Digitized by the Internet Archive in 2011 with funding from The Library of Congress http://www.archive.org/details/completetreatise02lang « 1? A COMPLETE TREATISE ECTRO-DEPOSITION OF METALS : COMPRISING ELECTRO-PLATING AND GALVANOPLASTIC OPERATIONS, THE DEPOSITION OF METALS BY THE CONTACT AND IMMERSION PROCESSES, THE COLORING OF METALS, LACQUERING, 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 LATEST GERMAN EDITION OF DR. GEORGE LANGBEIN, n PROPRIETOR 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." SEVENTH EDITION, REVISED AND ENLARGED. ILLUSTRATED BY ONE HUNDRED AND FIFTY-FIVE ENGRAVINGS. PHILADELPHIA : HENRY CAREY BAIRD & CO., INDUSTRIAL PUBLISHERS, BOOKSELLERS, AND IMPORTERS, 810 Walnut Street. 1913 Copyright, by HENRY CAREY BAIRD & CO. 1913. / ? ^\3- PRINTED AT THE WlCKERSHAM PRINTING HOUSE, 111-117 EAST CHESTNUT STREET, LANCASTER, PA.. U. S. A. ©CI.A357445 PREFACE TO THE SEVENTH AMERICAN EDITION. The number of American editions through which Dr. George Langbein's work, Handbuch der elecktrolytischen Metall-Nieder- schlage, has passed in rapid succession, and the continued demand for it, may be accepted as evidence that the book, written from a scientific, as well as practical, standpoint, has been found to fulfill the purpose for which it is primarily intended, namely to serve as a ready book of reference and practical guide to the electroplater, who, if he would be a master of his art, must be conversant with the scientific prin- ciples upon which it rests. In this the seventh American edition, now presented to the public, the general scheme and scope of the sixth edition have been retained, but a thorough revision has been made, and a good deal of new matter has been added. Due attention has been paid to all important innovations, and it has been endeavored to include all practical methods of plating which have become known since the publication of the sixth edition, as well as the most recent machinery and apparatus. The editor is under obligations to The Hanson & Van Winkle Co., of Newark, N. J., the well-known manufacturers of, and dealers in, electroplaters' supplies and to The Egyptian Lacquer Manufacturing Co., of New York, for valuable in- formation and engravings. He has also diligently consulted the leading trade journals and freely quoted from them, due credit having been given in the text ; but he would acknowl- edge his special indebtedness to " The Metal Industry." The publishers have spared no expense in the proper il- (iii) iv PREFACE TO THE SEVENTH AMERICAN EDITION. lustration 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. W. T. B. Philadelphia, October 15, 1913. 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, Vollstdndiges Handbuch der Galvanischen Mettall- Niederschlage, 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 refer- ence and a practical guide for the workshop. In fact, it is especially intended for the practical workman, wherein he can find advice and -information regarding the treatment of the objects while in the bath, as well as before and after electro- plating. The author, Dr. George Langbein, is himself a master of the art, being the proprietor of an extensive electro- plating establishment combined with a manufactory of chem- ical products, machinery and apparatus used in the industry. The results yielded by the modern dynamo-electric ma- chines, to which the great advance in the electro-plating art it largely due, are in every respect satisfactory, and the more so since the need of accurate, and at the same time handy, measuring instruments has also been supplied. With the assistance of such measuring instruments, the establishment of fixed rules regarding 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 observing the determined conditions, and pro- (v) VI PREFACE TO THE FIRST AMERICAN EDITION. vided with well-working measuring instruments, he can at once produce beautiful and suitable deposits of the various metals. The data referring to these current-conditions, according to measurements by Dr. Langbein, are given as completely as possible, 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 ad- vantages for certain uses is added, thus enabling the operator to select the bath most suitable for his special purpose. To the few formula? which have not been tested, a note to that effect is in each case appended, and they are only given with due reserve. To render the work as useful as possible, the most suitable formula? for plating by contact and immersion, as well as the best methods for coloring the metals, and the characteristic properties of the chemicals used in the industry, are given. However, the preparation of the chemicals has been omitted, since they can be procured at much less expense from 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 on " Useful Tables." added by him, may contribute to the usefulness of the treatise. Finally, it remains only to be stated that the publishers have spared no expense in the proper illustration and the mechanical production of the book ; and,, as is their universal practice, have caused it to be provided with a copious table of contents, and a very full index, which will add additional value by rendering any subject in it easy and prompt of reference. W. T. B. Philadelphia, July 1, 1891. CONTENTS. 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 Carlyle, 1800; Wollaston's observations, 1801; Cruikshank's investigations, 1803; Brugnatelli's experiments in electro-gilding, 1805; Sir Hum- phry 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 byPixii; Faraday's electrolytic law laid down and proved in 1833; Production of iridescent colors, in 1826, by Novili; Production of the amalgams of potassium and sodium, in 1853 by Bird . . 4 Discovery of the actual galvanoplastic process, in 1838, by Prof. Jacobi; Claims of priority of invention by T. Spencer, and C. J. Jor- dan; Labors of the Elkingtons and of De Ruolz; Murray's discov- ery, in 1840, of black-leading 5 Introduction, in 1843, of gutta-percha by Dr. Montgomery; First em- ployment, in 1840, of alkaline cyanides by Wright; Patent for the deposition of nickel, 1840; Origination of the term "electro-metal- lurgy" by Mr. Alfred Smee, 1841; Prof. Bcettger's discovery, in 1842, of the deposition of nickel from its double salt .... 6 (Vii) Vlll CONTENTS. PAGE 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; First magnetic machine that deposited silver on a prac- tical scale constructed, in 1844, by Woolwych; Attempts, since 1854, by Christoffle and Co., to replace their batteries by magneto-elec- trical machines; The Alliance machine; Objections to Wilde's machine; Dr. Antonio Pacinotti's invention, in i860, of the ring named after him. 7 Siemens' dynamo machine, 1866; Wheatstone's dynamo machine, 1867; Zenobe Gramme's machine, 1871; Hefner- Alteneck's machine, 1872; Siemens & Halske machine, 1874; S. Schuckert's machine; Impetus given to the electro-plating industry by the construction of suitable dynamo machines 8 II. THEORETICAL PART. CHAPTER II. Magnetism and Electricity. Magnetism. Loadstone or magnetic iron ore; Natural and artificial magnets . . 9 Definition of the magnetic poles; Neutral line or neutral zone; Mag- netic meridian; North and south poles; Phenomena of attraction and repulsion; Ampere's theory 10 Magnetic field n Electro-Magnetism . Direction of the reflection of a magnetic needle; Instruments for recog- nizing feeble currents u Galvanoscopes or galvanometers; Astatic galvanometer; Instruments for measuring the intensity of the current by the magnitude of the deflection of the magnetic needle; Definition of electro-magnets . 12 Expression of the magnitude of the magnetizing force of the current; Remanent or residual magnetism; Properties of an electro-magnet; Flow of the magnetic lines of force; Magnetic field . . . .13 Direction and magnitude of the field-force; Effect of the electro-magnet upon soft iron; Definition of permeability . . . . . .14 Magnitude of the magnetic induction; The solenoid . . . .15 Induction. Definition of induction 15 Primary, inducing or main current; Secondary, induced or induction- current 16 CONTENTS. IX PAGE Direction of the induced current ........ 17 Electro- magnetic alternating actions; Hand-rule for following the direction of the induced current ........ 18 Fundamental Principles of Electro-Technics. Electric units 18 Comparison of the electric current with a current of water . . . 19 Definition of current-strength; The coulomb; The ampere; Electro- motive force or tension . . The volt; Difference of electro-motive force or difference of potential The volt-ampere, or watt; Unit of electrical work; Electric resistance Electric resistance of the current; The ohm; Law of Ohm; Equations Examples to equations 22 Internal and external resistance; Decrease in electro-motive force . 23 Proportion of the current-strength to the resistance of the current; Equation for calculating the decreasing electro-motive force; Im- pressed electro-motive force; Specific resistances . . . .24 Specific resistances and coefficient of temperature of the metals . . 25 Coefficient of temperature; Law of Kirchhoff; Branching or distrib- uting the current; Main wire and branch wires . ... . .26 Summary of Kirchhoff 's law • - - ■ • • 2 7 Law of Joule 28 Frictional Electricity . Idio-electrics 28 Non-electrics; Good and bad conductors; Electroscope; Kinds of elec- tricity .29 Contact Electricity . Generation of a current of electricity by the contact of various metals; Potential; Difference of potential; Series of the electro-motive force of the metals 30 Galvanic current or hydro-electric current; Galvanic element or voltaic cell 31 Fundamental Chemical Principles . Action of moist air upon bright iron or steel; Action of heat upon red oxide of mercury; Synthetic and analytical chemical processes . . 32 Law of the conservation of matter; Chemical elements; Molecules; Atoms 33 Atomic weights; Symbols and their formation 34 Table of the atomic weights of the most important chemical elements, together with their symbols and atomic weights; Valence of the elements . 36 Equivalent weights or combining weights $7 Arrangement of the most important elements according to their va- lence; Metals and non-metals and their classification. . . .38 X CONTENTS. PAGB Metalloids; Properties of metals and non-metals 3Q Acids, bases, salts; Great affinity of the elements for oxygen . . 40 Acids and their properties; Haloid acids; Oxy-acids; Bases; Hydroxyl group; Salts and their properties 41 Neutralization; Reagent papers 42 Formation of new products by the neutralization between acids and bases 43 Formation of salts from the acids; Neutral salts 44 Acid salts; Equations showing the difference between neutral and acid salts; Nomenclature of salts 45 Fundamental Principles of Electro- Chemistry \ Electrolytes; Conductors and non-conductors; Conductors of the first, and of the second, class Electrolysis; Electrodes; Ions; Cations; Anions; Properties of the ions Theory of solutions; A solution not merely a mechanical mixture; Vari- ous kinds of solutions Experiment with cupric sulphate solution; Law followed by the gases Osmotic pressure Electrolytic dissociation; Clausius' theory; Raoult's method of de termining the molecular weights of dissolved bodies . Discovery, by Arrhenius, regarding the conductivity of solutions Migration of the ions; Energy; Definition of energy; Mechanical work ............ Force and counter-force; Law of the conservation of force and work Processes on the electrodes; Electrolysis of a solution of potassium disulphate ........... Electrolysis of very dilute hydrochloric acid, and of sodium hydroxide Electrolysis of a solution of cupric sulphate Electrolysis of a silver bath containing potassium-silver cyanide . Laws of Faraday Proportion of the quantity of substances which is separated on the electrodes, to the strength of the electric current Second law of Faraday as expressed by v. Helmholz; Electro-chemi cal equivalent, and its definition Table of electro-chemical equivalents; Solution-tension of metals. Osmotic theory of the production of the current, according to Nernst Process which takes places in a cell Determination of the electro-motive force of a cell Additional chemical processes which take place in a cell; Polarization and its occurrence. ......... Counter-current or polarization-current ...... Origin of the electro-motive force of the polarization-current; Decom position-pressure .......... Decomposition-values of solutions; Velocity of ions Transport-values of the ions 46 47 49 50 5i 52 S3 54 55 56 57 58 59 60 61 63 64 65 66 67 68 69 CONTENTS. XI III. SOURCES OF CURRENT. CHAPTER III. Voltaic Cells, Thermo-Piles, Dynamo-Electric Machines, Accumulators. Voltaic cells; Conversion of chemical energy into electrical energy; Inconstant cells 70 Constant cells; Voltaic pile; Trough battery; Local action; Amalga- mation 71 Smee cell 72 Avoidance of polarization; Daniell cell ....... 73 Meidinger cell 74 Bunsen cell; Artificial carbon 75 Processes in the Bunsen cell; Forms of Bunsen cells . . . -76 Improved Bunsen cell; Location of Bunsen cells . . . . .78 Dupre's substitute for sulphuric and nitric acids for filling cells . . 79 Treatment of Bunsen cells ......... 80 Advisability of having duplicate set of porous clay cups; Renewal of the acid; Leclanche cell 81 Cupric oxide cell 82 Cupron cell 83 Plunge batteries , 84 Plunge battery constructed by Fein 85 Stoehrer's plunge battery; Dr. G. Langbein's plunge battery . . 86 Bichromate cell; Coupling cells 87 Coupling for electro-motive force; Coupling for quantity of current, or parallel coupling; Mixed coupling or group coupling. . . .89 Thermo-electric piles; Discovery by Prof. Seebeck . . . .90 Noe's and Clamond's thermo-electric piles 91 Giilcher's thermo-electric pile . . . . . . . .92 Dynamo-electric machines ......... 93 Fundamental principle of dynamo-electric machines . . . .94 Windings; Armature 95 Separate parts of the dynamo-machine; The frame; Magnetic winding or field winding; Two-polar and four-polar type of dynamo . . 96 Remanent magnetism; Self excitation; Foreign or separate excitation; Armature or inductor; Ring armature; Drum armature; Ring arma- ture winding 97 Drum armature winding 98 Chief difference between the modes of winding 99 Slotted armature; Commutator . . 100 Xll CONTENTS. *AGE Brushes; Choice of material for the brushes; Copper and brass gauze brushes 101 Boudreaux brushes; Brush holders; Brush rocker .... 102 Direct current dynamos; Series wound machines; Shunt-wound dynamo 103 Two-pole wound dynamos 104 Compound -wound dynamos 105 Multi-polar type of dynamo manufactured by The Hanson & Van Winkle Co., and its armature 106 Motor-generator sets manufactured by the same firm .... 109 Data for the most suitable machine . . . . . . . no Secondary cells (accumulators); Plante's practical application of ac- cumulators, and his accumulator in Use of lead grids by Faure; Chemical processes in the accumulator; Elb's theory 112 Liebenow's theory; Common form of an accumulator; Maintenance of accumulators. . . . , 116 Mode of charging a cell . . . . . . .. . -H7 Coupling accumulators; Ampere hours capacity 118 IV. PRACTICAL PART. CHAPTER IV. Arrangement of Electro-Plating Establishments in General. Light and ventilation in plating rooms 119 Heating the plating room 120 Renewal of water; Floors of plating rooms . . . . . . 121 Size of plating rooms; Grinding and polishing rooms .... 122 Exhaust fans 123 Distance between machines; Transmission 124 Electro-Plating Arrangements in Particular. Parts of the actual electro-plating plant; Current density . . . 124 Electro-chemical equivalent of the ampere-hour; Determination of the quantity of deposit and the time required 126 Determination of the current-output 127 Electro-motive force in the bath; Determination of the resistance of the electrolyte 128 Electro-motive counter force of polarization 130 Determination of the electro-motive counter-force 131 Scattering of the current lines. 132 CONTENTS. Xlll PAGE A. INSTALLATION WITH CELLS. Coupling of cells 132 Examples of coupling 133 Current regulation 135 Current regulator, resistance board, or rheostat; Conditions upon which the action of the resistance board is based .... 136 Modes of coupling the resistance board 137 Current indicator; Galvanometer 138 The Hanson & Van Winkle patent underwriters' rheostat . . . 140 The Hanson & Van Winkle Co.'s special rheostat .... 141 Indications made by the galvanometer; Validity of the deductions drawn from the position of the needle 143 Means of recognizing the polarity of the current; Measuring instru- ments; Ampere-meter or ammeter; Voltmeter 144 Instruments constructed according to Hummel's patent . . . 145 The Waverly voltmeter 146 The Weston ammeter; Arrangement of the switch-board, and ammeter with a bath operated by means of a battery; Voltmeter switch . . 147 Scheme showing the coupling of the main object-wire and of the main anode-wire, together with the resistance-boards, the voltmeter switch and two baths , 148 Dependence of the current-density on the electro-motive force . . 151 Conductors; Most suitable material for conducting the current; Loss of electro-motive force caused by conductors 152 Mounting of conductors; Main and branch conductors; Dimensions of conductors 153 Connection of main and branch conductors; Tanks; Welded steel tanks. 154 Construction of wooden tanks; Lead-lined tanks 155 Cement-lined tanks; Stoneware tanks . . . . ... . 156 Insulating joint; Conducting fixtures; Conducting rods. . . . 157 Binding posts and screws; Arrangement of objects and anodes in the bath 158 Supply of anodes; Anode-hooks 159 Slinging wires; Protection of the rods 160 Apparatus for cleansing and rinsing; Cleansing the objects from grease; Special table for this purpose 161 Drying the objects 163 Centrifugal dryer 164 B. INSTALLATION WITH DYNAMO-ELECTRIC MACHINES. Setting up and running a dynamo; Cause of most of the troubles with plating dynamos 164 Foundations for dynamos; Mode of ascertaining the direction of rota- tion; Belting. 165 Starting up; Proper position of the tips of the brushes; Adjustment of the brushes; Lubrication; Treatment of the commutator . . . 166 XIV CONTENTS. PAGE Choice of a dynamo 167 Impressed electro-motive force of the dynamo; Explanation by an ex- ample of the choice of a suitable dynamo 168 Destruction of an excess of electro motive force ..... 169 Advisability of using several dynamos with different impressed electro- motive forces 170 Principle of series-coupling of baths illustrated; Connection of the baths, resistance boards and measuring instruments to a shunt- wound dynamo 171 Parallel coupling and series-coupling of dynamo-machines; Rules to be observed in coupling several dynamos in parallel .... 172 When the coupling of dynamos in series may become necessary . . 174 Ground plan of an electro-plating plant with dynamo .... 175 Plating room and method of connecting dynamo, tanks and instru- ments according to the two-wire system 179 Three-wire system of current distribution; Plating room wired accord- ing to this system; Switch boards 180 C. INSTALLATION AND ACCUMULATORS. Use of an accumulator; Dynamos for supplying the accumulator. . 184 On what the magnitude of the performance of an accumulator de- pends; Ampere-hour capacity of an accumulator; Explanatory ex- ample 185 Diagram of connections for using storage batteries in connection with dynamos 186 CHAPTER V. Preparation of the 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 . Scratch-brushing; Various forms of brushes .... Treatment of scratch-brushes Circular scratch-brushes and their construction Various kinds of brushes suitable for the different operations The sand-blast and its use in cleaning; Types of sand-blast . Cleaning metallic articles in the tumbling barrel or drum Adjustable oblique tumbling barrel; Grinding; Grinding wheels and their construction ....... Grinding wheels of paste-board and of cork waste . Elastic wheel; Reform wheel; Emery for gluing . Treatment of the grinding wheels; Vienna lime . Removing emery and glue from worn leather-covered wood polishing wheels, and machine for that purpose; Grinding lathes 188 189 190 191 192 193 194 196 197 198 199 CONTENTS. XV PAGE Belt attachment combined with a double grinding lathe; Types of elec- trically driven grinding motors 202 Execution of grinding and brushing; Fiber brushes .... 204 Grinding iron and steel articles 205 Grinding brass and copper castings, sheets of brass, German silver, copper and zinc; Polishing 206 Foot-lathe for polishing; Union canvas wheel; Universal polishing wheel 207 Walrine wheel; Types of polishing lathes 208 Independent spindle polishing and buffing lathe 210 Electrically driven polishing and buffing lathes 211 Belt-strapping attachment; Polishing materials 212 Polishing with Vienna lime; Burnishing 213 B. MECHANICAL TREATMENT DURING AND AFTER ELECTRO-PLATING. Scratch-brushing the deposits, and its object 213 Porous formation of the deposit; Effect of scratch-brushing; Scratch- brushes for various purposes; Mode of operating with the hand ■ scratch-brush ........... 214 Scratch-brushing with the lathe brush; Drying the finished plated objects 215 Freeing nickel objects from moisture; Production of high luster; Polishing deposits of nickel, copper and brass, gold, silver and platinum; Operation of burnishing 216 Forms of burnishers; Cleansing the polished objects .... 217 Chemical Treatment. Pickling and dipping; Pickle for cast-iron and wrought-iron articles; Cleansing badly rusted iron articles ....... 218 Operation of pickling cast-iron ........ 219 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 Pickling zinc objects; Cleansing and brightening copper and its alloys; Preliminary pickle; Bright dipping bath 223 Use of potassium cyanide as a pickle; Mat-dipping .... 224 Preparation of a good mat dip; Mixture for the production of a mat- grained surface by pickling; Main points to be observed in pickling. 225 Absorbing plant for escaping acid vapors 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, copper, bronze, German silver and tombac 232 XVI CONTENTS. PAGE Electro-Plating Solutions (Electrolytes, Baths). Solvents; Spring and well waters 233 Distilled water, Rain water; Purity of chemicals; Examples of differ- ence in chemicals 234 Concentration of the baths; Conclusions which may be drawn from the specific gravity 235 Cause of dark or spotted nickeling; Difference in concentration in summer and in winter; Agitation of the baths 236 Uneven wearing of the anodes 22,7 Advantages claimed for constant agitation; Cause of changes in con- centration of the baths 238 Temperature of the baths; Boiling the baths, and utensils for the pur- pose 240 Use of nickeled kettles; Dissolving nickel salts soluble with difficulty; Working the bath with the current; Objections to this process. . 241 Filtering the baths; Prevention of impurities; Choice of anodes . . 242 Absorption of the deposit 243 Effect of the current-density 244 Current-output; Reaction of the baths 245 General qualifications an electro-plating bath should possess . . 246 CHAPTER VI. Deposition of Nickel and Cobalt. 1. deposition of nickel. Growth and popularity of nickel plating; Properties of nickel . . 247 Nickel salts 248 Conducting salts 249 Other additions to nickel baths; Boric acid 250 Substitution of glycerin for water in the preparation of nickel baths . 251 Effect of current-density; Electro-motive force; Reaction of nickel baths , 252 Formulas for nickel baths 253 Baths with the addition of chlorides 255 Nickel baths containing boric acid 256 Nickel baths for special purposes; For copper and copper alloys . . 258 For zinc; Bath yielding a very fine dark nickeling .... 259 Black nickeling 260 Bath for iron and copper alloys; Baths for the production of very thick deposits 262 Addition of carbon disulphide to nickel baths 263 Nickel bath without nickel salt; Prepared nickel salts .... 264 Correction of the reaction of nickel baths; Thick deposits in hot nickel baths 265 Foerster's experiments; Dr. George Langbein's experiments; Quick nickeling; Dr. Kugel's discovery 266 CONTENTS. XVII PAGE Thick deposits in cold nickel baths ....... 267 Coehn and Siemens' experiments with electrolytes containing nickel salts and magnesium salts; Nickel anodes; Elliptic anodes patented by The Hanson & Van Winkle Co 268 Objection to the use of insoluble anodes 271 Proportion of cast to rolled anodes 273 Cause of a reddish tinge on the anodes 274 Uneven solution of the anodes; Scattering of current lines; Execu- tion of nickeling; Removal of grease from the objects . . . 275 Previous coppering or brassing of certain objects; Security against rust. 276 Nickeling parts of bicycles; Means for preventing the rusting of the basis-metal . 277 Over-nickeling or burning and means of avoiding it . . . 278 Normal deposition and criterion for judging it; Most suitable current- density for nickeling .......... 279 Advisability of the use of a voltmeter and ammeter, as well as of a rheostat; Production of a very thick deposit; Solid nickeling . . 280 Faulty arrangement of anodes; Suspension of the objects ... . 281 Nickeling of cavities and profiled objects; Use of the hand anode; Ex- periments in nickeling the inside of brass tubes 282 Polarization; Reason why iron requires a stronger current for nickel- ing than copper alloys, and zinc a stronger one than iron. . . 284 Stripping defective nickeling 285 Stripping acid 286 Removal of the nickel coating by mechanical means; Stripping by electrolysis 287 Remedy against the yellowish tone of the nickeling; Defective nickel- ing; Resume of the principal defects which may occur in nickeling, and remedies. 288 Refreshing nickel baths 290 Treatment of the articles after nickeling; Polishing nickel deposits; Cleansing polished objects 291 Calculation of the nickeling operation . . . • . . . . 292 Nickeling small and cheap objects in large quantities .... 293 Types of mechanical electro-plating apparatus 295 Lifting device for raising and lowering the plating barrel . . . 297 Nickeling sheet-zinc; Preliminary grinding or polishing the sheets . 298 Construction of cloth bobs; Mode of polishing the sheets . . . 299 Automatic polishing machines ........ 300 Freeing zinc sheets from grease . 301 Nickeling the sheets; Advantages of coppering or brassing the sheets. 302 Dimensions of tanks for nickeling the sheets; Anodes for nickeling sheet-zinc ............ 304 Alkalinity of the baths for nickeling sheet-zinc; Polishing the nickeled sheets 305 Nickeling tin-plate, copper and brass sheets, sheet-iron and sheet-steel. 306 XV111 CONTENTS. Nickeling wire . . • 3°7 Nickeling knife-blades, sharp instruments, etc 310 Nickeling skates; Nickeling soft alloys of lead and tin . . . .311 Nickeling printing plates; Hard nickeling and baths for that purpose. 312 Recovery of nickel from old baths; Deposition of nickel alloys . . 314 Nickel bronze; Deposit of German silver 315 Examination of nickel baths; Determination of the content of acid . 316 Methods for the examination of baths; Gravimetric analysis; Volu- metric analysis 3 l & Electrolytic method of analysis, and apparatus for that purpose . . 319 2. DEPOSITION OF COBALT. Properties of cobalt; Baths for plating with cobalt; Cobalting copper plates for printing 323 Determination of the quantity of copper dissolved in stripping the co- - bait deposit from cobalted copper plates; Warren's cobalt solution . 324 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 326 Copper cyanide baths, and their preparation; Formation of cupric cyanide 3 2 7 Stockmeyer's experiments; Hossauer's copper bath .... 328 Copper baths for iron and steel articles 329 Stockmeyer's copper bath 330 Copper baths with sulphate of copper (blue vitriol) . . . .331 Use of cupro-cupric sulphite for the preparation of copper baths; Cop- per bath recommended by Pfanhauser 332 Copper bath for small zinc objects; Prepared copper salts . . . 333 Copper baths without potassium cyanide; Bath for coppering zinc ob- jects; Weill's copper bath 334 Walenn's and Gauduin's copper baths; Tanks for potassium-copper cyanide baths 335 Copper anodes; Formation of slime on the anodes; Execution of copper-plating . . . 336 Causes of copper baths yielding no deposit at all or only a slight one, and their remedies 337 Scouring and pickling the articles to be coppered; Treatment of de- fective places of the deposit; Washing the coppered objects . . 338 Prevention of stains; O. Schultz's method for removing hydrochloric acid from the pores and preventing the formation of stains; Polish- ing the coppered objects 339 Penetration of the deposit into the basis-metal; Coppering sheet-iron or sheet-zinc; Treatment of copper baths when they become inactive. 340 CONTENTS. XIX PAGE Coppering small articles in quantities; Inlaying of depressions of cop- pered art castings with black 341 Examination of copper baths containing potassium cyanide . . . 342 Determination of potassium cyanide . . 343 Determination of copper by electrolysis 345 Volumetric determination of copper 346 2. DEPOSITION OF BRASS. Constitution and varieties of brass . 348 Behavior of brass towards acids; Brass baths, their composition and preparation 349 Rules for baths containing more than one metal in solution; Brass bath according to Roseleur t . . 350 Other brass baths . . . . . . . . . . 351 Use of cupro-cupric sulphite and cuprous oxide for the preparation of brass baths 352 Bath for brassing zinc; Bath for brassing wrought iron, cast iron and steel . 353 Solution for transferring any copper-zinc alloy which serves as anode; Irregular working of fresh baths; Prepared brass salts . . . 354 Tanks for brass baths; Brass anodes; Execution of brassing; On what the color of the deposit depends 355 Formation of slime on the anodes, and what it indicates . . . 356 Remedies for the sluggish formation of the deposit .... 357 Effect of too great an excess of potassium cyanide; Treatment of a brass bath that has not been used for some time .... 358 Production of a brass deposit which is to show a tone resembling gold; Importance of the distance of the objects to be brassed from the anodes 359 Brassing of unground iron casting; Examination of brass baths; De- termination of free potassium cyanide and the content of copper . 360 Volumetric determination of zinc; Deposits of tombac .... 362 • Deposits of bronze 363 Method of preparing a bronze bath. 364 CHAPTER VII. Deposition of Silver. Properties of silver 365 Silver baths, their composition, preparation and treatment . . . 366 Advantage of silver baths prepared with silver chloride. . . . 367 Silver bath for a heavy deposit (silvering by weight); Preparation of a bath with silver chloride; Preparation of silver chloride . . . 368 Preparation of a bath with silver cyanide; Preparation of silver cyanide. 369 Silver bath for ordinary electro-silvering; Tanks for silver baths; Treat- ment of the silver baths; Silver anodes; Potassium cyanide required for the bath 370 XX CONTENTS. PAGE Indication of the presence of too much or not enough potassium cyanide. 371 The behavior and appearance of the anodes as criteria of the content of potassium cyanide in the bath; Regulating the content of potassium cyanide 37.2 Keeping the bath constant by silver anodes ...... 373 Proper treatment of baths made with silver chloride; Gradual thicken- ing of the baths 374 Determination of the proper proportion of silver and excess of potas- sium cyanide in the bath; Agitation of silver baths; Contrivances to keep the articles in gentle motion 375 Addition of certain substances to silver baths; Preparations for bright plating 377 Yellow tone of silvering 379 Silver alloys; Areas silver-plating 380 Experiments in areas silver-plating 381 Execution of silver-plating; Silver-plating by weight; Freeing from grease; Pickling and rubbing; Amalgamating (quicking). . . 382 Slinging wires; Methods of depositing an extra heavy coating of silver on the convex surfaces of spoons and forks ..... 383 Silver-plating the steel blades of table knives 385 Determination of weight of deposit . 386 Roseleur's plating balance 388 Plating balance, together with rheostat, voltmeter ahd silver bath . 390 Voltametric balance; Copper voltameter ...... 392 Advantages and disadvantages of the voltametric balance . . . 393 Neubeck's combination 394 Voltametric controlling apparatus 396 Calculation of the weight of the silver deposit from the current- strength used 398 Mat silver 400 Polishing the deposits; Ordinary silver-plating; Quicking solution; Direct silvering of Britannia, tin, German silver .... 401 Australian patent for directly silver-plating iron and steel; Stopping- off, and varnish for that purpose ........ 402 Special application of electro-silvering; Silvering of fine copper wire; Incrustations with silver and gold 403 Imitation of niel or nielled silvering; Nielling upon brass . . . 404 Old (antique) silvering; Oxidized silver 405 Brown tone on silver 406 Yellow color on silvered articles: Stripping silvered articles. . . 407 Determination of silver-plating; Process for the determination of genuine silvering used by the German custom-house officers . . 408 Examination of silver baths; Determination of free potassium cyanide, and of potassium carbonate ......... 409 Calculation of the quantity of barium cyanide required for the con- version of the quantity of potassium carbonate found. . . . 410 contp:nts. xxi PAGE Table for the use of a 20% per cent, barium cyanide solution; Deter- mination of the silver by the electrolytic method . . . .411 Recovery of silver from old silver baths, etc. ..... 412 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 . . , 415 Shell-gold or painters' gold; Gold baths their composition, prepara- tion and treatment . . . . . . . . . 416 Baths for cold gilding; Effect of too large an excess of potassium cyanide. 417 Bath with yellow prussiate of potash for cold gilding .... 418 Baths for hot gilding 419 Preparation of gold baths with the assistance of the electric current . 420 Gold anodes; Management of gold baths; Use of insoluble platinum anodes; Use of steel anodes and experiments with them . . . 421 Advantages claimed for steel anodes; Use of carbon anodes; Platinum anodes for coloring the deposit 423 Cause of unsightly and spotted deposits; Tanks for gold baths . . 424 Heating the baths 425 Execution of gold-plating; Gilding without a battery; Preparation of the articles for gilding 426 Current-strength for gilding; Agitation of the objects in the bath . 427 Gilding the inner surfaces of hollow-ware; Process of gold-plating in the cold, and in the hot, bath 428 Polishing the gold deposits , 429 Red gilding; Determination of the content of copper required for obtaining a beautiful red gold 430 Plating rings, watch chains, and other objects of base metal with red gold; Green gilding 431 Rose-color gilding; Rose gold solution . 432 Method of gilding which is a combination of fire-gilding with electro- deposition . 433 Mat gilding; Matting with the sand blast and by chemical or electro- chemical means 434 Coloring of the gilding 435 Gilder's wax; Process to give gilded articles a beautiful, rich appear- ance 436 Method of improving bad tones of gilding; Incrustations with gold; Gilding of metallic wire and gauze; J. W. Spaeth's machine for this purpose 437 Stripping gold from gilded articles; Electrolytic smoothing and polish- ing scratched or rubbed rings 440 Determination of genuine gilding; Examination of gold baths; De- termination of gold by the electrolytic method 441 Recovery of gold from gold baths, etc 442 XX11 CONTENTS. PAGE CHAPTER X. Deposition of Platinum and Palladium. I. deposition of platinum. Properties of platinum; Platinum baths, their composition, prepara- tion and treatment 444 Boettger's bath; Preparation of platoso-ammonium chloride; Platinum bath patented by the Bright Platinum Plating Co.; Jordis's platinum bath 445 Management of platinum baths; Execution of platinum plating . . 446 Production of heavy deposits; Process for plating directly, without previous coppering, iron, nickel, cobalt, and their alloys with platinum 447 Recovery of platinum from platinum solutions . . . . 448 2. deposition of palladium. Properties of palladium 448 Bertrand's palladium bath; Pilet's bath for plating watch movements. 449 CHAPTER XI. deposition of tin, zinc, lead, and iron, i. deposition of tin. Properties of tin; Moire metallique on tin; Tin baths, their composi- tion, preparation and treatment 450 Tinning of objects of zinc, copper, and brass; Experiments with Sal- zede's bronze bath 451 Neubeck's bath; Management of tin baths; Process of tin-plating . 452 2. DEPOSITION OF ZINC. Properties of zinc 453 Value of electro-zincking. . . . . . . . 454 Comparative experiments regarding zincking by the hot process and by electro-deposition; Disadvantages of hot galvanizing; Loss of zinc in electro-zincking .......... 455 Drawbacks of both processes; Preece's test for judging the thickness of the coating of zinc obtained by hot galvanizing; Burgess's method of testing the power of resistance of coatings obtained by electro- zincking . . . . 456 Zinc baths; Dr. Alexander's patented zinc bath 458 Decision of the Circuit Court of the United States for the District of New Jersey in regard to the Alexander patent; Recent investigations regarding the electrolysis of zinc; Regenerative process . . . 459 Addition of aluminium-magnesium alloy and of dextrose to zinc baths. 460 Addition of pyridine, and of glucosides; Formula for an alkaline zinc bath 461 Formulas for zinc baths; Importance of using zinc salts free from other metals 462 CONTENTS. XX111 PAGE Zinc anodes; Treatment of zinc baths 463 Loss of zinc by the formation of basic zinc salts; Heating the baths for strongly profiled objects 464 Tanks for zinc baths; Execution of zincking . . . . . 465 Zincking of sheet iron 466 Zincking of pipes , 467 Zincking of wrought iron girders, T-i r o n > U-i ron > L.-i r °n, etc.; Pro- filed anodes 468 Zincking of wire, steel tapes, cords, etc 469 Zincking of screws, nuts, rivets, nails, tacks, etc.; Zinc alloys, and their deposition 47 1 3. DEPOSITION OF LEAD. Properties of lead; Lead baths, their composition and preparation; Anodes for lead baths 47 2 Metallo-chromes (Nobili's rings, iridescent colors, electrochromy) . 473 4. DEPOSITION OF IRON (STEELING) . Principal practical use of the electro-deposition of iron; Iron (steel) baths, their composition and preparation 475 Management of iron baths ......... 476 Execution of steeling . . 477 CHAPTER XII. Deposition of Antimony, Arsenic, Aluminium, i. deposition of antimony. Properties of antimony; Antimony baths, their composition and pre- paration; Explosive power of antimony deposits 478 Non-explosive deposit of antimony; Antimony bath which yields good results . 479 2. DEPOSITION OF ARSENIC. Properties of arsenic; Arsenic baths, their composition, preparation and treatment . . . . 479 Cause of defective deposits 480 Solutions for coloring articles black 481 3. DEPOSITION OF ALUMINIUM. Non-feasibility of depositions of aluminium from aqueous solutions of its salts; Aluminium baths offered by dealers, and the results of test- ing them 483 4. DEPOSITION UPON ALUMINIUM. Difficulties met with in the electro-deposition of other metals upon aluminium; Behavior of aluminium towards the usual cleansing agents 484 XXIV CONTENTS. PAGE Coppering aluminium previous to plating and copper bath for this pur- pose; Villon's process of plating aluminium; Prof. Nees's process; Burgess and Hambuechen's method ....... 485 Gottig's process; Electro-deposits upon aluminium produced by the Mannesmann Pipe Works, Germany 486 CHAPTER XIII. Deposition by Contact, by Boiling, and by Friction. Theory of contact-deposition; Deposits by immersion or boiling; Plat- ing by means of a brush or by friction. . . ". . . . 487 Limits of the application of the contact-process; Drawbacks of the process 488 Contact-metals; Properties of the electrolytes for the contact-process . 489 Means of increasing the conductivity of the electrolytes containing potassium cyanide; Promotion of the attack of the contact-metal; Plating small objects in quantities; Useless reduction of metal in contact-deposition 4go Methods to avoid the reduction of metal on the wrong place; Defects of the contact-process; Nickeling by contact and boiling; Stolba's process of nickeling . 491 Processes for nickeling small articles; Use of aluminium-contact in place of zinc-contact 492 Darlay's patented process of nickeling 493 Chemical process of Darlay's electrolyte; Cobalting by contact and boiling 494 Coppering by contact and dipping; Liidersdorff's solution; Bacco's copper bath .' 495 Darlay's patented bath 496 Chemical process of Darlay's formula; Brush coppering . . . 497 Coppering iron and steel objects, steel pens, needles' eyes, etc.; Brass- ing by contact; Darlay's bath 498 Silvering by contact, immersion and friction; Bath for contact-silver- ing of copper and brass objects 499 Darlay's patented bath; Silvering by immersion and solution for this purpo'se 500 Preparation of solution of sodium sulphite 501 Ebermayer's silver immersion-bath; Process of coating with a thin film of silver small articles, such as hooks and eyes, pins, etc. . . 503 Cold silvering with paste; Composition of the argentiferous paste . 504 Graining; Process of graining parts of watches 505 Preparations for graining; Preparation of silver powder . . . 506 Composition of resist 507 Gilding by contact, by immersion, and by friction; Formulas for con- tact gold baths 508 Gilding by immersion (without battery or contact) and formulas for this purpose 509 CONTENTS. XXV Gilding by friction; Reddish gilding by friction; Solution for gilding by friction . . . . . . . ... • • • 5!0 Platinizing by contact; Tinning by contact and by boiling; Baths for tinning by contact 5 11 Zilken's patented bath for tinning by contact; Darlay's cold tin bath; Tinning solution for iron and steel articles 5 12 Tinning solutions for small brass and copper articles . . . . 513 A characteristic method of tinning by Stolba; Zincking by contact, and solution for this purpose; Darlay's bath; Process for coating brass and copper with a bright layer of zinc 514 Deposition of antimony and of arsenic by immersion . . . . 515 CHAPTER XIV. Coloring of Metals. Means by which metal coloring may be effected; Requirements for the practice of coloring 5*6 Coloring of copper; Production of all shades from the pale red of cop- per to a dark chestnut-brown; Brown color on copper; Brown layer of cuprous oxide on copper; Brown of various shades on copper . 518 Brown on copper by the Chinese process; Gold-yellow on copper; Manduit's process of bronzing copper; Yellowish-brown on copper . 519 Dark brown to black on copper; Red to violet shades on copper; Cuivre-fumk Black color on copper; Mat-black on copper .... Patina; Definitions of patina and patinizing; Artificial patina- cesses of patinizing ........ Donath's process; Imitation of genuine green patina . Blue-green patina; Brown patina; Patina for copper and brass; gray on copper Various colors upon massive copper; Coloring brass and bronzes Lustrous black on brass; Black color on brass optical instruments . 526 Steel-gray on brass; Silver color on brass; Pale gold color on brass; Straw color, to brown, through golden yellow, and tombac color on brass; Color resembling gold on brass 5 2 7 Brown color called bronze Barbidienne on brass 5 2 8 Coloring bronze articles dead-yellow or clay-yellow; Coloring brass articles in large quantities brown by boiling; Violet and cornflower blue on brass. . 5 2 9 Ebermayer's experiments in coloring brass 530 Coloring zinc; Black on zinc 53 1 Gray, yellow, brown to black colors upon zinc; Brown patina on zinc; Various colors on zinc S3 2 Gray coating on zinc; Bronzing, and yellow shades on zinc; Coloring iron; Browning gun barrels; Lustrous black on iron. . . . 533 Meritens' process for obtaining a bright black color on iron. . . 534 Pro- 520 5 2 i 522 523 Steel • 5 2 4 • 5 2 5 XXVI CONTENTS. PAGE Mat black coating upon clock cases of iron and steel — Swiss mat; Blue color on iron and steel; Brown-black coating with bronze luster on iron; To give iron a silvery appearance with high luster . . . 535 Coloring of tin; Bronze-like patina on tin; Sepia-brown tone upon tin; Dark coloration upon tin; Electrochroma ..... 536 CHAPTER XV. Lacquering. Application of lacquer; Drying the lacquered objects .... 538 Development in the art of lacquer making, and most noted improve- ments in lacquers; Pyroxyline lacquers, and their properties . . 539 Lacquering by dipping 540 Appearance of rainbow colors upon objects lacquered with pyroxyline lacquer; Production of various shades of color; Special invisible lacquer for ornamental cast and chased interior grille, rail and en- closure work 541 Satin finish lacquer; Dip lacquer for pickled castings to be copper- plated and oxidized 542 Helios dip lacquer; Old brass or brush-brass finishes .... 543 Brush-brass finish lacquers . . . 544 Egyptian brush-brass dip lacquer and brush-brass thinner; Brass bed- stead lacquering 545 Dead black lacquers 546 Dead black lacquer as a substitute for Bower-Barff .... 547 Spraying of lacquers; The spraying machine and its application . . 548 Equipment to be used ' . . . 549 Management of lacquers for spraying 550 Lacquers for spraying manufactured by The Egyptian Lacquer Manu- facturing Co.; Spraying black lacquers; Priming lacquer . . 551 Water-dip lacquers and their use . 553 Points to be followed when using water-dip lacquers .... 554 CHAPTER XVI. 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; Vessels used in the establishment not to be used for drinking purposes .... 555 Precautions in handling potassium cyanide and its solutions; Sensi- tiveness of many persons to nickel solutions; Poisoning by prussic acid, potassium cyanide and by cyanide combinations; Poisoning by copper salts 556 Poisoning by lead salts; by alkalies; by mercury salts; by sulphuretted hydrogen; by chlorine, sulphurous acid, nitrous and hyponitric gases. 557 CONTENTS. XXV11 PAGE CHAPTER XVII. Galvanoplasty (Reproduction). Definition of galvanoplasty proper; Application of galvanoplasty; In- vention of the process .......... 558 I. GALVANOPLASTY IN COPPER. Properties of copper deposited by electrolysis; Composition of the bath for depositing copper; Investigations by Hiibl and by Forster. 559 Formation of spongy and sandy deposits; Investigations by Mylius and Fromm, and by Lenz and Soret 560 Classification of the processes used in galvanoplasty; Galvanoplastic deposition in the cell apparatus; Simple apparatus frequently used . 561 Large apparatus; French form of cell apparatus 562 German form of cell apparatus 563 Copper bath for the cell apparatus 564 Freeing the bath from an excess of sulphuric acid; Decrease of the content of copper in the bath; Table of the content of blue vitriol at different degrees of Baume 565 Electro-motive force in the cell-apparatus, and its regulation; Galvano- plastic deposition by the battery and dynamo; Arrangement for the employment of an external source of current 566 Regulation of the current; Deposition with the battery; Cells . . 567 Deposition with the dynamo; Dynamos suitable for the purpose; Electro-motive force for the slow process 568 Combination of dynamos with a motor-generator ..... 569 Coupling the baths; Coupling in series 570 Mixed coupling or coupling in groups 571 Electro-motive force with baths coupled in parallel, and with baths coupled in groups 57 2 Combined operation with dynamo and accumulators; Disadvantage of interrupting the galvanoplastic deposition of copper .... 573 Copper bath for galvanoplastic deposition with a separate source of current; Functions of the sulphuric acid 574 Bath for the reproduction of shallow as well as of deep moulds; Prop- erties of the deposited copper; Bath for copper printing plates; Influence of the temperature of the electrolyte on the mechanical properties of the copper 575 Current conditions; Color of the deposit as a criterion of the quality . 576 Table showing the results of Hiibl's experiments 577 Causes of brittle copper deposits; Forster's and Hiibl's investigations. 578 E. Miiller and P. Behntje's investigations on the effects of organic additions; Duration of deposition. ....... 579 Table of the duration of deposition for electrotypes 0.18 millimeter thick with different current-densities; Nitrate baths . . . . 580 Agitation of the baths 581 XXV111 CONTENTS. PAGE Sand's experiments . 582 Stirring contrivances; Agitation of the bath by blowing in air; Agita- tion by flux and reflux . 583 Arrangement of the baths for this purpose 584 Necessity of keeping agitated baths clean; Filtering; Maximowitschs' , plan for agitating the baths 585 Anodes; Effect of impurities in the anodes; Anode slime . . . 586 Forster's experiments; Tanks; Rapid galvanoplasty .... 587 Principles upon which the process of rapid galvanoplasty is based . 588 Bath for shallow impressions" of autotypes, wood-cuts, etc.; Heating the bath; Danger of the crystallization of blue vitriol; Agitation of the bath. . . . • . 590 Current-density for this bath; Knight's process of coppering matrices. 591 Bath for deep depressions; Rudholzner's process 592 Quality of the copper deposit; Treatment of rapid galvanoplastic baths 593 Examination of the acid copper baths; Determination of free acid; Volumetric determination of the content of copper . . . . 594 Electrolytic determination of the copper. 595 Operations in galvanoplasty for graphic purposes; Preparation of the moulds (matrices) in plastic material . 596 Moulding in gutta-percha, and in wax 597 Mixtures for moulding in wax 598 Wax-melting kettles; Preparing the wax for receiving the impression; Moulding box . . . 599 Modern method of operation; Presses; The toggle press . . . 600 Hydraulic press 601 Metal matrices 602 Dr. E. Albert on the rational preparation of metal matrices. . . 603 Basis for the solution of the problem; Explanation of the process. . 605 Fischer's process; Kunze's method , . . 609 Further manipulation of the moulds; Removal of inequalities and eleva- tions; Making the moulds conductive; Black-leading the moulds and machines for this purpose 610 Black-leading by the wet process 612 Electrical contact; Trimming and wiring gutta-percha moulds; Feelers; Preparation of gutta-percha moulds for suspension in the bath . . 613 Process for black-leaded wax moulds; Hook for suspension in the bath; Preventing the copper deposit from spreading; Treatment of very deep forms 614 Suspending the moulds in the bath; Detaching the deposit or shell from the mould . . . . . . . . . . .615 Moulding and melting table for wax moulds Backing the deposit or shell . Finishing; Saw table . . ... Planing or shaving machines . 616 617 618 619 CONTENTS. XXIX Copper deposits from metallic surfaces; Process of making a copy directly from a metallic surface without the interposition of wax or gutta-percha 620 Coppering stereotypes 622 Coppering zinc plates; Preparation of type matrices; Treatment of originals of hard lead or similar alloys; Electro-etching . . . 623 Covering or etching ground; Work of the engraver .... 624 Photo-engraving and processes used ....... 625 Photo-galvanography 626 Collographic printing; Zincography 627 Process of transferring hy reprinting 628 Etching with the assistance of the electric current .... 629 Heliography 630 Electro-engraving; Rieder's patented process ..... 631 Apparatus for electro-engraving ........ 632 Galvanoplastic reproduction of plastic objects; Reproduction of busts, vases, etc.; Materials for the moulds . . . . -, s . . . 634 Moulding surfaces in relief and not undercut; Dissection of the ob- jects; Moulding with oil gutta-percha . 635 Preparation of oil gutta-percha; Moulding with gutta-percha; Metallic moulds, and metallic alloys for this purpose 636 Plaster of Paris moulds and their preparation. ..... 637 Moulding large objects 638 Rendering plaster-of-Paris moulds impervious ..... 639 Metallizing or rendering the moulds conductive; Metallization by the dry way; Metallization by metallic powders 640 Metallization by the wet way 641 Parkes' method of metallization 642 Lenoir's process— Galvanoplastic method for originals in high relief . 643 Gelatine moulds, and directions for making them. .... 644 Special applications of galvanoplasty; Nature printing .... 645 Production of copper tubes; Corvin's niello 646 Plates for the productions of imitations of leather; Incrusting galvano- plasty ... 647 Rendering the objects impervious 648 Copper bath and current conditions; Neubeck's investigations of the work in the cell-apparatus; Additional manipulation of the deposits; Philip's process of coating laces and tissues with copper . . . 649 Coating grasses, leaves, flowers, etc., with copper; Providing wooden handles of surgical instruments with a galvanoplastic deposit of cop- per; Coppering busts and other objects of terra-cotta, stoneware, clay, etc. . 650 Protecting mercury vessels of thermometers by a galvanoplastic de- posit of copper; Coppering mirrors; Galvanoplastic decorations on glass and porcelain ware 651 XXX CONTENTS. PAGE A. A. LeFort's process for silver deposit on glass and china; Prepara- tion of metallized silver 652 Grinding the paint 653 Firing the objects 654 Plating the objects, and bath for this purpose 655 Decorating umbrella and cane handles of celluloid with a metallic de- posit; Coppering baby shoes, carbon pins and carbon blocks, rolls of steel and cast iron, pump pistons, etc., steel gun barrels, candela- bra, stairs, and structural parts of buildings of rough castings . . 656 II. GALVANOPLASTY IN IRON (STEEL) . First production of serviceable iron electrotypes; Klein's bath . . 657 Lenz's investigations; Dr. George Langbein's investigations . . 658 Precautionary measures to counteract the spoiling of the deposits; Contrivance for mechanically interrupting the current . . . 659 Neubeck's experiments; Properties of electrolytically deposited iron; Advantages of^teeled copper electrotypes 660 III. GALVANOPLASTY IN NICKEL. Production of nickel electrotypes in an indirect way .... 661 Cold nickel bath for the direct method; Requirements for working with the direct process of deposition . . . . . . . . 662 Most suitable electro-motive force; Devices for preventing the nickel deposit from rolling off 663 Nickel matrices 664 Mode of effecting an intimate union of the copper casing with the nickel ............. 665 Matrices of massive nickel and cobalt . 666 IV. GALVANOPLASTY IN SILVER AND GOLD. Difficulties in the preparation of reproduction in silver and gold; Moulding of the originals . . . . . . . . , 667 Baths for galvanoplasty in silver, and in gold 668 CHAPTER XVIII. Chemicals Used in Electro-Plating and Galvanoplasty. 1. acids. Sulphuric acid (oil of vitriol) 669 Recognition of sulphuric acid; Nitric acid (aqua fortis, spirit of nitre) and its recognition; Hydrochloric acid (muriatic acid) and its recog- nition; Hydrocyanic acid (prussic acid) 670 Recognition of hydrocyanic acid; Citric acid and its recognition; Boric acid (boracic acid) and its recognition 671 Arsenious acid (white arsenic, arsenic, ratsbane) and its recognition; Chromic acid and its recognition; Hydrofluoric acid . . . . 672 Recognition of hydrofluoric acid . . . . . . . 673 CONTENTS. XXXI II. ALKALIES AND ALKALINE EARTHS. Potassium hydrate (caustic potash); Sodium hydrate (caustic soda); Ammonium hydrate (ammonia or spirits of hartshorn) . . . 67s Recognition of ammonium hydrate; Calcium hydrate (burnt or quick lime) 674 III. SULPHUR COMBINATIONS. Sulphuretted hydrogen (sulphydric acid, hydrosulphuric acid) and its recognition; Potassium sulphide (liver of sulphur) .... 674 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) . . 675 Ferric sulphide. . . 676 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) 676 Arsenious chloride; Copper chloride; Tin chloride — a. Stannous chlo- ride or tin salt and its recognition, b. Stannous chloride; Zinc chlo- ride (hydrochlorate or muriate of zinc) ; Butter of zinc, and its recog- nition 677 Chloride of zinc and ammonia; Nickel chloride and its recognition; Cobaltous chloride and its recognition; Silver chloride . . . 678 Recognition of silver chloride; Gold chloride (terchloride of gold, auric chloride) and its recognition; Platinic chloride and its recog- nition 679 V. CYANIDES. Potassium cyanide (white prussiate of potash) 680 Comparative table of potassium cyanide with different content; Copper cyanide and its recognition 682 Zinc cyanide (hydrocyanate of zinc, prussiate of zinc); Silver cyanide (prussiate or hydrocyanate of silver) ; Potassium ferrocyanide (yellow prussiate of potash), and their recognition ...... 683 VI. CARBONATES. Potassium carbonate (potash) and its recognition; Acid potassium carbonate, commonly called bicarbonate of potash; Sodium car- bonate (washing soda); Sodium bicarbonate (baking powder) . . 684 Calcium carbonate (marble, chalk); Copper carbonate, zinc carbonate, nickel carbonate, and their recognition 685 Cobaltous carbonate 686 XXX11 CONTENTS. VII. SULPHATES AND SULPHITES. Sodium sulphate (Glauber's salt); Ammonium sulphate, potassium- aluminium sulphate (potash-alum), and their recognition; Alu- minium-alum ........... 686 Recognition of aluminium-alum; Ferrous sulphate (sulphate of iron, protosulphate of iron, copperas, green vitriol), and its recognition; Iron-ammonium sulphate; Copper sulphate (cupric sulphate, blue vitriol or blue copperas) , and its recognition 687 Zinc sulphate (white vitriol), nickel sulphate, and their recognition; Nickel-ammonium sulphate ......... 688 Recognition of nickel-ammonium sulphate; Cobalt-ammonium sul- phate; Sodium sulphite and its recognition; Sodium bisulphite . 689 Cuprous sulphite . . . . 690 VIII. NITRATES. Potassium nitrate (saltpetre, nitre), and its recognition; Sodium nitrate (cubic nitre or Chile saltpetre) ; Mercurous nitrate. . . 690 Mercuric nitrate (nitrate of mercury), and its recognition; Silver nitrate (lunar caustic) . . . . 691 IX. PHOSPHATES AND PYROPHOSPHATES. Sodium phosphate, sodium pyrophosphate, and their recognition; Ammonium phosphate 692 X. SALTS OF ORGANIC ACIDS. Potassium bitartrate (cream of tartar) 692 Potassium-sodium tartrate (Rochelle or Seignette salt), and its recog- nition; Antimony potassium tartrate (tartar emetic), copper acetate (verdigris) and their recognition 693 Lead acetate, and its recognition; Sodium citrate 694 Appendix. Contents of vessels; To find the number of gallons a tank or other vessel will hold; Avoirdupois weight; Troy weight .... 695 Imperial fluid measure; Table of useful numerical data; To convert Fahrenheit thermometer degrees (F.) to Centigrade degrees (C); To convert Centigrade degrees to Fahrenheit degrees . . . 696 Table for the conversion of certain standard weights and measures . 697 Table of solubilities of chemical compounds commonly used in electro- technics. 798 Content of metal in most commonly used metallic salts. . . 700 Table showing the electrical resistance of pure copper wire of various diameter; Resistance and conductivity of pure copper at different temperatures 701 Table of hydrometer degrees according to Baume, at 63.5° F., and their weights by volume; Table of bare copper wire for low voltages. 702 Index . . . . • . 703 ELECTRO-DEPOSITION OF 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 solution of its salts by the electric current, the simple reduc- tion which takes place by the immersion of one metal in the solution of another, may be omitted. This mode of reduction was well known to the alchemist Zozimus, who described the reduction 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 dis- covery. Galvani observed, while dissecting a frog on a table, whereon stood an electric machine, that the limbs suddenly became convulsed by one of his pupils touching the crural nerve with the dissecting-knife at the instant of taking a spark from the conductor of the machine. The experiment was several times repeated, and it was found to answer in all cases when a metallic conductor was connected with the nerve, but not otherwise. He observed that muscular contractions were 1 Z ELECTRO-DEPOSITION OF METALS. 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 contractions were produced by the same agent. From a course of experiments, Galvani drew the erroneous inference that these muscular contractions wero caused by a fluid having its seat in the nerves, which through the metallic connections flowed over upon the mus- cles. Everywhere, in Germany, England and France, emi- nent scientists hastened to repeat Galvani's experiments, 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 experiment, it was absolutely necessary for the metallic con- nection to consist of two different metals coming in contact with each other. From this he drew the inference that the agent producing 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 dis- similar 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 consisted 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 OP ELECTRO-METALLURGY. 3 Nicholson and Carlisle, in 1800, were the first to decompose water electrolytically into hydrogen and oxygen, using a Volta pile. The method has only acquired practical im- portance during the last few years. Wollaston, in 1801, found that if a piece of silver in contact with a more positive metal, for instance, zinc, be immersed in copper solution, the silver will be coated with copper, and this coating will stand burnishing. Cruikshank, in 1803, investigated the behavior of solutions of nitrate of silver, sulphate of copper, acetate of lead, and of several 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 sus- pended in the solution from the positive pole. He also ob- served that the positive plate, if it consisted of an oxidizable metal, was dissolved. One of the greatest discoveries connected with the subject, however is that of Sir Humphry Davy, in 1807, when by decomposing potassium hydroxide and sodium hydroxide by ' means of a powerful electric current he obtained 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 current. It was known long before this that powerful electric discharges affect the magnetic needle. It had, for instance, been observed that the needle of a ship's compass struck by lightning had lost its property of indicating the North Pole, and several physicists, among them Franklin, had succeeded in producing the same phenomena by heavy discharges of the electrical machine, but they were satisfied with the supposition 4 ELECTRO-DEPOSITION OF METALS. 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 the construction of the galvanoscope or galvanometer, an instrument 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 in- duced in the contiguous wire is not constant, because after a few oscillations the magnetic needle returned to the position occupied 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 combi- nations by the same current are proportional to their chemical equivalents, was laid down and proved in 1833, and upon this Faraday based the measurements of the current-strength by chemical deposition, as, for instance, that of water, in the voltmeter. Of the practical electro-chemical discoveries there remains 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. HISTORICAL REVIEW OP ELECTRO-METALLURGY. 5 The actual galvanoplastic process, however, dates from 1838. In the spring of that year Prof. Jacobi made known to the Academy of Sciences of St. Petersburg his discovery of the utility of galvanic electricity as a means of reproducing objects of metal. He produced an exact mould of metals and artistic objects by means of wax or plaster, and then coated every detail of the surface of this mould with very fine graphite, thus rendering it electrically conductive. He then suspended the mould from the negative pole (cathode) of an electrolytic bath containing a suitable metallic salt, and formed the posi- tive pole of the same metal ; on passing an electric current through this bath the mould became lined with very fine particles of metal, forming a continuous and compact surface. The metal forming the anode was gradually dissolved in the bath as fast as it was deposited on the cathode. Hence, Jacobi must be considered the father of galvanoplasty in so far as he was the first to utilize and give practical form to the discoveries made up to that time. Though Jacobi's process was published in the English periodical, " 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 invention, 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 metallic objects 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 pdrpose, 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. 6 ELECTRO-DEPOSITION OF METALS. 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 solutions of metallic cyanides in potassium cyanide prevails at the present time, and the results obtained thereby have not been surpassed by any other practice. 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. Boettger, 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, Boettger'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 w T e are also in- HISTORICAL REVIEW OP ELECTRO-METALLURGY. 7 ■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 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 Birm- ingham, England. The Woolrych machine stands 5 feet high, 5 feet long, and 2J feet wide. As early as 1854, Christofle & Co. endeavored to replace their batteries by magnetic-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 objection- able on account of its heating while working, and the conse- quent frequent interruptions in the operations. In 1860 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 ma- chines, steel magnets had been used, and their magnetism not being constant, the effect of the machine was consequently also not constant. Furthermore, they generated alternately nega- O ELECTRO-DEPOSITION OF METALS. tive 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 electro-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 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- magnets. 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. By the construction of suitable dynamo-machines a mighty impetus was given to the electro-plating industry. They sup- planted the ordinary cell apparatus formerly used and ren- dered possible the production of electrolytically nickeled, coppered and brassed sheet-steel and tin-plate, as well as that of electrolytically zincked sheets, wire, building materials, etc. All these processes will be fully discussed, in the practical part, of this work. 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 prop- erty 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 4 ), 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 Thes- saly, in the neighborhood of which it was found. In the tenth or twelfth century it was discovered that this stone has the property of pointing north and south when suspended by a thread. This property was turned to advantage in naviga- tion and the term load stone (" leading stone ") was applied to the magnesian stone. If a natural loadstone be rubbed over a bar of steel, its characteristic properties will be com- municated 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 (9) 10 ELECTRO-DEPOSITION OF METALS. 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 possesses no attractive force, is termed the neutral line or neutral 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 en- sues 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 sec- ond north pole, or a south pole near another south pole, mutual repulsion is observed, and th-e 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 — MAGNETISM AND ELECTRICITY. 11 are arranged irregularly ; during magnetization they are made to move parallel to one another, and as the magnetiza- tion 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. 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 12 ELECTRO-DEPOSITION OF METALS. 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 opposed, and hung by a long fiber of twisted silk, with the lower needle in the coil and the upper one above it. The advantage thus gained is twofold : The system is astatic, un- affected, or nearly so, by the magnetism of the earth ; and the needles being both acted upon in the same manner by the current, are urged with much greater force than one alone would be, all the actions of every part of the coil being strictly concurrent. 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 magnetic, the greater the number of turns of the coil, and the: more intense the current passing through the turns. MAGNETISM AND ELECTRICITY. 13 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 iron. This remaining magnetism is called remanent or residual magnetism. An electro-magnet possesses the same properties as an ordi- nary magnet, and, like it, has a north pole and a south pole, Fig. 1. / / ' / / s \ / / / as well as a magnetic field, through which its influence ex- tends. Place a piece of paper above an electro-magnet and sift uniformly 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 proportion^, lines of filings are formed from the north pole to the south pole. This experiment demon- strates 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 influ- ence is called the magnetic field. The lines of force flow from the north pole to the south pole, where they combine, and flow 14 ELECTRO-DEPOSITION OF METALS. back through the iron bar to the north pole, as shown in the accompanying illustration, Fig. 1. The dotted lines also take actually 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, the latter being on all points struck at right angle by the lines of force. By placing a bar of soft iron, a b, in the proximity of a mag- Fig. 2. /^/VM;-ii;.i\ivv\-;//////';;-ij»\\\ N o* \ \ 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- 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 1 MAGNETISM AND ELECTRICITY. 15 . square centimeter of cross-section of a material, is called the magnitude of the magnetic induction of the material in question. Eyery 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 other hand, opposes far greater resistance, and, hence, the density of the 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 re- pelling 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 16 ELECTRO-DEPOSITION OF METALS. magnetic needle of a multiplier, M, which is connected with the ends of a, the deflection of the needle showing that the current produced in a by the current in b moves in an oppo- site 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 interrupted, the magnetic needle swings to the opposite direction, thus indicating the formation Fig. 3. •of a current in a, which passes through it in the same direc- tion 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 a current of opposite direction, but when interrupted, a current of the same direction. In the same manner as closing and opening the main cur- MAGNETISM AND ELECTRICITY. 17 rent, 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 con- tiguous 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 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, 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 decreases with the magnitude of the number of lines of force. 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 2 18 ELECTEO-DEPOSTTION OF METALS. 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 Fleming's hand rule, which is as follows : Hold the thumb and the first and the middle fingers of the right hand as nearly as possible at right angles to each other, as shown in Fig. 4, so as to represent three rectangular axes in. space. If the thumb points in the direction of motion, and. Fig. 4. the forefinger points along the direction of the magnetic lines,, then the middle finger will point in the direction of the in- duced electro-motive force. 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 expressed 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- MAGNETISM AND ELECTRICITY. 19 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 Fig. 5. the force of the current of water is expressed according to the quantity of water which runs out in the time-unit, it follows 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 20 ELECTKODEPOSITION OF METALS. the same cross-section, it will be found that a greater number 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 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 1 gramme hydrogen 96,540 coulombs must migrate through the elec- trolyte. The unit of current-strength is called the ampere, i. e., a cur- rent which every second carries 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 1 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 cor- MAGNETISM AND ELECTRICITY. 21 responds 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- 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 22 ELECTRO-DEPOSITION OE METALS. 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. . 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 K (1) - = resistance (W), u 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 W indi- 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 ; that is, the current-strength is equal to the electro-motive force divided by the resistance. Example to equation 1. If through a circuit closed by a long MAGNETISM AND ELECTRICITY. 23 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 1 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? JO volts K = o amperes. 2 ohms 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 wl and w2, equation 3 assumes the following aspect : E (4) - ^J w W + wl + w2 J - 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 If.. A cell possesses an internal resist- ance of 0.3 ohm and an electro-motive force of 1.8 volts, and the resistance of the conducting wire, wl, is 1 ohm and that of the electrolyte 0.5 ohm. The current-strength then amounts tolamp^re( a3+ 1 1 8 +a5 = l). If a determined current-strength flows through a resistance, ■a decrease of electro-motive force results in the resistance, ex- actly as in a water-conduit the pressure of the column of water is decreased with the length of the pipe, a decrease in pressure taking place. It might be said that the resistance consumes 24 ELECTRO-DEPOSITION OF METALS. the pressure, and the greater the resistance of a conductor is,, the less the current-strength will be, since, if in the equation 3 the divisor grows, the current-strength, J, must become less. According to the law of Ohm, the following proposition here holds good : The current-strength is inversely proportional to the sum of {he- 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 (5) W = - The decreasing electro-motive force, according to the law of Ohm, is calculated by the following equation, in which a denotes the decrease in electro-motive force, J the qurrent- 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 proportional 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- MAGNETISM AND ELECTRICITY. 25- 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 jDOssesses 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. 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. The specific resistance c of the metals at 59° F., and the co- efficient of temperature a (see later on) amount to for : Aluminium . Antimony . . Bismuth . . Brass .... Copper . . . German silver Gold ...'.. Iron .... Lead .... Manganin . . Mercury . . Nickel . . . Xickelin . . . Platinum . . Silver . . . . Steel ....'. Tin .... . Zinc . . . - c. x a ' 0.029 0.0039 0.475 * 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 0.10 0.0048 0.207 0.0039 0.455 0.00002 0.953 0.0009 0.15 0.0036 0.435 to 0.340 0.000025 0.15 to 0.094 0.0024 0.016 0.0038 0.50 to 0.168 0.0040 0.10 0.0042 0.065 0.0040 ■26 ELECTRO-DEPOSITION OF METALS. 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, [+a(t 2 — t,)], in which Wt 2 is the resistance at the higher temperature t 2 , and Wtj, the resistance at the lower temperature t x , and the magnitude a, the number of ohms the resistance increases by a rise of 1° 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 2 =-Wt 2 [1— a (t 2 — 10]. 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. 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, 1, 2, and 3, branch off, and b, ■the. junction at which they meet. If a current-meter (see later MAGNETISM AND ELECTRICITY. 27 on) be placed in the main wire, and one in each of the branch wires, it will be found that the sum of the current-quantities flowing through the separate branch wires is equal to the current-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 Fig. 6. that the branch wire 1 is shorter than 2 or 3, and hence pos- sesses less resistance. 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-idres distribute themselves in inverse proportion to 'their resistances. In the practical part of this work the further conclusions resulting from the law of Kirchhoff will be referred to. 28 ELECTRO-DEPOSITION OF METALS. 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 produced by the passage of a determined current- strength through a determined resistance, increases in the same ratio as the duration 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 magni- tude of the resistance, and, hence, that the quantity of heat becomes larger as the resistance increases. It has further been, established that the quantity of heat produced in a de- termined resistance during a determined 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. J 2 . W. t. If Q is the quantity of heat developed in calories, J is the current-strength in amperes which flows through the resist- ance, W the resistance through which J flows, and t the space of time in seconds of the passage of the 'current ; C is a con- stant 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. Frictional 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 MAGNETISM AND ELECTRICITY. 29 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, from which hangs by a silken thread or hair a pith 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. 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 or positive, and resinous or negative electricity, and it has been found that electricities of a similar name attract, and electricities of an opposite name repel each other. Contact Electricity. However, a current of electricity is generated not only by friction, but also by the contact of various metals. In the 30 ELECTRO-DEPOSITION OF METALS. same manner as the copper and iron in Galvani's experiments with the frog-leg, other metals and conductors of electricity also become 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 be- comes more strongly positively electric than when in contact with copper ; whilst, however, copper in contact with zinc is negatively excited, in contact with platinum it becomes posi- tively electric. The metal which has become positively electric is said to have the higher potential, i. e., it possesses a larger measure of electricity than the metal which has become negatively elec- tric, 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 charges is, and this difference in the charges of two bodies is called difference of potential. 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 intro- ducing 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 xMAGNETISM AND ELECTRICITY. 31 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 continuous. 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 suppo- sition 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 tho osmotic pressure. It is first of all necessary to explain the fundamental chemical principles, since without a knowledge of them, the subsequent sections could not be understood. Fundamental Chemical Principles. 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 ex- amination ; it remains the same steel which had been origin- ally 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 chemical principles, are of an entirely dif- ferent nature, we having constantly to deal with changes in substance, as may be shown hy the following examples. •32 ELECTRO-DEPOSITION OF METALS. 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 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 quanti- ties 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 MAGNETISM AND ELECTRICITY. 66 weight never occurs. The weight of the resulting compound is invariably equal to the sum of the weight of the bodies entering into the reaction. This furnishes proof that the most import- ant law of the indestructibility and non-creation of weighable substance in nature, which is known as the law of the conserva- tion 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 quan- tity by weight of iron can only combine, under the co-opera- tion 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 pro- portion. 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 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 3 34 ELECTRO-DEPOSITION OF METALS. 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 highest 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- stance, represented by the letter H, from the word Hydrogenium; Oxygen by 0, 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 furnished with an additional characteristic letter. Thus, for instance, boron is represented by the letter B ; barium by Ba ; bismuth by Bi ; bromine by Br. MAGNETISM AND ELECTRICITY. 35 International Table of the Atomic Weights of the Most Important Elements, (1911). Name of Element. Aluminium Antimony . Arsenic . . Barium . . Bismuth . Boron . . Bromine . Cadmium . Calcium . Carbon . . Chlorine . Chromium. Cobalt . . Copper . . Fluorine . Gold . . . Hydrogen . Iodine . . Iron . . . Symbol. Atomic Weight. Al 27.1 Sb 120.2 As 74.96 Ba 137.37 Bi 208.0 B 11.0 Bi- 79.92 Cd 112.40 Ca 40.09 C 12.0 CI 35.46 Cr 52.0 Co 58.97 Cu 63.57 F 19.0 Au 197.2 H 1.008 I 126.92 Fe 55.85 Name of Element. Lead . . . . Magnesium . Manganese . Mercury . . Nickel . . . Nitrogen . . Osmium . . Oxygen . . . Phosphorus , Platinum . . Potassium . . Selenium . . Silicon . . . Silver . . - Sodium . . . Sulphur . . Tin . . . . Zinc .... Symbol. Pb Mg Mn Hg Ni N Os O P Pt K Se Si Ag Na S Sn Zn Atomic Weight. 207.10 24.32 54.93 200.0 58.68 14.01 190.9 16.00 31.04 195.2 39.10 79.2 28.3 107.88 23.00 32.07 119.0 65.37 The symbols not only represent the elementary bodies, but also their fixed quantities by weight, so that, for instance, the symbol Ni means 58.68 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 salt consists of 23.00 parts by weight of sodium and 35.46 parts by weight of chlorine, which together form 58.46 parts by weight of common salt. If several atoms of an element are present in a compound, this is denoted by numbers which are written to the right of the symbol, below, as proposed by Poggendorf, or above, as proposed by Berzelius, and still used at the pres- ent by a few people. Water, for instance, contains 2 atoms hydrogen (H) and one atom oxygen (O), and hence its formula 36 ELECTRO-DEPOSITION OF METALS. is H 2 0, which indicates that 2 parts by weight of hydrogen, together with 16 parts by weight of oxygen, form 18.016 parts by weight of water. The symbols may be said to constitute the chemical alpha- bet and the formulas may be considered as the words of the chemical language. By means of the symbols and formulas it is made possible, to express in the most simple manner, the chemical processes 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 endeavored to explain the nature of a chemical process, be translated into this chemical language, the equa- tions read as follows : 1. 2Fe 2 + 30 2 + 6H 2 = 4Fe 3 (OH) 8 . 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 hydrogen ; 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, phos- phorus, arsenic and antimony, fix three atoms of hydrogen, and finally, the elements of the fourth group, carbon and silicon, may combine with four atoms of hydrogen. Hence, we must ascribe a particular function of affinity to each ele- MAGNETISM AND ELECTRICITY. 37 ment 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 chemically equivalent. Tn chemical compounds, such equiv- alent elements may replace each other atom for atom, such substitution being also possible in elements of dissimilar val- ence, but it must take place in such a manner that a bivalent atom replaces two hydrogen atoms, a trivalent atom three hydrogen atoms, so that an equal number of valences is always exchanged. 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 35.46 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 16 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 16 to 2. Since the elements, nitro- gen, 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 — ! — = 4.67 parts by weight of nitrogen are substituted for 1 o part by weight of hydrogen. Finally, one atom of carbon or of silicon is equivalent to 4 parts by weight of hydrogen, or 1 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 1 part by weight of 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. 38 ELECTRO-DEPOSITION OF METALS. 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, trivalent in one combination and quinquivalent in another. Combinations of phosphorus with chlorine may serve as an example. Together they form a combination, PC1 3 , as well as one PC1 5 ;-in the first case 3 atoms of chlor- ine or 3 X 35.46 parts by weight are equivalent to 1 atom of phosphorus or 31.04 parts by weight. This capacity of differ- ent elements of being endowed with totally unequal valence, forces us to the assumption that valence is not a characteristic property of the elements, but is dependent on the nature of the elements combining 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, mercury. Bivalent and trivalent elements: Iron, cobalt, nickel, man- ganese. Trivalent elements : Boron, aluminium, gold. Trivalent and quinquivalent elements : Oxygen, phosphorus, arsenic, antimony, bismuth. Quadrivalent elements: Carbon, silicon, tin, platinum. Later on", in the section on the fundamental principles of electro-chemistry, in speaking of the development of the laws of Faraday, these groups will have to be referred to, and their importance will then become evident. Metals and non-metals. In accordance with the greater or less conformity of their physical j^roperties, the elements have, for the sake of expediency, been sub-divided into two sections, MAGNETISM AND ELECTRICITY. 39 namely, metals and non-metals, the latter being also called metalloids. The first section embraces the elements the prin- ciple characteristics of which are that they show metallic luster, are opaque or at the utmost translucent in thin laminae, are, as a rule, fairly malleable and ductile, and with the one exception of mercury, are all solid bodies at ordinary temper- atures and pressures, 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 differ- ent from those presented by compounds of the metals with oxygen. These differences will later on be referred to in de- tail. A very remarkable difference of the utmost importance, especially for our purpose, is in the action of the electric cur- rent upon the combinations between metals and metalloids, the metals being always deposited on the electro-negative pole, and the metalloids 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 considera- tions cannot be reached, and the classification as regards some elements turns out different according to whether one or the other behavior is first taken into consideration. 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 40 ELECTRO-DEPOSITION OF METALS. 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, silicon. 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 be- havior will have to be somewhat more closely considered, because we are thereby directed to extremely important classes of chemical 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 re- action with it. In the processes enacted thereby, the large class of oxides is formed, and the chemical process in which an absorption of oxygen takes place is generally called oxida- tion, while the term reduction 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 litmus previously reddened. The oxides of the first kind are chiefly formed with the co-operation of the ele- ments belonging to the metalloids, while those of the second class contain 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. MAGNETISM AND ELECTRICITY. 41 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, a& 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 assistance 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 hydroxy I groups, OH. Accord- ing to their valence the metals combine with one or more hydroxyl groups to bases. Salts. The groups of chemical combinations above referred' 42 ELECTRO-DEPOSITION OF METALS. 1;o, 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 com- bination 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 combination, 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 be- come 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 MAGNETISM AND ELECTRICITY. 43 the process 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 desirable to gain an insight into the chemical trans- formations 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 neutral- ization, 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, consists of sodium (Na) and chlorine (CI), and hence consti- tutes the well-known common salt (NaCl). However, in ad- 44 ELECTRO-DEPOSITION OF METALS. dition to the common salt, water (H 2 0) has also been formed by the chemical process, as shown by analysis. 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 w r ith 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 examples we have to write HC1 -f NaOH = H 2 + NaCl. Hydrochloric acid. Sodium hydrate. Water. Sodium chloride (common salt). H 2 S0 4 + 2KOH = H 2 + K 2 S0 4 . Sulphuric acid. Potassium hydrate. Water. Neutral potassium sulphate. i These formulas show plainly the connection which exists be- tween the acids, bases and salts. The formation of salts from the acids is thus 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 valence 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, MAGNETISM AND ELECTRICITY. 45 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 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 mole- cule. 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 suffi- ciently 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 saturating the sulphuric acid with caustic soda, i. e., by compounding the sulphuric acid with caustic soda up to the neutral reaction. The two processes just described are explained by the follow- ing equations, which also show distinctly the difference between neutral and acid salts : -1. H 2 S0 4 + NaOH = NaHS0 4 + H 2 0. Sulphuric acid. Sodium Acid sodium Water, hydrate. sulphate. 2. H 2 S0 4 + 2NaOH = Na 2 S0 4 + H 2 0. Sulphuric acid Sodium Neutral sodium Water, hydrate. sulphate. In an analogous manner, as a dibasic acid is capable of forming 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 46 . ELECTRO-DEPOSITION OF METALS. 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 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 conductors, 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 second 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 MAGNETISM AND ELECTRICITY. 47. current, a chemical change is 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. 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 constituent of the acid on the positive electrode. The ions separated on the negative electrodes are called cations and, hence, in the above-mentioned examples, sodium and hydrogen are the cations of sodium chloride, or of the acid. The cations 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 48 ELECTRO-DEPOSITION OF METALS. in solution, while the element hydrogen is gaseous and but very slightly soluble in water. Further, while the hydrogen- ion determines the characteristic properties of the acids, hy- drogen gas exhibits none of these properties, and the hydrogen- ion 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 •constituents, and this chlorine-ion possesses the same properties exhibited 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 possess- ing 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 elementary one ; and the reason for these different conditions and prop- erties will be more accurately known after we have to some extent become acquainted with 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 process 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 laws 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. MAGNETISM AND ELECTRICITY. 49 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 vessel 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 ac- quired 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 filled 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 re- moved from the water and the bladder be punctured with a pin, the pressure which had existed becomes plainly percepti- ble by a jet of fluid being forced upward. By exact investiga- tions of the magnitude of osmotic pressure it has been ascer- tained that it is proportioned 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 4 50 ELECTRO-DEPOSITION OF METALS. to Avogadro's law equal volumes of different gases under the same conditions of temperature and pressure contain equal numbers of molecules, and the weights of these gases are thus in the same ratio as their respective molecular weights. 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 num- ber of dissolved molecules in the same volume of solvent (equimolecular solutions) exert, under the same conditions of temperature, 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-law T s 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 de- composed, and that the 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 opposite 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 direc- tion presented by the action of the current, i. e., the positive molecular particles will wander with the direction of the cur- rent 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 MAGNETISM AND ELECTRICITY. 51 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. e., solutions which contain an equal number of dissolved molecules in the same volume of solvent; show the same elevation of the boil- ing 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 in equimolecular solutions furnished 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 com- pared with equimolecular solutions of many organic sub- stances, they caused under entirely equal conditions, a higher elevation of the boiling point or depression 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 assumption 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 results as regards elevation of the boiling point and depression of the freezing point, possessed the common property of con- cluding 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 Hoft's law requires, and it would therefore be but natural to suppose that sub- stances which give too large pressures in aqueous solutions are dissociated. He further found that dissociation increases with increasing dilution, and he established the law that for every 52 ELECTRO-DEPOSITION OF METALS. 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. It further follows that it is the ions which take charge of the '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 cations 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 •conducted through the electrolyte, the ions are attracted by the electrodes, the positively charged cations 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 may be 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 various 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 MAGNETISM AND ELECTRICITY. 53 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 opposite directions. Both these propositions may be com- bined to the proposition of the conservation of force and work 7 w r hich reads : No quantity of force and no quantity of ivork are lost; the force and ivork 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- tion al 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 con- servation 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 54 ELECTRO-DEPOSITION OF METALS. the elements yield a portion of their content of energy, gen- erally in the form of heat, though sometimes also with lumin- ous phenomena, so that the content of energy in the combina- tion is less than the content of energy of the elements before their union. If now a solution of the combination in water be prepared, 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 entering into chemical processes with the constituents of the electrolyte or with the electrodes, as may be shown by the following 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, ^-Ko | S0 4 -^ 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, MAGNETISM AND ELECTRICITY. 55 is shown by the abundance of hydrogen * which escapes in the electrolysis of the potassium disulphate. On the other hand, the acid residue S0 4 migrates to the anode, which, as it consists of insoluble platinum, cannot saturate the acid residue, and the latter is also transposed with water according to the following equation : S0 4 + H 2 0' = H 2 S0 4 + 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 f 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 H- 2H 2 = 4HC1 + 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- *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. f 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 Chemie," I. p. 203. 56 ELECTRO-DEPOSITION OF METALS. 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 : 40H = 2H 2 + 2 Hydroxide. Water. Oxygen. 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 (blue vitriol) CuS0 4 is to be electrolyzed. The copper ions migrate to the cathode <-Cu | S0 4 — > 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 residue becomes saturated with copper, dissolving approx- imately 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 H 2 S0 4 , 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 MAGNETISM AND ELECTRICITY. 57 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 : CuS0 4 + H 2 = Cu + H 2 S0 4 Cupric sulphate. Hydrogen. Copper. Sulphuric acid. In the electrolysis of a silver bath containing potassium- silver cyanide (KAgCN 2 ), potassium-ions and silver cyanide- ions (AgCN 2 *) appear : (a) — | <-K | AgCN 2 -> | + 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 : (6) K + KAgCN 2 = Ag'+ 2KCN. Potassium-ion. Potassium silver 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 : (c)Ag + CN = AgCN Silver. Cyanogen. Silver cyanide. (d) 2AgCN + 2KCN = 2KAgCN 2 Silver cyanide. Potassium cyanide. Potassium silver cyanide. *Hittorf, Ostwald's Klassiker, 23, § 45. 58 ELECTRO-DEPOSITION OF METALS. 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 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 : The quantity of substances which is liberated on the electrodes is directly proportional to the strength of the electric current which has been conducted through the electrolytes, and the time. Fig. 7. By conducting the current through a closed decomposing cell, Fig. 7, filled with acidulated water and furnished with two platinum electrodes which are connected with the poles •of a source of current, oxygen is evolved on the positive elec- trode, 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 MAGNETISM AND ELECTRICITY. 59 produced by a current of fixed strength within a determined time can be readily ascertained. If now a current of double the strength be for the same length of time passed through the decomposing cell, the quantity of oxyhydrogen gas pro- duced 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 an- other, which contained electrolytes of different compositions, and determined quantitatively the separations of cations 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 solu- tion 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- mined previous to electrolysis, are rinsed in water, next in alcohol, and finally in ether. They are then thoroughly dried and again weighed to determine the quantities of metal sepa- rated in the individual cells. The following quantities were found : Electrolyte. ■Quantity of sepa- f rated cations. . \ For 1 mg. H are separated . . . Atomic weights. . I. Dilute sulphuric acid 1:15. 67 ccm. H = 6.00 mg. H 1 mg. H 1 II. Potassium silver cyanide KAgC'y 2 . 650 mg. Ag. 108.33 mg. Ag. 108 III. Cupric sulphate CuS0 4 . 190 mg. Cu 31.66 mg. Cu 63.3 IV. Cuprous chloride CuCl. 380 mg. Cu 63.3 mg. Cu 63.3 00 ELECTRO-DEPOSITION OF METALS. From this it follows that the separated quantities of cations, 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 mg. 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 bi valence 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 converts them into other combinations. It has previously been mentioned that for the development of 1 g. hydrogen, 96540 coulombs must pass through the electrolyte. 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 Electro-chemical equivalent, i. e., the number of coulombs which split off in one second the portion of atomic weights of the cations (metals) or of the anions referred to a valence and expressed in grammes, i. e., the gramme-equivalent. Hence, for the separation of 1 gramme-equivalent of copper = 31.65, or of 1 gramme-equivalent of silver = 108,96540 coulombs 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 ex- pressed : The quantities of the different ions combined with equal MAGNETISM AND ELECTRICITY. 61 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 simultaneously 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 9654-0 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. 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 Deposit in Specific Equivalent. 1 Ampei-e-hour Gravity. 0.104 0.0375 0.00009 0.415 1.4940 6.8 0.258 0.9322 5.7 0.305 1.1001 8.7 0.329 1.1858 8.8 0.658 2.3717 8.8 0.681 2.4513 19.2 2.043 7.3560 19.2 0.193 0.6950 7.8 0.289 1.0423 7.8 1.071 3.8580 11.3 0.304 1.0945 8.6 0.504 1.8160 21.4 1.118 4.0248 10.5 0.308 1.1094 7.3 0.616 2.2180 7.3 0.339 1.2200 7.2 Solution-tension of metals. A fluid evaporates on the surface until the vapor-pressure produced is equal to the evaporation- tension of the fluid. Analogous to this process is the osmotic pressure which a salt exercises when dissolved in water, a pressure which increases with the quantity of the salt until it 62 ELECTRO-DEPOSITION OF METALS. is in equilibrium with the solution-tension. According to Nernst, every metal when immersed in an electrolyte also possesses the power conditional to its chemical nature to give off metal atoms as ions (cations) to the solution, and this power is called solution-tension. The solution-tension is the greater the smaller the number of cations which are already present in the electrolyte ; if, on the other hand, the electrolyte contains a great number of cations derived from the dissociation of the salt, the osmotic pressure may overbalance the solution-tension, or the osmotic pressure may be equal to the solution-tension. In the first case, when the solution-tension preponderates, the metal will give up to the solution cations 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 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 given up to the solution by the zinc so long as the solution-tension of the zinc overbalances the osmotic pressure of the dissolved zinc-ions. When an equilibrium between osmotic pressure and solution-tension 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 give up to the 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-tension of the cop- per, and hence not only counteracts the formation of new copper-ions, but carries positive copper-ions from the electro- lyte to the copper, the latter receiving thereby a positive MAGNETISM AND ELECTRICITY. 63 charge, while the fluid surrounding the copper becomes negative. However, no matter whether the solution-tension may con- siderably overbalance the osmotic pressure, by the mere dip- ping of the metal in the electrolyte the quantity of ions which are newly formed will always be small, because by reason of the electrostatic attraction of the cations by the negatively- charged metal, there will take place on the contact-surface between the metal and the electrolyte an accumulation of cations, the osmotic pressure of which will consequently be increased, and counteract the solution-tension. 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 sulphate solution, and copper in cupric sulphate solution, such as a Daniell 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-tension ; 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-tension 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 '64 ELECTRO-DEPOSITION OF METALS. now by means of a metallic wire the zinc be outside of the solutions connected with the copper, thus, establishing a closed circuit, the following process takes place : The positive elec- tricity in the copper migrates through the wire to the zinc, and neutralizes 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 gives up cojDper-ions to the copper, whereby the latter is again charged with positive •electricity. On the other hand, after the exchange of elec- tricities in the zinc by the solution-tension, 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 sulphate solution to the copper, or until all the zinc is ionized, i. e., dissolved. Nernst's conception of the solution-tension of the metals is analogous to that of the osmotic pressure, the impelling force •of a Daniell battery having the character of a pressure, and for that reason Ostwald designates a galvanic battery as a machine driven by osmotic pressure, eventually by electrolytic solu tion-tension . The electro-motive force of such a cell is mainly determined by the magnitude of the solution-tension of the metals. In the closed cell the metal gives up with greater solution-tension its atoms as ions into the electrolyte in which it is confined, while the cations 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 cations of its electrolyte separate non-electrically, the cathode. Since the cations are discharged on the cathode, the latter is also called the conducting elec- trode, 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. MAGNETISM AND ELECTRICITY. 65 The solution-tension 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 cations 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 dissolved zinc is deposited on the cathode. By the anion SO 4 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 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 oxidizing 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 to 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 5 66 ELECTRO-DEPOSITION OF METALS. 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 SO 4. migrate to the electrode connected with the positive pole, where they dissolve copper, thus giving up fresh copper-ions- to 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 point, thus indicating the absence of a counter-current ; the electrodes have proved them- selves as non-polarizable. 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 snlphurie acid (H 2 S0 4 ), the latter is decomposed into hydrogen-ions which go to the platinum cathode while the S0 4 -ions 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 con- sequence being that from the hydrogen of the cathode a counter-current flows to the oxygen of the anode, which is in- dicated when the primary current is interrupted by the needle of the galvanometer, instead of merely returning to the O point, deflecting in a direction opposite to that of the previous deflection, and returning to the point only after the equal- ization of the charges in the electrodes. The counter-current or polarization-current appears also MAGNETISM AND ELECTRICITY. 67 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 copper, 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 gener- ated, and consequently flows in a direction opposite to that of the main current, which passes from the zinc to the copper. The electro-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 plat- inum electrodes, zinc separates on the cathode while chlorine 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-tension, 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 permanently 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 68 ELECTRO-DEPOSITION OF METALS. charge of the ions. The decomposition-values of solutions which separate metals vary. Le Blanc found as decomposi- tion-values of solutions which contained per liter one combin- ing 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 decomposition 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, 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 elec- trolyte, must be equal, was an erroneous one. The mobility of the ions varies, and depends on their nature. If, for in- stance, hydrochloric acid be electrolyzed, the hydrogen-ion migrates about five times as rapidly to the cathode as the chlorine-ion to the anode. The cations and anions of the metallic salts act in a similar manner, and consequently a greater concentration will take place on the cathode and a re- duction in the content of metal on the anode, when the anions migrate more slowly than the cations ; and vice versa, concen- tration will increase on the anode when the anions migrate more rapidly than the cations. MAGNETISM AND ELECTRICITY. 69 The middle layer of the electrolyte always remains un- changed and of the same concentration, the changes in con- centration 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 cations 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 w T ill 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 detailed description of all the forms of voltaic cells, because the number of such constructions is very large, and the num- ber of those which have been successfully and permanently introduced 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- tension of the metals or the osmotic pressure of the solutions, and we know further that in a voltaic cell chemical energy is converted into electrical energy. In speaking of polarization which is formed when two different metals dip in one fluid, we have seen that the hydrogen liberated on the copper in a Volta cup cell generates a counter-current which weakens the principal current. This hydrogen appearing on the posi- tive 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 (70) SOURCES OF CURRENT. 71 way or by chemical agents which oxidize it, are called constant cells. 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 trough 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 •connected 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 amalgama- tion is also a protection against the above-mentioned chemical work of the cell, the hydrogen bubbles adhering so firmly during the interruption 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 72 ELECTRO-DEPOSITION OF METALS. 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 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 a suitable solution of mercury salt and rub with a woolen rag. A suitable solution is prepared by dissolv- ing 10 parts by weight of mercurous nitrate in 100 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 12 parts of hydro- chloric acid and 100 of water, or by dissolving 10 parts by weight of potassium mercuric cyanide and 2 parts potassium cyanide in 100 parts of water. In order to preserve as much as possible the coating of mercury upon the zinc, sulphuric acid saturated with neutral mercuric sulphate is used for the cells. For this purpose frequently shake the concentrated sulphuric acid (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 of the addition of mercuric sulphate, Bouant recom- mends to compound the dilute sulphuric acid with 2 per cent, of a solution obtained as follows : Boil a solution of 3^ ozs. of nitrate of mercury in 1 quart of water, together with an excess of a mixture of equal parts of mercuric sulphate and mercuric chloride, and, after cooling, filter and use the clear solution. Smee cell. This cell consists 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 of silver may be employed without fear of its bending out of shape and making a short circuit. Platinizing is effected by suspending SOURCES OF CURRENT. 73 the silver plates in a vessel filled with acidulated water, add- ing 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 man- ner is a black powder which roughens the surfaces, in conse- quence of which the bubbles of hydrogen become readily de- tached, and polarization is less than with silver plates not platinized. The use of electrolytically-prepared 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 the United States with silver and gold plating solutions. 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 hydrogen evolved to water, or, in other words, which immediately oxi- dizes the hydrogen to water. From this conviction originated the so-called constant cells with two fluids, the first of these cells being, in 1829, constructed 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 earthen- ware pot and a zinc rod suspended in the latter. The glass vessel is filled with saturated blue vitriol solution, a small piece of blue vitriol being added, and the porous earthenware pot with dilute sulphuric acid about 1 part of acid to 12 to 20 parts of water. The acid residue S0 4 migrates to the positive zinc, and there forms zinc sulphate, while the hydrogen which is liberated on Fig. 8. 74 ELECTRO-DEPOSITION OF METALS. Meidinger cell. Fig. 9. the electro-negative copper, reduces from the blue vitriol solution an equivalent quantity of copper, which is deposited upon the electro-negative plate according to the following equation : CuS0 4 + 2H = Cu + H 2 S0 4 Cupric sulphate. Hydrogen. Copper. Sulphuric acid. Thus the hydrogen is removed by its combining with the acid-residue S0 4 to sulphuric acid. A drawback of the Daniell cell is that the blue vitriol solution diffuses into the porous pot, where it is decomposed by the zinc on coming in contact with it, and the copper is separated upon the zinc, the efficiency being thus destroyed, or at least very much weak- ened. The electro-motive force of the Daniell cell is quite exactly 1.1 volt. This may be considered a modified Daniell cell. Like the Callaud cell, it has no porous partition, the mixture of the two fluids being retarded by their different specific gravities. The form of the Meid- inger cell, as most generally used, is shown in Fig. 9. * Upon the bottom of a glass vessel, A, provided at b with a shoulder, stands a small glass cylinder, K, which contains the electro-negative copper cylinder D; from the latter a conducting wire leads to the exterior. Upon the shoulder, at 6, rests the zinc cylinder Z, which is also provided with a conducting wire leading to the exterior. The balloon C closes the vessel by being placed upon it. The balloon is filled with pieces of blue vitriol and Epsom salt solution. The entire cell is also filled with Epsom salt solution (1 part Epsom salt to 5 water.) In the balloon C concentrated solution of blue vitriol is formed which flows into the glass cylinder K. If the battery is not SOURCES OF CURRENT. 75 closed, the concentrated copper solution remains quietly stand- ing in K, its greater specific gravity preventing it from rising higher and reaching the zinc. If, however, the current be closed, zinc is dissolved, while metallic copper is separated from the blue vitriol solution, and concentrated solution flows from the balloon G to the same extent as the blue vitriol solu- tion in D becomes dilute by the separation of copper. Hence the action of the cell remains constant for quite a long time, and of all the modified forms of Daniell's cell consumes the least blue vitriol for a determined quantity of current. How- ever, in consequence of its great internal resistance (3 to 5 ohms, according to its size) its current-strength is small. The electro-motive force of the Meidinger cell is 0.95 volt. Bunsen cell. Bunsen, in 1841, replaced the expensive plati- num by prisms cut from gas-carbon, which is still less electro- negative than platinum, and very hard and solid, so that it perfectly resists the action of the nitric acid. In place of the gas-carbon an artificial carbon may be prepared by kneading a mixture of pulverized coal and coke with sugar solution or syrup, bringing the mass under pressure into suitable iron moulds and heating it red-hot, the air being excluded. After cooling the carbon is again saturated with sugar solution (others 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.,. the removal of the hydrogen-bubbles which produce polariza- tion, is most effectively assisted by the nitric acid, the hy- drogen being oxidized to water according to the following equation, while the nitric acid is reduced to nitric oxide: 76 ELECTRO-DEPOSITION OF METALS. 2HN0 8 Nitric acid. + 6H Hydrogen. 2NO Nitric oxide. 4H 2 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 migrates to the zinc and combines with it to zinc sul- phate (ZnS0 4 ) as illustrated by the following scheme : Sulphuric acid | Nitric acid H 2 S0 4 2HNO, Carbon ( + )C \< / ■ \ / \ ZnS0 4 (Zinc sulphate) 2HN0 3 (Nitric acid) H 2 (Hydrogen) \ At / K,0, Nitrogen tetroxide +2H 2 Water. To prevent the two fluids from mixing, the use of a porous partition is required, the same as in DanielFs cell. Figs. 10, 11 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 SOURCES OF CURRENT. 77 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 bind- ing-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 transmission of the current. The other vessel is filled with Fig. 10. Fig. 11. Fig. 12. dilute sulphuric acid (1 part by weight of sulphuric acid of 66° Be. — 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. 11 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 advantageous, because its effective zinc surface can be kept larger. 78 ELECTRO-DEPOSITION OF METALS. Fig. 12 shows a plate cell such as is chiefly used for plunge batteries. Fig. 13 shows an improved Bunsen cell of great power. It is particularly adapted for use with nickel, copper, brass or bronze solutions. It has an electro-motive force of 1.9 volts. Where the absence of power prevents the use of a dynamo, a battery of these cells is very suitable for nickel plating. 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 (0.5 to 0.25 ohm, according to Fig. 13. 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. The 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- SOURCES OF CURRENT. 79' 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. 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, con- centrated sulphuric acid 400, sodium nitrate 500, and bichro- mate 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 chrom- ium 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 work- ing for six days, from morning to evening, without refilling being required. During the night the batter}^ remained filled, but inactive. The solution is obtained by treating Langbein's chromic iron powder with concentrated sulphuric acid and carefully diluting with water. 80 ELECTRO-DEPOSITION OF METALS. The electro-motive force of a cell filled with this solution is 1.8 volts. Considering the lasting quality and great con- stancy, and consequent cheapness, as well as freedom from odor of this solution, it would appear to be the most suitable. 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 £ to | 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 pur- pose the carbons are placed £ to 1 inch deep in melted paraffine and allowed to remain 10 minutes. On the sides where the armature comes in contact with the carbon, an excess of par- affine 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 71. 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° Be. 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 SOURCES OF CURRENT. 81 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 sticks of wood laid across the glass vessel to drain off. In put- ting the cells 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, being 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 Leclanche 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 6 82 ELECTRO-DEPOSITION OF METALS. 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. 14 which possesses certain 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, coiled in the form of a spiral, which is suspended from an Fig. 14. ebonite cover carrying a terminal connected with the zine. 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 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 SOURCES OP CURRENT. 83 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- 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 regener- ation of these plates was still more troublesome. By treat- ment with various chemical agents, Dr. Bottcher, of Leipsie, has succeeded 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 intro- duced into commerce. Cupron 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 84 ELECTRO-DEPOSITION OF METALS. zinc dissolves, zinc-oxide-soda being formed according to the following scheme, while the cuprous oxide is reduced to copper: Cuprous oxide CuO( + ) _ Zn{ONa). l 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 her- metical closing of the former also apply to the latter. An addition of sodium hyposulphite to the caustic soda solution is recommended 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 - 5 V part of mercuric sulphate in 100 parts of water, and adding 38 parts of pure concentrated sulphuric acid, being employed. SOURCES OP CURRENT. 85 A plunge battery, as constructed by Fein, consists of a wooden box, which contains in two rows six vessels into which dip the zinc and carbon plates. The latter are secured to wooden cross-pieces furnished with handles, and may be maintained at any height desired by the notches in the stand- ards. According to the current-strength required the plates are allowed to dip in more or less deeply. In using the above-mentioned chromic acid solution origin- Fig. 15. 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 86 ELECTRO-DEPOSITION OF METALS. Fig. 16. electro-plating operations requiring a constant current for some time, but they may be employed for temporary use. If plunge batteries are to be used for constant work in elec- tro-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. 15) the porous clay cup is omitted, the massive carbon cylinders K, K, etc., being each 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. 16 shows a plunge battery manufactured by Dr. G. Langbein & Co., the details of which will be readily understood without further description. The zinc plates dip in the diaphragms, which are filled with a mixture of 26 lbs. of water and 2 lbs. of sulphuric acid free from arsenic, in which 2f ozs. of amalgamating salt have previously been dissolved. The carbon plates dip into the glass vessels, which contain a solution of commercial crystallized chromic acid in the pro- portion of 1 part acid to 5 water. In place of this pure chromic acid the following mixture may also be used : 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 SOURCES OF CURRENT. 87 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. Bichromate cell. 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 advantage- ously employed. In the bottle A two long strips of carbon united above by a metallic connection are fastened, parallel to one another, to a vul- canite stopper, and are there connected with the binding-screw ; these form the neg- ative element, and pass to the bottom of the bottle. Between them is a short, thick strip of 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. 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 wi : w + wi By now combining several such cells, say n cells, to a bat- tery, the electro-motive force of the latter will become n.E, but the internal resistance n.w, and with the same closed cir- cuit as the single cell had, the external resistance wi will not increase. Hence the current-strength of these n elements has to be written n.E J = n.w. + wi 00 ELECTRO-DEPOSITION OF METALS. 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 in- creases n-times. Thus the current-strength approaches more and more the limit of value E? == 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 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- ly strength approaches more and more the value — wi Hence, it follows that the enlargement of the surface of the exciting pair of plates produces an increase in 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 Fig. 18. *fa Vfa V^CD Vmzd V= practice, we find that the cells may be coupled in various ways according to requirement. 1. 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. 18), the current passes four times in succession through an SOURCES OP CURRENT. 89' equalty large layer 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. 19. Fig. 20. 2. By connecting four cells alongside of each other, i. e., all the zinc plates and all the carbon plates one with another (Fig. 19), 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 coupling for quantity of current, or coupling in parallel. 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. 20, whereby, according to what has above been said, the electro-motive force, as well as the current-strength, is increased. This mode of connection 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- 90 ELECTRO-DEPOSITION OF METALS. plater may couple Lis cells in either way. We will here only mention the proposition deduced from Ohm's law, that a num- ber of voltaic cells yield the maximum of current-quantity when they are so arranged that the internal resistance of the 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 elements 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. B. Thermo-Electric Piles. Although thermo-electric piles are only used in isolated Fig. 21. cases for electro-plating operations, for the sake of complete- ness their nature and best-known forms will be briefly men- tioned. Professor Seebeck, of Berlin, observed in 1823, that elec- SOURCES OF CURRENT. 91 tricity is developed when the soldered joints of two metals are unequally heated ; hence, while electricity can be converted into heat, heat vice versa can be converted into electricity. Noe's thermo-electric pile (Fig. 21) consists of a series of small cylinders composed of an alloy of 36 J parts of zinc and 62 J parts of antimony for the positive element and stout Ger- man silver as the negative element. The soldering consists of tin. The junctions of the elements are heated by small gas jets, and the alternate junctions are cooled by the heat being conducted away by large blackened sheets of thin copper. A pile of twenty pairs has an electro-motive force of 1.9 volts. Clamond's thermo-electric pile (Fig. 22) also consists of a zinc- Fig. 22. antimony alloy, but in place of German silver, ordinary tinned sheet iron is employed. To insure good contact be- tween 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 92 ELECTRO-DEPOSITION OF METALS. succeeding series by asbestos disks. With the consumption of about 6 J cubic feet of gas per hour, such a pile deposits 0.7 oz. of copper, which corresponds to an intensity of about 17 amperes. Quicker' s thermo-electric pile, invented in 1890, is shown in Fig. 23. 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 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 Fig 23. 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'jnto 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- SOURCES OF CURRENT. 93 tions are soldered long copper strips secured in notches in the slate plate. They 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 10 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 l-eVI- 5200 = 0.20 heat-unit. These correspond to 1208 volt-amperes, 1 volt-ampere being equal to 0.00024 heat- unit. Hence, in Giilcher'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 \ per cent, in the outer circuit. 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 elec- tricity, in the dynamo-electric machine a conversion of me- chanical energy into electrical energy takes place. 94 ELECTRO-DEPOSITION OE METALS. 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 : 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. 24. Fig. 24. 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 SOURCES OF CURRENT. . 95 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 direc- tion of the arrow, out from the plane of the illustration to- wards 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 greater, the greater the velocity with which the wires, or con- ductor forming the windings, are moved through the mag- netic field. If the length of the conductors be increased by enlarging 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 strength- ened, 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 perpen- dicularly cut by the conductor. ■yt> ELECTRO-DEPOSITION OF METALS. Separate parts of the dynamo- electric machine. The frame. The production of the magnetic field has for a long time been 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. Fig. 25 shows a two-polar, and Fig. 26 a four-polar type of Fig. 25. Fig. 26. 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 W. v. Siemens, the electric current gener- ated in the armature is utilized for the excitation of the mag- netic field. The dynamo-electric principle is based upon the following : Lines of force, few in number, are present from a jprevious excitation in every magnet frame, and this is called SOURCES OP CURRENT. 97 remanent magnetism (see p. 13). In revolving the armature the existence of this small number of lines of force suffices for the induction of a weak current which is partly conducted through the magnet winding, the magnetic field being 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 wind- ing, until the frame is saturated with lines of force. This process is called self-excitation, while the term foreign or sepa- rate 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- ings wrapped around it. The iron body cannot be made of one piece because rotatory 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 armature. 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. 27 represents a scheme of such ring-winding. iVand S are the two field magnets of the frame. Every two of the continuous 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 7 98 ELECTRO-DEPOSITION OF METALS. under the poles. In revolving the armature from 0° to 90°, the generation of current decreases, from 90° to 180° it de- creases, from 180° to 270° it increases in a reverse sense, and from 270° to 300° it again decreases. Thus, currents flowing alternately in opposite directions, the so-called alternating currents are generated, and their conversion into constant Fig. 27. ISO. currents of uniform direction is effected by the commutator. At 0° and at 180°, the generation of current is equal to 0, and at these points the current changes its direction ; the line 0° to 180° is called the neutral zone. In the drum armature the conducting wires are wound upon the armature-core parallel to its axis, carried on the faces of the core around the core-shaft, and the ends of every two coils SOURCES OF CURRENT. 99 lying alongside each other on a face are connected, one with the other, and with a segment of the commutator. Fig. 28 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 indicate the connection of the coils upon the commutator-side Fig. 28. and with the commutator, and the dotted lines, the coil-con- nections 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 100 ELECTRO-DEPOSITION OF METALS. run on the faces as well as in the interior of the bore, which are of no importance as regards the generation of the current 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 suit- able 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 run- Fig. 29. ning rather around the copper wires through the iron. How- ever, 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 armatures 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 amatures. Fig. 29 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 seg- ments and fastened to the armature-shaft. It is insulated SOURCES OF CURRENT. 101 with mica. The segments consist of copper, tombac, or brass and are insulated from each other as well as from the com- mutator 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 segment. The function of the commutator consists in converting the alternating currents of the windings generated by induction into constant currents of uniform direction. As seen from Fig. 27, currents of opposite direc- tions 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 wind- ings is carried along as positive 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 previ- ously shown, the direction of the current in both halves is different. Brushes. The function of the brushes is to take off the cur- rent from the commutator. For such dynamo-electric ma- chines as here come into question, the brushes are of fine copper or brass wire-gauze, or of very thin metal-plate. Car- bon brushes are often used for dynamo-electric motors. The choice of material for the brushes depends on the prop- 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 removed by frequent blowing out with a pair of bellows, or a similar instrument, may readily cause short-circuiting. 102 ELECTRO-DEPOSITION OF METALS. Brushes of twisted, thin inetal-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 oxidizing 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 passage of the current from the commutator to the brushes. This, on the one hand, results in the commu- tator and brushes becoming 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 elas- tically 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 furni shed with two thick copperbolts 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 insu- lating material, and secured to the rocker by insulated nuts. 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. SOURCES OF CURRENT. 103 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 Direct current dynamos. If the whole of the current 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 combination 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 direc- tion. The plating dynamos on the market to-day are what is technically known as "shunt-wound" 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. 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- 104 ELECTRO-DEPOSITION OF METALS. 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. Fig. 30 illustrates a two-pole shunt-wound dynamo, and Fig. 31 a two-pole shunt-wound dynamo for high current- strengths. In Fig. 30 the frame is of cast-steel and the bearing plates are screwed to it. In Fig. 31 the pillow-blocks and frame are mounted upon a common cast-iron plate. . The armature is of the slotted drum type described in Fig. SO. Fig. 29. 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 thus excluded, as is invariably the case with wires secured by means of screws to the commutator. An abundance of cop- per cross-sections being used, the degree of efficiency of the dynamo is an excellent one. To decrease friction, the portions SOURCES OF CURRENT. 105- of the steel armature shaft which run in the journal boxes of phosphor-bronze, as well as the latter themselves, are highly 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 revolutions is a moderate one, and consequently the con- sumption 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. Fig. 31. 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, pass- ing 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 armature winding and increased magnetic reaction caused by the armature current is provided for. 106 ELECTRO-DEPOSITION OF METALS. Fig. 32 shows a multi-polar type of "dynamo manufactured by The Hanson & Van Winkle Co., Newark, N. J. The frame is made of a high-grade cast iron, having a high mag- netic permeability. The poles are made of soft rolled steel with cast-iron shoes. Field coils are 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. Fig. 32. The armature, Fig. 33, is of the toothed type. The core is built up of thin soft steel discs, and is insulated on both sides smd assembled on a spider constructed to insure the greatest -amount of ventilation. The armature coils are made in a form and perfectly insu- lated. The slots in which the coils rest are also insulated, so that there is no chance for a ground. The segments of the commutator are forged from pure cop- per carefully insulated with the best mica. The radials from the bars are so set that a steady current of air is thrown on (the commutator and brushes. SOURCES OF CURRENT. 107 The bearings are self-aligning, boxes are made of special bronze, and are provided with large oil-wells and automatic oiling-rings. Fig. 33. This machine will run continuously under full load with a rise of temperature above the surrounding atmosphere not Fig. 34. exceeding 55° F. in the accumulator, and something less in windings. 108 ELECTRO-DEPOSITION OF METALS. . Fig. 34 shows a separately excited dynamo of the multi- polar type manufactured • by The Hanson & Van Winkle Co., Newark, N. J. It is a very popular form of generator, the- field being excited from an external circuit, usually 1 10 or 220 volts D. C. The capacity is 4000 amperes at 6 volts. The commercial efficiency is high, 86 per cent. — the electrical efficiency averages 93 per cent. This form of dynamo is fur- nished for both two and three wire systems of current distribu- tion. The frame and pole pieces are of steel. For the frame a special, soft grade is used, having a high magnetic perme- ability. 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 improvements 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 manufacturer had to rely upon the generation of the electric current by batteries. The latter, at the very best, are trouble- some to manage ; they only give out their full power w T hen 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 atten- tion. Even when working on a small scale, it is cheapest to SOURCES OF CURRENT. 109 procure a small gas or other motor for driving a small dynamo, the lathes, and grinding and polishing machines. Most cities and towns are now supplied with electric light from central stations, and thus the means are furnished to smaller plants to avail themselves of the use of electricity without the necessity of installing their own source of power. From such central stations the conductors are fed with cur- rents of 110 or 220 volts. Hence the wires from the power circuit can be directly connected with a motor-generator, which is constructed for the respective voltage and converts Fig. 35. 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 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. 35 shows a 150-ampere motor-generator set, and Fig. 36, 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 110 ELECTRO-DEPOSITION OF METALS. whole outfit being mounted on a substantial iron base. There is no loss of power as in the caee when belts are used, so the full capacity of the generator is available. In many instances 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. Th is,of course, increases the cost of installation. With the motor- Fig. 36. 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. To enable the manufacturer of dynamos to suggest the most suitable machine the following data should be submitted to him: 1. Variety, size, and number of the baths which are to be fed by the machine. 2. The average surface of the articles in the bath, or their maximum surface, and the metals of which they consist. SOURCES OF CURRENT. Ill 3. Whether at one time many, and at another time few,, articles are suspended in the bath. 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- 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 prac- tically 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 solu- tion, 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 connected one with the other, while the plates with uneven numbers, 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 touch- ing 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. 112 ELECTRO-DEPOSITION OF METALS. Hence, in charging, a conversion of electrical energy into chemical energy takes place and, in discharging, a recon- version 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- 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 sulphuric acid, and the positive plates with one of minium and sulphuric acid. The current reduces the litharge and peroxidizes 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 sulphurie 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- SOURCES OF CURRENT. 113 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 for- mation of lead disulphate must chiefly take place on the posi- tive electrodes, since the anion (the sulphuric acid residue) migrates to the positive pole, and by the action of the water the lead disulphate is decomposed to lead peroxide and free sulphuric acid. 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 + pole of the dynamo and the negative plate with the — pole, decomposition of sulphuric acid takes place, the hydrogen migrating to the negative elec- trode, 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 ) 2 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 2 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 = Pb0 2 + 2H 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- 114 ELECTRO-DEPOSITION OP METALS. 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 per- oxide 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 nega- tive electrode, in consequence of which, by the decomposition of the sulphuric acid, the anion S0 4 migrates to the positive lead electrode, and forms lead sulphate, while the hydrogen separated 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 Pb + S0 > . = PbS0 ' Lead. Sulphuric acid residue. Lead sulphate. On the + electrode Pb0 * . + 2H = Pb0 + H *° 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 S0 4 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 SOURCES OF CURRENT. 115 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 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 : 2PbS0 4 + 2H 2 = Pb + 4H + Pb0 2 + 2S0 4 . The anions sulphuric acid and lead peroxide migrate to the positive pole and the cations 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 required, or, in other words, whose decomposition-point is lowest, 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 elec- trodes would soon be exhausted, further charging can only take place when from the lead sulphate formed on the elec- trodes, fresh molecules are brought into solution, by the dis- sociation of which the precipitated ions are replaced, and charging is only finished when all the lead sulphate is dis- solved and separated as lead peroxide and lead-sponge. "With a further passage hydrogen-ions, which possess the next 116 ELECTRO-DEPOSITION OF METALS. highest decomposition-point, are separated. The above-de- scribed 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. According to Liebenow'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 as- sumes that at the moment of discharge, the latter are con- verted into bivalent lead-ions, the dissolving lead peroxide furnishing additional quadrivalent lead-ions, while at the moment of charging the bivalent lead-ions are converted into quadrivalent ones, 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. 37 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. 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 1.21. 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, SOURCES OF CURRENT. 117 which can only be removed with difficulty, and by this for- mation of crystals the accumulator acquires a very great re- sistance. 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 "boiling" 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 sulphuric acid of 1.05 specific gravity. Fig. 37. By the formation of lead peroxide and its subsequent reduc- tion, the positive electrodes readily undergo changes in vol- ume, they being liable to buckling and the scaling off of active mass ; lead-crystals of considerable length may deposit on % the negative electrodes, both these occurrences giving rise to short-circuiting. Hence, the accumulator should be fre- quently inspected, 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 118 ELECTRO-DEPOSITION OF METALS. 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, charging 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 interrupting 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 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- mentioned 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 ESTABLISHMENT IN GENERAL. Although rules valid for all cases cannot be given, be- cause 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, nevertheless, certain main features which must be taken into consideration 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 (119) 120 ELECTRO-DEPOSITION OF METALS. 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 batteries 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 temper- ature 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 ELECTRO-PLATING ESTABLISHMENTS. 121 indifferent to the plating solution suspended in the bath. In this manner baths of 1000 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 current 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 tempera- ture 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 lowest point, which also serves for the reception of the rinsing 122 ELECTRO-DEPOSITION OF METALS. 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 w r hen 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 number 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 requir- ing the use of emery, or coarse grinding powders, should be performed in the actual grinding room, as well as the grinding upon stones and scratch-brushing by means of rapidly revolv- ELECTRO-PLATING ESTABLISHMENTS. 123 ing steel scratch-brushes. Articles already plated are, of 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 & suitable apparatus for keeping the dust out of the room. If this cannot be done, wooden frames covered with packing- oloth, placed opposite the polishing lathes, render good ser- vice; the packing-cloth by being frequently moistened with water retains a large portion of the dust. Many of the states now have laws compelling firms to install some kind of apparatus to keep the dust out of the room. There are many schemes of installing these exhaust fans, the most common of which is, according to T. C. Eichstaedt,* as follows: A fan or blower of sufficient capacity for the number of lathes in use is generally placed at one end of the room, driven by a belt or directly connected with a motor. The latter is the most economical and the better of the two. Then the polishing and buffing lathes are placed in a straight line and a large galvanized iron pipe, having openings with intake pipes and hoods for each wheel, is run to the floor behind each lathe. * Metal Industry, March, 1913. 124 ELECTRO-DEPOSITION OF METALS. 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 electricalty-driven grinding and polish- ing 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 Treatment." Electro-plating Arrangements in Particular. The actual electro-plating plant consists of the following parts : 1. The sources of current (batteries or d} 7 namo-electric machines) with auxiliary apparatus. 2. The current-conductors. 3. The baths, consisting of the vats, the plating solutions, 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 ELECTRO-PLATING ESTABLISHMENTS. 125 sufficent 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 centi- meters, a current 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 de- composition of the electrolyte did not amount to 2.5 volts. As previously mentioned, a Bunsen cell furnishes about 1.8 volts, and to 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 im- pediment 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 126 ELECTRO-DEPOSITION OF METALS. definite time can be readily calculated. The electro-chemical equivalent has been referred to on p. 60, and it has been established that it represents the number of coulombs which separates 1 gramme-equivalent of metal per second. When by 1 coulomb, i. e., by 1 ampere, 0.3290 mg. copper per second is separated from cupric oxide salts, 1.184 gr. copper' are separated 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 equiv- alent 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 cur- rent-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-strength. 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 -iV millimeter thickness with a current-density of 0.4 ampere. First calculate the weight of the deposit by mul- tiplying the surface in square millimeters with the thickness and specific gravity. One square decimeter is equal to 10,000 square millimeters, which, multiplied by T V 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 -fV 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- ELECTRO-PLATING ESTABLISHMENTS. 127 density of 0.4 ampere is required, and 1 ampere deposits, ac- cording to the table given on p. 61, ] .1094 grammes in 1 hour, \ ampere deposits 0.4437 gramme in 1 hour, and, therefore, about 19f 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 1.10 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 \ 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 remain about 4f hours in the bath for the deposi- tion 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 thor- oughly. 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. 61) how much metal should have been precipitated in the time consumed by the current- 128 ELECTRO-DEPOSITION OF METALS. strength used ; the result will be the theoretical current-output. The practical current-output in per cent, is found by multi- plying 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 (1.1094 X 1.5 X 3) 4.923 grammes of nickel. Hence, the practical current-output attained is 4.925 : 4.45 = 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 . calculati the time the re _ 100 S suit obtained above would have to be multiplied by the fraction _ , and for calculating the current- <;urrent-output in per cent. strength the quotient is likewise to be multiplied by the frac- 100 ;tion : 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 •electromotive 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, ■n . \ ,,, , , i . Specific resistance X dm. electrode-distance Resistance of the electrolyte = -£ — dm. object-surface. ELECTRO-PLATING ESTABLISHMENTS. 129 According to p. 21, 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 electro- lyte, 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 cur- rent-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 •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 : 92 X 1 2 W= - ' IQ0 ' = 0.01104 ohm. From this the electro-motive force, E, required to send the current-strength, J, through the bath is calculated : E = J X W = 125 X 0.01104 = 1.38 volt. However, this is valid only for the normal temperature of 18° C. (64.40° F.). If the electro-motive force has to be calculated, which is required at a higher temperature, for sending 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. 26, whereby, if the tem- perature of the bath is 24° C. (75.2° F.), the equation assumes the following form : 9 130 ELECTRO-DEPOSITION OF METALS. Specific resistance = 0.92 (1 — 0.0113 X 6) = 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 18° C, the product subtracted from 1, 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 18° 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 0.858 X 1.2 n _ nn [ W = jqq = 0.0103 ohm, and the electro-motive force, E, which is capable of forcing 125 amperes through the resistance of 0.0103 ohm : E = J X W = 125 X 0.0103 = 1.287 volt. If the electrolyte is 6° C. colder than 18° C, the formula is 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 + 0.0113 X 6) = 0.9824 ohm ; the resistance of the bath is then : W^ - 982 ^ 12 = 0.01178 ohm, 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 consider- ation. The causes of polarization have been explained on p. 65 ; it being partly due to the formation of gas-cells during ELECTRO-PLATING ESTABLISHMENTS. 131 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 b}^ 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 required 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 essen- tially 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 re- turns 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. 132 ELECTRO-DEPOSITION OF METALS. When the magnitude of the counterforce has been determined by experiment as above described, the electro-motive force of the 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 b}' 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 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 disregarded, 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 subsequent 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- ELECTRO-PLATING ESTABLISHMENTS. 133 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 requires for its decomposition a current of 2.5 volts of electro- motive force. Now since, according to p. 78, a Bunsen cell devel6ps 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 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 1 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. 88 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- 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- 134 ELECTRO-DEPOSITION OF METALS. 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 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 Fig. 38. 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 19, or perspectively in Fig. 38. 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 ELECTRO-PLATING ESTABLISHMENTS. 135 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 thickness 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. 18. 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 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 suspended 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 suffi- ciently plated, or too late, when the deposit already shows the consequences of too strong a current. 136 ELECTRO-DEPOSITION OF METALS. For the control of the current an instrument called a cur- rent-regulator, resistance board or rheostat has been devised, which allows of the current-strength of a battery being re- duced without the necessity of uncoupling cells. It is obvious that the current of a battery, if too strong, can be weakened by decreasing the number of cells forming the battery, and also by decreasing the surface of the anodes, because the ex- ternal resistance is thereby increased. This coupling and uncoupling of cells is, however, not only a time-consuming, but also a disagreeable, labor ; and it is best to use a resistance Fig. 39. Fig. 40. TetheBWsh. To the J3cff> board with which, by the turn of a lever, the desired end is attained. Figs. 39 and 40 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 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- ELECTRO-PLATING ESTABLISHMENTS. 137 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. 39 the conducting wire coming 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, Fig. 41. BATH 'f\tavXfi.Ui\ BATTERY 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 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 re- sistance board, it is more advantageous to couple the spirals in parallel, and not one after the other, as in Figs. 41 and 42. 138 ELECTRO-DEPOSITION OF METALS. The resistance 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. 41. In the other mode of coupling, Fig. 42, the resistance lies in shunt to the circuit, it being coupled parallel to it. Accord- ing to Kirchoff's law, if there be a branching-off of the ■current, the sum of the current-strengths in the separate Fig. 42. bat a Jii&vlWcK/ BATTERY branches is just as great as the current-strength prior to and after branching 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. 42) represents such a branching-oft of the current ; the 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. ELECTRO-PLATING ESTABLISHMENTS. 139 The 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-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 two cells, it is of advantage to use a horizontal galvanometer (Fig. 43). It is screwed to a table by means of a few brass screws in such a FlG - 43 - position that the needle in the north posi- tion, which it occupies, points to 0° when no current passes through the instru- ment. Articles of iron and steel must, of course, be kept away from the instrument. For stronger currents it is better to combine a vertical galvano- meter with the switch-board and fasten it to the same frame, as shown in Fig. 44. The screw of the lever of the switch- board is connected with one end of the copper strip of the vertical galvanometer, while the other is connected with the screw on the right side of the switch-board, in which is se- cured the wire leading 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 other end, which is in con- 140 ELECTRO-DEPOSITION OF METALS. nection with the bath, is secured in the binding-screw on the Fig. 44. opposite side marked " weak." The entire arrangement will be perfectly understood from Figs. 44 and 45. Fig. 45. Fig. 46 shows the Hanson & Van Winkle Patent Under- ELECTRO-PLATING ESTABLISHMENTS. 141 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. 46. Fig. 47 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 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 142 ELECTRO-DEPOSITION OF METALS. 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 resistance of the exterior closed circuit (conducting-wires, baths and anodes), it is evident that a bath with slighter re- sistance, when worked with the same battery and containing Fig. 47. the same surface of anodes and objects, will cause the needle to deflect more than a bath of greater resistance under other- wise 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 conditions, are of great value. Suppose a nickel bath to work always with the same surfaces ELECTRO-PLATING ESTABLISHMENTS. 143 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 25°, 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 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- 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 being in this case greater, a deflection to 10°, 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 deductions must always be drawn with due consideration to the conditions, namely, surfaces of objects and anodes, and distance between them. It frequently happens that, in consequence of defective con- tacts with the binding-screws of the battery, or by the con- ductors 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 144 ELECTRO-DEPOSITION OF METALS. 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. e., 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 batten- current flows out from the positive pole through the conduct- ing 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 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 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 dis- cussed 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 ammeter 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 construc- tions 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 cur- ELECTRO-PLATING ESTABLISHMENTS. 145 rent. 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 cur- rent-conditions, this mode of working requires far more atten- tion than when by simply reading off the deflection of the needle on the measuring 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 convenience, 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 pre- viously 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. 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 calcu- lation 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 frequently 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 sensitive, 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 attracted by a current-conductor. In the scheme, Fig. 48, S is a circular current-conductor, consisting of a greater or smaller number of copper-wire coils. In the interior is a piece of thin sheet- 10 146 ELECTRO-DEPOSITION OF METALS. Fig. 48. iron, E, connected with an axis of revolution, a. G is a weight which is to be lifted by the attractive force of the cur- rent 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 alike with the exception of the coil S. In the voltmeter it consists of many windings of thin copper wire, and in the ammeter of but a few windings of stout copper wire, or in instruments for great current-strength, of a massive bent piece of copper. Fig. 49 shows the " Waverly " voltmeter, manufactured by Fig. 49. the Hanson and Van Winkle Co., Newark, N. J. It is in- tended for direct current circuits only; to 10 volts. It is furnished with binding posts for fourteen tanks, thus enabling ELECTROPLATING ESTABLISHMENTS. 147 the operator to use only one instrument in obtaining the read- ing of any number of tanks up to fourteen, by simply moving the switch lever to the tank numbers indicated on the switch of the instrument, and when used in connection with the patent tank rheostat, will enable the operator to reproduce at all times the same electrical conditions which by observation and experience he has found necessary in order to obtain a satisfactory deposit of uniform thickness and color in the shortest possible time. Fig. 50 shows the Weston ammeter. The ammeter is Fig. 50. placed in one conductor only, either in that of the objects or -of the anode, and thus the whole of the current must pass through it. The voltmeter, however, is connected with both conductors. On the point where the electro-motive force is to be measured, one of the binding posts of the voltmeter is con- nected by means of a copper wire with the object-conductor, and the other, with the anode-conductor. Fig. 51 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 an expense to furnish 148 ELECTRO-DEPOSITION OF METALS. each bath with a special voltmeter. However, this is unneces- sary, 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 Fig. 51. required, the construction of which will be seen from Figs. 52 and 53. Fig. 52 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 R 1 and R 2 , the voltmeter V, switch U, and the two baths. In Fig. 53 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 U consists of a brass lever, mounted with a brass foot,. upon a board. In the foot is a ELECTRO-PLATING ESTABLISHMENTS. 149 screw, with which is connected by a 0.039-inch thick copper wire one of the pole-screws of the voltmeter. 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 FiCx 52. switch), which serve for the reception of the 0.039-inch 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 voltmeter is directly con- 150 ELECTRO-DEPOSITION OF METALS. nected 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 i^; the screw marked "weak" of the resist- ance board R x is connected by a wire of corresponding thick- ness with the object-wire of bath I, and at the same time with the binding-screw 1 of the switch. The resistance board R 2y of the bath II, is in the same manner connected with the main object-wire, the bath, and the binding-screw 2 of the switch ; Fig. 53. also the resistance boards R 3 and R± of the baths III and IV, which are not shown in the illustration. With the main anode-wire each bath is directly connected by conducting the current to an anode-rod of the bath by means of binding- screws and a stout copper wire, and establishing a metallic connection between this anode-rod and the next one. How- ever, instead of connecting both, the current may also be con- ducted 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 ELECTRO-PLATING ESTABLISHMENTS. 151 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 2 ; hence the voltmeter V will indicate the 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 is thrown out, and the voltmeter indicates the electro-motive force in 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-strength 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 152 ELECTRO-DEPOSITION OF METALS. 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 a't the bath, the current-density must also increase, because, according to the law of Ohm, the current-strength is equal to 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 remains the same and the dividend be increased. Hence the current-density becomes greater. Now, as for the production of a useful deposit, a certain current-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 t|ie 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 ELECTRO-PLATING ESTABLISHMENTS. 153 regards dimensions, and it is recommended to entrust the installation of such, constructions only to competent hands -capable 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 decrease 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 from the source of current to the baths, while the latter branch off from them to the separate baths. The positive main conductor or anode conductor is con- nected with the + 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 con- ductors 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, cither 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. 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- 154 ELECTRO-DEPOSITION OF METALS. rent-strength one square millimeter of copper cross-section, it 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 couplings, Fig. 54, securing them by means of screws, and filling any intermediate space with solder. If the round main conductors are to be run at an angle, the coupling, Fig. 55, is used, and the T-coupling, Fig. 56, 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 by means of a piece of copper-sheet and screws, the contact surfaces having been first tinned to prevent oxidation. Fig. 54. Fig. 55. Fig. 56. Tanks. The choice of material for the construction of tanks to hold the plating solutions depends on the nature and properties of the latter. Solutions containing potassium cyanide require tanks of stoneware, enameled cast-iron or impregnated wood. Welded steel tanks constructed by the oxy-acetylene welding process are also largely used for cyanide solutions, soap solutions, electric cleaners, etc. 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. ELECTRO-PLATING ESTABLISHMENTS. 155 Wooden tanks must be carefully constructed, and should be securely clamped together with strong iron bars, riveted and bolted, as shown in Fig. 57. 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 1J 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 0.118-inch thick, and the seams soldered with pure lead, are quite suitable. Care must, Fig. 57. of course, be taken that neither the conducting rods nor the articles suspended in the bath and the anodes come in contact 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, be- cause with too small a distance, metal from the solution is precipitated upon the lead lining. The latter always becomes electric, which, however, does not matter, and if the anodes are at a greater distance from it than the objects no metal is precipitated upon it. If for the better exhaustion of the baths the anodes are suspended at a slight distance from the sides? 156 ELECTRO-DEPOSITION OP METALS. •it is advisable to 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 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, 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. When using lead steam coils or loops in plating tanks or those arranged for electric cleaning, the coil ends entering and . ELECTRO-PLATING ESTABLISHMENTS. 157 returning from the solution should be connected to the heat- ing system with insulating joints, Fig. 58, in order to prevent leakage of the electric Fig. 58. current. 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 con- necting the conducting rods. The cross-sections of the conducting rods are, on the one hand, dependent on the maximum current-strength which without 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 conduction, 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 158 ELECTRO-DEPOSITION OF METALS. effected by means of binding-posts and screws of the improved forms shown in Fig. 59, 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 Fig. 59. No. 1. No. 3. No. 4. No. 2. 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 surrounded as much as possible by anodes, i. e., the positive- ELECTRO-PLATING ESTABLISHMENTS. 159 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. For large round objects it is better to entirely surround them with anodes, if it be not preferred to turn them fre- quently, so that all sides and portions gradually feel the effect of the immediate 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; the surface to be plated being, of course, turned towards the anodes. There shonld 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 permissible in gold and silver baths. The anodes should not be too thin, because the thinner they 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. 60). 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 160 ELECTRO-DEPOSITION OF METALS. Fig. 60. Fig. 61. 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 there- fore, not liable to corrosion ; but the anodes are then not completely 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. 61). 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 w r ire gauge being generally employed for such light work as spoons, forks and' table utensils. 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 advisable 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- ELECTRO-PLATING ESTABLISHMENTS. 161 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 im- pediment 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 preparatory cleans- ing processes three vessels with water, which has to be fre- quently 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. 62. It consists of 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 11 162 ELECTRO-DEPOSITION OF METALS. 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. 66 these Fig. 62. tanks are indicated by 11 and 12. The two marked 11 con- tain dilute sulphuric acid for pickling iron and steel articles, while those marked 12 contain dilute potassium c} 7 anide solu- tion for pickling copper and its alloys, and Britannia, etc. For cleansing 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 every- ELECTRO-PLATING ESTABLISHMENTS. 163 thing 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 tempera- ture of the latter. How the water is heated makes no dif- Fig. 63. ference, and depends on the size of the establishment. The heated objects are then immediately dried in a box filled with •dry, fine sawdust that of boxwood, maple, or other wood free from tannin being suitable for the purpose. A steam sawdust box very suitable for the purpose is made in four removable sections, which consist of a smooth galvanized iron box, hot air chamber with asbestos lining closely built, f-inch steam radiator, and a rigid stand made of 1^-inch angle iron. To overcome various troubles and difficulties connected 164 ELECTRO-DEPOSITION OF METALS. with drying by means of sawdust mixed with the articles: placed in the pan and heated, steam drying barrels have been introduced. One type is practically the same as the oblique tilting tumbling barrel in common use for cleaning metallic surfaces, except that it is jacketed and otherwise constructed to allow a circulation of steam about the inner barrel, auto- matic ejection of the condensation, still allowing the barrel to- be tilted. A barrel load can be thoroughly dried in a few minutes, especially if the work is shaken out of hot water. It will be readily understood that the rolling over and over of the hot barrel thoroughly mixes the work and sawdust, liberates the steam and precludes the possibility of water- marks, etc., and further, brightens the goods at the same time. A centrifugal dryer for small work, supplied by The Han- son & Van Winkle Co., N. J., is shown in Fig. 63. This machine should be used where mechanical plating apparatus is installed, one to three minutes only being necessary for drying small work. The machine is furnished with or with- out hoist, and is fitted with ball bearings. It can be supplied; with a tapered steel pan or a perforated straight-sided steel or copper basket for holding the work. 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^ following considerations should govern the choice of location : The dynamo should not be exposed to moisture nor to the dirt. ELECTRO-PLATING ESTABLISHMENTS. 165 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 foundation. 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 vertically 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 giving 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. After the machine has been properly set and belted, it re- 166 ELECTRO-DEPOSITION OF METALS. mains to start it up. Before starting, remove the bearing caps and pour a small quantity of oil on the bearings ; loosen tbe- screw holding the rocker-arm in position, and be prepared to shift the rocker-arm backward or forward, so as to get tho 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. 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 dirty, after cleaning with No. sandpaper (emery should ELECTRO-PLATING ESTABLISHMENTS. 167 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 previ- ously mentioned, shunt-wound and compound-wound dynamos 168 ELECTRO-DEPOSITION OF METALS. are at present largely used. Their construction has already been explained, and there remains now only the question what size dynamo, i. 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 required for each bath. The sum of the current re- quired for the separate bath, with an allowance of 20 to 25 per cent, for an 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 ^ to | 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 re- quired 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 3.0 to 3.5 volts are required ; for brassing also 0.35 ampere ELECTRO-PLATING ESTABLISHMENTS. 169 •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 3.6 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 economic loss, it follows that the impressed electro-motive force of the dynamo should not be greater than absolutely necessary, 170 ELECTRO-DEPOSITION OF METALS. so that it can be reduced by a regulator to the lowest per- missible 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 objects From what has been said, it will be seen that voltmeters are indispensable for electro-plating plants in order to be constantly informed as to the electro-motive force pre- vailing 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 3J volts, a large number of silver and tin baths and acid copper baths for galvanoplasty (with the exception of those for rapid gal- vanoplasty), for which an impressed electro-motive force of 2 volts is quite sufficient, it would by all means be more judic- ious to use for the first-named baths a special dynamo with an impressed electro-motive 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 unequal resistances and unequal electro surfaces, are con- ELECTKO-PLATING ESTABLISHM ENTS. 171 nected, baths requiring an equal, or approximately equal, current-strength may be coupled one after the other, i. e., in series. This principle of series-coupling of baths is illustrated by Fig. 64. 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. 64. 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 100 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- ing instruments to a shunt-wound dynamo is shown in Fig. 172 ELECTRO-DEPOSITION OF METALS. 65, 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 fill- ing all demands, even at the busiest season. The installation of two dynamos allows of the business being carried on with- out 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 question 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 ad- ditional 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 had been excited to the same voltage. If this were not done, the current of greater ELECTRO-PLATING ESTABLISHMENTS. 173 H 174 ELECTRO-DEPOSITION OF METALS. 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 + 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 eh 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-wire system. One conductor is branched off from the -f- pole of one dynamo, the second from the — pole of the other dynamo, and the third, called the neutral or middle conductor, from the junction of the dyna- ELECTRO-PLATING ESTABLISHMENTS. 175 mos coupled in series. Between the last-mentioned neutral 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 neutral conductor. Ground plan of an electro-plating plant with dynamo. This in the most simple form is shown in Fig. 66. 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. 66. NN 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. 1, and is screwed to the wall. The main conductors, marked — and +, 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 connected 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 ; M Ni, nickel baths ; Ku, copper cyanide bath ; Mg, brass bath ; S K, acid copper bath ; Si, silver bath ; and Go, gold bath. Each of the first-named five baths has its own resist- ance-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 176 ELECTRO-DEPOSITION OF METALS. it be preferred to feed these baths with a special machine of less voltage. Fig. 66. / /// J J i // / t?jf/M{/i Z }JJjJMjJJj-£I2±> ' Z2 l Z2 I 72. t / / t > 7, mm @ -k BDE1 Oh ux V, / / / ./ / V / Vm 777 V777 ZZLLULLLLUJJ ///////./ // /// ///, LLUL L/fZ rFniA ELECTRO-PLATING ESTABLISHMENTS. 177 From Fig. 66 it will be seen that the current weakened by the resistance-boards 7 and 8 serves for conjointly feeding the 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 jacketed 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. In- stead of the preparatory cleansing with hot lye, which saponi- fies the. oil, the objects may be brushed off with benzine, oil of turpentine or petroleum, the principal thing being the re- moval of the greater portion of the grease and dirt, so that the final cleansing, which is effected with lime paste, may not re- quire too much time and labor. It is also advisable to cleanse the objects, in one way or the other, immediately after grind- ing, 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. 161, and illustrated by Fig. 62. Referring again to Fig. 66, 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 immediately brought into the bath. 12 178 ELECTRO-DEPOSITION OF METALS. H W is the hot-water reservoir in which the plated objects are heated to the temperature of the hot water, so that they may quickly dry in the subsequent rubbing in the saw-dust box Sp. Before polishing the deposits, iron and steel objects are thoroughly dried in the drying chamber T(Fig. 66), heated either by steam or direct fire. By finally adding to the appli- ELECTRO-PLATING ESTABLISHMENTS. 179 ances a large table, 13, for sorting and tying the objects on the copper wires, and a few shelves not shown in the illustration, everything necessary for operating without disturbance will have been provided. 25 ^ s. CD ■^^-e^^"^ 1 <4 ie i-r^' - i T iii ng ii o o t- LU z -l> UJ V 1. it Z h- sor 0: z (i 2( ZCJ Z o en Z < < Z ct UJ UJ z zo hi ? .1 Ill h- 1 $ v=u hZZZ < o oo t— Hi- hi- Q HEOS NNEC NNEC NNEC ROD 0E RC cooouo ckuiz V UUU Q X J j5jZ rt wnoh LtJ oSl ZJ O O era >0| -c act" LJ05 O 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 maintenance 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 trouble- some, and the use of mixed anodes is decidedly to be pre- ferred, 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 varia- tions 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 If ozs., chemically pure boric acid (crys- tallized) 10| 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 carbonate 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 * In place of nickel carbonate, nickel hydrate may as well be used. 17 258 ELECTRO-DEPOSITION OF METALS. 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 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 b} r 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 J ozs., potassium citrate 7 ozs., ammonium chloride 7 ozs., water 10 to 12 quarts. For copper and copper-alloys : Electro-motive force at 10 cm. electrode-distance, 1.5 to 1.7 volts. Current-density, 0.45 to 0.5 ampere. DEPOSITION OF NICKEL AND COBALT. 259 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 10J ounces of nickel sulphate and 3J 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, for instance, tops, candlesticks, mountings, etc. 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 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 nickel- ing 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, 6J ozs., sodium pyrophosphate, 26J ozs., water, 10 quarts. For copper and its alloys : Electro-motive force, at 10 cm. electrode-distance, 3.5 volts. Current 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 pre- cipitated 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 w r ater. This bath yields a dark nickeling particularly 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. 260 ELECTRO-DEPOSITION OF METALS. For the same purpose a nickel solution compounded^ with a large quantity of ammonia, hence an ammoniacal nickel solution has been recommended. However, experiments with this solution alwaj^s yielded lighter tones than bath IX. Special advantages cannot be claimed for this so-called dark nickeling since in arsenic and antimony we have more effective and more reliable expedients. Black nickeling. Black deposits of nickel are frequently used particularly for decorative purposes. For the production of such deposits general directions may be given as follows: 1. A strong bath has to be used. 2. Apply a weak current. For the production of a uniform black deposit the current- strength should not exceed 1 volt. From the manner in which the deposit commences to form, it can readily be recog- nized whether the current is of suitable strength. The first film of deposit upon the object is iridescent, i. e., shows rain- bow colors and does not extend over the entire surface. The deposit next acquires a bluish tone until finally a black coat- ing is formed. If the deposit acquires immediately in the commencement of the operation a uniform color, the current is too strong. The deposit should form slowly ; it should, as mentioned above, at first be iridescent and the black deposit appear only after one or two minutes. It is of sufficient thickness as soon as the desired color appears. Very thick deposits are apt to peel off, they being more or less brittle. With the use of a weak current 30 to 60 minutes will be re- quired for the production of a deposit of sufficient thickness. 4. A large number of nickel anodes should be used. Old anodes are to be preferred, they yielding nickel more readily than new ones. 5. Any acid which may be present in the bath should be neutralized by the addition of nickel carbon- ate, a neutral bath yielding a better deposit than one even only slightly acid. A black nickel bath of the following composition yields a very uniform black deposit : Water 4J quarts, double sul- phate of nickel and ammonium 10 ozs., ammonium sulpho- DEPOSITION OF NICKEL AND COBALT. 261 cyanate 1 oz., zinc sulphate 1 oz. This bath practically con- tains exclusively double nickel salts which dissolve in water. If in cold weather crystallizing takes place, the bath has to be heated. It is best to keep the temperature of the bath at from 70° to 100° F.; at a higher temperature the deposit readily acquires a gray color. At a temperature of below 59° F. some nickel salts readihy crystallize out, and besides the bath does not work well. A gray color of the deposit is an indication of too strong a current, this being also the case when streaks are formed upon the object. With the use of an old bath it may happen that it becomes acid and it will be noticed that a black coating is not produced, even by reducing the current-strength. The bath then very likely contains free acid, and the best means of neutralizing it is the addition of nickel carbonate. In case the latter is not available, ammonia may be used. Test the bath with litmus paper. If before adding the nickel carbon- ate or ammonia, blue limus paper when dipped into the bath turns red, the bath is acid. Add nickel carbonate until no more of it dissolves, although a small excess is no disadvan- tage. On the other hand, with the use of ammonia care must be had that no more than required for neutralization is added. When the limit is reached at which the color of either blue or red litmus paper is no longer changed, no more ammonia should be added. Black nickel deposits frequently come from the bath with the proper black color and otherwise without defect, but when rinsed and dried have a brown tone. This can be removed by immersion in chloride of iron solution. The latter does not attack the black nickel deposit, provided the objects are not left too long in it, a moment's immersion being sufficient, after which they are rinsed and dried. The chloride of iron bath is composed of: Chloride of iron 8J ozs., hydrochloric acid 18 drachms, water 4j quarts. Black nickel deposits when exposed to the influence of atmospheric air gradually acquire a brown color which, how- 262 ELECTRO-DEPOSITION OF METALS. ever, is only superficial and can be wiped off. To prevent such tarnishing a coat of lacquer is as a rule applied to the nickeled object. Black nickel deposits are much used as a priming in the application of mat black lacquers to automobile parts and for other purposes, where as durable a coating as possible is desired. If the lacquer is applied without previously giving the brass a suitable black nickel deposit, every tiny scratch or peeling-off becomes perceptible, which is prevented by the black nickel deposit underneath the lacquer. A black nickel bath of the following composition has been recommended by Blauet : Water 95 gallons, nickel-ammonium sulphate 12 ozs., potassium sulphocyanide 2£ ozs., copper carbonate 2 ozs., arsenious acid 2 ozs. Dissolve the nickel salt in the water and add the potassium 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. If in time a gray sediment is formed, some potassium sulphocyanide and copper carbonate have to be added. X. A fairly good nickel bath for many purposes is obtained from a solution of nickel-ammonium sulphate 22J ozs., mag- nesium sulphate 11J 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, how- ever, 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. For the production of very thick deposits a bath composed DEPOSITION OF NICKEL AND COBALT. 263 of nickel sulphate 17.63 ozs. and sodium citrate 17.63 ozs. dissolved in 2f gallons of water has also been recommended. Pfanhauser has changed these proportions to nickel sulphate 14.11 ozs. and 12.34 ozs. sodium citrate dissolved in 2f gal- lons of water. This bath is said ' to be available chiefly for the production of nickel cliches and thick deposits. It has, however, the drawback of all nickel baths prepared with large quantities of organic combinations of requiring a high electro- motive force and of readily becoming mouldy. It can, how- ever be highly recommended for nickeling articles with sharp edges and points, for instance, knives, scissors, etc., it being quite indifferent towards changes in the current proportions, so that even with • a higher than the normal electro-motive force and a greater current-density the objects do not readily over-nickel. The deposit is very soft, and hence in grinding such nickeled instruments peeling-olf of the deposit takes place more rarely than with objects nickeled in baths of dif- ferent composition. Electro-motive force at 10 cm. electrode- distance, 3 volts ; current-density, 0.35 ampere. According to an English formula, 17.63 ozs. nickel sulphate, 9 ozs. 5 J drachms tartaric acid and 2.4 ozs. caustic potash are dissolved in 2f gallons of water. The results with this bath were only moderate. It has not been deemed necessary to give additional form- ulas 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 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. Accord- ing to Bruce, such an. addition prevents the nickel deposit from becoming dull when reaching a certain thickness, but repeated experiments made strictly in accordance with the directions given did not confirm this statement. 264 ELECTRO-DEPOSITION OF METALS. The general remark may here be adder] that freshly pre- pared nickel baths mostly work correctty 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 suspend 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 & nickel bath without nickel salt. t 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 depo- sition may be effected with quite a feeble current. Before the solution acquires the capacity of depositing, quite a strong current has to be conducted through the bath until the com- mencement of a proper reduction of nickel. This bath is only suitable for coloring very cheap articles, it being impos- sible 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 DEPOSITION OF NICKEL AND COBALT. 265 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 re- quired 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. 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 minutes be overcome by the addition of an acid, and accord- ing to the composition of the bath, its neutrality or slightly acid reaction 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. Thick deposits in hot nickel baths. Nickel baths, more or less highly heated, have for years been used for nickeling, the purpose 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 consequence of the contraction in cooling. 266 ELECTRO-DEPOSITION OF METALS. The results obtained in heated baths were, however, un- satisfactory, since, if the current was not carefully regulated, the deposit 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 de- posits 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. of 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. 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 acidulated with sulphuric acid.f * Zeitschrift fur Elektrochemie, 1897 to 1898, p. 160. f German patent, 117054. DEPOSITION OF NICKEL AND COBALT. 267 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 deposits 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 introduction of hydrogen. Agitation by blowing in air is not permissible on account of oxidation of the ethyl-sulphate combinations 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. In an electrolyte of given composition, which has to be constantly kept slightly acid with acetic 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- 268 ELECTRO-DEPOSITION OF METALS. percha matrices, galvanoplastic nickel deposits 6 millimeters- in thickness, the metal proving thoroughly homogeneous and firmly united throughout its entire thickness. Coehn and Siemens * found that from electrolytes which contain 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-mentioned 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 anodes, as a rule, with ease. If the latter dissolve only with difficulty they fail in their object of replacing the nickel metal withdrawn 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. Attention may here be called to the elliptic anodes, Fig. 110, 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 deposit as disintegration takes place from all sides of the- anode ; consequently the molecules are distributed uniformly *Zeitschrift fur Elektrochemie, 1902, S. 591. DEPOSITION OF NICKEL AND COBALT. 269 Fig. 110. throughout the solution, and not only hasten the deposit, but .give a heavier 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 de- sirable to put in more nickel, the old ones which take up practically no room in the tank, can re- main until entirely con- sumed, and as a result there is practically no scrap nickel to dispose of at half price. Fig. Ill shows the small loss in the use of the elliptic anode. The weight of the orginal plate was 16 pounds. Percentage of waste only 5 per cent. Fig. 112 shows the or- iginal 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 is almost as heavy as the same section •of the original plate. The ■original weight of the plate was 13| lbs. Waste 2 lbs. Percentage of waste 14.6 per cent. Another form of the old-style plate is shown in Fig. 113. The original weight 270 ELECTRO-DEPOSITION OP METALS. was 17 J lbs. Weight of scrap 4| lbs. Perceiitage of waste 27.4 per cent. The examples shown in the illustrations were Fig. 111. TTTTt - | - 10 oz. 12 oz. 14 oz. ? 13 oz. I0 °z 16 LBS, taken from a lot of scrap returned to the manufacturers. The scrap from the elliptic anode came from a large stove concern Fig. 112. Fig. 113. --'--- -— " 4 1 lbs. and the flat scrap also from a stove manufacturer. Elliptic anodes are furnished in all commercial metals. DEPOSITION OF NICKEL AND COBALT. 271 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 suffi- cient 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 will here be over- thrown by practical reasons, it only requiring to be demon- 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 insoluble anodes need not be taken into consideration, be- cause for large surfaces of objects correspondingly large sur- faces of platinum anodes would have to be present, as other- wise the resistance of thin platinum sheets would be consider- able. But such an expensive arrangement would be justifiable only if actual advantages were obtained, which is not the- 272 ELECTRO-DEPOSITION OF METALS. case, because, though the platiiium does absolutely not dis- solve, the deficiency of metallic nickel in the bath caused by such anodes 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 conjunction 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 de- posit 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 separate 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- 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 car- bon becoming 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 f of its length, is fitted with anodes. If, for instance, a tank is 120 centimeters long in the clear and 50 DEPOSITION OF NICKEL AND COBALT. 273 centimeters deep, the width of the nickel anodes laid alongside one another should be about 80 centimeters, and their length about | 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 smallest 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 shpuld 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 veiy hot, have, to be sure, the disadvantage of becoming brittle, and crumbling before they are entirety 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- 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 18 274 ELECTRO-DEPOSITION OF METALS. 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 less 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 reddish coloration also appears when an analysis shows the anodes, as well as the bath, to be absolutely free from cop- per. It is 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 con- ducting a strong current through the bath. Pfanhauser is of the opinion that this reddish tinge is due to a separation of copper. In fact, even the purest brands of anodes contain traces of copper, but, on the other hand, the nickel salts are at present furnished mostly entirely free from copper, and a nickel bath would have to be worked for a long time before a content of copper would be transferred to it from DEPOSITION OF NICKEL AND COBALT. 275 the anodes. An experiment showed that a bath prepared with nickel salt absolutely free from copper produced a slight red film upon a new anode without the current having been in action ; a bright steel-sheet served as anode. This does not indicate the separation of copper, as its derivation would in this case be inexplicable. The anodes are 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 dis- proportionate solution of the anodes may, however, also be noticed 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. Execution 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 cleaned, and on the correct current-strength. The mechanical preparation of the objects has been dis- cussed on page 188 et seq. The directions for the removal of grease, etc., given on p. 276 ELECTRO-DEPOSITION OF METALS. 228, also apply to objects to be nickeled. In executing the operations, it should always be borne in mind that though dirty, greasy parts become coated with niokel, the deposit im- mediately peels off by polishing, because an intimate union of the deposit with the basis-metal is effected with only per- fectly 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, Ger- man silver, etc.), as well as iron and steel, are directly nick- eled, zinc, tin, Britania and lead are generally first coppered or brassed. With a suitable composition of the nickel bath and some experience, the last-mentioned metals may also be directly nickeled ; but, as a rule, previous coppering or brassing is preferable, 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 advantage 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 DEPOSITION OF NICKEL AND COBALT. 277 directions given on page 228, previous coppering is not neces- sary. The case, however, is different if the copper deposit is pro- duced in order to act as a cementing agent for two nickel deposits. 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 generall} 7 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 la} T ers 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 consoli- dated 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 objects 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 : 278 ELECTRO-DEPOSITION OF METALS. The objects are provided with an electro-deposit of zinc. This deposit is scratch-brushed, coppered in the copper cya- nide 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 produced upon the object with the use of a cold ethyl sulphate nickel bath, or a hot quick nickeling bath (see pp. 266 et seq.). TJie 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 or 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. This phenomenon is due to the hydrogen being condensed and retained by the deposit, which is thereb}'' 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 DEPOSITION OF NICKEL AND COBALT. 279 hanging 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. 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 portions 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 regularity. 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 stronger 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 elements, or diminishing the anode-surface, or finally by suspending 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 0.3 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 current-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 280 ELECTRO-DEPOSITION OF METALS.. 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. 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. e.,. to effect the first deposit of nickel, with the use of a strong- current, 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 1 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, how- ever, 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 nor- mal current to allow them to remain in the bath until a mat- bluish shine appears ; this is an indication that the deposit has acquired considerable thickness, provided the bath has- DEPOSITION OF NICKEL AND COBALT. 281 not been alkaline. In alkaline baths this dull deposit is fre- quently 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 mat appearing objects are permitted to remain longer in the bath without scratch-brushing, the mat bluish tone soon passes into a mat 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 rub- bing a nickeled corner or edge of the object rapidly and with energetic pressure upon a piece of planed soft wood until it becomes 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 suspending them between two rows of anodes suffices. Round objects with a large diameter should be quite surrounded with anodes, and be as nearly as possible equi- distant from them. This arrangement should especially not be neglected where a heavy and uniform deposit of nickel is to be applied 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 282 ELECTRO-DEPOSITION OB^ METALS. thicker deposit than the inside surfaces, and the thickness of the deposit 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 3f to 5f inches, for objects with depressions and cavities it must be larger, if it is not preferred to make use of the methods described later on. However, a deposit of a uniform thickness cannot be obtained by this means, because the portions nearer to the anodes will acquire a thicker de- posit 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 preferred. This, of course, renders it necessary for a workman to stand alongside the bath and execute the opera- tion by hand ; but as the small anode can be brought within •a few millimeters of the surface of the article, and at this dis- tance 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 in 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 DEPOSITION OP NICKEL AND COBALT. 283 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 showed through. On the other hand, in the bath without ammonium chloride the end of the tube turned towards the anode, to be sure, became mat, but did not peel off in polishing, and nickeling in the interior of the 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 articles form an exception to the general rule in so far as by reason of the highly positive properties of zinc, the resist- ance of the bath may be slighter than the 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 another, 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 covered surface acquires only a slight deposit. That the objects must not touch the anodes need scarcely be mentioned. 284 ELECTRO DEPOSITION OF METALS. 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 b} 7 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. 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 different metals in a fluid a counter or polarization current is generated, 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, how- ever, greater when iron objects are suspended in' the bath, and still greater with zinc surfaces which are to be nickeled, be- cause 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 introduced at the bath, the latter is weakened, and the more so the stronger the counter-current is. This explains why iron requires 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 con- ducted into the bath, which, by its sufficiently, large electro- motive force can overcome the counter-current, and the con- sequences of the reversal of the current can be prevented by using the galvanometer and observing the deflection of its- needle, which (according to p. 143) in proper time indicates DEPOSITION OF NICKEL AND COBALT. 285 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 overcome the action of these metallic surfaces as regards the formation of the counter-current. 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 generally used. It is, however, well to acquaint the oper- ator 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 nickel. Defective nickeling must, as a rule, be completely removed before the objects can be nick- eled, since the second deposit does not adhere to the previous •one, but frequently peels off in polishing or by slightly bend- ing the object. The reasons for this behavior are : 1. Like iron, nickel readily oxidizes on the surface, but this oxidation is not so heavy as to be perceptible. Previous to nickeling this oxide has not been completely removed and in the case of quite old plated objects the nickel has had a chance to oxidize. Nickel, however, adheres firmly only to metallic nickel and not to the oxide ; hence the second deposit peels •off. 2. In case the deposit is comparatively new and has not been exposed for some time to the action of atmospheric air, the peeling off of nickel deposited upon nickel is, as a rule, caused by the polishing material remaining upon the surface. Vienna lime and similar agents which contain paraffin and other mineral fats and wax are much used for polishing nickel. These substances partially penetrate into the pores of the deposited nickel or remain upon the surface. By the ordinary means of cleaning the mineral fats or wax are not 286 ELECTRO-DEPOSITION OF METALS. removed, the consequence being that the second deposit of nickel does not adhere. With the use of animal fats, which readily saponify, as polishing agents, the case is not so bad, but even under these conditions, the nickel has a tendency to peel off. It must be borne in mind that as previously men- tioned, all electrolytically produced deposits are composed of a net- work of ver}' minute crystals, the deposit being thus of a porous nature. In polishing larger or smaller quantities of the polishing agent penetrate into these pores, and their com- plete removal is a very difficult matter. For the removal of the nickel coating the following strip- ping 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 sul- phuric acid, since considerable heat is generated when this acid is mixed with water. When the entire quantity of sul- phuric 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 arti- cles 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- 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 DEPOSITION OF NICKEL AND COBALT. 287 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 afterward 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. Many nickel-plated iron and steel objects are so cheap that it does not pay to strip the nickel from them, and it is best to throw them on the scrap pile. In some cases, however, for instance, surgical instruments, fire-arms, fine cutlery and other more expensive articles, it is frequently desirable to re- move the old nickel deposit. To be sure, nitric acid would remove the nickel, but it also attacks iron and steel and causes pitting. For stripping such articles by electrolysis the following bath has been recommended : Water 1 lb., potas- sium cyanide 1.8 ozs., yellow prussiate of potash 0.5 oz. The iron or steel object to be stripped is suspended as anode in the bath, which should be used at a temperature of 122° F. A sheet of iron or steel serves as cathode. For stripping a thin 288 ELECTRO-DEPOSITION OF METALS. deposit only a few hours are required, but a whole day for thick deposits. However, the operation requires no special attention, as the iron or steel surface is not attacked and there is no danger of pitting. The current-strength should be the same as usually employed for nickel-plating. 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 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 dissolved, and the nickeling will show a pure white tone. As nickel anodes contain, as a rule, iron, a minute quantity of this metal is deposited together with the nickel, and the latter is inclined to form a mat surface or to tarnish. If the objects are to be polished this does not matter, but if they are not to be polished slight mat stains frequently appear upon the surface after drying. Such stains can be removed by the use of a bath of dilute hydrochloric acid (2 parts water, 1 part acid). After thoroughly rinsing the object in water, immerse it for a moment in the acid bath, and then rinse again care- fully. Now, without drying, draw the object through a soap- bath and rinse again. Since the soap solution leaves a thin film of oil upon the nickel surface not much water will adhere to it, and it will quickly dry. It will be found that the mat spots have disappeared or the stains are scarcely perceptible. 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 coloration is due to the chemical action of the nickel solution upon the metals constituting the objects. This phe- DEPOSITION OF NICKEL AND COBALT. 289 nomenon is frequently observed in nickeling zinc articles. Remedy : Increase the current or diminish the area of sus- pended 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 ascer- tained by testing 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 clean- ing them ; or, the conducting 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 generally be remedied by working the bath two or three hours, if it is not over-concentrated and the cause, as above mentioned, has 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 insufficient 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. 19 290 ELECTRO-DEPOSITION OF METALS. 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 de- fective deposit, or, if it cannot be entirely removed, coppering. 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 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 distance ; 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,. DEPOSITION OF NICKEL AND COBALT. 291 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- ductivit}'- 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 ad- visable 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. 216). To give the objects the highest luster possible, it is advisable finally to polish them upon a woolen brush with dry Vienna lime. 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 thick- ness and hardness. Knife blades and surgical instruments with sharp edges require special care in polishing, which will later on be re- ferred to. Cleansing polished objects. After polishing, the nickeled 292 ELECTRO-DEPOSITION OF METALS. objects, 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. 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, pol- ishing 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 grind- ing, 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 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 sell- ring 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 DEPOSITION OF NICKEL AND COBALT. 293 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 Fig 114. 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 bundles in order to effect a change of position of the objects 294 ELECTRO-DEPOSITION OF METALS. 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 stoneware 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 basket. During the operation the articles must be con- stantly shaken, and as nickel baths, as a rule, do not conduct sufficiently 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. 114) and constantly shakes Fig. 115. and turns it. For nickeling in the dipping basket it is further advisable to heat the nickel bath. In place of a stoneware dipping basket, a basket tray of brass wire, Fig. 115, 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 1\ 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, especially if, with the other hand, the articles are constantly stirred by means of a glass or wooden rod. DEPOSITION OF NICKEL AND COBALT. 295 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 quan- tities. It will be further referred to under " Deposition of Cobalt." 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 con- trivances mentioned the anodes are placed outside of the •drum, and the latter acts as a diaphragm with great resist- ance, a very high electro-motive force is required for the pro- duction of the deposit, 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, 296 ELECTRO-DEPOSITION OP METALS. while the positive current is carried to the plates occupying a 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. 116 shows a mechanical electro-plating apparatus patented and manufactured by The Hanson and Van Winkle Co., Newark, N. J. The apparatus complete consists of an Fig. 116. outer wooden tank for containing the solution, a perforated revolving plating barrel, made of wood or celluloid in which to hold and tumble the work while deposition is going on, and necessary rods and connections. The size of the perfora- tions required in the plating barrel depends on the class and shape of the work to be plated. The perforations should be as large as possible without allowing the work to slip through or catch in them. The barrel is entirely submerged, thus permitting a much larger quantity of work in each batch. DEPOSITION OF NICKEL AND COBALT. 297 The drive is from the outside, thus avoiding the use of belts running in the solution. The barrel is removable at any- time without throwing off the belt or interfering with the drive. For raising and lowering the plating barrel a lifting device is very convenient. Fig. 117 shows a hand-wheel lift- ing device. In operation it raises and lowers the plating bar- rel in a perpendicular direction, and when the barrel is sus- pended above the tank for a few seconds will allow the Fig. 117. solution to drip directly back into the tank. This reduces the loss of solution to a minimum and overcomes the difficulty of a wet and sloppy floor. 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- '298 ELECTRO-DEPOSITION OF METALS. -anode ; hence a regular and even deposit is obtained. These anodes are cast in all metals with square copper hooks attached. 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 intelligence of the operator than any other electro-plating pro- cess, 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 surface, as well as of the proper anode surface, and the most suitable composition and treatment of the nickel baths. 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 bear- DEPOSITION OF NICKEL AND COBALT. 299 ings secured in a hanging cast-iron frame by a set screw and safety keys, or preferably as shown in Fig. 101, since with this construction an injury to the grinder by the lathe jump- ing out is impossible. The bobs, when new, have on an average a diameter of 12 to 16 inches, and a. width of 5f 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 unsteadil} 7 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 pro- duced 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 conveniently 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. 118) 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 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 pro- jecting 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 Fig. 118. 300 ELECTRO-DEPOSITION OF METALS. 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 f of the sur- face 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 r the oil and polishing dirt are removed by dry polishing, after- providing 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 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 DEPOSITION OF NICKEL AND COBALT. 301 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 Muller * avoids the above-mentioned drawbacks by obliquely standing polishing rolls. In KorHer'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. 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 " * German patent, 49736. t German patent, 89648. 302 ELECTRO-DEPOSITION OF METALS. 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 observ- ing 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 nickeling 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 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. However, 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 DEPOSITION OP NICKEL AND COBALT. 303 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 pale yellow or greenish. When brassing 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 304 ELECTRO-DEPOSITION OF METALS. 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^ feet wide, and 2^ to 2J feet deep. In such tanks sheets 6 \ feet long and \\ feet wide can be conveniently nickeled. With the use of a nickel bath according to formula VIII, p. 258, for nickeling sheet-zinc, the most suitable electro-motive force is 3.5 volts and 1 ampere current-density per square deci- 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-ammo- nium sulphate without the addition of conducting salts, or in baths containing 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 DEPOSITION OF NICKEL AND COBALT. 305 '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 1\ 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 re- stored 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 salts. When the sheets have been sufficiently nickeled, they are allowed to drain off, then plunged into hot water, and, after removing 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 un- nickeled 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 effected by placing them upon supports and pressing against the revolving bob as previously described, the sheets being, how- ever, only moderately moistened with oil, and not too much 20 306 ELECTRO-DEPOSITION OF METALS. 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 bending and rebending several times without, the deposit of nickel breaking or peeling off. Nickeling tin-plate. — For handsome and durable nickeling,, iin-plate also requires previous coppering. Deposition is effected with a less powerful current than for sheet-zinc. Freeing from grease is done in the same manner as above- described. For preparatory polishing of tin-plate, the use of a polish- ing 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 1 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 DEPOSITION OF NICKEL AND COBALT. 307 them before nickeling with a large, broad fiber brush (p. 204) 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 succeeded by brushing, as described on page 205. After preparing a sufficiently smooth surface, the sheets are at once rubbed with a rag moistened with petroleum, or, if preferred, with a rag and pulverized Vienna lime. They are then scoured wet in the manner described for sheet-zinc. The scouring 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 current-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 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 212° 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 308 ELECTRO-DEPOSITION OF METALS. 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, accord- ing 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. Nickel- ing the wire in coils, however, cannot be done, as only the upper windings exposed to the anodes would acquire a coat of nickel. Hence it becomes necessary to unwind the coil, and for continuous working pass the wire at a slow rate through the cleansing and pickling baths, as well as the nickel bath, and hot water reservoir, as shown in Fig. 119, in cross-section, and in Fig. 120, in ground plan. The unwinding of the wire is effected by a slowly revolving shaft, upon which the nickeled wire again coils itself; but in the illustration the shaft is omitted. In Fig. 120 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 6 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 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 carrying the wires over the roll d, negative electricity is con- ducted to them. From the roll d, the wires run over the roll- bench s (Fig. 119) 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 DEPOSITION OF NICKEL AND COBALT. 309 apparatuses are not shown in the illustration), to be again wound in coils. In case a high polish is required, the nick- v5* # H >/^V. CO' tew , V,*. / ■ I \Vs\ rnun 4w- sill yifif u eled wires may be run under pressure through leather cheeks dusted with Vienna lime. 310 ELECTRO-DEPOSITION OF METALS. 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 precaution- ary 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 sup- port of felt or cloth, so that the edge sinks somewhat into the support, without, however, cutting into it. The edge is then held downward, and thus together with the support brought against the revolving 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 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. DEPOSITION OF NICKEL AND COBALT. 311 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 oiher 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 finer 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, 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 brass- ing is not advisable, waste in consequence of peeling off being frequently the result. 312 ELECTRO-DEPOSITION OF METALS. 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 suit- able composition of the nickel baths and the manipulation required will here be given. The nickel baths according to formula I (page 253) and formula VII (page 257) 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 edition 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. 257. In case the metal salts should contain free acids add, previous to the addition of the boric 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. 253 and. DEPOSITION OF NICKEL AND COBALT. 313 257), and the process of hard nickeling does not essentially differ 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-copper 0.11 inch thick, and £ to 1 inch wide, of the form shown in Fig. 121. 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. Fig. 121. covered with a strong current. When everywhere coated' with nickel, the current is weakened and the deposit allowed gradually to augment. With an average duration of nickel- ing 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- -314 ELECTRO-DEPOSITION OF METALS. 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 elec- tros, pickling with potassium cyanide solution, after freeing .from grease, must not be omitted. The nickeled 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 ineffi- ciency 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 reduction of the foreign metals is inconvenient and connected with expense 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." Deposition 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 combination, especially, all tones from copper-red to gold- shade may be obtained, according to which metal predomi- nates, or according to the current-strength which is conducted into the bath, as is also the case in brassing. DEPOSITION OF NICKEL AND COBALT. 315 A suitable bath for coating metallic articles with an alloy •of nickel, copper and tin, for which the term nickel-bronze is proposed, 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, dis- solved in a concentrated solution of sodium pyrophosphate, while chloride of tin is directly dissolved in sodium pyro- phosphate until the turbidity, at first rapidly disappearing, disappears but slowly. Nothing definite can be said in regard to the mixing pro- portions of these three solutions, because the proportions will have to be varied according to the desired color of the de- posit. 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 •German 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 cyanide. The precipitate is then filtered off, washed, dis- solved in 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. 316 electro-deposition of metals. Examination of Nickel Baths. The reaction of the nickel baths have previously been briefly referred to, but the subject must here be more closely considered. 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 derivation. If, for instance, in consequence of insufficient solution of nickel, free sulphuric acid appears on the anodes, the bath be- comes at the same time 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 litmus-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 formula? 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 red- den it. In this case red congo paper, which is not changed 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. DEPOSITION OF NICKEL AND COBALT. 317 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 organic 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 sulphuric 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 recognized, 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 ammonia formed. With this process there will generally be connected an increase in the content of the 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 operation, 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 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- 318 ELECTRO-DEPOSITION OF METALS. 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 arriv- ing at incorrect results by the use of inaccurately prepared standard solutions. For this reason directions for the prepa- ration of standard solutions are omitted, and the methods of examination 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 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 DEPOSITION OF NICKEL AND COBALT. 319' the beaker with a glass rod, add standard soda solution from, a glass burette provided with a glass cork and divided into-n,- 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 colorization 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 previously 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 fol- lows : 1 cubic centimeter of standard soda solution neutralizes 0.049 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 centi- meters of the fluid containing sulphuric acid, 5.4 cubic centi- meters of standard soda solution were required, then the content of sulphuric acid amounts to 5.4x0.049=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- based upon the fact that the metallic solution contained in a* platinum dish is decomposed by the current, and the metah 320 ELECTRO-DEPOSITION OF METALS. precipitated 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 shown in Fig. 122. 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 Fig. 122. 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 mov- able support or holder. The latter is carefully insulated from the rod of the stand and connected with the positive pole of the source of current. During electrolysis the platinum dish is covered with a perforated watch-glass to prevent possible •loss by the evolution of gas. DEPOSITION OF NICKEL AND COBALT. 321 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 analy- sis 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 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 22 322 ELECTRO-DEPOSITION OF METALS. 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. absolutely 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 at 212° F. in an air-bath. The weight of the precipitate of metallic nickel obtained by weighing the platinum dish gives the content of nickel am- monium sulphate in grammes per liter of bath b} 7- multiplying by 335. From the increase in the content of nickel ammo- DEPOSITION OF NICKEL AND COBALT. 323 ilium sulphate shown by the analysis, it can be readily cal- culated 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 (Co = 58.97 parts by weight) 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 capable 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 w r ith cobalt, the baths given under " Nickeling " may be used by substituting for the nickel salt a correspond- ing quantity of cobalt salt. By observing the rules given for nickeling, 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 valu- able 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- 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, 324 ELECTRO-DEPOSITION OF METALS. and the plates are to be electro-plated with the use of a moderate 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 10J 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. Prof. Sylvanus Thompson's solutions for the electro-deposi- tion of cobalt, patented by him in 1887, yield very satisfactory results : I. Double sulphate of cobalt and ammonium 16 ozs., mag- nesium sulphate 8 ozs., ammonium sulphate 8 ozs., citric acid 1 oz., water 1^ gallons. II. Cobalt sulphate 8 ozs., magnesium sulphate 4 ozs., ammonium sulphate 4 ozs., water 1^ gallons. It is best to use the solutions warm, at about 95° F. To determine whether copper, and how much of it, is dis- solved 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 sul- phuric 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 exhibit- ing no trace of corrosion. The experiment proved that there is no danger of destroying the copper plate b} r stripping the cobalt deposit with dilute sulphuric acid, provided the opera- tion 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 DEPOSITION OF NICKEL AND COBALT. 325 suitable for electro-plating small articles in quantities. For the preparation of this bath, dissolve 3J ounces of chloride of cobalt in as little water as possible, and compound the solution with concentrated solution of Rochelle salt until the volumi- nous precipitate at first formed is almost entirely redissolved, and then filter. Bring the bath into a vessel and place the latter in a clay cup filled with concentrated solution of chlo- ride 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 suffi- ciently heavy to bear vigorous polishing with the bob. Coat- ing zinc in the same manner was not successful. CHAPTER VII. DEPOSITION OF COPPER, BRASS AND BRONZE. 1. Deposition of Copper. Properties of copper. Copper (Cu = 63.57 parts by weight) lias 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 becomes gradually coated with a green deposit of basic car- bonate. 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 read- ily attacked by nitric acid, but is slowly dissolved when im- mersed in heated hydrochloric 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 potas- sium cyanide dissolves copper. Sulphuretted hydrogen black- ens 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 dis- cussed 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 suc- ceeding processes of nickeling, silvering, or gilding, or to pro- (326) DEPOSITION OF COPPER, BRASS AND BRONZE. 327 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- further 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 freq uently- BY CONTACT, BY BOILING, AND BY FRICTION. 489' changed. On the other hand, the constant increase of dis- solved contact-metal in the electrolyte constitutes a drawback, and is the cause of the electrolytes, as a rule, giving out long, before their content of metal is exhausted. Finally, the reduction 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 electrolyte, metals reducible by the current. Furthermore, the quantities of metal deposited upon the aluminium can be dissolved with nitric acid without materially attacking the contact-metal. Darlay has recommended magnesium as a contact-metal (German patent 127,464). It presents, however r no advantage, on the one hand, on account of its high price and, on the other, by reason of the deficient results in connec- tion with the baths of the above-mentioned patent. The electrolytes serving for depositions by contact must possess definite properties if they are to yield good results. Since the currents generated by contact are weak, the elec- trolyte 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 77 grains of crystallized sodium phos- phate, 46^ grains of caustic potash, 15^ grains of neutral chlo- ride 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 dissolv- ing the contact-metal, whether it be zinc, cadmium, aluminium, 490 ELECTRO-DEPOSITION OF METALS. 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 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 suitable, 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 pro- moted by sufficient alkalinity of the electrolyte, mostly in connection with chlorides, in a few rarer cases without chlo- rides, 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 pyrophosphates 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 regen- eration, which as a rule is not so readily done, and thus in [practice the contact-process becomes quite expensive. It must BY CONTACT, BY BOILING, AND BY FRICTION. 491 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 thin deposits can be produced, which do not afford protection against atmospheric influences, and are not sufficiently re- sistant 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 ^re provided, either mechanically by rolling or welding, or electrolytically by deposition, with the same metal contained in solution 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 combina- tions a portion 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 with- drawn 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 «team 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. According to Franz Stolba, articles can be sufficiently nick- eled in 15 minutes by boiling them, mixed with fragments of zinc in a solution of nickel sulphate. A copper kettle tinned 492 ELECTRO-DEPOSITION OF METALS. inside is to be used. 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 contact process becomes a boiling process. The articles are to be boiled for 30 to 60 minutes in a 10 per cent, zinc chloride solution to which is added enough nickel sulphate to give the solution a deep green color. However, Stolba's process cannot be recommended to the nickel-plater. To be sure a thin nickel deposit of a light color might be obtained upon brass articles, but that on iron objects generally turned out dark and mostly stained. The nickeling is so thin that it will not stand polishing with any kind of pressure, and the cheapness claimed for the process is- quite illusive, the solution soon becoming useless by reason of the absorption of copper, iron, etc., from the metals to be- nickeled. For small articles, which are not to be nickeled with the- assistance of the current, one of the following processes is to- be preferred : By boiling a solution of 8| ozs. of nickel-ammonium sul- phate and 8^ 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 sheet-zinc 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. 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 BY CONTACT, BY BOILING, AND BY FRICTION. 493 •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 slightly 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 those 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 fulfill nothing further than the general conditions given in detail on p. 487 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. 489). 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 " Electro- 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. 488, 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. In his patent specification, Darlay gives the following com- position of the electrolyte which is to be used hot : Water 1 quart, nickel chloride 1\ drachms, sodium phos- 494 ELECTRO-DEPOSITION OF METALS. phate 8£ ozs., ammonium chloride 11J drachms, ammonium carbonate and sodium carbonate each 4f 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. 489. 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 Darlay'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. 259 under formula IX for nickeling with an external source of current, should be suit- able 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 so- lution 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., crystallized ammonium chloride 0.07 oz., water 1 quart. Heat the bath to between 104° and 122° F., and immerse the pre- viously cleansed and pickled articles in it, bringing them in contact with a bright zinc surface not too' small ; for small BY CONTACT, BY BOILING, AND BY FRICTION. 495- 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 satisfactory results are obtained in this bath, the reaction of aluminium in cobalt solutions thus appearing to be different from that in nickel solutions. What has been said in re- gard to Darla} r 's contact process for nickeling applies also to cobalting. For cobalting small objects in quantities, the reader is re- ferred to Warren's process, p. 324. Coppering by Contact and Dipping. According to Liidersdorff, 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 10| 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 stir- ring, pure whiting until effervescence is no longer perceptible. Filter off the fluid from the tartrate of lime, separate and wash the precipitate, so that the filtrate, inclusive of the wash water, amounts to 10 or 12 quarts, and dissolve in it If 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. 334, under formula X. The bath is to be heated to between 185° 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 quantities are quickly and nicely coppered. According to Bacco, a copper bath in which zinc may be coppered by immersion, and iron and other metals in contact 496 ELECTRO-DEPOSITION OF METALS. 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 -iV 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 extent 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 formula 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 cyanide "is exactly to be adhered to" in order to prevent a deposit of copper upon the contact-body — an aluminium BY CONTACT, BY BOILING, AND BY FRICTION. 497 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 potassium 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, potassium 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 accurately-fixed content of potassium cyanide" in Dar- lay'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 sep- arated 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 aluminium-contact can be employed for cop- pering 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 b} 7 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, each provided with a brush, preferably so wide that the entire surface of the object to be treated can be coated with one ap- * 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. 32 498 ELECTRO-DEPOSITION OF METALS. plication. One of the vessels contains a strongly saturated solution of caustic soda, and the other a strongly saturated solution of blue vitriol. For coppering, the well-cleansed object is first uniformly coated with a brushful of the caustic soda solution, and then also with a brushful of the blue vitriol solution. A quite thick film of copper is immediately de- posited 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, If ozs. of blue vitriol, and If 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 brassing 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 autovolt brass bath, and yields- thin brass deposits of an agreeable color and good luster : Water 1 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 BY CONTACT, BY BOILING, AND BY FRICTION. 499 98 per cent, potassium cyanide the bath yielded no deposit, one 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 lamina?, 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 alu- minium, and that deposition by contact is consequently con- nected 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 1 quart, crystallized silver nitrate 0.52 oz., 60 per cent, potassium cyanide 1.4 ozs. 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. 500 ELECTRO-DEPOSITION OF METALS. According to Darlay's German patent, 128,318, the follow- ing baths serve for silvering by contact with aluminium : Water 1 liter (2.11 pints), silver nitrate 30 grammes (0.7 oz.), potassium cyanide 10 grammes (0.35 oz.), caustic potash 4 grammes (0.14 oz.). Information regarding the content in percent, 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 specifica- tion, should read 0.05 kilogramme of silver nitrate instead of 0.5 kilogramme. This, calculated to 1 liter, gives 2 grammes instead 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 immei'sion. For silvering coppered or brassed objects by immersion, the following solution may be used : Water 1 quart, silver nitrate 0.35 oz., 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 BY CONTACT, BY BOILING, AND BY FRICTION. 501 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 2f to 5J drachms of potassium cyanide per quart. Should this prove ineffectual, the content of silver is nearly ex- hausted, and the bath is evaporated to dryness, and the resi- due 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- ing to Roseleur, very suitable for silvering by immersion. The solution is prepared by pouring into moderately concen- trated 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 commences to lose its effect. If, however, the bath is not capable of dissolving the silver sulphide formed, concen- trated solution of sodium sulphite has to be added. For the preparation of the solution of sodium sulphite, Roseleur recommends the following method : Into a tall vessel of glass or porcelain (Fig. 134) introduce 5 quarts of water and 4 pounds of crystallized soda, after pouring 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 sul- phuric acid, washing the gas in a Woulff bottle filled an inch or so deep with water, and introducing it into the bottle con- taining 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 502 ELECTRO-DEPOSITION OF METALS. escapes with effervescence. 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 quan- tity 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 Fig. 134. 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 BY CONTACT, BY BOILING, AND BY FRICTION. 503 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 silver 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 bath, a mat 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 decomposition gradually 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 1 quart of water which con- tains 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 with- drawn may be replaced by the addition of moist silver oxide as long as complete 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 dilu- ting 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 re- quire to be boiled for a longer time. The process is as follows : 504 ELECTRO-DEPOSITION OF METALS. 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 decom- posed 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 heaping 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 sil- ver paste must be added. If finally the bath acquires a green- ish color, caused by dissolved copper, it is no longer suitable for the purpose, and is then evaporated and added to the sil- ver 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 b}' 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 suffi- cient quantity to form the ingredients into a stiff paste. II. Silver in the form of freshly precipitated chloride of sil- BY CONTACT, BY BOILING, AND BY FRICTION. 505 ver * 0.35 oz., potassium cyanide 1.05 ozs., sufficient water to- 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 does excellent service: Silver in the form of chloride of silver 0.35 oz., cream of tartar 0.7 oz., common salt 0.7 oz., and sufficient water to form the mixture of the ingredients into a stiff paste. Another composition is as follows : Chloride of silver 1 part, pearl ash 3, common salt 1J, 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 sil- vered, 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 prelim- inary operation called graining, by which a grained and slightly dead appearance is given to the articles. Marks of the file are obliterated b}' rubbing upon a whetstone, and lastly upon an oil stone. Any oil or grease is removed hj 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 flat heads. The- parts are then thoroughly rubbed over with a brush entirely free from grease, and dipped into a paste of water and very fine 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- * From 0.56 oz. of nitrate of silver. 506 ELECTRO-DEPOSITION OF METALS. in a weak mercurial solution, composed of water 1\ gallons, nitrate or binoxide of mercury T V oz., sulphuric acid \ oz., which slightly whitens the copper. The pieces are passed quickly through the solution and then rinsed. This opera- tion gives strength to the graining, which without it possesses 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 pro- portion of cream of tartar is greater, but it is then more diffi- cult to scratch-brush. The silver powder is obtained as follows: Dissolve in a glass or porcelain vessel § oz. of crystallized nitrate of silver in 1\ gallons of distilled water, and place 5 or 6 ribbands of cleansed copper, f inch wide, in the solution. These ribbands 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 ribbands. 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 oipon 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 BY CONTACT, BY BOILING, AND BY FRICTION. 507 of paste is added two or three times and rubbed in the manner indicated. 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, the pieces are washed and scratch-brushed. The brushes employed 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 operation or uncovering 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 giv- ing 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 covering 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 gilding bath. A good compo- sition is : Yellow wax, 2 parts by weight ; translucent rosin, 3J ; extra-fine red sealing-wax, 1J ; polishing rouge, 1. Melt the rosin and sealing-wax in a porcelain 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 stir- ring until the mixture becomes solid, otherwise all the rouge will fall to the bottom. The flat parts to receive this resist are slightly heated, and then covered with the mixture, 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 508 ELECTRO-DEPOSITION OF METALS. long wires, and their flexibilit} 7 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 saw-dust. The holes of the pinions are cleansed and polished with small pieces of, very white, soft wood, the friction of which is suffi- cient 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 Contact, 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 T prussiate of potash 1 oz., potash 1 oz., common salt 1 oz., water 1 quart. The bath is prepared as given for formula III under " Deposition of Gold." For use, heat it to boiling. II. Chemically pure crystallized sodium phosphate 2.11 ozs. r neutral crystallized sodium sulphite 0.35 oz., potassium cya- nide 0.28 oz., fine gold (as chloride) 15.43 grains, water 1 quart. The bath is prepared as given for formula V under " Depo- sition of Gold." Temperature for contact-gilding 185° to 194° F. If red gilding is to be effected in this bath a corres- BY CONTACT, BY BOILING, AND BY FRICTION. 509 ponding addition of potassium-copper cyanide has to be made, 1\ 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 ■contact. 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. Gilding by immersion {without battery or contact). The fol- lowing two formulas have proved very useful : I. Crystallized sodium pyrophosphate 2.82 ozs., 12 per cent, prussic acid 4.51 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 dis- advantage of rapidty decomposing, and consequently can seldom be completely exhausted. In this respect the follow- ing formula answers much better. II. Crystallized sodium phosphate 2.82 drachms, chem- ically 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 | of the water, and the potassium cyanide and chloride of gold in the remaining J, 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 2f drachms of potassium cya- nide, 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 suitable for contact gilding. 510 ELECTRO-DEPOSITION OF METALS. 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 with the rag, with the thumb, with the cork. It is chiefly em- 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 partial^ to finely-divided metallic gold. This tinder is then rubbed in a porcelain mortar to a fine, uniform powder. To gild with this powder, dip into it a charred cork moist- ened with vinegar or salt water and rub, with not too gentle a pressure, 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 powder takes badly. After gilding, the surface may be care- fully 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 thicken- ing 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 Pe} r raud, the orig- inators of this method, describe the operation as follows : Articles of other metals than zinc are placed in a bath consist- ing of concentrated solution of ammonium chloride, in which BY CONTACT, BY BOILING, AND BY FRICTION. 511 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 composi- tion, dissolve 11.28 drachms of chloride of gold in a like quantity of water, and add a solution of 2.11 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 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 158° 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 suit- able for giving a thin coat of platinum to fancy articles. He recommends a solution of 0.35 oz. of chloride of platinum and 7 ozs. of common salt in 1 quart of water, which is made alka- line 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. 512 ELECTRO-DEPOSITION OF METALS. 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 pickled objects in contact with pieces of zinc or, 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 pre- pared 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, Zilk'en 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 15f ozs., and 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 process, 8 to 10 hours. Darlay uses for a cold tin bath with aluminium-contact : Water 10 quarts, stannous chloride 1.05 ozs., potassium cyanide 1.41 ozs., caustic soda 1.76 ozs. It might be advisable to heat the bath to at least between 113° 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 BY CONTACT, BY BOILING, AND BY FRICTION. 513 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 ad- dition 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 be polished by scratch-brushing, or scouring with saw- dust in the tumbling barrel. Tinning by boiling in the above betth 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 so- lution of equal parts of tin-salt and common salt in rain-water. The manipulation is the same as given above. 33 514 ELECTRO-DEPOSITION OF METALS. 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 so- lution 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 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 128319) 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 194° 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. BY CONTACT, BY BOILING, AND BY FRICTION. 515 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 OF METALS. Metal coloring and bronzing is an important branch of the metal industry, its object being, on the one hand, to em- bellish the original metallic surface and, on the other, to protect it from the influence of atmospheric air, moisture, various gases, etc. Although, strictly speaking, these opera- tions do not form a part of a work on the electro-deposition of metals and cannot be adequately treated within the limits of a chapter, a few methods and approved formulas will here be given since the electro-plater is frequently forced to make use of one or the other method to furnish basis-metals or electro-deposits in certain shades of colors demanded by customers. Metal coloring may be effected by electrolytic, chemical and mechanical means. Methods of coloring electrolytically have been given under Deposition of Nickel (black nickel- ling), and under Deposition of Antimony and Arsenic. Mechanical methods of coloring require the use of pigments, bronze powders, varnishes, etc. and cannot be here fully de- scribed. To the electro-plater the most important of these operations is lacquering which will be described in the next chapter. Attention will here be given chiefly to coloring metals by chemical means. The practice of coloring metals requires considerable talent for observation and a certain knowledge of the behavior of metals or metallic alloys towards the chemical substances used. Especially in coloring alloys, for instance, brass, their per- (516) COLORING OP METALS. 517 rentage composition makes a difference, and patinas can be produced upon a brass richer in zinc, which cannot be ob- tained upon an alloy richer in copper. Hence instructions for patinizing have to be changed in one or the other direc- tion, and this problem cannot be readily solved without a certain chemical knowledge. The temperature of the solu- tions used is also of great importance, and the directions given in this respect must be accurately observed. 1. Coloring copper. — With the use of chemicals nearly all colors can be produced upon copper, as well as upon other metals and alloys, by first coating them electrolytically with copper and afterwards coloring the deposit. For the produc- tion of yellow and brown, alkaline sulphides are, for instance, used, for green, copper salts, for black, metallic silver, bis- muth, platinum, etc. All shades from the pale red of copper 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 uniformly 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 tem- perature must be, and the longer it must act upon the object. When sufficiently heated, the dry powder is removed by brush- ing 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 produced in this manner is very warm, and resists the action of the air. 518 ELECTRO-DEPOSITION OF METALS. Brown color on copper. — Apply to the thoroughly cleansed object a paste made of verdigris 3 parts, ferric oxide 3, sal ammoniac 1, and sufficient vinegar and heat until the paste turns black, then wash and dry the object. By the addition of some blue vitriol to the paste the color may be darkened to chestnut-brown. A brown layer of cuprous oxide on copper is produced as fol" lows : After polishing the articles with pumice powder apply with a brush a paste made of verdigris 4 parts, ferric oxide 4, finely rasped horn shavings 1, and a small quantity of vinegar. Dry, heat over a coal fire, wash, and smooth with the polish- ing stone. A brown color is also obtained by brushing to dryness with a hot solution of 1 part of potassium nitrate, 1 of common salt, 2 of ammonium chloride, and 1 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 produced as follows : Place the articles, previously freed from grease and pickled, in a solution of 5£ ozs. of copper sulphate, and 2f ozs. potassium chloride heated to 140° F. until the desired tone is produced. Then brush with a soft brass-wire brush, rinse again for a short time in the pickle, and finally wipe dry with a soft cloth. Brown of various shades on copper is produced as follows : COLORING OF METALS. 519 Bring the objects previously cleansed and pickled into a solu- tion of liver of sulphur 1£ ozs., or a solution of trichloride of antimony (butter of antimony) 1| ozs. in water 1 quart. When the desired tone is produced, rinse the objects thor- oughly in water and dry. The shade of the color may be varied by the concentration of the bath as well as by the length of time of its action. The color is finally fixed by rubbing with a rag saturated with oil varnish or by rubbing heated wax upon the object. A beautiful brown on copper by the so-called Chinese process is produced as follows : Crystallized verdigris 2 parts, cinnabar 2, ammonium chloride 5, finely powdered alum 5, intimately mixed and made into a thin paste with water or wine vinegar. Apply this paste with a brush to the polished surfaces. Then heat uniformly over a coal fire and when cold wash carefully with water. By the addition of copper sulphate a color shad- ing more into chestnut-brown is obtained, and by the addition of borax one shading more into yellow. Gold-yellow on copper. Treat the objects with a hot solution diluted with water, of mercury 10 parts and zinc 1 part in hydrochloric acid, to which some pulverized tartar has been added. 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 pro- duces tones from bronze Barbedienne to antique green patina, according 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. Yellowish-brown on copper is produced by boiling the objects in a saturated solution of potassium chloride and ammonium nitrate. By heating the objects after drying them, a more reddish-brown color is obtained. 520 ELECTRO-DEPOSITION OF METALS. Dark brown to black on copper is obtained by dissolving nitrates of bismuth, copper, silver or cupriferous silver in water and adding some nitric acid. Copper to which such a fluid has been applied is, when heated, colored brown with the use of bismuth, and black with the use of copper and sil- ver salts. Very dark Slack is produced by placing the objects for half an hour over a vessel containing a saturated solution of liver of sulphur to which some hydrochloric acid has been added. The luster may be increased by rubbing with a woolen cloth and a waxed brush. Bed to violet shades on copper articles. According to a pro- cess patented in Germany by M. Mayer, the highly polished copper article is electrolytically provided with a thin deposit of arsenic or antimony. For the preparation of the bath, solu- tion of an antimony or arsenic salt is poured into a ferric chloride solution till the precipitate formed redissolves. A sheet of iron may serve as anode. The articles thus treated are then heated to cherry red and again polished. It is claimed that the electro-deposit as a carrier of oxygen effects a uniform oxidation of the copper underneath, but at the same time prevents it from becoming too highly oxidized so that by heating a layer of oxide is chiefly formed. The coating thus obtained shows red to violet shades, adheres firmly and resists physical as well as chemical influences. Copper is colored blue-black by dipping the object in a hot solution of 11^ drachms of liver of sulphur in 1 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 COLORING OF METALS. 521 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. Mat-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 drjnng over a coal fire. These manipulations are to be re- peated until the formation of a uniform mat-black. A solution recommended for obtaining a deep black color on copper and its alloys is composed as follows : Copper nitrate 100 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, heating the work on a hot plate until the copper salt is de- composed into the black copper oxide. It would be difficult to heat large articles on a hot plate, but a closed muffle- furnace would give better results than an open coal fire. In any case heating should not be continued longer than neces- sary to produce the change mentioned above. Black color on copper, coppered objects and alloys rich in copper. For this purpose Dr. Groschuff gives the following directions : Heat a suitable quantity of 5 per cent, soda lye in a vessel of glass, porcelain, stoneware or enameled iron to 212° F., add 1 per cent, powdered potassium persulphate and immerse the article previously secured to a wire; an evolu- 522 ELECTRO-DEPOSITION OF METALS. tion of oxygen will be perceptible. The article is moved to and fro in the hot bath till the black color desired is pro- duced which, with smaller articles, is generally the case within five minutes. Should the evolution of oxygen cease previous to this, add 1 per cent, more of potassium persulphate. The article presenting at first a velvety appearance is rinsed in cold water, dried with a soft towel and rubbed ; it will then be of a deep black color with mat luster. The solution may also be used for coloring black a large number of alloys with a high percentage of copper. Gen- erally speaking, more time is required for coloring alloys than copper. Patina. This term is applied to the beautiful green colors antique statues and other art-works of bronze have acquired by long exposure to the action of the oxygen, carbonic acid, and moisture of the air, whereby a thin layer of copper car- bonate is formed upon them. It has been sought to accelerate by chemical means the formation of the patina thus slowly produced by the action of time and the term patinizing has been applied to the production of such colors. 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 vari- ous 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 60° F., the process is several times repeated. The composition of the metal to which the patiniz- ing fluid is to be applied, exerts an influence upon the forma- tion of a patina of good qualit}^, the latter being most readily COLORING OF METALS. 523 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 ver- digris, but possess less resistance towards water. Coatings produced w T ith ammoniacal fluids have a dull, earthy appear- ance, and a blue-green to gray-green color. Yellow-green tones are obtained 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 be changed into blue-green, only ammonium carbonate solution 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 ammonium chloride in vinegar, the action of the solution being accelerated by the addition of verdigris. A solution of 9 drachms of ammonium chloride and 2J drachms of potas- sium 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 ap- plication, 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 patina are thus fulfilled. If the patina is to show a more bluish tone, brush the objects with a solution of 4^ ozs. of ammonium carbonate and 1 J ozs. of am- monium chloride in 1 quart of water, to which a small quan- tity of gum tragacanth may be added. 524 ELECTRO-DEPOSITION OF METALS. A blue-green patina, much used in Paris, is produced by heating in the following solution : Water 500 grammes, cor- rosive sublimate 2.5 grammes, saltpetre 8.6 grammes, borax 5.6 grammes, zinc oxide 11.3 grammes, copper nitrate 22 to 22.5 grammes. A brown patina is obtained with the following solution : Oxalic acid 3 grammes, sal ammoniac 15 grammes, distilled water 280 grammes. 'The article is to be frequently brushed with the solution ; this process requires considerable time. Patina for copper and brass. The production of two fine tones of color upon copper and brass articles is due to the fact that ammonia attacks and eventually dissolves copper. The following directions are given by La Nature : If to objects of copper is to be given the appearance of very antique art objects recently dug up, it is only necessary to immerse them in ammonia. The effect does not show itself immediately, but only after 24 hours. A beautiful dark green coating, which adheres quite firmly, is formed. By allowing the copper object to remain for several days in the fluid the sur- face is more strongly attacked and the antique effect is heightened. Another kind of patina which cannot be produced upon copper but only upon brass is obtained by immersing the object in a hot, nearly boiling, mixture of 75 cubic centimeters of ammonia, the same quantity of water and 10 grammes of potash. A uniform durable patina shows itself in half a minute. By allowing the article to remain. longer in the solu- tion the patina acquires, without being materially altered, a steely bluish-gray luster. To produce a steel-gray color upon copper, immerse the clean and pickled objects in a heated solution of chloride of anti- mony in hydrochloric acid. By using a strong electric cur- rent 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 1 COLORING OP METALS. 525 quart of hydrochloric acid, 0.125 quart of nitric acid, If ozs. of arsenious 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 If and lampblack J. Then dissolve in a quart of water, 4J ozs. of sodium hyposulphite, and in another quart of water, 14J drachms of blue vitriol, 5 J drachms of crystallized verdigris, and 7f 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 167° and 176° F. By dipping articles of copper, brass, or nickel in the hot solution they become im- mediately 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 protected 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. 2. Coloring brass and bronzes. Most of the directions given for coloring copper are also available for brass and bronzes, especially those for the production of patinas and the oxidized tones by a mixture of ferric oxide and blacklead. 526 ELECTRO-DEPOSITION OF METALS. Many colorations on brass are, however, effected only with difficulty, and are partially or entirely unsuccessful as, for instance, 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 cop- per salts so that a small excess remains undissolved, or, in other words, that the ammonia is saturated with copper. The carbonate of copper is prepared by mixing hot solutions of equal parts of blue vitriol and of soda, filtering off and wash- ing 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. Black color on brass optical instruments is produced by plac- ing the brass in a solution of platinum or chloride of gold mixed with stannous nitrate. The Japanese bronze brass with a solution of copper sulphate, alum and verdigris. Success in bronzing depends on the temperature of the alloy, the propor- tions of metals used in the alloy, drying, and many other COLORING OF METALS. 527 small details which can be learned only by practical experi- ence. Steel gray on brass. — Use a mixture of 1 lb. of strong hydro- chloric acid with 1 pint of water to which are added 5£ ozs. of iron filings and a like quantity of pulverized antimony sulphide. Hydrochloric acid compounded with white arsenic is also recommended for the purpose. The mixture is brought into a lead vessel, and the object dipped in it should be in contact with the lead of the vessel, or be wrapped around with a strip of lead. Solution of antimony chloride produces a gray color with a bluish tinge, and a hot solution of arsenious chloride in a small quantity of water a steel gray color. Silver color on brass. Dissolve in a well-glazed vessel 1^ ozs. cream of tartar and \ oz. of tartar emetic in 1 quart of hot water, and add to the solution If ozs. of hydrochloric acid, 4 J ozs. of granulated, or better, pulverized tin and 1 oz. of powdered antimony. Heat the mixture to boiling and im- merse 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. Pale gold color on brass. 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 \ hour. Then add a solution of 3.6 parts by weight in 10 parts by weight of hot water. Use the bath at a temperature of 176° F. Straw color, to brown, throvgh 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 1 quart of water, and add If 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. Color resembling gold on brass, according to Dr. Kayser: Dissolve 8J drachms of sodium hyposulphite in 17 drachms 528 ELECTRO-DEPOSITION OF METALS. of water, and add 5.64 drachms of solution of antimonious chloride (butter of antimony). Heat the mixture 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 become gray. Brown color, called bronze Barbedierine, on brass. This beau- tiful color may be produced as follows : Dissolve b} 7 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 tur- bidity 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 satisfactorily, add some antimonious sulphide. The solution decomposes 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 1 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 auran- tiannm) with 1 part of finely pulverized bloodstone, and tritu- COLORING OF METALS. 529 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 ammonium 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. Dead red color on brass. Suspend the articles, previously thoroughly freed from grease, in a solution of equal parts of potassium-lead oxide and red prussiate of potash heated to 122° F. until they have acquired a sufficiently dark color. . For coloring brass articles in large quantities brown by boiling, the following solution is recommended : Water 1 quart, potas- sium chromate 1J ozs., nickel sulphate 1J ozs., potassium permanganate 4 J drachms. 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: Dissolve in 1 quart of water 4^ ozs. of sodium hyposulphite, 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 hyposulphite of soda, solution of hyposulphite of lead is formed, which decomposes slowly and separates sulphide of lead, which precipitates upon 34 530 ELECTRO-DEPOSITION OP METALS. the brass objects, and, according to the thickness 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 Ger- man patent for it. He dissolves in 6J 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 1 oz. of chloride of tin in §■ pint of water, mixing the solution, heating, and pouring 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 1000, give b}^ 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 1000 of water, and adding 100 of caustic soda until a precipitate is formed, and boiling the objects in the solution, & gray- brown color is obtained, which can be made darker by the addition of colcothar. (Stains are readily formed. Brassed zinc ac- quires a pleasant pale-brown.) IV. With 50 parts by weight of caustic soda, 50 of sulphide of antimony, and 500 of water, a pale fig-brown color is pro- duced. (Fig-brown could not be obtained, the shade being rather dark olive-green.) COLORING OF METALS. 531 V. By boiling 400 parts by weight of water, 25 of sulphide of antimony and 600 of calcined soda, and filtering the hot solution, 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 ob- tained. (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 brown 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 broivn-yellow color, playing into a magnificent red. (The results obtained were only in- different.) 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 ob- tained. The formula, however, is not available for brassed zinc. 3. Coloring zinc. Direct coloring of zinc does not give, as a rule, reliable results, and it is therefore recommended to first copper or tin the zinc and color the coating thus obtained. Black on zinc. a. Dissolve crystallized copper nitrate 2 parts and copper chloride 2 parts in acidulated water 64 parts, and add to the solution hydrochloric acid of 1.1 specific gravity 8 parts. The resulting fluid has a slightly bluish color. A sheet of zinc, previously scoured bright by means of dilute hydrochloric acid and fine sand, will, when immersed in the fluid, immediately be colored intensely black. By removing the sheet thus treated, at once from the fluid and rinsing it without loss of time in a large quantity of pure water and allowing it to dry, the black coating will adhere very firmly to the zinc. b. Dip the object in a boiling solution of pure green vitriol 5.64 ozs. and ammonium chloride 3.17 ozs. in 2§- quarts of 532 ELECTRO-DEPOSTTION OF METALS. water. Remove the loose black precipitate deposited upon the object by brushing, again dip the object in the hot solu- tion and then hold it over a coal fire until the ammonium chloride evaporates. By repeating the operation three or four times, a firmly adhering black coating is formed. Gray, yellow, brown to black colors upon zinc. — Bring the articles into a bath which contains 6 to 8 quarts of water, 3J ozs. of nickel-ammonium sulphate, 3J ozs. of blue vitriol and 3 \ 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 de- termined shades will soon be learned by practice. When colored, the articles are thoroughly rinsed, dried, without rub- bing, 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. Brown patina on 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 consist- ing of a solution of 5.29 ozs. of blue vitriol and 2.82 ozs. of potassium chlorate in one quart of water at J 40° 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 re- placed 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 2.11 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. COLORING OF METALS. 533 A gray coating on zinc is obtained by a deposit of arsenic in a heated bath composed of 2.82 ozs. of arsenious acid, 8.46 drachms of sodium pyrophosphate and If 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 1 part by weight of crystallized verdigris, 1 of tartar, and 2 of crystallized soda. Red-brown shades on zinc. Rub with solution of copper chloride in ammonia. Yellow-brown shades on zinc. Rub with solution of copper chloride in vinegar. 4. Coloring iron. Browning of gun barrels. Apply a mix- ture of equal parts of butter of antimony 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 15J 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 15J 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 manganous oxide has been stirred. Lustrous black on iron. Apply solution of sulphur in tur- pentine prepared by boiling on the water-bath. After the 534 ELECTRO-DEPOSITION OF METALS. evaporation of the turpentine a thin layer of sulphur remains upon the iron, which on heating 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 it 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 experi- ment was repeated with larger plates, when a good blue-black color was obtained on the anode in half a hour. On drying in sawdust 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 appearance was almost identical with the black 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 per- ceptible change took place after the connection had been made with the dynamo for a quarter of an hour. After the inter- val of one hour a slight darkening occurred, but the effect * Sulphur dissolved in linseed oil. COLORING OF METALS. 535 was much less than that produced in five minutes in aerated water. 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 mat black coating upon clock cases of iron and steel — the so-called Swiss mat — is not produced by the electric process, 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, allowed to dry, and then steamed. For the production of a very strong mat, the process is to be twice or three times repeated. By one operation a beautiful black with semi-luster is obtained. Blue color on iron and steel. Immerse the article in | per cent, solution of red prussiate of potash mixed with an equal volume of |- per cent, solution of ferric chloride. Brown-black coating with bronze luster on iron. Heat the bright objects and brush them over with saturated potassium dichromate solution. When dry, heat them over a charcoal fire, and wash until the water running off shows no longer a yellow color. Repeat the operation twice or three times. A similar coating is obtained by heating the iron objects with a solution of 10 parts by weight of green vitriol and 1 part of sal ammoniac in water. To give iron a silvery appearance with high luster. — Scour the polished and pickled iron objects with a solution prepared as follows: Heat moderately 1J ozs. of chloride of antimony, 0.35 ozs. of pulverized arsenious acid, 2.82 ozs. of elutriated blood- stone with 1 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 de- posited, which is the more lustrous the more carefully the iron has previously been polished. 536 ELECTRO-DEPOSITION OF METALS. 5. Coloring of tin. — A bronze-like patina on tin may be ob- tained by brushing the object with a solution of If ozs. of blue vitriol and a like quantity of green vitriol in 1 quart of water, and moistening, when dry, with a solution of 3J ozs. of verdi- gris in 10J ozs. of vinegar. When dry, polish the object with a soft waxed brush and some ferric oxide. The coating thus obtained being not durable, must be protected by a coating of lacquer. Durable and very warm sepia-brown tone upon tin and its al- loys. — 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 solu- tion. 6. Coloring of Silver. — See " Deposition of Silver. " Electrochroma. The process for the production of colors on metals by electro-deposition, known under this term, is the invention of Mr. F. Arquimedas Rojaz. By this method either deposits or smuts of any desired color or texture can be pro- duced upon any metal used as a cathode. The anodes used are of pure carbon, no metal of any sort being put into the tank containing the plating solution except the work itself. In starting to color a piece of metal, be it brass, copper, tin, lead or iron, etc., the metal is first dipped into a cleaning solution, then into a hot water bath, next into the tank containing the solution for whatever background color is desired. A current of 8 to 12 volts pressure with a strength of 1 ampere per square inch of surface is used. After an immersion in the tank for from two to three minutes the work is dipped into hot water, and from there into a tub containing a dip solution. Here the finish of the process takes place, and the beautiful shades of color are produced. A piece of work, such as a lock plate for a store, may be given a green verde smut in the plating tank and then be changed to a light blue background in the dip tub- Gold finishes, rose antique and green, may be produced at COLORING OP METALS. 537 will in a few seconds of time, without any gold in the solu- tion. All of the solutions used in the process are fully protected by patents and are furnished ready for use. They are said to be made up of more than half a dozen elements, the propor- tions of which are so evenly balanced that a slight variation in the amounts used of each ingredient will throw the entire solution out of gear. CHAPTER XV. 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 ob- ject 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 applied, 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 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 trans- parent, 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. (538) LACQUERING. 539 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 the use to which the lacquered metal is subjected. 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 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 Lastina, Pyramide and Obelisk, etc., were introduced to the trade in America as early as 1876, and were 540 ELECTRO-DEPOSITION OF METALS. gradually adopted until early in the 80's, when their use be- came general, and since then they have become known throughout all parts of America and Europe. Pyroxyline 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 perfect]}' 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 ad- vantage of the lacquer — especially as regards the metallic objects — is that the coating in consequence of its physical constitution preserves the character of the bases. In accord- ance 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 w T ith 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. 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 100° to 120° F., if possible using a thermometer. Dip lacquers will dry in the air, but baking improves the finish. The receptacle for holding the lacquer and thinner for dip- ping purposes, should be either of glass, stoneware, chemically enameled iron, or a tin-lined wooden box — the preference be- LACQUERING. 541 ing in the order named. Lacquer or thinner should never be placed in copper or galvanized iron tanks. For thinning the lacquer when it has become too thick by the evaporation of the solvent, use the thinner which is recom- mended for each particular grade of lacquer. The appearance of rainbow colors upon objects lacquered with pyroxyline lacquer is due either to insufficient cleanli- ness, especially to the presence of grease upon the objects, or to the lacquer having been too much diluted. Objects to be lacquered should be freed from grease by the use of platers' compound, rinsed in hot water, dried in thinner and then lacquered. The use of benzine, aside from the danger it en- tails, is not always effective in removing grease from the pores of the metal. After cleaning, the polished surface of the work should 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, or correct the tendency to rainbow colors by adding more undiluted lacquer to the mix- ture. In adding thinner to lacquer it is always advisable to give it plenty of time to act upon the pigment in the lacquer. This can be facilitated by stirring with a wooden paddle. 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 dry, then suspending the objects for a few seconds in golden-yellow, red, green, etc., d}^es, known as dipping colors, next washing in water and finally drying. By mixing the coloring dyes in various pro- portions nearly every desired tone of color can be obtained. Special invisible lacquer for ornamental cast and chased interior grille, rail and enclosure ivork. This lacquer is made in three grades for use, 1, with the brush ; 2, with the spraying machine ; and 3, as a dip lacquer. Its presence cannot be detected on any of these sensitive finishes, and the fine mat finishes are left without the slightest luster after it has been 542 ELECTRO-DEPOSITION OF METALS. applied thereto. It can be mixed with the pigment fillings so much used in cast ornamental mountings, figured mould- ing for the verds, Florentine, rose and antique effects. Sand- blasted and brushed plain parts will not take on a sheen from this lacquer and will, therefore, not make a contrast in the lights of the filled and smooth portions of the work. The fine reliefs in these finishes, it has been found, will not be disturbed because of the lacquer softening the pigments when it is applied by spraying. In use this lacquer can be thinned so as to flow away from the various parts that make up a grille or rail without leaving any lines or waves, or causing glossy places or variations of lines. This lacquer is made by The Egyptian Lacquer Manufacturing Co., of New York, and with it the rich subdued effects of dead, mat, sanded and semi-dead finishes can be protected without in the least affecting their appearance. Satin finish lacquer is made by the same concern just men- tioned ; it comes in two grades, one for brush and the other for dip work. Its purpose is to maintain the light, but some- what solid, effect in which body color rather than tints pre- dominate ; its deadness gives to these body effects a plastic appearance. It can be used to protect a velvet-like tint re- sembling the ground gold, frosting or satin finish seen in ormolu and colonial gold, as well as dead and dull surfaces, or unpolished, lusterless and mat gold and mat silver. It can also be used to create a dead luster, or a deadened lustrous surface, for example, on mat designs upon a lustrous ground, where the lacquer lights up the satin finish. Jewelry, silver and novelty manufacturers can use it for general finishing of their work, as it will not alter the sensitive metal colorings, nor will it fill up to a gloss delicately brushed, satined, or chased surfaces or smut tints. Dip lacquer for pickled castings to be copper-plated and oxi- 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- LACQUERING. 543 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 of the metal and to the smut left from the oxidation when not scratch-brushed. This is a very rapid and inexpensive process since it does away with the costly operations of polishing, scratch-brushing and cleaning ; the finish depends entirely upon the life and luster of the lacquer, hence it is best to use one of the lacquers now designated. With helios dip lacquer, special, which is made by The Egyptian Lacquer Manufacturing Co., of New York, a fine luster is given to the dead backgrounds and a bright and lustrous finish to the smooth parts of the work and in many respects this lacquer renders the work equal to that which has been polished. Many other lacquers which have been tried dry down to the natural deadness of the metal finish and consequently the effect of the plating and oxidizing is lost, or, if not entirely lost, is not brought out in its right color. Old brass or brush-brass finishes. From 90 to 95 per cent of all brass for gas and electric fixtures, bedsteads and similar work is finished in brush-brass. Lacquers are specially made for the high gloss effects, as well as for the dull, or antique finish. As this finish is more susceptible to tarnish and stain than any other known finish, it is important that precise particulars be given as to the handling of this work prelim- inary to lacquering. For instance, where this work is finished with pumice, sand, flint, etc., and water, as most of it is, it should, as fast as completed be placed in a tank containing borax solution made by dissolving 1 lb. powdered borax in hot water and adding enough water to make 5 gallons. Use cold. Let the work accumulate in the solution until ready to lacquer. Then rinse the work in hot water and dip it in thinner. It will dry without stain by hanging up for a moment or two, when it should be immediately lacquered. Where " old brass composition " or emery and oil is used, the work should be cleaned from grease in " plater's com- 544 ELECTRO-DEPOSITION OF METALS. pound " or some other non-tarnishing cleaner, and can be placed in the borax -solution as fast as finished on the brush. It is then rinsed in hot (not too hot) water, dried in thinner, and immediately lacquered. Wiping the surface with a soft cloth or chamois skin does not remove the moisture from the metal. This is particularly apparent when there is much humidity in the air, and ver- digris or oxide rapidly forms in the scratches made by the abrasive materials and causes much subsequent trouble. The heat of the oven converts this moisture, combined with the oxide, into steam which penetrates the lacquer and causes staining of the film. Sawdust should never be used for drying metals given an old-brass finish. Brush brass finish lacquers. This very sensitive and easily discolored finish is readily marred by the use of an inefficient transparent dip lacquer. No existing finish requires more exacting and careful treatment than the brush brass finish, the finely brushed lines attracting and retaining substances which tarnish it readity. As a rule these substances are not visible, and cannot be easily removed by ordinary cleaning methods. After a time every speck of dirt shows under the lacquer coating, and is the cause of the various discolorations often seen in brush brass finish ; they vary from the tints shading into the browns to tints running into the greens, and are in almost every instance caused by the oxidizing influ- ences of contaminating matters left upon or attracted by the metal before it has been lacquered. When work is handled in large quantities these imperfections are especially notice- able, for such work cannot always be inspected one piece at a time. The old method of drying the buffed and smooth-sur- faced finishes with sawdust and then rubbing them with a soft muslin material is inadequate as well as uncertain for the brush brass ; in fact this process primarily causes the imper- fections which it is intended to prevent. At any rate, the result is necessarily doubtful when brush brass is dried in this way and allowed to stand for even a very short time before it is protected with lacquer. LACQUERING. 545 Egyptian brush brass dip lacquer and brush brass thinner, made by the Egyptian Lacquer Manufacturing Co., of New York, meets the necessary and varied conditions called for by this finish. After the brush brass has been washed in plater's compound and well rinsed in cold and hot waters, the work is first dipped into the brush brass thinner, which absorbs all moisture left on the metal and removes whatever impurities may have been attracted to it, and prepares the work for its dip into the brush brass dip lacquer. By the dip into the thinner a chemically pure metal surface is provided for the reception of the lacquer coating, and this guarantees the brush brass finish itself against discoloration, since 'the lacquer has been applied to a practically chemically clean and pure surface. Brush brass work which cannot be conveniently dip- lacquered should be spray-lacquered in preference to lacquer- ing with a brush, because the fine irregularities of the brushed surface of the metal retard the free flow of a brush lacquer. In other words, a brush lacquer cannot be applied quite as effectively as on a smooth finish, for, owing to the irregu- larities of the metal surface spoken of, an obstruction is placed in the way of the flowing of the lacquer when it is applied with a brush, because with the use of the latter the separa- tions in the lacquer, due to the uneven distribution of it from the bristles of the brush, sometimes leave minute parts of the surface unlacquered and the irregularities of the brushed metal surface prevent the lacquer from spreading over these minutely exposed lines. Thus when applying the lacquer with a brush it happens now and then that the exposed and unlacquered portions tarnish and destroy the appearance of the entire work. On large articles the lacquer should be sprayed, and the article itself turned by mechanical means during the application of the lacquer, so as to give momentum to its flow, thereby insuring its even distribution. Brass bedstead lacquering. Complaints of the same kind, namely, streaks in lacquered work, have been the cause for 35 546 ELECTRO-DEPOSITION OF METALS. replacing brush lacquering of brass bedsteads by the spray. Since the vogue for satin and drawn emery finishes have taken the place of the old English gilt bedstead finish the spraying process has become even more necessary. The unusual depth of the cut in the metal surface made by these finishes has cre- ated a new problem for lacquer makers. The lacquer used on this work should be unusually heavy, in fact heavy enough and dense enough to fill these abnormally penetrated surfaces, for the lacquer film must in all instances be built up so as to protect the highest exposed points of this finish. The lacquer for this finish must be applied with a spray since it is neces- sary that a thick and plastic coating should be applied, one indeedwhich when dry shall be hard and tough enough to resist marring from the usual rough and severe treatment to which a bedstead is subjected. Dead black lacquers produce imitation dead and mat 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 180° 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 process may be completed in a few hours, where it will re- LACQUERING. 547 quire from one to five days to secure the same finish with japan, and besides all the equipment necessary for the latter will be entirely 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 lacquer. 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 transparent 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 finished 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 are 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-Barff. 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 com- mensurate 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 other similar solutions. A coating of these mixtures is 548 ELECTRO-DEPOSITION OF METALS. 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 uncertain 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 mat 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 spraying machine consists of a pump, called a com- pressor, generating the air, transferring the air to a storage tank. If this pump is automatic, copper flexible tubing is used, if stationary, a gas pipe. The storage tank which holds the air, has a gauge indicating the number of pounds carried. A safety valve is also on the tank to control the air. These tanks vary a great deal ; it depends entirely upon the number of cups drawing off the air and the air must be regulated ac- cordingly. It will run from 18 lbs., and in some cases as high as 60. There is a rubber hose of flexible copper tube LACQUERING. 549 connected to the storage tank long enough to cover the entire work -bench to which the cups are fastened. The cup or con- tainer is an atomizer throwing a spray very much the same as a perfume atomizer, although it is made in sizes from half a pint to a quart. Cups or containers are made both of glass and metal. Some prefer the glass for the reason that it is possible to see the lacquer in the container at any time. Glass cups have, however, the drawback of liability of breakage which may result from careless or rough usage about the shop, and besides some sprays are so constructed that under certain conditions it is an easy matter for the air pressure to be acci- dentally switched directly into the container, and with a pres- sure of 40 lbs. both container and lacquer are destroyed. For these reasons it would seem that metal containers are to be preferred. The spray ma}^ be gauged by a small catch on the side of the nozzle. This style of sprayer is considered very practical, although there are many more complicated ones in the market. The equipment to be used in producing the air, storing it and in forcing it to the spray in a pure condition should be of sufficient capacity and be provided with the proper appli- ances to guard against fluctuations which in the flow of the lacquer stream itself interferes with the continuous flow of the lacquer. This flow of necessity must be uniform in strength and outflow, else the results cannot fail to be irregular. It naturally follows that the compressor which regulates this must be such as to be capable of sustaining this pressure uninterruptedly. The quality of the lacquering changes with the irregularity of the pressure. The air should be taken from a part of the building which is far removed from the steam exhausts or other localities where the air or atmosphere is impure or moist ; the drier the air, the less condensed water will enter into the pipe line. The air should be stored in a tank close to where the spray is in use, for this helps in the precipitating of impurities just before it goes into the lacquer, and the extra volume close at hand steadies the pressure. A 550 ELECTRO-DEPOSITION OF METALS. reducing valve in the line between the tank and spray, which can be drained occasionally, is another precaution which may be provided against the admission of water. The addition of a filter will be found to be of great advantage, as it will catch the most minute particles of oil, moisture and dirt just before the air reaches the flexible hose to which the spray is attached. Assuming that both the pressure and clean air referred to can be relied upon, then the next thing necessary is to use the lacquer in as heavy a condition as possible. By this is meant that it should be neither too heavy nor too light for the air to raise it to the nozzle, atomize it and apply it by flowing it out from the spray upon the work in an even and heavy film. The lacquer should never be thinned so as to make it easier in the spray, for in that case the lacquer will create runs upon the surface of the work; if unusual thinning is necessary to get an even flow from the spray then either the pressure or the adjustment of the spray, or the spray itselt, is at fault. While the lacquer is being applied from the spray the work which is being lacquered should be kept moving in a revolv- ing motion in order to insure an even distribution of the lac- quer, and avoid an uneven distribution of it ; in other words, to prevent matting. 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 fixtures ; another for silver and white metals ; another for builders' hardware. With these when applied uniformly, the lacquer spreads evenly and covers the surface entirely with- out break, and presents an unusually uniform appearance with- LACQUERING. 551 out disfiguring blotches or patches, indicating an unequal thick- ness of lacquer. Most of the lacquers which we have seen tested were 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 satisfac- tory work with these machines. Spraying black lacquers. By applying the black lacquers with a spra}' various finishes heretofore made with either baking enamels or japans can now be finished with black lacquer. Whenever great durability and toughness are essen- tial and where the fine finish made with the black lacquer is but a secondary consideration, a priming lacquer should be first applied to the work ; after this the black lacquer should be sprayed over it. Such a finish makes up in toughness and tenacity the slight runs in its appearance. A second coating of black lacquer without this priming coat will not be proof against the hard usage to which some of these finishes are frequently exposed. A coat of priming lacquer is of great advantage in many instances where the metal surface is not of an adhesively magnetic nature, or on a metal that cannot be entirely pre- vented from taking an oxide if exposed to the air even only during the short time of lacquering. The coat of priming lacquer is also a desirable preventative where large quan- tities of work are being lacquered and where cleanliness of the work cannot always be absolutely relied upon. Peeling and chipping, either or both, are often caused by the inex- perience of the lacquerer in mixing the lacquer ; if the body is thinned to the extent that it weakens the binding qualities of the material something of the kind is bound to happen. Since the advent of antique effects, such as mission and Flemish, and other dark and subdued finishes on furniture, etc., the manufacturers of art metal goods have given close attention to having their goods in conformity with the furni- ture and trimmings in buildings. 552 ELECTRO-DEPOSITION OF METALS. 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 unless 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 obviated and the finish cannot be otherwise than perfect, and the lacquer 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 inter- stices or on the flattest surface, with artistic perfection. 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 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 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 uni- formity. 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. LACQUERING. 553 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 finished in bulk by basket dipping. Tarnish affects this finish almost instantly if it is allowed to dry and then lacquered in the usual way ; therefore the lacquering must be carried out as soon as the dipping process has been finished. The most flagrant example of tarnishing is in the case of plated work, particularly 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 tarnishing, and the result is either the increase in labor in handling the goods, or the production of a large amount of imperfect 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 pro- 554 ELECTRO -DEPOSITION OF METALS. tection 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 building 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- 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 XVI. 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 electro- 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. Those 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 overcome 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 protect the skin from the corrosive action of the lye. It should be a rule for every employee in the establishment not to drink from vessels used in electro-plating manipula- (555) 556 ELECTRO-DEPOSITION OF METALS. tions ; 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 morning 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 re- quires 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 dxops of blue 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 contact with nickel baths without being subject to such erup- tions. 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. Poisoning by prussic acid, potassium cyanide and cyanide com- binations. — In cases of internal poisoning first aid must be quickly rendered and a physician immediately called. There is but little hope of saving the life of a person poisoned by prussic acid, as well as when potassium cyanide or soluble cyanide combinations in large quantities have been taken into the stomach. In such cases solution of acetate of iron should be quickly administered and the patient made to inhale some chlorine prepared by putting a teaspoonful of chloride of lime in water acidulated with a small quantity of sulphuric acid. Water as cold as possible should at intervals be also poured over the head of the patient. 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 HYGIENIC RULES FOR THE WORKSHOP. 557 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 of this mixture 5 or 6 tablespoonfuls, 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 sulpliuretted hydrogen. — The patient should be made to inhale the vapor of chlorine from chlorine water, Javelle water, or bleaching-powder. Energetic friction, espe- 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, mo- lasses candy, and licorice paste. Milk is excellent. CHAPTER XVII. 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 serving -as a mould. By means of galvanoplasty we are enabled to produce a simple, smooth plate of copper of such homogeneity as never shown by rolled copper, and such copper plates are 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 re- quired, 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. Jacobi, 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 conductive, and depositing upon it copper, thus obtaining a true copy of the original. (558) GALVANOPLASTY (rEPKODUCTION). 559 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 Jacobi ; 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 can be deposited chemically pure, and in this state is less subject to change than ordinary 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 (8.85) lies 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 copper sulphate (blue vitriol). Smee proved by experiments that, with as intense 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 hydrogen is liberated, copper in a sandy, pulverulent form is obtained, and in 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. 560 ELECTRO-DEPOSITION OF METALS. Hiibl worked with 5 per cent, neutral and 5 per cent, acid solutions, as well as with 20 per cent, neutral and 20 per cent, acid solutions. The neutral solutions were prepared by boil- ing 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, solu- tion less brittle 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 formation of very fine-grained deposits even with very slight current-densities, and it would seem that the brittleness of copper deposited from the acid baths is influ- enced 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 electrolytic- ally 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. GALVANOPLASTY (REPRODUCTION). 561 A. Galvanoplastic Reproduction 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 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. 1. 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 the Daniell cell, and the cell apparatus is actually a Daniell cell, closed in itself, 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 copied with the zinc of the porous 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 objects to be moulded. Forms of cells. The form and size of the simple cell-appa- ratus vary very much according to the purpose for which the latter 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 36 562 ELECTRO-DEPOSITION OF METALS. Fig. 135. from the zinc plates get only too easily upon the object to be reproduced and cause holes in the deposit, while with the vertical arrangement the progress of deposition can at any time be controlled by lifting out the objects without taking the apparatus apart, as in the case with the horizontal arrange- ment. Hence, only such apparatus in which the zinc plates and the objects to be moulded are arranged vertically oppo- site 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. 135. 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 0.79 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 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 sup- plement 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. 136 shows the French form of cell apparatus. In the middle of the vat, and in the direction of its length, is dis- GALVANOPLASTY (REPRODUCTION). 563 posed a row of cylindrical cells, close to each other, each pro- vided with its zinc cylinder. A thin metallic ribbon is con- nected 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 in contact with the metallic bands of the ledges, and therefore, in connection with the zincs. Fig. 136. The German form of cell apparatus is shown in Fig. 137. It is provided with long, narrow, rectangular cells of a corres- pondingly greater height than the column of fluid. Across the vat are placed three conducting rods connected with each other by binding screws and copper wire. To the center rod, which lies over the cells, are suspended the zinc plates by means of a hook, while the outer two 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. 564 ELECTRO-DEPOSITION OF METALS. 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 100-quart bath, with an addition of about 3 \ to 4^ lbs. of sulphuric acid of 60° 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 in- creasing the content of acid in the latter. If the generation Fig, 137. 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 manufacture of cliches. It may therefore happen that after working the copper bath GALVANOPLASTY (REPRODUCTION). 565 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 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 10 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, filled with blue vitriol crystals, in the bath. Since directions are frequently found in which the blue vitriol solutions to be used are given according to their weights b} r volume or degrees of Be., a table showing the content of blue vitriol is given below. Degrees Be. 5° 10° 12° 15° 16° 17° 18° 19° 20° 21° 22° This solution contains crystallized blue vitriol. 5 per cent. 11 " 13 " 17 " 18 " 19 " 20 " 21 " 23 " 24 " 25 " 566 ELECTRO-DEPOSITION OF METALS. 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 matrices 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 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 sel- dom used, at least not for the production of electros. It is, however, occasionally employed for the reproduction of ob- jects of art with very high reliefs, so as to cover them as uni- formly as possible and quite slowly with copper. The cell 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 be 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 galvanoplastic 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 cop- per 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. 44 and 45, pp. 140, 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 satura- ted with blue vitriol, the content of copper being thus, if not GALVANOPLASTY (REPRODUCTION). 567 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. 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 principal 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 purpose. Since the copper bath for galvanoplastic purposes requires 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. 19, p. 89) 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 suit- able of all for continuous working, but by reason of their slight current strength a large number of them would have to be used. 5 68 ELECTRO-DEPOSITION OF METALS. All that has been said under " Installations with Cells," p. 132, in regard to conducting the current, rheostats, conduct- ing rods, anodes, etc., applies also to plants for the galvano- plastic deposition of copper with batteries. b. Depositions ivith the Dynamo. The improvements in dynamos have also benefited indus- trial galvanoplasy, and problems can now be solved in a much shorter time and with much greater ease than in a cell appa- ratus, without having to put up with the obnoxious 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 suffices 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 deposits 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 depositions. For depositing copper according to the old pro- GALVANOPLASTY (REPRODUCTION). 569 cess there should, for instance, be available a large current- strength with only 1 to 1.5 volts, while for a rapid galvano- plastic 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 destroyed 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 on). 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 Fig. 138. central station, the construction being such that the dynamo which is perhaps only temporarily in use can be readily disengaged. Fig. 138 shows such a double aggregate, built by the firm of Dr. G. Langbein & Co. for the German Imperial Printing Office. 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 repeti- 570 ELECTRO-DEPOSITION OF METALS. tion, we refer to what has been said on this subject under "Arrangement of Electro-plating Establishments," the direc- tions 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 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. With the baths coupled in series the cathode (object) sur- faces in all the baths should be 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 + pole 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. 64). With this simple 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 consideration. 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 GALVANOPLASTY (REPRODUCTION). 571 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. Fig. 139. 4np£Kner£/> rt RHEOSTAT 4-^- (7y 1LTHETED In large galvanoplastic plants the advantages derived from this mixed coupling are 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 immediately done, irregularities in working will result. If, however, the baths be combined in groups in the manner shown in Fig. 139, only the cathode-surfaces of each of the groups coupled in parallel, need to be of the same size, or ap- proximately so, and with the observation of this condition it 572 ELECTRO-DEPOSITION OF METALS. is entirely indifferent 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 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 decimeters 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 X 2 = 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 the bath electro- GALVANOPLASTY (REPRODUCTION). 573 motive force be also 1.25 volts and the current-density 2 am- peres, then there will be required, 300 X2= 600 amperes, and 1.25 X 3 = 3.75 volts, or practically, 4 volts impressed electro-motive force. c. Combined Operation ivith 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. 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 accumulators. 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, as blisters are readily formed, or the deposit peels 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 fin- ishing matrices which are suspended late in the afternoon, after working hours. In order to avoid repetition, the reader is referred to what has been said on p. 184 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 hath, 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. 574 ELECTRO-DEPOSITION OF METALS. 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 18° Be., which is brought up to 22° Be. by the addition 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, because the addition of sulphuric acid will vary according to the current-strength available, 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 prevent 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. 50, 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 cation of the sulphuric acid — the hydrogen-ions — migrates to the cathode, and effects the decomposition of the blue vitriol, an equivalent quantitj^ 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 GALVANOPLASTY (REPRODUCTION). 575 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 4f to 6^ lbs. The bath is prepared as follows : Dissolve 48J lbs. of blue vitriol in pure warm water, and, to avoid spurting, add gradu- ally, stirring constantly, the sulphuric acid. At the normal temperature of 59° F. the bath may be worked with a current- density of up to 2 amperes, and if the bath be agitated, the current-density may be up to 3 amperes. Properties of the deposited copper. — As regards elasticity, strength and hardness of galvanoplastic copper deposits, Hiibl determined that copper of great tenacity, but possessing less hardness and strength, is deposited from a 20 per cent, solu- tion with the use of a current- density of 2 to 3 amperes. For copper printing plates a 20 per cent, solution compounded with 3 per cent, sulphuric acid, and current-density of 1.3 amperes 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 compounded 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 unfavorably influenced at a higher temperature. 576 ELECTRO-DEPOSITION OF METALS. 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 pro- portion 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 precipi- tated upon the moulds. If the zinc-surfaces of the clay cells are very large 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 desirable 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 proportions of 1 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 ma- trix-surface. If the zinc-surface should be smaller, stronger acid ma}' 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 ap- plies 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 comparatively rapid deposition without detriment to the quality of the de- posit. According to the composition of the bath, a fixed minimum GALVANOPLASTY (REPRODUCTION). 577 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 : Minimum and maximum current-density per 15.5 square inches. Blue vitriol solution. With solution at rest. Amperes. With solution gently agitated. Amperes. 15 per cent, blue vitriol, without sulphuric acid ... 15 per cent, blue vitriol, with 6 per cent, sulphuric acid . . 20 per cent, blue vitriol, without sulphuric acid 20 per cent, blue vitriol, with 6 per cent, sulphuric acid .... 2.6 to 3.9 1.5 " 2.3 3.4 " 5.1 2.0 " 3.0 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. 575, 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 J, to at the utmost 1 J, 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 37 578 ELECTRO-DEPOSITION OF METALS. coupling the separate weaker cells alongside each other also suffices. When all 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 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 towards 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 current 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 electro-motive force have to be properly regulated by means of a rheostat. Brittle copper deposits may be caused, not only by an unsuit- able 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 the use of hooks coated with rubber solution in benzol for suspending the cathodes a protection against the attacks of the electrolyte and the air, and smooth copper de- posits of a beautiful velvety appearance were obtained, but they were so brittle that they could not be detached without breaking from the basis. The deposit contained small quan- tities of carbonaceous substances, which could have been de- rived only from a partial solution of the rubber. Hiibl also describes the fact of having obtained brittle cop- per by the electrolyte having been contaminated by a small quantity of gelatine which had passed into solution in the preparation of an electrotype upon heliographic gelatine reliefs. GALVANOPLASTY (REPRODUCTION). 579 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 tlacquer was not perfectly hard, and it was observed that by reason of an accidental contamination of the electro- lyte with gelatine, deposits were formed which showed the branched formation of crystals similar to an arbor Saturni, and were extremely brittle. Erich Miiller and P. Behntje * have recently investigated the effects of such organic additions (colloids) on blue vitriol solutions, additions of gelatine, egg albumen, gum, and starch being drawn upon for comparing the effects. After an elec- trolysis for 15 hours, the deposits obtained from baths com- pounded 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 run- ning 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 b}' analysis. Further experiments proved that the above-mentioned 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 pro- duce, by an addition of gelatine, a lustrous coppering from acid copper baths. The properties 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 produc- tion of a deposit entirely depends, according to what has been * Zeitschrift far Elektrochemie, XII, 317. 580 ELECTRO-DEPOSITION OF METALS. said on p. 124, on the current-density used. One ampere de- posits 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 1 ampere current-density, there are required - 8 t 9 tV°- == 75 hours. By tak- ing the thickness of a deposit as 0.18 millimeter, which suf- fices for all purposes of the graphic industry, then 1 square decimeter will weigh 89 X 0.18 = 16.02 grammes, and for their deposition with 1 ampere current-density will be re- quired', in round numbers, xnf= 13-J- 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 formation of a deposit 1 millimeter thick, so that the calcula- tion of the time required for depositing a copper film of a thickness different from 0.18 millimeter can be readily made by multiplying 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 1 millimeter thickness requires 0.5 ampere 27 hours 150* hours 0.75 " 18 a 101'J " 1.0 13i a 75 u 1.5 9 <; 50 '• 20 6| " 37J It 2.5 5* • '( 30 11 3.0 4* it 25 " 4.0 3f 1 1 18| " 5.0 2| a 15 " 6.0 2\ (i 12 J " 7.0 " 2 it lOf cc 8.0 " ItV it 9* u 9.0 " 1* a 8J Nitrate baths. — To shorten the duration of deposition, baths GALVANOPLASTY (REPRODUCTION). 581 have been 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, ammo- nium chloride is added. Independent of the fact that de- posits obtained in these baths are inferior in quality to those produced in blue vitriol baths, such baths require frequent corrections, 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 pro- cess, there is no necessity for nitrate baths. Agitation of the baths. — From Hiibl'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 unexceptional manner, the bath must be kept entirely homo- geneous in all its parts. "When a copper bath is at rest, and the operation of deposition is in progress, the following pro- cess 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 be- come poorer in copper, and consequently specifically lighter, rise on the cathodes to the surface. These layers contain more sulp*huric acid than the lower ones, hence their resist- ance is slighter and their conducting power greater, the latter being still further increased by the layers heated by the cur- rent 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 582 ELECTRO-DEPOSITION OP METALS. 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-surface is kept back. The concentration of the upper layers of fluid may finally happen to become so slight that the 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 cur- rent-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 pro- duction of serviceable deposits under such conditions is of course impossible. 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 * Zeitschrift fur physikalishe Chemie, xxxv, 641. GALVANOPLASTY (REPRODUCTION). 583 being that deposition is effected with greater rapidity. These experiences gathered in electro-metallurgical operations on a large scale, have been advantageously applied to galvano- plasty. 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 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 advantage 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 per- forations 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 pressing 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. 584 ELECTRO-DEPOSITION OF METALS. The baths are arranged in the form of steps. Near the bottom each bath is provided with a leaden outlet-pipe (Fig. 140), which terminates above the next bath over a distribut- ing 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 reser- voir, 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 become too low. Over A a wooden frame cov- ered with felt may be placed ; the copper solution 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 insolu- ble particles becoming detached from the anodes sink to the bottom and have no injurious effect upon the deposit. On the other hand, in agitated GALVANOPLASTY (REPRODUCTION). 585 baths, they remain suspended in the electrolyte, and it may 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 excresences 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 into the collecting reservoir. Solutions agi- tated 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 recom- mended, it is best to sew them in some kind of fabric, for in- stance, muslin, the fibers of which have been impregnated with ethereal paraffine 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 chem- ically pure anodes in the same manner. In case no means for agitating the bath should be available, good results may, according to Maximowitsch, be obtained by the following arrangement : The electrodes are placed hori- zontally and in such a manner that in the bath the anodes are over the cathodes. The new solution is thus formed in the upper portions of the bath on the anodes and being specifically heavier than the old exhausted solution sinks to the bottom where it displaces the exhausted solution poor in copper, the latter being by reason of its slighter specific gravity forced up- wards. Hence, without the use of any mechanical contriv- ance the freshly-formed solution is constantly mixed with the old solution. To prevent small particles of metal from the anodes falling upon the cathodes and there giving rise to the evolution of gas, 586 ELECTRO-DEPOSITION OF METALS. a frame filled with unbleached, undyed silk is placed between the two electrodes. For the production of a beautiful, dense and firm deposit, according to this process, Schonbeck recommends the follow- ing bath: Crystallized blue vitriol 125 lbs., concentrated sul- phuric acid 12J lbs., water 500 lbs. Current- density per square decimeter electrode surface 6 to 10 amperes ; electro-motive force for every ampere 0.8 volt ; electrode distance 8 centimeters. 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 residue formed upon them will be, and this residue in time deposits 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 residues 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 (4.15 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- tained. By raising the temperature of the electrolyte to 140° F. the quantity of anode slime increased considerably, and at GALVANOPLASTY (REPRODUCTION). 587 1 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 analogous observations in the electrolysis of gold chloride solution containing hydrochloric acid, and based upon these observations, 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 = CuSO, + 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 0.11 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 men- tioned, may have an injurious effect. Rapid galvanoplasty. Thus far galvanoplastic baths with an average content of 22 per cent, of blue vitriol and 2 to 3 per cent, of sulphuric acid have only been referred to. Such baths were exclusively used up to the end of 1899. The current-density employed in practice amounted to scarcely more than 25 amperes, 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 search for ways and means to attain this object. 588 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 reduction 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 formation 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 sulphuric 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 reduction at high current densities, there is danger of hydrogen-ions being brought to separate as h} r drogen 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 sul- phuric acid participate equally, according to Hiibl, in con- ducting the current ; while with a content of 5 per cent, of acid, the conduction 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 de- GALVANOPLASTY (REPRODUCTION). 589 posited copper 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 electro- lyte, 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 re- liable in practical rapid galvanoplasty, and the necessity for other compositions will scarcely arise. 590 ELECTRO-DEPOSITION OF METALS. For shallow impressions of autotypes, wood-cuts, etc. — In a 100 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 tem- perature 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 detri- mental 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 crystal- lization of blue vitriol if the work-room is not kept at an even temperature, or the bath is not worked for one or more days in succession. 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 precaution, 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, b} r means of a copper paddle fitted to the front of the tank and driven bv means of a band from GALVANOPLASTY (REPRODUCTION). 591 a transmission. It is placed about six inches above the bot- tom of the tank and, the paddles being set at an angle of 45°, a vigorous motion of the lower layers towards the surface is effected. If the above-mentioned conditions be observed, the current- dendty 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 ap- proximately be 6 volts. When working on an average with 6 amperes per square decimeter, a deposit of 0.15 millimeter thick will in this bath be obtained in 1J to If 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 blow- ing in air, and to resume agitation and increase the current- strength only after the matrices are coated with copper. Thus, according to the size of the galvanoplastic plant, it ma} 7 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 fil- ings, which is much liked, is not applicable in rapid galvano- plasty. 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 592 ELECTRO-DEPOSITION OF METALS. difficult to obtain with the above-mentioned high current- densities unexceptionable electrotypes from matrices produced 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 \ 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 100-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 advantage- ously 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| volts. The copper deposit attains in 2^ hours a thickness of 0.15 millimeter, and in 2£ hours one of 0.18 millimeter. Higher current-densities are also permis- sible, 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 GALVANOPLASTY (REPRODUCTION). 593 the printing faces of the electrotypes are thus most surely avoided. Heating the baths may be omitted in plants lacking the necessary 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 readily understood from what has been said above. On the one hand, the baths must not be allowed to cool to a tempera- ture 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 de- tached 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, without recasting and rolling, suspended as anodes in the bath. The use of rolled anodes is therefore absolutely neces- sary, 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. 38 594 ELECTRO-DEPOSITION OF METALS. Examination of the Acid Copper Baths. The copper withdrawn from the bath by deposition is only 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 described 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, 10 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 1 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 Haen's 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 -^ liter, neutralize the free acid by the addition of dilute soda lye until a precipitate of bluish cupric hydrate, which does not disap- GALVANOPLASTY (REPRODUCTION). 595 pear even with vigorous shaking, commences to separate. Now add, drop by drop, dilute sulphuric acid until the pre- 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 100 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 1 cubic centimeter of decinormal solution corresponds to 0.0249 gramme of blue vitriol (= 0.0003 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 centi- meters of strong nitric acid, fill the dish up to within 1 centi- meter of the rim with distilled water, and electrolyze with a current-strength ND 100 = 1 ampdre. Deposition of copper is finished when a narrow strip of platinum sheet placed over the rim of the dish and dipping into the fluid shows in 10 minutes no trace of a copper de- posit, which is generally the case in 3J hours. The deposit is then washed without interrupting the current, rinsed with alcohol and ether, and dried for a short time at 212° 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. 596 ELECTRO-DEPOSITION OF METALS. If now the content of free acid and of the blue vitriol in the bath has been ascertained, a comparison with the contents 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 carbon- ate have to be added, and each gramme of copper carbonate increases 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 a 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 determi- nation of the content of copper and free sulphuric acid will suffice. However, with baths, 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 deposits 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, it has to be prepared by moulding the original either in a plastic mass which, on hardening, will retain the forms and GALVANOPLASTY (REPRODUCTION). 597 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. 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 in 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, earthy 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 become highly plastic by heating, without, however, becoming sticky, and finally it should rapidly harden. The most simple way of softening gutta-percha is to immerse it in water of 170° to 190° F. When thoroughly softened no hard lumps should be felt on kneading with the hands, which should be kept thoroughly moistened with water during the operation. A fragment of the gutta-percha corresponding to the size of the object to be moulded is then rolled into a plate about £ to f inch thick. To facilitate the detachment of the mould after cooling, the surface of the gutta-percha which is to receive the impression 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 598 ELECTRO-DEPOSITION OF METALS. preparing moulds, but, like stearine, it is according to the temperature now softer and now harder, which must be taken into consideration. In the cold state 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 ; various formulas for such compositions recommended by dif- ferent authors are here given : a. White wax 120 parts, stearin 50, tallow 30, Syrian asphalt 40, elutriated graphite 5. (G. L. von Kress). b. Yellow beeswax 700 parts, paraffin 100, Venetian tur- pentine 55, graphite 1 75 ; or, cake wax 50 parts, yellow wax 50, ceresin 15, Venetian turpentine 5. (Karl Kempe). c. Wax 20 parts, thick turpentine 20, rosin 10, graphite 50. (Hackewitz). By reason of its large content of graphite, this composition which is excellent in every respect, can be recommended for taking moulds from objects which can be black-leaded only with difficulty. d. Yellow wax 900 parts, Venetian turpentine 135, graphite 22. (Urquhart). e. Pure beeswax 850 parts, crude turpentine 100, elutri- ated graphite 50. (Furlong). The mixture is to be freed from all moisture by boiling in a steam pot for 2 hours. In the hot season of the year it is recommended to add 50 parts of burgundy pitch to impart greater hardness to the wax. /. Pfanhauser recommends the following composition es- pecially for taking moulds from undercut objects. The mass is very elastic and objects with quite wide projecting portions can, with care, be moulded with it. Yellow beeswax 400 parts, ozocerite 300, paraffine 100, Venetian turpentine 60, elutriated graphite 100. For use in the summer months the composition of the mass is as follows : Yellow beeswax 250 parts, ozocerite 450, paraffin 50, Ve- netian turpentine 35, elutriated graphite 180. 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 GALVANOPLASTY (REPRODUCTION). 599 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. To avoid overheating it is advisable not to melt the wax mixture over an open fire, and a jacketed kettle heated by steam or gas is generally used. With the use of steam, the latter passes through a valve into the jacket while the con- densed water is discharged through another valve. When gas is used the space between the jacket and kettle is filled with water, the latter being from time to time replenished as evaporation progresses. 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 transferred 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 suffi- cient size with shallow sides about £ inch in depth ail 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. 600 ELECTRO-DEPOSITION OF METALS. 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 shaving 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 in- jury- The wax plates prepared according to the process just 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 cap- able of giving a gradual and powerful pressure. Fig. 141 represents a form of moulding press in common use, and known as the " toggle " 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 form being placed on the bed. The well black-leaded case is attached b}' 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 GALVANOPLASTY (REPRODUCTION). 601 read}', 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 pressure, causing the face of the type form to impress itself into the exposed moulding surface. Fig. 141. Fig. 142 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 602 ELECTRO-DEPOSITION OF METALS. the cistern below the cylinder, and is furnished with a gradu- ated adjustable safety-valve to give any desired pressure. Metal matrices. — Attempts have for many years been made to mould originals in lead, since lead matrices possess many advantages 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, Fig. 142. objects readily liable to injury, such as wood cuts, composi- tions, etc., could not withstand the pressure required for im- pression in lead plates, and were demolished ; steel plates at the utmost were capable of standing the high pressure. Serviceable results were not obtained, even with the use of very thin lead foil backed, in pressing, with moist paste-board or gutta-percha, because the portions of the lead foil subject to the most severe demands would tear. GALVANOPLASTY (REPRODUCTION). 60S 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, tjiat the compo- sition down to the quads is impressed before the shades, for instance, of a wood cut or an autotype, are finished. In mak- ing impressions, 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 depressions. Notwithstanding the enormous ductility of lead, the lead foil could not satisfy these demands on ex- tension and, in consequence 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. 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 correspond- ing to the dark portions of the original can only be impressed when the moulding material has been forced into the last cor- ner of the deepest depressions of a printing form,*is not pre- meditated nor one by choice, but is conditioned on the physical * Zur Theorie und Praxis der Metall-matrize, 1905. 604 ELECTRO-DEPOSITION OF METALS. properties of the material itself. The pressure required to force the moulding material into the smallest depressions cannot be applied 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 soft 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 commencement of the pressure the lateral escape is avoided, whereby the moulding material yields first in the direction ot 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 furlher drawback that the lead firmly settles in these smallest depressions, thus rendering the original useless. Besides, there is no type composition, no wood-cut, etc., the printing elements of which, especially when standing isolated, GALVANOPLASTY (REPRODUCTION). 605 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 impressions, since the difference in height between printing and justifying surface is about 1 cieero = 4.5 millimeters. Hence, with the means hitherto available, the production of matrices, either with thin or thick metal plates, was imprac- ticable, and until lately recourse had to be had to the old and qualitatively inferior wax and gutta-percha matrices, till Dr. Albert, in 1903, succeeded in finding a method for the rational production of metal matrices. This method is based upon a number of inventions patented in all civilized countries, and the characteristic features of the process 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 the thickness of the plate to be materially less than the relief difference of the printing form. 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 ex- pedient 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 606 ELECTRO-DEPOSITION OF METALS. extent the larger and wider the sunk surface is, the electro automatically receiving thereby all the white portions of such depth that they do not smear in printing. The process may be explained by Figs. 143 and 144. Fig. 143 represents the arrangement of the platen, lead plate, and soft intermediate layer previous to the moment of impression. The material used for the intermediate layer must possess certain properties and must be softer than the moulding material. It should be compressible without materi- ally yielding laterally under pressure and, by reason of elas- ticity or internal 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 Fig. 143. must not be too soft in the sense of its affinity to a liquid aggregate state, as, for instance, heated wax, but it should be 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 shavings 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 tendency to equalize the change suffered in form counteract the lateral yielding, or other checks have to be arranged. Besides, a certain degree of GALVANOPLASTY (REPRODUCTION). 607 elasticity is useful for bending the lead plate on the free-lying places. 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 com- mencement of pressure, the lateral yielding of the interme- diate layer. The latter important property was in former experiments neutralized by moistening the paper. In Fig. 144 the platen has sunk so that the intermediate Fig. 144. layer opposite to the places o o' ', from which the first counter, pressure emanates, is compressed to one-half of its original volume. At the moment when the intermediate layer has by compression 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 o o' . On the places opposite to u u f , the lead, which lies here perfectly free, and hence exerts no counter-pressure, is at the same time pressed into the hol- low 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 rest- ing upon supports 6 feet apart is more bent by a weight than one whose supports are only 3 feet apart. 608 ELECTRO-DEPOSITION OF METALS. This also answers technical requirements, since the white portions 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 yielding body, which, as regards its extensibility parallel to the impression-plane, was checked by its texture or otherwise. By this bending process the pressure required for impres- sion was under certain circumstances reduced to one-tenth of its former magnitude, so that metal matrices could also be produced 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 1000 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 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 GALVANOPLASTY (REPRODUCTION). 609 phenomena appearing in other methods of impressing, namely, that it is impossible for the process of impression being affected by occluded 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 instance, only 55 seconds were required for impressing a form of the "Woche," and not quite two minutes for one of the " Berliner Illustrierte Zeitung." For impressing illustration- forms of the same size without letters, only half the above- mentioned time was necessary. Thus there is no difficulty whatever in executing impres- sions of any size. Fischer endeavors to attain the same object as Dr. Albert by the use of lead plates with corrugated backs, small pyramids j AAA Aj aD0U t 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 otherwise high pressure required being thus effected. Now, suppose in Fig. 144, instead of an elastic intermediate layer, a lead plate with corrugated back is placed upon the form, the small pyramids which are opposite to the portion o o' of the printing form are first compressed, while the part of the lead plate corresponding to the portion u u' is bent through by the pressure exerted .by the platen upon the points of the corrugations, the latter being thereby not very much flattened. If now the pressure be increased the lead plate is first flattened at o o' , and then 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. 39 610 ELECTRO-DEPOSITION OF METALS. 3. Further manipulation of the moulds. — The moulds when detached from the original show in addition to the actual impression 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 ap- pearance. A more modern instrument for this purpose is so arranged that the flame can be regulated by the finger pres- sing 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 elec- trotype 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, b} 7 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. The next process is 4. Making the moulds 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 material 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. Black-leading the moulds is performed either by hand or more commonly by machines. GALVANOPLASTY (REPRODUCTION). 611 Fig. 145 shows one of these machines with its cover re- 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 Fig. 145. is placed an apron which catches the powder, which is again used. Another construction of a black-leading machine is shown in Fig. 146, the details of which will be understood without lengthy description. The moulds are placed upon the slowly revolving, horizontal wheel, upon which the brush moves rapidly up and down with a vertical, and at the same time 612 ELECTRO-DEPOSITION OF METALS. lateral, vibrating motion. The black-leading space being closed air-tight, scattering of black-lead dust is entirely pre- vented, 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 electrot}^pers prefer the wet process as it is claimed to work more quickly and neatly, producing moulds that are thinly, evenly and perfectly covered. The Fig. 146. moulds are placed upon a shelf in a suitable receptacle, and a rotary pump forces an emulsion of graphite and water over their surface through a traveling fine rose-nozzle. Black-leading machines have recently been introduced, their action being based upon the principle of the blast. The graph- ite powder is by means of a current of strongly-compressed air carried with considerable force towards the surface of the mould to be black-leaded. The process of making the moulds GALVANOPLASTY (REPRODUCTION). 613 ■conductive according to this system, is claimed to be thorough and complete and quickly accomplished. However, many operators prefer black-leading by hand, especially moulds of autotypes, the lines remaining sharper. 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 0.31 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 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 depressions. 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 copperplate being melted in on the edge of the mould and the latter secured to the conducting rod by means of a hook. Gutta-percha moulds, being specifically lighter than the copper bath, would float in it, and have, therefore, to be loaded by securing heated pieces of lead to the backs. 614 ELECTRO-DEPOSITION OF METALS. Fig. 147. For black-leaded wax moulds the process is as follows : A bright copper plate 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 removed with a knife. The shape of the mould- holder is shown in the accompanying illustration, Fig. 147. 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. 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- GALVANOPLASTY (REPRODUCTION). 615 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 ex- cess 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 £ 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- rices should be provided with a protecting layer of celluloid or other suitable material to prevent them from becoming cop- pered. 7. Detaching the deposit or shell from the mould, a. From 616 ELECTRO-DEPOSITION OF METALS. 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 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 Fig. 148. 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. In larger establishments, a cast-iron moulding and melting table, such as is shown in Fig. 148, is used for wax moulds. The planed table plate is hollow, and by means of tongues GALVANOPLASTY (REPRODUCTION). 617 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 ver}^ 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.* 8. Backing the deposit or shell. The face of the electro is first freed from all residues by careful burning off over a flame *Dr. E. Albert, " Zur Theorie und Praxis der Metall-Matrize," p. 10. 618 ELECTRO-DEPOSITION OF METALS. and washing with benzine, and scoured bright with whiting and hydrochloric acid. The edges are then trimmed with shears to the width of a finger from the picture. The tinning of the back of the shell is the next operation, and has for its object the strengthening 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 allow- ing hydrochloric acid to take up as much zinc as it will dis- solve, and diluting with about one-third 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 stereotype 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 thickness 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. An alloy of lead 100 parts, tin 3 and and antimony 4 is also recommended as very suitable. 9. Finishing. — For this purpose the plates go first to the saw table (Fig. 149) for the removal of the rough edges by means GALVANOPLASTY (kEPRODUCTION). 619 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, types of which are shown in Figs. 150 and 151, Fig. 150 being a shaving machine with steam one way, and Fig. 151 one with steam both ways. By means of a straight-edge, the Fig. 149. plates are then tested as to their being level, and any un- eveness is rectified 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 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. 620 ELECTKO-DEPOSITION OF METALS. 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. Fig. 150. Copper deposits from metallic surfaces. — It remains to say a few w r ords 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. GALVANOPLASTY (REPRODUCTION). 621 Hence, the metallic original must first undergo special prepa- ration, 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, which is a good conductor, but prevents the adherence of the deposit to the original. For the purpose of silvering, free the Fig. 151. surface of the metallic original (of brass, copper, or bronze) from grease, and pickle it by washing with dilute potassium cyanide solution (1 part potassium cyanide to 20 water). Then brush it over with a solution of 4J drachms of silver nitrate and 1 oz. 6 drachms of potassium cyanide (98 per cent.) 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- 622 ELECTRO-DEPOSITION OF METALS. 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 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 metallic 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. 368) 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 desired 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, how- ever, 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 thorough!}' GALVANOPLASTY (REPRODUCTION). 623 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- antimony-bismuth alloy) indifferent towards the acid copper bath. It is best to brass zinc originals, and to give the brass de- posit higher lustre by polishing with Vienna lime powder upon a small flannel bob. They are then freed from grease by brushing with quicklime, silvered by the method previously given, and iodized. The surfaces which are to remain free from deposit 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 be- fore 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 624 ELECTRO-DEPOSITION OF METALS. 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. 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, 1 paft 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 constant!}', 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, however, injuring the metal, and finishes his work by nar- rower 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 GALVANOPLASTY (REPRODUCTION). 025 to etching with nitric acid or, more recently, with ferric chlo- ride. After the at first weak acid has acted for a short time, the finest lines have acquired 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 becoming 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. 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 : 1. 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. e., 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 40 626 ELECTRO-DEPOSITION OF METALS. the diapositive, the layer of chromium and gelatine is hard- ened, the process taking place in the same gradations of tone as conditioned by the diapositive. After sufficient exposure 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 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 pre- ceding 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 man- ipulations for the preparation of the printing plates required for this purpose differ but little from those for photo-galvan- ography. Pour over a glass plate, 0.19 to 0.27 inch thick, a layer of chrome-gelatine, which, however, must not be colored, and GALVANOPLASTY (REPRODUCTION). 627 place the plate in a drying-oven heated to 113° 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 portions which have become insoluble by exposure to light are very susceptible to fat colors. If now such a glass plate be wiped over wdth 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. 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 activ- ity, 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 print- ing result in the white portions of the picture should be as deep as possible. It is obvious that this requirement makes the highest demands on the etching process, and that long experience and perseverance are required to achieve excel- lency 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 defects 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 adheres 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. 628 ELECTRO-DEPOSITION OF METALS. 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 same manner, the manipulations are repeated until the plate has the necessary depth for printing. Finally, all un- necessary 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 pur- pose, 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 ex- posed to the light. The result is the same as has been de- scribed under photo-engraving, a picture being obtained which is exactly treated as the reprinted drawings, i. ■ '&&{*/.&&. v '"''////"/ '4'w:'/, W///7////'' ""'/,?. ','/'/<■''"',/ ///"/y'i ', ', '//"/' C'. > vs/, 4 S '//, '',///,■>///,//,/ ''A "v', i'//''/' '"'//■ V'/p/'//'//'/"/', "''/'/'/if**. Fig. 153. deposits 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 distance of about 3 millimeters, as shown in Fig. 152 in front view, and in Fig. 153 in section. 664 ELECTRO-DEPOSITION OF METALS. The object of this contrivance is that upon the careful ty 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 ot 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 become inti- mately attached to 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. 154 and 155, 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 potassium 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 tie 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 rapidty, 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 electrotypes, which without doubt includes electrolyticalty prepared matrices for casting type, the influence of the tern- GALVANOPLASTY (REPRODUCTION). G65 perature 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 fiir Schriftgiesserei " obtained a pat- ent, the characteristic feature of which is that zinc can be directly cast around the face " without further galvanoplastic reinforcement." 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 reinforced to the customary thickness by a galvano- plastic deposit of copper. It is obvious that a thickness of 0.1 to 0.25 millimeter 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 casting 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 enveloped 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. 312 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 bath has to be brushed over with nitric acid, rinsed, and without delay brought into the copper bath. 666 ELECTRO-DEPOSITION OF METALS. The omission of these manipulations, which require dex- terity, may have been the cause why no more favorable results were obtained by former experiments to leinforce thinner nickel deposits by copper to a thickness of 2 millimeters, the nickel deposits becoming detached from the copper when the matrix was in use. If, however, in accordance with the sug- gestions 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. 266 were used. They contained in 100 quarts, 77 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 con- stantly 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 insulat- ing 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 dur- ing which time the current must in no wise be interrupted, and the original, especially in the beginning, be vigorously GALVANOPLASTY (REPRODUCTION). 667 shaken, a nickel deposit about 0.25 millimeter in thickness is obtained. This deposit, as previously described, is reinforced iii 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. 267, 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 pre- sents many difficulties. While copper is reducible in a com- pact 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 alka- line solutions attack moulds of fatty substances, such as wax and stearine, consequently also, plaster-of-Paris moulds im- pregnated with these substances, as well as gutta perch a 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 dis- solving 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. 668 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 gen- tle force, the oil gutta-percha being in a hardened state suffi- ciently 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 powder, thoroughly rubbing the latter with a brush into the depressions, 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) If 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 fulmi- nating gold) 1 oz., 99 per cent, potassium cyanide 3J ozs., water 1 quart. Current-density, 0.1 ampere. Electro-motive force at 10 cm. electrode-distance, 0.4 volt. CHAPTER XVIII. CHEMICALS USED IN ELECTRO-PLATING AND GALVANOPLASTY. Below the characteristic properties of the chemical prod- ucts employed in the workshop will be briefly discussed, and the reactions indicated which allow of their recognition. It frequently happens that the labels become detached from the bottles and boxes, thus rendering the determination of their contents necessary. I. Acids. 1. Sulphuric acid (oil of vitriol). — Two varieties of this acid are found in commerce, viz.. fuming sulphuric acid (disul- phuric 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 1.87 to 1.89. The only purpose for which fuming sulphuric acid is used in the electroplating 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 galvano- plastic 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 con- stant 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 substances, and hence has (669) 670 ELECTRO-DEPOSITION OP METALS. to be kept in bottles with 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 sul- phate. 2. Nitric acid (aqua fortis, 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 cop- per, brown-red vapors are evolved. For the determination of dilute nitric acid, add a few drops of it to green vitriol solu- tion, when a black-brown coloration will be produced on the point of contact. 3. Hydrochloric 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 dis- tinguished from other acids. The specific gravity of the strongest hydrochloric acid is 1.2. The crude acid of com- merce 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 distilled water, a heavy white precipitate is formed, which becomes black by exposure to the light. 4. Hydrocyanic acid (prussic acid). — This extremely poison- ous 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 CHEMICALS USED IN ELECTRO-PLATING. 671 cherry laurel, bitter almonds, the stones of the apricot, of 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 potassa in old silver baths. The inhalation 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 solu- tion 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 pre- cipitated, 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.). Accord- ing 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 solution, the latter acquires a brown color, the color becoming 672 ELECTRO-DEPOSITION OF METALS. more intense on drying. Alkalies impart to turmeric paper a similar coloration, which, however, disappears on immersing the paper in dilute hydrochloric acid. 7. Arsenious acid (ivhite arsenic, arsenic, ratsbane). — It gen- erally occurs in the shape of a white powder, and sometimes in vitreous-like lumps, resembling porcelain. For our pur- poses the white powder is almost exclusively used. It is slightly soluble in cold water, and more readily so in hot water and hydrochloric 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 solu- tion of nitrate of silver, a yellow precipitate of arsenate of silver is obtained. The ammoniacal solution of nitrate of silver is prepared 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, ver} r 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 alumin- CHEMICALS USED IN ELECTRO-PLATING. 673 ium dead white. Great care must be observed in working with the acid, since not only the aqueous solution, but also the vapors, have an extremely corrosive effect upon the skin and respiratory 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 alcohol ; by absorbing carbonic acid from the air it rapidly becomes converted into the carbonate, and thus loses its caustic properties. It should, therefore, be kept in well-closed vessels. Substances 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 ob- jects 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 freeing 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- 43 674 ELECTRO-DEPOSITION OF METALS. ing 24.2 per cent, of ammonia gas) ; of 0.920 specific gravity (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 preparation of fulminating gold, and as an addition to some copper 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 em- ployed 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 of sulphur). — It forms a hard CHEMICALS USED IN ELECTRO-PLATING. 675 green-yellow to pale-brown mass, with conchoidal fracture. It 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, sulphuretted hydrogen is evolved with effervescence, sulphur being at the same time separated. 16. Ammonium 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 sul- phur. It is used for the same purpose as liver of sulphur. 17. Carbon disulphide 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 char- acteristic 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 sulphide 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- cum) 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 ammonium 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 676 ELECTRO-DEPOSITION OF METALS. dull yellow powder. Specific gravity 3.46. It is soluble in the alkalies and spirits of sal ammoniac. 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 precipitating 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 dissappear 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 2J 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 tinning, 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 trichloride (butter of antimony). — A cr} 7 stalline mass which readily deliquesces in the air. Its solution in hydrochloric 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 potash lye. The solution serves for coloring brass steel-gray, and for browning gun-barrels. CHEMICALS USED IN ELECTRO-PLATING. 677 24. Arsenious chloride. — A thick, oily fluid, which evaporates in the air with the emission of white vapors. 25. Copper chloride. — Blue-green crystals readily soluble in water. The concentrated solution is green, and the dilute solution 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 exposure to the air becomes turbid ; by adding, however, hydrochloric 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 preparation 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 solu- ble and deliquescent. The salt prepared by evaporation gen- erally 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. 678 ELECTRO-DEPOSITION OF METALS. 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 solder- ing, and zincking by contact. 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. 31. 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, con- geals to a transparent, tenacious, horn-like mass. Silver chloride is practically insoluble in water, but dissolves with CHEMICALS USED IN ELECTRO-PLATING. 679 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 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 articles 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 me- tallic gold and chlorine gas. By mixing its aqueous solution with ammonia, a yellow-brown powder consisting of fulminat- ing gold is formed. In a dry state this powder is highly ex- plosive, 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 com- binations 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 680 ELECTRO-DEPOSITION OF METALS. platoso-ammonium chloride on mixing concentrated platinie chloride solution with a few drops of saturated sal ammoniac solution. V. Cyanides. 34. Potassium cyanide (white prussiate 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, product 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 pre- paration 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 ex- CHEMICALS USED IN ELECTRO-PLATING. 681 posed to the air it becomes deliquescent, and is decomposed b}' 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, 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 resultant product contains 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 similar behavior, it being less soluble than the potassium double salt and as the electro-motive forces for decomposing the potassium and sodium double salts vary, the use of a mix- ture of potassium cyanide and sodium cyanide is, to say the least, not rational. For certain purposes the electro-plater should demand 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 somewhat 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 to- wards the air and in dissolving is the same as that of the pure product. 682 ELECTRO-DEPOSITION OF METALS. 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 predom- inates, 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. 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 98 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 = 1.2o0 parts = 1.40.0 parts = 1.660 parts = 2.180 parts. 0.820 part = 1 part — 1.143 parts = 1.333 parts = 1.780 parts. 0.714 part = 0.875 part = 1 part = 1.170 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 part = 0.750 part == 1 part. 35. Copper cyanide. — There is a cuprous and a cupric cj^a- nide ; that used for electro-plating purposes being a mixture of both. It is a green-brown powder, which should not be entirely 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- copper cyanide, i. e., a combination of copper cyanide with potassium cj^anide, 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 solutions, in hydrochloric acid, to dryness on a. water-bath, wherein care must be taken not to inhale the vapors, and dissolving the residue in water, a green-blue solution is obtained which acquires a deep blue color by the addition of ammonia in excess. CHEMICALS USED IN ELECTRO-PLATING. 683 36. Zinc cyanide {hydrocyanate of zinc, prussiate 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 potassium-zinc cyanide, which is used for brass baths. Recognition. — By evaporating zinc cyanide, or its solution, with an excess of hydrochloric acid on the water-bath, zinc chloride remains behind, which is recognized by the same re- action given under zinc chloride. 37. 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, how- ever, 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 potas- sium cyanide, but is only slightly soluble in ammonia, differ- ing in this respect from silver chloride. It forms a double salt with potassium cyanide — potassium-silver cyanide — and as such is employed 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 re- quired, the solution exhibiting a pale yellow color. It pre- cipitates nearly all the metallic salts from their solutions, some of the precipitates being soluble in an excess of the pre- cipitating agent. This salt is not poisonous. It serves for the preparation of silver and gold baths ; its employment, however, offering over potassium cyanide no advantages, unless the non-poisonous properties be considered as such. Recognition. — When the j'ellow solution is mixed with ferric chloride, a precipitate of Berlin blue is formed ; by blue vitriol solution a brown-red precipitate is obtained. (584 ELECTRO- DEPOSITION OF METALS. VI. Carbonates. 39. Potassium carbonate (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 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 objects 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 carbo'aate or monopotassic carbonate, com- monly called bicarbonate of potash. — Colorless, transparent, crystals, which at a medium temperature dissolve to a clear solution in 4 parts of water. It is not deliquescent; however, on boiling 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 commerce 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, re- maining 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 CHEMICALS USED IN ELECTRO-l'LATING. 685 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 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 substance, 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 ribband of bright sheet-iron in the solution, copper separates 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 alka- line carbonate is a combination of zinc carbonate with zinc oxyhydrate. 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 quan- 686 ELECTRO-DEPOSITION OF METALS. tity of ammonia, nickel oxyhydrate is precipitated, which, by adding 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. 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- CHEMICALS USED IN ELECTRO-PLATING. 687 * alum. On exposing ammonium-alum to a red heat, the am- monium sulphate is lost, pure alumina remaining behind. Ammonium-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 ammonia becomes perceptible. 52. Ferrous sulphate (sulphate of iron, protosulphate 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 sulphate, the sulphate of copper and of zinc, as well as ferric sulphate. 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 hy rubbing acquires the luster of gold. 53. Iron-ammonium sulphate. — Green crystals which are constant 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 pos- sess a pure blue color but shows a greenish luster, is contam- inated 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 688 ELECTRO-DEPOSITION OF METALS. 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 sulphate in the cold, and nearly 100 parts at the boiling- point. Zinc sulphate is employed for the preparation of brass and zinc baths, as well as for mat 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 b} 7 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 color- ing 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 dissolving only 5.5 parts of it. It is used for the same pur- CHEMICALS USED IN ELECTRO-PLATING. 689 poses 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 concen- trated solution with the same volume of strong potash or soda lye, no odor of ammonia is perceptible, while nickel-ammon- ium 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 taste. They are constant in the air and readily dissolve in water, the solution showing a red color. By heating the crystals 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. Co bait- 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 alka- line reaction due to a small content of sodium carbonate. It is employed in the preparation of gold, brass, and copper baths, for silvering by immersion, etc. Recognition. — The solution when mixed with dilute sul- phuric 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 44 690 ELECTRO-DEPOSITION OP METALS. 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- 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 ace- tate 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 mat luster upon gold and gilding. For these purposes it may, however, be replaced b}' 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 bitar- trate saturated at the ordinary temperature, a crystalline pre- cipitate of tartar is formed. 63. Sodium nitrate (cubic nitre or Chile saltpetre). — Colorless crystals, deliquescent and very soluble in water ; the solution shows a neutral reaction. It is used for the same purposes as potassium nitrate. 64. Mercurous 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 CHEMICALS USED IN ELECTRO-PLATING. 691 of yellow-red vapors, into yellow-red mercuric oxide, which, on further heating, entirely evaporates. With a small quan- tity 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 em- \ ployed 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 : 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 ribband 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 gra}^ 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. 692 ELECTRO-DEPOSITION OF METALS. 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 re- action. 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 alka- line reaction. Sodium pyrophosphate also occurs in com- merce in the form of an anhydrous white powder, though it may here be said that the directions for preparing baths refer to the crystallized 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 showing an acid reaction, should be rejected. It is em- ployed in the preparation of platinum baths. X. Sails 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 pow- dered state, purified tartar is called cream of tartar. It is employed for the preparation of the whitening silver baths, CHEMICALS USED IN ELECTRO-PLATING. 693 for those of tin, and for the silvering paste for silvering by friction, and in scratch-brushing different deposits. 71. Potassium-sodium tartrate (Roclielle or Seigneite 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 temperature. 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 decomposed in the single cell apparatus. 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 slight 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, in- soluble in an excess of the cold acid. Sulphuretted 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 copper and brass baths, for the production of artificial patinas, for coloring, gilding, etc. Recognition. — On pouring sulphuric acid over copper ace- 694 ELECTRO-DEPOSITION OF METALS. tate, 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 crystals 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. 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. Avoirdupois Weight. = Ounces. = Drams. = Grains. = Grams. 1 Pound ...•".. 1 Ounce 1 Dram 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 Pound 1 Ounce 1 Pennyweight .... 12 1 0.05 240 20 1 5,760 480 24 372.96 31.08 1.55 (695) 696 APPENDIX. Imperial Fluid Measure. i Gallon i Quart I Pint i Fluid Ounce . . . i Fluid Dram . . . i Minim £ CO -0 a 3 a II Ph li EtrO II 4 8 160 i 2- 40 0.5 I 20 0.025 O.O5 1 0.0031 O.O062 0.125 0.00005 0.0001 0.0021 ■26 is 1280 320 160 0.0167 76,800 j 19,200 9,600 480 60 1 _g II u II II 70,000 277.276 4-541 17,5°° 69 310 I-I35 8,75° 34-659 0.567 437-5 1-733 0.0284 54-7 0.217 0.0035 0.91 0.0036 0.00006 •s-I U o 4.541 I.I35-2 576.6 283.8 35-5 0.59 Table of Useful Numerical Data. •03937 inches •3937° " 3-937°o " 39.37000 " 1 gram. 1000 a 1 ounces by 315.271; y *>J 1 J I measure. 1 millimeter equals 1 centimeter " 1 decimeter " 1 meter " 1 cubic centimeter of water equals 1 liter " 1 liter " 1 1 gallon ( or 1 60 fluid \ , ounces) equals J 1 gallon " 277.276 cubic ins 1 pint (or 20 fluid 1 - .. > 34-659 " ounces equals J 1 fluid ounce " 1-733 " 1 liter " 61.024 " I avoirdupois pound equals f liters. 7000. grains. 1 troy pound equals 1 avoirdupois ounce "> equals J I troy ounce equals 1 avoirdupois drm. ) equals J 1 troy pennyweight "1 equals 1 gram equals I kilogram equals 1 liter of water equals 1 cubic inch of water ) equals J I cubic centimeter of \ water equals > 1 kilogram equals 5760. grains. 437-5 480. " 27-34 " 24. " '5-43 " 15432. 15432. 252.5 35.274 avoir- dupois ozs To convert Fahrenheit thermometer degrees (F.) to Centigrade degrees (C), first subtract 32, then multiply by 5, and divide by 9. r - 5(F-- 32) 9 To convert Centigrade degrees to Fahrenheit degrees, multiply by 9, divide by 5, then add 32. 9 C + 32 APPENDIX. 697 0) mvo O rovO i t-~ o cm ^t-vo (J\ i O e 3 n t-OO rOvO O « vo *\0 00 H i tj-vo r^. on o cm m in o vo ro -. ON O CM ") O "^t-00 rO\0 ON CM VO i oo rooo --a-co cm t-N m 273 S Og.6 O O covo co onvo cm on m « co in OOwHwroro^in invo OOCOOOOOOOO ON -^-CO rOOO vO-'hCMOcOvOTr-CMOOOOONO 1 'oo ■<*■ on ■■*■ o **■ oo moo rt- on -*■ on < Of Pints equals Cubic Inches. t^ >*■ O. -^-oo ro o>^o ro o-vo «oo -<*■ 10 w 1-^ ro 000 r~vo ro r^ n nmvo ro cy>MD w 0*0 n cm/in r-^ ro r*. 0' -a- c~- m -**- a\ rood ro c^. ei t~. h \o ro cj-vd h n « « m covo O ro rsO -^-r^-H -3-01 rooo m H h w (N M ro rovo O ro OIHH NfO 000 t^.\o in CM* ONVO* CM ON in M NfOO^O ffiNd r>. w vo ro owo cm m t-. -*■ i— h t*- o> roco mvo m cm N cm ro rovo o rfiNt t-t H H CO Of Cubic Inches equals Pints. o o o o O O H ooo -*• r-* rovD ONCO t-^ M M N (N « M ^*-vo 00 H M H K M « -3"VO 00 OHHHUMNrO'-a* O IN "^VO OO O O H fOiTNCMN ^vO 00 invo r>.co 0000 000 t*-. OOOOOmhcmcOtI-O O CM -» t>. H •^•00 h ^o\ "**CO w vo O -* O co*o ro nnco rooo ^00 ro t-s. 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( . 1 " ! erg 5(5 c-s in m Cs. in H SO CM inomoinoooo t^s coco tonne in OoooOwMCMCMroTi-'4-in invo inomoinoooooooooo CM 00 Th SOnO CM roiOHvO CM M M M H CO "^-VO (n. roco ^-ONino inomo mo mo NONO CM COmHVO CM t>. roco i- om 00000 O m m 1 -*vO r-OiO 3 v a a cr ^ 3 c; rpvo ro onnd cm on m h 00 tJ- on moo mr-»cMvo wmo mMvo wvo hvo m ro -» q o o o o o q o q o m h w r^ n m co m r-. m m on m t^ m m ooo co S\o m . HHMNCMrommr*»MinoNO\ °J "? W . ^ " *\* N . °°. ^ °? "* °° « NO O ^-00 CMVO0 OOOO ONONO»ON ONCO CO SSrh mcm int-sOeM 10 is d «' in 6 vd h" n« n moo* -<*-oo* cm'vo" mtNrt iAonononononon HMMMCMCM«mt^OCMmrN,ocMmovOHtNCM t^. moo conh m on on HHMM«CMCMinrN.ocMinrN.ocMinovOw\om q h i cm m *■*• mvo r^oo on o m cm m ■*■ mvo tN.oo oooooooooooooooo m cm m •»*■ mvo tN-oo o o o o o o o h cm ro --*- m o 698 APPENDIX. 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 + 700 -)- 20 + 8 cubic inches. But a reference to the sixth column shows that 1000 cubic inches = 16,385.92 cubic centimeters. 700 K = 11,470.10 20 if = 32772 8 « = i3*-°9 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 167 F. 4 9-5 2.7 29 140 149 95 80 very soluble very soluble. 133 very soluble. 11.6 43.3 at 167 F. 30.5 63.7 at 158 F. 7-4 20 soluble very soluble. 37 203 61 333 soluble soluble. very soluble very soluble. 45-35 very soluble. 48 139 3i-5 71-5 6-57 54 decomposable decomposable. decomposable decomposable. APPENDIX. 699 Table oj Solubilities of Chemical Compounds Commonly Used in Electro- Technics. — Continued. 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 dicbromate 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 ioo 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. c.65 1.25 9.8 357-5 0.4 6.9 109 156 94 154 soluble decomposable. 8.0 98 28 5° soluble soluble. 21. 1 247 6.45 very soluble. 12.5 IOO 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 21 5. 6° F. 108.5 163 96.x 213 65 102 at 140 F. 20 15° 6.8 93 9 42.5 2 5 IOO soluble soluble. 271 decomposable. 125.7 343-3 300 very soluble. 138.2 653.6 700 APPENDIX. Content of Metal in the Most Commonly Used Metallic Salts. Metallic Combination. Formula. 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 . . (NH 4 ) 2 Co(S0 4 ) 2 +6H 2 CoCl.,+ 6H. 2 CoS0 4 +7H 2 Cu(C 2 H 3 2 ) 2 +H 2 2CuCO s (CuOH) 2 CuCl 2 +2H 2 Cu 3 (CN) 4 + 5 H 2 CuO CuS0 4 +5H 2 Cu 2 FeS0 4 + 7H 2 AuCL,-)-x ag AuCl 3 -|x ag (NH 4 )Fe(S0 4 ) 2 +6H 2 Pb(C 2 H,0 2 ) 2 + 3 H 2 Pb(N0 3 ) 2 HgCl 2 Hg,(N0 3 ) 2 (NH 4 ) 2 Ni(S0 4 ) 2 +6H 2 NiCO s 4NiO, 5H 2 NiCl 2 4-6H,0 NiCl 2 fNi(OH) 2 +H.,0 (separated \ at 212 F.) Ni(NCQ 2 +6H 2 Ni-A NiS0 4 +7'H,0 PtCl 4 + 5 H 2 (NH 4 ) 2 PtCl B K 4 Cu 2 (CN) 6 K 2 Hg(CN) 4 KA g (CN) 2 K 2 Zn(CN) 4 AgCl AgCN AgN0 3 SnCl 2 +2H ? NH 4 ZnCl s +2H 2 ZnCO a Zn(OH) 2 ZnCl 2 Zn(CN) 2 ZnSQ 4 +7H 2 t SIS. o ^ U 14.62 ! 24.68 20.92 3I-87 55-2o 37-°7 5 6 -5° 79-83 25.40 88.79 20.14 50 to 52 48 to 49 14.62 , 54-57 62.51 73-87 79-36 14.94 57-87 24.63 45-3° 63-34 18.97 71.00 22.01 45-66 43-91 28.83 53-56 54.20 26.35 68.20 80.57 64.98 52.45 28.98 29.05 47.84 56.59 22.73 APPENDIX. 701 Table Showing the Electrical Resistance of Pure Copper Wire of Various Diameters. Number of Number of No. of wire, feet required No. of wire, feet required Birmingham Resistance of to give Birmingham Resistance of to give wire gauge. i foot in ohms. resistance wire gauge. 1 foot in ohms. resistance O.OOOO516 of 1 ohm. of 1 ohm. OOOO 19358 17 O.OO316 316.I OOO O.OOOO589 16964 18 O.OO443 225-5 OO O.OOO0737 I3562 19 O.OO603 105-7 O O.OOOO922 IOS57 20 O.O0869 115. 1 I O.OOOII8 8452.6 21 O.OIO4O 96.2 2 O.OCOI32 7575-1 22 0.01358 73-6 3 O.OOOI59 6300.1 23 O.OI703 58.7 4 O.OCOI88 53I9-9 24 0.02200 45-5 5 0.000220 4545-9 25 O.02661 37-6 6 O.CCO258 387 -3 26 O.O3286 304 7 O.OOO329 3°43-4 27 O.O4159 24.0 8 O.OOO39I 2 557-i 28 O.05432 18.4. 9 O.OOO486 2057.7 29 O.063OO 15-9 IO O.OOO593 1686.5 30 0-07393 !3-5 n O.OOO739 i35 2 -5 31 O.IO646 9-4 12 O.OO0896 1 1 16.0 32 O.I3T44 7.6 13 O.OO 1 180 847-7 33 O.16634 6.0 14 O.OOI546 647.0 34 O.21727 4.6 *5 O.OO2053 487.0 35 O.42583 2.4 16 O.OO2520 396.8 36 O.66537 r -5 Resistance and Conductivity of Pure Copper at Different Temperatures. Centigrade temperature. Resistance. Conductivity. Centigrade temperature. i6 c Resistance. Conductivity. o° I .OOOOO I .OOOOO I.06168 .94190 I I. OO38 1 .99624 17 I.06563 .93841 2 I.O0756 •99250 18 I.06959 •93494 3 1-01135 .98878 19 I.07356 •93H8 4 1-01515 .98508 20 I.07742 .92814 5 1.01896 . -98139 21 1. 08 1 64 •92452 6 1.02280 .97771 22 I-08553 .92121 7 1.02663 .97406 23 I.08954 .91782 8 1.03048 .97042 24 I.O9365 •91445 9 I-03435 .96679 25 I.09763 .91110 10 1.03822 .96319 26 I.IOl6l .90776 11 1. 04 1 99 •95970 27 I. IO567 •90443 12 1.04599 •95603 28 I.II972 .90113 13 1.04990 •95247 29 I.II882 •89784 14 1.05406 •94893 30 I.I 1 782 .89457 15 I-05774 •94541 702 APPENDIX. Table of Hydrometer Degrees according to Baume, at 63.5° 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. o 1 .0600 19 1.1487 38 1-3494 57 1.6349 i 1.0068 20 1.1578 39 1.3619 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 l -°3S3 24 '•«955 43 1.4I43 62 I-73I3 6 1.0426 25 1.2053 44 1.4281 63 1.7520 7 1. 050 1 26 1-2153 45 1. 442 1 64 1-7731 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 Ti 1.0810 30 1.2569 49 1.5012 68 1,8632 12 1.0890 31 1.2677 5° 1.5167 69 1.8871 *3 1.0972 32 1.2788 5 1 I-5325 70 1.9117 14 1-1054 33 1. 2901 52 I-5487 7i i.937o J 5 1.1138 34 1.3015 53 1.5652 72 1.9629 16 1. 1 224 35 i-3i3i 54 1.5820 17 1.1310 36 1.3250 55 1-5993 18 1. 1398 37 I-3370 i 56 1.6169 Table of Bare Copper Wire for Low Voltage. bo 3 >. CuO 3 >> u c p.— M s fail P. U M 4> U rt * P.U V V CO 0) rt (\ _£'*" 2 ° S GO