 articles suspended in the bath and the anodes come in contact 
 
158 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 with the lead lining, and therefore the conducting rods should 
 not be laid directly upon the tanks, but placed upon a few thick 
 strips of dry wood. Further, the anodes should be suspended 
 at a sufficient distance from the lead lining, because with too 
 small a distance, metal from the solution is precipitated upon the 
 lead lining. The latter always becomes electric, which, how- 
 ever, does not matter, and if the anodes are at a greater dis- 
 tance from it than the objects no metal is precipitated upon it. 
 If for the better exhaustion of the baths the anodes are sus- 
 pended at a slight distance from the sides, it is advisable to 
 
 Fig. 63. 
 
 ^ 
 
 protect the lead lining with thin wooden boards, or to insulate it 
 by giving it two coats of asphalt-lacquer. However, for this 
 purpose asphalt-lacquer prepared from the residues of the tar 
 industry is not available, and a solution of Syrian asphalt, with 
 a small quantity of Venice turpentine in benzine should be 
 employed. 
 
 Based upon careful investigations, such lead-lined tanks have 
 been used for large copper and brass baths containing potassium 
 cyanide without the slightest injury to the baths. If even a 
 film of lead cyanide is formed upon the lead, it is insoluble in 
 excess of potassium cyanide, and hence is entirely indifferent 
 as regards the bath. However, for nickel baths containing 
 
ELECTRO-PLATING ESTABLISHMENTS. I 59 
 
 large quantities of acetates, citrates and tartrates, these lead- 
 lined tanks cannot be recommended, since these salts possess a 
 certain power of dissolving lead oxide. However, the use of 
 such baths has been almost entirely abandoned, and the small 
 quantities of organic acid which occasionally serve for correct- 
 ing the reaction of a nickel bath need not be taken into con- 
 sideration. The lead lining might be dispensed with if it were 
 not for the difficulty of keeping wooden tanks tight. Many 
 plating solutions impair the swelling power of the wood, and 
 with even a slight change in the temperature the tanks become 
 pervious, the evil in time increasing. Tanks lined with lead v 
 on the other hand, remain tight, and have the advantage that 
 the baths can be boiled in them by means of steam introduced 
 through a lead coil in the tanks. 
 
 For large baths containing potassium cyanide, holders of brick 
 laid in cement may also be used, or holders of boiler-plate lined 
 with a layer of cement. For nickel baths cement-lined tanks 
 cannot be recommended. If a tank of that kind is to be used, 
 direct contact of the nickel solution with the cement lining 
 should be prevented by applying to the latter at least two coats 
 of asphalt-lacquer. Stoneware tanks do not bear heating. 
 
 Conducting fixtures. These include the conducting rods 
 which serve for suspending the objects and anodes, and are laid 
 across the tanks, as well as the binding-posts and screws and 
 copper-connections used for connecting the conducting rods. 
 
 The cross-sections of the conducting rods are, on the one 
 hand, dependent on the maximum current-strength which with- 
 out greater resistance is to pass through them, and, on the 
 other, on the weight of the objects and anodes to be suspended 
 in the bath. The conducting rods may be drawn of hard cop- 
 per, or for not considerable current-strengths may be made of 
 brass or copper tubing with insertions of iron rods. Bi-metal, 
 i. e., iron rods upon which has been deposited by electrolytic 
 methods a coat of copper adequate to the current-strength, may 
 be highly recommended. By reason of the intimate union of 
 the copper with the iron, the latter takes part in the conduc- 
 
l6o ELECTRO-DEPOSITION OF METALS. 
 
 tion, which is, as a rule, not the case with copper tubes with 
 insertions of iron rods, in consequence of the formation of oxide 
 and defective contacts. 
 
 It is advantageous to provide the narrow sides of the tanks 
 with semicircular notches for the conducting rods to rest in, to 
 prevent their rolling away. When using stoneware tanks the 
 conducting rods are laid directly upon the tanks. Tanks of other 
 material must be provided with an insulated rim of wood, or 
 the rods are insulated by pushing pieces of rubber tubing over 
 their ends. According to the size of the bath, 3, 5, 7, or more 
 conducting rods, best of pure massive copper, or if this is too 
 expensive, of strong brass tubing with iron rods inside, are 
 used. 
 
 The rods carrying the anodes, as well as those carrying the 
 objects, must be well connected with each other. This is ef- 
 fected by means of binding-posts and screws of the improved 
 forms shown in Fig. 64, Nos. 1 and 2 being rod connections 
 for tanks. No. 4, or double connection, is a very convenient 
 form, as it can be adapted to so very many changes. The 
 three-way connection, No. 3, is so well known that it hardly 
 needs an explanation. 
 
 Arrangement of objects and anodes in the bath. To secure 
 the uniform coating of the objects with metal they must be sur- 
 rounded as much as possible by anodes, i. e., the positive-pole 
 plates of the metal which is to be deposited. For flat objects, 
 it suffices to suspend them between two parallel rows of anodes, 
 the most common arrangement being to place three rods across 
 the bath, the two outermost of which carry the anodes, while 
 the objects are secured to the center rod. For wide baths five 
 conducting rods are frequently used, but they should always be 
 so arranged that a row of objects is between two rows of anodes. 
 The arrangement frequently seen with four rods across the 
 baths, of which the outermost carry anodes, and the other two, 
 objects, is irrational if the objects are to be uniformly plated on 
 all sides, because the sides turned towards the anodes are 
 coated more heavily than those suspended opposite to the other 
 row of objects. 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 161 
 
 For large round objects it is better to entirely surround them 
 with anodes, if it be not preferred to turn them frequently, so 
 that all sides and portions gradually feel the effect of the imme- 
 diate vicinity of the anodes. (See "Nickeling.") 
 
 For objects to be plated on one side only the center rod may 
 be used for the anodes and the two outer ones for the objects ; 
 
 Fig. 64. 
 
 No. 2. 
 
 the surface to be plated being, of course, turned towards the 
 anodes. 
 
 There should be an ample supply of anodes in the bath. In 
 baths of base metals the anode-surface should at least be equal 
 in size to the surface to be plated ; an exception being permis- 
 sible in gold and silver baths. 
 
 The anodes should not be too thin, because the thinner they 
 1 1 
 
162 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Fig. 65. 
 
 Fig. 66. 
 
 are, the greater the resistance. Copper, brass and nickel 
 anodes should not be less than 3 millimeters thick, and the 
 hooks by which they are suspended 
 should be correspondingly thick and 
 numerous. 
 
 The anodes are suspended from the 
 cross-rods by strong hooks of the same 
 metal, so that they can be entirely im- 
 mersed in the bath (Fig. 65). Hooks of 
 another soluble metal would contaminate 
 the bath by dissolving in it, and this 
 must be strictly avoided, as it would 
 cause all sorts of disturbances in the 
 correct working of the bath. In case 
 hooks of another metal, except platinum, are used, the anodes 
 must be suspended so that they project above the surface of 
 the liquid, and the hooks not being immersed are, therefore,, 
 not liable to corrosion ; but the anodes are then not com- 
 pletely used up, the portion dipping in the solution being 
 gradually dissolved, whilst the portion projecting above the 
 fluid remains intact. Instead of wire hooks, strips of the 
 same metal as the anodes and fastened to them by a rivet may 
 also be used (Fig. 66). 
 
 For suspending the objects, lengths of soft, pure copper wire,. 
 technically called slinging wires, are used. They are simply 
 suitable lengths of copper wire of a gauge to suit the work in 
 hand, wire No. 20 Birmingham wire gauge being generally 
 employed for such light work as spoons, forks and table uten- 
 sils. Wire of a larger diameter should be employed for large 
 and heavy goods. The immersed ends of these wires becoming 
 coated with the metal which is being deposited, they should be 
 carefully set aside each time after use, and when the deposit 
 gets thick it should be stripped off in stripping acid, and the 
 wire afterwards annealed and straightened for future use. 
 
 To keep the rods clean and to protect them from the fluid 
 draining off from the articles when taken from the bath, it is ad- 
 
ELECTRO- PLATING ESTABLISHMENTS. 1 65 
 
 visable to cover them with a roof of strips of wood (A)> or a 
 semi-circular strip of zinc coated with ebonite lacquer; by this 
 means the frequent scouring of the rods, which otherwise is 
 necessary in order to secure a good contact with the hooks of 
 the anodes, is done away with. 
 
 It need scarcely be mentioned that the anodes and the ob- 
 jects to be plated must not touch each other, as short-circuiting 
 would take place on the point of contact. 
 
 The plating solutions, briefly called baths or electrolytes, 
 will be especially discussed in speaking of the various electro- 
 plating processes. Other rules for suspending the objects will 
 be mentioned under " Nickeling," and are valid for all other 
 electro-plating processes. 
 
 Apparatus for cleansing and rinsing. It remains to consider 
 the cleansing and rinsing contrivances, without which it would 
 be impossible to carry on electro-plating operations. Every 
 electro-plating establishment, no matter how small, requires at 
 least one tub or vat in which the objects can be rubbed or 
 brushed with a suitable agent in order to free them from grease. 
 This is generally done by placing a small kettle or stoneware 
 pot containing the cleansing material at the right-hand side of 
 the operator alongside the vat or tub. Across the latter, which 
 is half filled with water, is laid a board of soft wood covered 
 with cloth, which serves as a rest for the objects previously 
 tied to wires. The objects are then scrubbed with a brush, or 
 rubbed with a piece of cloth dipped in the cleansing agent. The 
 latter is then removed by rinsing the objects in the water in the 
 tub and drawing them through water in another tub. By this 
 cleansing, process a thin film of oxide is formed upon the metals, 
 which would be an impediment to the intimate union of the 
 electro-deposit with the basis-metal. This film of oxide has to 
 be removed by dipping or pickling, for which purpose another 
 vat or tub containing the pickle, the composition of which 
 varies according to the nature of the metal, has to be provided. 
 After dipping, the objects have to be again thoroughly rinsed 
 in water to free them from adhering pickle, so that for the 
 
1 64 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 preparatory cleansing processes three vessels with water, which 
 has to be frequently renewed, as well as the necessary pots for 
 pickling solutions, have to be provided. 
 
 Larger plants require a special table for freeing the objects 
 from grease. Such a table is shown in Fig. 6j. It consists of 
 
 Fig. 67. 
 
 a box furnished with legs, and is divided by four partitions into 
 two larger and three smaller compartments. Boards covered 
 with cloth are laid over the larger compartments, upon which 
 the objects are brushed with lime- paste for the final thorough 
 freeing from grease. Over each of these compartments is a 
 rose provided with a cock, under which the objects are rinsed 
 with water. The outlets for the waste water from the large 
 compartments are in the bottom of the box and are provided 
 with valves. Of the smaller compartments, the one in the 
 center serves for the reception of the lime paste (see " Chemi- 
 cal Treatment"), while the others contain each two pots or 
 small stoneware tanks with pickling fluid. In Fig. 70 these tanks 
 
ELECTRO -PLATING ESTABLISHMENTS. 1 65 
 
 are indicated by 11 and 12. The two marked 11 contain 
 dilute sulphuric acid for pickling iron and steel articles, while 
 those marked 12 contain dilute potassium cyanide solution for 
 pickling copper and its alloys, and Britannia, etc. For cleans- 
 ing smaller articles, four men can at one time work on such a 
 table ; but for cleansing larger articles only two. For an 
 establishment which does not require such a large table, one 
 with a larger and two smaller compartments may be used. 
 The advantages of such a box-table are that everything is 
 handy together; that the pickle, in case a pot should break, 
 cannot run over the floor of the workshop; and that the latter 
 is not ruined by pickle dropping from the objects. The small 
 box on the side of the table serves for the reception of the 
 various scratch-brushes. 
 
 After having received the electro-deposit, the objects have to 
 be again rinsed in cold water, which can be done in one of the 
 three tanks or with the rose-jet, and finally have to be immersed 
 in hot water until they have acquired the temperature of the 
 latter. How the water is heated makes no difference, and 
 depends on the size of the establishment. The heated objects 
 are then immediately dried in a box filled with dry, fine saw- 
 dust — that of maple, poplar, or other wood free from tannin 
 being suitable for the purpose. 
 
 B. Installations with Dynamo- Electric Machines. 
 
 Setting up and running a dynamo. Most of the troubles 
 with plating- dynamos are caused by neglecting one or more of 
 the conditions necessary for their proper operation, and are 
 not due to any defects in the machines themselves. The 
 troubles most frequently encountered are, in order of their 
 frequency, as follows: First, insufficient or variable speed. 
 Second, improper setting of the brushes, and the use of im- 
 proper lubricants and cleaning material on the commutator. 
 Third, poor oil, or an insufficient, or too great, an amount of 
 oil in the bearings. Fourth, overloading the machine. 
 
 It is important that the dynamo be properly placed, and the 
 
1 66 ELECTRO-DEPOSITION OF METALS. 
 
 following considerations should govern the choice of location : 
 The dynamo should not be exposed to moisture nor to the dirt 
 and dust of the polishing room. Cleanliness is a necessity. 
 A cool, well-ventilated room should be chosen. This is im- 
 portant, for a well-ventilated machine will do more work with 
 less wear on parts than one unfavorably placed. The machine 
 should not be boxed in, as this will make it run hotter than it 
 otherwise would. Not only this, the mere fact of having it 
 totally boxed in precludes the probability of receiving the 
 proper amount of attention. 
 
 Except on the larger sizes of machines a special foundation 
 is not mechanically necessary, providing the floor is fairly solid. 
 On account, however, of dirt getting into the running parts 
 when the floor is cleaned, it is always well to raise the machine 
 from six to twelve inches above the floor. For a small dynamo 
 a well-made box of two-inch lumber will afford an ample foun- 
 dation. For the larger sizes two or three strips of 6-inch x 6- 
 inch yellow pine may be used. In either case the box or 
 strips should be solidly nailed or bolted to the floor and the 
 machine secured to its base with four lag screws of the proper 
 size. 
 
 The direction of rotation may be ascertained by an inspec- 
 tion of the brushes, the commutator running away from the 
 brushes. One of the troubles mentioned above, namely, vari- 
 able speed, may be remedied to a large extent by a suitable 
 belt, run in the proper manner. The counter-shaft should never 
 be run directly over the dynamo, but should be placed far 
 enough to one side so that the belt will run diagonally and in 
 such a direction that the under side of the belt does the work. 
 This is on account of the fact that when the belt is running ver- 
 tically or diagonally with the upper side doing the work it 
 stretches and sags away from the pulley when a heavy load is 
 thrown on the dynamo, thus given less pull as the necessity for 
 a greater pull increases, Use good, pliable, single belting with 
 the hair side of the belt to the pulley on smaller and medium- 
 size machines. For the larger sizes a thin, double belt may be 
 used. 
 
ELECTRO-PLATING ESTABLISHMENTS. 1 67 
 
 After the machine has been properly set and belted, it re- 
 mains to start it up. Before starting, remove the bearing caps 
 and pour a small quantity of oil on the bearings ; loosen the 
 screw holding the rocker-arm in position, and be prepared to 
 shift the rocker-arm backward or forward, so as to get the 
 brushes on the neutral or non-sparking line, as it often happens 
 that the rocker-arm has been shifted from its proper position 
 in transportation. 
 
 The proper position for the tips of the brushes on all ma- 
 chines of either the bipolar or multipolar type is about opposite 
 the center of the poles. The tips of the brushes should also be 
 spaced at even intervals, this being, on the two-pole machine, 
 diametrically opposite to each other; on the four-pole machine, 
 one-quarter of the circumference from each other ; on the six- 
 pole machine, one-sixth of the circumference, and so on. The 
 exact position of the brushes (that is, where they run spark- 
 lessly) can only be ascertained by trial. This adjustment should 
 be made, in case it is necessary, as soon as the machine starts 
 up, for if it is allowed to run any length of time while sparking, 
 the commutator will be cut badly, and may necessitate taking 
 out the armature and truing up the commutator. In case this 
 is necessary, a sharp diamond-point tool should be used with a 
 moderate speed, and the commutator should be finished with a 
 fine second-cut file, and then with No. o sandpaper and oil. 
 After the proper adjustment of the brushes has been made, 
 take an oil-can, and while the machine is running, pour oil 
 .slowly into the oil-well until the oil- rings take it up properly 
 and carry it to the top of the bearings, where it enters the dis- 
 tributing slot. If too little oil is in the well and the rings do 
 not dip into it sufficiently deep, they will rattle around and 
 spatter oil, whereas if too much oil is put in, it will run out at 
 the ends of the bearings and get into the belt, winding and 
 •commutator of the machine. 
 
 While the commutator should never be allowed to become 
 greasy or dirty, it is equally important that it should not be 
 run perfectly dry, so that the brushes cut. When it becomes 
 
1 68 ELECTRO-DEPOSITION OF METALS. 
 
 dirty, after cleaning with No. o sandpaper (emery should never 
 be used) it should be re-oiled by rubbing it with a woolen 
 cloth moistened with kerosene oil, or with the very smallest 
 amount of lubricating oil. The quality and kind of oil used for 
 the bearings is important, and a regular dynamo oil should be 
 used. Under no circumstances should vegetable or animal oil 
 (such as castor or sperm oil) be used, but a light grade of 
 mineral dynamo oil. 
 
 The brushes should not only be properly set as regards their 
 position around the commutator, but they should have careful 
 individual setting. They should have a fair and even bedding 
 on the commutator, and not touch on the heel or toe or on 
 either edge, as the object is to get full contact surface between 
 the brushes and the commutator. If the commutator is kept 
 in proper shape and the brushes once properly set, it will not 
 be necessary to adjust them often. As it is practically impos- 
 sible to make a perfectly accurate setting of the brushes, and it 
 takes them some few days to get worn down to a good con- 
 tact, it will be seen that it does more harm than good to be 
 continually re-setting them. If the ends of the brushes get 
 very ragged, they should, in the case of wire-gauze brushes, 
 be carefully trimmed with a pair of shears, and in the case of 
 strip- copper brushes, filed with a fine second-cut file. The 
 tension spring on the brush holder should be adjusted to make 
 a light but positive contact, for if there is too much pressure, 
 the brushes will cut the commutator, causing it to wear away 
 rapidly. 
 
 If there is any doubt about which is the positive and which 
 is the negative pole of the dynamo, the polarity may be readily 
 determined after starting up, by running two small wires from 
 the dynamo and placing the ends in a glass of acidulated water. 
 Around one of these wires more bubbles of gas will be thrown 
 off than around the other, the one evolving the greater amount 
 of gas being the negative pole, to which the work should be 
 attached. 
 
 Choice of a dynamo. For electrolytic processes, as pre- 
 
ELECTRO PLATING ESTABLISHMENTS. 169' 
 
 viously mentioned, shunt-wound dynamos are at present largely 
 used. Their construction has already been explained, and 
 there remains now only the question what size dynamo, *". e., 
 of what capacity as regards current-strength and electro-motive 
 force, is to be selected for a plant. 
 
 We have learned that a certain object-surface requires a 
 certain current-strength. Hence for plants with different baths, 
 it is only, necessary to fix the largest object-surface in square 
 decimeters which is to be suspended in the separate baths and 
 to multiply this number of square decimeters by the current- 
 density in amperes, in order to find the supply of current re- 
 quired for each bath. The sum of the current required for the 
 separate bath, with an allowance of 20 to 25 per cent, for ani 
 eventual enlargement, gives the current-strength the dynamo 
 must furnish. It must of course be taken into consideration 
 whether all the baths are to be in constant operation at the 
 same time or not. In the latter case a smaller current-strength 
 will of course suffice, and a smaller type of dynamo answer the 
 purpose. 
 
 The impressed electro-motive force of the dynamo should be 
 such that, taking into consideration the decline of the electro- 
 motive force in the conductors, it is, at the greatest current- 
 capacity, about y to y 2 volt greater than the highest electro- 
 motive force of a bath required. 
 
 For the purpose of explaining by an example the choice of 
 a suitable dynamo, let us suppose that a nickel bath with an 
 object surface of 50 sq. decimeters ; a potassium cyanide copper 
 bath with an object surface of 30 sq. decimeters ; a brass bath 
 with an object surface of 40 sq. decimeters ; a silver bath with 
 an object surface of 10 sq. decimeters, are to be fed with 
 current. 
 
 The standard current-densities and electro-motive forces 
 required for the separate baths are given later on when speaking 
 of them. It will there be found that the current- density for 
 nickeling brass amounts to about 0.4 ampere, the electro- 
 motive force being 2.5 volts; for coppering, 0.35 ampere and 
 
I/O ELECTRO-DEPOSITION OF METALS. 
 
 3.0 to 3.5 volts are required ; for brassing also 0.35 ampere and 
 3.0 to 3.25 volts; while for silvering 0.2 ampere and 1 volt are 
 on an average used. This amounts to 
 
 For nickel bath 50 sq. decimeters X 0.4 ampere = 20 amperes. 
 For copper bath 30 sq. decimeters X 0.35 ampere = 10.5 amperes. 
 For brass bath 40 sq. decimeters X 0.35 ampere = 14 amperes. 
 For silver bath 10 sq. decimeters X 0.2 ampere = 2 amperes. 
 
 46.5 amperes. 
 
 Hence 46.5 amperes are required for the simultaneous 
 operation of these four baths, and a dynamo of 50 amperes 
 current-strength and 4 volts impressed electro-motive force 
 would have to be selected, since, taking into consideration a 
 permissible decline of electro-motive force of 10 per cent. = 
 0.4 volt in the conductors, there are still at disposal ?>-6 volts, 
 while the greatest electro-motive force required amounts to 3.5 
 volts. 
 
 Since the various baths of a larger establishment possess 
 different resistances and cannot always be charged with the 
 same object-surfaces, they have to be operated in parallel. 
 This renders it necessary that for each separate bath working 
 with a lower electro-motive force, the excess of electro-motive 
 force as existing in the main conductor has to be destroyed by 
 a resistance, called the main-current regulator or bath-current 
 regulator. Hence as many main-current regulators must be 
 provided as there are baths, and the regulators have to be 
 exactly calculated and constructed for the required effect. 
 Thus in the above-mentioned example, the bath-current regu- 
 lators, with an electro-motive force of 3.6 volts in the main 
 conductor, must let pass for a nickel bath 20 amperes and 
 destroy 1.1 volts; let pass for a copper bath 10.5 amperes and 
 destroy 0.6 to 0.35 volt; let pass for a brass bath 14 amperes 
 and destroy 0.6 to 0.35 volt; let pass for a silver bath 2 amperes 
 and destroy 2.6 volts. 
 
 Since every destruction of electro-motive force means an eco- 
 nomic loss, it follows that the impressed electro-motive force of 
 
ELECTRO- PLATING ESTABLISHMENTS. I/I 
 
 the dynamo should not be greater than absolutely necessary, so 
 that it can be reduced by a regulator to the lowest permissible 
 limit, and this limit should be constantly maintained. Thus, 
 when the electrode surfaces in the bath are changed, and there 
 is consequently also a change in the impressed electro-motive 
 force, the latter can be properly adjusted by the regulator. If 
 this were not done, and the impressed electro-motive force 
 would become considerably greater, the bath-current regulators 
 calculated for the destruction of a fixed electro-motive force 
 •would no longer be capable of fulfilling their object. From 
 what has been said, it will be seen that voltmeters are indis- 
 pensable for electro-plating plants in order to be constantly 
 informed as to the electro-motive force prevailing at the baths, 
 and, if necessary, to correct it. 
 
 By reason of the economic loss connected with the destruc- 
 tion of an excess of electro-motive force, it may also have to be 
 taken into consideration whether in larger plants it would not 
 be better to use several dynamos with different impressed 
 electro-motive forces than a single dynamo with an impressed 
 electro-motive force required for the greatest electro-motive 
 force for the baths. Suppose, for instance, there are present in 
 a larger plant, in addition to nickel, brass and copper cyanide 
 baths, which require a voltage of up to 3^ volts, a large num- 
 ber of silver and tin baths and acid copper baths for galvano- 
 plasty (with the exception of those for rapid galvanoplasty), 
 for which an impressed electro-motive force of 2 volts is quite 
 sufficient, it would by all means be more judicious to use for 
 the first-named baths a special dynamo with an impressed 
 electromotive force of 4 volts, and for the last-mentioned baths 
 a dynamo with a voltage of 2 volts. 
 
 Another question to be considered in the choice of a dynamo 
 is, whether one or several accumulator cells are to be charged 
 from it. This will be later on referred to. 
 
 While, when baths are coupled in parallel, each bath receives 
 its supply of current from the main conductor, and such parallel 
 coupling is always required when baths of different nature, with 
 
I7-> 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 unequal resistances and unequal electrode surfaces, are con- 
 nected, baths requiring an equal, or approximately equal, 
 current-strength may be coupled one after the other, *'. e., in 
 series. This principle of series-coupling of baths is illustrated 
 by Fig. 68. 
 
 The current passes through the anodes of the first bath into 
 the electrolyte, flows through the latter and passes out through 
 the object-wire. From there it goes through the anodes of the 
 next bath to the objects contained in it, and so on, until it 
 returns through the object-wire of the last bath to the source 
 of current. 
 
 Thus for series coupling of the baths, a dynamo with a 
 
 Fig. 68. 
 
 greater impressed electro-motive force than the sum of the 
 electro-motive forces of all the baths coupled one after the 
 other has to be selected. On the other hand, baths coupled 
 one after the other do not require a greater current-strength 
 than a single bath. Suppose four baths, each charged with 
 ioo square decimeters of cathode- and anode-surfaces are 
 coupled one after the other, and the electro-motive force of one 
 bath amounts to 1.25 volts and the current-density to 2 amperes. 
 Then there will be required for one bath 100 X 2 = 200 
 amperes and 1.25 volts, and for four baths coupled one after 
 another, 200 amperes and 1.25 X 4 = 5 volts. 
 
 The connection of the baths, resistance boards and measur- 
 
ELECTRO-PLATING ESTABLISHMENTS. 173 
 
 ing instruments to a shunt-wound dynamo is shown in Fig. 69, 
 and requires no further explanation. The resistance board at 
 the right is the field resistance board, the other two belonging 
 to the two baths which are coupled in parallel. 
 
 Parallel coupling and series coupling of dynamo-machines. 
 In establishing a larger electro-plating plant, the question may- 
 arise whether it would not be advisable to install two smaller 
 dynamos instead of a single larger one capable of filling all 
 demands, even at the busiest season. The installation of two 
 dynamos allows of the business being carried on without 
 serious interruption in case one of the machines requires 
 repairing, and in dull times one dynamo would, as a rule, be 
 sufficient. In case two dynamos are installed, the main con- 
 ductors must of course have the required cross-sections corre- 
 sponding to the total current-strength of both machines. 
 
 It, however, happens very frequently that as the plant be- 
 comes larger by reason of an increase in the number of baths, 
 a larger supply of current will in time be required. The ques- 
 tion then arises whether to sell the old dynamo, which may be 
 difficult, especially if it is of an obsolete pattern, or whether to 
 supply the deficit of current by installing an additional dynamo. 
 In such case, if the baths are not to be divided into groups, 
 one of them being furnished with current from one dynamo and 
 the other from the second machine, but both the dynamos are 
 to be connected to a common main conductor, the cross- 
 section of the latter must first of all be increased so as to be 
 capable of carrying the total current-strength of both dynamos 
 without material decrease in electro-motive force. Whether for 
 this purpose a new conductor of larger cross-section is to be 
 used, or whether a supplementary conductor is in a suitable 
 manner to be connected with the old one, is best left to the 
 judgment of the person entrusted with the installation. 
 
 In coupling several dynamos in parallel to a common con- 
 ductor, care must in all cases be taken to connect a dynamo to 
 one already in operation only after it has been excited to the 
 same voltage. If this were not done, the current of greater 
 
174 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 
 f*e 
 
 
 
 Q 
 
 
 ^ 
 
ELECTRO-PLATING ESTABLISHMENTS. I 75. 
 
 electro-motive force of the dynamo in operation would flow 
 from the main conductor to the other dynamo, and the first 
 dynamo would thus be short-circuited by the brushes, com- 
 mutator and armature of the second one. No current would 
 pass into the baths, but the second dynamo would run as a 
 motor. To prevent this, a switch has to be placed between 
 every dynamo and the main conductor. If one dynamo 
 already furnishes current, the second dynamo has at first to be 
 set in operation with the switch open, until its voltmeter shows 
 the same voltage as possessed by the other dynamo. The 
 switch is then closed, and the desired current-strength gen- 
 erated by means of the shunt-regulator. It is obvious that for 
 coupling in parallel, only dynamos which yield the same 
 voltage are suitable, while a difference in capacity as regards 
 current-strength is no obstacle. 
 
 The poles of a similar name of the various machines must of 
 course be connected to one and the same circuit. 
 
 Coupling of dynamos in series may become necessary when 
 baths require a greater electro-motive force than can be fur- 
 nished by a single machine, for instance, in case baths are 
 coupled one after the other. For coupling in series only 
 dynamos which furnish with the same voltage the same current- 
 strength are suitable. Coupling is effected so that the -f- pole 
 of one dynamo is connected with the — pole of the other one, 
 hence in the same manner as cells and accumulators are 
 coupled. 
 
 Coupling in series of dynamos may also be used if there are 
 baths requiring great electro-motive force, for instance, for 
 plating en masse in the mechanical apparatus (see later on), 
 while baths requiring a considerably lower electro-motive force 
 are to be fed from the same source of current. 
 
 In such case, it is advisable to construct the conductors 
 according to the three-conductor system. One conductor is 
 branched off from the + pole of one dynamo, the second from 
 the — pole of the other dynamo, and the third, called the 
 intermediary conductor, from the junction of the dynamos 
 
176 ELECTRO-DEPOSITION OF METALS. 
 
 coupled in series. Between the last-mentioned intermediary 
 conductor and an outside conductor is the lower electro- 
 motive force as furnished by one dynamo, but between the two 
 outside conductors, the sum of the electro-motive forces of 
 both dynamos. Hence the baths requiring a large electro- 
 motive force are to be coupled between the outside conductors, 
 and the baths requiring a low electro-motive force between an 
 outside and the intermediary conductor. 
 
 Ground plan of an electro-plating pla?tt with dynamo. This 
 in the most simple form is shown in Fig. 70. In order to make 
 the sketch more distinct, the measuring instruments have been 
 omitted. Their arrangement will be understood from what 
 has been previously said, and from Fig. 70. 
 
 A7V" 1 is a dynamo-electric machine of older construction. 
 The resistance-board belonging to the machine, which is placed 
 in the conductor, is indicated by No. I, and is screwed to the 
 wall. The main conductors, marked — and -f, run along the 
 wall, from which they are separated by wood, and consist of 
 rods of pure copper 0.59 inch in diameter. The rods are con- 
 nected with each other by brass coupling-boxes with screws. 
 From the negative pole and the positive pole of the machine to 
 the object-wire and anode-wire lead two wires, each 0.27 inch 
 in diameter ; one end of each is bent to a flat loop and secured 
 under the pole-screws of the machine, while the other ends are 
 screwed into the second bore of the binding-screws screwed 
 upon each conductor. To the right and left of the machine the 
 baths are placed ; Zn, indicating zinc bath ; Ni Ni, nickel baths ; 
 Ku, copper cyanide bath ; Mg, brass bath ; 5" A", acid copper 
 bath; Si, silver bath; and Go, gold bath. Each of the first- 
 named five baths has its own resistance-board, designated by 2, 
 3,4, 5, 6. However, before reaching the acid copper bath, and 
 the silver and gold baths, the current is conducted through two 
 resistance-boards, 7 and 8. Since these baths require a current 
 of only slight electro-motive force, it is necessary to place two, 
 and in many cases even three or four resistance-boards, one 
 after another, unless it be preferred to feed these baths with a 
 special machine of less voltage. 
 
ELECTRO-PLATfNG ESTABLISHMENTS. 
 
 177 
 
 From Fig. 70 it will be seen that the current weakened by 
 the resistance-boards 7 and 8 serves for conjointly feeding the 
 
 y^z ■, \ zzriTTin^jri::: , 
 
178 ELECTRO-DEPOSITION OF METALS. 
 
 acid-copper, silver, and gold baths. Hence, practically, only 
 one bath can be allowed to work at one time, as otherwise each 
 bath would have to be provided with as many resistance-boards 
 as would be required for the reduction of the electro-motive 
 force. For want of space the gold bath is placed in the sketch 
 behind the silver bath ; but as their resistances are not the 
 same, they must also be placed parallel. 
 
 L is the lye-kettle. It serves for cleansing the objects by 
 means of hot caustic potash or soda lye, from grinding and 
 polishing dirt and oil. For larger plants the use of a jacket- 
 kettle is advisable. By the introduction of steam in the jacket 
 the lye is heated without being diluted. The same object is 
 attained by placing a steam coil upon the bottom of the kettle. 
 Of course, heating may also be effected by a direct fire. 
 Instead of the preparatory cleansing with hot lye, which 
 saponifies the oil, the objects may be brushed off with benzine, 
 oil of turpentine or petroleum, the principal thing being the 
 removal of the greater portion of the grease and dirt, so that 
 the final cleansing, which is effected with lime paste, may not 
 require too much time and labor. It is also advisable to cleanse 
 the objects, in one way or the other, immediately after grinding, 
 as the dirt, which forms a sort of solid crust with the oil, is 
 difficult to soften and to remove when once hard. 
 
 The table which serves for the further cleansing of the 
 objects has already been described on p. 164, and illustrated 
 by Fig. 67. 
 
 Referring again to Fig. 70, between the lye-kettle L and the 
 box-table, is a frame, 14, for the reception of brass and copper 
 wire hooks of various sizes and shapes suitable for suspending 
 the objects in the bath. 
 
 The reservoir W, filled with water, standing in front of the 
 machine, serves for the reception of the cleansed and pickled 
 objects, if for some reason or other they cannot be imme- 
 diately brought into the bath. 
 
 H W is the hot-water reservoir in which the plated objects 
 are heated to the temperature of the hot water, so that they 
 
ELECTRO -PLATING ESTABLISHMENTS. 
 
 179 
 
 may quickly dry in the subsequent rubbing in the saw-dust box 
 Sf>. Before polishing the deposits, iron and steel objects are 
 thoroughly dried in the drying chamber T (Fig. 70), heated 
 
 
 
 
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i8o 
 
 ELECTRO-DEPOSITION OF METALS. 
 
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 Figs. 71a and 71b show a plating-room recently fitted up by 
 the Hanson & Van Winkle Co., of Newark, N. J. The arrange- 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 
 181 
 
 ment will be readily understood from the illustrations, so that a 
 detailed description is not necessary. 
 
 Switch-boards. In the sketch, Fig. 70, the resistance-board 
 belonging to each bath is secured to the wall in the immediate 
 neighborhood of the bath. This arrangement has the advan- 
 tage that the operator can, directly after suspending the objects, 
 conveniently effect regulation from the bath itself. The resist- 
 ances and measuring instruments, as well as the switches, may, 
 however, be also arranged alongside each other on a switch- 
 board. Where a large number of baths are in operation, 
 
 Fig. 72. 
 
 several such switch-boards will, of course, have to be provided 
 to avoid the necessity of the operator having to walk too great 
 a distance from the bath to the switch-board. 
 
 Fig. 72 shows such a switch-board, upon which are mounted 
 the dynamo resistance, the resistance for the accumulator, two 
 resistances for two baths, three amperemeters, a voltmeter with 
 switch, current indicator, as well as switches for engaging and 
 disengaging the machine as well as the accumulator. For the 
 sake of neatness the conductors and connections are on the 
 back of the switch-board. 
 
 A marble slab with a wood rim is the best material for a 
 
1 82 ELECTRO-DEPOSITION OF METALS. 
 
 switch-board. Marble or slate is absolutely required if the 
 arrangements for starting the electro-motors of the aggregates 
 or transformers are mounted upon the switch-board. If, in 
 such a case, the latter were of wood, there would be danger of 
 ignition by reason of the heating of the spirals, etc. Wooden 
 switch-boards may, however, be used for measuring instru- 
 ments and resistances not especially subject to heating. 
 
 The suggestions and directions given in the section " Installa- 
 tion with Cells " as regards regulation of current, measuring 
 instruments, conductors, tanks for solutions, etc., apply also to 
 installations with dynamos, and the reader is referred to that 
 section. 
 
 C. Installations and Accumulators. 
 
 Only in rare cases will an electroplating plant be operated 
 by an accumulator alone. 
 
 For larger establishments, where deposits requiring many 
 hours for finishing are made, for instance, in copper and nickel 
 galvanoplasty, silvering by weight, etc., the use of an accumu- 
 lator, in addition to a dynamo, is of great advantage, since the 
 process of depositing need not be interrupted during the noon 
 intermission or, in case it is not finished in the evening, during 
 the night, such interruptions affecting in various ways the 
 quality of the deposit. 
 
 However, even for depositing processes requiring a shorter 
 time, for instance nickeling, an accumulator gives the oppor- 
 tunity of turning the working power to better advantage. Sup- 
 pose, for instance, that bicycle parts which are to be solidly 
 nickeled have to remain in the bath for I y 2 hours. However, 
 the steam engine, and consequently the dynamo, are stopped 
 at 12 M. (noon), and hence no objects can be brought into the 
 bath after 10:30 a. m., as otherwise they would not be finished 
 by noon, and an interruption in the nickeling process has to be 
 avoided. If, however, an accumulator can during the noon 
 hour be used for feeding the baths, objects can be suspended 
 up to that time in the baths and taken from them finished 
 when the noon-hour expires and operations are recommenced. 
 
ELECTRO-PLATING ESTABLISHMENTS. I 83 
 
 The same can be done in the evening, and thus by the use of 
 an accumulator the producing power of an electro-plating plant 
 can be materially increased. 
 
 If an accumulator is thus to be made use of, a dynamo of an 
 adequately larger size has to be selected so that in addition to 
 the depositing work, the accumulator can at the same time be 
 charged by direct current from the dynamo. 
 
 In establishments where the current is generated by a motor- 
 generator or transformer fed from a central station, an accumu- 
 lator is a good investment, since in this case the operating 
 current is constantly at disposal and the motor-generators and 
 transformers can consequently run day and night. 
 
 Instead of feeding the baths and the accumulator simultane- 
 ously with current from a larger dynamo, two dynamos may, 
 of course, also be used, one of them supplying the baths and 
 the other the accumulator. 
 
 The magnitude of the performance of an accumulator de- 
 pends on the current-strength which it is to yield for a certain 
 time. As previously stated, the value ampere-strength X hours 
 is called the ampere-hour capacity of an accumulator. Hence 
 the question arises for how long the accumulator is to do the 
 work of the dynamo while the latter is not running, and what 
 current-strength is during this time to be transmitted from the 
 accumulator to the bath. If, now this ampere-hour capacity is 
 known, as well as the maximum current-strength required for 
 feeding the bath from the dynamo, we also know the current- 
 strength which the dynamo must have. 
 
 To explain this by an example, we will suppose that the bath 
 requires at a maximum 200 amperes, and that the dynamo has 
 to directly feed the bath for four hours and at the same time 
 charge a cell, which, when the dynamo stops, is to discharge 
 for two hours with 200 amperes to the bath. The cell must 
 therefore have a capacity of 400 ampere-hours, and taking into 
 consideration the fact that for charging at least 10 per cent, 
 more charging current is necessary than corresponds to the 
 discharging current, 440 amperes will have to be used for one 
 
1 84 ELECTRO-DEPOSITION OF METALS. 
 
 hour in order to charge the cell, or 220 amperes for two hours, 
 140 amperes for four hours. Since the dynamo, previous to 
 being stopped, has directly to yield for four hours to the bath, 
 200 amperes, there are four hours at disposal for charging the 
 cell, and the dynamo must therefore have a capacity of 
 200 -j- 110 = 310 amperes. 
 
 The diagram Fig. 73 shows the connection of a plant as 
 installed by the Electro-Chemical Storage Battery Co., of New 
 York. 
 
 By suitable manipulation of the switches and rheostats it is 
 possible to make the following connections : 1 . The dynamo 
 alone can be used on the baths. 2. The batteries alone can 
 be used on the baths. 3. The dynamo can be used on the 
 baths and the batteries charged with the excess-current, while 
 at the same time steadying the dynamo current. 4. The 
 dynamo and batteries can be used in multiple on the baths, 
 giving a greatly increased capacity. 
 
ELECTRO-PLATING ESTABLISHMENTS. 
 Fig. 73. 
 
 185 
 
CHAPTER V. 
 
 PREPARATION OF THE METALLIC OBJECTS. 
 
 As previously stated, the metallic objects to be plated have 
 to undergo both a mechanical and chemical preparation, and 
 each of these processes will be considered separately. 
 
 A. Mechanical Treatment Previous to Electro- Plating. 
 
 If the objects are not to be plated while in a crude state, 
 which is but rarety feasible, the mechanical treatment consists 
 in imparting to them a cleaner surface by scratch-brushing, or a 
 smoother and more lustrous one by grinding and polishing. It 
 may here be explicitly stated that scratch-brushing of plated 
 objects is not to be considered a part of their preparation, 
 since such scratch-brushing is executed in the midst of, or after 
 the plating process, its object being to effect an alteration of 
 the electro-deposits in more than one direction, and not the 
 cleansing of the surface of the metallic base. The following 
 directions, therefore, apply only to scratch-brushing of objects 
 not yet plated. The scratch-brushing of electro- deposits will 
 be considered later on. In regard to grinding, we have to deal 
 with the subject only in so far as it relates to smoothing rough 
 surfaces by the use of grinding powders possessing greater 
 hardness than the metal to be ground. With grinding in the 
 sense of instrument-grinding, the primary object of which is to 
 provide the instrument with a cutting edge, we have nothing 
 to do. 
 
 As some platers seem to have wrong ideas regarding the 
 electro-plating process, it may here be mentioned that the de- 
 posit is formed exactly in correspondence with the surface of 
 the basis-metal. If the latter has been made perfectly smooth 
 by grinding and polishing, the deposit will be of the same 
 
 ( 186 ) 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 I8 7 
 
 nature ; but if the basis surface is rough, the deposits also will 
 be rough. Hence it is wrong to suppose that by electro-plat- 
 ing a rough surface can be converted into a lustrous one, and 
 that pores, holes or scratches in the basis-metal can be filled 
 by plating. In order to obtain a deposit which is to acquire 
 high luster by polishing, it is absolutely necessary to bring the 
 basis into a polished state by mechanical treatment. In doing 
 this it is not necessary to go so far as to produce high luster, 
 but fine scratches, which would be an impediment to attaining 
 high luster after plating, must be removed. 
 
 Fig. 74. 
 
 Fig. 75. 
 
 Fig. 77. 
 
 Scratch-brushing may be effected either by hand or by a 
 scratch-brush lathe. For hand-work, scratch-brushes of more 
 or less hard brass or steel wire, according to the hardness of the 
 metal to be manipulated, are used. Various forms of brushes 
 are employed, the most common ones being shown in the 
 accompanying illustrations (Figs. 74 to 82). 
 
 Fig. 81 shows a whip brush for frosting or satin finish, and 
 Fig. 82 the plater's lathe goblet scratch-brush. 
 
1 88 ELECTRO-DEPOSITION OF METALS. 
 
 In scratch-brushing it is recommended first to remove, or at 
 least to soften, the uppermost hard and dirty crust (the scale) 
 by immersing the objects in a pickle, the nature of which 
 depends on the variety of metal, so that a complete removal of 
 all impurities and non-metallic substances may be effected by 
 means of the scratch-brush in conjunction with sand, pumice- 
 stone, powder, or emery. The composition of pickles will be 
 given later on. Scratch-brushing is complete only when the 
 article shows a clean metallic surface, otherwise the brushing 
 
 Fig. 78. 
 
 Fig. 70. 
 
 Fig. 
 
 tlw^ 
 
 '¥ 
 
 Fig. 82. 
 
 (scouring) must be continued. Scratch-brushes must be care- 
 fully handled and looked after, and their wires kept in good 
 order. When they become bent they have to be straightened,, 
 which is most readily effected by several times drawing the 
 brush, held in a slanting position, over a sharp grater such as 
 is used in the kitchen. By this means the wires become dis- 
 entangled and straightened out. 
 
 Hand scratch-brushing being slow and tedious work, large 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 189 
 
 establishments use circular scratch-brushes which are attached 
 to the spindle of a lathe. These circular brushes consist of 
 round wooden cases in which, according to requirement, 1 to 
 6 or more rows of wire bundles (see Fig. 83) are inserted. 
 
 Brushes with wooden cases are, however, more suitable for 
 scratch-brushing deposits than for cleansing the metallic base, 
 since for the latter purpose a more energetic pressure is usually 
 applied, in consequence of which the bundles bend and even 
 break off, if the wire is anyways brittle. For cleansing purposes 
 a circular scratch-brush, which the workman can readily re- 
 furnish with new bundles of wire, deserves the preference. It 
 is constructed as follows: Around iron disk about o. 1 1 inch 
 thick, and from 5 ^ to 7^ inches in diameter, is provided in the 
 centre with a hole so that it can be conveniently placed upon 
 the spindle of the lathe. At a distance of from 0.19 to 0.31 
 
 Fig. 83. 
 
 inch from the periphery of the disk, holes 0.079 to 0.1 1 inch in 
 diameter are drilled, so that between each two holes is a distance 
 of 0.15 inch. Draw through these holes bundles of wire about 
 3.93 inches long, so that they project an equal distance on 
 both sides. Then bend the bundles towards the periphery, 
 and on each side of the iron disk place a wooden disk 0.31 to 
 0.39 inch thick. The periphery of the wooden disk, on the side 
 next to the iron disk, should be turned semi-annular, so that 
 the wooden disks when secured to the spindle press very lightly 
 upon the wire bundles, and the latter remain very mobile. 
 When a circular scratch-brush constructed in this manner and 
 secured to the lathe is allowed to make from 1800 to 2000 
 revolutions per minute, the bundles of wire, in consequence of 
 
190 ELECTRO-DEPOSITION OF METALS. 
 
 the centrifugal force, stand very rigid, but being mobile will 
 give way under too strong a pressure without breaking off, and 
 can thus be utilized to the utmost. When required, the iron 
 disk can be refurnished with wires in less than half an hour. 
 An error frequently committed is that the objects to be cleansed 
 are pressed with too heavy a pressure against the wire brushes. 
 This is useless, since only the sharp points of the wire are 
 effective, the lateral surfaces of the bundles removing next to 
 nothing from the articles. 
 
 Brushes. A definition of these instruments is unnecessary, 
 and we shall simply indicate the various kinds suitable to the 
 different operations. 
 
 The fire-gilder employs, for equalizing the coating of amal- 
 gam, a long-handled brush, the bristles of which are long and 
 
 Fig. 85. Fig. 86. 
 
 very stiff. The electro-gilder uses a brush (Fig. 84) with long 
 and flexible bristles. 
 
 For scouring with sand and pumice-stone alloys containing 
 nickel, such as German silver, which are difficult to cleanse in 
 acids, the preceding brush, with smaller and stiffer bristles, is 
 used. 
 
 The gilder of watch-works has an oval brush (Fig. 85), with 
 stiff and short bristles for graining the silver. 
 
 The galvanoplastic operator, for coating moulds with black- 
 lead, besides a number of pencils, uses also three kinds of 
 brushes — the watchmaker's (Fig. 86), a hat brush, and a 
 blacking-brush. The bronzer uses all kinds of brushes. 
 
 Brushes are perfectly freed from adherent grease by washing 
 with benzine or carbon disulphide. 
 
 In large establishments engaged in electro-plating cast-iron 
 without previous grinding, the use of the sand-blast, in place of 
 the circular wire brush, has been introduced with great advan- 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 191 
 
 tage. Objects with deep depressions, which cannot be reached 
 with the scratch-brush, as well as small objects, which cannot 
 be conveniently held in the hand and pressed against the re- 
 volving scratch-brush, can be brought by the sand-blast into a 
 state of sufficient metallic purity for the electro-plating process. 
 
 However, while circular scratch-brushes impart to the objects 
 a certain, though not very great luster, the metal portions are 
 matted by the sand-blast, and the latter is frequently employed 
 for matting entire lustrous surfaces or for producing contrasts, 
 for instance, mat designs upon lustrous grounds, or vice versa. 
 
 Fig. 87 shows such a sand-blast. The compressed air, the 
 
 Fig. 87. 
 
 pressure of which should be at least equal to that of a column 
 of water i8*/£ inches high, passes through the blast-pipe A into 
 a nozzle running horizontally through the machine, carries 
 along a jet of sand, and hurls the latter upon the objects placed 
 underneath the nozzle. The objects are placed upon sheet-iron 
 plates or in sheet-iron boxes and very slowly passed below the 
 nozzle, the motion being effected by the shafts BB with the use 
 of rubber belts. To avoid dust, the machine is provided with 
 
192 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Fig, 
 
 SIEVE 
 H rji 1 1 m ] 1 1 1] 1 u UJ 
 
 ȣL 
 
 
 a jacket of sheet-iron or wood ; a few windows enable the 
 operator to watch the progress of the operation. 
 
 Figs. 88 and 89 show a complete portable sand-blast outfit, 
 which has been designed and placed on the market by Leiman 
 Bros., Newark, N. J. The outfit is all mounted upon a small 
 platform truck, which can be readily moved from place to place 
 to suit the demands of the work. At one end of the platform 
 is located the electric motor, which receives current from the 
 nearest circuit. This drives the pressure-blower from which 
 the air, after passing through the oil separator, enters the pipe 
 which delivers the air at the nozzle. 
 
 The nozzle of the machine is a long, straight piece of ordi- 
 nary iron pipe without the tapered hole usually used, and there 
 
 is therefore very little wear. 
 The air goes directly from the 
 compressor to the mixing cham- 
 ber at the base of the nozzle, the 
 vacuum created there drawing 
 the sand through the sand feed- 
 pipe from the tank. As the 
 sand reaches the mixing cham- 
 ber it receives the full pressure 
 of the air, driving it through the 
 nozzle without the necessity of 
 making the nozzle tapered in 
 order to increase the pressure. 
 In this way not only can a 
 larger nozzle be used, thereby 
 covering a much larger surface 
 with a given pressure of air, but 
 it may be longer, even to the 
 extent of several feet, enabling 
 the operator to stand at a dis- 
 tance from his work with just as 
 satisfactory results. The fact 
 that the air does not go through the machine itself does away 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 193 
 
 with the necessity of making it of steel, and it is therefore made 
 of heavy galvanized iron. In the top of the tank is a depressed 
 sieve which sifts the sand automatically. The machine holds 
 enough sand for three or four hours' continuous work. 
 
 The operation of the apparatus is controlled by the one sim- 
 ple valve at the bottom, which starts and stops, as well as 
 regulates, the flow of sand. All that is necessary is to turn the 
 valve and point the nozzle on to the work. This sand-blast can 
 be used for cleaning castings of any kind, and for frosting glass, 
 hardware, gas and electric fixtures and all metals. Sea sand 
 
 Fig. 
 
 Je.pr&sseB 
 
 or sand of any quality, as well as the various grades of flint or 
 carborundum, may be used, depending on the class of work to 
 be sand-blasted — whether the very roughest of steel or iron or 
 the very finest of finished brass or bronze. This material is 
 first thoroughly dried and thrown into the sieve at the top of 
 the machine where it is sifted, dropping into the bottom of the 
 machine ready for use. 
 
 The uses to which a sand-blast can be put are very numerous. 
 The frosting or satin-finishing of silverware and other articles, 
 engraving or stenciling of metal or glass, inlaying, removing 
 13 
 
194 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 scale, etc., the nature of the'work being governed by the fine- 
 ness of the sand used as well as the pressure. 
 
 If a clean metallic surface is at one time to be given to a large 
 number of small articles, such as buckles, steel beads, metal 
 buttons, steel watch chains, ferrules, etc., a tumbling barrel or 
 drum is frequently used (Fig. 90). It generally consists of a 
 cylindrical or polygonal box having a side door for the intro- 
 duction of the work, together with sharp sand or emery, and is 
 mounted horizontally on an axis furnished with a winch or 
 pulley, so as to be revolved either by hand or power, as may 
 be desired. In order to prevent certain objects, like hooks for 
 ladies' dresses and the like, from catching each other and com- 
 
 Fig. 90. 
 
 bining into a mass, a number of nails or wooden pegs are fixed 
 in the interior of the drum. 
 
 For ordinary polishing the articles are brought into the 
 tumbling barrel together with small pieces of leather waste 
 (leather shavings), and taken out in one or two days. How- 
 ever, to produce an actually good polish a somewhat more 
 complicated method has to be pursued. The articles are first 
 freed from adhering scale by washing in water containing 5 per 
 cent, of sulphuric acid, then rinsed and dried in a drying cham- 
 ber, or in a pan over a fire. They are next brought into the 
 tumbling barrel together with sharp sand, such as is used in 
 glass-making, and revolved for about 12 hours, when they are 
 taken from the barrel and freed from the admixed sand by sift- 
 ing. They are then returned to the barrel, together with soft, 
 
PREPARATION OF THE METALLIC OBJECTS. 1 95 
 
 fibrous sawdust, to free them from adhering sand, and at the 
 same time to give them a smoother surface. They are now 
 again taken from the barrel, freed from sawdust, and returned 
 to the barrel, together with leather shavings. They now re- 
 main in the barrel until they have acquired the desired polish^ 
 which, according to the size and shape of the articles and the 
 degree of polish required, may frequently take two weeks or 
 more. Articles of different shapes and sizes are best treated 
 together, time being thereby saved. The process is also accel- 
 erated by adding some fat oil to the leather shavings, which, 
 of course, must be omitted when, after long use, the shavings 
 have become quite greasy. The barrel should be filled about 
 half full, otherwise the articles do not roll freely, and polishing 
 is retarded. On the other hand, when the barrel is less than 
 half full there is danger of the articles bending, or in case they 
 are hardened, for instance buckles, of breaking. 
 
 For many purposes polishing in the tumbling barrel is of 
 great advantage, since, independent of its cheapness, the sharp 
 edges of the articles are at the same time rounded off. How- 
 ever, with articles the edges of which have to remain sharp, the 
 process cannot be employed. 
 
 The tumbling barrel in which the articles are treated with 
 sand cannot be used for polishing with leather shavings, it 
 being next to impossible to free it entirely from sand. The 
 barrels should make from 50 to 70 revolutions per minute; if 
 allowed to revolve more rapidly, the articles take part in the 
 revolutions without rolling together, which, of course, would 
 prevent polishing. 
 
 The brightening of articles of iron and steel may be simpli- 
 fied by using water to which 1 per cent, of sulphuric acid has 
 been added. The barrel used for the purpose must, of course, 
 be water-tight. By the addition of sand the process is acceler- 
 ated. Nickel and copper blanks for coins are also cleansed in 
 this manner. They are brought into the tumbling barrel, to- 
 gether with a pickling fluid, and, when sufficiently treated, are 
 taken out, rinsed, dried in sawdust, and finally stamped. 
 
?96 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Fig. 91. 
 
 Fig. 91 shows a form of an adjustable, oblique tumbling- 
 barrel, adapted to clean, smooth, 
 brighten, and polish nearly every 
 variety of iron and brass goods. The 
 simplicity and durability of the con- 
 struction and the rapidity with which 
 the work is done are distinct advan- 
 tages. The machine can be used 
 wet or dry. It is adjustable by screw 
 and wheel to any working elevation 
 up to 50 . The machine shown in 
 the illustration is designed to carry 
 a barrel 24 inches in diameter, but 
 larger or smaller barrels can be used. 
 Grinding. Wooden wheels cov- 
 ered with leather coated with emery of various degrees of fine- 
 ness are almost exclusively used for grinding metallic objects 
 preparatory to the plating process. The 
 wooden wheels are made of thoroughly- 
 seasoned poplar, in the manner shown in 
 Fig. 92. The separate pieces are radi- 
 ally glued together, and upon each side in 
 the center a strengthening piece is glued 
 and secured with screws, so that each 
 segment of the wheel is connected with 
 the strengthening piece. The center of 
 the wheel is then provided with a hole corresponding to the 
 diameter of the spindle of the grinding lathe, to which it is 
 secured by means of wedges. The periphery, as well as the 
 sides, is then turned smooth. A good quality of leather, previ- 
 ously soaked in water and cut into strips corresponding to the 
 width of the wheel is then glued to the periphery, and still fur 
 ther secured by pins of soft wood. When the glue is dry the 
 wheel is again wedged upon the spindle and the leather care 
 fully turned ; it is then ready for coating with emery. 
 
 With the use of grinding wheels of oak or walnut, covering 
 
 Fig. 92. 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 with leather may be omitted, and the emery can be applied 
 directly to the wheels. However, leather-covered wheels are to 
 be preferred since, by reason of their elasticity, better results 
 in grinding are obtained than with uncovered wheels of the 
 above-mentioned varieties of wood. 
 
 For grinding soft metals, hard, impregnated felt wheels " set 
 up" with glue and emery are also employed. 
 
 For grinding profiled articles preference should be given to 
 wheels without leather covering, and the grinding surface 
 should be fitted to the profile of the article to be ground by 
 cutting with a turning tool. 
 
 Grinding wheels of paste-board and of cork waste have re- 
 cently been introduced. The former are made by coating on 
 both sides thin, round disks of paste-board with glue mixed 
 with emery, and then gluing a sufficient number of such disks 
 one upon the other to form a wheel of the desired width. The 
 wheel is finally subjected to strong pressure under a hydraulic 
 press, and dried. However, as these wheels have disappeared 
 from commerce, it may be assumed that they have not stood 
 the test in practice. The same may 
 be said of cork wheels. The so- 
 called elastic wheel has also not an- 
 swered the demands made in prac- 
 tice. The cementing material in the 
 case consisted of a gum or rubber- 
 likemass, which to be sure imparted . 
 great elasticity to the wheel, but when 
 the latter became hot during grind- 
 ing, the mass softened and smeared. 
 
 The so-called reform wheel, Fig. 
 93, has a better prospect of general 
 introduction. The leather covering 
 does not consist of a single strap, but 
 
 pieces of leather, 3 to 5 millimeters thick, are placed alongside 
 each other and secured by means of a sort of dove-tailing to an 
 iron rim, which is screwed upon the wooden disk. According 
 
 mm 
 
 lira 
 
I98 ELECTRO-DEPOSITION OF METALS. 
 
 to the length of the pieces of leather a greater or smaller 
 degree of elasticity is attained. One covering lasts at least 
 five to eight times as long as the covering with leather straps, 
 and leather-waste, otherwise of scarcely any value, may be 
 employed for the covering. 
 
 For grinding soft metals, hard impregnated felt wheels coated 
 by means of glue with emery are also used. 
 
 For gluing with emery three different kinds of emery are 
 used, a coarse quality ( Nos. 60 to 80) for preparatory grind- 
 ing, a finer quality (No. 00) for fine grinding, and the finest 
 quality ( No. 0000) for imparting luster. The wheels thus 
 coated are termed respectively " roughing wheel," " medium 
 wheel," and " fine wheel." With the first the surface of the 
 objects are freed from the rough crust. The coarse-grained 
 emery used for this purpose, however, leaves scratches, which 
 have to be removed by grinding upon the medium wheel until 
 the surfaces of the objects show only the marks due to the 
 finer quality of emery, which are in their turn removed by the 
 fine wheel. 
 
 In most cases brushing with a circular bristle brush may be 
 substituted for the last grinding, the articles being moistened 
 with a mixture of oil and emery No. 0000. Care must be had 
 not to execute the brushing nor the grinding with the finer 
 quality of emery in the same direction as the preceding grind- 
 ing, but in a right angle to it. 
 
 Treatment of the grinding wheels. — The coating of the 
 roughing wheels with emery is effected by applying to them a 
 good quality of glue and rolling them in dry, coarse emery 
 powder. For the medium and fine wheels, however, the emery 
 is mixed with the glue and the mixture applied to the leather. 
 When the first coat is dry, a second is applied, and finally a 
 third. The whole is then thoroughly dried in a warm place. 
 Before use, a piece of tallow is held to the revolving disk for 
 the purpose of imparting a certain greasiness to it, and in order 
 to remove any roughness due to an unequal application of the 
 emery, it is smoothed by pressing a smooth stone against it. 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 199 
 
 While the preparatory grinding upon the roughing wheel is 
 executed dry, i. e., without the use of oil or fat, in fine grinding, 
 the objects are frequently moistened with a mixture of oil and 
 the corresponding No. of emery. When the layer of emery is 
 used up, the remainder is soaked with warm water and scraped 
 off with a dull knife. The leather of the disks on which oil or 
 tallow has been used is then thoroughly rubbed with caustic 
 lime or Vienna, lime* to remove the greasiness, which would 
 prevent the adherence of the layer of glue and emery to be 
 
 Fig. 94. 
 
 applied later on. When the leather is thoroughly dry a fresh 
 layer of emery may at once be applied. 
 
 To prevent the leather from absorbing an excess of water 
 when moistening the old layer of glue and emery for the pur- 
 pose of softening it, it is advisable to apply moderately wet clay 
 
 * Vienna lime is prepared from a variety of dolomite which is first burned, then 
 slaked, and finally ignited for a few hours. It consists of lime and magnesia, and 
 should be kept in well-closed cans, as otherwise it absorbs carbonic acid and mois- 
 ture from the air, and becomes useless. 
 
200 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 to the layer and allow it to remain for a few hours when the 
 scraping-off of the emery can be readily effected. 
 
 Grinding lathes. For use, the grinding wheels are wedged 
 upon a conical cast-steel spindle provided with a pulley and 
 running in bearings, as plainly shown in Fig. 94. The cast-iron 
 standards are screwed to the floor; the wooden bearings can 
 be shifted forward and backward by wedges and secured in a 
 determined position by a set screw, thus facilitating the removal 
 
 Fig. 95. 
 
 of the spindle after throwing off the belt. The wheels being 
 wedged upon a conical spindle, they always run centrically. 
 Changing of the wheels requires but a few seconds, and on ac- 
 count of the slight friction of the points of the spindle in the 
 wooden bearings, the consumption of power is very slight. 
 
 To avoid the necessity of throwing off the belt while chang- 
 ing the grinding wheels, double machines (Fig. 95) are used, 
 the principle of conical spindles being, however, preserved. 
 The shaft is provided with loose and fast pulley and coupling 
 lever. 
 
 Fig. 96 illustrates a similar machine with ring-oiling. 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 20I 
 
 Fig. 97 represents a belt-attachment combined with a double 
 grinding lathe, as constructed by the firm of Dr. G. Langbein 
 & Co. The apparatus can be readily secured by means of 
 screws to the lathe, and is readily removed. It allows of 
 grinding-wheels, brushes, etc., being attached to both ends of 
 the shaft, while the belt can at the same time be used. 
 
 Fig. 96. 
 
 Electrically- driven grinding motors have been previously re- 
 ferred to. Fig. 98 shows a grinder of this type manufactured 
 by the Hanson & Van Winkle Co., Newark, N. J. It is of the 
 ribbed type, and is furnished in various sizes. The switch, 
 starting box and regulator are contained within the stand, with 
 the operating handles extending through a suitable opening. 
 An important feature of this machine is the ability of the oper- 
 ator to regulate the speed of the wheels, running them at the 
 speeds most suitable for the work in hand. This regulation of 
 the speed is accomplished by the simple movement of a handle, 
 the speed remaining practically constant at any point. 
 
 A smaller type of the same machine is very suitable for use 
 by manufacturers, jewelers, dentists, instrument makers, etc. 
 
202 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 These grinding motors, as well as the polishing motors to be 
 described later on, have the advantage of occupying no more 
 •space than that is usually required by a belt-driven lathe, while 
 the full motive power is applied, without loss, directly to the 
 grinding wheels. They also possess the advantage of being 
 
 Fig. 97. 
 
 PS 
 
 (J 
 
 
 portable, and in a few moments' time „can be moved to any 
 part of the factory that may be best suited for the purpose re- 
 quired, making it possible to take the motor to the work when 
 desired/ instead of bringing the work to the motor. 
 
 Execution of grinding and brushing. — Grinding is executed 
 by pressing the surfaces to the ground against the face of the 
 wheel, moving the objects constantly to and fro. The opera- 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 203 
 
 tion requires a certain manual skill, since, without good reason, 
 no more should be ground away on one place than on another. 
 Special care and skill are required for grinding large round 
 surfaces. 
 
 If the objects are not to be treated with the fine wheel, fine 
 grinding is succeeded by brushing with oil and emery by means 
 of circular brushes formed of bristles set in disks of wood. 
 Genuine bristles being at present very expensive, vegetable 
 fiber, so-called fibers, has been successfully substituted for 
 
 Fig. 98. 
 
 them, the wooden wheel being replaced by an iron case, in the 
 bell-shaped cheeks of which the fiber-bundles are secured by 
 means of strong nuts. Before use it is advisable to saturate 
 the fiber-bundles with oil in order to deprive them of their 
 brittleness, and thus improve their lasting quality. 
 
 The grinding lathe (Fig. 99) is provided with a tampico 
 brush, this fiber being particularly adapted for rough,. quick 
 work. It can, of course, be just as well placed upon the con- 
 ical spindles of double machines. The iron case is provided 
 with a conical hole corresponding exactly to the conical spin- 
 
204 
 
 ELECTRO-DEPOSITION OF METAl.^. 
 
 die, the large frictional surface preventing the turning of the 
 brush upon the spindle, or its running off. 
 
 In regard to grinding the various metals, the procedure, 
 according to the hardness of the metal, is as follows: 
 
 Iron and steel articles are first ground upon the roughing 
 wheel, then fine-ground upon the medium wheel, and finally 
 upon the fine wheel, or brushed with emery with the circular 
 brush. Very rough iron surfaces may first be ground upon 
 
 Fi<;. 99. 
 
 Fig. 100. 
 
 solid emery wheels before being worked upon the roughing 
 wheel. 
 
 For depressed surfaces which cannot be reached with the 
 large emery wheels, small walrus-hide wheels coated with glue 
 and emery are placed upon the point of the spindle of a 
 polishing lathe. 
 
 Brass and copper castings are first ground upon roughing 
 wheels which have lost part of their sharpness and will no 
 longer attack iron. They are then ground fine upon the medium 
 wheel, and finally polished upon cloth or felt wheels (bobs). 
 (See below, under "Polishing") 
 
 Sheets of brass, German silver and copper, as furnished by 
 
PREPARATION OF THE METALLIC OBJECTS. 205 
 
 rolling-mills, are only brushed with emery and then polished 
 with Vienna lime or rouge upon bobs. 
 
 Zinc castings, as, for instance, those produced in lamp fac- 
 tories, are first thoroughly brushed by means of circular 
 brushes and emery, and then polished upon cloth bobs. 
 
 Sheet zinc is only polished with Vienna lime and oil upon 
 cloth bobs secured to the spindle shown in Fig. 106. 
 
 Polishing. — As will be seen from the foregoing, polishing 
 serves for making the articles read)', i. e., the final luster is im- 
 parted to them upon soft polishing wheels with the use of fine 
 polishing powders. The polishing wheels or bobs of fine felt, 
 shirting, or cloth, are secured to the polishing lathe, and, ac- 
 cording to the hardness of the metal to be polished, make 2000 
 to 2500 revolutions per minute. A foot-lathe, such as is shown 
 in Fig. 100, makes generally not over 1800 revolutions per 
 minute. Cloth bobs are made by placing pieces of cloth one 
 upon another in the manner described under " Nickeling of 
 sheet zinc," cutting out the center so as to correspond to the 
 diameter of the spindle, and securing the disks of cloth by 
 means of nuts between two wooden cheeks upon the spindle of 
 the polishing lathe. In place of cloth bobs, solid wheels of 
 felt or wooden wheels covered with a layer of felt may be used, 
 especially for polishing smooth objects without depressions, 
 the fineness and softness of the felt depending on the degree of 
 polish to be imparted and the hardness of the metal to be 
 manipulated. 
 
 Fig. 101 shows the patented triplex buff manufactured by 
 Zucker & Levett & Loeb Co., New York. It is made of standard 
 grades of muslins, and can be furnished stitched or not, as 
 desired. 
 
 The secret of the great wearing qualities of the triplex buff is 
 in the fold, the prime object of which is to produce a cross- 
 cutting or diagonal surface on the cutting face of the buff, the 
 buff being made of a succession of folds so formed as to offer 
 a greater surface to the work and, at the same time, to save 
 composition. The mesh of the fabric crossing as described 
 
206 
 
 ELECTRO-DEPOSITION OF METALS. 
 Fig. ioi. 
 
 3 ,v t vv"v"^ 
 
 Fig. io2. 
 
 prevents the material from pulling out or fraying on the work- 
 ins edge. 
 
 An excellent polishing-wheel is 
 the Union canvas wheel, made by 
 the Hanson & Van Winkle Co., of 
 Newark, N. J. It is shown in Fig.. 
 102. It is not glued, but by a spe- 
 cial process the weight is reduced, 
 the elasticity and flexibility are in- 
 creased, and a cloth face is obtained,, 
 which combined with the glue, pre- 
 sents a surface that will hold emery 
 better than any other wheel. Being 
 of a flexible nature, it easily adjusts 
 itself to the irregularities of the 
 work. No special skill is required 
 to use it, and there is less tendency to "-gouge" the work or 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 207 
 
 spoil design. The wheel will do more work with one " setting- 
 up " than any other. It is durable and easily kept in balance. 
 Another wheel of great flexibility and elasticity is the wal- 
 rine wheel manufactured by the same firm. On account of 
 its flexibility and elasticity, combined with its hardness, it is 
 recommended for hard grinding, and the fact that its face can 
 
 Fig. 103. 
 
 be turned to any shape — at the same time preserving all the 
 characteristics of hide wheels— will place it before sea-horse 
 or walrus on its merits. One advantage of this wheel is its 
 pliability, which allows it to adjust itself to any inequalities in 
 the coat of emery, and consequently it wears evenly, and being 
 
208 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 lighter than any other serviceable wheel, it is much less liable 
 to injure lathe bearings. 
 
 Fig. 104. 
 
 Fig. 103 shows a substantial foot-power grinding and polish- 
 ing lathe. It is noiseless, and with friction-clutch attachment a 
 speed of 2500 to 3000 revolutions per minute can be maintained 
 
 IjiHH 
 
 without effort. There is nothing better for gunsmiths, black- 
 smiths, skate-grinders, locksmiths, bicycle repair shops, jewelers. 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 209 
 
 It is so constructed as to be very rigid and strong to prevent 
 vibration. It is furnished by the Hanson & Van Winkle Co. 
 
 Double polishing lathes according to American patterns, 
 Figs. 104 and 105, are used for polishing objects of not too 
 large dimensions. These polishing lathes are manufactured in 
 several sizes, the largest capable of using wheels 15 inches 
 diameter and 5 inches face. Fig. 104 shows a 10-inch polish- 
 ing head to be screwed to a bench. 
 
 Fig. 105 illustrates a 14-inch ring-oiling polishing machine. 
 The head is constructed so as to give plenty of room between 
 
 Fig. 106. 
 
 the wheels and the column, thus making the machine of special 
 advantage where awkward pieces are to be handled, as bicycle, 
 chandelier, and similar classes of work. The bearings provided 
 are peculiar to the machine, the boxes being so constructed 
 that the spindle has four bearings, thus affording a good sup- 
 port and making the machine a stiff and durable one. 
 
 The polishing lathe shown in Fig. 106 serves chiefly for pol- 
 ishing large sheets, the latter being placed upon a smooth, 
 wooden support which rests upon the knees of the workman, 
 as will be described later on in speaking of nickeling sheet-zinc. 
 
 Fig. 107 shows an independent spindle polishing and buffing 
 14 
 
2IO 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 lathe manufactured by the Hanson & Van Winkle Co., Newark 
 N. J. In designing this lathe further demands for economy' 
 viz.. power, shafting and belting have been anticipated' 
 Countershafts, loose pulleys and incidental belting are dis- 
 pensed with. To accomplish this, a single driving pulley and 
 double friction cones, securely housed in the lathe head, as 
 shown in the illustration, are used on the lathe. 
 
 Ftg. 107. 
 
 The forged steel clutches are operated by small hand levers 
 above the casing. A study of the illustration will show the 
 great strength and large provision for wear in the double fric- 
 tion cones, as well as the spindle bearings, and the means for 
 oiling. 
 
 The lathe spindle is of large diameter, carefully ground and 
 polished ; it runs smoothly and noiselessly and without end play 
 Throwing off the clutch brings a brake into action and stops the 
 spindle instantly, while the reverse motion releases the brake 
 
PREPARATION OF THE METALLIC OBJECTS. 211 
 
 and starts the spindle immediately. This is done at either end 
 without interference or waiting ; as a result there is no lost time 
 for either operator, which means a saving of from one to three 
 hours per day. 
 
 The pedestal flares at the back so that the lathe can be belted 
 from below, a method now used in many shops, and always to 
 be preferred, as it gives a room entirely clear of belts. 
 
 Electrically-driven polishing and buffing lathes are now in 
 frequent use. The high speed at which emery and polishing 
 wheels are run necessitate tight belts, heated bearings, and the 
 
 Fig. io8. 
 
 dirt carried by the belt. All this is overcome in these ma- 
 chines. They can be placed so as to secure the best light, the 
 speed is constant, and no power is used in driving the counter- 
 shaft when not in use. The machines are furnished with and 
 without stand. 
 
 Fig. 1 08 shows a type of polisher manufactured by the Han- 
 son & Van Winkle Co. It has all the good points of the 
 grinder (Fig. 99) manufactured by the same firm. 
 
 The belt strapping attachment or endless belt machine shown 
 
212 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 in Fig. 109 is manufactured by the Hanson & Van Winkle Co 
 of Newark, N. J. The demand for machines of this character 
 for polishing bicycle parts has greatly increased, and improve- 
 ments have from time to time been made, culminating in the 
 present construction, which is much more solid and the adjust- 
 ment of the tension of the belt can be done without interfering 
 with the operator. There are fewer parts used than in previous 
 machines, and with the flanged wheels that are supplied to go 
 
 Fig. ioq. 
 
 on the pulley lathe, and with the rubber endless belts from 1 to 
 3 inches wide and up to 12 feet in length, make this machine 
 available for all purposes. It is equally available to manufac- 
 turers of saddlery and carriage hardware, and on irregularly 
 shaped articles that cannot be conveniently polished on a circu- 
 lar wheel. 
 
 No shop is now complete without one or more flexible shafts 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 213 
 
 for grinding, polishing and buff- 
 ing. In many ways it will be 
 found a profitable and econom- 
 ical device. For cleaning and 
 grinding heavy castings, for pol- 
 ishing and buffing all metal and 
 glass, it is a most indispensable 
 tool where power is or can be 
 used to advantage. These shafts, 
 Fig. no, are made in standard 
 sizes, from ^-inch diameter 
 core, suitable for very light 
 work, to 13^-inch core, capable 
 of driving a 3-inch drill in iron 
 or steel. 
 
 Fig. 1 1 1 shows the flexible 
 shaft with part of case and core 
 cut away to show the method of 
 construction. 
 
 Fig. in. 
 
 Fig. 1 shows complete shaft with drill on one end. Fig. 2 
 
214 ELECTRO-DEPOSITION OF METALS. 
 
 shows manner of " laying up " the shaft, and the construction 
 of case. Fig. 3, section showing hand piece, shaft case, and 
 end nut, to which are attached the tools to be used. Fig. 4, 
 section of pulley end. 
 
 Letter references : AA, shaft case ; B, section of shaft and 
 case; C, cord to draw pulley to any desired direction; D, 
 driving belt. 
 
 This mode of construction insures stability and great tor- 
 sional strength, and, at the same time, entire flexibility at right 
 angles to the axis. 
 
 Polishing materials. — According to the hardness of the 
 material to be polished, rouge (ferric oxide, colcothar) tripoli, 
 Vienna lime, etc., in the state of an impalpable powder, and 
 generally mixed with oil, or sometimes with alcohol, are used 
 as polishing agents. For hard metals, an impalpable rouge of 
 great hardness (No. F of commerce) is employed, for softer 
 metals, a softer rouge (No. FFF), or Vienna lime, tripoli, etc. 
 
 It is of advantage to melt the rouge with stearine and a small 
 quantity of tallow, and cast the mixture in moulds with the aid 
 of strong pressure. The sticks thus formed are sufficiently 
 greasy to render the use of oil superfluous. In order to im- 
 pregnate the surface of the polishing bob with the polishing 
 material, hold one of the sticks for a second against the revolv- 
 ing wheel, and then polish the objects by pressing them against 
 the wheel, diligently moving them to and fro. The polishing 
 bob must not be too heavily impregnated with rouge, since a 
 surplus of the latter smears instead of cutting well. 
 
 In polishing with Vienna lime it is expedient to moisten the 
 objects to be polished with stearine oil, and saturate the polish- 
 ing wheels by pressing a piece of Vienna lime against them. 
 However, this causes a great deal of dust, which not only 
 incommodes the workman, but is also injurious to the respira- 
 tory organs. It is therefore recommended to remove the dust 
 by means of an exhauster. 
 
 Another process of polishing, called burnishing, is executed 
 by means of tools usually made of steel for the first or ground- 
 
PREPARATION OF THE METALLIC OBJECTS. 21 5 
 
 ing process, or of a very hard stone, such as agate or blood- 
 stone, for finishing. Burnishing is applied to the final polish- 
 ing of deposits of the noble metals, and will be referred to 
 later on. 
 
 B. Mechanical Treatment During and After Electro-plating. 
 
 In this connection, scratch-brushing the deposits will be first 
 considered, the object of this operation being, on the one hand 
 to promote the regular formation of certain deposits, and, on 
 the other, to affect the physical properties of the deposits, and 
 finally to ascertain whether the deposit adheres to the basis- 
 metal. 
 
 If it is noticed by the irregular formation of the deposit that 
 the basis-metal has not been cleaned with sufficient care by the 
 preparatory scratch-brushing, the object has to be taken from 
 the bath and the defective places again scratch-brushed with 
 the application of water and sand, or pumice-stone, when the 
 object is again pickled and replaced in the bath. 
 
 On the other hand, the deposits always form more or less 
 porous, they having, so to say, a net-like structure, though it 
 may not be visible to the naked eye. By scratch-brushing, 
 the meshes of the net are made closer by particles of metals 
 being forced into them by the' brush, and the deposit is thus 
 rendered capable of receiving additional layers of metal. 
 Furthermore, by scratch-brushing, dull deposits acquire a 
 certain luster, which is enhanced by the subsequent polishing 
 process. Finally, by an unsparing application of the scratch- 
 brush, it will be best seen whether the union of the deposit with 
 the basis-metal is sufficiently intimate to stand, without becom- 
 ing detached, the subsequent mechanical treatment in polishing. 
 
 According to the object in view, and the hardness of the de- 
 posit to be manipulated, scratch-brushes of steel or brass wire 
 are chosen. For nickel, which, as a rule, requires scratch- 
 brushing least, and chiefly only for the production of very thick 
 deposits, steel wire of 0.2 millimeter thickness is taken; for 
 deposits of copper, brass, and zinc, brass wire of 0.2 millimeter; 
 
216 ELECTRO-DEPOSITION OF METALS. 
 
 for silver, brass wire of 0.15 millimeter; and for gold, brass 
 wire of 0.07 to 0.1 millimeter. Scratch-brushing is seldom 
 done dry. The tool as well as the pieces should be constantly 
 kept wet with liquids, especially such as produce a lather in 
 brushing, for instance, water and vinegar, or sour wine, or solu- 
 tions of cream of tartar or alum, when it is desired to brighten 
 a gold deposit which is too dark. However, the liquid most 
 generally used is a decoction of licorice-root, of horse-chestnut, 
 of marshmallow, of soap-wort, or of the bark of Panama-wood, 
 all of which, being slightly mucilaginous, allow of a gentle 
 scouring with the scratch-brush, with the production of an 
 abundant lather. A good adjunct for scratch-brushing is a 
 shallow wooden tub containing the liquid employed, with a 
 board laid across it nearly level with the edges, which, how- 
 ever, project a little above. This board serves as a rest for the 
 pieces. 
 
 The hand scratch-brush, when operating upon small objects, 
 is held by the workman in the same manner as a paint brush, 
 and is moved over the object with a back and forward motion 
 imparted by the wrist only, the forearm resting on the edge of 
 the tub. For larger objects, the workman holds his extended 
 ringers close to the lower part of the scratch-brush, so as to 
 give the wires a certain support, and, with raised elbow, strikes 
 the pieces repeatedly, at the same time giving the tool a sliding 
 motion. When a hollow is met with, which cannot be scoured 
 longitudinally, a twisting motion is imparted to the tool. 
 
 Scratch-brushing by means of circular scratch-brushes is 
 effected in a lathe. The lathe-brush is mounted upon a spindle 
 and is provided above with a small reservoir to contain the lub- 
 ricating fluid, a small pipe with a tap serving to conduct the 
 solution from this to a point immediately above the revolving 
 brush. The top of the brush revolves towards the operator, 
 who presents the object to be scratch-brushed to the bottom. 
 The brush is surrounded by a wooden cage or screen to prevent 
 splashing. To protect the operator against the water projected 
 by the rapid motion, there is fixed to the top of the frame a 
 
PREPARATION OF THE METALLIC OBJECTS. 21 7 
 
 small inclined board, which reaches a little lower than the axis 
 of the brush without touching it. This board receives the pro- 
 jected liquid, and lets it fall into a zinc trough, which forms 
 the bottom of the box. Through an outlet provided in one of 
 the angles of the trough, a rubber tube conveys the waste 
 liquid to a reservoir below. After scratch-brushing every trace 
 of the lubricating liquid must be washed away before placing 
 or replacing the objects in the bath. 
 
 Drying. — The finished plated objects are first rinsed in clean 
 water to remove the solution constituting the bath adhering to 
 them. They are next immersed in hot water, where they re- 
 main until they have acquired the temperature of the water, and 
 are then quickly rubbed with dry, hot sawdust. It is best to 
 use sawdust of soft wood, free from tannin, such as maple, 
 poplar, or pine. Oak sawdust is not suitable for the purpose 
 on account of its content of tannin, which imparts a dirty 
 coloration to the deposits. Boxwood sawdust, though much 
 used, is not sufficiently absorbent, and sticks to the moist 
 objects. The sawdust used must be freed from coarser particles 
 of wood by sifting. For holding the sawdust, a zinc box with 
 double bottom is frequently used, which is heated by waste 
 steam or some other process. In order to remove all moisture 
 from the pores it is advisable to place plated objects of iron 
 and steel for a few hours in an oven heated to between 140 
 and 1 75 F. 
 
 For drying small work centrifugal dryers have been de- 
 signed. Time, heat, and sawdust are saved by their use, a 
 much greater bulk of work can be handled in a day, and the 
 staining of work which has been nickeled greatly reduced. 
 The work is dried in 1 to 3 minutes. Such a machine is a very 
 useful adjunct where a mechanical plating apparatus (see 
 Chapter VI, Deposition of Nickel) is installed. A very good 
 method of freeing nickeled objects from all moisture which 
 may have collected in the pores is to immerse them for about 
 ten minutes in boiling linseed oil, and, after allowing them to 
 drain off, to remove the adhering oil by rubbing with sawdust. 
 
2l8 ELECTRO-DEPOSITION OF METALS. 
 
 According to some electro -platers, the deposit of nickel thus 
 treated loses its brittleness and will stand bending several 
 times, for instance, wire, sheets, etc., without breaking. Ex- 
 periments made by Dr. George Langbein did not confirm these 
 statements, but the security against rust of nickeled-iron objects 
 is found to be considerably enhanced by boiling in linseed oil. 
 
 Production of high luster. When dry, the plated objects are 
 highly polished, this being effected by means of polishing bobs 
 of fine felt, cloth or flannel, with the use of polishing composi- 
 tions, Vienna lime, etc., or by burnishing with tools of steel and 
 of agate or blood-stone. 
 
 Nickel deposits are almost without exception polished upon 
 cloth or felt bobs with rouge or Vienna lime. An excellent 
 material for nickel finishing also is the Victor white polish 
 prepared by Zucker & Levett & Loeb Co., New York. It is 
 very efficient and economical and made in two grades — regular 
 and greasy. 
 
 Copper and brass deposits are polished with fine flannel bobs, 
 the polishing powder being applied very sparingly. Deposits 
 of tin are generally only scratch-brushed, it being impossible 
 to impart great luster to this metal by polishing with bobs. 
 After drying, the deposit is polished with whiting. Deposits 
 of gold and silver as well as of platinum are polished by burn- 
 ishing, the steel burnisher being used for the grounding pro- 
 cess, and an agate or bloodstone burnisher for finishing. The 
 operation of burnishing is carried on as follows : Keep the tool 
 continually moistened with soap-suds. Take hold of the tool 
 very near to the end, and lean very hard with it on those parts 
 which are to be burnished, causing it to glide by a backward 
 and forward motion without taking it off the piece. When it is 
 requisite that the hand should pass over a large surface at once 
 without losing its point of support on the work bench, be care- 
 ful in taking hold of the burnisher to place it just underneath 
 the little finger. By these means the work is done more 
 quickly, and the tool is more solidly fixed in the hand. The 
 burnishers are of various shapes to suit the requirements of 
 
PREPARATION OF THE METALLIC OBJECTS. 
 
 219 
 
 different kinds of work, the first rough burnishing being often 
 done by instruments with comparatively sharp edges, while the 
 finishing operations are accomplished with rounded ones. Fig. 
 112 illustrates the most common forms of burnishers of steel 
 and agate. Both must be free from cracks and highly polished. 
 To keep them free from blemishes they are from time to time 
 polished by vigorously rubbing them with fine tin putty, rouge, 
 or calcined alum upon a strip of leather fastened upon a piece 
 
 Fig. 112. 
 
 of wood which is placed in a convenient position upon the 
 work bench. 
 
 Cleansing the polished objects. The objects to which high 
 luster has been given by means of Vienna lime and oil, or rouge 
 have to be freed from adhering polishing dirt. With flat, 
 smooth objects, this is effected by wiping with a flannel rag 
 and Vienna lime, and with those having depressions or matted 
 surfaces, by brushing with a soft brush and soap water, and 
 then drying in sawdust. 
 
220 ELECTRO-DEPOSITION OF METALS. 
 
 Cleansing is very much facilitated by brushing the polished 
 articles upon a small cloth or flannel bob. 
 
 Chemical Treatment. 
 
 While it is the aim of the mechanical treatment to prepare, 
 on the one hand, a pure metallic surface, and on the other, a 
 smooth one, the chemical preparation of the objects serves the 
 purpose of facilitating the mechanical treatment by softening 
 and dissolving the impurities of the surface, and of freeing the 
 mechanically treated objects from adhering oil, grease, dirt, etc., 
 so as to bring them into the state of absolute purity required for 
 the electro-plating process. 
 
 Pickling and dipping. The composition of the pickling 
 liquor varies according to the nature of the metal to be treated. 
 
 Cast-iron and wrought-iron articles are pickled in a mixture 
 of i part by weight of sulphuric acid of 66° Be", and 15 parts 
 by weight of water.* 
 
 To cleanse badly rusted iron articles without attacking the 
 iron itself, it is recommended to pickle them in a concentrated 
 solution of chloride of tin, which, however, should not contain 
 too much free acid, otherwise the iron is attacked. Bucher 
 recommends a pickle composed as follows: Dissolve 3^ ozs. 
 of chloride of tin in I quart of water, and 1 ]4 drachms of tar- 
 taric acid in 1 quart of water. Pour the former solution into 
 the latter, and add 20 cubic centimeters of indigo solution 
 diluted with 2 quarts of water. The object of the addition of 
 indigo is not intelligible. 
 
 An excellent pickle for iron is also obtained by mixing 10 
 quarts of water with 28 ozs. of concentrated sulphuric acid, dis- 
 solving 2 ozs. of zinc in the mixture, and adding 12 ozs. of 
 nitric acid. This mixture makes the iron objects bright, while 
 in dilute sulphuric or hydrochloric acid they become black. 
 
 For many cases pickling may advantageously be effected in 
 the electrolytic way. Suspend the articles in a weak acid bath 
 (hydrochloric or sulphuric acid), connect them with the posi- 
 
 *The acid should be poured into the water, not the water into the acid. 
 
PREPARATION OF THE METALLIC OBJECTS. 22 1 
 
 live pole of a source of current, and suspend opposite to them 
 a sheet of metal (copper or brass), which is connected with 
 the negative pole. 
 
 According to a patent of the Vereinigten Elektrischen Gesell- 
 schaften, Vienna and Buda-Pest, a 20-per cent, alkaline solution 
 of common salt or of Glauber's salt is used for electrolytic 
 pickling, the metal to be pickled serving as anode. By the 
 passage of the current, the electrolyte is broken up into sodium- 
 ions, which are separated on the cathodes, and SO + and 
 chlorine-ions, which are separated on the anodes, the pickling 
 effect being produced by the latter ions. 
 
 This electrolyte may also be used for freeing sheet metal, for 
 instance, sheet-iron, which is to be zincked, from grease, and 
 at the same time pickling it. For this purpose the sheet-iron 
 is suspended to the anode and object-rods of the bath, and a 
 current allowed to enter through the anodes, the sheets serving 
 as cathodes, being thereby freed from grease by the secondarily 
 formed caustic soda. When this has been done, the direction 
 of the current is reversed, the former cathodes becoming now 
 the anodes, and the former anodes, the cathodes. The first 
 having been previously freed from grease are now pickled by the 
 separated anions, while the latter are freed from grease. When 
 pickling is finished, the sheets which have served last as anodes, 
 are taken from the bath and replaced by fresh sheets, and the 
 -direction of the current having been changed, the operation is 
 repeated, a continuous process of freeing from grease and 
 pickling being thus possible. With about 90 amperes and 4 
 volts per square meter, pickling, according to the " Metallar- 
 beiter," requires about half an hour. 
 
 To render possible the removal in the electrolytic way of the 
 layer of hard solder remaining after soldering bicycle frames 
 and thus to allow of perfect enameling, the following method 
 is, according to Burgess,* generally adopted in this country. 
 The parts to be soldered together were simply dipped in hard 
 
 * Electro-chemical Industry, 1904, No. 1. 
 
222 ELECTRO-DEPOSITION OF METALS. 
 
 solder whereby a thin layer of hard solder remained upon the 
 parts thus treated. To remove this by filing proved expensive, 
 and to dissolve by cyanides and solutions of double chromates 
 required much time, and was imperfect. With the assistance of 
 the electric current and the use of a suitable electrolyte the hard 
 solder is completely and rapidly removed without attacking the 
 steel. A suitable electrolyte for the purpose is a 5-per cent, 
 sodium nitrate solution. In consequence of electrolysis some 
 sodium nitrate is formed, and this makes the iron or steel pas- 
 sive, i. c, deprives it of the power to be attacked by the elec- 
 trolyte, while the hard solder is completely dissolved. It must, 
 however, be borne in mind that after several days' electrolysis 
 the steel does no longer remain passive, but is perceptibly 
 attacked by the electrolytic pickle, this being due to the fact 
 that the electrolyte becomes alkaline and then contains free 
 ammonia. The latter must therefore be every day neutralized 
 by the addition of dilute sulphuric acid. The sodium nitrate 
 used for the preparation of the electrolyte should not contain 
 much chloride, as otherwise the iron is attacked. 
 
 The correct progress of the operation is recognized by the 
 rapid solution of the hard solder, a brown layer remaining 
 behind, which can readily be rubbed off. If, however, a thick, 
 greenish, firmly adhering slime forms on the anodes, the elec- 
 trolyte has become alkaline, and when a brownish foam and 
 precipitate appear upon the surface of the electrolyte, the 
 alkalinity has become so great that the steel is also attacked. 
 The hard solder electrolytically dissolved from the steel frame 
 is precipitated as copper and zinc hydroxide by the caustic 
 soda secondarily formed on the cathode. This precipitate has 
 from time to time to be removed from the bath. The most 
 suitable current-density is 0.8 to 1.2 amperes with 3 to 5 volts. 
 
 The duration of pickling depends on the more or less thick 
 layer of scale, etc., which is to be removed or softened. The 
 process may be considerably assisted and the time shortened by 
 frequent scouring with sand or pumice. The pickled articles 
 are rinsed in cold water, then immersed in hot water, and dried 
 
PREPARATION OF THE METALLIC OBJECTS. 223 
 
 in sawdust. In order to neutralize the acid remaining in the 
 pores, it is advisable to make the rinsing water alkaline by the 
 addition of caustic potash or soda, etc. 
 
 Zinc objects are only pickled when they show a thick layer 
 of oxide, in which case pickling is also effected in dilute sul- 
 phuric or hydrochloric acid, and brushing with fine pumice. 
 A very useful pickle for zinc consists of sulphuric acid IOO parts 
 by weight, nitric acid 100, and common salt I. The zinc ob- 
 jects are immersed in the mixture for one second, and then 
 quickly rinsed off in water which should be frequently changed. 
 
 Copper, and its alloys brass, bronze, tombac and German silver \ 
 are cleansed and brightened by dipping in a mixture of nitric 
 acid, sulphuric acid, and lampblack, a suitable pickle consisting 
 of sulphuric acid of 66° Be., 50. parts by weight, nitric acid of 
 36 Be., 100, common salt 1, and lampblack 1. In order to 
 remove the brown coating, due to cuprous oxide, the objects 
 are first pickled in dilute sulphuric acid, and then dipped for a 
 few seconds, with constant agitation, in the above-mentioned 
 pickle until they show a bright appearance. They are then 
 immediately rinsed in water to check any further action of the 
 pickle. 
 
 If objects of copper or its alloys are not to be subjected, after 
 pickling to further mechanical treatment, or are to be at once 
 placed in the electro-plating bath, it is best to execute the pick- 
 ling process in two operations by treating them in a preliminary 
 pickle and brightening them in the bright-dipping bath. The 
 preliminary pickle consists of nitric acid of 36 Be., 200 parts 
 by weight, common salt 1, lampblack 2. In this preliminary 
 pickle the articles are allowed to remain until all impurities are 
 removed, when they are rinsed in a large volume of water, 
 dipped in boiling water, so that they quickly dry, and plunged 
 into the bright-dipping bath, which consists of nitric acid of 40 
 Be., 75 parts by weight, sulphuric acid of 66° Be., 100, and 
 common salt 1. It is not advisable to bring the objects which 
 have passed through the preliminary pickle and rinsing water 
 directly, while still moist, into the bright-dipping bath, since 
 
224 ELECTRO-DEPOSITION OF METALS. 
 
 for the production of a beautiful, pure luster the introduction of 
 water into the bright-dipping bath must be absolutely avoided. 
 
 Hence the objects treated in the preliminary pickle should 
 first be dried by heating in hot water, shaking the latter off. 
 
 Potassium cyanide, dissolved in ten times its weight of water, 
 is often used instead of the acid pickle for brass, especially when 
 it is essential that the original polish upon the objects should 
 not be destroyed, as in the preparation of articles for nickel- 
 plating. The objects should remain in this liquid longer than 
 in the acid pickle, because the metallic oxides are far less 
 soluble in this than in the latter. In all cases the final clean- 
 ing in water must be observed. 
 
 All acid pickles used for different kinds of work should be 
 kept distinct from each other, so that one metal may not be 
 dipped into a solution containing a more electro-negative metal, 
 which would deposit upon it by chemical exchange. 
 
 The pickled objects must not be unnecessarily exposed to the 
 air, and should be transferred as quickly as possible from the 
 pickle to the wash-waters, and then to the electro-plating bath, 
 or, if this is not feasible, kept under pure water. Pickled ob- 
 jects which are not to be plated are carefully washed in water, 
 which should be frequently changed, then rinsed, drawn 
 through a solution of tartar, and dried by dipping in hot water 
 and rubbing with sawdust. 
 
 Places soldered with soft solder, as well as parts of iron, be- 
 come black by pickling, and have to be brightened by scour- 
 ing with pumice, or by scratch-brushing. 
 
 Matt-dipping. Objects of brass or other alloys of copper 
 are frequently to be given a dead surface so that after plating 
 they show a beautiful matt luster. Very fine effects may by 
 this means be obtained, especially in the bronze-ware industry. 
 Matting may be effected in various ways. Every bright dip 
 acts as a matt dip if the objects are exposed to its effect for a 
 longer time and at a higher temperature. Matting is, however, 
 more effective by adding zinc sulphate to the dip, the matting 
 being the more pronounced, the more zinc sulphate has been 
 added. 
 
PREPARATION OF THE METALLIC OBJECTS. 225 
 
 A good matt dip is prepared by pouring a solution of 0.35 
 oz. of zinc sulphate in 3^ ozs. of water in a cold mixture of 
 6yi lbs. of nitric acid of 36 Be., 4.4 lbs. of sulphuric acid of 
 66° Be., and ^ oz. of common salt. According to the shade 
 of matt desired, the objects are allowed to remain in the dip 
 for 2 to 10 minutes. The objects, which on coming from the 
 matt-dip show a faded, earthy appearance, are rapidly drawn 
 through a clean bright dip, whereby they acquire the matt 
 luster, and are then quickly rinsed in a large volume of water. 
 
 For the production of a matt-grained surface by pickling, 
 the following mixture may be recommended : Saturated solu- 
 tion of potassium dichromate 1 part by volume, and concen- 
 trated hydrochloric acid 2 parts by volume. In this mixture 
 the brass articles are allowed to remain several hours. They 
 are then rapidly drawn through the bright-dipping bath and 
 rinsed in a larger volume of water frequently renewed. 
 
 A delicate matted surface may be produced by electrolytic 
 pickling or etching. The process is the same as described 
 above under iron. 
 
 Other methods of matting will be given under " Gilding." 
 
 Generally speaking, it may be said that less depends on the 
 composition of the pickle than on quick and skilful manipula- 
 tion ; and as good results have always been obtained with the 
 above-mentioned mixture, there is no reason for repeating the 
 innumerable receipts given for pickles. The main points are to 
 have the acid mixture as free from water as possible, further to 
 develop hyponitric acid which is effected by the reduction of 
 nitric acid in consequence of the addition of organic substances 
 (lampblack, sawdust, etc.), and of chlorine, which is formed by 
 the action of the sulphuric acid upon the common salt. The 
 volume of the dipping bath should not be too small, since in 
 pickling the acid mixture becomes heated and the increased 
 temperature shows a very rapid, frequently not controllable, 
 action, so that a corrosion of small articles may readily take 
 place. It is therefore necessary to allow the acid mixture, 
 after its preparation, to thoroughly cool off. Pour the sulphuric 
 15 
 
226 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 acid into the nitric acid {never the reverse!), and allow the 
 mixture, which thereby becomes strongly heated, to cool off to 
 at least the ordinary temperature. 
 
 In order to be sure of the uniform action of the pickle upon 
 all parts, it is, in all cases, advisable previous to pickling to free 
 the articles from grease by one of the methods given later on. 
 
 In pickling abundant vapors are evolved which have an in- 
 jurious effect upon the health of the workmen, and corrode 
 metallic articles exposed to them. The operation should, 
 
 Fig. 113. 
 
 therefore, be conducted in the open air, or under a well- 
 drawing vapor-flue. 
 
 In large establishments it may happen that the quantity of 
 escaping acid vapors is so large as to become a nuisance to the 
 neighborhood, which the propietors may be ordered by the 
 authorities to abate. The evil is best remedied by a small 
 absorbing plant, as follows : 
 
 Connect the highest point of the vapor-flue D (Fig. 113) by 
 a wide clay pipe R with a brick reservoir, A, laid in cement, so 
 that R enters A a few centimeters above the level of the fluid, 
 
PREPARATION OF THE METALLIC OBJECTS. 227 
 
 kept constantly at the same height by the discharge pipe b. 
 Above, the reservoir is closed by an arch through which the 
 water conduit W is introduced. Below the sieve S, which is 
 made of wood and coated with lacquer, a wide clay pipe R 
 leads to the chimney of the steam boiler; or the suction pipe of 
 an injector is introduced in this place, into which the air from 
 the vapor-flue is sucked through the reservoir and allowed to- 
 escape into the open air or into a chimney. Through the man- 
 hole M, the sieve-bottom 5 of the reservoir is filled with large 
 pieces of chalk or limestone. The manner of operating is now 
 as follows : A thin jet of water falls upon S, where it is dis- 
 tributed and runs over the layer of chalk. The air of the pick- 
 ling room saturated with acid vapor moves upward in conse- 
 quence of the draught of the chimney of the steam boiler, the 
 injector, or the ventilator, and yields its content of acid to the 
 layer of chalk, while the neutral solution of calcium nitrate and 
 calcium chloride, which is thus formed, runs off through b. 
 
 The absorption of the acid vapors may, of course, be effected 
 by apparatus of different construction, but the one above de- 
 scribed may be recommended as being simple, cheap, and 
 effective. 
 
 The considerable consumption of acid for pickling purposes 
 in large establishments makes it desirable to regain the acid 
 and metal contained in the exhausted dipping baths. The 
 following process has proved very successful for this purpose: 
 Mix the old dipping baths with ^ their volume of concentrated 
 sulphuric acid, and bring the mixture into a nitric acid distill- 
 ing apparatus. Distil the nitric acid off at a moderate temper- 
 ature, condense it in cooled clay coils, and collect it in glass 
 balloons. To the residue in the still ,add water, precipitate 
 from the blue solution, which contains sulphate of copper and 
 zinc, the copper with zinc waste, and add zinc until evolution 
 of hydrogen no longer takes place. Filter off the precipitated 
 copper through a linen bag, wash, and dry. The fluid running 
 off, which contains zinc sulphate, is evaporated to crystalliza- 
 tion and yields quite pure zinc sulphate, which ma)' be sold to 
 dye-works, or for the manufacture of zinc-white. 
 
22 S ELECTRO-DEPOSITION OF METALS. 
 
 According to local conditions, for instance, if the zinc sul- 
 phate cannot be profitably sold in the neighborhood, or zinc 
 waste cannot be obtained, it may be more advantageous to omit 
 the regaining of zinc from the dipping baths. In this case the 
 fluid which is obtained by mixing the contents of the still with 
 water is compounded with milk of lime until it shows a slightly 
 acid reaction. The gypsum formed is allowed to settle, and 
 after bringing the supernatant clear fluid into another reservoir, 
 the copper is precipitated by the introduction of old iron. The 
 first rinsing waters in which the pickled objects are washed are 
 treated in the same manner. The precipitated copper is 
 washed and dried. 
 
 Removal of grease and cleansing. These two operations 
 must be executed with most painstaking exactness because on 
 them chiefly depends the success of the electro-plating process. 
 Their object is to remove every trace of impurity, be it due to 
 the touching with the hands or to the manipulation in grind- 
 ing and polishing, and to get rid of the layer of oxide which is 
 formed in removing the grease with lyes and other agents. 
 
 According to the preparatory treatment of the articles, the 
 removal of grease is a more or less complicated operation. 
 Large quantities of oily or greasy matter should be removed 
 by washing with benzine or petroleum, it being advisable to 
 execute this operation immediately after grinding and polish- 
 ing, so that the oil used in these operations has no chance of 
 hardening, as is frequently the case with articles preparatively 
 polished with Vienna lime and stearine oil. Instead of clean- 
 ing with benzine or petroleum, the articles, as far as their 
 nature allows, may be boiled in a hot lye consisting of I part of 
 caustic potash or soda in 10 of water, until all the grease is 
 saponified, when the dirt, consisting of grinding powder, can be 
 readily removed- by brushing. In place of solution of caustic 
 alkalies, hot solution of soda or potash may be used, but its 
 action is much slower and offers no advantages. Objects of 
 tin, lead and Britannia must be left in contact with the lye for 
 a short time only, as otherwise they are attacked by it. 
 
PREPARATION OF THE METALLIC OBJECTS. 229 
 
 The articles thus freed from the larger portion of grease are 
 first rinsed in water, and then, for the removal of the last traces 
 of grease, are brushed with a bristle brush and a mixture of 
 water, quicklime and whiting until, when rinsed in water, all 
 portions appear equally moistened and no dry spots are visible. 
 
 The lime mixture or paste is prepared by slaking freshly- 
 burnt lime, free from sand, with water to an impalpable pow- 
 der, mixing I part of this with 1 part of fine whiting, and adding 
 water, stirring constantly, until a paste of the consistency of 
 syrup is formed. 
 
 The shape of many objects presents certain difficulties in the 
 removal of grease, as the deeper portions cannot be reached 
 with the brush, as, for instance, in skates, which often are to 
 be nickeled in a finished state. In this case the objects are 
 drawn in succession through three different benzine vessels. In 
 the first benzine most of the grease is dissolved, the rest in 
 the second, while the third serves for rinsing off. When the 
 benzine in the first vessel contains too much grease, it is emp- 
 tied and filled with fresh benzine, and then serves as the third 
 vessel, while that which was formerly the second becomes the 
 first, and the third the second. After rinsing in the third ben- 
 zine vessel, the objects are plunged in hot water, then for a few 
 seconds dipped in thin milk of lime, and finally thoroughly 
 rinsed in water. It is recommended not to omit the treatment 
 with milk of lime of objects freed from grease with benzine. 
 
 Electro-chemical cleaning. It has been found that alkaline 
 substances, such as sodium carbonate, potassium carbonate, 
 potassium hydroxide and sodium hydroxide in solution, in 
 varying degrees of concentration and with small proportions of 
 potassium cyanide added, will with a sufficiently strong electric 
 current of from 4 to 8 volts, and at a temperature nearly boil- 
 ing, develop sufficient hydrogen to remove entirely all organic 
 substances from the surface of the metal, thereby leaving it 
 chemically clean. 
 
 This method has brought into the market several new com- 
 binations which are sold under the name of electro chemical 
 cleaning salts, and have given very satisfactory results. 
 
230 ELECTRO-DEPOSITION OF METALS. 
 
 In a paper read at the convention of the American Brass 
 Founders' Association, at Toronto, Canada, 1908, Charles H. 
 Proctor, in speaking of electro-chemical cleaning baths and 
 their application, says:* 
 
 "The action of an electro-cleanser is similar to the action of 
 an electro-plating bath. The only difference as far as the de- 
 velopment of gases is concerned, is that no metal being in solu- 
 tion and the anode being insoluble, no metal is deposited. But 
 with a strong current a copious evolution of oxyhydrogen gas 
 is developed upon the articles, which attacks the organic mat- 
 ter upon the surface, practically lifting it off and by rapid evo- 
 lution of the gases carries it to the surface. The small quan- 
 tity of potassium cyanide contained in solution absorbs the 
 slight oxidation that might be upon the surface, and by the 
 combined action produces a surface clean enough, after wash- 
 ing in clear water, for any deposits. 
 
 " The arrangement of an electro-cleaning bath is very simple. 
 Prepare a wrought-iron tank of proportions best adapted to the 
 amount of work to be cleansed. This should be heated with 
 steam coils of iron. Across the top of the tank an insulated 
 frame should be constructed. Upon this frame place three 
 conducting poles, as on the regular plating bath. To the two 
 outside poles the positive current should be carried direct. 
 This can best be accomplished with at least J^-inch copper- 
 wire flexible cables. To the center pole the negative current 
 is connected with cables of the same dimensions; no rheostats 
 are necessary. The stronger the current the greater the evolu- 
 tion of gases and the quicker the cleansing operation is accom- 
 plished. 
 
 " Although direct contact can be made with the positive cur- 
 rent to the tank itself, in practice better results have been ob- 
 tained with anodes of sheet-iron not more than 6 inches wide 
 and of a length in proportion to the depth of the tank. 
 
 " The electro-cleaning solution should consist (for ordinary 
 
 *The Metal Industry, June, 1908. 
 
PREPARATION OF THE METALLIC OBJECTS. 23 1 
 
 purposes) of 3 to 4 ozs. caustic potash to each gallon of water, 
 and to every 100 gallons of solution 8 ozs. cyanide of potas- 
 sium. This can be varied according to conditions. It is ad- 
 visable to add at least ^ lb. cyanide each week. Where the 
 articles, such as iron or steel, contain much oil or grease upon 
 the surface, the density of the solution can be increased. For 
 articles of brass, copper or bronze that have been polished, 
 use a solution of carbonate of soda in the proportion of 2 ozs. 
 soda and y 2 oz. caustic potash to each gallon of water, with 
 the addition of 4 ozs. of cyanide to every 100 gallons of solu- 
 tion. If much organic matter is upon the surface of the articles 
 to be cleansed, it is advisable where an air pressure can be 
 obtained from an ordinary blower, to arrange a pipe so that 
 the current of air can be deflected upon the surface of the solu- 
 tion, thus keeping the center of the solution clear of the in- 
 soluble substances that arise to the surface. When the 
 cleanser is at rest, as much of this matter should be removed 
 as possible. 
 
 " It should be the aim of the operator to use the same 
 methods of avoiding all unnecessary contamination as he would 
 in electrodepositing baths. It is obvious even to those who 
 have not practiced this method of cleansing metallic articles 
 that large quantities of work can be treated very rapidly, and 
 this is the case especially where frames or racks are used in the 
 plating operations. On occount of the rapidity of operation 
 and the efficiency of the bath, this method of cleansing should 
 be a part of the labor-saving devices used in all great com- 
 mercial establishments engaged in the electroplating of metals." 
 
 To avoid subsequent touching with the hands the objects, 
 before freeing them from grease, must of course be tied to the 
 metallic wires (of soft copper) by which they are suspended 
 in the electro-plating bath. In removing the grease by the 
 wet method a layer of oxide scarcely perceptible to the eye is 
 frequently formed upon the metals. This layer of oxide has to 
 be removed, the liquid used for the purpose varying, of course, 
 with the nature of the layer. 
 
232 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Objects of iron and steel, as well as of zinc, are momentarily- 
 plunged in a mixture of sulphuric acid I part by weight and 
 water 20 parts, and quickly rinsed off in clean water. Highly 
 polished objects of iron and steel, after being treated with this 
 mixture, are best again rapidly brushed with lime paste, and, 
 after rinsing off quickly, immediately brought into the electro- 
 plating bath. 
 
 Copper, brass, bronze, German silver, and tombac are best 
 cleaned with a dilute solution of potassium cyanide, I part of 
 60 per cent, potassium cyanide in 15 to 20 of water. The 
 objects are then quickly rinsed off and placed in the electro- 
 plating bath. 
 
 Lead and Britannia may be treated with water slightly 
 acidulated with nitric acid. 
 
 The difficult and dangerous operation of tilting heavy carboys 
 
 Fig. 114. 
 
 Fig. 115. 
 
 
 containing acid is overcome by the use of the Hanson & Van 
 Winkle acid pump shown in Figs. 114 and 115. In using this 
 pump it is not necessary for two men to handle a carboy. A 
 workman carries the acid pitcher or receptacle to the carboy ; 
 one end of the pump tube is placed in the acid, the rubber- 
 cork making" an air-tight joint in the neck of the carboy, and 
 
PREPARATION OF THE METALLIC OBJECTS, 233: 
 
 the other end of the pump is carried to the .pitcher. On. 
 pumping a steady flow of acid is obtained. 
 
 Electro-plating Solutions (Electrolytes, Baths). 
 
 Next to the proper mechanical and chemical preparations of 
 the. objects, the success of the process of electro-deposition de- 
 pends on the suitable composition of the electro-plating solu- 
 tions, electrolytes, or baths, and the proper current-strength 
 which is conducted into the baths for the precipitation of the 
 metals. In regard to the latter the most essential conditions 
 have already been discussed in Chap. IV., " Electro-plating 
 Plants in General," and will be further referred to in speaking 
 of the several electro-plating processes. Hence, the general 
 rules which have to be observed in the preparation of the baths 
 will first be considered. 
 
 Solvents. — With the exception of the baths prepared with 
 glycerin according to the patent of Marino, water is the solvent 
 used in the preparation of all baths, and its constitution is by 
 no means of such slight importance as is frequently supposed. 
 
 Spring and well water often contain considerable quantities 
 of lime, magnesia, common salt, iron, etc., the presence of which 
 may cause various kinds of separations in the baths. On the 
 other hand, river water is frequently impregnated to such an 
 extent with organic substances that its employment without 
 previous purification cannot be recommended. No doubt, dis- 
 tilled water, or in want of that rain water, is the most suitable 
 for the preparation of baths. However, rain water collected 
 from metal roofs should not be used, nor that running off from 
 other roofs, it being contaminated with dust. When used, it 
 should be caught in vessels of glass, earthenware, or wood, free 
 from tannin and filtered. Where river or well water has to be 
 employed, thorough boiling and filtering before use are abso- 
 lutely necessary in order to separate the carbonates of the alka- 
 line earths held in solution. By boiling, a possible content of 
 sulphuretted hydrogen is also driven off. 
 
 Purity of chemicals. Another important factor is the purity 
 
234 ELECTRO-DEPOSITION OF METALS. 
 
 of the chemicals used for the baths, the premature failure of the 
 latter being in most cases caused by the unsuitable nature of 
 the chemicals, which also frequently give rise to abnormal 
 phenomena inexplicable to the operator. Chloride of zinc, for 
 instance, may serve as an example. It is found in commerce 
 in very varying qualities, it being prepared for dyeing purposes 
 with about 70 per cent, actual content of chloride of zinc, for 
 pharmaceutical purposes with about 90 per cent., and for 
 electro-plating purposes with 98 or 99 per cent. Now it will 
 readily be seen that if an operator who is preparing a brass 
 bath according to a formula which calls for pure chloride of 
 zinc uses a preparation intended for dyeing purposes, there will 
 be a deficiency of metallic zinc in the bath, and the content of 
 copper in the bath being too large in proportion to the zinc 
 present, will cause reddish shades in the deposits. 
 
 Likewise, in case the operator uses potassium cyanide of low 
 content, when the formula calls for a pure article with 98 per 
 cent., he will not be able to effect the solution of copper or 
 zinc salts with the quantity prescribed. Furthermore, potas- 
 sium cyanide, in the preparation of which prussiate of potash 
 containing potassium sulphate is used, will cause, by reason of 
 the formation of potassium sulpho-cyanide, various disturbing 
 influences (formation of bubbles in the deposit), the explana- 
 tion of which is difficult to the operator, who, trusting to the 
 purity of the chemicals, seeks elsewhere for the causes of the 
 abnormal phenomena. 
 
 Sodium suphite may in similar manner cause great annoy- 
 ance if the suitable preparation is not used. There is a crystal- 
 lized neutral salt which is employed for many gold baths, and 
 also the bisulphate of soda in the form of powder which serves 
 for the preparation of copper and brass baths. If the latter 
 should be used in the preparation of gold baths, the gold 
 would be reduced from the solution of its salts and precipitated 
 as a brown powder. 
 
 Or, if in preparing nickel baths, a salt containing copper is 
 used, the nickeling will never be of a pure white color, but 
 
PREPARATION OF THE METALLIC OBJECTS. 235 
 
 show shades having not even a distant resemblance fo the color 
 of nickel. 
 
 The above-mentioned examples will suffice to show how 
 careful the operator must be in the selection of the sources 
 from which he obtains his supplies. It may be here mentioned 
 that all the directions given in the following pages refer to 
 chemically pure products ; where products of a lower standard 
 may be used their strength is especially given. 
 
 Concentration of baths. — For the concentration of the various 
 baths no general rules can be laid down ; neither can the de- 
 termination of the density of the baths by the hydrometer be 
 relied on. If electro-plating solutions consisted of nothing but 
 the pure metallic salts, the specific gravity, which is indicated 
 by the hydrometer-degrees, might serve for an estimation of 
 their value. But such an estimation is often apt to prove de- 
 ceptive, since, to decrease the resistance, the baths also require 
 conducting salts, and by the addition of a larger quantity of 
 them, the specific gravity of a bath may be increased to any 
 extent without the content of the more valuable metal being 
 greater than in a bath showing fewer hydrometer-degrees. 
 
 When the operator is acquainted with the composition of the 
 baths, and knows how many degrees Be. a fresh bath should 
 show when correctly prepared, he can draw a conclusion as to 
 the condition of the bath by changes in the specific gravity. 
 If, for instance, a nickel bath when freshly prepared shows the 
 standard specific gravity — yo° Be. — for nickel baths, and it 
 shows later on 90 Be., the greater specific gravity is due either 
 to evaporation of water or to excessive refreshing or strengthen- 
 ing of the bath. Such a bath generally yields dark or spotted 
 nickeling, the deposit is formed in a sluggish manner, and 
 readily scales off with a stronger current. The operator in 
 this case may recognize from the hydrometer that the cause of 
 these phenomena is not due to a contamination of the bath, but 
 to its over-concentration. Baths, when too concentrated, 
 readily deposit salts in crystals on the anodes and the sides of 
 the tanks, which should by no means take place, and there is 
 
236 ELECTRO-DEPOSITION OF METALS. 
 
 even danger of microscopic crystals depositing upon the 
 articles and causing holes in the deposit. 
 
 A plating bath should never be poor in metal, as otherwise 
 it soon becomes exhausted, and besides the deposits form more 
 slowly and with less density than in baths with a correct con- 
 tent of metal. 
 
 Hence in summer when the temperature of the bath, is nat- 
 urally higher, they can be made more concentrated than in 
 winter. If crystals are separated, even when a bath shows a 
 temperature of 5 8° F., they should be removed and dissolved 
 in hot water. The solution is returned to the bath and water 
 is added to the latter until the formation of crystals ceases. 
 
 Agitation of the baths. In order that all the strata of the 
 bath may show an equal content of metal, it is advisable in the 
 evening, after the day's work is done, to thoroughly stir up the 
 solution with a wooden crutch. For practical reasons the baths 
 are generally made one-quarter to one-third deeper than corre- 
 sponds to the lengths of the objects to be plated. In conse- 
 quence of this, the strata of fluid between the anodes and the 
 objects become poorer in metal than those on the bottom, and 
 the object of stirring up is to restore the same concentration to 
 all portions of the bath. 
 
 While stirring up the bath, it is also advisable to see whether 
 any metallic articles have become detached from the slings and, 
 dropped to the bottom of the vat. Such articles must be taken 
 out, since they are dissolved by some baths, the latter being 
 thereby spoiled. This examination must be especially thor- 
 ough with nickel baths. 
 
 The strata of fluid which come in contact with the anodes 
 become, by the absorption of metal, specifically heavier than 
 the other strata and sink to the bottom of the tank, while, on 
 the other hand, the strata of fluid which yield metal to the 
 articles become specifically lighter and rise to the top. A 
 partial compensation, of course, takes place by diffusion, but 
 not a complete one, and from this cause arise several annoy- 
 ances. The heavier and more saturated fluid offering greater 
 
PREPARATION OF THE METALLIC OBJECTS. 237 
 
 resistance to the current, the anodes are attacked chiefly on 
 
 the upper portions where the specifically lighter 
 
 layer of fluid is; practically this is proved by the IG " " 
 
 appearance of the anodes, which, at first square, 
 
 after being for some time used assume the shape | 
 
 shown in Fig. 1 16. 
 
 On the other hand, the portions of the cathodes 
 (objects) which come in contact, near the surface, 
 with strata of fluid poor in metal, acquire a deposit 
 of less thickness than the lower portions which dip 
 into the bath where it is richer in metal. Now if 
 the bath also contains free acid, and if there is a considerable 
 difference in the specific gravity of the lower and upper strata 
 of fluid, the electrode, which touches both strata, produces a 
 current, the effect of which is that metal dissolves from the 
 upper portions and deposits upon the lower. This explains 
 the phenomenon that a deposit on the upper portions of the 
 objects may be redissolved, even when a current, which, how- 
 ever, must be very weak, is conducted into the bath from an 
 external source. 
 
 Many authors, therefore, go so far as to demand that during 
 the electro-plating process the baths should be kept in con- 
 stant agitation by mechanical means. This, however, is 
 scarcely necessary, because a homogeneity of the solution is 
 to a certain extent effected by the agitation of the fluid in 
 suspending and taking out the objects. Hence as long as 
 objects are put in and taken out, an agitation naturally takes 
 place in which all the strata of fluid between the objects and 
 anodes take part, while only the deepest strata, which do not 
 come into contact with the objects and the anodes, remain in a 
 state of stagnation. 
 
 Constant agitation of the plating solution is of advantage in 
 silvering, and in galvanoplastic reproduction in the acid copper 
 bath, in which the articles have to remain four to five, and eight 
 to ten hours. With constant agitation of the bath it is possi- 
 ble to work with a greater electro- motive force, whereby the 
 
238 ELECTRO-DEPOSITION OF METALS. 
 
 deposits are finished in a shorter time; and in silvering, the 
 formation of current-streaks is, to a certain extent, avoided ; and 
 in galvanoplastic reproduction, the formation of so-called 
 blooms. In nickeling, with constant agitation of the bath, 
 heavier deposits can, without doubt, be obtained in a shorter 
 time and without premature deadening of the deposit. 
 
 Henry Sand * draws attention to the fact that, according to 
 all known experience, the greater current densities which are 
 permissible in the electrolysis of given metal salt solutions, de- 
 pend solely on the rapidity of the renewal of the fluid on the 
 electrode. In his opinion it is very probable that, in the depo- 
 sition of metals, the cathode potential in itself is independent 
 of the current-density, further that the quality of the metal-de- 
 posits is but slightly influenced by the current-density, and 
 that the great variations in the nature of the deposits with 
 different current-densities is almost exclusively due to local 
 changes in concentration. 
 
 These changes in concentration — the impoverishment in 
 metal ions of the electrolyte on the place where it comes in 
 contact with the cathode — is, according to Daneel f caused, on 
 the one hand, by the separation of metal ions on the cathode; 
 further, in complex salt solutions, by the accumulation of ions 
 of the salt which with the metal salt forms the complex com- 
 bination, and by the conveyance by the current of the metal in 
 those complex salt solutions which form complex anions con- 
 taining the metal to be separated, and migrate away from the 
 cathode to the anode. 
 
 The impoverishment in metal ions would proceed still more 
 rapidly but for the counter-action of certain forces. First of 
 all, diffusion has to be taken into consideration : it causes the 
 entrance of strata of fluid richer in metal into those poorer in 
 metal, and it is greatest on the sides where impoverishment has 
 progressed furthest. Further, fresh ions are constantly sup- 
 
 * Zeitschrift fiir Elecktrochemie, 1904, S. 452. 
 fZeitschrift fiir Elektrochemie, IX, 763. 
 
PREPARATION OF THE METALLIC OBJECTS. 239 
 
 plied by dissociation, and by solutions of the simple as well as 
 the complex salts which contain the metal in the kathion, 
 impoverishment is counteracted by the conveyance of metal by 
 the current. 
 
 When working with low current-densities in an electrolyte, 
 even when the latter is at rest, the slighter concentration of 
 ions appearing on the cathode is to a certain extent obviated 
 by diffusion of fluid richer in metal ; hence under such condi- 
 tions good deposits are obtained without agitation of the elec- 
 trolyte. 
 
 The case, however, is different when in the same electrolyte 
 depositions are made with high current- densities, serviceable 
 deposits being only obtained so long as sufficient concentration 
 of metal ions is present on the points of contact of the electro- 
 lyte with the cathode. However, as diffusion is no longer 
 sufficiently great to replace the content of metal separated, 
 hydrogen ions are next separated, together with the metal ions 
 supplied by diffusion, which causes, almost without exception, 
 the formation of spongy deposits. Hence in rapid electrolysis 
 for which high current-densities are employed, the local ex- 
 haustion of the layers on the cathode has to be prevented by 
 vigorous agitation of the electrolyte. 
 
 Constant agitation effects also the more rapid removal of the 
 hydrogen-bubbles which form on the articles, but the same end 
 is attained without complicated contrivances by the operator 
 accustoming himself to strike the object-rod a slight blow with 
 the finger each time he suspends an object* 
 
 Temperature of the baths. The temperature required for the 
 electro-plating solutions has already been referred to on p. 123, 
 where also the means have been given for bringing baths which 
 have cooled down too much to the proper degree of temper- 
 ature. Baths which are to be used cold should under no cir- 
 cumstances show a temperature below 59 F., it being best to 
 maintain them at between 64. 5 and 68° F. 
 
 The warmer a bath is, the less its specific resistance and the 
 greater its conducting power, because the salts dissolved in the 
 
240 ELECTRO-DEPOSITION OF METALS. 
 
 bath are more dissociated than when the electrolyte is cold. 
 In warm solutions the hydrogen-bubbles separated by the 
 cathodes escape much more rapidly than in cold electrolytes, 
 and consequently there is less chance of hydrogen occlusion 
 which, according to general opinion, is the principal cause of 
 the deposit peeling off. 
 
 Boiling the baths. Boiling is required in the preparation of 
 many baths, if, after cooling, they are to yield good and certain 
 results. The kettles and boiling-pans used for the purpose are 
 of various shapes, hemispherical or with flat bottom, and are 
 made of different materials, those of enameled iron, or, for 
 small baths, of porcelain or earthenware, being best. The 
 enamel of the iron kettles must be of a composition which is 
 not attacked by the bath. Notwithstanding their enamel these 
 vessels become gradually impregnated with the solutions they 
 have held, and it is risky to employ them for different kinds of 
 baths. Thus, an enameled kettle which has been used for sil- 
 vering will not be suitable, even after the most thorough wash- 
 ing, for a gold bath, as the gilding will certainly be white or 
 green, according to the quantity of silver retained by the ves- 
 sel. The use of metal vessels should be avoided. Copper and 
 brass baths may, however, be boiled in strong copper kettles, 
 though they are somewhat attacked. A copper kettle, after 
 being freed from grease and scoured bright, may be provided 
 with a thick deposit of nickel, by filling it with a nickel bath, 
 connecting it with the negative pole of a strong battery or 
 dynamo machine, and suspending in it a number of nickel an- 
 odes connected with the positive pole. Such nickeled kettle 
 may be used for boiling nickel baths, but enameled kettles or 
 large dishes of nickel-sheet, or vessels lined with lead, deserve 
 the preference. Generally speaking, nickel baths do not require 
 actual boiling, but the nickel salts and certain conducting salts 
 which constitute the baths, dissolve with difficulty in cold water, 
 and hence solution is effected in hot water. 
 
 When, for the preparation of nickel baths, nickel salts soluble 
 with difficulty have to be dissolved with the assistance of heat, 
 
PREPARATION OF THE METALLIC OBJECTS. 24 1 
 
 and no suitable vessel is available for the purpose, solution may 
 be effected as follows : Bring pure water in a bright copper 
 kettle to the boiling-point. Pour the hot water into a clean 
 wooden bucket holding from 8 to 10 quarts, and add the quan- 
 tity of nickel salt corresponding to the quantity of water. Stir 
 with a wooden crutch until solution is complete. Repeat the 
 operation until all the salt required is dissolved. 
 
 For very large baths this process would, however, require 
 too much time, and it is, therefore, advisable to use a large 
 round or oval wooden tank, or a tank lined with pure sheet 
 lead. The contents of the tank are heated by means of a lead 
 coil through which steam is introduced. 
 
 Working the baths with the current. In case boiling of large 
 quantities of fluid is not feasible, the same object may be at- 
 tained by working the bath for some time with the electric cur- 
 rent. The anode rods are hung full of anodes and, a few plates 
 of the same kind of metal having been secured to the object- 
 rods, a current of medium strength is conducted into the bath 
 until an object, from time to time suspended in the bath, is 
 properly covered with a deposit. This process is frequently 
 used with great success for large brass baths. 
 
 Objections have been made to the process because it is some- 
 times carried too far, the solution becoming thereby demetal- 
 lized(?). However, there is no reason for objecting to a pro- 
 cess because some operators carry it out in a bungling manner, 
 and in our opinion a bath which cannot stand working for sev- 
 eral days with the current without becoming poor in metal, is 
 not of the proper composition. 
 
 Filtering the baths. Should the solutions after their prepara- 
 tion, and, if necessary, boiling, not be perfectly clear, they have 
 to be filtered. For large baths this is best effected by means 
 of felt filter bags, and for smaller baths, especially those of the 
 noble metals, with filtering paper. This removal of the parti- 
 cles held in suspension is necessary to prevent their deposition 
 upon the objects, which might cause small holes in the deposit, 
 as well as roughness and other defects. It is still better to 
 16 
 
242 ELECTRO-DEPOSITION OF METALS. 
 
 allow the baths to clarify by standing quietly, and to draw off 
 the clear solution by means of a siphon. The turbid residue 
 is then filtered. 
 
 Prevention of impurities. To secure lasting qualities to the 
 baths they must be carefully protected from every possible 
 contamination. When not in use for plating they should be 
 covered to keep out dust. The objects before being placed in 
 the baths should be free from adhering scouring material or 
 dipping fluid, which otherwise might, in time, spoil the bath. 
 The cleansing of the anode and object rods by means of sand- 
 paper, or emery-paper, should never be done over the bath, 
 so as to avoid the danger of the latter being contaminated by 
 the oxides of the metal constituting the rods falling into it. 
 When a visible layer of dust has collected upon the bath, it 
 must be removed, as otherwise particles of dust might deposit 
 upon the objects and prevent an intimate union of the deposit 
 with the basis-metal. With large baths the removal of the 
 layer of dust is readily effected by drawing a large piece of 
 filtering or tissue paper over the surface, and repeating the 
 operation with fresh sheets of clean paper until all the dust is 
 removed. Small baths should be filtered. 
 
 The choice of anodes is also an important factor for keeping 
 the baths in good condition, as well as for obtaining good 
 results. The anodes should always consist of the metal which 
 is deposited from the solution ; and the metal used for them 
 must be pure and free from all admixtures. To replace as 
 much as possible the metal withdrawn from the bath by the 
 electro-plating process, the anodes must be soluble; and it is 
 wrong if, for instance, nickel baths are charged with insoluble 
 anodes of carbon ; or for smaller baths, of sheet platinum, pro- 
 vided the chemical composition of the bath does not in part 
 demand insoluble anodes. Insoluble anodes cause a steady 
 and rapid declination in the content of metal, an excessive for- 
 mation of acid in the bath, and, by the detachment of particles 
 of carbon, a contamination of the solution. Further particulars 
 in regard to anodes will be given in discussing the separate 
 baths. 
 
PREPARATION OF THE METALLIC OBJECTS. 243 
 
 Absorption of the deposit. When upon a pure metallic sur- 
 face another metal is electro-deposited, the first portion of the 
 deposit penetrates into the basis-metal, thus forming an alloy. 
 This may be readily proved by repeating Gore's experiments.. 
 If a thick layer of copper be precipitated upon a platinum 
 sheet, and then heated to a dark-red heat, the deposit can be 
 entirely peeled off. By then heating the platinum sheet with 
 nitric acid, and thoroughly washing with water, it appears, after 
 drying, entirely white and pure. By reheating the sheet, the 
 surface becomes again blackened by cupric oxide, and by fre- 
 quently repeating the same operation, a fresh film of cupric 
 oxide will always be obtained. 
 
 This penetration of the deposit into the basis-metal, however, 
 does not merely take place during electro-plating, but also later 
 on ; and it may frequently be observed that, for instance, zinc 
 objects only slightly coppered or brassed, after some time be- 
 come again white. Since this also happens when the deposits 
 are protected by a coat of lacquer against atmospheric influ- 
 ences, the only explanation of the phenomenon can be that the 
 deposit is absorbed by the basis-metal, which is also confirmed 
 by analysis. This fact must be taken into consideration if dur- 
 able deposits are to be produced. 
 
 Effect of the current-de7isity. A greater or smaller current- 
 density used in operating is not without influence upon the 
 electrolytes. The greater the current-density is, the more 
 metal will be deposited on the cathode, while on the anode, 
 the oxidation of the metal and its solution into acid residues 
 cannot take place in the same measure, the result being further 
 decompositions, oxygen gas being liberated. In consequence 
 of this there appear also greater differences in concentration 
 than when depositing with less current-density and, as regards 
 concentration, the electrolyte will remain most constant when 
 working with a smaller current-density. 
 
 For depositions upon strongly profiled objects a medium 
 current-strength will prove most suitable. Daneel * pictures 
 
 * Zeitschrift fur Elektrochemie, IX, 763. 
 
244 ELECTRO-DEPOSITION OF METALS. 
 
 the process as follows: If a deposit is made upon an article 
 with elevations and depressions, the current-lines will crowd 
 together towards the elevated points, i. e., those nearer to the 
 anodes, since the current always chooses the most convenient 
 way. Now owing to the deposit an impoverishment in metal 
 In the electrolyte takes place on the elevated portions, and the 
 consequence is that on these portions the separation-tension is 
 increased. However when the latter is increased the current- 
 lines will turn towards more favorable portions richer in metal 
 ions, i. e., those lying deeper, until an impoverishment in metal 
 ions there also takes place. From this it follows that with a 
 medium current-strength the current lines cannot permanently 
 favor any particular portions of the cathodes, and the deposit 
 must become uniform. Should an unequal impoverishment 
 take place on the electrode it would be overcome by short- 
 closed circuits formed there, which means that they cannot 
 distribute themselves unequally over the surface of the cathode. 
 
 With very small current-densities the process would be dif- 
 ferent. When the current-density is so small that an im- 
 poverishment in metal ions on the entire electrode can be 
 prevented by diffusion, the current lines will permanently 
 crowd together upon the more elevated portions, and the de- 
 posit will grow there, while less metal deposits in the de- 
 pressions. 
 
 In practice it has been found that a great distance of the 
 anodes from the profiled cathodes, thorough agitation of the 
 electrolyte, not too great a conductivity of the latter, and a 
 normal current-density, are the best auxiliaries for obtaining 
 deposits of uniform thickness, and where these do not suffice 
 recourse may be had for depressions to the hand anode (see 
 later on). 
 
 Current-output. In the theoretical part it has already been 
 stated that the separation-products of electrolysis are fre- 
 quently subject to secondary decomposition. Thus, the hydro- 
 gen escaping on the cathodes means a loss of electrolyzing 
 effect of the current, and it is obvious that the quantity of the 
 
PREPARATION OF THE METALLIC OBJECTS. 245 
 
 deposit obtained does thereby not come up to the values which, 
 according to the laws of Faraday, should be obtained. The 
 quantities of deposit produced in practice referred to the theo 
 retically calculated quantities, are called the current-output. 
 
 Reaction of the baths. A distinction is made between acid, 
 alkaline, neutral, and potassium cyanide baths. The reaction 
 of a bath is determined by means of suitable reagent papers. 
 Thus, blue litmus paper, for instance, indicates the acid nature 
 of a bath when by being dipped in it, it acquires a red color. 
 All acids redden blue litmus paper, though many metallic salts 
 of a perfectly neutral character produce the same change in 
 color, and it is therefore necessary to make additional tests. 
 Tropaeolin paper, for instance, which possesses a yellow color, 
 is only changed by mineral acids, the yellow color being con- 
 verted into violet. A bath, which reddens blue litmus paper 
 and colors tropaeolin paper violet, contains without doubt, a 
 free inorganic acid, while a bath which only reddens blue lit- 
 mus paper, but does not change tropaeolin paper does not 
 contain a free inorganic acid, but an organic acid (citric, 
 tartaric acids), and with a content of certain inorganic salts 
 may also be free from organic acid. 
 
 An alkaline reaction of the bath is indicated by red litmus 
 paper acquiring a blue color, while neither blue or red litmus 
 paper is changed when the electrolyte is neutral. 
 
 In a normal state, potassium cyanide baths always show an 
 alkaline reaction ; deviations from this condition will be later 
 on referred to. 
 
 The general qualifications which an electro-plating bath should 
 possess are as follows : 
 
 1. It should possess good conducting power. 
 
 2. It must exert a sufficient dissolving effect upon the anodes. 
 
 3. It must reduce the metal in abundance and in a reguline 
 state. 
 
 4. It must not be chemically decomposed by the metals to 
 be plated, hence not by simple immersion; the adherence of 
 the deposit to the basis-metal being in this case impaired. 
 
 5. It must not be essentially decomposed by air and light. 
 
CHAPTER VI. 
 
 DEPOSITION OF NICKEL AND COBALT, 
 i. Deposition of Nickel. 
 
 ALTHOUGH nickel-plating is of comparatively recent origin, 
 it shall be first described, since chiefly by reason of the devel- 
 opment of the dynamo-electrical machine it has steadily grown 
 in popularity and become an industry of great magnitude and 
 importance. The great popularity which nickel-plating enjoys 
 is due to the excellent properties of the nickel itself — the 
 almost silvery whiteness of the metal, its cheapness as com- 
 pared with silver, and the hardness of the electro-deposited 
 metal, which give the coating great power to resist wear and 
 abrasion ; its capability of taking a high polish ; the fact that 
 it is not blackened by the action of sulphurous vapors which 
 rapidly tarnish silver, and finally the fact that it exhibits but 
 little tendency to oxidize even in the presence of moisture. 
 
 Properties of nickel. — Pure nickel is a lustrous, silvery-white 
 metal with a slight steel-gray tinge. It is hard, malleable and 
 ductile. Its specific gravity varies from 8.3 (cast nickel plates) 
 to 9.3 (wrought or rolled plates). It melts at about the same 
 temperature as iron, but is more fusible when combined with 
 carbon. It is slightly magnetic at ordinary temperatures, but 
 loses this property on heating to 68o° F. 
 
 The metal is soluble in dilute nitric acid, concentrated nitric 
 acid rendering it passive, i. e., insoluble. In hydrochloric and 
 sulphuric acids it dissolves very slowly, especially when in a 
 compact state. 
 
 Certain articles, for instance, hot fats, strongly attack nickel, 
 while vinegar, beer, mustard, tea and other infusions produce 
 stains; hence, the nickeling of culinary utensils or the use of 
 
 ( 246 ) 
 
DEPOSITION OF NICKEL AND COBALT. 247 
 
 nickel-plated sheet-iron for that purpose cannot be recom- 
 mended. 
 
 The chemical equivalent of nickel is 29.3. 
 
 Nickel salts. The first requisite in preparing nickel baths is 
 the use of absolutely pure chemicals, and in choosing the nickel 
 salts to be especially careful that they are free from salts of iron, 
 Copper and other metals. Furthermore, it is not indifferent 
 what kind of nickel salt is used, whether nickel chloride, nickel 
 sulphate, the double sulphate of nickel and ammonium, etc., but 
 the choice of the salt depends chiefly on the nature of the metal 
 which is to be nickeled. There are a large number of general 
 directions for nickel baths, of which nickel chloride, ammonio- 
 nickel chloride, nickel nitrate, etc., form the active constituents, 
 and yet it would be a grave mistake to use these salts for nick- 
 eling iron, because the liberated acid if not immediately and 
 completely fixed by the anodes in dissolving, imparts to the iron 
 objects a great tendency to the formation of rust. Iron objects 
 nickeled in such a bath, to be sure, come out faultless, but in a 
 short time, even if stored in a dry place, portions of the nickel 
 layer will be observed to peel off, and by closely examining 
 them it will be seen that under the deposit a layer of rust has 
 formed which actually tears the nickel off. The use of nickel 
 sulphates or of the salts with organic acids is, therefore, consid- 
 ered best. It might be objected that the liberated sulphuric 
 acid produces in like manner a formation of rust upon the iron 
 objects; but according to long experience and many thorough 
 examinations, such is not the case, the tendency to the forma- 
 tion of rust being only imparted by the use of the chloride and 
 nitrate. 
 
 Of the nickel salts with organic acids, the citrate and tartrate, 
 have been frequently employed. Nickel citrate in watery solu- 
 tion is not particularly well dissociated, requires a greater elec- 
 tro-motive force and is quite indifferent towards variations in 
 the latter, this being the chief reason for its use in nickeling 
 sharp ground instruments. Nickel lactate, according to Jordis's 
 patent,* yields, to be sure, beautiful, lustrous deposits in thin 
 
 *Jordis, Elektrolyse wassriger Metallsalzlosungen, S. 78. 
 
248 ELECTRO-DEPOSITION OF METALS. 
 
 layers, but is not serviceable for heavy nickeling since, as the 
 inventor himself admits, deposits in thicker layers tear. Of 
 materially greater advantage is the use of the combinations of 
 nickel with the ethyl sulphates * and their derivatives. Accord- 
 ing to experiments made in Dr. Langbein's laboratory, the 
 ethyl sulphate solutions of metals are very energetically dissoci- 
 ated and permit the production of very thick deposits without 
 peeling off or tearing, such as cannot be obtained in the cold 
 bath in any other nickel solution ; they are distinguished by 
 great homogeneity and toughness. 
 
 Conducting salts. — To decrease the resistance of the nickel 
 solutions, conducting salts are added to them, which are also 
 partially decomposed by the current. Like the use of nickel 
 chloride in nickeling iron, an addition of ammonium chloride, 
 which is much liked, cannot be recommended, though the 
 subsequent easy deposition of nickel with a comparatively 
 weak current invites its employment. 
 
 For copper and its alloys, zinc, etc., the chlorine combina- 
 tions may be used, but for nickeling iron they must be avoided 
 as the source of future evils. 
 
 The use of sodium acetate, barium oxalate, ammonium 
 nitrate, ammonium-alum, etc., we consider unsuitable, and 
 partially injurious, and are of the opinion that with few excep- 
 tions, which will be referred to later on, potassium, sodium, 
 ammonia or magnesia are best for bases of the conducting salts. 
 
 The effect of the ions separated from the different conduct- 
 ing salts varies very much ; the potassium ion acts different 
 from the sodium ion, and the latter different from the mag- 
 nesium ion, and an idea of this difference in action of the 
 various ions can be formed by preparing, according to formula 
 VIII, one nickel bath with potassium citrate and another with 
 sodium citrate. While the bath prepared with the potassium 
 salt works quite well in the deeper portions on zinc, that pre- 
 pared with the sodium salt is far less effective, and several 
 
 * German patent, No. 134,736. 
 
DEPOSITION OF NICKEL AND COBALT. 249 
 
 other proofs derived from practice could be mentioned. An 
 attempt to explain these facts must at present be abstained 
 from as this suggestion cannot yet be proved by experiment so 
 that no objection to it could be raised. 
 
 Other additions. — Some other additions to the nickeling bath 
 which are claimed to effect a pure silver-white deposit have 
 been recommended by various experts. Thus, the presence 
 of small quantities of organic acid has been proposed ; for 
 instance, boric acid by Weston, benzoic acid by Powell, and 
 citric acid or acetic acid by others. The presence of small 
 quantities of free acid effects without doubt the reduction of a 
 whiter nickel than is the case with a neutral or alkaline solu- 
 tion. Hence a slightly acid reaction of the nickeling bath, due 
 to the presence of citric acid, etc., with the exclusion of the 
 strong acids of the metalloids, can be highly recommended. 
 The quantity of free acid, however, must not be too large, as 
 this would cause the deposit to peel off. 
 
 Boric acid, recommended by Weston as an addition to nickel- 
 ing and all other baths, has a favorable effect upon the pure 
 white reduction of the nickel, especially in nickeling rough 
 castings, i. e., surfaces not ground. Weston claims that boric 
 acid prevents the formation of basic nickel combinations on the 
 objects, and that it makes the deposit of nickel more adherent, 
 softer, and more flexible. Whether with a correct current- 
 strength, basic nickel salts, to which the yellowish tone of the 
 nickeling is said to be due, are separated on the cathode, is not 
 yet proved, and would seem more than doubtful. The action 
 of the boric acid has not yet been scientifically explained, but 
 numerous experiments have shown that the deposition of nickel 
 from nickel solution containing boric acid is neither more ad- 
 herent nor softer and more flexible than that from a solution 
 containing small quantities of a free organic acid. Just the 
 reverse, the deposition is harder and more brittle in the pres- 
 ence of boric acid, and different results may very likely be due 
 to the employment of varying current-densities. 
 
 In view of the fact that in the electrolysis of watery solutions, 
 
250 ELECTRO-DEPOSITION OF METALS. 
 
 water also takes part in the processes enacted on the electrodes, 
 and that the hydrogen appearing on the cathode promotes the 
 formation of spongy, pulverulent and dull deposits, Marino * 
 wants to substitute glycerin for water. Since many metallic 
 salts dissolve only to a slight degree in glycerin, the content of 
 metal in a glycerin bath is very low, and the resistance of the 
 cold bath so great that enormous voltages are needed for the 
 separation of metals, nickel, for instance, requiring more than 
 20 volts, and with an electro-motive force of 3 to 4 volts de- 
 posits can only be produced when the baths have been heated 
 to quite a high temperature. However, according to Foerster 
 and Langbein's experiments, the deposits do not possess the 
 good qualities claimed by the patent, and cannot be forced to 
 such thickness as, for instance, is with the greatest ease attained 
 in nickel ethyl-sulphate baths. 
 
 The owners of the Marino patent have apparently themselves 
 recognized the disadvantages of the glycerin electrolyte, and 
 have applied for a patent, according to which, 15 to 50 per 
 cent, of glycerin is to be added to solutions of metallic salts in 
 water. The glycerin is claimed to act as depolarizer, and allow 
 of the production of lustrous nickel deposits of great homo- 
 geneousness. However, the correctness of these statements 
 may be doubted, since by experiments made in this direction, 
 it was found impossible to produce a better technical effect 
 with such an addition of glycerin than without it, in properly- 
 prepared baths. 
 
 It may here again be emphasized that the compositions of 
 the electrolyte must vary according to the results desired, and 
 that it is impossible to attain with one electrolyte all the pos- 
 sible properties of the deposit. 
 
 Moreover, the addition of glycerin to aqueous electrolytes 
 has for a long time been known through the English patents 
 5300 and 22855, an d it might be supposed that if such an ad- 
 dition were of special advantage it would have long ago come 
 into general use. 
 
 * German patent, No. 104111. 
 
DEPOSITION OF NICKEL AND COBALT. 25 I 
 
 Effect of current-density. A slighter current-density always 
 and under all conditions causes the deposition of a harder and 
 more brittle nickel than a current of medium strength, while 
 with too great a current-density, the metal is separated in pul- 
 verulent form. However, as will be shown later on, nickel can 
 also be deposited with a high current-density provided the 
 baths are of proper composition, and agitated. 
 
 Electro-motive force. The electro-motive force given for all 
 the baths is valid for the normal temperature of 59 to 64. 4 F. 
 and an electrode-distance of 10 cm. It has previously been 
 mentioned, that with an increasing temperature of the electro- 
 lyte its specific resistance becomes less, but grows as the tem- 
 perature decreases, less electro-motive force being required in 
 the first case, and more in the latter. 
 
 The greater the electrode-distance in a bath is, the higher the 
 electro-motive force which is required. A statement in figures 
 of the changes in electro-motive force for the various electrode- 
 distances will not be given because, on the one hand, the nec- 
 essary electro-motive force is readily determined by a practical 
 experiment, and, on the other, a calculation in advance of the 
 electro-motive force might lead to wrong conclusions in so far 
 as the specific resistance of the electrolyte is subject to change, 
 and the value of the electro-motive force of the counter current 
 varies very much for the objects suspended as cathodes, accord- 
 ing to the nature of the basis-metal of which they are composed. 
 For this reason a statement of the specific resistances of the 
 bath prepared according to the directions given below is also 
 omitted, because such statements would be valid only for 
 freshly-prepared baths. 
 
 Reaction of nickel baths. All nickel baths work best when 
 they possess a neutral or slightly acid reaction. Hence blue 
 litmus-paper should be only slightly reddened, and red congo 
 paper must not be changed at all. Baths prepared with boric 
 acid form an exception, as they may show quite a strong acid 
 reaction. An alkaline reaction of nickel baths is absolutely 
 detrimental, such baths depositing the metal dull and with a 
 yellowish color, and do not yield thick deposits. 
 
252 ELECTRO-DEPOSITION OF METALS. 
 
 Formulas for nickel baths. I. The most simple nickel bath' 
 consists of a solution of 8 parts by weight of pure nickel ammo- 
 nium sulphate in 100 parts by weight of distilled water. 
 
 Electro-motive force at 10 cm. electrode-distance, 3.0 volts. 
 
 Current-density, 0.3 ampere. 
 
 The solution is prepared by boiling the salt with the corres- 
 ponding quantity of water, using in summer 10 parts of nickel 
 salt to 100 of water, but in winter only 8 parts, to prevent the 
 nickel salt from crystallizing out. This bath which is fre- 
 quently used, possesses, however, a considerable degree of re- 
 sistance to conduction, and hence requires a strong current 
 for the deposition of the nickel. It also requires cast-nickel 
 anodes, since with the use of rolled anodes nickeling proceeds 
 in a very sluggish manner. However, the cast anodes rapidly 
 render the bath alkaline, necessitating a frequent correction of 
 the reaction. 
 
 To decrease the resistance, recourse has been had to certain 
 conducting salts, and, below, the more common nickel baths 
 will be discussed, together with their mode of preparation and 
 action, as well as their availability for certain purposes. 
 
 II. Nickel ammonium sulphate 17 ozs., ammonium sulphate 
 17 ozs., distilled water 10 quarts. 
 
 Electro motive force at 10 cm. electrode-distance, 1.8 to 2 
 volts. 
 
 Current-density, 0.35 ampere. 
 
 Boil the salts with the water, and, if the solution is too acid, 
 restore its neutrality by ammonia; then gradually add solution 
 of citric acid until blue litmus-paper is slowly but perceptibly 
 reddened. The bath deposits rapidly, it possessing but little 
 resistance, and all metals (zinc, lead, tin and Britannia, after 
 previous coppering) can be nickeled in it. However, upon 
 rough castings and iron, a pure white deposit is difficult to 
 obtain, frequent scratch-brushing with a medium hard-steel 
 brush being required. On account of the great content of sul- 
 phate of ammonium in the bath, the nickel deposit piles up 
 especially on the lower portions of the objects, which, in conse- 
 
DEPOSITION OF NICKEL AND COBALT. 253 
 
 quence, readily become dull {burn or over-nickel, for which see 
 later on), while the upper portions are not sufficiently nickeled. 
 For this reason the objects must be frequently turned in the 
 bath so that the lower portions come uppermost. This piling- 
 up of the deposit also frequently prevents the latter from ac- 
 quiring a uniform thickness. 
 
 III. Nickel ammonium sulphate 25^ ozs., ammonium sul- 
 phate 8 ozs., crystallized citric acid 1 ^ ozs., water 10 to 12 
 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 2.0 to 2.2 
 volts. 
 
 Current- density, 0.34 ampere. 
 
 The bath is prepared in the same manner as the preceding, 
 the salts being dissolved in boiling water, and ammonia added 
 until blue litmus paper is only slightly reddened. 
 
 This bath was formerly in general use in this country and is 
 to some extent at present employed, especially for nickeling 
 ground articles. It has the drawback of requiring very careful 
 regulation of the current to avoid peeling off. According to 
 experiments made by Dr. Langbein it would be better to de- 
 crease the content of ammonium sulphate to 0.8 oz. 
 
 The reaction of this bath should be kept only very slightly 
 acid or still better, neutral, and it is best to use an equal num- 
 ber of cast and rolled nickel anodes. 
 
 If, after working for some time, the objects nickel dark an 
 addition of nickel sulphate is advisable, if the reaction is cor- 
 rect and perhaps not alkaline. 
 
 IV. Nickel-ammonium sulphate 23 ozs., ammonium chloride 
 (crystallized) 11^ ozs., water 10 to 12 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 1.5 volts. 
 
 Current- density, 0.55 ampere. 
 
 The bath is prepared in the same manner as given for II. 
 and III. It nickels very rapidly and quite .white, but the de- 
 posit is soft, and hence care must be had in polishing upon 
 cloth or felt bobs, the corners and edges of the objects espec- 
 ially requiring careful handling. On account of the danger of 
 
254 ELECTRO-DEPOSITION OF METALS. 
 
 peeling off, a heavy deposit of nickel cannot be obtained in this 
 bath, since, in consequence of the rapid precipitation, the de- 
 posit condenses and absorbs hydrogen, is formed with a coarser 
 structure, and turns out less uniform and dense. These phe- 
 nomena are a hindrance to a heavy deposit, which, if it is to 
 adhere, must be homogeneous and dense. 
 
 As previously mentioned, baths with the addition of chlorides, 
 as xvell as those prepared with nickel chloride and nickel nitrate, 
 are not suitable for the solid nickeling of iron. They are, how- 
 ever, well adapted to the rapid light nickeling of cheap brass 
 articles. To obtain nickeling of a whiter color, only 7 ozs. in 
 place of 1 1 y 2 ozs. of ammonium chloride and 33^ ozs. of boric 
 acid may be dissolved with the assistance of heat. The bath 
 then requires 1.8 to 2 volts. 
 
 V. Nickel chloride (crystallized) 17^2 ozs., ammonium 
 chloride (crystallized) 17% ozs., water 12 to 15 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 1.75 to 2 
 volts; for zinc, 2.8 to 3 volts. 
 
 Current-density, 0.5 ampere. 
 
 This bath is prepared by dissolving the salts in hike-warm 
 water and adding ammonia until the bath shows a very slightly 
 acid, or a neutral, reaction. The bath deposits readily and is 
 especially liked for nickeling zinc castings. 
 
 All the drawbacks of the preceding bath as regards the 
 nickeling of iron apply also to this bath, only to a still greater 
 extent. Rolled nickel anodes have to be exclusively used. 
 
 Nickel BatJ is Containing Boric Acid. 
 
 VI. Weston recommends the following composition for 
 nickel baths: Nickel chloride 17^ ozs., boric acid 7 ozs., water 
 20 quarts; or nickel-ammonium sulphate 35 ozs., boric acid 
 17^ ozs., water 25 to 30 quarts. Both solutions are said to 
 be improved by adding caustic potash or caustic soda so long 
 as the precipitate formed by the addition dissolves. 
 
 These compositions, however, cannot be recommended, be- 
 cause the baths work faultlessly for a comparatively short time 
 
DEPOSITION OF NICKEL AND COBALT. 255 
 
 only. All kinds of disturbing phenomena very soon made 
 their appearance, the deposit being no longer white but black- 
 ish, and the baths soon failing entirely. Kaselowsky's formula 
 yields similar results. This bath is prepared by dissolving, 
 with the assistance of heat, 35/^ ozs. of nickel-ammonium sul- 
 phate and 17^5 ozs. of boric acid in 20 quarts of water. This 
 bath also generally fails after two or three months' use. The 
 cause of this has to be primarily sought for in the fact that baths 
 prepared with boric acid require, according to their composi- 
 tion, a definite proportion between rolled and cast nickel anodes. 
 If rolled anodes are exclusively used, free sulphuric acid is 
 soon formed, which causes energetic evolution of hydrogen on 
 the articles, but prevents a vigorous deposit and imparts to the 
 latter a tendency to peel off. The same thing happens when 
 a nickel salt not entirely neutral has been used in the prepara- 
 tion of the bath. If, on the other hand, cast nickel anodes 
 alone are employed, the bath soon becomes alkaline, with tur- 
 bidity and the formation of slime, and the deposit turns out 
 gray and dull before it possesses sufficient thickness. 
 
 From the foregoing it will be readily understood that the 
 nickel salt used must be neutral, and that the proportion of 
 rolled to cast anodes must be so chosen that the free sulphuric 
 acid formed on the cast anodes is neutralized, but that the 
 acidity of the bath dependent on the free boric acid is con- 
 stantly maintained. 
 
 A recent author argues in support of Haber's proposition 
 that the effect produced by the use of mixed anodes, i. e., 
 rolled and cast anodes, might be attained by regulating the 
 anode current-density by the use of definite dimensions of the 
 anodes in such a way that the electrolyte, as regards its com- 
 position, remains constant. For practical purposes this would 
 only be feasible without trouble, if approximately the same 
 object-surface is always present in the bath, otherwise the main- 
 tenance of the adequate anode current-density must be managed 
 by taking out or suspending anodes according to the varying 
 object-surfaces. However, this is far more troublesome, and 
 
256 ELECTRO-DEPOSITION OF METALS. 
 
 the use of mixed anodes is decidedly to be preferred, it having 
 been shown in the Galvanic Institute of Dr. George Langbein, 
 that by this means the reaction of a bath can for years be kept 
 constant even with considerable variations in the size of the 
 object-surface. 
 
 Such a bath containing boric acid may advantageously be 
 prepared as follows : 
 
 VII. Nickel-ammonium sulphate 21 ozs., chemically pure 
 nickel carbonate 1 ^ ozs., chemically pure boric acid (crys- 
 tallized) io}4 ozs., water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 2.25 to 2.5 
 volts. 
 
 Current-density, 0.35 ampere. 
 
 Boil the nickel-ammonium sulphate and the nickel carbon- 
 ate* in the water until the evolution of bubbles of carbonic 
 acid ceases and blue litmus-paper is no longer reddened. 
 After allowing sufficient time for settling, decant the solution 
 from any undissolved nickel carbonate, and add the boric acid. 
 Boil the whole a few minutes longer, and allow to cool. If the 
 nickel salt contains no free acid, boiling with the nickel car- 
 bonate may be omitted. The solution shows a strongly acid 
 reaction, which must not be removed by alkaline additions. 
 
 The proportion of cast to rolled anodes used in this bath is 
 dependent on the quality of the anodes. The use of readily- 
 soluble cast anodes requires the suspension in the bath of more 
 rolled anodes than when cast anodes dissolving with difficulty 
 are employed, since the surfaces of the latter, in consequence 
 of rapid cooling, are not readily attacked. The proportion has 
 likewise to be changed, with the use of soft- or hard-rolled 
 anodes. Hence the proper proportion will have to be estab- 
 lished by frequently testing the reaction of the bath. For this 
 purpose the following rules may be laid down: Blue litmus- 
 paper must always be perceptibly and intensely reddened, but 
 congo-paper should not change its red color, for if the latter 
 
 * In place of nickel carbonate, nickel hydrate may as well be used. 
 
DEPOSITION OF NICKEL AND COBALT. 257 
 
 turns blue it is an indication of the presence of free sulphuric 
 acid in the bath, which has to be neutralized by the careful 
 addition of solution of soda or potash until a fresh piece of 
 congo-paper dipped in the bath remains red. Ammonia can- 
 not be recommended for neutralizing free sulphuric acid in 
 this bath. Red litmus-paper must retain its color, for if it 
 turns blue, the bath has become alkaline, and fresh boric acid 
 has to be dissolved in the previously heated bath until a fresh 
 piece of blue litmus-paper acquires an intense red color, or 
 pure dilute sulphuric acid has to be added to the bath, stirring 
 constantly, until blue litmus-paper is reddened, avoiding, how- 
 ever, an excess which is indicated by red congo-paper turning 
 blue. 
 
 This bath is equally well adapted for nickeling ground ob- 
 jects, as well as for rough castings, the latter acquiring a pure 
 white coating of nickel if thoroughly scratch-brushed, and the 
 bath shows a normal acid reaction. 
 
 Below are given a few other formulae for nickel baths which 
 may be advantageously used for special purposes, but not for 
 nickeling all kinds of metals with equally good results. 
 
 VIII. Nickel sulphate 10^ ozs., potassium citrate 7 ozs., 
 ammonium chloride 7 ozs., water 10 to 12 quarts. 
 
 For copper and copper-alloys: Electro-jnotive force at 10 cm. 
 electrode-distance, 1.5 to 1.7 volts. 
 
 Current- detisity, 0.45 to 0.5 ampere. 
 
 For zinc : Electro-motive force at 10 cm. electrode-distance, 
 2 to 2.5 volts. 
 
 Current- density, 0.8 to 1 ampere. 
 
 To prepare the bath dissolve 10 ^ ounces of nickel sulphate 
 and 3*^ ounces of pure crystallized citric acid in the water ; 
 neutralize accurately with caustic potash, and then add the 
 ammonium chloride. This bath is especially adapted for the 
 rapid nickeling of polished, slightly coppered zinc articles. 
 Deposition is effected with a very feeble current, without the 
 formation of black streaks, such as are otherwise apt to appear 
 in nickeling with a weak current. The deposit itself is dull 
 17 
 
258 ELECTRO-DEPOSITION OF METALS. 
 
 and somewhat gray, but acquires a very fine polish and pure 
 white color by slight manipulation upon the polishing wheels. 
 With a stronger current the bath is also suitable for the direct 
 nickeling of zinc articles ; it must, however, be kept strictly 
 neutral. The bath works with rolled anodes, and when it has 
 become alkaline, requires a correction of the reaction by citric 
 acid. 
 
 IX. Nickel phosphate, 6j4, ozs., sodium pyrophosphate, 26^ 
 ozs., water, 10 quarts. 
 
 For copper and its alloys: Electro-motive force, at 10 cm. 
 electrode-distance, 3.5 volts. 
 
 Cur rent- density, 0.5 ampere. 
 
 For the preparation of the nickel phosphate dissolve 12 ozs. 
 of nickel sulphate in 3 quarts of warm water and 10 ozs. of 
 sodium phosphate in another 3 quarts of warm water. Mix the 
 two solutions, stirring constantly, and filter off the precipitated 
 nickel phosphate. 
 
 Dissolve the sodium pyrophosphate in 8 quarts of warm 
 water, add the nickel phosphate, which soon dissolves by thor- 
 ough stirring, and make up the bath to 10 quarts by adding 
 water. 
 
 This bath yields a very fine dark nickeling upon iron,, brass, 
 and copper, as well as directly, without previous coppering 
 upon sheet zinc and zinc castings, and may be advantageously 
 used for decorative purposes where darker tones of nickel are 
 required. For zinc, work with 3.8 volts and 0.55 ampere. 
 
 For the same purpose a nickel solution compounded with a 
 large quantity of ammonia, hence an ammoniacal nickel solu- 
 tion has been recommended. However, experiment with this 
 solution always yielded lighter tones than bath IX. 
 
 A black nickel bath of the following composition has been 
 recommended by Blauet : Water 95 gallons, nickel-ammonium 
 sulphate 1 oz. and 3 drachms, potassium sulphocyanide 4^ 
 drachms, copper carbonate 3 drachms, arsenious acid 3 
 drachms. 
 
 Dissolve the nickel salt in the water and add the potassium 
 
DEPOSITION OF NICKEL AND COBALT. 259 
 
 sulphocyanide. Then dissolve, at about 176 F., the copper 
 carbonate by treatment with ammonium carbonate or potas- 
 sium cyanide, and add the solution, while lukewarm to the 
 bath. Finally add the arsenious acid. The latter seems not 
 to be consumed. If in time a gray sediment is formed, some 
 potassium sulphocyanide and copper carbonate have to be 
 added. 
 
 Prepared black nickeling salt is furnished by the Hanson & 
 Van Winkle Co. 
 
 X. A fairly good nickel-bath for electro-platers having but a 
 feeble current at their disposal is obtained from a solution of 
 nickel-ammonium sulphate 223^ ozs., magnesium sulphate 
 11)4 ozs > water 10 to 12 quarts. 
 
 For iron and copper alloys: Electro -motive force at 10 cm. 
 electrode-distance, 4 volts. 
 
 Current-density, 0.2 ampere. 
 
 This bath deposits with ease, and a heavy coating can be 
 produced on iron without fear of the disagreeable conse- 
 quences of bath IV. Even zinc may be directly nickeled in it 
 with a comparatively feeble current. The deposit, however, 
 turns out rather soft, with a yellowish tinge, and the bath does 
 not remain constant, but fails after working at the utmost three 
 or four months, even cast anodes being but little attacked. 
 
 Below are given the compositions of a few nickel baths 
 which have been highly recommended: — 
 
 ju, XI. Pure nickel sulphate 35^ ozs., neutral ammonium tar- 
 trate 26^ ozs., tannin yj grains, water 20 quarts. Neutral 
 ammonium tartrate is obtained by saturating a solution of tar- 
 taric acid with ammonia. The nickel salt must also be neutral. 
 For this purpose dissolve the above-mentioned ingredients in 3 
 or 4 quarts of water and boil the solution for % hour, then add 
 enough water to make 20 quarts of fluid, and filter. The bath 
 is said to yield. a very white, soft, and homogeneous deposit of 
 any desired thickness, without roughness or danger of peeling 
 off. On rough or polished castings thick deposits may be ob- 
 tained at a cost scarcely exceeding that of coppering. Gal- 
 
260 ELECTRO-DEPOSITION OF METALS. 
 
 vanoplastic reproduction may also be effected in this bath. 
 For those who wish to try the bath it may be mentioned that 
 the most suitable electro-motive force is 3.5 volts; current- 
 density, 0.3 ampere. 
 
 XII. An English formula is as follows: Dissolve ijyi ozs. 
 of nickel sulphate, 9^ ozs. of tartaric acid, and 2 X A ozs. of 
 caustic potash in 10 quarts of water. 
 
 XIII. For nickeling small articles the following bath is 
 claimed to yield excellent results: Nickel-ammonium sulphate 
 64 ozs., ammonium sulphate 20^ ozs., crystallized citric acid 
 
 4^ ozs - 
 
 For the production of very thick deposits, the following bath 
 
 has been recommended: Nickel sulphate 16 ozs., sodium 
 citrate 10 ozs., water 10 quarts. This bath is said to be 
 especially useful in preparing nickel cliches. However, numer- 
 ous experiments proved it to possess the disadvantages of all 
 nickel baths prepared with large quantities of organic com- 
 binations, and, for the special purpose for which it is recom- 
 mended, no better results were obtained than with any other 
 nickel bath rationally composed for heavy deposits. However, 
 for nickeling articles with sharp edges and points, for instance, 
 knives, scissors, etc., this bath is very suitable, it being quite 
 indifferent towards current conditions, so that even with a 
 higher electro- motive force than the normal one and greater 
 current-density, the articles do not readily over-nickel. The 
 deposit is quite soft, and in grinding such nickeled instruments, 
 peeling-off of the nickel layer happens less frequently than with 
 instruments nickeled in other baths. Electro-motive force at 
 10 cm. electrode-distance, 3.0 volts. Current-density, 0.33 
 ampere. 
 
 We herewith conclude the formulas for nickel baths, because 
 no better results were obtained from other receipts which have 
 been published and which have been thoroughly tested, than 
 from those given above. In most cases success with them fell 
 far short of expectation. 
 
 Some authors have recommended for nickeling a solution of 
 
DEPOSITION OF NICKEL AND COBALT. 26 r 
 
 nickel cyanide in potassium cyanide, but experiments failed to 
 obtain a proper deposition of nickel. 
 
 The addition of carbon disulphide to nickel baths, which has 
 been recommended by Bruce, is not advisable. According to 
 Bruce, such an addition prevents the nickel deposit from be- 
 coming dull when reaching a certain thickness, but repeated 
 experiments made strictly in accordance with the directions 
 given did not confirm this statement. 
 
 The general remark may here be added that freshly-prepared 
 nickel baths mostly work correctly from the start, though it 
 may sometimes happen that the articles first nickeled come 
 from the bath with a somewhat darker tone. In this case sus- 
 pend a few strips of iron or brass-sheet to the object-rod ; allow 
 the bath to work for one or two hours, when nickeling will 
 proceed faultlessly. If, however, such should not be the case, 
 ascertain by a test with the hydrometer whether the specific 
 gravity of the bath is too high. If the deposit does not turn 
 out light, even after dilution, it is very likely that the nickel salt 
 contains more than traces of copper, or, with black-streaked 
 nickeling, zinc. 
 
 It has also been observed that the deposit frequently peels 
 off when, for the purpose of neutralization, additions have been 
 made to the nickel baths. This phenomenon disappears in a 
 few days, but it demonstrates that, instead of correcting the 
 reaction of the bath by the addition of acids or alkalies, it 
 should be done by increasing the rolled anodes in case the 
 bath shows a tendency to become alkaline, or to increase the 
 cast anodes in case the bath becomes too acid. 
 
 A few words may here be said in regard to what may be 
 termed a nickel bath without nickel salt. It simply consists of 
 a 15 to 20 per cent, solution of ammonium chloride, which 
 transfers the nickel from the anodes to the articles. Cast 
 anodes are almost exclusively used for the purpose, and deposi- 
 tion may be effected with quite a feeble current. Before the 
 solution acquires the capacity of depositing, quite a strong cur- 
 rent has to be conducted through the bath until the commence- 
 
2o2 ELECTRO-DEPOSITION OF METALS. 
 
 merit of a proper reduction of nickel. This bath is only suit- 
 able for coloring- very cheap articles, it being impossible to 
 produce solid nickeling with it. It is here mentioned because 
 it may serve as a representative of a series of other electro- 
 plating baths in which the transfer of the metal is effected by 
 ammonium chloride solution without the use of metallic salts, 
 for instance, iron, zinc, cobalt, etc. 
 
 Prepared nickel salts. As previously mentioned, there is a 
 large number of receipts for nickel baths, some of them being 
 entirely unsuitable, while others are only available for certain 
 purposes. Hence, it is impossible, even for the skilled oper- 
 ator, to separate the good receipts from the bad ones, if he is 
 not qualified to do so by many years' experience and a thor- 
 ough knowledge of chemistry. The choice is still more diffi- 
 cult for the beginner and layman, and it is recommended to 
 them to get their supply of suitable baths from well-known 
 dealers in electro-plating supplies. 
 
 By prepared nickel salts are understood preparations which, 
 in addition to the most suitable nickel salt, contain the required 
 conducting salt for the decrease of the resistance, and further 
 such additions as promote a pure white separation of nickel, and 
 are necessary for the continuously good working of the bath. 
 i Correction of the reaction of nickel baths. When after long 
 use a nickel bath has become alkaline, which is readily deter- 
 mined by a test with litmus paper, this defect can in a few min- 
 utes be overcome by the addition of an acid, and according to 
 the composition of the bath, its neutrality or slightly acid reac- 
 tion can be restored by citric, acetic, sulphuric, boric acids, 
 etc. The use of hydrochloric acid for this purpose, which has 
 been recommended, is not advisable. In most cases it will be 
 best to employ dilute sulphuric acid, provided an excess of it be 
 avoided, which is recognized by red congo-paper turning blue. 
 
 When a bath contains too much free acid, the latter may be 
 removed by an addition of ammonia, ammonium carbonate, 
 potash or nickel carbonate, the choice of the agent to be used 
 depending on the composition of the bath. 
 
DEPOSITION OF NICKEL AND COBALT. 263 
 
 Thick deposits in hot nickel baths. Nickel baths, more or less 
 highly heated, have for years been used for nickeling, the pur- 
 pose being, on the one hand, the production in a shorter time 
 of a thick deposit, and on the other, it was expected that the 
 product thus obtained would become especially dense in con- 
 sequence of the contraction in cooling. 
 
 The results obtained in heated baths were, however, unsatis- 
 factory, since, if the current was not carefully regulated, the 
 deposits peeled off readily, and the polished nickeling became 
 dull on exposure to the air. 
 
 The unsatisfactory results might primarily have been due to 
 an unsuitable composition of the electrolytes. Foersters's* 
 experiments have shown that almost perfectly smooth deposits 
 of 0.5 to 1 millimeter thickness may be obtained in absolutely 
 neutral nickel solutions with a high content of nickel — 1 oz. or 
 more per quart — if. kept at a temperature of 122 to 194 F., 
 for instance, in solutions containing 5 ozs. nickel sulphate per 
 quart, at 167 to 176 F. Electro-motive force, at an electrode- 
 distance of 4 cm., 1.3 volts; current-density, 2 to 2.5 amperes. 
 
 Exhaustive experiments made by Dr. George Langbein led 
 to the result that deposits of great thickness may also be pro- 
 duced in slightly acidulated nickel baths of suitable composi- 
 tion, at a temperature kept constant at from 185 to 194 F. 
 In a bath which contained 12.34 ozs - °f nickel sulphate and 
 6.34 ozs. of sodium sulphate or magnesium sulphate per quart, 
 and which was slightly acidulated with acetic acid, deposits of 
 0.5 millimeter thickness were in 12 hours obtained, the current- 
 density amounting to 4 amperes. 
 
 For nickeling flat objects the current-density may, however, 
 be materially increased, one of up to 8 amperes or more being 
 permissible. By reason of the rapidity with which thick de- 
 posits can be produced in hot baths of the above-mentioned 
 composition, the term quick nickeling has been applied to this 
 process. 
 
 *Zeitschrift fLir Elektrochemie, 1897 to 1898, p. 160. 
 
264 ELECTRO-DEPOSITION OF METALS. 
 
 Independent of Dr. Langbein, Dr. Kugel discovered that 
 thick deposits of nickel can be obtained in a hot nickel bath of 
 nickel sulphate and magnesium sulphate very slightly acidu- 
 lated with sulphuric acid.* 
 
 While, in order to avoid the formation of roughness and 
 bud-like excrescences, Foerster found agitation of the electro- 
 lytes of the composition mentioned by him of advantage, Dr. 
 Langbein obtained smoother deposits when the electrolyte was 
 not mechanically agitated, and the fluid was only slowly mixed 
 through by heating with a steam coil. 
 
 Upon flat objects, for instance, sheets, very uniform deposits 
 1 millimeter or more in thickness are very rapidly obtained, as 
 well as upon round objects, if care be taken to have, by the 
 use of anodes of the same shape, a uniform anode-distance 
 from all object surfaces. However, the production of such de- 
 posits of entirely uniform thickness upon articles with high 
 relief has thus far not been successfully accomplished by. Dr. 
 Langbein with the use of the above-mentioned electrolytes. 
 
 Thick deposits in cold nickel baths. By the use of an electro- 
 lyte which contains nickel ethyl sulphate (German patent, No. 
 134736) or the ethyl sulphates of the alkalies or alkaline 
 earths, deposits of any desired thickness can be produced if the 
 bath be constantly agitated by mechanical means or the intro- 
 duction of hydrogen. Agitation by blowing in air is not per- 
 missible on account of oxidation of the ethyl-sulphate com- 
 binations by the oxygen of the air. 
 
 Continued experiments with such ethyl-sulphate combina- 
 tions by Dr. G. Langbein & Co. resulted in finding formulas 
 for prepared nickel salts from the solutions of which thick de- 
 posits of nickel capable of being polished can in a few minutes 
 be obtained in the cold way. The formulas for these different 
 prepared nickel salts will not be given as they are protected by 
 patents. The salts are known in commerce as Mars, Lipsia, 
 Germania and Neptune. 
 
 * German patent, 11 7054. 
 
DEPOSITION OF NICKEL AND COBALT. 265 
 
 In an electrolyte of given composition, which has to be con- 
 stantly kept slightly acid with acetie acid nickeling may for 
 weeks be carried on at the ordinary temperature without any 
 peeling-off of the deposit being noticed, and, in this respect, 
 this bath surpasses all other known baths. In the course of 
 six weeks, Dr. Langbein has produced upon gutta-percha 
 matrices, galvanoplastic nickel deposits 6 millimeters in thick- 
 ness, the metal proving thoroughly homogeneous and firmly 
 united throughout its entire thickness. 
 
 Coehn and Siemens * found that from electrolytes which con- 
 tain nickel salts and magnesium salts, weighable quantities of 
 magnesium are under certain conditions separated together 
 with the nickel, and they succeeded in depositing alloys con- 
 taining approximately 90 per cent, of nickel and 10 per cent, 
 of magnesium. According to the above-mentfoned authors, 
 the behavior of the nickel-magnesium alloys in the electrolytic 
 separation differs essentially from that of nickel, they showing 
 especially no tendency towards peeling off. 
 
 Nickel anodes. Either cast or rolled nickel plates are used 
 as anodes, they, of course, having to be made of the purest 
 quality of nickel. Every impurity of the anode passes into the 
 bath, and jeopardizes, if not at first, then finally, its successful 
 working. Rolled anodes dissolve with difficulty and cast an- 
 odes, as a rule, with ease. If the latter dissolve only with diffi- 
 culty they fail in their object of replacing the nickel metal with- 
 drawn from the bath by the nickeling process. 
 
 As regards solubility, electrolytically produced nickel anodes 
 stand between rolled and cast anodes. 
 
 The anodes should not be too thin, otherwise they increase 
 the resistance. For small baths rolled anodes 2 to 3 milli- 
 meters thick are generally used. For larger baths, it is better 
 to use plates 3 to 10 millimeters thick, while the thickness of 
 cast anodes may vary from 3 to 10 millimeters, according to 
 their size. 
 
 * Zeitschrift fiir Elektrochemie, 1902, S. 591. 
 
266 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Attention may here be called to the elliptic anodes, Fig. 117, 
 patented by the Hanson & Van Winkle Co., Newark, N. J. 
 
 The great advantage claimed 
 in the use of these elliptic 
 anodes over the old style flat 
 plate is the uniformity of de- 
 posit as disintegration takes 
 place from all sides of the 
 anode ; consequently the 
 molecules are distributed 
 uniformly throughout the 
 solution, and not only hasten 
 the deposit, but give a 
 heaver deposit in a given 
 time. Another important 
 feature in these anodes is 
 the fact that they wear down 
 evenly to a small, narrow 
 strip, and when worn down 
 to such a point that it seems 
 desirable to put in more 
 nickel, the old ones which 
 take up practically no room 
 in the tank, can remain until 
 entirely consumed, and as a 
 result there is practically no 
 scrap nickel to dispose of at 
 half price. Fig. 118 shows 
 the small loss in the use 
 of the elliptic anode. The 
 weight of the original plate 
 was 16 pounds. Percentage 
 of waste only 5 per cent. 
 Fig. 119 shows the orig- 
 inal shape of the flat plate still largely used and the character 
 of the wear. The top part of the scrap-plate with its two ears 
 
DEPOSITION OF NICKEL AND COBALT. 267 
 
 is almost as heavy as the same section of the original plate. 
 
 Fig. 118. 
 
 11 oz. 
 
 4 OZ. I3 oz 
 
 10 oz. 
 
 16 LBS. 
 
 The original weight of the plate was 13^3 lbs. Waste 2 lbs. 
 Percentage of waste 14.6 per cent. The examples shown in 
 
 Fig. 119. 
 
 Fig. 120. 
 
 the illustrations were taken from a lot of scrap returned to the 
 
268 ELECTRO-DEPOSITION OF METALS. 
 
 manufacturers. The scrap from the elliptic anode came from 
 a large stove concern and the flat scrap also from a stove 
 manufacturer. Elliptic anodes are furnished in all commercial 
 metals. 
 
 Fig. 1 20 shows the silverite anode manufactured by Zucker 
 & Levett & Loeb Co., New York. It is formed with columns 
 extending downward. It exposes to the solution a very large 
 metal surface of extremely light weight, and insures long life to 
 the anode and very little waste of metal. These anodes are 
 made with pure malleable wire hooks cast welded to them, or 
 with the older form of ears intended to be used with regular 
 copper hooks. The anodes are made of any length desired. 
 
 The use of insoluble anodes of retort carbon or platinum, 
 either by themselves, or in conjunction with nickel anodes, as 
 frequently recommended by theorists, is not advisable. The 
 harder and the less porous the nickel anode is, the less it is 
 attacked in the bath and the less it fulfills the object of keeping 
 constant the metallic content of the solution. On the other 
 hand, the softer and the more porous the anode is, the more 
 readily it dissolves, because it conducts the current better and 
 presents more points of attack to the bath ; and the more it is 
 dissolved, the more metal is conveyed to the bath. With the 
 sole use of rolled anodes and working with a feeble current, 
 free acid is formed in the bath ; on the other hand, by working 
 with cast anodes alone, the bath readily becomes alkaline. 
 Now it would appear that the possibility of a bath also becom- 
 ing alkaline even with the sole use of rolled anodes, especially 
 when working with a strong current, has led to the proposition 
 of suspending in the bath, besides the nickel anodes, a sufficient 
 number of insoluble anodes in order to effect a constant 
 neutrality of the bath. It would lead too far to go into the 
 theory of the secondary decompositions which take place in a 
 nickel bath, to prove that, though neutrality is obtained, it can 
 only be done at the expense of the metallic content of the 
 bath. Hence, this impracticable proposition shall here be 
 overthrown by practical reasons, it only requiring to be demon- 
 
DEPOSITION OF NICKEL AND COBALT. 269 
 
 strated that in baths becoming alkaline the content of nickel 
 also decreases steadily though slowly. This fact in itself shows 
 that in order to save the occasional slight labor of neutralizing 
 the bath, the decrease of the metallic content should not be 
 accelerated by the use of insoluble anodes. 
 
 For larger baths the use of expensive platinum anodes as in- 
 soluble anodes need not be taken into consideration, because 
 for large surfaces of objects correspondingly large surfaces of 
 platinum anodes would have to be present, as otherwise the 
 resistance of thin platinum sheets would be considerable. But 
 such an expensive arrangement would be justifiable only if 
 actual advantages were obtained, which is not the case, because, 
 though the platinum does absolutely not dissolve, the defici- 
 ency of metallic nickel in the bath caused by such anudes must 
 in some manner be replaced. 
 
 The insoluble anodes of gas-carbon, which have frequently 
 been proposed, are attacked by the bath. Particles of carbon 
 become constantly detached, and floating upon the bath, de- 
 posit themselves upon the objects and cause the layer of nickel 
 to peel off. Furthermore, by the use of nickel anodes in con- 
 junction with carbon anodes, the current, on account of the 
 greater resistance of the latter, is forced to preferably take its 
 course through the metallic anodes, in consequence of which 
 the articles opposite the nickel anodes are more thickly nickeled 
 than those under the influence of the carbon anodes. With 
 larger objects this inequality in the thickness of the deposit is 
 again a hindrance to obtaining layers of good and uniform 
 thickness, such as are required for solid nickeling. Since the 
 current preferably seeks its compensation through these sepa- 
 rate metallic anodes, they are more vigorously attacked than 
 when nickel plates only are suspended in the bath. 
 
 With nickel baths which contain a considerable amount of 
 ammonium chloride, the use of a few carbon anodes along with 
 the rolled nickel anodes may be permissible, since these baths 
 strongly attack even the rolled anodes, and thereby convey to 
 the bath sufficient quantities of fresh nickel. Such baths con- 
 
270 ELECTRO-DEFOSITION OF METALS. 
 
 taining ammonium chloride, as a rule, become very rapidly 
 alkaline, so that frequent neutralization becomes inconvenient. 
 However, in this case, it is advisable to place the carbon anodes 
 in small linen bags which retain any particles of carbon becom- 
 ing detached, the latter being thus prevented from depositing 
 upon the articles in the bath. 
 
 According to long practical experience, the best plan is to 
 use rolled and cast anodes together in a bath which does not 
 contain chlorides, and to apportion the anode surface so that 
 an anode-rod, about 2 /^ of its length, is fitted with anodes. If, 
 for instance, a tank is 120 centimeters long in the clear and 50 
 centimeters deep, the width of the nickel anodes laid alongside 
 one another should be about 80 centimeters, and their length 
 about 3/5 of the depth of the tank, hence 30 centimeters. For 
 each anode-rod, 8 anodes, each 30 centimeters long and 10 
 centimeters wide, would, therefore be required. 
 
 The proportion of cast to rolled anodes depends on the com- 
 position of the bath, but it may be laid down as a rule, that 
 baths with greater resistance require more cast anodes, and 
 baths with less resistance more rolled anodes. Baths with the 
 greatest resistance, for instance, that prepared according to 
 formula I require only cast anodes, while baths with the small- 
 est resistance, for instance, those containing ammonium chloride, 
 may to advantage work only with rolled anodes ; baths with 
 medium resistance require mixed, anodes. 
 
 The proper proportion has been established when, after work- 
 ing for some time, the original reaction of the bath remains as 
 constant as possible. When the bath is observed to become 
 alkaline, the number of rolled anodes should be increased, but 
 when the content of acid increases they should be decreased, 
 and the number of cast anodes increased. 
 
 Cast anodes, especially those not cast very hot, have, to be 
 sure, the disadvantage of becoming brittle, and crumbling 
 before they are entirely consumed. Nickel anodes cast in 
 iron moulds are so hard on their surfaces as to resist the action 
 of the bath, and dissolve only with difficulty, so that the con- 
 
DEPOSITION OF NICKEL AND COBALT. 271 
 
 tent of metal of the bath is only incompletely replenished. 
 Anodes cast in sand moulds, and slowly cooled, are porous 
 and consequently dissolve readily, but by reason of their por- 
 osity their interior portions are also attacked. If such an 
 anode be broken, it will be found that the interior contains a 
 black powder (nickel oxide) which novices sometimes believe 
 to be carbon. In fact cases have been heard of that customers 
 have complained that the anodes furnished them were not 
 nickel anodes at all, but simply carbon plates coated with a 
 layer of nickel. 
 
 The cast anodes suspended to the ends of the conducting 1 
 rods are especially strongly attacked, and, therefore, when 
 rolled and cast anodes are used together, it is best to suspend 
 the latter more towards the center, and the former on the ends 
 of the rods. 
 
 These drawbacks, however, are not sufficient to prevent 
 the use of a combination of cast and rolled anodes when re- 
 quired by the composition of the bath. The brittle remnants 
 of the anodes are thoroughly washed in hot water, dried, and 
 sold. 
 
 Rolled nickel anodes are liable to corrosion, and may be 
 used up to the thickness of a sheet of paper before they fall to 
 pieces. It is, however, best to replace them by fresh anodes 
 before they become too thin, since with the decrease in thick- 
 ness their resistance increases. 
 
 It is best to allow the anodes to remain quietly in the bath, 
 even when the latter is not in use, they being in this case not 
 attacked. By frequently removing and replacing them they 
 are subject to concussion, in consequence of which they 
 crumble much more quickly than when remaining quietly in 
 the bath. 
 
 In the morning, before nickeling is commenced, the anodes 
 will frequently show a reddish tinge, which is generally ascribed 
 to a content of copper in the bath or in the anodes. This red- 
 dish coloration also appears when an analysis shows the anodes, 
 as well as the bath, to be absolutely free from copper. It is 
 
272 ELECTRO-DEPOSITION OF METALS. 
 
 very likely due to a small content of cobalt, from which nickel 
 anodes can never be entirely freed. It would seem that by the 
 action of a feeble current cobaltous hydrate is formed, which, 
 however, immediately disappears on conducting a strong cur- 
 rent through the bath. 
 
 The anodes aie supported by pure nickel wire 0.11 to 0.19 
 inch thick, or by strips of nickel sheet riveted on. 
 
 It has previously been mentioned that the anodes in baths at 
 rest are frequently more strongly attached at the upper, than at 
 the lower, portions, because specifically lighter layers of fluid 
 are present on top and heavier ones below, and the current 
 takes the road where there is the least resistance. This dispro- 
 portionate solution of the anodes may, however, also be no- 
 ticed in baths which are agitated, and consequently in which 
 no layers of different specific gravities are present. The lower 
 and side edges will be found more corroded than the middle 
 portions of the anodes, and the backs opposite to which no 
 objects are suspended appear also strongly attacked. These 
 observations render plausible Pfanhauser's supposition that the 
 current does not in all places migrate directly and in straight 
 lines from the anodes to the cathodes, but that, as with the 
 magnetic lines of force, this migration takes place in curves, 
 especially when the anode-surface is small in proportion to the 
 cathode-surface. Pfanhauser has applied the term scattering 
 of current lines to this migration of the current in curves, and 
 has noticed that it grows with the electrode-distance, and 
 decreases as the electro-surfaces are increased. 
 
 Process of nickeling. Next to the correct composition of the 
 bath and the proper selection of the anodes, the success of the 
 nickeling process depends on the articles having been carefully 
 freed from grease and cleansed, and on the correct current- 
 strength. 
 
 The mechanical preparation of the objects has been dis- 
 cussed on p. 186, et seq. 
 
 The directions for the removal of grease, etc., given on p. 
 228, also apply to objects to be nickeled. In executing the 
 
DEPOSITION OF NICKEL AND COBALT. 273 
 
 operations, it should always be borne in mind that though 
 dirty, greasy parts become coated with nickel, the deposit im- 
 mediately peels off by polishing, because an intimate union of 
 the deposit with the basis-metal is effected with only perfectly 
 clean surfaces. Touching the cleansed articles with the dry 
 hand or with dirty hands must be strictly avoided; but, if large 
 and heavy objects have to be handled, the hands should first 
 be freed from grease by brushing with lime and rinsing in 
 water, and be kept wet. 
 
 As previously mentioned? the cleansed objects must not be 
 exposed to the air, but immediately placed in the bath, or, if 
 this is not practicable, be kept under clean water. 
 
 While copper and its alloys (brass, bronze, tombac, German 
 silver, etc.), as well as iron and steel, are directly nickeled, zinc, 
 tin, Brittania and lead are generally first coppered or brassed. 
 
 With a suitable composition of the nickel bath and some ex- 
 perience, the last-mentioned metals may also be directly nick- 
 eled ; but, as a rule, previous coppering or brassing is prefer- 
 able, the certainty and beauty of the result being thereby 
 considerably enhanced. 
 
 Security against rust. — By many operators it is preferred to 
 copper iron and steel articles previous to nickeling, it being 
 claimed that by so doing better protection against rust is 
 secured. However, comparative experiments have shown that 
 with the thin coat of copper which, as a rule, is applied, this 
 claim is scarcely tenable, and the conclusion has been reached 
 that a thick deposit of nickel obtained from a bath of suitable 
 composition protects the iron from rust just as well and as long 
 as if it had previously been slightly coppered. It cannot be 
 denied that previous coppering of iron articles has the advan- 
 tage that in case the articles have not been thoroughly 
 cleansed, the deposit of nickel is less liable to peel off, because 
 the alkaline copper bath completes the removal of grease ; but 
 with objects carefully cleansed according to the directions 
 given on page 228, previous coppering is not necessary. 
 
 The case, however, is different if the copper deposit is pro- 
 18 
 
274 ELECTRO-DEPOSITION OF METALS. 
 
 duced in order to act as a cementing agent for two nickel de- 
 posits. If, for instance, parts which have previously been 
 nickeled and from which the old deposit cannot be removed 
 by mechanical means, are to be re-nickeled, coppering is re- 
 quired, because the new deposit of nickel adheres very badly 
 to the old. Where articles are to be protected as much as 
 possible from rust, coppering is advisable, but the best success 
 is attained by a method different from the one generally pur- 
 sued. In nickeling, for instance, parts of bicycles which are 
 exposed to all kinds of atmospheric influences, they are first 
 provided with a thick deposit of nickel, then with a thick coat 
 of copper, and finally, again nickeled, they thus being twice 
 nickeled. It has previously been mentioned that every de- 
 posit is formed net-like, the meshes of the net being larger or 
 smaller, according to the nature of the metal deposited. If 
 now thick layers of two different metals are deposited one on 
 the top of the other, the net-lines of one deposit do not con- 
 verge into those of the previous deposit, but are deposited be- 
 tween them, thus consolidating the net. It will now be readily 
 understood that by the subsequent polishing the further con- 
 solidation of the deposits will be far more complete than when 
 the basis-metal receives but one deposit, which is to be con- 
 solidated by polishing. It is a remarkable fact that the porosity 
 of the nickel-deposit varies if the article is nickeled in several 
 baths of different composition. Thus denser deposits may be 
 obtained by suspending the articles in two or three baths, 
 which proves that the different resistances of the respective 
 baths of one and the same metal exert an influence upon the 
 greater or slighter density of the net. 
 
 However, under certain conditions, even iron and steel ob- 
 jects doubly nickeled in the above-described manner, do not 
 offer a sure guarantee against rusting of the basis-metal, and 
 to absolutely prevent the latter, the following means may be 
 adopted : 
 
 The objects are provided with an electro-deposit of zinc. 
 This deposit is scratch-brushed, coppered in the copper cyan- 
 
DEPOSITION OF NICKEL AND COBALT. 275 
 
 ide bath, rinsed in water, and finally nickeled, at first with a 
 strong current, which is after a few minutes reduced to the 
 normal current-density. It is recommended to polish the 
 objects thus treated with circular brushes, and not use polish- 
 ing wheels which may cause them to become heated, because 
 by such heating blisters are readily formed. 
 
 Another plan is as follows : The objects are first coppered in 
 the copper cyanide bath. The thickness of this deposit is then 
 increased to 0.15 or 0.2 millimeter in the acid copper bath (see 
 Galvanoplasty). It is then polished and nickeled. Or, if there 
 is sufficient time, a very thick deposit of nickel is directly pro- 
 duced upon the object with the use of a cold ethyl sulphate 
 nickel bath, or a hot quick nickeling bath (see pp. 263 et seq.). 
 
 The objects should never be suspended in the bath without cur- 
 rent, since the baths, with few exceptions, exert a chemical 
 action upon many metals, which is injurious to the electro- 
 plating process, and especially with nickel baths it is necessary 
 to connect the anode-rods and object-rods before suspending 
 the objects. 
 
 Over-nickeling. An error is frequently committed in nickel- 
 ing with too strong a current, the consequence being that the 
 deposit on the lower portions of the objects soon becomes' dull 
 and gray-black, while the upper portions are not sufficiently 
 nickeled. This phenomenon is due to the reduction of nickel 
 with a coarse grain in consequence of too powerful a current, 
 and is called burning ox over-nickeling. A further consequence 
 of nickeling with too strong a current is that the deposit readily 
 peels off after it reaches a certain thickness. The phenomenon 
 is due to the hydrogen being condensed and retained by the 
 deposit, which is thereby prevented from acquiring greater 
 thickness. 
 
 Especially do those objects suspended on the ends of the 
 rods nickel with great ease. This evil can be avoided by hang- 
 ing on both ends of the rods a strip of copper-sheet about 0.39 
 inch wide, and of a length corresponding to the depth of the 
 bath. 
 
2/6 ELECTRO-DEPOSITION OF METALS. 
 
 Normal deposition. The following criteria may serve for 
 judging whether the nickeling progresses with a correct cur- 
 rent-strength : In two, or at the utmost three, minutes, all por- 
 tions of the objects must be perceptibly coated with nickel, 
 but without a violent evolution of gas on the objects. Small 
 gas bubbles rising without violence and with a certain regu- 
 larity are an indication of the operation progressing with regu- 
 larity. If, after two or three minutes, the objects show no 
 deposit, the current is too weak, and in most cases the objects 
 will have acquired dark, discolored tones. In such case, either 
 a stionger current must be introduced by means of the rheostat, 
 or, if the entire volume of current generated already passes into 
 the bath, the object-surface has to be decreased, or, if this is 
 not desired, the battery must be strengthened by adding more 
 elements, or by fresh filling, etc. 
 
 If, on the other hand, a violent evolution of gas appears on 
 the objects, and the latter are well covered in a few seconds, 
 and the at first white and lustrous nickeling changes in a few 
 minutes to a dull gray, the current is too strong, and must be 
 weakened either by the rheostat, or by uncoupling a few ele- 
 ments, or diminishing the anode-surface, or finally by suspend- 
 ing more objects in the bath 
 
 These criteria also apply to nickeling with the dynamo. 
 
 The most suitable current-density for nickeling varies very 
 much, as will be seen from the preceding explanations. For 
 the ordinary cold electrolysis it varies for copper, brass, iron, 
 and steel from o.j to 1.5 amperes, while zinc, previously cop- 
 pered, requires 1 to 1.2 amperes. In the hot nickel bath the 
 current-density may be up to 5 and more amperes. 
 
 In nickeling zinc objects greater currenL-density and higher 
 electro-motive force are required. If the current is not of suffi- 
 cient strength, black streaks and stains are formed, zinc is dis- 
 solved, and the nickel bath spoiled. These evils are frequently 
 complained of by nickel-platers who have not a clear percep- 
 tion of the prevailing conditions (see polarization-current). A 
 vigorous evolution of gas must take place on the zinc objects, 
 otherwise a serviceable deposit will not be obtained. 
 
DEPOSITION OF NICKEL AND COBALT. 277 
 
 In most cases the electro-plater will in a few days learn cor- 
 rectly to judge the proper current-strength by the phenomena 
 presented by the objects, and if he closely follows the direc- 
 tions given but few failures will result. It may here be again 
 repeated that the use of a voltmeter and ammeter, as well as of 
 a rheostat, greatly facilitates a correct estimate of the proper 
 current-strength, and these instruments should for the sake of 
 economy never be omitted in fitting up an electro-plating plant. 
 
 It is in every case advisable first to cover the objects, i. <?., to 
 effect the first deposit of nickel, with the use of a strong cur- 
 rent, in order to withdraw the metals from the action of the 
 solution. The current is then reduced to a suitable strength 
 and nickeling finished with this current. With a current thus 
 regulated, the objects may be allowed to remain in the bath for 
 hours, and even for days. It is further possible to nickel by 
 weight and attain deposits of considerable thickness. 
 
 If very thick deposits of nickel are to be produced in the 
 ordinary bath, the objects must be frequently turned, as the 
 lower portions are more heavily nickeled than the upper; fur- 
 ther, as soon as the deposit acquires a dull bluish luster, it has to 
 be thoroughly scratch-brushed, in doing which, however, the 
 objects must not be allowed to become dry. After scratch- 
 brushing it is advisable to cleanse the deposit once more with 
 the lime-brush, and after rinsing replace the objects in the bath. 
 If burnt places cannot be brightened and smoothed with the 
 scratch-brush, the desired end is readily attained with the 
 assistance of emery paper or pumice. 
 
 For solid nickeling it suffices for most articles, with a normal 
 current to allow them to remain in the bath until a matt bluish 
 shine appears; this is an indication that the deposit has ac- 
 quired considerable thickness, provided the bath has not been 
 alkaline. In alkaline baths this dull deposit is frequently 
 formed before the deposit has attained considerable thickness 
 and this may cause errors, if the reaction of the bath is not 
 frequently controlled. 
 
 If the matt-appearing objects are permitted to remain longer 
 
278 ELECTRO-DEPOSITION OF METALS. 
 
 in the bath without scratch-brushing, the matt bluish tone soon 
 passes into a matt gray, and all the metal deposited in this 
 form must be polished away in order to obtain a bright luster. 
 
 Whether the deposit of nickel is sufficiently heavy for all 
 ordinary demands is, according to Fontaine, shown by rubbing 
 a nickeled corner or edge of the object rapidly and with ener- 
 getic pressure upon a piece of planed soft wood until it be- 
 comes hot. The nickeling should bear this friction. This test 
 can be recommended as perfectly reliable. 
 
 Faulty arrangement of anodes. If the objects, after having 
 been suspended for some time in the bath, are only partially 
 nickeled, it is very likely due to the defective arrangement 
 of the anodes. This occurs chiefly with large round objects 
 and with articles having deep depressions (cups, vases, etc.). 
 It is, of course, supposed that the wires to which the objects 
 are suspended in the bath have a sufficiently large cross-section 
 to carry the current required for nickeling the entire surface of 
 the object. 
 
 For flat objects it is sufficient to suspend them between two 
 rows of anodes. Round objects with a large diameter should 
 be quite surrounded with anodes, and be as nearly as possible 
 equidistant from them. This arrangement should especially 
 not be neglected where a heavy and uniform deposit of nickel 
 is to be given to round or half-round surfaces — for instance, 
 large half-round stereotype plates for revolving presses. 
 
 The arrangement of two object-rods between two anode-rods 
 is permissible only for small and thin articles such as safety- 
 pins, crochet needles, lead-pencil holders, etc. For articles 
 with larger surfaces it is decidedly objectionable, because the 
 sides of the articles turned towards the anodes acquire a thicker 
 deposit than the inside surfaces, and the thickness of the de- 
 posit decreases with the distance from the anodes. 
 
 Nickeling of cavities and profiled objects. While for smooth 
 articles the most suitable distance of the anodes from the objects 
 is 3^ to 5^ inches, for objects with depressions and cavities 
 it must be larger, if it is not preferred to make use of the 
 
DEPOSITION OF NICKEL AND COBALT. 279 
 
 methods described later on. However, a deposit of a uniform 
 thickness cannot be obtained by this means, because the por- 
 tions nearer to the anodes will acquire a thicker deposit than 
 the cavities ; hence the use of a small hand anode, which is 
 connected by means of a thin, flexible wire with the anode-rod, 
 and introduced into the depressions and cavities, is to be pre- 
 ferred. This, of course, renders it necessary for a workman to 
 stand alongside the bath and execute the operation by hand ; 
 but as the small anode can be brought within a few millimeters 
 of the surface of the article, and at this distance slowly moved 
 around it, a correspondingly thick deposit is in a short time 
 formed. 
 
 At any rate baths in which objects with depressions and 
 profiled articles are to be nickeled must possess greater resist- 
 ance than baths for nickeling flat articles, and it is inexplica- 
 ble why a bath with a large content of ammonium chloride 
 and consequently slight conducting resistance can be recom- 
 mended, as has been done, for nickeling hollow articles. 
 When baths containing ammonium chloride are used for nick- 
 eling articles with deep cavities the portions nearest to the 
 anodes will frequently be found overnickeled — burnt — before 
 the deepest portions are at all covered with nickel, and if the 
 operator waits until the deposit upon the latter portions has 
 acquired the desired thickness, the deposit already peels off 
 from the former portions, and frequently before that time. By 
 comparative experiments in nickeling the inside of brass tubes, 
 15 millimeters in diameter, it was found that in a bath with 
 great resistance, as well as one with slight resistance, nickeling 
 was equally well effected. However, the phenomenon of peel- 
 ing off, above referred to, appeared in the bath which contained 
 ammonium chloride when the ends of the .120 -millimeter long 
 tubes turned away from the anode, were still so slightly nick- 
 eled that the basis-metal shone through. On the other hand, 
 in the bath without ammonium chloride the end of the tube 
 turned towards the anode, to be sure, became matt, but did not 
 peel off in the polishing, and nickeling in the interior of the 
 
280 ELECTRO-DEPOSITION OF METALS. 
 
 tube had progressed well to the opposite end, the basis-metal 
 there being well covered. 
 
 In nickeling lamp-feet of cast-zinc, the use of the hand- anode 
 can scarcely be avoided if the depressed portions also are to be 
 provided with a uniformly good deposit. Moreover, zinc arti- 
 cles form an exception to the general rule in so far as by reason 
 of the highly positive properties of zinc, the resistance of the 
 bath may be slighter than for baths for nickeling copper and 
 its alloys, as well as iron and steel. 
 
 Besides the above-mentioned general rules for nickeling, 
 which also hold good for other electro-plating purposes, the 
 following may be given : 
 
 In suspending the objects in the bath, rub the metallic hooks 
 or wires, with which they are secured to the rods, a few times 
 to and fro upon the rod, in order to be sure that the place of 
 contact is purely metallic. It is also well to acquire the habit 
 of striking the rod a gentle blow with the finger every time 
 when suspending an object, the gas-bubbles settling on the 
 articles becoming thereby detached and rising to the surface. 
 It is further advisable, before securing the objects to the object- 
 rod, to move them up and down several times ; so to say, shake 
 them beneath the fluid, whereby, on the one hand, the layers 
 poorer in metal are mixed with those richer in metal, and, on 
 the other, any dust which may float upon the bath and settle 
 on the objects is removed. 
 
 The objects suspended in the bath should not touch one an- 
 other, nor one surface cover another, and thus withdraw it from 
 the direct action of the anode. In the first case stains will 
 readily form on the places of contact, and, in the latter, the cov- 
 ered surface acquires only a slight deposit. That the objects 
 must not touch the anodes need scarcely be mentioned. 
 
 Objects with depressions and cavities should be suspended 
 in the bath so that the air in the depressions and cavities can 
 escape, which is effected by turning the depression upwards, 
 or, if there are several depressions on opposite sides, by turn- 
 ing the articles about after being introduced into the bath. 
 
DEPOSITION OF NICKEL AND COBALT. 2,8 1 
 
 Air-bubbles remaining in the hollows prevent contact with the 
 solution, no deposit being formed on such places. 
 
 Polarization. It remains to say a few words in regard to the 
 so-called polarization phenomena. In the theoretical part of 
 this work, it has been shown that by dipping two plates of dif- 
 ferent metals in a fluid a counter or polarization current is gen- 
 erated, which is the stronger the greater the difference in the 
 potentials of the two metals in the solution is. If the anodes 
 in a nickel bath consist of nickel and the objects of copper, the 
 counter-current will be slight. It becomes, however, greater 
 when iron objects are suspended in the bath, and still greater 
 with zinc surfaces which are to be nickeled, because with the 
 solutions here in question, zinc possesses towards nickel an 
 essentially higher potential. Now, since the counter-current 
 flows in a direction opposite to that of the current intro- 
 duced at the bath, the latter is weakened, and the more so the 
 stronger the counter-current is. This explains why iron re- 
 quires a stronger current for nickeling than copper-alloys, and 
 zinc a stronger one than iron. 
 
 Now it may happen that the counter-current becomes so 
 strong as to entirely check the effect of the main current, and 
 even to reverse the latter, the consequence being that, in the 
 first case, the formation of the deposit is interrupted, and, in 
 the latter, that the deposit is again destroyed, and the metals 
 of which the articles consist dissolve and contaminate and spoil 
 the bath. To avoid this, a main current must be conducted 
 into the bath, which, by its sufficiently large electro-motive 
 force can overcome the counter-current, and the consequences 
 of the reversal of the current can be prevented by using the 
 galvanometer and observing the deflection of its needle, which 
 (according to p. 146) in proper time indicates the appearance 
 of a reversed current. Now if a nickel-plater has only a slight 
 current at his disposal, it follows from the above explanation 
 that, before nickeling the more electro-positive metals, such as 
 iron, tin, zinc, it is best first to copper them, and thereby over- 
 come the action of these metallic surfaces as regards the forma- 
 tion of the counter-current. 
 
282 ELECTRO-DEPOSITION OF METALS. 
 
 It happens comparatively seldom that the counter-current 
 becomes so strong as to destroy the deposits formed, because 
 for nickeling powerful Bunsen cells with two acids, or a dynamo 
 with at least 4 volts' impressed electro-motive force, are gener- 
 ally used. It is, however, well to acquaint the operator with 
 all possible contingencies, and to explain the reason why the 
 articles are preferably covered with a strong current. Sprague 
 recommends an initial current of 5 volts' electro- motive force, 
 but in most cases one of 3.5 volts suffices for nickeling iron 
 and copper alloys. 
 
 Stripping defective nickeling. Defective nickeling must, as a 
 rule, be completely removed before the objects can be re- 
 nickeled, since the second deposit adheres bady to the previous 
 one, especially if the latter has become dry. The removal of a 
 nickel-deposit is in most cases a disagreeable labor, which, 
 however, can most assuredly be saved if the utmost .care and 
 painstaking cleanliness are observed in freeing the articles from 
 grease, and in regulating the current. For the removal of the 
 nickel coating the following stripping acid, which may be used 
 either cold or tepid, has been recommended : Sulphuric acid 
 of 66° Be., 4 lbs. ; nitric acid of 40 Be., 1 lb. ; water about 
 1 pint. First put the water in a stoneware jar and cautiously 
 add, a little at a time, the sulphuric acid, since considerable 
 heat is generated when this acid is mixed with water. When 
 the entire quantity of sulphuric acid has been added, pour in 
 the nitric acid, when the bath is ready for use. In making up 
 the stripping bath, the proportions of the acids may be varied, 
 but the foregoing will be found to answer every purpose. An 
 addition of 8 ozs. of potassium nitrate to the bath has also been 
 recommended. 
 
 When stripping nickel-plated articles in the above bath it is 
 necessary to watch the operation attentively, since some articles 
 are very lightly coated and a momentary dip is frequently 
 sufficient to deprive them of their nickel. Other articles which 
 have been thoroughly well nickeled, but require from some 
 accidental cause to be stripped and re-nickeled, will need im- 
 
DEPOSITION OF NICKEL AND COBALT. 283 
 
 mersion for several minutes — indeed well-nickeled articles may 
 occupy nearly half an hour in stripping before the underlying 
 surface is entirely bare. The operation of stripping should be 
 conducted in the open air, or in a fire-place, so that the acid 
 fumes, which are very pernicious, can escape freely. The 
 articles should be attached to a stout copper wire, and after a 
 few moments' immersion should be removed from the bath to 
 see how the operation progresses, it being absolutely necessary 
 that the work should not remain in the stripping solution one 
 instant after the nickel is removed. The object is then trans- 
 ferred to a large volume of cold water, and after washing twice 
 or three times in fresh water is ready for the subsequent stages 
 of the process. When stripping has been properly effected, 
 the underlying metal exhibits a bright, smooth surface, giving 
 little evidence of the mixture having acted upon it. 
 
 Many platers, however, prefer to remove the nickel-coating 
 mechanically by brushing with emery. From depressions it is 
 as much as possible removed with the brush, after which the 
 object is freed from grease and pickled, and coppered before 
 nickeling. In this case the layer of copper serves for cement- 
 ing together the old and new deposits, and there will be no 
 danger of the new deposit peeling off in polishing. 
 
 It has also been proposed to strip by electrolysis by making 
 the object the anode in an old nickel bath. Attention is 
 equally necessary in conducting this process to guard against 
 any attack upon the basis-metal ; but since it is impossible to 
 prevent all action, no bath which is to be afterwards employed 
 for depositing the metal should be used for this purpose, as it 
 will become gradually charged with impurities. A 10 per 
 cent, solution of sulphuric acid in water may be equally readily 
 adapted to the electrolytic stripping. 
 
 As a remedy against the yellowish tone of the nickeling, 
 Pfanhauser recommends suspending the nickeled articles, im- 
 mediately after taking them from the nickel bath, as anodes in 
 a nickel bath acidulated with citric or hydrochloric acid, a piece 
 of sheet nickel serving as the cathode, and to allow the current 
 
284 ELECTRO-DEPOSITION OF METALS. 
 
 to act for a few seconds. It is claimed that thereby the basic 
 nickel salts separated together with the nickel, and to which, 
 according to Pfanhauser, the yellowish tinge is due, are dis- 
 solved, and the nickeling will show a pure white tone. 
 
 Defective nickeling. The following is a brief resume of the 
 principal defects which may occur in nickeling, as well as the 
 means of avoiding them: 
 
 1. The articles do not become coated with nickel, but acquire 
 discolored, generally darker, tones. Reason : The current is 
 either too feeble to effect the reduction of nickel, and the col- 
 oration is due to the chemical action of the nickel solution upon 
 the metals constituting the objects. This phenomenon is fre- 
 quently observed in nickeling zinc articles. Remedy : Increase 
 the current or diminish the area of suspended objects; also 
 examine whether the current actually passes into the bath, 
 otherwise clean the places of contact. 
 
 2. A deposition of nickel takes place, but it is dark or spotted 
 or marbled, even with a sufficiently strong current. Reasons : 
 The bath is either alkaline, which has to be ascertained by test- 
 ing with litmus-paper, and, if so, the slightly acid reaction of 
 the bath has to be restored by the addition of a suitable acid;. 
 or, the bath is too concentrated, in which case a separation of 
 crystals will be observed — this is remedied by diluting with 
 water; or, the nickel solution is very poor in metal, which can 
 be remedied by the addition of nickel salt; it should also be 
 tested as to the admixture of copper, the production of dark 
 tones being frequently due to this — in this case the bath is 
 allowed to work for some time, and if the content of copper is 
 inconsiderable a white deposit will soon be obtained ; or, the 
 cleaning and pickling of the articles have not been thoroughly 
 done, which is remedied by again cleaning them ; or, the con- 
 ducting power of the bath is insufficient, which is remedied by 
 the addition of a suitable conducting salt. 
 
 When freshly-prepared baths yield dark nickeling, it can gen- 
 erally be remedied by working the bath two or three hours, if 
 it is not over-concentrated and the cause, as above-mentioned,, 
 
DEPOSITION OF NICKEL AND COBALT. 285 
 
 lias to be looked for in a small content of copper in the nickel 
 salt. 
 
 3. A yellowish tinge of the nickeling. Reason : Alkalinity 
 of the bath. Remedy : See under 2 ; or, with cast-iron, an in- 
 sufficient metallic surface, which is remedied by repeating the 
 scratch-brushing; or, unsuitable composition of the bath. 
 
 4. The objects rapidly acquire a white deposit of nickel, but 
 the color soon changes to a dull gray-black, especially on the 
 lower edges and corners. Reason : Too strong a current. 
 Remedies : Regulating the current, or suspending more objects, 
 or uncoupling elements. Frequent turning of the articles. 
 
 5. The nickeling is white, but readily peels off by scratching 
 with the finger nail, or by the action of the polishing wheel. 
 Reasons : The current is too strong, which is remedied as under 
 4; or, the bath is too acid — this is remedied by the addition of 
 ammonia, potassium carbonate, or nickel carbonate, according 
 to the composition of the bath ; or, freshly-prepared nickel bath 
 or freshly-made additions, this being remedied by working the 
 bath and by very careful regulation of the current in nickeling 
 during the first days; or, insufficient cleaning and pickling, 
 which is remedied by thorough cleaning after removing the 
 defective deposit, or, if it cannot be entirely removed, copper- 
 ing. 
 
 6. Though nickeling may proceed in a regular manner, some 
 places remain free from deposit. Reasons : Either the surfaces 
 of some of the objects touch one another; or, are stained by 
 having been touched with dirty fingers ; or, air bubbles are 
 inclosed in cavities. Remedy : Removal of the causes. 
 
 7. The deposit appears with small holes. Reason : A de- 
 posit of particles of dust upon the objects. Remedy : Remove 
 the dust from the surface. When there is a general turbidity 
 of the bath in consequence of alkalinity, add the most suitable 
 acid, and boil and filter the bath ; or, insufficient removal of gas 
 bubbles from the objects. Remedy: Shake the object- rods by 
 blows with the finger. 
 
 8. Deposition takes place promptly upon the portions of the 
 
286 ELECTRO-DEPOSITION OF METALS. 
 
 objects next to the anodes, while deeper portions remain free 
 from nickel or become black. Reason: Too slight a distance 
 of the objects from the anodes. Remedy: Increasing the dis- 
 tance ; with large depressions, treatment with the hand-anode. 
 
 Refreshing nickel baths. — According to their composition, 
 the amount of work performed, and the anodes used, the baths 
 will in a shorter or longer time require certain additions in 
 order to keep their action constant. By "refreshing" is not 
 understood the small addition of acid or alkali from time to 
 time required for restoring the original reaction of the baths,, 
 but additions intended to increase the metallic content and the 
 diminished conductivity. 
 
 The metallic content is increased by boiling the bath with 
 some of the nickel salt used in its preparation, while the con- 
 ductivity is improved by adding, at the same time, so much 
 conducting salt as is necessary to restore the electro-motive 
 force originally required. Nothing definite can, of course, be 
 said in regard to the quantity of such additions, it being advis- 
 able to observe their effect on a small portion of the bath, so as 
 to be sure not to spoil the entire bath. 
 
 Nickel baths bear, as a rule, refreshing several times, but as 
 in the course of time they take up impurities, even when the 
 greatest care is exercised, it is best to refresh them at the 
 utmost twice, and then to renew them entirely. 
 
 The treatment of the articles after nickeling, as well as after 
 all electro-plating processes, has already been described, and 
 it is only necessary here to refer again to the fact, that with 
 articles of iron and steel, immersion in boiling water before 
 drying in sawdust is absolutely necessary, and subsequent 
 drying in a drying chamber is also a great safeguard as regards 
 stability and protection against rust. 
 
 Nickel deposits are polished upon felt wheels or bobs of cloth, 
 muslin or flannel, with the use of Vienna lime, rouge, Victor 
 white polish, etc. (See "Polishing," p. 218.) To give the 
 objects the highest luster possible, it is advisable finally to 
 polish them upon a woolen brush with dry Vienna lime. 
 
DEPOSITION OF NICKEL AND COBALT. 287 
 
 Sharp edges, corners and raised portions should be held only 
 with slight pressure against the polishing wheels, they being 
 more strongly attacked by them than flat surfaces. The latter 
 can stand a stronger pressure without fear of cutting through 
 the deposit, provided the latter is of sufficient thickness and 
 hardness. 
 
 Knife blades and surgical instruments with sharp edges re- 
 quire special care in polishing, which will later on be referred to. 
 
 Cleansing polished objects. After polishing, the nickeled ob- 
 jects, especially those with depressions, have to be freed from 
 polishing dirt by brushing with hot soap-water, or dilute hot 
 caustic lye, or benzine, then rinsed in hot water and dried in 
 clean, fine sawdust. 
 
 Calculation of the nickeling operation. Many inquiries re- 
 garding the mode of calculating the price to be charged for 
 nickeling objects give rise to the following remarks: If the 
 same article with the same definite surface is always to be 
 nickeled, the calculation is quite simple. From the current- 
 strength and the time required for nickeling, the weight of the 
 nickel-deposit can be readily determined by keeping in view 
 that 1 ampere theoretically deposits in 1 hour 1.1 gramme of 
 nickel, or about 1 gramme if the current output be taken into 
 consideration. The value of the ascertained weight has to be 
 determined by taking the cost of the anodes as the basis, and 
 from this is calculated the constant price of the separate piece. 
 To this has to be added the wages for grinding, polishing and 
 nickeling, as well as the amount of power required, which, 
 according to the motors in use, has to be established by a 
 special calculation ; further, the materials used for grinding, 
 polishing, freeing from grease, etc., and a certain profit. 
 However, in most cases it is scarcely possible to make such 
 detailed calculations in electro-plating establishments in which 
 the most diverse objects have to be nickeled, because, on the 
 one hand, the determination of the surface of the separate 
 objects would be difficult and time-consuming, and on the 
 other, it would be very troublesome, in consequence of the 
 
288 ELECTRO-DEPOSITION OF METALS. 
 
 change of the object-surfaces in the bath, to keep an accurate 
 account of the current- strength and time required for the 
 separate objects. 
 
 To attain the object, it has in practice proved the simplest 
 plan to take as a basis the wages paid to the grinder and 
 polisher, and multiply them by 4, in order to obtain the selling 
 price of the work furnished. The selling value thus deter- 
 mined includes all expenses and a fair profit. Somewhat more 
 will have to be allowed for particularly complicated objects 
 which require assistance with the hand-anode. This mode of 
 calculation has on the whole been found to answer for solid, 
 heavy nickeling. For light nickeling — coloring white in the 
 nickel bath — the selling value might be too high. An extra 
 charge will of course have to be made for repairing articles 
 which are received for nickeling. 
 
 When objects already ground and polished are sent in to be 
 nickeled, the above-mentioned mode of calculation is of course 
 not applicable. In that case it has to be calculated how much 
 a charge of a bath must bring, in order to cover expenses and 
 a certain profit, and from that the approximate selling value of 
 the nickeling work may be determined. 
 
 Nickeling small and cheap objects in large quantities. This is 
 effected by stringing the objects, if feasible, upon a copper wire, 
 and placing a large glass bead between every two objects, to 
 prevent the surfaces from sticking together in the bath. Such 
 objects being generally only slightly nickeled, it suffices to 
 allow them to remain for a few minutes only in the bath with a 
 strong current, it being advisable to diligently shake the bun- 
 dles in order to effect a change of position of the objects and 
 prevent their touching one another, notwithstanding the glass 
 bead placed between them. 
 
 Very small objects, such as rivets, pins, etc., which cannot be 
 strung upon wire, are nickeled in dipping baskets of stone ware 
 or wire. To the bottom of the dipping basket is secured a 
 copper or brass wire, which is connected with the object-rod, 
 and the articles, not too many at a time, are then placed in the 
 
DEPOSITION OF NICKEL AND COBALT. 
 
 289 
 
 basket. During the operation the articles must be constantly 
 shaken, and as nickel baths, as a rule, do not conduct suffi- 
 ciently well to properly nickel the objects in the basket, it is 
 advisable to hold with one hand an anode, connected by a 
 flexible wire with the anode-rod, in the basket, while the other 
 hand holds the basket (Fig. 121) and constantly shakes and 
 turns it. For nickeling in the dipping basket it is further ad- 
 visable to heat the nickel bath. 
 
 Fig. 121. 
 
 In place of a stoneware dipping basket, a basket tray of 
 brass wire, Fig. 122, to which are soldered two copper wires 
 for suspending it to the object-rod, may preferably be used. 
 From the soldered places a few copper wires extend to the 
 bottom of the basket. To prevent the basket from becoming 
 covered with nickel it is coated with asphalt varnish. At a 
 •distance of about 2^ to 3 inches below the basket an anode is 
 arranged in horizontal position, while with one hand a hand- 
 anode is held over the small articles in the basket. By this 
 arrangement a thicker deposit is more rapidly obtained, especi- 
 19 
 
290 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 ally if, with the other hand, the articles are constantly stirred 
 by means of a glass or wooden rod. 
 
 Warren has described a solution of nickel and one of cobalt 
 which can be decomposed in a simple cell apparatus. With 
 the nickel solution, which was prepared by dissolving 100 parts 
 by weight of nickel chloride in as little water as possible and 
 mixing with a concentrated solution of 500 parts of Rochelle 
 salts, no satisfactory results could be obtained. The cobalt 
 solution however yielded good results, and would seem to be 
 suitable for electro-plating small objects in large quantities. It 
 will be further referred to under "Deposition of Cobalt." 
 
 Fig. 122. 
 
 In the last few years a number of contrivances for electro- 
 plating small articles in large quantities have been patented, 
 the articles to be plated being, as a rule, contained in a revolv- 
 ing perforated drum. The drums of some of the contrivances 
 are constructed of non-conducting material so that the articles 
 receive the current through copper or other metallic strips, 
 which are secured in the inside walls of the drums, and are 
 brought in various ways in contact with the source of current. 
 In other contrivances, for instance, the apparatus of Smith & 
 Deakin, metallic pins capable of being turned around the shaft, 
 which is in contact with the negative pole of the source of 
 current, reach to the layer of articles in the drum, and effect 
 the re-transmission of the current. Since in the contrivances 
 mentioned the anodes are placed outside of the drum, and the 
 latter acts as a diaphragm with great resistance, a very high 
 electro-motive force is required for the production of the de- 
 
DEPOSITION OF NICKEL AND COBALT. 29 1 
 
 posit, independent of the fact that the articles being in constant 
 motion already require an essentially higher electro-motive 
 force. 
 
 In another class of apparatus, the six or eight-cornered drum 
 is constructed of the same metal which is to be deposited. 
 Every metal plate forming one side is insulated from the next 
 plate. The plates which, while the drum is revolving, occupy 
 the lowest position and upon which the articles for the time 
 being rest, are brought into contact with the negative pole of 
 the source of current by a commutator of special construction, 
 while the positive current is carried to the plates occupying a 
 
 Fig. i 23. 
 
 . / 
 
 higher position, they thus acting as anodes. In this type of 
 apparatus the high resistance due to the arrangement of the 
 anodes on the outside is overcome, but the commutator with 
 the sliding contact constitutes a very sensitive part of the 
 construction. 
 
 Fig. 123 shows the improved mechanical electro-plating 
 apparatus patented and manufactured by Hanson & Van 
 Winkle Co., Newark, N. J. The apparatus complete consists 
 
292 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 of wood tank, revolving plating barrel, all necessary rods and 
 ■connections and a special patent countershaft. Both the 
 •electrical and mechanical features have received close attention 
 and have been much simplified. The barrel is entirely sub- 
 merged, thus permitting a much larger quantity of work in 
 each batch. The drive is from the outside, thus avoiding the 
 use of belts running in the solution. Two speeds are provided 
 
 Fig. 124. 
 
 for. The barrel is removable at any time without throwing oft" 
 the belt or interfering with the drive. 
 
 In connection with this apparatus the use of patent curved 
 elliptic anodes, as shown in the illustration is recommended. 
 The anode is curved to fit the periphery of the revolving bar- 
 rel, and when an anode is hung on each side of the tank, the 
 barrel holding the work is equidistant at all times from the 
 anode; hence a regular and even deposit is obtained. These 
 anodes are cast in all metals with square copper hooks at- 
 tached. 
 
DEPOSITION OF NICKEL AND COBALT. 293 
 
 A mechanical plating apparatus patented and manufactured 
 by Zucker & Levett & Loeb Co., New York, is brought into 
 commerce under the name of the rotoplater, Fig. 124. It con- 
 sists of a wooden tank to hold the solution and anodes, also a 
 hexagonal cylinder, which contains the work to be plated. 
 The cylinder is provided with sliding perforated panels of wood 
 or hard rubber, and is revolved slowly in the solution by means 
 of a belt running from the ordinary form of counter-shaft. The 
 cylinder is also fitted with a crank and gear by which it is 
 lifted clear of the solution when receiving or discharging work, 
 and this device acts without interfering in any way with the 
 drive, and at the same time dispenses with the need for an 
 overhead hoist. The machine is entirely self-contained, and 
 needs only to be placed in position and connected with the 
 dynamo and countershaft to be ready for use. Curved anodes 
 are used, so that the work and the anode surface are equi- 
 distant at all times. 
 
 The above-described mechanical electro-plating devices are 
 equally well adapted for zincking articles in large quantities, 
 such as screws, nails, rivets, etc., as well as for brassing, 
 coppering, etc. 
 
 Nickeling sheet-zinc. The nickeling of sheet-zinc has been 
 surrounded with a great deal of mystery by those engaged in 
 its manufacture, which may, perhaps, be excusable on the 
 ground that there is scarcely another branch of the electro- 
 plating industry in which experience had to be acquired at the 
 sacrifice of so much money and time as in this. Nevertheless, 
 the nickeling of sheet-zinc makes no greater demand on the in- 
 telligence of the operator than any other electro-plating process, 
 it requiring only an accurate consideration of the relations of 
 the electric behavior of zinc towards nickel ; consequently, a 
 knowledge of the strength of the counter-current and of the 
 chemical behavior of zinc towards the nickel solution, which 
 may readily dissolve the zinc ; further, a correct estimation of 
 the proper current-strength required for a determined zinc sur- 
 face, as well as of the proper anode-surface, and the most suit- 
 able composition and treatment of the nickel bath's. 
 
294 ELECTRO-DEPOSITION OF METALS. 
 
 With due observation of. these conditions, the nickeling of 
 sheet-zinc is accomplished as readily as that of other metals ; 
 and the suggestions to first cover the sheets in a bath with a 
 strong current, and finish nickeling with a weaker current, or to 
 amalgamate the zinc before nickeling, need not be considered. 
 
 Below the conditions required for nickeling sheet-zinc, and 
 the execution of the process itself, together with the pre- 
 liminary and final polishing of the sheets, will be found fully 
 described. 
 
 The preliminary grinding or polishing is effected upon broad 
 cloth wheels (buffs) formed of separate pieces of cloth. The 
 polishing lathes run with their points in movable bearings se- 
 cured in a hanging cast-iron frame by a set screw and safety 
 keys, or preferably as shown in Fig. io6 5 since with this con- 
 struction an injury to the grinder by the lathe jumping out is 
 impossible. 
 
 The bobs, when new, have on an average a diameter of 1 2 to 
 16 inches, and a width of 5% to 8 inches. The principal point 
 in the construction of these bobs is uniform weight on all sides, 
 quiet running and the possibility of a good polish without 
 great exertion depending on this. Bobs not well balanced run 
 unsteadily and jump, thereby producing fine scratches upon the 
 sheet. The bobs are constructed as follows : A square piece 
 of cloth if folded fourfold and the closed point cut off with a 
 pair of scissors, so that on unfolding the cloth, the hole produced 
 by the cut is exactly in the center of the cloth disk. According 
 to the diameter of the spindle more or less is cut away, but in 
 every case just sufficient for the piece of cloth to be conven- 
 iently pushed upon the spindle. The latter, which is provided 
 with a pulley and a hoop against which the pieces of cloth fix 
 themselves, as well as with a nut and screw for securing them, is 
 vertically fastened in a vise, and the separate pieces of cloth are 
 pushed upon it so that the second piece placed in position 
 forms an angle of about 30 (Fig. 125) with the first, the 
 operation being thus continued until the bob has the desired 
 width. Next a small, but very strong iron disk is laid upon 
 
A 
 
 Fig. 
 
 125. 
 
 i '<», • 
 
 . !.,'-• 
 
 "■«; •' «.*i 
 
 DEPOSITION OF NICKEL AND COBALT. 295 
 
 the cloth bob, and the separate pieces are pressed together as 
 
 firmly as possible with the screw. The 
 
 spindle is then placed in the bearings, and 
 
 after adjusting the belt upon the pulley the 
 
 bob is revolved, a sharp knife being held 
 
 against it to remove the projecting corners. 
 
 In polishing sheet-zinc the bobs make 
 
 2,200 to 2,500 revolutions per minute, 
 
 according to whether finely rolled or 
 
 rougher sheets are to be polished. 
 
 For the purpose of preparatory polishing, the operator places 
 the sheet upon a support of hard wood of the same size and 
 form as the sheet, and grasps the two corners of the sheet 
 nearest to his body, together with the support, with the hands, 
 applying with the balls of the hands the necessary pressure to 
 hold the sheet upon the support. The lower half of the sheet, 
 that furthest from the body, rests upon the knees of the opera- 
 tor, and with them he presses the sheet against the polishing 
 wheel, constantly moving at the same time, and at not too slow 
 a rate, the knees from the right to the left, then from the left to 
 the right, and so on. Previous to polishing, a streak of oil 
 about two inches wide is applied by means of a brush to the 
 center of the sheet in the visual line of the operator, and the 
 revolving bob is impregnated with Vienna lime by holding a 
 large piece of it against it, when polishing of the lower portion 
 of the sheet begins. When about § of the surface has thus 
 been polished, the sheet is turned round and the remaining 
 portion subjected to the same process. The sheet is then 
 closely inspected to see whether there are still dirty or dull 
 places, and, if such be the case, it is polished once more, after 
 moistening it with some oil and again impregnating the bob 
 with Vienna lime. The sheet being sufficiently polished, the 
 oil and polishing dirt are removed by dry polishing, after pro- 
 viding the bob with sufficient Vienna lime, so that the sheets 
 when finished show no streaks of dirt or oil. 
 
 Sheets 50x50, 100x50, and also 150x50 centimeters, can 
 
296 ELECTRO-DEPOSITION OF METALS. 
 
 in this manner be readily polished, but it is a difficult feat, 
 mostly subject to the risk of producing bent places, to polish 
 sheets 6 feet long upon the knees. Numerous attempts have 
 therefore been made to construct automatic machines for con- 
 veniently polishing sheets 12 or more feet long. 
 
 Several such automatic polishing machines have been de- 
 scribed and illustrated in the fifth edition of this book, but, 
 while they furnish a quite good polish, they have, on the one 
 hand, the drawback that thin sheets are readily creased or 
 wound around the polishing roll, and, on the other hand, that 
 the sheets are with great violence thrown out by the polishing 
 roll if this is not prevented by placing another sheet over a 
 portion of the sheet to be polished, and passing it together 
 with the latter under the roll. This, however, has the draw- 
 back that the covered portion of the first sheet is not polished, 
 and has to be again passed under the polishing roll, and the 
 place where the edge of the second sheet has rested upon the 
 first sheet shows a mark formed by pressure, which, as a rule, 
 is not desirable. 
 
 The polishing machine constructed according to the patent 
 of Hille and Midler * avoids the above-mentioned drawbacks 
 by obliquely standing polishing rolls. In KorBer's f construc- 
 tion two polishing rolls move in opposite directions. The 
 sheets are pressed against the rolls by an oscillating table so 
 that first one and then the other portion of the table is alter- 
 nately advanced towards the corresponding polishing roll. 
 
 In the construction patented by Dr. Langbein & Co., the 
 drawbacks of throwing out and crumpling the sheets is over- 
 come by the arrangement of two polishing bobs, which alter- 
 nately stand still and revolve, however, in opposite directions. 
 The table consists of two movable halves; while one of the 
 halves, in an elevated position, presses the sheet carried by the 
 transport-rolls against the revolving polishing bob, the other 
 half is lowered and its polishing bob remains stationary. 
 
 * German patent, 49736. t German patent, 89648. 
 
DEPOSITION OF NICKEL AND COBALT. 297 
 
 When a certain length of the sheet has been polished the 
 second polishing bob revolving in an opposite direction is put 
 in action, a constant stretching of the sheet being thereby 
 effected. 
 
 Freeing zinc sheets from grease . This is best effected in two 
 operations, first dry and then wet. For the dry process use a 
 very soft piece of cloth and, after dipping it in Vienna lime, 
 very finely pulverized and passed through a hair sieve, rub 
 over the sheet in the direction of a right angle to the polishing 
 streaks, applying a very gentle pressure. For the wet process, 
 dip a moist piece of cloth, or a soft sponge free from sand, into 
 a paste of impalpable Vienna lime, whiting and water, and go 
 carefully over the sheet so that no place remains untouched. 
 Then rinse the sheet under a powerful jet of water, best under 
 a rose, being particularly careful to remove all the lime, going 
 over the sheet, if necessary, with a soft, wet rag, and ob- 
 serving whether all parts appear evenly moistened. If such be 
 the case, cleaning is complete, otherwise the sheet has to be 
 once more treated with lime. 
 
 If the sheets are to be nickeled on only one, side, two of them 
 are placed together with their unpolished sides and fastened on 
 the two upper corners with binding screws to which is soldered 
 a copper strip about 0.39 inch wide, by which they are sus- 
 pended to the conducting rods. Plating is then at once pro- 
 ceeded with, without allowing the sheets to remain exposed to 
 the air longer than is absolutely necessary. Special care must 
 be had that the lime does not dry, as this would produce stains. 
 
 With sheets 50 x 50 centimeters, two binding screws suffice 
 for suspending the sheets to the conducting rods. With sheets 
 100 centimeters long, three binding screws are generally used, 
 with sheets 150 centimeters long, five, and with lengths of 200 
 centimeters, six, or more, so that the current required for nick- 
 eling finds a sufficient cross-section. 
 
 Some manufacturers nickel the cleansed sheet without pre- 
 vious coppering or brassing, and claim special advantages for 
 such direct nickeling. This may be done with a bath of nickel 
 
298 ELECTRO-DEPOSITION OF METALS. 
 
 sulphate and potassium citrate without, or with a greater or 
 smaller addition of ammonium chloride, according to the surface 
 to be nickeled and the intensity of current at disposal. How- 
 ever, sheet-zinc directly nickeled does not show the warm, full 
 tone of sheets previously coppered or brassed ; besides, direct 
 nickeling requires a far more powerful current, so that it is not 
 even more economical. 
 
 For the nickeling process itself, it is indifferent whether the 
 sheets are previously coppered or brassed, but the choice be- 
 tween the two is controlled by a few features which must be 
 mentioned. The nickel deposit upon brassed sheets shows a 
 decidedly whiter tone than that upon coppered sheets, and 
 brassing would deserve the preference if this process did not 
 require extraordinarily great care in the proper treatment of the 
 bath, the nickel deposit readily peeling off, generally in the bath 
 itself, which seldom or never occurs with coppered sheet, and 
 then may generally be considered due to insufficient cleaning 
 or other defective manipulation. 
 
 This peeling-off of the nickel deposit may be prevented by 
 giving due consideration to the conditions, and avoiding, on the 
 ■one hand, too large an excess of potassium cyanide in the brass 
 bath, and, on the other, by regulating the current so that no 
 pale yellow or greenish brass is precipitated. Since nickeling 
 with a strong current requires only a few minutes for a deposit 
 of sufficient thickness capable of bearing polishing, it is gener- 
 ally desired to brass the sheets at the same time, so that the 
 operation may proceed rapidly and continuously. To do this, 
 a very powerful current has to be conducted into the brass bath, 
 the result being that a deposit with a larger content of zinc and 
 a correspondingly lighter color is formed, but also with a 
 coarser, less adherent structure, and this is the principal reason 
 why the nickel deposit, together with the brass deposit, peels 
 off. To avoid this, the brassing must be done with a current 
 so regulated that the deposit precipitates uniformly, adheres 
 firmly, and is not porous ; the correct progress of the operation 
 is recognized by the color being more like tombac, and not 
 
DEPOSITION OF NICKEL AND COBALT. 299 
 
 pale yellow or greenish. When brass has to be done quickly 
 the content of copper in the brass bath must be increased to 
 such an extent that a powerful current produces a deposit of 
 the above-mentioned color, and, hence, too large an excess of 
 potassium cyanide must be strictly avoided. 
 
 It will' be seen that brassing requires a certain attention 
 which is not necessary in coppering, and therefore the latter is 
 to be preferred. 
 
 For coppering, one of the baths, formulas III to VII, given 
 under "Deposition of Copper" can be used, to which, for this 
 special purpose, more potassium cyanide may be added. The 
 sheets should remain in this bath no longer than required to 
 uniformly coat them with a beautiful red layer of copper, and 
 under no circumstances must they be allowed to remain until 
 the coppering commences to become dull or even discolored. 
 They should come from the bath with a full, or at least half, 
 luster. 
 
 When taken from the copper bath the sheets are thoroughly 
 rinsed in a large water reservoir, the contents of which must be 
 frequently renewed, care being had to remove any copper 
 solution adhering to the unpolished sides which are not to be 
 nickeled, since that would soon spoil the nickel bath. The 
 sheets are then immediately brought into the nickel bath, it 
 being best to suspend two, three, or four of them at the same 
 time, to prevent one from being more thickly nickeled than the 
 other, and take them out the same way. In suspending the 
 sheets in the bath, care should be had to bring them as soon as 
 possible in contact with the conducting rod, a neglect of this 
 rule being apt to produce blackish streaks and stains. 
 
 The tanks used for nickeling sheet-zinc are generally about 
 7 feet long in the clear, 1^3 feet wide, and 2]/^ to 2^ feet deep. 
 In such tanks sheets 6^ feet long and i 1 /^ feet wide can be 
 conveniently nickeled. 
 
 With the use of a nickel bath according to formula VIII, p. 
 257, for nickeling sheet-zinc, the most suitable electro-motive 
 force is 3.5 volts and I ampere current-density per square deci- 
 
300 ELECTRO-DEPOSITION OF METALS. 
 
 meter, in order to obtain in three minutes an effective deposit. 
 After working for some time this bath also requires a stronger 
 electro-motive force. 
 
 If zinc is to be nickeled in baths conducting with greater 
 difficulty, for instance, in a simple solution of nickel-ammon- 
 ium sulphate without the addition of conducting salts, or in 
 baths conducting boric acid, 1.2 to 1.5 amperes and 7 volts 
 must be allowed for 1 square decimeter, if nickeling is to be 
 effected in the above-mentioned space of time. 
 
 For nickeling sheet-zinc, rolled anodes are, as a rule, only 
 used, except when working with baths containing boric acid. 
 The anode surface must at least be equal to that of the zinc 
 surface. The distance between the anodes and the sheets 
 should be from 3 to 3^ inches, and when the current-strength 
 is somewhat scant the distance may be reduced to 2^ inches. 
 The nickel anodes have to be taken from the bath once daily 
 and scoured bright with scratch- brushes and sand. For the 
 rest, all the rules given for nickel anodes are valid. 
 
 Baths used for nickeling sheet-zinc soon become alkaline in 
 consequence of the powerful current used, which is shown by 
 red litmus-paper turning blue. The alkalinity also manifests 
 itself by the bath becoming turbid and the nickeling not turn- 
 ing out pure white. The slightly acid reaction required is 
 restored by citric acid solution. The appearance of the dreaded 
 black streaks and stains is due either to the current itself being 
 too weak, or to its having been weakened by an extremely 
 great resistance of the nickel bath ; also to an insufficient me- 
 tallic surface of the anodes, which may be either too small or 
 not sufficiently metallic on account of tarnishing; and finally 
 to an excessive alkalinity of the bath, or insufficient contact of 
 the hooks with the connecting rods. 
 
 The metallic content of the bath must from time to time be 
 strengthened by the addition of nickel salt, and the bath filtered 
 at certain intervals. When the conductivity abates, it has to 
 be restored by the addition of conducting-salt. 
 
 When the sheets have been sufficiently nickeled, they are 
 
DEPOSITION OF NICKEL AND COBALT. SOT 
 
 allowed to drain off, then plunged into hot water, and, after re- 
 moving the binding screws, dried by gentle rubbing with fine 
 sawdust free from sand and passed through a fine sieve to 
 separate pieces of wood. In all manipulations, the unnickled 
 sides are placed together, while a piece of paper of the size and 
 form of the sheets is laid between the nickeled sides. 
 
 The nickeled sheets are finally polished, which is affected by 
 placing them upon supports and pressing against the revolving 
 bob as previously described, the sheets being, however, only 
 moderately moistened with oil, and not too much Vienna lime 
 applied to the bob. Polishing is done first in one direction and 
 then in another, at a right angle to the first. After polishing, 
 the sheets are finally cleansed with a piece of soft cloth and 
 impalpable Vienna lime, when they should show a pure white 
 lustrous nickeling, free from cracks and stains, and bear bend- 
 ing and rebending several times without the deposit of nickel 
 breaking or pealing off. 
 
 Nickeling tin-plate. — For handsome and durable nickeling, 
 tin-plate also requires previous coppering. Deposition is 
 effected with a less powerful current than for sheet-zinc. Free- 
 ing from grease is done in the same manner as above described. 
 
 For preparatory polishing of tin-plate, the use of a polishing 
 compound free from lime and grease is recommended, since a 
 good polish on tin cannot be obtained with Vienna lime and 
 ■oil. Nickeled tin-plate may be polished with Vienna lime and 
 stearine oil. 
 
 It may be here mentioned as a remarkable fact that freshly 
 nickeled tin-plate will stand every kind of manipulation, such 
 as stamping, edging, pressing, etc., but after having been stored 
 for a few months, the layer of nickel frequently peels of by 
 these operations. 
 
 . Nickeling copper and brass sheets. — The treatment of these 
 sheets differs from that of sheet-zinc in that the rough sheets 
 are first brushed with emery and then polished with the bob. 
 After treating the sheets with hot caustic lye or lime-paste, 
 they are pickled by brushing them over with a solution of I 
 
302 ELECTRO-DEPOSITION OF METALS. 
 
 part of potassium cyanide in 20 parts of water. They are then 
 thoroughly and rapidly rinsed, and immediately brought into 
 the bath. To avoid peeling off, the current-density should not 
 exceed 0.4 ampere. 
 
 Nickeling sheet-iron and sheet-steel. — Only the best quality of 
 sheet should be used for this purpose. After rolling, the 
 sheets are freed from scales by pickling, then passed through 
 the fine rolls, and finally again pickled. If the nickeled sheets 
 are not to exhibit a high degree of polish, it suffices to brush 
 them before nickeling with a large, broad, fiber brush (p. 202) 
 and emery No. 00. But for a high luster, such as is generally 
 demanded, the sheets have first to be ground. For fine grind- 
 ing the pickled sheets, broad massive wood rolls, turned and 
 directly glued with emery, are used. These wheels are 10 to 12 
 inches in diameter, and 2 to 4 or more inches long, according 
 to the size of the sheets. For the first grinding, the wheels are 
 coated with glue and rolled in emery No. 100 to 120, according 
 to the condition of the sheets, while emery No. 00 is applied to 
 the wheels used for the fine grinding. The grinding is suc- 
 ceeded by brushing, as described on p. 203. 
 
 After preparing a sufficiently smooth surface, the sheets are 
 at once rubbed with a rag moistened with petroleum, or, if pre- 
 ferred, with a rag and pulverized Vienna lime. They are then 
 scoured wet in the manner described for sheet-zinc. The scour- 
 ing material must be liberally applied, especially if the sheets 
 are to be directly nickeled without previous coppering, the 
 latter being, however, quite advisable. After rinsing off the 
 lime-paste, the sheets are without loss of time brought into the 
 nickel bath. 
 
 For nickeling, a bath free from chlorine should by all means 
 be used in order to protect the sheets from rusting. The cur- 
 rent-density should be 0.4 ampere, with which the sheets 
 acquire in ^ hour a deposit of sufficient thickness. With the 
 use of cold quick nickeling baths the same thickness of the 
 deposit may be obtained in 15 minutes. It is not advisable to 
 attempt to obtain a heavy deposit in a shorter time, because it 
 
DEPOSITION OF NICKEL AND COBALT. 303. 
 
 would lack density which, by reason of greater protection 
 against rust, is the principal requisite for nickeled sheet-iron. 
 
 After nickeling, the sheets are rinsed in clean water, then 
 plunged into hot water, and dried by rubbing with warm saw- 
 dust. After this operation, it is recommended to thoroughly 
 dry the sheets in an oven heated to between 176 to 21 2° F., 
 to expel any moisture from the pores, and then to polish them 
 with Vienna lime and oil, or with rouge. 
 
 Nickeling wire. Nickeling of wire of iron, brass or copper 
 is scarcely ever done on a large scale. It is, however, believed 
 that the nickeling of iron and steel wires — for instance, piano- 
 strings — might be of advantage to prevent rust, or at least to 
 retard the commencement of oxidation as long as possible. 
 
 To nickel single wires cut into determined lengths, according 
 to the general rules already given, is simple enough ; but this 
 method cannot be pursued with wire several hundred yards 
 long, rolled in coils, as it occurs in commerce. Nickeling the 
 wire in coils, however, cannot be done, as only the upper wind- 
 ings exposed to the anodes would acquire a coat of nickel. 
 Hence it becomes necessary to unwind the coil, and for con- 
 tinuous working pass the wire at a slow rate through the cleans- 
 ing and pickling baths, as well as the nickel bath, and hot 
 water reservoir, as shown in Fig. 126, in cross-section, and in 
 Fig. 127, in ground plan. 
 
 The unwinding of the wire is effected by a slowly revolving 
 shaft, upon which the nickled wire again coils itself; but in the 
 illustration the shaft is omitted. In Fig. 127 four wires run 
 over the four rolls a, mounted upon a common shaft, to the 
 rolls b upon the bottom of the tank A, whereby they come in 
 contact with a thickly-fluid lime-paste in the vat, and are freed 
 from grease. From the rolls b the wires run through the 
 wooden cheeks i, lined with felt, which retain the excess of 
 lime-paste, and allow it to fall back into the tank. The wires 
 then pass over the roll c to the roll d. Between these two rolls 
 is the rose g, which throws a powerful jet of water upon the 
 wires, thereby freeing them from adhering lime-paste. The 
 
;o4 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 roll d, as well as its axis, is of brass, and to the latter is con- 
 nected the negative pole of the battery or dynamo, so that by 
 
 - » 
 
 w r 
 
 ■CF 
 
 'w" 
 
 
 i m «: 
 
 Li, 
 
 
 -v 
 li 
 
 carrying the wires over the roll d, negative electricity is con- 
 ducted to them. From the roll d, the wires run over the roll- 
 
DEPOSITION OF NICKEL AND COBALT. 305 
 
 bench s (Fig. 126) to the tank C, which contains the nickel 
 solution, so that they are subjected to the action of the anodes 
 arranged in this tank on both sides of the wires. The wires then 
 pass over the roll e, are rinsed under the rose h, and run finally- 
 through a hot-water reservoir and sawdust (these two appara- 
 tuses are not shown in the illustration), to be again wound in 
 coils. In case a high polish is required, the nickeled wires may 
 be run under pressure through leather cheeks dusted with 
 Vienna lime. 
 
 Nickeling knife-blades, sharp surgical instruments, etc. Con- 
 siderable trouble is frequently experienced in nickeling sharp- 
 edged instruments, the edges and points being spoiled either 
 by the deposit of nickel or in polishing. And yet such instru- 
 ments can be readily nickeled in such a manner that the edges 
 remain in as good condition as before. 
 
 If new instruments which have never been used are to be 
 nickeled, no special preparation is required, it being only nec- 
 essary to free them at once from grease and bring them into 
 the bath. But instruments which have been used or, by bad 
 treatment have become partly or entirely covered with rust, 
 must be first freed from rust by chemical or mechanical treat- 
 ment, and then polished. The marks left by the stone or emery 
 wheel are effaced by means of the circular brush, this treatment 
 being necessary to obtain perfect nickeling. But, in brushing, 
 the edges are rendered dull if special precautionary measures 
 are not used. For instance, the edge of a knife-blade must 
 never come in contact with the brush. This is prevented by 
 firmly pressing the blade flat upon a soft support of felt or 
 cloth, so that the edge sinks somewhat into the support, with- 
 out, however, cutting into it. The edge is then held downward, 
 and thus together with the support brought against the revolv- 
 ing brush. In this manner the blades may be vigorously 
 brushed without fear of spoiling the edges. 
 
 The treatment for giving them a high polish after nickeling is 
 the same. Freeing from grease may be done in the usual 
 manner with lime-paste ; but must also be effected upon a soft 
 20 
 
306 ELECTRO-DEPOSITION OF METALS. 
 
 support, the same as in polishing. After thorough rinsing in 
 clean water, the separate pieces, without being previously cop- 
 pered, are brought directly into the nickel bath, the composi- 
 tion of which must, of course, be suitable for nickeling steel 
 articles. The instruments are first coated with the use of a 
 strong current, so that deposition takes place slowly and with 
 great uniformity. 
 
 In suspending the articles in the bath, care should be had 
 that neither a point nor an edge is turned towards the anodes. 
 It is best to use a bath with anodes on one side only, and to 
 suspend the blades with their backs towards the anodes. If, 
 for any reason, the instruments are to be suspended between 
 two rows of anodes, the edges should be uppermost, as near as 
 possible to the level of the bath ; but they should never hang 
 deep or downwards. 
 
 These precautionary measures may be omitted by using for 
 nickeling such articles with sharp edges, the bath consisting of 
 nickel sulphate and sodium citrate, which has been previously 
 mentioned. In this bath, the edges and points of the instru- 
 ments do not burn as readily as in other nickel baths, and the 
 deposited nickel being soft, it does not show a tendency to 
 peeling off when, after nickeling, the edges of the instruments 
 are sharpened. 
 
 The plated instruments are given a fine luster by polishing, 
 but during this operation they must always be exposed upon 
 a soft support, as above described, to the action of a felt wheel, 
 or, still better, of a cloth bob. 
 
 In nickeling skates it is advisable to suspend them so that the 
 runners hang upwards and that the running surfaces are level 
 with the surface of the bath, because if the deposit upon the 
 running surfaces is too thick, it peels off readily when injured 
 by grains of sand upon the ice. 
 
 Nickeling of soft alloys of lead and tin, with or without addi- 
 tion of antimony, as are used for siphon-heads, etc., is effected, 
 in case the objects have already a high luster, by freeing them 
 from grease with whiting and a small quantity of Vienna lime, 
 
DEPOSITION OF NICKEL AND COBALT. 307 
 
 then rinsing in water, lightly coppering, or better, brassing, and 
 finally nickeling in a bath containing chlorine. 
 
 If the objects require preparatory polishing, use a polishing 
 compound free from lime and grease, as given under nickeling 
 of tin-plate, rinse with benzine, immerse in hot water, and free 
 from grease with whiting and Vienna lime. Then brass, nickel: 
 and polish. Direct nickeling without previous brassing is not 
 advisable, waste in consequence of peeling off being frequently 
 the result. 
 
 Nickeling printing plates (stereotypes, cliches, etc.). The ad- 
 vantages of nickeling stereotypes, etc., over steeling will be 
 referred to under "Steeling," and hence only the most suitable 
 composition of the nickel baths and the manipulations required 
 will here be given. 
 
 The nickel baths according to formula I (page 252) and 
 formula VII (page 256) are the most suitable for simple 
 nickeling, because the ammonium sulphate not being present 
 in too great an excess, as well as the presence of boric acid, 
 causes the nickel to separate with considerable hardness. With 
 nickeled stereotypes three times as large an addition can be 
 printed as with plates of the same material not nickeled. 
 
 Hard nickeling. It being a well-known fact that a fused 
 alloy of nickel with cobalt possesses greater hardness than 
 either of the metals by themselves, experiments proved that an 
 electro-deposited nickel-cobalt alloy exhibited the same be- 
 havior, the greatest degree of hardness being attained with an 
 addition of cobalt varying between 25 and 30 per cent. For 
 this deposit the term hard nickeling is proposed, the most suit- 
 able bath for the purpose being prepared according to the 
 following formula : 
 
 Nickel-ammonium sulphate 21.16 ozs., cobalt-ammonium 
 sulphate 5.29 ozs., crystallized boric acid 8.8 ozs., water 10 to 
 12 quarts. 
 
 To prepare the bath dissolve the constituents by boiling as 
 given under formula VII, p. 256. In case the metal salts should 
 contain free acids add, previous to the addition of the boric 
 
3o8 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 acid, a small quantity of nickel carbonate. The boric acid 
 must not be neutralized and the bath should work with its acid 
 reaction. Mixed anodes in the proportion of ^ cast and ^ 
 rolled, are to be suspended in the bath. 
 
 The bath prepared according to formula No. II deserves the 
 preference, it yielding a harder deposit than bath No. I. 
 
 For the rest, the treatment of the baths is the same as that 
 given for nickel baths of similar composition ( pp. 252 and 256), 
 and the process of hard nickeling does not essentially differ 
 
 Fig. 128. 
 
 from ordinary nickeling. The suspending hooks are soldered 
 to the backs of the plates by means of the soldering-iron and a 
 drop of tin ; or the plates are secured in holders of sheet-cop- 
 per 0.1 1 inch thick, and ^ to 1 inch wide, of the form shown 
 in Fig. 128. The printing surface is freed from grease by 
 brushing with lime-paste, rinsing in water, and then brushing 
 with a clean brush to remove the lime from the depressions. 
 The plates are then hung in the bath and covered with a strong 
 current. When everywhere coated with nickel, the current is 
 
DEPOSITION OF NICKEL AND COBALT. 309 
 
 weakened and the deposit allowed gradually to augment. 
 With an average duration of nickeling of 15 to 20 minutes, 
 with 2.8 to 3 volts, the deposit will, as a rule, be sufficiently 
 resisting. 
 
 Stereotypes of type metal, after being freed from grease, are 
 best lightly coppered in the acid copper bath, then rinsed and 
 brought into the nickel bath. Zinc etchings are first coppered, 
 not too slightly, in the copper cyanide bath, rinsed, and sus- 
 pended in the nickel bath with a very strong current. With 
 too weak a current, black streaks are formed, zinc is dissolved, 
 and both the plate and bath are spoiled. With copper electros, 
 pickling with potassium cyanide solution, after freeing from 
 grease, must not be omitted. 
 
 The nickled plates are rinsed in water, then plunged in hot 
 water, and dried in sawdust, when the nickeled printing surface 
 may be brushed over with a brush and fine whiting, it being 
 claimed that plates thus treated take printing-ink better, while 
 the first impressions of plates not brushed with whiting are 
 somewhat dull. 
 
 Nickel-facing is especially suitable for copper plates for 
 color-printing, the nickel not being attacked like copper or iron 
 by cinnabar. 
 
 Recovery of nickel from old baths. At the present price of 
 nickel its recovery from old solutions scarcely pays. The inef- 
 ficiency of the bath is in most cases due to two causes : It has 
 either become too poor in metal or it contains foreign metallic 
 admixtures. In the first case, the expense of evaporating, to- 
 gether with the further manipulations, is out of proportion to the 
 value of the nickel recovered, and, in the second case, the re- 
 duction of the foreign metals is inconvenient and connected 
 with expenses which make it unprofitable. The recovery of 
 nickel from old baths which have become useless, by the elec- 
 tric current with the use of carbon-plate anodes, as here and 
 there recommended, is the most disastrous and expensive of 
 all, and can only be condemned. 
 
 For nickeling by contact and boiling, see special chapter, 
 " Depositions by Contact." 
 
310 ELECTRO-DEPOSITION OF METALS. 
 
 Depositions of nickel alloys. — From suitable solutions of the 
 metallic salts nickel may be deposited together with copper and 
 tin, as well as with copper and zinc. With the first combina- 
 tion, especially, all tones from copper-red to gold-shade may 
 be obtained, according to which metal predominates, or accord- 
 ing to the current-strength which is conducted into the bath, 
 as is also the case in brassing. 
 
 A suitable bath for coating metallic articles with an alloy of 
 nickel, copper and tin, for which the term nickel-bronze is pro- 
 posed, is obtained by dissolving the metallic phosphates in 
 sodium pyrophosphate solution. By mixing solution of blue 
 vitriol with solution of sodium phosphate, cupric phosphate is 
 precipitated, which is filtered off and washed. In the same 
 manner nickel phosphate is prepared from a solution of nickel 
 sulphate. These phosphates are then, each by itself, dissolved 
 in a concentrated solution of sodium pyrophosphate, while 
 chloride of tin is directly dissolved in sodium pyrophosphate 
 until the turbidity, at first rapidly disappearing, disappears but 
 slowly. 
 
 Nothing definite can be said in regard to the mixing propor- 
 tions of these three solutions, because the proportions will have 
 to be varied according to the desired color of the deposit. The 
 operator, however, will soon find out, of which solution more 
 has to be added to obtain the tone desired. 
 
 For depositing a nickel-copper-zinc alloy solutions of cupric 
 sulphate (blue vitriol) and zinc oxide in potassium cyanide to 
 which is added an ammoniacal solution of nickel carbonate, 
 may be advantageously used. As will be seen a deposit of 
 German silver can be obtained with the use of this solution if 
 the latter contains the metals in the same proportions as Ger- 
 man silver, and German silver anodes are used. 
 
 According to a French process, a deposit of German silver 
 may be obtained as follows : Dissolve a good quality of Ger- 
 man silver in nitric acid and add, with constant stirring, solution 
 of potassium cyanide until all the metal is precipitated as cyan- 
 ide. The precipitate is then filtered off, washed, dissolved in 
 
DEPOSITION OF NICKEL AND COBALT. 3 1 I 
 
 potassium cyanide, and the solution diluted with double the 
 volume of water. This process, however, does not seem very 
 feasible, since nickel separates with difficulty from its cyanide 
 combination. 
 
 Examination of Nickel- Baths. 
 
 The reaction of the nickel baths have previously been briefly 
 referred to, but the subject must here be more closely con- 
 sidered. 
 
 For the determination of the content of acid, a different 
 method must be adopted according to the composition of the 
 bath, i. e., whether it has been prepared with an addition of 
 citric acid, boric acid, etc. The reddening of blue litmus-paper 
 simply indicates the presence of free acid in the bath, but leaves 
 us in the dark as to which acid is present, and as to its deriva- 
 tion. 
 
 If, for instance, in consequence of insufficient solution of 
 nickel, free sulphuric acid appears on the anodes, the bath be- 
 comes at the same times poorer in nickel in proportion to the 
 increase in the content of free sulphuric acid. If we have to 
 deal with a bath prepared from nickel-ammonium sulphate with 
 an addition of ammonium sulphate, but without organic acids, 
 the reddening of blue limus-paper will at once indicate a con- 
 tent of free sulphuric acid, if the bath was neutral in the begin- 
 ning. It is, however, quite a different matter when a bath con- 
 taining boric acid is examined. In the formulae for preparing 
 these baths, it has been seen that before adding the boric acid, 
 any free sulphuric acid of the nickel salt present is to be re- 
 moved by treating the solution with nickel carbonate or nickel 
 hydrate. After adding the boric acid, blue litmus-paper is 
 strongly reddened, and this acidity due to the boric acid is to 
 be maintained in the bath. However, in consequence of the 
 use of too large a number of cast anodes, free sulphuric acid 
 may form in the bath and this, together with boric acid, can- 
 not be recognized by blue litmus-paper, since both acids 
 redden it. In this case red congo paper, which is not changed 
 
312 ELECTRO-DEPOSITION OF METALS. 
 
 by boric acid, but is turned blue by sulphuric acid, has to be 
 used. If red congo paper is colored blue, it is a sure proof 
 that, besides boric acid, free sulphuric acid is present, which 
 has to be neutralized for the bath to work in a correct manner. 
 
 The process is again different when a bath prepared with an 
 addition of citric acid is to be examined. This organic acid 
 colors certain varieties of commercial congo paper blue, just 
 as sulphuric acid does, and hence tropaeolin paper has to be 
 used, which is not altered by citric acid, but is colored violet 
 by free sulphuric acid. 
 
 If a nickel bath has been prepared with the addition of or- 
 ganic salts, for instance, sodium citrate, ammonium tartrate or 
 others, the formation of free sulphuric acid in the bath cannot 
 at first be determined with reagent papers, because the sul- 
 phuric acid decomposes the organic salts, neutral sulphates 
 being formed, and a quantity of organic acid equivalent to the 
 sulphuric acid is liberated. For this reason the content of 
 metal in the bath declines, though the presence of sulphuric 
 acid cannot be established, because the sulphuric acid formed 
 by electrolysis is not consumed for the solution of nickel on the 
 anodes, but for the decomposition of the organic salts. 
 
 Now let us suppose the reverse, namely, that in a nickel 
 bath prepared with the addition of one of the above-mentioned 
 acids, free ammonia appears in consequence of the sole use of 
 cast anodes, and of the decomposition of ammonium sulphate by 
 a strong current. This phenomenon cannot at once be recog- 
 nized, because the ammonia is first fixed by the free acid, and 
 the bath becomes neutral or alkaline only when all the free 
 acid which was present has been consumed for fixing the am- 
 monia formed. With this process there will generally be con- 
 nected an increase in the content of metal, and it will be seen, 
 without further explanation, that for the accurate determination 
 of the processes and alterations in a nickel bath when in oper- 
 ation, the quantitative determination of the free acids, and as 
 much as possible, that of the content of metal, is required. 
 Although it may be said that the busy electro-plater will 
 
DEPOSITION OF NICKEL AND COBALT. 313 
 
 frequently not feel inclined to familiarize himself with the 
 methods of testing, and seldom have the necessary time for 
 executing the determinations of the content of metal, neverthe- 
 less the methods will here be described with sufficient detail, so 
 that those who wish to examine their baths in this respect will 
 find the necessary instructions. To be sure, if the electro- 
 plater himself is not a practical analytical chemist he will have 
 to be taught by some one thoroughly conversant with the sub- 
 ject, the management of the analytical balance, how to execute 
 the weighings, etc. It is also advisable to procure the stand- 
 ard solutions required for volumetric analysis from a reliable 
 chemical laboratory, in order to avoid the possibility of arriving 
 at incorrect results by the use of inaccurately prepared stand- 
 ard solutions. For this reason directions for the preparation 
 of standard solutions are omitted, and the methods of examina- 
 tion in use for our purposes will now be given. 
 
 The examinations may be made by gravimetric analysis 
 (analysis by weight), volumetric analysis (analysis by meas- 
 ure), and by electrolytic analysis. The first method is based 
 chiefly upon the precipitation in an insoluble form of the con- 
 stituent to be determined, and filtering, washing, drying, and 
 weighing the precipitate. This method requires considerable 
 knowledge of chemistry and analytical skill, and should only 
 be resorted to by those not versed in analysis when other 
 more practical methods for the determination of the contents, 
 such as volumetric and electrolytic methods, are not known. 
 
 Volumetric analysis is based upon a very different principle 
 from that of gravimetric analysis. The constituent to be ascer- 
 tained is quantitatively determined by means of a standard 
 solution, enough of which is used until the final reaction shows 
 that a sufficient quantity has been added. From the known 
 content of the standard solution the constituent to be deter- 
 mined is then calculated. This may be explained by an 
 example. For instance, the content of sulphuric acid in a 
 fluid is to be determined. Measure the quantity of fluid by 
 means of a pipette which up to a mark holds exactly 10 cubic 
 
314 ELECTRO-DEPOSITION OF METALS. 
 
 centimeters. Allow the fluid to run into a clean beaker, dilute 
 with about 30 cubic centimeters of water, and heat to about 
 122 F. Now, while constantly stirring the fluid in the beaker 
 with a glass rod, add standard soda solution from a glass 
 burette provided with a glass cork and divided into y 7 cubic 
 centimeters until a piece of congo paper when touched with 
 the glass rod is no longer colored blue. The addition of the 
 standard soda solution must, of course, be effected with great 
 care. So long as the congo paper shows a vivid blue color, a 
 larger quantity may at one time be added, but when the color- 
 ization becomes less vivid, the solution is added drop by drop 
 so as to be sure that the last drop is just sufficient to prevent 
 the blue coloration which was still perceptible after the addition 
 of the previous drop. The drop-test must, of course, be made 
 upon a dry portion of the congo paper, which has not been pre- 
 viously moistened. When no blue coloration appears after the 
 last drop has been added, it is a proof that all the sulphuric 
 acid present has been neutralized by the standard soda solution. 
 The number and fractions of cubic centimeters consumed are 
 then read off on the burette, and the quantity of sulphuric acid 
 present is calculated as follows : 1 cubic centimeter of standard 
 soda solution neutralizes o.o_j9 gramme of sulphuric acid 
 (H 2 S0 4 ), and hence the quantity of sulphuric acid is obtained 
 by multiplying the number of cubic centimeters of standard 
 soda solution by 0.049. Now, since 10 cubic centimeters were 
 measured off by the pipette and titrated, the number found is 
 multiplied by 100, which gives the content of sulphuric acid in 
 1 liter of the fluid. 
 
 If, for instance, for the neutralization of 10 cubic centimeters 
 of the fluid containing sulphuric acid, 5.4 cubic centimeters of 
 standard soda solution were required, then the content of sul- 
 phuric acid amounts to 5.4 X 0.049 = 0.2646 gramme, or in 1 
 liter to 0.2646 X 100 = 26.46 grammes. 
 
 The electrolytic method of analysis is available only for the 
 determination of such metals as can be completely separated 
 in a coherent form from their solutions by the current. It is 
 
DEPOSITION OF NICKEL AND COBALT. 
 
 315 
 
 based upon the fact that the metallic solution contained in a 
 platinum dish is decomposed by the current, and the metal pre- 
 cipitated upon the platinum dish. After washing and drying, 
 the dish is weighed and the weight of the precipitated metal is 
 obtained by deducting the weight of the platinum dish without 
 precipitate, which, of course, has been ascertained before 
 making the experiment. 
 
 The apparatus generally used for electrolytic analysis is 
 
 Fig. 129. 
 
 shown in Fig. 129. The platinum dish, holding about % liter, 
 rests upon a metal ring which is secured to the rod of the 
 stand, and is in contact with the negative pole of the source of 
 current. Into the dish, at a distance of 1 or 2 centimeters 
 from the bottom, dips a round platinum disk bent like the 
 bottom, or a spiral of platinum wire, 1 millimeter thick, which 
 serves as an anode and is secured by platinum wire in a movable 
 support or holder. The latter is carefully insulated from the 
 rod of the stand and connected with the positive pole of the 
 
3 16 ELECTRO-DEPOSITION OF METALS. 
 
 source of current. During electrolysis the platinum dish is 
 covered with a perforated watch-glass to prevent possible loss 
 by the evolution of gas. 
 
 Since many precipitates have to be washed without inter- 
 rupting the current, it is best to use the washing contrivance 
 shown in the illustration to prevent the precipitated metal from 
 being redissolved by the electrolyte. With the upper clip 
 closed, the shorter leg of the siphon is dipped into the dish. 
 The lower clip is then closed and the upper one opened until 
 the short leg is filled with water. The upper clip is then 
 closed and the lower one opened, whereby the dish is emptied. 
 The clip of the longer leg of the siphon is then closed, the 
 uppermost clip opened, and the dish filled up to the rim with 
 water. The uppermost clip is then closed, the lower one 
 opened, and the dish emptied the second time, the operation 
 being repeated until the precipitate and dish are thoroughly 
 washed. 
 
 Since for complete electrolytic precipitation it is essential to 
 operate with correct electro-motive forces, it is advisable to use 
 an accurate ammeter adjusted to 0.05 to 2.5 amperes, as well 
 as a voltmeter. 
 
 The current for electrolysis may be supplied by cells, a 
 thermo-electric pile, a dynamo, or an accumulator, but the 
 necessary regulating resistances must in every case be provided. 
 
 Let us now return to the examination of nickel baths. If by 
 qualitative analysis the presence of free sulphuric acid in the 
 bath has been established, it can be at once assumed that the 
 content of nickel has from the first declined. Hence it will 
 scarcely be worth while to determine by volumetric analysis 
 the quantity of free sulphuric acid present, and to calculate 
 from this the quantity of nickel carbonate or nickel hydrate 
 required for neutralization. It will be only necessary to add to 
 the bath, stirring constantly, small portions of the nickel salt 
 rubbed up with water, until a fresh test with congo paper 
 shows no blue coloration. The addition of a small excess of 
 nickel carbonate or nickel hydrate is unobjectionable. Besides 
 
DEPOSITION OF NICKEL AND COBALT. 317 
 
 neutralizing the free sulphuric acid, care should at the same 
 time be taken to prevent its further formation by increasing 
 the number of cast-nickel anodes. The case is similar when a 
 nickel bath prepared with organic salts, for instance, with 
 potassium citrate or sodium citrate, is to be examined. Even 
 if it is shown by the reaction that no free sulphuric acid is 
 present, the content of nickel, as previously mentioned, may 
 have decreased, and the content of free organic acid increased. 
 The latter may, however, be neutralized by the addition of 
 nickel carbonate or nickel hydrate and, hence, the determina- 
 tion of the content of acid by volumetric analysis is not abso- 
 lutely necessary. 
 
 When, on the other hand, a nickel bath has become alkaline, 
 the determination of the free alkali by volumetric analysis will 
 be of little value, and it will, according to the composition of 
 the bath, suffice to neutralize it with dilute sulphuric acid, or 
 acidulate it with an organic acid. Since, however, baths which 
 have become alkaline possess a higher content of nickel than 
 the normal bath, an electrolytic determination of the nickel 
 may be of use in order to calculate accurately the quantity of 
 water which has to be added to reduce the content of nickel to 
 the normal quantity. 
 
 If the bath has been prepared with nickel ammonium sul- 
 phate with additions of ammonium sulphate, or boric acid, or 
 if it contains only very small quantities of organic acids, it can 
 be directly electrolyzed. 
 
 Bring by means of the pipette exactly 20 cubic centimeters 
 of the bath into the platinum dish, add 4 grammes of ammo- 
 nium sulphate and 35 to 40 cubic centimeters of ammonia of 
 0.96 specific gravity and electrolyze with a current-density = 
 0.6 ampere, until no dark coloration appears after adding a 
 drop of ammonium sulphate to a few cubic centimeters of the 
 electrolyte. Rinse the dish, together with the precipitate, with 
 water, remove the water by rinsing with absolute alcohol, rinse 
 the dish with pure ether and dry it at 21 2° F. in an air-bath. 
 The weight of the precipitate of metallic nickel obtained by 
 
3 I 8 ELECTRO-DEPOSITION OF METALS. 
 
 weighing the platinum dish gives the content of nickel ammo- 
 nium sulphate in grammes per liter of bath by multiplying by 
 335. From the increase in the content of nickel ammonium 
 sulphate shown by the analysis, it can be readily calculated 
 how much water has to be added to the bath to reduce it to 
 the original content. 
 
 If a nickel bath contains large quantities of organic acids, 
 precipitate 20 cubic centimeters of the bath with sodium sul- 
 phide solution, filter and wash the precipitate, dissolve it in 
 nitric acid, and evaporate the solution with pure sulphuric acid 
 upon the water-bath to drive off the nitric acid. The residue 
 is treated as above described. 
 
 2. Deposition of Cobalt. 
 
 Properties of cobalt. Cobalt has nearly the same color as 
 nickel, with a slightly reddish tinge ; its specific gravity is 8.7. 
 It is exceedingly hard, highly malleable and ductile, and capa- 
 ble of taking a polish. It is slightly magnetic, and preserves 
 this property even when alloyed with mercury. It is rapidly 
 dissolved by nitric acid, and slowly by dilute sulphuric and 
 hydrochloric acids. 
 
 For plating with cobalt, the baths given under "Nickeling" 
 may be used by substituting for the nickel salt a corresponding 
 quantity of cobalt salt. By observing the rules given for nick- 
 eling, the operation proceeds with ease. Anodes of metallic 
 cobalt are to be used in place of nickel anodes. 
 
 Nickel being cheaper and its color somewhat whiter, electro- 
 plating with cobalt is but little practiced. On account of the 
 greater solubility of cobalt in dilute sulphuric acid, it is, how- 
 ever, under all circumstances, to be preferred for facing valuable 
 copper plates for printing. 
 
 According to the more or less careful adjustment of such 
 plates in the press, the facing in some places is more or less 
 attacked, and it may be desired to remove the coating and 
 make a fresh deposit. For this purpose Gaiffe has proposed 
 the use of cobalt in place of nickel, because the former dis- 
 
DEPOSITION OF NICKEL AND COBALT. 319 
 
 solves slowly but completely in dilute sulphuric acid. He 
 recommends a solution of 1 part of chloride of cobalt in 10 of 
 water. The solution is to be neutralized with aqua ammonia, 
 and the plates are to be electro-plated with the use of a moder- 
 ate current. 
 
 Cobalt precipitated from its chloride solution, however, does 
 not yield a hard coating, and hence the following bath is 
 recommended for the purpose : Double sulphate of cobalt and 
 ammonium 21 ozs., crystallized boric acid 10^ ozs., water 10 
 quarts. 
 
 The bath is prepared in the same manner as No. VII, given 
 under " Deposition of Nickel." It requires an electro-motive 
 force of 2.5 to 2.75 volts; current density, 0.4 ampere. 
 
 To determine whether copper, and how much of it, is dissolved 
 in stripping the cobalt deposit from cobalted copper plates, a 
 copper plate with a surface of 7^ square inches was coated with 
 7.71 grains of cobalt and placed in dilute sulphuric acid (1 part 
 acid of 66° Be. to 12.5 parts of water). After the acid had 
 acted for 14 hours the cobalt deposit was partially dissolved, 
 and had partially collected in laminae upon the bottom of the 
 vessel, the copper plate being entirely freed. On weighing 
 the copper-plate it was shown that it had lost about 0.0063 per 
 cent., this loss being apparently chiefly from the back of the 
 plate, the engraved side exhibiting no trace of corrosion. The 
 experiment proved that there is no danger of destroying the 
 copper plate by stripping the cobalt deposit with dilute sul- 
 phuric acid, provided the operation is executed with due care 
 and attention. 
 
 Warren has described a cobalt solution which can be decom- 
 posed in a single-cell apparatus, and for this reason would seem 
 suitable for electro-plating small articles in quantities. For the 
 preparation of this bath, dissolve 3*^ ounces of chloride of 
 cobalt in as little water as possible, and compound the solution 
 with concentrated solution of Rochelle salt until the voluminous 
 precipitate at first formed, is almost entirely redissolved, and 
 then filter. Bring the bath into a vessel and place the latter in 
 
320 ELECTRO-DEPOSITION OF METALS. 
 
 a clay cup filled with concentrated solution of chloride of 
 ammonium or of common salt, and containing a zinc cylinder. 
 Connect the objects to be plated to the zinc by a copper wire, 
 and allow them to dip in the cobalt solution. With a closed 
 circuit the objects become gradually coated with a lustrous 
 cobalt deposit which, after 2 hours is sufficiently heavy to bear 
 vigorous polishing with the bob. Coating zinc in the same 
 manner was not successful. 
 
CHAPTER VII. 
 
 DEPOSITION OF COPPER, BRASS AND BRONZE. 
 
 i. Deposition of Copper. 
 
 Properties of copper. Copper has a characteristic red color, 
 and possesses strong luster. It is very tenacious, may be rolled 
 to thin laminae, and readily drawn into fine wire. The specific 
 gravity of wrought copper is 8.95, and of cast 8.92. Copper 
 fuses more readily than gold, but with greater difficulty than 
 silver. 
 
 In a humid atmosphere containing carbonic acid, copper be- 
 comes gradually coated with a green deposit of basic carbonate. 
 When slightly heated it acquires a red coating of cuprous oxide, 
 and when strongly heated a black coating of cupric oxide with 
 some cuprous oxide. Copper is most readily attacked by nitric 
 acid, but is slowly dissolved when immersed in heated hydro- 
 chloric or sulphuric acid. With exclusion of the air, it is not 
 dissolved by dilute sulphuric or hydrochloric acid, and but 
 slightly with admission of the air. Liquid ammonia causes a 
 rapid oxidation of copper in the air and the formation of a blue 
 solution. An excess of potassium cyanide dissolves copper. 
 Sulphuretted hydrogen blackens bright copper. 
 
 Copper baths. The composition of these baths depends on 
 the purpose they are to serve, and below are mentioned the 
 most approved baths, with the exception of the acid copper 
 bath used for plastic deposits of copper, which will be discussed 
 later on under " Copper galvanoplasty." 
 
 In most cases the more electro-positive metals, zinc, iron, tin, 
 etc., are to be coppered either as preparation for the succeed- 
 ing processes of nickeling, silvering, or gilding, or to protect 
 them against oxidation, or for the purpose of decoration. The 
 21 ( 321 ) 
 
322 ELECTRO-DEPOSITION OF METALS. 
 
 above-mentioned electro-positive metals, however, decompose 
 acid copper solutions and separate from them pulverulent cop- 
 per, while an equivalent portion of zinc, iron, tin, etc., is dis- 
 solved. For this reason, such solutions cannot be used for 
 coating these metals, and alkaline copper baths are exclusively 
 employed, which may be arranged under two groups — those 
 containing potassium cyanide, and those without it. 
 
 Copper cyanide baths are prepared by dissolving cupric salts, 
 for instance, cupric acetate (verdigris), cupric sulphate (blue 
 vitriol), or cuprous compounds, such as cuprous oxide, in 
 potassium cyanide, the salts being thereby converted into 
 potassium-copper cyanide, which is the effective constituent of 
 all copper cyanide baths. 
 
 By compounding a solution of a cupric salt with potassium 
 cyanide, cupric cyanide is formed, which is very unstable,, 
 rapidly changing by exposure into cupro-cupric cyanide and 
 cyanogen gas. To avoid this loss of cyanogen, sulphites are 
 added, which, according to one view, effect a reduction of the 
 cupric salts to cuprous salts, which dissolve in potassium 
 cyanide without cyanogen being liberated, while, according to 
 another, hydrocyanic acid is produced from cyanogen gas and 
 sodium sulphate, water being decomposed, and forms with the 
 sodium carbonate present, sodium cyanide, the latter becom- 
 ing again active in converting the cupro-cupric cyanide into 
 the soluble double salt. It is possible that both the reactions 
 mentioned above partly appear together. 
 
 By using from the start cuprous oxide, the latter can without 
 loss of cyanogen be converted into potassium-copper cyanide. 
 
 In accordance with this, there will be given in the formulas 
 for the preparation of potassium-copper cyanide baths in which 
 cupric salts are used, larger or smaller additions of bisulphite 
 of soda and alkaline carbonates, the former serving the purpose 
 of decreasing the loss of cyanogen, and the latter being intended 
 to fix any free acid formed. 
 
 Stockmeier was the first to take the trouble of calculating 
 the combinations formed after the conversion of the separate 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 323 
 
 constituents of the copper baths, and Jordis has adopted the 
 same course, in order to obtain a standard formula. Both 
 these authors recommend not to produce the copper combina- 
 tion actually subjected to electrolysis in the bath by repeated 
 conversions of salts, but to prepare this combination by itself,, 
 and to dissolve it direct in water in order to obtain the finished 
 copper bath. It has been shown in practice that this method 
 is quite practicable provided certain points are taken into con- 
 sideration. However, the rational composition of a bath with 
 potassium cyanide, which has been produced by conversion 
 from the salts, cannot be judged according to whether the sep- 
 arate salts were present in stoichoimetrical proportions for the 
 smooth conversion into new combinations without receiving in 
 the bath an excess from one or the other substance. In prac- 
 tice it has long been known that an excess of sodium bisulphite 
 has a very beneficial effect upon the separation of a lustrous 
 copper, and prevents it from rapidly turning into a dull earthy 
 gray, this effect being very likely due to the prussic acid lib- 
 erated by the sulphurous acid. This one example may prove 
 that standard formulas erected upon theoretical maxims should 
 be accepted with due caution by the practical electro-plater, 
 and that, under certain conditions, additions will have to be 
 made to baths prepared according to such standard formulas if 
 the result is to be as good as that from baths prepared accord- 
 ing to older formulas. 
 
 Hossauer prepares a copper bath by dissolving 3^ ozs. of 
 copper cyanide in a solution of 17^2 ozs. of JO per cent, potas- 
 sium cyanide in 3 quarts of water, boiling, filtering, and diluting 
 with 7 quarts of water, to a 10-quart bath. This bath works 
 very well when heated to between 1 1 3 and 122 F., but when 
 used cold requires a very strong current. 
 
 Copper baths for iron and steel articles. — I. To be used at the 
 ordinary temperature. Water 10 quarts, bisulphite of soda in 
 powder 7 ozs., crystallized carbonate of soda 14 ozs., neutral 
 acetate of copper 7 ozs., 75 per cent, potassium cyanide 7 ozs., 
 ammonia 4.4 ozs. 
 
324 ELECTRO-DEPOSITION OF METALS. 
 
 II. For hot coppering {at between 140 and ijS° F.). Water 
 10 quarts, bisulphite of soda in powder 2^ ozs., crystallized 
 
 ■carbonate of soda 7 ozs., neutral acetate of copper 7 ozs., 75 
 per cent, cyanide of potassium 6^ ozs., ammonia 4 ozs. 
 
 The baths are best prepared as follows: Dissolve the bisul- 
 phite and carbonate of soda in one-half of the water, the potas- 
 sium cyanide in the other half, and mix the copper salt with 
 the ammonia ; then pour the blue ammoniacal copper solution 
 into the solution of the soda salts, and finally add the potassium 
 cyanide solution ; the bath will then be clear and colorless. 
 Boiling, though not absolutely necessary, is of advantage, after 
 which the solution is to be filtered. 
 
 According to thorough investigations made, the excess of 
 carbonate of soda in formula I serves no special purpose, but 
 on the contrary, in many cases, is directly detrimental ; neither 
 is the use of ammonia of any special advantage, and it may just 
 as well, or rather better, be omitted. Further, the use of sepa- 
 rate baths for cold and warm coppering is at least questionable. 
 It is believed that a single bath suffices for both cases, heating 
 having been found of special advantage only for rapid and 
 thick coppering, or for obtaining particular shades which are 
 produced with difficulty in the cold bath, but without trouble 
 in the heated bath. 
 
 It should be borne in mind that potassium cyanide solutions 
 are still more rapidly decomposed when heated than when used 
 cold, and consequently the consumption of potassium cyanide 
 in heated baths is considerably greater than in cold baths. Re- 
 course to heating should, therefore, only be had when the in- 
 tended result cannot by any other means be obtained. 
 
 The following formula may be highly recommended, a copper 
 bath composed according to it always yielding good and sure 
 results. 
 
 III. Water 10 quarts, crystallized carbonate of soda 8^ ozs., 
 crystallized bisulphite of soda 7 ozs., neutral acetate of copper 
 7 ozs., 98 or 99 per cent, potassium cyanide 83^ ozs. 
 
 Electromotive force at 10 cm. electrode-distance, 3 volts. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 325 
 
 Current- density, 0.35 ampere. 
 
 The bath is prepared as follows : Dissolve in 7 quarts of 
 warm water the carbonate of soda, gradually add the bisulphite 
 of soda to prevent violent effervescence, and then add, with 
 vigorous stirring, the acetate of copper in small portions. 
 Dissolve the potassium cyanide in 3 quarts of cold water, and 
 mix both solutions when the first is cold. By thorough stirring 
 with a clean wooden stick, a clear solution is quickly obtained, 
 which is allowed to settle and siphoned off clear. If after the 
 addition of the potassium cyanide the bath should not become 
 colorless, or at least wine-yellow, add a small quantity more of 
 potassium cyanide. 
 
 When conversion is complete, the bath contains potassium- 
 copper cyanide, potassium acetate, sodium acetate, sodium 
 sulphate, and potassium cyanide in excess in addition to 
 sodium bisulphite. 
 
 For certain purposes, for instance, for the production of a 
 very close, thick deposit, as required for cast-iron door knobs, 
 etc., it is advisable to double the content of metal. For the 
 preparation of such a copper bath, it is only necessary to dis- 
 solve double the quantities of the salts given in formula III in 
 10 quarts of water. 
 
 Stockmeier recommends the following copper bath r 
 
 Illtf. Water 10 quarts, neutral bisulphite of soda 8^4 ozs., 
 98 or 99 per cent, potassium cyanide 7 ozs., crystallized car- 
 bonate of soda 6 ozs., crystallized acetate of copper 7 ozs. 
 
 Dissolve the first mentioned three salts together in half the 
 quantity of water, and the acetate of copper in the other half, 
 and pour the last solution into the first, stirring constantly. It 
 is recommended to add to this bath JJ to 123 grains of bisul= 
 phite of soda per quart. 
 
 In preparing copper baths, the acetate of copper prescribed 
 in the preceding formulae may be replaced by the carbonate or 
 sulphate, the substitution of the latter, after its previous con- 
 version into carbonate, being of special advantage in order not 
 to thicken the bath by the potassium sulphate formed by re- 
 
326 ELECTRO-DEPOSITION OF METALS. 
 
 ciprocal decomposition. The following formula is especially 
 suitable for the use of sulphate of copper (blue vitriol) : 
 IV. Blue vitriol ...... 10*^ ozs. 
 
 Crystallized carbonate of soda . . 10^ ozs. 
 
 Water . . . . . . .10 quarts. 
 
 Pulverized bisulphite of soda ... 7 ozs. 
 Crystallized carbonate of soda . . S}4 ozs. 
 
 98 to 99 per cent, potassium cyanide . 8}£ ozs. 
 
 Electro-motive force at 10 cm. electrode-distance, about 3 
 volts. 
 
 Current-density, 035 ampere. 
 
 First dissolve the 10^ ozs. of blue vitriol and the 10^ ozs. 
 of crystallized carbonate of soda, each by itself, in hot water, 
 and mix the two solutions. Allow the precipitate of carbonate 
 of copper to settle, and pour off the supernatant clear fluid. 
 Then pour upon the precipitate 5 quarts of water, add the 
 bisulphite of soda, next the carbonate of soda, and mix this 
 solution with the solution of the potassium cyanide in 5 quarts 
 of water. The fluid rapidly becomes clear and colorless, when 
 it is boiled and filtered. 
 
 V. Water 15 quarts, cupron (cuprous oxide) 2>% ozs., 
 99 per cent, potassium cyanide 10^ ozs., bisulphite of soda 
 10^ ozs. 
 
 Electro-motive force at 10 cm. electrode-distance, 2.8 volts. 
 
 Current-density, 0.3 ampere. 
 
 For the preparation of the bath, dissolve the potassium cya- 
 nide in about 3 quarts of the water (cold), stir in gradually the 
 cupron, then add the solution of the bisulphite of soda in 3 
 quarts of the water, and with the remaining 9 quarts of water 
 make up the bath to 1 5 quarts. 
 
 As previously mentioned, an addition of sulphites to the cu- 
 prous oxide solution is not required since no cyanogen escapes. 
 However, in dissolving cuprous oxide in potassium cyanide 
 there is formed, in addition to potassium-copper cyanide, potas- 
 sium hydroxide (caustic potash) the presence of which in the 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 327 
 
 bath is for various reasons not desirable. A sufficient quantity 
 of bisulphite of soda to convert the caustic potash into neutral 
 potassium sulphite is therefore added, while the corresponding 
 portion of bisulphite is converted into neutral sodium bisul- 
 phite. A sufficient excess of bisulphite of soda for the exertion 
 of the above-mentioned favorable effects upon the coppering 
 process remains behind. 
 
 Dr. Langbein has introduced in the copper-plating industry 
 the cupro-cupric sulphite. It dissolves in potassium cyanide 
 without noticeable formation of cyanogen, since it contains 
 more than the sufficient quantity of sulphurous acid required 
 for the reduction of the portion of cupric oxide present. Suit- 
 able formulas for copper baths with cupro-cupric sulphite are : 
 
 VI. Water 10 quarts, 99 per cent, potassium cyanide S}4 
 ozs., ammonium soda if ozs., cupro-cupric sulphite 4^ ozs., 
 or, 
 
 Via. Water 10 quarts, 60 per cent, potassium cyanide 14 
 ozs.,- cupro-cupric sulphite 4^ ozs. 
 
 Dissolve the salts in the order given, stirring constantly, and 
 then add the remaining 5 quarts of water. 
 
 The deposits obtained in these baths are of a beautiful warm | 
 color, very adherent and dense. 
 
 Pfanhauser recommends the following bath, in which sepa- 
 rately prepared crystallized potassium-copper cyanide, in addi- 
 tion to suitable conducting salts, which are wanting in Hos- 
 sauer's formula, is used: 
 
 VII. Water 10 quarts, ammonia-soda 2>% ozs., anhydrous 
 sodium sulphate 7 ozs., crystallized potassium-copper cyanide 
 10*^ ozs., potassium cyanide 0.35 ozs. • 
 
 For the preparation of the bath the salts are to be dissolved 
 in a suitable quantity of water, stirring constantly. 
 
 Electro-motive force at an electrode distance of 15 cm., 2.7 
 volts for iron, 3.2 volts for zinc. Current-density 0.3 ampere. 
 
 For small zinc objects which are to be coppered in a basket, 
 baths III, IV, and V, may be used, or those up to and includ- 
 ing VII, which are to be heated and compounded with a small 
 
328 ELECTRO- DEPOSITION OF METALS. 
 
 additional quantity of potassium cyanide. For the same pur- 
 pose, Roseleur recommends the following bath : 
 
 VIII. Water 10 quarts, neutral crystallized sodium sulphate 
 I ^ ozs., neutral cupric acetate 8 ozs., 75 per cent, potassium 
 cyanide I2 1 /} ozs -> ammonia 3 ozs. 
 
 The bath is prepared in the same manner as the baths given 
 under formulas I to III. 
 
 Prepared coppering salts. Combinations under various names 
 (Schering: triple metal salts; Langbein Co.: double metal 
 salts) are now brought into commerce, and are quite convenient 
 for the preparation of copper baths (and brass baths) in so far 
 that only one weighing of the substance is required. 
 
 As regards their composition these preparations are v com- 
 binations of potassium-copper cyanide (relatively potassium- 
 zinc cyanide) with alkaline sulphites, such as, for instance, are 
 formed by dissolving cupro-cupric sulphite in potassium cyan- 
 ide and subsequent evaporation to dryness. As the copper 
 content in Langbein Co's. double copper salt amounts to from 
 20 to 21 per cent., copper baths with any desired content of 
 metal can in a very simple manner be prepared. Thus, for 
 instance, a copper bath with 92.59 grains of copper per quart 
 is obtained by dissolving 6.6 lbs. of double copper salt in 100 
 quarts of water; and a copper bath with 138.88 grains of cop- 
 per per quart, by dissolving 9.9 lbs. of double copper salt 
 in 100 quarts of water. It may be added that there is very 
 seldom occasion to exceed 138.88 grains of copper per liter. 
 
 As these preparations can contain but a small content of free 
 potassium cyanide to prevent them from absorbing moisture 
 when stored, it is advisable to dissolve in the baths prepared 
 from them 46 to 78 grains of 99 per cent, potassium cyanide. 
 It has also proved of advantage to add certain conducting salts, 
 for instance, neutral sodium sulphite in order to effect a better 
 anodal solution of the copper. 
 
 A copper salt brought into commerce by the Hanson & Van 
 Winkle Co. of Newark, N. J., under the name of ruby oxide, may 
 to advantage be used in making copper solutions, it being 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 329 
 
 claimed to give a much deeper red deposit than is possible to> 
 obtain with a carbonate solution. 
 
 Copper baths without potassium cyanide. Of the many direc- 
 tions for the preparation of these baths, only a few need here 
 be mentioned. 
 
 For coppering zinc objects, Roseleur recommends the follow- 
 ing bath : 
 
 IX. Water 10 quarts, tartar, free from lime, 6.7 ozs., crystal- 
 lized carbonate of soda 15 ozs., blue vitriol 6.7 ozs., caustic soda 
 lye of 16 Be., ^ lb. 
 
 To prepare this bath, dissolve the tartar and the crystallized 
 carbonate of soda in ^ of the water, and the blue vitriol in the 
 remaining ^, and mix both solutions. Filter off the precipitate,, 
 dissolve it in the caustic soda lye, and add this solution to the 
 other. 
 
 This bath works very well, and may be recommended to 
 electro-platers who copper zinc exclusively ; though even for 
 this purpose the baths prepared according to III, IV and V, 
 answer equally well. 
 
 Weill obtains a deposit of copper in a bath consisting of a 
 solution of blue vitriol in an alkaline solution of tartrate of 
 potassium or sodium. Such a bath is composed as follows: 
 
 X. Water 10 quarts, potassium sodium tartrate (Rochelle 
 salt) 53 ozs., blue vitriol io}4 ozs., 60 per cent, caustic soda 
 28 ozs. 
 
 The chief purpose of the large content of caustic soda is to 
 keep the tartrate of copper, which is almost insoluble in water, 
 in solution. According to Weil, the coppering may be exe- 
 cuted in three different ways, as follows : 
 
 The iron articles tied to zinc wires, or in contact with zinc 
 'strips, are brought into the bath ; the coppering thus taking 
 place by contact. Or, porous clay cups are placed in the bath 
 containing the articles ; these clay cups are filled with soda lye 
 in which zinc plates connected with the object-rods are allowed 
 to dip, the arrangement in this case forming a cell with which, 
 by the solution of the zinc in the soda lye, a current is pro- 
 
330 ELECTRO-DEPOSITION OF METALS. 
 
 cluced, which affects the decomposition of the copper solution 
 and the deposition. When saturated with zinc the soda lye 
 becomes ineffective, and according to Weil, it may be regen- 
 erated by the addition of sodium sulphite, which separates the 
 dissolved zinc as zinc sulphide. The third metJwd of coppering 
 consists in the use of the current of a battery or of a dynamo- 
 machine, in which case copper anodes have, of course, to be 
 employed. According to the method used, coppering is 
 effected in a shorter or longer time. In contact-coppering at 
 least six hours were required for the production of a tolerably 
 heavy deposit, and with the use of a current generated by an 
 external source, no other advantage over potassium copper 
 cyanide baths could be noticed than that being free from potas- 
 sium cyanide, it is not poisonous. However, the danger in the 
 use of copper cyanide baths is generally overestimated by the 
 laymen, there being actually none, if proper care be observed. 
 
 Another copper bath recommended by Walenn consists of a 
 solution of equal parts of neutral tartrate of ammonia and potas- 
 sium cyanide, in which 3 to 5 per cent, of copper (in the form 
 of blue vitriol or moist cupric hydrate) is dissolved. The bath 
 is to be heated to about 140 F. 
 
 Gauduiri s copper bath consists of a solution of oxalate of 
 copper with oxalate of ammonia and free oxalic acid. Fon- 
 taine asserts that the bath works well when heated to between 
 14O and 150 F. 
 
 Tanks for potassium copper cyanide baths. Copper baths con- 
 taining cyanide cannot be brought into pitched tanks, tanks of 
 stoneware and enameled iron being used for smaller baths, and 
 for larger ones, basins of brick set in cement, or iron reservoirs 
 lined with cement. Wooden tanks lined with celluloid are also 
 useful. For large baths containing potassium cyanide wooden 
 tanks lined with lead can be used without disadvantage, since a 
 slight coating of cyanide of lead which may be formed upon 
 the lead, is insoluble in potassium cyanide, and even if a small 
 quantity of cyanide of lead would be dissolved in the bath by 
 the presence of organic acids, a separation of lead • besides 
 copper upon the cathodes does not take place. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 33 1 
 
 Copper anodes. For this purpose it is best to use annealed 
 sheets of pure copper about 0.11 to 0.19 inch thick. They 
 should first be for some time pickled in dilute sulphuric acid, 
 and then scratch-brushed, in order to give them a pure metallic 
 surface. 
 
 The anode-surface should be as large as possible, at least as 
 large as the object-surface suspended in the bath. 
 
 In all baths containing cyanide the anodes become in a com- 
 paratively short time coated with a greenish slime which con- 
 sists of basic cuprous cyanide, and is mostly soluble in excess 
 of potassium cyanide. When a very thick formation of such 
 slime takes place, potassium cyanide is wanting and has to be 
 added. 
 
 In addition to this coat of cuprous cyanide, there may also 
 be formed upon the anode a brown film of para- cyanide which 
 adheres very tenaciously and cannot be removed with potas- 
 sium cyanide, but has to be taken off by scratch-brushing or 
 scouring with pumice. When coppering with small anode-sur- 
 faces, and potassium cyanide is at the same time wanting, the 
 coat may become so thick that no current passes into the bath, 
 and consequently no deposit is formed. This feature may even 
 appear when the bath contains a sufficient excess of potassium 
 cyanide, because the cyanide formed in abundance on the 
 anode by high current-densities cannot with sufficient rapidity 
 be dissolved by the potassium cyanide. In this case, recourse 
 must also be had to scouring the anodes, and then increasing 
 the anode-surfaces. The anodes are best suspended to the 
 anode-rods by means of copper bands riveted on. 
 
 Execution of copper-plating. — The general rules given under 
 nickeling, as regards the suitable composition of the bath, 
 correct selection of anodes, careful scouring and pickling of the 
 objects, and proper current- strength also apply to copper- 
 plating. 
 
 In copper baths containing cyanide, too large an excess of 
 potassium cyanide, to be sure, produces an evolution of hydro- 
 gen-bubbles on the objects, but it yields either no deposit at 
 
$$2 l'l ECTRO-PEPOSITION OF METALS. 
 
 all or only a slight one, which readily peels oft". If this phe- 
 nomenon is noticed after an addition of potassium cyanide is 
 made, the excess has to be removed by adding' a copper salt, 
 best, cupro-cupric cyanide. For this purpose triturate the 
 latter with a small quantity of the copper bath in a small por- 
 celain mortar to a thinly-fluid paste, and add the latter to the 
 bath, stirring vigorously for some time. After each addition, 
 see whether an object suspended in the bath becomes rapidly 
 and properly coppered and. if such be not the case, repeat 
 the addition of cupro-cupric cyanide until the bath works in a 
 faultless and correct manner. 
 
 1 [owever, deposition may also fail by reason of an insufficient 
 addition of potassium cyanide. This is recognized by the 
 heavy formation of froth on the anodes and the appearance of 
 a pale blue color in the fluid, though this ma}' also be caused 
 by the content of metal in the bath being too small. While in 
 the first case, the simple addition of 15 to 30 grains of potas- 
 sium cyanide per quart will cause the bath to deposit in the 
 proper manner, in the second case, solution of copper cyanide 
 in potassium cyanide is required in order to increase the con- 
 tent of metal, and it is advisable to add at the same time a 
 small quantity of carbonate of soda and of bisulphite of soda. 
 In place of preparing a solution of copper cyanide in potassium 
 cyanide, it is recommended to use crystallized copper cyanide. 
 which can be obtained from manufacturers oi chemicals, and 
 dissolve it in hot water. 
 
 Many platers are of the opinion that the articles to be copper- 
 plated do not require very careful cleaning and pickling before 
 plating, because this is sufficiently effected by the baths them- 
 selves, by those containing potassium cyanide, as well as by 
 those with alkaline organic combinations. This opinion, how- 
 ever, is wrong. It is true the potassium cyanide dissolves a 
 layer of oxide, but not, or at least very incompletely, any grease 
 present upon the articles, and hence it is advisable to free 
 objects intended for coppering as thoroughly from grease as 
 those to be nickeled. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 333 
 
 The preliminary scouring and pickling of the articles to be 
 coppered are executed according to the directions given on p. 
 220. The same precautions referred to under " Deposition of 
 Nickel" have to be used in suspending the objects in the bath, 
 and the directions given there for the suitable arrangement of 
 the anodes, etc., also apply to coppering. However, as a cop- 
 per bath conducts better than a nickel bath, the distances be- 
 tween the anodes and the objects may, if necessary, be some- 
 what greater. 
 
 With a proper arrangement of the anodes and correct regu- 
 lation of the current, the objects should be entirely coated with 
 copper in a few minutes after being suspended in the bath. In 
 five to ten minutes the objects are taken from the bath and 
 brushed with a scratch-brush of not too hard brass wires, 
 whereby the deposit should everywhere show itself to be dur- 
 able and adherent. Defective places are thoroughly scratch- 
 brushed, scoured, and pickled ; the objects are then returned 
 to the bath. For solid and heavy plating, the objects remain in 
 the bath until the original luster and red tone of the coppering 
 disappear and pass into a dull, discolored brown. At this 
 stage the objects are again scratch-brushed until they show luster 
 and the red copper color, and in doing this it is of advantage to 
 moisten them with tartar water. They are then again returned 
 to the bath, where they remain until the dull, discolored tone 
 reappears. They are then taken out, scratch-brushed bright, 
 rinsed in several clean waters, plunged into hot water, and 
 finally dried, first in sawdust and then thoroughly, at a high 
 temperature, in the drying chamber. 
 
 Special attention must be paid to the thorough washing of 
 the coppered objects, because, if a trace of the bath contain- 
 ing cyanide remains in the depressions or pores, small, dark, 
 round stains appear on those places, which cannot be removed, 
 or at least only with great difficulty, they reappearing again in a 
 short time after having been apparently removed. This forma- 
 tion of stains appears most frequently upon coppered (as 
 well as brassed) iron and zinc castings, which cannot be pro- 
 
334 ELECTRO- DEPOSITION OF METALS. 
 
 duced without pores. To prevent the formation of these stains 
 the following method is recommended : Since the rinsing in 
 many waters, and even allowing the objects to lie for hours in 
 running water, offer no guarantee that every trace of fluid con- 
 taining cyanide has been removed, the objects are brought into 
 a slightly acid bath which decomposes the fluid, a mixture of I 
 part of acetic acid and 50 parts of water being well adapted for 
 the purpose. The objects are allowed to remain in this mix- 
 ture for three to five minutes, when they are rinsed off in water 
 and dipped for a few minutes in dilute milk of lime. They are 
 finally rinsed and dried. Coppered castings thus treated will 
 in most cases show no stains. 
 
 O. Shultz obtained a patent for the following method for re- 
 moving the hydrochloride acid from the pores, and for prevent- 
 ing the formation of stains: The plated objects are placed in a 
 room which can be hermetically closed. The air is then re- 
 moved from the room by the introduction of steam of a high 
 tension and by means of an air-pump, and water is sprinkled 
 upon the objects. By this treatment in vacuum the fluid in the 
 pores comes to the surface, and the salt solution is removed by 
 the water sprinkled over the articles. 
 
 After drying, the deposit of copper, if it is to show high 
 luster, is polished with soft wheels of fine flannel and dry Vienna 
 lime. Commercial rouge FFF, moistened with a little alcohol, 
 is also an excellent polishing agent for copper and all other 
 soft metals. 
 
 As is well known, massive copper rapidly oxidizes in a 
 humid atmosphere, and this is the case to a still greater extent 
 with electro-deposited copper. Hence, the coppered objects, 
 if they are not to be further coated with a non-oxidizing metal, 
 have to be provided with a colorless, transparent coat of lac- 
 quer (sec "Lacquering," Chapter XIV). 
 
 It frequently happens that slightly-coppered (as well as 
 slightly-brassed) objects, especially of zinc, after some time, be- 
 come entirely white and show no trace of the deposit. This is 
 due to the deposit penetrating into the basis-metal, as already 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 335 
 
 explained. Lacquering in this case is of no avail, the deposit 
 also disappearing under the coat of lacquer. The only remedy 
 against the phenomenon is a heavier deposit. 
 
 If the coppered objects are to be coated with another metal, 
 drying is omitted, and after careful rinsing they are directly 
 brought into the respective bath, or into the quicking pickle, if, 
 as, for instance, in silvering, quicking has to be done. In such 
 cases, where the copper deposit serves only as an intermediary 
 for the reception of another metallic coating, the objects need 
 not be coppered as thickly, as previously described, by treating 
 them three times in the bath. Preliminary coppering for 5 to 
 IO minutes suffices in all cases, which is succeeded by scratch- 
 brushing in order to be convinced that the deposit adheres 
 firmly, and that the basis-metal is uniformly coated. The 
 objects are then suspended in the bath for from 5 to 10 minutes 
 longer with a weak current. 
 
 In coppering sheet-iron or sheet- zinc which is to be nickeled, 
 the sheets are taken from the bath after 3 to 5 minutes, at any 
 rate while they still retain luster, scratch-brushing being in this 
 case omitted. For coppering such sheets a current-density of 
 0.5 ampere and an electro-motive force of 3.5 to 4 volts is re- 
 quired. 
 
 The treatment of copper baths when they become inactive, 
 or show other abnormal features, has already been referred to. 
 
 When, as is frequently done, a fluid prepared by dissolving 
 cuprous oxide in potassium cyanide is used in place of solution 
 of crystallized potassium copper cyanide in water, for increas- 
 ing the content of metal, it must not be forgotten to add the 
 corresponding quantity of bisulphite of soda for the conversion 
 of the caustic potash formed into potassium sulphate. 
 
 All other general rules for plating baths given under " Elec- 
 tro-plating Solutions," Chapter V., must here also be observed. 
 
 In the course of time, copper-cyanide baths become thick in 
 consequence of the decomposition of the potassium cyanide 
 and the accumulation of alkaline carbonate and other products 
 of transformation formed thereby, the additions for refreshing 
 
336 ELECTRO-DEPOSITION OF METALS. 
 
 the baths also partly contributing thereto. While the normal 
 specific gravity of freshly-prepared baths is, according to their 
 composition, from 5° to 7 Be., the baths after having been in 
 operation for several years may show ii° Be. and more. It is 
 frequently found that coppering in baths which have become 
 thick is not effectual, the deposit not adhering so well and not 
 showing the brilliant color of copper as when produced in a 
 fresh bath. The only remedy for this is diluting the bath with 
 water to 6° or J° Be., increasing the content of metal by add- 
 ing highly concentrated solution of potassium copper cyanide, 
 and decomposing the alkaline carbonates, or at least a greater 
 portion of them, by conducting sulphurous acid into the bath, 
 or by dissolving bisulphite of soda in it. 
 
 Coppering small articles in quantities. If a large quantity of 
 small articles is at one time to be coppered in dipping baskets, 
 it is recommended to use the baths quite hot, this causing, to 
 be sure, a considerably larger consumption of potassium cyanide 
 than in cold baths. For the rest, the process is the same as 
 that given for nickeling small objects in quantities. 
 
 If very large quantities of small objects have continually to 
 be coppered, one of the mechanical plating contrivances re- 
 ferred to in Chapter VI will do good service. 
 
 The inlaying of depressions of coppered art-castings with 
 black may be done in different ways. Some blacken the ground 
 by applying a mixture of spirit lacquer with lampblack and 
 graphite, while others use oil of turpentine with lampblack and 
 a few drops of copal lacquer. A very thin nigrosin lacquer 
 mixed with finely pulverized graphite is very suitable for the 
 purpose. When the lacquer is dry the elevated places which 
 are to show the copper color are cleansed with a linen rag 
 moistened with alcohol. 
 
 Electrolytically coppered articles may be inlaid black by 
 coating them, after thorough scouring and pickling, with 
 arsenic in one of the baths given under " Electro-deposition of 
 Arsenic," and, after drying in hot water and sawdust, freeing 
 the surfaces and profiles, which are to appear coppered, from 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 337 
 
 the coating of arsenic by polishing upon a felt wheel. If this 
 polishing is to be avoided, the portions which are not to be 
 black may be coated with stopping-off varnish, and arsenic 
 deposited upon the places left free. 
 
 For coppering by contact and boiling, see special chapter, 
 " Depositions by Contact." 
 
 For coloring, pcitinizing and oxidizing of copper, see the 
 proper chapter. 
 
 Examination of Copper-baths Containing Potassium Cyanide. 
 In the preceding sections several characteristic indications 
 which serve for the qualitative examination of these baths have 
 already been given. Like all baths containing potassium 
 cyanide, their original composition gradually suffers extensive 
 alterations by the decomposition of the potassium cyanide, 
 which by the carbonic acid of the air is changed to potassium 
 carbonate and hydrogen cyanide, and spontaneously also to 
 ammonia and potassium formate. The potassium cyanide is 
 also split up by the current, potassium hydroxide being 
 formed, together with decomposition of water, which by the 
 carbonic acid of the air is gradually converted into potash, 
 while hydrogen cyanide and hydrogen escape. Under certain 
 conditions an oxidation of the potassium cyanide to potassium 
 cyanite may also take place. 
 
 The excess of potassium cyanide required for the correct 
 performance of the copper-bath is therefore gradually con- 
 sumed, and the bath, at first of a wine-yellow color, acquires a 
 blue coloration, and does no longer yield a good deposit. 
 When such is the case, the same quantity of copper which is 
 withdrawn from the bath by the deposit, is not dissolved from 
 the anodes, and, hence, the determination of the content of free 
 potassium cyanide, as well as that of the content of copper, may 
 at times be necessary. A determination of the potassium car- 
 bonate (potash) formed in the bath and its removal, or con- 
 version into potassium cyanide by the addition of the corre- 
 sponding quantity of barium cyanide solution, which will be 
 22 
 
338 ELECTRO-DEPOSITION OF METALS. 
 
 referred to under silver baths, cannot be recommended. This 
 determination in copper-baths which contain, as is generally 
 the case, sulphides, is troublesome, and an accumulation of 
 potash in copper baths does not produce the same evils as in 
 a silver bath. If, however, a copper bath, after working for 
 years, has become thick in consequence of a large content of 
 potash, it can be renewed without considerable expense, or, if 
 this is not desired, it can be regenerated by diluting with water,, 
 and increasing the content of copper and of potassium cyanide. 
 
 Hence, the determination of the free potassium cyanide 
 (i. e., not fixed on copper), and that of the copper will here 
 only be discussed. 
 
 Determination of potassium cyanide. — The best and most 
 rapid method for this purpose is by titrating with decinormal 
 solution of silver nitrate. Silver nitrate and potassium cyanide 
 form finally potassium nitrate and insoluble silver cyanide, the 
 latter, however, being redissolved to potassium silver cyanide 
 so long as free potassium cyanide is present. Since potassium 
 silver cyanide contains two molecules of cyanogen, one mole- 
 cule of silver nitrate corresponds to two molecules of potassium 
 cyanide, and I cubic centimeter of decinormal solution of silver 
 nitrate corresponds to 0.013 gramme of potassium cyanide. 
 
 Bring, by means of a pipette, 5 cubic centimeters of the 
 copper bath into a beaker having a capacity of about ^ liter. 
 Dilute with about 150 cubic centimeters of water, add one or 
 two drops of saturated common salt solution, and then, whilst 
 constantly stirring the fluid in the beaker, allow to flow in from 
 the burette silver nitrate solution so long as the precipitate 
 formed dissolves rapidly. 
 
 When solution becomes sluggish, add, stirring constantly, 
 silver nitrate solution drop by drop, waiting after the addition 
 of each drop until the fluid has again become clear. When 
 the fluid does not become clear after adding the last drop, and 
 it shows a slight turbidity, no more free potassium cyanide is 
 present. By multiplying the cubic centimeters of decinormal 
 solution of silver nitrate used by 2.6, the content of potassium 
 cyanide per liter of bath is found. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 339 
 
 Suppose, for instance, for 5 cubic centimeters of bath, 2.2 
 cubic centimeters of silver solution have been used, then 1 liter 
 of the bath contains 2.2 X 2.6 = 5.72 grammes of free potassium 
 cyanide, because I cubic centimeter of silver solution corre- 
 sponds to 0.013 grammes of potassium cyanide, therefore 2.2 
 cubic centimeters — 2.2 . 0.013 = 0.0286 grammes, from which 
 results by calculation 
 
 5 : 0.0286= 100: x 
 
 x = 5.72 grammes. 
 
 If now the initial content of free potassium cyanide in the 
 freshly prepared bath has been determined, a later determina- 
 tion will show the deficiency of it which has taken place. It 
 must, however, be taken into consideration that the potassium 
 formate formed by the decomposition of the potassium cyanide 
 may, up to a certain degree, apparently fill the role of the 
 potassium cyanide, in so far as it decreases the conducting re- 
 sistance of the bath, but it does not contribute to the solution 
 of the anodes. Hence, if the established deficiency of potas- 
 sium cyanide would be replaced by equally large quantities of 
 the salt, there would be danger of too much of it getting into 
 the bath, and the latter would conduct too readily, which would 
 result in the deposit precipitating too rapidly and turning out 
 less adherent. 
 
 Hence, it is evident that analytical methods alone are not 
 sufficient for maintaining entirely constant baths containing po- 
 tassium cyanide, and practical experience and a good faculty of 
 observation are required if the results of analysis are to be util- 
 ized for the correction of the baths. The potassium formate 
 can neither be removed from the bath nor can it be quanti- 
 tatively determined, and since its action in the bath is not accu- 
 rately known, it can only be stated from practical experience, 
 that under normal conditions only about 60 per cent, of the de- 
 ficiency of free potassium cyanide in a copper bath should be 
 replaced by pure potassium cyanide. 
 
34-0 ELECTRO-DEPOSITION OF METALS. 
 
 Determination of copper. This may be effected by electrolytic 
 or volumetric analysis. 
 
 For the determination of copper by electrolysis, measure off by 
 means of the pipette, 10 cubic centimeters of the copper bath, 
 and allow the fluid to run into a porcelain dish having a capa- 
 city of 150 to 200 cubic centimeters. Add 10 cubic centime- 
 ters of pure strong hydrochloric acid, cover the dish with a 
 watch glass, and heat upon the water bath. When evolution of 
 gas ceases, carefully remove the watch glass, rinse off adhering 
 drops with a small quantity of distilled water into the dish, and 
 evaporate the contents of the latter nearly to dryness. Now add 
 about 1 cubic centimeter of strong nitric acid, swing the dish to 
 and fro so that all portions of the residue are moistened by the 
 acid, heat for a short time, and then add 32 cubic centimeters 
 of pure dilute sulphuric acid (1 part acid, 2 parts water), with 
 which the contents of the dish are heated, until every trace of 
 odor of hydrochloric and nitric acids has disappeared. Now 
 pour the copper solution into the platinum dish serving for 
 electrolysis, rinse the porcelain dish with distilled water, adding 
 the wash-water to the contents of the platinum dish, fill the lat- 
 ter up to within I centimeter of the rim with water, add 2 cubic 
 centimeters of pure concentrated nitric acid, and electrolyze 
 with a current-strength of ND 100= 1 ampere, i. e,, 1 ampere 
 for 100 square centimeters surface of the platinum dish which 
 serves as cathode. 
 
 The copper separates with a bright red color, adhering 
 firmly to the platinum dish which is connected with the nega- 
 tive pole of the source of current. That the separation of 
 copper is finished is recognized by a narrow strip of platinum 
 sheet, when suspended in the platinum dish, showing in 15 
 minutes no trace of coppering; or by a few. drops of the solu- 
 tion when brought together with a drop of yellow prussiate of 
 potash solution, producing no red coloration. 
 
 When by one of the above-mentioned means the complete 
 separation of the copper has been ascertained, the platinum 
 dish is washed, without interruption of the current, the water 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 3 4. 1 
 
 removed by rinsing the dish with absolute alcohol, and the lat- 
 ter removed by rinsing with ether. Dry for a short time in an 
 air bath at 21 2° F., and weigh the dish together with the pre- 
 cipitate of copper. By deducting the weight of the dish, the 
 weight of the copper is obtained, and, since 10 cubic centi- 
 meters of the bath were electrolyzed, the weight of the copper 
 multiplied by 100 gives the contents of copper in grammes in 
 1 liter of copper bath. 
 
 The volumetric determination of copper is based upon the 
 principle that solution of sulphate or chloride of copper forms, 
 with potassium iodide, copper iodide, whilst free iodine is at 
 the same time formed, one atom of liberated iodine correspond- 
 ing to one molecule of copper salt. This free iodine is de- 
 termined by titration with a solution of sodium hyposulphite of 
 known content, and the content of copper is calculated from 
 the number of cubic centimeters of the solution used. For the 
 recognition of the final reaction, the blue coloration, which 
 originates when starch solution combines with free .iodine, is 
 utilized. There are required a decinormal iodine solution 
 which contains per liter exactly 12.7 grammes of re-sublimated 
 iodine dissolved in potassium iodide, and a decinormal solution 
 of sodium hyposulphite, of which 10 cubic centimeters diluted 
 with water and compounded with a small quantity of starch 
 solution must exactly use 10 cubic centimeters of iodine solu- 
 tion to give a permanent blue coloration by the formation of 
 iodine-starch. 
 
 The mode of operation is as follows : Heat in a porcelain 
 dish 10 cubic centimeters of the copper bath with 10 cubic 
 centimeters of strong hydrochloric acid, evaporate nearly to 
 dryness with 1 cubic centimeter of strong nitric acid and 2 
 cubic centimeters of hydrochloric acid, and heat upon the 
 water bath until the nitric acid is entirely removed. The resi- 
 due is dissolved in water with the addition of a small quantity 
 of dilute hydrochloric acid. The clear solution is brought into 
 a measuring flask holding 100 cubic centimeters, the dish is 
 rinsed with water, the free acid neutralized by the addition of 
 
342 ELECTRO-DEPOSITION OF METALS. 
 
 dilute soda lye until a precipitate of bluish copper hydrate 
 commences to separate, which after vigorous shaking does not 
 disappear. Now add, drop by drop, hydrochloric acid until the 
 precipitate just dissolves, fill the flask up to the ioo-centimeter 
 mark with water, and mix by shaking. Of this solution bring 
 by means of the pipette, IO cubic centimeters into a glass of 
 ioo cubic centimeters capacity, and provided with a glass 
 stopper, add 10 cubic centimeters of a 10 per cent, potassium 
 iodide solution, dilute with a small quantity of water, close the 
 glass with the stopper, and let it stand for 10 minutes. Now 
 add from a burette, decinormal solution of sodium hyposulphite 
 until the iodine solution has become colorless, and then add a 
 few cubic centimeters more. Next bring into the flask a few 
 drops of starch solution, and then add from another burette, 
 decinormal iodine solution until a blue coloration is just per- 
 ceptible. By deducting the cubic centimeters of iodine solution 
 used from the cubic centimeters of sodium hyposulphite solu- 
 tion, it will be known how many cubic centimeters of the latter 
 solution have been used for fixing the iodine liberated by 
 the reciprocal action between copper solution and potassium 
 cyanide solution. Since I cubic centimeter of a sodium hypo- 
 sulphite solution, which is equivalent to the decinormal iodine 
 solution, corresponds to 0.0063 gramme of copper, therefore, 
 as 1 cubic centimeter of the bath has been titrated, the number 
 of cubic centimeters found has to be multiplied by 6.3 to find 
 the content of copper per liter of copper bath. 
 
 Suppose to 10 cubic centimeters of the copper solution mixed 
 with potassium iodide has been added 2.8 cubic centimeters of 
 sodium hyposulphite solution, and for titrating back the excess 
 0.7 cubic centimeters of iodine solution had been used up to 
 the appearance of the blue coloration, then 2.8 — 0.7 = 2.1 
 centimeters have been used, which multiplied by 6.3 gives 13.3 
 grammes as the content of copper per liter of bath. 
 
 If now a deficiency of copper has been established by one or 
 the other method, the original content of copper can be readily 
 restored by the addition of crystallized potassium-copper cya- 
 nide. This salt, when pure, contains about 30 per cent, copper. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 343 
 
 Suppose, when first prepared, the bath contained 15 grammes 
 of copper per liter, and it has been shown by analysis that it. 
 now contains only 13,3 grammes, then a deficiency of 1.7 
 grammes of copper has to be made up. Since 100 grammes 
 of potassium-copper cyanide contain 30 grammes of copper, 
 then 
 
 3 : 100= 1.7 : x 
 
 ~* = 3-57 
 
 and hence 3.57 grammes of potassium-copper cyanide per liter 
 have to be dissolved in the bath. It is advisable to electrolyti- 
 cally determine in the previously described manner, after first 
 destroying the cyanogen combinations, the content of copper 
 in the potassium-copper cyanide to be used for strengthening 
 the bath, so that in case the salt shows a smaller content of 
 copper, the proper quantity of it may be added. 
 
 2. Deposition of Brass. 
 
 Brass is an alloy of copper and zinc, whose color depends on 
 the quantitative proportions of both metals. The alloys known 
 as yellow brass, red brass {similor, tombac), consist essentially 
 of copper and zinc, while those known as bell metal, gun metal, 
 and the bronzes of the ancients are composed of copper and tin. 
 Modern bronzes contain copper, zinc and tin. 
 
 The behavior of brass towards acids is nearly the same as 
 that of copper. It oxidizes, however, less rapidly in the air, is 
 harder than copper, malleable, and can be rolled and drawn 
 into wire. 
 
 Brass baths. In accordance with the plan pursued in this 
 work only the most approved formulas, the greater portion of 
 which has been practically tested, will be given. More recent 
 propositions which cannot be recognized as improvements 
 over the older directions, will be critically commented upon. 
 There is a large number of receipts for brass baths which show 
 such remarkable difference in the proportions of the two metals 
 that, on more closely examining them, even the layman can, at 
 
344 ELECTRO-DEPOSITION OF METALS. 
 
 the first glance, discover the doubtful result. Thus, for in- 
 stance, Russell and Woolrich recommend a bath in which the 
 quantity of copper salt to zinc salt is in the proportion of 
 10: i. Other authors give the following proportions: Copper 
 i to zinc 8 (Hecren) ; copper I to zinc 2 (Salzede, Kruel) ; 
 copper 2 to zinc I (Newton). These examples will show the 
 difference of opinion regarding the suitable composition of 
 brass baths. 
 
 An electro-plater understanding all the conditions and the 
 effect of the current-strength might possibly obtain a deposit 
 of brass even from baths which show such abnormal proportions 
 of mixture as those made up according to the directions by 
 Russell, Heeren, and others, but how many conditions have 
 thereby to be taken into consideration will be shown later on. 
 We share the opinion of Roseleur that a brass bath containing 
 copper and zinc salts in nearly equal proportions is the most 
 suitable and least subject to disturbances. A brass bath is to 
 be considered as a mixture of solutions of copper cyanide and 
 zinc cyanide, or of other copper-zinc salts, in the most suitable 
 solvent. Now, since a solution of copper cyanide requires a 
 different current-strength from one of zinc salt, it will be seen 
 that according to the greater or smaller current-strength, now 
 more of the one, and now more of the other, metal is deposited,, 
 which, of course, influences the color of the deposit. Hence 
 the proper regulation of the current is the chief condition for 
 obtaining beautiful deposits, let the bath be composed as it may. 
 
 For all baths containing more than one metal in solution, it 
 may be laid down as a rule that the less positive metal is first 
 deposited. In a brass bath, copper is the negative, and zinc the 
 positive metal ; and hence a weaker current deposits more 
 copper, in consequence of which the deposit becomes redder,, 
 while, vice versa, a more powerful current decomposes, in addi- 
 tion to the copper solution, also a larger quantity of zinc solu- 
 tion, and reduces zinc, the color produced being more pale 
 yellow to greenish. By bearing this in mind it is not difficult 
 to obtain any desired shades within certain limits. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 345 
 
 I. Brass bath according to Roseleitr. — Blue vitriol and zinc 
 sulphate (white vitriol ), of each 5^ ounces, and crystallized 
 carbonate of soda 15^ ounces. Crystallized carbonate of 
 soda and bisulphite of soda in powder, of each 7 ounces, 98 per 
 cent, potassium cyanide 8^ ounces, arsenious acid 30^ grains, 
 water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 2.6 to 2.8 
 volts. 
 
 Current-density , 0.32 ampere. 
 
 The bath is prepared as follows : In 5 quarts of warm water 
 dissolve the blue vitriol and the zinc sulphate ; and in the other 
 5 quarts the 15^ ounces of carbonate of soda; then mix both 
 solutions, stirring constantly. A precipitate of carbonate of 
 copper and carbonate of zinc is formed, which is allowed 
 quietly to settle for 10 to 12 hours, when the supernatant clear 
 fluid is carefully poured off, so that nothing of the precipitate 
 is lost. Washing the precipitate is not necessary. The clear 
 fluid poured off is of no value and is thrown away. Now add 
 to the precipitate so much water that the resulting fluid 
 amounts to about 6 quarts, and dissolve in it, with constant 
 stirring, the carbonate and bisulphite of soda, adding these 
 salts, however, not at once, but gradually, in small portions, to 
 avoid foaming over by the escaping carbonic acid. Dissolve 
 the potassium cyanide in 4 quarts of cold water and add this 
 solution, with the exception of about l / 2 pint, in which the 
 arsenious acid is dissolved with the assistance of heat, to the 
 first solutions, and finally add the solution of arsenious acid in 
 the y 2 pint of water retained, when the bath should be clear 
 and colorless. If after continued stirring, particles of the pre- 
 cipitate remain undissolved, carefully add somewhat more 
 potassium cyanide until solution is complete. 
 
 The addition of a small quantity of arsenious acid is claimed 
 to make the brassing brighter; but the above-mentioned pro- 
 portion of 30^ grains for a 10-quart bath must not be ex- 
 ceeded, as otherwise the color of the deposit would be too light 
 and show a gray tone. 
 
346 ELECTRO-DEPOSITION OF METALS. 
 
 II. Crystallized carbonate of soda 10}4 ounces, pulverized 
 bisulphite of soda 7 ounces, neutral acetate of copper 4.4 
 ounces, pulverized chloride of zinc 4.4 ounces, 98 per cent, 
 potassium cyanide 14. 11 ounces, arsenious acid 30^ grains, 
 water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance 2.6 to 2.8 
 volts. 
 
 Current density 0.32 ampere. 
 
 The preparation of this bath is more simple than that of the 
 preceding. 
 
 Dissolve the carbonate and bisulphite of soda in 4 quarts of 
 water, then mix the acetate of copper and chloride of zinc with 
 2 quarts of water, and gradually add this mixture to the solu- 
 tion of the soda salts. Next dissolve the potassium cyanide in 
 4 quarts of water, and add this solution to the first, retaining, 
 however, a small portion of it, in which dissolve the arsenious 
 acid with the assistance of heat. Finally add the arsenious 
 acid solution, when the bath will become clear. If, however, 
 the solution should not be clear and colorless, or at least wine- 
 yellow, after adding the potassium cyanide, an additional small 
 quantity of the latter may be used, avoiding, however, a con- 
 siderable excess. 
 
 For brassing iron in this bath, the quantity of carbonate of 
 soda may be increased up to 35 ozs. for a 10-quart bath. This 
 is also permissible, when in plating zinc articles with a heavy 
 deposit of brass, frequent scratch-brushing is to be avoided. 
 It would seem that a large content of carbonate of soda in the 
 bath retards to a considerable extent the brass color from 
 changing into a discolored brown, though the brilliancy of the 
 deposit appears to suffer somewhat. When boiled for I to 2 
 hours, or worked through with the current for 10 to 12 hours, 
 the bath prepared according to formula II. works very well. 
 
 Cupro-cupric sulphide and cuprous oxide may also be advan- 
 tageously used for the preparation of brass baths. Suitable 
 formulas for them are as follows: 
 
 \\a. Pure crystallized zinc sulphate (zinc vitriol or white vit- 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 347 
 
 riol) 5^ ozs., crystallized carbonate of soda 7 ozs., pulverized 
 bisulphite of soda 4% ozs., ammonium-soda 5^ ozs., 99 per 
 cent, potassium cyanide 10^ ozs., cupro-cupric sulphide 35- 
 ozs., water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode distance, 2.8 volts. 
 
 Current- density, 0.5 ampere. 
 
 The bath is prepared as follows: Dissolve the zinc sulphate 
 in 5 quarts of water and the crystallized carbonate of soda in 
 4 quarts of warm water, and mix the two solutions. When the 
 precipitate of zinc carbonate, which is formed, has completely 
 settled, siphon off the supernatant fluid as much as possible, 
 and throw the lye away. 
 
 Dissolve the bisulphite of soda, the ammonium-soda, and the 
 potassium cyanide in 5 quarts of water, add the cupro-cupric 
 sulphide, stirring constantly, and when solution is complete, 
 add the precipitate of zinc carbonate. 
 
 This bath yields beautiful pale yellow deposits of a warm 
 brass tone. 
 
 Wb. Potassium cyanide 10*^ ozs., cuprous oxide 3 ozs., zinc 
 chloride 2^ ozs., bisulphite of soda 7 ozs., water 10 quarts. 
 
 Dissolve the potassium cyanide in 5 quarts of water, add the 
 cuprous oxide and stir until solution is complete. Dissolve 
 the bisulphite of soda and the zinc chloride in the other 5 
 quarts of water, and mix the two solutions, stirring vigorously. 
 
 If metallic cyanides are to be used for the preparation of 
 brass baths, the following formula may be recommended : 
 
 III. Crystallized carbonate of soda 10^ ozs., pulverized 
 bisulphite of soda 7 ozs., copper cyanide and zinc cyanide of 
 each 3^ ozs., water 10 quarts, and enough 98 per cent, potas- 
 sium cyanide to render the solution clear. 
 
 To prepare the bath dissolve the carbonate and bisulphite of 
 soda in 2 or 3 quarts of water, rub in a porcelain mortar the cop- 
 per cyanide and zinc cyanide with a quart of water to a thin 
 paste, add this paste to the solution of the soda salts, and 
 finally add, with vigorous stirring, concentrated potassium 
 cyanide solution until the metallic cyanides are dissolved. 
 
34§ ELECTRO-DEPOSITION OE METALS. 
 
 Dilute the volume to io quarts, and, for the rest, proceed as 
 given for formulas I and II. 
 
 Brass baths may in a still more simple manner be prepared 
 by using the double cyanides, potassium-cupric cyanide and 
 potassium-zinc cyanide. 
 
 Ilia. Potassium-cupric cyanide (crystallized) 5^ ozs., potas- 
 sium-zinc cyanide (crystallized) 5^ ozs., crystallized bisul- 
 phite of soda Sy( ozs., 98 per cent, potassium cyanide 11% 
 drachms, water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 3 volts. 
 
 Current-density, 0.3 ampere. 
 
 The bath is prepared by simply dissolving the salts in warm 
 water of about 122° F. 
 
 For brassing sine exclusively, Roseleur recommends the fol- 
 lowing bath : 
 
 IV. Dissolve 9^ ozs. of crystallized bisulphite of soda and 
 14 ozs. of 70 per cent, potassium cyanide in 8 quarts of water, 
 and add to this solution one of 4^ ozs. each of neutral acetate 
 of copper and crystallized chloride of zinc, 5^ ozs. of aqua 
 ammonia of 0.9 10 specific gravity, and 2 quarts of ^vater. 
 
 For brassing wrougkl-iron, cast-iron and steel, Gore highly 
 recommends the following composition ; 
 
 IVa. Dissolve 35% czs. of crystallized carbonate of soda, 7 
 ozs. of pulverized bisulphite of soda, 13^ ozs. of 98 per cent, 
 potassium cyanide in S quarts of water; then add, stirring con- 
 stantly, a solution of fused chloride of zinc 33^ ozs., and 
 neutral acetate of copper 4^ ozs., in 2 quarts of water. Boil 
 and filter. The bath works well, best with an electro-motive 
 force of 3.75 volts, and also takes readily on cast-iron. 
 
 A solution for transfcring any copper- zinc alloy which serves 
 as anode, is composed, according to Hess, as follows: 
 
 V. Sodium bicarbonate, 14 j£ ozs., crystallized ammonium 
 chloride 9^3 ozs., 98 per cent, potassium cyanide 2^ ozs., 
 water 10 quarts. 
 
 Cast metal plates are to be used as anodes. Transfer begins 
 after a medium strong current has for a few hours passed 
 through the bath. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 349 
 
 This bath is also well adapted for the deposition of tombac 
 with the use of tombac anodes. Most suitable electro-motive 
 force, 3 to 3.5 volts. 
 
 Fresh brass baths work, as a rule, more irregularly than any 
 other baths containing cyanide, the deposit being cither too red 
 or too green or gray, while frequently one side of the object is 
 coated quite well, and the other not at all. To force the bath 
 to work correctly it must be thoroughly boiled, the water which 
 is lost by evaporation being replaced by the addition of dis- 
 tilled water or pure rain water. If boiling is to be avoided, the 
 bath, as previously mentioned, is worked through for hours, and 
 even for days, with the current, until an object suspended in it 
 is correctly brassed. 
 
 Prepared brass salts. Regarding these salts, we refer to what 
 has been said in reference to coppering salts, p. 328. For a 
 100-quart brass bath, with 92.59 grains of brass, use 6.6 lbs. of 
 double brass salt and 7 ozs. of 98 to 99 per cent, potassium 
 cyanide, and for a 100-quart brass bath with 13S.8S grains of 
 brass per quart 9.9 lbs. of brass double salt and 7 ozs. of 98 to 
 99 per cent, potassium cyanide. 
 
 As for copper baths prepared with double salt3, an addition 
 of 30 to 46 grains of potassium cyanide per liter and of a suit- 
 able conducting salt (neutral sodium sulphite) may be recom- 
 mended. 
 
 Tanks for brass baths. What has been said on this subject 
 under tanks for copper cyanide baths (p. 330) applies also to 
 brass baths. 
 
 Brass anodes. Sheets of brass, annealed and pickled bright, 
 not rolled too hard and of as nearly as possible the same com- 
 position and color as the deposit is to have, are used as anodes. 
 
 Cast anodes have the advantage of being more readily solu- 
 ble, and therefore keep the content of metal in the bath more 
 constant than rolled brass anodes. However, the latter answer 
 very well if care is taken to from time to time increase the con- 
 tent of metal in the bath. The anode-surface in the bath 
 should be as large as possible, since with slight anode current- 
 
350 ELECTRO-DEPOSITION OF METALS. 
 
 densities the formation of slime on the anodes is less than when 
 the contrary is the case. 
 
 Execution of brassing. As previously mentioned, the color 
 of the deposits depends on the quantitative proportions of the 
 two metals deposited, a weaker current' depositing predom- 
 inantly copper, and a stronger current more zinc. Hence by 
 the use of a rheostat it is in the power of the operator to effect 
 within the limits which are given by the resistances of the 
 rheostat, deposits of brass alloys of a redder or more pale 
 yellow to greenish color, according to whether the resistance is 
 increased or decreased. 
 
 However, according to the composition of the brass bath, 
 and especially with baths which have for a long time been in 
 use, a determined color of the alloy to be deposited cannot be 
 produced with the assistance of the rheostat. In such case the 
 content of metal in the bath which is required and lacking for 
 the production of a determined color, must be augmented by 
 the addition of solution of the respective metallic salts, or in 
 the form of double salt. 
 
 Suppose a bath which originally contained copper and zinc 
 salts in equal proportions has been long in daily use. Now, 
 since brass contains more copper than zinc the deposit will be 
 richer in copper, and it is evident that more of the latter will 
 be withdrawn from the bath than of zinc, and finally a limit will 
 be reached when the bath with a current suitable for the de- 
 composition of the solution will deposit a greenish or gray 
 brass, and with a weaker current produce no deposit whatever. 
 The only remedy in such a case is the addition of sufficient 
 solution of copper cyanide in potassium cyanide, so that, even 
 with quite a powerful current, a deposit of a beautiful brass 
 color is produced, the shades of which can then again be con- 
 trolled with the assistance of the rheostat. Instead of dissolv- 
 ing copper cyanide in potassium cyanide, it is better to directly 
 use crystallized potassium-copper cyanide. However, it must 
 not be forgotten that every addition of a metallic salt momen- 
 tarily initates the brass bath, making it, so to sav, sick, and to 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 351 
 
 confine this feature to the narrowest limit, an addition of car- 
 bonate and bisulphite of soda, or only of neutral bisulphite of 
 soda, should at the same time be made, and the bath be 
 worked through with the current as previously described, until 
 a test shows that it works in a regular manner. The effect of 
 the addition cannot be controlled in any other way, and more 
 might be added than is required and desirable. If, however, 
 the quantity of the addition is shown not to be sufficient, the 
 operation is continued till the object is attained. 
 
 As in the copper bath, an abundant formation of slime on 
 the anodes indicates the want of potassium cyanide in the bath. 
 In this case the evolution of gas-bubbles on the objects is very 
 slight, and the deposit forms slowly. This is remedied by an 
 addition of potassium cyanide. However, in brass baths con- 
 taining the standard excess of free potassium cyanide, the for- 
 mation of slime has also a disturbing effect, when the baths are 
 for a longer time worked without interruption. The solution 
 by the potassium cyanide of the bath of the metallic cyanides 
 formed on the anodes takes place more slowly than their forma- 
 tion. If the operation of the bath is for some time interrupted, 
 gradual solution takes place and the greater part of the slime 
 on the anodes disappears. However, with an uninterrupted 
 use of the bath, the layer of slime frequently increases to such 
 an extent that the current cannot flow through the anodes into 
 the bath. In such a case, the further increase of the content 
 of potassium cyanide would not be advisable, since it would 
 exceed the limit admissible for a dense deposit; frequent me- 
 chanical cleaning of the anodes is then the best remedy. A 
 particularly dense slime on the anodes is yielded by baths which 
 contain small quantities of conducting salts, such, for instance, 
 as are prepared from the double and triple salts. By giving 
 such baths additions of sulphites or chlorides a less compact 
 slime is formed which is favorable for solution in potassium 
 cyanide. This effect is without doubt due to the anions of the 
 conducting salts appearing on the anodes. 
 
 The sluggish formation of the deposit, however, may also be 
 
352 ELECTRO-DEPOSITION OF METALS. 
 
 due to a want of metallic salts. In this case not only potassium 
 cyanide, but also solution of copper cyanide and zinc cyanide 
 in potassium cyanide, has to be added. For this purpose pre- 
 pare a concentrated solution of potassium cyanide in water, and 
 a solution of equal parts of blue vitriol and zinc sulphate in 
 water. From the latter, precipitate the copper and zinc as car- 
 bonates with a solution of carbonate of soda as given in formula 
 I. After allowing the precipitate to settle, pour off the clear 
 supernatant fluid, and add to the precipitate, stirring vigorously, 
 of the potassium-cyanide solution until it is dissolved; if heat- 
 ing takes place thereby, add from time to time a little cold 
 water. Add this solution with a small excess of potassium 
 cyanide, and the addition of carbonate or bisulphite of soda, to 
 the bath, and boil the latter or work it through with the cur- 
 rent. A more simple method is to procure copper cyanide and 
 zinc cyanide, or concentrated solutions of these combinations, 
 from a dealer in such articles. In the first case, rub in a mortar 
 equal parts of zinc cyanide and copper cyanide with water to a 
 thinly-fluid paste. Pour this paste into a potassium-cyanide 
 solution, containing about 7 ozs. of potassium cyanide to the 
 quart, as long as the metallic cyanides dissolve quite rapidly by 
 stirring. When solution takes place but slowly, stop the addi- 
 sion of paste. A still more simple way is to buy crystallized 
 potassium-copper cyanide and potassium-zinc cyanide, dissolve 
 these salts in suitable quantitative proportions, and add the 
 solution to the bath. 
 
 When a brass bath contains too great an excess of potassium 
 cyanide, a very vigorous evolution of gas takes place on the 
 objects, but the deposit is formed slowly or not at all ; besides, 
 the deposit formed has a tendency to peel off in scratch-brush- 
 ing. In this case the injurious excess has to be removed, 
 which is effected by pouring, whilst stirring vigorously, a quan- 
 tity of the above-mentioned thinly-fluid paste of zinc cyanide 
 and of copper cyanide into the bath. The addition of metallic 
 cyanides is continued only so long as they dissolve with 
 rapidity, so as not to fix all the free potassium cyanide of the 
 bath. 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 353 
 
 When a brass bath has not been used for some time a white 
 film frequently forms on its surface. This is best removed by 
 pushing it by means of a piece of twisted paper into one corner 
 of the bath, and lifting it off with a shallow dish. It may then 
 be dissolved, eventually by heating, in a small quantity of potas- 
 sium cyanide and the solution added to the bath. 
 
 To avoid unnecessary repetition we refer, as regards the pro- 
 duction of thick deposits, scratch-brushing and polishing of the 
 plated articles, to what has been said under " Execution of 
 Coppering," the directions given there being also valid for 
 brassing. 
 
 The deposition of several metals from a common solution is 
 not an easy task, and requires attention and experience. If, 
 however, the directions given in this chapter are followed, the 
 operator will be able to conduct, after short experience, the 
 brassing process with the same success as one in which but one 
 metal is deposited. 
 
 Special attention must be paid to frequent thorough mixing 
 of the contents of the bath, so that the fluids are renewed on the 
 cathodes, because otherwise, by reason of the fluid becoming 
 poor in metal, the deposit would show different compositions, 
 and consequently other colors. 
 
 For the production of deposits of brass which are to show a 
 tone resembling gold, it has been recommended to add to the 
 brass bath an aluminium salt, aluminium chloride, aluminium 
 sulphate, etc. Such baths have been offered to laymen as 
 aluminium-bronze baths, with the assurance that the deposit 
 obtained from them consists of an alloy of aluminium and 
 brass, and possesses the same power of resisting atmospheric 
 influences as aluminium-bronze. Although these commenda- 
 tions are evident!)' misleading, because, notwithstanding innum- 
 erable receipts for the production of electro-deposits of alu- 
 minium, the reduction of this metal from solutions of its salts 
 has thus far not been successfully accomplished. Deposits pro- 
 duced in such brass baths, compounded with aluminium salts, 
 were subjected to examination, and in no case was it possible 
 23 
 
354 ELECTRO-DEPOSITION OF METALS. 
 
 to establish even the slightest trace of aluminium in the deposit. 
 However, notwithstanding that a reduction of aluminium does 
 not take place, the influence of an addition of an aluminium salt 
 to brass baths, as regards the result of the brass tone, cannot 
 be denied, but up to the present time it has been impossible to 
 find an explanation of this fact. If a brass bath, prepared 
 according to the formulas given above be compounded with 35 
 to 40 grains of aluminium chloride per quart of bath, the result- 
 ing deposit shows a warmer, more sad brass tone than that 
 yielded by a bath without such an addition, and if the bath is 
 somewhat rich in copper, the color of the deposit almost resem- 
 bles red gold. However, greater power of resisting atmospheric 
 influence could not be noticed, neither can such be expected, 
 since the deposit consists solely of zinc or copper. 
 
 It remains to be mentioned that in brassing the distance of 
 the objects to be plated from the anodes is of considerable 
 importance. If objects with deep depressions or high reliefs 
 are suspended in the brass bath, it will be found that, with the 
 customary distance of 3^ to 5%^ inches from the anodes, the 
 brassing of the portions in relief nearest to the anodes will turn 
 out a lighter color than that of the depressed portions, which 
 will show a redder deposit, the reason for this being that the 
 current acts more strongly upon the portions in relief, and con- 
 sequently deposits more zinc than the weaker current, which 
 strikes the depressions. To equalize this difference the objects 
 have to be correspondingly further removed from the anodes, 
 with lamp-feet up to 9^ inches, and even more, when a deposit 
 of the same color will be everywhere formed. 
 
 The brassing of unground iron-castings is especially trouble- 
 some, and in order to obtain a beautiful and clean deposit the 
 preliminary scratch-brushing has to be executed with special 
 care; but even then the color of the brass deposit will some- 
 times be found to possess a disagreeable gray tone. This is 
 very likely largely due to the quality of the iron itself, and it is 
 advisable first to give the casting a thin coat of nickel or tin, 
 upon which a deposit of brass of the usual brilliancy can be 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 355 
 
 produced. In baths serving for brassing iron articles, a large 
 excess of potassium cyanide must be avoided. It is, however, 
 an advantage to increase the content of carbonate of soda. 
 
 Inlaying of brassed objects with black is done in the same 
 manner as described under " Deposition of Copper." 
 
 Brassing by contact will be referred to in the chapter " Depo- 
 sitions by Contact." 
 
 For oxidizing, patinizing and coloring of brass, see special 
 chapter. 
 
 Examination of brass baths. The characteristic indications 
 by which a deficiency, and too large an excess of potassium 
 cyanide in the bath, as well as an insufficient content of metal, 
 may be recognized, have already been discussed, and it is here 
 only necessary to refer to the quantitative determination of the 
 separate constituents. 
 
 Free potassium cyanide and the content of copper are deter- 
 mined in the same manner as described under copper baths 
 containing potassium cyanide. Hence the only determination 
 of zinc has here to be considered. For making this determi- 
 nation it is necessary to destroy the cyanide combinations, and 
 entirely to remove the copper. For this purpose bring by 
 means of the pipette 10 cubic centimeters of the brass bath 
 into a porcelain dish, .and proceed in the same manner as 
 given on page 336 for the determination of copper by electro- 
 lysis. Dissolve the evaporated residue in the dish in water, 
 adding a few drops of pure hydrochloric acid. Then bring the 
 solution into a capacious beaker, dilute with water to about 
 250 cubic centimeters, and heat to boiling. Now add about 
 10 cubic centimeters of pure dilute sulphuric acid (1 : 10) and 
 stirring constantly, mix with a solution of 2.5 grammes of 
 crystallized sodium. Copper sulphide is separated while the 
 sulphurous acid escapes. Cover the beaker with a watch-glass, 
 let it stand for 15 minutes, and then filter off the precipitate. 
 Wash the filter thoroughly with sulphuretted-hydrogen water, 
 and evaporate the filtrate together with the wash waters to 
 about 100 to 150 cubic centimeters. The solution contains all 
 the zinc, and can be at once titrated (see below). 
 
356 ELECTRO-DEPOSITION OF METALS. 
 
 For the determination of zinc by electrolysis, heat the solu- 
 tion to boiling, mix it with solution of sodium carbonate in 
 excess, and after the precipitate of basic zinc carbonate has 
 settled, filter it off. Dissolve the precipitate in the filter with 
 pure dilute sulphuric acid, bring the filtrate together with the 
 waters used for thoroughly washing the filter into a clean 
 beaker, and neutralize accurately with sodium carbonate. 
 
 Now bring into the platinum dish, previously coppered, 5 
 grammes of potassium oxalate, and 2 grammes of potassium 
 sulphate dissolved in a small quantity of water, fill the platinum 
 dish up to within I centimeter from the rim with distilled water, 
 and electrolyze with a current-density of ND 100=0.5 ampere. 
 The dull, bluish-white deposit of zinc is treated with water, then 
 with alcohol and ether, dried in the exsiccator over sulphuric 
 acid and weighed. The determined weight of the zinc deposit 
 multiplied by 100 gives the content of zinc in grammes per liter 
 of brass bath. 
 
 For the volumetric determination of the zinc, about 100 to 150 
 cubic centimeters of the zinc solution resulting after the pre- 
 cipitation of the copper are used. The determination is based 
 upon the principle that potassium ferrocyanide solution pre- 
 cipitates the zinc from the solution, and that complete precipi- 
 tation is indicated by an excess of potassium ferrocyanide, 
 yielding a brown coloration with uranium acetate. If now the 
 content of the potassium ferrocyanide solution is known, the 
 quantity of it used gives the content of zinc. It is best to use 
 a solution which contains per liter 32.45 grammes of pure crys- 
 tallized potassium ferrocyanide, every cubic centimeter of this 
 solution corresponding to O.oi gramme of zinc. Add, stirrring 
 constantly, from a burette potassium ferrocyanide solution to 
 the zinc solution in a beaker until a drop of the fluid brought 
 upon a strip of filtering paper previously saturated with uranium 
 acetate solution and again dried, just shows the commencement 
 of a brown coloration. 
 
 Since 10 cubic centimeters of the brass bath were used for 
 the determination, the number of cubic centimeters of potas- 
 sium ferrocyanide solution consumed gives the quantity of zinc 
 
DEPOSITION OF COPPER, BRASS AND BRONZE. 357 
 
 in grammes per liter of brass bath. Suppose 6 cubic centime- 
 ters of solution have been consumed, they would correspond to 
 0.06 gramme zinc (0.01 X 6). Hence since in 10 cubic centi- 
 meters of bath 0.06 gramme of zinc is present, the bath con- 
 tains 6 grammes (0.06 X 100) of zinc per liter. 
 
 If thus a deficiency of zinc in the bath, due to long-continued 
 working, has been determined the initial content can be readily 
 restored by the addition of pure potassium zinc cyanide. The 
 latter contains 26 per cent, of zinc, and the quantity required 
 to be added is determined in the same manner as with a copper 
 bath (see p. 342.) 
 
 Deposits of tombac, i. e., deposits having the color of tombac, 
 are obtained by increasing the content of copper in the brass 
 baths. 
 
 The following formula gives a tombac bath which works well : 
 
 Crystallized potassium copper cyanide 7 ozs., crystallized 
 potassium-zinc cyanide 3^ ozs., crystallized neutral bisulphite 
 of soda 8%^ ozs., potassium cyanide ^ oz., water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode distance, 3 volts. 
 
 Current-density, 0.3 ampere. 
 
 It is of special advantage for the deposition of tombac to 
 heat the bath to between 86° and 95 F., the resulting deposits 
 being of a more uniform color than at the ordinary temperature. 
 
 For tombac deposits the transferring solution, according to 
 Hess (see "Deposition of Brass," Formula V), may also be 
 employed, tombac sheets being used as anodes. 
 
 Deposits of bronze. Plating of metallic objects with bronze, 
 i. e., a copper-tin alloy, or an alloy of copper, tin and zinc, is but 
 seldom practiced, the bronze tone being in most cases imitated 
 by a brass deposit with a somewhat larger content of copper. 
 
 For coating wrought and cast-iron with bronze, Gountier rec- 
 ommends the following solution : 
 
 Yellow prussiate of potash 10^ ozs., cuprous chloride 5^ 
 ozs., stannous chloride (tin salt) 14 ozs., sodium hyposulphite 
 14 ozs., water 10 quarts. 
 
 According to Ruolz, a bronze bath is prepared as follows: 
 Dissolve at 122° to 140 F., copper cyanide 2.1 1 ozs., and 
 
358 ELECTRO-DEPOSITION OF METALS. 
 
 oxide of tin 0.7 o/s., in 10 quarts of potassium-cyanide solution 
 of 4 Be. The solution is to be filtered. 
 
 Eisner prepares a bronze bath by dissolving 21 ozs. of blue 
 vitriol in 10 quarts of water, and adding a solution of 2^ ozs. 
 of chloride of tin in potash lye. 
 
 Salzede recommends the following bath, which is to be used 
 at between 86° and 95 ° F. : Potassium cyanide 3^ ozs., car- 
 bonate of potash 35 y ozs., stannous chloride (tin salt) 0.42 
 oz., cuprous chloride y, oz., water io quarts. 
 
 Weil and Newton claim to obtain beautiful bronze deposits 
 from solutions of the double tartrate of copper and potash, and 
 the double tartrate of the protoxide of tin and potash, with 
 caustic potash, but fail to stale the proportions. 
 
 The above formula: are here given with all reserve, since ex- 
 periments with them failed to give satisfactory results. With 
 Gountier's, Ruolz's, and Eisner's baths no deposit was obtained, 
 but only a strong evolution of hydrogen, while even with a 
 strong current, Salzedc's bath did not yield a bronze deposit, 
 but simply one of tin. 
 
 The following method of preparing a bronze bath may be 
 recommended: Prepare, each by itself, solutions of phosphate 
 of copper and stannous chloride (tin salt) in sodium pyrophos- 
 phate. From a blue vitriol solution precipitate, with sodium 
 phosphate, phosphate of copper, allow the latter to settle, and 
 after pouring oil' the clear supernatant fluid, bring it to solution 
 by concentrated solution of sodium pyrophosphate. On the 
 other hand, add to a saturated solution of sodium pyrophos- 
 phate, solution of tin salt, as long as the milky precipitate 
 formed dissolves. Of these two metallic solutions, add to a 
 solution of sodium pyrophosphate, which contains about iy 
 ozs. of the salt to the quart, until the precipitate appears 
 quickly and of the desired color. For anodes, use cast bronze 
 plates, which dissolve well in the bath. Some sodium phos- 
 phate has from time to time to be added to the bath, and if the 
 color becomes too light, solution of copper, and if too dark, 
 solution of tin. 
 
 For nickel-bronze, sec- p. 310. 
 
CHAPTER VIII. 
 
 DEPOSITION OF SILVER. 
 
 Properties of silver. — Pure silver is the whitest of all known 
 metals. It takes a fine polish, is softer and less tenacious than 
 copper, but harder and more tenacious than gold. It is very 
 malleable and ductile, and can be obtained in exceedingly thin 
 leaves and fine wire. Its specific gravity is 10.48 to 10.55, 
 according to whether it is cast or hammered. It melts at about 
 1832 F. It is unacted upon by the air, but in the atmosphere 
 of towns it gradually becomes coated with a film of silver 
 sulphide. It is rapidly dissolved by nitric acid, nitrogen diox- 
 ide being evolved. Hydrochloric acid has but little action 
 upon it even at a boiling heat; when heated with concentrated 
 sulphuric acid it yields sulphur dioxide and silver sulphate. 
 
 Chlorine acts upon silver at the ordinary temperature. Silver 
 has great affinity for sulphur, and readily fuses with it to silver 
 sulphide. Sulphuretted hydrogen blackens silver, brown-black 
 silver sulphide being formed (tarnishing of silver in rooms in 
 which gas is burned). Such tarnishing is most readily removed 
 by potassium cyanide solution. 
 
 Concentrated sulphuric acid combines at a boiling point with 
 silver to silver sulphate, sulphurous acid escaping. Nitric acid 
 readily dissolves silver at a gentle heat, and at a higher tem- 
 perature with considerable violence, silver nitrate (lunar caustic) 
 being formed while nitrogen dioxide escapes. Watery chromic 
 acid converts silver into red silver chromate, and this conver- 
 sion is made use of as a test for silvering. By touching silver 
 or genuine silver-plating with a drop of a solution obtained by 
 dissolving potassium dichromate in nitric acid of 1.2 specific 
 gravity, a red stain is formed. 
 
 (359) 
 
360 ELECTRO-DEPOSITION OF METALS. 
 
 Electro-plating with silver was, of all electro-metallurgical 
 processes, the first which was carried on on a large scale and 
 has reached enormous proportions. Large quantities of silver 
 are annually consumed for this purpose, and it is to be re- 
 gretted that no accurate statistics regarding this consumption 
 are available. 
 
 Silver baths. The longer an electro-plating process has 
 been carried on, the greater, as a rule, the number of existing 
 formula? for baths will be ; but silver baths are an exception to 
 this rule. If it is taken into consideration that silver-plating has 
 been practically carried on for more than sixty years, the num- 
 ber of formula? might be expected to be at least equal to those 
 for nickel-plating, which is of much more recent origin. Such, 
 however, is not the case, and chiefly for the reason that the 
 attempts to improve the silver baths, which were made either 
 with a view to banish the poisonous potassiifm cyanide from 
 the silver-plating industry, or otherwise to advance the plating 
 process, could absolutely show no better results than the baths 
 used by the first silver-platers. However, that attempts to 
 make such improvements have not been entirely abandoned is 
 shown by Zinin's proposition to substitute solution of silver 
 iodide in potassium iodide for a solution containing potassium 
 cyanide, or by Jordis' proposition to use silver lactate baths. 
 While the bath according to Zinin yields bad results as com- 
 pared with the old baths containing potassium cyanide, quite 
 good silvering is obtained with a bath according to Jordis, but 
 independent of the fact that the bath contains no potassium 
 cyanide, no special advantages could be established. Hence 
 there is no good reason for including other directions for silver 
 baths in this work which is primarily intended for practical use, 
 and only formula? for the most approved baths will be given. 
 
 However, before describing the preparation of the baths, a 
 few words may be said in regard to the old dispute whether it 
 is preferable to use silver cyanide or silver chloride. Without 
 touching upon all the arguments advanced, it may be asserted, 
 by reason of' conscientious comparative experiments, that the 
 
DEPOSITION OF SILVER. 36 1 
 
 results are the same, and that the life of the bath is also the 
 same, whether one or the other salt has been used in its original 
 preparation. From the chemical view-point, preference had 
 to be given to silver cyanide, but in practice, baths prepared 
 with silver chloride were found to possess certain advantages, 
 and theory has furnished an explanation of them. 
 
 One of these advantages is found in the fact that by reason 
 of the potassium chloride formed, the resistance of a bath pre- 
 prepared with silver chloride is considerably less than that of a 
 silver cyanide bath, and, with the same current-density, the 
 latter, therefore, requires a greater electro-motive force. 
 
 Theoretically, preference has further to be given to silver 
 chloride, because a portion of the potassium chloride formed is 
 dissociated, and potassium-ions and chlorine-ions thus get into 
 the solution. These potassiums-ions augment the potassium- 
 ions which are present as a result of the dissociation of the 
 potassium cyanide and silver cyanide and thus increase the 
 efficiency. On the other hand, in addition to cyanogen-ions, 
 chlorine-ions are separated on the anodes and augment the 
 supply of silver-ions in the electrolytes. Furthermore, the 
 presence of potassium chloride facilitates the conversion of the 
 silver cyanide formed on the anodes into potassium silver 
 cyanide, according to the following equation : 
 
 2AgCy + KC1 = KAgCy, + AgCl 
 
 Silver cyanide. Potassium chloride. Potassium silver Silver chloride. 
 
 cyanide. 
 
 While, according to this, preference may be given to silver 
 chloride for the preparation of silver baths, and the more so as 
 it is more easily prepared than silver cyanide, yet for 'refresh- 
 ing the baths, which becomes from time to time necessary, to 
 increase their content of silver, recourse must be had to silver 
 cyanide, because with the use of silver chloride for this pur- 
 pose, the baths would become thick in consequence of a con- 
 stant supply of further quantities of potassium chloride, and the 
 silver separate with a coarse structure. 
 
362 ELECTRO-DEPOSITION OF METALS. 
 
 Silver-bath for a heavy deposit of silver (silvering by weight). 
 
 I. 98 to 99 per cent, potassium cyanide 14 ozs., fine silver as 
 silver chloride 8^ ozs., distilled water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 0.75 volt. 
 
 Current density, 0.3 ampere. 
 
 la. 98 to 99 percent, potassium cyanide 8^ ozs., fine silver 
 as silver cyanide 8 3^ ozs., distilled water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, I volt. 
 
 Current density, 0.3 ampere. 
 
 Preparation of bath I. with silver chloride. Dissolve 14 ozs. 
 of chemically pure nitrate of silver, best the crystallized and not 
 the fused article, in 5 quarts of water, and add to the solution 
 pure hydrochloric acid, or common salt solution, with vigorous 
 stirring or shaking, until a sample of the fluid filtered through 
 a paper filter forms no longer a white caseous precipitate of 
 silver chloride when compounded with a drop of hydrochloric 
 acid. These, as well as the succeeding operations, until the 
 silver chloride is ready, have to be performed in a darkened 
 room, as silver chloride is partially decomposed by light. Now 
 separate the precipitate of silver chloride from the solution by 
 filtering, using best a large bag of close felt, and wash the pre- 
 cipitate in the felt bag with fresh water. Continue the washing 
 until blue litmus paper is no longer reddened by the wash- 
 water, if hydrochloric acid was used for precipitating, or, if 
 common salt solution was used, until a small quantity of the 
 wash-water, on being mixed with a drop of lunar caustic solu- 
 tion, produces only a slight milky turbidity and no precipitate. 
 Now bring the washed silver chloride in portions from the felt 
 bag into a porcelain mortar, rub it with water to a thin paste, 
 and pour the latter into the potassium cyanide solution consist- 
 ing of 14 ozs. of 98 per cent, potassium cyanide in 5 quarts of 
 water, in which, by vigorous stirring, the silver chloride gradu- 
 ally dissolves. All the precipitated silver chloride having been 
 brought into solution, dilute with water to 10 quarts of fluid, 
 and boil the bath, if possible, for an hour, replacing the water 
 lost by evaporation. A small quantity of black sediment con- 
 
DEPOSITION OF SILVER. 363 
 
 taining silver thereby separates, from which the colorless fluid 
 is filtered off. This sediment is added to the silver residues, 
 and is worked together with them for the recovery of the silver 
 by one of the methods to be described later on. 
 
 Preparation of bath la with silver cyanide. Dissolve 14 
 ounces of chemically pure crystallized nitrate of silver in 5 
 quarts of water, and precipitate the silver with prussic acid, 
 adding the latter until no more precipitate is produced by the 
 addition of a few drops of prussic acid to a filtered sample of 
 the fluid. Now filter, wash, and proceed for the rest exactly 
 as stated for the bath with silver chloride, except that only 8^ 
 ounces of potassium cyanide are taken for dissolving the silver 
 cyanide. In working with prussic acid avoid inhaling the 
 vapor which escapes from the liquid prussic acid, especially in 
 the warm season of the year; and be careful the acid does not 
 come in contact with cuts on the hands. It is one of the most 
 rapidly-acting poisons. 
 
 Silver cyanide may also be prepared as follows : Dissolve 
 14 ounces of chemically pure crystallized nitrate of silver in 5 
 quarts of water, and add moderately concentrated potassium 
 cyanide solution until no more precipitate is formed, avoiding, 
 h'owever, an excess of the precipitating agent, as it would again 
 dissolve a portion of the silver cyanide. The precipitated 
 silver cyanide is filtered off, washed and dissolved in potassium 
 cyanide, as above described. 
 
 The preparation of the silver bath according to the above 
 formulae is more conveniently effected by using pure crystal- 
 lized potassium-silver cyanide in the following proportions : 
 
 lb. 98 per cent, potassium cyanide, 6% to 7 ozs. ; crystal- 
 lized potassium-silver cyanide, 17 yi ozs.; distilled water, 10 
 quarts. 
 
 Electro-motive force and current density as for la. 
 
 The salts are simply dissolved in the cold water. 
 
 The baths prepared according to formulae I, la or lb serve 
 chiefly for the production of a heavy deposit upon German 
 silver articles, especially table and other household utensils. 
 
364 ELECTRO-DEPOSITION OE METALS. 
 
 Of course, they may also be used for plating other metals by 
 weight. 
 
 Silver bath for ordinary electro-silvering. II. 98 per cent, 
 potassium cyanide, 6^ to 7 ounces; fine silver (as silver 
 nitrate or chloride), 3^ ounces; distilled water, 10 quarts. 
 
 Electro-motive force, for silver chloride, at 10 cm. electrode- 
 distance, 1.25 volts. 
 
 Current density, 0.3 ampere. 
 
 To prepare the bath dissolve 5^ ounces of chemically pure 
 crystallized nitrate of silver in 5 quarts of distilled water ; in the 
 other 5 quarts of water dissolve the potassium cyanide, and 
 mix both solutions. Or, if chloride of silver is to be used, pre- 
 cipitate the solution of 3^ ounces of the silver salt in the same 
 manner as given for formula I ; wash the precipitated chloride 
 of silver, and dissolve it in the potassium cyanide solution. 
 
 \\a. 98 per cent, potassium cyanide if ozs., crystallized potas- 
 sium-silver cyanide 7 ozs., distilled water, 10 quarts. 
 
 Dissolve the salts in the cold water. 
 
 For the preparation of silver baths double and triple silver 
 salts are brought into commerce by some manufacturers. 
 
 Such salts require simply dissolving in water. However, 
 they offer no special advantages since the preparation of baths 
 according to formulas lb and \\a can scarcely be surpassed as 
 regards simplicity. 
 
 Tanks for silver- baths. As receptacles for silver baths, tanks 
 of stone-ware and enameled iron tanks, as well as wood tanks 
 lead lined and coated or lined with celluloid can only be used. 
 
 Treatment of the silver baths. — Silver anodes. Frequently 
 the error is committed of adding too much potassium cyanide 
 to the bath. A certain excess of it must be present, and in 
 the formulas given, this has been taken into consideration. 
 For dissolving the silver cyanide prepared from 14 ounces of 
 nitrate of silver, as given in formula \a, only about 5^ ounces 
 of potassium cyanide are required, and the consequence of 
 working with such a bath, devoid of all excess, would be that, 
 on the one hand, the bath would offer considerable resistance 
 
DEPOSITION OF SILVER. 365 
 
 to the current, and, on the other, that the deposit would not be 
 uniform and homogenous, and the anodes would be coated with 
 silver cyanide. Hence, with the use of a normal current, about 
 0.35 to 0.42 ozs. more of potassium cyanide is added per quart 
 of bath. However, when working with a stronger current, this 
 excess would already be too large, and the deposit would not 
 adhere properly, and rise up in scratch-brushing. And, again, 
 with a very weak current, the baths can without disadvantage 
 stand a larger excess. As a rule, however, the proportions 
 between fine silver and potassium cyanide given in the above 
 formulae may be considered as normal, and with the current- 
 densities prescribed, a deposit of fine structure, which adheres 
 firmly, will result. 
 
 By reason of the slight electro-motive force required for sil- 
 vering, in plating larger object-surfaces, the cells are not 
 coupled one after the other for electro-motive force, but in par- 
 allel. In no case must an evolution of hydrogen be perceptible 
 on the objects, and the current must be the more weakened, 
 the larger the excess of potassium cyanide in the bath. 
 
 In the silver baths prepared according to the formulas given 
 above, the excess of potassium cyanide amounts to 0.35 to 
 0.42 oz. per quart, and is only increased in silver baths which 
 are to serve for the direct silvering of tin and of alloys with a 
 large content of nickel, as will be shown later on. Baths for 
 ordinary, as well as light, silvering, with 0.35 oz. of silver per 
 quart, would only require an excess of 0.17 oz. of potassium 
 cyanide. However, since the larger excess of 0.35 oz. is no 
 disadvantage, and allows of working with less electro-motive 
 force, it is generally preferred. The electro-motive force given 
 for the separate formulas is applicable only when the anode- 
 surface is of the same size, or approximately so, as the object- 
 surface. If, for reasons of economy, the work is carried on 
 with considerably smaller anode-surfaces, the electro-motive 
 force has to be adequately increased in order to conduct into 
 the bath a quantity of current corresponding to the normal 
 current-density. 
 
366 ELECTRO-DEPOSITION OF METALS. 
 
 Whether too much, or not enough, potassium cyanide is 
 present in the bath is indicated by the appearance of the plated 
 objects and the properties of the deposit, as well as by the 
 behavior of the anodes in the bath during and after silvering. 
 It may be accepted, as a rule, that with a moderate current 
 the object should, in the course of io to 15 minutes, be coated 
 with a thin, dead-white film of silver. If this be not the case, 
 and the film of silver shows a meager bluish-white tone, potas- 
 sium cyanide is wanting. However, if, on the other hand, the 
 dead-white deposit forms within 2 or 3 minutes, and shows 
 a crystalline structure, or a dark tone playing into gray-black, 
 the content of potassium cyanide in the bath is too large, pro- 
 vided the current is not excessively strong. If copper and 
 brass become coated with silver without the co-operation of 
 the current, the bath contains also too much potassium cyanide. 
 
 In silver-plating, even if the objects are to be only thinly 
 coated, insoluble platinum anodes should never be used, but 
 only anodes of fine silver, which are capable of maintaining the 
 content of silver in the bath quite constant. From the behavior 
 and appearance of the anodes, a conclusion may also be drawn 
 as to whether the content of potassium cyanide in the bath is 
 too large or too small. If the anodes remain silver-white dur- 
 ing plating, it is a sure sign that the bath contains more potas- 
 sium cyanide than is necessary and desirable; but, if they turn 
 gray or blackish, and retain this color after plating, when no 
 current is introduced into the bath for a quarter of an hour or 
 more, potassium cyanide is wanting. On the other hand, the 
 correct content of potassium cyanide is present, when the 
 anodes acquire during the plating process a gray tone, which, 
 after the interruption of the current, gradually changes back to 
 a pure white. 
 
 The proposition to use, in place of silver anodes, steel sheets 
 as anodes for silver baths cannot be approved, especially when 
 chloride of silver has been used for the preparation of the bath 
 or other chlorides are present in it. The chloride-ions would 
 bring iron into solution and this would form potassium ferro- 
 cyanide with the potassium cyanide. 
 
DEPOSITION OF SILVER. 367 
 
 If it is shown by the process of silvering itself, or by the ap- 
 pearance of the articles or of the anodes, that potassium cyanide 
 is wanting in the bath, it should be immediately added, though 
 never more than 30 to 37^ grains per quart of bath at one 
 time, so as to avoid going to the other extreme. Too large a 
 content of potassium cyanide is remedied by adding to the 
 bath, stirring constantly, a small quantity of cyanide or chloride 
 of silver rubbed with water to a thinly-fluid paste, whereby the 
 excess is rendered harmless in consequence of the formation of 
 the double salt of silver and potassium cyanide. Instead of 
 such addition, the current may, however, be used for correcting 
 the excess. For this purpose suspend as many silver anodes 
 as possible to the anode-rods, but only a single anode as an 
 object to the object-rod, and allow the current to pass for a 
 few hours throwgh the bath, whereby the excess of potassium 
 cyanide is removed or rendered harmless by the dissolving 
 silver. 
 
 The bath can be kept quite constant by silver anodes, pro- 
 vided potassium cyanide be regularly added at certain inter- 
 vals, and the anode-surface is equal to that of the objects to be 
 plated. But since, on account of the expense, a relatively 
 small anode-surface is frequently used, the content of silver in 
 a bath continuously worked will finally become lower, and 
 augmentation, by the addition of silver, will be required. The 
 manner of effecting this augmentation depends on whether the 
 baths are used for plating by weight or for lighter silvering, or 
 whether the baths are worked, without stopping, from morning 
 till evening. For replacing the deficiency in baths prepared 
 according to formulae I and la, it is advisable to use exclusively 
 solution of silver cyanide in potassium cyanide, or of crystal- 
 lized potassium-silver cyanide in water. 
 
 It has previously been mentioned that with proper treatment 
 baths made with chloride of silver have the same duration of 
 life as those prepared with silver cyanide. The chief feature 
 of such proper treatment is not to use chloride of silver dis- 
 solved in potassium cyanide for augmenting the content of 
 
368 ELECTRO-DEPOSITION OF METALS. 
 
 silver, but to employ silver cyanide instead, since by the use of 
 
 the tenner, the bath thickens in consequence of the potassium 
 chloride which is simultaneously introduced. The ettect of 
 such thickening is that the deposits are formed less homo- 
 geneously and with coarser structure. 
 
 A gradual thickening of the bath may also take place if po- 
 t.'ssium cyanide containing potash is used, instead of the prep- 
 aration free from potash, and of 98 to 00 per cent, purity. Even 
 pure fused potassium cyanide produces a thickening of the 
 bath, which, however, progresses very slowly. This thickening- 
 is due to a portion of the excess of potassium cyanide being 
 by the action of the air converted into potassium carbonate, 
 and if the quantity of the latter exceeds % oz. per quart, it has 
 to be neutralised. For this purpose, prussic acid was formerly 
 used in order to effect a conversion of the potassium carbonate 
 into potassium cyanide. It is, however, a well-known fact that 
 carbonic acid decomposes the potassium cyanide, potassium 
 carbonate and prussic acid being formed, and the addition of 
 prussic acid would therefore appear not very suitable for attain- 
 ing the object in view. 
 
 It is better to use solutions of calcium cyanide or barium 
 cyanide, and add them so long as a precipitate of calcium car- 
 bonate or barium carbonate is formed. The solutions should, 
 however, be freshly prepared. The precipitate formed is 
 allowed to settle when the clear solution is siphoned oft", and 
 the residue altered through a paper filter. 
 
 Since, as mentioned above, the proportion of excess of potas- 
 sium cyanide to the content of silver undergoes changes accord- 
 ing to the proportion of the object-surface to the anode-surface. 
 the temperature of the bath, etc.. it becomes necessary to add 
 one or the other in order to maintain the proper proportions 
 and the effective working of the bath. 
 
 To determine rapidly whether the bath contains silver and 
 xcess of potassium cyanide in proper proportions, the follow- 
 ing methods may be used: Dissolve t gramme (. 1 5-43 grains") 
 of chemically pure crystallized nitrate of silver in 20 grammes 
 
DEI'OSrnON OK SILVER. 369 
 
 (0.7 oz.) of water and gradually add this solution, whilst con- 
 stantly stirring with a glass rod, to [00 grammes (3.52 ozs.) 
 of the silver bath in a beaker, as long as the precipitate of silver 
 cyanide formed dissolves by itself. If, after adding the entire 
 quantity of silver solution, the precipitate dissolves rapidly, 
 too large an excess of potassium cyanide is present in the bath ; 
 and vice versa, if the precipitate does not completely dissolve, 
 after stirring, potassium cyanide is wanting. 
 
 The quantitative determination of the content of potassium 
 cyanide and of silver will be described later on under " Exam- 
 ination of Silver Baths." 
 
 Agitation of silver baths. In heavy silver-plating constant 
 agitation of the strata of fluid is of decided advantage, grooves 
 and blooms being otherwise readily formed upon the plated 
 objects, especially when the baths are over-concentrated or 
 thickened. The depressed grooves can only be explained by 
 the fact that the strata of fluid on the cathodes having become- 
 specifically lighter by yielding metal are subject to a current 
 towards the surface; the lower strata richer in silver give rise 
 to heavier deposits on the lower cathode portions, so that agi- 
 tation of the bath becomes an actual necessity. 
 
 With a bath in constant agitation a greater current-density 
 may be used, the deposits, notwithstanding the greater current- 
 density forming with finer structure and in a correspondingly 
 shorter time, which is especially noteworthy for heavy silvering. 
 To keep the articles in gentle motion while in the bath, one- 
 method is to connect the suspending rods to a frame of iron 
 having four wheels, about 3 inches in diameter, connected to it, 
 which slowly travel to and fro to the extent of 3 or 4 inches 
 upon inclined rails attached to the upper edge of the tank, the 
 motion, which is both horizontal and vertical, being given by 
 means of an eccentric wheel driven by steam power. By an- 
 other arrangement, the frame supporting the articles does not 
 rest upon the tank, but is suspended above the bath, and re- 
 ceives a slow swinging motion from a small eccentric or its 
 equivalent. In the Elkington establishment at Birmingham the 
 24 
 
370 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 following arrangement is in use : All the suspending rods of the 
 bath rest upon a copper mounting, which, by each revolution 
 of an eccentric wheel, is lifted about ^ inch, and then returned 
 to its position. The copper mounting is connected to the main 
 negative wire of the dynamo-machine by a copper cable. The 
 same object may also be attained by giving the articles a hori- 
 zontal, instead of a vertical motion, as shown in Fig. 130, in 
 which the motion is produced by an eccentric wheel on the side. 
 With equal, if not better, success the mechanically-moved 
 stirring apparatus, which will be described under " Copper 
 
 Fig. 130. 
 
 Galvanoplasty," may be used. In this apparatus several glass 
 rods movable around a pivot keep the bath in constant motion. 
 Where such a stirring apparatus cannot be conveniently 
 arranged, the motion of the bath may be produced by intro- 
 ducing, by means of a pump, air on the bottom of the tank. 
 
 A singular phenomenon in regard to silver baths, which 
 has not yet been explained, may here be mentioned. A small 
 addition of certain, and especially of organic, substances, which, 
 however, must not be made suddenly or in too large quanti- 
 ties, produces a fuller and better-adhering deposit of greater 
 luster than can be produced in fresh baths. Elkington ob- 
 
DEPOSITION OF SILVER. 37 1 
 
 served that an addition of a few drops of carbon disulphide 
 to the bath made the silvering more lustrous, while others 
 claim to have used with success solutions of iodine in chloro- 
 form, of gutta-percha in chloroform, as well as heavy hydro- 
 carbons, tar, oils, etc. 
 
 Some preparations which have been recommended for this 
 "bright" plating may here be given. Bring 6 ozs. of carbon 
 disulphide into a stoppered bottle and add I gallon of the usual 
 plating solution. Shake the mixture thoroughly and then set 
 it aside for 24 hours. Add 2 ozs. of the resulting solution to 
 every 20 gallons of ordinary plating solution in the vat, and 
 stir thoroughly. This proportion must be added every day, 
 but where the mixture has been used every day, less than this 
 may be used at a time. This proportion is claimed to give a 
 bright deposit, but by adding a larger amount a dead surface 
 may be obtained very different from the ordinary dead surface. 
 
 Another method of preparing a solution for bright-plating is 
 as follows: Put 1 quart of ordinary silver-plating solution into 
 a large stoppered bottle. Now add 1 pint of strong solution 
 of cyanide, and shake well ; 4 ozs. of carbon disulphide are 
 then added, as also 2 or 3 ozs. of liquid ammonia, and the 
 bottle again well shaken, the latter operation being repeated 
 every two or three hours. The solution is then set aside for 
 about 24 hours, when it will be ready for use. About 2 ozs. of 
 the clear liquid may be added to every 20 gallons of plating 
 solution, and well mixed by stirring. A small quantity of the 
 brightening solution may be added to the bath every day, and 
 the liquid then gently stirred. In course of time the disulphide 
 solution acquires a black color; to modify this a quantity of 
 strong cyanide solution, equal to the brightening liquor which 
 has been removed from the bottle, should be added each time. 
 In adding the disulphide solution to the plating bath, an excess 
 must be avoided, otherwise the latter will be spoilt. Small 
 doses repeated at intervals is the safer procedure, and less 
 risky than the application of larger quantities, which may ruin 
 the bath. 
 
372 ELECTRO-DEPOSITION OF METALS. 
 
 A very simple way to prepare the brightening solution is 
 to put 2 or 3 ozs. of carbon disulphide into a bottle which 
 holds rather more than half a gallon. Add to this about 3 
 pints of old silver solution and shake the bottle well for a 
 minute or so. Then nearly fill the bottle with a strong solu- 
 tion of cyanide, shake well as before, and set aside for at least 
 24 hours. Add about 2 ozs. (not more) of the brightening 
 liquor, without shaking the bottle, to each 20 gallons of solu- 
 tion in the plating vat. Even at the risk of a little loss from 
 evaporation, it is best to add the brightening liquor to the bath 
 the last thing in the evening, when the solution should be well 
 stirred so as to thoroughly diffuse the added liquor. The 
 night's repose will leave the bath in good working order for 
 the following morning. 
 
 A silver bath, as shown by experience, becomes without 
 doubt better in the degree in which it takes up small quantities of 
 organic substances from the air and from dust; but numerous 
 experiments have failed to confirm Elkington's observation 
 that the formation of the deposit or its appearance is essentially 
 influenced by the addition of carbon disulphide or any of the 
 above-mentioned solutions of organic origin either in very small 
 or considerable quantities. Many baths have been entirely 
 spoiled by an attempt to change them into bright-working 
 baths by the addition of such ingredients, and hence it is best 
 to leave such experiments alone. It may, however, be stated 
 that by the addition of a few drops of liquid ammonia, fresh 
 silver baths accommodate themselves more rapidly to regular 
 performance. 
 
 Yellow tone of silvering. After plating, the objects fre- 
 quently show, instead of a pure white, a yellow tone, or they 
 become yellow in the air, which is ascribed to the formation of 
 basic silver salts in the deposit. To overcome this evil it has 
 been proposed to allow the objects to remain in the bath for a 
 lew minutes after interrupting the current, whereby the basic 
 salts are dissolved by the potassium cyanide of the bath; or 
 the same object is attained by inverting the electrodes for a 
 
DEPOSITION OF SILVER. $7$ 
 
 few seconds, after plating, thus transforming the articles into 
 anodes. The electric current carries away the basic salt of 
 silver in preference to the metal. This operation should, of 
 course, not be prolonged, otherwise the silver will be entirely- 
 removed from the objects, and will be deposited on the anodes. 
 For the same purpose some electro-platers hold in readiness a 
 warm solution of potassium cyanide, in which they immerse the 
 plated articles for half a minute. 
 
 Silver alloys. It has been proposed to add to the silver baths 
 a solution of nickelous cyanide in potassium cyanide in order 
 to obtain a deposit of a silver-nickel alloy, which is claimed to 
 be distinguished by its greater hardness and the property of 
 not turning so readily dark. Numerous experiments with 
 solutions of cyanide of silver and nickelous cyanide in potas- 
 sium cyanide in all possible proportions, and with various 
 electro-motive forces, and subsequent analysis of the deposits 
 obtained, showed, however, only inconsiderable traces of nickel 
 in the silver deposit, which had but a very slight influence 
 upon the hardness and durability of the silver. 
 
 The London Metallurgical Co. endeavors to attain greater 
 hardness and power of resistance of the silver by adding zinc 
 cyanide or cadmium cyanide, and has given to this process the 
 name of areas silver-plating. According to the patent, an addition 
 of 20 to 30 per cent, of zinc or cadmium to the silver prevents 
 the tarnishing of the plating, and besides the deposit is claimed 
 to be lustrous and hard. For areas silver-plating the appropriate 
 quantity of zinc or cadmium, or a mixture of both metals, is 
 converted into potassium-zinc cyanide or potassium-cadmium 
 cyanide, and this solution is mixed with a corresponding quan- 
 tity of solution of potassium-silver cyanide, with a small excess 
 of potassium cyanide. Sheets of a silver-zinc or a silver-cad- 
 mium alloy are used as anodes. 
 
 This method has been favorably commented upon by 
 Sprague, Urquart and others, and some English platers claim 
 that for many articles, especially bicycle parts, areas silvering 
 may be substituted for nickeling. However these favorable 
 
374 ELECTRO-DEPOSITION OF METALS. 
 
 opinions were not confirmed by the following experiments 
 made by Dr. Langbein regarding the value of this process as a 
 substitute for silver-plating instruments and articles of luxury. 
 
 A bath was prepared which contained per quart 231^ troy 
 grains of fine silver and JJ troy grains cadmium in the form of 
 cyanide double salts with a small excess of potassium cyanide. 
 The most suitable tension of current for the decomposition of 
 a pure potassium-cadmium cyanide solution which contained 
 per quart 154 troy grains of cadmium with the same excess of 
 potassium cyanide as the above-mentioned mixture, was found 
 to be 2 volts. 
 
 In electrolyzing the cadmium-silver bath with 0.75 volt, a 
 uniform silver-white deposit similar to that of pure silver was at 
 first formed. However, after two hours the deeper places of 
 the objects suspended in the bath showed crystalline excres- 
 cences which felt sandy, and could be rubbed off with the 
 fingers. After scratch-brushing the articles and again suspend- 
 ing them in the bath, these sandy, non-adhering metallic de- 
 posits were rapidly reformed. An analysis of the deposit 
 separated from the articles showed 96.4 per cent, silver, and 
 3.2 per cent, cadmium. This deposit could, without difficulty, 
 be polished with the steel like a pure silver deposit, and hence 
 its hardness would not seem greater than that of pure silver. 
 Its capability of resisting hydrogen sulphide as compared with 
 pure silver was scarcely greater. 
 
 In another experiment electrolysis was effected with 1.25 
 volts. The deposit showed from the start a coarser structure, 
 and the formation of the sandy non-adhering deposit took place 
 much more rapidly. But, on the other hand, the hardness of 
 the reduced coherent metal was greater than that of pure 
 silver, and also its power of resisting hydrogen sulphide. An 
 analysis of the deposit showed 92.1 per cent, silver and 7.8 per 
 cent, cadmium. In both cases the deposit was dull like that of 
 pure silver. 
 
 With a greater electro-motive force the quantity of cadmium 
 in the deposit increased, and the hardness of the latter became 
 
DEPOSITION OF SILVER. 375 
 
 correspondingly greater. However, these deposits could not 
 be considered serviceable for the above-mentioned purpose, 
 because they could not be made of sufficient thickness as re- 
 quired for solid silver-plating of forks and spoons. 
 
 In Dr. Langbein's opinion, the decomposition-pressures of a 
 solution of potassium-silver cyanide and of one of potassium- 
 cadmium cyanide lie too far apart to obtain without delay de- 
 posits of even composition and of sufficient density and thick- 
 ness. 
 
 Execution of silver-plating — A. Silver-plating by weight. — 
 Copper, brass, and all other copper alloys may be directly 
 plated after amalgamating (quicking), whilst iron, steel, nickel, 
 zinc, tin, lead, and Britannia are first coppered or brassed, and 
 then amalgamated. 
 
 The mechanical and chemical preparation of the objects for 
 the silver-plating process is the same as described on page 186 
 et. seq. To obtain well-adhering deposits great care must be 
 exercised in freeing the objects from grease, and in pickling. 
 As a rule, objects to be silver-plated are ground and polished. 
 However, polishing must not be carried too far, since the de- 
 posit of silver does not adhere well to highly-polished surfaces ; 
 and in case such highly-polished objects are to be silvered it is 
 best to deprive them of their smoothness by rubbing with 
 pumice powder, emery, etc., or by pickling. 
 
 The treatment of copper and its alloys, German silver and 
 brass, which have chiefly to be considered in plating by weight 
 is, therefore, as follows : 
 
 1 . Freeing from grease by hot potash or soda lye ( 1 part of 
 caustic alkali to 8 to 10 parts of water), or by brushing with 
 the lime-paste mentioned on page 228. 
 
 2. Pickling in a mixture of 1 part, by weight, of sulphuric 
 acid of 66° Be. and 10 of water. This pickling is only required 
 for rough surfaces of castings, ground articles being immedi- 
 ately after freeing from grease treated according to 3. 
 
 3. Rubbing with a piece of cloth dipped in fine pumice 
 powder or emery, after which the powder is to be removed by 
 washing. 
 
376 ELECTRO-DEPOSITION OF METALS. 
 
 4. Pickling in the preliminary pickle, rinsing in hot water, 
 and quickly drawing through the bright-dipping bath (page 
 223), and again thoroughly rinsing in several waters. 
 
 5. Amalgamating {quicking) by immersion in a solution of 
 mercury, called the quicking solution. This consists of a solu- 
 tion of 0.35 ounce of nitrate of mercury in I quart of water, to 
 which, while constantly stirring, pure nitric acid in small por- 
 tions is added until a clear fluid results. A weak solution of 
 potassium-mercury cyanide in water is, however, to be pre- 
 ferred, because the acid quicking solution mentioned above 
 makes the metals brittle. A quicking solution for silver-plating 
 by weight consists of: Potassium-mercury cyanide, 14 drachms 
 to 1 oz. : 99 per cent, potassium cyanide, 14 drachms; water, 1 
 quart. Care must be taken to bring the quicked objects into 
 the bath as rapidly as possible, otherwise thin objects are liable 
 to become brittle. The amalgam formed upon the surface 
 penetrates to the interior of thin sheets if this action is not 
 prevented by an immediate deposition of silver and the forma- 
 tion of silver amalgam. In the quicking solution the objects 
 remain only long enough to acquire a uniform white coating, 
 when — 
 
 6. They are rinsed in clean water, and gone over with a soft 
 brush in case the quicking shows a gray, instead of a white 
 tone. 
 
 The articles are now brought into the silver bath, and 
 secured to the object rods by slinging wires of pure 
 copper or, still better, of pure silver. The latter 
 have the advantage that when by reason of a de- 
 posit of considerable thickness having been formed 
 upon them, they have become useless for suspend- 
 ing the articles, they can be directly converted into 
 silver nitrate by dissolving in nitric acid, and used 
 for the preparation of fresh baths, or for strengthen- 
 ing old baths. 
 
 When certain objects, for instance, forks and 
 spoons, are to be plated, copper wires may be bent in the man- 
 
DEPOSITION OF SILVER. 377 
 
 ner shown in Fig. 131. To prevent the deposition of silver 
 upon the portions of the wire which do not serve for the pur- 
 pose of contact, they are coated with fused ebonite mass or 
 gutta-percha, only the loop in which the fork or spoon is hung 
 and the upper end for suspending to the object-rod being left 
 free. Silver wires are also better for this purpose. 
 
 In order to secure an extra heavy coating of silver on the 
 convex surfaces of spoons and forks which, being subject to 
 greater wear than the other parts, require extra protection, 
 some plating establishments use a frame in which the articles 
 supported therein by their tips are placed horizontally in a shal- 
 low silver bath, and immersed just deep enough to allow the 
 projecting convexities to dip into the bath. By this artifice 
 these portions are given a second coating of silver of any desired 
 thickness. This mode of procedure, which is termed " sec- 
 tional " plating, accomplishes the intended purpose nicely and 
 satisfactorily. In some establishments the silvered forks and 
 spoons are placed between plates of gutta-percha of corre- 
 sponding shape, and held together by rubber bands. In these 
 plates the portions to be provided with an extra coating of 
 silver are cut out. By suspending the forks and spoons thus 
 protected in the bath, the unprotected places receive a further 
 layer of silver, the outlines of which are later on smoothed 
 down with burnishers. The second object may also be attained 
 by coating the places which are to receive no further deposit 
 with " stopping-off " varnish (see later on). 
 
 According to German patent No. 76975, sheets of celluloid 
 or similar substances are suspended as shields between the 
 inside portions of spoons and the anodes. By this means the 
 deposit of silver on these portions, which are subject to less 
 wear is only slightly augmented, while the outside portions 
 acquire a heavier deposit. 
 
 To attain the same object, J. Buck * suspends a frame in 
 such a manner that every two spoons are turned with their in- 
 
 * German patent 126053 (expired). 
 
378 ELECTRO-DEPOSITION OF METALS. 
 
 side portions towards each other, and anodes are arranged only 
 on the outside portions. 
 
 When commencing the operation of silver-plating, introduce 
 into the bath at first a somewhat more powerful current, so 
 that the first deposition of silver takes place quite rapidly, and 
 after 3 minutes regulate the current so that in 10 to 15 minutes 
 the objects are coated with a thin, dull film of silver. At this 
 stage take them from the bath, and after seeing that all portions 
 are uniformly coated, scratch-brush them with a brass brush, 
 which should, however, not be too fine. In doing this the de- 
 posit must not raise up. If at this stage the objects stand 
 thorough scratch-brushing, raising of the deposit in burnishing 
 later on need not be feared. 
 
 Any places which show no deposit are vigorously scratch- 
 brushed with the use of pulverized tartar, then again carefully 
 cleansed by brushing with lime-paste to remove any impurities 
 due to touching with the hands, pickled by dipping in potas- 
 sium cyanide solution, again rinsed, quicked, and after careful 
 rinsing returned to the bath. Special care must be taken not 
 to contaminate the bath with quicking solution as this would 
 soon spoil it. 
 
 The objects now remain in the bath at a normal current- 
 density until the deposit has acquired a weight corresponding 
 to the desired thickness. Knives, forks and spoons receive a 
 deposit of 2.1 1 to 3.52 ozs. of silver per dozen. 
 
 Determination of weight. In order to control the weight of 
 the deposit proceed as follows : Remove one of the pans of a 
 sensitive beam balance and substitute for it a brass rod which 
 keeps the other pan in equilibrium. Under this rod place a 
 vessel filled with pure water, and of sufficient diameter and 
 depth to allow of the article suspended to the rod dipping en- 
 tirely into the water without touching the sides of the vessel. 
 Suppose now that several dozen spoons of the same size and 
 shape are at the same time to be provided with a deposit of a 
 determined weight, it suffices to control the weight of the de- 
 posit of a single spoon, and when this has acquired the neces- 
 
DEPOSITION OF SILVER. 
 
 379 
 
 sary deposit all the other spoons will also be coated with a 
 deposit of silver of the same thickness as the test spoon. The 
 spoons having been quicked and carefully rinsed, one of them 
 is suspended to the brass rod of the balance so that it dips en- 
 tirely under water. The equilibrium is then re-established by 
 placing lead shot upon the pan of the scale, and adding the 
 
 Fig. 132. 
 
 weight corresponding to the deposit the spoon is to receive. 
 Now bring the weighed spoon together with the rest into the 
 bath, and proceed with the silvering process in the ordinary 
 manner. After some time the weighed spoon is taken from the 
 bath, rinsed in water, and hung to the brass rod of the scale. 
 If it does not restore the equilibrium of the latter, it is returned 
 
;8o 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 to the bath, and after some time again weighed, and so on 
 until its weight corresponds to that of the lead shot and weight 
 placed in the pan of the scale, when it is assumed that the 
 other objects have also received their proper quantity and that 
 the operation is complete. 
 
 A more complete weighing apparatus is the metallometric 
 balance first used by Brandely, and later on improved be Rose- 
 leur. The apparatus, which is shown in Fig. 132, is designed 
 for obtaining deposits of silver " without supervision and with 
 constant accuracy, and which spontaneously breaks the current 
 when the operation is terminated." It is manufactured in 
 various sizes, suitable for small or large operations. 
 
 It consists of: I. A wooden vat, the upper edge of which 
 carries a brass winding-rod having a binding screw at one end 
 to receive the positive conducting wire of the battery. From 
 this rod the anodes are suspended, which are entirely immersed 
 in the solution, and communicate with brass cross-rods by 
 means of platinum wire hooks. These cross-rods are flattened 
 at their ends so that they may not roll, and at the same time 
 have a better contact with the " winding-rod." 
 2. A cast-iron column screwed at its base to 
 the side of the vat, and which carries near the 
 top two projecting arms of cast-iron, the ex- 
 tremities of which are vertical and forked, and 
 may be opened or closed by iron clamps. 
 These forks are intended for sustaining the 
 beam and preventing the knives from leaving 
 their bearings under the influence of too vio- 
 lent oscillations. In the middle of the two arms 
 are two wedge-shaped recesses of polished 
 steel to receive the knife edges of the beam. 
 One of the arms of the column carries at its 
 end a horizontal ring of iron in which is fixed 
 a heavy glass tube supporting a cup of pol- 
 ished iron which is insulated from the column (Fig. 133). 
 This cup has at its lower part a small pocket of lamb-skin 
 
 Fig. i- 
 
DEPOSITION OF SILVER. 38 1 
 
 or of India rubber, which by means of a screw beneath may- 
 be raised or lowered. This flexible bottom allows the operator 
 to lower or raise at will the level of the mercury introduced 
 afterwards into the iron cup. Another lateral screw permits 
 connection to be made with the negative electrode. 3. A cast- 
 iron beam carrying in the middle two sharp knife edges of the 
 best steel hardened and polished. At each extremity there are 
 two parallel bearings of steel separated by a notch, and intended 
 for the knife-edges of the scale-pan that receives the weights, 
 and those of the frame supporting the articles to be plated. 
 One of the arms of the beam is provided with a stout platinum 
 wire, placed immediately above and in the center of the cup of 
 mercury. According as the beam inclines one way or the other, 
 this wire plays in or out of the cup. 4. A scale pan for weights, 
 with two knife-edges of cast steel, which is attached to four 
 chains supporting a wooden pan for the reception of weights. 
 A smaller pan above is intended for the weights corresponding 
 to that of the silver to be deposited. 5. The frame for support- 
 ing the articles to be plated, which is also suspended from two 
 steel knife-edges, and the rod of which is formed of a stout 
 brass tube attached below to the brass frame proper, which last 
 is equal in dimensions to the opening of the vat, and supports 
 the rods to which the articles are suspended. 
 
 It must, however, be borne in mind that the weight of a body 
 immersed in water is less than when weighed in the air, it being 
 as much less as the weight of the volume of fluid displaced by 
 it. The specific gravity of silver is 10.5, hence 1 cubic centi- 
 meter of silver weighs 10.5 more than 1 cubic centimeter of 
 water, so that 10.5 grammes of silver weighed in the air weigh 
 only 10.5 — 1 = 9.5 grammes when immersed in water. Since 
 the specific gravity of the silver bath is greater than that of 
 water — of fresh baths about 5 Be = 1.035 — IO -5 grammes of 
 silver, while immersed in the silver bath weigh only 10.5 — 1.035 
 = 9.465 grammes. Hence for the determination of the weight 
 to be placed in the scale-pan, which corresponds to the actual 
 weight of the silver deposit, the desired weight of the deposit 
 
2,82 ELECTRO-DEPOSITION OF METALS. 
 
 has to be multiplied by 9.465 and divided by 10.5, or what 
 amounts lo the same thing, multiplied by 0.901. Suppose 300 
 grammes of silver are to be deposited upon forks, knives and 
 spoons, not 300 grammes, but only 300X0.901=270.3 
 grammes have to be placed in the scale-pan. The weight of 
 the articles themselves is not taken into account as the objects 
 are tared under the solution and remain in the same bath-fluid to 
 
 Fig. 134. 
 
 the end of the process. Hence, according to the above calcula- 
 tion, the weight, to be placed in the scale-pan should, in round 
 figures, be 10 per cent, less than the desired weight of silver. 
 However, as silver also deposits on the slinging wires, it has 
 been shown that a reduction of 4 to 5 per cent, of the weight is 
 about the right thine. 
 
DEPOSITION OF SILVER. 383 
 
 Fig. 134 shows a metallometric balance in operation, as 
 coupled with the rheostat, voltmeter, and the silver bath, and 
 will be understood without further explanation. These metal- 
 lometric balances must of course be very carefully constructed 
 so as to render possible accurate weighings with a load of 
 about 1 1 lbs. They are used by most large silver-plating 
 establishments for forks, knives and spoons. They may also 
 be employed to advantage in plating coffee-pots, tea-pots, 
 sugar bowls, etc., but with such articles special attention has 
 to be paid in order to obtain a deposit of uniform thickness 
 upon all portions of the anode arrangement. It is evident that 
 with the use of straight silver anodes the portions of round 
 vessels nearest to the anodes will receive a thicker deposit of 
 silver than the portions at a greater distance from them. How- 
 ever, this also happens in every silver bath in operation not 
 connected with a metallometric balance, the latter indicating 
 of course only the total weight of deposit upon all the articles 
 in the bath, and means for the formation of a uniform deposit 
 on all portions must therefore be provided. This is effected by 
 the use of cylindrically bent anodes suspended around the 
 objects at equal distances ; further by frequently changing the 
 position of the objects so as to bring the more remote portions 
 nearer to the anodes. 
 
 For the determination of the weight of the deposit, Pfanhauser 
 Jr. uses a voltametric balance,* a combination of a voltameter 
 with a balance, the principle of which, according to Ferchland,f 
 is similar to Edison's registering voltameter, and has for some 
 time been practically utilized by Prof. Domalipj in Prague. 
 
 A copper voltameter is an apparatus which allows of the 
 determination of the quantity of current conducted in a certain 
 time through an acid copper sulphate solution (water 35 ozs., 
 copper sulphate 7 ozs., concentrated sulphuric acid 1 ^ ozs., 
 alcohol y oz.) by the quantity of copper electrolytically separ- 
 
 * German patent 120843. 
 
 t Zeitschrift fur Elektrochemie, 1891, No. 71. 
 
 X Ahrens. Handbuch der Elektrochemie, ii, Aufl. S. 151. 
 
384 ELECTRO-DEPOSITION OF METALS. 
 
 ated on the cathode. Two copper anodes dip into the solution 
 and between them' is a copper cathode. The weight of the 
 latter is exactly determined, and after the current has for an 
 accurately measured time passed through the voltameter, is 
 washed with water, rinsed with alcohol, dried and again weighed. 
 From the increase in weight the quantity of current which has 
 passed through the voltameter can be readily calculated, since 
 one ampere deposits in one hour 1.1858 grammes of copper. 
 
 Now by placing such a copper voltameter in the current-con- 
 ductor of a silver bath so that the current passes through the 
 bath and the voltameter one after the other, the same quantity 
 of current must pass through the bath as well as the voltameter 
 since, according to Kirchhoff's law, the current- strength is 
 equally great in all points of a current-circuit. According to 
 Faraday's law, the quantities of metals deposited are propor- 
 tional to their electro-chemical equivalents and hence the 
 quantity of copper separated will be to the quantity of silver 
 deposited as 1.858 : 4.0248 ; thus when the quantity of copper 
 separated is known, the weight of the silver deposit can be 
 readily calculated. 
 
 In Pfanhauser's voltameter balance the copper cathode is by 
 means of a conductor suspended to the metal-beam of a smaller 
 balance, the equilibrium being restored by placing weights or 
 shot in the scale-pan on the other end of the beam. Now in 
 order to determine the weight adequate to the desired deposit 
 in the silver bath, the weight has to be multiplied by 1.1858 
 and divided by 4.0248. The number of grammes found is the 
 weight the copper-deposit in the copper voltameter must attain 
 to correspond to the desired weight of the deposit in the silver 
 bath. The weight thus determined has to be placed in the pan 
 of the scale. When the deposit has acquired the desired weight 
 the current is automatically interrupted by a contrivance simi- 
 lar to that described when speaking of the metallometric 
 balance. 
 
 As compared with the metallometric balance, the voltametric 
 balance possesses advantages and disadvantages, the latter being 
 
DEPOSITION OF SILVER. 385 
 
 chiefly that besides the swelling up of the deposit in the volta- 
 meter which has to be taken into consideration, the reduction 
 of the weight of silver to be deposited to the weight of the 
 copper-deposit to be placed in the scale-pan, may readily lead 
 to errors, if left to the ordinary workman. To be sure this can 
 be avoided by consulting tables which are furnished with the 
 balance. 
 
 It must furthermore be borne in mind that the voltametric 
 balance gives reliable results only when the current-output of 
 the silver bath remains constant and is exactly equal to that of 
 the copper solution in the voltameter, a third correction of the 
 weight being otherwise required. The current-output in the 
 voltameter is 100, but that of fresh silver baths does not reach 
 this height. According to numerous determinations by Friess- 
 ner, executed in Dr. G. Langbein & Co.'s electro chemical 
 laboratory, the current-output in cyanide silver baths varies 
 according to whether the bath is at rest or in motion, the cur- 
 rent-output with 0.3 ampere current-density being in a bath 
 which contains per liter 25 grammes of silver as silver cyanide 
 and 27 grammes 99 per cent, potassium cyanide, 99.63 per 
 cent, without agitation of the bath and 99.18 per cent, with 
 agitation, hence 0.45 per cent, less in the latter case. 
 
 The increased electro-motive force when a voltametric bal- 
 ance is placed in the current-circuit must also not be lost sight 
 of. Since the voltameter solution and the silver bath are 
 coupled one after the other, about double the electro-motive 
 force is required and this greater performance of work increases 
 the cost of current. However, this is not of sufficient import- 
 ance to prevent the use of voltametric balances. 
 
 The advantages of a voltametric balance consist in that it 
 is not necessary to place it in the vicinity of the bath. It may 
 be located in a special dry-room where it is not exposed to the 
 effects of the damp atmosphere of the work-room. However 
 these effects are, as a rule over-estimated, since metallometric 
 balances with knife-edges of specially prepared steel, which 
 quite well resists the action of rust, working in agate^_bearings, 
 25 
 
386 ELECTRO-DEPOSITION OF METALS. 
 
 have been known to work with great accuracy after having been 
 in use for fifteen years. The slighter load of the beams is also 
 in favor of metallometric balances so that they can be of lighter 
 construction. 
 
 Metallometric as well as voltametric balances have the draw- 
 back that the current must pass through the beam and other 
 sensitive parts to reach the bath. To prevent corrosions on the 
 contacts and avoid large sparks on the sensitive portions, special 
 protective measures are required which render the construction 
 both more complicated and more expensive. 
 
 The advantage of metallometric balances, namely, simple 
 attendance and, when due care is observed, absolute certainty 
 of results, may be advantageously utilized, together with the 
 advantages of voltametric balances, i. e., slighter load and loca- 
 tion at any desired distance from the bath, by the following 
 combination devised by Neubeck. 
 
 If in front of the silver bath be placed a smaller controlling 
 bath of exactly the same composition as the silver bath in 
 operation, or in other words, is taken from the latter, the cur- 
 rent-output of both these baths must be the same, provided the 
 current-density is the same. Now by using as cathodes for this 
 controlling bath very thin silver sheets — 0.05 to 0.1 millimeter 
 thick — with a total surface approximately equal to that of the 
 objects in the bath, the weight of the cathodes will, on the other 
 hand, be materially less than that of the articles in the bath, for 
 instance, of an equally large surface represented by spoons, and 
 consequently the balance can be of lighter construction, while, 
 on the other hand, the current-density in the controlling bath 
 will be approximately equal to that in the silver bath. 
 
 One dozen spoons weighs on an average 540 to 550 grammes 
 and has a surface of about 13.2 square decimeters. The same 
 surface in silver sheet, 0.1 millimeter thick, weighs about 70 
 grammes and in silver sheet 0.05 millimeter thick about 35 
 grammes. Hence the load of the ware is, in the commence- 
 ment, jy 2 to 15 times less than with the metallometric balance 
 and when, on attaining a thickness of about Y / 2 millimeter, the 
 cathodes are reversed, always only half as great. 
 
DEPOSITION OF SILVER. 
 
 387 
 
 Now by allowing the current to pass through the controlling 
 bath and then through the silver bath, exactly the same 
 quantity of silver is deposited in the former as in the latter; 
 thus by connecting the cathodes of the controlling bath with a 
 balance the quantity of metal deposited in the silver bath upon 
 the objects can be accurately determined. 
 
 These considerations led to the construction of the volta- 
 metric controlling apparatus, Fig. 135, which can be connected 
 with any kind of cheap beam-balance. The apparatus * con- 
 structed by Dr. G. Langbein & Co., is arranged as follows: 
 
 Fig. 135. 
 
 The screw 1 secured to the anode-frame (Fig. 135) is 
 directly connected with the anode wire. Upon the anode-frame 
 of copper sit the conducting rods 9, 9, 9, etc., for the anodes, 
 the latter being secured to them by means of platinum wire. 
 To the rod 16 is secured the movable cathode from 7 to which 
 the thin cathode sheets are suspended by means of platinum 
 wire. The current enters the bath through the binding post 1, 
 
 * German patent. 
 
3»S8 ELECTRO-DEPOSITION OF METALS. 
 
 the anode-rods 9, and the anodes, passes to the cathodes, and 
 returns through the cathode-frame 7 to the source of current so 
 long as the screw 2 fixed to the support 17 dips, by reason of 
 the load of the balance, into the mercury vessel 3. The latter 
 is secured to the anode-frame 7 and conductively connected 
 with it. The celluloid disk 10 serves the purpose of protecting 
 the bath from mercury, which may be spilled by careless hand- 
 ling, passing into it. 
 
 When the cathodes have attained the required weight the 
 flow of current to the bath is interrupted by the beam of the 
 balance tilting over. The two steel pins 4 and 5, which are in- 
 sulated from the mercury vessel 3, dip thereby into the mer- 
 cury cups 6 fixed below them on the movable arm of the 
 support 17 and insulated one from the other, the short-circuit 
 of the bell wire being thus affected. The wire 1 1 leads direct 
 to the bell 13, while a second wire 12 leads through the spirals 
 14 to the support 17 and from there through spiral 15 to the 
 bell. When the pins 4 and 5 dip into the mercury cups, 6, a 
 second connection with the bell is made and the latter rings so 
 long as the pins 4 and 5 dip into the mercury. 
 
 Contrary to the principle of the metallometric and the volta- 
 metric balances, the beam and other portions of the balance are 
 here entirely excluded from the current-circuit. Hence, any 
 ordinary beam-balance can be used and no corrosion of sensi- 
 tive portions of the balance by sparks takes place. 
 
 When the cathodes of the controlling bath have attained a 
 thickness approximately the same as that possessed by the 
 silver anodes of the bath in the commencement of the opera- 
 tion, they are used as anodes by suspending them to the anode- 
 rods, while the anodes which have become thinner are sus- 
 pended as cathodes. 
 
 With this arrangement there is to be sure, the same drawback 
 as with the voltamctric balance, namely, that by reason of the 
 baths being coupled one after the other, double the electro- 
 motive force than that used for a silver bath connected with a 
 metallometric balance is required. The interest, which, how- 
 
DEPOSITION OF SILVER. 389 
 
 ever, amounts to very little, on the dead metallic silver in the 
 controlling bath may also be called a disadvantage. On the 
 other hand, the controlling apparatus has the advantage that 
 two or more silver baths of the same composition can be con- 
 nected with it when the same quantity of silver is to be de- 
 posited upon approximately the same object-surface in each 
 bath. 
 
 The case is somewhat different when the baths in operation 
 are of considerable size and furnished with many object-rods. 
 In order to obtain the same current-density in the actual silver 
 bath as in the controlling bath, the latter would have to be of 
 quite large dimensions and require so much electrode-material 
 as to cause considerable expense for providing it. In such a 
 case the advantages presented by the same composition of the 
 operating bath and the controlling bath, have to be abandoned 
 and the controlling bath has to be used as a copper voltameter. 
 Since in the copper solution depositions can be made with cur- 
 rent densities up to 1.5 amperes per square decimeter only one- 
 fifth part of the object-surface in the operating bath is required 
 as cathode-surface in the controlling copper bath. Of course 
 the weight of the desired silver-deposit, reduced to copper, 
 which is found from tables furnished with the apparatus, has to 
 be placed in the scale-pan. The tables are calculated for cur- 
 rent-outputs of from 98 to 99.6 per cent, in T x - - per cent, for 
 baths for silvering by weight with 25 grammes of fine silver as 
 silver cyanide and 25 grammes of of 99 per cent, potassium 
 cyanide, and a current-density of 0.3 ampere per square deci- 
 meter. Hence the current-output of the bath to be used has to 
 be determined and the weights of copper corresponding to the 
 silver deposit are then found in the table for the determined 
 current-output. As the current-output is subject to change by 
 the bath becoming gradually contaminated by foreign metals, 
 which cannot be avoided in silvering metals, for instance, zinc 
 and copper, soluble in potassium cyanide, it will be necessary 
 to determine the current-output at least twice a year. 
 
 As previously mentioned the current-output is materially 
 
390 ELECTRO-DEPOSITION OF METALS. 
 
 smaller when the bath is agitated than when it is at rest, and 
 hence the controlling silver bath cannot be used for agitated 
 baths because, in order to obtain accurate weighing results, 
 agitation of the controlling bath has to be avoided. In this 
 case the copper solution (see p. 383) has also to be used with 
 reference to the tables for the respective current-output. How- 
 ever, when the controlling apparatus works with the copper 
 solution, it still has the advantage of no current passing 
 through sensitive portions of the balance, and thus they are 
 not subject to wear. 
 
 Calculation of the weight of the silver deposit from the current- 
 strength used. This can be done if the current conducted into 
 the bath during silvering be constantly kept at the same 
 strength, and the current- output of the bath be taken into con- 
 sideration. According to the table on p. 60, one ampere de- 
 posits in 1 hour 4.0248 grammes of silver, hence after t hours 
 with a current-strength i : 4.0248 xixt grammes of silver will 
 be deposited, if the current-output amounts to 100. However, 
 the latter is, as a rule, only 98 to 99 per cent., and the value 
 obtained is therefore to be multiplied by the fraction tVo or to\. 
 in order to determine the actual weight of the deposit. 
 
 Attention must, however, be drawn to the fact that it is very 
 difficult to keep the current-strength quite constant for a longer 
 time, especially where numerous baths are connected to a com- 
 mon circuit, and for this reason a calculation, based upon the 
 measurement of the current-strength, will very likely be in 
 most cases impracticable. 
 
 For the calculation of the time which has been consumed for 
 depositing a certain weight of silver when the current-strength 
 is known, the desired weight of the deposit has to be divided 
 by the product from current-strength times chemical equiva- 
 lent of the silver, and the value found multiplied by VV°- or -V /- 
 
 If, for instance, 50 grammes of silver are to be deposited 
 upon one dozen spoons, and the current-strength be 3.2 
 amperes and the current-output 99 per cent., the time is found 
 from the following calculation : 
 
DEPOSITION OF SILVER. 391 
 
 50XIOO 50OO 
 
 — — = 3-9 2 hours = 3 hours 55 minutes. 
 
 3.2X4.0248x99 1275.05 
 
 If the current-strength is to be calculated, which is required 
 to produce in a given time a determined thickness of deposit, 
 the product from the desired thickness in millimeters, times the 
 object-surface in square decimeters, times the specific gravity 
 of the metal to be deposited, times 1000, has to be divided by 
 the product from time, times electro-chemical equivalent, times 
 current-output. Suppose, for instance, the desired thickness 
 of the deposit is to be 0.1 millimeter, the object-surface 1.5 
 square decimeter, the specific gravity 10.5, the time 4 hours, 
 the electro-chemical equivalent 4.025, and the current-output 
 98 per cent., then the current-strength required is : 
 
 0.1 x 1.5 x 10. ox 100 1575 
 
 o 3 — — zrz — 0.99 ampere. 
 
 4x4.0248x98 1577.72 ^ 
 
 When the articles have received a deposit of the required 
 weight, they are treated for the prevention of subsequent yel- 
 lowing according to one of the methods given on p. 372, then 
 scratch-brushed bright with the use of decoctions of soap-root, 
 plunged in hot water and dried in sawdust. 
 
 Matt silver. — Articles which are to retain the beautiful crys- 
 talline dead white with which they come from the bath are, 
 without touching them with the fingers or knocking them 
 against the sides of the vessel, rinsed thoroughly in clean 
 water, plunged into very hot, distilled water, and then sus- 
 pended free to dry. Immediately after drying they are to be 
 provided with a thin coat of kristalline or zapon to protect the 
 dead-white coating, which readily turns yellow, and, moreover, 
 is very sensitive. 
 
 Polishing the deposits. — The silvered articles having been 
 scratch-brushed, must finally be polished, which may be effected 
 upon a fine felt wheel with the use of rouge, but imparting high 
 luster by burnishing is to be preferred, the deposit being first 
 treated with the steel burnisher, and then with the stone bur- 
 nisher, as explained on p. 218. 
 
392 ELECTRO-DEPOSITION OF METALS. 
 
 In some establishments in which plated table-ware in large 
 quantity is turned out, ingeniously-devised burnishing machines 
 driven by power are in use, by which much of the manual labor 
 is saved. The knife, spoon, etc., each supported by its tips 
 in a suitable holder, are very slowly rotated, while the bur- 
 nishing-tool moves quickly over the surface, performing the 
 work rapidly and satisfactorily. 
 
 When burnishing is completed, the surface is wiped off" lon- 
 gitudinally with an old, soft calico rag. Sawdust, hard cloth, 
 and tissue paper produce streaks. 
 
 B. Ordinary silver-plating. — Objects which are to receive a 
 deposit of less thickness have to undergo exactly the same 
 operations described under plating by weight, the only differ- 
 ence being that for quicking a weaker solution ( I 5 to 3 I grains 
 of nitrate of mercury to I quart of water), or very dilute solution 
 of potassium-mercury cyanide (77 grains of potassium-mercury 
 cyanide and 77 grains of potassium cyanide to I quart of water) 
 is used, and that the objects remain a shorter time in the bath. 
 
 Direct silvering of Britannia, tin., German silver. As pre- 
 viously mentioned, iron, steel, zinc and tin should first 
 be coppered or brassed. However, tin and Britannia may also 
 be directly plated, but the bath must be rich in silver and con- 
 tain a large excess of potassium cyanide. Further, the current 
 should be so strong that the articles acquire a blue-gray color. 
 They are then suspended in the silver bath of normal composi- 
 tion, and plating is finished with a normal current. 
 
 The same process is also suitable for plating articles of Ger- 
 man silver rich in nickel. In polishing such articles it is fre- 
 quently observed that the deposit rises, but by plating in the 
 above-mentioned preparatory bath, and finishing in the normal 
 bath, the deposit will very well bear polishing with the steel. 
 
 For silver-plating Britania ware and articles of tin, Gore 
 recommends the following process. Boil the articles in caustic 
 potash solution, scratch-brush them, and plate them prepara- 
 tively with a strong current and the use of large anode-surfaces 
 in a hot silver bath ( 194 F.), and then finish deposition to the 
 desired thickness in the ordinary cold silver bath. 
 
DEPOSITION OF SILVER. 393 
 
 According to an Australian patent, the following process is 
 claimed to yield good results in directly silver-plating iron and 
 steel : The article to be plated having first been dipped in hot 
 dilute hydrochloric acid is brought into solution of mercury 
 nitrate and then connected with the zinc pole of a Bunsen ele- 
 ment. It becomes quickly coated with a layer of mercury when 
 it is taken out, washed and brought into an ordinary silver 
 bath. When covered with a layer of silver of sufficient thick- 
 ness, it is heated to 572 F., the mercury evaporating at this 
 temperature. It is claimed that silver deposited in this man- 
 ner adheres more firmly than by any other process, but it is 
 doubtful whether for solid silver-plating this method can replace 
 previous coppering. 
 
 Stopping off. If certain parts of a metallic article are not to 
 receive a deposit, as for instance, when a contrast is to be ef- 
 fected by depositing different metals upon the same object, these 
 parts are covered or " stopped-off," with a varnish. Stopping- 
 off varnish is prepared by dissolving asphalt or dammar with 
 an addition of mastic in oil of turpentine. Apply with a brush, 
 and after thoroughly drying the articles in the drying-chamber, 
 place them for an hour in very cold water, whereby the varnish 
 hardens completely. After plating, the varnish is removed, 
 best with benzine, the article plunged in hot water, and dried in 
 sawdust. 
 
 For a varnish that will resist the solvent power of the hot 
 alkaline gilding liquid, Gore recommends the following compo- 
 sition : Translucent rosin 10 parts, yellow beeswax 6, extra- 
 fine red sealing-wax 4, finest polishing rouge 3. 
 
 Quick-drying, stopping-off varnishes, which harden immedi- 
 ately at the ordinary temperature and resist cyanide baths, are 
 now found in commerce. 
 
 Special applications of electro-silvering. — It remains to men- 
 tion a few special applications of electro-silvering as well as 
 processes of decorating with silver by electrical and chemical 
 means. 
 
 Silvering of fine copper wire is effected in an apparatus", 
 
394 ELECTRO-DEPOSITION OF METALS. 
 
 which is described and illustrated in Chapter IX, " Deposition 
 of Gold," where further details will be found. Luster is imr 
 parted to the silvered wire by drawing through a draw-plate. 
 
 Incrustations with silver {and gold, and other metals). — By 
 incrusting is understood the inlaying of depressions, produced 
 by engraving or etching upon a metallic body, with silver, gold 
 and other metals, such as Japanese incrustations, which are 
 made by mechanically pressing the silver or gold into the de- 
 pressions. Such incrustations, however, can also be produced 
 by electro- deposition, the process being as follows : The design 
 which is to be incrusted upon a metal is executed with a pig- 
 ment of white-lead and glue-water or gum-water. The portion 
 not covered by the design is then coated with stopping-off 
 varnish. The article is next placed in dilute nitric acid, 
 whereby the pigment is first dissolved, and next the surface 
 etched, which is allowed to progress to a certain depth. 
 Etching being finished, the article is washed in an abundance 
 of water and immediately brought into a silver or gold bath, 
 in which, by the action of the current, the exposed places 
 are filled up with metal. This being done, the stopping-off 
 varnish is removed with benzine, the surface ground smooth, 
 and polished. In this manner one article may be incrusted 
 with several metals ; for instance, brass may be incrusted with 
 copper, silver and gold, and by oxidizing or coloring portions 
 of the copper beautiful effects can be produced. The principal 
 requisites for these incrustations are manual skill and much 
 patience. Expensive apparatus is not required, every skilled 
 electro-plater being able to execute the work. 
 
 Imitation of nicl or nielled silvering. By nielling is under- 
 stood the inlaying of designs produced either by engraving or 
 stamping, with a black mixture of metallic sulphides. The niel- 
 ling powder is prepared by melting silver 20 parts by weight, 
 copper 90 parts and lead 150 parts. To the liquid metallic 
 mass add 26^ ozs. of sulphur and 3^ oz. of ammoniun chloride, 
 quickly cover the crucible, and continue heating until the ex- 
 cess of sulphur is volatilized. Then pour the contents of the 
 
DEPOSITION OF SILVER. 395 
 
 crucible into another crucible, the bottom of which is covered 
 about Y^ inch deep with flowers of sulphur, cover the crucible 
 and allow the mixture to cool. When cold bring the contents 
 once more to the fusing point, and pour the fused mass in a 
 thin stream into a bucket filled with water, whereby granulated 
 metal is formed, which can be readily reduced in a mortar to a 
 fine powder, This powder is mixed with ammonium chloride 
 and gum-water to a thin paste. This paste is brought into the 
 designs produced by engraving or stamping, and after drying 
 burnt-in in a muffle. When cold, any roughness is removed 
 by grinding, and after polishing a sharp, black design in white 
 silver is obtained. 
 
 To imitate niel by electro-deposition, the design is executed 
 upon the surface with a pigment consisting of white lead and 
 glue- or gum-water. The portions which are to remain free are 
 coated with stopping-off varnish, and the design is uncovered 
 by etching with very dilute nitric acid. The article is then 
 brought as the anode into dilute solution of ammonium sul- 
 phide, while a small sheet of platinum connected to the nega- 
 tive pole is dipped into the solution. Sulphide of silver being 
 formed, the design becomes rapidly black-gray, and after re- 
 moving the stopping-off varnish with benzine, stands out in 
 sharp contrast from the white silver. 
 
 Upon brass, nielling may be imitated by silvering the article 
 and then engraving the design, by which the silver is removed 
 and the brass uncovered. The article is then brought into the 
 black bright-dip, by which the uncovered brass is colored black 
 while the silvered portions remain unchanged. If portions in 
 relief are to be made black, the silvering is removed by grind- 
 ing the article dipped into cream of tartar solution, and then 
 brought into the black bright-dip. This process is largely em- 
 ployed by manufacturers of buttons when silvered buttons are 
 to be supplied with the name of the firm and the quality num- 
 ber in black. 
 
 Old {antique) silvering. — To give silvered articles an antique 
 appearance coat them with a thin paste of 6 parts graphite, I 
 
396 ELECTRO-DEPOSITION OF METALS. 
 
 red ochre and sufficient spirits of turpentine. After drying, 
 gentle rubbing with a soft brush removes the excess of powder, 
 and the reliefs are set off (discharged) by means of a rag 
 dipped into alcohol. 
 
 A tone resembling antique silvering is also obtained by 
 brushing the silvered articles with a soft brush moistened with 
 very dilute alcoholic solution of chloride of platinum. 
 
 In order to impart the old silver tinge to small articles, such 
 as buttons, rings, etc., they are agitated in the above-mentioned 
 paste, and then " tumbled " with a large quantity of dry saw- 
 dust until the desired shade is obtained. 
 
 With the use of the electric current and carbon anodes, 
 antique silver may be produced as follows: Bring the silvered 
 articles, previously thoroughly freed from grease, into the silver 
 bath at an electro-motive force of 4 to 5 volts, and allow them 
 to remain for a few minutes until they become covered with a 
 uniform blue-gray deposit. They are then thoroughly rinsed 
 in water, and the raised portions rubbed with very fine pumice, 
 to lay bare the silver. If surfaces are to appear in antique 
 silver, the deposit is only sufficiently removed with pumice for 
 the silver to shine through, and the surface to show the proper 
 antique-silver tone. 
 
 Oxidized silver. — This term is incorrect, as by it is under- 
 stood not an oxidation, but a combination with sulphur or 
 chlorine. Solution of pentasulphide of potassium (liver of 
 sulphur of the shops) is generally used for the purpose. Im- 
 merse the articles in a solution of 2.75 drachms of liver of 
 sulphur and ^]4 drachms of ammonium carbonate in 1 quart 
 of water heated to 1 76 F., and allow them to remain until they 
 have acquired the desired dark tone. Immediately after im- 
 mersion, the articles become pale gray, then darker, and finally, 
 deep black-blue. For coloring in this manner, the silvering 
 should not be too thin. For articles with a very thick deposit 
 of silver, solution of double the strength may be used. Very 
 slightly silvered articles cannot be oxidized in this manner, as 
 the bath would remove the silvering, or under the most favor- 
 
DEPOSITION OF SILVER. 397 
 
 able circumstances produce only a gray color. If the operation 
 'is not successful, and the articles come from the bath stained, 
 or otherwise defective, dip them in a warm potassium cyanide 
 solution, which rapidly dissolves the silver sulphide formed. 
 
 A yellow color is imparted to silvered articles by immersion 
 in a hot concentrated solution of chloride of copper, rinsing 
 and drying. 
 
 For silvering by contact, boiling and friction, see special 
 chapter " Depositions by Contact." 
 
 Stripping silvered articles. — When a silvering operation has 
 failed, or the silver is to be stripped from old silvered articles, 
 different methods have to be used according to the nature of 
 the basis-metal. Silvered iron articles are treated as the anode 
 in potassium cyanide solution in water (i : 20), the iron not 
 being attacked by potassium cyanide. As cathode suspend 
 in the solution a few silver anodes or a copper-sheet rubbed 
 with an oily rag ; the silver precipitates upon the copper 
 sheet but does not adhere to it. Articles, the basis of which 
 is copper, are best stripped by immersion in a mixture of 
 equal parts of anhydrous (fuming) sulphuric acid and nitric 
 acid of 40 Be. This mixture makes the copper passive, it 
 not being attacked while the silver is dissolved. Care must, 
 however, be had not to introduce any water into the acids, nor 
 to let them stand without being hermetically closed, since by 
 absorbing moisture from the air they become dilute, and may 
 then exert a dissolving effect upon the copper. The fuming 
 sulphuric acid may also be highly heated in a shallow pan of 
 enameled cast iron. Then at the moment of using it pinches of 
 dry and pulverized nitrate of potassium (saltpeter) are thrown 
 into it, and the article, held with copper tongs, is plunged into 
 the liquid. The silver is rapidly removed, while the copper or 
 its alloys is but slightly corroded. According to the rapidity 
 of the solution, fresh additions of saltpeter are made. All the 
 silver has been dissolved when, after rinsing in water and dip- 
 ping the articles into the cleansing acids, they present no brown 
 or black spots, that is to say, when they behave like new. In 
 
398 ELECTRO-DEPOSITION OF METALS. 
 
 this hot acid stripping proceeds more quickly than in the cold 
 acid mixture, but the latter acts more uniformly. 
 
 Determination of silver-plating. — By applying to genuine 
 silver-plating a drop of nitric acid of 1.2 specific gravity, in 
 which red chromateof potash has been dissolved to saturation, 
 a red stain of chromate of silver is formed. According to 
 Griiger, this method may also be used, to a certain extent, for 
 the recognition of any other white metal which may be mistaken 
 for silver. A drop of the mixture applied to German silver be- 
 comes brown, no red stain appearing after rinsing with water; 
 upon Britannia the drop produces a black stain; zinc is etched 
 without a colored spot remaining behind ; upon amalgamated 
 metals a brownish precipitate is formed, which does not adhere 
 and is washed away by water; upon tin the drop also acquires 
 a brownish color, and by diluting with water a yellow precipi- 
 tate is formed ; upon lead a beautiful yellow precipitate is 
 formed. 
 
 Custom-house officers in Germany are directed bylaw to use 
 the following process for the determination of genuine silver- 
 plating : Wash a place on the article with ether or alcohol, dry 
 with blotting paper, and apply to the spot thus cleansed a drop 
 of i to 2 per cent, solution of crystallized bisulphite of soda 
 prepared by boiling 1.05 ozs. of sodium sulphite and 2.36 
 drachms of flowers of sulphur with 0.88 oz. of water until the 
 sulphur is dissolved, and diluting to 1 quart of fluid. Allow 
 the drop to remain upon the article about ten minutes and then 
 rinse off with water. Upon silver articles, a full, round, steel- 
 gray spot is produced. Other white metals and alloys, with 
 the exception of amalgamated copper, do not show this phe- 
 nomenon, there appearing at the utmost a dark ring at the edge 
 of the drop. Amalgamated copper is more quickly colored, 
 and acquires a more dead-black color than silver. 
 
 Examination of silver baths. 
 
 For the quantitative examination of silver baths, the determi- 
 ination of the content of free potassium cyanide and of metallic 
 
DEPOSITION OF SILVER. 399 
 
 silver as well as of the potassium carbonate which is formed by 
 the action of air,. etc., upon the potassium cyanide, has to be 
 taken into consideration. 
 
 Regarding the determination of the free potassium cyanide, 
 the reader is referred to the method given under " Examination 
 of copper baths containing potassium cyanide," and what has 
 been said there in reference to replacing the deficiency also 
 applies here. 
 
 The potassium carbonate which is formed in constantly 
 increasing quantities in the bath, is best removed by the addi- 
 tion of barium cyanide solution, whereby, in consequence of 
 reciprocal decomposition, potassium cyanide is formed, while 
 barium carbonate in an insoluble state is separated. 
 
 The determination of the potassium carbonate present in the 
 bath is desirable, so as to be able on the one hand, to calculate 
 the quantity of barium cyanide required for its decomposition 
 and, on the other, to become acquainted with the quantity of 
 free potassium cyanide formed thereby. 
 
 The determination of the potassium carbonate is affected as 
 follows : Bring by means of the pipette, 20 cubic centimeters of 
 silver bath into a beaker, dilute with 50 cubic centimeters of 
 water, and compound with barium nitrate solution in excess. 
 Allow to settle for some time, then filter through not too large 
 a paper filter, taking care that the entire precipitate reaches the 
 filter, and wash the filter thoroughly with water until a few 
 drops of the filtrate, when evaporated upon a platinum sheet, 
 leave no residue. Now take the filter, together with the resi- 
 due, carefully from the funnel, bring it into a beaker, and add 
 water, as well as a carefully measured quantity of standard nitric 
 acid, which should, however, be somewhat larger than required 
 for dissolving the barium carbonate. While solution is being 
 effected, keep the beaker covered with a watch glass, and then 
 rinse any drops appearing upon the latter into the beaker by 
 means of distilled water. Add to the solution, as an indicator, 
 a few drops of methyl-orange, whereby the solution is colored 
 red, and add, while stirring constantly, from a burette, stand- 
 
400 ELECTRO-DEPOSITION OF METALS. 
 
 ard soda solution until the red color of the solution passes into 
 yellow. By now deducting the cubic centimeters of soda solu- 
 tion used from the cubic centimeters of standard nitric acid 
 added to the solution of the barium carbonate, and multiply- 
 ing the number of the remaining cubic centimeters of standard 
 nitric acid by 3.45, the quantity of potassium carbonate in 
 grammes present in 1 liter of silver bath is obtained. 
 
 Now the quantity of barium cyanide has to be calculated, 
 which is required for the conversion of the quantity of potas- 
 sium carbonate found, into potassium cyanide with the separa- 
 tion of barium carbonate. It is best to use a 20)^ per cent, 
 barium cyanide solution, and since 1 gramme of potassium 
 carbonate requires for conversion 1.36 grammes of barium 
 cyanide, 6.80 grammes of 20 per cent, barium cyanide solution 
 are necessary for the purpose, and each gramme of potassium 
 carbonate yields 0.942 gramme of potassium cyanide. Hence 
 for the determination of the potassium cyanide present after 
 the destruction of the potassium carbonate, there has to be 
 added to the potassium cyanide found by titration, the content 
 of free potasium cyanide calculated from the conversion with 
 barium cyanide. If this shows a deficit as compared with the 
 original content, it is to be made up by adding only about one- 
 half the quantity, for the same reason as given in speaking of 
 the copper bath, namely, because the potassium formate, which 
 is at the same time formed, performs the function of the potas- 
 sium cyanide. 
 
 To save calculation a table by Steinach and Buchner for the 
 use of a 20^ per cent, barium cyanide solution is here given: 
 
DEPOSITION OF SILVER. 
 
 4OI 
 
 Potassium carbonate in 
 
 For 1 liter of silver bath have to be added 
 
 
 
 1 liter of silver bath. 
 
 20)2 P er cent, barium cya- 
 
 Potassium cyanide 
 
 
 nide solution. 
 
 formed thereby. 
 
 1 gramme 
 
 6.7 grammes 
 
 0.95 gramme 
 
 2 " 
 
 13-4 
 
 ' 
 
 1.90 " 
 
 3 " 
 
 20.1 ' 
 
 c 
 
 2.85 " 
 
 4 " 
 
 26.8 
 
 
 3.80 « 
 
 5 
 
 33-5 
 
 
 4.70 " 
 
 6 
 
 40.2 ' 
 
 
 5-7° 
 
 7 " 
 
 46.9 
 
 
 6.65 
 
 8 
 
 53-6 
 
 
 7.60 
 
 9 " 
 
 60.3 
 
 
 8-55 " 
 
 10 
 
 67.0 ' 
 
 
 9.50 
 
 11 
 
 73-7 
 
 
 10.40 " 
 
 12 " 
 
 80.4 
 
 
 11.40 " 
 
 13 " 
 
 87.1 ' 
 
 
 12.35 
 
 14 " 
 
 93-9 
 
 
 13.30 
 
 15 
 
 100.5 
 
 
 14.20 " 
 
 For the determination of the silver, the electrolytic method is 
 the most simple and suitable in so far as the silver bath can be 
 directly used for the purpose. 
 
 Bring by means of the pipette into the platinum dish 10 
 cubic centimeters of the silver bath, or 20 cubic centimeters 
 if the bath is weak; add, according to the greater or smaller 
 excess of the potassium cyanide present, x / 2 to 1 gramme of 
 potassium cyanide dissolved in water, and dilute up to 1 or 1 y 2 
 centimeters from the edge of the dish. Heat, by means of a 
 small flame, the contents of the dish to from 140 to 149 F., 
 and maintain this temperature as nearly constant as possible. 
 Electrolysis is effected with a current density NDioo = o.o8 
 ampere. Complete precipitation, which requires 3 to 3^ 
 hours, is recognized by ammonium sulphide producing no dark 
 coloration of the fluid. The dish is then washed, without inter- 
 rupting the current, rinsed with alcohol and ether, dried for a 
 short time at 21 2° F., and weighed. The weight of the pre- 
 cipitate multiplied by 100 gives the content of silver in grammes 
 per liter of bath. If 20 cubic centimeters of silver bath have 
 been electrolyzed, multiply only by 50. 
 
 If the analysis has shown a deficit of silver in the bath, it can 
 26 
 
402 ELECTRO- DEPOSITION OF METALS. 
 
 be readily replaced. For strengthening the bath it is best to 
 use pure crystallized potassium-silver cyanide, which in round- 
 numbers contains 50 per cent, of silver. Suppose the bath con- 
 tains per liter 2 grammes of silver less than it should, then for 
 each liter of bath (52: 100 ==2 :x; x = 3.8 grammes), 3.8 
 grammes of pure crystallized potassium-silver cyanide have to 
 be added. 
 
 The more troublesome volumetric analysis may be omitted, 
 it offering no advantage over the electrolytic method. 
 
 Recovery of silver from old silver baths, etc. — Old solutions 
 which contain silver in the form of a silver salt are easily treated. 
 It is sufficient to add to them, in excess, a solution of common 
 salt, or hydrochloric acid, when all the silver will be precipi- 
 tated in the state of chloride of silver, which, after washing, may 
 be employed for the preparation of new baths. 
 
 For the recovery of silver from solutions which contain it as 
 cyanide, the solutions may be evaporated to dryness, the resi- 
 due mixed with a small quantity of calcined soda and potassium 
 cyanide, and fused in a crucible, whereby metallic silver is 
 formed, which, when the heat is sufficiently increased, will be 
 found as a button upon the bottom of the crucible ; or if it is not 
 desirable to heat to the melting-point of silver, the fritted mass 
 is dissolved in hot water, and the solution containing the soda 
 and cyanide quickly filtered off from the metallic silver. The 
 evaporation of large quantities of fluid, to be sure, is inconven- 
 ient, and requires considerable time. But the reducing process 
 above described is without doubt the most simple and least 
 injurious. 
 
 According to the wet method, the bath is strongly acidulated 
 with hydrochloric acid, provision being made for the effectual 
 carrying-off of the hydrocyanic acid liberated. Remove the 
 precipitated chloride of silver and cyanide of copper by filtra- 
 tion, and, after thorough washing, transfer it to a porcelain dish 
 and treat it, with the aid of heat, with hot hydrochloric acid, 
 which will dissolve the cyanide of copper. The resulting 
 chloride of silver is then reduced to the metallic state by mix- 
 ing it with four times its weight of crystallized carbonate of 
 
DEPOSITION OF SILVER. 403 
 
 soda, and half its weight of pulverized charcoal. The whole is 
 made into a homogeneous paste, which is thoroughly dried, and 
 then introduced into a strongly-heated crucible. When all the 
 material has been introduced, the heat is raised to promote 
 complete fusion and to facilitate the collection of the separate 
 globules of silver into a single button at the bottom of the cru- 
 cible, where it will be found after cooling. If granulated silver 
 is wanted, pour the metal in a thin stream, and from a certain 
 height, into a large volume of water. 
 
 A very simple method is as follows : Bring the silver bath 
 into flasks, mix the contents of the flask with zinc dust (zinc 
 in a finely-divided state) in the proportion of about *^ oz. per 
 quart of bath, and shake thoroughly 5 or 6 times every day. 
 In five days, all the silver is precipitated. Decant the clear 
 liquid from the precipitate, wash the latter several times with 
 water, and dissolve the zinc contained in the precipitate in pure 
 hydrochloric acid. The silver remains behind in a pulverulent 
 form, and may be dissolved in nitric acid, worked up into sil- 
 ver chloride or silver cyanide. In place of zinc, aluminium 
 powder may be used for precipitation, the excess of aluminium 
 being then dissolved by caustic potash, or caustic soda 
 solution. 
 
 From acid mixtures used for stripping, the silver may be ob- 
 tained as follows: Dilute the acid mixture with 10 to 20 times 
 the quantity of water, and precipitate the silver as chloride of 
 silver by means of hydrochloric acid. Interrupt the addition 
 of hydrochloric acid, when a drop of it produces no more pre- 
 cipitate of chloride of silver in the clear fluid. The precipi- 
 tated chloride of silver is filtered off, washed, and either directly 
 dissolved in potassium cyanide, or the silver is regained as 
 metal by fusing the chloride of silver with calcined soda, and 
 wood charcoal powder, previously thoroughly mixed. 
 
 Still more simple is the reduction of the chloride of silver by 
 pure zinc. For this purpose suspend the chloride of silver by 
 water, add hydrochloric acid, and place pure zinc rods or 
 granulated zinc in the fluid. While zinc dissolves, metallic 
 silver is separated, which is filtered off, washed and dried. 
 
CHAPTER IX. 
 
 DEPOSITION OF GOLD. 
 
 Gold is generally found in the metallic state. It is one of the 
 metals possessing a yellow color. Precipitated from its solution 
 with green vitriol (ferrous sulphate) or oxalic acid, it appears 
 as a brown powder without luster, which on pressing with the 
 burnisher acquires the color and luster of fused gold. Pure 
 gold is nearly as soft as lead, but possesses considerable tenacity. 
 In order to increase the hardness when used for articles of 
 jewelry and for coinage, it is mixed with silver or copper. 
 The " fineness of gold," or its proportion in the alloy, is usually 
 expressed by stating the number of carats present in 24 carats 
 of the mixture. Pure gold is stated to be 24 carats "fine;" 
 standard gold is 22 carats fine; 18 carats gold is a mixture of 
 18 parts of gold and 6 of alloy. Gold is the most malleable and 
 ductile of the metals. It may be beaten out into leaves not ex- 
 ceeding xo.Wo of a millimeter in thickness. When beaten 
 out into thin leaves and viewed by transmitted light, gold ap- 
 pears green; when very finely divided it is dark red or black. 
 The specific gravity of fused gold is 19.35, and tnat of precipi- 
 tated gold powder, from 19.8 to 20.2. Pure gold melts at about 
 2016 F., and in fusing exhibits a sea-green color. The melt- 
 ing-points of alloyed gold vary according to the degree of fine- 
 ness. Thus, 23 carat gold melts at 2012 F. ; 22 carat at 
 2009 ; 20 carat at 2002 ; 18 carat at 1995 ; 15 carat at 
 1992 ; 13 carat at 1990 ; 12 carat at 1987 ; 10 carat at 
 1982 ; 9 carat at 1979 ; 8 carat at 1973 ; 7 carat at i960 . 
 The fineness of gold may be approximately estimated by means 
 of the touch-stone, a basaltic stone formerly obtained from Asia 
 Minor, but now procured from Saxony and Bohemia. The 
 sample of gold to be tested is drawn across the stone, and the 
 
 ( 404 ) 
 
DEPOSITION OF GOLD. 405 
 
 streak of metal is treated with dilute nitric acid. From the 
 rapidity of the action and the intensity of the green color pro- 
 duced due to the solution of the copper, as compared with 
 streaks made by alloys of known composition — the assayer is 
 enabled to judge of the proportion of inferior metal which is 
 present. Gold preserves its luster in the air, and is not acted 
 upon by any of the ordinary acids. Nitric, hydrochloric, or 
 sulphuric acid by itself does not dissolve gold, but it dissolves 
 in an acid mixture which develops chlorine, hence in aqua regia 
 (nitro-hydrochloric acid). 
 
 The gold found in commerce under the name of shell-gold or 
 painter ' s gold, which is used in painting and for repairing 
 smaller defects in electro-gilding, is prepared by triturating 
 waste in the manufacture of leaf gold with water, diluted honey, 
 or gum-water. Gold solution may also be precipitated with 
 antimonic chloride. The resulting precipitate is triturated with 
 barium hydrate, extracted with hydrochloric acid, and after 
 washing, the gold powder is triturated with gum arabic solution. 
 
 Gold baths. Gold-plating may be effected in a hot or cold 
 bath, large objects being generally plated in the latter, and 
 smaller objects in the former. The hot bath has the advantage 
 of requiring less current-strength, besides yielding deposits of 
 greater density and uniformity, and of sadder, richer tones. 
 Hot baths work with a moderate content of gold — 11^ to 
 125^ grains per quart of bath — while cold baths should con- 
 tain not less than 54 grains per quart. 
 
 Some authors — for instance, Eisner, Briant, Selm, and others 
 — give the preference to baths prepared with potassium ferro- 
 cyanide ; while others, like Elkington and Regnault, work with 
 a solution of gold-salt and potassium bicarbonate; and Buttger, 
 Leuchtenberg, and others recommend a solution of cyanide of 
 gold in potassium cyanide. With proper treatment of the bath, 
 good results may be obtained with either. However, the use of 
 baths prepared with potassium ferrocyanide cannot be recom- 
 mended on account of the secondary decompositions which 
 take place during the operation of plating, and because the 
 
406 ELECTRO-DEPOSITION OF METALS. 
 
 baths do not dissolve the gold anodes. In the following, only 
 approved formulae for the preparation of gold baths will be 
 given : — 
 
 I. BatJi for cold gilding. — Fine gold in the form of fulmi- 
 nating gold 54 grains, 98 per cent, potassium cyanide 0.35 to 
 0.5 oz. (according to the current-strength used), water I quart. 
 
 Electro-motive force at 10 cm. electrode-distance, and with 
 the use of O.35 oz. of potassium cyanide, 1.35 volts; with the 
 use of 0.5 oz. of potassium cyanide, 1.2 volts. 
 
 Current-density, 0.15 ampere. 
 
 To prepare this bath, dissolve 54 grains of fine gold in aqua 
 regia in a porcelain dish heated over a gas or alcohol flame, and 
 evaporate the solution to dryness. Continue the heating until 
 the solution is thickly-fluid and dark brown, and on cooling 
 congeals to a dark brown mass. Heating too strongly should 
 be avoided, as this would cause decomposition and the auric 
 chloride would be converted into aurous chloride, and even- 
 tually into metallic gold and chlorine, which escapes. The 
 neutral chloride of gold formed in this manner is dissolved in 
 1 pint of water and ammonia added to the solution as long 
 as a yellow-brown precipitate is formed, avoiding, however, 
 a considerable excess of ammonia. The precipitate of ful- 
 minating gold is filtered off, washed, and dissolved in 1 quart 
 of water containing 0.5 oz. of potassium cyanide in solution. 
 The solution is boiled, replacing the water lost by evapora- 
 tion, until the odor of ammonia which is liberated by dissolv- 
 ing the fulminating gold in potassium cyanide disappears, when 
 it is filtered. Instead of dissolving the gold and preparing 
 neutral chloride of gold by evaporating, it is more convenient 
 to use 108 grains of chemically pure neutral chloride of gold 
 as furnished by chemical works, and precipitate the fulminat- 
 ing gold from its solution. 
 
 Too large an excess of potassium cyanide yields gold depos- 
 its of an ugly, pale color. When working with a more power- 
 ful current, the excess of potassium cyanide need only be slight ; 
 with a weaker current it may be larger. 
 
DEPOSITION OF GOLD. 407 
 
 The fulminating gold must not be dried, as in this condi- 
 tion it is highly explosive, but should be immediately dissolved 
 while in a moist state. 
 
 If the cost of a bath for cold gilding with such a high con- 
 tent of gold as given in formula I should appear too great, only 
 27 grains of gold per quart may be used. With a suitable 
 electro-motive force, deposits of a beautiful, sad-yellow color 
 are thus also obtained. Such a bath is yielded by the follow- 
 ing formula : 
 
 la. Fine gold in the form of neutral gold chloride 27 grains, 
 98 to 99 per cent, potassium cyanide 0.26 oz., water 1 quart. 
 
 Electro-motive force at 10 cm. electrode-distance, 2.0 volts. 
 
 Current-density, 0.15 ampere. 
 
 For cold gilding, Roseleur recommends the following bath: 
 
 II. Fine gold as neutral chloride of gold, 0.35 oz. ; 98 per 
 cent, potassium cyanide, 0.7 oz. ; water, 1 quart. 
 
 Electro-motive force at 10 cm. electrode-distance, about 1.5 
 volts. 
 
 Current density, 0.12 ampere. 
 
 Dissolve the gold-salt from 0.35 oz. of fine gold or about 0.7 
 oz. of neutral chloride of gold in */ 2 pint of the water, and the 
 potassium cyanide in the other y 2 pint of water, and after 
 mixing the solutions boil for half an hour. The preparation of 
 this bath is more simple than that of formula I, but the color 
 of the gold deposit obtained with the latter is warmer and sad- 
 der. The high content of gold in the bath, prepared according 
 to formula II, readily causes a red-brown gold deposit, and 
 hence special attention has to be paid to the regulation of the 
 current. 
 
 For those who prefer gold baths prepared with yellow prus- 
 siate of potash instead of potassium cyanide, the following 
 formula for cold-gilding is given : 
 
 III. Yellow prussiate of potash (potassium ferrocyanide), 
 0.5 oz. ; carbonate of soda, 0.5 oz. ; fine gold (as chloride of 
 gold or fulminating gold), 30.75 grains; water, 1 quart. 
 
 Electro-motive force at 10 cm. electrode-distance, 2 volts. 
 
408 ELECTRO-DEPOSITION OF METALS. 
 
 Current-density, 0.15 ampere. 
 
 To prepare the bath, heat the solutions of the yellow prussi- 
 ate of potash and of the carbonate of soda in the water to the 
 boiling-point, add the gold-salt, and boil % hour, or with use 
 of freshly precipitated fulminating gold, until the odor of am- 
 monia disappears. After cooling, the solution is mixed with a 
 quantity of distilled water, corresponding to the water lost by 
 evaporation, and filtered. This bath gives a beautiful bright 
 gilding upon all metals, even upon iron and steel. 
 
 The yellow prussiate of potash baths are deservedly popular 
 for decorative gilding, when gold deposits of different colors 
 are to be produced upon an object. Certain portions have 
 then to be covered with stopping-off varnish, the latter being 
 less attacked by this bath than by one containing an excess of 
 potassium cyanide. 
 
 This bath is especially suitable for the so-called clock gild- 
 ing. The articles are first provided with a heavy deposit of 
 copper in the alkaline copper bath, then matt-coppered in the 
 acid copper bath, next drawn through the bright-pickling bath, 
 thoroughly rinsed, and finally gilded in the bath heated to 
 about 122 F. 
 
 Gold bath for hot gilding. — IV. Fine gold (as fulminating 
 gold) 15.4 grains, 98 per cent, potassium cyanide 77 grains, 
 water 1 quart. 
 
 Electro-motive force at 10 cm. electrode-distance, 1.0 volt. 
 
 Current-density, 0.1 ampere. 
 
 This bath is prepared in the same manner as that according 
 to formula I, from 15.4 grains of fine gold, which is converted 
 into neutral chloride of gold by dissolving in aqua regia and 
 evaporating; or dissolve directly 29.32 to 30.75 grains of 
 chemically pure neutral chloride of gold in water, precipitate 
 the gold as fulminating gold with aqua ammonia, wash the pre- 
 cipitate, dissolve it in water containing the potassium cyanide, 
 and heat until the odor of ammonia disappears, replacing the 
 water lost by evaporation. This bath yields a beautiful sad 
 gilding of great warmth. All that has been said in regard to 
 
DEPOSITION OF GOLD. 4O9 
 
 the content of potassium cyanide in the bath prepared accord- 
 ing to formula I also applies to this bath. The temperature 
 should be between 158 and 176 F., and the current-strength 
 2.0 to 2.5 volts. 
 
 Roseleur recommends for hot gilding: 
 
 V. Chemically pure crystallized sodium phosphate 2.1 1 ozs., 
 neutral sodium sulphite 0.35 oz., potassium cyanide 30.86 
 grains, fine gold (as chloride) 15.43 grains, distilled water I 
 quart. 
 
 Electro-motive force at 10 cm. electrode distance 1.5 volts. 
 
 Current- density, 0.12 ampere. 
 
 If this bath is to serve for directly plating steel, only half the 
 quantity of potassium cyanide is to be used, and the objects 
 should be covered with the use of a somewhat greater electro- 
 motive force. Increasing the content of neutral sodium sul- 
 phite to 0.5 or 0.7 oz. also appears advisable. 
 
 Dissolve in a porcelain dish, with the aid of moderate heat, the 
 sodium phosphate and sodium sulphite, and when the solution 
 is cold, add the neutral chloride of gold prepared from 15.43 
 grains of gold = about 30.86 grains of commercial chloride of 
 gold, and the potassium cyanide. For use, heat the bath to 
 between 158 and 167 F. 
 
 For the preparation of gold baths for hot and cold gilding, 
 double gold salts and triple gold salts, as well as gold solutions, 
 as brought in commerce by some manufacturers may also be used. 
 
 Many gold-platers prepare their gold baths with the assist- 
 ance of the electric current. For this purpose prepare a solu- 
 tion of 3.52 ozs. potassium cyanide (98 to 99 per cent.) per 
 quart of water and, after heating to between 122 and 140 F., 
 conduct the current of two Bunsen cells through two sheets of 
 gold, not too small, which are suspended as electrodes in the 
 potassium cyanide solution. The action of the current is inter- 
 rupted when the solution is so far saturated with gold that an 
 article immersed in it and connected to the negative pole in 
 place of the other gold sheet, is gilded with a beautiful warm 
 tone. By weighing the sheet of gold serving as anode, the 
 
410 ELECTRO-DEPOSITION OF METALS. 
 
 amount of gold which has passed into the solution is ascer- 
 tained. According to English authorities, a good gold bath 
 prepared according to this method should contain 3.52 ozs. of 
 potassium cyanide and 0.7 oz. of fine gold per quart of water. 
 
 The only advantage of this mode of preparing the bath is that 
 it excludes a possible loss of gold, which may occur in dissolv- 
 ing gold, evaporating the gold solution, etc., by breaking the 
 vessel containing the solution. However, by using commercial 
 chemically pure chloride of gold such loss is avoided, and the 
 bath prepared according to the formulae given yields richer 
 tones than a gold bath produced by electrolysis. Besides, the 
 preparation of the gold bath with the assistance of the electric 
 current can only be considered for smaller baths, since the sat- 
 uration of a larger volume of potassium cyanide solution re- 
 quires considerable time, and the potassium cyanide is strongly 
 decomposed by long heating. 
 
 Gold anodes. Management of gold baths. — It is advisable to 
 keep the content of gold in the baths prepared according to 
 the different formulae as constant as possible, which is best 
 effected by the use of fine gold anodes. 
 
 Insoluble platinum anodes are better liked in gilding than 
 for all other electro-plating processes, partly because they are 
 somewhat cheaper, and partly because they are recommended 
 in most books on the subject. However, a bath which has 
 become low in gold does not yield a beautiful gold color, and 
 has to be frequently strengthened by the addition of chloride 
 of gold or concentrated solution of fulminating gold in potas- 
 sium cyanide, the preparation of which consumes time and 
 causes expense, so that the use of gold anodes is the cheapest 
 in the end, especially with the present high price of platinum. 
 
 The use of steel anodes for cold and warm cyanide gold 
 baths, advocated by some, cannot be recommended. Every 
 gilder knows from experience that, when the enamel of the tanks 
 containing the gold baths becomes defective, the baths in a 
 short time fail. The reason for this is simply that the iron on 
 the defective places of the tank decomposes the gold bath, me- 
 
DEPOSITION OF GOLD. 411 
 
 tallic gold being reduced. Iron, in this respect, acts like zinc, 
 which, in a still shorter time, precipitates metallic gold from 
 gold baths. Now, when iron anodes remain suspended in the 
 baths, a reduction of gold takes place, while a quantity of iron 
 equivalent to the reduced gold is dissolved, and, in the form of 
 ferric oxide, falls to the bottom of the vat. 
 
 In hot gold baths this separation of gold proceeds still more 
 rapidly and the content of potassium cyanide in the bath is 
 destroyed, yellow prussiate of potash being formed. The 
 argument made in favor of the use of steel anodes, that the old 
 practitioners often added intentionally yellow prussiate of 
 potash to their baths to heighten the gold tone is fallacious. 
 A plater who works with gold baths prepared with yellow 
 prussiate of potash cannot expect to replace the gold by the 
 solution of the gold anodes, and when working with gold 
 cyanide and potassium cyanide baths there is no inducement 
 for gradually changing the bath into a yellow prussiate of 
 potash bath by the use of steel anodes. 
 
 According to one statement, a hot gold bath with steel anodes 
 showed, after being electrolyzed for 70 hours, scarcely a trace 
 of iron. To ascertain the correctness of this statement by an 
 experiment, a gold bath prepared according to formula IV 
 was electrolyzed at 15 8° F., with a blue annealed steel anode 
 weighing 12.092 grammes. During the first two hours only a 
 moderate yellow-reddish bloom of iron salt was perceptible on 
 the anode, which became detached from the latter and fell to 
 the bottom of the beaker. The bloom, however, became 
 gradually heavier, the bottom of the beaker was covered with 
 a precipitate of a yellow-brown color, the previously colorless 
 bath acquired a yellow color, and after electrolyzing for five 
 hours, the blue color of the anode had largely disappeared. 
 The anode weighed now 11.822 grammes, and had conse- 
 quently lost 2.2 per cent. After again suspending it in the 
 bath it was more rapidly attacked in consequence of the de- 
 struction of the blue annealing color, which retarded corrosion. 
 After five more hours the anode weighed 11. 105 grammes, the 
 
412 ELECTRO -DEPOSITION OF METALS. 
 
 loss being therefore 8.16 per cent. The bath now showed a 
 deep yellow color, and the precipitate on the bottom of the 
 beaker had increased, while small, lighter flakes of ferric 
 hydrate spun around in the bath and attached themselves to 
 the anode. Electrolysis was now discontinued, since the last 
 mentioned phenomena proved the uselessness of steel anodes 
 for the reasons given under "Deposition of Nickel and Cobalt." 
 
 As regards the advantage claimed for the use of steel anodes, 
 that a large anode-surface corresponding to the object-surface 
 can be rendered effective without taxing too severely the 
 pocket-book of the gilder, it may be said that the same object 
 can in a more rational manner be attained by employing carbon 
 anodes, which to prevent contamination of the bath by parti- 
 cles of carbon, are placed in linen bags. Crosses and balls of 
 unusually large dimensions for church towers have frequently 
 been gilded in Dr. Geo. Langbein & Co.'s establishment, for 
 which a large anode-surface was required in order to obtain a 
 uniformly heavy deposit, and in such cases carbon anodes of 
 the best quality of retort graphite were used. These anodes, 
 to be sure, become saturated with gold bath, and for that rea- 
 son cannot be used for other baths. When not required for 
 some time, they are kept in a vessel filled with clean water, and 
 the latter is added to the bath to replace that lost by evapora- 
 tion. 
 
 The employment as anodes of platinum strips or platinum 
 wire may, perhaps, be advocated for coloring the deposit, /. e., 
 for the purpose of obtaining certain tones of color when gilding 
 in the hot bath. By allowing the platinum anode to dip only 
 slightly in the bath a pale gilding is obtained, because the cur- 
 rent thereby becomes weaker; by immersing the anode deeper 
 the color becomes more yellow, and by immersing it entirely 
 the tone becomes more reddish. 
 
 However, instead of producing these effects of the current- 
 strength by the anode, which requires the constant presence of 
 the operator, it is better to obtain the coloration by means of 
 the rheostat. By placing the switch upon " strong," a reddish- 
 
DEPOSITION OF GOLD. 413 
 
 gold tone is obtained, and by placing it upon "weak," a paler 
 gold tone, while the beautiful gold-yellow lies in the middle 
 between the two extremes. However, since even with the use 
 of gold anodes the content of gold in the bath is not entirely 
 restored, the bath has after some time to be strengthened, which 
 is effected by a solution of fulminating gold or chloride of 
 gold in potassium cyanide, according to the composition of the 
 bath. 
 
 The excess of potassium cyanide must not be too large, 
 otherwise the gilding will be pale ; but, on the other hand, it 
 must not be too small, since in this case quite a strong current 
 would have to be used to effect a normal deposition of gold, 
 which, besides, would not be dense and homogeneous. Too 
 small a content of potassium cyanide is indicated by the gold 
 anodes showing dark streaks. 
 
 As in the silvering baths, the excess of potassium cyanide in 
 the gold baths is also partially converted into potassium carbo- 
 nate by the action of air, heat, etc., and it is, therefore, advis- 
 able from time to time to add a small quantity of potassium 
 cyanide. 
 
 The presence of larger quantities of organic substances which 
 may get into the bath by dust or some other way, shows itself, 
 as a rule, by a brownish coloration. Such baths rarely yield a 
 beautiful gold color, but deposit gold of a dark tone. 
 
 Unsightly and spotted deposits are also caused by a con- 
 tamination of gold baths with compounds of lime which reach 
 the bath by the use of water containing much lime, or by 
 insufficient removal of lime paste after freeing the objects from 
 grease. 
 
 Tanks for gold baths. Gold baths for cold gilding are kept 
 in tanks of stoneware or enameled iron, or small baths in glass 
 tanks, which, to protect them against breaking, are placed in a 
 wooden box. Baths for hot gilding require enameled iron 
 tanks in which they can be heated by a direct fire, or better, 
 by placing in hot water (water bath), or by steam. For small 
 gold baths for hot gilding, a porcelain dish resting upon a 
 
414 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 short-legged iron tripod may be used (Fig. 136). Beneath 
 the iron tripod is a gas burner supplied with gas by means of a 
 flexible India-rubber tube connected to an ordinary gas burner 
 Across the porcelain dish are placed two glass rods, around 
 which the pole-wires are wrapped. 
 
 In heating larger baths in enameled tanks over a direct 
 Inc- ,t may happen that on the places most exposed to the 
 heat the enamel may blister and peel off; it is, however, 
 better to heat the baths in a water or steam bath. For this 
 purpose have made a box of stout iron or zinc sheet about 
 H mch wider and longer, and about 4 inches deeper than the 
 
 Fig. 136. 
 
 J w\ 
 
 enameled tank containing the gold bath. To keep the level of 
 the water constant, the box is to be provided with a water 
 '"let- and overflow-pipe. In this box place the tank so that its 
 edges rest upon those of the box, and make the joints tight 
 with tow. The water-bath is then heated over a gas flame or 
 "Pon a hearth, the water lost by evaporation being constantly 
 "Placed, so that the enameled tank is always to half its height 
 surrounded by hot water. For heating by steam the arrange- 
 ment is the same, only a valve for the introduction, and a pipe 
 for the discharge, of steam, are substituted for the water inlet- 
 and overflow-pipe. 
 
DEPOSITION OF GOLD. 415 
 
 Execution of gold-plating. — Most suitable current-density, 
 0.15 to 0.2 ampere. Like all other electro-plating operations, 
 it is advisable to effect gold-plating with an external source of 
 current, that is, to use a battery or other source of current 
 separated from the bath, and to couple the apparatuses as pre- 
 viously described and illustrated by Figs. 50 and 51. 
 
 To be sure, there are still gilders who gild without a battery 
 or separate external source of current and obtain good results, 
 the process being, as a rule, employed only in gilding small 
 articles. The apparatus used for this purpose consists of a glass 
 vessel containing the gold solution compounded with a large 
 excess of potassium cyanide, and a porous clay cup filled with 
 very dilute sulphuric acid or common salt solution, which is 
 placed in the glass vessel-. Care should be taken to have the 
 fluids in both vessels at the same level. Immerse in the clay 
 cup an amalgamated zinc cylinder or zinc plate, to which 
 a copper wire is soldered. Outside the cup this copper wire is 
 bent downwards, and the article to be gilded, which dips in the 
 gold solution, is fastened to it. In working with this apparatus 
 there is always a loss of gold, since the gold solution penetrates 
 through the porous cup, and on coming in contact with the 
 zinc is reduced by it, the gold being separated as black powder 
 upon the zinc. In cleaning the apparatus this black slime has 
 to be carefully collected and worked for fine gold. 
 
 For the sake of greater solidity, only articles of silver and 
 copper and its alloys should be directly gilded, while all other 
 metals are best first brassed or coppered. Cleaning from 
 grease and pickling is done in the same manner, as described 
 on page 228. The preparation of the articles for gilding differs 
 from that of silvering only in that the surfaces, which later on 
 are to appear with high luster, are not artificially roughened 
 with emery, pumice, or by pickling, because, on the one hand, 
 the gold deposit seldom needs to be made extravagantly heavy, 
 and the rough surface formed would require more laborious 
 polishing with the burnishers ; and, on the other, the gold de- 
 posits adhere quite well to highly-polished surfaces, provided 
 
41 6 ELECTRO-DEPOSITION OF METALS. 
 
 the current-strength is correctly regulated, and the bath ac- 
 curately composed according to one of the formulas given. 
 Ouicking the articles before gilding, which is recommended by 
 some authors, is not necessary. 
 
 The current-strength must, under no circumstances, be so 
 great that a decomposition of water, and consequent evolution 
 of hydrogen on the objects, takes place, since otherwise the gold 
 would not deposit in a reguline and coherent form, but as a 
 brown powder. By regulating the current-strength so that it 
 just suffices for the decomposition of the bath, and avoiding a 
 considerable surplus, a very dense and uniform deposit is 
 formed ; and by allowing the object to remain long enough in 
 the bath, a beautiful, matt gold deposit can be obtained in all 
 the baths prepared according to the formulae given. It may, 
 however, be mentioned that this mode of matt gilding is the 
 most expensive, since it requires a very heavy deposit, and it 
 will, therefore, be better to matten the surface previous to gild- 
 ing, according to a process to be described later on. 
 
 Constant agitation of the objects in the bath, or of the latter 
 itself, is of great advantage for obtaining good gilding. It is 
 evident that by reason of the small amount of metal in the gold 
 baths, especially in warm ones, the strata of fluid on the cath- 
 odes becomes rapidly poor in metal and if care be not taken 
 to replace them by strata of fluid richer in gold, disturbances 
 in deposition will result. 
 
 For gilding with cold baths, two freshly-filled Bunsen cells 
 coupled for electro- motive force suffice in almost all cases, while 
 for hot baths one cell is, as a rule, sufficient, if the anode sur- 
 face is not too small. The more electro-positive the metal to 
 be gilded is, the weaker the current can and must be. 
 
 Though gold solutions are good conductors and, therefore, 
 the portions of the articles which do not hang directly opposite 
 the anodes gild well, for solid plating of larger objects it is 
 recommended to frequently change their positions except when 
 they are entirely surrounded by anodes. 
 
 The inner surfaces of hollow-ware, such as drinking-cups, 
 
DEPOSITION OF GOLD. 417 
 
 milk pitchers, etc., are best plated after freeing them from 
 grease and pickling, by filling the vessel with the gold bath and 
 suspending a current-carrying gold anode in the center of the 
 vessel, while the outer surface of the latter is brought in con- 
 tact with the negative conducting wire. The lips of vessels are 
 plated by placing upon them a cloth rag saturated with the 
 gold bath and covering the rag with the gold anode. 
 
 For gold-plating in the cold bath the process is as follows: 
 The objects, thoroughly freed from grease and pickled (and if 
 of iron, zinc, tin, Britannia, etc., previously coppered), are 
 suspended in the bath by copper wires, where they remain 
 with a weak current until in about 8 or 10 minutes they appear 
 uniformly plated. At this stage they are taken from the bath, 
 rinsed in a pot filled with water, and the latter, after having 
 been used for some time, is added to the bath to replace the 
 water lost by evaporation. The articles are finally brushed 
 with a fine brass scratch-brush and tartar solution, thoroughly 
 rinsed, again freed from grease^by brushing with lime-paste 
 and then returned to the bath, where they remain until they 
 have acquired a deposit of sufficient thickness. 
 
 If the articles are to have a very heavy deposit it is advisa- 
 ble to scratch-brush them several times with the use of tartar 
 or its solution. For gold plating by weight the same plan as 
 given for silver-plating by weight (p. 278) is pursued. 
 
 For gold-plating with the hot bath, the operations are the same, 
 with the exception that a weaker current is introduced into the 
 bath and the time of the plating process shortened. Frequent 
 scratch-brushing also increases the solidity of the deposit and 
 prevents its prematurely turning to a dead brown-black. Since 
 in hot plating more gold than intended is readily deposited, it 
 is especially advisable to place a rheostat and voltmeter in the 
 circuit, as otherwise the operator must remain standing along- 
 side of the bath and regulate the effect of the current by 
 immersing the anodes more or less. 
 
 When taken from the bath, the finished gilded objects should 
 show a deep yellow tone, which, after polishing, yields a full 
 27 
 
41 8 ELECTRO-DEPOSITION OF METALS. 
 
 gold color. If the objects come from the bath with a pale gold 
 tone, the deposit, after polishing, shows a meager, pale gold 
 color, which is without effect. Gold deposits of a dark or 
 brown color also do not yield a sad gold tone. 
 
 With a somewhat considerable excess of potassium cyanide, 
 and if the objects to be plated are not rapidly brought in con- 
 tact with the current-carrying object rod, hot gold baths cause 
 the solution of some metal. Therefore, when silver or silver- 
 plated objects are constantly plated in them they yield a some- 
 what greenish gilding inconsequence of the absorption of silver, 
 or a reddish gilding due to the absorption of copper, if copper 
 or coppered articles are constantly plated in them. Hence, for 
 the production of such green or reddish color, gold-plating 
 baths which have thus become argentiferous or cupriferous, 
 may be advantageously used. In order to obtain a deposit of 
 green or red gold with fresh baths, the tone-giving addition of 
 metal must be artificially effected, as will presently be seen. 
 
 If, however, such extreme tones are not desired, the content 
 of gold in the baths may be exhausted for preliminary plating 
 with the use of platinum anodes, the sad gold color being then 
 given in a freshly prepared bath. 
 
 The gold deposits are polished in the same manner as silver 
 deposits, with the burnisher and red ochre, and moistening 
 with solution of soap, decoction of flaxseed, or soap-root, etc. 
 For less heavy gilding the articles, previous to gilding, are 
 given high luster, and after gilding, burnished with rouge and 
 buckskin. 
 
 Red-gilding. — In order to obtain a red gold with the formulae 
 given, a certain addition of copper cyanide dissolved in potas- 
 sium cyanide has to be made to them. The quantity of such 
 addition cannot be well expressed by figures, since the current 
 strength with which the articles are plated exerts considerable 
 influence. It is best to triturate the copper cyanide in a mor- 
 tar to a paste with water, and add of this paste to a moderately 
 concentrated potassium cyanide solution as long as copper 
 cyanide is dissolved. Of this copper solution add, gradually 
 
DEPOSITION OF GOLD. 419 
 
 and in not too large portions, to the gold solution until, with 
 the current strength used, the gold deposit shows the desired 
 red tone, and if fine gold anodes are used, the bath is kept con- 
 stant with this content of copper by an occasional addition of 
 the above-mentioned copper solution. 
 
 The absorption of copper in the bath may also be effected 
 by suspending, in place of gold anodes, anodes of copper or 
 copper-gold alloys, for instance, fourteen-carat gold, and allow- 
 ing the current to circulate (suspension of a few gold anodes 
 to the object-rod). The direct addition of copper cyanide, 
 however, deserves the preference. 
 
 In place of preparing the solution of copper cyanide in potas- 
 sium cyanide, commercial crystallized potassium-copper cyan- 
 ide may be used. It is dissolved in warm water, and of the 
 solution a sufficient quantity is gradually added to the gold- 
 bath. 
 
 For the determination of the content of copper required for 
 the purpose of obtaining a beautiful red gold, a bath for hot 
 gilding which contained 10.8 grains of gold per quart was com- 
 pounded with a solution of copper cyanide in potassium cyanide 
 with 1.08 grains content of copper. The tone of the gilding, 
 which previously was pure yellow, immediately passed into a 
 pale red gold. By the further addition of 1.08 grains of cop- 
 per, a fiery red gold tone was obtained, while a third addition 
 of 1.08 grains of copper yielded a color more approaching that 
 of copper than of gold. These experiments show that 20 per 
 cent, of copper of the weight of gold contained in the bath 
 seems to be the most suitable proportion for obtaining a beau- 
 tiful red gold. 
 
 Rings, watch-chains, and other objects of base metal are fre- 
 quently to be plated with red gold, so as to show no percep- 
 tible sign of having been attacked by nitric acid, even after 
 remaining in it for several hours.. This may be effected by first 
 giving the objects a deposit of a strongly yellow color by gild- 
 ing in a bath containing 10.8 to 15.43 grains of gold per quart, 
 and then coloring them in the red gilding bath. This process 
 
420 ELECTRO-DEPOSITION OF METALS. 
 
 may be called an imitation of mechanical gold plating, and is 
 frequently made use of in the jewelry industry. 
 
 Green gilding. To obtain greenish gilding, solution of 
 cyanide or chloride of silver in potassium cyanide has to be 
 added to the gold bath. It is not easy to prepare greenish 
 gilding of a pleasing color, and to obtain it the current-strength 
 must be accurately proportioned to the object-surface, since with 
 too weak a current silver predominates in the deposit, the gild- 
 ing then turning out whitish, while too strong a current deposits 
 too much gold in proportion to silver, the gilding becoming 
 yellow, but not green. 
 
 Rose-color gilding may be obtained by the addition of suit- 
 able quantities of copper and silver solutions, but such colora- 
 tion requires much attention and thought. 
 
 For the sake of completeness, a method of gilding which is 
 a combination of fire-gilding with electro-deposition, may here 
 be mentioned, though experiments made with it failed to show 
 the advantages claimed for it, because it does not yield as dense 
 a deposit as fire-gilding, nor can the volatilization of mercury 
 be avoided, the latter operation being the most dangerous part 
 of fire-gilding. 
 
 According to Du Fresne, the process is as follows : 
 
 The articles are first coated with mercury, with the assistance 
 of the current, in a mercurial solution consisting of cyanide of 
 mercury in potassium cyanide, with additions of carbonate and 
 phosphate of soda, then gilded in an ordinary gilding-bath, 
 next again coated with mercury, then again gilded, and so on, 
 until a deposit of sufficient thickness is obtained. The mer- 
 cury is then evaporated over glowing coals, and the articles, 
 after scratch-brushing, are burnished. 
 
 According to another process, the articles are gilded in a bath 
 consisting of 98 per cent, potassium cyanide 1.2 ozs., cyanide 
 of gold 92^ grains, cyanide of mercury 22^ grains, distilled 
 water 1 quart, a strong current being used. When the objects 
 are sufficiently gilded, the mercury is evaporated in the above- 
 mentioned manner, and the objects are scratch-brushed, and 
 finally polished. 
 
DEPOSITION OF GOLD. 42 I 
 
 Matt gilding. — As previously mentioned, a beautiful matt 
 gold deposit may be obtained by the use of any of the formulas 
 given, and a current correctly regulated, and allowing sufficient 
 time for gilding. The heavy deposit of gold required for this 
 process makes it, however, too expensive, and it is, therefore, 
 advisable to produce matt gilding by previously matting the 
 basis-surface, since then a thinner deposit of gold will answer 
 very well. The process of graining will be referred to later on 
 under " Silvering by Contact," etc. 
 
 Another method is to matt the first slight deposit by means 
 of brass or steel-wire brushes, and then to give a second deposit 
 of gold, which also turns out matt upon the matted surface. 
 The character of the matt produced depends on the thickness 
 of the wire of the brushes. Thicker wire gives a matt of a 
 coarser grain, and thinner wire one of a finer grain. 
 
 Objects may be readily matted with the use of the sand 
 blast, after which they are quickly drawn through the bright 
 dipping bath, thoroughly rinsed and brought into the gold bath. 
 
 Matting by chemical or electro- chemical means is effected by 
 one of the following methods. 
 
 For this purpose the mixture of I volume of saturated solu- 
 tion of bichromate of potash and 2 volumes of concentrated 
 hydrochloric acid, mentioned on p. 225, may be used. Brass 
 articles are allowed to remain several hours in the mixture, 
 and are then quickly drawn through the bright-dipping bath. 
 Copper alloys might also be successfully matted by suspending 
 them as anodes in a mixture of 90 parts water and 10 parts 
 sulphuric acid, and drawing the matted articles through the 
 bright-dipping bath. 
 
 Or, they are matt-silvered, and the gold is deposited upon 
 the matted layer of silver. Articles gilded upon a matt silver 
 basis, however, acquire before long an ugly appearance, since 
 in an atmosphere containing sulphuretted hydrogen the silver 
 turns black, even under the layer of gold and shines through". 
 
 More advantageous is the process of providing the articles 
 with a matt copper coating in the acid galvanoplastic bath. 
 
422 ELECTRO-DEPOSITION OF METALS. 
 
 They are then drawn through a not too strong pickle, rinsed, 
 and gilded. This process is used for the so-called French clock 
 gilding, and yields a very sad, beautiful gilding. The articles 
 consisting of zinc are first heavily coppered in a cyanide cop- 
 per bath, then matted in the acid copper bath (see " Galvano- 
 plasty "), care being taken that the slinging wire is in contact 
 with the object-rod, which conducts the current, before the 
 coppered zinc object is suspended in the bath. This process 
 of coppering zinc in the acid copper bath is, however, quite 
 a delicate operation, and it will frequently be noticed, even 
 with apparently very heavy coppering in the cyanide copper 
 bath, that in suspending the articles in the acid bath, brownish- 
 black places appear on which, by contact of the acid bath with 
 zinc, copper in a pulverulent form is deposited. When this is 
 observed, the articles must be immediately taken from the bath, 
 thoroughly scratch-brushed, and again thoroughly and heavily 
 coppered in the cyanide copper bath, before replacing them in 
 the acid copper bath, It may be recommended to provide 
 the coppered zinc articles with a thick deposit of nickel, and 
 then to copper them matt in the acid bath, the percentage of 
 unsuccessful coppering being much smaller than without pre- 
 vious nickeling. The matt-coppered articles are rapidly drawn 
 through the bright-dipping bath and then gilded, the bath pre- 
 pared according to formula III, and heated to about 140 F., 
 being very suitable for the purpose. 
 
 Coloring of the gilding. — It has been repeatedly mentioned 
 that the most rational and simple process of giving certain 
 tones of color to the gilding is by means of a stronger or weaker 
 current. Many operators, however, cling to the old method of 
 affecting the coloration by gilder's wax or brushing with certain 
 mixtures, and for this reason this process, which is generally 
 used for coloring fire-gilding, shall be briefly mentioned. 
 
 To impart to the gold-deposit a redder color, the gilding-wax 
 is prepared with a greater content of copper, while for greenish 
 gilding more zinc-salt is added. There are innumerable re- 
 ceipts for the preparation of gilding-wax, nearly every gilder 
 
DEPOSITION OF GOLD. 423 
 
 having his own receipt, which he considers superior to all 
 others. Only two formulae which yield good results will have 
 to be given one (I) for reddish gilding and one (II) for green- 
 ish gilding. 
 
 I. Wax 12 parts by weight, pulverized verdigris 8, pulver- 
 ized sulphate of zinc 4, copper scales 4, borax 1, pulverized 
 bloodstone 6, copperas 2. 
 
 II. Wax 12 parts by weight, pulverized verdigris 4, pulver- 
 ized sulphate of zinc 8, copper scales 2, borax 1, pulverized 
 bloodstone 6, copperas 2. 
 
 Gilder's wax is prepared as follows : Melt the wax in an iron 
 kettle, add to the melted mass, while constantly stirring, the 
 other ingredients, pulverized and intimately mixed, in small 
 portions, and stir until cold, so that the powder cannot settle 
 on the bottom or form lumps. Finally, mould the soft mass 
 into sticks about j^ inch in diameter. 
 
 Gilder's wax is applied as follows : Coat the heated gilded 
 articles uniformly with the wax, and burn off over a charcoal 
 fire, frequently turning the articles. After the wax flame is 
 extinguished, plunge the articles into water, scratch-brush with 
 wine-vinegar, dry in sawdust, and polish. 
 
 To give gilded articles a beautiful, rich appearance, the fol- 
 lowing process may also be used : Mix 3 parts by weight of 
 pulverized alum, 6 of saltpetre, 3 of sulphate of zinc, and 3 of 
 common salt, with sufficient water to form a thinly-fluid paste. 
 Apply this paste as uniformly as possible to the articles by 
 means of a brush, and after drying, heat the coating upon an 
 iron plate until it turns black ; then wash in water, scratch- 
 brush with wine-vinegar, dry and polish. 
 
 According to a French receipt, the same result is attained by 
 mixing pulverized blue vitriol 3 parts by weight, verdigris 7, 
 ammonium chloride 6, and saltpetre 6, with acetic acid 31; 
 immersing the gilded articles in the mixture, or applying the 
 latter with a brush ; then heating the objects upon a hot iron 
 plate until they turn black, and, after cooling, pickling in con- 
 centrated sulphuric acid. 
 
424 
 
 ELECTRO- DEPOSITION OF METALS. 
 
 Some gilders improve bad tones of gilding by immersing the 
 articles in dilute solution of nitrate of mercury until the gilding 
 appears white. The mercury is then evaporated over a flame 
 and the articles are scratch-brushed. Others apply a paste of 
 pulverized borax and water, heat uniil the borax melts, and 
 then quickly immerse in dilute sulphuric acid. 
 
 Incrustations with gold are produced in the same manner as 
 incrustations with silver, described on p. 394. 
 
 Gilding of metallic wire and ganzc. — Fine wire of gilded 
 
 Fig. 137. 
 
 copper and brass is much used in the manufacture of metallic 
 fringes and lace, for epaulettes and other purposes. The fine 
 copper and brass wires being drawn through the draw-irons 
 and wound upon spools by special machines, and hence not 
 touched by the hands, freeing from grease may, as a rule, be 
 omitted. The first requisite for gilding is a good winding ma- 
 chine, vvhich draws the wires through the gold bath and wash- 
 boxes, and further effects the winding of the wire upon spools. 
 The principal demand made in the construction of such a ma- 
 chine is that by means of a simple manipulation a great varia- 
 
DEPOSITION OF GOLD. 425 
 
 tion in the speed with which the wire or gauze passes through 
 the gold bath can be obtained. This is necessary in order to 
 be able to regulate the thickness of the gilding by the quicker 
 or slower passage of the wire. A machine well adapted for 
 this purpose is that constructed by j. W. Spaeth, and shown in 
 Fig. 137. 
 
 The variation in the passage of the wire is attained by the 
 two friction-pulleys F, which sit upon a common shaft with the 
 driving pulley R, and transmit their velocity by means of the 
 friction-pistons KK' to the friction-pulley F ', which is firmly 
 connected to the belt-pulley R driving the spool spindle. Since 
 by a simple device the pistons K and K' may be shifted, it is 
 clear that the transmission of the number of revolutions from 
 F to F is dependent on the position of the friction-pistons K 
 and K' , and that the velocity will be the greater the shorter the 
 distance they are from the center of friction-pulleys F and F. 
 In order that the friction between F, K and F may always be 
 sufficient for the transmission of the motion, even when the 
 pistons are worn, four weights, G, are provided, which press 
 the above-mentioned parts firmly against each other. 
 
 In front of each spool of this machine is inserted a small 
 enameled iron tank which contains the gold bath, and is heated 
 by a gas flame to about 167 F. Between this bath and the 
 winding machine is another small tank with hot water in which 
 the gilded wire is rinsed. 
 
 The wire unwinds from a reel placed in front of the gold 
 baths, run over a brass drum which is connected to the nega- 
 tive pole of the source of current and transmits the current to 
 the wire. The dipping of the wire into the gold bath is 
 effected by porcelain drums, which are secured to heavy pieces 
 of lead placed across the tanks, as shown in Fig. 138. The 
 gilded wire being wound upon the spools of the winding ma- 
 chine, these spools are removed and thoroughly dried in the 
 drying chamber. The wire is then again reeled off onto a 
 simple reel, in doing which it is best to pass it through between 
 two soft pieces of leather to increase its luster. 
 
426 ELECTRO-DEPOSITION OF METALS. 
 
 For gilding wire the most suitable gold bath is that prepared 
 according to formula IV. The electro-motive force should be 
 from 6 to 8 volts, in order to produce a deposit of sufficient 
 thickness, even when the wire passes at the most rapid rate 
 through the bath. For this reason a dynamo with a voltage of 
 io volts is almost exclusively used for wire gilding. 
 
 As a rule an anode of platinum — a strip of platinum sheet — 
 of the same length as the tank is placed upon the bottom of the 
 latter, and connected by means of platinum wire to the positive 
 pole of the source of current. The use of gold anodes for wire 
 gilding is not required, since the small gold baths — generally 
 only 2 to 4 quarts — are as far as possible to be worked till ex- 
 hausted, when they are replaced by fresh baths. 
 
 In place of platinum anodes, Stockmeir recommends the 
 
 Fig. 138. 
 
 use of blued Bessemer steel anodes for wire gilding. In this 
 case there can be no objection to steel anodes, because the 
 baths are rapidly exhausted, and then go amongst the gold- 
 residues. But, nevertheless, the use of an indestructible plati- 
 num anode would appear to deserve the preference, the baths 
 being without doubt kept cleaner than with steel anodes. 
 
 Silver-plated wires are, as a rule, to be gilded, and since the 
 color of the basis-metal exerts an influence upon the gilding, 
 Stockheimer recommends brassing the silver-plated or solid 
 silver wires previous to gilding, because a gold-deposit of less 
 thickness than for covering the white silver, would thus be re- 
 quired. The proposition to gild nickeled wires, in place of 
 silver-plated wires, because they are less subject to rapid dis- 
 coloiation in an atmosphere containing sulphuretted hydrogen, 
 also deserves consideration. 
 
DEPOSITION OF GOLD. 427 
 
 Removing gold from gilded articles. — " Shipping." — Gilded 
 articles of iron and steel are best stripped by treating them as 
 anodes in a solution of from 2 and 2^ ozs. of 98 per cent, 
 potassium cyanide in I quart of water, and suspending a copper 
 plate greased with oil or tallow as the cathode. Gilded silver- 
 ware is readily stripped by heating to ignition, and then im- 
 mersing in dilute sulphuric acid, whereby the layer of gold 
 cracks off, the heating and subsequent immersion in dilute sul- 
 phuric acid being repeated until all the gold is removed. Be- 
 fore heating and immersing in dilute sulphuric acid, the articles 
 may first be provided with a coating of a paste of ammonium 
 chloride, flowers of sulphur, borax and nitrate of potash which 
 is allowed to dry. On the bottom of the vessel containing the 
 dilute sulphuric acid, the gold will be found in laminae and 
 scales, which are boiled with pure sulphuric acid, washed and 
 finally dissolved in aqua regia, and made into chloride of gold 
 or fulminating gold. 
 
 To strip articles of silver, copper or German silver which will 
 not bear heating, the solution of gold may be effected in a mix- 
 ture of 1 lb. of fuming sulphuric acid, 2.64 ozs. of concentrated 
 hydrochloric acid, and 1.3 ozs. of nitric acid of 40 Be. Dip 
 the articles in the warm acid mixture, and observe the progres- 
 sive action of the mixture by frequently removing the articles 
 from it. The articles to be treated must be perfectly dry be- 
 fore immersing in the acid mixture, and care must be had to 
 preserve the latter from dilution with water in order to prevent 
 the acids from acting upon the basis-metal. 
 
 The process by which scratched or rubbed rings are, so to 
 say, electrolytically smoothed and polished, may be called a sort 
 of stripping. For this purpose the rings are suspended as 
 anodes in a bath consisting of : Water 1 quart, yellow prussiate 
 of potash 1 oz., 99 per cent, potassium cyanide T \ ozs. By 
 conducting a current of high electro-motive force, of about 20 
 to 25 volts, through the bath any roughness or unevenness is in 
 a few minutes removed, and the rings will be almost perfectly 
 smooth when taken from the bath. A sheet of gold or platinum 
 is used as cathode. 
 
428 ELECTRO-DEPOSITION OF METALS. 
 
 Determination of genuine gilding. — Objects apparently gilded 
 are rubbed upon the touchstone, and the streak obtained is 
 treated with pure nitric acid of 1.30 to 1.35 specific gravity. 
 The metal contained in the streak thereby dissolves, and as far 
 as it is not gold, disappears, while the gold remains behind. 
 The stone should be thoroughly cleansed before each operation, 
 and the streak should be made, not with an edge or a corner of 
 the object to be tested, but with a broader surface. If no gold 
 remains upon the stone, but there is, nevertheless, a suspicion 
 of the article being slightly gilded, proceed with small articles 
 as follows : Take hold of the article with a pair of tweezers, and 
 after washing it first with alcohol, and then with ether, and 
 drying upon blotting paper, pour over it in a test glass, cleansed 
 with alcohol or ether, according to the weight of the article, 
 0.084 to 5-^4 drachms of nitric acid of 1.30 specific gravity free 
 from chlorine. The article will be immediately dissolved, and 
 if it has been gilded never so slightly, perceptible gold spangles 
 will remain upon the bottom of the glass. 
 
 Examination of Gold Baths. 
 
 The determination of free potassium cyanide and of the 
 potassium carbonate which is formed, is effected in the same 
 manner as given under " Examination of copper baths and of 
 silver baths." 
 
 The determination of the gold is effected by the electrolytic 
 method. With baths poor in gold, 50 cubic centimeters are 
 used for electrolysis, and with baths rich in gold, 25 cubic 
 centimeters. After diluting with water to within 1 centimeter 
 of the rim of the platinum dish, the liquid is electrolyzed for 
 about three hours with a current-density ND 100 = 0.067 
 ampere, the complete separation of the gold being recognized 
 by a platinum strip suspended over the rim of the dish and 
 dipping into the fluid showing in fifteen minutes no trace of a 
 separation of gold. 
 
 The dish is then washed, rinsed with alcohol, and dried at 
 212 F. To obtain the content of gold in grammes per liter of 
 
DEPOSITION OF GOLD. 429 
 
 bath, multiply the weight of the precipitate by 20, when 50 
 cubic centimeters, or by 40, when 25 cubic centimeters, of the 
 bath has been used. 
 
 The content of gold in the baths declines constantly, especi- 
 ally with the use of platinum and carbon anodes. For strength- 
 ening the bath neutral gold chloride dissolved in potassium 
 cyanide is used, 2 grammes neutral gold chloride and 1.4 
 grammes 99 per cent, potassium cyanide dissolved in a small 
 quantity of water or directly in the bath, being required for 
 every gramme of gold deficit in the baths. 
 
 The determination of gold described above is suitable only 
 for baths prepared with potassium cyanide, which contain the 
 gold in the form of potassium-gold cyanide. The determina- 
 tion of gold in baths prepared with yellow prussiate of potash 
 is more difficult and should be made by a skilled analyst. 
 
 Recovery of gold from gold baths, etc. — To recover the gold 
 from old cyanide gilding baths, evaporate the baths to dryness, 
 mix the residue with litharge, and fuse the mixture. The gold 
 is contained in the lead button thus obtained. The latter is 
 then dissolved in nitric acid, whereby the gold remains behind 
 in the form of spangles. These spangles are filtered oft and 
 dissolved in aqua regia. 
 
 The following method is used for the recovery of gold by the 
 wet process: The bath containing gold, silver and copper is 
 acidulated with hydrochloric acid, which causes a disengage- 
 ment of hydrocyanic acid. This gas is extremely poisonous, 
 for which reason the operation should be carried on in the open 
 air, or where there is a good draught or ventilation to carry off 
 the fumes. A precipitate consisting of the cyanides of gold 
 and copper and chloride of silver is formed. This is well 
 washed and boiled in aqua regia, which dissolves the gold and 
 copper as chlorides, leaving the chloride of silver behind. The 
 solution containing the gold and copper is evaporated nearly 
 to dryness in order to remove the excess of acid, the residue is 
 dissolved in a small quantity of water, and the gold precipitated 
 therefrom as a brown, metallic powder by the addition of sul- 
 phate of iron (copperas). The copper remains in solution. 
 
430 ELECTRO-DEPOSITION OF METALS. 
 
 Finely divided zinc — so-called zinc-dust — is an excellent 
 agent for the precipitation of gold in a pulverulent form from 
 cyanide gilding baths. By adding zinc-dust to an exhausted 
 cyanide gilding bath, and thoroughly shaking or stirring it 
 from time to time, all the gold is precipitated in two or three 
 days. The quantity of zinc required for precipitation depends 
 of course on the quantity of gold present, but generally speak- 
 ing, y 2 lb., or at the utmost I lb., of zinc-dust will be required 
 for ioo quarts of exhausted gilding bath. 
 
 The pulverulent gold obtained is washed, treated first with 
 hydrochloric acid to remove adhering zinc-dust, and next with 
 nitric acid to free it from silver and copper. 
 
 From the acid mixtures serving for matt pickling gold, or 
 for stripping, the gold is precipitated by solution of sulphate of 
 iron (copperas) added in excess. The gold present is precipi- 
 tated as a brown powder mixed with ferric oxide. This powder 
 is filtered off and treated in a porcelain dish with hot hydro- 
 chloric acid, which dissolves the iron. The gold which remains 
 behind is then filtered off, and, after washing, dissolved in aqua 
 regia in order to work the solution into fulminating gold or 
 neutral chloride of gold. 
 
 For gilding by contact, boiling and friction, see special chap- 
 ter " Deposition by Contact." 
 
CHAPTER X. 
 
 DEPOSITION OF PLATINUM AND PALLADIUM. 
 
 i. Deposition of Platinum. 
 
 Properties of platinum. — Pure platinum is white with a gray- 
 ish tinge. It is as soft as copper, malleable and very ductile. 
 At a white heat it can be welded, but is fusible only with the 
 oxyhydrogen blowpipe or by the electric current. Its specific 
 gravity is 21.4. 
 
 Air has no oxidizing action upon platinum. It is scarcely 
 acted upon by any single acid ; prolonged boiling with con- 
 centrated sulphuric acid appears to dissolve the metal slowly. 
 The best solvent for it is aqua regia, which forms the tetrachlo- 
 ride, PtCl 4 . Chlorine, bromine, sulphur and phosphorus com- 
 bine directly with platinum, and fusing saltpetre and caustic 
 alkali attack it. 
 
 Besides, in the malleable and fused state, platinum may be 
 obtained as a very finely divided powder, the so-called platinum 
 black, which is precipitated with zinc from dilute solution of 
 platinum chloride acidulated with hydrochloric acid. 
 
 Platinum baths. — In view of the valuable properties of plat- 
 inum of oxidizing only under certain difficult conditions, of 
 possessing an agreeable white color, and of taking a fine polish, 
 it seems strange that greater attention has not been paid to the 
 electro-deposition of this metal than is actually the case. The 
 reason for this may perhaps be found in the fact that the baths 
 formerly employed for experiments possessed serious defects, 
 causing the operator many difficulties, and besides, allowed 
 only of the production of thin deposits. Giving due consider- 
 ation to the requirements of the process of electro-deposition 
 of platinum, and with the use of a suitable bath, deposits of 
 
 (43i) 
 
432 ELECTRO-DEPOSITION OF METALS. 
 
 platinum of a certain thickness can be readily produced, and 
 necessary conditions will be described under " Treatment of 
 Platinum Baths." 
 
 The platinum baths formerly proposed did not yield satis- 
 factory results, because the content of platinum was too small 
 in some of them, while with others dense deposits could not be 
 obtained. A more recent formula by Bottger, however, gives 
 quite a good bath. A moderately dilute, boiling-hot solution 
 of sodium citrate is added to platoso-ammonium chloride until 
 an excess of the latter no longer dissolves, even after continued 
 boiling. The following proportions have been found very 
 suitable: Dissolve \J% ozs. of citric acid in 2 quarts of water, 
 and neutralize with caustic soda. To the boiling solution add, 
 whilst constantly stirring, the platoso-ammonium chloride 
 freshly precipitated from 2.64 ozs. of chloride of platinum, 
 heat until solution is complete, allow to cool, and dilute with 
 water to 5 quarts. To decrease the resistance of the bath, 0.7 
 or 0.8 oz. of ammonium chloride may be added; a larger 
 addition, however, will cause the separation of dark-colored 
 platinum. 
 
 The platoso-ammonium chloride is prepared by adding to a 
 concentrated solution of platinic chloride, concentrated solution 
 of ammonium chloride until a yellow precipitate is no longer 
 formed on adding a further drop. The precipitate is filtered 
 off and brought into the boiling solution of sodium citrate. 
 The bath works very uniformly if the content of platinum is 
 from time to time replenished. 
 
 " The Bright Platinum Plating Company," of London, has 
 patented the following composition of a platinum bath: Chlor- 
 ide of platinum 0.98 oz., sodium phosphate 19^ ozs., ammo- 
 nium phosphate 3.95 ozs., sodium chloride 0.98 oz., and borax 
 0.35 oz., are dissolved, with the aid of heat, in 6 to 8 quarts of 
 water, and the solution is boiled for 10 hours, the water lost by 
 evaporation being constantly replaced. The results obtained 
 with this bath were not much better than with Bottger's. 
 
 Jordis obtained useful results from a platinum lactate bath 
 
DEPOSITION OF PLATINUM AND PALLADIUM. 433 
 
 prepared by transposition from platinic sulphate with ammo- 
 nium lactate. There are, however, difficulties in obtaining 
 platinic sulphate of uniform composition.* 
 
 Dr. W. H. VVahl gives the following directions for preparing 
 platinum baths : f 
 
 Alkaline platinate bath. — Platinic hydrate, 2 ozs. ; caustic 
 potassa (or soda), 8 ozs.; distilled water, 1 gallon. 
 
 Dissolve one-half of the caustic potassa in a quart of distilled 
 water, add to this the platinic hydrate in small quantity at a 
 time, facilitating solution by stirring with a glass rod. When 
 solution is effected, stir in the other half of alkali dissolved in a 
 quart of water ; then dilute with enough distilled water to form 
 one gallon of solution. To hasten solution, the caustic alkali 
 may be gently heated, but this is not necessary, as the platinic 
 hydrate dissolves very freely. This solution should be worked 
 with a current of about two volts, and will yield metal of an 
 almost silvery whiteness upon polished surfaces of copper and 
 brass, and quite freely. There should be slight, if any, percep- 
 tible evolution of hydrogen at the cathode, but a liberal evolu- 
 tion of oxygen at the anode. An addition of a small proportion 
 of acetic acid to this bath improves its operation where a heavy 
 deposit is desired. The anode must be of platinum or carbon, 
 and owing to the readiness with which the metal is deposited, 
 an excess of anode-surface is to be avoided. Articles of steel, 
 nickel, tin, zinc, or German silver will be coated with black and 
 more or less non-adherent platinum ; but by giving objects of 
 these metals a preliminary thin electro-deposit of copper in the 
 hot cyanide bath they may be electro-platinized in the alkaline 
 platinate bath equally as well as copper. The bath may be 
 worked hot or cold, but it is recommended to work it at a tem- 
 perature not exceeding ioo° F. It may be diluted to one-half 
 the strength indicated in the formula and still yield excellent 
 results. The surface of the objects should be highly polished 
 
 * Jordis, Die Elektrolyse wasseriger Metallsalzlosungen, 1901. 
 t Journal of the Franklin Institute, July, 1890. 
 28 
 
434 ELECTRO-DEPOSITION OF METALS. 
 
 by buffing or otherwise prior to their introduction into the bath, 
 if the resulting deposit is designed to be brilliant. 
 
 The deposition of platinum takes place promptly. In five 
 minutes a sufficiently heavy coating will be obtained for most 
 purposes. The deposited metal is so soft, however, that it re- 
 quires to be buffed very lightly. A heavier deposit will appear 
 gray in color, but will accept the characteristic luster of plati- 
 num beneath the burnisher. 
 
 An oxalate solution is prepared by dissolving I oz. of platinic 
 hydrate in 4 ozs. of oxalic acid and diluting the solution to the 
 volume of one gallon with distilled water. The solution should 
 be kept acidified by the occasional addition of some oxalic acid. 
 The simplest plan of using this bath, which requires no atten- 
 tion to proportions, is simply to work with a saturated solution 
 of the oxalate, keeping an undissolved excess always present at 
 the bottom of the vessel. An addition of a small quantity of 
 oxalic acid now and then will be found advantageous. The 
 double salts of oxalic acid with platinum and the alkalies may 
 be formed by saturating the binoxalate of the desired alkali 
 with platinic hydrate and maintaining the bath in normal 
 metallic strength by the presence of an undissolved residuum 
 of platinous oxalate. 
 
 The double oxalates are not so soluble in water as the simple 
 salt. The oxalate bath, both of single and double salts, may be 
 worked cold or hot (though not to exceed 150 F.) with a 
 current of comparatively low pressure. The metal will deposit 
 bright, reguline and adherent on copper and brass. Other 
 metallic objects must receive a preliminary coppering as above. 
 The deposited metal is dense, with a steely appearance, and 
 can be obtained of any desired thickness. 
 
 The deposit obtained in the oxalate bath is sensibly harder 
 than that from the alkaline platinate bath, and will bear buffing 
 tolerably well. 
 
 The phosphate bath may be prepared by the following 
 formula: 
 
 Phosphoric acid, syrupy (specific gravity 1.7), 8 ozs., plati- 
 nic hydrate 1 to I yi ozs., distilled water I gallon. 
 
DEPOSITION OF PLATINUM AND PALLADIUM. 435 
 
 The acid should be moderately diluted with distilled water 
 and the solution of the hydrate effected at the boiling tempera- 
 ture. Water should be added cautiously from time to time to 
 supply that lost by evaporation. When solution has taken 
 place, the same should be diluted with sufficient water to make 
 the volume 1 gallon. The solution may be worked cold or 
 heated to ioo° F., and with a current much stronger than that 
 required for the platinates and oxalates. The ammonio (and 
 sodio) platinic phosphates may be formed from the simple 
 phosphate by carefully neutralizing the solution of the phos- 
 phate with ammonia (or soda) ; then adding an excess of 
 phosphoric acid, or enough to dissolve the precipitate formed, 
 and an additional quantity to insure a moderate amount of free 
 phosphoric acid in the bath. The phosphate baths will be 
 maintained of normal strength by additions of platinic hydrate, 
 the solutions of which will need to be assisted by heating the 
 bath, preferably at the close of each day's work. The metal 
 yielded by the electrolysis of these phosphate solutions is 
 brilliant and adherent. It has the same steely appearance as 
 that exhibited by the oxalate solutions, but to a less pro- 
 nounced degree. The physical properties of the deposited 
 metal are in other respects like those described in connection 
 with that obtained from the oxalate baths. 
 
 Management of platinum baths. Copper and brass may be 
 directly plated with platinum, but iron, steel and other metals 
 are first to be coppered, otherwise they would soon decompose 
 the platinum bath, independent of the fact that an unexcep- 
 tionable deposit cannot be produced upon them without the 
 cementing intermediary layer of copper. 
 
 Platinum baths must be used hot, and even then require an 
 electromotive force of 5 to 6 volts, and hence, in plating with a 
 battery at least three, or better four, Bunsen cells must be 
 coupled one after the other. An abundant evolution of gas 
 must appear on the objects and anodes. The anode-surface 
 (platinum anodes) must not be too small, and should be only 
 at a few centimeters' distance from the objects. Since the 
 
436 ELECTRO-DEPOSITION OF METALS. 
 
 platinum anodes do not dissolve, the content of platinum in the 
 bath decreases constantly, and the bath must from time to time 
 be strengthened. For this purpose, the bath, prepared accord- 
 ing to Bottger's formula, is heated in a porcelain dish or 
 enameled vessel to the boiling-point, a small quantity of fresh 
 solution of sodium citrate is added and platoso-ammonium 
 chloride introduced so long as solution takes place. A con- 
 centrated solution of platoso-ammonium chloride in sodium 
 citrate (so-called platinum essence) may be kept on hand and 
 a small quantity of it be at intervals added to the bath. Baths 
 prepared according to the English method are strengthened 
 by the addition of platinum chloride. 
 
 Execution of platinum plating. The objects, thoroughly 
 freed from grease and, if necessary, coppered, are suspended 
 in the bath heated to between 176° and 194 F., and this tem- 
 perature must be maintained during the entire operation. The 
 current should be of sufficient strength and the anodes placed 
 so close to the objects that a liberal evolution of gas appears 
 on them. For plating large objects, it is recommended to go 
 round them, at a distance of 0.31 to 0.39 inch, with a hand- 
 anode of platinum sheet which should not be too small and 
 should be connected to the anode-rod. When the current has 
 vigorously acted for 8 to 10 minutes, the objects are taken from 
 the bath, dried and polished. However, for the production of 
 heavy deposits — for instance, upon points of lightning rods — 
 the deposit is vigorously brushed with a steel-wire scratch- 
 brush or fine pumice-powder. The objects are then once more 
 freed from grease and returned for 10 or 15 minutes longer to 
 the bath to receive a further deposit of platinum with a weaker 
 current, which must, however, be strong enough to cause the 
 escape of an abundance of gas-bubbles. The objects are then 
 taken out, and after immersion in hot water, dried in sawdust. 
 The deposit is then well burnished, first with the steel tool and 
 finally with the stone, whereby the gray tone disappears and 
 the deposit shows the color and luster of massive platinum 
 sheet. Points of lightning-rods platinized in this manner were 
 
DEPOSITION OF PLATINUM AND PALLADIUM. 437 
 
 without flaw after an exposure to atmospheric influences for 
 more than six years. 
 
 Recovery of platinum from platinum solutions. — From not 
 too large baths, precipitation of the platinum with sulphuretted 
 hydrogen is the most suitable method, and preferable to evap- 
 orating and reducing the metal from the residue. The process 
 is as follows : Acidulate the platinum solution with hydrochloric 
 acid ; and, after warming it, conduct sulphuretted hydrogen into 
 it. The metal (together with any copper present) precipitates 
 as sulphide of platinum. The precipitate is filtered off, dried, 
 and ignited in the air, whereby metallic platinum remains be- 
 hind. From larger baths the platinum may be precipitated by 
 suspending bright sheets of iron in the acidulated bath. In 
 both cases the precipitated platinum is treated with dilute nitric 
 acid in order to dissolve any copper present. After filtering 
 off and washing the pure platinum, dissolve it in aqua regia. 
 The solution is then evaporated to dryness in the water bath, 
 and the chloride of platinum thus obtained may be used in 
 making a fresh bath. Precipitation by zinc sheets or zinc dust 
 can also be recommended. 
 
 2. Deposition of Palladium. 
 
 Properties of palladium. — Palladium, when compact, has a 
 white color and possesses a luster almost equal to that of silver. 
 Its specific gravity is about 12.0; it is malleable and ductile, 
 and may be fused at a white heat. In the oxy-hydrogen flame 
 it is volatilized, forming a green vapor. It is less permanent in 
 the air than platinum. It is dissolved by nitric acid ; it is 
 scarcely attacked, however, by hydrochloric or sulphuric acid. 
 Hydriodic acid and free iodine coat it with the black palladium 
 iodide. 
 
 On account of the high price of its salts, palladium has been 
 but little used for electro-plating purposes; nor, for the same 
 reason, is it likely to be more extensively employed in the 
 future. 
 
 According to M. Bertrand, the most suitable bath consists of 
 
438 ELECTRO-DEPOSITION OF METALS. 
 
 a neutral solution of the double chloride of palladium and 
 ammonium, which is readily decomposed by 3 Bunsen cells 
 coupled one behind the other (therefore about 5.4 volts). A 
 sheet of palladium is used as anode. 
 
 A solution of palladium cyanide in potassium cyanide does 
 not yield as good results as the above bath. 
 
 Palladium is entirely constant in the air, and in color closely 
 resembles silver. It possesses further the property of not 
 being blackened by sulphuretted hydrogen, and for this reason 
 it is sometimes employed for coating silver-plated metallic 
 articles. 
 
 Palladium has also of recent years been employed for plat- 
 ing watch movements. According to M. Pilet, 4 milligrammes 
 (about -pf grain) of palladium are sufficient to coat the works of 
 an ordinary-sized watch. M. Pilet recommends the following 
 bath: Water 2 quarts, chloride of palladium 5^ drachms, 
 phosphate of ammonia 3^ ozs., phosphate of soda 17 }4 ozs., 
 benzoic acid 2^ drachms. 
 
 Deposits of iridium and rhodium have recently been pro- 
 duced from baths similar in composition to those mentioned 
 under palladium. But as these metals would be used for plat- 
 ing purposes only in isolated cases, it is not necessary to enter 
 into details. 
 
CHAPTER XI. 
 
 DEPOSITION OF TIN, ZINC, LEAD AND IRON. 
 i. Deposition of tin. 
 
 Properties of tin. — Tin is a white, highly lustrous metal. It 
 possesses but little tenacity, but has a high degree of mallea- 
 bility, and tin-foil may be obtained in leaves less than -^ thof 
 a millimeter in thickness. Tin melts at about 446 F., and 
 evaporates at a high temperature. The fused metal shows 
 great tendency to crystallize on congealing. By treating the 
 surface of melted tin with a dilute acid, the crystalline structure 
 appears in designs {moire metallique}, resembling the ice- 
 flowers on frosted windows. 
 
 Tin remains quite constant even in moist air, and resists the 
 influence of an atmosphere containing sulphuretted hydrogen. 
 Strong hydrochloric acid quickly dissolves tin on heating, 
 hydrogen being evolved and stannous chloride formed. Dilute 
 sulphuric acid has but little action on the metal; when heated 
 with concentrated sulphuric acid, sulphur dioxide is evolved. 
 Dilute nitric acid dissolves tin in the cold without evolution of 
 gas ; concentrated nitric acid acts vigorously upon the metal, 
 whereby oxide of tin, which is insoluble in the acid, is formed. 
 Alkaline lyes dissolve the metal to sodium stannate, hydrogen 
 being thereby evolved. 
 
 Tin baths. The bath used by Roseleur for tinning with the 
 battery works very well. It is composed as follows : 
 
 I. Pyrophosphate of soda 3.5 ozs., tin salt (fused) 0.35 oz., 
 water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance, 1.25 volts. 
 
 Current-density, 0.25 ampere. 
 
 f 439) 
 
440 ELECTRO-DEPOSITION OF METALS. 
 
 To prepare the bath dissolve the pyrophosphate of soda in 
 io quarts of rain water, suspend the tin-salt in a small linen 
 bag in the solution, and move the bag to and fro until its con- 
 tents are entirely dissolved. 
 
 Objects of zinc, copper and brass are directly tinned in this 
 bath. Articles of iron and steel are first coppered or prelimi- 
 narily tinned by boiling in a bath given later on under tinning 
 by contact, the deposit of tin being then augmented in bath I 
 with the battery current. Cast-tin anodes as large as possible 
 are used, which, however, will not keep the content of tin in 
 the bath constant. It is therefore necessary, from time to time, 
 to add tin-salt, which is best done by preparing a solution of 
 3.5 ozs. of pyrophosphate of soda in I quart of water and in- 
 troducing into the solution tin-salt as long as the latter dis- 
 solves clear. Of this tin-essence add to the bath more or less, 
 as may be required, and also augment the content of pyrophos- 
 phate of soda, if notwithstanding the addition of tin-salt, the 
 deposition of tin proceeds sluggishly. 
 
 Though the bath composed according to formula I suffices 
 for most purposes, an alkaline tin bath, first proposed by 
 Eisner, and later on recommended by Maistrasse, Fearn, Birg- 
 ham and others, with or without addition of potassium cyanide, 
 may be mentioned as follows : 
 
 II. Crystallized tin-salt 0.7 ozs., water 1 quart, and potash 
 lye of io° Beaume until the precipitate formed dissolves. 
 
 As seen from the formula the solution of tin-salt is com- 
 pounded with potash lye of the stated concentration (or with 
 a solution of 1 oz. of pure caustic potash in water), until the 
 precipitate of stannous hydrate again dissolves. 
 
 Some operators recommend the addition of 0.35 oz. of potas- 
 sium cyanide to the solution. 
 
 In testing Salzede's bronze bath (p. 358), it was found to 
 yield quite a good deposit of tin directly upon cast iron, and it 
 was successfully used for this purpose by omitting the cuprous 
 chloride, and using instead 0.88 oz. of stannous chloride, so 
 that the composition became as follows : 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 44 1 
 
 Ha. 98 per cent, potassium cyanide 3.5 ozs., carbonate of 
 potassium 3S}i ozs., stannous chloride 0.88 ozs., water 10 
 quarts. With 4 volts a heavy deposit was rapidly obtained. 
 
 Very good results were obtained in a hot bath (158 to 194 
 F.), first made public by Neubeck, which consists of: 
 
 III. 70 per cent, caustic soda 35 y^ ozs., ammonium-soda 
 35^ ozs., fused tin-salt 7 ozs., water 10 quarts. 
 
 Electro-motive force at 10 cm. electrode-distance and 15 5 
 F., 0.8 volt. 
 
 Current- density, 1 ampere. 
 
 The chemicals are successively dissolved in the water. 
 When the bath commences to work sluggishly, about 0.35 to 
 0.5 oz. of fused tin-salt has to be added. 
 
 Management of tin baths. — Tin baths should not be used at a 
 temperature below 68° F. Too strong a current causes a 
 spongy reduction of the tin, which does not adhere well, while 
 with a suitable current-strength quite a dense and reguline de- 
 posit is obtained. Cast-tin plates, with as large a surface as 
 possible, are used as anodes. The choice of the tin-salt exerts 
 some influence upon the color of the tinning. By using, for 
 instance, crystallized tin-salt, which is always acid, in preparing 
 the bath according to formula I, a beautiful white tinning with 
 a bluish tinge is obtained, which, however, does not adhere so 
 well as that produced with fused tin-salt. Again, the latter 
 yields a somewhat dull gray layer of tin, and, therefore, the 
 effects of the bath will have to be corrected by the addition of 
 one or the other salt. 
 
 As previously mentioned, iron and steel objects are best sub- 
 jected to a light preliminary tinning by boiling. However, in- 
 stead of this preliminary tinning, they may first be electro- 
 coppered and, after scratch-brushing the copper deposit, 
 brought into the tin bath. 
 
 Process of tin-plating. — From what has been said, it will be 
 evident that the execution of tin-plating is simple enough. 
 After being freed from grease, and pickeled, the objects are 
 brought into the bath and plated with a weak current. For 
 
44 2 ELECTRO-DEPOSITION OF METALS. 
 
 heavy deposits the objects are frequently taken from the bath 
 and thoroughly brushed with a brass scratch-brush, not too 
 hard, and moistened with dilute sulphuric acid (i part acid 
 of 66° Be. to 25 water) and, after rinsing in water, are re- 
 turned to the bath. If, with the use of too strong a current, 
 the color of the deposit is observed to turn a dark dull gray, 
 scratch-brushing must be repeated. When the tinning is fin- 
 ished the articles are brushed with a brass scratch-brush and 
 decoction of soap-root, then dried in sawdust, and polished 
 with fine whiting. 
 
 For tinning by contact and boiling, see special chapter, 
 " Depositions by Contact." 
 
 2. Deposition of Zinc. 
 
 Properties of Zinc. — Zinc is a bluish-white metal, possessing 
 high metallic luster. It melts at 776 F. At the ordinary 
 temperature zinc is brittle, but it is malleable at between 21 2° 
 and 300 F., and can be rolled into sheets. At 392 ° F. it 
 again becomes brittle, and may be readily reduced to powder. 
 The specific gravity of zinc varies from about 6.86 to J. 2. 
 When strongly heated in the air, or in oxygen, it burns with a 
 greenish-white flame, producing dense white fumes of the 
 oxide. 
 
 In moist air it becomes coated with a thin layer of basic 
 carbonate, which protects the metal beneath from further 
 oxidation. Pure zinc dissolves slowly in the ordinary mineral 
 acids, but the commercial article containing foreign metals is 
 rapidly attacked, hydrogen being evolved. 
 
 Since zinc is a very electro-positive metal and precipitates 
 most of the heavy metals from their solutions, especially cop- 
 per, silver, lead, antimony, arsenic, tin, cadmium, etc., this being 
 the reason why in dissolving impure zinc, the admixed metals 
 do not pass into solution so long as zinc in excess is present. 
 Potash and soda lyes attack zinc, especially when it is in con- 
 tact with a more electro-negative metal, hydrogen being evolved. 
 
 Zinc in contact with iron protects the latter from rust, and 
 also prevents copper from dissolving when in contact with it. 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 443 
 
 Up to within a few years, objects were, as a rule, zincked by 
 the so-called galvanizing process, and electro-plating with zinc 
 was only used for parts which could not stand hot galvanizing, 
 for instance, finer qualities of cast-iron objects or parts of 
 machines, such as parts of centrifugals for sugar houses. 
 
 Further researches and practical experience in this line led 
 to the application of zinc by the electrolytic cold process to 
 other objects, such as sheet-iron and iron for constructive pur- 
 poses. Thus, for instance, all the iron in lengths of up to 36 
 feet and 7 feet 6 inches projection used in the construction of 
 the palm houses in the new botanical garden at Dahmen- 
 Berlin were electro-plated with a thick deposit of zinc, and by 
 thorough investigations of the authorities it has been shown 
 that, as regards protection from rust, the iron thus plated with 
 zinc is at least not inferior to iron zincked by the hot process. 
 
 Electro-zincking has also proved of value for protecting the 
 tubes of the Thornycroft boiler and several plants of this char- 
 acter are now in operation. Of great importance is also the 
 electro-zincking of iron and steel network for corsets. 
 
 Electro-zincking is also of great advantage for small iron 
 articles, for instance, screws and nuts, since the worms do not 
 fill up with metal, as is the case in the hot process, and conse- 
 quently do not require re-cutting. 
 
 While in the further manipulations, such as bending, punch- 
 ing, etc., of sheets, angle-iron, "|~-iron, pipes, etc., zincked by 
 the hot galvanizing process, the layer of zinc readily cracks off, 
 the electro-deposit adheres very firmly, if the basis-metal has 
 been properly cleansed ; and if the deposit is not of excessive 
 thickness, which would be entirely useless, it cannot be de- 
 tached by bending and beating. If it be further taken into 
 consideration that in zincking by the hot galvanizing process 
 much more zinc than is necessary for the protection against 
 rust adheres to the objects, that the loss of zinc by the forma- 
 tion of hard zinc (an iron-zinc alloy) is considerable, and that 
 it is quite expensive to keep the plant in repair, it will have to 
 be admitted that in an economical aspect also, zincking with 
 the assistance of the current presents many advantages. 
 
444 ELECTRO-DEPOSITION OF METALS. 
 
 Exhaustive comparative experiments regarding zincking by 
 the hot process and by electro-deposition (cold process), have 
 been published by Burgess.* These experiments relate to the 
 duration of protection of the basis-metal, adhering power of the 
 zinc coating, ductility and flexibility of the latter, uniformity of 
 the coatings as regards strength and density, as well as resist- 
 ance against mechanical wear. The results of the experiments 
 were as follows : 
 
 The disadvantages of hot-galvanizing are : Considerable con- 
 sumption of heat and a material loss of zinc by oxidation on 
 the surface of the fused zinc, by alloying with the cover of sal- 
 ammoniac, and by the formation of hard zinc — a zinc-iron alloy 
 which is formed at the expense of the walls of the iron tank. 
 Burgess estimates the loss of zinc at 50 per cent, of the zinc 
 used, and only a portion of it can be regained by a special 
 process. 
 
 On the other hand, in electro-zincking no loss by heat is 
 incurred, and hence such articles as steel-wire, steel-springs,, 
 etc., can be zincked, the treatment of which, at the temperature 
 of the melted zinc, would be out of the question. Electro- 
 zincking of certain kinds of work is now specified by the Gov- 
 ernments of Great Britain and Germany, and the United States 
 Government has installed at its various shipyards complete 
 equipments for the purpose of treating articles by the electri- 
 cal method. 
 
 The loss of zinc in electro-zincking is nominal and the wear 
 of the vessels used is less than 10 per cent, per annum, while 
 in the hot process it amounts to from 50 to 100 per cent. 
 
 By electro-deposition articles of any size may be zincked ; 
 the bath is always ready for use, and the thickness of the coat- 
 ing can be controlled and regulated, which in hot galvanizing 
 is possible only to a limited degree. Both processes possess 
 the drawback of never yielding coatings of uniform thickness; 
 the edges of hot-zincked pieces, especially of those which come 
 
 * Lead and Zinc News, 1904, viii, Nos. 8 to io. 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 445 
 
 last from the bath, are smeared over, i. e., they are more 
 heavily zincked than others while, by reason of the current- 
 density being greater on these portions, the edges of sheets 
 zincked by electro-deposition are also more heavily zincked 
 than parts in the center of the sheets. 
 
 The usual method of determining, by immersion in a 20 per 
 cent, copper sulphate solution, the thickness of the coating of 
 zinc obtained by hot-galvanizing, was found by Burgess to 
 be quite unsuitable for judging the thickness and quality of 
 electro-zincking. This test, known as Preece's test, consists in 
 placing the galvanized iron in the copper solution for y 2 to 1 
 minute, and continuing the immersions until the test-piece 
 shows a red deposit of copper, which is a true indication that 
 the zinc has been penetrated and the iron exposed. In Ger- 
 many it is, as a rule, required that hot-galvanizing must stand 
 for at least 30 seconds constant immersion before the red cop- 
 per color appears ; so long as the coating of zinc is intact there 
 is only a black coloration. On applying Preece's test to 
 electro-zincked articles, it was found that they would not stand 
 as many immersions in the copper solution as coatings obtained 
 by hot-galvanizing but nevertheless they were more resisting 
 to atmospheric influences. For testing the power of resistance 
 of the coatings, Burgess, therefore, made use of dilute sulphuric 
 acid and found that an electro-deposited coating % the weight 
 of one produced by hot-galvanizing possesses the same power 
 of resisting corrosion as the latter, and that for coatings of 
 equal thickness the proportion of the resisting power is as 
 10:1. This superiority of electro-zinking has to be ascribed 
 to the greater purity of the deposit effected by electro-deposi- 
 tion. 
 
 On measuring the adhesive power, Burgess ascertained quite 
 different values from those of hot-galvanizing. With electro- 
 deposited zinc the force required to tear the coatings from the 
 basis-metal (iron) amounted on an average to 482 lbs. per square 
 inch, and only to 280 lbs. for coatings obtained by hot-gal- 
 vanizing. Hence the adhesive power of electro-deposited 
 coatings is materially greater. 
 
44 6 ELECTRO-DEPOSITION OF METALS. 
 
 Attempts were made to ascertain the ductility and flexibility 
 of the coatings by rolling. However, no positive results were 
 obtained, some deposits becoming thereby more or less cracked,, 
 while others remained intact. The flexibility of the deposit is. 
 without doubt affected by the reaction of the bath, and it has 
 been observed that from very slightly acid electrolytes, with an 
 electro-motive force of 1.5 amperes, deposits free from cracks 
 were obtained while very brittle deposits were obtained from 
 more strongly acid solution with the same current-density. 
 Burgess's experiments in this respect only made sure of the fact 
 that there is no material difference in the behavior of hot- and 
 cold-galvanized sheets with coatings of equal thickness. In all 
 cases the zinc, when subjected to rolling, showed a tendency to 
 separate from the basis-metal; the zinc detached from electro- 
 zincked sheet, however, possessed greater strength and was less 
 brittle than that from hot- galvanized sheet. 
 
 On examining the detached coatings under the microscope 
 it was further found that, contrary to the generally accepted 
 opinion, the coating produced by hot-galvanizing was far more 
 porous than that obtained by electro-deposition. An electro- 
 deposit of less than 100 grammes zinc per square meter surface, 
 was to be sure also porous, but with a thickness of 200 grammes 
 zinc per square meter the pores had grown together. 
 
 The resistance against mechanical wear was apparently the 
 same with the different deposits of equal thickness. Only in 
 one case the electro-deposit proved of less value than the hot- 
 galvanizing, namely, when electro-zincked sheets were subjected 
 by heating and cooling to frequent and considerable changes in 
 temperature, blisters were more frequently formed, and the zinc 
 became detached to a greater extent than was the case with 
 hot- galvanized sheet. This shows that electro-zincked sheets 
 should not be used for heating pipes for high temperatures. 
 Blistering is less to be feared with temperatures not exceeding 
 that of steam of 3 atmospheres. 
 
 Zinc baths. While flat articles can be readily coated with a 
 firmly-adhering layer of zinc of uniform thickness, the produc- 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 447 
 
 tion of such a deposit upon large, shaped articles and profiled 
 objects is attended with difficulties, because zinc baths do not 
 work quite well in the deeper portions. As will be seen later 
 on, these difficulties may be overcome, on the one hand, by- 
 heating the baths and, on the other, by the use of anodes with 
 somewhat the same profile as the article to be zincked, so that 
 all portions of it are as nearly as possible at the same distance 
 from the anodes. 
 
 In plating articles with depressions, better results are obtained 
 by depositing not pure zinc, but zinc in combination with other 
 metals. Of course, zinc must be largely in excess if the deposit 
 is to have the same effect as pure zinc in protecting the plated 
 article from rust. By the addition of salts of magnesium and 
 aluminium to the zinc bath, Schaag, Dr. Alexander and others 
 have endeavored to deposit zinc in combination with these 
 metals. While the possibility of depositing aluminium from 
 aqueous solutions is doubtful, it is very likely that in Schaag's? 
 as well as in Dr. Alexander's patented process neither the mag- 
 nesium nor the aluminium is the effective agent, but the tin or 
 mercury salts which are also added to the bath. But such ad- 
 ditions are nothing new, since deposits of zinc-tin alloys with or 
 without mercury salts have for many years been produced. 
 The same object is attained by an addition of tin and nickel to 
 the zinc bath, and experiments have conclusively shown that 
 deposits upon iron produced in such a bath protect the iron 
 from rust as well as a deposit produced in a bath of pure zinc, 
 or in Dr. Alexander's zinc baths, the patents for which are now 
 expired. The good effect of aluminium sulphate in zinc baths 
 might solely be due to the fact that the acidity of the baths is 
 longer maintained. 
 
 In connection with the Alexander patents it may here be 
 stated that an important decision was rendered by Judge Cross 
 of the Circuit Court of the United States for the District of New 
 Jersey, in favor of the Hanson & Van Winkle Co., of Newark, 
 N. J., and Chicago, 111., and against the United States Electro- 
 Galvanizing Co. of Brooklyn, owners of these patents. The 
 
44§ ELECTRO-DEPOSITION OF METALS. 
 
 decision ends as follows: "For the following, among other 
 reasons, then, the defendant does not infringe; it does not make 
 the alloyed coating of the patent, employs no basic salts, but 
 rather makes and maintains throughout an acid bath ; does 
 not use chloride of aluminium in its salts, does not use any 
 organic substance with its salts or bath, or any equivalent 
 thereof, and its bath is composed in part of different ingredi- 
 ents from the complainants, is prepared differently and under 
 different conditions, and its ingredients, in so far as they are the 
 same, appear in the different proportions. The bill of com- 
 plaint will accordingly be dismissed, with costs." 
 
 Whatever may be said of the validity of the Alexander patents 
 as against others, as against the salts and processes of the Han- 
 son & Van Winkle Co., the patent is of no effect. The largest cold 
 galvanizers of this country have been fitted up by the experts 
 of this company. 
 
 While the protection against rust of deposits from alloy- 
 baths is about the same as from pure zinc baths, the use of the 
 latter, without the addition of foreign metals can nevertheless 
 be recommended, since with a suitable composition of the bath 
 and proper arrangement of the anodes perfect zinc deposits can 
 in all cases be obtained. 
 
 During the last few years several investigators have occupied 
 themselves with the electrolysis of zinc, and numerous proposi- 
 tions have been advanced, but space will not permit to consider 
 them here. Cowper-Coles used an electrolyte which consisted 
 of zinc sulphate with an addition of ferric sulphate, the effect of 
 which was to prevent a formation of zinc oxide in the deposit. 
 Later on, he proposed to electrolyze a pure solution of zinc 
 sulphate with lead anodes in order to prevent the bath from 
 becoming alkaline, and to neutralize the excess of acid formed 
 with zinc dust in a special tank. 
 
 By this method zinc coatings of quite good quality are ob- 
 tained and the drawback connected with the use of zinc anodes 
 is avoided. As disadvantages may be mentioned, the con- 
 siderably greater electro-motive force required with the use of 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 449 
 
 insoluble lead anodes and the consequently larger cost of cur- 
 rent, and further the operating expenses caused by the ap- 
 paratus for forcing the bath liquor into the regenerating vats. 
 
 Although not within the scope of this work, it may here be 
 mentioned that Sherard Cowper-Coles has recently inverted a 
 dry process of galvanizing to which the term " Sherardizing " 
 has been applied. It owes its existence to the peculiar prop- 
 erties of zinc-dust, and in practice is performed as follows : The 
 articles to be coated are placed in a suitable retort — usually a 
 cast-iron drum — and covered with commercial zinc-dust; the 
 retort is closed as tightly as possible, and even luted, to pre- 
 vent the egress of the vapor, which is at a higher pressure than 
 the atmosphere of the oven. The time during which the retort 
 or drum will be left in the oven will depend on the deposit it is 
 desired to get. The retort is allowed to cool by natural means 
 and the articles are taken out. * 
 
 Dr. Szirmay and von Kollerich want to add solution of mag- 
 nalium (aluminium-magnesium alloy) in sulphuric acid and 
 dextrose to white vitriol (zinc sulphate) solution. In dissolv- 
 ing magnalium, aluminium sulphate and magnesium sulphate 
 are formed. Neither aluminium or magnesium in watery solu- 
 tions are reducible as metals by the current, as they oxidize at 
 the moment of reduction, water being decomposed. The effect 
 of the aluminium sulphate with its acid reaction is simply that 
 the bath does not readily become alkaline, while the magnesium 
 sulphate acts as a conducting salt, the separated magnesium- 
 ions of it causing the secondary reduction of zinc from the sul- 
 phate solution. The addition of carbohydrates to which dex- 
 trose belongs, which became known through the English patent 
 No. 1 269 1, 1897, is claimed to prevent the formation of sponge, 
 which, however, according to experiments made in Dr. Lang- 
 bein's laboratory, is the case only to a limited extent. An 
 addition of dextrose appears to have the further effect of the 
 bath working better in the deeper portions and the deposits 
 
 * Alfred Sang in " Electro-chemical and Metallurgical Industry." 
 29 
 
450 ELECTRO-DEPOSITION OF METALS. 
 
 turning out less tufaceous. The deposits frequently come from 
 the bath with a slight luster, this being especially the case when 
 electrolysis is for some time continued after the addition of the 
 dextrose. 
 
 According to Goldberg (German patent 15 1336) an addi- 
 tion of pyridine to zinc baths is claimed to effect a dense de- 
 posit of zinc of a beautiful white color and velvety appearance. 
 On testing this process these claims were found to be correct, 
 and furthermore such a bath works better in the depression. 
 
 Classen has patented the addition of glucosides, and claims 
 to obtain thereby the deposition of lustrous zinc coatings. 
 
 The reason why in baths of the compositions formerly given, 
 actually thick deposits without showing a spongy structure 
 could not be obtained, is found in the fact that these baths 
 contained too little metal and had an unsuitable, generally alka- 
 line, reaction. Even when electrolysis has only been carried 
 on for a short time, alkaline baths do not yield a coherent and 
 purely metallic deposit of zinc, a basic zinc oxide being re- 
 duced together with the metallic zinc, which readily gives rise 
 to the formation of sponge. 
 
 The formula for an alkaline zinc bath, namely, 1]/, ozs. of 
 white vitriol dissolved in 1 quart of water, and adding potash 
 lye until the precipitated zinc hydroxide is again dissolved, 
 which was given in former editions of this work, yields quite 
 fair results. These baths work best when, in place of potash 
 or soda lye, ammonia is used for precipitating and dissolving 
 the zinc hydroxide, and the baths contain a large excess of am- 
 monia. Hence, in the above-mentioned formula, the potash 
 lye should be replaced by ammonia and, in addition to the 
 quantity required for the solution of the precipitate formed, 
 enough of it should be used to impart to the bath a strong odor 
 of ammonia. However, by reason of this odor of ammonia, 
 the operation of such a bath becomes disagreeable, and even 
 injurious to health. 
 
 In order to force the bath to work better in the deeper por- 
 tions, mercury salts in the form of potassium mercuric cyanide, 
 
DEPOSITION OP "JIN, ZINC, LEAD AND ICON' 451 
 
 may be added to alkaline baths. It must, moreover, be borne 
 in mind that an addition of mercury is of advantage because 
 the anodes are thereby superficially amalgamated and kept in 
 a purely metallic state. In alkaline zinc baths particularly, an 
 abundant coat of zinc hydroxide is formed upon the anodes, 
 and because this coat does not dissolve to the same extent as 
 it is formed, it has to be frequently removed by mechanical 
 means. 
 
 Below formulas for zinc baths which have stood the test for 
 a long time are given. 
 
 I. Chemically pure crystallized zinc sulphate 44 lbs., pure 
 crystallized sodium sulphate 8.8 lbs., chemically pure zinc 
 chloride, 2.2 lbs., crystallized boric acid 1.1 lbs., dissolved in 
 water to a 100 quart bath. 
 
 lilectro-motive force at 10 cm. electrode-distance and 64. 4 F., 
 1.1, 1.5, 1.8, 2.2, 2.4, 2.7, 3.7 volts. 
 
 Current- density at 64. 4 F„ 0.55, 0.75,0.95, 1.15, 1.25, 1.45, 
 1.9 amperes. 
 
 Electro motive force at io cm. elect rode- distance and at \ 13 
 F., 0.9, 1.05, r.25, 1.40, 1.8, 2.0, 2.3, 3.5 volts. 
 
 Current- density at J f 3 F., 0.7, 0.8, I .O, I.I, 1.4, 1.55, 1.8, 
 2.75 amperes. 
 
 This bath as well as others of similar composition will stand 
 eon iderably higher current-densities if provision is made for 
 vigorous agitation of the electrolyte, U agitation is Lo be 
 avoided an increase of the content of zinc salt and boric acid is 
 of advantage. 
 
 To prepare the bath, dissolve- the zinc sulphate, the zinc 
 chloride and sodium sulphate (Glauber's salt; in luke-warm 
 water. Heat a portion of this fluid to about 194 F., dissolve 
 in it the boric acid, and mix itwith the other solution. An ad- 
 dition of 0.8 to j oz. of dextrose per quart is recommended. 
 
 For the production of a good depos t of zinc it. is of im- 
 portance to use zinc salts free from other metals, it having been 
 shown that a content of foreign metals, especially iron, causes 
 disturbances. 
 
452 ELECTRO-DEPOSITION OF METALS. 
 
 The reaction of the bath should be kept slightly acid, so that 
 blue litmus paper is intensely reddened, but congo paper is not 
 perceptibly blued. The bath gradually loses its acid reaction 
 and does not work as well, the deposit becoming darker instead 
 of pale gray, and inclining towards the formation of sponge. 
 It should then be acidulated by the addition of pure dilute sul- 
 phuric acid. For flat objects (sheets, etc.) the bath may be 
 used cold, but for profiled objects, such as angle-iron, beams, 
 etc., it is advisable to heat it to between 104 and 122 F. 
 
 II. Crystallized sodium citrate 5.5 lbs., chemically pure zinc 
 chloride 8.8 lbs., pure crystallized ammonium chloride 6.6 lbs. 
 Dissolve with water to a lOO-quart bath. 
 
 Electro-motive force at 10 cm. electrode-distance and at 64.4 
 F., 0.8, 1.0, 1. 5, 1.8, 2.2, 3.4 volts. 
 
 Cnrre7it-density at 64.4 F., 0.7, 0.9, 1.4, 1.7, 1.9, 3.0 amperes. 
 
 Electro-motive force at 10 cm. electrode-distance and 1 13 F., 
 0.8, 1.0, 1.5, 1.75, 2.5, 3.2 volts. 
 
 Current-density at 1 13 F., 1.0, 1.25, 1.9, 2.3, 3.2, 4.3 amperes. 
 
 The bath is prepared by dissolving the constituents in the 
 water, which should not be too cold ; best luke-warm. What 
 has been said under formula I in reference to the reaction also 
 applies to this bath. 
 
 Zinc anodes. Treatment of zinc baths. — For anodes it is best 
 to use very pure rolled-zinc sheets 0.1 1 to 0.19 inch or more in 
 thickness. Strips of zinc riveted to the anodes with zinc rivets 
 serve for suspending the anodes to the anode rods. For 
 zincking sheet-iron, wire, etc., on a large scale, cast zinc anodes 
 may be preferred on account of being cheaper. It must, how- 
 ever, be borne in mind that cast anodes readily crumble, 
 especially when they have frequently to be cleansed mechan- 
 ically by scraping and scratch- brushing for the removal of the 
 basic zinc salts forming on them. The loss of zinc caused by 
 the formation of basic zinc salt and by crumbling is consider- 
 able, and according to Covvper-Coles may be as large as 30 
 per cent, of the entire consumption of zinc. This estimate, 
 however, appears to be excessive : to be sure the formation of 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 453 
 
 a coat on the anodes as well as the crumbling of the anodes is 
 disagreeable, but it cannot be considered a direct loss since the 
 zinc salt as well as the detached crumbs of metal can, by dis- 
 solving in sulphuric acid, be converted into zinc sulphate, and 
 the latter be used for strengthening the bath. The surface of 
 the anodes should be as large as possible. Rolled anodes also 
 become readily coated with a layer of basic zinc salt, and it is 
 advisable from time to time to remove this layer by scratch- 
 brushing. The coating thus removed may be dissolved in 
 dilute sulphuric acid and added to the bath as neutral zinc solu- 
 tion. As previously mentioned, the zinc baths should show a 
 perceptibly acid reaction in order to avoid as much as possible 
 the formation of sponge, and therefore the reaction should at 
 short intervals be tested and, if necessary, corrected by the 
 addition of dilute sulphuric acid. 
 
 The zinc anodes should be removed from the bath when the 
 latter is not in operation, otherwise the free acid of the bath 
 would be neutralized by the solution of zinc and it would have 
 to be again acidified. 
 
 Although the zinc baths, without exception, work well at a 
 temperature of 64. 4 to 68° F. upon flat articles, it is recom- 
 mended, in view of the slight electro- motive force required, to 
 keep them somewhat warmer. 
 
 For zincking strongly-profiled objects it is advisable to heat 
 the baths to between 104 and 11 3° F., since at a higher tem- 
 perature the deposit penetrates better into the deeper portions. 
 Anodes with profiles similar to those of the objects are used. 
 As shown by the current conditions given with the formulas for 
 the baths, a fixed current-density is not obligatory in electro- 
 zincking. For the bath, according to formula I, 1.25 to 1.5 
 amperes may be designated as the lowest rational current- 
 density, at which 5.29 to 6.34 ozs. of zinc per square meter 
 (10.76 square feet) are in one hour deposited. With heated 
 and agitated baths, the maximum current-density may be given 
 as about 3 amperes, with which 12.91 ozs. of zinc per square 
 meter are in one hour deposited. However, in certain cases, 
 
454 ELECTRO-DEPOSITION OF METALS. 
 
 this current-density may be exceeded. For baths, according 
 to formula II, it is best to use a slighter current-density. 
 Should it, however, be necessary to work with higher current- 
 densities, provision has to be made for a sufficiently acid reac- 
 tion and thorough agitation in order to avoid the formation of 
 sponge. In zincking, agitation of the baths is of special value, 
 and, if possible, should never be omitted. 
 
 Tanks for zinc baths. — For smaller baths it is best to use 
 stoneware vessels, while for larger baths, tanks of pitch-pine, or 
 still better, of wood lined with lead, may be employed. Zinc 
 salt solutions gradually impair the swelling capacity of wood, 
 and even pitch-pine tanks, most carefully built, commence in 
 the course of time to leak. For this reason tanks of wood 
 lined with lead, or of sheet-iron, deserve the preference. Brick 
 tanks lined with cement may also be used, provided several 
 coats of thinly-fluid asphalt lacquer be applied to the cement 
 lining to prevent the latter from being attacked by the acid 
 baths. 
 
 Heating the zinc baths is best effected by steam introduced 
 through a hard lead (alloy of antimony and lead) coil on the 
 bottom of the tank. 
 
 Execution of zincking. — Since the principal object of elec- 
 tro-zincking is to prevent rusting, embellishing the metallic 
 objects being only in very rare cases effected, the mechanical 
 refinement of the surface by grinding is as a rule omitted, a 
 purely metallic surface free from scale being produced in a 
 cheaper manner. 
 
 This is done by pickling, scratch-brushing, scrubbing with 
 sand in a drum, or by the sand-blast. The latter deserves the 
 preference for large quantities of small articles, as well as for 
 objects with not too large surfaces. For freeing large surfaces 
 of sheets from scale, the use of the sand-blast is, however, too 
 expensive on account of the great consumption of power, and, 
 besides, takes too much time. 
 
 In electro-zincking particularly, the mode of operating de- 
 pends entirely on the nature and form of the objects, and it is, 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 455 
 
 therefore, advisable to discuss separately the various manipula- 
 tions required for certain objects. 
 
 Zincking sheet-iron. — When the sheets have been freed from 
 grease by means of hot alkaline lyes or lime paste, they are 
 pickled in dilute sulphuric or hydrochloric acid, and the 
 loosened scale is removed by scouring with fire brick and sand. 
 The use of a pickle of hydrochloric acid 2 parts, sulphuric 
 acid of 66° Be., 1 part, and water 17 parts is also of advantage. 
 To what extent the electrolytic method of pickling, previously 
 referred to, can be used to advantage for this purpose, has thus 
 far not been practically determined. By the use of a sand- 
 blast the cleanest and most complete results are obtained, but 
 the expense for power has to be taken into consideration. 
 
 As in all other electro-plating processes, a purely metallic 
 surface free from scale is an absolutely necessary condition for 
 a well-adhering deposit of zinc. Portions of the sheets coated 
 with scales, would come out zincked, but in the further manip- 
 ulation of the sheets, the layer of zinc becomes detached, and 
 this must be avoided. 
 
 The pickled and scoured sheets, generally in lengths of 6 
 feet and 1 foot wide, are secured to binding screws and brought 
 into the zinc bath, that given under formula I being especially 
 suitable for the purpose. Heating the bath to between 104 
 and 1 1 3 ° F., and vigorous agitation by blowing in air, or by 
 means of a mechanical contrivance, allows of working with a 
 current-density oi 2*4 amperes, and, if necessary, more, at 
 which a sufficiently heavy deposit to protect the objects from 
 rust is in 20 to 25 minutes obtained. 
 
 In working on a large scale, it is advisable to couple the 
 baths in series and to zinc in each bath 3 sheets, each 2x1 
 meters, with a total surface of 12 square meters per bath. 
 Hence, for zincking the sheets on both sides and working with 
 a current-density of 2.5 amperes per square decimeter, there 
 will be required for four baths in series, each with 12 square 
 meters of surface, a dynamo of 12 x 250 = 3000 amperes, and 
 the electro-motive force should be 12 volts, 2 X A to 3 volts be- 
 
456 ELECTRO-DEPOSITION OF METALS. 
 
 ing required per bath. With such a plant working for 10 
 hours, 340 to 360 sheets, each 2 x 1 meters, can be zincked on 
 both sides so as to protect them from rust, and by working day 
 and night, 820 to 850 sheets. 
 
 When zincking is finished, the sheets are rinsed in water, 
 then immersed in boiling water until they have acquired the 
 temperature of the latter, and finally set up free, or hung up to 
 dry. The hot sheets then dry in a few minutes. 
 
 The zincked sheets show a pale-gray, matt, velvety appear- 
 ance, and are generally used in this state. If the zinc deposit 
 is to be lustrous, the sheets are scratch-brushed, best dry, with 
 steel scratch-brushes. 
 
 Zincking of pipes. The pipes are freed from scale either by 
 means of the sand blast or by pickling and scouring. To pro- 
 tect the screw threads from the pickle, they are coated with 
 tallow which, however, previous to zincking, has to be re- 
 moved with hot soda lye or rubbing with benzine, and care 
 must be had thoroughly to free them from grease with lime 
 paste. 
 
 The pipes, best four or six pieces one above the other, are 
 placed upon a frame which also serves for conducting the cur- 
 rent, and, if they are of considerable diameter, it is advisable to 
 turn them 90 when half the time for zincking has expired, in 
 order to obtain a uniform deposit. 
 
 While in zincking straight flat sheets, the distance of the 
 anodes from the cathodes need only be 1.96 to 2.35 inches, the 
 distance of the zinc anodes from the pipes should be the greater, 
 the larger the diameter of the latter is. Pipes of very large 
 diameter are best suspended alongside each other, instead of 
 one above the other, a row of anodes of zinc sheet suitably 
 bent being arranged between every two pipes. Frequent turn- 
 ing of the pipes is required, and uniform zincking is promoted 
 by heating the bath and by vigorous agitation. The further 
 manipulation of the zincked pipes is similar to that given for 
 sheets. 
 
 Zincking the insides of the pipes is a more difficult opera- 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 457 
 
 tion. To commence with it is, as rule, a difficult task to find 
 out whether pickling and scratch-brushing has been sufficiently 
 done and a pure metallic surface has everywhere been pro- 
 duced. Special directions for inside zincking depend partly on 
 the diameter, and it can only be said in general that it is best 
 to zinc the pipes while in a vertical or half- lying position and 
 to provide for a constant renewal of the electrolyte in the in- 
 terior. 
 
 Zincking of wrought- iron girders, f-iron, \J-iron, \_-iron, etc. 
 The cheapest plan of freeing the objects from scale is by pick- 
 ling in dilute sulphuric or hydrochloric acid and vigorous 
 scrubbing with sand, or scratch-brushing. The use of a trans- 
 portable sand blast is also very suitable, but this method is 
 more expensive than the former. 
 
 For the uniform zincking of such profiled objects, the use of 
 flat zinc anodes is not practicable, far more zinc being deposited 
 upon the edges and surfaces next to the anodes than upon the 
 depressed portions. Hence, in addition to heating and vigor- 
 ously agitating the bath, recourse must be had to profiled anodes 
 corresponding to the shape of the object to be zincked, the 
 object of such profiled anodes being solely to bring all por- 
 tions of the objects at as nearly an equal distance as possible 
 from the anodes. 
 
 The profiled anodes may be made by bending zinc sheets into 
 the proper shape, or what is better, by riveting or screwing 
 square cast-zinc bars to the zinc sheets, this being of advantage, 
 for instance, in zincking girders. Figs. 139 and 140 show the 
 arrangement of the anodes, and require no further explanation. 
 
 In zincking profiled objects, it is of advantage to add to the 
 bath prepared according to formula I, 0.8 oz. of dextrose per 
 quart, the bath working better in the deeper portions with such 
 an addition than without it. Of still greater advantage is the 
 pyridine- zinc bath according to Goldberg. 
 
 Zincking of wire, steel tapes, cords, etc. — Under this heading 
 will chiefly be considered iron and »steel wire which is to be 
 protected from rust by a deposit of zinc. As previously men- 
 
45S 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 tioned when speaking of nickeling wire, the latter has to be 
 uncoiled and passed at a suitable rate of speed through the 
 pickling solutions and the zinc bath. 
 
 Bright-drawn iron and steel wire, requiring but little prepar- 
 atory work, is most suitable for zinking. It suffices for coils 
 of such wire, when free from rust, to push them upon a shaft 
 of corresponding diameter, and bring the whole into a tank 
 with hot soda lye, which is furnished with bearings for the 
 shaft. From this tank the wire, freed from grease by the hot 
 lye, passes through a few felt rolls or cloth cheeks supplied 
 with thin lime paste, an additional freeing from grease being 
 
 Fig. 139. 
 
 Fig. 140. 
 
 iiiillfiilglllgilgilil 
 
 thus, for the sake of greater security, effected. The wire is 
 then brought under a rose for the removal by water of adhering 
 lye and lime, then slides over a metallic roll which is in contact 
 with the negative pole of the source of current, and passes into 
 the zinc bath. In the latter zinc anodes are arranged below 
 and above the lengths of wires running parallel to each other. 
 Such zinc baths for wire zincking are from 20 to 26 feet long. 
 The average velocity with which wire 0.039 inch in diameter 
 passes through the bath is about 20 feet per minute. For wire 
 of less diameter the velocity may be increased to 59 feet, while 
 
DEPOSITION QF TIN, ZINC, LEAD AND IRON. 459 
 
 for wire of greater diameter it has to be correspondingly de- 
 creased. 
 
 When the wire comes from the bath it is conducted through 
 a tank containing boiling water, and is then reeled up. The 
 contrivances for reeling up the wire are best driven by an 
 electro-motor with the use of a starting resistance for regulating 
 the turns, it being thus possible to choose and change at will 
 the velocity of the passage of the wire in the bath. 
 
 Zincking of wires produced by rolling is not quite so simple. 
 Such wire, which is readily recognized by its black appearance, 
 is coated with a scale, which adheres very firmly by reason of 
 the rolling process. Previous to zincking, such wire has to be 
 carefully freed from scale in order to obtain a purely metallic 
 surface. This may be accomplished in various ways, the 
 method selected depending en the nature and properties of the 
 material to be manipulated. 
 
 Experiments in cleansing such wire by means of the sand 
 blast did not yield satisfactory results, the process being too 
 slow notwithstanding the use of suitable annular blast-pipes. 
 Hence recourse will have to be had to pickling in acids, but 
 many kinds of wire and steel tapes stand pickling only for a 
 very short time, they readily becoming brittle. Wire which 
 does not show this drawback is pickled until the scale is parti- 
 ally dissolved, or at least very much loosened. After rinsing 
 in water, it is immersed in boiling water so that it will dry 
 rapidly and then, for the removal of the loosened scale, passed 
 by means of a suitable contrivance through the scratch-brushing 
 machine. Wire which will not bear pickling at all, or only for 
 a very short time, has to be brightened by mechanical means, 
 either by the drawing-plate, or by conducting it over revolv- 
 ing, hard grindstones or emery wheels provided with insertions 
 for holding it. 
 
 Zincking of screws, nuts, rivets, nails, tacks, etc. Such small 
 objects are freed from grease either by means of the sand blast 
 or in tumbling barrels with the use of wet, sharp sand. When 
 the latter process is employed, the objects have of course to be 
 immediately zincked to prevent rusting. 
 
460 ELECTRO DEPOSITION OF METALS. 
 
 For zincking quantities of such small objects, one of the me- 
 chanical plating contrivances referred to under " Depositions of 
 Nickel " is very suitable. When zincking is effected in baskets 
 the position of the objects has to be frequently changed by 
 stirring in order to insure a uniform deposit. 
 
 The bath prepared according to formula II, when heated, is 
 very well adapted for zincking small objects in large quantities. 
 With the use of a mechanical plating apparatus, it is possible 
 in consequence of the constant agitation, to work with high 
 current- densities and to deposit a correspondingly large quan- 
 tity of zinc in a comparatively short time. 
 
 The further manipulation of the zincked small objects con- 
 sists in washing them in baskets and drying them quickly by 
 immersion in boiling water and shaking with heated clean saw- 
 dust, though the latter operation may be omitted. 
 
 For zincking by contact, see special chapter " Depositions by 
 Contact." 
 
 Zinc alloys. — The production of the principal zinc alloy, 
 brass, by the electric method, having already been mentioned, 
 and also that of a zinc-nickel-copper alloy (German silver), it 
 remains to give an alloy of zinc with tin, or of zinc, tin and 
 nickel, which can be produced by the same means. 
 
 A suitable bath for depositing this alloy consists of: Chlo- 
 ride of zinc 6% drachms, crystallized stannous chloride 9 
 drachms, pulverized tartar 9 drachms, pyrophosphate of soda 
 2 3^ drachms, water I quart. Dissolve the salt at a boiling 
 heat, and filter the cold solution, when it is ready for use. For 
 anodes, cast plates of equal parts of tin and zinc are used. 
 
 These deposits have no special advantages, but, on the other 
 hand, a deposit containing zinc in large excess has the same 
 effect of protecting iron from rust as a deposit of pure zinc. 
 
 By preparing a bath which contains as conducting salt sodium 
 citrate, and ammonium chloride and the chlorides of the metals 
 in the proportion of 4 zinc chloride to 1 tin chloride, a deposit 
 is obtained, which not only is a perfect protection against rust, 
 but also enters far better into depressions than pure zinc. By 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 46 1 
 
 adding to the bath a small quantity of chloride of mercury, or 
 of nickel, alloys of zinc, tin, mercury, or of zinc, tin and nickel 
 are formed, which are distinguished from pure zinc deposits by 
 a finer structure. 
 
 3. Deposition of Lead. 
 
 The properties of lead only interest us in so far as it is less 
 attacked by most mineral acids than any other metal, and ob- 
 jects have been coated with it, in order to protect them against 
 the action of such agents. For decorative purposes electro- 
 deposits of lead are scarcely used, and those as a protection 
 against chemical influences cannot be produced of sufficient 
 thickness for that purpose. 
 
 Lead baths. — I. Dissolve, by continued boiling, caustic pot- 
 ash 1.75 ozs. and finely pulverized litharge 0.17 oz. in 1 quart 
 of water. 
 
 II. According to Watt, the following solution is used : Ace- 
 tate of lead 0.17 oz., acetic acid 0.17 oz , water 1 quart. 
 
 The bath prepared according to formula I deserves the 
 preference. 
 
 Lead baths require anodes of sheet-lead or cast-lead plates, 
 a weak current and, in order to produce a dense deposit of 
 some thickness, the objects have to be frequently scratch- 
 brushed. Iron is best previously coppered. Peroxide of lead 
 is separated on the anodes, and they have to be frequently 
 cleansed with a scratch-brush. The formation of peroxide of 
 lead on the anodes is utilized for the production of the so- 
 called Nobili's rings (electrochromy), which will be mentioned 
 below. 
 
 To coat gun barrels and other articles of steel or iron with 
 peroxide of lead as a protection against rust, suspend the 
 bright articles as anodes in a solution of nitrate of lead mixed 
 with ammonium nitrate. 
 
 Mctallo- chromes {Nobili's rings, iridescent colors, electro- 
 chromy). The reduction of peroxide of lead upon the anodes 
 or upon objects suspended as anodes, produces superb effects 
 
462 ELECTRO-DEPOSITION OF METALS. 
 
 of colors. For the production of such colors, a bath is pre- 
 pared by boiling for half an hour 3^ ozs. of caustic potash, 
 14 drachms of litharge, and I quart of water. The operation 
 is as follows: Suspend the articles, carefully freed from grease 
 and pickled, to the anode-rods, and with a weak current intro- 
 duce in the lead solution a thin platinum wire connected with 
 the object-rod by flexible copper wire, without, however, touch- 
 ing the article. The latter will successively become colored 
 with various shades — yellow, green, red, violet and blue. By 
 the continued action of the current, these colors pass into a 
 discolored brown, which also appears in the beginning if the 
 current be too strong, or the platinum wire be immersed too 
 deep. Such unsuccessful coloration has to be removed by 
 rapidly dipping in nitric acid, and, after rinsing in water, sus- 
 pending the article in the bath. For coloring not too large 
 surfaces, a medium-sized Bunsen cell is, as a rule, sufficient, if 
 the platinum wire be immersed about ^ inch. 
 
 Colors of all possible beautiful contrasts may be obtained by 
 perpendicularly placing between the objects to be colored and 
 the platinum wire a piece of stout parchment paper, or pro- 
 viding the latter with many holes or radial segments. 
 
 Another process of producing these effects of colors is as 
 follows: Prepare a concentrated solution of acetate of lead 
 (sugar of lead), and after filtering, pour it into a shallow por- 
 celain dish. Then immerse a plate of polished steel in the 
 solution, and allow it to rest upon the bottom of the dish. Now 
 connect a small sheet of disc copper with the wire proceeding 
 from the zinc element of a constant battery of two or three cells, 
 the wire connected with the copper element being placed in 
 contact with the sLeel plate. If now the copper disc be brought 
 as close to the steel plate as possible without touching it, in a 
 few moments a series of beautiful prismatic colorations will ap- 
 pear upon the steel surface, when the plate should be removed 
 and rinsed in clean water. These colorations are films of lead 
 in the form of peroxide, and the varied hues are due to the 
 difference in thickness of the precipitated peroxide of lead, the 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 463 
 
 light being reflected through them from the polished metallic 
 surface beneath. By reflected light every prismatic color is 
 visible, and by transmitted light a series of prismatic colors 
 complementary to the first colors will appear occupying the 
 place of the former series. The colors are seen to the greatest 
 perfection by placing the plate before a window with the back 
 to the light, and holding a piece of white paper at such an angle 
 as to be reflected upon its surface. The colorations are not of 
 a fugitive character, but will bear a considerable amount of 
 friction without being removed. In proof of the lead oxide 
 being deposited in films or layers, it may be stated that if the 
 deposit be allowed to proceed a few seconds be} r ond the time 
 when its greatest beauties are exhibited, the coloration will be 
 less marked, and become more or less red, green or brown. If 
 well rubbed, when dry, with the finger or fleshy part of the 
 hand, a rich blue-colored film will be laid bare by the removal 
 of the delicate film above it. 
 
 The plan recommended by Mr. Gassiot to obtain the metallo- 
 chromes is to place over the steel plate a piece of cardboard or 
 parchment paper cut into some regular design, and over this a 
 rim of wood, the copper disc being placed above this. Very 
 beautiful effects are obtained when a piece of fine copper wire 
 is turned up in the form of a ring, star, cross or other pattern, 
 and connected with the positive electrode, this being in fact one 
 of the simplest and readiest methods of obtaining the colorations 
 upon the polished metal. Metallochromy is extensively em- 
 ployed in Nuremberg to ornament metallic toys. It has been 
 adopted in France for coloring bells, and in Switzerland for 
 coloring the hands and dials of watches. In using the lead 
 solutions to produce metallochromes, it must be remembered 
 that metallic lead becomes deposited upon the cathode, conse- 
 quently the solutions in time become exhausted, and must 
 therefore be renewed by the addition of the lead salt. 
 
 For the preparation of iridescent sheets, i. e., nickeled zinc 
 sheets coated with peroxide of lead, a sheet of lead of the same 
 size as the sheets to be made iridescent is used as object, and a 
 
464 ELECTRO-DEPOSITION OF METALS. 
 
 current of about 2^ volts is employed. The slime formed in 
 the bath must from time to time be removed, as otherwise the 
 tones of color will not turn out pure. 
 
 4. Deposition of Iron (Steeling ). 
 
 The principal practical use of the electro-deposition of iron 
 is to coat printing plates of softer metal to increase their wear- 
 ing qualities. We are indebted to Bottger for calling attention 
 to the employment of iron deposits, but notwithstanding the 
 efforts of many scientific and practical men to improve the 
 process, the expectation entirely to replace copper galvano- 
 plasty for cliches by iron-galvanoplasty has not been fulfilled. 
 
 Only such baths as are suitable for steeling will here be 
 given. Solutions for the production of thick iron deposits, and 
 the conditions under which they can be obtained, will be re- 
 ferred to later on under " Galvanoplasty in Steel." 
 
 Iron {steel) baths. I. According to Varrentrapp : Pure green 
 vitriol 4 l /i ozs., ammonium chloride 3^ ozs., water I quart. 
 
 Electro-motive force at 10 cm. electrode-distance 1.0 volt. 
 
 Current-density, 0.2 ampere. 
 
 Boil the water for l / 2 hour to expel all air, and, after cooling, 
 add the green vitriol and ammonium chloride. By the action 
 of the air, and the oxygen appearing on the anodes, this bath 
 is readily decomposed, insoluble basic sulphate of iron being 
 separated as a delicate powder, which has to be frequently re- 
 moved from the fluid by filtering. To decrease decomposition, 
 the double sulphate of iron and ammonium, which can be more 
 readily obtained pure and free from oxide, may be used. 
 
 II. Ammonium chloride 3^ ozs., water 1 quart. 
 
 Electro-motive force at 10 cm. electrode-distance, i.O volt. 
 
 Current- density, 0.2 ampere. 
 
 This neutral solution of ammonium chloride may be made 
 into an iron bath by hanging in it iron sheets as anodes, sus- 
 pending an iron or copper plate as cathode, and allowing the 
 current to circulate until a regular separation of iron is attained, 
 which is generally the case in 5 to 6 hours. Although a sepa- 
 
DEPOSITION OF TIN, ZINC, LEAD AND IRON. 465 
 
 ration of hydrated oxide of iron also takes place in this bath, it 
 does so in a less degree than in that prepared according to 
 formula I. For the production of not too heavy a deposit of 
 iron, some operators claim to have obtained the best results 
 with this bath. 
 
 According to Bottger, the following bath serves for steeling: 
 Ha. Potassium ferrocyanide (yellow prussiate of potash) 0.35 
 oz., Rochelle salt 0.7 oz., distilled water 200 cubic centimeters. 
 To this solution is added a solution of 1.69 drachms of persul- 
 phate of iron in 50 cubic centimeters of water, whereby a 
 moderate separation of Berlin blue takes place. Then add, 
 drop by drop, whilst stirring constantly, solution of caustic 
 soda until the blue precipitate has disappeared. The clear, 
 slightly yellowish solution thus obtained can be used directly 
 for steeling. 
 
 A heavy and very hard deposit of iron is obtained in a bath 
 of the following composition. 
 
 III. Ammonio-ferrous sulphate 1^ ozs., crystallized citric 
 acid 0.88 oz., water I quart; sufficient ammonia for neutral or 
 slightly acid reaction. 
 
 Electro-motive force at 10 cm. electrode-distance, 2.0 volts. 
 
 Current- density , 0.3 ampere. 
 
 Management of iron-baths. — As previously mentioned, the 
 insoluble precipitate from time to time formed in the bath has 
 to be removed by filtration. This precipitate is, however, very 
 delicate, and when stirred up might settle upon the objects and 
 prevent the adherence of the deposit. It is, therefore, advisable 
 to use for steel baths, tanks of much greater depth than corre- 
 sponds to the height of the objects, whereby the stirring-up of 
 the sediment in suspending the objects is best avoided. 
 
 With the use of steel anodes the baths may become readily 
 acid. This can be avoided by suspending a few small linen 
 bags filled with carbonate of magnesia in the bath. On the 
 other hand, anodes of soft iron make the electrolyte alkaline, 
 and when such anodes are employed, the reaction of the bath 
 must from time to time be tested and the neutral reaction be 
 30 
 
466 ELECTRO-DEPOSITION OF METALS. 
 
 restored by the addition of very dilute sulphuric acid, or better, 
 citric acid. 
 
 Deposits produced in an iron bath which has become alka- 
 line show slight hardness, form very rapidly with a matt ap- 
 pearance and have a tendency to peel of. 
 
 Execution of steeling. — The cleansed and pickled objects are 
 placed in the baths according to formulae I and II, with a 
 current of 1.5 to 2 volts, and the anodes at a distance of 4 to 
 4^ inches, after which the current is reduced to I volt. To 
 produce iron deposits of any kind of thickness, the escape of 
 the hydrogen bubbles which settle on the objects must be pro- 
 moted by frequent blows with the finger upon the object-rod. 
 When steeling is finished, the articles are thoroughly rinsed, 
 then plunged into very hot water, and, after drying in sawdust, 
 placed for several hours in a drying chamber heated to about 
 212 F., to expel all moisture from the pores. 
 
 Steeling of printing plates has the advantage over nickeling, 
 that when the plates are worn they can be rapidly freed from 
 the deposit by dilute sulphuric acid or very dilute nitric acid, 
 and resteeled. It has been ascertained by experiments that 
 the capability of resistance of steeled plates is less than that of 
 nickeled plates, 200,000 impressions having been made with 
 the latter without any perceptible wear. 
 
 For steeling printing plates a bath prepared according to 
 formula II or III is very suitable. 
 
CHAPTER XII. 
 
 DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM, 
 i. Deposition of Antimony. 
 
 Properties of antimony. — Electro-deposited antimony pos- 
 sesses a gray luster, while native, fused antimony shows a silver- 
 white color. Antimony is hard, very brittle, and may easily be 
 reduced to powder in a mortar. It melts at 842 F., and at a 
 strong red heat takes fire and burns with a white flame, forming 
 the trioxide. Its specific gravity is 6.8. It is permanent in the 
 air at ordinary temperatures. Cold, dilute, or concentrated 
 sulphuric acid has no effect upon antimony, but the hot con- 
 centrated acid forms sulphide of antimony. By nitric acid the 
 metal is more or less energetically oxidized, according to the 
 strength and temperature of the acid. 
 
 Antimony baths. — Electro-depositions of antimony are but 
 seldom made use of in the industries, though they are very 
 suitable for decorative contrasts. This is no doubt due to the 
 fact that a thoroughly reliable bath yielding deposits without 
 the appearance of drawbacks during the operation is thus far 
 not known. 
 
 For the special study of electro-depositions of antimony we 
 are indebted to Bottger and Gore, the latter having discovered 
 the explosive power of deposits of antimony deposited from a 
 solution containing chloride or hydrochloric acid. 
 
 According to Gore, a bath consisting of tartar emetic 3 ozs., 
 tartaric acid 3 ozs., hydrochloric acid 4^ ozs., and water, 1 
 quart, yields a gray, crystalline deposit of antimony. This bath 
 requires a current of about 3 volts. The deposit possesses the 
 property of exploding when scratched or struck with a hard 
 
 (467) 
 
458 ELECTRO-DEPOSITION OF METALS. 
 
 object. The explosion is attended by a cloud of white vapor, 
 and sometimes by a flash of light, considerable heat being 
 always evolved. This explosibility is due to a content of anti- 
 mony chloride. Bottger found 3 to 5 per cent, of chloride of 
 antimony in the deposit, and Gore 6 per cent. A similar ex- 
 plosive deposit is obtained by electrolyzing a simple solution of 
 chloride of antimony in hydrochloric acid (liquid butter of an- 
 timony, liquor stibii chlorati) with the current. 
 
 A lustrous, non-explosive deposit of antimony is obtained by 
 boiling 4.4 ozs. of carbonate of potash, 2.1 1 ozs. of pulverized 
 antimony sulphide, and I quart of water for I hour, replacing 
 the water lost by evaporation, and filtering. Use the bath 
 boiling hot, employing cast antimony plates or platinum sheets 
 as anodes. 
 
 An antimony bath which yields good results is composed as 
 follows : 
 
 Schlippe's salt I 3^ ozs., water 1 quart. Dissolve the salt in 
 the water. Electro-motive force required, 4 volts. An un- 
 pleasant feature of this bath is that during electrolyzing sul- 
 phuretted hydrogen escapes, which limits its application. 
 
 2. Deposition of Arsenic. 
 
 Properties of arsenic. — Arsenic has a gray-white color, a 
 strong metallic luster, is very brittle, and evaporates at a red 
 heat. In dry air arsenic retains its luster, but soon turns dark 
 in moist air. It is scarcely attacked by dilute hydrochloric 
 and sulphuric acids, while concentrated sulphuric acid, as well 
 as nitric acid, oxidizes it to arsenious acid. If caustic alkalies 
 are fused together with arsenic, a portion of the latter is con- 
 verted into alkaline arsenate. 
 
 Arsenic baths. — Deposits of arsenic are more frequently used 
 than antimony deposits for decorative purposes, in order to 
 produce a blue-gray tone of a certain warmth, which is very 
 effective in combination with bright copper, brass, etc. 
 
 A solution suitable for depositing arsenic upon all kinds of 
 metals is as follows: 
 
DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 469 
 
 I. Pulverized arsenious acid I ^ ozs., crystallized pyrophos- 
 phate of soda 0.7 oz., 98 per cent, potassium cyanide 1 ^ ozs., 
 water 1 quart. 
 
 Dissolve the pyrophosphate of soda, and the potassium 
 cyanide in the cold water, and after adding, whilst stirring, the 
 arsenious acid, heat until the latter is dissolved. In heating, 
 fumes containing prussic acid escape, the inhalation of which 
 must be carefully avoided. The bath is used warm, and requires 
 a vigorous current of at least 4 volts, so that, at the least, 3 
 Bunsen cells have to be coupled for electro-motive force. 
 After suspending the objects they are first colored black-blue, 
 the color passing with the increasing thickness of the deposit 
 into pale blue, and finally into the true arsenic gray. Platinum 
 sheets or carbon plates are to be used as anodes. 
 
 In place of the bath prepared according to formula I, a solu- 
 tion of the following composition may be used : 
 
 II. Sodium arsenate 1 ^ ozs., 98 per cent, potassium cyanide 
 0.8 oz., water 1 quart. Boil the solution for half an hour, then 
 filter and use it at a temperature of at least 167 to 176 F., 
 with a strong current. It yields a good deposit. 
 
 Large baths, to be used cold, must be more concentrated, 
 and require a stronger current than hot baths. 
 
 When the baths begin to work irregularly and sluggishly, 
 they have to be replaced by fresh solutions. 
 
 The same rules as for other electro-plating processes are to 
 be observed in depositing arsenic and antimony. 
 
 However, attention may here be called to one feature 
 which is frequently the cause of defective deposits. When, for 
 instance, mountings of zinc, such as are used for book covers, 
 jewel boxes, etc., are to be provided with a deposit of copper 
 and arsenic, and hence are to show two colors, it is necessary 
 to first copper them. After polishing and cleaning the cop- 
 pered mountings, the places which are not to receive the blue- 
 gray deposit of arsenic are coated with stopping-off varnish. 
 When articles thus treated, after being again freed from grease 
 and pickled, are brought into the arsenic bath, they frequently 
 
470 ELECTRO-DEPOSITION OF METALS. 
 
 show ugly stains the size of a pin-head. This feature, how- 
 ever, does not appear when the articles before being brought 
 into the bath are drawn through water acidulated with a small 
 quantity of nitric acid (about */j oz. of nitric acid to I quart of 
 water), and thoroughly rinsed in clean water. 
 
 Electro-depositions of chromium, tungsten, cadmium and 
 bismuth have thus far not become of any practical importance, 
 and their discussion may, therefore, with good reason, be omit- 
 ted. As regards silver-cadmium deposits the reader is referred 
 to Areas-silvering under " Deposition of Silver." 
 
 3. Deposition of Aluminium. 
 
 There is actually no reason or authority for the heading of 
 this section, but it has been introduced because inquiries are 
 frequently received as to whether baths for the deposition of 
 aluminium can be furnished. 
 
 A number of receipts for the preparation of aluminium baths 
 have been published, but in testing them nothing further could 
 be obtained than the confirmation of the fact that the deposi- 
 tion of aluminium from aqueous solutions of its salts by the 
 current upon the cathode has thus far not been feasible. 
 
 Reports have from time to time appeared in newspapers of 
 the iron construction of tall buildings having been provided 
 with a heavy deposit of aluminium, and even the processes used 
 have been fully described. It is to be regretted that such 
 elaborate reports are even admitted into scientific journals, 
 though the separation of romance from truth could be readily 
 accomplished by a conscientious examination. Unscrupulous 
 dealers offer their customers aluminium baths, charging a high 
 price for them, and on testing a deposit produced with such 
 baths, it has frequently been found to consist solely of tin. 
 Others, who actually had faith in the value of their invention 
 have submitted for examination objects plated with aluminium 
 by their processes. On testing such deposits it was found that 
 in one case, it consisted of a thin deposit of zinc, the origin of 
 
DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 47 1 
 
 which was due to zinckiferous aluminium salts, and in other 
 cases, of a deposit of iron due to the same cause. 
 
 The concurrence of the above-mentioned influences and the 
 recent rapid development of the aluminium industry explains 
 the demand for aluminium baths by many electro-platers. 
 However, without entering into scientific reasons, which would 
 not be within the scope of this work, it can here only be re- 
 peated that the reduction of metallic aluminium from its solu- 
 tions will very likely remain an empty dream. 
 
 4. Depositions upon Aluminium. 
 
 The electro-deposition of other metals upon aluminium pre- 
 sents many difficulties which are chiefly due to the behavior of 
 this metal towards the plating baths. The deposits to be sure 
 are formed, but they possess no adherence, and especially baths 
 containing potassium cyanide yield the worst results in conse- 
 quence of the effect of alkaline solutions upon the basis-metal. 
 Since the production of aluminium has so largely increased, 
 and a great number of articles of luxury and for practical use 
 are now made of this metal, the need of decorating such articles 
 by electro-plating or covering them entirely with other metals 
 has been felt, since the color of aluminium is by no means a 
 sympathetic one. Look into a show window where aluminium 
 articles are exposed — nothing but gray in gray. Offended, the 
 eye of the observer turns away, and seeks a more agreeable 
 resting-place. 
 
 Aluminium behaves so differently from other metals towards 
 the cleansing agents generally used, that different methods from 
 those previously described have to be employed in preparing 
 it for plating. Nitric acid has almost no effect on aluminium, 
 and pickle just a little ; but, on the other hand, the metal is 
 attacked by concentrated hydrochloric acid, dilute hydro- 
 fluoric acid, and especially by alkaline lyes. Hence, if polished 
 articles of aluminium are to be prepared for plating, alkaline 
 lyes will have to be avoided in freeing them from grease, it 
 being best to use only benzine for the purpose. Unpolished 
 
472 ELECTRO-DEPOSITION OF METALS. 
 
 articles may without hesitation be freed from grease with caus- 
 tic potash or soda lye, and, for the production of a dead white 
 surface, be for a short time pickled in dilute hydrofluoric acid, 
 and then thoroughly rinsed in running water. 
 
 For producing an electro-deposit upon aluminium it has been 
 considered advisable to first copper the metal, and the Alu- 
 minium Gesellschaft of Neuhausen recommends for this pur- 
 pose a solution of nitrate of copper. But the adherence of the 
 copper proved also insufficient, because in the subsequent sil- 
 vering, nickeling, etc., the deposit raised up. 
 
 The copper bath recommended by Delval, consisting of 
 sodium pyrophosphate 3 ozs., copper sulphate (blue vitriol) 
 y oz., sodium bisulphite y oz., water 1 quart, also proved 
 unreliable. 
 
 According to another patented process, plating of aluminium 
 is claimed to be effected successfully, and without defect, by 
 lightly coating the metal with silver amalgam by boiling in a 
 silver bath compounded with potassium-mercury cyanide. 
 However, this treatment did not always yield reliable results. 
 
 According to Villon, articles of aluminium are to be im- 
 mersed for one hour in a bath consisting of glycerin $y ozs., 
 zinc cyanide 0.88 oz., zinc iodide 0.88 oz., and then heated to 
 a red heat. When cold, they are washed with a hard brush 
 and water, and brought into the gold or silver bath. The suc- 
 cess of this process seems also questionable. 
 
 The best and most reliable process is without doubt the one 
 patented, in 1893, by Prof. Nees. It consists in first immersing 
 the aluminium articles previously freed from grease in caustic 
 soda lye until the action of the lye upon the metal is recognized 
 by gas bubbles rising to the surface. The articles without 
 being previously rinsed are then for a few minutes immersed in 
 a solution of 77 troy grains of chloride of mercury, rinsed, 
 again brought into the caustic soda lye, and then, without 
 rinsing, suspended in the silver bath. The deposit of silver 
 thus obtained adheres very firmly, and can be scratch-brushed, 
 and polished with the steel without raising up. It can also be 
 
DEPOSITION OF ANTIMONY, ARSENIC, ALUMINIUM. 473 
 
 directly gilded, brassed, or, after previous coppering in the 
 potassium cyanide copper bath, provided with a heavy deposit 
 of nickel and polished upon polishing wheels. 
 
 Burgess and Hambuechen * found it best to first zinc the 
 aluminium in an acid zinc bath containing 1 per cent, fluoric 
 acid ; the fluoric acid acts as a solvent upon the film of oxide 
 formed so that the deposit is effected upon a pure metallic 
 surface. According to these authors, the aluminium article is 
 to be immersed in dilute fluoric acid until its surface appears 
 slightly rough and attacked. It is then to be rinsed in water, 
 and for a few seconds immersed in a bath of sulphuric acid 
 100 parts and nitric acid 75 parts. It is then again thoroughly 
 rinsed in water, next brought into a zinc bath of 15 Be., con- 
 sisting of zinc sulphate and aluminium sulphate, and acidulated 
 with 1 per cent, of fluoric acid or the equivalent quantity of 
 potassium fluoride, and zincked for 15 to 20 minutes. For 
 subsequent silvering or gilding the zinc deposit is first cop- 
 pered in the potassium cyanide copper bath. 
 
 According to Gottig, a thin, firmly-adhering deposit of cop- 
 per is first to be produced upon the aluminium by triturating 
 blue vitriol solution with tin-powder and whiting ; or a tin de- 
 posit is to be produced by applying stannous chloride-ammo- 
 nium chloride solution by means of a soft brass brush. 
 
 The Mannesmann Pipe Works, Germany, produce durable 
 electro-deposits by brushing the aluminium with solutions of 
 sulphide of gold and sulphide of silver in balsam of sulphur f 
 and volatile oils, and burning in the metals in a muffle, under 
 exclusion of the air, at 840 to 930 F. Thin layers of metal 
 which are reduced adhere firmly to the aluminium, and are 
 then provided with any electro-deposit desired. According to 
 a process patented by the same corporation, the articles are 
 provided with a firmly adhering (?) film of zinc by immersing 
 them in boiling solution of zinc dust in caustic soda, and are 
 then electro-plated. 
 
 * Electro-chemical Industry, 1904, No. 3. 
 f Solution of sulphur in linseed oil. 
 
474 ELECTRO-DEPOSITION OF METALS. 
 
 However, in view of the fact that all the methods mentioned 
 above partly yield uncertain results, it has recently been pro- 
 posed first to provide the aluminium in readily-fusible metallic 
 salts (cupric chloride, tin salt) with a coat of these metals, and 
 then treat it further in aqueous electrolytes. 
 
CHAPTER XIII. 
 
 DEPOSITION BY CONTACT, BY BOILING, AND BY FRICTION. 
 
 If a sheet of metal, for instance, copper, be brought into 
 a solution which contains the kathions of a metal of slighter 
 solution-pressure (p. 60), for example, a solution of potassium- 
 silver cyanide in water with an excess of potassium cyanide, 
 which has been heated to about 158 F., the following process 
 takes place: By the osmotic pressure (p. 48) the metal-ions, in 
 this case silver-ions, are reduced upon the copper sheet, the 
 osmotic pressure of the solution being thereby decreased. In 
 consequence of this decrease in the osmotic pressure, copper- 
 ions can be forced into the solution by the solution-pressure, 
 while additional silver-ions are brought to separate upon the 
 copper sheet. Hence, during the formation of the deposit, a 
 solution of the metal to be coated in the case in question, cop- 
 per, takes place at the same time, this process coming to a 
 standstill when the copper sheet has been covered with an co- 
 herent coat of silver, which prevents further solution of copper 
 in the electrolyte. 
 
 The process may also be explained in a different way, 
 namely, that by the immersion in the silver solution the copper 
 is negatively charged, positive silver-ions being by reason of 
 electro-static attraction attracted and reduced on the copper. 
 
 The deposits produced in this manner are generally known 
 as deposits by immersion, or when the electrolyte is highly 
 heated, by boiling. 
 
 The same process takes place when metallic objects are 
 plated by applying by means of a brash or by friction an 
 electrolyte which contains a metal with slighter solution-pressure 
 than possessed by the metal of an object to be coated. 
 
 (475) 
 
476 ELECTRO-DEPOSITION OF METALS. 
 
 Since the more electro-positive metals of the old series of 
 electro-motive force possess a greater solution-pressure than 
 the electro-negative metals, it may be briefly stated, that 
 electro-positive metals when immersed in suitable solutions of 
 electro- negative metals reduce the latter, and, under certain 
 conditions, become coated with them so that a coherent de- 
 posit is formed. 
 
 From the process above described, according to which re- 
 duction only takes place till the electro-positive metal has been 
 provided with a coherent coating of the electro-negative metal, 
 it is plain that such deposits can be only very thin and cannot 
 be increased by continued action of the electrolyte, except re- 
 course be had to other means. 
 
 The process, however, is a different one when a deposit is to 
 be produced by the contact of one metal with another in an 
 electrolyte. If a copper sheet dipping in a potassium cyanide 
 solution of potassium-silver cyanide be touched with an electro- 
 positive metal, for instance, a zinc rod or a zinc sheet, the 
 latter dipping also in the electrolyte, an electric current is 
 generated which reduces silver-ions on the copper sheet, while 
 on the zinc sheet zinc-ions are forced into solution. However, 
 even when the copper sheet has been covered with a coherent 
 deposit of silver, the reduction of the latter goes on in so far as 
 the silver which is also reduced upon the zinc, and which 
 interrupts contact with the electrolyte, as well as prevents fur- 
 ther migration of zinc-ions into the solution, is only from time 
 to time removed. 
 
 The contact processes can, however, be applied only to a 
 limited extent. On the one hand, the formation of uniformly 
 heavy deposits upon the metallic objects is excluded, because 
 by reason of the greater current-densities appearing at the 
 point of contact with the contact metal, a heavier reduction of 
 metal takes place there than on the portions further removed 
 from the point of contact, except the latter be frequently 
 changed. On the other hand, the constant increase of dis- 
 solved contact-metal in the electrolyte constitutes a drawback, 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 477 
 
 and is the cause of the electrolytes, as a rule, giving out long 
 before their content of metal is exhausted. Finally, the reduc- 
 tion of metal upon the contact-metal is not a desirable feature. 
 
 As contact-metals, zinc, cadmium and aluminium are chiefly 
 used. In many cases, aluminium being a highly positive metal, 
 considerably surpasses in its effect the first-mentioned metals, 
 and possesses the advantage of not bringing into the electro- 
 lyte, metals reducible by the current. Furthermore the quanti- 
 ties of metal deposited upon the aluminium can be dissolved 
 with nitric acid without materially attacking the contact-metal. 
 Darlay has recently recommended magnesium as a contact- 
 metal (German patent 127,464). It presents, however, no ad- 
 vantage, on the one hand, on account of its high price and, on 
 the other, by reason of the deficient results in connection with 
 the baths of the above-mentioned patent. 
 
 The electrolytes serving for depositions by contact must pos- 
 sess definite properties if they are to yield good results. 
 
 Since the currents generated by contact are weak, the electro- 
 lyte should possess good conductivity so that the reduction of 
 metal does not take place too slowly, and it must attack — 
 chemically dissolve — the contact-metal, as a current can only 
 be generated if such be the case. Let us consider, for instance, 
 a well-known gold bath for hot gilding by contact, which con- 
 tains in 1 quart of water: jj grains of crystallized sodium 
 phosphate, 46^ grains of caustic potash, i$% grains of neutral 
 chloride of gold, and 0.56 oz. of 98 per cent, potassium cyanide. 
 It will be found that only a slight portion of the potassium 
 cyanide is consumed for the conversion of the chloride of gold 
 into potassium-gold cyanide, the greater portion of it serving 
 to increase the conductivity of the electrolyte. The caustic 
 potash, together with the sodium phosphate, effects the alka- 
 linity of the bath which is required for attacking and dissolving 
 the contact-metal, whether it be zinc, cadmium, aluminium, 
 or magnesium. The effect of the alkaline phosphate as such, 
 is claimed to be that the deposit of metal which results not 
 only upon the objects in contact with the contact-metal, but 
 
478 ELECTRO-DEPOSITION OF METALS. 
 
 also upon the latter itself, does not firmly combine with it, but 
 can be readily removed by scratch-brushing. 
 
 For increasing the conductivity of electrolytes containing 
 potassium cyanide, a greater or smaller excess of the latter is 
 used either by itself or in combination with chlorides, for in- 
 stance, ammonium chloride or sodium chloride, nearly all 
 known baths for contact-deposition containing these salts in 
 varying quantities. For nickel and cobalt baths, an addition 
 of ammonium chloride, in not too small quantity, is most suit- 
 able, it assisting materially the attack upon the contact-metal 
 and may in some cases serve for this purpose by itself without 
 the co-operation of an alkali. 
 
 The attack on the contact-metal is most effectually promoted 
 by sufficient alkalinity of the electrolyte, mostly in connection 
 with chlorides, in a few rarer cases without chlorides, and as 
 previously mentioned, occasionally by chlorides alone without 
 the co-operation of an alkali. 
 
 In judging the formulas for contact baths to be given later 
 on, the effects here explained will have to serve as a basis. 
 
 Small objects in quantities are generally plated in baskets 
 made of the contact-metal, and, as previously mentioned, the 
 deposition of quantities of the same metal with which the 
 objects are to be coated upon the contact-body cannot be 
 avoided. To be sure, claim is made in a few patents to pre- 
 vent deposition upon the contact-metal and to keep the con- 
 tact-body free by certain additions, for instance, alkaline pyro- 
 phosphates and phosphates, but experiments failed to prove 
 the correctness of these claims. 
 
 The useless reduction of metal is one of the many weak 
 points of the contact-process. The bath thereby becomes 
 rapidly poor in metal, requires frequent refreshing or regenera- 
 tion, which as a rule is not so readily done, and thus in prac- 
 tice the contact-process becomes quite expensive. It must 
 further be borne in mind that so soon as reduction of metal 
 upon the contact-body takes place, the formation of a deposit 
 upon the object ceases, this being the reason why only very 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 479 
 
 thin deposits can be produced, which do not afford protection 
 against atmospheric influences, and are not sufficiently resistant 
 to mechanical attack. 
 
 To avoid as much as possible the drawback of metal being 
 reduced on the wrong place, Dr. G. Langbein & Co. use, ac- 
 cording to a method for which a patent has been applied for, 
 baskets of contact-metal, the outsides of the latter, which do 
 not come in contact with the objects, being insulated from the 
 electrolyte by enameling, or coating with hard rubber, cellu- 
 loid or similar materials capable of resisting the hot solution. 
 Or, they use baskets of contact-metal the outsides of which are 
 provided, either mechanically by rolling or welding, or electro- 
 lytically by deposition, with the same metal contained in solu- 
 tion in the electrolyte, the baskets being thus protected from 
 the deposit; while, in addition, a partial regeneration of the bath 
 is in many cases attained. With certain combinations a por- 
 tion of the electro-negative metal or alloy combined with the 
 contact-metal or fixed insulated from it, passes into solution, 
 and partly replaces the metal which has been withdrawn from 
 the bath and deposited upon the objects. 
 
 Further drawbacks of the contact process are, working with 
 baths almost boiling hot, and the consequent evolution of 
 steam which is injurious to the workmen as well as to the work- 
 rooms. 
 
 Hence, the contact process is suitable only for coating — so 
 to say coloring — objects in large quantities with another metal, 
 when no demands as regards solidity of the deposit are made. 
 
 Nickeling by Contact and Boiling. 
 
 Franz Stolba has described a nickeling process by contact, 
 which is executed as follows : 
 
 In a bright copper kettle heat to boiling a concentrated solu- 
 tion of zinc chloride with an equal or double the volume of 
 soft water, and then add, drop by drop, pure hydrochloric acid 
 until the precipitate formed by diluting the zinc chloride solu- 
 tion with water disappears. Then add as much zinc powder as 
 
480 ELECTRO-DEPOSITION OF METALS. 
 
 will lie upon the point of a knife, the effect of this addition 
 being that the copper of the kettle so far as it comes in contact 
 with the solution is in a few minutes zincked. Now bring into 
 the kettle sufficient nickel salt, best nickel sulphate, to color 
 the fluid perceptibly green. Then introduce the articles to be 
 nickeled together with small pieces of sheet-zinc or zinc wire, 
 so as to present many points of contact, and continue boiling. 
 With a correct execution of the process it is claimed the articles 
 will be uniformly nickeled in 15 minutes. If such be not the 
 case, the boiling must be continued, fresh pieces of zinc added, 
 or, if the solution does not appear sufficiently green, fresh nickel 
 salt introduced. 
 
 For the success of the process several conditions are neces- 
 sary. The metallic articles must be thoroughly freed from 
 grease, as otherwise no deposit of nickel is formed on the 
 greasy places. In boiling, the solution must not become turbid 
 by the separation of basic zinc salt, nor acid, by free hydro- 
 chloric acid, otherwise the nickeling will be dull and blackish. 
 Hence, any turbidity must be at once removed by adding, drop 
 by drop, hydrochloric acid, and too great acidity, by the care- 
 ful addition of solution of carbonate of soda. The articles thus 
 nickeled are to be thoroughly washed with water, dried, and 
 polished with whiting. 
 
 Since stains are readily formed by this process, especially 
 when nickeling polished iron and steel articles, on the places 
 where the metal to be nickeled comes in contact with the zinc, 
 Stolba in later experiments omitted the zinc, and thus the con- 
 tact process becomes a boiling process. To a 10 per cent, 
 solution of zinc chloride add enough nickel sulphate to give the 
 solution a deep green color and then heat, best in a porcelain 
 vessel, to the boiling-point. Then without troubling about the 
 turbidity of the bath caused by the separation of a basic zinc 
 salt, immerse in it the objects, previously cleansed and freed 
 from grease, in such a way that they do not touch each other, 
 or at least in only a few places, and keep the whole boiling 30 
 to 60 minutes, from time to time replacing the water lost by 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 481 
 
 evaporation. The after-treatment is the same as given above 
 for the contact process. The deposit of nickel is, of course, 
 very thin. 
 
 Objects of steel, especially of hardened steel, resist nickeling 
 by boiling, and remain free from nickel even after boiling for 
 several hours. However, by using in place of the 10 per cent, 
 chloride of zinc solution, concentrated solution of chloride of 
 zinc, nickeling is claimed to be effected in half an hour. 
 
 However, Stolba's process cannot be recommended to the 
 nickel-plater. To be sure a thin nickel deposit of a light color 
 may be obtained upon brass articles, but that on iron articles 
 generally turned out dark and mostly stained. The process 
 may be suitable for the amateur but for professional work the 
 results are not sufficiently sure. Besides, it is necessary to 
 place the boiled iron and steel articles for several hours in lime 
 water to remove the zinc chloride lye and prevent its rust- 
 producing effect. The nickeling is so thin that it will not stand 
 polishing with vigorous pressure, and the cheapness of the pro- 
 cess is believed to be quite illusive, the solution soon becoming 
 useless by reason of the absorption of copper, iron, etc., from 
 the metals to be nickeled. 
 
 If small objects are positively not to be nickeled with the 
 current, one of the following processes is to be preferred. 
 
 By boiling a solution of 8)4 ozs. of nickel-ammonium sul- 
 phate and 8 x / 2 ozs. of ammonium chloride in 1 quart of water, 
 together with clean iron filings free from grease, and introduc- 
 ing into the fluid copper or brass articles, the latter become 
 coated with a thin layer of nickel capable of bearing light 
 polishing. 
 
 In place of iron filings, it is of greater advantage to bring the 
 objects to be coated in contact with a piece of zinc sheet of 
 not too small a surface, or to nickel them in an aluminium 
 basket. The hotter the solution is, the more rapidly coating 
 with nickel is effected, and when the bath is made slightly 
 alkaline with ammonia, iron objects also nickel quite well in an 
 aluminium basket. 
 31 
 
482 ELECTRO-DEPOSITION OF METALS. 
 
 In place of the zinc-contact, Basse & Selve use an aluminium 
 contact for nickeling (as well as for coppering and silvering). 
 According to the patent specification, objects nickel gray and 
 show no metallic luster when brought in a zinc basket into a 
 boiling solution of 20 parts of nickel-ammonium sulphate, 40 
 parts ammonium chloride and 60 parts water, which, after the 
 addition of a slight excess of ammonia and filtering, is rendered 
 slightly acid with citric acid. By substituting for the zinc 
 basket an aluminium basket, a lustrous, more firmly adhering 
 layer of nickel is in about two minutes obtained. 
 
 Still better results are obtained by keeping the bath slighly 
 alkaline with ammonia or ammonium carbonate. 
 
 A. Darlay has patented in France as well as in Germany a 
 process of nickeling (as well as cobalting) by aluminium or 
 magnesium contact. However, the object of the invention is 
 not the aluminium-contact, which has been known for a long 
 time, nor the special kinds of baths, the compositions of which 
 are similar to that of other known contact-baths, but the use of 
 the aluminium or magnesium contact in connection with baths 
 of exactly defined compositions. 
 
 These patented baths fulfil nothing further than the general 
 conditions given in detail on p. 476 et. seq., and which are also 
 fulfilled by most of the long known contact-baths as shown by 
 the bath for gilding by contact (p. 477). Darlay's patent is, 
 therefore, a combination-patent, and its right of existence ap- 
 pears rather doubtful in view of the fact that Basse and Selve's 
 patent has expired, and that baths of the composition of the 
 Darlay electrolytes have long been known and used for 
 deposition. 
 
 Darlay's baths are brought into commerce by " Elcctro- 
 metallurgie " under the name of autovolt baths, and in answer 
 to many inquiries it may here be stated that for the reason 
 given on p. 476, no heavier deposits can be produced with 
 these autovolt baths, than with the contact process in general, 
 and that this autovolt method shows the same drawbacks as all 
 other contact processes. 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 483 
 
 In his patent specification, Darlay gives the following com- 
 position of the electrolyte which is to be used hot : 
 
 Water 1 quart, nickel chloride 7*^ drachms, sodium phos- 
 phate 83^ ozs., ammonium chloride 11^ drachms, ammonium 
 carbonate and sodium carbonate each 4^ drachms. 
 
 The sodium phosphate is claimed to effect the production of 
 a bright attacking surface of the contact-metal, and the sodium 
 and ammonium carbonates, the alkaline reaction and, hence 
 the generation of the current, by dissolving the aluminium, 
 while the ammonium chloride produces good conductivity. As 
 regards the action of alkaline pyrophosphates, the reader is 
 referred to p. 477. 
 
 The inventor asserts that the proportions given above have 
 to be kept within quite narrow limits. With the exception of 
 the nickel chloride, the quantities of sodium phosphate and of 
 one of the other chemicals can without fear be increased 50 per 
 cent., the results thus obtained being still better than with 
 Darlny's formula. 
 
 The chemical process of Darlay's electrolyte consists no 
 doubt in that a transposition takes place between the nickel 
 chloride and the sodium phosphate, sodium chloride and nickel 
 phosphate being formed, which are soluble in the excess of 
 sodium phosphate, and are not precipitated by the alkaline 
 carbonates. 
 
 Hence the bath given on p. 258 under formula IX for nickel- 
 ing with an external source of current, should be suitable for 
 contact-nickeling with aluminium, if the quantity of sodium 
 phosphate be materially increased, the conductivity enhanced 
 by the addition of ammonium chloride, and the solution of the 
 aluminium promoted by adding caustic potash, caustic soda, or 
 better, alkaline carbonates. 
 
 Cobalting by Contact and Boiling. 
 
 Cobalting by contact is readily accomplished with the use of 
 the following bath: Crystallized cobalt sulphate 0.35 oz., crys- 
 tallized ammonium chloride 0.07 oz., water 1 quart. Heat the 
 
484 ELECTRO-DEPOSITION OF METALS. 
 
 bath to between 104 and 122 F., and immerse the previously 
 cleansed and pickled articles in it, bringing them in contact 
 with a bright zinc surface not too small ; for small articles a 
 zinc basket may be used. In 3 or 4 minutes the coating is 
 heavy enough to bear vigorous polishing. 
 
 It is a remarkable fact that with aluminium-contact no satis- 
 factory results are obtained in this bath, the reaction of alumi- 
 nium in cobalt solutions thus appearing to be different from 
 that in nickel solutions. What has been said in regard to Dar- 
 lay's contact process for nickeling applies also to cobalting. 
 
 For cobalting small objects in quantities, the reader is 
 referred to Warren's process, p. 319. 
 
 Coppering by Contact and Dipping. 
 
 According to Ludersdorff, a solution of tartrate of copper in 
 neutral potassium tartrate serves for this purpose. A suitable 
 modification of this bath is as follows: Heat 10 quarts of water 
 to 140 F., add 2 lbs. of pulverized tartar (cream of tartar) free 
 from lime, and lOyi ozs. of carbonate of copper. Keep the 
 fluid at the temperature above mentioned until the evolution of 
 gas due to the decomposition of the carbonate of copper ceases, 
 and then add in small portions, and with constant stirring, pure 
 whiting until effervescence is no longer perceptible. Filter off 
 the fluid from the tartrate of lime, separate and wash the precipi- 
 tate, so that the filtrate, inclusive of the wash water, amounts to 
 10 or 12 quarts, and dissolve in it 1^ ozs. of caustic soda and 
 1 oz. of 99 per cent, potassium cyanide. 
 
 With zinc-contact the bath works somewhat slowly, but more 
 rapidly with aluminium-contact. Zinc is coppered in this bath 
 by simple immersion. 
 
 The bath for coppering by contact, proposed by Weill, has 
 been given on p. 329, under formula X. The bath is to be 
 heated to between 1 8 5 ° and 194 F., and with zinc contact 
 yields a tolerably good deposit upon small iron objects. With 
 aluminium-contact, iron screws as well as iron articles in quan- 
 tities are quickly and nicely coppered. 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 485 
 
 According to Bacco, a copper bath in which zinc may be 
 coppered by immersion, and iron and other metals in contact 
 with zinc, is prepared by adding to a saturated solution of blue 
 vitriol, potassium cyanide solution until the precipitate of 
 cyanide of copper which is formed is again dissolved. Then 
 add T V to \ of the volume of liquid ammonia and dilute with 
 water to 7 Be. 
 
 The bath is to be heated to 194 F. To the same ex- 
 tent as zinc passes into solution the copper bath is gradually 
 changed to a brass bath. 
 
 Every strongly alkaline copper cyanide bath may serve for 
 coppering by contact, provided only a small quantity of free 
 potassium cyanide is present in the bath, and the latter is 
 heated to 194 F. 
 
 Zinc when used as a contact-metal shows the drawback of 
 the copper depositing quite firmly upon it, so that it has to be 
 removed by pickling in nitric acid. Furthermore, with the use 
 of zinc as contact-bodies, the content of free alkali has to be 
 much larger than with aluminium contacts, and so much zinc 
 passes, in the first case, into solution that, in place of copper 
 deposits, brass deposits with tones of color varying according 
 to the temperature are in a short time obtained. 
 
 According to Darlay's patent, an alkaline copper cyanide 
 bath heated to between 185 and 194 F. is to be used, the 
 electrolyte consisting of: 
 
 Water 1 quart, cupric sulphate 0.35 oz., potassium cyanide 
 0.42 oz., caustic soda 0.52 oz. 
 
 When in such formulas the quantity of potassium cyanide is 
 given without stating its content in per cent., it would, as a 
 rule, be understood to refer to the 98 or 99 per cent, article. 
 However, according to experiments made with Bacco's bath, 
 with the use of 98 per cent, potassium cyanide, the excess 
 would be too large, and it may be supposed that Darlay's for- 
 mula refers to 60 per cent, potassium cyanide. 
 
 However, in this respect, the patent specification does not 
 agree with the facts. For instance, the content of potassium 
 
486 ELECTRO-DEPOSITION OF METALS. 
 
 cyanide " is exactly to be adhered to " in order to prevent 
 a deposit of copper upon the contact-body — an aluminium 
 basket. However, no matter whether potassium cyanide with 
 a content of 60 per cent., or more is used, a heavy deposit 
 of copper is always formed upon the aluminium,* and the for- 
 mation of a deposit of copper upon the objects is not in the 
 least dependent upon adhering exactly to the quantity of potas- 
 sium cyanide given. 
 
 The chemical process of Darlay's formula consists therefore 
 in the conversion of cupric sulphate and potassium cyanide to 
 potassium-copper cyanide. With the use of 68 per cent, potas- 
 sium cyanide scarcely any free potassium cyanide is contained 
 in the bath, while with 98 per cent, potassium cyanide, free 
 potassium cyanide remains in the bath. If, now "the accur- 
 ately-fixed content of potassium cyanide" in Darlay's formula 
 refers to the 60 per cent, article, we come back to Bacco's 
 formula, in which just enough potassium cyanide is added to 
 the cupric sulphate solution to redissolve the separated cupro- 
 cupric cyanide, a content of free potassium cyanide being 
 avoided. Bacco effects alkalinity by ammonia and Darlay by 
 caustic soda. From this it will be seen that Darlay's formula 
 is very similar to Bacco's, and it is doubtful whether a patent- 
 right can be claimed on the substitution of caustic soda for 
 ammonia. At any rate, now that Basse and Selve's patent has 
 expired, it is obvious that Bacco's bath with the use of alu- 
 minium-contact can be employed for coppering by contact 
 without infringing on Darlay's patent. 
 
 The so-called brush-coppering, which has been recommended, 
 may here be mentioned. This process may be of practical 
 advantage for coppering very large objects which by another 
 method could only be coated with difficulty. The deposit of 
 copper is, of course, very thin. The process is executed as 
 follows: The utensils required are two vessels of sufficient size, 
 
 * According to experiments made by Friessner, about 90 per cent, of the metal 
 contained in the bath was deposited upon the contact-body, and only 10 per cent, 
 upon the objects. 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 487 
 
 each provided with a brush, preferably so wide that the entire 
 surface of the object to be treated can be coated with one ap- 
 plication. One of the vessels contains a strongly saturated 
 solution of caustic soda, and the other a strongly saturated solu- 
 tion of blue vitriol. For coppering, the well-cleansed object is 
 first uniformly coated with a brushful of the caustic soda solu- 
 tion, and then also with a brushful of the blue vitriol solution. 
 A quite thick film of copper is immediately deposited upon the 
 object. Care must be had not to have the brush too full, and 
 not to touch the places once gone over the second time, as 
 otherwise the layer of copper does not adhere firmly. 
 
 Many iron and steel objects, for instance, wire, springs, etc., 
 are provided with a thin film of copper in order to give them 
 a more pleasing appearance. For this purpose a copper solu- 
 tion of 10 quarts of water, 1 ^ ozs. of blue vitriol, and I ^ ozs. 
 of pure concentrated sulphuric acid may be used. Dip the 
 iron or steel objects, previously freed from grease and oxide, 
 for a moment in the solution, moving them constantly to and 
 fro; then rinse them immediately in ample water, and dry. 
 By keeping the articles too long in the solution the copper 
 separates in a pulverulent form, and does not adhere. 
 
 Steel pens, needles' eyes, etc., may be coppered by diluting the 
 copper solution just mentioned with double the quantity of 
 water, moistening sawdust with the solution, and revolving the 
 latter, together with the objects to be coppered, in a wooden 
 tumbling barrel. 
 
 Brassing by Contact. 
 
 Some older authors have given formulas for baths for brass- 
 ing by contact, but the results obtained are not very satisfactory. 
 
 Darlay has patented the bath given below. It is brought 
 into commerce under the name of antovolt brass bath, and 
 yields thin brass deposits of an agreeable color and good luster: 
 
 Water I quart, cupric sulphate 0.14 oz., zinc sulphate 0.35 
 oz., potassium cyanide 0.44 oz., caustic soda 0.52 oz. 
 
 On testing this formula it was found that with the use of 98 
 per cent, potassium cyanide the bath yielded no deposit, one 
 
488 ELECTRO-DEPOSITION OF METALS. 
 
 being, however, obtained with the 60 per cent, article. What 
 has been said in reference to the autovolt copper bath applies 
 also to the brass bath. 
 
 As previously mentioned, deposits produced by contact can- 
 not be obtained of any thickness, the contact-metal soon be- 
 coming covered with a deposit when the process comes to a 
 standstill. Aluminium, to be sure, relinquishes the deposited 
 metal in coherent laminae, this being promoted by the heavy 
 evolution of hydrogen. However, it shows also how large are 
 the quantities of metal which are deposited upon the aluminium, 
 and that deposition by contact is consequently connected with 
 a waste of metallic salts, which considerably increases the cost 
 of manufacture. For removing the deposit upon the aluminium 
 body, mixtures of nitric and sulphuric acids have to be used* 
 so that, in addition to the loss of metal, there is a considerable 
 consumption of acids. 
 
 Iron objects brassed in the above-mentioned baths have, to 
 be sure, quite a neat appearance, but soon commence to rust, 
 and for this reason cannot serve as substitutes for objects 
 thickly brassed by means of an external source of current. 
 
 Silvering by Contact, Immersion and Friction. 
 
 For contact-silvering of copper and brass objects the follow- 
 ing bath may be used : 
 
 Water I quart, crystallized silver nitrate 0.52 oz., 60 per cent, 
 potassium cyanide 1.4 oz. 
 
 The bath is to be somewhat heated, so that deposition does 
 not take place too slowly. Zinc is very suitable for a contact- 
 metal, but to avoid formation of stains, the contact-points have 
 to be frequently changed. 
 
 If iron articles are to be silvered, it is recommended to add 
 to the bath, heated to between 176 and 194 F., about 0.28 to 
 0.35 oz. of caustic soda, and to use an aluminium contact; for 
 smaller objects in quantities an aluminium basket. It is of 
 greater advantage, in all cases, first to brass or copper the iron 
 objects. 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 489 
 
 According to Darlay's German patent. 128,318, the follow- 
 ing baths serve for silvering by contact with aluminium : 
 
 Water 1 liter (2.1 1 pints), silver nitrate 20 grammes (0.7 oz.), 
 potassium cyanide 10 grammes (0.35 oz.), caustic potash 4 
 grammes (0.14 oz.). 
 
 Information regarding the content in per cent, for potassium 
 cyanide is wanting. Besides, the quantity of potassium cya- 
 nide in proportion to silver nitrate is too low, which may be 
 due to a typographical error, and it may be supposed that the 
 formula for a 25-liter bath, as given in the patent specification, 
 should read 0.05 kilogramme of silver nitrate instead of 0.5 
 kilogramme. This, calculated to 1 liter, gives 2 grammes in- 
 stead of 20 grammes of silver nitrate. 
 
 For silvering iron and steel in hot baths : 
 
 Water 1 quart, silver nitrate 0.44 oz., potassium cyanide 4.4 
 ozs., sodium phosphate 0.88 oz. 
 
 The object of the sodium phosphate here is not to prevent 
 the adhesion of the metal deposited upon the contact metal, 
 which is to be effected by the excess of potassium cyanide. 
 However, in experiments made with this bath, more silver was 
 deposited upon the contact-body than upon the objects. 
 
 Silvering by immersion. — For silvering coppered or brassed 
 objects by immersion, the following solution may be used : 
 
 Water 1 quart, silver nitrate 0.35 ozs., 98 per cent, potassium 
 cyanide 1.23 ozs. 
 
 To prepare the bath dissolve the silver salt in 1 pint of the 
 water, then the potassium cyanide in the remaining pint of 
 water, and mix the two solutions. The bath is heated in a 
 porcelain or enameled iron vessel to between 176 and 194° F., 
 and the thoroughly cleansed and pickled objects are immersed 
 in it until uniformly coated, previous quicking being not re- 
 quired. The deposit is lustrous if the articles are left but a 
 short time in the bath, but becomes dull when they remain 
 longer. In the first case the deposit is a mere film, and, while 
 it is somewhat thicker in the latter, it can under no circum- 
 stances be called solid. The thickness of the deposit does not 
 
49Q 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 increase by continued action, as much metal being dissolved as 
 silver is deposited, and the silver deposit prevents a further 
 dissolving effect upon the basis metal. 
 
 The bath gradually works less effectively, and finally ceases 
 to silver, when its action may be restored by the addition of 2^ 
 to 5^ drachms of potassium cyanide per quart. Should this 
 prove ineffectual, the content of silver is nearly exhausted, and 
 the bath is evaporated to dryness, and the residue added to the 
 silver waste. Frequent refreshing of the bath with silver salt 
 cannot be recommended, the silvering always turning out best 
 in a fresh bath. 
 
 A solution of nitrate of silver in sodium sulphite is, accord- 
 
 Fig. 141. 
 
 ing to Roseleur, very suitable for silvering by immersion. The 
 solution is prepared by pouring into moderately concentrated 
 solution of sodium phosphite, while constantly stirring, solution 
 of a silver salt until the precipitate of silver sulphide formed 
 begins to be dissolved with difficulty. The bath can be used 
 cold or warm, fresh solution of silver being added when it com- 
 mences to lose its effect. If, however, the bath is not capable 
 of dissolving the silver sulphide formed, concentrated solution 
 of sodium sulphite has to be added. 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 49 1 
 
 For the preparation of the solution of sodium sulphite, Rose- 
 leur recommends the following method : 
 
 Into a tall vessel of glass or porcelain (Fig. 141) introduce 5 
 quarts of water and 4 pounds of crystallized soda, after pour- 
 ing in mercury about an inch or so deep to prevent the glass 
 tube through which the sulphurous acid is introduced from 
 being stopped up by crystals. The sulphurous acid is evolved 
 by heating copper turnings with concentrated sulphuric acid, 
 washing the gas in a Woulff bottle filled an inch or so deep 
 with water, and introducing it into the bottle containing the 
 soda solution, as shown in the illustration. A part of the soda 
 becomes transformed into sodium sulphite, which dissolves, 
 and a part is precipitated as carbonate. The latter, however, 
 .is transformed into sodium sulphite by the continuous action 
 of sulphurous acid, and carbonic acid gas escapes with efferves- 
 cence. When all has become dissolved, the introduction of 
 sulphurous acid should be continued until the liquid slightly 
 reddens blue litmus paper, when it is set aside for 24 hours. 
 At the end of that time a certain quantity of crystals will be 
 found upon the mercury, and the liquid above, more or less 
 colored, constitutes the sodium sulphite of the silvering bath. 
 The liquid sodium sulphite thus prepared should be stirred 
 with a glass rod, to eliminate the carbonic acid which may still 
 remain in it. The liquid should then be again tested with blue 
 litmus paper, and if the latter is strongly reddened, carbonate 
 of soda is cautiously added, little by little, in order to neutralize 
 the excess of sulphurous acid. On the other hand, if red litmus 
 paper becomes blue, too much alkali is present, and more 
 sulphurous acid gas must be passed through the liquid, which 
 is in the best condition for our work when it turns litmus paper 
 violet or slightly red. The solution should mark from 22° to 
 20° Be., and should not come in contact with iron, zinc, tin, or 
 lead. 
 
 As will be seen, this mode of preparing the sodium sulphite 
 solution is somewhat troublesome, and it is therefore recom- 
 mended to proceed as follows : Prepare a saturated solution of 
 
492 ELECTRO-DEPOSITION OF METALS. 
 
 commercial sodium sulphite. The solution will show an alka- 
 line reaction, the commercial salt frequently containing some 
 sodium carbonate. To this solution add, while stirring, solu- 
 tion of bisulphite of sodium saturated at 122° F., until blue 
 litmus paper is slightly reddened. Then add to this solution 
 concentrated solution of nitrate of silver until the flakes of sil- 
 ver sulphide separated begin to dissolve with difficulty. 
 
 The immersion-bath, prepared according to one or the other 
 method, works well, the silvering produced having a beautiful 
 luster, such as is desirable for many cheap articles. If the 
 articles are allowed to remain for a longer time in the bat-h, a 
 matt deposit is obtained. For bright silvering, the bath should 
 always be used cold. It must further be protected as much as 
 possible from the light, otherwise gradual decomposition takes 
 place. 
 
 According to Dr. Ebermayer, a silver immersion-bath for 
 bright silvering is prepared as follows: Dissolve 1. 12 ozs. of 
 nitrate of silver in water, and precipitate the solution with 
 caustic potash. Thoroughly wash the silver oxide which is 
 precipitated, and dissolve it in I quart of water which contains 
 3.52 ozs. of potassium cyanide in solution, and finally dilute the 
 whole with one quart more water. For silvering, the bath is 
 heated to the boiling-point, and the silver withdrawn may be 
 replaced by the addition of moist silver oxide as long as com- 
 plete solution takes place. When the silvering is no longer 
 beautiful and of a pure white color, the bath is useless, and is 
 then evaporated. Experiments with a bath prepared according 
 to the above directions were never quite satisfactory. Better 
 results were, however, obtained by diluting the bath with 3 to 4 
 quarts of water and using it without heating. It then yielded 
 very nice, lustrous silvering. 
 
 The process of coating with a thin film, or rather whitening, 
 with silver, small articles, such as hooks and eyes, pins, etc., 
 differs from the above-described immersion method, which 
 effects the silvering in a few seconds, in that the articles require 
 to be boiled for a longer time. The process is as follows : 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 493 
 
 Prepare a paste from 0.88 oz. of silver nitrate precipitated as 
 silver chloride, cream of tartar 44 ozs., and a like quantity of 
 common salt, by precipitating the silver nitrate with hydro- 
 chloric acid, washing the chloride of silver and mixing it with 
 the above-mentioned quantities of cream of tartar and common 
 salt, and sufficient water to a paste, which is kept in a dark glass 
 vessel to prevent the chloride of silver from being decomposed 
 by the light. Small articles of copper or brass are first freed 
 from grease, and pickled. Then heat in an enameled kettle 
 3 to 5 quarts of rain-water to the boiling-point ; add 2 or 3 heap- 
 ing teaspoonfuls of the above-mentioned paste, and bring the 
 metallic objects contained in a stoneware basket into the bath, 
 and stir them diligently with a rod of glass or wood. Before 
 placing a fresh lot of articles in the bath, additional silver paste 
 must be added. If finally the bath acquires a greenish color, 
 caused by dissolved copper, it is no longer suitable for the pur- 
 pose, and is then evaporated and added to the silver residues. 
 
 Cold silvering with paste. — In this process an argentiferous 
 paste, composed as given below, is rubbed, by means of the 
 thumb, a piece of soft leather, or rag, upon the cleansed and 
 pickled metallic surface (copper, brass, or other alloys of cop- 
 per) until it is entirely silvered. The paste may also be rubbed 
 in a mortar with some water to a uniformly thin fluid mass, and 
 applied with a brush to the surface to be silvered. By allow- 
 ing the paste to dry naturally, or with the aid of a gentle heat, 
 the silvering appears. The application of the paste by means 
 of a brush is chiefly made use of for decorating with silver, 
 articles thinly gilded by immersion. For articles not gilded, 
 the above-mentioned rubbing-on of the stiff paste is to be 
 preferred. 
 
 Composition of argentiferous paste. — I. Silver in the form of 
 freshly precipitated chloride of silver,* 0.352 oz., common salt 
 0.35 oz., potash 0.7 oz., whiting 0.52 oz., and water a sufficient 
 quantity to form the ingredients into a stiff paste. 
 
 II. Silver in the form of freshly precipitated chloride of 
 silver * 0.35 oz., potassium cyanide 1.05 ozs., sufficient water to 
 * From 0.56 oz. of nitrate of silver. 
 
494 ELECTRO-DEPOSITION OF METALS. 
 
 dissolve these two ingredients to a clear solution, and enough 
 whiting to form the whole into a stiff paste. This paste is 
 also excellent for polishing tarnished silver; it is, however, 
 poisonous. 
 
 The following non-poisonous composition docs excellent ser- 
 vice : Silver in the form of chloride of silver 0.35 ozs., cream of 
 tartar 0.7 ozs., common salt 0.7 ozs., and sufficient water to form 
 the mixture of the ingredients into a stiff paste. 
 
 Another composition is as follows : Chloride of silver I part, 
 pearl ash 3, common salt 1^, whiting 1, and sufficient water to 
 form a paste. Apply the latter to the metal to be silvered and 
 rub with a piece of soft leather. When the metal is silvered, 
 wash in water, to which a small quantity of washing soda has 
 been added. 
 
 Graining. — In gilding parts of watches, gold is seldom di- 
 rectly applied upon the copper ; there is generally a preliminary 
 operation called graining, by which a grained and slightly dead 
 appearance is given io the articles. Marks of the file are ob- 
 literated by rubbing upon a whetstone, and lastly upon an oil 
 stone. Any oil or grease is removed by boiling the parts for a 
 few minutes in a solution of 10 parts of caustic soda or potash 
 in 100 of water, which should wet them entirely if all the oil 
 has been removed. The articles being threaded upon a brass 
 wire, cleanse them rapidly in the acid mixture for a bright luster, 
 and dry them carefully in white wood sawdust. The pieces are 
 fastened upon the even side of a block of cork by brass pins 
 with fiat heads. The parts are then thoroughly rubbed over 
 with a brush entirely free from grease, and dipped into a paste 
 of water and very find pumice-stone powder. Move the brush 
 in circles, in order not to rub one side more than the other; 
 thoroughly rinse in cold water, and no particle of pumice-stone 
 should remain upon the pieces of cork. Next place the cork 
 and the pieces in a weak mercurial solution, composed of water 
 iy 2 gallons, nitrate or binoxide of mercury T ^ oz., sulphuric 
 acid \ oz., which slightly whitens the copper. The pieces are 
 passed quickly through the solution and then rinsed. This 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 495 
 
 operation gives strength to the graining, which without it pos- 
 sesses no adherence. 
 
 The following preparations may be used for graining: I. 
 Silver in impalpable powder 2 ozs., finely-pulverized cream of 
 tartar 20 ozs., common salt 4 lbs. II. Silver powder 1 oz., 
 cream of tartar 4 to 5 ozs., common salt 13 ozs. III. Silver 
 powder, common salt, and cream of tartar, equal parts by 
 weight of each. The mixture of the three ingredients must be 
 thorough and effected at a moderate and protracted heat. The 
 graining is the coarser the more common salt there is in the 
 mixture, and it is the finer and more condensed as the propor- 
 tion of cream of tartar is greater, but it is then more difficult to 
 scratch-brush. The silver powder is obtained as follows ; Dis- 
 solve in a glass or porcelain vessel jA, oz - °f crystallized nitrate 
 of silver in 2^ gallons of distilled water, and place 5 or 6 
 ribands of cleansed copper, ^ inch wide, in the solution. 
 These ribands should be long enough to allow of a portion of 
 them being above the liquid. The whole is kept in a dark 
 place, and from time to time stirred with the copper ribands. 
 This motion is sufficient to loosen the deposited silver, and 
 present fresh surfaces to the action of the liquor. When no 
 more silver deposits on the copper the operation is complete, 
 and there remains a blue solution of nitrate of copper. The 
 silver powder is washed by decantation or upon a filter until 
 there remains nothing of the copper solution. 
 
 For the purpose of graining, a thin paste is made of one of 
 the above mixtures and water, and spread by means of a spatula 
 upon the watch parts held upon the cork. The cork itself is 
 placed upon an earthenware dish, to which a rotating move- 
 ment is imparted by the left hand. An oval brush with close 
 bristles, held in the right hand, rubs the watch parts in every 
 direction, but always with a rotary motion. A new quantity of 
 paste is added two or three times and rubbed in the manner in- 
 dicated. The more the brush and cork are turned the rounder 
 becomes the grain, which is a good quality, and the more paste 
 added the larger the grain. When the desired grain is obtained, 
 
496 ELECTRO-DEPOSITION OF METALS. 
 
 the pieces are washed and scratch-brushed. The brushes em- 
 ployed are of brass wire, as fine as hair, and very stiff and 
 springy. It is necessary to anneal them upon an even fire to 
 different degrees ; one soft or half annealed for the first opera- 
 tion or unco'vering the grain; one harder for bringing up the 
 luster; and one very soft or fully annealed, used before gilding 
 for removing any marks which may have been made by the 
 preceding tool, and for scratch-brushing after gilding, which, 
 like the graining, must be done by giving a rotary motion to 
 the tool. If it happens that the same watch part is composed 
 of copper and steel, the latter metal requires to be preserved 
 against the action of the cleansing acids and of the graining 
 mixture by a composition called resist. This consists in cover- 
 ing the pinions and other steel parts with a fatty composition 
 which is sufficiently hard to resist the tearing action of the 
 bristle and wire brushes, and insoluble in the alkalies of the gild- 
 ing bath. A good composition is: Yellow wax, 2 parts by 
 weight; translucent rosin, 3^ ; extra-fine red sealing-wax, I ^ ; 
 polishing rouge, I. Melt the rosin and sealing-wax in a porce- 
 lain dish, upon a water bath, and afterwards add the yellow wax. 
 When the whole is thoroughly fluid, gradually add the rouge 
 and stir with a wooden or glass rod, withdraw the heat, but 
 continue the stirring until the mixture becomes solid, otherwise 
 all the rouge will fall to the bottom. The flat parts to receive 
 this resist arc slightly heated, and then covered with the mix- 
 ture, which melts and is easily spread. For covering steel 
 pinions employ a small gouge of copper or brass fixed to a 
 wooden handle. The metallic part of the gouge is heated upon 
 an alcohol lamp and a small quantity of resist is taken with it. 
 The composition soon melts, and by turning the tool around 
 the steel pinion thus becomes coated. Use a scratch-brush 
 with long wires, and their flexibility prevents the removal of the 
 composition. When the resist is to be removed after gilding, 
 put the parts into warm oil or tepid turpentine, then in a very 
 hot soap-water or alkaline solution ; and, lastly, into fresh water. 
 Scratch-brush and dry in warm, white wood sawdust. The 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 497 
 
 holes of the pinions are cleansed and polished with small pieces 
 of very white, soft wood, the friction of which is sufficient to 
 restore the primitive luster. The gilding of parts of copper and 
 steel requires the greatest care, as the slightest rust destroys 
 their future usefulness. Should some gold deposit upon the 
 steel, it should be removed by rubbing with a piece of wood 
 and impalpable pumice dust, tin putty, or rOuge. 
 
 The gilding of the grained watch parts is effected in a bath 
 prepared according to formula I or III, given under "Deposi- 
 tion of Gold." 
 
 Gilding by Cotitact, by Immersion, and by Friction. 
 
 For contact-gilding by touching with zinc, formulas I, II, 
 IV and V, given in Chapter IX " Deposition of Gold " may 
 be used, IV and V being especially suitable, if the addition of 
 potassium cyanide is somewhat increased and the baths are 
 sufficiently heated. 
 
 A contact gold bath prepared with yellow prussiate of potash 
 according to the following formula also yields a good deposit. 
 
 I. Fine gold as chloride of gold 54 grains, yellow prussiate 
 of potash 1 oz., potash 1 oz., common salt I oz., water 1 quart. 
 
 The bath is prepared as given for formula III under " Depo- 
 sition of Gold." For use, heat it to boiling. 
 
 II. Chemically pure crystallized sodium phosphate 2.1 1 ozs., 
 neutral crystallized sodium sulphite 0.35 oz., potassium cyanide 
 0.28 oz., fine gold (as chloride) 15.43 grains, water I quart. 
 
 The bath is prepared as given for formula V under " Depo- 
 sition of Gold." Temperature for con tact-gilding 185 to 
 194 F. If red gilding is to be effected in this bath a corres- 
 ponding addition of potassium-copper cyanide has to be made, 
 7% grains sufficing for paler red, while 15 grains have to be 
 added for redder tones. 
 
 Gilding by contact is done the same way as silvering by con- 
 tact. The points of contact must be frequently changed, since 
 in the gold bath intense stains are still more readily formed 
 than in the silver bath. 
 32 
 
498 ELECTRO-DEPOSITION OF METALS. 
 
 Gilding by immersion {without battery or contact). — The fol- 
 lowing two formulas have proved very useful: 
 
 I. Crystallized sodium pyrophosphate 2.82 ozs., 12 percent, 
 prussic acid 4.5 1 drachms, crystallized chloride of gold 1. 12 
 drachms, water 1 quart. Heat the bath to the boiling-point, 
 and immerse the pickled objects of copper or its alloys, mov- 
 ing them constantly until gilded. Iron, steel, tin, and zinc 
 should be previously coppered, coating the objects with mer- 
 cury (quicking) being entirely superfluous. 
 
 All gold baths prepared with sodium pyrophosphate, when 
 fresh, give rapid and beautiful results, but they have the disad- 
 vantage of rapidly decomposing, and consequently can seldom 
 be completely exhausted. In this respect the following formula 
 answers much better. 
 
 II. Crystallized sodium phosphate 2.82 drachms, chemically 
 pure caustic potash 1.69 drachms, chloride of gold 0.56 
 drachm, 98 per cent, potassium cyanide 9.03 drachms, water 
 1 quart. Dissolve the sodium phosphate and caustic potash in 
 a^ of the water, and the potassium cyanide and chloride of 
 gold in the remaining y^, and mix both solutions. Heat the 
 solution to the boiling-point. This bath can be almost entirely 
 exhausted, as it is not decomposed by keeping. Should the 
 bath become weak, add about 2^ drachms of potassium 
 cyanide, and use it for preliminary dipping until no more gold 
 is reduced. To complete gilding, the objects subjected to such 
 preliminary dipping are then immersed for a few seconds in a 
 freshly-prepared bath of the composition given above. 
 
 The bath prepared according, to formula II is also very suit- 
 able for contact gilding. 
 
 The layer of gold produced by immersion is in all cases very 
 thin, since only as much gold is deposited as corresponds to the 
 quantity of basis-metal dissolved. For heavier gilding by this 
 process the action of zinc or aluminium contact will have to be 
 employed as auxiliary means. 
 
 Gilding by friction. — This process is variously termed gilding 
 tvitli the rag, with the thumb, with the cork. It is chiefly em- 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 499 
 
 ployed upon silver, though sometimes also upon brass and 
 copper. The operation is as follows: Dissolve 1.12 to 1. 69 
 drachms of chloride of gold in as little water as possible, to 
 which has previously been added 0.56 drachm of saltpetre. 
 Dip in this solution small linen rags, and, after allowing them 
 to drain off, dry them in a dark place. These rags saturated 
 with gold solution are then charred to tinder at not too great a 
 heat, whereby the chloride of gold is reduced, partially to 
 protochloride and partially to finely-divided metallic gold. 
 This tinder is then rubbed in a porcelain mortar to a fine, uni- 
 form powder. 
 
 To gild with this powder, dip into it a charred cork moistened 
 with vinegar or salt water and rub, with not too gentle a pres- 
 sure, the surface of the article to be gilded, which must be 
 previously cleansed from adhering grease. The thumb of the 
 hand may be used in place of the cork, but in both cases care 
 must be had not to moisten it too much, as otherwise the pow- 
 der takes badly. After gilding, the surface may be carefully 
 burnished. 
 
 Reddish gilding by friction is obtained by adding about 8 
 grains of cupric nitrate to the gold solution. 
 
 For gilding by friction, a solution of chloride of gold in an 
 excess of potassium cyanide may also be used, after thickening 
 the solution to a paste by rubbing in whiting. The paste is 
 applied to the previously zincked metals by means of a cork, a 
 piece of leather or a brush. Martin and Peyraud, the origin- 
 ators of this method, describe the operation as follows : Articles 
 of other metals than zinc are placed in a bath consisting of con- 
 centrated solution of ammonium chloride, in which has been 
 placed a quantity of granulated zinc. The articles are allowed 
 to boil a few minutes, whereby they acquire a coating of zinc. 
 For the preparation of the gilding composition, dissolve 11.28 
 drachms of chloride of gold in a like quantity of vvater, and 
 add a solution of 2.1 1 ozs. of potassium cyanide in as little 
 water as possible (about 2.8 ozs.) Of this solution add so 
 much to a mixture of 3.52 ozs. of fine whiting and 2.82 drachms 
 
500 ELECTRO-DEPOSITION OE METALS. 
 
 of pulverized tartar that a paste is formed which can be readily 
 applied with a brush to the article to be gilded. When the 
 article is coated, heat it to between 140 and I58°F. After 
 removing the dry paste by washing, the gilding appears and 
 can be polished with the burnisher. 
 
 Platinizing by Contact. 
 
 Though a thick deposit cannot be produced by the contact- 
 process, Fehling's directions may here be mentioned as suitable 
 for giving a thin coat of platinum to fancy articles. He recom- 
 mends a solution of 0.35 oz. of chloride of platinum and 7 ozs. 
 of common salt in 1 quart of water, which is made alkaline by 
 the addition of a small quantity of soda lye, and for use heated 
 to the boiling-point. 
 
 If larger articles are to be platinized by contact, free them 
 from grease, and after pickling, and if necessary, coppering 
 wrap them round with zinc wire, or place them upon a bright 
 zinc sheet, and introduce them into the heated bath. All the 
 remaining manipulations are the same as in other contact- 
 processes. 
 
 Tinning by Contact and by Boiling. 
 
 For tinning by zinc-contact in the boiling tin bath, the follow- 
 ing solutions are suitable: 
 
 According to Gerhold : Pulverized tartar and alum, of each 
 3.5 ozs., fused stannous chloride 0.88 oz., rain-water 10 quarts. 
 
 According to Roseleur: Potassium pyrophosphate 7 ozs., 
 crystallized stannous chloride (tin-salt) 0.38 oz., fused stan- 
 nous chloride 2.8 ozs., rain water 10 quarts. 
 
 It might be advisable to increase the content of potassium 
 pyrophosphate, and to add about 0.7 oz. of caustic soda. 
 
 According to Roseleur by immersion : 
 
 Potassium pyrophosphate 5.6 ozs., fused stannous chloride 
 1.23 ozs., rain-water 10 quarts. 
 
 For tinning by contact, heat the bath to boiling and suspend 
 the clean and picked objects in contact with pieces of zinc, or, 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 501 
 
 better, wrapped around with zinc wire spirals, care being had 
 from time to time to shift them about to prevent staining. 
 Large baths which cannot be readily heated are worked cold, 
 the objects being covered with a large zinc plate. In the cold 
 bath the formation of the tin deposit requires, of course, a 
 longer time. By using the electric current the deposit can be 
 made as heavy as desired. By immersion in the bath prepared 
 according to the last formula, zinc can only be coated with a 
 very thin film of tin. 
 
 For tinning by contact in a cold bath, Zilken has patented 
 the following solution: Dissolve with the aid of heat in 100 
 quarts of water, tin-salt 7 to 10.5 ozs., pulverized alum 10.5 
 ozs., common salt 15^ ozs -- an d pulverized tartar 7 ozs. The 
 cold solution forms the tin bath. The objects to be tinned are 
 to be wrapped round with strips of zinc. Duration of the pro- 
 cess, 8 to 10 hours. 
 
 Darlay uses for a cold tin bath with aluminium-contact : 
 
 Water 10 quarts, stannous chloride 1.05 ozs., potassium cya- 
 nide 1.4 1 ozs., caustic soda 1.76 ozs. 
 
 It might be advisable to heat the bath to at least between 
 1 13° and 122 F. For a hot tin bath Darlay uses : 
 
 Water 10 quarts, stannous chloride 0.88 oz., potassium cya- 
 nide 10.58 ozs., caustic soda 0.88 oz., sodium pyrophosphate 
 8.8 ozs. 
 
 The contact-body cannot be kept free from deposit by the 
 addition of potassium cyanide, and tinning is effected as well 
 without as with the addition of potassium cyanide. 
 
 Tinning solution for iron and steel articles. — Crystallized 
 ammonium-alum 7 ozs., crystallized stannous chloride 2.8 
 drachms, fused stannous chloride 2.8 drachms, rain-water 10 
 quarts. Dissolve the ammonium-alum in the hot water, and 
 when dissolved add the tin-salts. The bath is to be used boil- 
 ing hot and kept at its original strength by an occasional addi- 
 tion of tin- salt. The clean and pickled iron objects, after being 
 immersed in the bath, become in a few seconds coated with a 
 firmly-adhering film of tin of a dead, white color, which may 
 
502 ELECTRO-DEPOSITION OF METALS. 
 
 be polished by scratch-brushing, or scouring with sawdust in 
 the tumbling barrel. Tinning by boiling in the above bath is 
 the most suitable preparation for iron and steel objects which 
 are finally to be provided with a heavy electro-deposit of tin. 
 To insure entire success it is recommended thoroughly to 
 scratch-brush the objects after boiling, then to return them 
 once more to the bath, and finally to suspend them in a bath 
 composed according to formula I, Ila, or III, given under 
 " Deposition of Tin." 
 
 A tinning solution for small brass and copper articles (pins, 
 eyes, hooks, etc.), consists of a boiling solution of: Pulverized 
 tartar 3.5 ozs., stannous chloride (tin-salt) 14. 11 drachms, 
 water 10 quarts. After heating the bath to the boiling-point, 
 immerse the objects to be tinned in a tin basket, or in contact 
 with pieces of zinc in a stoneware basket. Frequent stirring 
 with a tin rod shortens the process. 
 
 A tinning solution highly recommended by Roseleur con- 
 sists of : 
 
 Crystallized sodium pyrophosphate 7 ozs., crystallized stan- 
 nous chloride 0.7 oz., fused stannous chloride 2.82 ozs., water 
 10 quarts. 
 
 The solution is prepared in the same manner as the preced- 
 ing one. 
 
 Another solution, given by Bottger, also yields good results: 
 Dissolve oxide of tin by boiling with potash lye, and place the 
 copper or brass objects to be tinned in the boiling solution in 
 contact with tin shavings. 
 
 Eisner s bath yields equally good results. It consists of a 
 solution of equal parts of tin- salt and common salt in rain-water. 
 The manipulation is the same as given above. 
 
 A characteristic method of tinning by Stolba is as follows : 
 Prepare a solution of 1.75 ozs. of tin-salt and 5.64 drachms of 
 pulverized tartar in one quart of water; moisten with this 
 solution a small sponge and dip the latter into pulverulent zinc. 
 By then rubbing the thoroughly cleansed and pickled articles 
 with the sponge, they immediately become coated with a film 
 
BY CONTACT, BY BOILING, AND BY FRICTION. 503 
 
 of tin. To obtain uniform tinning, the sponge must be re- 
 peatedly dipped, now into the solution, and then into the zinc- 
 powder, and the rubbing continued for a few minutes. 
 
 Zincking by Contact. 
 
 For zincking iron by contact, a concentrated solution of zinc 
 chloride and ammonium chloride in water is very suitable. 
 The objects are placed in the solution in contact with a large 
 zinc surface. 
 
 Darlay (German patent 1283 19) gives the following bath 
 which, with an aluminium contact is claimed to yield a useful 
 coating of zinc : 
 
 Water 10 quarts, zinc sulphate 0.35 ozs., potassium cyanide 
 1 oz., caustic soda 5.29 ozs. 
 
 It may be supposed that the bath is to be heated to between 
 170 and 1 94 F., though the patent specification is silent on 
 this point. Experiments to obtain, according to these direc- 
 tions, a good coating of zinc on iron did not yield satisfactory 
 results. 
 
 To coat brass and copper with a bright layer of zinc proceed 
 as follows : Boil for several hours commercial zinc-gray, i. e., 
 very finely-divided metallic zinc, with concentrated solution 
 of caustic soda. Then immerse the articles to be zincked in 
 the boiling fluid, when, by continued boiling, they will in a 
 short time become coated with a very bright layer of zinc. 
 When a copper article thus coated with zinc is carefully 
 heated in an oil bath to between 248 and 284 F., the zinc 
 alloys with the copper, forming a sort of bronze similar to 
 tombac. 
 
 Depositions of Antimony and of Arsenic by Immersion. 
 
 A heated solution of chloride of antimony in hydrochloric 
 acid — liquor stibii chlorati of commerce — deposits upon brass 
 objects immersed in it a coating of antimony of a steel-gray 
 color inclining to bluish. 
 
 A purer steel-gray color is obtained with the use of a hot 
 solution of arsenious chloride in water. 
 
CHAPTER XIV. 
 
 COLORING, PATINIZING, OXIDIZING, ETC., OF METALS — 
 LACQUERING. 
 
 THOUGH, strictly speaking, these operations do not form a 
 part of a work on the electro-deposition of metals, they require 
 to be mentioned, since the operator is frequently forced to 
 make use of one or the other method in order to furnish basis- 
 metals or electro deposits in certain shades of colors ordered. 
 
 By patina is understood the beautiful green colors, antique 
 statues and other art-works of bronze acquired by long expo- 
 sure to the action of the oxygen, carbonic acid, and moisture of 
 the air, whereby a thin layer of copper carbonate is formed 
 upon them. It has been sought to accelerate by chemical 
 means the formation of the patina thus slowly produced by the 
 influence of time, and the term patinizing has been applied to 
 this artificial production of colors. Without drawing a strict 
 line as to which processes have to be considered as coloring 
 and which as patinizing, the most approved methods for chang- 
 ing the color of the metals or of the deposits will be given. 
 
 It has to be particularly pointed out that the practice of 
 coloring requires considerable talent of observation and a cer- 
 tain knowledge of the behavior of metals or metallic alloys 
 towards the chemical substances used. 
 
 Especially in coloring alloys, for instance, brass, their per- 
 centage composition makes a difference, and patinas can be 
 produced upon a brass richer in zinc, which cannot be obtained 
 upon an alloy richer in copper. Hence, the instructions for 
 patinizing have to be changed in one or the other direction, 
 and this problem cannot be readily solved without a certain 
 chemical knowledge. 
 
 (504) 
 
COLORING, FATINIZING, OXIDIZING, ETC. 505 
 
 The temperature of the solutions which are used for patiniz- 
 ing is also of great importance, and the directions given in this 
 respect must be accurately observed. 
 
 1. Coloring of copper. — All shades from the pale-red of cop- 
 per to a dark chestnut-brown can be obtained by superficial 
 oxidation of the copper. For small objects it suffices to heat 
 them uniformly over an alcohol flame. With larger objects a 
 more uniform result is obtained by heating them in oxidizing 
 fluids or brushing them over with an oxidizing paste, the best 
 results being obtained with a paste prepared, according to the 
 darker or lighter shades desired, from 2 parts of ferric oxide 
 and 1 part of black-lead, or 1 part each of ferric oxide and 
 black-lead, with alcohol or water. Apply the paste as uni- 
 formly as possible with a brush, and place the object in a warm 
 place (oven or drying chamber). The darker the color is to 
 be the higher the temperature must be, and the longer it must 
 act upon the object. When sufficiently heated, the dry powder 
 is removed by brushing with a soft brush, and the manipulation 
 repeated if the object does not show a sufficiently dark tone. 
 Finally the object is rubbed with a soft linen rag moistened 
 with alcohol, or brushed with a soft brush and a few drops of 
 alcohol until completely dry, and then with a brush previously 
 rubbed upon pure wax. The more or less dark shade pro- 
 duced in this manner is very warm, and resists the action of 
 the air. 
 
 Brown color upon copper is obtained by applying to the 
 thoroughly cleansed surface of the object a paste of verdigris 
 3 parts, ferric oxide 3, sal ammoniac I, and sufficient vinegar, 
 and heating until the applied mixture turns black. The ob- 
 ject is then washed and dried. By the addition of some blue 
 vitriol, the color may be darkened to chesnut-brown. 
 
 In England a brown layer of cuprous oxide upon copper 
 articles is produced as follows : After polishing the articles with 
 pumice powder apply with a brush a paste of 4 parts of verdi- 
 gris, 4 parts of colcothar (ferric oxide), I part of finely-rasped 
 horn shavings and a small quantity of vinegar. Dry, heat over 
 a coal fire, wash, and smooth with the polishing stone. 
 
506 ELECTRO-DEPOSITION OF METALS. 
 
 A brown color is also obtained by brushing to dryness with a 
 hot solution of I part of potassium nitrate, I of common salt, 
 2 of ammonium chloride, and i of liquid ammonia in 95 of 
 vinegar. A warmer tone is, however, produced by the method 
 introduced in the Paris Mint, which is as follows : Powder and 
 mix intimately equal parts of verdigris and sal ammoniac. 
 Take a heaping tablespoonful of this mixture and boil it with 
 water in a copper kettle for about twenty minutes, and then 
 pour off the clear fluid. To give copper objects a bronze-like 
 color with this fluid, pour part of it into a copper pan; place 
 the objects separately in it upon pieces of wood or glass, so 
 that they do not touch each other, or come in contact with the 
 copper pan, and then boil them in the liquid for a quarter of 
 an hour. Then take the objects from the solution, rub them 
 dry with a linen cloth, and brush them with a waxed brush. 
 
 A beautiful and uniform brown tone on copper is obtained by 
 placing the objects previously freed from grease and pickled in 
 a solution of 5^ ozs. of copper sulphate, and 2^ ozs. potas- 
 sium chloride, heated to 140 F., until the desired tone is pro- 
 duced, then brushing with a soft brass-wire brush, again rinsing 
 for a short time in the pickle, and finally wiping dry with a 
 soft cloth. 
 
 According to Manduit, copper and coppered articles may 
 be bronzed by brushing with a mixture of castor oil 20 parts, 
 alcohol 80, soft soap 40, and water 40. This mixture produces 
 tones from bronze Barbtdienne to antique green patina, accord- 
 ing to the duration of the action. After 24 hours the article 
 treated shows a beautiful bronze, but when the mixture is 
 allowed to act for a greater length of time the tone is changed 
 and several different shades of great beauty can be obtained. 
 After rinsing, dry in hot sawdust, and lacquer with colorless 
 spirit lacquer. 
 
 A red-brown copper-tone of very beautiful effect, is pro- 
 duced in China, by the application of a paste consisting of 
 verdigris 2 parts, cinnabar 2 parts, ammonium chloride 5 parts, 
 alum 5 parts, and a sufficient quantity of vinegar, heating over 
 a coal fire, washing off, and repeating the process. 
 
COLORING, PATINIZING, OXIDIZING, ETC. 507 
 
 Copper is colored blue-black by dipping the object in a hot 
 solution of 1 1 y^ drachms of liver of sulphur in I quart of water, 
 moving it constantly. Blue-gray shades are obtained with 
 more dilute solutions. It is difficult to give definite directions 
 as to the length of time the solution should be allowed to act, 
 since this depends on its temperature and concentration. With 
 some experience the correct treatment, however, will soon be 
 learned. 
 
 The so-called cuivre-fume is produced by coloring the copper 
 or coppered objects blue-black with solution of liver of sulphur, 
 then rinsing, and finally scratch-brushing them, whereby the 
 shade becomes somewhat lighter. From raised portions which 
 are not to be dark, but are to show the color of copper, the 
 coloration is removed by polishing upon a felt wheel or bob. 
 
 Black color upon copper is produced by a heated pickle of 2 
 parts of arsenious acid, 4 of concentrated muriatic acid, 1 of 
 sulphuric acid of 66° Be., and 24 of water. 
 
 Matt-black on copper. Brush the object over with a solution 
 of 1 part of platinum chloride in 5 of water, or dip it in the 
 solution. A similar result is obtained by dipping the copper 
 object in a solution of nitrate of copper or of manganese, and 
 drying over a coal fire. These manipulations are to be repeated 
 until the formation of a uniform matt-black. 
 
 A solution recommended for obtaining a deep black color on 
 copper and its alloys is composed as follows : Copper nitrate 
 IOO parts, water 100 parts. The copper nitrate is dissolved in 
 the water, and the article, if large, is painted with it; if small, 
 it may be immersed in the solution. It is then heated over a 
 clear coal fire and lightly rubbed. The article is next placed 
 in, or painted, with a solution of the following composition : 
 Potassium sulphide 10 parts, water 100, hydrochloric acid 5. 
 
 More uniform results, however, are obtained by using a solu- 
 tion about three times more dilute than the above, viz.: Cop- 
 per nitrate 100 parts, water 300. Small work can be much 
 more conveniently treated by immersion in the solution, and 
 after draining off", or shaking off, the excess of the solution, 
 
508 ELECTRO-DEPOSITION OF METALS. 
 
 heating the work on a hot plate until the copper salt is decom- 
 posed into the black copper oxide. It would be difficult to 
 heat large articles on a hot piate, but a closed muffle-furnace 
 would give better results than an open coal fire. In any case 
 heating should not be continued longer than necessary to pro- 
 duce the change mentioned above. 
 
 Artificial patina. There are numerous directions for the 
 production of an artificial patina on metallic objects, and, in 
 conformity with the natural principle of formation, the various 
 artificial processes are based upon the slowest possible action 
 of the patinizing fluid. 
 
 To avoid stains the surfaces of the metallic objects should be 
 as bright as possible, and any adhering grease must first be 
 removed by washing with dilute soda lye. The objects are 
 then placed, without touching them with the bare hands, on 
 the bench or other place where they are to be patinized. 
 
 Patinizing is effected with a dilute solution applied with a 
 brush or sponge. After allowing the first application to dry at 
 a temperature of about 6o° F., the process is several times re- 
 peated. The composition of the metal to which the patinizing 
 fluid is to be applied, exerts an influence upon the formation 
 of a patina of good quality, the latter being most readily 
 formed upon bronze, while copper and brass are more difficult 
 to patinize ; alloys containing arsenic easily turn black. 
 
 Donath makes a distinction between acid and alkaline pat- 
 inizing fluids. The former contain acetic acid, oxalic acid, 
 hydrofluo-silicic acid, and the latter, ammonia, ammonium 
 carbonate, etc. Coatings effected with acids require a longer 
 time for their formation ; they are in the beginning less crys- 
 talline and at first blue-green, later on, of the color of verdigris, 
 but possess less resistance towards water. Coatings produced 
 with ammoniacal fluids have a dull, earthy appearance, and a 
 blue-green to gray-green color. Yellow-green tones are ob- 
 tained by the addition of chlorides — common salt, sal ammoniac 
 — to the solution, while copper nitrate or copper acetate yield 
 more blue-green colorations. If a yellow-green coloration is to 
 
COLORING, PATINIZING, OXIDIZING, ETC. 509 
 
 be changed into blue-green, only ammonium carbonate solu- 
 tion can subsequently be used. 
 
 Imitation of genuine green patina, as well as its rapid forma- 
 tion upon objects of copper, and of bronze and brass, is ob- 
 tained by repeatedly brushing the objects with solution of am- 
 monium chloride in vinegar, the action of the solution being 
 accelerated by the addition of verdigris. A solution of 9 
 drachms of ammonium chloride and 2^ drachms of potassium 
 binoxalate (salt of sorrel) in 1 quart of vinegar acts still better. 
 When the first coating is dry, wash the object, and repeat the 
 manipulations, drying and washing after each application, until 
 a green patina is formed. It is best to bring the articles after 
 being brushed over with the solution into a hermetically closed 
 box, upon the bottom of which a few shallow dishes containing 
 very dilute sulphuric or acetic acid and a few pieces of marble 
 are placed. Carbonic acid being thereby evolved, and the air 
 in the box being kept sufficiently moist by the evaporation of 
 water, the conditions required for the formation of genuine pat- 
 ina are thus filled. If the patina is to show a more bluish tone, 
 brush the objects with a solution of 4^ ozs. of ammonium 
 carbonate and 1 y 2 ozs. of ammonium chloride in 1 quart of 
 water, to which a small quantity of gum tragacanth may be 
 added. 
 
 The object is more rapidly attained by the use of a liquid 
 brought now in commerce under the name antique green pat- 
 ina. Shake the liquid thoroughly, pour a few drops upon a 
 glass plate, and triturate them uniformly with a pestle. Apply 
 by means of a brush, a coat, not too thick, to the dry objects 
 previously free from grease and pickled, allow to dry, and re- 
 peat the operation once more. Then dry the objects thor- 
 oughly at about 140 F., and scratch-brush with a delicate 
 steel or brass-wire brush when the patina appears with a slight 
 luster. 
 
 Commercial new green patina is applied in the same manner. 
 
 It is not considered necessary to give additional directions 
 for the production of a patina, those given above yielding reli- 
 able results. 
 
5IO ELECTRO-DEPOSITION OF METALS. 
 
 To produce a steel-gray color iipon copper immerse the clean 
 and pickled objects in a heated solution of chloride of antimony 
 in hydrochloric acid. By using a strong electric current the 
 objects may also be coated with a steel-gray deposit of arsenic 
 in a heated arsenic bath. 
 
 For coloring copper dark steel-gray, a pickle consisting of I 
 quart of hydrochloric acid, 0.125 quart of nitric acid, 1% ozs. 
 of arsenic acid, and a like quantity of iron filings is recom- 
 mended. 
 
 Various colors upon massive copper. — First draw the object 
 through a pickle composed of sulphuric acid 60 parts, hydro- 
 chloric acid 24.5, and lampblack 15.5; or of nitric acid 100 
 parts, hydrochloric acid lyi and lampblack %\ Then dissolve 
 in a quart of water, 4^ ozs. of sodium hyposulphite, and in 
 another quart of water, 14^ drachms of blue vitriol, 5^ 
 drachms of crystallized verdigris, and 7^ grains of sodium 
 arsenate. Mix equal volumes of the two solutions, but no 
 more than is actually necessary for the work in hand, and heat 
 to between \6j° and 176 F. By dipping articles of copper, 
 brass, or nickel in the hot solution they become immediately 
 colored with the colors mentioned below, one color passing 
 within a few seconds into the other, and for this reason the effect 
 must be constantly controlled by frequently taking the objects 
 from the bath. The colors successively formed are as follows: 
 
 Upon copper: Upon brass: Upon nickel: 
 
 Orange, Golden-yellow, Yellow, 
 
 Terra-cotta, Lemon color, Blue, 
 
 Red (pale), Orange, Iridescent. 
 
 Blood-red, Terra-cotta, 
 
 Iridescent. Olive-green. 
 
 Some of these colors not being very durable, have to be pro- 
 tected by a coat of lacquer or paraffine. It is further necessary 
 to diligently move the objects, so that all portions acquire the 
 same color. The bath decomposes rapidly, and hence only 
 sufficient for 2 or 3 hours' use should be mixed at one time. 
 
COLORING, PATINIZING, OXIDIZING, ETC. 5 I I 
 
 2. Coloring of brass and bronzes. — Most of the directions 
 given for coloring copper are also available for brass and 
 bronzes, especially those for the production of the green patina, 
 and the oxidized tones by a mixture of ferric oxide and black- 
 lead. 
 
 Many colorations on brass, however, are effected only with 
 difficulty, and are partially or entirely unsuccessful, as, for in- 
 stance, coloring black with liver of sulphur. As a pickle for 
 the production of a 
 
 Lustrous black on brass, the following solutions may be used : 
 Dissolve freshly precipitated carbonate of copper, while still 
 moist, in strong liquid ammonia, using sufficient of the copper 
 salts so that a small excess remains undissolved, or, in other 
 words, that the ammonia is saturated with copper. The car- 
 bonate of copper is prepared by mixing hot solutions of equal 
 parts of blue vitriol and of soda, filtering off and washing the 
 precipitate. 
 
 Dilute the solution of the copper, salt in ammonia with one- 
 fourth its volume of water, add 31 to 46 grains of graphite and 
 heat to between 95 ° and 104 F. 
 
 According to experiments in the laboratory of the Physikal- 
 isch-Technischen Reichsanstalt, the following proportions have 
 proved very effective: Copper carbonate 3^ ozs., liquid am- 
 monia 26^ ozs., and an addition of 5^ ozs. of water. Place 
 the clean and pickled articles in this pickle until they show a 
 full black tone, then rinse in water, immerse in hot water, and 
 dry in sawdust. The solution soon spoils, and hence no more 
 than required for immediate use should be prepared. 
 
 For black pickling in the hot way, a solution of 21 ozs. of 
 copper nitrate in 7 ozs. of water mixed with a solution of 3^ 
 grains of silver nitrate in % oz. of water, is recommended. 
 
 Black of a beautiful luster may be produced, especially upon 
 nickeled brass, by suspending the objects as anodes in a solu- 
 tion of lead acetate (sugar of lead) in caustic soda, using a 
 slight current density. 
 
 Steel-gray on brass is obtained by the use of a mixture of 1 lb. 
 
512 ELECTRO-DEPOSITION OF METALS. 
 
 of strong hydrochloric acid with I pint of water, to which are 
 added 5^ ozs. of iron filings and a like quantity of pulverized 
 antimony sulphide. 
 
 Hydrochloric acid compounded with arsenious acid is also 
 recommended for this purpose. The mixture is brought into a 
 lead vessel, and the objects dipped in it should come in contact 
 with the lead of the vessel, or be wrapped around with a strip 
 of lead. 
 
 Silver color on brass. Dissolve in a well-glazed vessel I y 2 
 ozs. cream of tartar and ]/ 2 oz. of tartar emetic in I quart of hot 
 water, and add to the solution 1 % ozs. of hydrochloric acid, 
 4^ ozs. of granulated, or better, pulverized tin and 1 oz. of 
 powdered antimony. Heat the mixture to boiling and immerse 
 the articles to be colored. After boiling at the utmost for half 
 an hour, the articles will be provided with a beautiful, hard and 
 durable coating. 
 
 A gray color with a bluish tint on brass is produced with a 
 solution of antimonious chloride (butter of antimony), while a 
 pure steel-gray color is obtained with a hot solution of arsenious 
 chloride with a little water. 
 
 A pale gold color on brass is obtained in the following bath : 
 Dissolve in 90 parts by weight of water, 3.6 parts by weight of 
 caustic soda and the same quantity of milk sugar. Boil the 
 solution x /± hour. Then add a solution of blue vitriol 3.6 parts 
 by weight in 10 of hot water, and use the bath at a temperature 
 of 176 F. 
 
 Straw color, to brown, through golden yellow, and tombac color 
 on brass may be obtained with solution of carbonate of copper 
 in caustic soda lye. Dissolve 5.25 ozs. of caustic soda in I 
 quart of water, and add 1 ^ ozs. of carbonate of copper. By 
 using the solution cold, a dark, golden-yellow is first formed, 
 which finally passes through pale brown into dark brown with a 
 green luster. Coloration is more rapidly effected by using the 
 solution hot. 
 
 A color resembling gold on brass is, according to Dr. Kayser, 
 obtained as follows: Dissolve S}4 drachms of sodium hyposul- 
 
COLORING, PATINIZING, OXIDIZING, ETC. 513 
 
 phite in 17 drachms of water, and add 5.64 drachms of solution 
 of antimonious chloride (butter of antimony). Heat the mix- 
 ture to boiling for some time, then filter off the red precipitate 
 formed, and after washing it several times upon the filter with 
 vinegar, suspend it in 2 or 3 quarts of hot water ; then heat and 
 add concentrated soda lye until solution is complete. In this 
 hot solution dip the clean and pickled brass objects, removing 
 them frequently to see whether they have acquired the desired 
 coloration. By remaining too long in the bath, the articles be- 
 come gray. 
 
 Brown color, called bronze Barbedienne, on brass. — This beau- 
 tiful color may be produced as follows : Dissolve by vigorous 
 shaking in a bottle, freshly prepared arsenious sulphide in 
 liquid ammonia, and compound the solution with antimonious 
 sulphide (butter of antimony) until a slight permanent turbidity 
 shows itself, and the fluid has acquired a deep yellow color. 
 Heat the solution to 95 ° F., and suspend the brass objects in 
 it. They become at first golden-yellow and then brown, but 
 as they come from the bath with a dark dirty tone, they have 
 to be several times scratch-brushed to bring out the color. If, 
 after using it several times, the solution fails to work satisfac- 
 torily, add some antimonious sulphide. The solution decom- 
 poses rapidly, and should be prepared fresh every time it is to 
 be used. 
 
 A suitable solution may also be prepared by boiling 0.88 oz. 
 of arsenious acid and I oz. of potash in 1 pint of water until the 
 acid is dissolved and, when cold, add 250 cubic centimeters of 
 ammonium sulphide. According to the degree of dilution, 
 brown to yellow tones are obtained. 
 
 By this method only massive brass objects can be colored 
 brown. To brassed zinc and iron, the solution imparts brown- 
 black tones, which, however, are also quite beautiful. 
 
 Upon massive brass, as well as upon brassed zinc and iron 
 
 objects, bronze Barbedienne may be produced as follows: Mix 
 
 3 parts of red sulphide of antimony {stibium sulfuratum anran- 
 
 tianum) with 1 part of finely pulverized bloodstone, and tritu- 
 
 33 
 
514 ELECTRO-DEPOSITION OF METALS. 
 
 rate the mixture with ammonium sulphide to a not too thickly- 
 fluid pigment. Apply this pigment to the objects with a brush, 
 and, after allowing to dry in a drying-chamber, remove the 
 powder by brushing with a soft brush 
 
 In Paris bronze articles are colored dead-yellow or clay -yellow 
 to dark brown by first brushing the pickled and thoroughly 
 rinsed objects with dilute ammonium sulphide, and, after dry- 
 ing, removing the coating of separated sulphur by brushing. 
 Dilute solution of sulphide of arsenic in ammonia is then ap- 
 plied, the result being a color resembling mosaic gold. The 
 more frequently the arsenic solution is applied, the browner the 
 color becomes. By substituting for the arsenic solution one of 
 sulphide of antimony in ammonia or ammonium sulphide, 
 colorations of a more reddish tone are obtained. 
 
 A dark red brown color upon brass is produced by suspend- 
 ing the articles, previously thoroughly freed from grease, in a 
 solution of equal parts of potassium-lead oxide and red prus- 
 siate of potash heated to 122° F. The articles are allowed to 
 remain in the solution until they have acquired a sufficiently 
 dark color. 
 
 For coloring brass articles in large quantities brown by boil- 
 ing the following solution is recommended : Water I quart, 
 potassium chromate \% ozs., nickel sulphate \% ozs., potas- 
 sium permanganate Jj grammes. 
 
 Solution of blue vitriol and potassium permanganate serves 
 the same purpose. However, after boiling, the articles must 
 not be scratch-brushed, but after drying rubbed with vaseline. 
 
 Violet and cornflower-blue upon brass may be produced as 
 follows: Dissolve in I quart of water 4^ ozs. of sodium hypo- 
 sulphite, and in another quart of water 1 oz. 3^ drachms of 
 crystallized lead acetate (sugar of lead), and mix the solutions. 
 Heat the mixture to 176 F., and then immerse the cleansed 
 and pickled articles, moving them constantly. First a gold 
 yellow coloration appears, which, however, soon passes into 
 violet and blue, and if the bath be allowed to act further, into 
 green. The action is based upon the fact that in an excess of 
 
COLORING, PATINIZING, OXIDIZING, ETC. 515 
 
 hyposulphite of soda, solution of hyposulphite of lead is formed, 
 which decomposes slowly and separates sulphide of lead, which 
 precipitates upon the brass objects, and, according to the thick- 
 ness of the deposit, produces the various lustrous colors. 
 
 Upon the same action is based the spurious gilding of small 
 silvered brass and tombac articles. Though this process has 
 been known for many years, Joseph Dittrich obtained a German 
 patent for it. He dissolves in 6*4 lbs. of water, 10^ ozs. of 
 sodium hyposulphite, and 3^ ozs. of lead acetate (sugar of 
 lead). 
 
 Similar lustrous colors are obtained by dissolving 2. 11 ozs. 
 of pulverized tartar in 1 quart of water, and I oz. of chloride of 
 tin in y 2 pint of water, mixing the solution, heating, and pour- 
 ing the clear mixture into a solution of 6.34 ozs. of sodium 
 hyposulphite in 1 pint of water. Heat this mixture to 176 F., 
 and immerse the pickled brass objects. 
 
 Ebermayer 's experiments in coloring brass. — Below the results 
 of Ebermayer's experiments are given. In testing the direc- 
 tions, the same results as those claimed by Ebermayer were not 
 always obtained ; and variations are given in parentheses. 
 
 I. Blue vitriol 8 parts by weight, crystallized ammonium 
 chloride 2, water 100, give by boiling a greenish color. (The 
 color is olive-green, and useful for many purposes. The color- 
 ation, however, succeeds only upon massive brass, but not upon 
 brassed zinc.) 
 
 II. Potassium chlorate 10 parts by weight, blue vitriol 10, 
 water iooo, give by boiling a brown-orange to cinnamon-brown 
 color. (^Only a yellow-orange color could be obtained.) 
 
 III. By dissolving 8 parts by weight of blue vitriol in ioco 
 of water, and adding 100 of caustic soda until a precipitate is 
 formed, and boiling the objects in the solution, a gray-brown 
 color is obtained, which can be made darker by the addition of 
 colcothar. (Stains are readily formed. Brassed zinc acquires 
 a pleasant pale-brown. ) 
 
 IV. With 50 parts by weight of caustic soda, 50 of sulphide 
 of antimony, and 500 of water, a pale jig-brown color is pro- 
 
5 16 ELECTRO-DEPOSITION OF METALS. 
 
 duced. (Fig-brown could not be obtained, the shade being 
 rather dark olive-green^ 
 
 V. By boiling 400 parts by weight of water, 25 of sulphide 
 of antimony and 600 of calcined soda, and filtering the hot solu- 
 tion, mineral kermes is precipitated. By taking of this 5 parts 
 by weight and heating with 5 of tartar, 400 of water, and 10 of 
 sodium hyposulphite, a beautiful steel-gray is obtained. (The 
 result is tolerably sure and good). 
 
 VI. Water 400 parts by weight, potassium chlorate 20, nickel 
 sulphide 10, give after boiling for some time a brozvn color, 
 which, however, is not formed if the sheet has been pickled. 
 (The brown color obtained is not very pronounced.) 
 
 VII. Water 250 parts by weight, potassium chlorate 5, car- 
 bonate of nickel 2, and sulphate of ammonium and nickel 5, 
 give, after boiling for some time, a brown-yellow color, playing 
 into a magnificent red. (The results obtained were only indif- 
 ferent. ) 
 
 VIII. Water 250 parts by weight, potassium chlorate 5, and 
 sulphate of nickel and ammonium 10, give a beautiful dark 
 brown. Upon massive brass a good dark brown is obtained. 
 The formula, however, is not available for brassed zinc. 
 
 3. Coloring zinc. — The results obtained by coloring zinc 
 directly according to existing directions cannot be relied on, 
 and it is, therefore, recommended to first copper the zinc and 
 then color the coppering. Experiments in coloring zinc black 
 with alcholic solution of chloride of antimony according to 
 Dullos's process gave no useful results. Puscher's method is 
 better. According to it, the objects are dipped in a boiling 
 solution of 5.64 ozs. of pure green vitriol and 3.17 ozs. of am- 
 monium chloride in 2 x / 2 quarts of water. The loose black pre- 
 cipitate deposited upon the objects is removed by brushing, the 
 object again dipped in the hot solution, and then held over a 
 coal fire until the ammonium chloride evaporates. By repeat- 
 ing the operation three or four times, a firmly-adhering black 
 coating is formed. To color zinc black with nitrate of manga- 
 nese, as proposed by Neumann, is a tedious operation, it 
 
COLORING, PATINIZING. OXIDIZING, ETC. 517 
 
 requiring to be repeated seven or eight times. It is done by 
 dipping the object in a solution of nitrate of manganese and 
 heating over a coal fire, the manipulation, being repeated until 
 a uniform dead black is obtained. 
 
 Gray, yellow, brown to black colors upon zinc are obtained by 
 bringing the articles into a bath which contains 6 to 8 quarts of 
 water, 33^ oz. of nickel-ammonium sulphate, 3^ ozs. of blue 
 vitriol and ^yi ozs. of potassium chlorate. The bath is to be 
 heated to 140 F. By increasing the content of blue vitriol a 
 dark color is obtained, and a brighter one with the use of a 
 larger proportion of nickel salt. The correct proportions for 
 the determined shades will soon be learned by practice. 
 When colored, the articles are thoroughly rinsed, dried, with- 
 out rubbing, in warm sawdust, and finally rubbed with a flannel 
 rag moistened with linseed oil, whereby they acquire deep luster, 
 and the coating becomes more durable. 
 
 For the production of a beautiful brown patina upon zinc, 
 the objects are first coppered in a copper bath containing 
 potassium cyanide, then in the acid-copper bath, rinsed, and 
 finally suspended in a pickle consisting of a solution of 5.29 
 ozs. of blue vitriol and 2.82 ozs. of potassium chlorate in one 
 quart of water at 140 F., until they show the desired brown 
 tone. They are then rinsed in water, scratch-brushed with a 
 fine brass-brush, for a short time replaced in the pickle, again 
 thoroughly rinsed in water, and dried with a soft cloth. 
 
 By suspending zinc in a nickel bath slightly acidulated with 
 sulphuric acid, a firmly adhering blue-black coating is, after 
 some time, formed without the use of a current. This coating 
 is useful for many purposes. A similar result is obtained by 
 immersing the zinc objects in a solution of 2.1 1 ozs. of the 
 double sulphate of nickel and ammonium and a like quantity of 
 crystallized ammonium chloride in 1 quart of water. The 
 articles become first dark yellow, then successively, brown, 
 purple-violet and indigo-blue, and stand slight scratch-brushing 
 and polishing. 
 
 A gray coating on zinc is obtained by a deposit of arsenic in 
 
5 I 8 ELECTRO-DEPOSITION OF METALS. 
 
 a heated bath composed of 2.82 ozs. of arsenious acid, 8.46 
 drachms of sodium pyrophosphate and 1 ^ drachms of 98 per 
 cent, potassium cyanide, and 1 quart of water. A strong cur- 
 rent should be used so that a vigorous evolution of hydrogen 
 is perceptible. Platinum sheets or carbon plates are used as 
 anodes. 
 
 A sort of bronzing on zinc is obtained by rubbing it with a 
 paste of pipe-clay to which has been added a solution of I part 
 by weight of crystallized verdigris, 1 of tartar, and 2 of crys- 
 tallized soda. 
 
 Red-brown shades on zinc. — Rub with solution of chloride of 
 copper in liquid ammonia. 
 
 Yellow-brown shades on zinc. — Rub with solution of chloride 
 of copper in vinegar. 
 
 4. Coloring of iron. — The browning of gun-barrels is effected 
 by the application of a mixture of equal parts of butter of anti- 
 mony and olive oil. Allow the mixture to act for 12 to 14 
 hours, then remove the excess with a woolen rag and repeat 
 the application. When the second application has acted for 12 
 to 24 hours, the iron or steel will be coated with a bronze- 
 colored layer of ferric oxide with antimony, which resists the 
 action of the air, and may be made lustrous by brushing with a 
 waxed brush. 
 
 A patina which protects metals — iron, zinc, tin, etc. — from 
 rust, is, according to Haswell, obtained as follows : The article, 
 previously freed from grease and pickled, is suspended as 
 negative electrode in a solution of 15^/3 grains of ammonium 
 molybdate and j^ oz. of ammonium nitrate in 1 quart of water. 
 A weak current should be used — 0.2 to 0.3 ampere per 15^ 
 square inches. 
 
 To protect gun barrels and other articles of iron and steel 
 from rust, they are, according to Haswell, suspended as anodes 
 in a bath consisting of a solution of lead nitrate and sodium 
 nitrate, into which maganous oxide has been stirred. 
 
 A lustrous black on iron is obtained by the application of 
 solution of sulphur in spirits of turpentine prepared by boiling 
 
COLORING, PATINIZING, OXIDIZING, ETC. 5 19 
 
 upon the water bath. After the evaporation of the spirits of 
 turpentine a thin layer of sulphur remains upon the iron, which 
 on heating the article immediately combines with the metal. 
 
 A lustrous black is also obtained by freeing the iron articles 
 from grease, pickling, and after drying, coating with sulphur 
 balsam,* and burning in at a dark-red heat. If pickling is 
 omitted, coating with sulphur balsam and burning-in must be 
 twice or three times repeated. 
 
 The same effect is produced by applying a mixture of three 
 parts flowers of sulphur, and 1 part graphite with turpentine, 
 and heating in the muffle. 
 
 According to Meritens a bright black color can be obtained 
 on iron by making it the anode in distilled water, kept at 158 
 F., and using an iron plate as cathode. The method was 
 tested as follows : A piece of bright sheet pen-steel was placed 
 in distilled water and made the anode by connecting with the 
 positive pole of a plating dynamo, and a similar sheet was con- 
 nected with the negative pole to form the cathode. An electro- 
 motive force of 8 volts was employed. After some time a dark 
 stain was produced, but it lacked uniformity. The experiment 
 was repeated with larger plates, when a good blue-black color 
 was obtained on the anode in half a hour. On drying in saw- 
 dust the color appeared less dense, and inclined to a dark straw 
 tint. The back of the plate was also colored, but not regularly. 
 The face of the cathode was discolored with a grayish stain on 
 the side opposite to the anode, but on the other side the ap- 
 pearance was almost identical with the back of the anode. The 
 water became of a yellowish color. 
 
 Fresh distilled water was then boiled for a long time so as to 
 expel all trace of oxygen absorbed from the atmosphere, and the 
 experiment repeated as in the former cases. No perceptible 
 change took place after the connection had been made with the 
 dynamo for a quarter of an hour. After the interval of one hour 
 a slight darkening occurred, but the effect was much less than 
 that produced in five minutes in aerated water. 
 
 * Sulphur dissolved in linseed oil. 
 
520 ELECTRO-DEPOSITION OF METALS. 
 
 The action of the liquid in coloring the steel is evidently one 
 of oxidation, due to the dissolved oxygen, which becomes more 
 chemically active under the influence of the electric condition, 
 and gradually unites with the iron. 
 
 The matt black coating upon watch cases of iron and steel — 
 the so-called Swiss matt — is not produced by the electric pro- 
 cess, but by a slow process of oxidation, ferroso-ferric oxide 
 being formed. The objects, previously cleaned from grease 
 with the greatest care, are brushed over by means of a sponge 
 or brush with a ferric chloride solution, called ferroxydin Y 
 allowed to dry, and then steamed. For the production of a 
 very strong matt, the process is to be twice or three times re- 
 peated. By one operation a beautiful black with semi-luster is 
 obtained. 
 
 According to Bottger a durable blue on iron and steel may 
 be obtained by dipping the article in a ^ per cent, solution of 
 red prussiate of potash mixed with an equal volume of a ^ 
 per cent, ferric chloride solution. 
 
 A brown-black coating with bronze luster on iron is obtained 
 by heating the bright iron objects and brushing them over 
 with concentrated solution of potassium dichromate. When 
 dry, heat them over a charcoal fire, and wash until the water 
 running off shows no longer a yellow color. Repeat the opera- 
 tion twice or three times. A similar coating is obtained by 
 heating the iron objects with a solution of io parts by weight 
 of green vitriol and I part of sal ammoniac in water. 
 
 To give iron a silvery appearance zvitJi high luster. — Scour 
 the polished and pickled iron objects with a solution prepared 
 as follows: Heat moderately iy2 ozs. of chloride of antimony, 
 0.35 oz. of pulverized arsenious acid, 2.82 ozs. of elutriated 
 bloodstone with I quart of 90 per cent, alcohol upon a water 
 bath for half an hour. Partial solution takes place. Dip into 
 this fluid a tuft of cotton and go over the iron portions, using 
 slight pressure. A thin film of arsenic and antimony is thereby 
 deposited, which is the more lustrous the more carefully the 
 iron has previously been polished. 
 
COLORING, PATINIZING, OXIDIZING, ETC. 52 1 
 
 5. Coloring of tin. — A bronze-like . patina on tin may be ob- 
 tained by brushing the object with a solution of 1 ^ ozs. of 
 blue vitriol and a like quantity of green vitriol in I quart of 
 water, and moistening, when dry, with a solution of 3*^ ozs. of 
 verdigris in \o]/ 2 ozs. of vinegar. When dry, polish the object 
 with a soft waxed brush and some ferric oxide. The coating 
 thus obtained being not very durable, must be protected by a 
 coating of lacquer. 
 
 Durable and very warm sepia-brown tone upon tin and its 
 alloys. — Brush the object over with a solution of 1 part of plat- 
 inum chloride in 10 of water, allow the coating to dry, then 
 rinse in water, and, after again drying, brush with a soft brush 
 until the desired brown luster appears. 
 
 A dark coloration is also obtained with ferric chloride 
 solution. 
 
 6. Coloring of silver. — See "Deposition of Silver." 
 
 Lacquering. 
 
 In the electro plating industry recourse is frequently had to 
 lacquering in order to make the deposits more resistant against 
 atmospheric influences, or to protect artificially prepared colors, 
 patinas, etc. Thin, colorless shellac solution, which does not 
 affect the color of the deposit or of the patinizing, is, as a rule, 
 employed, while in some cases colored lacquers are used to 
 heighten the tone of the deposit, as, for instance, gold lacquer 
 for brass. 
 
 The lacquer is applied with a flat fine fitch brush, the object 
 having previously been heated hand-warm. The brush should 
 be frequently freed from an excess of lacquer, and the lacquer 
 be applied as uniformly as possible without undue pressure of 
 the brush. An excess of lacquer, which may have been ap- 
 plied, is removed by means of a dry brush. 
 
 The lacquer for immediate use is kept in a small glass or 
 porcelain pot, across the top of which a string may be stretched. 
 This string is intended for removing by wiping the excess of 
 lacquer taken up by the brush. Crusts of dried-in lacquer 
 
522 ELECTRO-DEPOSITION OF METALS. 
 
 should be carefully removed, and the contents of the small pot 
 should under no conditions be poured back into the can, as 
 otherwise the entire supply might be spoiled. 
 
 After lacquering, the object is dried in an oven at a temper- 
 ature of between 140 and 158 F., small irregularities being 
 thereby adjusted, and the layer of lacquer becoming transparent, 
 clear and lustrous. 
 
 Electro-plated articles which are to be lacquered must be 
 thoroughly rinsed and dried to remove adhering plating solu- 
 tion from the pores, otherwise ugly stains will form under the 
 coat of lacquer. 
 
 If it becomes necessary to thin a spirit lacquer, only absolute 
 alcohol, i. e., alcohol free from water, should be used for the 
 purpose, since alcohol containing water renders the coat of 
 lacquer muddy and dull. 
 
 The development in the art of lacquer-making has advanced 
 with, and in a measure kept pace with that made in the electro- 
 deposition of metals. With the use of new metals, the intro- 
 duction of new and altered formulas and processes for finishing 
 metals, the employment of new and different chemicals, in fact, 
 with every change or alteration in the methods of finishing and 
 using metals — changes have been made in the nature of the 
 lacquers employed in their protection. 
 
 Lacquers to be acceptable to the metal worker must be per- 
 fectly adapted to each special use, and not only suit the varied 
 metals, finishes and conditions of the work, but also meet and 
 overcome difficulties arising from, for instance, the influence of 
 climatic changes and use to which the lacquered metal is sub- 
 jected. Many cases of trouble in the finishing of metal may 
 now be traced to the use of an improper lacquer for the par- 
 ticular metal or finish. Thus ingredients and chemicals which 
 from their nature are antagonistic to a bronze metal and detri- 
 mental to it should not be included in a lacquer for bronze, 
 although the same ingredients may be beneficial to a silver, gold 
 or aluminium surface. 
 
 The most noted improvements have been effected in lacquers 
 
COLORING, PATINIZING, OXIDIZING, ETC. 523 
 
 for brass bedsteads, gas and electric fixtures, black lacquers, 
 and the lacquers made with the special object of saving time in 
 their application and money in their use. 
 
 A review of all the lacquers made for the above-mentioned 
 purposes is not within the province of this work, and we must 
 therefore confine ourselves to the enumeration of the newest 
 and most important ones for general use, with which we have 
 become familiar. 
 
 Pyroxyline lacquers. — These lacquers, known under various 
 names, such as zapon, kristalline, etc., were introduced to the 
 trade in America during 1884, and since then they have become 
 known throughout all parts of America and Europe. Pyroxy- 
 line lacquer represents a clear, almost colorless fluid, and smells 
 something like fruit-ether, reminding one of bananas. It is 
 chiefly used as a dip lacquer, though there is also a brush- 
 lacquer, which is applied with a brush, like spirit-lacquer. 
 
 The lacquer possesses the following good properties : The 
 transparent, colorless coat obtained with it can be bent with the 
 metallic sheet to which it has been applied without cracking. 
 It is so hard that it can scarcely be scratched with the finger- 
 nail, shows no trace of stickiness, and it is perfectly homogene- 
 ous even on the edges. This favorable behavior is very likely 
 due to the slow evaporation of the solvent, and the fact that the 
 lacquer quickly forms a thickish, tenacious layer, which though 
 moved with difficulty, is not entirely immobile. Another advan- 
 tage of the lacquer — especially as regards the metallic objects 
 — is that the coating in consequence of its physical constitu- 
 tion preserves the character of the bases. In accordance with 
 the nature of pyroxyline, the coating is not sensibly affected by 
 ordinary differences in temperature, and does not become dull 
 and non-transparent, as is the case with resins in consequence 
 of the loss of molecular coherence. It can be washed with 
 soap and water, and protects metals coated with it from the 
 action of the atmosphere. It may also be colored, but, of 
 course, only with coloring substances — mostly aniline colors — 
 which are soluble in the solvent used. 
 
524 ELECTRO-DEPOSITION OF METALS. 
 
 A useful pyroxyline lacquer may be prepared as follows:* 
 Bring collodion-cotton, i, e., soluble pyroxyline, such as is used 
 by photographers, into a box which can be hermetically closed, 
 and place upon the bottom of the box a dish containing sul- 
 phuric acid. The purpose of this is to dry the collodion-cotton, 
 which requires from 36 to 48 hours. The collodion-cotton is 
 then brought into a large bottle, and three to four times its 
 quantity by weight of very strong alcohol poured over it. In a 
 few days the greater portion of it is dissolved, when the clear so- 
 lution is poured into another bottle. Add to the clear solution 
 more collodion-cotton, about 25 to 30 per cent, of the weight 
 of the quantity originally used, and the resulting product forms 
 an excellent cellulose lacquer, which rapidly hardens to a per- 
 fectly transparent and very glossy coating. For diluting cellu- 
 lose lacquers it is best to use wood spirit. To color them, 
 dissolve an aniline color in strong spirits of wine, add a cor- 
 responding quantity of the solution to the lacquer, and shake 
 vigorously. 
 
 For lacquering articles by dipping, they should be as clean 
 as for plating, and so arranged that the lacquer will run off 
 properly. Allow them to drip over the drip tank until the 
 lacquer stops flowing. Dry in a temperature of ioo° F., if 
 possible, using a thermometer. Dip lacquers will dry in the 
 air, but baking improves the finish. Use a tin-lined wooden 
 tank for holding the lacquer, or a chemically enameled iron 
 tank or a glass tank. When not in use cover with a wooden 
 or sheet galvanized cover. 
 
 For thinning the lacquer when it has become too thick by 
 the evaporation of the solvent, use the so-called thinner, which 
 consists of acetone, benzine and amyl acetate. 
 
 The appearance of rainbow colors upon objects lacquered 
 with pyroxyline lacquer is due either to insufficient cleanliness, 
 especially to the presence of grease upon the objects, or to the 
 
 * For detailed information regarding the manufacture of these lacquers, the reader 
 is referred to "Cellulose and Cellulose Products." By Dr. Josef Bersch. Henry C. 
 Baird & Co., Philadelphia, 1904. 
 
COLORING, PATINIZING, OXIDIZING, ETC. 525 
 
 lacquer having been too much diluted. Objects to be lacquered 
 should be freed from grease by means of a linen rag saturated 
 with benzine, and must not be touched with the hands. If the 
 rainbow colors are due to the lacquer having been too much 
 thinned, let the vessel containing it stand uncovered for some 
 time in a place free from dust, so that it becomes somewhat 
 more concentrated by the evaporation of the solvent. 
 
 Very nice shades of color can be produced by coating the 
 objects, previously well cleansed from grease, with lacquer by 
 dipping, allowing the coat to become almost dry, then suspend- 
 ing the objects for a few seconds in golden-yellow, red, green, 
 etc., essences, known as dipping colors, next washing in water 
 and finally drying. By mixing the dipping colors in various 
 proportions nearly every desired tone of color can be obtained. 
 
 Special invisible lacquer for grille work. It is made for both 
 dip and brush work and when applied to the objects its pres- 
 ence cannot be detected, the dead, matt, grille finish being left 
 absolutely lusterless. In use it can be thinned so as to flow 
 away from the numerous parts that make up a grille, without 
 leaving any runs or waves to cause glossy places. This lac- 
 quer is made by the Egyptian Lacquer Manufacturing Co., of 
 New York and with it the rich subdued effects of dead, matt, 
 sanded, and semi-dead finishes can be protected without in the 
 least affecting their appearance. 
 
 Satin finish lacquer. This lacquer is also made by the 
 above-mentioned firm. It comes in two grades, one for brush 
 and the other for dip work. Its purpose is to maintain the 
 light, but somewhat solid, effect in which body color rather 
 than tints predominate. It can be used to protect a velvet- 
 like tint resembling the ground gold, frosting or satin finish 
 seen in ormolu and colonial gold, as well as on a dull or dead 
 surface, or unpolished, lusterless, matt gold and matt silver. 
 It can also be used to give a dead luster, or a deadened lus- 
 trous surface, for instance, on matt designs upon a lustrous 
 ground. The lacquer lights up the satin finish. 
 
 Dip lacquer for pickled castings to be copper-plated and oxi- 
 
526 ELECTRO-DEPOSITION OF METALS. 
 
 dized. Articles made from iron and steel castings that are 
 pickled or water-rolled, or from hot-rolled steel, where the 
 scale is pickled off, or any other similar work which is pre- 
 pared by the same inexpensive method, when copper-plated 
 and oxidized, must be lacquered with a lacquer which will 
 give life to the naturally dead surface. The pickled objects 
 must not be exposed to the air and should be transferred as 
 quickly as possible from the pickle to the wash-waters and then 
 to the electro-plating bath. 
 
 Helios Dip Lacquer, Special, made by the Egyptian Lacquer 
 Manufacturing Company of New York, has been found to give 
 a fine luster to the dead backgrounds and a finish on the 
 smooth parts equal to work that has been polished. Many 
 other lacquers as a rule, dry down to the natural deadness of 
 goods finished in this way and, therefore, the plating and oxi- 
 dizing is not brought out to their right color. 
 
 Dead black lacquers produce imitation dead and matt finishes. 
 These are variously known as imitation Bower Barff, wrought 
 iron, ebony or rubber finishes. If the same preliminary steps 
 are taken in preparing metal goods for the black lacquers as 
 for japan and enamel, just as durable and lasting results will be 
 obtained in a small fraction of the time and at a minimum cost 
 in labor. The best class of japanning on iron castings, hot or 
 cold rolled steel requires two coats of either thin japan or some 
 other similar preparation, each coat requiring several hours' 
 baking, and usually a delay of several days before the surface 
 of the last coat is in condition to be rubbed down. 
 
 To get the same results with the black lacquers on sand 
 pitted cast iron, two coats of metallic filler, applied with a brush, 
 baked a short time at about i8o° F. to harden, and then 
 rubbed down with fine emery cloth or No. 2 garnet paper, fol- 
 lowed by one or two air-drying coats of lacquer will be suffi- 
 cient. On smooth surfaced metals one or two thin coats of 
 lacquer can be applied in place of the metallic filler as a base 
 for the final coat. In many cases one coat of the lacquer will 
 be found sufficient to give the desired finish, and the entire 
 
COLORING, PATINIZING, OXIDIZING, ETC. 527 
 
 process may be completed in a few hours, where it will require 
 from one to five days to secure the same finish with japan, and 
 besides all the equipment necessary for the latter will be en- 
 tirely eliminated. 
 
 If desired, the metal can be given a light copper plate and 
 then be oxidized as a base for the finishing coat of black lac- 
 quer. 
 
 For high luster finishes such as are obtained with enamels, 
 glossy, black lacquers are used, and to increase the brilliancy 
 and high luster the same as with enameled goods which are 
 given a finishing coat of baking varnish, a high grade of trans- 
 parent lacquer is used over the glossy black lacquer the same 
 as the varnish on the enamel. 
 
 On goods made from non-ferrous metals, such as high-grade 
 optical goods, opera and field glasses, and all classes of instru- 
 ment work, where sliding tubes and other parts are to be fin- 
 ished with a glossy or dead black lacquer, where both beauty 
 and great durability are the chief essentials, the surface of the 
 brass should be first prepared by chemically blacking the 
 metal with copper-ammonia or any other good black dip. 
 Then a filling coat of any black lacquer, preferably a dead 
 black should be used. The surface is then in perfect condition 
 for the finishing coat of black lacquer. A black background 
 and very adhesive surface is obtained by this method, and the 
 finish will withstand the hard usage these goods are made for. 
 
 Dead black lacquer as a substitute for Bower-Barjf. The 
 genuine Bower-Barff is a matted black finish for iron and steel. 
 It is produced by heat and steam liberating the oxygen from 
 the iron and forming magnetic oxide. 
 
 The oven and other equipment required for this finish is not 
 practicable in the average factory, as the demand for goods in 
 this finish, outside builders' hardware, is not commensurate 
 with the cost of providing and maintaining a plant for this 
 purpose. 
 
 A number of imitation finishes are made, by using solutions 
 of sulphur and linseed oil, sulphur, graphite and turpentine, and 
 
528 ELECTRO-DEPOSITION OF METALS. 
 
 other similar solutions. A coating of these mixtures is applied 
 and the metal heated to a red heat to burn it in or else the 
 goods are baked in a muffle. But they are all slow and uncer- 
 tain processes, and some kind of special equipment must be 
 provided to do this work. 
 
 The method for obtaining this finish most in use, and for 
 which any plating room is equipped, is by using an antique 
 black or Bower-Barff lacquer. Such lacquer has a number of 
 advantages over the above-described processes, which can 
 only be used on iron or steel; the lacquer will give the finish 
 on any metal. 
 
 To get the Bower-Barff on iron or steel the metal should 
 first be lightly copper-plated and oxidized ; and if brass or 
 bronze is used it is only necessary to oxidize the metal with 
 any black dip, or electro-oxidize. Then the antique black 
 lacquer is applied for the finish. The lacquer can also be lightly 
 sand-blasted if an increased matt is desired. 
 
 In the above-described processes good results are obtained 
 by the use of the following lacquers, made by the Egyptian 
 Lacquer Manufacturing Co. of New York, Dead Blacks, Egyp- 
 tian Antique Blacks, Ebony, and Rubber Finish Lacquers. 
 
 Spraying of Lacquers. — The application of lacquers by the 
 pneumatic air spray having for the last few years been gradu- 
 ally adopted, has proved advantageous in finishing various 
 goods, the success in application depending upon many minor 
 details of manipulation ; these come readily to the lacquerer 
 while using the spray. 
 
 The high pressure used drives the lacquer onto the object, 
 after which, however, the liquid must take care of itself, and it 
 must then flow together into a smooth surface, or else the whole 
 process is worthless. 
 
 The spraying-on of lacquers to be successfully used depends 
 not only upon the nature of the articles sprayed, but upon the 
 lacquer itself. Special lacquers have been made for these pur- 
 poses, and with them success may readily be obtained. A 
 special lacquer has been made for lamps, chandeliers and gas 
 
COLORING, PATINIZING, OXIDIZING, ETC. 529 
 
 fixtures ; another for silver and white metals; another for build- 
 ers' hardware. With these when applied uniformly, the lacquer 
 spreads evenly and covers the surface entirely without break, 
 and presents an unusually uniform appearance without disfig- 
 uring blotches or patches, indicating an unequal thickness of 
 lacquer. 
 
 The lacquers which we have seen tested were all made by 
 The Egyptian Lacquer Manufacturing Company of New York. 
 In many instances it will be found that ordinary operators with 
 less skill than the trained lacquerer can do very satisfactory 
 work with these machines. 
 
 Spraying black lacquers. — Since the advent of antique effects, 
 such as mission and Flemish, and other dark and subdued, fin- 
 ishes on furniture, etc., the manufacturers of art metal goods 
 have given close attention to having their goods in conformity 
 with the furniture and trimmings in buildings. 
 
 They have found the dead black lacquers the best for this 
 purpose, and the question of application has been solved by 
 the spray, as it was impossible to get the fine results they re- 
 quire by either brushing or dipping the black lacquers, for un- 
 less the operator was skilled in the application of lacquers by 
 these methods there would be such imperfections as streaks, 
 laps, runs or drip. With the spray all these difficulties are ob- 
 viated and the finish cannot be otherwise than perfect, and the 
 laquer thereby used to the best advantage, with the fine result 
 intended for it by the makers. 
 
 To use the spray successfully for this purpose, the base used 
 in the lacquer must be adapted to go through the spray nozzle 
 without clogging and going onto a surface lumpy. With the 
 spray any of the Blacks proposed by The Egyptian Lacquer 
 Manufacturing Co. can be applied on all classes of metals, 
 whether of a design with deep indentations or interstices or on 
 the flattest surface, with artistic perfections. 
 
 The same can be said about the finishing of other goods, 
 such as slate electric switchboards, gas stoves, heaters, steel or 
 other box enclosures, cast parts, steel or brass stampings, or, in 
 34 
 
530 ELECTRO-DEPOSITION OF METALS. 
 
 fact, all other articles made from any of the metals or any of the 
 alloys. 
 
 The Black Lacquers will retain their original finish and re- 
 main black under this heat. And there is no other black made 
 that will adorn this class of goods the same from the points of 
 beauty, durability and salableness. Stoves and heaters have 
 large and porous surfaces as the sheet metal is left in its 
 natural condition just as it comes from the rolling mill, and for 
 this reason it has been found difficult to apply the black 
 lacquer with a brush, but the spray puts it on perfectly, and 
 transforms it from an object of roughness to one of uniformity. 
 To avoid marring the nickel trimmings during the operation of 
 spraying, a mask or other covering is used to protect those 
 parts, and it is then a very rapid process. 
 
 This also applies to all other articles constructed from the 
 same material and on the same order of the stoves and heaters. 
 
 On other metal goods, where designs or ornaments are to be 
 put on, with black or other colored lacquers, stencils are used,. 
 and the lacquers sprayed onto it. With the spray application 
 there will be no runs or other disfigurement of the design. 
 
 The spray, with the blacks or other colored lacquers, can be 
 used. 
 
 Water-dip lacquers and their use. — These lacquers are not, as 
 often believed, lacquers in which water is used. Their name 
 is derived from the fact that after the metal has been dipped 
 or plated, it may, while wet and without drying it, be dipped 
 into the lacquer without in any way affecting the metal finish. 
 
 The advantage of water-dip lacquers is readily appreciated 
 by the manufacturers who are rapidly adopting them for many 
 classes of small work. They are especially well adapted for 
 bright-dipped finishes, such as are usually used in basket work. 
 Tarnish affects this finish almost instantly if it is allowed to 
 dry and then lacquered in the usual way; therefore the lacquer- 
 ing must be carried out as soon as the dipping process has been 
 finished. 
 
 The most flagrant example of tarnishing is in the case of 
 
COLORING, PATINIZING, OXIDIZING, ETC. 53 1 
 
 plated work, particulary goods copper-plated, and to prevent 
 tarnishing, such goods must be lacquered at once. Even the 
 customary drying-out will usually not suffice to prevent the tar- 
 nishing, and the result is either the increase in labor in hand- 
 ling the goods, or the production of a large amount of imper- 
 fect goods. 
 
 The method of drying work in sawdust before lacquering, 
 with the consequent carrying of sawdust into the lacquer, and 
 the frequent discoloration of the finish by wet sawdust, can be 
 entirely eliminated, and this one important improvement alone 
 in handling such work has brought about an extensive use for 
 the water-dip lacquers. 
 
 Since the advent of mechanical platers water-dip lacquers 
 have another and new field, as the goods plated in this way can 
 be put into a mesh basket as soon as taken from the plater and 
 lacquered, which not only gives the finish immediate protec- 
 tion but is in keeping with the quickness and low cost of this 
 method. 
 
 Points to follow when using water- dip lacquers for small 
 work, such as cupboard catches, window fasteners, cheap build- 
 ing and trunk hardware, coat hooks, tacks, furniture nails, and 
 other small specialties and novelties. The work may be placed 
 in a wire mesh basket, rinsed in cold and hot water, dipped into 
 the lacquer, which can be used so thin that there will be no 
 accumulation or drip left, and the work can be dried in bulk 
 without the pieces sticking together. The goods thus lacquered 
 can be put right into a box and sent to the shipping room, 
 where they will dry out hard and with a high luster. 
 
 The Water-Dip Lacquers, made by The Egyptian Lacquer 
 Manufacturing Company of New York, contain ingredients 
 which permit lacquering in bulk of small brass-plated work, 
 copper acid-dipped or oxidized finishes being rinsed in either 
 hot or cold water, and without drying dipped directly into the 
 lacquer. Electro-deposited copper oxidizes rapidly, and espe- 
 cially so in a humid atmosphere. An instant application of 
 these lacquers, while the work still retains its luster is recom- 
 
532 ELECTRO-DEPOSITION OF METALS. 
 
 mended. It is very desirable for bulk, basket or en masse 
 lacquering. 
 
 A large collection of small articles can be perfectly lacquered 
 by simple immersion. 
 
 Syphon out the water every morning from the lacquering 
 tank, either with a rubber hose or by means of a faucet at the 
 bottom of the tank. 
 
 A wire screen, nickel-plated and with a coarse mesh, should 
 be placed in the lacquer jar or tank, three or four inches from 
 the bottom. This will prevent the work from being dipped 
 through the lacquer into the precipitated water, which lies at 
 the bottom of the jar. All dirt and foreign matter carried into 
 the lacquer with the work will sift through the screen and can 
 be drawn off with the water. 
 
CHAPTER XV. 
 
 HYGIENIC RULES FOR THE WORKSHOP. 
 
 In but few other branches of industry has the workman so 
 constantly to deal with powerful poisons as well as other sub- 
 stances and vapors, which are exceedingly corrosive in their 
 action upon the skin and the mucous membranes, as in eletroc- 
 plating. However, with ordinary care and sobriety, all influ- 
 ences injurious to health may be readily overcome. 
 
 The necessity of frequently renewing the air in the workshop 
 by thorough ventilation has already been referred to in chapter 
 IV, " Electro-plating Establishments in General." Workmen 
 exclusively engaged in pickling objects, are advised to neutral- 
 ize the action of the acid upon the enamel of the teeth and the 
 mucous membrane of the mouth and throat, by frequently 
 rinsing the mouth with dilute solution of bicarbonate of soda. 
 Workmen engaged in freeing the objects from grease lose, for 
 want of cleanliness, the skin on the portions of the fingers 
 which come constantly in contact with the lime and caustic 
 lyes. This may be evercome by frequently washing the hands 
 in clean water; and previous to each intermission in the work, 
 the workman should, after washing the hands, dip them in dilute 
 sulphuric acid, dry them, and thoroughly rub them with cos- 
 moline, or a mixture of equal parts of glycerine and water. 
 The use of rubber gloves by workmen engaged in freeing the 
 objects from grease cannot be recommended, they being ex- 
 pensive and subject to rapid destruction. It is better to wrap 
 a linen rag seven or eight times around a sore finger, many 
 workmen using this precaution to proteet the skin from the 
 corrosive action of the lye. 
 
 It should be a rule for every workman employed in an 
 
 (533) 
 
534 ELECTRO-DEPOSITION OF METALS. 
 
 electro-plating establishment not to drink from vessels used in 
 electro-plating manipulations; for instance, porcelain dishes, 
 beer glasses, etc. One workman may this moment use such a 
 vessel to drink from, and without his knowledge another may- 
 employ it the next moment for dipping out potassium cyanide 
 solution, and the first using it again as a drinking vessel may 
 incur sickness, or even fatal poisoning. 
 
 The handling of potassium cyanide and its solutions requires 
 constant care and judgment. Working with sore hands in 
 such solutions should be avoided as much as possible ; but if it 
 has to be done, and the workman feels a sharp pain in the sore, 
 wash the latter quickly with clean water, and apply a few drops 
 of green vitriol solution. 
 
 Many individuals are very sensitive to nickel solutions, 
 eruptions which are painful and heal slowly, breaking out upon 
 the arms and hands, while others may for years come in con- 
 tact with nickel baths without being subject to such eruptions. 
 In such cases prophylaxis is also the safeguard, i. e., to prevent 
 by immediate thorough washing the formation of the eruption 
 if the skin has been brought in contact with the nickel solution, 
 as, for instance, in taking out with the hand an object which 
 has dropped into a nickel bath. 
 
 Below will be found some directions for neutralizing, in case 
 of internal poisoning, the effects of the poison either entirely or 
 at least sufficiently to retard its action until professional aid 
 can be summoned. 
 
 Poisoning by hydrocyanic (prussic) acid, potassium cyanide, 
 or cyanides. — If prussic acid, or the cyanides, be concentrated 
 or have been absorbed in considerable quantity, their action is 
 almost instantly fatal, and there is little hope of saving the 
 victim, although everything possible should be tried. But if 
 these substances have been taken in very dilute condition, 
 they may not prove immediately fatal, and there is some hope 
 that remedial measures may be successfully applied. 
 
 In poisoning with those substances, water as cold as possible 
 should be run upon the head and spine of the patient, and he 
 
HYGIENIC RULES FOR THE WORKSHOP. 535 
 
 should be made to inhale, carefully and moderately, the vapor 
 •of chlorine water, bleaching powder, or Javelle water (hypo- 
 chlorite of soda). 
 
 Should these poisons be introduced into the stomach, there 
 should be administered as soon as possible the hydrate of 
 sesquioxide of iron, or, what is better, dilute solutions of the 
 acetate, citrate, or tartrate of iron. With proper precautions a 
 very dilute solution of sulphate of zinc may be given. 
 
 Poisoning by copper salts. — The stomach should be quickly 
 emptied by means of an emetic or, in want of this, the patient 
 should thrust his finger to the back of his throat and induce 
 vomiting by tickling the uvula. After vomiting, drink milk, 
 white of egg, gum-water, or some mucilaginous decoction. 
 
 Poisoning by lead salts requires the same treatment as poison- 
 ing by copper-salts. A lemonade of sulphuric acid, or an alka- 
 line solution containing carbonic acid, such as Vichy water or 
 bicarbonate of soda, is also very serviceable. 
 
 Poisoning by arsenic. — The stomach must be quickly emptied 
 by an energetic emetic, when freshly precipitated ferric hydrate 
 and calcined magnesia may be given as an antidote. Calcined 
 magnesia being generally on hand, mix it with 15 or 20 times 
 the quantity of water and give this mixture, 3 to 6 tablespoon- 
 fuls, every 10 to 15 minutes. 
 
 Poisoning by alkalies. — Use weak acids, such as vinegar, 
 lemon juice, etc., and in their absence sulphuric, hydrochloric 
 or nitric acid diluted to the strength of lemonade. After the 
 pain in the stomach has diminished, it will be well to adminis- 
 ter a few spoonfuls of olive oil. 
 
 Poisoning by mercury salts. — Mercury salts, and particularly 
 the chloride (corrosive sublimate), form with the white of egg 
 (albumen) a compound very insoluble and inert. The remedy, 
 albumen, is therefore indicated. Sulphur and sulphuretted 
 water are also serviceable for the purpose. 
 
 Poisoning by sulphuretted hydrogen. — The patient should be 
 made to inhale the vapor of chlorine from chlorine water, 
 Javelle water, or bleaching-powder. Energetic friction, espe- 
 
536 ELECTRO-DEPOSITION OF METALS. 
 
 cially at the extremities of the limbs, should be employed. 
 Large quantities of warm and emollient drinks should be given, 
 and abundance of fresh air. 
 
 Poisoning by chlorine, sulphurous acid, nitrous and hyponitric 
 gases. — Admit immediately an abundance of fresh air, and ad- 
 minister light inspirations of ammonia. Give plenty of hot 
 drinks and excite friction in order to conserve the warmth and 
 transpiration of the skin. Employ hot foot baths to remove 
 the blood from the lungs. Afterwards maintain in the mouth 
 of the patient some substance which, melting slowly, will keep 
 the throat moist, such as jujube and marshmallow paste,, 
 molasses candy, and licorice paste. Milk is excellent. 
 
CHAPTER XVI. 
 
 GALVANOPLASTY ( REPRODUCTION ) . 
 
 By galvanoplasty proper is understood the production, with 
 the assistance of the electric current, of copies of articles of 
 various kinds, true to nature, and of sufficient thickness to form 
 a resisting body, which may be detached from the object serv- 
 ing as a mould. 
 
 By means of galvanoplasty we are enabled to produce a sim- 
 ple, smooth plate of copper of such homogeneity as never 
 shown by rolled copper, such copper plates being used for 
 engraving. From a medal, copper-engraving, type or other 
 metallic object, a galvanoplastic copy may be made, which is 
 to be considered as the negative of the original, in so far as it 
 shows the raised portions of the original depressed, and the 
 depressed portions raised. If now from this negative a fresh 
 impression be made by galvanoplasty, the result will be a true 
 copy of the original, possessing the same sharpness and fine- 
 ness of the contours, lines and hatching. 
 
 A true reproduction of plastic works of art can in the same 
 manner be made, but a current-conducting surface is required 
 for effecting the deposit. As seen above, for the reproduction 
 of a metallic original, two galvanoplastic deposits are required, 
 one for the purpose of obtaining a negative, and the other in 
 order to produce from the negative the positive — a copy true 
 to the original. 
 
 Jacoby, the inventor of galvanoplasty, already endeavored to 
 avoid the process of two galvanoplastic deposits by making an 
 impression of the original in a plastic mass (melted rosin, wax, 
 or plaster of Paris), rendering this non-metallic negative con- 
 ductive, and depositing upon it copper, thus obtaining a true 
 copy of the original. 
 
 (537) 
 
538 ELECTRO-DEPOSITION OF METALS. 
 
 It is not within the scope of this work to describe the various 
 phases through which the art of galvanoplasty has passed since 
 its invention. In the historical part reference has been made 
 to several facts, such as making non-metallic impressions 
 (moulds or matrices) conductive by graphite, a discovery for 
 which we are indebted to Murray, and which was also made 
 independently by Jacoby ; further, the production of moulds in 
 gutta-percha; so that in this chapter we have solely to deal 
 with the present status of galvanoplasty. 
 
 I. Galvanoplasty in Copper. 
 
 Copper is the most suitable metal for galvanoplastic pro- 
 cesses, that which is precipitated by electrolysis showing the 
 following valuable properties : It may be precipitated chemic- 
 ally pure, and in this state is less subject to change than ordi- 
 nary commercial copper, or the copper alloys in general use, 
 its tensile strength being 20 per cent, greater than that of 
 smelted copper. Its hardness is also greater, while its specific 
 gravity (18.85) ues between that of cast and rolled copper. 
 
 The physical properties of copper deposited by electrolysis 
 are dependent upon the condition of the bath, as well as on the 
 intensity and tension of the current. 
 
 The bath used for depositing copper is in all cases a solution 
 of blue vitriol. Smee proved by experiment that, with as in- 
 tense a current-strength as possible without the evolution of 
 hydrogen, the copper is obtained as a tenacious, fine-grained 
 deposit. But when the current-strength is so intense that hy- 
 drogen is liberated, copper in a sandy, pulverulent form is 
 obtained, and in a coarsely crystalline form, when the current- 
 strength is very slight. 
 
 At a more recent period, Hiibl and Forster have instituted a 
 series of systematic experiments for the determination of the 
 conditions under which deposits with different physical prop- 
 erties are obtained. Forster, in addition, deserves credit for his 
 investigations of the anodal solution-processes. 
 
 Hiibl worked with 5 per cent, neutral and 5 per cent, acid 
 
GALVANOPLASTY (REPRODUCTION). 539 
 
 solutions, as well as with 20 per cent, neutral, and 20 per cent, 
 acid solutions. The neutral solutions were prepared by boiling 
 blue vitriol solution with carbonate of copper in excess, and the 
 acid solutions by adding 2 per cent, of sulphuric acid of 66° Be. 
 The result was that in the neutral 5 per cent, solution less brit- 
 tle deposits were obtained with a slight current-density than in 
 a more concentrated solution, though the appearance of the 
 deposits was the same. The experiments with acidulated baths 
 confirmed the fact that free sulphuric acid promotes the forma- 
 tion of very fine-grained deposits even with very slight current- 
 densities, and it would seem that the brittleness of copper depos- 
 ited from the acid baths is influenced less by the concentration 
 than by the current-density used. 
 
 With the use of high current-densities, spongy deposits of a 
 dark color, but frequently also sandy deposits of a red color, 
 are obtained from the neutral, as well as from acid, blue vitriol 
 solutions. These phenomena are directly traceable to the 
 effect of the hydrogen reduced on the cathodes. 
 
 However, such spongy deposits are also obtained with the 
 use of slight current-densities, when the concentration of the 
 electrolyte has become less by the exhaustion of the bath on 
 the cathodes, and Mylius and Fromm have shown that copper 
 reduced under such conditions had absorbed hydrogen, while 
 Lenz, in addition to hydrogen, found in a brittle copper de- 
 posit, carbonic oxide and carbonic acid. Soret also found 
 carbonic acid in addition to hydrogen, and attributes to it the 
 unfavorable effect, while he considers a content of hydrogen as 
 unessential for the mechanical properties of the electrolytically 
 deposited copper. 
 
 It is impossible to understand where the carbonic acid is to 
 come from, provided there has been no contamination of the 
 electrolyte by organic substances. 
 
 A. Galvanoplastic Reproductions for Graphic Purposes. 
 (Electrotypy.) 
 
 The processes used in galvanoplasty may be arranged in two 
 classes, viz., the deposition of copper with, or without, the use of 
 
54° ELECTRO-DEPOSITION OF METALS. 
 
 external sources of current, the first comprising galvanoplastic 
 deposits produced by means of the single-cell apparatus, and 
 the other those by the battery, thermo-electric pile, dynamo or 
 accumulator. 
 
 i . Galvanoplastic Deposition in the Cell Apparatus. 
 
 The cell apparatus consists of a vessel containing blue vitriol 
 solution kept saturated by a few crystals of blue vitriol placed 
 in a muslin bag, or a small perforated box of wood, stoneware, 
 etc. In this vessel are placed round or square porous clay 
 cells (diaphragms) which contain dilute sulphuric acid and a 
 zinc plate, the zinc plates being connected with each other 
 and with the objects to be moulded — which may be either 
 metallic or made conductive by graphite — by copper wire or 
 copper rods. 
 
 The objects to be moulded play the same role as the copper 
 electrode in a Daniell cell, and the cell apparatus is but a spe- 
 cies of Daniell cell in which the internal, instead of the external, 
 current is utilized. As soon as the circuit is closed by the 
 contact of the objects to be moulded with the zinc of the por- 
 ous cell, the electrolytic process begins. The zinc is oxidized 
 by the oxygen, and with the sulphuric acid forms zinc sulphate 
 (white vitriol), while the copper is reduced from the blue vitriol 
 solution and deposited in a homogeneous layer upon the articles 
 to be moulded. 
 
 Form of cells. — The form and size of the simple cell-apparatus 
 vary very much according to the purpose for which it is to be 
 used. While formerly a horizontal arrangement of the objects 
 to be copied and of the zinc plates was generally preferred, 
 because with this arrangement the fluids show a more uniform 
 concentration, preference was later on properly given to the 
 vertical arrangement. Particles becoming detached from the 
 zinc plates get only too easily upon the object to be reproduced 
 and cause holes in the deposit, while with the vertical arrange- 
 ment the progress of deposition can at any time be controlled 
 by lifting out the objects without taking the apparatus apart, as 
 
GALVANOPLASTY (REPRODUCTION). 
 
 541 
 
 is the case with the horizontal arrangement. Hence, only such 
 apparatus in which the zinc plates and the objects to be 
 moulded are arranged vertically opposite one to the other will 
 here be discussed. 
 
 A simple apparatus frequently used by amateurs for mould- 
 ing metals, reliefs, etc., is shown in Fig. 142. 
 
 In a cylindrical vessel of glass or stoneware filled with satu- 
 rated blue vitriol solution is^placed a porous clay cell, and in 
 the latter a zinc cylinder projecting about 0.039 to 0.079 inch 
 above the porous clay cell. To 
 the zinc is soldered a copper 
 ring, as plainly shown in the 
 illustration. The clay cell is 
 filled with dilute sulphuric acid 
 (1 acid to 30 water), to which 
 some amalgamating salt may be 
 suitably added. The articles to 
 
 Fig. 142. 
 
 be moulded are suspended to 
 the copper ring, care being had 
 to have the surfaces which are 
 to be covered near and opposite 
 to the cell. To supplement the 
 content of copper, small linen 
 or sail-cloth bags filled with blue 
 vitriol are attached to the upper edge of the vessel. 
 
 Large apparatus. — To cover large surfaces, large, square 
 tanks of stoneware, or wood, lined with lead, gutta-percha, or 
 another substance unacted upon by the bath are used. For 
 baths up to three feet long, stoneware tanks are to be preferred. 
 
 Fig. 143 shows the French form of cell apparatus. In the 
 middle of the vat, and in the direction of its length, is disposed 
 a row of cylindrical cells, close to each other, each provided 
 with its zinc cylinder. A thin metallic ribbon is connected 
 with all the binding screws of the cylinder, and is in contact at 
 its extremities with two metallic bands on the ledges of the 
 depositing vat. The metallic rods supporting the moulds are 
 
5 4 2 
 
 ELECTRO- DEPOSITION OF METALS. 
 
 in contact with the metallic bands of the ledges, and therefore,, 
 in connection with the zincs. 
 
 Fig. 143. 
 
 The German form of cell apparatus is shown in Fig. 144. 
 It is provided with long, narrow, rectangular cells of a corres- 
 pondingly greater height than the column of fluid. 
 
 Fig. 144. 
 
 Across the vat are placed three conducting rods connected 
 
GALVANOPLASTY (REPRODUCTION). 543 
 
 with each other by binding screws and copper wire. To the 
 centre rod, which lies over the cells, are suspended the zinc 
 plates by means of a hook, while the two outer rods serve for 
 the reception of the moulds. 
 
 The zinc surfaces in the simple apparatus should be of a size 
 about equal to that of the surfaces to be reproduced, if dilute 
 sulphuric acid (1 acid to 30 water) is to be used. 
 
 Copper bath for the cell apparatus. — This consists of a solu- 
 tion of 41 to 44 lbs. of pure blue vitriol free from iron, for a 
 lOO-quart bath, with an addition of about 3^ to 4^ lbs. of 
 sulphuric acid of 66° Be., free from arsenic. 
 
 •It is not customary to add to the copper bath serving for 
 graphic purposes a larger quantity of sulphuric acid than that 
 mentioned above, because acid diffuses constantly from the 
 fluid in the clay cells into the bath, thus gradually increasing 
 the content of acid in the latter. If the generation of current 
 is induced by acidulating the water in the clay cells, a further 
 addition of acid for the cells would actually not be required for 
 the progressive development of the current, since the acid- 
 residue formed by the decomposition of the blue vitriol 
 migrates from the zinc of the cells, and brings fresh zinc- ions 
 into solution. A diffusion of acid from the cells into the bath 
 would in this manner be avoided, and only the zinc-sulphate 
 solution formed would diffuse into the copper bath. It appears, 
 however, that without an occasional addition of a smalL quantity 
 of sulphuric acid to the cell-solution the process of deposition 
 runs its course very slowly, which is not desirable for the man- 
 ufacture of cliches. 
 
 It may therefore happen that after working the copper bath 
 for a long time, it contains too much acid, a portion of which 
 has to be removed. For this purpose the bath was formerly 
 mixed with whiting, and the gypsum formed filtered off. This 
 method, however, cannot be recommended, gypsum being not 
 entirely insoluble in water, and it is better to replace it by 
 cupric carbonate or cuprous oxide (cupron). If cupric car- 
 bonate be used, it is advisable thoroughly to stir the bath, or 
 
544 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 what is better, to boil it, so as to remove as completely as pos- 
 sible the carbonic acid. 
 
 By the diffusion of zinc sulphate solution from the clay cells, 
 the bath becomes gradually rich in zinc salt, and it will be 
 noticed that a certain limit — with a content of about io per 
 cent, zinc sulphate — the copper deposits turn out brittle. 
 The bath has then to be entirely renewed. 
 
 The content of copper in the bath decreases in accordance 
 with the copper deposited, and the concentration of the bath 
 would consequently become so low that useful deposits could 
 no longer be obtained, if care were not taken to replace the 
 copper. This is done by suspending perforated baskets of 
 stoneware or lead, filed with blue vitriol crystals, in the bath. 
 
 Since directions are frequently found to which the blue vitriol 
 solutions to be used are given according to their weights by 
 volume or degrees of Be., a table showing the content of blue 
 vitriol is given below. 
 
 Degrees Be. 
 
 5 1 " 
 io° 
 
 12° 
 
 '5 C 
 1 6° 
 
 17° 
 1 8° 
 19° 
 
 20° 
 21° 
 22° 
 
 This solution contains 
 crystallized blue vitriol. 
 
 5 per cent. 
 ii 
 
 13 " 
 
 17 « 
 
 18 " 
 
 19 " 
 
 20 " 
 
 21 " 
 23 
 
 24 " 
 
 25 » 
 
 Electro-motive force. — The effective electro-motive force in 
 the cell apparatus amounts to about 0.75 volt. It may be 
 regulated by either bringing the mattrices more closely to the 
 diaphragms, or removing them a greater distance from them. 
 In the first case, the resistance of the bath is decreased, the 
 current-density being consequently increased, while in the 
 
GALVANOPLASTY (REPRODUCTION). 545 
 
 other, the resistance of the bath is increased and the current 
 density decreased. 
 
 For regulating the electro- motive force a rheostat may also 
 be placed in the circuit, between the matrices and the zincs, 
 instead of connecting them directly by a copper wire. Although 
 this method is not in vogue, it is certainly recommendable. 
 
 For working on a large scale, the cell apparatus is but seldom 
 used, at least not for the production of electros. It is, however, 
 occasionally employed for the reproduction of objects of art 
 with very high reliefs, so as to cover them as uniformly as pos- 
 sible and quite slowly with copper. The cell apparatus is also 
 still liked for the production of matrices. 
 
 2. Galvanoplastic Deposition by the Battery and Dynamo. 
 
 Since it has been shown in the preceding section that a 
 cell apparatus is to considered as a Daniell cell closed in 
 itself, it will not be difficult to comprehend that in economical 
 respects no advantage is offered by the production of galvano- 
 plastic depositions by a separate battery, because in both cases 
 the chemical work is the same, and the zinc dissolved by the 
 use of the Daniell or Bunsen cell effects no greater quantity 
 of copper deposit in the bath than the same quantity of zinc 
 dissolved in the cells of the single apparatus. In other respects 
 the use of a battery, however, offers great advantages. 
 
 The employment of an external source of current requires 
 the same arrangement as shown in Figs. 50 and 51, pp. 142 and 
 143, copper anodes being placed in the bath and connected with 
 the anode pole of the battery. Copper being dissolved in the 
 anodes, the sulphuric acid residue which is liberated is satu- 
 rated with blue vitriol, the content of copper being thus, if not 
 entirely, at least approximately, kept constant. Furthermore, 
 no foreign metallic salts reach the bath, as is the case in the 
 simple apparatus, by zinc sulphate solution penetrating from 
 the clay cells and causing the formation of rough and brittle 
 deposits of copper. With the use of anodes of chemically pure 
 copper the bath will thus always remain pure. 
 35 
 
546 ELECTRO-DEPOSITION OF METALS. 
 
 The current may also be regulated within certain limits by 
 bringing the anodes more closely to the objects, or removing 
 them a greater distance from them. The principle advantage, 
 however, consists in that by placing a rheostat in the circuit 
 the current strength can be controlled as required by the dif- 
 ferent kinds of moulds. 
 
 a. Depositions with the Battery. 
 
 Cells. — The Daniell cell described on p. 71, yields an electro- 
 motive force of about 1 volt, and is much liked for this pur- 
 pose. Since the copper bath for galvanoplastic purposes re- 
 quires for its decomposition an electro-motive force of only 0.5 
 to 1 volt, it will be best for slightly depressed moulds to couple 
 the elements for quantity (Fig. 21, p. 88) alongside of each 
 other; and only in cases where the particular kind of moulds 
 requires a current of greater electro-motive force to couple two 
 cells for electro-motive force one after the other, an excess of 
 current being rendered harmless by means of the rheostat, or 
 by suspending larger surfaces. 
 
 Bunsen or Meidinger cells may, however, be used to great 
 advantage, since the zincs of the Daniell cells become tarnished 
 with copper, and have to be frequently cleansed if the process 
 is not to be retarded or entirely interrupted. The Bunsen cells 
 need only be coupled for quantity, their electro-motive force 
 being considerably greater. To be sure, the running expenses 
 are much greater than with Daniell cells, at least when nitric 
 acid is used for filling. The lasting constancy of the Meidinger 
 cells would actually make them the most suitable of all for con- 
 tinuous working, but by reason of their slight current- strength 
 a large number of them would have to be used. 
 
 All that has been said under " Installations with Cells," p. 135, 
 in regard to conducting the current, rheostats, conducting rods, 
 anodes, etc., applies also to plants for the galvanoplastic depo- 
 sition of copper with batteries. 
 
GALVANOPLASTY (REPRODUCTION). 547 
 
 b. Depositions with the Dynamo. 
 
 The improvements in dynamos have also benefited the in- 
 dustrial practice of galvanoplasty, and problems can now be 
 solved in a much shorter time and with much greater ease than 
 in the cell apparatus, without having to put up with the ob- 
 noxious vapors which make themselves very disagreeably felt 
 in working on a large scale with a simple apparatus. That the 
 use of a dynamo offers decided advantages is best proved by 
 the fact, that no galvanoplastic plant of any importance works 
 at present without one, and there can scarcely be any doubt 
 that establishments which still work exclusively with the simple 
 apparatus will be forced to make use of a dynamo, if they wish 
 to keep up with competition as regards cheapness and rapidity 
 of work. 
 
 Dynamos. — It is best to use a dynamo capable of yielding a 
 large quantity of current with an impressed electro-motive force 
 of 2, or, at the utmost, 3 volts, in case it is not to serve for 
 rapid galvanoplasty; for the latter a machine of 5 to 10 volts 
 impressed electro-motive force is required. For the old, slow 
 process by which deposits for graphic purposes are produced 
 in 5 to 6 hours, an impressed electro-motive force of 2 volts 
 suffice for baths coupled in parallel. If, however, there are to 
 be charged from the dynamo one or more accumulator cells, 
 which are to furnish current to the bath while the steam engine 
 is not running during the intermission of work, or to finish de- 
 posits after working hours, the impressed electro-motive force, 
 with cells coupled in parallel, must be 3 volts, and with cells 
 coupled in series in proportion to their number. 
 
 It may also happen that in a galvanoplastic plant currents of 
 greatly varying electro-motive force may be required for deposi- 
 tions. For depositing copper, according to the old process, 
 there should, for instance, be at disposal a great current- 
 strength with 1 to 1.5 volts, while for a rapid galvanoplastic 
 bath a current of 6 volts is at the same time to be used. If a 
 dynamo of 6 volts impressed electro-motive force were to be 
 used, the excess of electro-motive force would have to be de- 
 
54 8 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 stroyed by rheostats in front of the baths requiring a slight 
 electro-motive force, in case it is not convenient to couple these 
 baths in series (see later onV The destruction of electro-motive 
 force is, however, not economical, and, in such a case, the use 
 of two dynamos with different electro-motive forces is advisable. 
 It is best to combine both dynamos with a motor-generator, if 
 the plant is connected with a power circuit of a central station, 
 the construction being such that the dynamo, which is perhaps 
 only temporarily in use, can be readily disengaged. 
 
 Fig. 145 shows such a double aggregate, built by the firm of 
 Dr. G. Langbein & Co. for the German Imperial Printing Office. 
 
 Fig. 145. 
 
 The larger dynamo has a capacity of 1000 amperes and 2.5 
 volts, and the smaller one, one of 250 amperes and 6 volts. 
 
 Current-conductors of sufficient thickness, corresponding to 
 the quantities of current have to be provided to prevent loss of 
 current by resistance in the conductors. To avoid repetitions, 
 we refer to what has been said on this subject under "Arrange- 
 ment of Electro-plating Establishments," the directions there 
 given applying also to the galvanoplastic process. 
 
 Coupling the baths. — When coupling the baths in parallel, 
 each bath will have to be provided with a rheostat and am- 
 meter, while a voltmeter with a voltmeter switch may be em- 
 ployed in common for several baths. If the baths are of 
 
GALVANOPLASTY (REPRODUCTION). 549 
 
 exactly the same composition and the same electrode-distances 
 are maintained in them, regulation of the current by the shunt- 
 rheostat of the dynamo will suffice. 
 
 Coupling the baths in series may under certain conditions be 
 of advantage. In such a case, a dynamo of adequately higher 
 electro-motive force will of course have to be employed. 
 Coupling the baths in series implies that the cathode (object) 
 surfaces in all the baths are of the same size, or at least 
 approximately so. The baths are coupled in series by con- 
 necting the anodes of the first bath with the -f- poles of the 
 dynamo, the cathodes of the first bath with the anodes of the 
 second, the cathodes of the second with the anodes of the third, 
 and so on, and reconducting the current from the cathodes of 
 the last bath to the — pole of the dynamo (Fig. 68). 
 
 With this plain coupling in series, the impressed electro- 
 motive force is uniformly distributed in all the baths, so that 
 with four baths coupled in series, and an impressed electro- 
 motive force of 4 volts, an electro-motive force of 1 volt is pre- 
 sent in each bath if the conductivity resistance be left out of con- 
 sideration. Hence, it may be readily calculated how many 
 baths have to be coupled in series to utilize a given impressed 
 electro-motive force, when the electro-motive force required for 
 one bath is known. 
 
 If, for instance, there is a dynamo with 6 volts impressed 
 electro-motive force, and the electro-motive force required for 
 one bath is 1.5 volts, then 4 baths have to be coupled in series, 
 since they require 1.5 X 4 = 6 volts. If, however, only one volt 
 is required for one bath, then 6 baths will have to be coupled 
 in series, or, in case fewer baths are to be used, the impressed 
 electro-motive force of the dynamo has to be suitably regulated 
 by the shunt rheostat. 
 
 Besides, the simple coupling in series, mixed coupling, also 
 called coupling in groups, a combination of coupling in parallel 
 and in series, may be employed. This is effected by combin- 
 ing a number of baths to a group in parallel, and coupling 
 several such groups in series. 
 
550 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 The advantage offered by this mixed coupling to large gal- 
 vanoplastic plants is as follows : 
 
 With the simple couple in series, the electrode-surfaces in 
 all the baths must be of the same size. When finished objects 
 are taken from a bath, the current conditions are changed, until 
 in place of the object taken out fresh surfaces of the same size 
 are suspended in the bath, and as this cannot always be imme- 
 diately done, irregularities in working will result. If, however, 
 the baths be combined in groups in the manner shown in Fig. 
 146, only the cathode-surfaces of each of the groups coupled 
 
 Fig. 146. 
 
 W SHUNT %o rm „ s 
 
 in parallel, need to be of the same size, or approximately so, 
 and with the observation of this condition it is entirely indif- 
 ferent whether a bath of one group is not at all charged with 
 cathodes. 
 
 For the adjustment of any difference in the electro-motive 
 force in the baths of the separate groups, it is advisable to place 
 in each bath a rheostat in shunt-. 
 
 While with baths coupled in parallel the electro-motive force 
 of the dynamo corresponds to the requisite electro motive force 
 of one bath, but the current-strength is calculated from the sum 
 
GALVANOPLASTY (REPRODUCTION). 55 I 
 
 of all the cathodes present in the different baths, with baths 
 coupled in series only the total cathode surface of one bath is 
 decisive as regards the current-strength, the electro-motive force 
 of the machine resulting from the sum of the electro-motive 
 forces of the separate baths. With baths coupled in groups the 
 requisite impressed electro-motive force is calculated from the 
 number of groups of baths coupled in series, but the current- 
 strength from the total cathode-surface of only one group. 
 
 The following examples may serve as illustrations : Suppose 
 3 baths, each with 100 square decimeters cathode-surface, are 
 coupled in parallel, and the electro-motive force for one bath is 
 1.5 volts. Hence in the three baths there are 100 X 3 = 300 
 square dec'meters cathode surface, and if, for instance, one square 
 decimeter requires 2 amperes, then the 3 baths require 300 X 2 
 = 600 amperes. Thus the capacity of the dynamo must be 600 
 amperes, with an impressed electro-motive force of 1.5 volts, 
 but for practical reasons a machine of 2 volts should be 
 selected. 
 
 Suppose 4 baths, each charged with 100 square decimeters 
 cathode-surface, are coupled in series, and the bath electro- 
 motive force is 1.25 volts, and the current- density 2 amperes. 
 Hence there will be required, 100 X2= 200 amperes, and 1.25 
 X 4 = 5 volts. 
 
 Suppose 9 baths are coupled, mixed in three groups of 3 
 baths each, the latter being coupled in parallel, and the three 
 groups coupled in series. Now if each group be charged with 
 300 square decimeters cathode-surface and thebath electro- 
 motive force be also 1.25 volts and the current-density 2 am- 
 peres, then there will be required, 300 X 2 =600 amperes, and 
 1.25 X 3 = 3-75 volts, or practically, 4 volts impressed electro- 
 motive force. 
 
 c. Combined Operation with Dynamo and Accumulators. 
 
 When, as is frequently the case in galvanoplastic plants 
 working with the slow process of deposition, electrotypes have 
 to be finished in a hurry, recourse has to be had to night work. 
 
b^ 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 If the dynamo is not driven by a motor-generator fed from a 
 power circuit of a central station, it will be necessary to use for 
 night work either a cell apparatus, or to feed the bath from ac- 
 cumulators. 
 
 An interruption in the galvanoplastic deposition of copper 
 is a great drawback, because an additional deposit made after 
 the current has been interrupted adheres badly upon the one 
 previously made, blisters being readily formed, or the deposit 
 peeling off. The chief object in the use of an accumulator is 
 that it allows of the work being carried on during the noon 
 hour when the steam engine is generally stopped, and of finishing 
 matrices which are suspended late in the afternoon, after work- 
 ing hours. 
 
 In order to avoid repetition, the reader is referred to what 
 has been said on p. 182 et seq., in regard to the use of an ac- 
 cumulator in addition to the dynamo. 
 
 For galvanoplasty in copper by the slow process, one accu- 
 mulator cell of sufficient capacity to supply current for 2 or 3 
 hours is, as a rule, all that is required. This cell is charged 
 from the dynamo at the same time, while the latter directly 
 operates the bath, a machine with an impressed electro-motive 
 force of 3 volts being required for the purpose. 
 
 If several cells have to be used, it has to be decided accord- 
 ing to the capacity of the dynamo, whether they are to be 
 charged in parallel or in series. If great demands are for a 
 longer time made on the accumulators, it is advisable to use a 
 separate dynamo for charging purposes. 
 
 Copper baths for galvanoplastic depositions with a separate 
 source of current. — The directions for the composition of the 
 bath vary very much, some authors recommending a copper 
 solution of 1 8° Be., which is brought up to 22° Be. by the addi- 
 tion of pure concentrated sulphuric acid. Others again increase 
 the specific gravity of the bath up to 25 Be. by the addition 
 of sulphuric acid, while some prescribe an addition of 3 to 7 
 per cent, of sulphuric acid. 
 
 It is difficult to give a general formula suitable for all cases,. 
 
GALVANOPLASTY (REPRODUCTION). 553 
 
 because the addition of sulphuric acid will vary according to the 
 current strength at disposal, the nature of the moulds, and the 
 distance of the anodes from the objects. The object of adding 
 sulphuric acid is, on the one hand, to render the bath more 
 conductive and, when used in proper proportions, to make the 
 deposit more elastic and smoother, and prevent the brittleness 
 and coarse-grained structure which, under certain conditions, 
 appear. 
 
 However, it is also the function of the sulphuric acid to pre- 
 vent the primary decomposition of the blue vitriol, and to 
 effect in a secondary manner the reduction of the copper. As 
 has been explained on p. 49, acids, bases, and salts, dissociate 
 in aqueous solution, and only substances which dissociate 
 in aqueous solution are conductors of the electric current, 
 they being the better conductors, the greater their power 
 of dissociation is. The dilute sulphuric acid being much more 
 dissociated, takes charge in a much higher degree of con- 
 ducting the current than the less strongly dissociated blue 
 vitriol solution. Consequently the kathion of the sulphuric 
 acid' — the hydrogen-ions — migrates to the cathode, and effects 
 the decomposition of the blue vitriol, an equivalent quantity of 
 copper being reduced upon the cathode. 
 
 The addition of a large quantity of sulphuric acid, as recom- 
 mended by some authors, cannot be approved, it having been 
 found of advantage only in a few cases. 
 
 For depositing with a battery, somewhat more sulphuric 
 acid may for economical reasons be added to the bath than 
 when working with the current of a dynamo. The following 
 composition has in most cases been found very suitable for the 
 reproduction of shallow, as well as of deep, moulds : 
 
 Blue vitriol solution of 19%° Be. 100 quarts, sulphuric acid 
 of 66° Be. free from arsenic 4^ to 6 Y / 2 lbs. 
 
 The bath is prepared as follows : Dissolve 48^ lbs. of blue 
 vitriol in pure warm water, and, to avoid spurting, add grad- 
 ually, stirring constantly, the sulphuric acid. At the normal 
 temperature of 59 F. the bath may be worked with a current- 
 
5 54 ELECTRO-DEPOSITION OF METALS. 
 
 density of up to 2 amperes, and if the bath be agitated, the 
 current-density may be up to 3 amperes. 
 
 Properties of tJic deposited copper. — As regards elasticity, 
 strength and hardness of galvanoplastic copper deposits, Hubl 
 determined that copper of great tenacity, but possessing less 
 hardness and strength, is deposited from a 20 per cent, solution 
 with the use of a current-density of 2 to 3 amperes. 
 
 For copper printing plates a 20 percent, solution compounded 
 with 3 per cent, sulphuric acid, and current-density of 1.3 am- 
 peres was found most suitable by Giesecke. Dissolve for this 
 purpose 50.6 lbs. of blue vitriol for a 100 quart bath and add 
 6.6 lbs. of sulphuric acid. 
 
 Forster and Seidel have shown that the mechanical proper- 
 ties of the copper are materially influenced by the temperature 
 of the electrolyte. From Forster's investigations, with a 
 cathodal current-density of 1 ampere in an electrolyte com- 
 posed of 150 grammes blue vitriol and 50 grammes sulphuric 
 acid per liter, it appears that the copper obtained with the 
 electrolyte at 140 F. showed the greatest tenacity, it decreas- 
 ing again at a higher temperature while the strength slightly 
 increased. 
 
 The nature, i. e., the composition of the electrolyte also exerts 
 an influence upon the structure of the deposit. Forster com- 
 pounded the electrolyte previously used with a quantity of 
 sodium sulphate equivalent to that of the blue vitriol. The 
 result showed that the strength as well as the tenacity was un- 
 favorably influenced at a higher temperature. 
 
 Current conditions. — In order to obtain a dense, coherent and 
 elastic deposit in the acid copper bath, it is first of all necessary 
 to bring the current-strength into the proper proportion to the 
 deposition-surface, this applying to depositions in the simple 
 apparatus, as well as to that produced with an external source 
 of current. 
 
 The stronger the sulphuric acid in the clay cells of the simple 
 apparatus is, the more rapidly is the copper precipitated upon 
 the moulds. If the zinc-surfaces of the clay cells are very large 
 
GALVANOPLASTY (REPRODUCTION). 555 
 
 in proportion to the surfaces of the moulds, the deposition of 
 copper also takes place more rapidly. The rapid reduction of 
 copper, however, must above all be avoided if deposits of de- 
 sirable qualities are to be obtained, because a deposit of copper 
 forced too rapidly turns out incoherent, spongy, frequently full 
 of blisters and, with a very strong current, even pulverulent. 
 
 The color of the deposit is to some extent a criterion of its 
 quality, a red-brown color indicating an unsuitable deposit, 
 while a good, useful one may be counted upon when it shows 
 a beautiful rose color. 
 
 For filling the clay cells, it has previously been stated that 
 the acid is to be diluted in the proportion of I part of concen- 
 trated sulphuric acid of 66° Be. to 30 parts of water, the zinc 
 surface being supposed to be of about the same size as the 
 matrix-surface. If the zinc-surface should be smaller, stronger 
 acid may be used, and if it be larger, the acid may be more 
 dilute. The proper concentration of the acid in the clay cells 
 is readily ascertained from the progressive result of the deposit 
 and its color. 
 
 What has been said in reference to the current-strength 
 applies also to the deposition of copper with a separate source 
 of current (battery or dynamo). The current-strength must 
 be so adjusted by means of a rheostat as to allow of compar- 
 atively rapid deposition without detriment to the quality of the 
 •deposit. 
 
 According to the composition of the bath, a fixed minimum 
 and maximum current-density corresponds to it, which must 
 not be exceeded if serviceable deposits are to be obtained. 
 There is, however, a further difference according to whether 
 the bath is at rest or agitated. Hiibl obtained the following 
 results : 
 
556 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Blue vitriol solution. 
 
 15 percent, blue vitriol, without sulphuric 
 
 acid 
 
 15 per cent, blue vitriol, with 6 per cent. 
 
 sulphuric acid 
 
 20 percent, blue vitriol, without sulphuric 
 
 acid 
 
 20 per cent, blue vitriol, with 6 per cent. 
 
 sulphuric acid 
 
 Minimum and maximum current-density 
 per 15.5 square inches. 
 
 With solution at 
 
 rest. 
 
 Amperes. 
 
 2.6 to 3.9 
 
 i-5 " 2 -3 
 
 3-4 " 5 1 
 
 2.0 " 3.0 
 
 With solution gently 
 agitated. 
 Amperes. 
 
 3.9 to 5.2 
 
 2.3 " 3.0 
 
 5.1 " 6.8 
 
 3.0 " 4.0 
 
 Touching the addition of sulphuric acid, it was shown that 
 no difference in the texture of the deposit is perceptible if the 
 addition of acid varies between 2 and 8 per cent. 
 
 The most suitable current-density for the production of good 
 deposits with a bath of the composition given on p. 554, when 
 at rest, is for slow deposition 1 to 2 amperes per square deci- 
 meter of matrix surface, and when the bath is agitated 2 to 3 
 amperes. The current-densities for rapid galvanoplastic baths 
 will be given later on. 
 
 Since for ordinary, strongly acid copper baths an electro- 
 motive of y 2 , to at the utmost 1^, volts is required, the more 
 powerful Bunsen cells will have to be coupled alongside each 
 other, while of the weaker Daniell or Lallande cells, two, or of 
 the Meidinger cells, three, will have to be coupled one after the 
 other, and enough of such groups have to be combined to 
 make their active zinc-surfaces of nearly the same size as the 
 surfaces of the matrices. However, for strongly acid baths 
 coupling the separate weaker cells alongside each other also 
 suffices. 
 
 When all the parts of the matrices, as well as the deeper por- 
 tions, are covered with copper, the current is weakened in case 
 a deposit of a pulverulent or coarse-grained structure appears 
 on the edges of the moulds, and it is feared that the deposit 
 
GALVANOPLASTY (REPRODUCTION). 557 
 
 upon the design or type might also turn out pulverulent. The 
 current need not be weakened more than is necessary to prevent 
 the dark deposits on the edges from progressing further to- 
 wards the interior of the mould-surfaces. If, by reason of too 
 strong a current, pulverulent copper has already deposited upon 
 the design or type, and the fact is noticed in time and the cur- 
 rent suitably weakened, the deposit can generally be saved by 
 the layers being cemented together by the copper which is 
 coherently deposited with the weaker current. 
 
 In depositing with the dynamo, the current-density and elec- 
 tro-motive force have to be properly regulated by means of a 
 rheostat. 
 
 Brittle copper deposits may be caused, not only by an unsuit- 
 ble composition of the electrolyte, improper current-densities 
 and impure anodes (see later on), but also by contamination of 
 the bath with non-metallic substances, certain organic sub- 
 stances especially having an unfavorable effect upon the prop- 
 erties of the copper deposit. 
 
 Forster found that by using for suspending the cathodes, 
 supports which had been coated with rubber solution in benzol 
 is a protection against the attacks of the electrolyte and the 
 air, smooth copper deposits of a beautiful velvety appearance 
 were to be sure obtained, but they were so brittle that they 
 could not be detached unbroken from the basis. The deposit 
 contained small quantities of carbonaceous substances which 
 could have been derived only from a partial solution of the 
 rubber. 
 
 Hiibl also describes the fact of having obtained brittle copper 
 by the electrolyte having been contaminated by a small quan- 
 tity of gelatine which had passed into solution in the prepara- 
 tion of an electrotype upon heliographic gelatine reliefs. Dr. 
 Langbein had frequently occasion to notice, that baths in 
 tanks lined with lead, and provided with a coat of asphalt and 
 mastic dissolved in benzol, yielded brittle copper when the 
 coat of lacquer was not perfectly hard, and it was observed 
 that by reason of an accidental contamination of the electrolyte 
 
558 ELECTRO DEPOSITION OF METALS. 
 
 with gelatine, deposits were formed which showed the branched 
 formation of crystals similar to an arbor Saturni, and were ex- 
 tremely brittle. 
 
 Erich Miiller and P. Behntje * have recently investigated the 
 effects of such organic additions (colloids) on blue vitriol solu- 
 tions, additions of gelatine, egg albumen, gum, and starch being 
 drawn upon for comparing the effects. After an electrolysis 
 for 15 hours, the deposits obtained from baths compounded 
 with gum and starch solutions showed no material difference in 
 appearance from deposits obtained with the same current- 
 strength from pure acidulated blue vitriol solution. Deposits 
 obtained from baths to which gelatine and egg albumen had 
 been added, however, had lustrous streaks running from top to 
 bottom. The weight of these deposits was, moreover, greater 
 than that of the copper obtained from pure solution, and the 
 presence of gelatine in the deposit could be established by 
 analysis. Further experiments proved that the above-men- 
 tioned phenomena were dependent on the current-density, and. 
 with smaller additions of gelatine, and 3.5 amperes, thoroughly 
 homogeneous, mirror-bright copper coatings could be obtained, 
 thus rendering it possible to produce, by an addition of gela- 
 tine, a lustrous coppering from acid copper baths. The prop- 
 erties of this copper are, however such as are not desirable for 
 galvanoplastic purposes. 
 
 It is therefore absolutely necessary to exclude such organic 
 substances, even if only dissolved in traces, from contact with 
 the electrolyte. 
 
 Duration of deposition. — The time required for the production 
 of a deposit entirely depends, according to what has been said 
 on p. 127, on the current density used. One ampere deposits 
 in one hour 1.18 grammes of copper, and from this, when the 
 current-density is known, the thickness acquired by the deposit 
 in a certain time can be readily calculated. 
 
 A square decimeter of copper, 1 millimeter thick, weighs 
 about 89 grammes, and to produce this weight with I ampere 
 
 * Zeitschrift fiir Elektrochemie. XII. 317. 
 
GALVANOPLASTY (REPRODUCTION). 
 
 559 
 
 current-density, there are required y 8 T 9 8=75 hours. By taking 
 the thickness of a deposit as 0.18 millimeter, which suffices for 
 all purposes of the graphic industry, then I square decimeter 
 will weigh 89 X 0.18 = 16.02 grammes, and for their deposition 
 with 1 ampere current-density will be required, in round num- 
 bers, y/f =13^ hours. 
 
 Below is given the duration of deposition for electrotypes 
 0.18 millimeter thick with different current-densities, and in 
 addition the time is stated which would be required for the for- 
 mation of a deposit 1 millimeter thick, so that the calculation of 
 the time required for depositing a copper film of a thickness 
 different from 0.18 millimeter can be readily made by multi- 
 plying the number of hours in the third column by the desired 
 thickness of the copper. 
 
 With a current-density of 
 
 Duration of deposition for 
 0.18 millimeter thick- 
 ness of copper 
 
 A deposit of 
 thickness 
 
 1 millimeter 
 requires 
 
 0.5 ampere 
 
 27 
 
 hours 
 
 *S°% 
 
 hours 
 
 0.75 
 
 18 
 
 " 
 
 IOI M 
 
 
 ' 
 
 1.0 " 
 
 I3K 
 
 " 
 
 75 
 
 
 
 1.5 
 
 9 
 
 u 
 
 50 
 
 
 EC 
 
 2.0 " 
 
 6% 
 
 it 
 
 37K 
 
 
 t 
 
 2.5 
 
 1% 
 
 " 
 
 30 
 
 
 ' 
 
 3.0 
 
 4 l A 
 
 " 
 
 25 
 
 
 1 
 
 4.0 
 
 3* 
 
 " 
 
 18% 
 
 
 I 
 
 5.0 
 
 2% 
 
 " 
 
 15 
 
 
 « 
 
 6.0 
 
 *y± 
 
 u 
 
 i?K 
 
 
 ' 
 
 7.0 
 
 2 
 
 it 
 
 ™% 
 
 
 t 
 
 8.0 
 
 ir'o 
 
 a 
 
 9.1 
 
 
 t 
 
 9.0 
 
 ~/2 
 
 a 
 
 8K 
 
 
 i 
 
 Nitrate baths. — To shorten the duration of deposition, baths 
 were a few years ago recommended which, in place of blue 
 vitriol, are prepared with cupric nitrate, and which by reason 
 of being more concentrated will bear working with greater 
 current-densities. To further increase their conducting power, 
 ammonium chloride is added. Independent of the fact that 
 deposits obtained in these baths are inferior in quality to those 
 produced in blue vitriol baths, such baths require frequent cor- 
 
560 ELECTRO-DEPOSITION OF METALS. 
 
 rections, they becoming readily alkaline in consequence of the 
 formation of ammonia. Besides, in view of the short time 
 required for deposition by the rapid galvanoplastic process, 
 there is no necessity for nitrate baths. 
 
 Agitation of the baths. — From Hubl's table it will be seen that 
 a copper bath in motion can bear considerably higher current- 
 densities, and hence will work more rapidly than a bath at rest. 
 In electrolytically refining copper it was found that, if the 
 process of reducing the copper is to proceed in an unexcep- 
 tional manner, the bath must be kept entirely homogeneous 
 in all its parts. When a copper bath is at rest, and the opera- 
 tion of deposition is in progress, the following process takes 
 place : The layers of fluid on the anodes having by the solution 
 of copper become specifically heavier, have a tendency to sink 
 down, while layers of fluid which have become poorer in cop- 
 per, and consequently specifically lighter, rise on the cathodes 
 to the surface. These layers contain more sulphuric acid than 
 the lower ones, hence their resistance is slighter and their con- 
 ducting power greater, the latter being still further increased by 
 the layers heated by the current also rising to the surface. In 
 consequence of this process there will be a variable growth in 
 thickness of the deposit, and various phenomena may appear 
 which, according to the composition of the layers in question, 
 can be theoretically established. If the intermixture of the 
 electrolyte has not progressed to any great extent, and thus 
 there are no great differences, as regards composition, between 
 the upper and lower layers of the fluid, the deposit will be quite 
 uniformly formed upon the lower as well as upon the upper 
 portions of the cathodes, although it will be somewhat thicker 
 on the lower portions, which dip into the more concentrated 
 copper solution, than on the upper portions. This difference 
 in thickness in favor of the lower cathode-surfaces will become 
 more pronounced as the concentration of the lower layers of 
 the fluid increases, while the growth in thickness on the upper 
 cathode-surfaces is kept back. The concentration of the upper 
 layers of fluid may finally happen to become so slight that the 
 
GALVANOPLASTY (REPRODUCTION). 561 
 
 hydrogen-ions do not meet with sufficient blue vitriol for de- 
 composition, and hydrogen will consequently be separated and 
 the formation of a sandy or spongy deposit noticed. 
 
 It may, however, also happen that a current of slight electro- 
 motive force cannot overcome the greater resistance of the 
 more concentrated lower layers of fluid, and in consequence 
 passes almost exclusively through the upper layers. So long 
 as the hydrogen- ions find sufficient blue vitriol and the current- 
 density is slight, the growth of the deposit on the upper 
 cathode-surfaces may, in this case, progress, while it comes to 
 a stand-still on the lower ones. 
 
 Experiments by Sand * have shown that in consequence of 
 local exhaustion of blue vitriol in an acid copper bath more than 
 60 per cent, of the current is, notwithstanding natural diffusion, 
 consumed for the evolution of hydrogen. The production of 
 serviceable deposits under such conditions is of course impos- 
 sible. 
 
 By constant agitation of the bath, the layers poorer in metal, 
 which have deposited copper on the cathodes, are rapidly re- 
 moved, and layers of fluid richer in metal are conveyed to the 
 cathodes, the greatest possible homogeneity of the bath being 
 thus effected, and the operation of deposition becoming 
 uniform. 
 
 Baths in motion show less inclination to the formation of 
 buds and other rough excrescences, and hence the current- 
 density may be greater than with solutions at rest, the result 
 being that deposition is effected with greater rapidity. These 
 experiences gathered in electro-metallurgical operations on a 
 large scale, have been advantageously applied to galvanoplasty. 
 
 Stirring contrivances. — Constant agitation of the copper bath 
 may be effected in various ways. A mechanical stirring con- 
 trivance may be provided, or agitation may be effected by 
 blowing in air, or finally, by the flux and reflux of the copper 
 solution. 
 
 With the use of a stirring apparatus, stirring rods of hard 
 
 * Zeitschrift fiir physikalishe Chemie. xxxv. 641. 
 36 
 
562 ELECTRO-DEPOSITION OF METALS. 
 
 rubber or glass which are secured to a shaft running over the 
 bath, swing like pendulums, between the electrodes. This 
 motion of the shaft is effected by means of leverage driven 
 from a crank pulley. The stirring rods should not move with 
 too great rapidity, otherwise the slime from the anodes, which 
 settles in the bath, might be stirred up. 
 
 Agitation of the bath has also been effected by slowly re- 
 volving, by means of a suitable mechanism, cast copper anodes 
 of a square cross-section, this mode of motion having the ad- 
 vantage of very thoroughly mixing the electrolyte without 
 being too violent. 
 
 If the bath is to be agitated by blowing in air, the latter is 
 forced in by means of a pump through perforated lead pipes,' 
 arranged horizontally about two inches from the bottom of the 
 tank. 
 
 It is best to use a small air compressor in connection with an 
 air chamber provided with a safety valve. The quantity of air 
 to be conveyed to the perforated lead pipes is regulated by 
 means of a cock or valve. The number and size of the perfor- 
 ations in the lead coil must be such that the air passes out as 
 uniformly as possible the entire length of the pipe, so that all 
 portions of the electrolyte are uniformly agitated. For smaller 
 baths an ordinary well-constructed air-pump suffices for press- 
 ing in the air. 
 
 Agitation of the bath by flux and reflux of the solution may 
 be effected in various ways, and is especially suitable where 
 many copper baths are in operation. 
 
 The baths are arranged in the form of steps. Near the 
 bottom each bath is provided with a leaden outlet-pipe (Fig. 
 147), which terminates above the next bath over a distributing 
 gutter, or as a perforated pipe h. From the last bath the 
 copper solution flows from a reservoir, E, from which it is 
 forced by means of a hard-rubber pump, i, into the reservoir, 
 A, placed at a higher level. From A it again passes through 
 the baths B, C and D. A leaden steam-coil may, if necessary,, 
 be placed in A, to increase the temperature, if it should have 
 
GALVANOPLASTY (REPRODUCTION). 
 
 563 
 
 become too low. Over A a 
 wooden frame covered with felt 
 may be placed ; the copper solu- 
 tion flowing upon the frame and 
 passing through the felt, is 
 thereby filtered. 
 
 While agitation of the bath 
 presents great advantages, there 
 is one drawback connected with 
 it, which, however, should not 
 prevent its adoption. With 
 baths at rest, dust and insoluble 
 particles becoming detached 
 from the anodes sink to the 
 bottom and have no injurious 
 effect upon the deposit. On 
 the other hand, in agitated 
 baths, they remain suspended ;* 
 in the electrolyte, and it may S 
 happen that they grow into the 
 deposit, giving rise to the for- 
 mation of roughnesses (buds). 
 Everywhere that such rough- 
 ness is formed, it increases more 
 rapidly in proportion to the 
 other smooth portions of the 
 cathode, and these excrescences 
 frequently attain considerable 
 thickness, which is not at all 
 desirable. 
 
 It is, therefore, advisable to 
 make provision for keeping such 
 baths perfectly clean. Baths 
 agitated by flux and reflux can 
 be readily filtered, as described 
 above, previous to their passing 
 
564 ELECTRO-DEPOSITION OF METALS. 
 
 into the collecting reservoir. Solutions agitated by a stirring 
 contrivance, or by blowing-in air, should be occasionally allowed 
 to rest and settle. The perfectly clear solution is then siphoned 
 off, and the bottom layers are freed from insoluble particles by 
 filtering. With the use of impure anodes, which, however, 
 cannot be by any means recommended, it is best to sew them 
 in some kind of fabric, for instance, muslin, the fibres of which 
 have been impregnated with ethereal pararhne solution to make 
 them more resistant towards the action of the sulphuric acid. 
 In order to keep the electrolyte as clean as possible, it is best 
 to treat chemically pure anodes in the same manner. 
 
 Anodes. — Annealed sheets of the purest electrolytic copper 
 should be suspended in the bath. Impure anodes introduce 
 other metallic constituents into the bath, and the result might 
 be a brittle deposit. The use of old copper boiler sheets, so 
 frequently advocated, is decidedly to be rejected. 
 
 The more impurities the anodes contain, the darker the re- 
 sidue formed upon them will be, and this residue in time de- 
 posits as slime upon the bottoms of the tanks. Anodes of 
 electrolytically deposited, and therefore perfectly pure, copper 
 also yield a residue, which, however, is of a pale brown ap- 
 pearance, and consists of cuprous oxide and metallic copper. 
 It is recommended daily to free the anodes from adhering re- 
 sidues by brushing, so as to decrease the collection of slime in 
 the bath. The anodes of baths in motion are best sewed, as 
 above described, in a close fabric to retain insoluble particles. 
 
 In connection with his previously mentioned experiments, 
 Forster ascertained that with the use of ordinary copper, at 0.3 
 ampere current-density, about 7.4 grammes (4.1 5 drachms) of 
 red-brown anode slime with 60 to 70 per cent, of copper, par- 
 tially in the form of cuprous oxide, were at the ordinary tem- 
 perature obtained from 6.6 lbs. of anode-copper. On the other 
 hand, at a temperature of 104 F., only 24 grammes (1.25 
 drachms) of a pale-gray slime consisting chiefly of silver, lead, 
 lead sulphate, and antimony combinations with only a slight 
 content of copper were under otherwise equal conditions ob- 
 
GALVANOPLASTY (REPRODUCTION). 565 
 
 tained. By raising the temperature of the electrolyte to 140 
 F., the quantity of anode slime increased considerably and at I 
 ampere current-density amounted to about twenty times as 
 much. The slime, in addition to a smaller quantity of the 
 above-described pale-gray slime, contained larger quantities of 
 well-formed lustrous copper crystals which could scarcely be 
 derived from the rolled copper anodes. Wohlwills made ana- 
 logous observations in the electrolysis of gold chloride solution 
 containing hydrochloric acid, and based upon these observa- 
 tions, Forster assumes that at the higher temperature the anode 
 copper sends forth augmented univalent cuprous-ions into the 
 copper solution, the cuprous sulphate solution formed being 
 decomposed to cupric sulphate (blue vitriol) while copper is 
 separated, according to the following equation: 
 
 Cu 2 S0 4 = CuS0 4 + Cu. 
 
 Cuprous sulphate. Cupric sulphate. Copper. 
 
 The anode surfaces should be at least equal to that of the 
 moulds, and for shallow moulds, the distance between them and 
 the anodes may be from 2 to 3 inches, but for deeper moulds 
 it must be increased. 
 
 Tanks. — Acid-proof stoneware tanks serve for the reception 
 of the acid copper baths, or for larger baths, wooden tanks 
 lined with pure sheet-lead about o.n to 0.19 inch thick, the 
 seams of which are soldered with pure lead. It should be borne 
 in mind that a coat of lacquer, as previously mentioned, may 
 have an injurious effect. 
 
 Rapid galvanoplasty. — Thus far we have only discussed the 
 galvanoplastic baths with an average content of 22 per cent, of 
 blue vitriol and 2 to 3 per cent, of sulphuric acid, which, up to 
 the end of 1899, were exclusively used. The current-density 
 employed in practice amounted to scarcely more than 2.5 am- 
 peres, and the customary thickness of 0.15 to 0.18 millimeters 
 for electrotypes was at the best attained in 4^ to 5 hours. 
 
 The much-felt want of producing galvanoplastic deposits of 
 sufficient thickness in a materially shorter time gave rise to seek 
 for ways and means to attain this object. 
 
566 ELECTRO-DEPOSITION OF METALS. 
 
 Taking into consideration the fact that a larger quantity of 
 copper can in a shorter time be deposited with the use of higher 
 current-densities, the conditions under which the use of higher 
 current-densities becomes possible without leading to the re- 
 duction of a useless, brittle or pulverulent deposit had to be 
 ascertained. By the investigations of Hiibl it had been shown 
 that the production of good deposits is by no means dependent 
 on a high content of sulphuric acid in the electrolyte, but that 
 acidulating the copper bath only so far as to prevent the forma- 
 tion of basic salts suffices. 
 
 It was further known that by the bath containing a large 
 quantity of sulphuric acid, the solubility of blue vitriol is de- 
 creased, and since good deposits can with high current- 
 densities be obtained only from highly-concentrated blue vitriol 
 solutions, the reduction of the content of sulphuric acid became 
 an absolute necessity. 
 
 There is, however, still another reason why copper baths 
 working with high current-densities can only be compounded 
 with small quantities of sulphuric acid. It has previously been 
 mentioned that the sulphuric acid is dissociated into hydrogen- 
 ions and S0 4 -ions, and that hydrogen-ions effect the reduction 
 of copper in a secondary manner. By a small addition of sul- 
 phuric acid, this secondary reduction is to be largely avoided, 
 and the copper is to be brought to separate chiefly in a primary 
 manner, because by reason of the accelerated process of reduc- 
 tion at high current densities, there is danger of hydrogen-ions 
 being brought to separate as hydrogen gas on the cathodes, 
 which might give rise to the formation of a sandy or spongy 
 deposit. 
 
 In a 20 per cent, blue vitriol solution compounded with 1 per 
 cent, of sulphuric acid, the copper solution and the sulphuric 
 acid participate equally, according to Hiibl, in conducting the 
 current; while with a content of 5 per cent, of acid, the conduc- 
 tion of the current is almost exclusively taken charge of by the 
 acid-ions. Thus, the smaller the content of free sulphuric 
 acid, the greater the quantity of primarily deposited copper 
 
GALVANOPLASTY (REPRODUCTION). 567 
 
 will be, and the less the danger of hydrogen-occlusion, or the 
 formation of a hydrate. 
 
 However, a smaller content of sulphuric acid in the electrolyte, 
 together with a greater content of blue vitriol, is by itself not 
 sufficient for removing the possibility of the formation of 
 spongy deposits caused by the layers of fluid on the cathode 
 having become poorer in metal. Provision has to be made' 
 for the vigorous agitation of the electrolyte, so that the layers 
 poor in metal on -the cathode are constantly replaced by layers 
 richer in metal, a discharge of hydrogen-ions on the cathodes 
 being thus best prevented; and coherent copper- deposits of 
 great hardness and sufficient tenacity for graphic purposes are 
 even with very high current-densities obtained. 
 
 This process, based upon the principles above mentioned, 
 was perfected in 1900, and the term rapid galvanoplasty has 
 been applied to it. 
 
 It is obvious that the term rapid galvanoplastic bath cannot 
 be claimed solely for one composition, but that all acid copper 
 baths which yield deposits in a materially shorter time than 
 was formerly possible may thus be designated. According to 
 the objects the rapidly-working baths are to serve, it would 
 even be rational that their compositions should vary, as will be 
 directly, seen. 
 
 While shallow impressions, for instance, autotypes, wood- 
 cuts, etc., only require a very small addition of sulphuric acid, 
 for deep impressions of set-up type a larger content of sulphuric 
 acid is necessary, especially when the type has been set with 
 low spaces. For the reproduction of moulds of objects of art 
 in very high relief, rapid galvanoplasty is only within certain 
 limits applicable. 
 
 Below will be given two compositions of rapid galvanoplastic 
 baths, which are considered the highest and lowest limits, 
 though it is not to be understood that good results cannot be 
 obtained with baths containing more or less blue vitriol and 
 sulphuric acid. These two baths, however, have proved reli- 
 able in practical rapid galvanoplasty, and the necessity for 
 other compositions will scarcely arise. 
 
568 . ELECTRO-DEPOSITION OF METALS. 
 
 For shallow impressions of autotypes, wood-cuts, etc. — In a 
 ioo quart bath : 74.8 lbs. of blue vitriol, 0.44 lb. of sulphuric 
 acid of 66° Be. 
 
 Dissolve the blue vitriol with the assistance of heat. 
 
 This bath being oversaturated with blue vitriol, crystals 
 would be formed, which must by all means be avoided, and for 
 this purpose the bath has to be constantly kept at a tempera- 
 ture of about 78. 8° to 82. 4 F. At this temperature the bath 
 shows about 25 Be, and at 64. 4 F., 27 Be. 
 
 Heating the bath is best effected by means of a lead coil on 
 the bottom of the lead- lined tank, through which steam is 
 introduced until the bath shows the desired temperature. 
 Since, by reason of the high current-densities, the temperature 
 of the bath is still further increased, which might be detrimental 
 with the use of wax moulds, the lead coil should be furnished 
 with an additional branch for the introduction of cold water in 
 case the temperature becomes excessive. 
 
 It is not likely that a larger bath of the above-mentioned 
 composition will cool off enough over night for the crystalliza- 
 tion of blue vitriol, especially if it is covered and the work-room 
 is not exceedingly cold. There is danger of the crystallization 
 of blue vitriol if the work-room is not kept at an even tempera- 
 ture, or the bath is not worked for one or more days in succes- 
 sion. In the latter case it is advisable, the evening before work 
 is stopped, to heat the bath more than usual and dilute it with 
 water. The quantity of the latter which has to be added to 
 make up what may in a certain time be lost by evaporation 
 will soon be learned by experience. If, for the sake of precau- 
 tion, the bath is covered, it will be found ready for work when 
 operations are resumed. 
 
 In order to obtain deposits of good quality with high current 
 densities, vigorous agitation of the bath is required. This is 
 most uniformly effected by blowing in air by means of an air 
 compressor. The bath may also be agitated, though less uni- 
 formly so in all portions, by means of a copper paddle fitted to 
 the front of the tank and driven by means of a band from a 
 
GALVANO PLASTY (REPRODUCTION). 569 
 
 transmission. It is placed about six inches above the bottom of 
 the tank and, the paddles being set at an angle of 45 °, a vigor- 
 ous motion of the lower layers towards the surface is effected. 
 
 If the above-mentioned conditions be observed, the current- 
 density for this bath may amount up to 6 amperes per square 
 decimeter, and with a distance of about 6 centimeters of the 
 cathodes from the anodes, the electro-motive force will approx- 
 imately be 6 volts. When working on an average with 6 am- 
 peres per square decimeter, a deposit of 0.15 millimeter thick 
 will in this bath be obtained in 1 ^ to 1 ^ hours. 
 
 With the use of gutta-percha matrices, the bath may be 
 somewhat more heated than when working with wax moulds, 
 and still higher current-densities than those given above may 
 be employed, the deposit being then finished in a still shorter 
 time. It is, however, advisable not to carry the work of the 
 current to an excess, otherwise the copper might readily show 
 properties not at all desirable. 
 
 It may, under certain circumstances be advantageous, nay 
 even necessary, to face the black-leaded matrices with copper 
 at a somewhat slighter current-density, while the bath is at rest, 
 i. e., not agitated by a stirring contrivance, or by blowing in 
 air, and to resume agitation and increase the current strength 
 only after the matrices are coated with copper. Thus, accord- 
 ing to the size of the galvanoplastic plant, it may be desirable 
 to have a smaller coppering bath not furnished with a stirring 
 contrivance, from which the matrices, after having been faced 
 with copper, are transferred to the agitated bath. 
 
 It may here be remarked that Knight's process of coppering 
 the matrices with neutral blue vitriol solution and iron filings, 
 which is much liked, is not applicable in rapid galvanoplasty. 
 In suspending such matrices coated with copper in the rapid 
 bath, the slight copper-film is, so to say, burnt, and a proper 
 deposit can no longer be effected. 
 
 In a bath of the composition given above, it is sometimes 
 difficult to obtain with the above-mentioned high current- 
 densities unexceptionable electrotypes from matrices produced 
 
570 .ELECTRO-DEPOSITION OF METALS. 
 
 from deep and steep set-up type. The shallow portions, to be 
 sure, copper well, but the copper does not spread into the 
 deeper portions, and holes are left. By the addition of certain 
 substances, for instance, alcohol, this drawback can, to be sure, 
 be somewhat improved, but not entirely removed, and for this 
 reason such matrices are further worked in a bath, the compo- 
 sition of which is given below. It is, however, preferable to 
 preparatively copper such type-compositions, especially when 
 low spaces have been used, and after about yi hour to transfer 
 the matrices to the rapid galvanoplastic bath. By working in 
 this manner, the electrotypes will be free from holes, and fin- 
 ishing even the largest customary forms will not require more 
 than 2 hours. 
 
 For deep impressions. — In a ioo quart bath : 57.2 lbs. of blue 
 vitriol, 1.76 lb. of sulphuric acid. 
 
 It is recommended not to deposit at a lower temperature of 
 the bath than 68° F., though with this concentration the 
 danger of crystallization is less. For heating and cooling the 
 electrolyte, a lead coil, as previously described, is advan- 
 tageously used, and provision for thorough agitation has to be 
 made. This bath is generally allowed to work with 4.5 to 5 
 amperes current-density, the electro-motive force, with a dis- 
 tance of 6 centimeters of the anodes from the cathodes, amount- 
 ing then to about 4^2 volts. The copper deposit attains in 
 2*4 hours a thickness of 0.15 millimeter, and in 2^ hours one 
 of 0.18 millimeter. Higher current-densities are also per- 
 missible, and the operator will soon find out how far he can go 
 in this respect. 
 
 Deeper forms become well covered, especially if, according 
 to Rudholzner's proposition, about 1 lb. of alcohol is added. 
 But, nevertheless, it is recommended to preparatively copper 
 in the ordinary acid copper bath impressions of very steep 
 set-up type with low spaces, as with the use of high current- 
 densities the streaks which are temporarily formed upon the 
 printing faces of the electrotypes are thus most surely avoided. 
 
 Heating the baths may be omitted in plants lacking the nee- 
 
GALVANOPLASTY (REPRODUCTION). 571 
 
 -essary contrivances. The blue vitriol solution must then be of 
 such a composition as to preclude all danger of blue vitriol 
 crystallizing out even at the lowest temperature of the work- 
 room. Somewhat lower current-densities corresponding to the 
 slighter concentration have of course to be used. 
 
 Regarding the quality of the copper deposit effected with 
 high current-densities, it may be said that its tenacity is good, 
 better in the second bath than in the one first mentioned, but 
 in all cases sufficient for the electrotypes. The copper is how- 
 ever, decidedly somewhat harder than that deposited from the 
 ordinary baths as proved by its slight wear in printing. 
 
 The treatment of the rapid galvanoplastic baths will be read- 
 ily understood from what has been said above. On the one 
 hand, the baths must not be allowed to cool to a temperature 
 at which the blue vitriol would no longer be held in solution, 
 but would crystallize; and, on the other, the reaction has from 
 time to time to be tested with red congo paper which must 
 acquire a plainly-perceptible blue color. If such is not the 
 case, no, or too little, free sulphuric acid is present in the bath, 
 and brittle deposits will be formed which cannot be detached 
 whole from the matrices. When this is noticed add 0.44 lb. 
 of sulphuric acid per 100 quarts of bath, or 1.76 lb. to the bath 
 for deep impressions. 
 
 The excess of acid is very rapidly consumed with the use of 
 copper plates which have been electrically deposited and, with- 
 out recasting and rolling, suspended as anodes in the bath. 
 The use of rolled anodes is therefore absolutely necessary, and, 
 as previously described, they should be sewed in a close fabric 
 to avoid contamination of the bath by the anode-slime formed, 
 and by small copper crystals. 
 
 Special attention should be paid to furnish the matrices with 
 conductors of sufficiently large cross-section corresponding to 
 the great current-strengths. This will later on be referred to. 
 
 Examination of the Acid Copper Baths. 
 The copper withdrawn from the bath by deposition is only 
 
572 ELECTRO-DEPOSITION OF METALS. 
 
 partially restored, but not entirely replaced, by the anodes, 
 and hence the content of copper will in time decrease, and the 
 content of free acid increase. The deficiency of copper can, 
 however, be readily replaced by suspending bags filled with 
 blue vitriol in the bath, while too large an excess of acid is 
 removed by the addition of copper carbonate or cuprous oxide 
 cupron). 
 
 However, in order not to grope in the dark in making such 
 corrections of the bath, it is necessary to determine from time 
 to time the composition of the copper solution as regards the 
 content of copper and acid, for which purpose the methods de- 
 scribed below may be used. 
 
 Determination of Free Acid. — The free acid is determined by 
 titrating the copper solution with standard soda solution, congo- 
 paper being used as an indicator. Bring by means of a 
 pipette, io cubic centimeters of the copper bath into a beaker, 
 dilute with the same quantity of distilled water, and add drop 
 by drop from a burette standard soda solution, stirring con- 
 stantly, until congo paper is no longer colored blue when 
 moistened with a drop of the solution in the beaker. Since I 
 cubic centimeter of standard soda solution is equal to 0.049 
 gramme of free sulphuric acid, the cubic centimeters of stand- 
 ard soda solution used multiplied by 4.9 give the number of 
 grammes of free sulphuric acid per liter of bath. 
 
 Volumetric determination of the content of copper according to 
 Haeris method. — This method is based upon the conversion of 
 blue vitriol and potassium iodide into copper iodide and free 
 iodine. By determining the quantity of separated free iodine 
 by titrating with solution of sodium hyposulphite of known 
 content, the content of blue vitriol is found by simple calcu- 
 lation. The process is as follows: Bring 10 cubic centimeters 
 of the copper bath into a measuring flask holding T ^ liter, 
 neutralize the free acid by the addition of dilute soda lye until 
 a precipitate of bluish cupric hydrate, which does not disap- 
 pear even with vigorous shaking, commences to separate. 
 Now add, drop by drop, dilute sulphuric acid until the pre- 
 
GALVANOPLASTY (REPRODUCTION). 573 
 
 cipitate just dissolves ; then fill the measuring flask up to the 
 mark with distilled water, and mix by vigorous shaking. Of 
 this solution bring 10 cubic centimeters by means of a pipette 
 into a flask of lOO cubic centimeters' capacity and provided 
 with a glass stopper; add 10 cubic centimeters of a 10 per 
 cent, potassium iodide solution ; dilute with some water, and 
 allow the closed vessel to stand about 10 minutes. Now add 
 from a burette, with constant stirring, a decinormal solution of 
 sodium hyposulphite until starch-paper is no longer colored 
 blue by a drop of the solution in the flask. Since i cubic 
 centimeter of decinormal solution corresponds to 0.0249 
 gramme of blue vitriol (_ 0.C003 gramme of copper), the 
 content of blue vitriol in one liter of the solution is found by 
 multiplying the number of cubic centimeters of decinormal 
 solution used by 24.9. For the correctness of the result it is 
 necessary that the copper bath should be free from iron. 
 
 The electrolytic determination of the copper being more simple, 
 it is to be preferred to the volumetric method. Bring by means 
 of the pipette 10 cubic centimeters of the copper bath into 
 the previously weighed platinum dish, add 2 cubic centimeters 
 of strong nitric acid, fill the dish up to within 1 centimeter of 
 the rim with distilled water, and electrolyze with a current- 
 strength ND lOO = 1 ampere. 
 
 Deposition of copper is finished when a narrow strip of plati- 
 num sheet placed over the rim of the dish and dipping into 
 the fluid shows in 10 minutes no trace of a copper deposit, 
 which is generally the case in 3^ hours. The deposit is then 
 washed without interrupting the current, rinsed with alcohol 
 and ether, and dried for a short time at 21 2° F. in the air-bath. 
 The increase in weight of the platinum dish multiplied by 100 
 gives the content of metallic copper in grammes per 1 liter of 
 bath. To find the content of blue vitriol, multiply the found 
 content of. copper per liter by 3.92, or multiply the content of 
 copper determined in 10 cubic centimeters of bath by 3.92. 
 
 If now the content of free acid and of the blue vitriol in the 
 bath has been ascertained, a comparison with the contents 
 
574 ELECTRO-DEPOSITION OF METALS. 
 
 originally present in preparing the bath will show how many 
 grammes per liter the content of acid has increased, and how 
 many grammes the content of copper has decreased. Then by 
 a simple calculation it is found how much dry pure copper 
 carbonate has to be added per liter of solution to restore the 
 original composition. For each gramme more of sulphuric 
 acid than originally present, 1.26 grammes of copper carbonate 
 have to be added, and each gramme of copper carbonate in- 
 creases the content of blue vitriol 2.02 grammes per liter of 
 bath. By reference to these data the operator is enabled to 
 calculate whether the quantity of copper carbonate added for 
 the neutralization of the excess of free acid suffices to restore 
 the original content of blue vitriol, or whether, and how much, 
 blue vitriol per liter has to be added. 
 
 With the use of baths in which the solutions circulate, the 
 additions are best made in the reservoir placed at higher 
 level, into which the solution constituting the bath is raised 
 by means of a pump. The composition of such baths, con- 
 nected one with the other, is the same, and a single determina- 
 tion of the content of copper and free sulphuric acid will 
 suffice. However, with baths, the the contents of which do not 
 circulate and are not mixed, a special determination has to be 
 made for each bath, and the calculated additions have to be 
 made to each separate bath. 
 
 Operations in Galvanoplasty for Graphic Purposes. 
 
 The manipulations for the production of galvanoplastic de- 
 posits for printing books and illustrations will first be described. 
 
 1. Preparation of the moulds {matrices) in plastic material. 
 If a negative of the original for the production of copies is not 
 to be made by direct deposition upon a metallic object, the 
 negative has to be prepared by moulding the original either in 
 a plastic mass which, on hardening, will retain the forms and 
 lines of the design to the finest hatchings, or in a material, 
 which plastic itself, retains the impression unaltered. Suitable 
 materials for this purpose are: Gutta-percha, wax (stearine, 
 etc.), and lead. 
 
GALVANOPLASTY (REPRODUCTION). " 5/5' 
 
 The preparation of moulds in gutta-percha and wax will first 
 be described, and the production of metallic matrices will be 
 referred to in the next section. 
 
 a. Moulding ih' gutta-percha. — For the reproduction of. the 
 fine lines of a wood-cut or copper-plate, pure gutta-percha,, 
 freed by various cleansing processes from the woody fibers, 
 earthly substances, etc., found in the crude product, is very 
 suitable. Besides the requisite degree of purity, the gutta- 
 percha should possess three other properties, viz., it must be- 
 come highly plastic by heating, without, however, becoming 
 sticky, and finally in should rapidly harden. 
 
 The most simple way of softening gutta-percha is to place it" 
 in water of 170 to 194 F. When thoroughly softened no: 
 hard lumps should be felt in kneading with the hands, in doing 
 which the latter should be kept thoroughly moistened with 
 water. A fragment corresponding to the size of the object to 
 be moulded is then rolled into a plate about ^ to ^ inch, 
 thick. To facilitate the detachment of the mould after cooling, 
 the surface of the gutta-percha which is to receive the impres- 
 sion, should be well brushed with black lead (plumbago or 
 graphite), an excess of it being removed by blowing. 
 
 The original (wood-cut, autotype, set-up type, etc.) must be 
 firmly locked in the usual manner, and the surface is then 
 cleansed from dirt and stale ink by brushing with benzine, 
 When dry it is brushed over with plumbago, an excess of it 
 being removed by means of a bellows. 
 
 The black-leaded surface of the warm gutta-percha plate is 
 then placed upon the black leaded face of the original, and 
 after gently pressing the former with the hand upon the latter, 
 the whole is placed in the press. 
 
 b. Moulding in Wax. — Beeswax is a very useful material for 
 preparing moulds, but, like stearine, it is according to the tem- 
 perature now softer and now harder, which must be taken into 
 consideration. In the cold, pure beeswax is quite brittle, and 
 apt to become full of fissures in pressing. To decrease the 
 brittleness certain additions are made to the wax. Urquhart 
 
57^ ELECTRO-DEPOSITION OF METALS. 
 
 recommends the following mixture, which is frequently used in 
 England: Beeswax 85 parts by weight, Venice turpentine 13, 
 black lead finely pulverized 2. 
 
 G. L. v. Kress recommends the following mixture : Pure wax 
 42.32 ozs., Syrian asphalt 14. 11 ozs., stearine 14 to 21 ozs., 
 tallow 10^ ozs., black-lead finely pulverized 1^. 
 
 Melt the asphalt over a moderate fire, then introduce the 
 wax, stearine and tallow, and when all is melted, add the 
 graphite, and stir until the mixture commences to congeal. 
 
 The following mixture has been proposed by Furlong: Pure 
 beeswax 29^ ozs., crude turpentine 3^ ozs., graphite 1% ozs. 
 The mixture is to be freed from all moisture by boiling in a 
 steam kettle for 2 hours. In the hot season of the year it is 
 recommended to add 5 per cent, of Burgundy pitch in order to 
 impart greater hardness to the wax. 
 
 For the reason mentioned above the proportions given in the 
 formulas cannot always be strictly adhered to, and one has to 
 be guided by prevailing conditions. If the wax turns out rather 
 brittle somewhat more tallow or turpentine has to be added, 
 and, on the other hand, in the hot season of the year when the 
 wax is too soft, a smaller quantity of turpentine or tallow will 
 have to be used. 
 
 In order to avoid overheating it is advisable not to melt the 
 wax mixture over a direct fire, jacketed kettles heated by steam 
 or gas being generally used for the purpose. When gas is used, 
 the space between the jacket and kettle is filled with water, 
 which, as evaporation progresses, has from time to time to be 
 replenished. 
 
 Two wax-melting kettles will be required, because the wax, 
 which has been in contact with the bath, has to be entirely freed 
 from water in the one kettle before it can be again used for 
 moulding. The dehydrated wax is then tranferred to the other 
 kettle. 
 
 To prepare the wax for receiving the impression, pour the 
 melted composition in the mould-box, which is a tray of 
 sufficient size with shallow sides about y£ inch in depth all 
 
GALVANOPLASTY (REPRODUCTION). 577 
 
 round, and with* a continuation of the bottom plate on one of 
 the shorter sides for about 3 inches beyond the box, to allow of 
 its being supported by hooks from the conducting rods of the 
 bath. The moulding-box is placed upon a level surface and 
 filled to the brim. Air bubbles and other impurities forming 
 on the surface are at once removed by a touch with a hot iron 
 rod. 
 
 The surface of the wax, while still luke-warm, is then dusted 
 over with the finest plumbago. The black-leaded original is 
 then placed, face downwards, upon the wax surface and sub- 
 mitted to intense pressure. When black- leading has been 
 carefully done, the original can be readily and perfectly de- 
 tached from the mould. Some operators apply a light coat of 
 oil to the original in place of black-leading it, but care must be 
 taken not to leave any considerable portion of oil upon the 
 original. 
 
 In this country, before the impression is taken, the wax plate 
 or wax mould is frequently treated as follow : Black-lead and 
 water are mixed to the consistency of cream. The mixture is 
 carefully and uniformly applied to the wax plate and rubbed 
 dry with the hand. 
 
 The method above described, according to which the melted 
 wax is poured in the moulding-box is constantly more and 
 more abandoned, the work being generally done as follows: 
 
 Lead plates, the size of the original to be moulded, are cast, 
 laid upon the wax-moulding table, and enclosed by a rim of the 
 depth of the required thickness of the wax plate. The box 
 thus formed is then filled to the brim with melted wax, air- 
 bubbles and other impurities being removed, any excess of wax 
 cut off, and the mould black-leaded by means of a soft brush. 
 In some galvanoplastic plants the moulded wax plates, previous 
 to making the impressions, are planed perfectly level by a shav- 
 ing machine. While gutta-percha matrices will bear quite 
 vigorous treatment with the brush, care must in this respect be 
 exercised with wax matrices to prevent injury. 
 
 The wax plates prepared according to the process just 
 37 
 
578 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 described are black-leaded and laid upon the •originals to be 
 moulded, the whole being then placed under the press. 
 
 2. Presses. — For making the impressions of the form in the 
 moulding composition, a moulding press is used which is capable 
 of giving a gradual and powerful pressure. Fig. 148 represents 
 
 Fig. 148. 
 
 a form of moulding press in common use, and known as the 
 " to ggle " press. It consists of a massive frame having a planed, 
 movable bed, over which a head is moved on pivots and counter- 
 balanced by a heavy weight, as shown, so that it can be readily 
 thrown up, having the bed exposed, the black-leaded type- 
 
GALVANOPLASTY (REPRODUCTION), 
 
 5 79 
 
 form being placed on the bed. The well black-leaded case is 
 attached by clamps to the movable head, or the form (also 
 black- leaded) is laid face down on the case, and the head is 
 then turned down and held in place by the swinging bar 
 (shown turned back in the cut). All being ready, the toggle- 
 pressure is put on by means of the hand-wheel and screw, the 
 result being to raise the bed of the press with an enormous 
 
 Fig. 149. 
 
 pressure, causing the face of the type-form to impress itself 
 into the exposed moulding surface. 
 
 Fig. 149 represents a form of ''hydraulic press" less com- 
 monly used than that just described. It is provided with 
 projecting rails and sliding plate, on which the form and case 
 are arranged before being placed in the press. The pump, 
 which is worked by hand, is supported by a frame-work on 
 the cistern below the cylinder, and is furnished with a grad- 
 uated adjustable safety-valve to give any desired pressure. 
 
580 ELECTRO-DEPOSITION OF METALS. 
 
 Metal matrices. — Attempts have for many years been made to 
 mould originals in lead since lead matrices possess many advan- 
 tages over gutta-percha and wax matrices as they do not require 
 to be rendered conductive by black-leading, and no changes 
 in dimensions take place in consequence of the transition from 
 the heated into the cold state. However, objects readily liable 
 to injury, such as wood cuts, compositions, etc., could not with- 
 stand the pressure required for impression in lead plates, and 
 were demolished ; steel plates at the utmost were capable of 
 standing the high pressure. Serviceable results were not ob- 
 tained, even with the use of very thin lead foil backed, in pres- 
 sing, with moist paste-board or gutta-percha because the 
 portions of the lead foil subject to the most severe demands 
 would tear. 
 
 To Dr. E. Albert of Munich is due the credit of having dis- 
 covered the cause to which these failures were due, and of 
 having devised a method for the rational preparation of metal 
 matrices. 
 
 Dr. Albert says in reference to this matter * : " Every gal- 
 vanoplastic operator knows that in making impressions of forms 
 of mixed composition and illustration, that the composition 
 down to the quads is impressed before the shades, for instance, 
 of a wood cut or an autotype are finished. In making impres- 
 sions, the moist paste-board referred to above acted exactly in 
 the same manner as wax or gutta-percha softened by heating; 
 i. e. by the moist paste-board the lead foil had to be pressed 
 first into the deeper, and finally into the more shallow depres- 
 sions. Notwithstanding the enormous ductility of lead, the lead 
 foil could not satisfy these demands on extension and, in con- 
 sequence of this over-demand, tore in many places. Hence 
 this process was not available for general practice, it being at 
 the utmost suitable only for forms with very slight differences 
 in level, and even not for this purpose with the large forms now 
 in general use. 
 
 *Zur Theorie unci Praxis der Metall-matrize. 1905. 
 
GALVANOPLASTY (REPRODUCTION). 581 
 
 It must be borne in mind that, for instance, upon a square 
 millimeter of an autotype there are 36 depressions into which 
 the lead foil has to be pressed and to 144 side-walls per square 
 millimeter of which it has to attach itself. Especially with 
 under-etched printing forms considerable force is required to 
 detach the matrix from the moulding material, and it is there- 
 fore impossible with larger forms to manipulate the lead foil 
 which, for the sake of decreasing the pressure, has to be very 
 thin so as to maintain at the same time a level surface. 
 
 This method of impression by which the parts corresponding 
 to the dark portions of the original can only be impressed when 
 the moulding material has been forced into the last corner of 
 the deepest depressions of a printing form, is not premeditated 
 nor one by choice, but is conditional on the physical properties 
 of the material itself. The pressure required to force the 
 moulding material into the smallest depressions cannot be ap- 
 plied so long as the moulding material has a chance to escape 
 into an empty space. 
 
 In consequence of this property the matrices have to under- 
 go extensive manipulations, since the large angular elevations 
 which correspond to the depressions of the printing form would 
 prevent the further development of the electro, especially also 
 the formation of the copper-deposit upon the matrix. Hence 
 the prominent portions have to be removed in the known 
 manner. 
 
 This necessary after-manipulation would of course be im- 
 practicable with matrices of thin lead foils, and for this reason 
 also the method is not available for line-etching, wood-cut, and 
 composition. 
 
 In the preceding it has been specified as characteristic of the 
 bodies hitherto used for the preparation of matrices that the 
 impression of the deepest depressions takes place before that of 
 the more shallow ones ; with sofc metals, particularly with lead, 
 just the reverse is the case. The interior coherence of the 
 body-molecules, is so much greater in comparison with wax 
 and gutta-percha mass, or moistened paste-board, that at the 
 
582 ELECTRO-DErOSITION OF METALS. 
 
 commencement of the pressure the lateral escape is avoided, 
 whereby the moulding material yields first in the direction of 
 the pressure and fills the smallest depressions. Only with in- 
 creasing pressure which is necessary for forcing the lead into 
 the deeper depressions of the printing form, the lead also 
 begins to yield laterally in the region of the portions pressed 
 first. 
 
 Independent of the fact that the small points already im- 
 pressed which correspond to the smallest impressions of the 
 printing form, are again impressed, this pushing of the lead has 
 the further drawback that the lead firmly settles in these 
 smallest depressions, thus rendering the original useless. 
 
 Besides there is no type composition, no wood-cuts, etc., the 
 printing elements of which, especially when standing isolated, 
 could withstand the enormous pressure which has to be used 
 for forcing a lead-plate at least 5 millimeters thick into the 
 large depressions. However, such a thickness of the lead-plate 
 would be necessary just as with wax and gutta-percha impres- 
 sions, since the difference in height between printing and justi- 
 fying surface is about one cicero=4.5 millimeters. 
 
 Hence, with the means hitherto available, the production of 
 matrices, either with thin or thick metal plates^ was impracticable 
 and until lately recourse had to be had to the old and qualita- 
 tively inferior wax and gutta-percha matrices, till Dr. Albert, 
 in 1903, succeeded in finding a method for the rational produc- 
 tion of metal matrices. 
 
 This method is based upon a number of inventions patented 
 in all civilized countries, and the characteristic features of the 
 processes will here be briefly given. 
 
 The basis for the solution of the problem rested upon the 
 adoption of such a thickness of the metal-plate, that the man- 
 ipulations required for the production of the matrix and its 
 after-manipulations without deformation could be effected by 
 the hand of any workman ; as well as upon a new method of 
 impressing which would render it possible for thickness of the 
 plate to be materially less than the relief difference of the print- 
 in e form. 
 
GALVANOPLASTY ( REPRODUCTION ) , 
 
 583 
 
 While in the production of medals and coins by means of 
 galvanoplasty, the problem consists in a perfectly detached 
 reproduction of all the differences in level of the original, with' 
 an electro for graphic purposes, the impression of the matrix in 
 the large depressions is only a matter of technical necessity so 
 that in the subsequent use of the electro for printing the white 
 portion will not smear. This knowledge led to the expedient 
 of pressing or bending by means of a support of a soft body, 
 the about 2 millimeters thick lead, plates only so far into the 
 above-mentioned depressions as required for technical reasons. 
 
 Hence this method of impression is based upon a combina- 
 tion of pressing and bending. The lead is bent to a greater 
 extent, the larger and wider the sunk surface is, the electro 
 
 Fig. 150. 
 
 automatically receiving thereby all the white portions of such 
 depth that they do not smear in printing. 
 
 The process maybe explained by Figs. 149 and 150. 
 
 Fig. 149 represents the arrangement of the platen, lead plate, 
 and soft intermediate layer previous to the moment of impres- 
 sion. The material used for the intermediate layer must pos- 
 sess certain properties and must be softer than the moulding 
 material. It should be compressible without materially yield- 
 ing laterally under pressure and, by reason of elasticity or inter- 
 nal friction, also oppose a certain resistance to compression in 
 order to bend with this resisting power of the lead-plate where 
 the latter lies hollow. On the other hand, it must not be too 
 soft in the sense of its affinity to a liquid aggregate state, as, 
 
5§4 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 for instance, heated wax, but it should be more more porously 
 soft either in conformity with its nature or its arrangement. 
 In principle, the latter is generally based upon the production 
 of many empty intermediate spaces in the material (wood shav- 
 ings and snow are softer than wood and ice), or upon placing 
 many thin layers of the material one above the other. Such 
 bodies can be compressed without yielding too much laterally. 
 If the character of the body approaches more the liquid state, 
 more elastic properties have to be added, which by their ten- 
 dency to equalize the change suffered in form counteract the 
 lateral yielding, or other checks have to be arranged. Besides 
 a certain degree of elasticity is useful for bending the lead-plate 
 on the free-lying places. 
 
 Fig. 151. 
 
 Such an intermediate layer may appropriately consist of a 
 number of layers of paper. Such a layer, by reason of the 
 character of the paper fiber itself, as well as of the intermediate 
 layer of air, is soft and elastic as regards the direction vertical 
 to the impression-plane, while, on the other hand the texture of 
 the paper-stuff affords the necessary checks in the direction 
 parallel to the impression-plane to prevent after the commence- 
 ment of pressure, the lateral yielding of the intermediate layer. 
 The latter important property was in former experiments 
 neutralized by moistening the paper. 
 
 In Fig. 15 1 the platen has sunk so that the intermediate layer 
 opposite to the places 0' , from which the first counter-pres- 
 sure emanates, is compressed to one-half of its original volume. 
 At the moment when the intermediate layer has by compression 
 
GALVANOPLASTY (REPRODUCTION). 585 
 
 acquired the degree of hardness of the moulding material, it is 
 forced by the next increase in pressure into the small depressions 
 of the plane 0' . On the places opposite to u u' , the lead, 
 which lies here perfectly free and, hence exerts no counter-pres- 
 sure, is at the same time pressed into the hollow space u u' by 
 the resisting force of the intermediate layer. 
 
 The same is also the case opposite to the places m m' , but 
 the bending takes place in a less degree, just as a board resting 
 upon supports 6 feet apart is more bent by a weight than one 
 whose supports are only 3 feet apart. 
 
 This also answers technical requirements, since the white por- 
 tions smear the more readily in the press, the greater their 
 dimensions are. 
 
 Thus there had always been made the gross error of treating 
 according to the same principles which had proved good for 
 wax and gutta-percha, a body, such as lead, of an entirely 
 different physical character. The process of pressing had in 
 the main to be excluded, and a bending process substituted 
 for it. This was rendered possible by a suitable thickness of 
 the moulding material, and by backing it with a soft and yield- 
 ing body, which, as regards its extensibility parallel to the im- 
 pression-plane, was checked by its texture or otherwise. 
 
 By this bending process the pressure required for impression 
 was under certain circumstances reduced to one-tenth of its 
 former magnitude, so that metal matrices could also be pro- 
 duced from wood-cuts and composition. 
 
 This reduction in pressure is least manifest with printing 
 forms with many very fine and crowded printing elements, for 
 instance, autotypes, for which, according to the character of 
 the picture, a pressure of 500 to icoo kilogrammes per square 
 centimeter is required ; this is more than hitherto used for wax 
 and gutta-percha. 
 
 The problem of the production of metal matrices was thus 
 solved only for forms of moderate size, since, although the 
 pressure had been largely reduced by the selection of a correct 
 thickness of the lead-plate and by backing the latter with a 
 
586 ELECTRO-DEPOSITION OF METALS. 
 
 soft, elastic body, it was nevertheless much greater than that 
 required for wax and gutta-percha. The ordinary hydraulic 
 presses, with some few hundred atmospheres, were therefore 
 not available for impressing larger forms. 
 
 By the use of successive partial pressure with the simultan- 
 eous introduction of side-pressure, Dr. Albert has succeeded in 
 increasing, at a small expense, about twenty times the capacity 
 of every press now in use. 
 
 The gradual progression of a limited pressure over the entire 
 printing form also prevents the extremely troublesome phe- 
 nomena appearing in other methods of impressing, namely, that 
 it is impossible for the process of impression being affected 
 by included air, the latter having at any time a chance to 
 escape. 
 
 The impressions being automatically effected, there is no loss 
 of time worth speaking of with this method. Thus, for in- 
 stance, only 55 seconds were required for impressing a form of 
 the " Woche," and not quite two minutes for one of the " Ber- 
 liner Illustrierte Zeitung." For impressing illustration-»forms of 
 the same size without letters, only half the above-mentioned 
 time was necessary. 
 
 Thus there is no difficult)'' whatever in executing impressions 
 of any size. 
 
 Fischer endeavors to attain the same object as Dr. Albert by 
 the use of lead plates with corrugated backs, small pyramids 
 
 f ^^ /v 1 about 2 to 3 millimeters high being thus formed. 
 
 These corrugations act like Albert's elastic intermediate layer 
 in so far that the lead plates are not pressed, but bent, into the 
 deep portions of the printing form, a reduction in the other- 
 wise high pressure required being thus effected. Now, suppose 
 in Fig. 151, instead of an elastic intermediate layer, a lead plate 
 with corrugated back is placed upon the form, the small pyra- 
 mids which are opposite to the portion 0' of the printing form 
 are first compressed, while the part of the lead plate corre- 
 sponding to the portion u u' is bent through by the pressure 
 
GALVANOPLASTY (REPRODUCTION). 587 
 
 exerted by the platen upon the points of the corrugations, the 
 latter being thereby not very much flattened. If now the pres- 
 sure be increased the lead plate is first flattened at 0', and now 
 the actual impression, i. e., pressing the lead into the design of 
 the original or into the composition begins. 
 
 Kunze does not use corrugated lead plates, but provides the 
 platen with corrugations, and combines therewith a process of 
 successive partial pressure invented by him. (German patent 
 applied for.) As the patent has not yet been granted, details 
 of the process cannot be given. 
 
 3. Further manipulation of the moulds. — The moulds when 
 detached from the original show in addition to the actual im- 
 pression certain inequalities which have to be removed. 
 
 With gutta-percha moulds such inequalities in the shape of 
 elevations are carefully pared away with a sharp knife, while 
 with wax moulds they are melted down. For this purpose 
 serves a brass tube about 4 inches long, drawn out to a fine 
 point and connected by means of a rubber tube with a gas jet. 
 By opening the gas-cock more or less, the gas burns with a 
 larger or smaller pointed flame, and the brass tube is guided 
 by the hand, so that the elevations are melted down and the 
 deeper portions of the electrotype will present a smooth appear- 
 ance. A more modern instrument for this purpose is so ar- 
 ranged that the flame can be regulated by the finger pressing 
 upon a rubber bulb. However, not only the inequalities are 
 melted down, but the upper edges of the steep contours of the 
 impression are melted together, and melted wax is built up all 
 around in order to- enlarge the depressions in the electrotype 
 and avoid cutting. The wax is readily built up by holding in 
 one hand a thin stick of wax at a distance of about 0.19 inch 
 from the edge of the impression and at about the same distance 
 above the mould, and melting off the wax, drop by drop, by 
 means of a pointed flame guided by the other hand. One drop 
 is placed close alongside the other, and when the entire edge 
 of wax is thus completed it is made perfectly smooth by again 
 melting with the pointed flame. 
 
588 ELECTRO- DEPOSITION OF METALS. 
 
 The next process is 
 
 4. Making the mould conductive, without which a galvano- 
 plastic deposit would be impossible. Black-lead is almost 
 exclusively used for this purpose, and must be of the purest 
 quality and in a most minute state of division. The best mate- 
 
 Eig. 152. 
 
 rial for this purpose is prepared from the purest selected Ceylon 
 graphite, which is ground by rolling with heavy iron balls until 
 it is reduced to a dead black, impalpable powder. 
 
 Biack- leading the moulds is performed either by hand or 
 more commonly by machines. 
 
 Fig. 152 shows one of these machines with its cover re- 
 
GALVANOPLASTY (REPRODUCTION). 
 
 589 
 
 moved to exhibit its construction. It has a traveling carriage 
 holding one or more forms, which passes backward and for- 
 ward, under a laterally vibrating brush. Beneath the machine 
 is placed an apron which catches the powder, which is again 
 used. 
 
 Another construction of a black-leading machine is shown 
 in Fig. 153, the details of which will be understood without 
 lengthy description. The moulds are placed upon the slowly 
 
 Fig. 153. 
 
 revolving, horizontal wheel, upon which the brush moves 
 rapidly up and down with a vertical, and at the same time 
 lateral, vibrating motion. The black-leading space being closed 
 air-tight, scattering of black-lead dust is entirely prevented, 
 the excess of black-lead collecting in a vessel placed in the 
 pedestal. 
 
 On account of the dirt and dust caused by the dry process 
 of black-leading, some electrotypers prefer the wet process in- 
 
590 ELECTRO-DEPOSITION OF METALS. 
 
 vented by Mr. Silas P. Knight, of New York. This process 
 is designed to work more quickly and neatly, producing 
 moulds that are thinly, evenly, and perfectly covered. The 
 moulds are placed upon a shelf in a suitable receptacle, and a 
 rotary pump forces an emulsion of graphite and water over 
 their surfaces through a traveling fine rose-nozzle. This pro- 
 cess is pronounced to be rapid, efficient, neat and economical. 
 
 5. Electrical contact. — The black-leaded moulds have now to 
 be provided with contrivances for conducting the current upon 
 the black-leaded surface. 
 
 With gutta-percha moulds, the edges are trimmed off to 
 within 0.19 to 0.3 1 inch of the impression. In two places on 
 the edges of the mould holes are made by means of an awl. 
 Through these holes stout copper wires doubled together are 
 drawn, so that after twisting them together they lie firmly on 
 the edge of the mould. These wires serve for suspending the 
 mould to the conducting rod, and previous to twisting them 
 together, two fine copper wires, the so-called feelers, are placed 
 between them and the edge of the mould. The object of these 
 thin wires being to effect the conduction of the current to the 
 lower portions of the mould, they must be firmly secured in 
 twisting together the suspension-wires. 
 
 However, before allowing these feelers to rest upon the black- 
 leaded surface, the place of contact of the wire with the mould 
 is again thoroughly brushed with black-lead, in order to be 
 sure that the the current will not meet with resistance on these 
 points. With very large moulds it is advisable to use more 
 than two feelers and to arrange them especially in deeper de- 
 pressions. The thickness of the feelers should be about that of 
 horse-hair. 
 
 No black-lead should get on the edges or back of the mould, 
 otherwise copper would also be deposited on them. 
 
 In place of the wires for suspending the mould, the method 
 for wax moulds described below may also be applied, a small, 
 hot copper plate being melted in on the edge of the mould and 
 the latter secured to the conducting rod by means of a hook. 
 
GALVANOPLASTY (REPRODUCTION). 
 
 591 
 
 Fig. 154. 
 
 Gutta-percha moulds, being specifically lighter than the cop- 
 per bath, would float in it, and have, therefore, to be loaded by 
 securing heated pieces of lead to the backs. 
 
 For black-leaded wax moulds the process is as follows: A 
 bright copperplate about 1. 18 inches square and 0.039 inch 
 thick is melted in on the upper edge of the mould, and the 
 edges are leveled by means of a pointed flame, so as to pro- 
 duce a smooth joint between the copper plate and wax surface. 
 This place is again thoroughly black-leaded with the hand, and 
 the edges, having been first beveled, are then melted together 
 with the flame. The wax over the hole in the lead plate 
 through which the hook of the mould-holder is pushed is 
 finally freed from wax with a knife. The shape of the mould- 
 holder is shown in the accompanying illustration, Fig. 154. 
 The hook to which the mould is suspended is insulated from 
 the rest of the holder by hard rubber plates, and , the screw- 
 threads by hard rubber boxes, so that the 
 lead plate which comes in contact with the 
 hook receives no current, and no copper can 
 deposit upon it. The small, square block 
 cast on the holder lies perfectly level upon 
 the copper plate in the mould, a good and 
 abundant conduction of current being thus 
 effected, such as is absolutely required, for 
 instance, for rapid galvanoplasty. 
 
 To prevent the copper deposit from spread- 
 ing much beyond the impression towards the 
 edge, it has been proposed to cover these 
 portions of the mould with strips of glass, 
 hard rubber, or celluloid. For this purpose 
 heated glass strips, 0.15 inch wide and 0.19 
 inch high, are pressed about 0.079 inch deep into the wax 
 mould so as to form a closed frame around the impression. 
 Strips of hard rubber or celluloid of the above-mentioned width 
 and height, are fastened together with copper pins. By these 
 means the object in view is perfectly attained. 
 
59 2 ELECTRO-DEPOSITION OF METALS. 
 
 With very deep forms of type, it is sometimes of advantage 
 to first coat the black-leaded surface with copper, in order to 
 obtain a uniform deposit in the bath. The process is as fol- 
 lows: Pour alcohol over the black-leaded form, let it run off,, 
 and then place the form horizontally over a water trough. 
 Now pour over the form blue vitriol solution of 15 to 16 Be., 
 dust upon it from a pepper-box some impalpable fine iron 
 filings and brush the mixture over the whole surface, which 
 thus becomes coated with a thin, bright, adherent film of 
 copper. Should any portion of the surface after such treat- 
 ment remain uncoppered, the operation is repeated. The 
 excess of copper is washed off and the form, after being 
 provided with the necessary conducting wires, is ready for the 
 bath. 
 
 Gilt or silvered black-lead is also sometimes used for very 
 deep forms. It is, however, cheaper to mix the black-lead 
 with l / h its weight of finest white bronze powder from finely 
 divided tin. When forms thus black-leaded are brought into 
 the copper bath, the particles of tin become coated with 
 copper, also causing a deposit upon the black-lead particles in 
 contact with them. 
 
 6. Suspending the mould in the bath. Previous to suspend- 
 ing the mould in the copper bath, it has to be perfectly freed 
 from every particle of black lead which might give rise to 
 defects in the deposit. 
 
 Strong alcohol is then poured over the mould, the object of 
 this being to remove any traces of greasy impurities, which are 
 readily dissolved and removed by the alcohol. Moulds thus 
 treated at once become uniformly wet in the bath, which, if 
 this precaution be omitted, is not the case, and causes an 
 irregular formation of the deposit (by air-bubbles). 
 
 The moulds are suspended in the bath in the manner above 
 described, special attention being paid to having them hang 
 parallel to the anodes so that all portions of them may receive 
 a uniform deposit. 
 
 Before being suspended in the bath, the backs of lead mat- 
 
GALVANOPLASTY (REPRODUCTION). 
 
 593 
 
 rices should be provided with a protecting layer of celluloid or 
 other suitable material to prevent them from becoming cop- 
 pered. 
 
 7. DetacJiing the deposit or shell from the mould, a. From 
 gutta-percha moulds. When the mould has acquired a deposit 
 of sufficient thickness, it is taken from the bath, rinsed in water, 
 and all edges which might impede the detachment of the de- 
 posit from the mould are removed with a knife. The deposit 
 is then gradually lifted by inserting under one corner a flat 
 horn plate, or a thin dull brass blade, and applying a very 
 
 Fig. 155. 
 
 moderate pressure. Particles of gutta-percha which may still 
 adhere to the deposit, are carefully burnt off over a flame. 
 
 b. From wax moulds. Wax moulds are placed level upon 
 a table, and hot water is several times poured over them. By 
 pushing the finger-nail under one corner of the deposit, it can 
 readily and without bending be detached from the softened 
 wax. If not successful at first, continue pouring hot water 
 over the mould until the deposit can be detached without 
 difficulty. 
 38 
 
594 ELECTRO -DEPOSITION OE METALS. 
 
 In larger establishments, a cast-iron moulding and melting 
 table, such as is shown in Fig. 155, is used for wax moulds. 
 The planed table plate is hollow, and by means of tongues 
 cast to the plate the steam which is introduced is forced to 
 uniformly heat the entire plate. The electrotypes are placed 
 upon the plate, the wax side down. The wax melts and runs 
 through stop- cocks on the side into a jacketed copper kettle, 
 which can be heated by steam for melting the wax. The iron 
 ledges screwed upon the table plate are made tight with as- 
 bestos paper, so that the wax cannot run off except through 
 the stop-cocks. 
 
 If the table is to be used for moulding the wax plates, cold 
 water, instead of steam, is allowed to circulate through the 
 hollow table plate, whereby rapid congealing of the wax is 
 effected. 
 
 Two such kettles are required, since the wax which has been 
 in contact with the bath has to be for several hours heated in 
 one of the kettles to render it free from water before it can be 
 again used for moulding. The wax freed from water is brought 
 into the kettle and used for moulding wax plates. 
 
 c. From metal-matrices. If the matrix has been free from 
 fat, the deposit adheres very firmly, and cannot be lifted off in 
 the ordinary manner as with gutta-percha matrices ; nor can 
 the deposit be separated from the lead by melting the latter, as 
 with the temperature required for this purpose, the copper shell 
 might be damaged. 
 
 Albert found that by allowing the metal matrix together 
 with the copper deposit to float upon readily fusible metallic 
 alloys with many free calories, the deposit, in consequence of 
 the unequal expansion of the metals, can completely and 
 without injury be separated. By detaching the deposit in this 
 manner, Albert succeeded in using the lead matrix freed from 
 the deposit four times for the preparation of electros, the last 
 electro thus made being not inferior in quality to the first one.* 
 
 * Dr. E. Albert, " Zur Theorie und Praxis der Metall-Matrize," p. 10. 
 
GALVANOPLASTY (REPRODUCTION). 595 
 
 8. Backing the depositor shell. — The tinning of the back of the 
 shell is the next operation, and has for its object the strength- 
 ening of the union between the shell and the backing metal. 
 For this purpose the back of the shell is cleansed by brushing 
 with " soldering fluid," made by allowing hydrochloric acid to 
 take up as much zinc as it will dissolve, and diluting with about 
 Y^ of water, to which some ammonium chloride is sometimes 
 added. Then the shell, face down, is heated by laying it upon 
 an iron soldering plate, floated upon a bath of melted stereo- 
 type metal, and, when hot enough, melted solder (half lead and 
 half tin) is poured over the back, which gives it a clean, bright 
 metallic covering. Or, the shell is placed downward in the 
 backing-pan, brushed over the back with the soldering fluid, 
 alloyed tinfoil spread over it, and the pan floated on the hot 
 backing metal until the foil melts and completely covers the 
 shell. When the foil is melted the backing-pan is swung on to 
 a leveling stand, and the melted backing metal is carefully 
 poured on the back of the shell from an iron ladle, commenc- 
 ing at one of the corners and gradually running over the sur- 
 face until it is covered with a backing of sufficient thickness. 
 Another method is as follows: After tinning the shell it is 
 allowed to take the temperature of the backing metal on the 
 floating iron plate. The plate is then removed from the melted 
 metal, supported in a level position on a table having project- 
 ing iron pins, on which it is rested, and the melted stereotype 
 metal is carefully ladled to the proper thickness on the back of 
 the tinned shell. This process is called "backing." The thick- 
 ness of the metal-backing is about an eighth of an inch. A 
 good composition for backing metal consists of lead 90 parts 
 tin 5, and antimony 5. 
 
 9. Finishing. — For this purpose the plates go first to the saw 
 table (Fig. 156) for the removal of the rough edges by means 
 of a circular saw. The plates are then shaved to take off any 
 roughness from the back and make them of even thickness. 
 In large establishments this portion of the work, which is very 
 laborious, is done with a power planing or shaving machine, 
 
596 
 
 ELECTRO-DEPOSITION OE METALS. 
 
 types of which are shown in Figs. 157 and 158, Fig. 157 being 
 a shaving machine with steam one way, and Fig. 158 one with 
 steam both ways. By means of a straight edge, the plates are 
 then tested as to their being level, and any uneveness is recti- 
 fied by gentle blows with a polished hammer, care being taken 
 not to damage the face. The plate then passes to the hand- 
 shaving machine, where the back is shaved down to the proper 
 
 Fig, 156. 
 
 thickness, smooth and level. The edges of the plate are then 
 planed down square and to a proper size, and finally the plates 
 are mounted on wood type-high. Book-work is generally not 
 mounted on wood, the plates being left unmounted and finished 
 with beveled edges, by which they are secured on suitable 
 plate-blocks of wood or iron supplied with gripping pieces, 
 which hold them firmly at the proper height and enable them 
 to be properly locked up. 
 
GALVANOPLASTY ( REPRODUCTION). 
 
 597 
 
 Copper deposits from metallic surfaces. — It remains to say a 
 few words about the process, by which a copy may be directly 
 made from a metallic surface without the interposition of wax 
 or gutta-percha. If the metallic surface to be moulded were 
 free from grease and oxide, the deposit would adhere so firmly 
 as to render its separation without injury almost impossible. 
 
 Fig. 157. 
 
 Hence, the metallic original must first undergo special prepara- 
 tion, so as to bring it into a condition favorable to the detach- 
 ment of the deposit. This is done by thoroughly rubbing the 
 original with an oily rag, or, still better, by lightly silvering it 
 and exposing the silvering for a few minutes to an atmosphere 
 of sulphuretted hydrogen, whereby silver sulphide is formed, 
 
193 
 
 ELECTRO- DEPOSITION OF METALS. 
 
 which is a good conductor, but prevents the adherence of the 
 deposit to the original. For the purpose of silvering, free the 
 surface of the metallic original (of brass, copper, or bronze) 
 from grease, and pickle it by washing with dilute potassium 
 cyanide solution ( I part potassium cyanide to 20 water). 
 Then brush it over with a solution of 4.% drachms of silver 
 nitrate and I oz. 6 drachms of potassium cyanide (98 per cent.) 
 
 Fig. 158. 
 
 in one quart of water; or, still better, immerse the original for 
 a few seconds in this bath, until the surface is uniformly coated 
 with a film of silver. The production of the layer of silver sul- 
 phide is effected according to the process described later on. 
 The negative thus obtained is also silvered, made black with 
 sulphuretted hydrogen, and a deposit of copper is then made, 
 which represents an exact copy of the original. Instead of 
 sulphurizing the silvering with sulphuretted hydrogen, it may 
 also be iodized by washing with dilute solution of iodine in 
 
GALVANOPLASTY (REPRODUCTION). 599 
 
 alcohol. The washed plate, prior to bringing it into the copper 
 bath, is for some time exposed to the light. 
 
 To prevent the reduction of copper on the back of the me- 
 tallic original to be copied, it is coated with asphalt lacquer, 
 which must be thoroughly dry before bringing into the bath. 
 When the deposit of copper is of sufficient thickness, the plate 
 is taken from the bath, rinsed in water, and dried. The edges 
 are then trimmed off by filing or cutting to facilitate the sepa- 
 ration of the shell from the original. 
 
 Of course only metals which are not attacked by the acid 
 copper solution can be directly brought into the bath. Steel 
 plates must therefore first be thickly coppered in the alkaline 
 copper bath, and even this precaution does not always protect 
 them from corrosion. It is therefore better to produce in 
 a silver bath (formula I., p. 362) a copy in silver of sufficient 
 thickness to allow of the separation of both plates. The silver 
 plate is iodized, and from it a copy in copper is made by the 
 galvanoplastic process. The copper plate thus obtained is an 
 exact copy of the original, and after previous silvering, the de- 
 sired number of copies may be made from it. 
 
 Other operations which may have to be done in galvano- 
 plastic plants, for instance, coppering of zinc etchings, and of 
 stereotypes, and nickeling and cobalting the latter, as well as 
 electrotypes, have already been described in the part devoted 
 to Electro-plating, so that few words will here suffice. 
 
 Stereotypes are, as a rule, coppered in the acid copper bath, 
 stereotype metal being not attacked by it. The bath, however, 
 should not have a large content of free sulphuric acid. In order 
 to have the copper adhere well, the plates previous to being 
 brought into the bath must, of course, be thoroughly freed from 
 grease by brushing with warm soda solution and whiting. 
 
 Zinc plates are thoroughly freed from grease, and then cop- 
 pered or brassed. Nickeling is effected according to the pro- 
 cess given under " Deposition of Nickel." 
 
 Preparation of type-matrices. — The process varies according 
 to whether the originals consist of zinc or of a material (lead- 
 
600 ELECTRO-DEPOSITION OF METALS. 
 
 antimony-bismuth alloy) indifferent towards the acid copper 
 bath. 
 
 It is best to brass sine originals, and to give the brass deposit 
 higher lustre by polishing with Vienna lime powder upon a 
 small flannel bob. They are then freed from grease by brush- 
 ing with quicklime, silvered by the method previously given, 
 and iodized. The surfaces which are to remain free from de- 
 posit are stopped off with wax, and the originals placed in the 
 acid copper bath, care being taken to bring them in contact 
 with the current-carrying conducting rod before immersion in 
 the bath. 
 
 Originals of hard lead or similar alloys, after having been 
 suitably prepared, may be directly suspended in the copper 
 bath, since a heavy copper deposit can be quite readily de- 
 tached from them, though slightly oiling them will do no harm. 
 
 The current-density for depositing must be slight to prevent 
 formation of buds. The deposit is generally made 0.079 to 
 0.098 inch thick, when it is detached from the original, and 
 after filing the edges backed with zinc or brass. The matrix is 
 finally justified. 
 
 Regarding nickel matrices, see " Galvanoplasty in Nickel." 
 
 Electro-etching. — It is in place here to discuss the process of 
 electro-etching, it being chiefly applied in the graphic indus- 
 tries, and a few methods of etching, which are not executed by 
 electrical means, will first be referred to. 
 
 Methods of dissolving the various metals by acids were 
 probably known many centuries ago, it being beyond doubt 
 shown by the notable productions of the goldsmiths, as well as 
 of the armorers, about the year 1400, that they possessed a 
 knowledge of etching. It may also be supposed that the niello 
 work of the goldsmiths was the forerunner of copper engraving, 
 an art still highly appreciated at the present day, and the earliest 
 impression of which dates from the year 1446. 
 
 There are four different methods of copper engraving, but 
 that in which etching plays an important role, would seem to 
 be the most interesting. 
 
GALVANOPLASTV (REPRODUCTION). 60 I 
 
 To protect separate portions of metallic surfaces from the 
 action of the acid, a so-called covering or etching ground is 
 used which consists of a mixture of 2^ parts asphalt, 2 parts 
 wax, i part rosin and 2 parts black pitch, applied hot. 
 
 The copper engraver uses for his work another composition 
 of resins, and it is here given because this covering ground has 
 proved capable of resisting 25 per cent nitric acid. Yellow 
 wax 4 parts, Syrian asphalt 4, black pitch 1, and white Bur- 
 gundy pitch 1. Melt the ingredients and when the mixture 
 boils, gradually add, whilst stirring constantly, 4 parts more of 
 pulverized Syrian asphalt. Continue boiling until a sample 
 poured upon a stone and allowed to cool breaks in bending. 
 Then pour the mixture into cold water and shape it into small 
 balls, which for use are dissolved in oil of turpentine. 
 
 Upon a heated plate, ground perfectly level, the copper en- 
 graver then applies the above-mentioned covering ground so 
 thin that the metallic surface appears golden-yellow. The 
 covering ground is next blackened by means of a wax torch, 
 and the outlines of the picture to be made are then sketched. 
 
 Now commences the work which shows the artistic talent of 
 the engraver. With a fine etching-needle, he scratches the 
 contours of the picture into the covering ground, without, how- 
 ever, injuring the metal, and finishes his work by narrower and 
 wider lines until the desired effect is believed to be produced. 
 
 However, to make this work fit to be printed, the lines of 
 the picture must lie depressed in the metal plate. For this 
 purpose the plate is surrounded with a wax rim and subjected 
 to etching with nitric acid or, more recently, with ferric chlor- 
 ide. After the at first weak acid has acted for a short time, the 
 finest lines have attained the required depth. The fluid is then 
 poured off and the fine lines are stopped off, when etching is 
 recommenced. Thus progressing, a picture with, lines becom- 
 ing constantly deeper, as well as broader, is formed, the result 
 finally showing the artistic talent of the engraver. The plate 
 is cleansed and handed to the printer, or it may be steeled or 
 manifolded by galvanoplasty. 
 
602 ELECTRO-DEPOSITION OF METALS. 
 
 While speaking of this process of copper-engraving, our at- 
 tention is involuntarily directed to a very interesting achieve- 
 ment, which deserves mention in connection with the work of 
 the etcher and of the operator in galvanoplasty. The process is 
 
 Photo engraving, by means of which copper plates, as well as 
 small and also very extensive pictures, of such high artistic 
 value can be produced that they form at present an important 
 branch of the art business. 
 
 Former investigators have shown : 
 
 i . That of all the varieties of glue, gelatine possesses the 
 greatest swelling capacity. 
 
 2. That when mixed with potassium dichromate and ex- 
 posed to the action of light, gelatine becomes insoluble, i. <?., 
 it loses entirely its power of swelling. 
 
 Upon this is based the following process : Take a sheet of 
 well-sized paper and make a rim around it, about 0.39 inch 
 high, by turning up the sides. The paper thus prepared, 
 which now forms a sort of dish, is placed upon a perfectly 
 level surface and a solution, consisting mostly of gelatine col- 
 ored black, is poured over it. Such paper is found in com- 
 merce under the name of black pigment paper. It is immersed 
 in solution of ammonium dichromate, dried in a dark room and 
 stored for use. 
 
 A perfect diapositive of the original is placed in a copying 
 frame and, after covering it with the prepared pigment paper, 
 the frame is closed. 
 
 By the rays of light which strike the prepared paper through 
 the diapositive, the layer of chromium and gelatine is hardened 
 in the same gradations of tone as conditioned by the diaposi- 
 tive. When sufficiently exposed to the light, the pigment 
 paper is placed in a water-bath, and a quite perceptible picture 
 in relief will in a short time appear. The portions, which had 
 not been exposed to the light, swell up very much and lose the 
 greater part of the coloring matter mixed with the gelatine. 
 The result is, therefore, the reverse of the diapositive used. 
 
 By means of an ingenious contrivance, a layer of impalpable 
 
GALVANOPLASTY (REPRODUCTION). 603 
 
 asphalt powder has in the meanwhile been applied to a finely 
 ground copper-plate, and melted upon it. The above-men- 
 tioned chrome-gelatine picture is now placed upon the plate 
 and is made to adhere by rubbing. The paper can now be 
 readily detached, while the picture adheres to the copper-plate. 
 The gelatine-layer forms the protection from the effect of the 
 etching with ferric chloride. 
 
 It will be readily understood that for this, and all the preced- 
 ing manipulations, great skill and years of experience are 
 required in order to produce such results as we have occasion 
 to admire in the art stores. 
 
 If galvanoplasty is to be employed for the production of such 
 copper-plates, a glass or metal plate is used and coated with 
 the chrome-gelatine above described. It is then exposed to 
 the light under a photographic glass negative, allowed to swell 
 up, and for a short time laid in a weak chrome alum solution. 
 The layer is then so hard as to allow of making a wax mould 
 and an electrotype. The process is called photo- galvanography . 
 
 The swelling power of gelatine, as well as its insolubility, has 
 led to the production of collographic printing. The manipula- 
 tions for the preparation of the printing plates required for this 
 purpose differ but little from those for photo-galvanography. 
 
 Pour over a glass plate, 0.19 to 0.27 inch thick, a layer of 
 chrome-gelatine, which, however, must not be colored, and 
 place the plate in a drying-oven heated to 11 3° F. The plate 
 is then exposed to the light under a photographic negative and 
 the layer of gelatine allowed to swell up. 
 
 Another property shown by chrome-gelatine is that the por- 
 tions which have become insoluble by exposure to light are 
 very susceptible to fat colors. If now such a glass plate be 
 wiped over with a moist sponge and then blackened all over by 
 means of a suitable color with the use of a roller, a picture 
 showing all the details of the negative used appears upon the 
 glass plate. By placing upon this picture a sheet of printing- 
 paper, and drawing both through the collographic printing- 
 press, the color adheres to the paper. 
 
604 ELECTRO-DEPOSITION OF METALS. 
 
 An etching process which includes all the improvements made 
 in metal etching, and which, by reason of the great progress 
 made in photography, has won a great field of activity, is 
 
 Zincography. — All plates produced by this process are in- 
 tended for book printing, and must show all the lines and 
 points of the picture in relief, while the parts which in printing 
 result in the white portions of the picture should be as deep as 
 possible. It is obvious that this requirement makes the high- 
 est demands on the etching process, and that long experience 
 and perseverance are required to achieve excellency in this 
 respect. 
 
 All former experiments will here be omitted, and only the 
 process which has proved of practical value will be described. 
 
 Freshly-made impressions are reprinted upon fine zinc plates 
 ground perfectly level, drawings executed with suitable ink 
 upon prepared paper being used in the same manner. 
 
 When the reprints have been successfully made and any de- 
 fects removed by retouching, very finely powdered rosin is 
 , poured upon the metal plate and rubbed with a brush into the 
 points and lines of the drawing. Since no rosin powder ad- 
 heres to the portions of the plate not printed on, the plate may 
 at once be laid upon the hot-plate and highly heated. The 
 rosin powder combines intimately with the printing ink, a layer 
 which well resists weak nitric acid being thus formed. 
 
 After etching for a short time with dilute nitric acid, fine 
 silvery edges produced by the washing away of the dissolved 
 metal appear on all the lines and points of the reprint. If 
 etching would now be continued, the lines and points would 
 also be laterally attacked by the acid. Over-etching would 
 thus take place, and all the fine portions of the picture disap- 
 pear. Hence a fresh protecting cover has to be applied, which 
 protects from corrosion, not only the surfaces of the lines and 
 points, but also the above-mentioned silvery edges. For this 
 purpose, the etcher uses a lithographic roller and a suitable 
 etching color. The drawing is then dusted over, and the plate 
 heated as previous to the first etching. Proceeding in the 
 
GALVANOPLASTY (REPRODUCTION). 605 
 
 same manner, the manipulations are repeated until the plate 
 has the necessary depth for printing. Finally, all unnecessary 
 metal is cut away with a fret-saw, and the etching having been 
 mounted on wood, is ready to be given to the printer. 
 
 If, however, the original handed in for reproduction, is to be 
 enlarged or reduced, a photographic negative of it is first made 
 and copied directly upon the zinc plate. For this purpose, a 
 coating of asphalt solution, or of a mixture of egg or glue with 
 ammonium dichromate, is applied to the zinc plate, and the 
 negative having been placed upon the latter, it is exposed to 
 the light. The result is the same as has been described under 
 photo-engraving, a picture being obtained which is exactly 
 treated as the reprinted drawings, i. e., powdered, heated, and 
 etched. 
 
 Another process of transferring is effected by reprinting : 
 
 A sheet of paper coated with chrome-gelatine is dried in a 
 dark room, placed in a copying frame under a negative and 
 exposed to the light until a beautiful, chestnut-brown picture 
 is perceptible. The chromium salt is dissolved in the water 
 bath, the picture inked with reprinting ink and, after drying, 
 transferred to the metal plate. 
 
 Up till now we have only spoken of points and lines, because 
 the originals have to be composed of such to be suitable for 
 the reproduction process. Photography, however, makes it 
 also possible to transform water-color paintings, photographs, 
 India-ink sketches, etc., into book-printing plates. 
 
 For this purpose the photographer uses a glass plate pro- 
 vided with a network of very fine lines, places it between the 
 sensitive glass plate and the original, and thus produces a neg- 
 ative, which, though composed of millions of small points, 
 nevertheless gives all the shadings of the original. This pro- 
 cess is called aiitotypy, and is at present used to such an extent 
 and has been brought to such a state of perfection, as to make 
 it difficult to say when the limit of what can be done by the 
 etching process in connection with photography may be 
 reached. 
 
6o5 ELECTRO-DEPOSITION OF METALS. 
 
 The achievements in photography widen almost daily the 
 field of activity of the etcher, and it may be anticipated that 
 printing plates will in this manner be produced which, when 
 printed in three colors, will yield impressions such as could 
 formerly only be attained by the lithographer with the use of 
 many stones. It is by no means impossible that the electric 
 current may before long be utilized in the execution of the 
 above-mentioned etching processes, and for this reason a few 
 hints will here be given which may be of use to the galvano- 
 plastic operator. 
 
 In etching steel, copper or zinc plates, in the ordinary way, 
 a covering ground, as previously mentioned, is applied to the 
 plate to be etched. The drawing is then transferred to the 
 covering ground and traced with the graver, taking care that 
 the tool lays bare the metal in all the lines. A rim of wax is 
 then made around the plate, and dilute nitric acid or another 
 solution poured over it. The basis-metal is attacked by the 
 acid and the drawing is thus etched. 
 
 The injurious acid vapors evolved thereby and the lateral 
 corrosion of the lines, as well as other drawbacks, have brought 
 about the execution of etching with the assistance of the elec- 
 tric current, the above-mentioned drawbacks being thereby ob- 
 viated, and more rapid and reliable working rendered possible. 
 The plate is treated in exactly the same manner as for ordinary 
 etching, but instead of furnishing it with a wax rim and pour- 
 ing acid over it, it is suspended in a suitable solution as anode 
 — hence connected with the positive pole — a metal plate of the 
 same size connected with the negative pole being suspended 
 parallel to it. The metal is dissolved by the acid-residue ap- 
 pearing on the positive pole. 
 
 For copper-plates which are to be etched, the ordinary acid 
 copper bath is used ; for zinc-plates, solution of zinc sulphate ; 
 for steel-plates, solution of copperas or of ammonium chloride ; 
 for brass, solution of ferric chloride. In place of the baths of 
 metallic salts, pure water slightly acidulated with sulphuric, 
 hydrochloric, or nitric acid may be used. 
 
GALVANOPLASTY (REPRODUCTION). 607 
 
 As covering or etching ground, the previously mentioned 
 mixture of rosin and wax, or the acid-proof varnish is used. 
 
 Since the current-strength is under perfect control, the etch- 
 ing may be carried to any depth desired. Some portions may 
 be less etched than others by taking the plate from the bath, 
 and, after washing and drying, coating the portions which are 
 not to be further etched with lacquer, and returning the plate 
 to the bath. 
 
 Printing plates in relief may in this manner be prepared by 
 slightly etching the bared design of a copper-plate in the gal- 
 vanoplastic copper bath, and then bringing the plate as object 
 in contact with the negative pole, while a plate of chemically 
 pure copper serves as anode. The deposited copper unites 
 firmly with the rough copper of the etched plates, and after re- 
 moving the etching-ground with benzine or oil of turpentine, 
 the design appears in relief. 
 
 Heliography. — The heliographic process, invented by Pretsch, 
 and improved by Scamoni, consists in taking by photography 
 a good negative of the engraving or other object to be repro- 
 duced, developing with green vitriol, reinforcing with pyrogallic 
 acid and silver solution, and then fixing with sodium hyposul- 
 phite solution in the same manner as customary for photo- 
 graphic negatives. A further reinforcement with chloride of 
 mercury solution then takes place until the layer appears light 
 gray. Now wash thoroughly, and intensely blacken the light 
 portions by pouring upon them dilute potassium cyanide solu- 
 tion. As in the photographic process, the solution must be 
 applied in abundance and without stopping, as otherwise 
 streaks and stains are formed. After washing, the plate is 
 dried, further reinforced, and finally coated with a colorless 
 negative varnish. From this negative a positive collodion 
 picture is taken, which is in the same manner developed, re- 
 inforced and fixed, the reinforcement with pyrogallic acid 
 being continued until the picture is quite perceptibly raised. 
 After careful washing, pour upon the plate quite concentrated 
 chloride of mercury solution, which has to be frequently re- 
 
60S ELECTRO-DEPOSITION OF METALS. 
 
 nevved, until the picture, at first deep black, acquires a nearly 
 white color, and the lines are perceptibly strengthened. Now 
 wash with distilled water, next with dilute potassium iodide 
 solution, and finally with ammoniacal water, whereby the pic- 
 ture acquires first a greenish, then a brown, and finally a violet- 
 brown, color. After draining, the plate may be progressively 
 treated with solutions of platinum chloride, gold chloride, 
 green vitriol and pyrogallic acid, the latter exerting a solidify- 
 ing effect upon the pulverulent metallic deposits. The metallic 
 relief is now ready ; the layer is slowly dried over alcohol, and 
 the plate, when nearly cold, quickly coated with a thin rosin 
 varnish, which, after momentary drying, remains sufficiently 
 sticky to retain a thin layer of black lead, which is applied with 
 a tuft of cotton. The edge of the plate is finally surrounded 
 with wax, and, after being wired, the plate is brought into the 
 galvanoplastic copper bath to be reproduced. 
 
 Electro-engraving. — Below an outline of Rieder's patented 
 process is given, it being supposed that the subject under dis- 
 cussion is the production of a die by means of which reliefs are 
 to be stamped in metal plates. 
 
 The relief is first produced in a material readily worked, for 
 instance, wood, wax, etc., and a copy of it made in plaster of 
 Paris. The plaster of Paris plate, which is about % to ^ inch 
 or more thick, is placed in a metal cylinder in such a manner 
 that a plaster of Paris surface of o.n to 0.15 inch depth pro- 
 jects above the edge of the cylinder. This cylinder containing 
 the plaster of Paris model is secured in a vessel containing 
 solution of ammonium chloride and a metal spiral connected 
 with the negative pole of the source of current. By a suitable 
 mechanical contrivance the vessel, together with the cylinder 
 containing the model, is pressed against the steel plate con- 
 nected with the positive pole. 
 
 The process is now as follows : The porous plaster of Paris 
 absorbs to saturation ammonium chloride solution. The steel 
 plate first comes in contact with the highest points of relief, 
 and the current becoming active, dissolves the steel on the 
 
GALVANOPLASTY (REPRODUCTION). 609 
 
 point of contact. The ferrous chloride solution which is formed 
 penetrates downwards into the capillaries of the plaster of Paris, 
 so that fresh quantities of the electrolyte constantly act upon 
 the steel plate. Etching thus progresses, and gradually every 
 portion of the plaster of Paris model comes in contact with the 
 steel plate, when etching is finished. 
 
 However, the practical execution of the work is not so simple 
 as the theoretical process above described. The carbon in the 
 steel and other admixtures, such as silicon, etc., prevent uniform 
 etching and must, therefore, from time to time, be mechanically 
 removed from the etching surface. For this purpose the ves- 
 sel containing the electrolyte, together with the model, has to 
 be lowered, the steel plate taken from the apparatus and 
 cleansed. It will, therefore, be readily understood that accu- 
 rate etching corresponding to the metal can only take place 
 when the principal parts, namely, the steel plate and model, 
 after cleansing, mathematically occupy exactly the same place 
 and position as before, so that the model presses accurately 
 against the same parts of the steel plate as in the beginning of 
 the etching operation. 
 
 Conjointly with Dr. Geo. Langbein & Co., Rieder has con- 
 structed an apparatus which works with such precision as to 
 fulfill all the above-mentioned conditions, and may be briefly 
 described as follows : * The plaster mould is secured by two 
 conical wedges to a cast-iron frame upon a vertically moving 
 table, the latter being set in motion by an eccentric. Above 
 this table is the clamping plate for the steel anode to be etched. 
 This clamping plate is also adjustable, and by a suitable con- 
 trivance can be set exactly parallel to the model. Cleansing 
 of the steel plate is effected by means of a carriage carrying a 
 revolving brush and worked by an eccentric ; the brush receives 
 water through a perforated pipe, and in addition a sponge roller 
 is carried over the model for the purpose of acidulating the 
 latter. 
 
 * Pfanhauser, Die Herstellung von Metallgegenstanden auf elektrolytischen Wege 
 und die Elektrogravure, 1903. 
 
 39 
 
6lO ELECTRO-DEPOSITION OF METALS. 
 
 The machine works as follows : By means of the movable 
 table the model is without shock and as elastically as possible 
 placed against the plate to be etched. After the plate and 
 model have been in contact for 15 seconds, the model is lifted 
 off and the cleaning process by brushing, etc., is effected. As 
 soon as the cleaning carriage is withdrawn, the model is again 
 brought against the steel-plate and the operation repeated. 
 
 Each electro-engraving is supplied with a model casting 
 arrangement, the frames of the machine being utilized for the 
 purpose. 
 
 The dynamo used has an impressed electro-motive force of 
 12 to 15 volts, and the current-strength for a plate of 200x300 
 millimeters is about 50 amperes, when the whole surfaces of the 
 plaster model has been brought in contact with the steel-plate. 
 An electro-engraving plant of this kind was exhibited at the 
 Paris Exposition in 1900. 
 
 The depth of the etching depends on the time of contact, but 
 it may be laid down as a rule that, according to the fineness of 
 the model 4 or 5 hours are required for a depth of I milli- 
 meter. The cleaning process above described may eventually 
 be effected with the assistance of an air compressor. Allowing 
 12 seconds as the duration of etching, about 600 to 800 etch- 
 ing periods must take place in order to etch to the depth of 1 
 millimeter. Experiments made on a large scale have proved 
 this method to be very suitable for many purposes, even if it 
 does not make hand-engravers superfluous. For the latter, 
 however, it is an excellent auxiliary for the purpose of obtain- 
 ing engravings absolutely true to nature from models in wax, 
 etc., and it allows of the preparation in a very short time of 
 engraved dies, plates, etc. The last retouching and polishing 
 have to be done by the hand of the engraver, because in ac- 
 cordance with the nature of the porous plaster-of-Paris model, 
 the etched surface shows but little luster. Further details 
 would not come within the compass of this work, and interested 
 parties are referred to the firm " Elektrograviire," Leipsic, 
 Saxony, Germany, who has secured the patents and constructs 
 the electro-engraving machines. 
 
GALVANOPLASTY (REPRODUCTION). 6ll 
 
 B. Galvanoplastic Reproduction of Plastic Objects. 
 
 The reproduction of busts, vases, etc., requires an entirely 
 different process of preparing the moulds than that described 
 as applied in the graphic arts, the material for moulding de- 
 pending on the nature of the original. Besides gutta-percha 
 and wax, readily fusible metals, oil gutta-percha, plaster of 
 Paris, and glue will have to be considered. If the original 
 bears heating to about 230 F., a copy in one of the readily 
 fusible alloys given later on may be made. If it will stand heat 
 and pressure, it is best to mould in gutta-percha, but if no pres- 
 sure and only slight heat can be used, recourse may be had to 
 oil gutta-percha. If neither heat nor pressure can be applied, 
 the moulds will have to be executed in plaster of Paris or in 
 glue. The manner of moulding and the material to be chosen 
 furthermore depend on whether surfaces in high relief or round 
 plastic bodies are to be copied, whether projecting portions are 
 undercut, and whether the mould can be directly detached, or, 
 if this is not the case, whether the original has to be dissected 
 and moulded in separate parts. 
 
 Regarding the practice of moulding, the reader is referred to 
 special works on that subject. Only the main points for the 
 most frequently occurring reproductions will here be given. 
 
 Surfaces in relief and not undercut are readily moulded in an 
 elastic mass, such as gutta-percha or wax; however, undercut 
 reliefs, and especially round plastic objects, mostly require a 
 plaster-of-Paris mould and are generally dissected. The dis- 
 section, of course, is not carried further than absolutely neces- 
 sary, because the separate parts must be united by a soldering 
 seam, which requires careful work, and the seam itself must be 
 worked over and made invisible. Hence the section should as 
 much as possible be made through smooth surfaces, edges, 
 etc., where the subsequent union by a soldering seam will 
 prove least troublesome ; cutting through ornaments or through 
 portions, the accurate reproduction of which is of the utmost 
 importance, should be avoided. Heads and busts are always 
 executed in a core mould and in portions, unless the entire 
 
6l2 ELECTRO-DEPOSITION OF METALS. 
 
 figure is to be deposited in one piece in a closed mould. The 
 section is made either through the center line of the head 
 through the nose, which, however, makes the subsequent union 
 very troublesome, if the copy is to be an exact reproduction of 
 the original, or the mould is divided from ear to ear, which has 
 the disadvantage that the deepest part of the mould correspond- 
 ing to the nose receives the thinnest deposit. It has, therefore, 
 been proposed to make two cuts so that three portions are 
 formed ; one cut from one ear at the commencement of the 
 growth of hair to the other ear ; and the second cut from one 
 ear in a downward direction below the lower jaw in the joint of 
 the head and neck, through this joint below the chin, and then 
 upwards to the other ear, and in front of it to where the hair 
 begins. In bearded male heads the cut follows the contour of 
 the beard and not the joint on the neck behind the beard. 
 
 Moulding with oil gutta-percha.— -Oil gutta-percha has the 
 advantage of allowing moulding without any pressure of the 
 largest shield-shaped or semi-circular objects with all the under- 
 cuts, which otherwise can only be accomplished with glue. 
 The mould can be readily detached from the original as well 
 as from the deposit, which is of great advantage. But, on the 
 other hand, oil gutta-percha deteriorates by frequent use, and 
 sticks to the mould when worked too hot, the result being that 
 it is difficult to detach from the original, and besides air bubbles 
 are formed. However, the heat must neither be too slight, 
 otherwise the sharpness of the impression would suffer. 
 
 Oil gutta-percha is prepared by heating in the water bath 
 ioo parts of gutta-percha, 10 parts of olive oil and 2 parts of 
 stearine. 
 
 The original, preferably of copper, should be slightly oiled. 
 It is laid upon an iron plate and the latter heated by a flame 
 until the original can be just for a moment retained in the hand. 
 The oil gutta-percha, previously heated in a sand bath and 
 thoroughly stirred, is then brought in a slow stream upon the 
 original. After allowing the oil gutta-percha to congeal super- 
 ficially, the original, together with the heating plate, is brought 
 into cold water, where complete congealing soon takes place. 
 
GALVANOPLASTY (REPRODUCTION). 613 
 
 For moulding in the press or by hand with oil gutta-percha, 
 the heated mass is poured into cold water and then kneaded to 
 the consistency of stiff dough. 
 
 Moulding with gutta-percha. — To mould round articles in 
 gutta-percha, the softened gutta-percha is kneaded with wet 
 hands upon the oiled original, or, in order to avoid some por- 
 tions receiving a stronger pressure than others, and to insure a 
 layer of gutta-percha of uniform thickness upon all parts, 
 moulding may also be executed in a ring or frame of iron or 
 zinc under a press. For the rest, all that has been previously 
 said in regard to moulding in gutta-percha is also applicable. 
 
 Metallic moulds. — The following metallic alloys have been 
 proposed for the preparation of moulds : 
 
 I. Lead 2 parts, tin 3, bismuth 5 ; fusible at 21 2° F. 
 II. Lead 5, tin 3, bismuth 8; fusible at 183 F. 
 
 III. Lead 2, tin 2, bismuth 5, mercury 1 ; fusible at 158 F. 
 
 IV. Lead 5, tin 3, bismuth 5, mercury 2 ; fusible at 127. 5 F. 
 The advantage of metallic moulds consists in the metal being 
 
 a good conductor of electricity, in consequence of which heavy 
 deposits of greater uniformity can be produced than with non- 
 metallic moulds which have been made conductive by black 
 lead. Nevertheless, they are but seldom employed, on account 
 of the crystalline structure of the alloys and the difficulty of 
 avoiding the presence of air bubbles. Bottger claims that a 
 mixture of lead 8 parts, tin 3, and bismuth 8, which is fusible 
 at 227 F., shows a less coarse-grained structure. 
 
 Fusible alloys containing mercury should not be used for 
 taking casts of metallic objects — iron excepted — as these will 
 amalgamate with the mercury and be injured. Moreover, 
 copper deposits obtained upon such alloys are very brittle, 
 which is due to the combination of the mercury with the de- 
 posited copper. 
 
 For moulding with metallic alloys, place the oiled object at 
 the bottom of a shallow vessel and pour the liquid metal upon 
 it; or pour the liquid metal into a box, remove the layer of 
 oxide with a piece of stout paper, and when the metal is just 
 beginning to congeal, firmly press the object in it. 
 
614 ELECTRO-DEPOSITION OF METALS. 
 
 Plaster-of- Paris moulds are used for making casts of portions 
 from originals which are so strongly undercut that a mould 
 consisting of one piece could not be well detached from them. 
 For taking casts from metallic coins and medals or from small 
 plaster reliefs, it is a very convenient material. The mode of 
 procedure is as follows : After the original model, say a medal, 
 has been thoroughly soaped or black-leaded, wrap round the 
 rim a piece of sufficiently stout paper or thin lead foil, and 
 bind it in such a manner by means of sealing-wax that the 
 face of the medal is at the bottom of the receptacle thus formed. 
 Then place the whole to a certain depth in a layer of fine sand, 
 which prevents the escape of the semi-fluid plaster of Paris 
 between the rim of the medal and the paper. Now mix plaster 
 of Paris with water to a thin paste, take up a small quantity of 
 this paste with a pencil or brush and spread it in a thin film 
 carefully and smoothly over the face of the medal, then pour 
 on the remainder of the paste up to a proper height, and allow 
 it to set. After a few minutes the plaster heats and solidifies. 
 Then remove the surrounding paper, scrape ofT with a knife 
 what has run between the paper and the rim of the medal, and 
 carefully separate the plaster cast from the model. If, instead 
 of applying the first layer with a brush, the whole of the plaster 
 were run at once into the receptacle, there would be great risk 
 of imprisoning air bubbles between the model and the mould, 
 which would consequently be worthless. The mould is finally 
 made impervious and conductive according to one of the 
 methods to be described later on. 
 
 The moulding in plaster of Paris in portions, when casts from 
 large plastic objects with undercut surfaces and reliefs are to be 
 taken, is troublesome work, because each separate mould must 
 not only be so that it can be readily separated without injury 
 to the original, but must also fit closely to its neighbors. 
 Hence thought and judgment are required to see of which parts 
 separate moulds are to be made, or, in other words, in how 
 many parts the mould is to be made. After determining on 
 the plan of the work, the mode of procedure is as follows: Oil 
 
GALVANOPLASTY (REPRODUCTION). 6l 5 
 
 a portion of the object, if it consists of metal, or soap it, if of 
 plaster of Paris, marble, wood, etc., and apply by means of a 
 brush a thinly-fluid paste of plaster of Paris, taking care that 
 no air bubbles are formed by the strokes of the brush. When 
 this thin coat is hard, continue the application of plaster of 
 Paris with a horn spatula until the coat has acquired a thick- 
 ness of ^ to i inch, and allow it to harden. Then separate the 
 mould, and after cutting or sawing the edges square and 
 smooth, replace it upon the portion of the original model cor- 
 responding to it, Now oil or soap the neighboring portions of 
 the model, and at the same time the smooth edges of the first 
 mould which come in contact with the mould now to be made, 
 and then proceed to make the second mould in precisely the 
 same manner as the first. When the second mould is hard, 
 trim the edges and replace it upon the model ; the same pro- 
 cess being continued until the entire original model is repro- 
 duced in moulds fitting well together. To prevent the finished 
 moulds from falling off, and to retain them in a firm position 
 upon the original model, they are tied with lead wire or secured 
 with catches of brass wire or sheet. When the moulds of the 
 larger portion of the model, for instance, one-half of a statue, 
 are finished, the so-called case or shell is made, i. e., the backs 
 of all the moulds are coated with a layer of plaster of Paris 
 which holds them together. This case is best made not too 
 thin in order to attain a better resisting power. 
 
 The entire model having been cast in the manner above de- 
 scribed, and the moulds provided with the case, the whole is 
 completely dried in an oven. 
 
 Rendering plaster-of- Paris moulds impervious. — The next 
 operation is to make the plaster of Paris impervious to fluids, 
 as otherwise by the moulds absorbing the acid copper bath, 
 copper would be deposited in the pores of the plaster and the 
 moulds be spoiled, while the copy would turn out rough in- 
 stead of having the smooth exterior of the model. To render 
 plaster of Paris and other porous substances impervious, they 
 are saturated with wax or stearine, or covered with a coat of 
 
6l6 ELECTRO-DEPOSITION OF METALS. 
 
 varnish, the latter process being generally employed for large 
 moulds. Apply a coat of thick linseed oil varnish to the face 
 of the mould, and, after drying, repeat the process until the 
 mould is considered to be sufficiently impervious. 
 
 Rendering the mould impervious with wax or stearine is a 
 better and more complete method. For this purpose place 
 the heated mould in a vat filled with melted wax or stearine, so 
 that the face does not come in contact with the wax but ab- 
 sorbs it by capillarity from the bath. However, as this cannot 
 be done in every case, the mould, if necessary, may be entirely 
 submerged in the melted wax until no more air-bubbles escape. 
 It is then taken from the bath and laid, face up, fn a drying; 
 oven, whereby the wax in melting oozes down, in consequence 
 of its gravity, the face of the mould being thus freed from an 
 excess of wax. 
 
 To prevent the removal of too much wax from the face, the 
 mould is cooled off with cold water the moment the excess of 
 wax is noticed to have penetrated from the face into the in- 
 terior. After drying the mould, the face is coated with gutta- 
 percha lacquer, in order to make the high reliefs, which may 
 have been too much freed from wax, impervious. Gutta- 
 percha lacquer is prepared as follows : 
 
 Bring into a wide-mouthed glass bottle provided with a glass- 
 stopper, gutta-percha cut up in small pieces, and fill the bottle 
 with a mixture of equal parts by volume of ether and benzoL 
 The bottle is allowed to stand for several weeks in a moder- 
 ately warm room, the contents being frequently shaken. In 
 this time as much gutta-percha as the solvent can absorb will 
 be dissolved. 
 
 For rendering impervious porous, non-metallic moulds upon 
 which copper is later on to be deposited, Greif has obtained a 
 patent on the following process : The impregnating agent con- 
 sists of about 70 parts coal-tar pitch, 20 parts retene (methyl- 
 propyl phenanthrene), and 10 parts naphthalene. The mix- 
 ture of the ingredients having been melted by steam, the body 
 to be impregnated is immersed in the liquid mass, and allowed 
 
GALVANOPLASTY (REPRODUCTION). 617 
 
 to remain in it a short time to become throughout impregnated. 
 An excess of the impregnating agent is readily removed by 
 allowing it to drain off. 
 
 Rendering the moulds conductive, or metallisation by the dry 
 way. — The moulds thus coated with varnish or impregnated 
 with wax are now rendered conductive with black-lead, this 
 operation being the same as that for moulds for the graphic 
 arts. 
 
 In some cases metallization by metallic powders is, however, 
 to be preferred to black-leading or metallizing by the wet way. 
 Metallic or bronze powders are metals in an exceedingly fine 
 state of division, of which, for galvanoplastic purposes, pure 
 copper "and brass powders only are of interest. Since such 
 metallic powders adhere badly to waxed surfaces, the mould 
 must be provided with a quick-drying coat of lacquer, upon 
 which, before it is completely dry, the powder is scattered or 
 sifted. When the lacquer is hard a smooth surface is produced 
 by going over the mould with a soft brush dipped in the metal- 
 lic powder, an excess being removed by a thin jet of water. 
 
 For many undercut or very deep portions which cannot be 
 thoroughly manipulated with the brush, metallization with 
 black-lead proves insufficient, and recourse will have to be 
 had to 
 
 Metallization by the wet way. — This method consists in the 
 deposition of certain metallic salts upon the moulds and their 
 reduction to metal or conversion to conductive sulphur combi- 
 nations. The process in general use is as follows : Apply with 
 a brush upon the mould a not too concentrated solution of 
 silver nitrate in a mixture of equal parts of distilled water and 
 90 per cent, alcohol. When the coat is dry expose it in a 
 closed box to an atmosphere of sulphuretted hydrogen. The 
 latter converts the silver nitrate into silver sulphide, which is a 
 good conductor of the current. For the production of the 
 sulphuretted hydrogen, place in the box, which contains the 
 mould to be metallized, a porcelain plate or dish filled with 
 dilute sulphuric acid (1 acid to 8 water), and add five or six 
 
6l8 ELECTRO-DEPOSITION OF METALS. 
 
 pieces of iron pyrites the size of a hazel-nut. The development 
 of the gas begins immediately, and the box should be closed 
 with a well-fitting cover to prevent inhaling the poisonous gas ; 
 if possible, the work should be done in the open air or under a 
 well-drawing chimney. The formation of the layer of silver 
 sulphide requires but a few minutes, and if not many moulds 
 have to be successfully treated, the acid is poured off from the 
 iron pyrites and clean water poured upon the latter so as not 
 to cause useless development of gas. 
 
 It has also been recommended to decompose the silver salt 
 by vapors of phosphorus and to convert it into silver phosphide, 
 a solution of phosphorus in carbon disulphide being used for 
 the purpose. The layer of silver salt is moistened with the 
 solution or exposed to its vapors. This method possesses, 
 however, no advantage over the preceding, because, on the one 
 hand, the phosphorus solution takes fire spontaneously, and, 
 on the other, the odor of the carbon disulphide is still more 
 offensive than that of sulphuretted hydrogen. 
 
 A somewhat modified method is given by Parkes as follows : 
 Three solutions, A, B, C, are required. Solution A is prepared 
 by dissolving 0.5 part of caoutchouc cut up in fine pieces in IO 
 parts of carbon disulphide and adding 4 parts of melted wax; 
 stir thoroughly, then add a solution of 5 parts of phosphorus in 
 60 of carbon disulphide together with 5 of oil of turpentine 
 and 4 of pulverized asphalt ; then thoroughly shake this mix- 
 ture, A. Solution B consists of 2 parts by weight of silver 
 nitrate in 600 of water; and solution C of 10 parts of gold 
 chloride in 600 of water. The mould to be metallized is first 
 provided with wires and then brushed over with, or immersed 
 in, solution A, and after draining off, dried. The dry mould is 
 then poured over with the silver solution (B) and suspended 
 free for a few minutes until the surface shows a dark luster. It 
 is then rinsed in water and treated in the same manner with the 
 chloride of gold solution (C), whereby it acquires a yellowish 
 tone, when, after drying, it is sufficiently prepared for the re- 
 ception of the deposit. Care must be taken in preparing solu- 
 
GALVANOFLASTY (REPRODUCTION). 619 
 
 tion A, carbon disulphide which contains phosphorus readily 
 taking fire. 
 
 It must, however, be confessed that in some cases, either one 
 of the above-mentioned methods may leave the operator in the 
 lurch. On the one hand, a small accumulation of silver-salt 
 solution in the deeper places cannot be well prevented, a 
 slightly crystalline layer of salt being thus formed, and on the 
 other, it has happened, that the layer of silver sulphide has 
 without discernible reason become detached .from the mould 
 in the copper bath, thus necessitating a repetition of the 
 process. 
 
 In many cases the following method has been successfully 
 used : Dilute iodized collodion solution, such as is used for 
 photographic purposes, with an equal volume of ether-alcohol, 
 and pour this solution quickly and without intermission over 
 the mould, the latter being inclined so that all portions of it 
 come in contact with the collodion solution, when the mould is 
 turned face down to allow an excess to run off. By manipulat- 
 ing with sufficient rapidity a film of collodion solution remains 
 upon the mould. This film, at the moment of congealing, is 
 exposed for 2 to 3 minutes to the action of a weak solution of 
 silver nitrate in water, the operation being best effected in a 
 darkened room. The collodion containing potassium iodide 
 forms with the silver bath, silver iodide, the previously clear 
 collodion layer becoming yellowish. In this state the mould is 
 taken from the silver bath, washed with a weak jet of water to 
 remove an excess of silver solution, and then for a few minutes 
 exposed to the sun. By this means a reduction of the silver 
 salt takes place, which is rendered still more intense by laying 
 the mould in a solution of copperas in water, alcohol and glacial 
 acetic acid, in the proportion of 1.76 ozs. copperas, I oz. glacial 
 acetic acid, 0.7 oz. alcohol per quart of water. The mould is 
 then rinsed in water and immediately brought into the copper 
 bath, the conduction of the current to the layer of silver having 
 been first effected by means of a few feelers. 
 
 In using this method it must be borne in mind that the col- 
 
620 ELECTRO-DEPOSITION OF METALS. 
 
 lodion layer will not bear rough handling, and injury of it, by 
 touching it with the hands or a strong jet of water, or by careless 
 application of the conducting wires (feelers), must be avoided. 
 When operating with the care required, the results are very 
 satisfactory and sure. 
 
 In place of iodized collodion, a mixture of equal parts of white 
 of egg and saturated common salt solution may be used, the 
 process for the rest being the same as above described. 
 
 Lenoir' s process — Galvanoplastic method for originals in high 
 relief. — Lenoir's method for reproducing statues in a manner 
 approaches in principle to that of the foundry. He begins by 
 making with gutta-percha a mould in several pieces, which are 
 united together so as to form a perfect hollow mould of the 
 original. This having been done, cover all the parts carefully 
 with black-lead. Make a skeleton with platinum wire, follow- 
 ing the general outline of the model, but smaller than the 
 mould, since it must be suspended in it without any point of 
 contact. If the skeleton thus prepared is enclosed in the 
 metallized gutta-percha mould, and the whole immersed in the 
 galvanoplastic bath, it will be sufficient to connect the inner 
 surface of the mould with the negative pole of the battery, and 
 the skeleton of platinum wires (which should have no points 
 of contact with the metallized surfaces of the mould) with the 
 positive pole, in order to decompose the solution of sulphate 
 of copper which fills the mould. When the metallic deposit 
 has reached the proper thickness the gutta-percha mould is 
 removed by any convenient process, and a faithful copy of the 
 original will be produced. Lead wires may be substituted for 
 the expensive platinum wires. This method requires a knowl- 
 edge of the moulder's art, so that good results can only be 
 obtained by an experienced hand. 
 
 Gelatine moulds. — Under certain conditions the elasticity of 
 gelatine allows of the possibility of its removal from undercut 
 or highly-wrought portions of the model, when it reassumes 
 the shape and position it had before removal therefrom. But 
 gelatine requires that the deposit shall be made rapidly, other- 
 
GALVANOPLASTY (REPRODUCTION). 621 
 
 wise it will swell and be partially dissolved by too long an 
 immersion in the copper bath. 
 
 To make a good gelatine mould, proceed as follows : Allow 
 white gelatine (cabinet-maker's glue) to swell for about 24. 
 hours in cold water, then drain off the water, and heat the 
 swollen mass in a water-bath until completely dissolved. 
 Compound the glue solution with pure glycerine in the pro- 
 portion of 5 to 10 cubic centimeters (0.24 to 0.3 cubic inch) 
 of glycerine to 30 grammes (1.05 ozs.) of gelatine, which 
 prevents the gelatine from shrinking in cooling. When some- 
 what cooled off, apply the gelatine to the oiled original, which 
 must be surrounded with a rim of plaster of Paris or wax, to 
 prevent the gelatine from running off; when cold, lift the gela- 
 tine mould from the model. Before metallizing and suspend- 
 ing in the copper bath, the mould has to be prepared to resist 
 the action of the latter, as otherwise it would at once swell and 
 be partially dissolved before being covered with the deposit. 
 This is effected by placing the mould in a highly concentrated 
 solution of tannin, which possesses the property of making 
 gelatine insoluble. 
 
 Brandley gives the following directions for preparing gelatine 
 solution with an addition of tannin, which renders the moulds 
 impervious to water: Dissolve 20 parts of the best gelatine in 
 100 of hot water, add y 2 part of tannic acid and the same quan- 
 tity of rock candy, then mix the whole thoroughly, and pour it 
 upon the model. 
 
 The same object is attained by the use of potassium dichro- 
 mate solution in place of tannin solution. In this case, the 
 potassium dichromate solution must be allowed to act in a 
 dark room, the mould being then for some time exposed to the 
 action of the sun. The chrome-gelatine layer formed upon the 
 surface does not swell up, and is insoluble, at least for the time 
 required to cover the mould with copper. Rendering glue 
 moulds conductive by means of black lead is, as a rule, imprac- 
 ticable, and metallization has to be accomplished by the wet 
 way in order to effect a rapid formation of the deposit. 
 
622 ELECTRO-DEPOSITION OF METALS. 
 
 Moulds rendered conductive by black lead should be rapidly 
 covered with copper while the bath is being agitated, because 
 a bath in which a considerable quantity of gelatine has been 
 dissolved, yields brittle copper, while by a very small quantity 
 of it, the density of the deposit is increased. 
 
 Special Applications of Galvanoplasty. 
 
 Nature printing, so named by Mr. v. Auer, Director of the 
 Imperial Printing Office at Vienna, has for its object the gal- 
 vanoplastic reproduction of leaves and other similar bodies. 
 The leaf is placed between two plates, one of polished steel, 
 the other of soft lead, and is then passed between rollers, which 
 exert a considerable pressure. The leaf thus imparts an exact 
 impression of itself and of all its veins and markings to the 
 lead, and this impression may be electrotyped, and the copper 
 plate produced used for printing in the ordinary way. Instead 
 of taking the impression in lead, it is advisable to use gutta- 
 percha or wax for delicate objects, which should previously be 
 black-leaded or oiled. In the same manner galvanoplastic 
 copies of laces, etc., may be obtained. 
 
 Elmore produces copper tubes by galvanoplastic deposition 
 by allowing the metallic core-bar to revolve slowly between 
 the anodes, while a polishing steel is by means of a mechanical 
 contrivance carried with strong pressure over the deposit, 
 whereby the latter is made dense and any roughness removed. 
 
 It would seem that the process for the production of copper 
 tubes, profiled hollow copper bodies, etc., patented by Ignaz 
 Klein, is better than Elmore's method. The black-leaded or 
 metallic core- bars are allowed to roll to and fro upon smooth 
 or profiled plates, the so-called milling plates, or the core-bars 
 are concentrically arranged around a cylindrical anode and 
 allowed with pressure to roll on an exterior round milling sur- 
 face. According to this method, the space in the baths can be 
 better utilized than in the Elmore process, and the deposit 
 shows excellent properties as regards uniform density and 
 power of resistance. 
 
GALVANOPLASTY (REPRODUCTION). 623 
 
 According to Dieffenbach and Limpricht's method (German 
 patent 125404) tubes and hollow bodies of copper of great 
 toughness and strength are obtained by allowing the metal 
 cores, or other cores rendered conductive in a suitable manner, 
 to revolve in an acid bath to which fine sand or, better, infuso- 
 rial earth has been added. The infusorial earth exerts a scour- 
 ing effect and removes any hydrogen bubbles which may have 
 been separated. Experiments made with this process yielded 
 copper tubes which on being tested showed excellent values as 
 regards strength. 
 
 Corviii s niello. — Corvin has invented a process of producing 
 inlaid work by galvanoplasty. The process is as follows : A 
 matrice of metal whose surface is finely polished is first made. 
 This matrice may be used for the production of numerous dup- 
 licates of the same kind of object. The incrustations (mother- 
 of-pearl, glass, ivory, amber, etc.) are then shaped by means 
 of a saw, files and other tools to the form corresponding to 
 that which they are to occupy in the design. The side of the 
 incrustation which is laid upon the matrice is, as a rule, smooth. 
 The shaped incrustations, smooth side down, are pasted on to 
 the parts of the model they are to occupy in the design. The 
 latter being thus produced, the backs of the non-metallic 
 laminae are metallized, and the portions of the metallic plate 
 left free are slightly oiled. By now placing the matrice thus 
 prepared in the galvanoplastic bath, the copper is deposited, 
 not only upon the metallic matrice, but also upon the back of 
 the inlaid pieces, the latter being firmly inclosed by the depos- 
 ited metal. When the deposited metal has acquired the de- 
 sired thickness, it is detached from the matrice, and incrustations 
 with the right side polished are thus obtained. The laminae 
 are more accurately and evenly laid in than would be possible 
 by the most skilled hand-work. 
 
 Plates for the production of imitations of leather are now fre- 
 quently prepared. The demand for alligator and similar 
 leathers is at the present time greater than the supply, and, 
 therefore, imitations are made by pressing ox-leather, the plate 
 
624 ELECTRO-DEPOSITION OF METALS. 
 
 being prepared by galvanoplasty, as follows : A large piece of 
 the natural skin or leather is made impervious to the bath by 
 repeated coatings with lacquer, and, when completely dry, 
 secured with asphalt lacquer to a copper or brass plate. The 
 leather is then black-leaded, and, after being made conductive 
 by copper wire or small lead plates, brought into the copper 
 bath. When the copper deposit has acquired the desired 
 thickness, the plate is further strengthened by backing with 
 stereotype metal. 
 
 Incrusting galvanoplasty . — This term may be applied to the 
 process by which a thick coat of copper, or of another metal, 
 is deposited upon an article. This deposit, however, is not 
 detached from the original, as in reproduction-galvanoplasty, 
 but remains upon it, the object being, as a rule, to embellish 
 the article or to give non-metallic articles the appearance of 
 metallic ones. 
 
 Non-metallic objects to be coated have also to be rendered 
 impervious to the electrolyte, great care being required in this 
 respect, since in case the acid copper bath penetrates into the 
 article to be coated, the deposit would later on effloresce and 
 peel off. 
 
 The objects may be rendered impervious by one of the 
 methods mentioned above, it being best, however, first to heat 
 them, as for instance, terra-cotta busts, and then place them in 
 melted wax, or mixtures of wax and paraffine. By heating, 
 the greater portion of the air is expelled from the pores, 
 the wax thus penetrating better and closing the pores. An 
 excess of wax is removed by draining off in a warm room (air- 
 bath), and when cold the objects are coated with gutta-percha 
 lacquer and metallized with black-lead. 
 
 However, it will frequently be impracticable to reach every 
 portion with the black-lead brush, and in this case it is recom- 
 mended to effect metallization by the wet way, as follows : 
 
 Coat the articles, previously rendered impervious, with a 
 thickly-fluid solution of shellac in alcohol, and allow them to 
 become thoroughly dry. Then immerse them for one minute 
 
GALVANOPLASTY (REPRODUCTION). 625 
 
 in saturated silver-nitrate solution in 4 parts of water and 6 
 parts of alcohol, and allow them to drain off. Bring the articles, 
 while still moist, into a vessel which can be closed air-tight, and 
 introduce sulphuretted hydrogen. A thin layer of silver sul- 
 phide will in a few minntesbe formed when the articles are taken 
 from the vessel and allowed to dry, the same manipulations be- 
 ing once or twice repeated. By operating in this manner, non- 
 success is next to impossible, because when the object is im- 
 mersed in the alcoholic silver-nitrate solution, the coat of 
 lacquer is superficially softened and absorbs silver nitrate, which 
 after its conversion into silver sulphide adheres very firmly after 
 drying, so that the layer of it becomes very seldom detached 
 in the bath. Should this nevertheless happen, it is generally 
 caused by the objects hot having been thoroughly dried be- 
 tween the separate operations. 
 
 Large objects which cannot be immersed will have to be 
 carefully brushed over with the solutions, or the latter be 
 poured over them. According to the nature of the objects to 
 be coated, the process may have to be somewhat modified, or 
 one of the methods already described will have to be employed. 
 This will soon be learned by experience. 
 
 Copper bath and current conditions. — Deposits for incrusting 
 galvanoplasty should be effected with very slight current- 
 densities in order to avoid roughness and a coarsely crystal- 
 line structure of the deposit. For many delicate objects to be 
 coated with copper, the use of the cell-apparatus is therefore 
 advisable. 
 
 Neubeck has recently investigated the work in the cell- 
 apparatus and its application to encrusting galvanoplasty, and 
 has found a copper bath which contains in 100 quarts, 44 lbs. 
 of crystallized blue vitriol and 13.2 lbs. of sulphuric acid of 66° 
 Be., to be especially valuable for the purpose. 
 
 In place of zincs, he used iron plates or iron tubes, and as 
 solution, one of sodium sulphate with the addition of a few 
 drops of sulphuric acid. The current generated by this ar- 
 rangement produces a very finely crystalline deposit free from 
 roughness and efflorescences. 
 40 
 
626 ELECTRO-DEPOSITION OF METALS. 
 
 Additional manipulation of the deposits. — The deposits of 
 copper produced by one or the other method require, as a 
 rule, additional mechanical manipulation to give the outlines 
 greater sharpness, and to the whole a more pleasing appear- 
 ance. This is done by chiseling to make, for instance, with 
 busts, the eyes, nose, ears, etc., more prominent. Scratch- 
 brushing, brushing, and polishing are applied if luster is to be 
 imparted to the deposits as is required for sufficiently effective 
 nickeling, gilding, etc. 
 
 Laces and tissues are, according to Philip, impregnated with 
 melted wax, and after removing an excess with blotting-paper, 
 they are made conductive by black-leading with a brush. It 
 is, however, preferable to metallize such delicate objects by the 
 wet way, employing one of the methods previously described. 
 
 Grasses, leaves, flowers, etc., are first dried and their former 
 shape and elasticity restored by placing them for a considerable 
 time in glycerine. They are then several times immersed in 
 gutta-percha lacquer, and metallized with silver nitrate solution 
 and sulphuretted hydrogen, or according to one of the other 
 processes described. 
 
 Wooden handles of surgical instruments are provided with a 
 galvanoplastic copper deposit to adapt them to the antiseptic 
 rules. The wood has to be protected from the bath-fluid pen- 
 etrating into it, by remaining for a considerable time in melted 
 wax, as otherwise the copper-deposit formed will be broken by 
 the swelling wood. Metallization may be effected by black- 
 lead, bronze powder or by the wet way, though black-leading 
 is the most simple method. The deposit is, as a rule, ground, 
 polished, and then nickeled. 
 
 Busts and other objects of terra-cotta, stoneware, clay, etc., are 
 immersed in melted wax and, after removing an excess of wax, 
 coated with gutta-percha lacquer. If there is no obstacle to 
 black-leading, this method may be used for metallization, other- 
 wise recourse will have to be had to one of the processes pre- 
 viously described. 
 
 When the copper deposit is finished the objects should be 
 
GALVANOPLASTY (REPRODUCTION). 627 
 
 thoroughly soaked in water, and then for a few hours placed in 
 a 5 per cent, yellow prussiate of potash solution for the neu- 
 tralization of any bath-residue which may still remain in some 
 of the pores. 
 
 To bring out sharp outlines, especially when the deposit is 
 quite thick, the coppered busts and other objects are chiseled, 
 scratch-brushed, and polished. They receive, as a rule, a 
 patina, according to one of the methods given in Chapter XIV, 
 or are brassed, silvered, or gilded. 
 
 The mercury vessels of thermometer siox vacuum and distilling 
 apparatus are as a protection given a galvanoplastic deposit of 
 copper. This is effected in the most simple manner by coating 
 the glass with copal lacquer and black-leading the layer of 
 lacquer, or applying bronze powder. The glass may also be 
 matted by the sand blast, or with fluoric acid, and directly 
 black-leaded, the black-lead adhering well to the matted glass 
 surface. 
 
 Mirrors are coppered to protect the thin layer of silver from 
 injury. For the success of coppering in the acid copper bath 
 without danger of the film of silver becoming detached, it is 
 necessary to use a weaker bath of at the utmost 8° to io° Be. 
 with 1 per cent, of free sulphuric acid, and to deposit with a 
 very slight current-density. 
 
 Glass and porcelain ware, for instance, tumblers, bowls, coffee 
 and tea sets, when furnished with galvanoplastic decorations in 
 copper or silver, produce beautiful effects. However, metalli- 
 zation by one of the processes thus far described is not practi- 
 cable, the high reliefs having to adhere firmly to the base, so as 
 not to become detached by cleansing or wear. 
 
 Metallization of the portions to be coated is effected by 
 painting the arabesques, flowers, monograms, etc., with solution 
 of Dutch gold, factitious silver, or platinum, and after drying, 
 burning in a muffle at a dark red heat. A lustrous layer of 
 metal firmly fused together with the glaze is thus obtained and 
 is without further preparation fit for coppering or silvering. 
 Still greater solidity is attained by triturating conducting silver 
 
028 ELECTRO-DEPOSITION OF METALS. 
 
 enamel with lavender oil upon a palette to a mass of the con- 
 sistency of paint, applying the latter with a brush and burning- 
 in the muffle. In addition to pure silver, the enamel contains 
 fluxing agents which effect a firm union of the silver with the 
 porcelain or glass. After burning in, the decorations are gone 
 over with a fine copper brush and, the conduction of the cur- 
 rent to the metallized portions having been effected by means 
 of .fine copper wires, the objects are brought into the galvano- 
 plastic bath. 
 
 Umbrella and cane handles of celluloid are decorated with a 
 metallic deposit by means of galvanoplasty. The simplest 
 mode of metallizing them is to paint the decorations with a 
 mixture of bronze powder and acetone. On the point of con- 
 tact, the acetone dissolves a small quantity of celluloid, the 
 latter thus becoming quite firmly united with the bronze pow- 
 der. After drying, an excess of non-adhering powder is re- 
 moved with a brush, and the objects are then brought into the 
 copper bath. 
 
 Baby-shoes for a keep-sake, are coppered by galvanoplasty, 
 and the deposit is patinized or silvered. Metallization is best 
 effected by applying several coats of copal lacquer, and black- 
 leading the layer of lacquer on the outside, while the inside, 
 which is more difficult of access, is made conductive by means 
 of bronze powder or by the wet way. 
 
 Carbon pins and carbon blocks for electro-technical purposes 
 are frequently coated with copper in order to effect a more 
 sure metallic contact in their mountings. The carbons are 
 impregnated with wax so as to prevent the blue vitriol solution 
 from penetrating. They are then brushed with quick lime and 
 without further preparation brought into the bath. 
 
 Rolls of steel and cast-iron, pump-pistons, etc., are first pro- 
 vided with as thick a deposit as possible in the cyanide cop- 
 per bath, and then brought into the galvanoplastic acid copper 
 bath. With a bath at rest the current density should not ex- 
 ceed 30 amperes per square meter, but with an agitated bath 
 up to 120 amperes may be used. 
 
GALVANOPLASTY (REPRODUCTION). 629 
 
 Steel gun barrels for marine purposes are treated in the same 
 manner, after all the portions which are not to receive a de- 
 posit of copper, have been thoroughly covered with a mixture 
 of wax, mastic and red lead. 
 
 Candelabra, stairs and structural parts of buildings of rough 
 castings require a somewhat modified treatment. While the 
 rolls and steel gun barrels previously referred to are always 
 turned smooth, rough iron castings are used for the above- 
 mentioned purposes, and the production in the potassium cya- 
 nide bath of a copper deposit of such thickness as not to 
 corrode the basis-metal in the acid copper bath is frequently 
 connected with difficulties. In a plant recently furnished by 
 Dr. Geo. Langbein & Co. for coppering rust-proof, and then 
 brassing structural parts of a post office building in Mexico, 
 the following plan was adopted : The rough castings were first 
 carefully cleaned by means of a sand blast and then heavily 
 nickeled; upon this nickel coating the I millimeter thick copper 
 deposit could without risk be produced in the acid copper bath. 
 The parts were then thoroughly rinsed, dried, brightened with 
 a brush and emery and, after carefully freeing from grease, 
 electrolytically provided with a heavy deposit of bronze, and 
 patinized. 
 
 It is believed that sufficient examples of the uses of galvano- 
 plasty have here been given. It allows of the most varied ap- 
 plications, and by studying the special processes described 
 above, the reader will be in a position to find out the most 
 suitable method for every other contingency. 
 
 II. Galvanoplasty in Iron (Steel). 
 
 Under " Deposition of Iron," the galvanoplastic produc- 
 tion of heavy detachable deposits of iron has already been 
 referred to. 
 
 Serviceable iron electrotypes were first produced about 1870, 
 by Klein, of St. Petersburg, and used for printing Russian bank 
 notes. Their preparation was, and is still, very troublesome, 
 success depending on the fulfillment of many conditions, so 
 
630 ELECTRO-DEPOSITION OF METALS. 
 
 that, notwithstanding continued experiments and the expense 
 of much labor, the former expectation of entirely supplanting 
 electrotypes in copper by cliches in steel has thus far not been 
 realized. 
 
 The bath used by Klein, and still employed for this purpose, 
 consists of a 10 per cent, solution of a mixture of equal parts 
 of ferrous sulphate (green vitriol) and magnesium sulphate 
 (Epsom salt). The solution has a specific gravity of 1.05. To 
 obtain successfully a serviceable electrotype from an original, 
 for instance, from a copper plate, which should previously be 
 silvered and coated with a thin layer of silver sulphide by 
 means of sulphuretted hydrogen, the following conditions have 
 to be fulfilled, according to Klein's statement: The bath must 
 be kept absolutely neutral, which is effected by suspending in 
 it linen bags filled with magnesium carbonate, and the current- 
 strength must be so regulated that absolutely no evolution of 
 hydrogen is perceptible on the anodes. Further, the plates 
 are every half hour to be taken from the bath and rinsed with 
 a powerful jet of water to remove any adhering gas-bubbles. 
 Care must be taken during this process that the plates do not 
 become dry, since fresh layers do not adhere well upon plates 
 which have become dry. 
 
 For the removal of adhering gas-bubbles, it has also been 
 proposed frequently to pass a feather over the plates. 
 
 It may here be mentioned that Lenz found a not inconsider- 
 able content of hydrogen in iron deposits, and also carbonic 
 acid, carbonic oxide, and nitrogen in varying quantities. How- 
 ever, examinations made by Dr. Geo. Langbein established 
 positively only a content of hydrogen, and it would seem that 
 this hydrogen, which is absorbed and tenaciously retained by 
 the deposit, is the cause of all the difficulties encountered in 
 the production of heavy iron deposits. 
 
 If, however, the occlusion of hydrogen is regarded as the 
 cause of the mischief, ways and means to counteract it as much 
 as possible may be found in the fact that iron deposited with 
 greater current-density is more brittle, shows a greater tendency 
 
GALVANOPLASTY (REPRODUCTION). 63] 
 
 to peel off in the bath, and contains a larger quantity of hydro- 
 gen than a deposit produced with slighter current-density. 
 
 In this respect experience gained in the electrolytic refining 
 of copper shows us the way in so far that for the production 
 of heavy deposits of iron, the bath must be kept in constant, 
 vigorous agitation, to remove, on the one hand, layers of fluid 
 poorer in metal from the cathode, and, on the other, to force, 
 by the agitation, the gas-bubbles adhering to the cathode to 
 escape. Further, deposition must be effected with so slight a 
 current-density that no evolution of hydrogen is perceptible 
 on the cathode, and a current-density of 0.25 ampere may be 
 designated as the maximum per 153^ square inches, with which 
 heavy deposits of iron can be produced. 
 
 To counteract the spoiling of the deposits, further precau- 
 tionary measures are, however, necessary, especially heating 
 the electrolyte, and from time to time interrupting the current. 
 In heated baths the escape of the gas is facilitated, especially 
 when the electrolyte is agitated, and hence adhering gas- 
 bubbles cannot remain long in one place. A constantly-re- 
 peated interruption of the current is of advantage and effective, 
 because metallic parts covered with a minimum quantity of 
 hydrogen cannot be coated with a fresh deposit until the hy- 
 drogen is removed by the agitation of the heated electrolyte. 
 Hence the interruption of the process of deposition would give 
 opportunity and time for the removal of the gas molecules 
 before further deposition takes place, and without a knowledge 
 of the more intimate processes, Klein succeeded in affecting the 
 interruption of the deposit, by taking the plates at short inter- 
 vals from the bath and removing the adhering gas by a power- 
 ful jet of water. 
 
 With the present state of galvanoplasty it is not necessary to 
 follow Klein's primitive method, and it would be more practical 
 to provide the positive conducting rod of the bath with a con- 
 trivance which mechanically effects the interruption of the cur- 
 rent. Suppose upon such a metallic conducting rod is mounted 
 a copper or brass wheel, which is secured to a pulley and re- 
 
632 ELECTRO-DEPOSITION OF METALS. 
 
 volves around the conducting rod, and half of the periphery 
 of which is insulated, and that upon the rod drags a metallic 
 brush which effects the transmission of the positive current. 
 Now, it will be seen that while the contact-wheel is revolving, 
 current is introduced only one-half the time and not during 
 the other half, and that by the rapidity of revolution of the 
 contact-wheel, the number of interruptions of the current can 
 be varied at will. 
 
 Since Neubeck has in a relatively very short time produced 
 in hot baths, deposits 1 to 2 millimeters thick, of coherent 
 form and good quality, the possibility is presented of making 
 steel electrotypes in an indirect way by obtaining first from the 
 impression a copper electrotype, from this a negative in copper, 
 and after silvering the latter, producing a heavy deposit of steel 
 upon it. 
 
 It may also be expected that by complying with the above- 
 mentioned conditions and the discovery of new methods, it will 
 be possible directly to produce steel electrotypes upon moulds 
 of gutta-percha or wax as is now successfully done with nickel. 
 
 It is well known that electrolytically deposited iron possesses 
 great hardness, and that such deposits well deserve the name 
 of steel deposits, their hardness being greater than that of iron, 
 and approaching that of steel. This feature cannot be ex- 
 plained otherwise than by the hydrogen absorbed by the de- 
 posit. Hence it will be seen that, on the one hand, this absorp- 
 tion of hydrogen has an injurious effect upon the separation of 
 iron, while, on the other, it imparts to the deposits the most 
 valuable property of great hardness. It would seem that the 
 quantities of iron first deposited upon the mould are, and can 
 be, richer in hydrogen in order to impart to the printing sur- 
 face the utmost possible hardness. However, in further strength- 
 ening and augmenting the deposit, our efforts must be directed, 
 by the reduction of the current, to deposit strengthening layers 
 as free from hydrogen as possible. 
 
 The question now arises, whether it is of greater advantage 
 to steel a copper electrotype in order to increase its power of 
 
GALVANOPLASTY (REPRODUCTION). 633 
 
 resistance, or whether it is better to produce an iron electrotype 
 and to strengthen its back in the acid copper bath. If the 
 above-expressed view that the layers of iron first deposited are 
 richer in hydrogen, and therefore harder, is correct, the prefer- 
 ence must be given to iron electrotypes, because with steeled 
 copper electrotypes the softer layers are exposed to wear, 
 while the harder layers lie upon the copper plate. The reverse 
 is the case with an iron electrotype, the first deposit, rich in 
 hydrogen, forming the printing face. 
 
 However, on the other hand, steeled copper electrotypes 
 have the advantage that, when worn, the old deposit of iron 
 can be readily removed by dilute sulphuric acid, and the elec- 
 trotypes resteeled, while worn iron electrotypes have to be 
 renewed. 
 
 III. Galvanoplasty in Nickel. 
 
 Although by the electro-deposition of nickel, electrotypes 
 are rendered fit for printing with metallic colors, which attack 
 copper, and their power of resisting wear is increased, the latter 
 advantage can to the fullest extent be obtained only by a thick 
 deposit. However, this always alters the design somewhat, 
 especially the fine hatchings, this being the reason why in 
 nickel-plating electrotypes a deposit of medium thickness is, as 
 a rule, not exceeded. If a hard nickel surface is desired, with- 
 out injury to the fine lines of the design, the layer of nickel has 
 to be produced by galvanoplasty, and the deposit of nickel 
 strengthened in the copper bath. 
 
 But upon black-leaded gutta-percha or wax moulds a nickel 
 deposit can only be obtained in fresh baths. The deposit, 
 however, is faultless only in rare cases, it generally showing 
 holes in the depressions. Hence the object has to be attained 
 in a round about way, the mode of procedure being as follows: 
 An impression of the original is taken in gutta-percha or wax, 
 and from this impression a positive cliche in copper is made. 
 The latter is then silvered, the silvering iodized as previously 
 described, and a negative in copper is then prepared from this 
 positive. The negative is again silvered, iodized, and then 
 
634 ELECTRO-DEPOSITION OF METALS. 
 
 brought into a nickel bath, where it receives a deposit of the 
 thickness of stout writing paper. It is then rinsed in water, and 
 the deposit immediately strengthened in the acid copper bath. 
 For the rest, it is treated like ordinary copper deposits. 
 
 If for the production of the nickel electrotype, a nickel bath 
 of the composition given on p. 264 and heated to between 185 
 and 1 94 F. is used, deposition may be made with high current- 
 densities — 5 amperes and eventually more — -so that a thickness 
 of 0.2 millimeter is in about 2^ hours attained. This deposit 
 is slightly coppered in the acid copper bath and backed. 
 
 In this manner nickel electrotypes of 15.74 x 11.81 inches 
 have been produced, but as will be seen for the purposes of 
 printing houses, the process is too troublesome and time-con- 
 suming, by reason of the necessary production of the copper 
 matrices. Hence the direct method of deposition upon black- 
 leaded gutta-percha or wax moulds is decidedly to be preferred. 
 
 This direct method requires a cold nickel bath, which yields 
 heavy deposits without the nickel rolling off, and for deposits 
 of a thickness suitable for printing, a few contrivances to pre- 
 vent spontaneous detachment of the nickel from the matrix. 
 , The electrolyte, according to patent No. 134736 given on page 
 264 is applicable to this purpose. With this electrolyte, de- 
 posits of 6 millimeters' thickness were without trouble produced 
 at the ordinary temperature upon gutta-percha. In testing 
 other nickel baths described or patented, not a single one was 
 found which allowed of obtaining useful nickel deposits directly 
 upon the matrices, the nickel always rolling off, and when the 
 latter drawback was prevented by suitable means, it was im- 
 possible to obtain a deposit of more than 0.05 millimeter thick- 
 ness, cracks being formed in the center. 
 
 In working with this direct process of deposition, it is abso- 
 lutely necessary always to keep the nickel bath slightly acidu- 
 lated, because in a neutral or alkaline electrolyte the deposit 
 becomes readily rough and forms with a dark color, which is 
 an indication of the formation of sponge. It is also of advan- 
 tage to keep the electrolyte constantly agitated. By reason of 
 
GALVANOPLASTY (REPRODUCTION). 
 
 635 
 
 the oxidation of the ethyl-sulpho combinations which takes 
 place, agitation, however, must not be effected by blowing in 
 air, but by mechanical means, or eventually by blowing in car- 
 bonic acid. 
 
 An electro- motive force of 2.2 volts and a current-density of 
 0.2 to 0.3 ampere proved most suitable for the production of 
 the above-mentioned nickel electrotypes of 6 millimeters in 
 thickness. The current output — about 70 per cent. — was not 
 particularly favorable, this being, however, of little importance 
 as compared with the advantages offered by the use of this 
 electrolyte. 
 
 It has previously been mentioned that in order to obtain de- 
 
 Fig. 159. 
 
 Fig. 161. 
 
 Fig. 162. 
 
 V' 1, '//// 1'S/ "/-. 
 
 '// / - > /, ■''/■-■ ■''■'/'-■- ■■'■■ 
 
 posits of greater thickness upon gutta-percha or wax, a few 
 contrivances are required to prevent the deposit from rolling 
 off. With the use of gutta-percha matrices there is less danger 
 of rolling off than with that of wax moulds, the tendency to 
 rolling off being much earlier shown by the latter. However, 
 in order to prevent failures, it is advisable not to omit these 
 devices even when working with gutta-percha matrices. 
 
 According to the patent specification, a groove undercut 
 towards the design and at a distance of about 3 millimeters 
 from it, is made all round, and - another such groove at a further 
 
636 ELECTRO-DEPOSITION OF METALS. 
 
 distance of about 3 millimeters, as shown in Fig. 159 in front 
 view, and in Fig. 160 in section. 
 
 The object of this contrivance is that upon the carefully black- 
 leaded grooves, nickel continuous with the nickel upon the 
 design is also deposited, and by reason of the undercutting 
 towards the design the nickel is thus prevented from rolling off 
 or becoming detached if, in consequence of the occlusion of 
 hydrogen, the deposit shows a tendency to bend up. 
 
 According to the above mentioned patent, the same effect 
 may also be attained by firmly securing a metallic edge all 
 round the design. While the nickel deposit cannot find a more 
 firm hold upon the black-leaded, but otherwise non-metallic 
 surfaces of the gutta-percha or wax matrices, it adheres very 
 firmly to the metallic edge, rolling off being thus prevented. 
 Dr. Langbein used thin brass strips, 0.1 millimeter thick and 5 
 millimeters wide which, as shown in Figs. 161 and 162, were 
 secured by small pins either to the impressed surface or to the 
 sides. Wires wound round the four sides of the matrix and 
 lying everywhere closely upon its black-leaded surface, may be 
 used in place of metal strips. It is advisable to place the 
 metal strips in a heated state upon the matrix and press them 
 gently into the matrix-material so that their surfaces lie per- 
 fectly level with the surface of the impression. The matrix and 
 the metal edge having been carefully black-leaded, the outside 
 of the latter is brushed over with a rag moistened with potas- 
 sium cyanide solution, care being taken not to damage the 
 black-leading of the metal towards the design. Then rinse the 
 matrix with alcohol and suspend it at once in the nickel bath, 
 the latter being kept at rest until the matrix is covered, and 
 then agitated. 
 
 Nickel matrices. — In casting type from copper matrices, the 
 latter oxidize quite rapidly, in consequence of which the edges 
 and lines especially lose sharpness, while the surfaces become 
 scarred. As early as 1883, Weston mentions in his English 
 patent 4784, the possibility of obtaining heavy deposits of solid 
 nickel, and that this invention is valuable for the production of 
 
GALVANOPLASTY (REPRODUCTION). 637 
 
 electrotypes, which without doubt includes electrolytically pre- 
 pared matrices for casting type, the influence of the temperature 
 of the liquid metal upon such nickel matrices being so slight 
 that they do not warp, etc. 
 
 Notwithstanding the fact that thus the employment of an 
 electrolytically-produced casting matrix of nickel was known, 
 the " Aktien-Gesellschaft fur Schriftgiesserei " obtained a patent, 
 the characteristic feature of which is that zinc can be directly 
 cast around the face "without further galvanoplastic reinforce- 
 ment." 
 
 Hence the above-mentioned patent cannot include such 
 nickel matrices in which by the deposition of nickel the face is 
 produced of a thickness which by itself is insufficient to allow 
 of the deposit being detached from the original without fear of 
 bending or breaking, the deposit requiring absolutely to be re- 
 inforced to the customary thickness by a galvanoplastic deposit 
 of copper. It is obvious that a thickness of 0.1 to 0.25 milli- 
 meter of nickel suffices to withstand the effect of temperature 
 and, when reinforced by copper, also the pressure in casting in 
 the machine. Reinforcement of the casing of the back with 
 copper has, however, the further advantage that in casting zinc 
 around the face, the zinc alloys to a certain degree with the 
 copper casting, thus uniting firmly with it, which is not the 
 case when zinc is cast around the pure nickel face not envel- 
 oped by copper, nickel not entering into a solid combination 
 with zinc. 
 
 Matrices electrolytically produced from cobalt also cannot 
 be claimed under the above-mentioned patent. In hardness, 
 cobalt is equal to nickel and. resists the hot-type metal as well, 
 possessing therefore all the properties required for casting 
 matrices. 
 
 The most suitable material for such matrices would be an 
 alloy of nickel and cobalt such as has been described on p. 307 
 as hard nickel alloy. 
 
 In order to effect an intimate union of the copper casing 
 with the nickel, the nickel deposit when taken from the nickel 
 
638 ELECTRO-DEPOSITION OF METALS. 
 
 bath has to be brushed over with nitric acid, rinsed, and with- 
 out delay brought into the copper bath. 
 
 The omission of these manipulations, which require dexterity, 
 may have been the cause why no more favorable results were 
 obtained by former experiments to reinforce thinner nickel 
 deposits by copper to a thickness of 2 millimeters, the nickel 
 deposit becoming detached from the copper when the matrix 
 was in use. If, however, in accordance with the suggestions 
 given above, the nickel deposit is made 0.1 to 0.25 millimeter 
 thick, and the back, which is to be reinforced, cleansed with 
 nitric acid and rinsed, and then as rapidly as possible brought 
 into the copper bath to be reinforced to 2.5 or 3 millimeters in 
 thickness, the copper will adhere firmly and a durable matrix 
 will be obtained. 
 
 By means of galvanoplasty matrices of massive nickel or 
 cobalt for use in the casting machine may even be produced. 
 However, by reason of their hardness, such massive nickel 
 matrices are justified with difficulty, and besides they are too 
 expensive. 
 
 While no experiments for the production of nickel matrices 
 have been made with Weston's baths, nickel deposits several 
 millimeters in thickness can without doubt be made with, them 
 by slightly changing their composition and heating them to 
 between 176 and 194 F. In the experiments made baths of 
 the composition given on p. 263 were used. They contained 
 in 100 quarts, JJ lbs. of nickel sulphate and 39.6 lbs. of mag- 
 nesium sulphate, and were always kept slightly acid with acetic 
 acid, the temperature during deposition being as constantly as 
 possible maintained at 194 F. 
 
 The originals have to be prepared in a manner different from 
 that for matrices in copper. In place of wax for insulating the 
 surfaces which are to receive no deposit, a material which does 
 not soften at 194 F. has to be used. For this purpose, it was 
 found most suitable to cast plaster of Paris around the original,, 
 or a paste of asbestos meal and water glass. By treatment for 
 10 hours in the hot nickel bath, during which time the current 
 
GALVANOPLASTY (REPRODUCTION). 639* 
 
 must in no wise be interrupted, and the original, especially in 
 the beginning, be vigorously shaken, a nickel deposit about 0.25 
 millimeter in thickness is obtained. This deposit, as previously 
 described, is reinforced in the acid copper bath to about 1.75 to 
 2.25 millimeters in thickness, and zinc having in the usual 
 manner been cast around it, is justified for the casting machine. 
 The production of nickel matrices may also be effected with 
 the use of the cold nickel bath described on p. 264, but much 
 more time is required. In this case the originals may of course 
 be insulated with wax. 
 
 IV. Galvanoplasty in Silver and Gold. 
 
 The preparation of reproductions in silver and gold presents 
 many difficulties. While copper is reducible in a compact state 
 from its sulphate solution, silver and gold have to be reduced, 
 from their double salt solutions — potassium silver cyanide and 
 potassium gold cyanide. However, these alkaline solutions 
 attack moulds of fatty substances, such as wax and stearine, 
 consequently also, plaster-of-Paris moulds impregnated with 
 these substances, as well as gutta-percha and gelatine. Hence, 
 only metallic moulds can be advantageously used, unless the 
 end is to be attained in a round-about way; that is, by first 
 coating the mould with a thin film of copper, reinforcing this 
 in the silver or gold bath, and finally dissolving the film of 
 copper with dilute nitric acid. 
 
 The double salt solutions mentioned above require a well- 
 conducting surface such as cannot be readily prepared by 
 black-leading, a further reason why metallic moulds are to be 
 preferred. 
 
 The simplest way for the galvanoplastic reproduction in gold 
 or silver of surfaces not in too high relief or too much under- 
 cut, is to cover the object with lead, silver or gold foil, and 
 pressing softened gutta-percha upon it. The foil yields to the 
 pressure without tearing, and adheres to the gutta-percha so 
 firmly that it can be readily separated together with it. This 
 method is of course only applicable if the originals to be 
 moulded can bear the pressure of the press. 
 
640 ELECTRO-DEPOSITION OF METALS. 
 
 With originals which cannot stand pressure, or have portions 
 in very high relief, or much undercut, oil gutta-percha may be 
 used. The original secured to a brass plate, having been 
 heated to between 122 and 140 F. and slightly oiled, the oil 
 gutta-percha in small cubes is applied so that one cube is first 
 placed upon the original and when soft, pressed firmly down 
 with the moistened finger, other cubes being then in the same 
 manner applied until the entire surface of the original is cov- 
 ered, when the whole is allowed to cool, which may be accel- 
 erated by placing it in very cold water. This impression can 
 be detached in good shape from the original by the use of 
 gentle force, the oil gutta-percha being in a hardened state suf- 
 ficiently pliable to allow of its being readily taken out from the 
 undercut portions. The face of the mould is next freed from 
 oil by means of alcohol, or by brushing with liquid ammonia, 
 and then dried. Now powder the mould with fine silver pow- 
 der, thoroughly rubbing the latter with a brush into the de- 
 pressions, so that it adheres firmly to the gutta-percha and after 
 blowing off an excess, bring the mould into the silver bath. 
 
 The most suitable composition of the galvanoplastic silver 
 bath is as follows : 
 
 Fine silver (in the form of silver cyanide) 1^ ozs., 99 per 
 cent, potassium cyanide 4^ ozs., water 1 quart. 
 
 Maximum current-density, 0.3 ampere. 
 
 A slighter current-density than that given above can only be 
 beneficial, and the electro-motive force should be as low as 
 possible, the best deposits having been obtained with 0.5 volt 
 and an electrode-distance of 10 centimeters. 
 
 For galvanoplasty in gold, the same process as described 
 above is used. Good results are obtained with a bath com- 
 posed as follows : 
 
 Fine gold (in the form of neutral chloride of gold or fulmin- 
 ating gold) 1 oz., 99 per cent, potassium cyanide 3^ ozs., 
 water 1 quart. 
 
 Current- density, 0.1 ampere. 
 
 Electro-motive force at 10 cm. electrode-distance, 0.4 volt. 
 
CHAPTER XVII. 
 
 CHEMICALS USED IN ELECTRO-PLATING AND GALVANOPLASTY. 
 
 Below the characteristic properties of the chemical products 
 •employed in the workshop will be briefly discussed, and the 
 reactions indicated which allow of their recognition. It fre- 
 quently happens that the labels become detached from the 
 bottles and boxes, thus rendering the determination of their 
 contents necessary. 
 
 I. Acids. 
 
 I. Sulphuric acid {oil of vitriol). — Two varieties of this acid 
 are found in commerce, viz., fuming sulphuric acid (disulphuric 
 acid) and ordinary sulphuric acid. The first is a thick oily 
 fluid, generally colored yellowish by organic substances, and 
 emits dense, white vapors in the air. Its specific gravity is 
 I.87 to 1.89. The only purpose for which fuming sulphuric 
 acid is used in the electro-plating art, is as a mixture with nitric 
 acid for stripping silvered objects. 
 
 Ordinary sulphuric acid has a specific gravity of 1.84. 
 Diluted with water it serves for filling the Bunsen elements and 
 as a pickle for iron ; in a concentrated state it is used in the 
 preparation of pickles and as an addition to the galvanoplastic 
 copper bath. The crude commercial acid generally contains 
 arsenic, hence care must be had to procure a pure article. In 
 diluting the acid with water, it should in all cases be added to 
 the water in a very gentle stream and with constant stirring, as 
 otherwise a sudden generation of steam of explosive violence 
 might result, and the dangerous corrosive liquid be scattered in 
 all directions. Concentrated sulphuric acid vigorously attacks 
 all organic substance, and hence has to be kept in bottles with 
 41 (641) 
 
642 ELECTRO-DEPOSITION OF METALS. 
 
 glass stoppers, and bringing it in contact with the skin should 
 be carefully avoided. 
 
 Recognition. — One part of the acid mixed with 25 parts of 
 distilled water gives, when compounded with a few drops of 
 barium chloride solution, a white precipitate of barium sulphate. 
 
 2. Nitric acid {aqua fords, spirit of nitre). — It is found in 
 trade of various degrees of strength. For our purposes, acid 
 of 40 and 30 Be is generally used. The acid is usually a 
 more or less deep yellow, and frequently contains chlorine. 
 The vapors emitted by nitric acid are poisonous and of a char- 
 acteristic odor, by which the concentrated acid is readily dis- 
 tinguished from other acids. It is used for filling the Bunsen 
 elements (carbon in nitric acid), and for pickling in combina- 
 tion with sulphuric acid and chlorine. On coming in contact 
 with the skin it produces yellow stains. 
 
 Recognition. — By heating the not too dilute acid with copper, 
 brown-red vapors are evolved. For the determination of dilute 
 nitric acid, add a few drops of it to green vitriol solution, when 
 a black-brown coloration will be produced on the point of 
 contact. 
 
 3. HydrocJiloric acid {muriatic acid). — The pure acid is a 
 colorless fluid which emits abundant fumes in contact with the 
 air, and has a pungent odor by which it is readily distinguished 
 from other acids. The specific gravity of the strongest hydro- 
 chloric acid is 1.2. The crude acid of commerce has a yellow 
 color, due to iron, and contains arsenic. Dilute hydrochloric 
 acid is used for pickling iron and zinc. 
 
 Recognition. — On adding to the acid, very much diluted with 
 distilled water, a few drops of solution of nitrate of silver in dis- 
 tilled water, a heavy white precipitate is formed, which becomes 
 black by exposure to the light. 
 
 4. Hydrocyanic acid (prussic acid). — This extremely poi- 
 sonous acid exists in nature only in a state of combination in 
 certain vegetables and fruits, and especially in the kernels of 
 the latter, as, for instance, in the peach, the berries of the 
 cherry laurel, bitter almonds, the stones of the apricot, of 
 
CHEMICALS USED IN ELECTRO- PLATING. 643 
 
 plums, cherries, etc. It may be obtained anhydrous, but in 
 this state it is useless, and very difficult to preserve from de- 
 composition. Diluted hydrocyanic acid is colorless, with a 
 bitter taste and the characteristic smell of bitter almonds. It is 
 employed in the preparation of gold immersion baths, and for 
 the decomposition of the potassain old silver baths. The inha- 
 lation of the vapors of this acid may have a fatal effect, as also 
 its coming in contact with wounds. 
 
 Recognition. — By its characteristic smell of bitter almonds. 
 Or mix it with potash lye until blue litmus paper is no longer 
 reddened, then add solution of green vitriol which has been 
 partially oxidized by standing in the air, and acidulate with 
 hydrochloric acid. A precipitate of Berlin blue is formed. 
 
 5. Citric acid. — Clear colorless crystals of 1.542 specific 
 gravity, which dissolve with great ease in both hot and cold 
 water. It is frequently employed for acidulating nickel baths, 
 and, combined with sodium citrate, in the preparation of plati- 
 num baths. 
 
 Recognition. — Lime-water compounded with aqueous solution 
 of citric acid remains clear in the cold, but on boiling deposits 
 a precipitate of calcium citrate. The precipitate is soluble in 
 ammonium chloride, but on boiling is again precipitated, and 
 is then insoluble in sal ammoniac. 
 
 6. Boric acid {boracic acid). — This acid is found in commerce 
 in the shape of scales with nacreous luster and greasy to the 
 touch ; when obtained from solutions by evaporation, it forms 
 colorless prisms. Its specific gravity is 1.435; it dissolves 
 with difficulty in cold water (1 part of acid requiring at 64.4 F. 
 28 of water), but is more rapidly soluble in boiling water (1 part 
 of acid requiring 3 of water at 212 F. According to Weston's 
 proposition, boric acid is employed as an addition to nickel 
 baths, etc. 
 
 Recognition. — By mixing solution of boric acid in water with 
 some hydrochloric acid and dipping turmeric paper in the solu- 
 tion, the latter acquires a brown color, the color becoming 
 more intense on drying. Alkalies impart to turmeric paper a 
 
644 ELECTRO-DEPOSITION OF METALS. 
 
 similar coloration, which, however, disappears on immersing 
 the paper in dilute hydrochloric acid. 
 
 7. Arsenious acid {white arsenic, arsenic, ratsbane*). — It gen- 
 erally occurs in the shape of a white powder, and sometimes in 
 vitreous-like lumps, resembling porcelain. For our purposes 
 the white powder is almost exclusively used. It is slightly sol- 
 uble in cold water, and more readily so in hot water and hy- 
 drochloric acid. Notwithstanding its greater specific gravity 
 (3.7), only a portion of the powder sinks to the bottom on 
 mixing it with water, another portion being retained on the 
 surface by air bubbles adhering to it. It is employed as an 
 addition to brass baths, further, in the preparation of arsenic 
 baths, for blacking copper alloys, and in certain silver whitening 
 baths. 
 
 Recognition. — When a small quantity of arsenious acid is 
 thrown upon glowing coals an odor resembling that of garlic is 
 perceptible. By mixing solution of arsenious acid, prepared by 
 boiling with water, with a few drops of ammoniacal solution of 
 nitrate of silver, a yellow precipitate of arsenate of silver is ob- 
 tained. The ammoniacal solution of nitrate of silver is pre- 
 pared by adding ammonia to solution of nitrate of silver until 
 the precipitate at first formed disappears. 
 
 8. Chromic acid. — It forms crimson -red needles, and also 
 occurs in commerce in the shape of a red powder. It is read- 
 ily soluble in water, forming a red fluid, which serves for filling 
 batteries. 
 
 Recognition. — Chromic acid can scarcely be mistaken for any 
 other chemical product employed by the electro-plater. A 
 very much diluted solution of it gives, after neutralization with 
 caustic alkali and adding a few drops of nitrate of silver solution, 
 a crimson-red precipitate of chromate of silver. 
 
 9. Hydrofluoric acid. — A colorless, corrosive, very mobile 
 liquid of a sharp, pungent odor. The anhydrous acid fumes 
 strongly in the air and attracts moisture with avidity. Hydro- 
 fluoric acid is used for etching glass and for pickling aluminium 
 dead white. Great care must be observed in working with the 
 
CHEMICALS USED IN ELECTRO-PLATING. 645 
 
 acid, since not only the aqueous solution, but also the vapors, 
 have an extremely corrosive effect upon the skin and respira- 
 tory organs. 
 
 Recognition. — By covering a small platinum dish containing 
 hydrofluoric acid with a glass plate free from grease, the latter 
 in half an hour appears etched. 
 
 II. Alkalies and Alkaline Earths. 
 
 10. Potassium hydrate {caustic potash). — It is found in com- 
 merce in various degrees of purity, either in sticks or cakes. 
 It is very deliquescent, and dissolves readily in water and alco- 
 hol; by absorbing carbonic acid from the air it rapidly becomes 
 converted into the carbonate, and thus loses its caustic proper- 
 ties. It should, therefore, be kept in well-closed vessels. Sub- 
 stances moistened with solution of caustic potash give rise to a 
 peculiar soapy sensation of the skin when touched. It should 
 never be allowed to enter the mouth, as even dilute solutions 
 almost instantaneously remove the lining of tender skin. 
 Should such an accident happen, the mouth should at once 
 be rinsed several times with water and then with very dilute 
 acetic acid. Pure caustic potash serves as an addition to zinc 
 baths, gold baths, etc. For the purpose of freeing objects from 
 grease the more impure commercial article is used. 
 
 11. Sodium hydrate {caustic soda). — It also occurs in com- 
 merce in various degrees of purity, either in sticks or lumps. 
 It is of a highly caustic character, resembling potassium hydrate 
 (see above) in properties and effects. It is employed for free- 
 ing objects from grease, for the preparation of alkaline tin and 
 zinc baths, etc. 
 
 12. Ammonium hydrate {ammonia or spirits of hartshorn). — 
 It is simply water saturated with ammonia gas. By' exposure 
 ammonia gas is gradually evolved, so that it must be kept in 
 closely-stoppered bottles, in order to preserve the strength of 
 the solution unimpaired. Four qualities are generally: found 
 in commerce, viz., ammonia of 0.910 specific gravity (contain- 
 ing 24.2 per cent, of ammonia gas); of 0.920 specific gravity 
 
646 ELECTRO-DEPOSITION OF METALS. 
 
 (with 21.2 per cent, of ammonia gas) ; of 0.940 specific gravity 
 with 15.2 per cent, of ammonia gas); and 0.960 specific grav- 
 ity (with 9.75 per cent, of ammonia gas). It is employed for 
 neutralizing nickel and cobalt baths when too acid, in the pre- 
 paration of fulminating gold, and as an addition to some cop- 
 per and brass baths. 
 
 Recognition. — By the odor. 
 
 13. Calcium hydrate {burnt or quick lime). — It forms hard, 
 white to gray pieces, which on moistening with water crumble 
 to a light white powder, evolving thereby much heat. Vienna 
 lime is burnt lime containing magnesia. Lime serves for free- 
 ing objects from grease, and for this purpose is made into a 
 thinly-fluid paste with chalk and water with which the objects 
 to be freed from grease are brushed. Vienna lime is much used 
 as a polishing agent. 
 
 III. Sulphur Combinations. 
 
 14. Sulphuretted hydrogen (sulphydric acid, hydrosulphuric 
 acid). — A very poisonous, colorless gas with a fetid smell re- 
 sembling that of rotten eggs. Ignited in the air, it burns with 
 a blue flame, sulphurous acid and water being formed. At the 
 ordinary temperature water absorbs about three times its own 
 volume of the gas, and then acquires the same properties as the 
 gas itself. Sulphuretted hydrogen serves for the metallizing of 
 moulds as described in the preceding chapter, where the manner 
 of generating it is also given. It is sometimes employed for the 
 production of " oxidized " silver. Care should be taken not to 
 bring metallic salts, gilt or silvered articles, or pure gold and 
 silver in contact with sulphuretted hydrogen, they being rapidly 
 sulphurized by it. 
 
 Recognition. — By its penetrating smell; further, by a strip of 
 paper moistened with sugar of lead solution becoming black 
 when brought into a solution of sulphuretted hydrogen or an 
 atmosphere containing it. 
 
 15. Potassium sulphide (liver 0/ sulphur). — It forms a hard 
 green-yellow to pale-brown mass, with conchoidal fracture. It 
 
CHEMICALS USED IN ELECTRO-PLATING. 647 
 
 readily absorbs moisture, whereby it deliquesces and smells of 
 sulphuretted hydrogen. It is employed for coloring copper 
 and silver black. 
 
 Recognition. — On pouring an acid over liver of sulphur, sul- 
 phuretted hydrogen is evolved with effervescence, sulphur being 
 at the same time separated. 
 
 16. A mmonium sulphide ( sulphydrate or hydrosulphate of am- 
 monia}. — When freshly prepared it forms a clear and colorless 
 fluid, with an odor of ammonia and sulphuretted hydrogen; by 
 •standing it becomes yellow, and, later on, precipitates sulphur. 
 It is used for the same purpose as liver of sulphur. 
 
 17. Carbon disnlphide or bisulphide. — Pure carbon disulphide 
 is a colorless and transparent liquid which is very dense, and 
 exhibits the property of double refraction. Its smell is charac- 
 teristic and most disgusting, and may be compared to that of 
 rotten turnips. It burns with a blue flame of sulphurous acid, 
 •carbonic acid being at the same time produced. It is used as 
 a solvent for phosphorus and rubber in metallizing moulds 
 according to Parkes' method. This solution should be very 
 carefully handled. 
 
 18. Antimony sulphide. — a. Black sulpJiide of antimony {sti- 
 bium sulfuratum nigrum} is found in commerce in heavy, gray 
 and lusterless pieces or as a fine black-gray powder, with slight 
 luster. It serves for the preparation of antimony baths, and 
 for coloring copper alloys black. 
 
 b. Red sulphide of antimony (stibium sulfuratum aurantia- 
 ciun) forms a delicate orange-red powder without taste or odor; 
 it is insoluble in water, but soluble in ammonium sulphide, 
 spirits of hartshorn and alkaline lyes. In connection with am- 
 monium sulphide or ammonia it serves for coloring brass 
 brown. 
 
 19. Arsenic trisulphide or arsenious sulphide (orpiment). — It 
 is found in commerce in the natural, as well as artificial, state, 
 the former occurring mostly in kidney-shaped masses of a lemon 
 color, and the latter in more orange-red masses, or as a dull 
 yellow powder. Specific gravity 3.46. It is soluble in the 
 alkalies and spirits of sal ammoniac. 
 
648 ELECTRO-DEPOSITION OF METALS. 
 
 20. Ferric sulphide. — Hard, black masses generally in flat 
 plates, which are only used for the generation of sulphuretted 
 hydrogen. 
 
 IV. Chlorine Combinations. 
 
 21. Sodium chloride {common salt, rock salt). — The pure salt 
 should form white, cubical crystals, of which 100 parts of cold 
 water dissolve 36, hot water dissolving slightly more. The 
 specific gravity of sodium chloride is 2.2. In electroplating 
 sodium chloride is employed as a conducting salt for some gold 
 baths, as a constituent of argentiferous pastes, and for precipi- 
 tating the silver as chloride from argentiferous solutions. 
 
 Recognition. — An aqueous solution of sodium chloride on 
 being mixed with a few drops of lunar-caustic solution, yields a 
 white caseous precipitate, which becomes black by exposure to 
 light, and does not disappear by the addition of nitric acid, but 
 is dissolved by ammonia in excess. 
 
 22. Ammonium chloride (sal ammoniac). — A white substance 
 found in commerce in the shape of tough fibrous crystals. It 
 has a sharp saline taste, and is soluble in 2^ parts of cold, and 
 in a much smaller quantity of hot water. By heat it is sub- 
 limed without decomposition. It serves for soldering and tin- 
 ning, and as a conducting salt for many baths. 
 
 Recognition. — By sublimation on heating. By adding to a 
 saturated solution of the salt a few drops of solution of platinum 
 chloride, a yellow precipitate of platoso-ammonium chloride is 
 formed. 
 
 23. Antimony tricliloride (butter of antimony). — A crystalline 
 mass which readily deliquesces in the air. Its solution in hydro- 
 chloric acid yields the liquor stibii chlorati, also called liquid 
 butter of antimony. It has a yellowish color, and on mixing 
 with water yields an abundant white precipitate, soluble in pot- 
 ash lye. The solution serves for coloring brass steel-gray, and 
 for browning gun barrels. 
 
 24. Arsenious chloride. — A thick, oily fluid, which evaporates 
 in the air with the emission of white vapors. 
 
CHEMICALS USED IN ELECTRO-PLATING. 649 
 
 25.. Copper chloride. — Blue-green crystals readily soluble in 
 water. The concentrated solution is green, and the dilute solu- 
 tion blue. On evaporating to dryness, brown-yellow copper 
 chloride is formed. It is employed in copper and brass baths 
 as well as for patinizing. 
 
 26. Tin chloride. — a. Stannous chloride or tin salt. A white 
 crystalline salt readily soluble in water, but its solution on ex- 
 posure to the air becomes turbid ; by adding, however, hydro- 
 chloric acid, it again becomes clear. On fusing the crystallized 
 salt loses its water of crystallization, and forms a solid non- 
 transparent mass of a pale yellow color — the fused tin salt. 
 The crystallized, as well as the fused, salt serves for the prepa- 
 ration of brass, bronze and tin baths. 
 
 Recognition. — By pouring hydrochloric acid over a small 
 quantity of tin salt and adding potassium chromate solution, 
 the solution acquires a green color. By mixing dilute tin salt 
 solution with some chlorine water and adding a few drops of 
 gold chloride solution, purple of Cassius is precipitated ; very 
 dilute solutions acquire a purple color. 
 
 b. Stannic chloride occurs in commerce in colorless crystals. 
 In the anhydrous state it forms a yellowish, strongly fuming 
 caustic liquid known as the " fuming liquor of Libadius." 
 
 27. Zinc chloride {hydrochlorate or muriate of zinc ; butter of 
 zinc). — A white crystalline or fused mass which is very soluble 
 and deliquescent. The salt prepared by evaporation generally 
 contains some zinc oxychloride, and hence does not yield an 
 entirely clear solution. It serves for preparing brass and zinc 
 baths, and its solution in nickeling by immersion, soldering, etc. 
 
 Recognition. — Solution of caustic potash separates a volumi- 
 nous precipitate of zinc oxyhydrate, which redissolves in an 
 excess of the caustic potash solution. By conducting sul- 
 phuretted hydrogen into a solution of a zinc salt acidulated 
 with acetic acid, a precipitate of white zinc sulphide is formed. 
 
 28. Chloride of zinc and ammonia. — This salt is a combina- 
 tion of zinc chloride and ammonium chloride, and forms very 
 deliquescent crystals. Its solution in water serves for soldering, 
 and zincking by contact. 
 
650 ELECTRO-DEPOSITION OF METALS. 
 
 29. Nickel chloride. — It is found in commerce in the shape 
 of deep green crystals and of a pale green powder. The latter 
 contains considerably less water and less free acid than the 
 crystallized article, and is to be preferred for electro-plating 
 purposes. The crystallized salt dissolves readily in water, and 
 the powder somewhat more slowly. Should the solution of the 
 latter deposit a yellow precipitate, consisting of basic nickel 
 chloride, it has to be brought into solution by the addition of 
 a small quantity of hydrochloric acid. Nickel chloride is em- 
 ployed for nickel baths. 
 
 Recognition. — By mixing the green solution of the salt with 
 some spirits of sal ammoniac, a precipitate is formed, which 
 dissolves in an excess of spirits of sal ammoniac, the solution 
 showing a deep blue color. 
 
 30. Cobaltous chloride. — It forms small rose-colored crystals, 
 which, on heating, yield their water of crystallization, and are 
 converted into a blue mass. The crystals are readily soluble 
 in water, while the anhydrous blue powder dissolves slowly. 
 Cobalt chloride is employed for the preparation of cobalt baths. 
 
 Recognition. — Caustic potash precipitates from a solution of 
 cobalt chloride a blue basic salt which is gradually converted 
 into a rose-colored hydrate, and, with the access of air, into 
 green-brown cobaltous hydrate. The aqueous solution yields 
 with solution of yellow prussiate of potash, a pale gray-green 
 precipitate. 
 
 3 1 . Silver chloride. — A heavy white powder which by ex- 
 posure to light becomes gradually blue-gray, then violet, and 
 finally black. When precipitated from silver solutions,, a case- 
 ous precipitate is separated. At 500 F. it fuses, without being 
 decomposed, to a yellowish fluid which, on cooling, congeals 
 to a transparent, tenacious, horn-like mass. Silver chloride is 
 practically insoluble in water, but dissolves with ease in liquid 
 ammonia and in potassium cyanide solution. It is employed 
 in the preparation of baths for silver-plating, for silvering by 
 boiling, and in the pastes for silvering by friction. 
 
 Recognition. — By its solubility in ammonia, pulverulent 
 
CHEMICALS USED IN ELECTRO-PLATING. 65 I 
 
 metallic silver being separated from the solution by dipping in 
 it bright ribands of copper. 
 
 32. Gold chloride ( terchloride of gold, muriate of gold, auric 
 chloride}. — This salt occurs in commerce as crystallized gold 
 chloride of an orange-yellow color, and as a brown crystalline 
 mass which is designated as neutral gold chloride, or as gold 
 chloride free from acid, while the crystallized article always 
 contains acid, and, hence, should not be used for gold baths. 
 Gold chloride absorbs atmospheric moisture and becomes re- 
 solved into a liquid of a fine gold color. On being moder- 
 ately heated, yellowish-white aurous chloride is formed, and on 
 being subjected to stronger heat, it is decomposed to metallic 
 gold and chlorine gas. By mixing its aqueous solution with 
 ammonia, a yellow-brown powder consisting of fulminating 
 gold is formed. In a dry state this powder is .highly explosive, 
 and, hence, when precipitating it from gold chloride solution 
 for the preparation of gold baths, it must be used. while still 
 moist. 
 
 Recognition. — By the formation of the precipitate of fulmi- 
 nating gold on mixing the gold chloride solution with ammo- 
 nia. Further, by the precipitation of brown metallic gold 
 powder on mixing the gold chloride solution with green vitriol 
 solution. 
 
 33. Platinic chloride. — The substance usually known by this 
 name is hydroplatinic chloride. It forms red-brown, very soluble 
 - — and in fact deliquescent — crystals. With ammonium chloride 
 it forms platoso-ammonium chloride. Both combinations are 
 used in the preparation of platinum baths. The solution of 
 platinic chloride also serves for coloring silver, tin, brass and 
 other metals. 
 
 Recognition. — By the formation of a precipitate of yellow 
 platoso-ammonium chloride on mixing concentrated platinic 
 chloride solution with a few drops of saturated sal ammoniac 
 solution. 
 
652 ELECTRO-DEPOSITION OF METALS. 
 
 V. Cyanides. 
 
 34. Potassium cyanide (white prussiatc of potash"). — For 
 electro-plating purposes pure potassium cyanide with 98 to 99 
 per cent., as well as that containing 80, 70 and 60 per cent., is 
 used, whilst for pickling the preparation with 45 per cent., is 
 employed. For the preparation of alkaline copper and brass 
 baths, as well as silver baths, the pure 98 to 99 per cent, pro- 
 duct is generally employed. However, for preparing gold 
 baths the 60 per cent, article is mostly preferred, because the 
 potash present in all potassium cyanide varieties with a lower 
 content renders fresh baths more conductive. However, gold 
 baths may also be prepared with 98 per cent, potassium cyanide 
 without fear of injury to the efficiency of the baths, while, under 
 ordinary circumstances, a preparation with less than 98 per 
 cent, may safely be used for the rest of the baths. However, 
 when potassium cyanide has to be added to the baths, as is 
 from time to time necessary, only the pure preparation free 
 from potash should be used, because the potash contained in 
 the inferior qualities gradually thickens the bath too much. 
 
 No product is more important to the electro-plater than 
 potassium cyanide. The pure 98 to 99 per cent, product is a 
 white, transparent, crystalline mass, the crystalline structure 
 being plainly perceptible upon the fracture. In a dry state it 
 is odorless, but when it has absorbed some moisture it has a 
 strong smell of prussic acid. It is readily soluble in water, and 
 should be dissolved in cold water only, since when poured into 
 hot water it is partially decomposed, which is recognized by the 
 appearance of an odor of ammonia. Potassium cyanide solution 
 in cold water may, however, be boiled for a short time without 
 suffering essential decomposition. Potassium cyanide must be 
 kept in well-closed vessels, since when exposed to the air it 
 becomes deliquescent, and is decomposed by the carbonic acid 
 of the air, whereby potassium carbonate is formed while prussic 
 acid escapes. It is a deadly poison and must be used with the 
 utmost caution. 
 
 While pure fused potassium cyanide of 98 to 99 per cent. 
 
CHEMICALS USED IN ELECTRO-PLATING. 653 
 
 could formerly be everywhere obtained in commerce, the pres- 
 ent commercial product consists, as a rule, of a mixture of 
 potassium cyanide and sodium cyanide. The reason for this is 
 that the dried yellow prussiate of potash was formerly fused by 
 itself, whereby one-third of its content of cyanogen was lost, 
 while, for the purpose of fixing this quantity of cyanogen, it is 
 now fused with metallic sodium. The resulting product con- 
 tains 78 per cent, potassium cyanide and 21 per cent, sodium 
 cyanide. 
 
 While for many electro-plating purposes, this mixture may 
 take the place of pure potassium cyanide, its use for some pro- 
 cesses, for instance, in the preparation of more concentrated 
 gold baths, is connected with certain drawbacks. While the 
 double salt — potassium-gold cyanide — dissolves very readily, 
 sodium-gold cyanide is less soluble and separates in the form 
 of a pale-yellow powder. Sodium-copper cyanide shows a simi- 
 lar behavior, it being less soluble than the potassium double 
 salt and as the electro-motive forces for decomposing the potas- 
 sium and sodium double salts vary, the use of a mixture of 
 potassium cyanide and sodium cyanide is, to say the least, not 
 rational. For certain purposes the electro-plater should de- 
 mand from his dealer pure potassium cyanide free from sodium 
 cyanide. 
 
 Potassium cyanide with 80, 70, 60 or 45 per cent, forms a 
 gray-white to white mass with a porcelain-like fracture. A pale 
 gray coloration is not a proof of impurities, being due to some- 
 what too high a temperature in fusing. These varieties are 
 found in commerce in irregular lumps or in sticks, the use of 
 the latter offering no advantage. Their behavior towards the 
 air and in dissolving is the same as that of the pure product. 
 
 Recognition. — By the bitter-almond smell of the solution. 
 By mixing potassium cyanide solution with ferric chloride and 
 then with hydrochloric acid until the latter strongly predomi- 
 nates, a precipitate of Berlin blue is formed. 
 
 The pure salt free from potash does not effervesce on add- 
 ing dilute acid, which is, however, the case with the inferior 
 qualities. 
 
654 
 
 ELECTRO-DEPOSITION OE METALS. 
 
 To facilitate the use of potassium cyanide with a different 
 content than that given in a formula for preparing a bath, the 
 following table is here given: 
 
 Potassium cyanide with 
 
 per cent. 
 
 80 per cent. 
 
 70 per cent. 
 
 60 per cent. 
 
 45 per cent. 
 
 By weight. 
 
 By weight. 
 
 By weight. 
 
 By weight. 
 
 By weight. 
 
 1 part = 
 
 = I.230 parts = 
 
 = 1.4CO parts = 
 
 1.660 parts 
 
 = 2.180 parts. 
 
 0.820 part = 
 
 = I part = 
 
 - 1. 143 parts = 
 
 x -333 P af ts 
 
 = 1.780 parts. 
 
 0.714 part = 
 
 = 0.875 P art - 
 
 = 1 part = 
 
 1.1 70 parts 
 
 = 1.550 parts. 
 
 0.615 part = 
 
 = 0.740 part = 
 
 = 0.857 part = 
 
 1 part 
 
 = 1.450 parts. 
 
 0.460 part = 
 
 = 0.562 part = 
 
 = 0.643 P art = 
 
 0.750 part 
 
 = I part. 
 
 35. Copper cyanide. — There is a cuprous and a cupric cya- 
 nide; that used for electro-plating purposes being a mixture of 
 both. It is a green-brown powder, which should not be en- 
 tirely dried, since in the moist state it dissolves with greater 
 ease in potassium cyanide than the dried product. 
 
 It is chiefly used in the form of a double salt potassium-cop- 
 per cyanide,./, e., a combination of copper cyanide with potas- 
 sium cyanide, in the preparation of copper, brass, tombac, and 
 red gold baths. 
 
 Recognition. — By evaporating a piece of copper cyanide the 
 size of a pea, or its solution, in hydrochloric acid, to dryness in 
 a water-bath, wherein care must be taken not to inhale the 
 vapors, and dissolving the residue in water, a green-blue solu- 
 tion is obtained which acquires a deep blue color by the addi- 
 tion of ammonia in excess. 
 
 36. Zinc cyanide (Jiydrocyanatc of zinc, prnssiate of zinc). — 
 A white powder insoluble in water, but soluble in potassium 
 cyanide, ammonia and the alkaline sulphites. The fresher it 
 is, the more readily it dissolves, the dried product dissolving 
 with difficulty. Its solution in potassium cyanide forms potas- 
 sium-zinc cyanide, which is used for brass baths. 
 
CHEMICALS USED IN ELECTRO- PLATING. 655 
 
 Recognition. — By evaporating zinc cyanide, or its solution, 
 with an excess of hydrochloric acid in the water-bath, zinc 
 chloride remains behind, which is recognized by the same re- 
 action given under zinc chloride. 
 
 $j. Silver cyanide {prussiate or hydrocyanate of silver). — A 
 white powder which slowly becomes black when exposed to 
 light. It is insoluble in water and cold acids, which, however, 
 will dissolve it with the aid of heat. At 750 F. it melts to a 
 dark red fluid, which, on cooling, forms a yellow mass with a 
 granular structure. It is readily dissolved by potassium cya- 
 nide, but is only slightly soluble in ammonia, differing in this 
 respect from silver chloride. It forms a double salt with potas- 
 sium cyanide — potassium-silver cyanide — and as such is em- 
 ployed in the preparation of silver baths. 
 
 38. Potassium ferro-cyanide (yellow prussiate of potash). — 
 It occurs in the shape of yellow semi-translucent crystals with 
 mother-of-pearl luster, which break without noise. Exposed 
 to heat they effloresce, losing their water of crystallization, and 
 crumbling to a yellowish-white powder. For the solution of 1 
 part of the salt, 4 of water of medium temperature are required, 
 the solution exhibiting a pale yellow color. It precipitates 
 nearly all the metallic salts from their solutions, some of the 
 precipitates being soluble in an excess of the precipitating 
 agent. This salt is not poisonous. It serves for the prepara- 
 tion of silver and gold baths ; its employment, however, offer- 
 ing over potassium cyanide no advantages, except the non- 
 poisonous properties be considered as such. 
 
 Recognition. — When the yellow solution is mixed with ferric 
 chloride, a precipitate of Berlin blue is formed ; by blue vitriol 
 solution a brown-red precipitate is obtained. 
 
 VI. Carbonates. 
 
 39. Potassium carbo7iate (potash). — It is found in commerce 
 in gray-white, bluish, yellowish pieces, the colorations being 
 due to admixtures of small quantities of various metallic oxides. 
 When pure it is in the form of a white powder, or in pieces the 
 
656 ELECTRO-DEPOSITION OF METALS. 
 
 size of a pea. The salt, being very deliquescent, has to be kept 
 in well-closed receptacles. It is readily soluble, and if pure, 
 the solution in distilled water should be clear. It serves as an 
 addition to some baths, and in an impure state for freeing ob- 
 jects from grease. 
 
 Recognition. — The solution effervesces on the addition of 
 hydrochloric acid. When neutralized with hydrochloric acid 
 it gives with platinum chloride a heavy yellow precipitate of 
 platinic potassium chloride, provided it be not too dilute. 
 
 40. Acid potassium carbonate or monopotassic carbonate, com- 
 monly called bicarbonate of potash. — Colorless, transparent crys- 
 tals, which at a medium temperature dissolve to a clear solution 
 in 4 parts of water. It is not deliquescent; however, on boil- 
 ing its solution it loses carbonic acid, and contains then only 
 potassium carbonate. It is employed for the preparation of 
 certain baths for gilding by simple immersion. 
 
 41. Sodium carbonate {washing soda). — It occurs in com- 
 merce as crystallized or calcined soda of various degrees of 
 purity. The crystallized product forms colorless crystals or 
 masses of crystals, which, on exposure to air, rapidly effloresce 
 and crumble to a white powder. By heating, the crystals also 
 lose their water, a white powder, the so-called calcined soda, 
 remaining behind. Soda dissolves readily in water, and serves 
 as an addition to copper and brass baths, for the preparation of 
 metallic carbonates, and for freeing objects from grease, the 
 ordinary impure soda being used for the latter purpose. 
 
 The directions for additions of sodium carbonate to baths 
 generally refer to the crystallized salt. If calcined soda is to 
 be used instead, 0.4 part of it will have to be taken for 1 part 
 of the crystallized product. 
 
 42. Sodium bicarbonate (baking powder). — A dull white 
 powder soluble in 10 parts of water of 68° F. On boiling, the 
 solution loses one-half of its carbonic acid, and then contains 
 sodium carbonate only. 
 
 43. Calcium carbonate {marble, chalk). — When pure it forms 
 a snow-white crystalline powder, a yellowish color indicating a 
 
CHEMICALS USED IN ELECTRO-PLATING. 657 
 
 content of iron. It is insoluble in water, but soluble, with 
 effervescence, in hydrochloric, nitric and acetic acids. In 
 nature, calcium carbonate occurs as marble, limestone, chalk. 
 
 In the form of whiting (ground chalk carefully freed from all 
 stony matter) it is used for the removal of an excess of acid in 
 acid copper baths, and mixed with burnt lime, as an agent for 
 freeing objects from grease. 
 
 44. Copper carbonate. — Occurs in nature as malachite and 
 allied minerals. The artificial carbonate is an azure-blue sub- 
 stance, insoluble in water, but soluble, with effervescence, in 
 acids. Copper carbonate precipitated from copper solution by 
 alkaline carbonates has a greenish color. Copper carbonate is 
 employed for copper and brass baths and for the removal of an 
 excess of acid in acid copper baths. 
 
 Recognition. — Dissolves in acids with effervescence ; on dip- 
 ping a riband of bright sheet-iron in the solution, copper sepa- 
 rates upon the iron. On compounding the solution with 
 ammonia in excess, a deep blue coloration is obtained. 
 
 45. Zinc carbonate. — A white powder, insoluble in water. 
 The product obtained by precipitating a zinc salt with alkaline 
 carbonate is a combination of zinc carbonate with zinc oxy- 
 hydrate. It serves for brass baths in connection with potassium 
 cyanide. 
 
 Recognition. — In a solution in hydrochloric acid, which is 
 formed with effervescence, according to the reactions given 
 under zinc chloride (27). 
 
 46. Nickel carbonate. — A pale apple-green powder, insoluble 
 in water, but soluble, with effervescence, in acids. It is em- 
 ployed for neutralizing nickel baths which have become acid. 
 
 Recognition.— -In hydrochloric acid, it dissolves, with effer- 
 vescence, to a green fluid. By the addition of a small quantity 
 of ammonia, nickel oxyhydrate is precipitated, which, by add- 
 ing ammonia in excess, is redissolved, the solution showing a 
 blue color. 
 
 47. Cobaltous carbonate. — A reddish powder, insoluble in 
 water, but soluble in acids, the solution forming a red fluid. 
 
 42 
 
658 ELECTRO-DEPOSITION OF METALS. 
 
 VII. Sulphates and Sulphites. 
 
 48. Sodium sulphate ( Glauber' s salt). — Clear crystals of a 
 slightly bitter taste, which effloresce by exposure to the air. 
 They are readily soluble in water. On heating, the crystals 
 melt in their water of crystallization, and when subjected to a 
 red heat, calcined Glauber's salt remains behind. It is used as 
 an addition to some baths. 
 
 49. Ammonium sulphate. — It forms a neutral, colorless salt,, 
 which is constant in the air, readily dissolves in water, and 
 evaporates on heating. It serves as a conducting salt for 
 nickel, cobalt and zinc baths. 
 
 Recognition. — By its evaporating on heating. A concen- 
 trated solution compounded with platinic chloride gives a yellow 
 precipitate of platoso-ammonium chloride, while a solution 
 mixed with a few drops of hydrochloric acid gives with barium 
 chloride a precipitate of barium sulphate. 
 
 50. Potassium aluminium sulphate (potash-alum). — Colorless 
 crystals or pieces of crystals with an astringent taste. It is 
 soluble in water, 12 parts of it dissolving in 100 parts of water 
 at the ordinary temperature. On heating, the crystals melt, 
 and are converted into a white, spongy mass, the so-called 
 burnt alum. Potash-alum serves for the preparation of zinc 
 baths and for brightening the color of gold. 
 
 Recognition. — On adding sodium phosphate to the solution 
 of this salt a jelly-like precipitate of aluminium phosphate is 
 formed, which is soluble in caustic potash, but insoluble in 
 acetic acid. 
 
 51. Ammonium-alum is exactly analogous to the above, the 
 potassium sulphate being simply replaced by ammonium sul- 
 phate. It is for most purposes interchangeable with potash- 
 alum. On exposing ammonium-alum to a red heat, the ammo- 
 nium sulphate is lost, pure alumina remaining behind. Ammo- 
 nium-alum is used for preparing a bath for zincking iron and 
 steel by immersion. 
 
 Recognition. — The same as potash-alum. On heating the 
 comminuted ammonium-alum with potash-lye, an odor of am- 
 monia becomes perceptible. 
 
CHEMICALS USED IN ELECTRO-PLATING. 659 
 
 52. Ferrous sulphate {sulphate of iron, protosulphaie of iron, 
 copperas, green vitriol). — Pure ferrous sulphate forms bluish- 
 green, transparent crystals of a sweetish astringent taste, which 
 readily dissolve in water, and effloresce and oxidize in the air. 
 The crude article forms green fragments frequently coated with 
 a yellow powder. It generally contains, besides ferrous sul- 
 phate, the sulphate of copper and of zinc, as well as ferric sul- 
 phate. Ferrous sulphate is employed in the preparation of 
 iron baths, and for the reduction of gold from its solutions. 
 
 Recognition. — By compounding the green solution with a few 
 drops of concentrated nitric acid, a black-blue ring is formed 
 on the point of contact. On mixing the lukewarm solution 
 with gold chloride, gold is separated as a brown powder, which 
 by rubbing acquires the luster of gold. 
 
 53. Iron-ammonium sulphate. — Green crystals which are con- 
 stant in the air and do not oxidize as readily as green vitriol. 
 100 parts of water dissolve 16 parts of this salt. It is used for 
 the same purposes as green vitriol. 
 
 54. Copper sulphate 'cupric sulphate, blue vitriol, or blue cop- 
 peras). — It forms large, blue crystals, of which 190 parts of cold 
 water dissolve about forty parts, and the same volume of hot 
 water about 200 parts. Blue vitriol which does not possess a 
 pure blue color but shows a greenish luster, is contaminated 
 with green vitriol, and should not be used for electro-plating 
 purposes. Blue vitriol serves for the preparation of alkaline 
 copper and brass baths, acid copper baths, etc. 
 
 Recognition. — By its appearance, as it can scarcely be mis- 
 taken for anything else. A content of iron is recognized by 
 boiling blue vitriol solution with a small quantity of nitric acid, 
 and adding ammonia in excess; brown flakes indicate iron. 
 
 55. Zinc sulphate {white vitriol). — It forms small colorless 
 prisms of a harsh metallic taste, which readily oxidize on ex- 
 posure to the air. By heating the crystals melt, and by heat- 
 ing to a red heat they are decomposed into sulphurous acid 
 and oxygen, which escape, while zinc oxide remains behind as 
 residue. 100 parts of water dissolve about 50 parts of. zinc 
 
660 ELECTRO-DEPOSITION OF METALS. 
 
 sulphate in the cold, and nearly IOO parts at the boiling-point. 
 Zinc sulphate is employed for the preparation of brass and zinc 
 baths, as well as for matt pickling. 
 
 Recognition. — By mixing zinc sulphate solution with acetic 
 acid and conducting sulphuretted hydrogen into the mixture, a 
 white precipitate of zinc sulphide is formed. A slight content 
 of iron is recognized by the zinc sulphate solution, made alka- 
 line by ammonia, giving with ammonia sulphide a somewhat 
 colored precipitate instead of a pure white one. However, a 
 slight content of iron does no harm. 
 
 56. Nickel sulphate. — Beautiful dark green crystals, readily 
 soluble in water, the solution exhibiting a green color. On 
 heating the crystals to above 536 F., yellow anhydrous nickel 
 sulphate remains behind. Like the double salt described be- 
 low, it serves for the preparation of nickel baths and for coloring 
 zinc. 
 
 Recognition. — By compounding the solution with ammonia 
 the green color passes into blue. Potassium carbonate pre- 
 cipitates pale green basic nickel carbonate, which dissolves on 
 adding ammonia in excess, the solution showing a blue color. 
 A content of copper is recognized by the separation of black- 
 brown copper sulphide on introducing sulphuretted hydrogen 
 into a heated solution previously strongly acidulated with 
 hydrochloric acid. 
 
 57. Nickel-ammonium sulphate. — It forms green crystals of a 
 somewhat paler color than nickel sulphate. This salt dissolves 
 with more difficulty than the preceding, 100 parts of water dis- 
 solving only 5.5 parts of it. It is used for the same purposes as 
 the nickel sulphate, and is also recognized in the same manner. 
 The following reaction serves for distinguishing it from nickel 
 sulphate : By heating nickel sulphate in concentrated solution 
 with the same volume of strong potash or soda lye, no odor 
 of ammonia is perceptible, while nickel ammonium sulphate 
 evolves ammoniacal gas which forms dense clouds on a glass 
 rod moistened with hydrochloric acid. 
 
 58. Cobaltous sulphate. — Crimson crystals of a sharp metallic 
 
CHEMICALS USED IN ELECTRO- PLATING. 66 1 
 
 taste. They are constant in the air and readily dissolve in 
 water, the solution showing a red color. By heating the crys- 
 tals lose their water of crystallization without, however, melting, 
 and become thereby .transparent and rose-colored. The salt is 
 used for cobalt baths for the electro- deposition of cobalt and 
 for cobalting by contact. 
 
 Recognition. — In the presence of ammoniacal salts, caustic 
 potash precipitates a blue basic salt, which on heating changes 
 to a rose-colored hydrate and, by standing for some time in 
 the air, to a green-brown hydrate. By mixing a concentrated 
 solution of the salt strongly acidulated with hydrochloric acid, 
 with solution of potassium nitrate, a reddish-yellow precipitate 
 is formed. 
 
 59. Cob alt- ammonium sulphate. — This salt forms crystals of 
 the same color as cobalt sulphate, which, however, dissolve 
 more readily in water. 
 
 60. Sodium sulphite and bisulphite. — a. Sodium sulphite. 
 Clear, colorless, and odorless crystals, which are rapidly trans- 
 formed into an amorphous powder by efflorescence. The salt 
 readily dissolves in water, the solution showing a slight alkaline 
 reaction due to a small content of sodium carbonate. It is em- 
 ployed in the preparation of gold, brass, and copper baths, for 
 silvering by immersion, etc. 
 
 Recognition. — The solution when mixed with dilute sulphuric 
 acid has an odor of burning sulphur. 
 
 b. Sodium bisulphite. — Small crystals, or more frequently in 
 the shape of a pale yellow powder with a strong odor of sul- 
 phurous acid and readily soluble in water. The solution shows 
 a strong acid reaction and loses sulphurous acid in the air. It 
 is employed in the preparation of alkaline copper and brass 
 baths. 
 
 Both the sulphite and bisulphite must be kept in well-closed 
 receptacles, as by the absorption of atmospheric oxygen they 
 are converted to sulphate. 
 
 61. Cuprous sulphite. — A brownish-red crystalline powder 
 formed by treating cuprous hydrate with sulphurous acid solu- 
 
662 ELECTRO-DEPOSITION OF METALS. 
 
 tion. It is insoluble in water, but readily soluble in potassium 
 cyanide, with only slight .evolution of cyanogen. It serves for 
 the preparation of alkaline copper baths in place of basic 
 acetate of copper (verdigris), blue vitriol, or cuprous oxide. 
 
 VIII. Nitrates. 
 
 62. Potassium nitrate {saltpetre, nitre). — It forms large, pris- 
 matic crystals, generally hollow, but also occurs in commerce 
 in the form of a coarse powder, soluble in 4 parts of water at a 
 medium temperature. The solution has a bitter, saline taste 
 and shows a neutral reaction. Potassium nitrate melts at a red 
 heat, and on cooling congeals to an opaque, crystalline mass. 
 It is employed in the preparation of desilvering pickle and for 
 producing a matt luster upon gold and gilding. For these 
 purposes it may, however, be replaced by the cheaper sodium 
 nitrate, sometimes called cubic nitre or Chile saltpetre. 
 
 Recognition. — A small piece of coal when thrown upon melt- 
 ing saltpetre burns fiercely. When a not too dilute solution of 
 saltpetre is compounded with solution of potassium bitartrate 
 saturated at the ordinary temperature, a crystalline precipitate 
 of tartar is formed. 
 
 63. Sodium nitrate (cubic nitre or Chile saltpetre). — Color- 
 less crystals, deliquescent and very soluble in water; the solu- 
 tion shows a neutral reaction. It is used for the same purposes 
 as potassium nitrate. 
 
 64. Metcurous nitrate. — It forms small, colorless crystals, 
 which are quite transparent and slightly effloresce in the air. 
 On heating, they melt and are transformed, with the evolution 
 of yellow-red vapors, into yellow-red mercuric oxide, which, 
 on further heating, entirely evaporates. With a small quantity 
 of water, mercurous nitrate yields a clear solution. By the 
 further addition of water it shows a milky turbidity, which, 
 however, disappears on adding nitric acid. It is employed for 
 quicking the zincs of the cells, and the objects previous to 
 silvering, and for brightening (with subsequent heating) gilding. 
 For the same purpose is also used : . , , 
 
CHEMICALS USED IN ELECTRO-PLATING. 663 
 
 65. Mercuric nitrate {nitrate of mercury). — This salt is ob- 
 tained with difficulty in a crystallized form. It is generally 
 sold in the form of an oily, colorless liquid which, in contact 
 with water, separates a basic salt. This precipitate disappears 
 upon the addition of a few drops of nitric acid, and the liquid 
 becomes clear. 
 
 Recognition. — A bright riband of copper dipped in solution 
 of mercurous or mercuric nitrate becomes coated with a white 
 amalgam, which disappears upon heating. 
 
 66. Silver nitrate {lunar caustic). — This salt is found in com- 
 merce in three forms : Either as crystallized nitrate of silver 
 in thin, rhombic, and transparent plates ; or in amorphous, 
 opaque, and white plates of fused nitrate ; or in small cylinders 
 of a white, or gray, or black color, according to the nature of 
 the mould employed, in which form it constitutes the lunar 
 caustic for surgical uses. For our purposes only the pure, 
 crystallized product, free from acid, should be employed. The 
 crystals dissolve readily in water. In making solutions of this 
 and other silver salts, only distilled water should be used ; all 
 other waters, owing to the presence of chlorine, produce a 
 cloudiness or even a distinct precipitate of silver chloride. 
 When subjected to heat the crystals melt to a colorless, oily 
 fluid, which, on cooling, congeals to a crystalline mass. Silver 
 nitrate is employed in the preparation of chloride and cyanide 
 of silver for silver baths. The solution in potassium cyanide 
 may also be used for silver baths. The alcoholic solution is 
 employed for metallizing non-conductive moulds for galvan- 
 oplastic deposits. 
 
 Recognition. — Hydrochloric acid and common salt solution 
 precipitate from silver nitrate solution silver chloride, which 
 becomes black on exposure to the light, and is soluble in am- 
 monia. 
 
 IX. Phosphates and Pyrophosphates. 
 
 67. Sodium phosphate. — Large, clear crystals, which readily 
 effloresce, and whose solution in water shows an alkaline reac- 
 
664 ELECTRO-DEPOSITION OF METALS. 
 
 tion. It is employed in the preparation of gold baths and for 
 the production of metallic phosphates for soldering. 
 
 Recognition. — The dilute solution compounded with silver 
 nitrate yields a yellow precipitate of silver phosphate. 
 
 68. Sodium pyrophosphate. — It forms white crystals, which 
 are not subject to efflorescence, and are soluble in 6 parts of 
 water at a medium temperature; the solution shows an alkaline 
 reaction. Sodium pyrophosphate also occurs in commerce in 
 the form of an anhydrous white powder, though it may here be 
 said that the directions for preparing baths refer to the crystal- 
 lized salt. It is employed in the preparation of gold, nickel, 
 bronze, and tin baths. 
 
 Recognition. — The dilute solution compounded with silver 
 nitrate yields a white instead of a yellow precipitate. . 
 
 69. Ammonium phosphate. — A colorless crystalline powder 
 quite readily soluble in water; the solution should be as neutral 
 as possible. A salt smelling of ammonia, as well as one show- 
 ing an acid reaction, should be rejected. It is employed in the 
 preparation of platinum baths. 
 
 X. Salts of Organic Acids. 
 
 70. Potassium bitartrate {cream of tartar). — The pure salt 
 forms small transparent crystals, which have an acid taste, and 
 are slightly soluble in water. The commercial crude tartar or 
 argol, which is a by-product in the wine-industry, forms gray 
 or dirty-red crystalline crusts. In a finely powdered state, puri- 
 fied tartar is called cream of tartar. It is employed for the 
 preparation of the whitening silver baths, for those of tin, and 
 for the silvering paste for silvering by friction, and in scratch- 
 brushing different deposits. 
 
 71. Potassium- sodium tartrate (Rochelle or Seignette salt). — 
 Clear colorless crystals, constant in the air, of a cooling, bitter, 
 saline taste, and soluble! in 2.5 parts of water of a medium tem- 
 perature. The solution shows a neutral reaction. This salt is 
 employed in the preparation of copper baths free from cyanide, 
 as well as of nickel and cobalt baths, which are to be decom- 
 posed in the single cell apparatus. 
 
CHEMICALS USED IN ELECTRO- PLATING. 665 
 
 Recognition. — By the addition of acetic acid the solution 
 yields an abundant precipitate of tartar. 
 
 72. Antimony-potassium tartrate {tartar emetic). — A white 
 crystalline substance, of which 100 parts of cold water dissolve 
 5 parts, while a like volume of hot water dissolves 50 parts. 
 The solution shows a slightly acid reaction. The only use of 
 this salt is for the preparation of antimony baths. 
 
 Recognition. — The solution of the salt compounded with sul- 
 phuric, nitric, or oxalic acid yields a white precipitate, insoluble 
 in an excess of the cold acid. Sulphurretted hydrogen imparts 
 to the dilute solution a red color. Hydrochloric acid effects a 
 precipitate, which is redissolved by the acid in excess. 
 
 73. Copper acetate {verdigris). — It is found in the market in 
 the form of dark green crystals showing an acid reaction, or as 
 a neutral bright green powder. 
 
 The crystallized copper acetate forms opaque dark green 
 prisms, which readily effloresce, becoming thereby coated with a 
 pale green powder. They dissolve with difficulty in water, but 
 readily in ammonia, forming a solution of a blue color. They 
 dissolve readily also in potassium cyanide and alkaline sulphites. 
 
 The neutral copper acetate forms a blue-green crystalline 
 powder, imperfectly soluble in water, but readily soluble in 
 ammonia, forming a solution of a blue color. 
 
 Copper acetate is used for preparing copperand brass baths, 
 for the production of artificial patinas, for coloring, gilding, etc. 
 
 Recognition. — On pouring sulphuric acid over copper acetate, 
 a strong odor of acetic acid is noticed ; with ammonia it yields 
 a blue solution. 
 
 74. Lead acetate {sugar of lead). — Colorless lustrous prisms 
 or needles of a nauseous sweet taste, and poisonous. The crys- 
 tals effloresce in the air, melt at 104 F., and are readily soluble 
 in water, yielding a slightly turbid solution. Lead acetate is 
 employed for preparing lead baths (Nobili's rings) and for 
 coloring copper and brass. 
 
 Recognition. — By compounding lead acetate solution with 
 potassium chromate solution, a heavy yellow precipitate of 
 lead chromate is formed. 
 
666 ELECTRO-DEPOSITION OF METALS. 
 
 75. Sodium citrate. — Colorless crystals, presenting a moist 
 appearance, which are readily soluble in water; the solution 
 should show a neutral reaction. This salt is employed in the 
 preparation of the platinum bath according to Bottger's for- 
 mula, and as conducting salt for nickel and zinc baths. 
 
APPENDIX. 
 
 Contents of Vessels. 
 
 To find the number of gallons a tank or other vessel will 
 hold, divide the number of cubic inches it contains by 231. 
 
 If rectangular, multiply together the length, breadth and 
 depth. 
 
 If cylindrical, multiply the square of the diameter by 0.7854, 
 and the product by the depth. 
 
 If conical, add together squares of diameters of top and 
 bottom, and the product of the two diameters. Multiply their 
 sum by 0.7854, and the resulting product by the depth. 
 Divide the product by 3. 
 
 If hemispherical, to three times the square of the radius at 
 top add the square of the depth. Multiply this sum by the 
 depth and the product by 0.5236. 
 
 A voirdupois Weight. 
 
 
 ■=■■ Ounces. 
 
 = Drams. 
 
 = Grains. 
 
 . = Grams. 
 
 
 16 
 1 
 0.062 
 
 256 
 
 16 
 
 1 
 
 7,000 
 437-5 
 27-34 
 
 453-25 
 
 28.33 
 
 1.77 
 
 Troy Weight. 
 
 
 = Ounces. 
 
 = Dwt. 
 
 = Grains. 
 
 — Grams. 
 
 1 Pennyweight . . 
 
 12 
 1 
 
 0.05 
 
 240 
 
 20 
 
 1 
 
 5,760 
 
 480 
 
 24 
 
 372.96 
 31.08 
 
 *-55 
 
 (667) 
 
668 
 
 ELECTRO-DEPOSITION OF METALS. 
 Imperial Fluid Measure. 
 
 
 D 
 
 o 
 II 
 
 c 
 
 E 
 
 II 
 
 •!« 
 
 3 3 
 
 II 
 
 •0 s 
 
 2. 2 
 E« 
 II 
 
 I 
 'c 
 
 % 
 
 II 
 
 c ■ 
 
 _M.S 
 ^ ■" 
 II 
 
 ■S-g 
 
 II 
 
 4J 
 
 E 
 II 
 
 V 
 
 ■M.i 
 
 us 
 
 11 u 
 
 
 4 
 
 i 
 
 °-5 
 0.025 
 0.0031 
 0.00005 
 
 8 
 
 2 
 
 1 
 
 0.05 
 
 0.0062 
 
 O.OOOI 
 
 160 
 40 
 20 
 
 I 
 
 O.I25 
 
 1280 
 
 320 
 
 160 
 
 8 
 
 1 
 
 0.0167 
 
 76,800 
 
 19,200 
 
 9,600 
 
 480 
 
 60 
 
 1 
 
 70,000 
 17,500 
 8,750 
 
 437-5 
 54-7 
 0.91 
 
 277.276 
 
 69.310 
 
 34-059 
 
 J-733 
 
 0.217 
 
 0.0036 
 
 4-541 
 
 I-I35 
 0.567 
 0.0284 
 0.0035 
 
 4.541 
 1,1352 
 576.6 
 283.8 
 
 35-5 
 o-59 
 
 i Pint 
 
 i Fluid Ounce.. . 
 i Fluid Dram... . 
 
 
 
 
 Table of Useful Numerical Data. 
 
 1 millimeter equals -03937 inches. 
 
 1 centimeter " -3937° " 
 
 1 decimeter " 3-937°° " 
 
 1 meter " 39.37000 " 
 
 1 cubic centimeter of -> 
 
 water equals ) ° 
 
 1 liter " 1000 " 
 
 1 liter 
 
 I 35-27 5l° uncesby 
 
 1 xjj 1 j 1 measure. 
 
 I gallon (or 160 fluid") ( - 
 
 liters. 
 
 ounces) equals 
 I gallon " 277.276 cubic ins. 
 
 1 pint (or 20 fluid \ 9 „ 
 
 ounces) equals I 
 1 fluid ounce " 1.733 " 
 
 I liter " 61.024 " 
 
 1 avoirdupois pounds) 
 
 equals. J 
 
 7000. 
 
 grains. 
 
 I troy pound equals 
 I avoirdupois ounce "i 
 
 equals J 
 
 I troy ounce equals 
 1 avoirdupois drm. "I 
 
 equals i 
 
 1 troy pennyweight "I 
 
 equals J 
 
 1 gram equals 
 I kilogram equals 
 I liter of water equals 
 1 cubic inch of water ) 
 
 equals i 
 
 1 cubic centimeter of \ 
 
 water equals / 
 I kilogram equals 
 
 5760. 
 437-5 
 480. 
 27-34 
 
 24. 
 
 15-43 
 15432. 
 15432. 
 
 252.5 
 
 grains. 
 
 1 . gram. 
 
 35.274 avoir- 
 dupois ozs. 
 
USEFUL TABLES. 
 
 669 
 
 *> (A u) 
 
 o u 
 
 CN mvo COAO Ov mvo 0"> 
 tN. -rtOO ONM lOO **O0 
 
 Mnoy3 h nwoo moo 
 d h en ^-vo" r>. <> d « co 
 
 mvo Ov CN vO Ov 
 -■l-OO W ts - 
 in 6 vO m 
 m m -«*-vo tN. o. o 
 
 t*- o cn "<*-vo o>h ror-%0 ■*}- t-» h -*oo h m o ■**- ( 
 
 " " O CN +NO^h -*J-vO CO H CflNQ ( 
 
 00 mvo ct>«vO 00 in cn ■**-(*>.< 
 
 00 rood "*t-oo" n r-s w in o -<too mvo ( 
 
 — O vo m tN. « 00 moo *<j-co cn 1 
 
 m ^vo t>>oo cn m in O vo ► 
 
 f K3P 
 
 '— v £ 
 O O 
 
 mvo en Ovvo cn omonoo in 
 OOHHWcncn-^io invo 
 OOOOOOOOOOO 
 
 ■ Ov -^OO moO vO ■**" tN O CO vO "<*- <N o 00 O 0. ov 
 
 (00 ■■+■ O ■* ov -^-oo moo 
 
 vO ^ CM Ov Ov 
 
 1 00 -<*• ov H" o> < 
 
 S S'S' 
 
 "Q cu -^ « 
 
 3^ rt £3 
 
 rj u 3 c 
 
 c 
 
 '\riH r^movinw t-^m o>co t*-vo in 
 vo" m owo" cn O'VO cn d'l^H smuo^ 
 •«*• ov moo m t-^ in t>. m vo m c>vo cn in 
 i mvo fONO •**- i>. m -^-o^ moo rovo 
 m h h cn cn cn en mvo o m t>. -^ 
 
 • t>. o mvo ovoo t^. in ■»*- 1 
 
 O o t-^vo ^- m w o 00 vO 
 
 OOOOOOOOOO 
 
 moo h «*- r- o mvo 00 iv,vo in if ( 
 
 M CN CN CN CN 
 
 «o 
 
 0) -"S-^O CO « "fl-vO C 
 
 OOOOO 
 
 ■ invo t^«co O Ov Ov OOO l>. 
 
 OOOOO 
 
 •^vo OOOOOOOOOOOih 
 
 O ■£ 
 
 
 moo -«*-oo conh'O o -*f o mvo 
 
 msn nh\o cn r-* m c 
 1 tN. Tt- t^. m ■* ov moo ' 
 
 ?-co m l~>. w vo -<t- o mvo flN." 
 
 ■ ^t- ov moo 
 
 1 "*■ •**- o^ moo 
 
 j 00 moo -**-co 
 
 100 -«i-h nmom^h cn 
 
 OOOOOOOOOOO 
 
 ■*t- mvo cn 00 -*■ O v 
 
 1 m -* ■* invo 
 
 h h cn cn cn m mvo < 
 i «f mvo r^oo 00 C 
 ■**-Ovo cnoo -^-m cn 
 e» m m ^ ■**■ »nvo* cn < 
 
 
 p«2 
 
 
 N rt-00 « 
 
 IT) o> t^vO ^" CO H O O t^^O N 
 
 tv CO OOO OO (^vO 
 
 »mHOD ^- ■ 
 
 •VO CO O. w 
 
 rt i! 
 
 U ~ IA 
 
 cc.S « " 
 
 OQg. 
 
 OS Q 
 
 >ooogooooo 
 -loq^pqinqinoin 
 
 ) in h vo* cn* i>- mod ^ Ov 
 
 q q q q q q o q o q m h « mvo 
 
 in O* in o" in o" m O* in o" o' d 0* 6 
 
 in m vo cn (^ mco ^-CMnO mo mo 
 
 m m -^-vO t^ovo « mmiHvo cn r>.m 
 
 m m m h m -<$-vo r-- m 
 
 mvo m o<vo 
 
 i 00 ^ o moo m tN. cn vo m 
 
 OOOOOOOOOOO 
 
 ) m vo m vo h m ■wo t^. ' 
 it^Hvoomomomt 
 
 i 00 m m 00 Th Ov moo cn 1 
 
 m m cn m^o 
 
 u o <u 
 
 >J3 > 
 
 Of Milli- 
 meters 
 equals 
 
 Inches. 
 
 
 
 
 
 
 
 
 
 CN vO 
 
 
 
 
 
 
 
 ■^t-oo m m 000 t^ c^vo mm^^i^H mocNvo mNtHW inw 
 cn cn mmmt->tH moNmt>.H m o-oo 00 r^vo vo m m ^*- m t-^. m •^■00 r^ 
 OOOOO OHHMCN cNmmmt-^Mmomt^iHin o>co 00 t>.vo m 
 
 
 
 
 
 
 M 11 
 
 m cn cn mmmi-^M 1000 
 
 Of Inches 
 equals 
 Milli- 
 meters. 
 
 CN 
 
 10 
 
 H 
 
 VO « 
 
 r* 
 
 « 00 m Tt-co cn vo 
 
 O "^-00 CN VO O 
 
 O O Ov Ov OOO CO NNvh 
 
 
 
 l^ 
 
 M 
 
 mt^.o cn movo m 
 
 H M CI N M IONO 
 
 MN ts mOO ^-CO CN VO 
 
 cn mt^o cn movo h 
 
 HHwCNCNCNmtN.0 
 
 nin n moo m (■** h in ov 
 cn mt^.0 cn movo h\o m 
 HMMCNCNCNinr-ocNin 
 
 H M CN 
 
 cn m rj- mvo t^oo o> 
 
 cn m rf mvo tN.00 0*00000000000 
 h s mt mvo t^.00 000 
 
670 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 From the above table any ordinary conversions up to 2000 units may be readily 
 made. For example : It is required to find the number of cubic centimeters equal 
 to 1728 cubic inches. 
 
 1728 = 1000 -f- 700 + 20 -f 8 cubic inches. 
 But a reference to the sixth column shows that 
 
 1000 cubic inches = 16,385.92 cubic centimeters. 
 700 " = 11,470.10 " " 
 
 20 " = 327.72 " " 
 
 8 " = 131.09 " " 
 
 Add together, and 1728 " 
 
 = 28,314.83 
 
 Table of Solubilities of Chemical Compounds Commonly Used in 
 Electro- Technics. 
 
 Names. 
 
 Acid potassium carbonate (bicarbonate of 
 potash) 
 
 Aluminium chloride 
 
 Aluminium sulphate (calculated to anhydrous 
 salt) 
 
 Ammonium alum 
 
 Ammonium chloride 
 
 Ammonium sulphate 
 
 Antimony potassium tartrate (tartar emetic) . 
 
 Arsenious acid 
 
 Boric acid 
 
 Cadmium chloride, crystallized 
 
 Cadmium sulphate 
 
 Chromic acid • 
 
 Citric acid 
 
 Cobalt ammonium sulphate (calculated to an- 
 hydrous salt) 
 
 Cobalt sulphate (calculated to anhydrous salt") 
 
 Copper acetate (verdigris) neutral 
 
 Copper chloride 
 
 Copper sulphate (blue vitriol) crystallized.... 
 
 Ferrous sulphate (green vitriol, copperas) 
 
 Gold chloride 
 
 Gold cyanide 
 
 Lead acetate (sugar of lead) 
 
 Lead nitrate 
 
 Magnesium sulphate (Epsom salt) 
 
 Mercuric chloride (corrosive sublimate) 
 
 Mercuric nitrate 
 
 Mercuric sulphate 
 
 Soluble in 100 parts by weight of 
 water at 
 
 50 F. 
 
 212° F. 
 
 Parts by weight. 
 
 Parts by weight 
 
 23 
 
 45 at 158 F. 
 
 400 
 
 very soluble. 
 
 35 
 
 1 130 
 
 9 
 
 422 
 
 33 
 
 73 
 
 73-6 
 
 97-5 
 
 5.2 
 
 28 at 1 67° F. 
 
 4 
 
 9-5 
 
 2-7 
 
 29 
 
 140 
 
 149 
 
 95 
 
 80 
 
 very soluble 
 
 very soluble. 
 
 133 
 
 very soluble. 
 
 1 1.6 
 
 43.3 at 167 F. 
 
 30.5 
 
 63.7 at I58°F. 
 
 74 
 
 20 
 
 soluble 
 
 very soluble. 
 
 37 
 
 203 
 
 61 
 
 333 
 
 soluble 
 
 soluble. 
 
 very soluble 
 
 very soluble. 
 
 45-35 
 
 very soluble. 
 
 48 
 
 139 
 
 3i-5 
 
 7>-5 
 
 6-57 
 
 54 
 
 decomposable 
 
 decomposable. 
 
 decomposable 
 
 decomposable. 
 
USEFUL TABLES. 
 
 671 
 
 Table of Solubilities of Chemical Compounds Commonly Used in 
 Electro- Tech n ics . — Con tin ned. 
 
 Names. 
 
 Mercurous nitrate 
 
 Mercurous sulphate 
 
 Nickel-ammonium sulphate (calculated to an- 
 hydrous salt) 
 
 Nickel chloride, crystallized 
 
 Nickel nitrate, crystallized. - 
 
 Nickel sulphate (calculated to anhydrous 
 salt) 
 
 Platinic chloride 
 
 Platoso-ammonium chloride 
 
 Potassium -aluminium sulphate (potash alum), 
 crystallized 
 
 Potassium bitartrate (cream of tartar) 
 
 Potassium carbonate (potash) 
 
 Potassium-copper cyanide 
 
 Potassium cyanide 
 
 Potassium dichromate 
 
 Potassium ferrocyanide (yellow prussiate of 
 potash) 
 
 Potassium-gold cyanide 
 
 Potassium nitrate (saltpetre) 
 
 Potassium permanganate 
 
 Potassium-silver cyanide 
 
 Potassium-sodium tartrate (Rochelle or Seig- 
 nette salt) 
 
 Potassium sulphide (liver of sulphur) 
 
 Potassium -zinc cyanide 
 
 Silver nitrate (lunar caustic) \ 
 
 Sodium bisulphite 
 
 Sodium carbonate, anhydrous (calcined soda) 
 
 Sodium carbonate (crystallized soda) 
 
 Sodium chloride (common salt) 
 
 Sodium dichromate 
 
 Sodium hydrate (caustic soda) 
 
 Sodium hyposulphite, sodium thiosulphate 
 
 (anhydrous salt) 
 
 Sodium phosphate 
 
 Sodium pyrophosphate 
 
 Sodium sulphate (Glauber's salt) 
 
 Sodium sulphite (neutral), crystallized 
 
 Stannic chloride 
 
 Stannous chloride (tin salt) 
 
 Tartaric acid 
 
 Zinc chloride 
 
 Zinc sulphate (white vitriol), crystallized .... 
 
 Soluble in 100 parts by weight of 
 water at 
 
 50° F. 
 
 212° F. 
 
 Parts by weight. 
 
 Parts by weight. 
 
 slightly soluble 
 
 slightly soluble. 
 
 very slightly soluble 
 
 decomposable. 
 
 3-2 
 
 28.6 
 
 50 to 66 
 
 very soluble. 
 
 slightly soluble 
 
 slightly soluble. 
 
 37-4 
 
 62 at 158 F. 
 
 soluble 
 
 very soluble. 
 
 0.65 
 
 1.25 
 
 9.8 
 
 357-5 
 
 0.4 
 
 6.9 
 
 109 
 
 156 . 
 
 94 
 
 *54 
 
 soluble 
 
 decomposable. 
 
 8.0 
 
 98 
 
 28 
 
 5° 
 
 soluble 
 
 soluble. 
 
 21. 1 
 
 247 
 
 6.45 
 
 very soluble. 
 
 12.5 
 
 100 
 
 58 
 
 very soluble. 
 
 very soluble 
 
 very soluble. 
 
 42 
 
 78.5 
 
 122 at 32 F. 
 
 714 at 185 F. 
 
 227 at 67° F. 
 
 1 1 1 1 at 230 F. 
 
 very soluble 
 
 very soluble. 
 
 12 
 
 45 
 
 40 
 
 540 at 219.2° F. 
 
 36 
 
 40.7 at 215.6 F. 
 
 108.5 
 
 163 
 
 96.1 
 
 213 
 
 65 
 
 102 at 140 F. 
 
 20 
 
 150 
 
 6.8 
 
 93 
 
 9 
 
 42-5 
 
 25 
 
 100 
 
 soluble 
 
 soluble. 
 
 271 
 
 decomposable. 
 
 125-7 
 
 343-3 
 
 300 
 
 very soluble. 
 
 138.2 
 
 653-6 
 
672 ELECTRO-DEPOSITION OF METALS. 
 
 Content of Metal in the Most Commonly Used Metallic Salts. 
 
 Metallic Combination. 
 
 Cobalt-ammonium sulphate, crystallized.. 
 
 Cobalt chloride 
 
 Cobalt sulphate, crystallized 
 
 Copper acetate, crystallized (verdigris) . . . 
 
 Copper carbonate 
 
 Copper chloride, crystallized 
 
 Copper cyanide 
 
 Copper oxide, black 
 
 Copper sulphate (blue vitriol), crystallized. 
 
 Cuprous oxide 
 
 Ferrous sulphate (green vitriol), crystal- 
 lized 
 
 Gold chloride (brown), technical. 
 
 Gold chloride (orange), technical 
 
 Iron-ammonium sulphate, crystallized.... 
 
 Lead acetate (sugar of lead), crystallized. 
 
 Lead nitrate, crystallized 
 
 Mercuric chloride 
 
 Mercurous nitrate 
 
 Nickel-ammonium sulphate, crystallized . . 
 
 Nickel carbonate, basic (separated at 
 212 F.) 
 
 Nickel chloride, crystallized 
 
 Nickel chloride, anhydrous 
 
 Nickel hydrate 
 
 Nickel nitrate, crystallized 
 
 Nickel oxide 
 
 Nickel sulphate, crystallized 
 
 Platinic chloride 
 
 Platoso-ammonium chloride 
 
 Potassium-copper cyanide, crystallized, 
 
 technical 
 
 Potassium mercuric cyanide 
 
 Potassium-silver cyanide, crystallized 
 
 Potassium-zinc cyanide, crystallized 
 
 Silver chloride 
 
 Silver cyanide 
 
 Silver nitrate, crystallized 
 
 Stannous chloride (tin-salt) 
 
 Zinc-ammonium chloride 
 
 Zinc carbonate 
 
 Zinc chloride 
 
 Zinc cyanide 
 
 Zinc sulphate (white vitriol), crystallized. . 
 
 
 o.SS 
 
 Formula. 
 
 tent 
 etal 
 :r ce 
 
 
 s= E a. 
 
 
 u 
 
 (NH 4 ) 2 Co(S0 4 ) 2 +6H 2 
 
 14.62 
 
 CoCl 2 +6H.,0 
 
 24.68 
 
 CoS0 4 +7H 2 
 
 20.92 
 
 Cu(C 2 H 3 2 ) 2 +H 2 
 
 31-87 
 
 2CuC0 3 (CuOH) 2 
 
 55-2° 
 
 CuCL,+2H 2 
 
 37-07 
 
 Cu 3 (CN) 4 + 5 H 2 
 
 56.50 
 
 CuO 
 
 79.83 
 
 CuS0 4 +5H 2 
 
 25.40 
 
 Cu 2 
 
 88.79 
 
 FeS0 4 + 7H.P 
 
 20.14 
 
 AuCl 3 +x ag 
 
 50 to 52 
 
 AuCl 3 -f-x ag 
 
 48 to 49 
 
 (NH 4 )Fe(S0 4 ) 2 +6H 2 
 
 14.62 
 
 Pb(C 2 PL,0 2 ) 2 +3H 2 
 
 54-57 
 
 Pb(N0 3 ) 2 
 
 62.51 
 
 HgCl 2 
 
 73-87 
 
 Hg,(N0 3 ) 2 
 
 79-36 
 
 (NH 4 ) 2 Ni(S0 4 ) 2 +6H 2 
 
 14.94 
 
 NiCO,4NiO, 5LLO 
 
 57-87 
 
 NiCl,+6H 2 
 
 24.63 
 
 NiCl, 
 
 45-3° 
 
 fNi(OH) 2 + H 2 (separated! 
 \ at 212 F.) / 
 
 63-34 
 
 Ni(NO,) 2 + 6H.,0 
 
 18.97 
 
 n. 2 o 3 
 
 71.00 
 
 NiS0 4 +7H 2 
 
 22.01 
 
 PtCl 4 +<;H 2 
 
 45.66 
 
 (NH 4 ) 2 PtCl 6 
 
 43-9i 
 
 K,Cu 2 (CN) 6 
 
 28.83 
 
 K 2 Hg(CN) 4 
 
 53-56 
 
 KAg(CN) 2 
 
 54.20 
 
 K 2 Zn(CN) 4 
 
 26.35 
 
 AgCl 
 
 68.20 
 
 AgCN 
 
 80.57 
 
 AgN0 3 
 
 64.98 
 
 SnCl 2 +2H 2 
 
 52.45 
 
 NH 4 ZnCl 3 +2H 2 
 
 28.98 
 
 ZnCO,Zn(OH) 2 
 
 29.05 
 
 ZnCl 2 
 
 47.84 
 
 Zn(CN) 2 
 
 56-59 
 
 ZnS0 4 -[- 7H 2 
 
 22.73 
 
USEFUL TABLES. 
 
 673 
 
 Table Showing the Electrical Resistance of Pine Copper Wire 
 of Various Diameters. 
 
 
 
 Number of 
 
 
 
 No. of 
 
 No. of wire, 
 
 
 feet required 
 
 No. of wire, 
 
 
 feet required 
 
 Birmingham 
 
 Resistance of 
 
 to give 
 
 Birmingham 
 
 Resistance ot 
 
 to give 
 
 -wire gauge. 
 
 1 foot in ohms. 
 
 resistance 
 of 1 ohm. 
 
 wire gauge. 
 
 1 foot in ohms. 
 
 resistance 
 of 1 ohm. 
 
 OOOO 
 
 O.OOOO516 
 
 19358 
 
 !7 
 
 O.OO316 
 
 316.I 
 
 OOO 
 
 O.OOOO589 
 
 16964 
 
 18 
 
 0-CO443 
 
 22 5-5 
 
 OO 
 
 O.OOOO737 
 
 I35 62 
 
 19 
 
 O.O0603 
 
 165-7 
 
 O 
 
 O.OOOO922 
 
 10857 
 
 20 
 
 0.00869 
 
 115.1 
 
 I 
 
 O.COOII8 
 
 8452.6 
 
 21 
 
 O.OIO4O 
 
 96.2 
 
 2 
 
 O.OOOI32 
 
 7575- 1 
 
 22 
 
 O.OI358 
 
 73-6 
 
 3 
 
 O.OOOI59 
 
 6300. 1 
 
 23 
 
 O.OI703 
 
 58.7 
 
 4 
 
 O.OOOI88 
 
 53I9-9 
 
 24 
 
 0.02200 
 
 45-5 
 
 5 
 
 O.O0O22O 
 
 4545-9 
 
 25 
 
 O.O2661 
 
 37- 6 
 
 6 
 
 O.OOO258 
 
 3870-3 
 
 26 
 
 O.O3286 
 
 30.4 
 
 7 
 
 O.OOO329 
 
 3°43-4 
 
 27 
 
 O.O4159 
 
 24.0 
 
 8 
 
 O.OOO39I 
 
 2557-1 
 
 28 
 
 0.05432 
 
 18.4 
 
 9 
 
 O.OOO486 
 
 2057.7 
 
 29 
 
 O.063OO 
 
 15-9 
 
 10 
 
 O.OCO593 
 
 1686.5 
 
 3° 
 
 0.07393 
 
 13-5 
 
 11 
 
 O.COO739 
 
 I352-5 
 
 31 
 
 O.I0646 
 
 9.4 
 
 12 
 
 O.OO0896 
 
 1 1 1 6.0 
 
 32 
 
 O.I3144 
 
 7-6 
 
 13 
 
 O.OO 1 180 
 
 847.7 
 
 33 
 
 O.16634 
 
 6.0 
 
 H 
 
 O.OOI546 
 
 647.0 
 
 34 
 
 O.21727 
 
 4.6 
 
 15 
 
 O.OO2053 
 
 487.0 
 
 35 
 
 O.42583 
 
 2.4 
 
 16 
 
 0.002520 
 
 396.8 
 
 36 
 
 O.66537 
 
 i-5 
 
 Resistance and Conductivity of Pure Copper at Different 
 Temperatures. 
 
 Centigrade 
 temperature. 
 
 Resistance. 
 
 Conductivity. 
 
 Centigrade 
 temperature. 
 
 Resistance. 
 
 Conductivity. 
 
 O 
 
 I .OOOOO 
 
 I .COOOO 
 
 1 6° 
 
 i. 06 1 68 
 
 .94190 
 
 I 
 
 I. OO38 1 
 
 .99624 
 
 17 
 
 1.06563 
 
 •93841 
 
 2 
 
 I.OO756 
 
 .99250 
 
 18 
 
 1.06959 
 
 •93494 
 
 3 
 
 IOII35 
 
 .98878 
 
 19 
 
 1.07356 
 
 .93148 
 
 4 
 
 I-OI5I5 
 
 .98508 
 
 20 
 
 1.07742 
 
 .92814 
 
 5 
 
 I. OI 896 
 
 •98139 
 
 21 
 
 1. 08 1 64 
 
 •92452 
 
 6 
 
 I.02280 
 
 .97771 
 
 22 
 
 1.08553 
 
 .92121 
 
 7 
 
 I.O2663 
 
 .97406 
 
 23 
 
 1.08954 
 
 .91782 
 
 8 
 
 I.03048 
 
 •97042 
 
 24 
 
 1.09365 
 
 .91445 
 
 9 
 
 I-03435 
 
 .96679 
 
 25 
 
 1.09763 
 
 .9IIIO 
 
 10 
 
 I.03822 
 
 .96319 
 
 26 
 
 1.10161 
 
 .90776 
 
 11 
 
 1. 04 1 99 
 
 •9597° 
 
 27 
 
 1. 10567 
 
 •90443 
 
 12 
 
 I.O4599 
 
 .95603 
 
 28 
 
 1.11972 
 
 .9OII3 
 
 13 
 
 I.O499O 
 
 .95247 
 
 29 
 
 1. 11882 
 
 .89784 
 
 H 
 
 I.05406 
 
 .94893 
 
 3o 
 
 1.1 1782 
 
 •89457 
 
 15 
 
 I.05774 
 
 •94541 
 
 
 
 
 43 
 
674 
 
 ELECTRO-DEPOSITION OF METALS. 
 
 Weight of Iron, Copper, and Brass Wire aiid Plates. 
 
 (Diameters and thickness determined by American gauge.) 
 
 
 
 Weight of wire per iooo 
 
 Weight of plates per 
 
 
 Size of 
 
 
 LINEAL FEET. 
 
 
 SQUARE FOOT. 
 
 
 No. of 
 
 each 
 
 No. 
 
 
 
 
 
 
 
 
 gauge. 
 
 
 
 
 ' 
 
 
 
 
 
 
 
 Wro't 
 iron. 
 
 Steel. 
 
 Copper. 
 
 Brass. 
 
 Wro't 
 iron. 
 
 Steel. 
 
 Copper. 
 
 Brass. 
 
 
 Inch. 
 
 Lis. 
 
 Lbs. 
 
 Lbs. 
 
 Lis. 
 
 Lbs. 
 
 Lis. 
 
 Lis. 
 
 Lis. 
 
 oooo 
 
 .46000 
 
 560.74 
 
 566.03 
 
 640.51 
 
 605.18 
 
 17.25 
 
 17.48 
 
 20.838 
 
 19.688 
 
 ooo 
 
 .40964 
 
 444.68 
 
 448.88 
 
 507-95 
 
 479-91 
 
 15-3615 
 
 15.5663 
 
 18.557 
 
 r 7-533 
 
 oo 
 
 .36480 
 
 352.66 
 
 355-99 
 
 402.83 
 
 380.67 
 
 13.68 
 
 13.8624 
 
 16.525 
 
 15-613 
 
 o 
 
 .32486 
 
 279.67 
 
 282.30 
 
 319.45 301.82 
 
 12.1823 
 
 12.3447 
 
 14.716 
 
 13.904 
 
 I 
 
 .28930 
 
 221.79 
 
 223.89 
 
 253-34 
 
 239-35 
 
 10.8488 
 
 10.9934 
 
 I3- io 5 
 
 12.382 
 
 2 
 
 .25763 
 
 175-89 
 
 *77-55 
 
 200.91 
 
 189.82 
 
 9.6611 
 
 9.7899 
 
 11. 671 
 
 11.027 
 
 3 
 
 .22942 
 
 I39-48 
 
 140.80 
 
 I59-3 2 
 
 150.52 
 
 8.6033 
 
 8.7180 
 
 10.393 
 
 9.8192 
 
 4 
 
 .20431 
 
 no 62 
 
 in. 66 
 
 126.35 
 
 119.38 
 
 7.6616 
 
 7-7638 
 
 9-2552 
 
 8.7445 
 
 5 
 
 .18194 
 
 87.720 
 
 88.548 
 
 100.20 
 
 94.666 
 
 6.8228 
 
 6.9137 
 
 8.2419 
 
 7.787 
 
 6 
 
 .16202 
 
 69.565 
 
 70.221 
 
 79.462 
 
 75-075 
 
 6.0758 
 
 6.1568 
 
 7-3395 
 
 6-9345 
 
 7 
 
 .14428 
 
 55-165 
 
 55.685 
 
 63.013 
 
 59-545 
 
 5.4105 
 
 5.4826 
 
 6.5359 
 
 6.1752 
 
 8 
 
 .12849 
 
 43-751 
 
 44.164 
 
 49.976 
 
 47.219 
 
 4.8184 
 
 4.8826 
 
 5 8206 
 
 5-4994 
 
 9 
 
 .11443 
 
 34-699 
 
 35.026 
 
 39.636 
 
 37-437 
 
 4.2911 
 
 4.3483 
 
 5.1837 
 
 4.8976 
 
 IO 
 
 .10189 
 
 27.512 
 
 27.772 
 
 31.426 
 
 29.687 
 
 3.8209 
 
 3-8718 
 
 4.6156 
 
 4.3609 
 
 ii 
 
 .000742 
 
 21.820 
 
 22.026 
 
 24924 
 
 23-549 
 
 3.4028 
 
 3.4482 
 
 4.1106 
 
 3-8838 
 
 12 
 
 .080808 
 
 I7-304 
 
 17.468 
 
 19.766 
 
 18.676 
 
 3-0303 
 
 3.0707 
 
 3.6606 
 
 3 4586 
 
 13 
 
 .071961 
 
 13.722 
 
 13851 
 
 15.674 
 
 14.809 
 
 2.6985 
 
 2-7345 
 
 3-2598 
 
 3-0799 
 
 14 
 
 .064084 
 
 10.886 
 
 10.989 
 
 12.435 
 
 11.746 
 
 2.4032 
 
 2-4352 
 
 2.9030 
 
 2.7428 
 
 15 
 
 .057068 
 
 8.631 
 
 8.712 
 
 9-859 
 
 9-3*5 
 
 2.1401 
 
 2.1686 
 
 2.5852 
 
 2.4425 
 
 16 
 
 .050820 
 
 6.845 
 
 6.909 
 
 7.819 
 
 7-587 
 
 1.9058 
 
 1.9312 
 
 2.3021 
 
 2.1751 
 
 *7 
 
 •045257 
 
 5-427 
 
 5-478 
 
 6.199 
 
 5-857 
 
 1. 6971 
 
 1. 7198 
 
 2.0501 
 
 r-937 
 
 18 
 
 .040303 
 
 4-304 
 
 4-344. 
 
 4.916 
 
 4.645 
 
 1.5114 
 
 I-53I5 
 
 1.8257 
 
 1-725 
 
 19 
 
 .035890 
 
 3-4I3 
 
 3-445 
 
 3.899 
 
 3.684 
 
 r-3459 
 
 1.3638 
 
 1.6258 
 
 i-536i 
 
 20 
 
 .031961 
 
 2.708 
 
 2-734 
 
 3-094 
 
 2.920 
 
 1. 1985 
 
 1. 2145 
 
 1.4478 
 
 r-3679 
 
 21 
 
 .028462 
 
 2.147 
 
 2.167 
 
 2.452 
 
 2.317 
 
 1.0673 
 
 1. 0816 
 
 1.2803 
 
 1. 2182 
 
 22 
 
 •025347 
 
 1.703 
 
 1. 719 
 
 1-945 
 
 1.838 
 
 •95051 
 
 .96319 
 
 1. 1482 
 
 1.0849 
 
 23 
 
 .022571 
 
 1-350 
 
 1.363 
 
 1-542 
 
 1-457 
 
 .84641 
 
 •8577 
 
 1.0225 
 
 .96604 
 
 24 
 
 .020100 
 
 1.071 
 
 1. 081 
 
 1.223 
 
 1. 155 
 
 •75375 
 
 .7638 
 
 ■9ro53 
 
 .86028 
 
 25 
 
 .017900 
 
 0.8491 
 
 0.8571 
 
 .9699 
 
 0.9163 
 
 .67125 
 
 .6802 
 
 .S1087 
 
 .76612 
 
 26 
 
 .015941 
 
 0.6734 
 
 0.6797 
 
 .7692 
 
 0.7267 
 
 •59775 
 
 .60572 
 
 .72208 
 
 .68223 
 
 27 
 
 .014195 
 
 0.5340 
 
 Q-539 1 
 
 .6099 
 
 0.5763 
 
 •53231 
 
 •53941 
 
 .64303 
 
 -60755 
 
 28 
 
 .012641 
 
 0.4235 
 
 0.4275 
 
 •4837 
 
 0.4570 
 
 •47404 
 
 .48036 
 
 •57264 
 
 •54103 
 
 29 
 
 .011257 
 
 o.3358 
 
 0-3389 
 
 .3835 
 
 0.3624 
 
 .42214 
 
 •42777 
 
 •50994 
 
 .48180 
 
 30 
 
 .010025 
 
 0.2663 
 
 0.2688 
 
 .3042 
 
 0.2874 
 
 •37594 
 
 .38092 
 
 •45413 
 
 .42907 
 
 3i 
 
 .008928 
 
 0.2113 
 
 0.2132 
 
 .2413 
 
 0.2280 
 
 •3348 
 
 •33926 
 
 .40444 
 
 .38212 
 
 32 
 
 .007950 
 
 0.1675 
 
 0.1691 
 
 •i9 r 3 
 
 0.1808 
 
 .29813 
 
 .3021 
 
 .36014 
 
 .34026 
 
 33 
 
 .007080 
 
 0.1328 
 
 0.1341 
 
 •1517 
 
 0.1434 
 
 • 2655 
 
 .26904 
 
 .32072 
 
 .30302 
 
 34 
 
 .006304 
 
 0.1053 
 
 0.1063 
 
 .1204 
 
 0.1137 
 
 .2364 
 
 •23955 
 
 •28557 
 
 .26981 
 
 35 
 
 .005614 
 
 0.08366 
 
 0.08445 
 
 .0956 
 
 0.1015 
 
 •21053 
 
 •21333 
 
 •2543 1 
 
 .24028 
 
 36 
 
 .005000 
 
 .06625 
 
 .06687 
 
 •0757 
 
 •0715 
 
 •1875 
 
 .19 
 
 • 2265 
 
 .2140 
 
 37 
 
 •oo4453 
 
 •05255 
 
 •05304 
 
 .06003 
 
 .05671 
 
 .16699 
 
 .16921 
 
 .20172 
 
 .19059 
 
 38 
 
 .003 165 
 
 .04166 
 
 .04205 
 
 .04758 .04496 
 
 .14869 
 
 .15067 
 
 .17961 
 
 •16973 
 
 39 
 
 ■003531 
 
 •03305 
 
 .03336 
 
 •03755 
 
 .03566 
 
 .13241 
 
 .13418 
 
 •15995 
 
 .1511 
 
 40 
 
 .003144 
 
 .02620 
 
 .02644 
 
 .02992 
 
 .02827 
 
 .1179 
 
 .11947 
 
 .14242 
 
 .13456 
 
 Specific 
 
 
 7-7747 
 
 7-847 
 
 8.880 
 
 8.336 
 
 7.200 
 
 7.296 
 
 8.698 
 
 8.218 
 
 Weight p 
 
 er 
 
 
 
 
 
 
 
 
 
 cubic f 
 
 
 185.874 i 
 
 90.45 
 
 554-988 1 
 
 524.16 
 
 450. 
 
 456. 
 
 543-6 
 
 5I3-6 
 
USEFUL TABLES. 
 
 675 
 
 Table of Hydrometer Degrees according to Baume, at 6j.^° F., 
 and their Weights by volume. 
 
 Degrees 
 Be. 
 
 Weight 
 
 by 
 volume. 
 
 Degrees 
 Be. 
 
 Weight 
 
 by 
 volume. 
 
 Degrees 
 Be. 
 
 Weight 
 
 by 
 volume. 
 
 Degrees 
 Be. 
 
 Weight 
 
 by 
 volume. 
 
 
 
 1 .0600 
 
 19 
 
 1. 1487 
 
 38 
 
 1-3494 
 
 57 
 
 1.6349 
 
 1 
 
 1.0068 
 
 20 
 
 1.1578 
 
 39 
 
 1.36-19 
 
 58 
 
 1.6533 
 
 2 
 
 1.0138 
 
 21 
 
 1. 1670 
 
 40 
 
 1-3746 
 
 59 
 
 1.6721 
 
 3 
 
 1.0208 
 
 22 
 
 1. 1763 
 
 4i 
 
 1.3876 
 
 60 
 
 1. 6914 
 
 4 
 
 1.0280 
 
 23 
 
 1.1858 
 
 42 
 
 1.4009 
 
 61 
 
 1.7m 
 
 5 
 
 I-0353 
 
 24 
 
 1-1955 
 
 43 
 
 1-4143 
 
 62 
 
 i-73'3 
 
 6 
 
 1.0426 
 
 25 
 
 1.2053 
 
 44 
 
 1. 4281 
 
 63 
 
 1.7520 
 
 7 
 
 1.0501 
 
 26 
 
 1-2153 
 
 45 
 
 1. 442 1 
 
 64 
 
 1-773 1 
 
 8 
 
 1.0576 
 
 27 
 
 1.2254 
 
 46 
 
 1.4564 
 
 65 
 
 1.7948 
 
 9 
 
 1.0653 
 
 28 
 
 1-2357 
 
 47 
 
 1.4710 
 
 66 
 
 1.8171 
 
 10 
 
 1.0731 
 
 29 
 
 1.2462 
 
 48 
 
 1.4860 
 
 67 
 
 1.8398 
 
 11 
 
 1.0810 
 
 30 
 
 1.2569 
 
 49 
 
 1. 5012 
 
 68 
 
 1.8632 
 
 12 
 
 1.0890 
 
 3i 
 
 1.2677 
 
 50 
 
 1.5167 
 
 69 
 
 1.8871 
 
 13 
 
 1.0972 
 
 32 
 
 1.2788 
 
 5i 
 
 !-5325 
 
 70 
 
 1.9117 
 
 14 
 
 1. 1054 
 
 33 
 
 1. 2901 
 
 52 
 
 1.5487 
 
 7i 
 
 1-937° 
 
 *5 
 
 1.1138 
 
 34 
 
 1.3015 
 
 53 
 
 1.5652 
 
 72 
 
 1.9629 
 
 16 
 
 1. 1 224 
 
 35 
 
 1-3131 
 
 54 
 
 1.5820 
 
 
 
 17 
 
 1.1310 
 
 36 
 
 1.3250 
 
 55 
 
 1-5993 
 
 
 
 18 
 
 1. 1398 
 
 37 
 
 1-337° 
 
 56 
 
 1. 6169 
 
 
 
 Comparison of the Scales of the Fahrenheit, Centigrade and 
 Reaumur Thermometers, and Rules for Converting one Scale 
 into another. 
 
 These three thermometers are graduated so that the range 
 of temperature between the freezing and boiling points of water 
 is divided by Fahrenheit's scale into 180 from 32°to2i2°) 
 by the Centigrade into 100 (from o° to ioo°), and by that of 
 Reaumur into 80 (from o° to 8o°) portions or degrees. 
 
 The spaces occupied by a degree of each scale are conse- 
 quently as i, \, and \ respectively, or as I, 1.8, and 2.25 ; and 
 the number of degrees denoting the same temperature, by the 
 three scales, when reduced to a common point of departure by 
 subtracting 32 from Fahrenheit's, are as 9, 5, and 4. Hence, 
 we derive the following equivalents : — 
 
 A degree of Fahrenheit's is equal to 0.5 of the Centigrade or 
 to 0.4 of Reaumur's; a degree of Centigrade is equal to 1.8 
 
676 ELECTRO-DEPOSITION OF METALS. 
 
 of Fahrenheit's or to 0.8 of Reaumur's; and a degree of 
 Reaumur's is equal to 2.25 of Fahrenheit's, or to 1.25 of the 
 Centigrade. 
 
 To convert degrees of Fahrenheit into the Centigrade or 
 Reaumur's, subtract 32 and multiply the remainder by f for 
 the Centigrade, or f for Reaumur's. 
 
 To convert degrees of the Centigrade or Reaumur's into 
 Fahrenheit, multiply the Centigrade by §-, or Reaumur's by 
 f, as the case may be, and add 32 to the product. 
 
INDEX. 
 
 ACCUMULATOR, chemical pro- 
 cesses in the, 1 15-120 
 common form of, 119 
 magnitude of the performance of, 
 
 183, 184 
 plant, 184, 185 
 Accumulators, 114-121 
 
 and dynamo, combined, galvano- 
 plastic operations with. 551, 552 
 coupling of, 121 
 installation with, 182-185 
 maintenance of, 120, 121 
 Acid, arsenious, b44 
 boric, 643, 644 
 chromic, 644 
 citric, 643 
 copper baths, examination of, 
 
 571-574 
 heating of, 568 
 tanks for, 565 
 
 determination of, 311-313 
 
 hydrochloric, 642 
 
 hydrocyanic, 642, 643 
 
 hydrofluoric, 644, 645 
 
 mixtures, recovery of silver from, 
 
 403 
 
 muriatic, 642 
 
 nitric, 642 
 
 potassium carbonate, 656 
 
 prussic, 642, 643 
 
 pump, 232, 233 
 
 regaining of, from dipping baths, 
 227, 228 
 
 residue, 53 
 
 salts, 44 
 
 sulphuric, 641, 642 
 
 vapors, absorbing plant for, 226, 
 227 
 Acids, 40, 641-645 
 
 bases, salts, 39-45 
 
 formation of salts from, 43, 44 
 
 organic, salts of, 664-666 
 Aggregate, double, 548 
 Albert, Dr., on metal matrices, 5S0- 
 
 587 
 Alexander's patents, 447, 44S 
 Alkalies and alkaline earths, 645, 646 
 poisoning by, 535 
 
 Alliance machine, 7 
 Alloys, lead and tin, soft, nickeling 
 of, 306, 307 
 metallic, first deposition of, 6 
 for moulds, 613 
 Aluminum, addition of, to zinc baths, 
 
 447 
 
 -contact for nickeling, 482 
 
 deposition of, 470, 471 
 
 depositions upon, 471-474 
 
 -magnesium alloy, addition of, to 
 ziuc baths, 449 
 Amalgamating articles to be silver- 
 plated, 376 
 Amalgamation, 69, 70 
 Amalgams, potassium and sodium, 4 
 Ammeter, 147 
 Ammonia, 645, 646 
 Ammonium-alum, 658 
 
 chloride, 648 
 
 hydrate, 645, 646 
 
 phosphate, 664 
 
 sulphate, 658 
 
 sulphide, 647 
 Ampere, 20 
 
 -meter, 147 
 
 -turn number, 12 
 Ampere's rule, 11 
 
 theory of molecules, 10 
 Analytical chemical process, 32 
 Anions, 46 
 Anode, 46 
 
 hooks, 162 
 Anodes, arrangement of, in the bath, 
 160-163 
 
 brass, 349, 350 
 
 cast and rolled, proportion of, 
 270, 271 
 
 choice of, 242 
 
 copper, 33 r 
 
 cover for, 162, 163 
 
 dimensions of, i6t, 162 
 
 elliptic, 266-268 
 
 faulty arrangement of, 278 
 
 for galvauoplastic bath, 564, 565 
 nickeling sheet-zinc, 300 
 
 gas-carbon, 269 
 
 gold, 410-413 
 
 (677) 
 
678 
 
 INDEX. 
 
 Auodes, insoluble, 26S-270 
 
 nickel, 265-272 
 
 silver, 364-369 
 
 silverite, 268 
 
 supply of. 161 
 
 suspension of, 162 
 
 uneven wear of, 237 
 
 zinc, 452-454 
 Antimony baths, 467, 468 
 
 deposition of, 467, 468 
 
 by imtnersiou, 503 
 
 -potassium tartrate, 665 
 
 properties of, 467 
 
 sulphide, 647 
 
 trichloride, 648 
 Aqua fortis, 642 
 Areas silver-plating, 373-375 
 Argentiferous paste, composition of, 
 
 493. 494 
 Argol, 664 
 Armature, 96, 98-102 
 
 windings, 101, 102 
 Arrhenius's investigations, 50 
 Arsenic baths, 468, 469 
 
 deposition of, 468-470 
 
 by immersion, 503 
 
 deposits, defective, 469, 470 
 
 poisoning by, 535 
 
 properties of, 46S 
 
 trisulphide, 647 
 
 white, 644 
 Arsenious acid, 644 
 
 chloride, 648 
 
 sulphide, 647 
 Artificial carbon, 73, 74 
 Astatic galvanometer, 11, 12 
 Atomic weights, 33 
 Atoms, 33 
 Auric chloride, 651 
 Autotypes, acid copper bath for, 568 
 Autotjpy, 605 
 Autovolt baths, 482 
 Avogrado's law, 50 
 Avoirdupois weight, 667 
 
 BABY shoes, galvanoplastic cop- 
 pering of, 628 
 Bacco's copper bath, 485 
 Backing deposits or shells, 595 
 
 -metal, "595 
 Baking powder, 656 
 Balance, metallometric, 380-383 
 
 voltametric, 383, 384 
 Barium cyanide, calculation of, 400, 
 
 401 
 Bases, 40 
 
 Basket tray, 289, 290 
 Baskets, dipping, 288, 289 
 
 Bath, arrangement of objects and 
 anodes in 
 the, 160- 
 163 
 switch-board 
 and am- 
 meter with 
 a, 150 
 electro-motive force in the, 131- 
 
 133 
 suspension of anodes in the, 162 
 Baths, 233-245 
 
 agitation of, 236-239 
 boiling of, 240, 241 
 concentration of, 235, 236 
 containing potassium cyanide, 
 
 holders for, 159 
 coupling of, for galvanoplastic 
 
 deposition, 548-551 
 electro-chemical cleaning, 230, 
 
 231 
 
 filtering the, 241, 242 
 for rapid galvanoplasty, 567, 568 
 galvanoplasty, current- 
 density for, 569 
 galvanoplastic, agitation of, 560- 
 
 564 
 prevention of impurities in, 242 
 reaction of, 245 
 temperature of, 239, 240 
 working of, with the current, 241 
 Battery, 30 
 
 galvanoplastic deposition with, 
 546 
 Baume hydrometer degrees, and their 
 
 weights 1 y volume, 675 
 Bell-metal, 343 
 
 Belt-attachment combined with a 
 grinding lathe, 201 
 or endless belt machine, 211, 
 212 
 Bicarbonate of potash, 656 
 Bichromate cell, bottle-form of, 85 
 Bicycle frames, removal of hard 
 
 solder from, 221, 222 
 Bicycles, nickeling parts of, 274 
 Bi-metal for rods, 159 
 Binding posts, 160 
 
 Bird, production of amalgams of po- 
 tassium and sodium bv, 4 
 Bivalent and trivalent elements, 37 
 
 elements, 37 
 Black lead, gilt or silvered, 592 
 -leading, 588-590 
 
 first application of, 5 
 machines, 588, 589 
 nickel bath, 258, 259 
 sulphide of antimony, 647 
 
INDEX. 
 
 679 
 
 Blue copperas, 659 
 vitriol, 659 
 
 copper baths with, 126 
 solution, effect of orgauic 
 additions to, 557, 558 
 electrolysis of, 55 
 Bobs, 205 
 
 construction of, 294, 295 
 Boettger, Prof., discoveries of, 6 
 Boric acid, 643, 644 
 
 addition of, to nickel baths, 
 
 249 
 nickel baths containing, 254- 
 256 
 Bower-Barff, dead black lacquer as a 
 
 substitute for, 527, 528 
 Bowls, galvanoplastic decorations on, 
 
 627, 628 
 Boxwood sawdust, 217 
 Branch conductors, 155, 156 
 
 wires, 26 
 Branching the current, 26 
 Brass and bronzes, coloring of, 511- 
 5i6 
 anodes, 349, 350 
 baths, 343-349 
 
 boiling of, 240 
 examination of, 355-357 
 lead-lined tanks for, 158, 159 
 tanks for, 349 
 bronze Barbedienne on, 513, 514 
 brown on, 513, 514 
 castings, grinding of, 204 
 cleansing of, 232 
 cornflower-blue on, 514, 515 
 dark red brown on, 514 
 deposit, sluggish formation of, 
 
 351, 352 
 deposition of, 343~357 
 deposits, polishing of, 218 
 
 showing a tone resembling 
 gold, 353 
 Ebermayer's experiments in col- 
 oring, 515, 516 
 etching of, 606, 607 
 gold color on, 512, 513 
 gray color with bluish tint on, 
 
 512 
 lustrous black on, 511 
 nickel bath for, 258 
 nielling upon, 395 
 pickling of, 223 
 salts, prepared, 349 
 scratch brushes for, 215 
 sheets, brushing of, 204, 205 
 
 nickeling of, 301, 302 
 silver color on, 512 
 
 Brass, spurious gilding of, 515 
 
 steel-gray on, 511, 512 
 
 straw color on, 512 
 
 tin bath for, 440 
 
 tinning solution for, 502 
 
 varieties of, 343 
 
 various colors on, 510 
 
 violet on, 514, 515 
 
 wire and plates, weight of, 674 
 
 zincking of, 503 
 Brassing by contact, 487, 488 
 
 execution of, 350-355 
 Bright dipping bath, 223, 224 
 
 silver-plating, 371, 372 
 Britannia, cleansing of, 232 
 
 silver plating of, 392 
 Bronze baths, 357, 358 
 
 Barbedienne on brass, 513, 514 
 
 cleansing of, 232 
 
 dead yellow or gray yellow to 
 dark brown color on, 514 
 
 deposition of, 357, 358 
 
 pickling of, 223 
 Bronzer, brushes used by the, 190 
 Bronzes, 343 
 
 and brass, coloring of, 511-516 
 Bruguatelli, first practical results in 
 
 electro-gilding attained by, 3 
 Bunsen cell, 73-80 
 
 processes in the, 74 
 
 cells, treatment of, 79, So 
 Brush-coppering, 486, 487 
 
 -holders, 103 
 
 -rocker, 103, 104 
 Brushes, 102, 103, 190 
 
 adjustment of, 167 
 
 proper position of the tips of, 167 
 Brushing and grinding, execution of, 
 
 202-205 
 Buff, triplex, 205, 206 
 Buffing, flexible shaft for, 212-214 
 
 lathes, 209-211 
 Burgess and Hambuechen's process 
 for depositions upon alumin 
 ium, 473 
 
 experiments by, regarding zinck- 
 ing by the hot and cold pro- 
 cess, 444-446 
 Burnishers, 218, 219 
 Burnishing, 214, 215 
 
 operation of, 218, 219 
 Burnt lime, 646 
 Busts, reproduction of, 611, 612 
 
 terra cotta, galvanoplastic de- 
 posit of copper on, 626, 627 
 Butter of antimony, 648 
 zinc, 649 
 
68o 
 
 INDEX. 
 
 CADMIUM silver bath, 374, 375 
 Calcium carbonate, 656, 657 
 hydrate, 646 
 Candelabra, galvanoplastic coppering 
 
 of, 629 
 Cane handles, galvanoplastic decora- 
 tions on, 628 
 Carbohydrates, addition of, to zinc 
 
 baths, 449, 450 
 Carbon anodes for gilding, 412 
 artificial, 73, 74 
 blocks, galvanoplastic coppering 
 
 of, 628 
 disulphide, 647 
 
 addition of, to nickel baths, 
 261 
 pins, galvanoplastic coppering 
 of, 628 
 Carbonates, 655-657 
 Castings, coppered, prevention of 
 stains on, 334 
 dip lacquer for, 525, 526 
 rough galvanoplastic coppering 
 of, 629 
 Cast-iron, bath for bronzing, 357 
 brass bath for, 348 
 pickling of, 220 
 rolls, galvanoplastic copper- 
 ing of, 628 
 Cathode, 46 
 Caustic potash, 645 
 
 soda, 645 
 Cell apparatus, 540-543 
 
 copper bath for, 543, 544 
 electro-motive force in, 544, 
 
 545 
 galvanoplastic deposition in, 
 
 540-545 
 determination of electro-motive 
 
 force of a, 63 
 galvanic, 30 
 voltaic, 30 
 Cells, coupling of, 87-89, 135-137 
 form of, 540-54} 
 installation with, 135-165 
 secondary; 114-121 
 voltaic, 68-89 
 Celluloid articles, galvanoplastic 
 
 decorations on, 628 
 Centigrade, Fahrenheit and Reaumur 
 thermometers, comparison of the 
 scales of, and rules for converting 
 one scale into another, 675, 676 
 Centrifugal driers, 217 
 Chalk, 656, 657 
 
 Chemical compounds, table of solu- 
 bilities of, 670, 671 
 elements, 33 
 
 Chemical elements, table of, with 
 their symbols and 
 atomic weights, 33, 34 
 valence of, 35-37 
 energy, conversion of, into elec- 
 trical energy, 68 
 formulas, 34, 35 
 
 processes, illustrations of, 31, 32 
 treatment of objects, 220-233 
 Chemicals, poisoning by, 534-536 
 purity of, 233-235 
 used in electro-plating and gal- 
 vanoplasty, 641-666 
 Chemistry, fundamental principles 
 
 of, 3 r "45 
 
 Chili saltpetre, 662 
 
 Chloride of zinc and ammonia, 649 
 
 Chlorine combinations, 648-651 
 poisoning by, 536 
 
 Christome & Co., early use of mag- 
 neto electrical machines by, 7 
 
 Chrome gelatine, 6' 13 
 
 Chromic acid, 644 
 
 solution, substitute for, 86, 
 
 S7 
 Chromium combination, soluble, 78 
 Circuit, electric resistance of the, 21 
 Citric acid, 643 
 
 Clamond's thermo electric pile, 92 
 Clausius, theory of, 49 
 Clay objects, galvanoplastic deposit 
 
 of copper on, 626, 627 
 Cleansing and rinsing apparatus, 
 163-165 
 
 polished objects, 219, 220 
 Cliches, nickeling of, 307-309 
 Cloth bobs, 205 
 Cobalt-ammonium sulphate, 661 
 
 baths, 319 
 
 deposition of, 318-320 
 
 properties of, 318 
 Cobalting by contact and boiling, 
 
 483, 484 
 Cobaltous carbonate, 657 
 
 chloride, 650 
 
 sulphate, 660, 661 
 Coefficient of temperature, 25, 26 
 Coffee sets, galvanoplastic decora- 
 tions on, 627, 628 
 Colcothar, 214 
 
 Cold silvering with paste, 493, 494 
 Coloring, patinizing, oxidizing, etc., 
 
 of metals. 504-521 
 Commutator, 102 
 Compound wound dynamo, 105 
 Concentration cells, 64 
 Conducting fixtures, 159, 160 
 
 rods, 159, 160 
 
INDEX. 
 
 68 1 
 
 Conducting salts, 248, 249 
 Conductors, 45, 155, 156 
 bad, 28 
 good, 28 
 
 of the first class, 45 
 second class, 45 
 Connection of main conductors and 
 
 branch conductors, 156, 157 
 Conservation of force and work, 52 
 Constant cells, 68 
 
 Contact and boiling, cobalting by, 
 .483, 484 
 nickeling by, 479- 
 
 .483 
 
 tinning by, 500-503 
 dipping, coppering by, 
 484-487 
 brassing by, 487, 488 
 -electricity, 29, 30 
 discovery of, 1 
 immersion and friction, gilding 
 by, 497-500 
 silvering by, 
 488-487 
 -metals, 417 
 platinizing by, 500 
 tinning by, 500, 501 
 zincking by, 503 
 Contacts, 155 
 Continuous-current wound dynamos, 
 
 104, 105 
 Copper acetate, 665 
 
 alloys, nickel bath for, 257, 258, 
 
 259 
 anodes, 331 
 bath, acid, current conditions for, 
 
 554-557 
 heating of, 568 
 for cell apparatus, 543, 544 
 incrusting galvanoplasty, 
 625 
 baths, 321-328 
 
 acid, examination of, 571- 
 
 574 
 tanks for, 565 
 boiling of, 240 ■ 
 containing potassium cyan- 
 ide, examination of, 337- 
 
 343 
 for galvanoplastic deposi- 
 tions with a separate 
 source of current, 552-554 
 lead-lined tanks for, 158, 159 
 without potassium cyanide, 
 
 329 
 wooden tanks for, 157, 158 
 black on, 507 
 blue-black on, 507 
 
 Copper, blue-gray shades on, 507 
 bronzing of, 506 
 brown on, 505, 506 
 carbonate, 657 
 castings, grinding of, 204 
 cleansing of, 232 
 coloring of, 505-510 
 cyanide, 654 
 
 baths, preparation of, 322 
 tanks for, 330 
 determination of, 340-343, 355, 35& 
 deposited, properties of, 554 
 deposition of, 321-345 
 deposits, brittle, cause of, 557, 
 558 
 
 from metallic surfaces, 597- 
 
 599 
 polishing of 2 [8 
 removal of hydrochloric acid 
 from the pores of, 334 
 early reduction of, 1 
 electrolytic determination of, 
 
 573. 574 
 electrotypes, steeled, 633 
 engraving, 600, 6or 
 faulty deposition of, 33:, 332 
 galvanoplasty in, 538-629 
 matt black on, 507, 508 
 metallic, regeneration of, 82 
 nickel bath for, 257, 258 
 pickling of, 223 
 plates, cobalting of, 318, 319 
 
 etching of, 606, 607 
 -plating, execution of, 331-337 
 printing plates, bath for, 554 
 properties of, 321 
 pure, resistance and conductivity 
 
 of, 673 
 red-brown on, 506 
 salts, poisoning by, 535 
 sandy deposits of, 539 
 scratch brushes for, 215 
 sheets, brushing of, 204, 205 
 
 nickeling of, 301, 302 
 spongy deposits of, 539 
 steel-grey on, 510 
 sulphate, 659 
 
 copper baths with, 326 
 tin bath for, 440 
 tinning solution for, 502 
 tubes, 622, 623 
 various colors on, 510 
 voltameter, 383, 384 
 volumetric determination of, 572, 
 
 573 
 wire and plates, weight of, 674 
 pure, table of electrical re- 
 sistance of, 673 
 
68: 
 
 INDEX. 
 
 Copper wire, silvering of, 393, 394 
 
 zinc alloy, solution for transfer- 
 ring, 348, 349 
 zincking of, 503 
 Copperas, 659 
 
 Coppered art-castings, inlaying of de- 
 pressions of, 336, 337 
 articles, formation of stains on, 
 
 333i 334 
 castings, prevention of stains on, 
 
 334 
 Coppering by contact and dipping, 
 484-487 
 matrices, 569 
 salts, prepared, 328, 329 
 small articles in quantities, 336 
 stereotypes, 599 
 zinc plates, 599 
 Cords, zincking of, 457-459 
 Cork waste grinding wheels, 197 
 Corvin's niello, 623 
 Coulomb, 20 
 Counter-current, 65 
 
 -force, 51 
 Coupling accumulators, 121 
 
 baths for galvanoplastic deposi- 
 tion, 548-55 ' 
 cells, 87-89, 135-137 
 dynamos, 173-176 
 of main object wire and main 
 anode wire together with the 
 resistance boards, voltmeter, 
 switch and two baths, 151-154 
 Covering ground, 601 
 Cowper-Coles, investigations of the 
 
 electrolysis of zinc by, 448, 449 
 Cream of tartar, 6?4 
 Cruikshank's investigations, 3 
 
 trough battery, 2 
 Cubic nitre, 662 
 Cuivre fume, 507 
 Cupric nitrate baths, 559, 560 
 oxide cell, 80-82 
 sulphate, 659 
 
 solution, electrolysis of, 55 
 Cupro-cupric sulphate, copper baths 
 
 with, 327 
 Cupron cell, 82, 83 
 Cuprous cyanide, formation of, on 
 copper anodes, 331 
 oxide, regeneration of, 82 
 sulphite, 661, 662 
 Current, branching or distributing 
 the, 26 
 conditions for acid copper bath, 
 
 554-557 
 encrusting gal- 
 vanoplasty, 625 
 
 Current-density, 127-131 
 
 dependence of, on electro- 
 motive force, 154, 155 
 effect of, 243, 244 
 for baths for rapid galvauo- 
 plasty, 569 
 galvanic, 30 
 hydro-electric, 30 
 indicator, 141-150 
 osmotic theory of the production 
 
 of, ft 1 -64 
 -output, 244, 245 
 primary, inducing, or main, 16 
 recognition of polarity of, 146, 
 
 147 
 regulation, 137-141 
 regulator, 138-140 
 secondary, induced, or induc- 
 tion, 16 
 sources of, 68-121 
 -strength, calculation of the 
 weight of the silver de- 
 posit from the, 390, 391 
 unit of, 20 
 working baths with the, 241 
 Currents, induced, law followed by, 
 
 18 
 Cyanide combinations of gold and 
 
 silver, 5 
 Cyanides, 652-655 
 
 metallic, first use of, of solutions 
 
 of, in potassium cyanide, 5 
 poisoning by, 534, 535 
 
 DANIELL cell, 71, 72 _ 
 chemical processes in the, 63, 64 
 Darlay's brassing bath, 4S7, 488 
 
 copper bath, 485, 486 
 
 nickeling bath, 482, 483 
 
 silvering bath, 489 
 
 tinning bath, 501 
 
 zincking bath, 503 
 Davy, Sir H., discovery of the metals 
 
 sodium and potassium by, 3 
 Decomposition-pressure, 66 
 
 -values of solutions, 66 
 Depolarization, 74 
 Deposit, absorption of the, 243 
 
 backing the, 595 
 
 detaching the, from moulds, 593, 
 
 594 
 formation of, 186, 187 
 Deposition by contact, by ■ boiling, 
 and by friction, 473-503 
 galvanoplastic, duration of, 558, 
 
 559 
 of aluminium, 470, 471 
 antimony, 467, 468 
 
INDEX. 
 
 68 3 
 
 Deposition of antimony, arsenic, alu- 
 minium, 467-474 
 of arsenic, 468-470 
 brass, 343~357 
 bronze, 357, 358 
 cobalt, 318-320 
 copper, 321-343 
 
 brass and bronze, 321-358 
 gold, 404-430 
 iron, 464-466 
 lead, 461-464 
 nickel, 246-318 
 
 alloys, 310, 311 
 and cobalt, 246-320 
 palladium, 437, 438 
 platinum, 431-437 
 
 and palladium, 431-438 
 silver, 359-403 
 tin, 439-442 
 
 zinc, lead, and iron, 439- 
 466 
 tombac, 357 
 zinc, 442-461 
 upon aluminium, 471-474 
 Deposits, calculation of time required 
 for a certain thickness of, 129, 130 
 Dextrose, addition of, to zinc baths, 
 
 449. 450 
 Dip lacquer for castings, 525, 526 
 Dipping and pickling, 220-228 
 baskets, 288, 289 
 bath, bright, 223, 224 
 baths, regaining acid and metal 
 
 from, 227, 228 
 vat, 163 
 Distributing the current, 26 
 Disulphuric acid, 641 
 Double connection, 160 
 Driers, centrifugal, 217 
 Drum armature, 100 
 Drying plated objects, 217, 218 
 Dynamo and accumulators, com- 
 bined, galvanoplastic operation 
 with, 551, 552 
 choice of a, 168-173 
 electric machine, frame of, 97-102 
 machines, 95-114 
 
 classification of, 97 
 fundamental principles 
 
 of, 95-97 
 installation with, 165-185 
 parallel and series coup- 
 ling of, 173-176 
 separate parts of, 97-104 
 various constructions of, 
 8 
 foundation for, 166 
 galvanoplastic deposition with, 
 547-551 
 
 Dynamo, location of, 165, 166 
 
 setting up and running a, 165-168 
 troubles with a, 165 
 
 EBERMAYER'S experiments in 
 coloring brass, 515, 516 
 silver-immersion bath, 492 
 Egyptian Lacquer Manufacturing Co., 
 
 lacquers made by, 525-532 
 Elb's theory of chemical processes in 
 
 the accumulator, 115-118 
 Electric current lines, scattering of, 
 
 134, 135 
 properties, effects aud 
 value of, compared 
 with a current of water, 
 1S-20 
 resistance to the, 14, 15 
 energy, conversion of chemical 
 
 energy into, 68 
 heating of nickel baths, 124 
 induction, discovery of, 4 
 resistance of the circuit, 21 
 
 unit of, 22 
 units, 18-24 
 work, unit of, 21 
 Electrically-driven polishing and 
 
 buffing lathes, 211 
 Electricity, frictional, 2S, 29 
 kinds of, 29 
 state of motion of, 3 
 unit of the quantity of, 20 
 Electro-chemical cleaning, 229-231 
 equivalent, 59 
 processes, investigators 
 of, 8 
 -chemistry, fundamental princi- 
 ples of, 45-67 
 -chromy, 461-463 
 -engraving, 608-610 
 -etching. 600-602 
 -gilder's brush, 190 
 -gilding, first practical results in, 3 
 -magnetic alternating actions, 18 
 
 induction machine, first, 4 
 -magnetism, 11-15 
 -magnets, 12 
 
 -metallurgy, first application of 
 the term, 6 
 historical review of, 1-8 
 -motive counter-force, determina- 
 tion of, 134 
 of polariza- 
 tion, 133- 
 
 135 
 force, coupling elements for, 
 88 
 
 dependence of current- 
 density on, 154-155 
 
684 
 
 INDEX. 
 
 Electro-motive force, difference of, 21 
 in the bath, 131-133 
 cell appara- 
 tus, 544, 545 
 series of, 30 
 unit of, 20 
 -plating apparatus, mechanical, 
 290-293 
 arrangements in particular, 
 
 127-185 
 chemicals used in, 641-666 
 establishments, arrangement 
 
 of, in general, 122-185 
 mechanical treatment during 
 and after, 
 215-220 
 previous to, 
 186-215 
 plant with dynamo, ground- 
 plans of, 176, 181 
 solutions, 233-245 
 -technics, fundamental princi- 
 ples of, 1S-2S 
 Electrodes, 46 
 
 processes on the, 53-56 
 Electrolysis, 46 
 
 determination of copper by, 340, 
 
 341 
 Faraday's laws of, 56-59 
 liberation of secondary products 
 
 by, 55 
 
 review of the history of the de- 
 velopment of, 1-8 
 Electrolyte, calculating the resist- 
 ance of the, 131-133 
 
 dissociation of the molecules of 
 
 a, 49 
 Electrolytes, 45, 46, 233-245 
 
 effect of current-density on, 243, 
 244 
 Electrolytic analysis, 314-316 
 
 determination of copper, 573, 574 
 dissociation, 49-51 
 pickling. 220, 221 
 Electropoiou, 77 
 
 Electrotypes, duration of deposition 
 for, 559 
 finishing of. 595, 596 
 iron, 629, 630 
 nickel, 637-639 
 Electrotypy, 539-610 
 Elements, chemical, 33 
 
 table of, with their 
 symbols and atomic 
 weights, 33, 34 
 valence of, 35-37 
 Elliptic anodes, 266-268 
 Eisner's tinning bath, 502 
 Emery, qualities of, 198 
 
 Energy, 51-53 
 
 Eyes and hooks, tinning solution for,. 
 
 502 • 
 Excitation, 98 
 
 FAHRENHEIT, Centigrade and 
 Reaumur thermometers, com- 
 parison of the scales of, and 
 rules for converting one scale 
 into another, 675, 676 
 Faraday, discovery of electric induc- 
 tion by, 4 
 laws of, 56-59 
 Feelers, 590 
 
 Fein's plunge battery, 83, 84 
 Felt wheels, 197, 198 
 Ferric oxide, 214 
 sulphide, 648 
 Ferrous sulphate, 659 
 Fibers, 203 
 Field, magnetic, it, 13 
 
 winding, 97 
 Fire-gilder's brush, 190 
 
 -gilding, combination of, with 
 electro deposition, 420 
 Flexible shafts, 212-2 14 
 Floors of plating room-, 124, 125 
 Flowers, galvanoplastic deposit of 
 
 copper on, 626 
 Foot-power grinding and polishing 
 
 lathe, 208, 209 
 Force, 51 
 
 Foreign excitation, 98 
 Forks, calculating the time for de- 
 positing a determined weight 
 of silver on, 129-131 
 extra heavy coating of silver on,. 
 377, 378 . 
 Forster, investigations by, 538 
 Four polar dynamo, 98 
 Frame of dynamo-electric machine, 
 
 97-102 
 French form of cell apparatus, 541, 
 
 542 
 Frictional electricity, 28, 29 
 work, 52 
 
 GALLONS, to find the number of, 
 a tank will hold, 667 
 Galvani, discovery of contact elec- 
 tricity by, 1 
 Galvanic cell, 30 
 
 current, 30 
 Galvanizing, cold, advantages of, 444 
 determination of the 
 power of resist- 
 ance of coating of 
 zinc obtained by 
 445. 446 
 
INDEX. 
 
 68 5 
 
 Galvanizing, hot, determination of 
 thickness of zinc 
 obtained by, 445 
 disadvantages of, 444 
 Galvanometer, 4, 11 
 coupling of, 141 
 horizontal, 142 
 
 indications made by the, 144-147 
 vertical, 142 
 Galvanoplastic baths, agitation of, 
 560-564 
 anodes for, 564, 
 
 565 
 deposition by battery and 
 dynamo, 545-571 
 duration of, 558, 559 
 dynamos for, 547-551 
 in the cell apparatus, 540- 
 
 545 
 with a separate source of cur- 
 rent, copper baths for, 
 
 55?~554 
 method for originals in high re- 
 lief, 620 
 operation, combined, with dy- 
 namo and accumulator, 
 55 1,. 552 
 process, discovery of, 4, 5 
 reproduction for graphic pur- 
 poses, 539-610 
 of plastic objects, 611-622 
 Galvanoplasty, 537-640 
 
 chemicals used in, 641-666 
 
 definition of, 537 
 
 for graphic purposes, operations 
 
 in, 574-622 
 in copper, 538-629 
 iron, 629-633 
 nickel, 633-639 
 silver and gold, 639, 640 
 incrusting, 624-626 
 rapid, 565-568 
 
 baths for, 567, 568 
 special applications of, 622-629 
 Galvanoscope, 4, 11, 12 
 Gas-carbon anodes, 209 
 Gauduin's copper bath, 330 
 Gauze, metallic, gilding of. 424-426 
 Gelatine moulds, 620-622 
 German form of cell apparatus, 542, 
 
 .543 
 silver, cleansing of, 232 
 deposit of, 310, 31 1 
 pickling of, 223 
 sheets, brushing of, 204 
 silver-plating of, 392 
 Gilded articles, giving a beautiful, 
 rich appearance to, 423 
 
 Gilder's wax, 422, 423 
 Gilding baths, 498, 499 
 by contact, 497, 498 
 
 immersion and friction, 
 497-500 
 friction or with the rag, thumb 
 
 or cork, 498-500 
 immersion, 498 
 carbon anodes for, 412 
 coloring of, 422, 423 
 genuine, determination of, 428 
 green, 420 
 
 improving bad tones of, 424 
 inner surfaces of hollow ware, 
 
 416, 417 
 matt, 421 
 
 metallic wire and gauze, 424-426 
 platinum anodes for, 410 
 preparation of articles for, 415, 
 
 416 
 red, 418, 419 
 reddish, 499 
 rose-color, 420 
 spurious, 5:5 
 steel anodes for, 410-412 
 without battery, 415 
 Girders, wrought-iron, zincking of, 
 
 457 
 Glass, galvanoplastic decorations on, 
 
 627, 628 
 Glauber's salt, 658 
 Glycerin, substitution of, for water, 
 
 250 
 Goblet scratch brush, 187 
 Gold anodes, 410-413 
 baths, 405-409 
 
 examination of, 428, 429 
 management of, 410-413 
 recovery of gold from, 429, 
 
 430 
 tanks for, 413, 414 
 chloride, 651 
 
 cyanide combinations of, 5 
 determination of, 428, 429 
 deposition of, 404-430 
 deposits, coloring of, 412, 413 
 polishing of, 218, 219, 418 
 expression of fineness of, 404 
 galvanoplasty in, 639, 640 
 incrustations with, 394 
 -plating, execution of, 415-418 
 properties of, 404 
 scratch brushes for, 216 
 stripping of, from gilded articles, 
 427 
 Graining, 494-497 
 
 preparation used in, 495 
 Gramme-equivalent, 59 
 
686 
 
 INDEX. 
 
 Gramme's machine, 7 
 Graphic purposes, galvanoplastic re- 
 productions for, 539- 
 610 
 operations in galvano- 
 plasty for, 574-622 
 Graphite, first use of, 5 
 Grasses, galvanoplastic deposit of 
 
 copper on, 626 
 Grease, removal of, and cleansing, 
 
 228-233 
 Green gilding, 420 
 
 vitriol, 659 
 Grille work, lacquer for, 525 
 Grinding, 196-198 
 
 and brushing, execution of, 202- 
 205 _ 
 polishing rooms, 125, 126 
 flexible shaft for, 212-214 
 lathes, 200-202 
 motors, 201, 202 
 wheels, 196-198 
 
 treatment of, 198-200 
 Group coupling, 89 
 Grove cell, 73 
 
 Giilcher's thermo-electric pile, 93, 94 
 Gun-barrels, browning of. 518 
 
 coating of, with lead per- 
 oxide, 461 
 -metal. 343 
 Gutta-percha, introduction of, 5 
 moulding in, 575 
 
 with, 613 
 moulds, detaching the de- 
 posit or shell from, 
 
 593 
 electrical contact for, 
 
 59°. 59 1 
 
 HALOID acids, 40 
 Hand-anode, 279 
 Hanson & Van Winkle Co., elliptic 
 anodes, pat- 
 ented by, 266- 
 268 
 
 mechanical 
 electro-plating 
 apparatus pat- 
 ented by, 291, 
 292 
 
 plan of a plating 
 room fitted up 
 by, 1S0, 181 
 
 polishing and 
 buffing lathes, 
 manufactured 
 by, 209-2 n 
 
 Hanson & Van Winkle Co., polish- 
 ing wheels man- 
 ufactured by, 
 206-208 
 rheostats manu- 
 factured by, 
 
 143. 144 
 types of dyna- 
 mos con- 
 structed by, 
 109, no 
 types of motor- 
 generators 
 constructed 
 by, in, 112 
 voltmeter man- 
 ufactured by, 
 149, 150 
 Hard nickeling, 307, 308 
 Hauck's thermo-electric pile, 93 
 Heating of plating rooms, 123, 124 
 HefnerAteneck's machine, 7 
 Heliography, 607, 60S 
 Helios dip lacquer, 526 
 Hittorf's investigations, 67 
 Hooks and eyes, silvering of, 492, 493 
 Horizontal galvanometer, 142 
 Hossauer's copper bath, 323 
 Hiibl, investigations by, 538, 539 
 Hydraulic press, 579 
 Hydrochlorate of zinc, 649 
 Hydrochloric acid, 642 
 
 dilute, electrolysis of, 
 
 54 
 removal of, from the 
 pores of copper 
 deposits, 334 
 Hydrocyauate of silver, 655 
 
 zinc, 654, 655 
 Hydrocyanic acid, 642, b43 
 
 poisoning by, 534, 535 
 Hydro electric current, 30 
 Hydrofluoric acid, 644, 645 
 Hydrogen-gas, 46, 47 
 
 -ion, 46, 47 
 Hydrometer degrees according to 
 Baume, and their weights by vol- 
 ume, 675 
 Hydroplatinic chloride, 651 
 Hydrosulphate of ammonium, 647 
 Hydrosulphuric acid, 646 
 Hydroxy 1 groups, 40 
 Hygienic rules for the workshop, 
 
 533-536 
 Hypomtrie gas, poisoning by, 536 
 
 TDIOELECTRICS, 28 
 
 I Imperial fluid measure, 668 
 
INDEX. 
 
 687 
 
 Inconstant cells, 68 
 
 Incrustations with silver, gold and 
 
 other metals, 394 
 Incrusting galvanoplasty, 624-626 
 Induced current, hand-rule for the 
 direction of, 18 
 law followed by, 18 
 or induction current, 16 
 Inducing current, 16 
 Induction, 15-18 
 
 electric, discovery of, 4 
 Inductor, 98-102 
 Inlaying of depressions of coppered 
 
 art-castings, 336, 337 
 Installation with accumulators, 182- 
 
 185 
 cells, 135-165 
 dynamo-electric ma- 
 chines, 165-185 
 Ions, 46, 47 
 
 migration of, 51 
 transport values of, 67 
 velocity of, 66, 67 
 Iridescent colors, 461-463 
 
 first production of, 4 
 Iron-ammonium sulphate, 659 
 
 badly rusted, cleaning of, 220 
 bath for bronzing, 357 
 
 coppering of, by immer- 
 sion. 485 
 baths, 464, 465 
 
 management of, 465, 466 
 black on, 518-520 
 blue on, 520 
 brass baths for, 346, 348 
 brown-black coating on, 520 
 castings, unground, brassing of, 
 
 354- 355 
 cleansing of, 232 
 coatingof, with leadperoxide,46i 
 coloring of, 518-520 
 copper baths for, 323, 324 
 deposition of, 464-466 
 electrotypes, 629, 630 
 galvanoplasty in, 629-633 
 grinding of, 204 
 nickel bath for, 258, 259 
 pickle for, 220 
 pickling of, 220 
 sheet, coppering of, 335 
 nickeling of. 302, 303 
 zinckiug of, 455, 456 
 silver-plating of, 393 
 silvering bath for, 489 
 silvery color on, 520 
 tinning solution for, 501, 502 
 treatment of, in the tumbling 
 
 barrel, 195 
 
 Iron wire and plates, weight of, 
 674 
 
 [ACOBY, Prof., discovery of the 
 J galvanoplastic process by, 4, 5 
 Jordan, C. J., claim of, 5 
 Joule's law, 27, 28 
 
 KATHIONS, 46 
 Keiser & Schmidt's plunge bat- 
 tery, 84 
 Kirchhoff's law, 26, 27 
 Knife blades, nickeling of, 305, 306 
 Knight's black-leading process, 590 
 process of coppering matrices, 
 
 569 
 
 Knives, calculating the time for de- 
 positing a determined weight ot 
 silver on, 129-131 
 
 Kristalline, 523, 524 
 
 LACES, galvanoplastic deposit of 
 copper on, 626 
 Lacquer, application of, 521 
 
 for grille work, 525 
 
 making, development in, 522, 523. 
 
 satin finish, 525 
 Lacquering, 521-532 
 Lacquers, dead black, 526-528 
 
 spraying of, 528-530 
 
 water-dip, and their use, 530-532 
 Lamp feet, nickeling of, 286 
 Langbein & Co.'s plunge battery, 86, 
 
 87 
 types of dynamos 
 constructed by, 98,. 
 105-107 
 Lathe goblet scratch-brush, 187 
 Lathes, grinding, 200-202 
 
 polishing, 209-211 
 Law of Joule, 27, 28 
 
 Kirchhoff, 26, 27 
 Ohm, 4, 22-24 
 Laws of Faradav, 56-59 
 Lead acetate, 665 
 
 and tin alloys, soft, nickeling of,. 
 
 3°^, 307 
 baths, 461 
 cleansing of, 232 
 deposition of, 461-464 
 -lined tanks, 158, 159 
 properties of, 461 
 salts, poisoning by, 535 
 Leather, plates for the production of 
 
 imitations, 623, 624 
 Leaves, galvanoplastic deposit of cop- 
 per on, 616 
 Leclanche cell, 80 
 
688 
 
 INDEX. 
 
 Leiruan Bros., sand-blast designed 
 by, 192, 193 
 
 Lenoir's process, 620 
 
 Liebenow's theory of chemical pro- 
 cesses in the accumulator, 118, 119 
 
 Light in plating-rooms, 121 
 
 Line, neutral, 10 
 
 Liver of sulphur, 646, 647 
 
 Loadstone, 9 
 
 Liidersdoiff's solution for coppering 
 by contact, 484 
 
 Lunar caustic, 663 
 
 Luster, high, production of, 218, 219 
 
 MACHINES, distance between, 126 
 Magnaliutn, addition of, to 
 zinc baths, 449 
 Magnesium, addition of, to zinc baths, 
 
 447 
 Magnet winding, 97 
 Magnetic field, 11, 13 
 
 induction, magnitude of, 14 
 iron ore, 9 
 lines of force, 13, 14 
 meridian, 10 
 
 needle, discover}- of the deflec- 
 tion of, 3 
 poles, 9 
 Magnetism, 9-1 1 
 
 and electricity, 9-67 
 remanent, 98 
 Magneto-electrical machines, early 
 
 use of, 7 
 Magnets, 9 
 
 Magnitude of magnetic induction, 14 
 Main conductors, 155, 156 
 
 and branch conductors, 
 
 connection of, 156, 157 
 
 current, 16 
 
 wire, 26 
 
 Mannesman Pipe Works, production 
 
 of deposits upon aluminium by, 
 
 473. 474 
 Marble, 656, 657 
 Marino's patent, 250 
 Matrices, coppering of, 569 
 
 in plastic material, preparation 
 
 of, 574-578 
 metal, 580-587 
 
 detaching the deposit or 
 shell from, 394 
 nickel, 636-639 
 Matt-dipping, 224-226 
 -gilding, 421 
 silver, 391 
 Matting, 224-226 
 
 by chemical or electro-chemical 
 means, 421, 422 
 
 Measure, imperial fluid, 668 
 Measures and weights, table for the 
 inter-conversion of certain stand- 
 ards, 669, 670 
 Measuring instruments, 147-150 
 Mechanical electro plating apparatus, 
 290-293 
 treatment during and after elec- 
 tro-plating, 215-220 
 previous to electro-plating, 
 186-215 
 work, 53 
 Meidinger cell, 72, 73 
 Mercuric nitrate, 663 
 Mercurous nitrate, 662 
 Mercury salts, poisoning by, 535 
 
 vessels of thermometers, galvan- 
 oplastic deposit of copper on, 
 b27 
 Meridian, magnetic, 10 
 Metal matrices, 580-587 
 
 detaching the deposit or 
 shell from, 594 
 regaining of, from dipping baths, 
 
 227, 228 
 table of content of, in metallic 
 salts, 672 
 Metallic moulds, 613 
 
 objects, preparation of, 186-245 
 salts, table of content of metai 
 
 in, 672 
 surfaces, copper deposits from, 
 
 597-599 
 Metallization by dry way, 617 
 by metallic powders, 617 
 wet way, 617-620 
 Matalloids, 38, 39 
 Metallo-chromes, 461-463 
 Metallometric balance, 380-383 
 Metals, 38, 39 
 
 coloring, patinizing, oxidizing, 
 
 etc., of, 504-531 
 deposition of several, from a com- 
 mon solution, 353 
 early reduction of, 1 
 incrustations with, 394 
 patina for the protection of, 518 
 series of electro-motive force of, 
 
 30 
 
 solution-pressure of, 60, 61 
 
 specific resistance of, 25 
 Mirrors, coppering of, 627 
 Mixed coupling, 89 
 Moire metallique, 439 
 Molecular conductivity, 50 
 
 weight of dissolved bodies, 
 method of determining, 49, 50 
 Molecule, 33 
 
INDEX. 
 
 689 
 
 Molecules, Ampere's theory of, 10 
 
 dissociation of, 49 
 Monopotassic carbonate, 656 
 Montgomery, Dr., introduction of 
 
 gutta-percha by, 5 
 Motor-generators, 111, 112 
 Motors, grinding, 201, 202 
 Mould-holder, 591 
 
 making the, conductive, 588-590 
 Moulding in gutta-percha, 575 
 in plaster of Paris, 614, 615 
 
 wax, 575-578 
 with gutta-percha, 613 
 metallic alloys, 613 
 oil gutta-percha, 612, 613 
 Moulds, detaching the deposit or 
 shell from, 593, 594 
 electrical contact for, 591-593 
 further manipulation of, 587 
 gelatine, 620-622 
 in plastic material, preparation 
 
 of, 574-578 
 metallic, 613 
 plaster of Paris, 614 
 rendering the, conductive, 617- 
 
 620 
 suspending the, in the bath, 592, 
 
 593 
 Multipliers, 11 
 Muriate of gold, 651 
 
 of zinc, 649 
 Muriatic acid, 642 
 Murray, discovery by, 5 
 
 ^] AILS, zincking of, 459, 460 
 i Nature printing, 622 
 Needles' eyes, coppering of, 487 
 Nees, Prof., process for depositions 
 
 upon aluminium by, 472, 473 
 Negative electricity, 29 
 
 electrode, 46 
 Nernst, osmotic theory of the pro- 
 duction of the current according 
 to, 61-64 
 Neubeck's investigations, 625 
 .Neutral base, 41 
 
 line or zone, 10 
 salts, 33 
 zone, 10, 100 
 Neutralization, 41 
 
 Nicholson and Carlisle, decomposi- 
 tion of water by, 3 
 Nickel alloys, deposition of, 310, 311 
 -ammonium sulphate, 660 
 and cobalt, deposition of, 246-320 
 anodes, 265-272 
 cast, 270, 271 
 faulty arrangement of, 278 
 
 44 
 
 Nickel anodes, reddish tinge on, 271, 
 272 
 
 rolled, 271 
 bath, normal current-density for 
 
 a, 127, 128 
 polarization in the, 281 
 without nickel salt, 261, 262 
 baths, additions to, 248-250 
 
 cold, thick deposits in, 264, 
 
 265 
 correction of the reaction of, 
 
 262 
 effect of current- density on, 
 
 251 
 electro-motive force for, 251 
 examination of, 311-318 
 formulas for, 252-260 
 heating of, 124 
 hot, thick deposits in, 263, 
 
 264 
 old, recovery of nickel from, 
 
 309 
 proportion of cast to rolled 
 
 anodes for, 270, 271 
 reaction of, 251 
 refreshing, 286 
 wooden tanks for, 157, 158 
 -bronze, 310 
 carbonate, 657 
 chloride, 650 
 -copper-zinc alloy, deposit of, 
 
 310,311 
 deposition of, 246-318 
 deposits, contrivances for the 
 prevention of, rolling off, 
 635, 636 
 polishing of, 218, 286, 287 
 test for sufficiently heavy, 
 
 278 
 very thick, bath for, 260 
 electrotypes, 637-639 
 
 bath for production of, 634 
 galvanoplasty in, 633-639 
 matrices, 636-639 
 normal deposition of, 276 
 properties of, 246, 247 
 salts, 247, 248 
 prepared, 262 
 solution of, 240, 241 
 scratch brushes for, 215 
 sulphate, 660 
 various colors on, 510 
 very thick deposits of, 277 
 Nickeled objects, freeing of, from 
 moisture, 217, 218 
 polished, cleansing of, 
 287 
 zinc sheet, iridescent, 463, 464 
 
690 
 
 INDEX. 
 
 Nickeling, aluminium contact for, 
 482 
 
 by contact and boiling, 479-483 
 
 cavities and profiled objects, 278- 
 281 
 
 copper sheets, 301, 302 
 
 defective, resume of, 284-286 
 stripping of, 282-284 
 
 bard, 307, 308 
 
 knife blades, 305, 306 
 
 lamp-feet, 280 
 
 most suitable current-density for, 
 276-278 
 
 operation, calculation of the, 287, 
 288 
 
 printing plates, 307-309 
 
 process of, 272, 273 
 
 quick, 263, 264 
 
 security against rust in, 273-275 
 
 sheet-iron, 302, 303 
 
 sheet-steel, 302, 303 
 
 small aud cheap objects in large 
 quantities, 288-293 
 
 solid, 277 
 
 surgical instruments, 305, 306 
 
 tin-plate, 301 
 
 treatment of articles after, 2S6, 
 287 
 
 wire, 303-305 
 
 yellowish tone of, 283, 284 
 
 zinc sheet, 293-301 
 Niel, imitation of, 394, 395 
 Niello, Corvin's, 623 
 Nitrate of mercury, 663 
 Nitrates, 662, 663 
 Nitre, 662 
 Nitric acid, 642 
 Nitrous gas, poisoning by, 536 
 Nobili, production of iridescent colors 
 
 by, 4 
 Nobili's rings, 461-463 
 Noe's thermo-electric pile, 90, 91 
 Nomenclature of salts, 44, 45 
 Non conductors, 45 
 
 -electrics, 28 
 
 -metals, 38, 39 
 North pole, 10 
 
 Numerical data, useful, table of, 668 
 Nuts, zincking of, 459, 460 
 
 OAK grinding wheels, 196, 197 
 sawdust, 217 
 Objects, arrangement of, in the 
 bath, 160-163 
 chemical treatment of, 220-233 
 metallic, preparation of, 1S6-245 
 Oersted, Prof., discoveries of, 3, 4 
 Ohm, law of, 4, 22-24 
 
 Oil gutta-percha, moulding with, 612,. 
 
 613 
 preparation of, 612 
 of vitriol, 641, 642 
 Organic acids, salts of, 664-666 
 Orpiment, 647 
 Osmotic pressure, 48, 49 
 
 theory of the production of the 
 current, 61-64 
 Oswald's designation of a galvanic 
 
 battery, 63 
 Over-nickeling, 275 
 Oxidized silver, 396, 397 
 Oxy acids, 40 
 Oxygen, 32 
 
 OACINOTTI'S ring, invention of, 
 
 Painter's gold, 405 
 Palladium baths, 437, 438 
 
 deposition of, 437, 438 
 
 properties of, 437 
 Paracelsus, 1 
 
 Paracyanide, formation of, on cop- 
 per anodes, 331 
 Parallel coupling, 89 
 Parke's process of metallization, 61S,. 
 
 619 
 Paste-board grinding wheels, 197 
 Patina, artificial, 508, 509 
 
 definition of, 504 
 
 for the protection of metals, 518 
 
 genuine green, imitation of, 509 
 Permeability, 14 
 Pfanbauser's voltametric balance, 
 
 383, 384 
 Phosphates and pyrophosphates, 663, 
 
 664 
 Photo-engraving, 602-604 
 
 -galvanography, 603, 604 
 Pickle, preliminary, 223 
 Pickling and dipping, 220-228 
 duration of, ,222 223 
 vat, 163 
 Pile of Volta, 2 
 Pins, nickeling of, 288 
 
 tinning solution for, 502 
 silvering of, 492, 493 
 Pipes, zincking of, 456, 457 
 Pixii, first electro-magnetic induction 
 
 machine constructed by, 4 
 Planing machines, 595, 596 
 Planters accumulator, 112 
 Plaster of Paris moulds, 614 
 
 rendering im- 
 pervious, 615- 
 617 
 Plated objects, drying of, 217, 218 
 
INDEX. 
 
 691 
 
 Platinic chloride, 651 
 Platinizing by contact, 500 
 Plating baths, heating of, 123, 124 
 rooms, floors of, 124, 125 
 heating of, 123, 124 
 light in, 122 
 
 renewal of water in, 124 
 size of, 125 
 
 ventilation in, 122, 123 
 Platinum anodes for gilding, 410 
 baths, 431-435 
 
 management of, 435, 436 
 deposition of, 431-437 
 deposits, polishing of, 218, 219 
 -plating, execution of, 436, 437 
 properties of, 431 
 recovery of, 437 
 Plunge batteries, 83-87 
 Poisoning by chemicals, 534-536 
 Polarity of current, recognition of, 
 
 146, 147 
 Polarization, 64-66, 281, 282 
 -current, 65 
 electro motive counter-force of, 
 
 133-135 
 
 magnitude of, 133, 134 
 Poles, attraction and repulsion of, 10 
 
 magnetic, 9 
 Polished objects, cleansing of, 219, 
 
 220 
 Polishing, 205-214 
 
 and grinding rooms, 125, 136 
 
 flexible shaft for, 212-214 
 
 in the tumbling barrel, 194-196 
 
 lathes, 209-211 
 
 machines for zinc sheet, 296, 297 
 
 materials, 214, 215 
 Porcelain, galvanoplastic decora- 
 tions on, 627, 628 
 Positive electricity, 29 
 
 electrode, 46 
 Potash, 655, 656 
 
 -alum, 658 
 
 bicarbonate of, 656 
 
 caustic, 645 
 Potassium-aluminium sulphate, 658 
 
 amalgam, 4 
 
 bitartrate, 664 
 
 carbonate, 655, 656 
 
 determination of, 399, 400 
 
 cyanide, 652-654 
 
 determination of, 338, 339, 
 
 355, 356 
 
 first use of solutions of me- 
 tallic cyanides in, 5 
 
 poisoning by, 534, 535 
 
 purity of, 234 
 
 use of, for pickling, 224 
 
 Potassium, discovery of, 3 
 
 disulphate solution, electrolysis 
 
 of a, 53, 54 
 ferro-cyanide, 655 
 hydrate, 645 
 nitrate, 662 
 
 -sodium tartrate, 664, 665 
 sulphide, 646, 647 
 Potential, 29 
 
 difference of, 21, 29 
 Preece's test, 445 
 Presses, 578-5S0 
 
 Prime & Son, perfection of the depo- 
 sition of metals by, 6, 7 
 Primary current, t6 
 Printing-plates, nickeling of, 307-309 
 Proctor, C. H., on electro chemical 
 cleaning baths and their applica- 
 tion, 230, 231 
 Protosulphace of iron, 659 
 Prussiate of potash, white, 652-654 
 yellow, 655 
 of silver, 655 
 zinc, 654, 655 
 Prussic acid, 642, 643 
 
 poisoning by, 534, 535 
 Pump pistons, galvanoplastic copper- 
 ing of, 628 
 Pyridine, addition of, to zinc baths, 
 
 45o 
 Pyrophosphates and phosphates, 663, 
 
 664 
 Pyroxyline lacquer, 523, 524 
 
 QUADRIVALENT elements, 37 
 Quick lime, 646 
 Ouicking articles to be silver-plated, 
 376 
 
 RAOUDT'S method of determining 
 the molecular weights of dis- 
 solved bodies, 49, 50 
 Ratsbane, 644 
 Reagent papers, 41 
 Reaumur, Centigrade and Fahren- 
 heit thermometers, comparison of 
 the scales of, and rules for convert- 
 ing one scale into another, 675, 676 
 Recovery of gold from gold baths, 
 429, 430 
 of nickel from old baths, 309 
 platinum from platinum solu- 
 tions, 437 
 silver from old silver baths, 
 402, 403 
 Red brass, 343 
 
 gilding, 418, 419 
 sulphide of antimony, 647 
 
692 
 
 INDEX. 
 
 Reddish gilding, 499 
 Reform wheel, 197, 198 
 Remanent magnetism, 98 
 Reprinting, process of transferring 
 
 by, 605 
 Reproduction, 537-641 
 Resinous electricity, 29 
 Resist, 497 
 Resistance board, 138-140 
 
 coupling of, 140, 141 
 electric, 21 
 
 unit of, 21 
 
 specific, 24, 25 
 
 Rheostat, 138-140 
 
 Patent Underwriters, 143 
 special, 143, 144 
 Rieder's process of electro-engraving, 
 
 608-610 
 Ring armature, 98-100 
 Rings, plating of, with red gold, 419, 
 420 
 scratched, smoothing and polish- 
 ing of, 427 
 Rinsing and cleansing apparatus, 
 
 163-165 
 Rivets, nickeling of, 288 
 zincking of, 459, 460 
 Rochelle salt, 664, 665 
 Rock salt, 648 
 Rods, conducting, 159, t6o 
 Rose-color gilding, 420 
 Rouge, 214 
 
 Ruolz, first deposition of metallic 
 alloys by, 6 
 
 OAIv AMMONIAC, 648 
 O Salt, common, 648 
 Saltpetre, 662 
 Salts, 40-45 
 
 acid, 44 
 
 formation of, from the acids, 43, 
 
 44 
 
 nomenclature of, 44, 45 
 
 neutral, 45 
 
 of organic acids, 664-666 
 Sand blasts, 190-194 
 Sand, experiments of, 561 
 Sawdust for drying, 217 
 Saw-table, 595 
 Scheele's observations, 5 
 Schuckert machine, 8 
 Scratch-brushes, 187. 215, 216 
 
 -brushing, 187-190, 215-217 
 Screws, zincking of, 459, 460 
 Secondary cells, 1 14—121 
 
 current, 16 
 Seebeck, Prof., discovery of, 90 
 Seignette salt, 664, 665 
 
 Self-excitation, 98 
 
 Separate excitation, 98 
 
 Series-wound dynamos, 104 
 
 Shafts, flexible, 212-214 
 
 Shaving machines, 595, 596 
 
 Sheets, large, polishing lathe for, 209 
 
 Shell-gold, 405 
 
 backing the, 595 
 
 detaching the, from the mould, 
 
 593. 594 
 Sherardizing, 449 
 Shunt-wound dynamos, 104, 105 
 Siemens' machine, 7 
 Siemens & Halske machine, 8 
 Silver alloys, deposition of, 373-375 
 anodes, 364-369 
 baths, 360-364 
 
 addition of organic sub- 
 stances to, 370-372 
 agitation of, 369, 370 
 current-density for, 128 
 determination of proper pro- 
 portions of silver and 
 potassium cyanide in, 368, 
 
 369 
 electrolysis of, 56 
 examination of, 398-402 
 old, recovery of silver from, 
 
 402, 403 
 steel sheets as anodes for, 
 
 366, 367 
 thickening of, 368 
 treatment of, 364-369 
 calculating the time for deposit- 
 ing a determined weight of, 
 129-131 
 chloride, 650, 651 
 cyanide, 655 
 
 combinations of, 5 
 deposit, calculation of the weight 
 of, from the current- 
 strength, 390, 391 
 determination of weight of, 
 
 .378-39° 
 deposition of, 359-403 
 deposits, polishing of, 218, 219, 
 
 39', 392 
 determination of, 401, 402 
 extra heavy coating of, 377, 378 
 first magnetic machine for the 
 
 deposition of, 7 
 galvanoplasty in, 639, 640 
 incrustations with, 394 
 matt, 391 
 nitrate, 663 
 
 -plating, bright, 371, 372 
 by weight, 375-392 
 determination of, 398 
 
INDEX. 
 
 693 
 
 Silver-plating, execution of, 375-393 
 preparation of objects for, 
 . 375, 376 
 oxidized, 396, 397 
 properties of, 359 
 recovery of, from old silver baths, 
 
 402, 403 
 scratch brushes for, 216 
 Silvered articles, stripping of, 397, 398 
 
 yellow color on, 397 
 Silvering, antique, 395, 396 
 baths, 488-490 
 by contact, 488, 489 
 
 immersion and friction, 
 488-497 
 immersion, 489-493 
 cold, with paste, 493, 494 
 nielled, imitation of, 394, 395 
 yellow tone of, 372, 373 
 Silverite anodes, 268 
 Similor, 343 
 Sine galvanometer, 12 
 Size of plating rooms, 125 
 Slinging wires, 162 
 Slotted armature, 102 
 Smee cell, 70, 71 
 Smee, discoveries by, 6 
 Soda, caustic, 645 
 Sodium amalgam, 4 
 bicarbonate, 656 
 bisulphite, 66 1 
 carbonate, 656 
 chloride, 648 
 citrate, 666 
 discovery of, 3 
 hydrate, 645 
 
 hydroxide, electrolysis of, 54 
 nitrate, 662 
 phosphate, 663, 664 
 pyrophosphate, 664 
 sulphate, 658 
 
 sulphite, preparation of, 491, 492 
 purity of, 234 
 Solder, hard, removal of, from bi- 
 cycle frames, 221, 222 
 Solubilities of chemical compounds, 
 
 table of, 670, 671 
 Solution-pressure of metals, 60, 61 
 Solutions, decomposition-values of,66 
 
 theory of, 47, 48 
 Solvents, 233 
 South pole, 10 
 Spaeth's machine for gilding wire 
 
 and gauze, 425, 426 
 Specific resistances, 24, 25 
 Spencer, T., claim of, 5 
 Spirit of hartshorn, 645, 646 
 nitre, 642 
 
 Spoons, calculating the time for de- 
 positing a determined weight 
 of silver on, 129-131 
 extra heavy coating of silver on, 
 
 377, 378 
 Spraying lacquers, 528-530 
 Stannic chloride, 649 
 Stannous chloride, 649 
 Steel anodes for gilding, 410-412 
 baths, 464, 465 
 brass bath for, 348 
 cleansing of, 232 
 coating of, with lead peroxide, 
 
 461 
 copper baths for, 323, 324 
 galvauoplasty in, 629-633 
 gold bath for, 409 
 grinding of, 204 
 
 gun barrels, galvanoplastic cop- 
 pering of, 629 
 nickeling of, by contact, 481 
 pens, coppering of, 487 
 plates, etching of, 606, 607 
 rolls, galvanoplastic coppering 
 
 of, 628 
 sheets, nickeling of, 302, 303 
 
 use of, as anodes for silver 
 baths, 366, 367 
 silvering bath for, 489 
 silver-plating of, 393 
 tapes, zincking of, 457-459 
 tinning solution for, 501, 502 
 treatment of, in the tumbling 
 barrel, 195 
 Steeling, 464-466 
 
 execution of, 466 
 Stereotypes, coppering of, 599 
 
 nickeling of, 307-309 
 Stirring contrivances, 561, 562 
 Stockmeier's copper bath, 325 
 Stoehrer's plunge battery, 85, 86 
 Stolba's method of tinning, 502, 503 
 process of nickeling by contact, 
 479-481 
 Stoneware objects, galvanoplastic de- 
 posit of copper on, 626, 627 
 Stopping-off, 393 
 
 Stripping defective nickeling, 282- 
 284 
 gold from gilded articles, 427 
 silvered articles, 397, 398 
 Sugar of lead, 665 
 Sulphate of iron, 659 
 Sulphates and sulphites, 658-662 
 Sulphur combinations, 646-648 
 Sulphuretted hydrogen, 646 
 
 poisoning by, 535, 
 536 r: 
 
694 
 
 INDEX. 
 
 Sulphuric acid, 641, 642 
 
 free, determination of, 
 
 Sulphurous acid, poisoning by, 536 
 
 Sulphydrate of ammonium, 647 
 
 Sulphydric acid, 646 
 
 Surgical instruments, galvanoplastic 
 deposit of copper on 
 wooden handles of, 
 626 
 nickeling of, 305, 306 
 
 Swiss matt, 520 
 
 Switchboards, i8r, 182 
 
 Symbols, 33, 34 
 
 Synthetic chemical process, 32 
 
 TABLE for freeing objects from 
 grease, 164, 165 
 Table for inter-conversion of certain 
 standard weights and meas- 
 ures, 669, 670 
 of chemical elements with their 
 symbols and atomic weights, 
 
 33. 34 
 content of metal in metallic 
 
 salts, 672 
 electrical resistance of pure 
 
 copper wire, 673 
 electro-chemical equivalents, 
 
 59, 60 
 hydrometer degrees according 
 to Baume and their weights 
 by volume, 675 
 resistance and conductivity of 
 pure copper at different tem- 
 peratures, 673 
 solubilities of chemical com 
 pounds commonly used in 
 electro-technics, 670, 671 
 useful numerical data, 668 
 weight of iron, copper, and 
 brass wire and plates, 674 
 Tacks, zincking of, 459, 460 
 Tampico brush, 203 
 Tangent galvanometer, 12 
 Tank, to find the number of gallons 
 
 a, will hold, 667 
 Tanks, 157-159 
 
 for copper cyanide baths, 330 
 galvanoplastic baths, 565 
 gold baths, 413, 414 
 sheet zinc, 299 
 silver baths, 364 
 zinc baths, 454 
 Tartar emetic, 665 
 Tea sets, galvanoplastic decorations 
 
 on, 627, 628 
 Temperature, coefficient of, 25, 26 
 
 Terchloride of gold, 651 
 
 Terra-cotta objects, galvanoplastic 
 
 deposit of copper on, 626, 627 
 Thermo-electric couple, 90 
 piles, 90-95 
 -electricity, 90 
 Thermometers, comparison of the 
 scales of, and rules for converting 
 one scale into another, 675, 676 
 Tin baths, 439-441 
 
 management of, 441 
 chloride, 649 
 coloring of, 521 
 dark coloration on, 521 
 deposition of, 439-442 
 -plate, nickeling of, 301 
 -plating, process of, 441, 442 
 properties of, 439 
 salt, 649 
 
 sepia brown on, 521 
 silver plating of, 392 
 Tinning by boiling, 502, 503 
 contact, 500, 501 
 
 and by boiling, 500- 
 
 5°3 
 zinc contact, 500 
 Tissues, galvanoplastic deposit of 
 
 copper on, 626 
 Toggle press, 578, 579 
 Tombac, 343 
 bath, 357 
 cleansing of, 232 
 deposition of, 357 
 pickling of. 223 
 spurious gilding of, 515 
 Touchstone, estimating the fineness 
 
 of gold by, 404, 405' 
 Transmission, 126, 127 
 Triplex buff, 205, 206 
 Tripoli, 214 
 
 Trivalent and quinquivalent ele- 
 ments, 37 
 elements, 37 
 Trough battery, 69 
 Troy weight, 667 
 Tumblers, galvanoplastic decorations 
 
 on, 627, 628 
 Tumbling barrel or drum, 194-196 
 Two-polar dynamo, 98 
 Type-matrices, preparation of, 599, 
 600 
 treatment of very deep forms of, 
 
 59 2 
 
 UMBRELLA handles, galvanoplas- 
 tic decoration on, 628 
 Union canvas wheel, 206, 207 
 Univalent elements, 37 
 
INDEX. 
 
 695 
 
 \7AP0RS, acid, absorbing plant for, 
 226, 227 
 Varnish, stopping off, 393 
 Vases, reproduction of, 611, 612 
 Ventilation in plating rooms, 122, 
 
 123 
 Verdigris, 665 
 Vertical galvanometer, 142 
 Vessels, content of, 667 
 Victoria white polish, 218 
 Vienna lime, 199, 214 
 Vitreous electricity, 29 
 Volt, 20 
 
 Volt-ampere, 21 
 Volta, discovery by, 2, 3 
 Voltaic cell, 30, 68, 69 
 
 pile, 2 
 Voltameter, copper, 383, 384 
 Voltametric balance, 383, 384 
 
 controlling apparatus, 3S7-390 
 Voltmeter switch, 150, T51 
 Voltmeters, 148, 149 
 Volumetric analysis, 313, 314 
 
 determination of copper, 341- 
 
 343, 572, 573 
 of zinc, 356, 357 
 
 WAHL, Dr. W. H., directions by, 
 for preparing platinum baths, 
 
 433-435 
 Walenn's copper bath, 330 
 Walnut grinding wheels, 196, 197 
 Walrine wheel, 207, 208 
 Warren's cobalt solution, 319, 320 
 Washing soda, 656 
 Watch cases, matt black coating on, 
 520 
 chains, plating of, with red gold, 
 
 419, 420 
 -movements, palladium bath for, 
 
 438 
 
 -works, brush for gilding, 190 
 Watches, graining parts of, 494, 495 
 Water, 233 
 
 decomposition of, 3 
 
 -dip lacquers and their use, 530- 
 
 53 2 , . 
 
 renewal of, in plating rooms, 
 
 124 
 substitution of glycerine for, 250 
 Watt, 21 
 
 Wax-melting kettles, 576 
 moulding in, 575~57 8 
 moulds, detaching the deposit or 
 shell from, 593, 594 
 electrical contact for, 591 
 Weight, avoirdupois, 667 
 troy, 667 
 
 Weights and measures, table for the 
 inter-conversion of certain stand- 
 ard, 669, 670 
 Weil's bath for coppering by contact, 
 484 
 copper bath, 329, 330 
 Weston ammeter, 150 
 
 nickel bath, 254 
 Wheatstone's machine, 7 
 Whip brush, 187 
 White arsenic, 644 
 
 prussiate of potash, 652-654 
 vitriol, 659, 660 
 Wilde machine, 7 
 Wire, gilding of, 424-426 
 main, 26 
 
 nickeling of, 302-305 . 
 zincking of, 457~459 
 Wires, branch, 26 
 Wollaston, discovery by, 3 
 Wood-cuts, acid copper bath for, 568 
 Wooden grinding wheels, 196, 197 
 
 tanks, 157 
 Woolrych, first magnetic machine for 
 
 the deposition of silver by, 7 
 Work, frictional, 52 
 tnechanical, 53 
 Workshop, hygienic rules for the, 
 
 533-536 
 Wright, first use of solutions of me- 
 tallic cyanides in potassium cy- 
 anide by, 5 
 Wrought-iron articles, pickling of, 
 220 
 bath for bronzing, 357 
 brass bath for, 348 
 girders, zincking of, 457 
 
 YBDDOW brass, 343 
 prussiate of potash, 655 
 
 ZAPON, 523, 524 
 Zilken's tinning bath, 501 
 Zinc alloys, deposition of, 460, 461 
 amalgamation of, 69, 70 
 and ammonia, chloride of, 649 
 anodes, 452-454 
 baths, 446-452 
 
 tanks for, 454 
 blue-black coating on, 517 
 brass bath for, 348 
 bronzing on, 518 
 carbonate, 657 
 
 castings, nickel bath for, 258 
 chloride, 649 
 
 qualities of, 234 
 solution, electrolysis of a, 
 65,66 
 
696 
 
 INDEX. 
 
 Zinc, coloring of, 516-518 
 -contact, tinning by, 500 
 coppering of, by immersion, 485 
 cyanide, 654, 655 
 deposition of, 442-461 
 determination of, 356, 357 
 etchings, nickeling of, 309 
 gray coating on, 517, 518 
 
 yellow, brown to black colors 
 on, 517 
 investigations regarding the elec- 
 trolysis of, 448, 449 
 nickel bath for, 257, 258 
 objects, copper baths for, 327, 
 
 328. 329 
 pickling of, 223 
 plates, coppering of, 599 
 
 etching of, 606, 607 
 properties of, 442 
 red-brown shades on, 518 
 scratch brushes for, 215 
 sheet, brassing of, 298, 299 
 coppering of, 299, 335 
 freeing of, from grease, 297 
 nickel bath for, 258 
 nickeling of, 293-301 
 nickeled, iridescent. 463, 464 
 peeling off of the nickel de- 
 posit from, 298, 299 
 polishing of, 205 
 
 machines for, 296, 297 
 preliminary polishing of, 295, 
 
 296 
 tanks for, 299 
 sulphate, 659, 660 
 tin bath for, 440 
 yellow-brown shades on, 518 
 
 Zincking brass, 503 
 by contact, 503 
 copper, 503 
 cords, 457-459 
 execution of, 454-460 
 nails, 459, 460 
 nuts, 459, 460 
 pipes, 456, 457 
 
 preparation of objects for, 454 
 rivets, 459, 460 
 screws, 459, 460 
 sheet-iron, 455, 456 
 steel tapes, 457-459 
 tacks, 459, 460 
 wire, 457-459 
 Zincography, 604, 605 
 Zone, neutral, 10, 100 
 Zozimus, reduction of copper by, 1 
 Zucker & Levett & Loeb Co., mechan- 
 ical electro- 
 plating appara- 
 tus manufac- 
 tured by, 293 
 patented triplex 
 buff manufac- 
 tured by, 205, 
 206 
 silverite anodes 
 man ufactured 
 by, 268 
 types of dynamos 
 constructed by, 
 107-109 
 types of motor- 
 generators con- 
 st rue ted by,. 
 112 
 
The Egyptian Lacquer Manafacturina Co., New York City. 
 
 LACQUERS. 
 
 IN 33 YEARS OF LACQUER EXPERIENCE WE 
 HAVE LEARNED: 
 
 That Lacquer should preserve the inetal finish 
 
 from what is hurtful. 
 That Lacquer should ward off decay in the inetal 
 
 finish and prevent its disease. 
 That a Lacquer good for Silver may be poor for 
 
 Builders' Hardware, Nickel, Bronze, Spelter, 
 
 etc., etc. 
 That a wise manufacturer uses Lacquer made by a 
 
 Lacquer Specialist. 
 
 WE ARE THE ONLY 
 
 Manufacturing Lacquer Specialists. 
 
 THE LATEST SPECIAL LACQUERS INTRO- 
 DUCED BY US ARE : 
 
 EGYPTIAN GAS AND ELECTRIC FIXTURE LAC- 
 QUERS (dip and brush) — the Standard Grades for 
 Fixture Work. 
 
 EGYPTIAN BLACK NICKEL LACQUER 
 
 which increases the depths of the color of the Black 
 Nickel finish and prevents the formation of iridescent 
 discoloration. 
 
 EGYPTIAN WATER DIP LACQUER 
 
 The work while wet — whether plated or acid-dipped — is 
 dipped directly into the Lacquer, ensuring a great saving 
 of time. 
 
 LACQUERS. 
 
The Egyptian Lacquer Manufacturing Co., New York City. 
 
 LA CQUE RS. 
 
 THE LATEST SPECIAL LACQUERS INTRO- 
 DUCED BY US ARE : 
 
 EGYPTIAN" LACQUERS to Produce an imitation Bower 
 Barff Finish. 
 
 EGYPTIAN BLACK LACQUERS for Electrical Apparatus. 
 
 EGYPTIAN LACQUERS LOR SILVER PLATE 
 
 Guaranteed to prevent pink, yellow or reddish tints. 
 Method of lacquering silver plate described in separate 
 article. 
 
 EGYPTIAN BEDSTEAD LACQUER: A close dupli- 
 cate to the Standard English Lacquer. 
 
 EGYPTIAN SPRAYING LACQUERS 
 
 Adapted for use With pneumatic spraying machine or air 
 brush. 
 
 EGYPTIAN BRUSH BRASS GAS FIXTURE LAC- 
 QUER used as a dip Lacquer. 
 
 EGYPTIAN DIP LACQUER FOR ROSE GOLD 
 
 the only Lacquer which will preserve the delicate and 
 supersensitive rose gold tint. 
 
 THE EGYPTIAN LACQUER MANUFACTURING CO., 
 
 GENERAL OFFICES : 
 
 152 FRONT STREET, NEW YORK CITY. 
 
 Orders may also be filled from our Chicago warerooms : 
 No. 176 South Clinton Street, Chicago, 111. 
 
 LACQUERS. 
 
Zucker & Levett & Loeb Co., New York, U. S. A. 
 
 WE MANUFACTURE . • . 
 
 A COMPLETE LINE OF 
 
 ELECTRO-PLATING 
 POLISHING AND GRINDING 
 
 SUPPLIES AND MACHINERY, 
 Likewise 
 
 VARIOUS CLEANING COMPOUNDS 
 
 FOR ALL METALS. 
 
 ESTIMATES FURNISHED ON 
 
 Plating and Polishing Outfits 
 
 For 
 NICKEL, BRASS, COPPER, BRONZE, SILVER, GOLD, ETC. 
 
 Electro=Galvanizing Plants 
 
 FURNISHED FREE OF ROYALTIES. 
 
 SEND FOR CATALOGUE. 
 
 ZUCKER & LEVETT & LOEB CO., 
 
 NEW YORK, U.S. A. 
 
 N. B.— For illustrations and descriptions of some of our Electro-plating Dynamos and other 
 apparatus, see pages 107, 108, 113, 206, and 267 of this work. , 
 
 SEE NEXT PAGE. 
 
Zucker <f- Levett <C Loeb Co., New York, U. S. A. 
 
 We are building- 
 
 GENERATORS 
 
 BOTH STANDARD AND THREE-WIRE SYSTEM 
 
 and have constructed them up to 12,500 amperes at 7 volts, which is the 
 largest low-voltage generator built in this country. We have been 
 specializing in these machines for a number of years, and believe we 
 have perfected one which gives the highest possible efficiency for a low 
 voltage generator. 
 
 TWO-BAR SILVERITE ANODE. 
 
 This makes a light sound anode which can be readily handled and 
 cleaned by a boy, and possesses all the advantages of the wider and 
 heavier four-bar Silverite. The Two-Bar Silverite is made standard 3h 
 inches wide and in various lengths. 
 
 We append herewith a table giving approximate weights of Two Bar 
 Silverite Anodes of different lengths. 
 
 Weight Table for Two Bar Silverite Nickel Anodes. 
 
 31" wide ..... 8 
 
 z\ " ..... 12 
 
 ;u " 14 
 
 3,1 " 16 
 
 3£ " 18 
 
 3£ " 20 
 
 Si " ..... 24 
 
 VICTOR WHITE POLISH. 
 
 Our Victor White Polish is a fine lime composition of our manu- 
 facture produced after long and careful experiment. This article is 
 made in three grades : Grade " K " which is our regular grade ; Grade 
 "N" which is greasy, and Grade "NN" which is very greasy. We 
 claim for our Victor White Polish that it gives the highest possible 
 luster in the shortest possible space of time ; in other words, the greatest 
 efficiency and economy. Each stick is packed in a separate tin can, 
 hermetically sealed, which does away with the danger of slacking, a 
 common fault witli the ordinary Vienna Lime Composition. 
 
 4 
 
 V long . . , 
 
 , . . about 
 
 6 
 
 pounds each 
 
 i a 
 
 u 
 
 9 
 
 <( 
 
 u 
 
 (1 
 
 a 
 
 10 
 
 (< 
 
 u 
 
 ; " . . . 
 
 u 
 
 11 
 
 a 
 
 a 
 
 I " . . . 
 
 <( 
 
 12 
 
 (( 
 
 a 
 
 i " . . . 
 
 it 
 
 14 
 
 11 
 
 u 
 
 [ " .-. . 
 
 it 
 
 17 
 
 u 
 
 u 
 
The Hanson & Van Winkle Co., Newark, N. J., IT. S. A. 
 MULTIPOLAR TYPE DYNAMOS. 
 
 We are prepared to 
 furnish this type dy- 
 namo in sizes ranging 
 from 800 to 6,000 am- 
 peres, either shunt or 
 compound wound, or 
 with fields wound for 
 separate excitation. We 
 can absolutely recom- 
 mend this type machine 
 as being the most com- 
 plete plating dynamo on 
 the market. 
 
 We can supply low-voltage dynamos direct connected to a motor of suitable size, the 
 whole outfit mounted on a substantial iron sub-base. Motors can be furnished in any volt- 
 age to suit conditions. 
 
 THE HANSON & VAN WINKLE CO., 
 
 NEWARK, N. J., U. S. A. CHICAGO, ILL., 
 
 219 Market St. 28 S. Canal St. 
 
The Hanson <('• Vein Winkle Co., Neivark, N. J., U. S. A. 
 
 THE H. & V. W. 
 PATENTED UNDERWRITER'S RHEOSTATS. 
 
 w 
 
 MADE IN ALL SIZES TO SUIT REQUIREMENTS. 
 
 WE MANUFACTURE 
 
 Multipolar dynamos, in various sizes, giving 5 and 10 Volts and 
 ranging from 800 to 5,000 Amperes on three-wire system, also 
 dynamos from 50 to 8,000 Amperes on two-wire system. 
 
 RHEOSTATS, 
 
 VOLTMETERS, 
 AMMETERS, 
 
 CONNECTIONS. 
 
 ANODES, ALL KINDS, 
 
 POLISHING MACHINERY, 
 POLISHING SUPPLIES, 
 
 POLISHING COMPOSITION, and 
 
 Everything Used in the Plating and Polishing Shop. 
 
 Special itemized estimates furnished for complete plants. 
 Write for dynamo information. 
 
 THE HANSON & VAN WINKLE CO., 
 
 MAIN OFFICE AND FACTORY, 
 NEWARK, N. J., U. S. A. 
 
 WESTERN BRANCH, 28 S. CANAL ST., CHICAGO. 
 
The Hanson & Van Winkle Co., Newark, N. J., U. S. A. 
 
 United States Patents June 22 1897 — Feb. 24 1923 Oct. 11, 1904, 
 
 March 24, 1908 — May 19, 1908. 
 
 Canadian Patents No. 58,205 and 97,852. 
 
 OTHER PATENTS PENDING. 
 
 IMPROVED MECHANICAL ELECTRO-PLATING APPARATUS. 
 
 TYPE B. 
 
 For electro-plating quantities of small work in bulk, saving 
 time, labor and expense. More than five hundred of these ma- 
 chines are in daily use, giving excellent results in plating Nickel, 
 Copper, Brass, Bronze and Zinc. 
 
 EVERYTHING USED IN THE PLATING 
 AND POLISHING SHOP. 
 
 Special itemized estimates furnished for complete plants. 
 
 THE HANSON & VAN WINKLE CO., 
 
 MAIN OFFICE AND FACTORY. 
 NEWARK, N". J., U. S. A., 
 
 WESTERN BRANCH, 28 S. CANAL ST., CHICAGO. 
 
The Hanson & Van Winkle Co., Newark, N. J., TJ. S. A. 
 
 NICKEL ANODES. 
 
 With the advances made in 
 nickel plating in the past years 
 the tendency has been to use 
 larger containers, which natur- 
 ally require anodes of increased 
 dimensions. To meet this 
 necessity various devices have 
 been tried in the way of crowd- 
 ing a larger number of plates 
 into the tank or using irregular 
 shapes, sometimes with cumber- 
 some attachments. After ex- 
 haustive experiments we have 
 at last solved the question, and 
 now offer to the trade our 
 patented Elliptic Anode. 
 
 For many years it lias been 
 customary to use flat nickel 
 Anodes, only because there was 
 nothing else obtainable, and 
 these flat plates are still in 
 general use by many large 
 establishments, which have 
 not taken time to investigate 
 the decided advantage and 
 economy in our late develop- 
 ments. 
 
 The patented Elliptic Anodes 
 possess many points of real 
 merit ; they are the result of 
 careful experiments covering- 
 several years, and they over- 
 come the disadvantages in all 
 other shapes. 
 
 Elliptic Anodes are 2.} inches 
 wide by K inches thick, and 
 are cast in any ordinary 
 length. 
 
 Experience shows that all 
 Anodes work more from the 
 edges than from the center, 
 showing conclusively that cir- 
 culation around the Anode is 
 necessary to get the greatest 
 amount of corrosion or disinte- 
 gration. 
 
 THE HANSON & VAN WINKLE CO., 
 
 NEWARK, N. J., U. S. A. CHICAGO, ILL., 
 
 219 Market St. 28 S. Canal St. 
 
The Hanson & Van Winkle Co., Newark, JV. J., tJ. S. A. 
 
 ELECTRO-GALVANIZING. 
 
 COLD PROCESS. NO ROYALTIES. 
 
 COMPLETE OUTFITS FURNISHED. 
 
 Samples Furnished without Charge, Estimates and 
 
 Information Furnished ©n Request. 
 
 AN ECONOMICAL AND PRACTICAL SUBSTITUTE 
 
 We have fitted up a number of plants which are operating pro- 
 fitably at an increased economy over the old method. The Elec- 
 tro-deposition of Zinc has been attempted for many years, but 
 within a short period only have practical commercial results been 
 obtained. With the advantages secured by the use of our Com- 
 pound Wound Dynamos as a source of current, we are now pre- 
 pared to fit up complete plants for galvanizing all iron or steel 
 articles, from small castings to a ship's anchor and chain. 
 
 A Plant for Electro-Gaivantzing Comprises: 
 
 Special Low Voltage Compound Wound Dynamo. 
 
 Electrical Measuring Instruments. 
 
 Electrical Connections. 
 
 Tank or Tanks for Solution, with Fittings. 
 
 Solution or Material for Solution. 
 
 Cast Anodes of superior quality and absolutely without Waste. 
 
 Cleaning Outfit for preparing work, including all tanks 
 
 and supplies necessary. 
 
 When Required We Send Our Expert for 
 Large Installations. 
 
 THE HANSON & VAN WINKLE CO., 
 
 MAIN OFFICE AND FACTORY, 
 
 NEWARK, N. J., U. S. A. 
 
 WESTERN BRANCH, 28 S. CANAL ST., CHICAGO. 
 
The Hanson & Van Winkle Co., Newark, N. J., U. S. A. 
 
 ALUMINUM DIPPSWG BASKETS 
 Made in Any Size or Shape. 
 
 We want especially to call your attention to Baskets made 
 of Aluminum as being particularly adapted for use in wash- 
 ing and dipping (except in potash) as the acids have practi- 
 cally no effect on them. 
 
 After thorough test we do not hesitate to recommend them. 
 They are very light, very durable, and will outlast the ordi- 
 nary dipping basket. 
 
 ■rffiiPWi 
 
 
 THE HANSON & VAN 
 
 NEWARK, N. J., U. S. A. 
 
 219 Market St. 
 
 CO., 
 
 CHICAGO, ILL., 
 
 28 S. Canal St. 
 
 LO 
 
OF 
 
 Practical and Scientific Boo^ 
 
 PUBLISHED BY 
 
 Henry Carey Baird & Co. 
 
 INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS- 
 
 810 Walnut Street, Philadelphia. 
 
 •if Any of the Books comprised in this Catalogue will he sent hy mail, fret ft 
 postage, to any address in the world, at the publication prices, 
 
 •** A Descriptive Catalogue, 90 pages, 8vo., will he sent free and free of postage 
 to any one in any part of the world, who will furnish his addressi 
 
 *•"• Where not otherwise stated, all of the Books in this Catalogue are booad 
 in muslin. 
 
 AMATEUR MECHANICS' WORKSHOP: 
 
 A treatise containing plain and concise directions for the manipula- 
 tion of Wood and Metals, including Casting, Forging, Brazing, 
 Soldering and Carpentry. By the author of the " Lathe and Itf 
 Uses." Seventh edition. Illustrated. 8vo. . . . $2.$t 
 
 ANDES.— Animal Fats and Oils: 
 
 Their Practical Production, Purification and Uses ; their Properties^ 
 Falsification and Examination. 62 illustrations. 8vo. . $4.00 
 
 ANDES.— Vegetable Fats and Oils: 
 
 Their Practical Preparation, Purification and Employment; theif 
 Properties, Adulteration and Examination. 94 illustrations. 8vo. 
 
 $4.00 
 
 ARLOT.— A Complete Guide for Coach Painters : 
 
 Translated from the French o f M. Arlot, Coach Painter, for 
 eleven years Foreman of Pain.mg to M. Eherler, Coach Maker, 
 Paris. By A. A. Fesquet, Chemist and Engineer. To which i» 
 added an Appendix, containing Informatios resnecting the Materials 
 and the Practice of Coach and Car Painting s^d Varnishing in the 
 United States and Great Britain i2mo. . . . £l>H 
 
HENRY CAREY BAlRD & CO.'S CATALOGUE. 
 
 IRMENGAUD, AMOROUX, AND JOHNSON.— The Practi 
 cal Draughtsman's Book of Industrial Design, and Ma 
 chinist's and Engineer's Drawing Companion : 
 
 Forming a Complete Course of Mechanical Engineering and Archi 
 tectural Drawing. From the French of M Armengaud the elder. 
 Prof, of Design in the Conservatoire of Arts and Industry, Paris, and 
 MM. Armengaud the younger, and Amoroux, Civil Engineers. Re 
 written and arranged with additional matter and plates, selections from 
 and examples of the most useful and generally employed mechanism 
 of the day. By William Johnson, Assoc. Inst. C. E. Illustrated 
 by fifty folio steel plates, and fifty wood-cuts. A new edition, 4to., 
 
 cloth #6.00 
 
 ARMSTRONG. — The Construction and Management of Steam 
 Boilers : 
 By R. Armstrong, C. E. With an Appendix by Robert Mallet, 
 C. E., F. R. S. Seventh Edition. Illustrated. 1 vol. i2mo. .60 
 
 ARROWSMITH.— The Paper-Hanger's Companion: 
 
 Comprising Tools, Pastes, Preparatory Work ; Selection and Flanging 
 of Wall- Papers ; Distemper Painting and Cornice-Tinting ; Stencil 
 Work; Replacing Sash-Cord and Broken Window Panes; and 
 Useful Wrinkles and Receipts, By James Arrowsmith. A New, 
 Thoroughly Revised, and Much Enlarged Edition. Illustrated by 
 25 engravings, 162 pages. (1905) .... $1.00 
 
 ASHTON. — The Theory and Practice of the Art of Designing 
 Fancy Cotton and Woollen Cloths from Sample : 
 Giving full instructions for reducing drafts, as well as the methods of 
 spooling and making out harness for cross drafts and finding any re- 
 quired reed; with calculations and tables of yarn. By Frederic T. 
 Ashton, Designer, West Pittsfield, Mass. With fifty-two illustrations. 
 One vol. folio #5°° 
 
 ASKINSON. — Perfumes and their Preparation: 
 
 A Comprehensive Treatise on Perfumery, containing Complete 
 Directions for Making Handkerchief Perfumes, Smelling-Salts, 
 Sachets, Fumigating Pastils ; Preparations for the Care of the Skin, 
 the Mouth, the Hair; Cosmetics, Hair Dyes, and other Toilet 
 Articles. By G.W. AsKINSON. Translated from the German by IsiDOR 
 Furst. Revised by Charles Rice. 32 Illustrations. 8vo. #3.00 
 
 BRONGNIART. — Coloring and Decoration of Ceramic Ware. 
 8vc< £2.50 
 
 BAIRD.— The American Cotton Spinner, and Manager's and 
 Carder's Guide: 
 A Practical Treatise on Cotton Spinning; giving the Dimensions and 
 Speed of Machinery, Draught and Twist Calculations, etc. ; with 
 notices of recent Improvements: together with Rules and Examples 
 ror making changes in the sizes and numbers of Roving and Yam. 
 Compiled from the papers <>f the late Robert H. Baird. 121110. 
 
 ,* 1 TO 
 
HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 BAKER. — Long-Span Railway Bridges : 
 
 Comprising Investigations of the Comparative Theoretical and 
 Practical Advantages of the various Adopted or Proposed Type 
 Systems of Construction ; with numerous Formulae and Tables. By 
 B. Baker. i2mo #1.00 
 
 BRANNT. — A Practical Treatise on Distillation and Rec- 
 tification of Alcohol : 
 Comprising Raw Materials ; Production of Malt, Preparation of 
 Mashes and of Yeast; Fermentation ; Distillation and Rectification 
 and Purification of Alcohol ; Preparation of Alcoholic Liquors, 
 Liqueurs, Cordials, Bitters, Fruit Essences, Vinegar, etc. ; Examina- 
 tion of Materials for the Preparation of Malt as well as of the Malt 
 itself; Examination of Mashes before and after Fermentation ; Alco- 
 holometry, with Numerous Comprehensive Tables ; and an Appendix 
 on the Manufacture of Compressed Yeast and the Examination of 
 Alcohol and Alcoholic Liquors for Fusel Oil and other Impurities. 
 By William T. Brannt, Editor of " The Techno-Chemical Receipt 
 Book." Second Edition. Entirely Rewritten. Illustrated by 105 
 engravings. 460 pages, 8vo. (Dec, 1903) . . . $4.00 
 
 BAKR.-A Practical Treatise on the Combustion of Coal : 
 Including descriptions of various mechanical devices for the Eco- 
 nomic Generation of Heat by the Combustion of Fuel, whether solid, 
 liquid or gaseous. 8vo. ....... $2.50 
 
 B ARR. — A Practical Treatise on High Pressure Steam Boilers: 
 Including Results of Recent Experimental Tests of Boiler Materials, 
 together with a description of Approved Safety Apparatus, Steam 
 Pumps, Injectors and Economizers in actual use. By Wm. M. Barr. 
 204 Illustrations. 8vo $3 00 
 
 BAUERMAN. — A Treatise on the Metallurgy of Iron : 
 
 Containing Outlines of the History of Iron Manufacture, Methods of 
 Assay, and Analysis of Iron Ores, Processes of Manufacture of Iron 
 and Steel, etc., etc. By H. Bauerman, F. G. S., Associate of the 
 Royal School of Mines. Fifth Edition, Revised and Enlarged. 
 Illustrated with numerous Wood Engravings from Drawings by J. B. 
 Jordan. i2mo, $2.oa 
 
 BRANNT.— The Metallic Alloys : A Practical Guide 
 
 For the Manufacture of all kinds of Alloys, Amalgams, and Solders, 
 used by Metal-Workers : together with their Chemical and Physical 
 Properties and their Application in the Arts and the Industries ; with 
 an Appendix on the Coloring of Alloys and the Recovery of Waste 
 Metals. By William T. Brannt. 45 Engravings. Third, Re- 
 vised, and Enlarged Edition. 570 pages. 8vo. . Net, $i>.oo 
 
 BEANS. — A Treatise on Railway Curves and Location of 
 Railroads : 
 By E. W. Beans, Ci E. Illustrated; i2mo. Tucks. . #1.50 
 
HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 BELL. — Carpentry Made Easy: 
 
 Or, The Science and Art of Framing on a New and Improved 
 System. With Specific Instructions for Building Balloon Frames, Barn 
 Frames, Mill Frames, Warehouses, Church Spires, etc. Comprising 
 also a System of Bridge Building, with Bills, Estimates of Cost, and 
 valuable Tables. Illustrated by forty-four plates, comprising nearly 
 200 figures. By William E. Bell, Architect and Practical Builder. 
 
 8vo. $5.00 
 
 8EMROSE. — Fret-Cutting and Perforated Carving: 
 
 With fifty-three practical illustrations. By W. Bemrose, Jr. I volt 
 
 quarto $2.50 
 
 BEMROSE.— Manual of Buhl-work and Marquetry: 
 
 With Practical Instructions for Learners, and ninety colored designs. 
 By W. Bemrose, Jr. i vol. quarto .... $3-oc 
 
 BEMROSE.— Manual of Wood Carving: 
 
 With Practical Illustrations for Learners of the Art, ?.nd Original and 
 Selected Designs. By William Bemrose, Jr. With an Intro 
 duction by Llewellyn Jewitt, F. S. A., etc. With 128 illustra- 
 tions, 4to. ......... $2.50 
 
 BERSCH.— Cellulose, Cellulose Products, and Rubber Sub- 
 stitutes : 
 Comprising the Preparation of Cellulose, Parchment-Cellulose, 
 Methods of Obtaining: Sugar, Alcohol and Oxalic Acid from Wood- 
 Cellulose ; Production of Nitro-Cellulose and Cellulose Esters ; 
 Manufacture of Artificial Silk, Viscose, Celluloid, Rubber Substi- 
 tutes, Oil-Rubber, and Faktis. By Dr. Joseph Bersch. Trans- 
 lated by William T. Brannt. 41 illustrations. (1904.) $3.00 
 BILLINGS.— Tobacco : 
 
 Its History, Variety, Culture, Manufacture, Commerce, and Various 
 Modes of Use. By E. R. Billings. Illustrated by nearly 200 
 engravings. 8vo. . . . . . . . $3 00 
 
 BIRD. — The American Practical Dyers' Companion: 
 
 Comprising a Description of the Principal Dye-Stuffs and Chemicals 
 used in Dyeing, their Natures and Uses ; Mordants and How Made ; 
 with the best American, English, French and German processes for 
 Bleaching and Dyeing Silk, Wool, Cotton, Linen, Flannel, Felt, 
 Dress Goods, Mixed and Hosiery Yarns, Feathers, Grass, Felt, Fur, 
 Wool, and Straw Hats, Jute Yarn, Vegetable Ivory, Mats, Skins, 
 Furs, Leather, etc., etc. By Wood Aniline, and other Processes, 
 together with Remarks on Finishing Agents, and instructions in the 
 Finishing of Fabrics, Substitutes for Indigo, Water-Proofing of 
 Materials, Tests and Purification of Water, Manufacture of Aniline 
 and other New Dye Wares, Harmonizing Colors, etc., etc. ; embrac- 
 ing in all over 800 Receipts for Colors and Shades, accompanied by 
 170 Dyed Samples of Raw Materials and Fabrics. By F. J. Bird, 
 Practical Dyer, Author of " The Dyers' Hand-Book." Svo. $5-°° 
 
HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 BLINN.— A Practical Workshop Companion for Tin, Sheet- 
 Iron, and Copper-plate Workers : 
 
 Containing Rules 'for describing various kinds of Patterns used by 
 Tin, Sheet-Iron and Copper-plate Workers ; Practical Geometry; 
 Mensuration of Surfaces and Solids ; Tables of the Weights of 
 Metals, Lead-pipe, etc. ; Tables of Areas and Circumference* 
 of Circles; Japan, Varnishes, Lackers, Cements, Compositions, etc., 
 etc. By Leroy J. Blinn, Master Mechanic. With One Hundred 
 and Seventy Illustrations. 121110. ..... $2.50 
 
 BOOTH.— Marble Worker's Manual: 
 
 Containing Practical Information respecting Marbles in general, theii 
 Cutting, Working and Polishing ; Veneering of Marble ; Mosaics ; 
 Composition and Use of Artificial Marble, Stuccos, Cements, Receipts, 
 Secrets, etc., etc. Translated from the French by M. L. Booth. 
 With an Appendix concerning American Marbles. i2mo., cloth #1.50 
 
 BRANNT.— A Practical Treatise on Animal and Vegetable 
 
 Fats and Oils : 
 Comprising both Fixed and Volatile Oils, their Physical and Chem- 
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 them, and Practical Rules for Testing them; as well as the Manufac- 
 ture of Artificial Butter and Lubricants, etc., with lists of American 
 Patents relating to the Extraction, Rendering, Refining, Decomposing, 
 and Bleaching of Fats and Oils. By William T. Brannt, Editor 
 of the " Techno-Chemical Receipt Book." Second Edition, Revised 
 and in a great part Rewritten. Illustrated by 302 Engravings. In 
 Two Volumes. 1304 pp. 8vo. ..... $10.00 
 
 BRANNT.— A Practical Treatise on the Manufacture of Soap 
 
 and Candles : 
 Based upon the most Recent Experiences in the Practice and Science ; 
 comprising the Chemistry, Raw Materials, Machinery, and Utensils 
 and Various Processes of Manufacture, including a great variety of 
 formulas. Edited chiefly from the German of Dr. C. Deite, A. 
 Engelhardt, Dr. C. Schaedler and, others; with additions and lists 
 of American Patents relating to these subjects. By Wm. T. Brannt. 
 Illustrated by 163 engravings. 677 pages. 8vo. . . $12.50 
 
 BRANNT— India Rubber, Gutta-Percha and Balata : 
 
 Occurrence, Geographical Distribution, and Cultivation, Obtaining 
 and Preparing the Raw Materials, Modes of Working and Utilizing 
 them, Including Washing, Maceration, Mixing, Vulcanizing, Rubber 
 and Gutta-Percha Compounds, Utilization of Waste, etc. By Will- 
 iam T. Brannt. Illustrated. i2mo. (1900.) . . #3-oo 
 
HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 BRANNT— WAHL.- The Techno-Chemical Receipt Book: 
 
 Containing several thousand Receipts covering the latest, most im- 
 portant, and most useful discoveries in Chemical Technology, and 
 their Practical Application in the Arts and the Industries. Edited 
 chiefly from the German of Drs. Winckler, Eisner, Heintze, Mier- 
 zinski, Jacobsen, Roller and Heinzerling, with additions by Wm. T. 
 Brannt and Wm. H. Wahl, Ph. D. Illustrated by 78 engravings. 
 l2mo. 495 pages #2.00 
 
 BROWN. — Five Hundred and Seven Mechanical Movements : 
 Embracing all those which are most important in Dynamics, Hy- 
 draulics, Hydrostatics, Pneumatics, Steam Engines, Mill and other 
 Gearing, Presses, Horology, and Miscellaneous Machinery ; and in- 
 cluding many movements never before published, and several of 
 which have only recently come into use. By Henry T. Brown. 
 l2mo #1.00 
 
 BUCKMASTER.— The Elements of Mechanical Physics: 
 By J. C. Buckmaster. Illustrated with numerous engravings. 
 l2mo. ^I.oo 
 
 BULLOCK.— The American Cottage Builder : 
 A Series of Designs, Plans and Specifications, from $200 to $20,000, 
 for Homes for the People ; together with Warming, Ventilation, 
 Drainage, Painting and Landscape Gardening. By John Bullock, 
 Architect and Editor of " The Rudiments of Architecture and 
 Building," etc., etc. Illustrated by 75 engravings. 8vo. 
 
 BULLOCK. — The Rudiments of Architecture and Building: 
 For the use of Architects, Builders, Draughtsmen, Machinists, En- 
 gineers and Mechanics. Edited by John Bullock, author of "The 
 American Cottage Builder." Illustrated by 250 Engravings. 8vo. #2.50 
 
 BURGH. — Practical Rules for the Proportions of Modern 
 Engines and Boilers for Land and Marine Purposes. 
 By N. P. Burgh, Engineer. i2mo. .... $1.50 
 
 BYLES. — Sophisms of Free Trade and Popular Political 
 
 Economy Examined. 
 
 By a Barrister (Sir John Barnard Byles, Judge of Common 
 
 Pleas). From the Ninth English Edition, as published by the 
 
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 Comprising the Grinding and Sharpening of Cutting Tools, Abrasive 
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HENRY CAREY BA1RD & CO.'S CATALOGUE. 
 
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 CABINET MAKER'S ALBUM OF FURNITURE. 
 
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HENRY CAREY BAIRD & CG.'S CATALOGUE. 
 
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HENRY CAREY BAIRD & CO.'S CATALOGUE. p 
 
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jo HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
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 DAVIS. — A Treatise on Steam-Boiler Incrustation and Meth- 
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 witli Bark, Extracts, Chrome and all Modern Tannages in General 
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 Based upon Actual Experience. By F. Dawidowsky, Technical 
 
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HENRY CAREY BAIRD & CO.'S CATALOGUE. n 
 
 DE KONINCK— DIETZ.— A Practical Manual of Chemical 
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 DUPLAIS. — A Treatise on the Manufacture and Distillation 
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 EDWARDS. — A Catechism of the Marine Steam-Engine, 
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12 HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 EDWARDS. — Modern American Marine Engines, Boilers, and 
 
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 Their Design and Construction. Showing the Present Practice of 
 
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 EISSLER.— The Metallurgy of Silver : 
 
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 FAIRBAIRN. — The Principles of Mechanism and Machinery 
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 FORSYTH.— Book of Designs for Headstones, Mural, and 
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 FRIEDBERG. Utilization of Bones by Chemical Means; 
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HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
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 GARDNER.— Everybody's Paint Book: 
 
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 GOTHIC ALBUM FOR CABINET-MAKERS: 
 
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14 HENRY CAREY BAIRD & CO.'S CATALOGUE 
 
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 Hand-Book of Useful Tables for the Lumberman, Farmer and 
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HENRY CAREY BAIRD & CO.'S CATALOGUE. 15 
 
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 JERVIS.— Railroad Property: 
 
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 KELLEY.— Speeches, Addresses, and Letters on Industrial and 
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t6 HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 KENTISH.^-A Treatise on a Box of Instruments, 
 
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 KICK.— Flour Manufacture. 
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 Imperial Regierungsrath, Professor of Mechanical Technology in the 
 imperial German Polytechnic Institute, Prague. Translated from 
 the second enlarged and revised edition with supplement by H. H. 
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 KINGZETT.— The History, Products, and Processes of the 
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 including the most Recent Improvements. By Charles Thomas 
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 KIRK.— The Cupola Furnace: 
 
 A Practical Treatise on the Construction and Management of Foundry 
 Cupolas. By Edward Kirk, Practical Moulder and Melter, Con- 
 suiting Expert in Melting. Illustrated by 78 engravings. Second 
 Edition, revised and enlarged. 450 pages. 8vo. 1903. $3-5° 
 
 LANDRIN.— A Treatise on Steel: 
 
 Comprising its Theory, Metallurgy, Properties, Practical Working, 
 and Use. By M. H. C. Landrin, Jr. From the French, by A. A. 
 
 Fesquet. i2mo $2.50 
 
 LANGBEIN.— A Complete Treatise on the Electro-DeposK 
 tion of Metals : 
 Comprising Electro-Plating and Galvanoplastic Operations, the De- 
 position of Metals by the Contact and Immersion Processes, the Color- 
 ing 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 De- 
 partment of the Ait. From the German of Dr. George Langbein, 
 with additions by Wm. T. Brannt. Fifth Edition, thoroughly revised 
 and much enlarged. 170 Engravings. 694 pages 8vo. 1905. #4.00 
 LARDNER.— The Steam-Engine : 
 
 For the Use of Beginners. Illustrated. l2mo. ... .60 
 LEHNER— The Manufacture of Ink: 
 
 (* Comprising the Raw Materials, and the Preparation df Waiting, 
 Copying and Hektograph Inks, Safety Inks, Ink Extracts and Pow- 
 ders, etc. Translated from the German of SlGMUND Lehner, with 
 additions by William T. Brannt. Illustrated. i2mo. $2-'oa 
 
rfEWRY CAREY BAIRD & CO.'S CATALOGUE. 17 
 
 LARKIN. — The Practical Brass and Iron Founder's Guide: 
 A Concise Treatise on Brass Founding, Moulding, the Metals and 
 their Alloys, etc.; to which are added Recent Improvements in the 
 Manufacture of Iron, Steel by the Bessemer Process, etc., etc. By 
 Tames Larkin, Jate Conductor of the Brass Foundry Department i« 
 Reany, Neafie & Co.'s Penn Works, Philadelphia. New edition, 
 revised, with extensive additions. 414 pages. 121110. . $2,50 
 
 LEROUX.-A Practical Treatise on the Manufacture of 
 Worsteds and Carded Yarns : 
 Comprising Practical Mechanics, with Rules and Calculations applied 
 to Spinning; Sorting, Cleaning, and Scouring Wools; the English 
 and French Methods of Combing, Drawing, and Spinning Worsteds, 
 and Manufacturing Carded Yarns. Translated from the French of 
 Charles Leroux, Mechanical Engineer and Superintendent of a 
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 Chemist and Engineer. Illustrated by twelve large Plates. To which 
 is added an Appendix, containing Extracts from the Reports of the 
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 appointed by the Council of the Society of Arts, London, on Woolea 
 and Worsted Machinery and Fabrics, as exhibited in the Paris Uni. 
 versal Exposition, 1867. 8vo. ..... $5.0© 
 
 kEFFEL. — The Construction of Mill-Dams : 
 Comprising also the Building of Race and Reservoir Embankments 
 And Head-Gates, the Measurement of Streams, Gauging of Water 
 Supply, etc. By James Leffel & Co. Illustrated by 58 engravings. 
 8vo. (Scarce.) 
 
 LESLIE.— Complete Cookery: 
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 LE VAN. — The Steam Engine and the Indicator: 
 
 Their Origin and Progressive Development ; including the Most 
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 cator-Cards. 469 pp. 8vo. ...... #2.00 
 
 LIEBER.— Assayer's Guide ; 
 Or, Practical Directions to Assayers, Miners, and Smelters, for the 
 Tests and Assays, by Heat and by Wet Processes, for the Ores of all 
 tj? principal Metals, of Gold and Silver Coins asid Alloys, and of 
 Coal, etc. By Oscar M. Lieber. Revised. 283 pp. l2mo. #1.50 
 
 tockwood's Dictionary of Terms : 
 
 Used in the Practice of Mechanical Engineering, embracing those 
 Current in the Drawing Office, Pattern Shop, Foundry, Fitting, Turn- 
 ing, Smith's and Boiler Shops, etc., etc., comprising upwards of Six 
 Thousand Definitions. Edited by a Foreman Pattern Maker, author 
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!8 HENRY CAREY BArRD & CO.'S CATALOGUE 
 
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 a Description of the Most Modern Appliances ior the Ornamentation 
 of Plane and Curved Surfaces, an Entirely Novl-1 Form of Lathe 
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 Art. Illustrated by 462 engravings. Seventh edition. 315 pages. 
 
 Svo $4-2$ 
 
 MAIN and BROWN. — Questions on Subjects Connected with 
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 And Examination Paper.-,; with Hints for their Solution. By 
 Thomas J. Main, Professor of Mathematics, Royal Naval College, 
 and Thomas Brown, Chief Engineer, R. N. 121110., cloth. $1.00 
 MAIN and BROWN. — The Indicator and Dynamometer: 
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 Portsmouth, and Thomas Brown, Assoc. Inst. C. E., Chief Engineei 
 R. N., attached to the R. N. College. Illustrated. Svo. . 
 MAIN and BROWN.— The Marine Steam-Engine. 
 
 By Thomas J. Main, F. R. Ass't S. Mathematical Professor at the 
 Royal Naval College, Portsmouth, and Thomas Brown, Assoc. 
 Inst. C. E., Chief Engineer R. N. Attached to the Royal Navai 
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 MAKINS.— A Manual of Metallurgy: 
 
 By George Hogarth Makins. 100 engravings. Second edition 
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 MARTIN.— Screw-Cutting Tables, for the Use of Mechanic^ 
 
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 Being a Complete and Practical Treatise on Direct-Acting Under 
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 MOLESWORTH. — Pocket-Book of Useful Formulae and 
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tlENRY CAREY BAIRD & CO.'S CATALOGUE l 9 
 
 MOORE.— The Universal Assistant and the Complete 9§B 
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 Containing over one million Industrial Facts, Calculations, Receipt^ 
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 The whole being adapted for convenient use by Engineers, Surveyor^ 
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 By Elwood Morris, C. E. 8vo $i.$q 
 
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 ( IQ °5) $3-75 
 
 NAPIER. — A System of Chemistry Applied to Dyeing. 
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 Third Edition, with Additions, consisting of New Formula for the 
 discharge from Tidal and Flood Sluices and Siphons; general infor- 
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 I2mo 55.50 
 
 IEWBERY. — Gleanings from Ornamental Art of everj 
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 Drawn from Examples in the British, South Kensington, Indian, 
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 1862, and the best English and Foreign works. In a series of ioa 
 exquisitely drawn Plates, containing many hundred examples. By 
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 NICHOLLS. —The Theoretical and Practical Boiler-Maker zni 
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 Foremen a - %d Workiny. Boiler-Makers. Iro»o, Copper, and Tinsmith* 
 
2 o HENRY CAREY BA1RD & CO.'s CAlALUGUE. 
 
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 NICHOLSON.— A Manual of the Art of Bookbinding : 
 
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 NORMANDY.— The Commercial Handbook of Chemical An* 
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 Or Practical Instructions for the Determination of the Intrinsic 01 
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 thick i2mo. ......... Scarce 
 
 NORRIS. — A Handbook for Locomotive Engineers and Ma 
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 Comprising the Proportions and Calculations for Constructing Loco 
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 etc., etc. By Septimus Norris, M. E. New edition. Illustrated, 
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 NYSTRGM. — A New Treatise on Elements of Mechanics : 
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 accompanied with an Appendix on Duodenal Arithmetic and Me 
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 NYSTROM.— On Technological Education and the Construc- 
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 For Naval and Marine Engineers. By John W. Nystrom, latt 
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 O'NEILL. — A Dictionary of Dyeing and Calico Printing: 
 Containing a brief account of all fhe Substances and Processes! ( 
 use in the Art of Dyeing and Printing Textile Fabrics ; with Pract?Cy 
 Receipts and Scientific Information. By Charles O'Neill, Analy* 
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 Chemist and Engineer. With an appendix on Dyeing and Calico 
 Printing, as shown at the Universal Exposition, Paris, 1867 8vo., 
 491 pages . . $3.00 
 
 ORTON. — Underground Treasures; r 
 
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 vi all the Useful Minerals within the United States. By James 
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 N. Y ; author of the "Andes and the Amazon," etc. A New Edi- 
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 Illustrated ........ $1.50 
 
HENRY CAREY BAIRD & CO.'S CATALOGUE. 21 
 
 OSBORN.— The Prospector's Field Book and Guide. 
 
 In the Search For and the Easy Determination of Ores and Other 
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 Engravings. Seventh Edition. Revised and Enlarged. 379 pages, 
 i2mo. (March, 1907) #1.50 
 
 ©SBORN — A Practical Manual of Minerals, Mines and Min 
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 Comprising the Physical Properties, Geologic Positions, Local Occur- 
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 LL. D., Author of " The Prospector's Field- Book and Guide." 171 
 engravings. Second Edition, revised. 8vo. . . . #4.50 
 OVERMAN— Thu Manufacture of Steel : 
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 A Handbook for Blacksmiths and Workers in Steel and Iron, Wagon 
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 ware, of Steel and Iron, and for Men of Science and Art. By 
 Frederick Overman, Mining Engineer, Author of the " Manu- 
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 A. A. Fesquet, Chemist and Engineer. l2mo. . . $1.50 
 OVERMAN. — The Moulder's and Founder's Pocket Guide : 
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 l2mo. , #1.50 
 
 PALLETT— The Miller's, Millwright's, and Engineer's Guide. 
 By Henry Pallett. Illustrated. i2mo. . . , £2.00 
 
22 riENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
 PERCY. — The Manufacture of Russian Sheet-Iron. 
 
 By John Percy, M. D., F. R. S. Paper. . . . 2 <i cts 
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 Practical Treatise on Gas and Ventilation. Illustrated. i2mo. $1.25 
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 POSSELT. — Recent Improvements in Textile Machinery Re- 
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 REGNAULT.- Elements of Chemistry: 
 
 By M. V. Regnault. Translated from the French by T. Forrest 
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 RICHARDS.— Aluminium : 
 
 Its History, Occurrence, Properties, Metallurgy and Applications, 
 
 including its Alloys. By Joseph W. Richards, A. C, Chemist and 
 
 Practical Metallurgist, Member of the Deutsche Chemische Gesell- 
 
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HENRY CAREY BAIRD & CO.'S CATALOGUE. K 
 
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 instruments. Elementary Instruction in Practical Mechanical Draw- 
 
24 HENRY CAREY BAIRD & CO.'S CATALOGUE. 
 
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 i2mo. .......... $2.00 
 
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 SMEATON- Builder's Pockti-Companion : 
 
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HENRY CAREY jdaIRD m lU.'S CAiALOGUE. 25 
 
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 SHERRATT.— The Elements of Hand-Railing : 
 
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26 HENRY CAREY BAIRt> & CO.'S CATALOGUE. 
 
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 TABLES SHOWING THE WEIGHT OF ROUND, 
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HENRY CAREY BAIRD & CO.'S CATALOGUE. 31 
 
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